STRUCTURE magazine | June 2016

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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STRUCTURE

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June 2016 51 EDITORIAL

7 Structural Engineering Licensure: Critical to Our Future

FEATURES STRUCTURAL REHABILITATION

66 Thinking Outside the Wooden Box

56 Leonard

By Kimberlee McKitish, P.E.

By Silvian Marcus, P.E., Hezi Mena, P.E. and Fatih Yalniz

PROFESSIONAL ISSUES

32

By Glenn R. Bell, P.E., S.E., SECB and Andrew W. Herrmann, P.E. STRUCTURAL DESIGN

12 Cross-Laminated Timber Structural Floor and Roof Design

70 Leadership Opportunities in Our Offices, in Our Associations, and in the Public Sector

By William D. Bast, P.E., S.E.

By Scott Breneman, Ph.D., P.E., S.E. INSIGHTS CONSTRUCTION ISSUES

16 Ensuring Quality Concrete

By J. Benjamin Alper, P.E., S.E. and

72 FHWA’s National Tunnel Inspection Program

By Brian J. Leshko, P.E.

Cawsie Jijina, P.E., SECB

20 Steel Rebar Coatings for Concrete Structures

By Fujian Tang, Ph.D. STRUCTURAL TESTING

24 The Design Professional’s Role in Special Inspections

Hat Truss-Supported Office Tower in Salt Lake City

By Mark Sarkisian, S.E., Peter Lee, S.E., Alvin Tsui, S.E. and Lachezar Handzhiyski, P.E.

37

Rising to the Clouds with Confidence

By Jon Galsworthy, Ph.D., P.Eng., P.E.

42

SPOTLIGHT BUILDING BLOCKS

28

75 170 Amsterdam

By Mukesh M. Parikh, P.E.

The Resilience-Based Design of the 181 Fremont Tower

STRUCTURAL FORUM

By Ibrahim Almufti, S.E., Jason Krolicki, S.E. and Adrian Crowther, P.E., C.Eng.

82 Five Tips for Engineering Managers

By Stan R. Caldwell, P.E., SECB

46

By Chris Kimball, S.E., P.E.

Preloading Approach to Column Removal in an Existing Building

HISTORIC STRUCTURES

By Pratik Shah, P.E.

60 John A. Roebling’s Niagara River Railroad Suspension Bridge – 1855

By Frank Griggs, Jr., D.Eng., P.E. STRUCTURAL ECONOMICS

63 Efficiency and Economy in Bridge and Building Structures – Part 2

By Roumen V. Mladjov, S.E.

51

IN EVERY ISSUE 8 Advertiser Index 10 Noteworthy 56 Resource Guide (Tall Buildings) 74 Bookcase 76 NCSEA News 78 SEI Structural Columns 80 CASE in Point

Tall Buildings Construction Moving Apace with New Products and Services

By Larry Kahaner

On the cover View from the clouds –- Jeddah Tower, designed by Adrian Smith + Gordon Gill Architects and Thornton Tomasetti, now under construction in Jeddah, Saudi Arabia. See feature article on page 37.

STRUCTURE magazine

5

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

June 2016

Editorial

Structural Engineering Licensure: new trends, new techniques and current industry issues Critical to Our Future

By Glenn R. Bell, P.E., S.E., SECB, F.SEI, F.ASCE and Andrew Herrmann, P.E., F.SEI, Pres 12. ASCE

W

hile certain jurisdictions of the U.S. have had structural engineering (SE) licensure separate from the more generic professional engineering (PE) licensure for over a century, an industry-wide promotion of SE licensure has gained momentum in the past several years. The authors, as strong proponents of SE licensure, wish to reinforce the critical nature of this movement to our future.

The U.S. Constitution does not grant federal jurisdiction over professional licensure, so this issue falls to the individual states. In the majority of states, structural engineers practice through professional engineering (PE) licenses.

In most states, a PE may perform structural engineering to the extent he or she feels qualified to do so. Eleven states have some form of SE Practice Act. (A Practice Act limits the practice of structural engineering on certain types of structures to engineers holding SE licensure.) Another eight states have SE Title Acts. (A Title Act permits PEs and CEs who meet specific SE requirements to use the title Structural Engineer, but it does not otherwise restrict or regulate practice beyond what a PE or CE can do.)

Formed in 2012, the Structural Engineering Licensure Coalition (SELC), a partnership of the Structural Engineering Institute of the American Society of Civil Engineers (SEI), the National Council of Structural Engineers Associations (NCSEA), the Structural Engineering Certification Board (SECB), and the Council of American Structural Engineers of the American Council of Engineering Companies (CASE), seeks to promote SE licensure. SELC does not propose federal SE licensure, but rather encourages the states’ adoption of SE licensure as a post-PE credential.

The need for separate SE licensure is a recognition of the explosion in the volume of structural engineering knowledge necessary to practice competently. One need only compare the 636 pages of ASCE/SEI 7-10 to its slim predecessor ANSI A58.1-1972 or the same explosion in the size of AASHTO’s highway bridge design code to appreciate the impact. We are, by necessity, more specialized and complex today.

Most of the arguments for SE licensure have focused on the current state of our profession. Equally important, if not more so, are future realities. As demanding as our profession is today, it’s getting rapidly ever more demanding.

Largely enabled by advances in technology, engineers are designing increasingly creative, complex, and sophisticated structures. As an example, straight lines and right angles have given way to compound curves and complex geometries that engage three-dimensional systems of structural elements supporting loads in ways not experienced in common beam-and-column structures. Structural systems are more daring, demanding a commensurate escalation of engineering skills.

The adoption of SE licensure on the west-coast, many years ago, was driven by the specialized skill set needed to design structures to resist severe earthquakes. Today, seismic design is substantially more complex and has been adopted broadly in the U.S. At the same time, we recognize the importance of terrorist threats, climate change, flooding, tsunamis, tornados, and hurricanes that require advanced structural considerations, such as analysis for nonlinear response or impact loading, which were not common even a few decades ago. The need to address extreme events is no longer a west-coast phenomenon.

It is commonplace throughout the U.S. STRUCTURE magazine

The sustainability imperative is driving more resource-efficient approaches to our design. The demand for more materially efficient, optimized structures is enabled by advances in technology and requires a more detailed understanding of the performance of construction materials than commonly held by engineers of the past. Also, highly efficient structures will be less forgiving for unforeseen threats. As such, structural engineers need a higher understanding of the performance of complex structures and increased precision in their analysis to maintain reliability.

One of the antidotes for overly complex, prescriptive codes and an enabler of creative, sustainable design is performance-based design (PBD).

Performance-based seismic design has become more commonplace.

Performance-based fire design has been practiced on an ad-hoc basis for many years. An appendix to upcoming ASCE 7-16 will introduce performance-based fire design to the code system. Recently SEI formed a new Board Level Committee to encourage the broad application of PBD to various loadings and forms of structural response. PBD requires an understanding of structural behavior beyond that necessary to design using prescriptive codes, mastery of risk assessment, and the strong ability to communicate performance expectations with stakeholders.

We must develop a more common basis for structural engineering registration in the U.S. to recognize the realities of the 21st Century.

Many U.S. structural engineers work throughout the country, and globally, diminishing the reasons for regional qualifications. Lack of more uniform acceptance of structural engineering qualifications is wasteful and discourages market efficiencies. The U.S. “national” building codes, once fractionalized on a regional basis, successfully unified into a single nationally applicable code and that has improved our industry.

Whether engineers work globally or locally, most of their design and construction projects today have international influence. In the U.S., we face competition from offshore engineers. Such competition will not abate.

At the same time, we have tremendous opportunities to contribute to the great need for a sustainably built environment across the world. We must become global players. Global presence will require structural engineers to be experts in regulatory, political, economic, cultural, language, and construction practices in societies very different from our own.

The global structural engineering community understands that it must become globally interoperable. The United Kingdom, through the Institution of Structural Engineers (IStructE), has had separate SE licensure (Chartering) for about a century. In pursuit of a global engineering platform, IStructE has been successful in promoting its Charter credential as an international standard. If we, as a U.S. structural engineering community, are to have our rightful place in the international community, we must have uniform SE licensure in the U.S. and join the movement for a global structural engineering platform.

Take a moment to step back from the din of the current debate and reflect on where our profession has been, where it is today, and where we need to go in the future. It is clear we meet our obligation to society and secure our future if we have a credential that demonstrates our mastery of the exploding knowledge required to perform structural engineering.

The qualifications to hold a PE alone do not suffice. SE licensure is critical for structural engineers to demonstrate that they have the broad knowledge, creativity, and innovation necessary to serve society, now and in the future.▪

7

June 2016

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Errata The author of the article Concrete Gravity Members (Engineer’s Notebook, STRUCTURE, September 2014) discovered an error after publication. The following corrections have been made in the flow chart in the online versions of the article. Visit www.STRUCTUREmag.org.

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21.13.3.2 should read, If Pu > Ag f 'c /10 21.1.4.3 should read, f 'c < 5000psi (LW)

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EDITORIAL STAFF Executive Editor Jeanne Vogelzang, JD, CAE execdir@ncsea.com Editor Christine M. Sloat, P.E. publisher@STRUCTUREmag.org Associate Editor Nikki Alger publisher@STRUCTUREmag.org Graphic Designer Rob Fullmer graphics@STRUCTUREmag.org Web Developer William Radig webmaster@STRUCTUREmag.org

EDITORIAL BOARD Chair Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@structuremag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA Dilip Khatri, Ph.D., S.E. Khatri International Inc., Pasadena, CA Roger A. LaBoube, Ph.D., P.E. CCFSS, Rolla, MO Brian J. Leshko, P.E. HDR Engineering, Inc., Pittsburgh, PA

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Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org June 2016, Volume 23, Number 6 ISSN 1536-4283. Publications Agreement No. 40675118.

Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student.

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STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

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Noteworthy

news and information

Jeanne Vogelzang to Retire

By Barry Arnold P.E., S.E., SECB, (NCSEA President 2014-15)

A

fter 20 years of loyal and dedicated service, Jeanne Vogelzang has announced her retirement. She will step down as Executive Director of the National Council of Structural Engineers Associations (NCSEA) effective June 30th.

Fortunately, Jeanne will continue serving NCSEA until the 2016 NCSEA Summit in September. She will work from Orange Beach, Alabama, where she and her husband, Marc Barter, will reside. We are delighted that Jeanne and Marc will no longer have to endure the trials of a long-distance relationship, and will be together and surrounded by family while Jeanne pursues and enjoys more personal interests like scuba diving and becoming a sommelier.

Jeanne is well known as a tireless advocate and fearless fighter for what is best and right for the structural engineering profession and, more specifically, for the practicing consulting engineer. She was often heard saying “Consulting structural engineers work harder than anyone I know and seldom get the respect and financial reward they deserve.”

While consulting structural engineers work diligently making a living, Jeanne works tenaciously, often behind the scenes, to make sure structural engineers and the structural engineering profession are well represented.

The late Gene Corley brought Jeanne to NCSEA. He knew her from her role as Structural Engineers Association of Illinois’s executive director and knew that she was the kind of person NCSEA needed. Hired in 1995, Jeanne took over a fledgling organization that had little to no financial foundation.

Her first instruction to the NCSEA Board was to raise the sum of $12,000, her yearly salary, which they did by writing personal checks.

She then proceeded to take the organization from 17 member associations to the 44 we have today. Jeanne has worked with every past president but one, Jim Cagley, the first.

Moreover, while Jim had left the board before Jeanne’s tenure, he was always a strong supporter of her work, recognizing that she took very good care of his idea, NCSEA.

NCSEA needed a Negotiator While reminiscing about Jeanne’s firm resolve to represent the best interests of the

profession, Michael J. Tylk, S.E. (NCSEA President 2001-02), recalled, “Jeanne, by herself, walked into a very contentious meeting with a CEO, CFO, and two attorneys and came out of the meeting with everything NCSEA wanted plus some.”

William D. Bast, P.E., S.E. (NCSEA President 2009-10) concurs. He emphasized that “Jeanne is a very formidable negotiator – something we often heard about and were fortunate to experience firsthand!” He added that “She is the type of advisor any President would want in their cabinet or on their board – smart, confident, never afraid to stand up to anyone, honest, truthful, wise, and gracious. She was never a Yes Woman – she could agree with you one minute on one topic, and vociferously disagree with you the next minute on a subsequent topic, without batting an eye.”

NCSEA needed an Advocate “Jeanne is exactly what NCSEA needed during our formative years,” said Ben Nelson, P.E., SECB (NCSEA President 2012-13).

He continued, “She advocated for NCSEA in our profession as fiercely and professionally as NCSEA advocates for the practicing structural engineer.”

Jeanne’s determination was an essential characteristic and vital to the success of

STRUCTURE magazine

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June 2016

NCSEA, as noted by Emile Troup, P.E., SECB (NCSEA President 1998-99). He said, “Jeanne helped NCSEA weather some tough early years as we were trying to expand the member base and survive, grow the magazine, and justify NCSEA as THE organization to represent structural engineers through their local member organizations.”

NCSEA needed a Visionary Sanjeev N. Shah, P.E., J.D. (NCSEA President 2002-03), when reflecting on Jeanne’s influence at Board meetings, said, “Jeanne Vogelzang, while the quietest one in a meeting, kept us on track by asking simple probing questions to keep us focused on what we were trying to achieve. Jeanne brought moments of levity and a whole lot of clarity into what, many times, would have become tedious (and yes, contentious) meetings.” He continued, “Though her title was Executive Director, she was more of a strategic advisor and facilitator.” He concluded by saying, “I learned a lot from Jeanne – be clear, be concise and, most importantly, walk the talk and have fun.”

Reflecting on Jeanne’s many contributions to NCSEA, Carrie Johnson, P.E., SECB (NCSEA President 2013-14) said that, “What strikes me is her passion for making NCSEA better. She constantly looked at things and thought ‘how could we do this better’ or ‘in what direction

should we head in the future?’ Without Jeanne’s passion, NCSEA would not be where it is today.”

Brian Dekker, P.E., S.E. (NCSEA President 2015-16) said, “There is no doubt that she has contributed more to this organization than any other individual. She spent the last 20 years setting us up for the next 20 years of success.”

NCSEA needed a Leader and Confidante James T. Slider, P.E. (NCSEA President 199798), referring to Jeanne, said that, “She was unflappable and always a lady. Jeanne is my friend, and I will always treasure that.”

Recalling his time serving with Jeanne, Greg Robinson, P.E. (NCSEA President 2006-07) said, “Jeanne worked tirelessly to return every call and email promptly. She worked way into the late evening hours and was back at work early the next morning. Jeanne, once given an idea, would act on it and carefully and methodically consider the options and implications.

She always treated every idea with respect. It was that ability that allowed NCSEA to grow and become what it is today.” Greg summed up his impressions about Jeanne by stating, “No one has encouraged, inspired and challenged our profession more than Jeanne.”

NCSEA needed Jeanne Jeanne came to NCSEA with impressive credentials. She is a licensed attorney, CPA, has an advanced degree in accounting and business management, and started her working career as a math teacher.

At NCSEA, she worked as Executive Director, Chief Executive, Chief Financial Officer, Accountant, In-house Counsel, Program Marketer, Investment Advisor, Negotiator, and NCSEA‘s Spokesperson/ Politician/Diplomat/Ambassador. She is the Chief Member Organization Liaison, Chief Committee Chair Liaison, and Entrepreneur and Champion of New Programs. During Jeanne’s 20 years of service, she handled all of NCSEA’s legal work. The organization never hired outside legal counsel for any reason. Also, Jeanne has served as Executive Director of the Structural Engineering Certification Board (SECB), NCSEA Media VP of Operations, and Executive Editor of STRUCTURE. James Malley, P.E., S.E., SECB (NCSEA President 2010-11) summed up Jeanne’s tenure with NCSEA when he stated, “Jeanne has been the one constant throughout the history of NCSEA. Presidents and Board

Members come and go, but Jeanne has been the thread that tied together the organization over the past twenty years. The continuity that she brought, with an institutional history, was critical to each year’s President and Board as NCSEA grew and developed.”

On behalf of all who have worked with Jeanne, I would like to express our most sincere gratitude and appreciation for her commitment to the improvement of the structural engineering profession and the continuous improvement of NCSEA into the fine organization it is today. Thank you, Jeanne, for your vision, passion, and devotion. We wish you all the best during your retirement.▪

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June 2016

Structural DeSign design issues for structural engineers

I

ncreased availability of cross-laminated timber (CLT) in North America, combined with successful use in projects worldwide, has generated interest in its properties and performance within the U.S. design community. With the inclusion of CLT in the 2015 International Building Code (IBC) and 2015 National Design Specification® (NDS®) for Wood Construction, curiosity is evolving, with some developers, architects and structural engineers using CLT in projects. One application under frequent consideration is the use of CLT within horizontal floor and roof systems to create longspanning structural decks. This article covers the available U.S. design standards and methods being used by engineers on these projects.

CLT in North America Cross-laminated timber is an engineered wood component manufactured from dimension lumber or structural composite lumber to create large, flat panels of solid wood. It is a member of a new class of massive (or “mass”) timber products – i.e., large-dimension engineered structural wood components that complement the dimension sawn lumber, solid sawn timbers, and structural composite lumber products frequently used in building framing. Other forms of mass timber construction include nail-laminated timber (NLT), glued-laminated timber (GLT) panels and solid panels of structural composite lumber materials. The large component sizes and strength of the mass timber panels allow these structural components to be an alternative to concrete, steel and masonry components in many building applications.

In North America, the availability and acceptance of CLT are relatively new; however, adoption is happening quickly considering the speed at which material design standards and building code modifications typically occur. The ANSIapproved product standard, ANSI/APA PRG 320 Standard for Performance-Rated Cross-Laminated Timber, provides a basis for standardization of CLT quality, manufacturing and structural properties for structural building applications in North America. Currently, there are three North American manufacturers of CLT with manufacturing certified to the ANSI/APA PRG 320 standard: Nordic Structures, Structurlam Products, and DR Johnson Wood Innovations. Additional companies are expected to begin manufacturing CLT for building applications shortly.

The size of manufacturing equipment and shipping constraints limits CLT panel sizes. North American-manufactured CLT is available in

Cross-Laminated Timber Structural Floor and Roof Design

By Scott Breneman, Ph.D., P.E., S.E.

Scott Breneman is Senior Technical Director of the Architectural and Engineering Solutions Team of WoodWorks – Wood Products Council. He can be reached at scott.breneman@woodworks.org.

The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

12 June 2016

Figure 1. CLT layup.

panels as large as 8 feet by 40 feet. While CLT is shipped anywhere in the U.S., it is not a “stock” product with material sitting at a local distribution center; panels are manufactured for specific projects. Design teams considering using CLT should work closely with manufacturers to understand availability and lead times. With extended lead times, importing CLT from overseas, notably Europe, is also possible.

CLT panels can be used in floor, roof, and wall framing. There are cases where buildings were constructed using CLT for all of the structural framing above the foundations, including walls, floors, and roofs. Other buildings use CLT for specific structural components such as floor decking.

U.S. Design Standardization A foundational document for designers using CLT in North America is the U.S. CLT Handbook, available free from www.rethinkwood.com. This Handbook covers a spectrum of topics relevant to the design of buildings using CLT, including structural properties, connections, enclosures, acoustics and fire performance. While not referenced by the building codes, this document provided a basis for early U.S. CLT applications through alternative means processes.

Building on and updating the structural provisions of the CLT Handbook, the building code-referenced 2015 NDS includes a new Chapter 10 covering engineering design of CLT. The NDS now includes provisions for dowel-type fasteners into CLT in Chapter 12. The calculated fire-resistance method of wood members in Chapter 16 of the NDS includes provisions to calculate up to a 2-hour structural fire-resistance rating of loaded CLT members. The calculated fire-resistance rating of CLT is based on ASTM E119 fire tests of structural CLT. For further information on the 2015 NDS changes, see the Code Updates article from the January 2015 edition of STRUCTURE.

MAJOR

Product quality and engineering standardization enabled explicit recognition of CLT in the 2015 IBC. CLT is identified as a structural material, defined in IBC Chapter 23 with reference to the PRG 320 standard and the 2015 NDS. CLT framing is allowed within Construction Types III, IV, and V, and for roof members in Types I and II roof assemblies requiring a 1-hour fire-resistance rating or less. IBC provisions for Type IV define minimum CLT material thickness for the use of CLT as a Heavy Timber floor (4 inches) and roof (3 inches).

OR

MIN

AXIS

IS

AX

CLT Manufacturing CLT is manufactured from dried dimension lumber with adhesives applied between laminations, similar to glulam members. As with plywood, CLT typically has an odd number of layers. The exterior layers are parallel and create the strong direction of a panel while perpendicular interior-only layers define its relatively weaker direction (Figures 1 and 2). Individual boards are dried to a moisture content of 12 +/- 3% and commonly finger-jointed into longer lengths before being assembled into a panel.

The PRG 320 standard specifies that the laminations have a 5/8-inch minimum and 2-inch maximum thickness. Laminations used in North American CLT are frequently from 2x4 and 2x6 boards. The PRG 320 standard covers CLT panels up to 20 inches thick.

With CLT construction, panels are dimensionally stable in both the major and minor panel axis (Figure 2). Dimensional changes across the thickness of the panel are limited because of the use of dried lumber during manufacturing.

PRG 320 defines seven stress grades of CLT panels, which provide minimum strength requirements using visually-graded or machine-graded dimension lumber. CLT grades E1 through E4 use machine stress-rated lumber for layers parallel to the major axis. CLT grades V1 through V3 use visually-graded lumber for layers parallel to the major axis. All CLT grades defined in PRG 320 use visually-graded lumber for layers perpendicular to the major axis. Manufacturers can also supply additional CLT grades.

Structural Properties of CLT For out-of-plane bending and shear behavior, and in-plane tension and compression behavior, the CLT layup creates a stronger and stiffer “major strength axis” and a weaker and softer “minor strength axis.”

Subscripts 0 and 90 are used to differentiate properties in the major and minor directions, respectively.

Out-of-Plane Bending Strength For out-of-plane flexural design, such as for gravity loads on a floor panel, the applied bending moment, Mb, must not be greater than the adjusted moment capacity and is written in the form:

Figure 2. CLT panel.

lb-ft/ft for the 7-ply E1. Conversion of a reference moment capacity to a Load and Resistance Factor Design (LRFD) moment capacity can be performed using the KF, φ, and λ factors listed in NDS Chapter 10.

Provided the reference bending capacity in the major and minor strength axes, FbSeff,0 and FbSeff,90, the flexural strength design checks at ASD levels are simply: Mb, 0 ≤ CD (∙) FbSeff,0 Mb,90 ≤ CD (∙) FbSeff,90 where (∙) provides for the atypical application of additional adjustment factors.

Out-of-Plane Shear Strength Out-of-plane (interlaminar or rolling shear) capacities are based on testing according to the principles of APA PRG 320: Vplanar ≤ Fs (Ib/Q)eff' where Vplanar is the applied shear demand and Fs(Ib/Q)eff' is the adjusted shear capacity which for ASD reduces to: Fs(Ib/Q)eff' = (∙) Fs(Ib/Q)eff Per NDS Chapter 10, the Load Duration Factor, CD, does not apply to this shear capacity check. Available CLT product reports use the term Vs for published values of the reference shear capacity, Fs(Ib/Q) eff, resulting in shear strength checks of: Vplanar,0 ≤ (∙) Vs,0 Vplanar,90 ≤ (∙) Vs,90 Out-of-Plane Stiffness PRG 320 and product reports provide calculated stiffness properties for flexural and shear deformation of CLT panels due to out-of-plane loads.

The panel stiffness properties provided are EIeff,0 and EIeff,90 for flexure

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where the adjusted moment capacity, Fb(Seff)', is calculated from the reference moment capacity, FbSeff, multiplied by adjustment factors presented in NDS Chapter 10. For allowable stress design (ASD), the load duration factor, CD, is applicable. Other adjustment factors including the wet service factor, CM, temperature factor, Ct, and beam stability factor, CL, are listed as potentially applicable to CLT panels in bending; however, they do not typically apply to CLT floor or roof panels within a building envelope.

The PRG 320 standard and manufacturers’ product reports provide the reference moment capacity, FbSeff, as an allowable design value. The major axis reference moment capacities in the CLT sections defined in PRG 320 range from 2,030 lb-ft/ft for the 3-ply V2 section to 18,375 STRUCTURE magazine

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Mb ≤ Fb (Seff)'

and GAeff,0 and GAeff,90 for shear deformations.

These effective stiffness values take into account the varying direction and grades of laminations.

As shown in Figure 2, the major strength axis of the CLT panel is typically aligned with the long direction of the panel. In typical floor or roof applications, CLT panels primarily act as a one-way system where multiple panels are installed adjacent to each other, spanning between perpendicular supports. CLT panels can be used in multiple-span configurations.

For such layouts, calculating floor or roof deflections under uniform loads can be performed by analyzing a strip (e.g., 1-foot width) of the CLT as a beam. Two-way spanning capabilities can be taken advantage of at corner overhangs and penetrations through panels. Using any structural analysis method with the capability to model the specific flexural and shear stiffness of the CLT, a designer can directly calculate internal forces and deflections as either a beam or two-way spanning floor system.

A simplified beam analysis method is presented in the 2015 NDS Section 10.4.1.1, where an apparent flexural stiffness, EIapp, combines the effective flexural and shear stiffness values. Commentary Section C10.4.1 provides an alternative formula of the apparent stiffness value, which can be used where effective bending and shear stiffness values are provided by the CLT manufacturer: EIeff Ks EIeff 1+ GAeff L2 The constant Ks depends on both the support conditions and applied loading pattern. For a single-span beam assuming pinned supports, Ks for uniformly distributed load equals 11.5 and Ks for a concentrated line load at mid-span equals 14.4. NDS Chapter 3 incorporates additional criteria regarding long-term deflection for CLT. EIapp =

CLT Floor Design for Vibration For many structural systems, designs of occupied floor systems are often governed by controlling floor vibrations for perceived occupant comfort and other serviceability concerns. CLT floor design is no different.

Prescriptive Span Limit One method proposed by researchers at FPInnovations (Hu and Gagnon, 2012) to help select a CLT section that will have acceptable performance to occupants for walking excitations is presented in the CLT Handbook Chapter 7. This approach calculates an acceptable span limit based on the section properties and has been calibrated to subjective performance evaluations of bare

CLT specimens. The recommended span limit can be written as: l≤

1 (EIapp)0.293 12.05 (ρA)0.122

where l is the span, EIapp is the apparent stiffness of a 1-foot strip of a simply supported single span under uniform load, ρ is the specific gravity of the CLT, and A is the cross-sectional area of the 1-foot wide strip of CLT. This approach also recommends keeping the fundamental frequency of CLT floors above 9 Hz. An estimate of the fundamental frequency of CLT as: f=

2.188 2l 2

√ EIρA

app

As EIapp in the above two equations depends on span length, application of these criteria requires iterative calculations to determine recommended span length for a given CLT section. As a convenience to designers, North American manufacturers publish the recommended span limit for standard CLT sections based on this approach.

The CLT Handbook recommends using the same limit for CLT floors with multiple spans, suspended ceilings and light-weight floor toppings. An interim suggestion for addressing heavy-weight floor toppings (>20 lbs./sq. ft.) is also provided.

Alternative Vibration Criteria With long spans or heavy floor loads, the period of vibration of floor systems can be difficult and uneconomical to keep above 9 Hz. Other established vibration criteria can be combined with an understanding of CLT floor behavior to design floors with acceptable vibration performance. One approach is the velocity control method included in the American Institute of Steel Construction Design Guide 11 (Murray et al., 2003) Chapter 6, which was used in the design of long-span CLT floors in the Timber Tower Research Project (SOM, 2013).

The velocity control method requires the selection of an acceptable velocity limit and loading condition. A two-dimensional analysis of the floor system can be performed to calculate the vibration response characteristics, including the period(s) of vibration. Alternative methods exist to estimate the floor flexibility including twoway spanning behavior, without performing a full two-dimensional plate analysis.

Advantages of general acceptance criteria, as in Design Guide 11 and standards such as ISO 10137, include being able to directly account for construction conditions that do not match the assumptions of the recommendations in the CLT Handbook and the ability to directly select more or less stringent design criteria

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June 2016

as appropriate for the project under design.

More accurate estimates of the floor stiffness and period through consideration of special boundary conditions, as in the Timber Tower Research Project, or by including the mass and stiffness contributions of topping slabs, as in Hamm et al. (2010), can explicitly consider floor configurations that are significantly outside the limitations of the recommended span-limit approach of the CLT Handbook.

Vibration-sensitive situations – e.g., the need to provide acceptable performance in response to rhythmic activities, or for sensitive equipment and occupancies – should receive much more rigorous evaluation than the methods outlined here.

CLT as Diaphragm While the structural design of CLT is included in provisions of the 2015 NDS, lateral force transferring diaphragm systems of CLT are not included in the 2015 Special Design Provisions for Wind and Seismic (SDPWS). CLT diaphragm connection and system performance with various connection details and loading conditions is an area of ongoing research. CLT floor and roof systems are currently designed and built using CLT as a diaphragm material in accordance with principles of engineering mechanics and provisions of the NDS for connections and member design. Because of the size and strength of CLT panels, CLT diaphragm behavior is significantly influenced by the strength, flexibility, and ductility of the connections between CLT diaphragm panels and other force-resisting components. Some connection details are similar to nailed wood structural panel-sheathed diaphragms. Other panel-to-panel connection details use proprietary self-tapping screws and can result in connections stronger and stiffer than nailed connections.

Conclusions While CLT is a relatively new building component to the U.S., product and design standards enable designers to design CLT floor and roof elements with confidence. The inclusion of CLT in the 2015 IBC and increasing North American manufacturing capabilities will likely lead to increased use of this innovative structural material. Also, organizations such as the Softwood Lumber Board, Binational Softwood Lumber Council, United States Department of Agriculture, Natural Resources Canada, and Canadian NEWBuildS Network are supporting considerable research to further support the use of CLT and other mass timber systems.▪ A similar article was published in the 2014 SEAOC Convention Proceedings.

Content reprinted with permission.

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ConstruCtion issues discussion of construction issues and techniques

O

ver the past decade, the use of highstrength concrete has gone from the exception to the norm. Uses of concrete strengths exceeding 10,000 psi are easily achievable on any building. The use of cold or hot weather concrete, high-performance concrete, self-consolidating concrete, architectural concrete, etc. is increasingly common, even for small projects. The material itself is not the same as it once was. The standard mixture of cement, water, stone and sand that the Romans perfected now regularly comes with a wide range of chemical admixtures that can vastly improve the composition, strength and performance capabilities of the concrete.

Most engineers may not be directly responsible for the concrete mix design; however, almost all structural engineers are responsible for the review and evaluation of the mix design for their project. Whereas the lab, plant, and contractor may be directly responsible for ensuring the concrete meets the specified design strength, it often falls to the Structural Engineer of Record to control the variables in the field conditions, assist in troubleshooting and make suggestions for improvement.

The goal of this article is to provide a general overview of primary concerns and highlight the many common issues experienced in the field on typical projects. For some professionals, this information may be new and informative, for others, it may just be a refresher.

Ensuring Quality Concrete From Mix to Plant to Placement

By J. Benjamin Alper, P.E., S.E. and Cawsie Jijina, P.E., SECB

The Pre-Concrete Conference J. Benjamin Alper is an Associate at Severud Associates and serves as the Quality Control Officer for Severud Associates’ inspection services. He can be reached at JAlper@severud.com.

Cawsie Jijina is a Principal at Severud Associates and serves as the Deputy Technical Director for Severud Associates’ inspection services. He can be reached at CJijina@severud.com.

The pre-concrete conference is the forum to get together all relevant players, architect, engineer, owner, contractor, concrete sub-contractor, concrete supplier, testing laboratory, special inspector, and ensure that the entire designconstruct team is on the same page. Even in small projects, it is essential to have this meeting as it can help avoid future misunderstandings, streamline the submittals process and expedite the project. Key components include an agenda, distributed before the meeting, a respectful discussion during the meeting, and timely written confirmation of the decisions arrived at during the meeting. On larger projects, a written acknowledgment of the Meeting Minutes by all attendees and relevant parties is mandatory.

The Mix One of the most important steps in ensuring concrete quality happens well before placement of the first batch of concrete. The concrete mix

16 June 2016

must be reviewed and approved by the Structural Engineer of Record (SEOR), and must happen well before the first placement of concrete occurs.

While the formats of design mixes will vary slightly between producers, the basic information required includes: ✓ Name of Project ✓ Date of Mix Design ✓ Compressive Strength of mix and Required Compressive Strength ✓ Number of days until specified strength is reached ✓ List of ingredients and their quantities ✓ Slump or Slump Flow ✓ Density ✓ Percentage of Air ✓ Type of Cement ✓ Supplementary Cementitious Materials ✓ Water to Cementitious Content Ratio ✓ Initial Setting Time Test results or trial data, mill reports for cement, and specification sheets on the admixtures to be used must accompany the mix design.

Admixture The admixtures available for concrete are numerous. While the discussion of each admixture is beyond the scope of this article, it is important to be aware of the general types of admixtures available. General categories for admixtures include: • Water Reducers/Superplasticizers – used to increase slump (and often strength) with less impact to the water to cementitious material ratio • Retarders/Accelerators – used to accelerate or delay the setting time of the concrete • Air-Entraining Admixtures – used to increase the air content of the concrete.

• Other – Corrosion Inhibitors, Coloring Admixtures, etc.

Test Results/Trial Data Per ACI 318, the design mix must achieve a required average compressive strength (f 'cr) higher than the design compressive strength (f 'c) specified. This requirement for the overstrength accounts for expected deviations in the strength of the delivered concrete. This design strength needs to be justified, either by field experience or by trial mix. The use of field experience to justify concrete strength involves the use of cylinder test results from previous placements to justify the specified strength.

ACI 318 provides factors for adjusting the field results based on the quantity of data sample available. For concrete strength substantiated based on field results, f 'cr is calculated as follows (Table 5.3.2.1 of ACI 318-11):

For f 'c equal to 5,000 psi or less, f 'cr shall be the greater of the following equations: f 'cr = f 'c + 1.34Ss f 'cr = f 'c + 2.33Ss – 500 For f 'c greater than 5,000 psi, f 'cr shall be the greater of the following equations: f 'cr = f 'c + 1.34Ss f 'cr = 0.90 f 'c + 2.33Ss where Ss is the sample’s standard deviation.

The use of trial mixes involves the preparation of several design mixes in a laboratory with varying water to cementitious ratios. The results are plotted on a graph of the trial mixes.

The mix is selected from the curve. For concrete strength substantiated based on trial mixes, f 'cr is as follows (Table 5.3.2.2 of ACI 318-11): For concrete strength less than 3,000 psi, f 'cr = f 'c + 1000psi.

For concrete strength between 3,000 psi and 5,000 psi (inclusive), f 'cr = f 'c + 1200 psi.

For concrete strength greater than 5,000 psi, f 'cr = 1.10 f 'c + 700 psi.

For example, for 6,000 psi concrete, the required average compressive strength of the trial mix must be at least: 7,300 psi (=1.10 * 6,000 psi + 700 psi).

Regardless of the methodology used in the mix design preparation, it is important to ensure that the results being used to justify the strength of the concrete are current, as many of the ingredients in the mix are natural and their properties can change over time.

Statistically, these methods should ensure that the average of the three concrete cylinder tests is greater than the specified f 'c virtually all the time. ACI 318 permits the use of concrete mixes without test data for concrete strengths of 5,000 psi and lower when permitted by the SEOR. This latitude is not recommended except in specific isolated circumstances. For high strength concrete mixes, the use of the higher f 'cr values, per ACI 363, is recommended.

Common Mix Design Issues ‘Old’ Mixes The attempted use of ‘old’ mixes (test results not current, typically greater than the past 24 months) by suppliers is not uncommon.

ACI 318-08 added the requirement that test results be no more than 12 months old. ACI 318-11 extended this period to 24 months.

As many of the materials are naturally derived, changes in sourcing or other changes may greatly impact the concrete performance.

Mix Not Appropriate for Use A lot of varying issues can fit in this category.

Most commonly, these issues are related to

the placement slump – for example, receiving a mix design with a 3-inch slump for a project where all concrete is to be pumped.

Other issues could include the use of larger than appropriate aggregate specified for a pump mix. Imagine if the contractor tried to pour self-consolidating concrete (SCC) in concrete stairs (a contractor seriously attempted this on one of the author’s projects). With the wide variety of available admixtures and concrete products, virtually every single desired performance requirement is attainable with the proper mix design, making the use of generic concrete mixes unacceptable.

Mix Usage Not Indicated Often there will be numerous design mixes on a project, their presence dictated by the need for varying design strengths or varying workability and performance concerns.

Clarity for a mix’s intended use is vitally important, and it is up to the structural engineer to issue clear and precise direction on this subject.

Materials Not Available There are times where the components that make up a concrete mix may not be readily available. Lately, with the closing of coal-fired power generation plants and the scarcity of steel mills, the procurement of Fly Ash and Blast Furnace Slag has become a serious issue. Slag can be shipped from as far away as Brazil. Approving a mix with a material that is not readily available is not beneficial to the project and not environmentally sustainable. While it should be the mix designer’s responsibility to ensure availability before sending the mix for approval, it is still good practice to question any products which you believe may not be readily available.

Compressive Strength Test Age Incorrect ACI 318 is explicit that compressive strength is based on 28 days unless the design drawings or specification indicate otherwise. For high strength concrete, 56-day and 90-day mixes are not uncommon. However, the design mix should achieve the specified strength within the period requested. ‘Slow’ mixes can sometimes affect the construction schedule as it relates to the removal of shores and reshoring operations. Remediation of structural elements where concrete has not met its design strength becomes more complicated when test information is unavailable for greater lengths of time.

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Problems with Test Data Errors in test data are hard to find and are mostly the results of a careless error by the preparer of the mix. These issues can include incorrectly specified concrete strength requirements (f 'cr), the omission of the modification factor for the standard deviation (Ss), and errors in numerous variables that make up data on which a mix design is based.

Mix Design Issues for High Rise Construction High Rise Construction, along with other construction with high concrete demands, bring its own set of issues specifically related to the concrete mix design. Selecting the appropriate mixes for these types of projects is complicated, but it is worth mentioning some of the most relevant issues.

High Compressive Strength Achieving high strength concrete goes beyond simple water to cementitious content ratio.

Special consideration needs to go to the admixtures and the aggregate used. Carefully choosing the aggregate from specific quarries is important, and the sourcing needs to be consistent throughout the project.

Modulus of Elasticity On tall buildings, it is often not only the strength but the stiffness of the concrete that is critical. The simple ACI equations to calculate the modulus of elasticity often are less accurate for higher strength concretes.

ACI 363 provides recommendations for adjusted values when using high strength concrete, but it is still often inaccurate when higher strength concretes come into play. The testing associated with the original code writing is one reason for this fall-off in accuracy. The majority of the prescribed provisions for elasticity, shear, etc. have their genesis in multiple concrete laboratory tests performed at a time when compressive strengths in the 4,000 psi to 5,000 psi range were standard. Extrapolation of these test results to concrete in the 10,000 psi and higher range is circumspect. It is, therefore, important to establish an appropriate testing program specifically tailored to the needs of your upcoming building. Tests to arrive at the correct Modulus of Elasticity (MOE) for a high strength design mix are time-consuming. Not all testing laboratories are equipped to perform them, and even lesser numbers of engineers and technicians are qualified to interpret the test results. continued on next page

These tests need to be planned and executed very early in the in the design to allow for adequate fine tuning of the design mix.

Extended Workability Because of the quantities of concrete, the thickness of the members being poured, and the heights to which the concrete needs to be pumped, concrete for tall buildings requires extended workability. Hydration control admixtures and other admixtures help in keeping concrete workable for extended periods. They also help slow down the hydration process in large concrete members.

Mix Design: Looking Forward As with many trends in the construction industry, there will be continued advances in concrete. Post-consumer recycled ground glass (ground glass harvested from municipal recycling programs) is already being tested as a substitute for Fly Ash and Blast Furnace Slag.

The concrete using this sustainable material was designed to attain strengths up to 14,000 psi and will be commercially used on a castin-place concrete building sometime in the next few months.

Reduction in Cement Because of the need to reduce the environmental impact of cement (one pound of cement releases one pound of carbon monoxide into the atmosphere), municipalities have considered or passed edicts which require a reduction in cementitious content in the production of concrete. If these efforts are successful, then they will undoubtedly affect mix designs in the future.

Self-Consolidating Concrete (SCC) The use of SCC to increase the speed of placement, quality of the finished surface and reduce labor costs is becoming more and more prevalent. In the future, more and more sites will be using SCC almost exclusively for formed members for these reasons.

From The Plant to the Site Few engineers ever see the inside of the concrete plant which batches and distributes the concrete to project sites. Most concrete projects do not require special inspections at the plant. The engineer is, therefore, reliant on the supplier to properly batch the concrete without supervision. It is important for checks and balances to occur on-site to help ensure that any potential issues with the concrete batching are caught and resolved before placement.

Initial Receipt of the Concrete on Site When concrete arrives at a construction site, the special inspector must check the batch ticket to ensure the concrete mix conforms to the approved mix. Thus, every truck must come with a computerized batch ticket. The batch ticket must indicate the truck number, the total batch size, the strength measured in psi, the batch time, and the amounts of materials added at the plant. The ticket should also indicate the percentage of moisture within the aggregate. The printout from the plant indicating concrete strength and batch size alone is not sufficient for verification of the mix design and any truck without a full batch ticket ought to be rejected since verification of the mix is not possible. It is imperative that this review happens when the truck first arrives on site. The Inspector should reject incorrect concrete mixes and instruct the truck to return to the plant.

Adding Water on Site The most common reason for low concrete test results is the addition of unauthorized water to the concrete mix at the site. Concrete must have no more water in it than is indicated in the approved mix design. The best method to ensure this is to prohibit the addition of any water on site. Unfortunately, when transit time to the site is excessive, and a loss of slump occurs by the time the concrete is ready to be placed on the site, the most common response is the addition of water. Occasionally, due to long travel times, a concrete batch plant will send a truck with less than the prescribed amount of water. In these cases, the plant, Special Inspector and SEOR have agreed on a plan of action to combat delayed arrivals and the balance of the water may be added to the concrete at the site.

After placing concrete from the truck, adding water to the mix is difficult since it is not possible to determine the quantity of concrete left in the truck nor the amount of water that can still be added. The contractor should be required to keep superplasticizer on site, to be used in specific instances to increase workability. The use of superplasticizer in this method should be planned with the SEOR in advance, along with other placement parameters like mixing times and ambient temperatures. Test cylinders need to be representative of the concrete being placed and need to be taken at the truck and the point of placement. In the event water was added to the concrete mix after the initial batching (either authorized or unauthorized), take test cylinders after all materials have been added.

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Site Testing The standard tests done at each site include slump, air entrainment, temperature, and unit weight. Less common, but very important, is microwave testing.

Microwave testing utilizes a microwave to remove the water from a concrete sample.

Measurements of the sample before and after being microwaved allow for a field determination of the actual amount of water in the specific concrete sample tested.

In high strength concrete, it is common to utilize this test for every concrete placement. For other projects, microwave testing may not be utilized but can be used as a tool in troubleshooting problems in the field. If concrete breaks are low on a project, implementing microwave testing can provide in situ information on the water to cementitious material ratio and can help pinpoint the issue, or at least eliminate the water content of the concrete as a potential issue.

When All Else Fails, Grab a Bucket The world is uncertain, and stuff happens.

Accordingly, basic contingencies need to be in place should things not go per the initial plan. One common issue is the concrete tester arriving late or not arriving at all. Without an inspector onsite, in most jurisdictions, no concrete can be placed.

Unfortunately, many concrete contractors will place the concrete which results in the unfortunate circumstance that “placed” concrete will need to be removed and replaced, or the concrete strength verification will need to be done by the removal and testing of concrete cores from major structural elements.

Neither option is desirable. One possible mitigation strategy is to fill several buckets with concrete, “rod” the concrete and then use this concrete mix to create cores. At a later date, test the cores and determine the strength after the application of appropriate reduction factors.

Low Breaks Happen Even after meticulous planning, inspection, and execution, statistically low concrete strengths can and will happen. The concrete special inspector must document where the concrete from each concrete truck is placed within the structure. This “placement map” can help determine the specific location where concrete with low strength was placed and can be very helpful in evaluating the structural impact and the design of remediation measures.

Concrete Placement Concrete placement consists of the conveying, depositing, and finishing of slabs and curing the concrete. Proper monitoring of each step is important. Once the concrete leaves the truck (or pump, or both) and placement begins, any changes that occur to the concrete will no longer be telegraphed through the concrete test cylinder results.

Conveying and Depositing The primary concern when conveying concrete from the mixing apparatus to the point of placement is to avoid concrete segregation. Common issues where segregation can occur are: Free Falling Concrete

Over Vibrating Concrete To properly consolidate the concrete, the use of a vibrator is required. However, the use of the vibrator as a tool to move the concrete can over-vibrate and segregate the concrete. Segregated concrete often happens in beams or shear walls where construction personnel will set up the concrete placement on one end of the structural element and attempt to use the vibrator to push the concrete across that element. The problem becomes moot when using self-consolidating concrete (SCC) since SCC negates the use of vibrators. SCC should be used in all formed members.

Concrete Not Vibrated Not vibrating concrete is only appropriate in a few instances. Even concrete on metal deck requires some form of vibration and consolidation, a condition often overlooked on steel framed buildings.

Curing Proper curing after placement is important.

It is not only a strength concern. Improper or no curing can affect the floor finishes and lead to shrinkage cracking. Curing options include wet curing and chemical curing. Address curing methods at the preconcrete conference. The concrete inspector needs to ensure utilization of proper curing methods. Hot and cold weather concrete placement procedures dictate to keep

Conclusion For quality concrete, the entire designconstruct team must understand the rules of concrete placement, execute an appropriate curing procedure and have pre-set corrective measures in place that can be cooperatively executed well before the first concrete placement.

For more information on mix design review and concrete placement and curing, some valuable resources include: • Manual of Concrete Practice (ACI), including the following sections: ACI 211.1-91 (Rev. 2009) Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete.

ACI 301-10 Specifications for Structural Concrete for Buildings.

ACI 302.1-04 Guide for Concrete Floor and Slab Construction.

ACI 305R-99 Hot Weather Concreting.

ACI 306R1-90 (Re-approved 2002) Cold Weather Concreting.

ACI 308 (Rev. 2008) Standard Practice for Curing Concrete.

ACI 318-14 Building Code Requirements for Reinforced Concrete.

• Design and Control of Concrete Mixes (PCA) • Manual of Standard Practice (CRSI) • Guidelines for Reviewing Concrete Mix Design (SEAONC) Please note that these resources along with the information in this article may vary based on your local building code.▪

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Dropping concrete from heights over the reinforcement in columns and walls can cause the aggregate to segregate. In general, concrete shall be dropped from a chute when there is a concern about segregation.

concrete in a specific temperature range during curing operations. A simple way to monitor these temperature changes is by using a calibrated maximum-minimum thermometer. Thermometers are available with a probe on one end that can be tucked under a blanket or in the concrete form. The probe will track the approximate temperature on the concrete surface during curing.

In addition to properly curing horizontal surfaces, the concrete cylinders taken need to be properly stored in an insulated curing box. During cold or hot weather days, the maximum-minimum thermometer can be used to monitor the temperature of the curing box. If there are low breaks during hot or cold weather, one of the first suspects is the curing method of the cylinders. By monitoring these temperatures, you can proactively eliminate this as a concern when low concrete breaks data.

Building Blocks updates and information on structural materials

S

teel rebar in concrete structures is usually protected by a passive film formed due to the alkaline environment of fresh concrete. However, this protective film can be destroyed by the ingress of chloride or carbonation of the concrete cover layer. Once damaged, corrosion initiates in the presence of oxygen and moisture. The volume of corrosion products is usually two to six times greater than the volume of the original steel it consumes, resulting in tensile stress in the surrounding concrete. When the stress reaches the tensile strength of concrete, cracking/spalling occurs in the concrete cover.

In the meantime, corrosion reduces the steelconcrete bond strength and the cross-sectional area of steel rebar. Therefore, steel reinforcement corrosion is one of the main causes of premature deterioration in reinforced concrete structures.

Many methods or techniques have been developed to protect steel rebar from corrosion in concrete structures, such as the addition of corrosion inhibitors or highperformance admixtures, use of protective coatings or corrosion resistant bars, and others. Among these methods, the use of protective coatings is one of the most effective and efficient methods because it can establish a physical and chemical barrier between the steel rebar and the corrosive environment.

This article presents protective coatings used to prevent steel rebar from corrosion in concrete structures, mainly focusing on hot dip galvanizing (HDG), fusion-bonded epoxy (FBE), and chemical reactive enamel (CRE).

Steel Rebar Coatings for Concrete Structures

By Fujian Tang, Ph.D.

Hot Dip Galvanizing (HDG) Fujian Tang is a Postdoctoral Research Fellow at Missouri University of Science and Technology. His research mainly includes steel reinforcement corrosion, steel rebar protective coatings, and development of optical fiber corrosion sensors. He may be reached at ftkr7@mst.edu.

The use of zinc as a coating to protect steel in concrete structures dates back to about 1900. In the following decades, especially after WWII, zinc was regularly used as a coating material for bridge and highway construction in the northern states of the U.S. and in Canada. Zinc coating protects steel rebar in two ways. First, it serves as a physical barrier between the steel bar and the corrosive environment. Second, it corrodes preferentially and provides sacrificial cathodic protection to the steel.

Zinc can be applied to the steel bar in a number of ways including hot dipping, electroplating, spraying and mechanical alloying. Hot dip galvanizing (HDG) is the most common method of zinc coating. The steel bar is immersed in a molten zinc bath at a temperature around 450°C (842°F). The metallurgical reaction takes place between the steel bar and the zinc, producing a series of iron-zinc alloy layers. Four typical layers are present from the steel substrate outwards, including the gamma layer (75% Zn, 25% Fe), the delta layer (90% Zn, 10% Fe), the zeta layer (94 % Zn, 6% Fe), and the eta layer (100% Zn) as shown in Figure 1a.

The unique structure of HDG coating offers many important advantages. First, it metallurgically bonds to the underlying steel, which avoids under-film corrosion. Second, the iron-zinc alloy layers are harder than the underlying steel, therefore producing a tough and abrasion resistant coating. In this regard, transportation and handling processes require no special care.

One concern for the use of HDG coated steel bar in concrete is that some chemical reactions occur when the zinc is in contact with the fresh concrete. The outer eta layer (pure zinc) will vigorously corrode until passivation occurs and the concrete hardens. The chemical reactions release hydrogen gas and produce calcium hydroxyzincate (CHZ) crystals, Ca(Zn(OH)3)2. On one hand, the hydrogen gas increases the porosity at the transitional zone between the coating and the surrounding concrete, resulting in a reduction in the bond strength. On the other hand, the CHZ crystals tightly adhere to the zinc surface and interact with the adjacent cement matrix, resulting in strengthening and densification of this zone. These two actions counteract each other in most cases. Therefore, most test results indicate that the use of HDG coated rebar has a negligible effect on bond strength of reinforcement in concrete.

Chemical reactions in fresh concrete also decrease the HDG coating thickness, shortening the service life of structures. Therefore, special treatment is usually made to passivate the zinc surface. For example, the freshly galvanized steel is usually quenched in water containing sodium dichromate. However, this practice is extremely limited due to growing concerns regarding both

Figure 1. Microstructure of (a) hot dip galvanized zinc (from American Galvanizer Association), (b) fusion-bonded epoxy, and (c) enamel.

20 June 2016

the human health risk and environmental hazards associated with the use of chromates.

Both laboratory and field studies show that the critical chloride corrosion threshold of HDG coated steel bar is greater than the threshold for conventional steel bar, and the average time to corrosion initiation in bridge decks for HDG coated steel is 4.8 years, compared with 2.3 years for bare steel bar. ASTM A767/A767M Standard Specification for ZincCoated (Galvanized) Steel Bars for Concrete Reinforcement specifies the use of HDG coated steel rebar in concrete structures.

Th e eff ectiveness of FBE coating in bridges in Pennsylvania and New York also protecting reinforcement steel against cor- indicated adhesion reduction within 6 to 10 rosion remains controversial. Several field years of placement in concrete. Most probstudies have reported good performance of lems are attributed to the breaks and defects FBE coated reinforcement after up to 20 in the coating during fabrication, transporyears of service. Other studies have reported tation, handling and concrete vibration. examples of failure after 10 to 15 years in Improvements have been made in the quality service. The most impressive example is the control of FBE-coated reinforcements regardcorrosion-induced cracking and spalling of ing reducing the numbers of breaks in the marine bridge substructures in the Florida coating and in improving its adhesion to the Keys in the mid-1980s, just seven years steel rebar. ASTM A775/A775M Standard after construction. Field studies performed Specification for Epoxy-Coated Steel Reinforcing 1 5/6/2016 4:37:38 PM betweenAutodesk-Structure-Magazine-05.2016.pdf 1996 and 1998 on some highway Bars and ASTM D3963/D3963M Standard

Fusion-Bonded Epoxy

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Fusion-bonded epoxy (FBE) coating was identified as an effective method of corrosion protection in the early 1970s when, in North America in the late 1960s, premature deterioration of highway bridge decks was discovered as a result of corrosion of the reinforcing steel. It remains the primary method to protect steel bar in concrete structures against corrosion damage. Based on the 2011 National Bridge Inventory, there are more than 74,097 bridge decks using epoxy-coated reinforcing steel, while only 1,072 decks utilize galvanized steel in the US. Epoxy commonly adheres to the steel bar through the electrostatic coating. In this process, mechanically blasted steel rebar is first heated to a temperature in the range of 180 to 250°C (356 to 482°F), and then the charged epoxy powder particles are electrostatically sprayed onto the hot steel bar. The epoxy powder melts, flows, and cures on the bar surface, which then is quenched in water at ambient temperature, finally producing a continuous protective coating. Figure 1b shows the typical microstructure of FBE coating on a steel substrate. Some air bubbles are present near the steel due to chemical reactions in the fusion process.

The epoxy coating has many advantages compared to other coatings. The fact that FBE does not get damaged when it is bent during fabrication is the most obvious. However, the weak bond with surrounding concrete and the underlying steel limits its use. ACI 318-14, Building Code Requirements for Structural Concrete, specifies at least a 20% increase in the development length for FBE coated steel bar compared to a conventional black steel bar. Moreover, extreme care is required when handling and transporting FBE coated rebar to avoid damage and prevent future under-film corrosion.

Comparison of HDG, FBE and CRE.

Properties & Performance

HDG

FBE

CRE

Microstructure

Layered zinc-iron alloys

Isolated air bubbles

Connected air bubbles

Adherence with Steel

Metallurgical bond

Physical bond

Chemical bond

Bond with Concrete

Chemical bond

Physical bond

Chemical bond

Special Handling

No

Yes

Yes

Abrasion Resistance

Excellent

Poor

Excellent

Corrosion Resistance

High

High

High

Chloride Threshold

High

High

Varying

Overlap Length

Equivalent to bare steel

Longer

Shorter

Cost (US$/lb.)

0.47

0.42

0.35

Specification for Fabrication and Jobsite Handling of Epoxy-Coated Steel Reinforcing Bars should be used to specify handling and fabrication of FBE coated rebar.

Chemically Reactive Enamel The technique of enameling dates back over 3000 years when it was used to decorate the surfaces of objects for aesthetic purposes.

During the industrial revolution, there was a resurgence in its use as a coating material applied to iron and steel for other purposes, such as corrosion protection, heat resistance, abrasion resistance, hygiene, and so on.

Today, enamel is widely used in domestic appliances, industrial environments, and the construction industry. In the home, cooking utensils are coated with enamel because it is easy to clean, can prevent the growth of bacteria, does not absorb odors, and is not attacked by food acids. In industry, it is commonly used as a protective coating for the interior of tanks, boilers, ovens, tubes and stove components. In the construction industry, enamel is used as decoration for cladding buildings or interior decor, as it combines a rigid steel substrate with various surface effects such as texture, reflectivity, salt and pepper effects and metallized colors.

Either a wet or dry process is used to apply enamel to a steel surface. For the wet process, steel is dipped into a vat containing enamel slurry or enamel slurry is sprayed on the surface of the steel. The steel with enamel slurry is moved into a furnace with a temperature between 750 and 850°C, where the enamel slurry dries, melts, and flows. After several minutes, it is moved out of the surface, cools down and hardens to a smooth, durable vitreous enamel on the steel. The dry application is carried out by electrostatic spraying before moving into the furnace. Figure 1c (page 20) shows the typical microstructure of enamel

Figure 2. Microstructure of (a) chemical reactive enamel (CRE), (b) double enamel, and (c) sand particle modified enamel.

coating on a steel substrate. Some air bubbles are present due to chemical reactions between the oxides in the enamel frits and the carbon in the steel in the firing process.

Use of enamel coating to protect steel rebar against corrosion in concrete structures was first investigated about ten years ago. Commercially available enamel was modified by adding Portland cement to produce a chemically reactive enamel (CRE) coating as shown in Figure 2a. This CRE coating not only improves the corrosion resistance of steel rebar but also enhances its bond strength with the surrounding concrete. However, the addition of Portland cement changes the microstructure of enamel coating from solid with isolated air bubbles (Figure 1c) to porous with connected channels (Figure 2a), reducing its corrosion resistance. Therefore, double layer enamel coatings (Figure 2b) and sand particle modified enamel (Figure 2c) coatings have been proposed and investigated. The double enamel consists of an inner black enamel and an outer CRE with the aim to improve its corrosion resistance through the inner black enamel and enhance the bond strength by the outer CRE. The sand particle was used to increase the bond strength through the rough surface and, in the meantime, maintain the corrosion resistance.

Despite these efforts, enamel coating has one fatal drawback, brittleness, which limits its wide application. It can be easily damaged during transportation and handling, causing potential pitting corrosion.

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Ongoing Research To sum up, none of these three coatings is perfect, and their properties and performance are summarized and compared in the Table. Chemical reactions in fresh concrete limits wide application of HDG coated steel bar; weak bond with underlying steel and surrounding concrete is the drawback of FBE coated steel bar; and brittleness of enamel coating restricts its application. Despite these limitations or drawbacks, extensive research efforts have been performed and continue to increase the performance of these coatings.

In a process to modify the dendritic microstructure by an alloying addition such as strontium, both the corrosion resistance and the mechanical properties of the HDG coating have been improved. The passivation of HDG coating before placing in concrete can be achieved by applying a cerium conversion coating, sol-gel coatings doped with organosilane and cerium, or a two-step roll coating phosphate/molybdate treatment. Adding nanoparticles can also improve the performance of the epoxy coating.

The incorporation of nanoparticles into epoxy resins offers environmentally benign solutions to enhance the integrity and durability of coatings, since the fine particles dispersed in coatings can fill cavities and cause crack bridging, crack deflection and crack bowing. For enamel coating, its brittleness can be reduced by adding fibers. Duplex coatings inherit the advantage and resolve the disadvantage of individual coating such as epoxy/zinc coating. Epoxy/enamel coatings have also been investigated.▪

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Structural teSting issues and advances related to structural testing

T

he National Council of Structural Engineers Associations (NCSEA) recently issued a position statement on special inspections clarifying their importance to protecting the public. One assertion made in this statement is that special inspections are “…essential for the satisfactory performance of any project.” While many design professionals have a very clear understanding of the special inspection requirements of the International Building Code (IBC), there are also many that still do not understand the importance of Chapter 17 nor the role they play in ensuring adequate performance of special inspections. Regardless of how special inspections are locally enforced, the Structural Engineer of Record (SER) has some very specific duties in regards to the special inspection program.

By adhering to the duties outlined in this article, you can help protect yourself from liability, provide a better product to the building owner, and provide an increased level of life safety.

The Design Professional’s Role in Special Inspections

By Chris Kimball, S.E., P.E., MCP, CBO

Chris Kimball is the Utah Regional Manager for West Coast Code Consultants, Inc. Mr. Kimball provides plan review services to many jurisdictions throughout the Western United States. He can be reached at chrisk@wc-3.com.

Design Professional in Responsible Charge

While structural plans typically list the special inspection and testing requirements for structural components, who is responsible for specifying the special inspection requirements for the nonstructural items? Section 1704.3 of the IBC states that the “…design professional in responsible charge shall prepare a statement of special inspections.”

The “design professional in responsible charge” for these nonstructural components is often the architect, mechanical engineer, or other members of the design team.

The entire design team should coordinate the overall special inspection and testing requirements for every project. The next step is to compile these requirements into one project-specific Statement of Special Inspections (SSI). The SSI can be included in the construction documents or as a separate document to be submitted to the building official. There are some jurisdictions that now specifically require the SSI to be included on one of the first sheets of the construction documents, and require it to note clearly all structural and nonstructural items that require special inspections and tests.

Statement of Special Inspections (SSI) As previously referenced, the design professional in responsible charge is required to provide an SSI for every project. The SSI provided on most projects is often missing many of the key components required by the IBC.

24 June 2016

Section 1704.3.1 of the IBC details the important requirements of an SSI. There are four key elements, described below.

1) Materials Chapter 17 of the IBC divides the types of materials requiring special inspections or tests into 16 major categories. The material categories listed in the IBC include: • Fabricators • Steel Construction • Concrete Construction • Masonry Construction • Wood Construction • Soils • Deep Foundations • Wind Resistance • Seismic Resistance Inspections • Seismic Resistance Testing • Sprayed Fire-Resistant Materials • Intumescent Coatings • EIFS • Fire-Resistant Penetrations • Smoke Control • Special Cases For clarification, this does not mean that only these items will require special inspections and tests. The last item, “special cases”, is a catchall category to cover items not specifically addressed. All items that are critical to lifesafety and property protection, and require special expertise, require special inspections.

Some specialty items that could also require special inspections and tests include deep excavation shoring, fiber-reinforced-polymer installations, etc.

2) Type & Extent of Inspections/Tests Not only should the materials, as noted above, be listed in the SSI, but the type and extent of the inspections and tests should be clarified. The IBC provides several examples as shown in Table 1605.3, Required Verification and Inspection of Concrete Construction.

Unfortunately, many design professionals rely too much on these IBC Tables and simply copy them to their general structural notes. With each new code cycle, more of these Tables from the IBC are now being removed. Instead, the actual special inspection and testing provisions are now simply referenced to the applicable design standard (i.e. AISC 360, AISC 341, TMS 402, etc.).

3) Seismic or Wind Requirements Too often, the SSI provided for a specific project does not list the specific seismic- and wind-related special inspections and tests as outlined in Sections 1705.10 through 1705.12 of the 2012 IBC. In previous versions of the IBC, the wind and seismic requirements had

separate sections within the code and were often overlooked. Now they are included specifically in Section 1705 as one of the 16 major categories noted previously. Each SSI should clearly define the specific wind and seismic requirements.

contractor, design team, authority having jurisdiction, and to the special inspection agency as to what specific inspections and tests are required.

Oversight of Special Inspections

4) Inspection or Test Frequency Since the term “Statement of Special Inspection” was added in the 2006 edition of the IBC, the requirement is to note specifically whether or not a particular special inspection or test is to be “continuously” or “periodically” performed. Terminology issues have become increasingly difficult now that referenced standards outline many of the special inspection requirements. Those standards, in some instances, do not use the same terminology as the IBC. Terminologies are clarified in the 2015 IBC, as it states, “…identification as to whether it will be continuous special inspection, periodic special inspection or performed in accordance with the notation used in the referenced standard where the inspections are defi ned.” Th e SSI must list the frequency of the special inspections or tests to be performed, regardless of the term used.

It is all too common for the SER to simply copy the special inspection tables from the IBC on their general structural note sheet and that is the extent of the SSI provided. The main problem with this practice is that the provisions laid out are not necessarily specific to the project in question.

As an example, the plans may include Table 1705.7 of the IBC, which covers the special inspection requirements for driven deep foundation elements, yet the project in question does not include any deep foundations.

Section 107.2.1 of the IBC notes that the construction documents “shall be of sufficient clarity to indicate the location, nature and extent of the work.”

The SSI should not provide extraneous information. As an example, if IBC Table 1705.3 (Required Verification and Inspection of Concrete Construction) was included in its entirety yet prestressed concrete or shotcrete will not be provided, then the SSI is not limited to the project in question. The SSI must provide a clear message to the owner,

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The SSI should be Project-Specific

The IBC requires that special inspection and testing reports be submitted directly to the building official and directly to the design professional in responsible charge. It further states that discrepancies brought to the attention of the contractor, which are not corrected

to-date, should be brought to the attention of both the building official and the design professional in responsible charge. This section highlights the key role that the SER has in ensuring the performance of special inspections, as required throughout the project. Not only should the SER be reviewing the special inspection reports to ensure construction of all items in accordance with the approved construction documents, but the SER should also be verifying inspections on all items which require inspections and testing and at the frequencies specified in the SSI. continued on next page

Performing Special Inspections Section 1704.2.1 of the IBC states that the “…design professional in responsible charge… are permitted to act as the special inspector for the work designed by them, provided they qualify as special inspectors.”

While it is true that very few design professionals have the requisite experience and training to perform ultrasonic testing of demand critical welds, the SER would be the ideal person to perform visual inspections of structural components.

The October 2006 edition of Civil + Structural Engineer magazine included a feature article entitled “The Practice of Special Inspections” (Eych, et. al.). In this article, the author states, “There is probably no single act that an engineer can do that is as effective at reducing his or her liability exposure as performing inspections during construction.”

This same article states, “It is not that the contractor (or special inspector [author comment]) is intentionally taking liberties with your design, but all of the tradesmen may not fully understand the subtleties of your drawings or your design intent.” Too often we point the finger of blame to the contractor or special inspector for missing items, yet sometimes they honestly may not know the importance of a certain detail, and they do not have the understanding of how things are supposed to work together as does the SER. The following experience highlights the importance of the SER on-site presence as much as possible, either as a special inspector or simply as a structural observer. A local

building inspector was concerned about a pedestrian bridge that spanned between two buildings, even though special inspections had occurred throughout the installation of the bridge structure. Something did not seem right to the city inspector prodding them to spend some time looking at the bridge details on the approved construction documents. The plans clearly called for a slip connection between the bridge and one of the buildings. After climbing the scaffolding and taking a look beneath the bridge, it was apparent that the required slip connection was not provided (see Figure).

While the support brackets were fabricated appropriately, with slots for the slip connection, the bracket was directly welded to the bridge structure, therefore creating a fixed connection.

Thank goodness for the city inspector and their inclination to take some extra time on this key detail. Even though special inspections occurred, the special inspector was more likely interested in ensuring that the weld was done correctly and not that the weld should never have been there in the first place. As this is a critical detail in the structural design, the SER would most likely have called it out to the contractor right away.

An article titled “Tornadoes Call QA-QC Into Question,” Engineering News Record (ENR) (Parsons, February 2016), highlights another example. This article discusses recent damage reports from 12 tornadoes across North Texas that occurred during the afternoon of December 26, 2015. A total of 13 people died during the event, and over

Prefabricated slot for bolted slip connection

A pre-fabricated slot for a bolted slip connection.

Note – just off the left edge of the photo are fillet welds of a bracket to the bridge structure.

$1.2 billion in damage was estimated. After the event, one of the volunteer inspectors noted that there were improper foundation connections and that there were no visible roof attachments. The article also stated that “all exterior and interior wall construction was inspected and approved by a thirdparty inspection firm at numerous intervals throughout the construction process.” This article highlights the need for the SER to take an active role as the special inspector whenever practical. The SER would more than likely take extra time to ensure that proper connections are provided on their projects, thus ensuring a complete load path is in place.

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The SER plays a key role in ensuring that special inspections and material testing are performed adequately on their projects. The SER works with the entire design team to create a detailed and project-specific SSI, providing oversight of the special inspection and testing reports provided during construction, and in performing special inspections and structural observations whenever possible. When the SER takes an active role in the special inspection program, they limit their liability, deliver a better product to the building owner, and ensure an increased level of life safety for the public.▪

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June 2016

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56 LEONARD

By Silvian Marcus, P.E., F. ASCE, Hezi Mena, P.E. and Fatih Yalniz

Villas in the sky.

T

he southwest corner formed by Leonard Street and Church Street in New York City is ground to the 56 Leonard project, a new and unique 57-story residential development comprising 480,000 square feet of gross area.

The current economic, cultural and social context of the real estate market in New York City requires serving a continuously changing and diverse group of buyers and investors from all over the world, which in turn has generated a very strong demand for excellence in analysis, design and construction of luxury residential buildings. In 56 Leonard, for instance, each floor gives the impression of being a singular, virtually independent structure carefully placed and balanced over yet another unique structural entity forming the floor below.

The resulting sensation is that of a vertical community of uniquely “stacked” homes. In fact, the residents of 56 Leonard will each live in a bright, inimitable private home reaching the sky.

Herzog & de Meuron, the architects behind this project, have been known for forward-thinking concepts throughout their careers. In the case of 56 Leonard, these concepts take the form of an innovative stack of individual homes suggesting the new idea of a vertical neighborhood in which each owner can choose a unique residence, albeit in the sky. The vertical neighborhood is a new paradigm in which the penthouse is no longer the single story breaking from the typical floor plan mold. An innovation of this scope and relevance certainly presents an excellent answer to the desire for traditional home ownership in an urban setting that is as unique as its occupants, while reducing the footprint of a conventional horizontal community of homes. In other words, the design of 56 Leonard successfully combines the idea of old-fashioned home ownership with the present vernacular of luxury urban living. The blending of traditional, present and future needs demanded not only the incorporation of forward-thinking solutions but also a complete vision of sustainable and resilient design.

The new tower has a height of 825 feet from the street level and a width of about 78 feet, which results in a daring slenderness ratio slightly above 10. The building includes three mechanical floors located at the 32nd, 46th, and 56th floors, with outrigger and belt wall systems placed on the first two of those stories. The highest residential floor is the 55th level. The 56th mezzanine floor houses a liquid tuned damper to provide adequate structural damping for occupant comfort.

STRUCTURE magazine

Foundation The foundation of 56 Leonard consists of 1,500-ton, 24-inch diameter caissons socketed in bedrock, and 180-ton end-bearing H-piles.

The lengths of caissons and piles range from 90 to 110 feet below the cellar level. Five-foot deep reinforced concrete caps structurally connect the caissons and piles. The caps serve as main supports for the vertical and lateral force-resisting systems.

The existing foundation walls on the north, east and south side of the site are a part of the new structure due to the adjacency of a Metropolitan Transportation Authority underground tunnel to the lot, as well as the column layout of the tower. The reuse of existing foundation walls not only contributed to the reduction of lateral support during the excavation process but also reduced the cost of construction.

Gravity System The tower at 56 Leonard is a reinforced concrete building. The structure is composed of cast-in-place concrete flat-plate slabs supported by reinforced concrete columns and shear walls.

To accommodate the varying apartment layouts throughout the building, which represented the main architectural concept, practically all of the columns had to be relocated from floor to floor by using walking columns. The structural solution was to introduce one- or two-story walls able to transfer the load from one column location above to a different location below. The eccentricity associated with the transfer of vertical load resulted in additional lateral forces, applied at the top and bottom of the transfer walls. Then, rational load paths to the shear walls, present in each story, transferred all additional lateral forces.

The building also has a great number of cantilevered slabs. The thickness of the slab controlled short cantilevers whereas larger ones utilized beams. The largest of cantilevers, which are about 25 feet long, were solved by creating a reinforced concrete Vierendeel truss extending over two stories and engaging the vertical members between them. This structural solution did not have an impact on the architectural intent.

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June 2016

Lateral System The combination of reinforced concrete shear walls and frame action between the flat plates and columns provided the lateral load-resisting system. The reinforced concrete core wall system is located at the center of the tower and acts as the main spine of the tower, providing not only support for gravitational loads but also resistance against wind and seismic forces.

The reinforced concrete core houses elevators and mechanical equipment, and is comprised of several walls connected to each other over access openings by reinforced concrete link beams. Wall thicknesses vary from 30 inches at lower levels to 12 inches at mid-height of the building.

Special enhancements to the lateral load-resisting system were provided to the main reinforced concrete core at the 32nd and 46th mechanical floors by connecting them to the perimeter columns using outriggers and belt walls in two orthogonal directions. The structural interaction between the core wall and perimeter columns induced by these special elements increased the overall building stiffness while significantly reducing lateral displacements.

The tower’s height, limited space and large slenderness ratio imposed stringent demands on the overall strength and stiffness of the structure. Those demands were met economically by using high-strength concrete of up to 12,000 psi. The specified concrete compressive strength ranges from 12,000 psi at the base of the building to 7,000 psi at the top. In addition to the compressive strength, it was necessary to specify a larger modulus of elasticity of concrete than that set by applicable building codes. This requirement aimed to increase the lateral stiffness of the core walls without imposing the premium associated with higher concrete compressive strength or the thickening of the walls. continued on next page

56 Leonard under construction.

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reducing and controlling lateral displacements and accelerations. An LSD, measuring 32 by 36 feet in plan and reaching 10 feet high, was placed at the 56th mezzanine floor. This addition kept lateral accelerations due to the wind within accepted industry limits.

The LSD placed at the top provided additional benefits to the project. While it kept building movement at an acceptable level of human comfort under wind loads, it also reduced the weight of the building thereby minimizing the number of additional materials that the structural system would otherwise require.

The structural analysis and design for the 56 Leonard project used finite element modeling software that assisted the engineering effort aimed at achieving precision during the design process. The modeling reduced the need for an overly conservative structural solution, which is an important factor that tends to influence construction expenditures negatively by requiring larger quantities of materials, which in turn produce a greater environmental and financial impact.

Summary 3D structural model.

Codes and Standards The primary design code for the project is the current New York City Building Code, including its amendments at the time of design.

However, in consideration of the unique distribution of masses throughout the building, it was essential to perform a series of projectspecific wind tunnel tests.

Rowan Williams Davies and Irvin Inc. (RWDI) wind tunnel facilities in Canada performed the tests at various stages of the design. The main objective was to ascertain the wind loading and wind-related response of the tower with respect to hurricane wind loads and human comfort criteria. High-Frequency Force Balance (HFFB) and aeroelastic tests, which are the prevalent methods for wind tunnel testing for tall buildings, were performed. These tests were able to provide design wind loads and main structural response in terms of acceleration.

An essential design requirement for 56 Leonard was the criteria regarding human comfort levels during high winds. Typically, the criteria for wind-induced motion have been established by experiments performed with different groups and ages of the population.

The motion perceived by building occupants is a function of the peak acceleration at the top occupied floor. Since the desired performance is solely for occupant comfort and not governed by structural safety or integrity, there are no specific requirements in building codes.

An exception to this is the acceptable acceleration suggested by the International Organization for Standardization (ISO). The corresponding acceleration of the structure is determined through wind tunnel testing of a solid model analyzed using the force balance method and by subjecting a flexible model to aeroelastic tests. Typically, various wind tests are carried out, each associated with wind events with periods of recurrence of 10 years, one year and one month. However, the most common performance criteria are given for wind events with a 10-year return period, for which acceptable accelerations guarantee human comfort in the range of 15 to 18 milli-g for residential buildings, and in the range of 20 to 25 milli-g for office buildings.

The iconic project of 56 Leonard presented an interesting challenge to the design team who answered by providing a redundant and resilient structural system comprised of a main core of shear walls, perimeter columns, and reinforced concrete flat slabs. Additionally, outriggers and belt wall systems were provided at two elevations of the tower to meet the required lateral stiffness. Furthermore, a Liquid Sloshing Damper was installed at the top of the building to guarantee human comfort during high wind events.

Each of the engineering techniques and tools used throughout the structural analysis and design of 56 Leonard supports not only the original aesthetics and architectural intent, but also provides a cohesive amalgamation of advantages. In a holistic approach, these multi-level strategies elegantly link the demands of today’s market with the traditional individualized character of home ownership, the protection of the environment for future generations, and the creation of a highly efficient and resilient structure. The complete yet detailed-oriented vision of the 56 Leonard design team produced a building that will be highly regarded in the long term, achieving consistency between the demands of current and new construction technologies and the social goal of meeting present and future sustainability mandates.▪

Liquid Sloshing Damper The wind tunnel study performed for the 56 Leonard project resulted in the incorporation of a Liquid Sloshing Damper (LSD) aimed at STRUCTURE magazine

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Silvian Marcus, P.E., F.ASCE, is the Director of Building Structures at WSP | Parsons Brinckerhoff in New York, NY. Mr. Marcus is a world-renowned engineer and has engineered a variety of domestic and international award winning projects.

Hezi Mena, P.E., is a Senior Vice President of Building Structures at WSP | Parsons Brinckerhoff. His experience is in design and construction of various large scale projects.

Fatih Yalniz is a Vice President of Building Structures at WSP | Parsons Brinckerhoff. Mr. Yalniz is involved with 3-dimensional computer analysis and design of lateral bracing systems for several high rise buildings.

Project Team Owner: Alexico Group/Hines Structural Engineer: WSP | Parson Brinckerhoff Design Architect: Herzog & de Meuron Architect: GHWA, Goldstein, Hill & West Architects June 2016

Elastocolor beats the elements

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MAPEI supplied three custom colors of Elastocolor Coat to meet aesthetic requirements.

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Hat Truss-Supported Office Tower in Salt Lake City

By Mark Sarkisian, S.E., Peter Lee, S.E., Alvin Tsui, S.E. and Lachezar Handzhiyski, P.E. 111 Main’s innovative “balanced” structural system supports the 25-story high-rise above an adjacent performing arts center.

I

n Salt Lake City, Utah, at 387 feet above grade, 111 Main has become the newest and one of the tallest additions to the skyline.

Currently under construction in the heart of the downtown City Center neighborhood, the roof hat-truss structure of the 25-story, 501,455 square foot Class A office tower was topped off this past January, with its loads successfully transferred from a temporary shoring support system to the permanent structural system during a one-day 12-hour period. Designed by architect and structural engineer of record Skidmore, Owings & Merrill LLP with VCBO Architecture and Dunn Associates Inc., the building’s structural engineering features an innovative and integrated solution to a complex site challenge – how to suspend a portion of the tower over an adjacent building.

Figures 1 and 2 show the building under construction and the final rendering, respectively.

Air Rights Collaboration An air rights agreement with the neighboring property owner defines the project site’s south property line. 111 Main is on a contiguous parcel with the new Salt Lake County Center for the Arts’ George S. and Dolores Doré Eccles Theater, which overlaps on the lower four stories and basement level of the tower footprint. The required structural system could not extend columns below the fifth level of the tower on the south side to accommodate the Eccles Theater under the southern portion of 111 Main’s tower. While the design development and construction of the two projects were undertaken simultaneously, in parallel but separate timeframes over three-plus

Figure 2. 111 Main rendering of design. Courtesy of Skidmore, Owings & Merrill LLP, 2016.

Figure 1. 111 Main under construction. Courtesy of City Creek Reserve, Inc.

years, the air rights collaboration allowed for adaptation of the final property line configuration, on the south side, to meet both project design objectives. Figure 3 shows an early concept design sketch of the building section and interface with the new performing arts center to the south.

“Balanced” Hat Truss Concept The design of the penthouse roof level comprises a “balanced” two-way steel hat truss system that supports all of the office tower’s 18 perimeter columns in an integrated load-balanced structure.

The system supports 20 suspended levels in the south side terminating at Level 5, and 23 suspended levels in the east, west and north sides terminating at Levels 2 and 3, such that no perimeter columns meet the ground level. The unequal bay sizes in the north (40 feet 3 inches) to south (45 feet) direction help to balance the

Figure 3. 111 Main site plan and section concept.

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Figure 4. 3D structural (REVIT) model.

eccentric loading caused by the unequal termination of floors in the north and south directions. The central reinforced concrete core walls provide the only connection of the tower to its foundation and transfer all gravity loads, as well as wind and seismic vertical and lateral loads. Conventional long-span, lightweight composite deck slab and steel floor framing construction connects the central core walls to the steel perimeter frame and suspended columns, providing clear span open office bays and a completely columnfree lobby at the tower’s base. Figure 4 shows the 3D structural REVIT (Autodesk) model with views looking from the northwest and southeast.

With 18 perimeter tower columns, only 7 of the 18 impacted the new performing arts center footprint at grade to the south. The design team considered several alternate schemes including onesided “eccentric” trusses, which created an undesirable 4¾-inch gravity “lean” to the south, while further considering vertical core wall post-tensioning to compensate for the eccentricities. The twoway hat truss system was selected, providing balance under gravity loads while NOT creating a penthouse roof outrigger truss system in resisting tower overturning seismic loads. Figure 5 shows the constructed penthouse roof hat truss system in shored condition just before load transfer in early January 2016.

Figure 5. Penthouse roof hat trusses just prior to load transfer. Courtesy of City Creek Reserve, Inc.

Superstructure Description Figure 6. Section through hat truss at top of core wall in transverse north-south direction.

Steel Hat Truss System The steel two-way hat truss system encompasses approximately 1870 tons of structural steel in support of the 18 suspended perimeter columns. Approximately 40% of building gravity dead and live loads are transferred at the roof penthouse hat trusses to the top of the reinforced concrete core wall superstructure via six steel spherical structural bearings. The bottom chords of the truss system, along with in-plane diaphragm bracing and the concrete deck slab, act as the framed mechanical penthouse floor framing at Level 25 just above the last occupied tenant space at Level 24.

The reinforced concrete core walls terminate just below the Level 25 bottom truss chords, as shown in the section in Figure 6. The top chords of the truss system, which include in-plane diagonal bracing, form the top of the roof penthouse. Throughout, the top to bottom chord centerline distance of the hat truss system is maintained at 28 feet 1½ inches deep. In plan, the trusses span over the core walls on three primary grid lines 30 feet apart in the north-south direction. In the east-west direction, two additional primary trusses span over the core walls separated by 42 feet 3 inches, with skewed truss cantilevers extending out from the concrete core to connect with perimeter 30-foot bay spacing.

Typical truss chord and diagonal members range from W14x398 to W14x730 Gr 50 ASTM A992 steel.

At the perimeter, in-plane “V” configured belt trusses act to pick-up each hanging column node connection below, at the V intersection, while also connecting to primary bottom and top truss chords. These perimeter trusses act to cantilever out 30 feet horizontally off the ends of the primary trusses to pick-up an additional “outlier” hanging column. There is a total of eight outliers with two at each corner picked up by the double cantilevered truss system. Perimeter WF column members, designed for both temporary shored compression loads and final hanging tension loads, range from W14x132 to W14x550 Gr 50 ASTM A992 steel. Perimeter truss cambers were set up +1½ inches at primary column “nodes” and +2 inches at outlier columns. The STRUCTURE magazine

Figure 7. Balanced two-way roof hat truss system.

3D layout configuration of the hat truss system above Level 25 is shown in Figure 7 along with typical shop fabricated built-up plate truss connection nodes as indicated in Figure 8 (page 34). At the four core wall corner structural bearing supports, the maximum connection node weighed 22 tons. The overall centerline footprint of the hat truss system is 130 feet by 150 feet.

Articulated Spherical Structural Bearings Six articulating spherical structural steel bearings are provided at the top of the reinforced concrete core wall superstructure to transfer compressive gravity and lateral loads from the penthouse roof hat trusses to the core walls extending to the deep piling foundation system. The bearings act as “pinned” connections, allowing for truss chord rotations in all directions as well as temperature movements under exposed environmental conditions. Seven W14x730 shear keys, with pockets at the top of the core walls, extend down from bottom truss chords providing horizontal shear bearing support. continue on next page

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Figure 9. Balanced two-way roof hat truss system.

Figure 8. Typical detailed shop fabricated built-up plate truss connection nodes.

The bearings, which measure 60 x 60 inches in plan, 16½ inches in height and are rated with a vertical capacity of 19,000 kips under combined vertical gravity and earthquake loads, include a 40-inch diameter articulated slider. Earthquake Protection Systems, Vallejo, CA, manufactured the bearings.

Ductile Reinforced Concrete Core Wall Superstructure

Figure 10. Construction placement of nodes at top of core walls. Courtesy of Sean Tuite, City Creek Reserve, Inc.

Located in a region of high seismicity near the active Salt Lake Segment of the Wasatch Fault Zone, 111 Main was designed to meet the requirements of the 2012 International Building Code (IBC) and ASCE 7-10 provisions. The superstructure construction incorporates a ductile reinforced concrete core wall system that exceeds the height limit of 160 feet per ASCE 7-10 Table 12.2.1. Thus, as an alternate design method permitted by IBC Section 104.11, performance-based seismic design procedures were adopted following the guidelines of the Pacific Earthquake Engineering Research Center (PEER) Tall Building Initiative Guidelines (TBI, 2010). This methodology and permit approval included a peer review process. The core walls are 30 inches thick, extending from the pile cap foundations to the top below the penthouse level.

Steel H-pile Deep Foundations A deep foundation system consisting of driven steel HP-piles, extending to depths of 100 feet and greater below grade, transfers the core wall loads. A total of 373 HP14x89 and HP14x117 piles, located primarily beneath the supporting core wall reinforced concrete pile caps, provide a balanced fixity of the core walls, with the center of gravity of the piling system in close alignment with the center of gravity of the core walls to minimize eccentric loading.

Temporary Shoring and Construction Sequencing The SOM design team proposed a “saddle cable” system concept to provide temporary shoring support for the seven interrupted columns to the south side above Level 5 over the performing arts center under construction below, as shown in Figure 13. In meeting a demanding construction schedule, over a 2-year period, STRUCTURE magazine

Figure 11. Placement of truss node connection at a top of articulated structural bearing. Courtesy of Sean Tuite, City Creek Reserve, Inc.

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Figure 12. Eccentricity of balanced concentric core loads with deep pile foundation.

Figure 13. Saddle cable system through core wall concept providing temporary shoring at Level 5.

the construction and engineering design-assist team developed a sequential, bottom-up staged construction sequence that allowed a conventional approach to the construction of the reinforced concrete core and steel composite floor framing system, level by level.

The collaborative team effort developed the saddle cable system anchored through the core walls north to south at Level 5 with temporary hydraulic jacks and additional steel temporary bracing as shown in Figures 14 and 15. Temporary hydraulic jacks were provided at the remaining shored eleven columns at Level 1. This system permitted the load transfer to occur after final construction of the roof hat truss system, in a single day with a synchronized construction sequence. With the unwavering support of the owner developer, City Creek Reserve, Inc., Salt Lake City, the design assist effort was led by general contractor Okland Construction Company, Inc. with SME Steel Contractors, Inc. and Hassett Engineering, Inc., exterior wall subcontractor Steel Encounters, Inc., and the SOM structure and architecture design team.

5 to lower the building at its perimeter columns approximately 3½ inches, transferring the compressive loads from the temporary shored columns to the roof hat truss system, reversing the stress in the perimeter columns from compression to tension. The 111 Main’s anticipated completion date is August 2016.▪

Acknowledgments The authors acknowledge key structural design contributions from Alessandro Beghini, P.E., and Alberto Lago, P.E. at SOM, as well as, Phil Miller, Tait Ketcham and Ron Dunn at Dunn & Associates, and Bill Gordon at Gordon Geotechnical in Salt Lake City, UT. Mark Mundy, Larry Lutton and Jeremy Stam at SME Steel led the construction sequencing design-assist team with Pat Hassett, S.E. and Jorien Baza, P.E. at Hassett Engineering, Dan Painter at SEI, and the whole amazing team at Okland Construction Company, Inc., Salt Lake City, UT.

Conclusion

Mark Sarkisian, S.E., (mark.sarkisian@som.com) is Partner, Peter Lee, S.E., (peter.lee@som.com) is Associate Director, Alvin Tsui, S.E., (alvin.tsui@som.com) is Associate, and Lachezar Handzhiyski, P.E., (lachezar.handzhiyski@som.com) is Design Engineer, Skidmore, Owings & Merrill LLP in San Francisco, CA.

With the hat truss construction completed, inspected and exterior wall glazing components installed through Level 18, on Saturday, January 9, 2016, at nine a.m., approximately 45 workers entered the shored building. The workers began a stepped construction sequence over the next 12-hours, using jacks at Levels 1 and Level

Figure 14. Temporary saddle cable system at Level 5 South. Courtesy of City Creek Reserve, Inc.

STRUCTURE magazine

Figure 15. Erection of temporary shoring and saddle cable system at Level 5 North. Courtesy of City Creek Reserve, Inc.

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RISING TO THE CLOUDS WITH CONFIDENCE The Upper-Level Wind Climate Assessment for the Jeddah Tower

By Jon Galsworthy, Ph.D., P.Eng., P.E.

“O

n a clear day, you can see forever,” the old song says.

From the windows of Saudi Arabia’s Jeddah Tower, eventually more than 1000 meters (3,281 feet) above the port city for which it is named (Figure 1), the old song will no longer be poetic hyperbole. The spectacular views are easy to imagine.

However, suppose the tune changes to “Stormy Weather.” It is much less romantic to picture a windstorm roaring outside your window when you are standing on the 167th floor.

In this situation, what will matter to occupants is the structure’s capacity relative to the demands such weather imposes. The task of characterizing windstorms for the structural engineering design of the Jeddah Tower was in the hands of the wind engineers of Rowan Williams Davies & Irwin Inc. (RWDI).

The challenge RWDI faced was that nobody had actually studied, in detail, what a windstorm does at such extreme heights above the earth’s surface.

Beyond Surface Models The first step in any wind engineering analysis is to develop an engineering model of the wind characteristics at the building site. The typical approach adopted for most buildings is to start with design wind speeds –provided in building codes or generated from statistical models derived from historical wind measurements – and then extrapolate up to the height of the building by using simplified engineering models of the planetary boundary layer. This layer is the portion of the atmosphere closest to the earth’s surface, where the wind speeds depend on the roughness of the surface terrain.

A consensus in the wind engineering consulting community is to rely on the standard engineering model of the planetary boundary layer developed by Deaves and Harris. Although a simplified model for very complex physical phenomena, it has proven effective for the design of many tall buildings.

For a structure of such an extreme height as the Jeddah Tower, the wind loads and wind-induced motions depend primarily on wind conditions near its top. However, it was recognized that the project might push the limits of the Deaves and Harris model.

Most structures sit entirely within the planetary boundary layer, the layer of the earth’s atmosphere closest to the ground that is most heavily affected by the properties of the underlying surface, such as terrain, urban surfaces, and interfaces between the land and water bodies. At its upper reaches, the tower enters a region above the boundary layer sometimes referred to as the free troposphere. This region is where the effects of larger masses of air called synoptic systems determine the weather with very little influence from boundary layer features.

These systems include features familiar from television weather maps, such as major storm fronts and low-pressure regions.

Ideally, wind engineers would develop and validate a new engineering model specific to this situation, but such an approach is not practical over the course of the design of a single project, even one so extreme as the Jeddah Tower. Instead, RWDI engineers had to find ways to STRUCTURE magazine

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Figure 1. Jeddah Tower, now under construction in Jeddah, Saudi Arabia. Courtesy of Jeddah Economic Company/ Adrian Smith + Gordon Gill Architecture.

June 2016

A Bigger Picture for Finer Detail

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Figure 2. Weather balloon data may underreport high winds. For example, on March 28 th, 1997, high surface winds prevented the evening balloon release.

determine the usefulness and limits of the standard model of the planetary boundary layer to ensure the safety and performance of the building. Their solution was to exploit additional data sources and advanced simulation techniques.

A First Approximation Weather balloons reach heights comparable to the Jeddah Tower, and beyond. They, therefore, provide a source of wind speed data that could be used to augment historical surface measurements. About 17 years’ worth of good-quality wind data were available from balloons released at the Jeddah International Airport. By interpolating measurements taken at various heights, data sets for the surface and 350, 600, and 1000 meters (1,148, 1,968 and 3,281 feet, respectively) were created.

From these data, RWDI could develop a statistical model to predict the frequency of wind speeds at each of these four heights.

The difficulty with this approach is that balloon measurements tend to underrepresent extreme wind events. Typically, balloons are launched only twice a day. If high winds occur between balloon ascensions, the peak wind speeds associated with that event are non-existent in the collected data. Furthermore, balloons are rarely released in high winds, so entire events may also be missed.

An example is shown in Figure 2, where a day-long high-wind event prevented a release, causing a 24-hour gap in the data. Also, further uncertainty to the analysis of balloon data is introduced due to the measurement duration of the wind speed. Rather than taking a long enough sample to determine the mean wind speed at each elevation as the balloon ascends, the wind speed is instead instantaneously measured and thus may reflect a localized gust.

To get the hourly resolution needed to model the wind climate at the upper reaches of the Jeddah Tower with greater confidence, RWDI adopted a second strategy: mesoscale modeling.

STRUCTURE magazine

To get the necessary wind climate detail, RWDI turned to the Weather Research and Forecast Model (WRF, pronounced “worf ”), which draws on the expertise and data of many governmental and academic institutions. This state-of-the-art weather model simulates atmospheric circulation at the mesoscale, that is, on scales ranging from hundreds of meters (feet) to thousands of kilometers (miles).

However, WRF could not pull historical data out of thin air. Thus, initial and boundary conditions for RWDI’s WRF model were set by using the Global Forecast System (GFS) reanalysis data, developed by the U.S. National Ocean and Atmospheric Administration (NOAA). This dataset is based on “reanalyzed” historical archives from a worldwide meteorological observation network. In the reanalysis, a mesoscale model is run in “hind-cast” mode on the archival data to retroactively simulate the weather, thus generating a fully detailed meteorological dataset (with a resolution of 1.0 degree everywhere on the planet) calibrated against measured values.

RWDI ran their WRF model in a “nested” approach, using three iterations on progressively finer grids (36, 12, and 4 km; 22, 7.5, 2.5 miles) centered on Jeddah. The model was also configured with a total of 35 vertical levels from the ground surface to 100 millibars (about 16,000 meters or nearly 10 miles above sea level). The vertical resolution was higher within the region of most interest, with 20 layers representing the region from ground level up to about 2000 meters (2,187 yards). This numerical strategy of nesting and vertical discretization offered a balance between computing requirements and detailed output specific to the project location.

The WRF simulations generated 87,000 records for each grid cell, giving hourly resolution for the period 2001 to 2010, inclusive. For each record, a vertical profile of wind speed and direction was extracted at the Jeddah Tower site and used in the subsequent analysis.

Validating the Detailed Model The next step was to determine whether this WRF model for the project location produced reasonable results. RWDI did an hour-byhour comparison of the two sources of surface wind data, checking the data generated by the WRF model at the tower versus the surface wind data measured at Jeddah International Airport.

As expected, the datasets were relatively well correlated, but they differed in two key ways: The WRF modeling data gave higher wind

Figure 3. Winds over Jeddah generated from vertical layers of WRF data, depicting a wind event with maximum speeds at approximately the 300-meter (984-foot) level and considerably lower speeds at the 1000-meter (3,281-foot) level.

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Figure 5. Comparison of vertical wind profiles from one of the highest wind events in the 10-year period modeled, with a comparison to a typical thunderstorm event.

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HEALTHCARE IN THE NORTHWEST

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speeds for milder wind conditions, and the airport data corresponded reviewed with a focus on the higher wind events at each height. Figure to higher wind speeds in stronger wind conditions.

5 shows two vertical profiles from separate strong wind events in the Several factors attributed to the differences, including inaccuracies 10-year period modeled. One profile indicates a very deep boundary associated with the inertia of rotating cup anemometers used at the airport; differences in upwind terrain between the Jeddah Tower site and the airport; the use of point measurements at the airport versus area-averaged speeds in WRF; and, known limitations associated with atmospheric physics modeled

by WRF, in particular for more localized weather phenomena such as thunderstorms.

The next step in validating the WRF data focused on high-wind events because those were of primary interest.

The wind engineers extracted records of strong windstorms from both WRF model and airport data, and plotted the time series for comparison. As an illustration, a strong wind event from the prevailing wind direction (north-south) is given in Figure 4. While there are some Swedish Edmonds, Edmonds, WA differences, the correlation between the WRF and, in general, surface data is very good. Wind events from east-west directions did show some differences between the datasets in wind speed and San Francisco Boise Seattle temporal shifts. These differences can be Los Angeles Phoenix Tacoma attributed to differences in site exposure, Long Beach St. Louis Lacey Pasadena Chicago Portland as mentioned earlier.

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Individual vertical profiles of winds San Diego Sacramento www.kpff.com were extracted from the WRF data and

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layer for much of the storm, as indicated by the consistent increase in wind speed with height. More frequently, though, these profiles show that the wind speed is higher near the surface while relatively benign at the top of the tower. This type of profile is consistent with thunderstorms where microbursts are created by cold air masses descending from a storm cell.

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Implications for Design To evaluate the implications of the data for the design of the building, RWDI engineers further compared the WRF simulation results and the analysis of the balloon data to the standard engineering model. Surprisingly, for heights of 350, 650, and 1000 m, the standard model was found to be quite conservative.

The profile wind speeds from the code were significantly higher than speeds obtained from both the airport data and the WRF model (Figure 6). This discrepancy indicates that the open profile assumed for the boundary layer and applied to wind speeds at the height of 10 meters is sufficiently conservative in accounting for the wind speeds aloft.

The demonstration that code wind profiles were conservative reassured the project design team and the owners, although this result did not prompt a reconsideration of the wind profiles for the project. It did, however, support a reduction of 20% in the wind speeds used to evaluate the serviceability of the structure, which allowed the design team to improve the performance of the building significantly from that perspective. Anchored in the actual, the RWDI analysis built a credible picture of the possible, allowing the project’s structural engineers to design a building where occupants can live safely at 167 stories above the ground.

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Figure 6. Summary of the wind climate assessment for Jeddah Tower.

(Local code specifies a 50-year return period 3-second gust wind speed of 42 m/s or 138ft/s.)

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Project Partners For these studies, consulting engineering firm RWDI (Guelph, Ontario, Canada) worked in close collaboration with the project team, which included the design architect Adrian Smith + Gordon Gill Architecture and the structural engineers Thornton Tomasetti (both based in Chicago, Illinois, USA).▪ A principal of RWDI, Jon Galsworthy, Ph.D., P.Eng., P.E., has participated in wind engineering analyses for numerous buildings and structures, including several super-tall buildings.

He is active in a number of technical committees, including the National Building Code of Canada, ASCE 7 Wind Load standard, and the ACI 307 Concrete Chimney wind-loading standard. Jon can be reached at jon. galsworthy@rwdi.com.

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June 2016

The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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The Resilience-Based Design of the 181 Fremont Tower

By Ibrahim Almufti, S.E., Jason Krolicki, S.E. and Adrian Crowther P.E., C.Eng., MICE

T

he 181 Fremont Tower, located in downtown San Francisco adjacent to the new Transbay Transit Center, will arguably be the most resilient tall building on the West Coast of the United States when completed in 2017. At that time, it will be the second tallest building in San Francisco (802 feet). The tower was designed to exceed CBC-mandated (California Building Code) earthquake performance objectives for new tall buildings by following a “resilience-based-design” approach. It was designed to achieve immediate re-occupancy and limited disruption to functionality after a 475-year earthquake (i.e. functionality is reestablished once utilities are restored) by targeting specific design criteria to achieve a “Gold” rating as outlined in the REDi Rating System (REDi, 2013). The US Green Building Council (USGBC) announced that satisfaction of the REDi guidelines may be used as a means to obtain the recently adopted LEED Resilient Design Pilot Credits. To achieve a “Gold” rating required that the structure is designed to remain essentially elastic (under 475-year shaking, which is approximately the recurrence interval for the CBC design basis earthquake, or DBE) and that the non-structural components are designed for more stringent force and displacement requirements relative to the code. The owners, Jay Paul Company, were also provided with additional recommendations for implementation of preparedness measures that would aid in achieving the enhanced performance objectives.

Background of Code-Based and Performance-Based Design Tall buildings in San Francisco and other West Coast cities are typically designed and assessed using a performance-based design approach (following the Pacific Earthquake Engineering Research Center (PEER) Tall Building Initiative guidelines or similar), primarily to circumvent height restrictions for certain lateral systems contained in the building code. Often, the earthquake performance objectives adopted are no more stringent than those outlined in modern building codes (i.e. low probability of collapse in an MCE, see ASCE 7-10) even though the loss of occupancy or functionality (in lower intensity shaking) in even a single tall building could have significant economic and societal repercussions.

In many cases, building owners are unaware of these potential consequences. They assume that meeting the minimum requirements of the building code will preserve their investment. This is a misconception of the code intent, shared by the public. PEER (Holmes et al., 2008) conducted a survey of building owners which found that their expectations for performance did not align with those outlined by the code. Tipler et al. (2014) found that tall reinforced concrete core-wall buildings, designed to meet state-of-the-art performancebased design guidelines (PEER-TBI, 2010), are still expected to suffer 15% financial loss and almost two years of downtime after 475-year earthquake shaking. This discrepancy suggests that our building codes are not aligned with public expectations.

STRUCTURE magazine

Figure 1. The 181 Fremont Tower with the Transbay Transit Center in the foreground.

Resilience-Based Design The owners of the 181 Fremont Tower envisioned a high-performance building, one which would incorporate innovative one-of-a-kind design strategies for sustainability (targeting LEED Platinum) through water savings and energy efficiency. They recognized that resilience is a natural extension of their enhanced sustainability objectives. After they had found that typical earthquake performance objectives did not align with their vision of a high-performance building, they elected to pursue a design strategy presented by the structural engineers to achieve “beyond code” earthquake resilience objectives.

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Achieving such high-performance targets requires a holistic “resilience-based-design” approach, which identifies and attempts to mitigate all threats that may hinder re-occupancy and functionality objectives through enhanced design of both structural and nonstructural components, and pre-disaster contingency planning. To supplement this approach, a site-specific loss assessment (based on FEMA P-58 (2013)), developed specifically for REDi, was used to verify the success in the design and planning measures to achieve the higher performance objectives. This method explicitly estimates downtime associated with specific recovery states such as re-occupancy and functionality, considering building damage, utility disruption, and external factors such as “impeding factors” (which delay the initiation of building repairs, e.g. the time it takes for a contractor to begin repairs).

of lateral forces from the condominium levels to the office levels. Large W14 sections make up the perimeter braces above Level 39. In general, vertical axial loads are resisted by welded steel box mega-columns (in the condominium levels, the columns are W14s), which vary in dimension but are commonly 36 inches by 36 inches at the base of the tower. Concrete fills the box columns up to Level 21. The mega-columns at the base support the entirety of the perimeter gravity loads; a transfer truss, which spans to the mega-columns, supports the perimeter frame system at Level 3. Since most of the lateral force is resisted at the base of these mega-columns, the designers could consider an uplifting solution to reduce column tension demands. A secondary system of special moment frames (generally W24s) transfer individual floor demands up or down to the mega-node locations (at Levels 3, 20, and 37).

The small footprint of the building (approximately 120 feet x 90 feet at the base and tapering to 95 feet x 80 feet at the roof ) did not allow for a core system in the office levels, so the lateral system is located entirely on the perimeter. In the condominium levels, there is a braced core of buckling restrained braces (BRBs) that act as a secondary system between the mega-nodes at Level 39 and the roof.

Structural System Description

Arup is the Structural Engineer of Record and Geotechnical Engineer of Record for the 181 Fremont Tower. The building has a steel core and perimeter framing with composite floors of concrete on steel framing. Above ground, it is 56 stories tall and the spire rises to a height of 802 feet. The lower 37 levels are offices and the upper levels are condominiums. It Structural Design will be the tallest mixed-use building on the West Coast when completed. Below ground, a 5-story concrete A key component of resilience-based design is to limit basement is supported on a concrete mat with 5-foot the damage to structural elements to essentially elastic or to 6-foot diameter concrete piles socketed into bedrock better. Any structural damage requiring significant repairs more than 200 feet below the ground surface. The piles could cause the building to receive a Restricted (yellow) control total and differential settlement due to the soft or Unsafe (red) post-earthquake placard which would Bay Muds and other soft soil layers immediately below impede the ability of residents/tenants to re-occupy grade, as the originally developed downtown site was the building or resume business operations. All of the reclaimed from San Francisco Bay (specifically, Yerba Figure 2. Rendering of the structural elements were designed to remain essentially Buena Cove). The seismic system consists of a dual structural system. elastic under 475-year earthquake shaking; the nonlinear system including a mega-frame. response history analysis verified this objective.

Figure 2 shows the structural system with the mega-frame highlighted For higher intensity shaking beyond the DBE, maximum-conin yellow. Mega-columns and mega-braces, which resist the global sidered earthquake (MCE) structural actions in each component lateral loads, make up the system. In the office levels, steel mega- were either designated as deformation-controlled or force-controlled, braces span from ground level to Level 20 and from Levels 20 to 37. following the methodology of PEER-TBI (2010). Acceptance Between Levels 37 and 39 (which house amenities and a mechani- criteria for deformation-controlled actions were adopted to limit cal level), an inverted chevron braced frame provides continuity the amount of damage at MCE. Force-controlled actions were

Figure 3. Schematic of damped mega-brace system.

STRUCTURE magazine

Figure 4. Close-up view of the dampers integrated within the brace system.

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PTFE bearings with excellent fatigue properties. This served to limit the wear from approximately 1500 km of anticipated travel distance.

Buckling restrained braces (BRBs) were also introduced into the load path of the mega-braces to act as a fuse in MCE shaking, protecting the primary and secondary braces, mega-columns, and dampers from damage.

Uplifting Megacolumns

Figure 5. Construction workers are lowering the mega-column base over the shear key.

typically designed for 1.5x mean MCE demands determined through non-linear response history analysis.

Non-Structural Design

Damped Mega-braces Since the tower is slender and lightweight, wind accelerations (particularly near the top) posed a potential issue due to stringent wind acceleration criteria in the condominium levels (at the fundamental period of the building of 7.5 seconds, approximately 10 milli-g peak acceleration under 1-year winds and 20 milli-g under 10-year winds).

The traditional approach for mitigating wind vibration is to incorporate a tuned mass damper (TMD), typically at or near the roof level of tall buildings. TMDs are not always an optimal choice since they are costly, heavy, relatively large, take up valuable real estate in the most desired locations and increase the gravity loads on the structure.

They are also not reliable in reducing seismic demands.

Therefore, an innovative viscous damping system was developed to fit within the architecturally expressed mega-brace design. The damped mega-brace system generates approximately 8% of critical damping, which has a significant effect in reducing both seismic and wind forces, particularly for a tall building that has very low (~2%) inherent damping. This freed-up space originally reserved for the TMD and allowed the owner to create an additional residential penthouse.

The mega-brace system is three braces in one (Figures 3 and 4, page 43). The middle (or “primary”) brace is a steel box section and the two outer (or “secondary”) braces are comprised of built-up plates attached to two viscous dampers at one end. As the building flexes laterally in a wind or earthquake event, large (elastic) strains develop in the very long primary braces. The result is approximately 6 inches of lengthening or shortening in the primary brace between the connected nodes. Since the secondary braces are connected to the same mega-nodes via dampers, this relative movement is utilized to activate the dampers and dissipate energy. The system was tuned to optimize the wind performance. However, the damping additionally benefitted the seismic response of the tower by reducing the earthquake demands across several modes of vibration. This contributed to keeping the structural system elastic in the 475-year earthquake.

For the mechanism described above to function properly, the relative movement of the mega-braces in the axial direction was allowed to slide freely as they cross each floor plate but was restrained from buckling in all other degrees of freedom by incorporating low-friction STRUCTURE magazine

The mega-columns were designed to uplift slightly (approximately 1 inch) at their bases in the MCE to significantly reduce the tension demands in the foundation and the mega-columns. The bases of the mega-columns were pre-tensioned with anchor rods extending below into the foundation so that uplift would not occur in wind or smaller earthquake events. Uplift would occur at a plane located just above the ground floor elevation, below the mega-column base plate and above a steel cruciform that rests upon the concrete pilaster embedded into the basement walls. A shear key (essentially a solid steel cylinder, similar to a pin in a BRB) was devised to transmit shear across this plane from the columns into the foundation in the event of uplift (Figure 5).

The performance of non-structural components is crucial to achieving the immediate re-occupancy and functionality objectives in the 475year earthquake. Following the REDi guidelines, the enhancements incorporated in the 181 Fremont Tower design include: • In tall buildings, elevators are crucial for not only continuity of operations but also for re-occupancy. To have the utmost confidence that at least one elevator would function after the 475-year earthquake, the guide rails and support brackets of one of the elevators that stops at every floor were upgraded to satisfy California hospital requirements (CBC, 2010). The 181 Fremont Tower is the first tower in the United States to utilize an elevator as a designated evacuation route.

Figure 6. The façade system was racked to high levels of drift and proven to remain weather-tight.

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• Noting the devastating consequences of stair failures in the Christchurch, NZ, earthquakes in 2010 and 2011, the structural engineers specified enhancements for the designbuild stairs to accommodate more movement and sustain less damage at MCE level relative to the requirements of the CBC (which references ASCE 7, Chapter 13). For stairs which relied on bearing support, Arup specified a minimum horizontal bearing seat of 1.5x mean MCE displacements.

The stairs were also required to retain their ability to carry dead and live loads under MCE level demands with minimal damage. A protective ‘moat’ was allowed for, within the stair shaft, to mitigate any partition wall damage and ensure pressurization.

• The façade was designed and tested to remain air- and weathertight after the 475-year earthquake. A full scale, three-story performance mock-up was tested and showed that the façade for 181 Fremont Tower is air- and water-tight up to drift limits of 2%, which far exceeds the expected drifts for 475-year shaking (Figure 6).

• Additional limitations were applied to Rp factors for the anchorage design of non-structural components and distribution systems to keep them essentially elastic under 475-year shaking. Further, a plan to confirm that the installation of non-structural components conformed to the drawings and specifications was agreed upon with the contractor.

As noted above, the accelerations are expected to be low relative to shorter buildings. Therefore, mechanical and other equipment are not anticipated to be damaged. However, while critical life-safety systems are required to be certified, the design team was encouraged to specify other seismically certified, non-essential equipment where possible. Also, there are emergency back-up systems which are designed to keep the essential functions of the building, including elevators, running for 8 hours after an earthquake.

Organizational Resilience through Preparedness There are a number of other earthquake preparedness and planning measures recommended to the owner and design team based on the REDi guidelines. These recommendations include: • Retain a qualified pre-certified professional who can perform an inspection quickly after an earthquake (for example, the City and County of San Francisco have developed a Building Occupancy Resumption Program (BORP) to facilitate this). A quick response aids in avoiding delays to re-occupancy.

• Due to the likelihood of utility disruption, maintain “hard” backup security measures (i.e. keys in addition to access codes) to ensure that non-tenants cannot access the building if the power goes out.

• Train and certify on-site facilities personnel to re-start elevators since they are required, by code, to incorporate a shakeactuated shut-down mode. Otherwise, it could take weeks for external vendors to re-start them.

• Plan for natural gas shut-off.

• Incorporate recommendations in an Owner’s Guideline to Earthquake Resilience for anchorage of heavy or mission-critical building contents, enhanced partition details, and food and water storage.

STRUCTURE magazine

Figure 7. At each end of the mega-brace, the connections are pinned. At the lower end (shown), BRBs are introduced into the load path of the secondary braces.

Conclusions While a resilience-based design approach is intended to extend beyond the typical purview of the structural engineer (to non-structural performance, contingency planning measures, and identification of threats outside the building envelope), skilled structural engineers are uniquely qualified to provide such expertise to owners and other stakeholders who demand “beyond code” performance.

In the future, it is hoped that enhanced re-occupancy and functionality objectives will be commonplace for tall buildings in high seismic regions because life-safety is no longer good enough for communities to achieve recovery quickly in the aftermath of a large earthquake. In the meantime, early adopters are critical in demonstrating that more resilient buildings can be designed and constructed for a little-to-no-cost premium and, by doing so, bring greater value to our community.▪

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Ibbi Almufti, S.E., is an Associate in the Advanced Technology + Research group in Arup’s San Francisco office and the Project Manager for the 181 Fremont Tower.

Jason Krolicki, S.E., is an Associate Principal at Arup and leads the Buildings Structures group in San Francisco.

Adrian Crowther, P.E., C.Eng., MICE, is a Senior Engineer in the Building group in Arup’s San Francisco office.

The online version of this article contains detailed references.

Please visit www.STRUCTUREmag.org.

June 2016

Figure 2.

Preloading Approach to Column Removal in an Existing Building

By Pratik Shah, P.E., LEED AP

475 Fifth Avenue is an existing building near Bryant Park at the intersection of 41st Street and Fifth Avenue in New York City. The 24-story, 1920s era building recently underwent a major renovation that required structural engineering designs to support the building’s architectural elements and to accommodate changes to the mechanical system. The structural scope for the project included strengthening the second-level flooring system for retail loading; framing of new mechanical penthouse; framing of new floor and wall openings to accommodate MEP ductwork and louvers; framing of new canopy, new stair crossover and closing abandoned shafts and openings. One challenging aspect of the project was to remove an existing column between Levels 1 and 2 located in the middle of the redesigned lobby (Figure 1). This column removal is the primary focus of this article.

The building’s structural system is a steel moment frame. The gravity system consists of a cinder concrete topping slab over a wire mesh reinforced concrete slab supported by steel beams spanning between girders. The girders are connected to the columns in both directions with moment connections, to resist lateral loads. All existing shear and moment connections were riveted, as is typical for buildings of this age. The original structural drawings for the building were unavailable, so all information necessary for design was obtained in the field.

Figure 1.

Figure 3.

STRUCTURE magazine

Exploratory Phase Since no structural drawings existed, DeSimone performed exhaustive exploratory work, including structural probes, walkthroughs, and field

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measurements. Structural steel coupon tests revealed the steel to be weldable and that it had a yield strength close to that of ASTM A36 steel. Concrete density tests were performed to determine the weight of the existing floor system, which was 110 lbs/ft3.

Analysis and Design of Transfer System Figure 1 indicates the portion of the frame where the column (labeled as column #60) is to be removed between the first and second floors. The spacing between columns was approximately 18 feet. A transfer girder was designed to span 36 feet to support the weight of the 23 floors above column #60 and transfer the load to the adjacent supporting columns (numbered #52 and #68). Based on the exploratory work, service gravity loads carried by each of the columns was estimated. The transfer girder was designed to be supported at Level 2 to maintain the floor-to-floor height at the ground floor lobby. For ease of delivery and rigging, the transfer girder was designed as back-to-back built-up channels. The individual channel members were delivered into the building through a window on Level 2 (Figure 2). They were connected using stiffener plates and cross bracing at the top and bottom (Figures 3 and 4). The supporting columns were coverplated to increase their capacity to support the additional load. Bearing and supporting brackets were designed to be welded directly to the columns to transfer the load to the girder. Existing footings (concrete piers) for column #52 and #68 were found to have enough reserve capacity to sup- Figure 4. port the additional load increase. However, lean concrete was poured around the top of the piers to increase confinement of the existing concrete at the point of load transfer. Finite element analysis, including an Eigenvalue buckling assessment, was performed to check stresses and the susceptibility to buckling of the transfer girder and supporting columns (Figure 5).

Preloading Approach to Column Removal In a conventional column removal, a transfer girder is installed and connected to the supporting columns. Then the column to be removed is attached to the transfer girder and cut below the girder. As illustrated in Figure 6 (page 48), the transfer girder is loaded instantaneously

from an undeformed state. This condition causes the girder and its supported levels to undergo deflection, instantaneously leading to potential serviceability issues such as cracks in the concrete floor, finishes, and partitions.

To counteract potential problems with the conventional approach, DeSimone employed an innovative preloading method to transfer the column load. The transfer girder was preloaded using hydraulic jacks to a load value equal to the service dead load supported by the column to-be-removed (column #60). This preload imposes an initial dead load deflection on the girder. Figure 4 shows details of this approach. First, two pairs of brackets are welded onto column #60, a pair of bearing brackets transfer the load from the column onto

Figure 5.

STRUCTURE magazine

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Level 5

Level 5

Level 5

Level 4

Level 4

Level 4

P

Level 3

Level 3

Level 3

Transfer Girder

Deflection of Transfer Girder only

Level 2

Level 2

Column to be removed 52

60

68

P/2 52

P/2 60

Figure 6.

Level 2

Deflection of Transfer Girder and Supported levels

68

P/2 52

Level 1

EXISTING BUILDING WHERE COLUMN IS TO BE REMOVED

Transfer Girder

P

Cumulative column load from all levels above

P

Hydraulic Jacks

P

P/2 60

68

Level 1

CONVENTIONAL APPROACH TO REMOVING EXISTING COLUMNS

Level 1

PRELOADING APPROACH TO REMOVING EXISTING COLUMNS

Remove column splice and install strain gage to measure upward deflection during jacking of column

ADVANTAGES OF PRELOADING APPROACH • By preloading the transfer girder with the help of hydraulic jacks to a load value equal to the cumulative load to be supported, only the transfer girder undergoes deflection, which eliminates deflection and hence, serviceability issues, of supported levels above.

• Load transfer to adjacent supporting columns is gradual.

• Fairly accurate value of the load supported by the transfer girder can be known at the time of preloading by measuring vertical movement of the column splice joint directly below the transfer girder.

the transfer girder, and a pair of brackets are used for jacking (Figure 7). A small gap was left directly below the bearing brackets to ensure that all the load during the preloading operation goes into the jacking brackets and that the bearing brackets are not engaged. The existing column splice for column #60 between Levels 1 and 2 was removed and strain gages were installed, at the splice, to monitor the vertical movement of the column during the jacking operation. The transfer girder was gradually preloaded to the service dead load value, or until vertical movement at the splice was detected by the strain gages. The hydraulic jacks were then locked and shim plates were introduced to close the gap between the bearing brackets and the transfer girder.

Once the shim plates were in place, the hydraulic jacks were removed, thereby disengaging the jacking brackets and transferring the load to bearing brackets. This process allowed for column #60 to be cut between Level 1 and 2. This preloading approach to column removal has several advantages over the conventional approach. The primary

advantage is that only the transfer girder undergoes deflection and the supported floors are unaffected, causing no serviceability issues on the supported levels. The finished lobby space without the existing column #60 is shown in Figure 8.

Figure 7.

Figure 8.

STRUCTURE magazine

Conclusion DeSimone successfully removed the column from the ground floor of an existing 24-story building using an innovative preloading approach. This approach helped minimize serviceability problems that are common in such projects.▪ Mr. Shah, P.E., LEED AP, is a Project Manager at DeSimone Consulting Engineers and has experience in designing new and renovation projects. He may be reached at pratik.shah@de-simone.com.

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June 2016

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TALL BUILDINGS CONSTRUCTION Moving Apace with New Products and Services

By Larry Kahaner

C

ompanies involved in tall building construction are continually offering new products and services to meet their customers’ demand.

“Business is great!” says Kord Wissmann, President of Geopier Foundation Company (www.geopier.com). “We continue to grow our resources to keep up with market demand and focus attention on clients. We are expanding our technologies and exploring and testing new possibilities that will continue to provide an intermediate foundation solution. We have also hired new employees ranging from additional regional engineers, engineers to assist in our design center, a director of business development and more office help.” Wissmann adds: “We continue to update our marketing efforts.

We are working toward a much more active presence in our regions as well as promoting ourselves through social channels and success stories that showcase our experience and expertise.”

Wissmann notes that, with the long-term rapid urban and industrial growth demands, there is more need than ever for ground improvement. “Geopier can develop the worst sites and soils and transform them to buildable, solid foundations. It is truly remarkable, and more ground improvement techniques like our rigid inclusions are being introduced to the market.”

One project that used the Geopier GeoConcrete system was The Grand, Phase 2, a 12-story condominium structure with two levels of below grade parking situated on the banks of the Grand River in Cambridge, Ontario. “The Geopier GeoConcrete Column system was selected for its cost, the speed of installation, and ability to provide high bearing capacity footing support,” Wissmann said. The foundations of this structure were subject to column loads of up to 1500 kips (6,675 kN), wall loads of up to 7 kips/ft (100 kN/m), and mat pressures of up to 8ksf (380 kPa). The Geopier GeoConcrete System was designed to limit total settlements to less than 1 inch and differential settlements to less than ¾ inches. Installation of the Geopier elements occurred as conducted from just above the bottom of footing elevation. The result of the full-scale load test completed on-site showed less than 0.18 inches (4.5 mm) of deflection at the maximum design load. (See ad on page 52.)

At S-Frame software (www.s-frame.com), CEO Marinos Stylianou says that the recent release of the S-FRAME R11.2 product suite is very well received by the structural engineering community. “R11.2 delivers significant updates and new functionality to our analysis and design products – S-FRAME, S-STEEL, S-PAD, S-CONCRETE, S-CALC, S-VIEW, and S-FOUNDATION.” He says these updates include new functionality and enhancements designed to improve clients’ user experience in five key areas: (a) Connectivity to industry standards REVIT 2016, AutoCAD, TEKLA 21,1, MS EXCEL, MS ACCESS; (b) Ability to automate repetitive tasks through a modern approach to automation using macros and the Python scripting language from within new products; (c) Improved productivity and faster product learning times by tightening the integration between analysis and steel and concrete design tasks; (d) Additional advanced material models and analysis capabilities to handle demanding modeling requirements, including STRUCTURE magazine

partial releases and material failure which are important in performance-based design studies; and (e) Addition concrete design codes for Eurocode 2 in ICD (Integrated Concrete Design) in S-FRAME and S-CONCRETE, their stand-alone concrete design solution.

Stylianou concludes: “We’ve also partnered with ADAPT Soft and provided our clients an integrated solution between S-FRAME’s S-CONCRETE and ADAPT’s Builder. The results from 2015 are very encouraging. The oil and gas industry has been negatively impacted by lower oil prices, but our clients are well diversified and global.

We’ve seen strong growth in the United States and Asia, especially from companies that chose to use our advanced structural analysis and design platform particularly for newer trend-setting tall buildings.” (See ad on page 4.)

At the Vulcraft /Verco Group, Division of Nucor (www.vulcraft.com), District Sales Manager John Cooper says that the Complex Composite Group (CCG) formed in 2012 is doing well and continues to grow.

“In 2012, our office started with just nine employees and has since grown to 25, with plans to add five more before the end of 2016. We have received new customers and several repeat customers.”

CCG’s main focus is to support customers’ needs for large complex projects that require composite metal decking in the non-residential structural steel construction market, says Cooper. “We now provide our customers with improved services in metal deck sales support nationwide, more accurate estimating, value engineering options, precision on-time CAD detailing, proactive project management, erector-friendly deck layout, and Tekla modeling software.” continued on next page

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As for recent projects, “Vulcraft/Verco CCG was an integral part of the construction of the 850,000-square foot Prudential Tower in Newark, NJ. CCG supplied and managed 1,015 tons of composite floor deck and accessories to the 20-story office tower,” Cooper says.

“Tekla BIMsight was utilized for the coordination of the structural steel components to increase productivity and accuracy. This was especially important given that the goal was to complete the skeleton before the cold Northeast winter arrived. CCG provided a Pour Stop detailing service to ensure all ‘Notches’ were provided in the correct locations for coordination with the curtain wall system. Pour Stop is a gauged steel product specialized to form the concrete slabs on a structural building. The Notches are located and then cut into the Pour Stop using a plasma cutter prior to fabrication. The successful completion

of the building’s steel structure was largely due to the coordination and teamwork of Cives Steel Company, the fabricator, Cornell & Company, the erector and Vulcraft, the metal deck supplier.”

According to Steven Powell, Executive Vice President at Star SeismicCorebrace (www.corebrace.com), the buckling restrained brace (BRB) is still growing in popularity. “From high rise buildings to bridges to industrial facilities, new applications are occurring.”

He notes that his company highlights to SEs the application of outriggers. “It uses an established product, a buckling restrained brace, but we are using it in a unique application as a structural fuse. This concept has been around probably for eight or nine years.

It started out with a few buildings here in the United States, and now it’s becoming more common around the world for high rise buildings. One limitation of high-rises is that the lateral resisting element, the core wall in the center of the building, is narrow and slender. By using an outrigger, we distribute the load to the outer super columns. It’s akin to a skier standing on his skis. It is easy to push over. However, if you take a pair of ski poles and stick your arms out, now it’s pretty hard to fall over on skis. That describes it in its simplest form. The product itself is not new, but the application of it is new.”

Powell says a limitation of core walls is their physical size. “You don’t want to eat up all your square footage in a high rise building by adding extra elevator banks and everything else. Also, increasing the wall thickness eliminates leasable square footage. By using the outrigger, you can reduce the thickness of the core walls. You are able to reduce the size of the foundations that the core wall sits on. You can distribute the loads out to these outrigger columns, and it just becomes a more economical system.”

He notes that Star Seismic and Corebrace joined in February, and the union is working well. “The companies decided that there were good parts about both companies and, if we put them together, the Give your structure stabilit y new form of Corebrace would be larger than the sum of its parts. It now gives us Work with Geopier’s geotechnical engineers to solve your ground the ability to use the best elements of both improvement challenges. Submit your project specifications to companies to service clients better and receive a customized feasibility assessment and preliminary cost produce superior performing buckling restrained braces.” estimate at geopier.com/feasibilityrequest.

Rich Madden, Marketing Director at New Millennium (www.newmill.com), 800-371-7470 would like SEs to know about Versa-Floor, geopier.com their Long-Span Composite Systems. info@geopier.com The advantages, according to Madden, are: • Clear spans up to 36 feet for open space designs ©2016 Geopier Foundation Company, Inc. The Geopier® technology and brand names are protected under U.S. patents • Integrates with any beam or walland trademarks listed at www.geopier.com/patents and other trademark applications and patents pending. Other foreign patents, patent applications, trademark registrations, and trademark applications also exist. bearing frame • Up to 40% less dead weight than cast-in-place concrete (CIP)

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Geopier Ground improvement controls structure settlement

STRUCTURE magazine

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June 2016

• Thinner floor optimizes story and building height • Predictable vibration behavior • Fire endurance ratings up to 4 hours • Flush spandrel beams for glass-curtain walls • Cleanly integrates MEP runs through the floor • Architecturally exposed finish options • Factory-applied primer paint options • Optional acoustical treatments Says Madden: “Versa-Floor can be used in multi-story residential buildings, commercial applications such as creating large bays designed for high-load combinations, retrofitting, healthcare, and special platforms. It is ideal for accelerated and safety-enhanced high-rise building construction, owing to a Panelized Delivery Method (PDM) whereby the floors are assembled in squares on the ground, then lifted into place.” (See ad on page 54.)

ITT Enidine Inc. (www.endine.com) is continually refining its designs of Fluid Viscous Damping (FVD) devices in response to technology and application advancement, says Ben Eder, Infrastructure Sales Manager – Americas.

“Our newest FVD technology, Series-UVD, utilizes a proprietary ultra-viscous silicone fluid, offering several advantages to traditional silicone hydraulic fluids. The use of ultra-viscous fluid allows for the design of an FVD to achieve a velocity exponent [damping alpha] as low as 0.1. Velocity exponents less than 0.4 are technically difficult, if not impossible, to achieve using traditional less viscous silicone fluids,” says Eder. “The nature of the extremely high viscosity lends itself to being leak-resistant. The primary point of failure of any hydraulic damping device, regardless of manufacturer, is the dynamic piston rod seal. When a damper is acted upon, the stroking of the

damper will wear the dynamic seal due to the friction between the piston rod OD surface and piston rod seal ID surface. Over time, the cumulative seal travel [wear] will eventually reach the point of creating potential leak paths. With a traditional less viscous silicone fluid, the leak path area required to produce a leak is significantly less than what is required to produce a leak using ultra-viscous fluid. Put simply, an FVD that utilizes an ultra-viscous fluid can accommodate much more cumulative seal travel before creating an actual leak path, which allows for longer damper life.”

Eder is beginning to see many SE firms engaging with their engineering team in early design phases of their projects to discuss application specifics and to learn about the potential solutions. He says this is a positive trend and can prove beneficial for everyone, from clients to SEs to building users. “Early engagement can help inform SEs of what an FVD is capable of achieving, as well as matching FVD designs and behavior to each specific application. Specifying the best technical and most economical FVD solution for supplementary damping in the early stages of development can translate to fewer design iterations and substantial savings for a client.” (See ad on page 55.)

At Hayward Baker (www.haywardbaker.com), Jeff Hill, Director, Business Development, sees increasing computer real-time data gathering. “This, in turn, makes our foundation systems more reliable and more cost effective. That’s where we’ve seen the biggest changes in the last, say, three years and what I perceive to be over the next five years.”

Hill says Hayward Baker is a full-scale foundation solution provider, and they optimize foundations using a variety of techniques depending upon conditions. “We tailor the foundation for the structure that they’re designing, with their allowable settlements and movements taken into account for making the system as optimal as possible.” continued on next page

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STRUCTURE magazine

3500 k Outrigger Viridian Tower, Manila, Phillipines

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In the future, Hill expects to see more design-builds and larger projects. “We are getting calls for what we call mega-projects where they’ve got a billion-dollar design/build project, and we think that trend will continue and it might even get larger.”

As for business conditions in general, Hill says, “Business is good in most of our geographies and most of our market segments. Of course, we have a few soft spots like oil.” (See ad on page 57.)

Business is also good for CTS Cement (www.ctscement.com), according to Susan Foster-Goodman, Director of Strategic Initiatives & Komponent. “We continue to see strong demand for our highperformance CSA cement-based product offerings for both the Rapid Set and Komponent product lines. The project efficiencies that can be achieved using rapid setting or shrinkage-compensating concrete materials offer value to the entire project team – owners, architects, engineers, and contractors alike. We help them meet demanding fast-track schedules without sacrificing durability, save time and money on more traditional project schedules and complex design/ build projects, and minimize maintenance costs and capital expenses related to repairs. This sparks a keen interest within the industry and provides new opportunities for growth.”

Foster-Goodman says that CTS Cement, founded on innovation, remains committed to providing the most innovative, high-performance concrete solutions in the industry. “We’ve recently developed two new Rapid Set products that add to our robust portfolio of concrete and concrete repair materials. The first is a rapid-setting WaterStop product designed to stop water leaks in concrete and masonry in less than five minutes and achieve structural strength in one hour. The second is a rapid hardening, multi-purpose repair mortar, Mortar Mix Plus, engineered with an integral corrosion inhibitor

for additional protection. It is ideal for wet environments where fast strength gain and sulfate resistance are essential.”

She would like SEs to know about innovation in their Komponent line that takes shrinkage-compensating concrete to a new level with their System-K offering. “System-K is a microfiber reinforced system for slab-on-grade applications. The K-Fiber used throughout the slab minimizes traditional reinforcement requirements. Perimeter steel is only required at slab edges, penetrations, and re-entrant corners to maximize the performance of the controlled expansion distinctive of shrinkage-compensating concrete. Thinner slabs are also viable,” she says.

“System-K also offers 90-95 percent reduction in control joint requirements and effectively negates shrinkage cracking. Panel sizes of 100-foot by100-foot up to 150 by 150-foot are common. Fewer joints and larger panel sizes significantly reduce the costs associated with tooling, cutting and treating control joints during installation as well as minimizing long-term joint maintenance and spall repair costs. Mobilizations and installation times can be reduced, saving time and money on the project,” says Foster-Goodman.

She concludes: “The move toward more integrated, collaborative design/build projects to optimize project efficiencies has prompted CTS to do the same – integrate one of our core products, Komponent, into a full line of innovative shrinkage-compensating concrete, low shrinkage concrete, and non-shrink grout solutions for slabs-on-grade, concrete containment, mass elements, specialty structures and more. System-K integrates value for the entire project team and performance for the owner by offering maximum durability and service life.” (See ad on page 59.)▪

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TALL BUILDINGS GUIDE

expertise in tall building design and construction

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American Wood Council Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org Product: Tall Wood Description: An industry term to identify mass timber buildings that exceed the height limit for wood buildings set by the current International Building Code. Includes any product currently permitted for use in Type IV construction, such as cross laminated timber, structural composite lumber, glued-laminated timber, and large section sawn lumber.

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Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

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Join us: SEAoP Jun 8, 2016 Villanova, PA NCSEA Sep 15-16, 2016 Orlando, FL

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Modeling has never been easier whether you’re doing a graphical layout, importing a BIM model (from Autodesk Revit Structure), or prefer spreadsheets. Full code checks and optimization for six different material types makes RISA your first choice in buildings.

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Historic structures significant structures of the past

T

he Niagara River gorge had long separated the United States from Canada.

It varied in depth up to 239 feet and in width generally between 800 and 1000 feet between the Falls and Lewiston. In 1845, Charles B. Stuart, then working on the location of the Great Western Railway in Canada, was looking for a way to connect his line with the Rochester and Niagara Falls branch of the New York Central. He proposed to span the gorge with a suspension bridge just above the Whirlpool.

Many thought his idea foolhardy as the only suspension bridges in the United States, other than some Finley bridges left over from the early part of the century, were Charles Ellet’s Fairmount Bridge over the Schuylkill River built in 1842 and John A. Roebling’s suspension aqueduct built across the Allegheny River in 1845. The English had given up on the use of suspension bridges for railways after Captain Samuel Brown’s attempt failed on the Stockton and Darlington Railway in the 1820s.

Stuart, however, did not share this belief and decided to send a circular letter to “a number of the leading Engineers of America and Europe, asking their opinion of the undertaking.” Of those who responded, only four thought the project feasible. Stuart wrote, “Charles Ellet, Jr., John A. Roebling, Samuel Keefer and Edward Serrell, alone favored the project...”

Ellet’s response stated in part: In the case which you have presented, I can, however, say this much with all confidence: A bridge may be built across the Niagara below the Falls, which will be entirely secure, and in all respects fitted for railroad uses. It will be safe for the passage of locomotive engines and freight trains, and adapted to any purpose for which it is likely to be applied...To build a bridge at Niagara has long been a favorite scheme of mine. Some twelve years ago I went to inspect the location, with a view to satisfy myself of its practicability, and I have never lost sight of the project since. I do not know in the whole circle of profession schemes a single project which it would gratify me so much to conduct to completion.

Roebling responded: I have bestowed some time upon this subject since the receipt of your letter, and have matured plans and working details. Although the question of applying the principle of suspension to railroad bridges has been disposed of in the negative by Mr. Robert Stephenson, when discussing the plan of the Britannia Bridge over the Menai, on the Chester and Holyhead Railway, I am bold enough to say that the celebrated Engineer has not at all succeeded in the solution of this problem. That a suspension bridge can be

John A. Roebling’s Niagara River Railroad Suspension Bridge – 1855

By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S.

Dr. Griggs specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an independent Consulting Engineer.

Dr. Griggs can be reached at fgriggsjr@verizon.net.

60 June 2016

Roebling’s Bridge 1855 to 1897, under deck wind cables not shown.

built to answer for a railroad, is proven by the Monongahela Bridge...The greater the weight to be supported, the stronger the cables must be, and as this is a matter of unerring calculation, there need be no difficulty on the score of strength.

The only question which presents itself is: can a suspension bridge be made stiff enough, as not to yield and bend under the weight of a railroad train when unequally distributed over it; and can the great vibration which result from the rapid motion of such trains, and which prove so destructive to common bridges, be avoided and counteracted?...I answer this in the affirmative, and maintain that wire cable bridges, properly constructed, will be found hereafter the most durable and cheapest railroad bridge for spans over one hundred feet...

In 1846, based on these responses, a charter was given to the Niagara Bridge Company by the State of New York and by the Provincial Parliament. By 1847, sufficient funds had been raised to retain an engineer and start construction. In February 1847, Ellet submitted a proposal stating: Immediately after inspecting the site, in eighteen hundred and forty-five, I gave the whole subject a careful investigation, and made a fair, but not extravagant, estimate of the cost of such a structure as I thought would be appropriate and of adequate strength.

This estimate amounted to two hundred and twenty thousand dollars for a railroad bridge competent to sustain the weight of locomotive engines and heavy freight trains, and one hundred and ninety thousand dollars for one suitable for common travel, with a railroad track in the centre, to be crossed by passenger and burthen cars drawn by horses.

When I made my estimate, I had in view a work of the first order, and as I do not wish to be in any way connected with one of a lower grade, I cannot offer to reduce my proposition.

But I will now repeat, that a secure, substantial and beautiful edifice, not one however, equal to the claim of the locality – for nothing can match that – but a noble work of art, which will form a safe and sufficient connection between the great Canadian and the New York railways, and stand firm for ages, may be erected over the Niagara river for the latter sum named…

Ellet’s (STRUCTURE, October 2006) proposal was accepted over Roebling’s, with modifications, on November 9th for the sum of $190,000. The span was to be 800 feet with a deck width of 28 feet. The deck would have two carriageways, two footways, and one railway track in the center of the floor. Ellet started by building a nine-foot wide suspension pedestrian and carriageway over the gorge to service the construction of the permanent bridge. There are several great stories concerning Ellet in the construction of this bridge.

One has to do with him offering anyone five dollars if they could fly a kite over the gorge and have it land on the other side so he could use the kite line to pull larger strings and ropes successively across the gorge. Another has to do with his first ride across the gorge in an iron basket shortly after he had succeeded in pulling a wire cable across. The last story has him riding his horse across the temporary bridge, before he had attached the railing, at a break-neck speed.

Later in the year, however, he had a disagreement with the directors “respecting the application of tolls taken on the footbridge, which after some litigation, ended by a compromise, by which Ellet relinquished his contract; and his work terminated on the twenty-seventh of December, eighteen hundred and forty-eight.” Ellet then returned to Wheeling to finish his 1,010-foot suspension bridge (STRUCTURE, May 2016) John Roebling (STRUCTURE, November 2006) would not take over the project until 1850. In 1847 and 1848, he, for the earlier competition, had worked out designs for a bridge all on one level and one with a double deck that located a single track railroad on the upper level and a roadway on a lower deck.

He offered to build the double deck bridge for $180,000 and to subscribe to $20,000 in stock in the bridge company.

While all this was going on, Edward W. Serrell (STRUCTURE, February 2012) spanned the gorge with a suspension bridge 1,043 feet long connecting Lewiston, New York, and Queenstown, Ontario, in 1851.

In 1864, Serrell removed his below deck wind cables during an ice jam and the bridge would eventually blow down. He had not yet replaced the wind cables when a windstorm came up contributing to the failure.

The fourth engineer who answered Stuart, Samuel Keefer, would also build a 1,268-foot span suspension bridge across the gorge at the Falls, but that would not be until 1869.

Roebling started work on the Niagara project in 1852. He provided all engineering services including design as well as construction supervision. The wire for his cables, one million

pounds worth, came from England, but his company supplied a significant amount of the wire used on the bridge in the under and above deck stays. He completed his 821-foot 6-inch span double-deck bridge in 1855. The onetrack railroad ran on the upper deck, and carriages and other vehicles passed on the lower deck.

He had a total of 64 stay cables of 13/8inch diameter, a total of 624 suspenders spaced 5 feet apart, four main cables 10 inches in diameter with 3,640 no. Section of double deck bridge.

9 gauge wires each and 56 under deck cables (river stays) anchored to the bedrock mile, for common or Railway travel, may on the banks of the river. He did not carry his be built, using iron for the cables, with stays over the top of towers and down to the entire safety. But by substituting the best anchorage but tied them directly to the cast quality of steel wire, we may nearly double iron roller plate at the top of the towers. The the span, and afford the same degree of four masonry towers were 15 feet square at security… As regards the success of your the base and 8 feet square at the top, with a work, more has been accomplished than height of 60 feet 6 inches. The length, center was promised… It is a great satisfaction to center of towers, was 821 feet 6 inches to me, that this work has turned out equal with a deck length of 800 feet. His stiffening to my promise, and also to know, that on trusses on each side were 18 feet deep, and taking leave of you, the mutual confidence were spaced 24 feet apart at the lower level that exists, will not undergo any change. and 25 feet apart on the upper level. The Roebling described the bridge in his Final diagonals were wrought iron rods 1-inch in Report to the Presidents and Directors of the diameter at an angle of 45° and crossed four Niagara Falls Suspension and Niagara Falls doubled wooden verticals spaced at 5 feet.

International Bridge Companies dated May In his final report to the Board, which was 1, 1855. It was also published in Papers and very complete, he also discussed Ellet’s earlier Practical Illustrations of Public Works of Recent bridge across the Niagara and the cause of the Construction both British and American by John failure of Ellet’s Bridge at Wheeling in 1854. Weale in London in 1856. Roebling was wrong Roebling proudly stated, about suspension bridges being the best choice One single observation of the passage for railroad bridges with spans over 100 feet. of a train over the Niagara Bridge will Time proved that long span simple trusses, convince the most skeptical that the praccantilever trusses, and continuous trusses were ticality of suspended railway bridges, so the most efficient for railroad purposes. much doubted heretofore, has been sucAfter traveling across the bridge, Mark Twain cessfully demonstrated... Bridges of half a commented, Then you drive over to Suspension Bridge and divide your misery between the chances of smashing down two-hundred feet into the river below, and the chances of having a railway-train overhead smashing down onto you. Either possibility is discomforting taken by itself, but, mixed together, they amount in the aggregate to positive unhappiness.

Over the years, Leffert L. Buck (STRUCTURE, December 2010) replaced some rusted wires at the anchorages, replaced the side trusses with iron, strengthened the anchorages and replaced the stone towers with iron, all without stopping traffic on the bridge. In 1897, he built a double deck braced spandrel steel arch bridge, under and around Roebling’s bridge, carrying two tracks on the upper level and transferring the load to the new bridge, also without stopTowers, approach to the lower deck, cables, and ping traffic.▪ side trusses.

STRUCTURE magazine

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June 2016

This article references several detailed Tables. Unfortunately, space constraints dictate not reprinting Table 1 from the May 2016 issue of STRUCTURE and providing the following Tables only in the online version of this article. The Tables are: Table 2: Steel and Cost Efficiency of Suspension and Cable-Stayed Bridges Table 3: Steel and Cost Efficiency for different Bridge Systems Table 5: Construction Time Efficiency of Bridges Table 6: Steel Efficiency for Long-Span Roof Structures Table 7: Steel Efficiency of Tall Buildings Please visit www.STRUCTUREmag.org to download these tables. There is a link to the PDF(s) at the top (right) of the online article.

E

fficiency and economy of structures are important parts of structural engineering. Efficiency and economy are not new ideas: engineers build many remarkable bridges and buildings under strict financial constraints.

Efficiency for Bridge Structural Systems Table 2 lists the cost and steel “efficiency coefficients” for suspension and cable-stayed bridges, including most of the longest span bridges in these two categories. In Table 3 are listed the cost and material efficiency coefficients for different structural bridge systems including representatives for each bridge system. Table 4 presents the best performance and the margins for the efficiency of the total groups (per this study) of structural systems (in establishing the average data, the highest and lowest coefficients for the group were eliminated). Table 5 lists the construction-time efficiency for bridges.

Exposed structures like bridges should be elegant: slender with simple forms and should harmonize with the surrounding environment.

There is a consensus among engineers and architects that a well-designed structure, using the right structural system, usually results in an elegant and well-proportioned bridge. Also, it is very important that an aesthetically attractive bridge is also efficient and economical.

Even when the challenge was about how to build a bridge with a record span length, the cost of the structure was always an issue that could abort or postpone the project for a long period (the Messina Strait Bridge is a good example). With the progress in structural analysis and software, high-strength properties of available structural materials and improved construction methods, today it is less of a problem to obtain a longer span than ever before. Now the greatest difficulty appears to be securing the needed funding for such projects.

For the same reason, engineers start paying more attention to the structural cost because using more efficient systems and technologies allows them to build “more bridge or building” (meaning more built area and longer free-of-column spans).

Different structural systems for bridges have a specific margin of efficiency coefficients for construction materials. For example – steel continuous girders have

2.55 to 3.0 kg/(L x m2); steel continuous trusses, about 1.8 kg/m3; chevron portals, 1.20 to 1.50 kg/(L x m2); cable-stayed, 0.62 to 2.46 kg/(L x m2); and suspension bridges, 0.62 to 0.98 kg/(L x m2). The Tables do not include the steel continuous trusses and chevron portals because of very limited information.

Two examples from the author’s experience demonstrate the possibilities provided by using the efficiency criteria: Akashi Kaikyo Bridge, with the longest bridge span of 1991 meters (or 6,532 feet), was completed in 1998.

As early as 1988, the author estimated a steel efficiency coefficient of 0.76 for the bridge, based on the limited information about this future structure at that time, using presumed similarity with other suspension bridges already completed in Japan. When, years later near the completion of the bridge, the final technical information for the bridge was made available, the steel efficiency came to 0.83, only 9% difference from the earlier estimate. The result was very close, especially considering that the Akashi Kaikyo Bridge had achieved a new world record with 1.41 times longer span than the previous record holder, the Humber Estuary Bridge. This example proves that an established criterion for bridge (or structure) efficiency can be a powerful tool for designers and developers in preliminary estimates of the material and cost required for new structures, even when new record-long spans are involved.

The replacement of the East Span of the San Francisco-Oakland Bay Bridge occurred from 2002 to 2015. During the period of review and system selection, members of the Engineering Design Advisory Panel (EDAP) for the new bridge, including the author, cautioned transportation authorities about the problems in selecting structural systems. For example, system selection for the “Skyway” and the self-anchored suspension (SAS) for the main span without providing, in advance, construction quantities and costs compared with other bridge systems would be problematic. Of special concern were the high selfweight of the concrete Skyway (resulting in higher seismic forces, heavier piers, and foundations) and the very high cost of the few self-anchored suspension systems built at the time, proposed for the

STRUCTURE magazine

Structural EconomicS cost benefits, value engineering, economic analysis, life cycle costing and more...

Efficiency and Economy in Bridge and Building Structures

63

Part 2: A Study for Structural Efficiency and Economy in Construction

By Roumen V. Mladjov, S.E.

Roumen V. Mladjov has more than 50 years in structural and bridge engineering and construction management. He lives in San Francisco, and his main interests are structural performance, efficiency, and economy. He can be reached at rmladjov@gmail.com.

The online version of this article contains detailed references. Please visit www.STRUCUTREmag.org.

Table 4. Summary of Bridge Steel, Concrete and Cost Efficiency.

Bridge Structural System Suspension Bridges Self-Anchored Suspension

L max note 1 meters (feet) min to max

L average meters

Steel/Area Average kg/m2 (lbs/ft 2)

Best

728 -1,991 (2,388 - 6,532)

1,209

677 (139)

0.62

Steel Efficiency

Cost Efficiency

Average

Cost/Area Average $/m2 ($/ft 2)

Best

Average

0.98

11,073 (1,029)

6.51

17.74

kg/m2 x Lav

$/m2 x Lav

112 - 385 (367 - 1,263)

267

1,013 (207)

2.77

5.51

30,044 (2,791)

12.13

83.50

126 - 1,104 (413 - 3,622)

513

442 (91)

0.62

2.46

6,969 (647)

7.45

35.27

Steel Arch Bridges

130 - 300 (427 - 984)

220

627 (128)

2.48

4.50

5,612 (521)

19.27

39.83

Steel Continuous Bridges

70 - 330 (230 - 1,083)

157

457 (94)

2.55

3.00

1,994 (185)

9.19

14.20

Concrete Arch Bridges

Cable-Stayed Bridges

200 - 323 (656 - 1,060)

235

573 (117)

2.52

6.47

5,251 (488)

21.82

51.41

Concrete Continuous Girders

110 - 250 (361 - 820)

179

656 (134)

2.90

5.54

5,068 (471)

12.20

70.39

Concrete Extradosed Bridges

100 - 180 (328 - 591)

132

521 (107)

2.58

4.98

4,727 (439)

20.57

58.84

Concrete/Area Average

Concrete Efficiency

m x10 /m x Lav

m /m (yd /yd )

Concrete Continuous Girders

110 - 250 (361 - 820)

179

2.31 (2.53)

6.71

18.43

5,068 (471)

12.20

47.61

Concrete Extradosed Bridges

100 - 180 (328 -591)

131

2.67 (2.93)

9.46

27.58

4,727 (439)

20.57

45.38

3

2

3

2

3

3

2

Note 1. L max and L average are for the bridges with available data part of this survey and do not include the maximum span lengths achieved with a particular structural system when there is not available information.

Note 2. The best performances (span length, minimum steel or concrete, minimum cost) are highlighted.

suspension portion of the bridge. The authorities ignored the warnings and, as a result, the already high estimated cost escalated to levels making this otherwise elegant bridge one of the most expensive in the world. This escalation is another example that demonstrates how established criteria for efficiency may have saved billions of dollars. As engineers can learn from successfully efficient projects, it is even more important to learn from the mistakes made in large and very expensive projects.

Efficiency for Long-Span and Tall Buildings Similar to bridges, the efficiency of singlelevel long-span structures for sports arenas, exhibition halls, aircraft hangars, etc., can be compared using the same efficiency coefficients; an example is given in Table 6.

For tall buildings or skyscrapers, a similar approach is used, replacing the span L with the height of the building H. Table 7 compares the steel efficiency for such buildings. In both Tables 6 and 7, only a few projects are listed to represent the structural systems.

Findings Based on the best-achieved steel efficiency coefficients, suspension bridges show the best performance (E/E coefficients) with coefficient 0.62 kg/(L x m2); followed by cable-stayed, 0.62 (same as the suspension, but with higher average coefficient); steel continuous and arch, 2.48 – 2.55; concrete continuous and “extradosed”, 2.58 –2.90; and concrete arch bridges, 2.52.

Based on cost (economy) coefficients, the suspension bridges are again the best with coefficient $6.51/(L x m2); followed by cable-stayed, $7.45; steel continuous, $9.19; concrete continuous, $12.20; steel arch bridges, $19.27; and concrete arch and “extradosed”, $20.57–21.82. Note that the lack of representation of pedestrian bridges in this article’s tables is indicative of their cost, as they are often significantly more expensive. For example, Calatrava’s Sundial Bridge at Redding, CA, has a cost of $15,670/m2. Juan Sobrino provides information for costs per meter square of several pedestrian bridges with spans of 150–200 meters ranging between $16,300/m2 and $57,400/m2. These costs are significantly higher than costs per m2 of suspension and cable-stayed bridges with spans exceeding 500–1000 meters (Tables 2 and 3).

The results above are from Table 3, where the suspension and the cable-stayed bridges are without competition for the first and second position of most efficient structures.

The highest efficiencies for suspension and cable-stayed bridges are valid only for the “classic” types of these structures. Selfanchored suspension bridges and suspended ribbon-decks are not as efficient (Tables 2 and 3).

Based on self-weight of the total structure, again the steel suspension, cable-stayed, continuous and arch bridges are more efficient than the remaining systems.

Based on construction time coefficients, the suspension and cable-stayed bridges are built faster than the remaining systems.

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Notes • Suspension and cable-stayed bridges are mostly steel structures, but they are often combined with concrete towers (pylons), composite steel-concrete decks, or both, thus making their rating more difficult.

• The reinforcing and tensioning steel efficiency coefficients (kg per square meter times the average span) used for concrete continuous and “extradosed” bridges (with 40- to 250-meter, or 131to 820-foot, spans) are more than the steel for longer cable-stayed spans (230 to 890 meters, or 754 to 2919 feet). The coefficients are closer to the steel used for suspension bridges with significantly longer spans (from 720 to 1990 meters, or 2362 to 6528 feet).

• Some recently built bridges in the country, highly acclaimed for their innovativeness and “efficiency”, actually exhibit poor performance in cost, materials and construction time efficiency.

• Some “signature” bridges tend to be between the least efficient and least economical; such bridge designs should be used very carefully unless donations from individuals or companies cover the costs and it is not a burden on state or federal budgets.

Conclusions and Recommendations • The data presented in this article can be used as a start for building a larger “Database” for efficiency of structures

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and corrections to remain competitive and provide motivation for further improvement. Being efficient and economical in the design will result in more economical constructions, reduced costs, materials and carbon footprint.

Structural efficiency has become a globally important issue as, in general, efficient constructions with their reduced “carbon footprint” help protect the environment.

Concrete, steel, and other materials have significant carbon dioxide emissions released during their production, manufacture and

construction. There is no better way for reducing the “carbon footprint” of the construction industry than reducing the quantity of structural materials used in construction.

Given the inherently competitive nature of structural engineering, we may slightly modify the Olympic Games motto, Citius, Altius, Fortius, as Faster, Higher, Stronger, Longer and Lighter. Thus, to the established competition criteria for higher, longer-span and stronger structures, we can also add those for faster and lighter (less consuming) structures.▪

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and structural systems. A more extensive Efficiency Database will provide very useful information and guidance for total efficiency and its elements: material, cost, construction time, weight for bridges, bridge systems, and other structures. By using the Database, engineers will be able to find the most efficient structures within the system groups and will learn how to further improve their projects based on the specific solutions for these best performance examples. At the same time, engineers will be able to avoid using systems that are significantly less efficient.

A developed Database will allow engineers to select the most appropriate concept for the overall project, the most important and challenging part of engineering.

Economy depends mainly on the design concept.

The expansion of this Database should be developed with the help of the State Departments of Transportation, design and construction companies, academia and the professional publications for engineers, architects and builders.

The goal should be to have the Database become a reliable guide for use by professional designers and builders, structural manufacturers, construction managers and owners of bridges and other structures.

The use of such a Database can save billions of dollars as early in the process as the selection of the structural system, thus saving necessary funding for construction and renovation of other structures.

All design and construction of bridges and other larger structure projects with a cost above $30 million, when funded by state or federal budgets (public taxpayer’s money), should be awarded only by design (or design-build) competitions. No such project should be approved if the material and cost efficiency coefficients for the project span exceed the typical E/E coefficients for such structures by 20 percent or more.

In the author’s opinion, engineers should monitor their own projects’ efficiency, comparing them to industry efficiency averages. This comparison will help engineers discover, at an early stage, whether their project requires adjustments

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Structural rehabilitation renovation and restoration of existing structures

S

tructural repairs are never “one size fits all” and, by combining flexibility and creativity, structural engineering professionals can employ innovative approaches to repair older wooden structures. These creative solutions can foster goodwill with existing clients, gain new design commissions, and help develop a reputation as a thought leader in the process. NuTec Design has been able to realize these benefits by embracing innovation and thinking “outside of the wooden box.” The case studies that follow focus on a roof renovation for a historic church and the repair of wood trusses in two different buildings in the same business park.

Historic Church Roof Renovation The first case study entailed a roof renovation for a historic church built in 1901 and located in Red Lion, PA (on the outskirts of York), as shown in Figure 1. On this project, the author’s firm was the second engineering firm called to investigate the church ceiling and roof. The client wanted to replace the existing slate roof with a new one, but during the original survey large cracks and deflections in the roof structure were discovered. These defects were due to the installation of a slate roof over the original builtup roofing material. The first engineering firm recommended a replacement of the entire roof structure. However, the cost associated with this replacement was too high for the client to absorb and created the possibility of damaging the historic plaster ceiling, so they opted for a second opinion. That was when NuTec received the call.

The overall construction is a multi-wythe masonry bearing wall with wood roof construction. Valley and ridge beams bear on the walls and support stick built trusses to create a vaulted

Thinking Outside the Wooden Box Creative Problem Solving for Repairing Wood Structures

By Kimberlee McKitish, P.E., LEED Green Associate

Kimberlee McKitish is a Structural Engineer with York, Pennsylvaniabased NuTec Design Associates, Inc. Kimberlee can be reached at kmckitish@nutecgroup.com.

ceiling space, attic floor, and roof rafters. The front auxiliary space and the front porch are framed independently. Figure 2 presents a 3D visual of the roof and ceiling framing.

During NuTec’s survey, several typical defects were observed throughout the structure. Cracks were noted in all of the ridge and valley beams and many of the rafters and vertical bracing members.

These cracks reduced the expected load-carrying capacity of the members. Bowing vertical bracing members, indicating significant load-demand in main members, were common across the structure and appeared to be due to the additional load from the slate roof.

Although the first survey stated that the existing members were not salvageable, in-depth analysis after the second survey indicated the existing members were not far over their demand-to-capacity values for the existing load conditions. The biggest concern was the slate roof built on top of layers of old roofing material. The slate roof was heavier than the original built-up roof, but the prior roof material was not removed as it should have been, compounding the problem of installing a heavier roof material.

The author’s firm recommended removing all the old roofing materials and then reinforcing the cracked members before laying the new slate roof. First, the damaged and deteriorated rafters were addressed. After the old roofing materials had been removed and the dead load relieved, the damaged rafter and vertical member sections were removed and replaced with 2x12 members.

The next step was to address the cracked valley beams. An epoxy crack injection system was used to fill the cracks, and then the damaged members were reinforced with 2x12s to support the new slate roof loads. The repairs were completed in 2010, and the structure has not exhibited deterioration based on subsequent, periodic structural inspections.

Figure 1. Exterior view of the historic church from Case Study one.

66 June 2016

Figure 2. Ceiling and roof framing from the church in Case Study one.

Commercial Business Park (Building 1) The second case study is a single-story manufacturing building located in Central Pennsylvania and is similar in construction to many of the buildings in the surrounding business park. The building, constructed in the 1940s, consists of wood trusses.

Within the last 20 years, the building was sold and the center bay replaced with a raised pre-engineered truss section. No modifications were done to the original wood trusses to support the additional drifted snow load due to the raised center roof portion. The client noticed cracks in the wood and engaged NuTec to complete a survey, analyze the trusses, and provide repair documents if necessary.

The overall construction of the building is a multi-wythe masonry bearing wall with integral piers. A raised center bay of 60-foot long pre-engineered steel frames was installed after the original building was constructed.

Wood trusses supported by the steel frames span approximately 60 feet and wood purlins, 20 feet long, span between them. There are a few interior walls built next to, or around the existing trusses. Refer to Figure 3 for a section displaying the truss construction and raised center bay.

During the survey, typical defects were noted throughout the structure. The defects noticed most frequently were checks in the top and bottom of many members through the member connections. These connections were comprised of 4-inch diameter split-rings. The checks at the member ends reduced the capacity of the connections. Some members had cracks against the wood grain, and most of the members had cracks through a portion of

Figure 3. Section of the pre-engineered metal bay and wood truss bay in the building from Case Study two.

the member length along the wood grain.

These cracks undermined the structural integrity of the members and reduced the load carrying capacity.

Five different options were evaluated, and order-of-magnitude estimates were developed for the main repairs to the structure: • Intermediate wood posts: $200,000 • Steel plate or channel reinforcement: $400,000 • Epoxy crack sealer system: $600,000 • Replacing or sistering the members: $800,000 • New steel beam, column, and foundation support system: $1,000,000 NuTec immediately disregarded the new steel beam and column option as it was the highest cost and would interfere with the manufacturing process, which drives the structure. The intermediate wood post option was similarly rejected due to manufacturing process interference. Replacing or sistering with wood members would be costly due to the size of the reinforcing required as a result of the amount of drifted snow from the raised center bay. Consequently, the client selected the option of reinforcing existing elements with steel plate or channel, a lesser cost option when compared to epoxy crack sealing. There were minimal utilities supported from the existing trusses that would be disturbed during the repair as well, making it the more cost-effective and least operational impact of all the repair options suggested.

The typical repair involved plating the bottom chord and center web members, in all trusses, to reinforce for the drifted snow load.

Members with significant cracks were then plated to improve the load carrying capacity.

Finally, the checks were filled with an epoxy crack sealer to repair the bearing of the split ring connection.

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Commercial Business Park (Building 2) The last case study is a manufacturing building located in Central Pennsylvania in the same business park as the previous case study.

Again, this building was constructed in the 1940s and employs wood trusses. This client owns approximately 13 similar buildings in this business park and they called NuTec because they had a truss failure in another building during a snow event.

A different engineering firm designed repairs in the failed building, utilizing new steel beams, columns, and concrete foundations. The invasiveness of the work necessitated the relocation of utilities and, as a result, all the utilities were brought up to code. The client did not feel this solution was optimal for their situation but wanted to ensure that their other buildings were safe for occupants. That is when the author’s team was asked to do a condition survey and provide recommendations.

Again, this is a single-story industrial building. The overall construction of the building is a multi-wythe masonry bearing wall with integral piers and interior wood columns. The piers and interior wood columns support the wood trusses and span approximately 60 feet with 20-foot wood purlins spanning between the trusses. Figure 4 (page 68) shows a 3D interior view of the building with the wood trusses highlighted in red.

During the survey, typical defects, similar to the previous case study, were noted throughout the structure. Also, the structure was littered with existing utilities and crane runway beams as illustrated in Figure 5 (page 68). The owner instructed the team not to disturb any of the existing utilities or crane beams, or disrupt the operation of the building. All of these existing

Figure 4. Interior view of the wood trusses in the building from Case Study three.

conditions and restrictions made for a unique and challenging repair project.

Again the same five options were considered, and order-of-magnitude estimates were prepared for the main repairs to the structure: • Intermediate wood posts: $200,000 • Replacing or sistering the members: $300,000 • Epoxy crack sealer system: $600,000 • Steel plate or channel reinforcing: $800,000 • New steel beam, column, and foundation support system: $1,000,000 Although the cost estimates are similar to the previous case study, replacing with wood members was cheaper than using steel plate and channels on this project. The building did not require reinforcing for snow drift, so the wood members were smaller and easier to handle. Furthermore, any steel reinforcing would have disrupted the utilities, causing relocation in some areas and resulting in higher costs due to the relocation.

The client immediately rejected new steel beams and columns. The steel approach was utilized in their first building, and they felt that the utility disruption and new foundations required to support the columns was not cost-effective. Intermediate wood posts were also not acceptable due to the disruption this would pose to the building operations, and replacing in-kind was ruled out due to the disruption of the existing utilities. The epoxy crack sealer was the option selected, as it was the lower cost option between the remaining two and it was the least invasive on the existing utilities.

Creative Engineering as a Marketing Tool Creative and flexible solutions can be used to market your company, generating many

different ways to gain new clients or design commissions. The author’s firm has experienced specific benefits.

Company exposure: Many prominent community leaders attend the church in the first case study. The consideration of options to save the church gained exposure for the firm, demonstrating their willingness to work with the community. This project preserved an important aesthetic in a historic church and caught the attention of those community leaders who will recognize this effort for the next project that requires a creative solution.

Set your company apart: Start to stand out as a firm with custom designs for buildings of a certain era or construction-type. Know how to work with inexpensive solutions that pose as little impact on facility function as possible. Incorporate creativity in your problem solving and leverage it to gain more business.

By working with the owner of the property in the business park example and providing a series of options, NuTec was able to work on eleven more buildings of similar construction in the same business park. This client is also a national property owner and solicited assistance on projects in other locations including sites around Central Pennsylvania and beyond.

Thought leadership: Thought leaders are recognized as the foremost authorities in their field. Their expert opinions are sought by others looking for information in that field. By building a portfolio in a specific or unique project type, one can gain recognition as a thought leader. Ultimately, the goal is to have prospects seek you out because of your unique knowledge or skill set. By engineering creative solutions, the author’s firm has become a thought leader in certain fields, with new and existing clients requesting expert opinion and engineering skills.

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Figure 5. An example of the utilities in the building from Case Study three.

Content Marketing: Creative engineering can lead to content marketing. You can start to generate blogs, case studies, and interviews to generate interest in your firm’s website.

This digital presence establishes your firm as a creative problem solver. NuTec has been approached to propose on projects due to content on their company blog, which has, in turn, led to creating valued partnerships with repeat clients.

Personal and professional brand: A personal brand is how professionals market themselves and their careers to others. Clients want to work with individuals they trust to design the best solution to fit their needs. By designing innovative and creative solutions for clients, you enhance your personal brand in the eyes of that client. The brand, in turn, increases the value of your company. You gain their respect and admiration, which will hopefully turn them into a repeat partner in the future.

In engineering, we are trained to look at things in black and white terms. However, there are many times when the best solution is in a gray area, where creativity and innovation reside. This is the time for multiple potential solutions that weigh all the variables that can influence the outcome.

In each case study, the individual concepts outlined were only a piece of the final solution for the client. As professionals, we have to balance client needs, cost, value, and engineering judgment to recommend a solution that fits a client’s budget, as well as the overall needs of the process or function of the space.▪

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Professional issues

issues affecting the structural engineering profession

Leadership Opportunities in Our Offices, in Our Associations, and in the Public Sector

By William D. Bast, P.E., S.E.

T

he world needs great leaders. We need better leaders in our government, in our companies, in our associations and organizations, and in our committees and teams. There are many articles and books published on leadership, but this article is based on my thirty years of working with structural engineering offices, associations, and committees. I have seen firsthand the many opportunities that are available where engineers can demonstrate leadership.

“An army of sheep lead by a lion... will always defeat an army of lions led by a sheep,” a quote attributed to Alexander the Great. I first heard it from Peter Rogers, the former CEO of Nabisco. He uses the quote in several of his talks to differentiate leadership and management. The internet contains many interpretations of what this quote means. However, in the context of leadership, I believe that it is clear – the army with a strong leader will defeat the army with a weak leader, even if the army with the weak leader is stronger.

This analogy has many connotations but, in business, it points to the importance of the need for strong leadership within a company.

A strong company needs strong leadership to be successful; a weak leader can weaken the strong members of the company. The weakening of the company also happens when a weak leader uses his or her authority to demoralize or make ineffectual the leaders and staff beneath him or her.

As a business owner and Past President of both the Structural Engineers Association of Illinois (SEAOI) and the National Council of Structural Engineer Associations (NCSEA), I have seen many opportunities for engineers to take on a leadership role and make a difference.

Leadership Opportunities within the Firm Principals of engineering firms and project engineers are the leaders of the firm. The decisions that they make or don’t make at the start of a project will often dictate the outcome and success of the project, months

or years later. The general direction for the procedures and methodology of the work to be performed by their staff, the design options to be pursued, the cost options to be weighed, and the nuances with the solutions must all be provided early on by these leaders for the team and the project to be successful.

One of my colleagues told me years ago that, as a principal of the firm, it is important to be very active in the beginnings of a project – setting the direction, goals, scope, strategies, and methodologies.

Then, as the project proceeds, it is best to fade into the background and let the staff execute the project and allow them to do what they do best.

Leadership Opportunities within Your Engineering Association On Sunday, July 2, 2000, three pieces of limestone fell from a building in Chicago, smashing a truck on the street but causing no bodily harm to pedestrians or workers.

The City of Chicago’s Law Department responded to the incident by initiating proceedings to take away the SE license of the Engineer of Record for the façade.

SEAOI backed the EOR, who had a stellar reputation and was a very diligent and talented man. The SEAOI staff issued a press release in support of the EOR and requested a thorough investigation of the incident. Partly through SEAOI’s efforts, as well as the substantial efforts of others, his license was not revoked.

The Leadership of NCSEA, SEI, and CASE have made a concerted effort and provided leadership in establishing SE licensure in all states. The commitment of the leadership of these organizations and their committees led to the formation of SELC (Structural Engineering Licensure Coalition). This organization has provided support and assistance to many states that were successful in obtaining SE Licensure, and many other states that are working toward SE licensure.

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Leadership Opportunities within the Public Sector Leadership opportunities in the public sector are abundant. To make a good decision, input from engineers is essential.

In late 2000, a City of Chicago Alderman proposed amending the façade ordinance to exclude the inspections of brick buildings. The Building Committee held a meeting shortly after announcing the proposed amendment, and I attended the meeting and signed up to testify before the committee. During my testimony, I stated that excluding brick buildings from the façade ordinance inspections had no technical merit or basis and that these buildings have all of the same problems as any other buildings clad in stone, terra cotta, or concrete.

After my testimony, the Chicago Alderman asked me, “Are you an engineer paid to do these inspections?” I answered in the affirmative. “Then no wonder you want to inspect the brick buildings, too!” he retorted. His response and challenge to my credibility gave me slight pause, but I reasoned that no matter what he or his committee believed, it was my responsibility as a leader to say and do what I believe is right regardless of the external pressures. I replied firmly, “You can say what you like, but the fact of the matter is that there is no technical reason to exclude brick buildings from complying with the ordinance!”

Fortunately, the committee made no decision that morning and reconvened the following week. At the next meeting, my colleagues from SEAOI were able to prepare a presentation that illustrated the façade problems of brick buildings, and the ordinance was not changed.

Leadership Requires Working Together On Saturday, March 9, 2002, a 100-footlong, custom-built scaffold collapsed while suspended midway up the 100-story John Hancock Center in Chicago, killing three people in a car on the street below.

SEAOI was contacted soon after the incident by the Building Owners and Managers Association (BOMA) of Chicago, asking

whether SEAOI was in favor of the new Scaffold Act that the City of Chicago’s Law Department had proposed in response to the incident. BOMA stated that the proposed ordinance would require all scaffolds in the City of Chicago to be certified by a structural engineer licensed in Illinois. The certification would apply to the rigging, as well as the shifting of all swing stage and pipe scaffolds.

Because there were over a thousand scaffolds in Chicago at the time, SEAOI realized that this Act could provide a lot of work for structural engineers. SEAOI also recognized that the cost would be an excessive burden to the building owners and, more importantly, they felt that the ordinance as proposed would not fix the problem.

SEAOI showed leadership by convening a committee to study the issue and propose alternate language to make the ordinance more effective and less costly. The committee was made up of an invited group of structural engineers, architects, contractors, and BOMA representatives. After a few meetings, the committee arrived at an alternative proposal which required all scaffold operators, workers, and inspectors to obtain a Scaffold Card, certifying their competence in the rigging and operation of swing stage and pipe scaffolds.

The proposal was sent to the City of Chicago’s Building Department, and it was approved. The whole process was a very rewarding experience because we were able to bring together all of the affected partners to arrive at a solution that was not a compromise, but a truly creative solution that was amenable to everyone.

The Attributes of Great Leaders From my experience, a leader’s attributes are varied but must include: • Being a servant leader. A servant leader is one who serves others, not expecting to be served. Being a servant leader means going to the end of the line and not taking the ‘first fruits’ because one happens to be at the front of the line.

• Being willing and determined to do the right thing regardless of the consequences or external pressures.

• Not worrying solely about political correctness, but saying and doing what you believe is right and exercising respect, tact and humility in your words.

• Looking for creative solutions to problems. Be willing to consider differing viewpoints before rendering conclusions.

• Staying within technical and objective limits and avoid the spin that can be applied by owners, developers, and attorneys to minimize your input and advice.

Conclusion Good leadership is hard to find and much in demand these days. Engineers can and need to step up and serve in leadership positions.

I urge you to get involved in your profession, your office, your community, and your families and churches – as leaders, leading the way with strength and humility.▪ Mr. Bast heads Thornton Tomasetti’s Renewal practice in Chicago, Illinois. He is a Past President of NCSEA, the Structural Engineers Foundation of Illinois, and the Structural Engineers Association of Illinois.

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STRUCTURE magazine

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InSIghtS

new trends, new techniques and current industry issues

FHWA’s National Tunnel Inspection Program

By Brian J. Leshko, P.E., F.SEI, F.ASCE

F

ollowing the tragic ceiling collapse in the Interstate 90 Connector Tunnel in Boston, Massachusetts, on July 10, 2006, the National Transportation Safety Board’s Highway Accident Report, NTSB Number HAR-07/02, identified several safety issues including, “inadequate regulatory requirements for tunnel inspections.” On July 6, 2012, President Obama signed the Moving Ahead for Progress in the 21st Century Act (MAP-21), which required the Secretary to establish national standards for tunnel inspections. Thus, the impetus for a tunnel safety inspection program can be traced back nearly ten years, with the requirement to develop national tunnel inspection standards mandated nearly four years ago.

Recognizing that the safety and security of the Nation’s tunnels are of paramount importance, Congress declared in MAP-21: it is in the vital interest of the country, to inventory, inspect and improve the condition of the Nation’s highway tunnels. The Federal Highway Administration (FHWA) has developed, over the last six years, tunnel inspection regulations (standards) and two supporting reference documents (a manual and specifications): • National Tunnel Inspection Standards (NTIS), • Tunnel Operation, Maintenance, Inspection and Evaluation (TOMIE) Manual, and • Specifications for the National Tunnel Inventory (SNTI).

The National Tunnel Inspection Standards (NTIS) establishes the regulations for the uniformity of tunnel inspections similar to the National Bridge Inspection Standards (NBIS) for bridges. The TOMIE Manual establishes procedures and practices for tunnel inspection and documentation of deficiencies similar to the Bridge Inspector’s Reference Manual (BIRM) for bridges. The SNTI enables the inspector to inventory and assess tunnel elements and functional systems similar to the AASHTO Manual for Bridge Element Inspection and the FHWA Recording and Coding Guide for bridges. Qualifications and responsibilities for tunnel program managers, tunnel inspection team leaders, tunnel load raters and tunnel inspectors, along with safety precautions and quality assurance and quality control, are detailed

HDR inspector using a bucket van to access the arched concrete roof of a tunnel during a routine inspection.

in these documents. Specific requirements for becoming a National Certified Tunnel Inspector (NCTI) were also delineated.

National Tunnel Inspection Standards (NTIS) Tunnels were not addressed in the National Bridge Inspection Standards (NBIS), bridge inspection manuals or training. In 2008, the FHWA initiated steps to implement the National Tunnel Inspection Standards (NTIS). The process began with the publication of the Advanced Notice of Proposed Rule-Making (ANPRM). After addressing the comments received on the ANPRM, a Notice of Proposed Rule-Making was developed and published in 2010; however, before completing the rule-making process in 2012, MAP-21 was signed into law. This highway law contained a number of tunnel inventory and inspection provisions which needed to be addressed. In July of 2013, the FHWA issued a Supplementary Notice of Proposed Rule-Making (SNPRM) to incorporate the new provisions and to seek comments. The final rule addressed the comments on the SNPRM. When published in the Office of the Federal Register on July 14, 2015, the NTIS became part of the Code of Federal Regulations – 23 CFR Part 650 Subpart E.

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The effective date for the NTIS was 30 days after publication; therefore, on August 13, 2015, the requirements began for all tunnels on public roads, on and off Federal-aid highways.

The intent of the new highway regulation is to establish a basis for uniform and consistent inventory and inspection procedures for all tunnels located on public roads. Under the NTIS, critical findings are to be reported to the FHWA and corrected promptly. The mandate calls for a national tunnel inventory and inspection program, tunnel routine inspection frequency of 24 months, training for tunnel inspectors, and a national certification program for tunnel inspectors.

Together with the National Highway Institute (NHI), the FHWA developed a comprehensive training course that provides national certification for tunnel inspectors.

Key inspection personnel, including the program manager and team leaders, are required to become Nationally Certified Tunnel Inspectors (NCTI). As a substitute for this certification, the NTIS also permits training which has been developed by the State and approved by the FHWA. To that end, the FHWA contracted with Michael Baker International to develop FHWA-NHI Course 130110 Tunnel Safety Inspection to provide instructorled comprehensive training for tunnel inspectors in accordance with the NTIS.

Brian J. Leshko (brian.leshko@hdrinc.com) is a Vice President, Principal Professional Associate and the Bridges & Structures Inspection Program Leader with HDR Engineering, Inc. in Pittsburgh, PA. He is a National Certified Tunnel Inspector, a FHWA-Certified Bridge Inspection Team Leader, and an NHI Certified Instructor.

Brian serves on the STRUCTURE Editorial Board, and he developed and is an instructor for the NHI 130110 Course.

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The course development team included HDR Engineering, Inc., with Subject Matter Experts (SMEs) for civil/structural, mechanical and electrical disciplines; and Engility with expertise in gaming simulation to develop the Virtual Tunnel Inspection (VTI) Computer Based Training (CBT) capstone exercise. The tunnel safety inspection course is comprised of modules covering Course Introduction, Overview of Tunnel Inspection, Tunnel Inspection Fundamentals, Inspection of Structural Tunnel Elements, Inspection of Civil Tunnel Elements, Inspection of Mechanical System Tunnel Elements, Inspection of Fire/Life Safety/Security System Tunnel Elements, Inspection of Electrical System Tunnel Elements, Inspection of Signage and Lighting System Tunnel Elements, and End of Course Review (including the VTI Exercise). The Baker+HDR Team was subsequently selected to deliver the new FHWA-NHI Course 130110 Tunnel Safety Inspection. Beginning with the first course offering in August 2015 (two weeks following the effective date of the NTIS), the Baker+HDR Team taught a total of 15 classes throughout the U.S. through May 2016. With each class averaging 30 attendees, to date, approximately 450 NCTIs have been issued.

For reference, the NTIS defines a tunnel as: “an enclosed roadway for motor vehicle traffic with vehicle access limited to portals, regardless of type of structure or method of construction, that requires, based on the owner’s determination, special design considerations to include lighting, ventilation, fire protection systems, and emergency egress capacity. The term ‘tunnel’ does not include bridges or culverts inspected under the National Bridge Inspection Standards (23 CFR 650 Subpart C – National Bridge Inspection Standards).” This definition is consistent with the definition used by the American Association of State Highway and Transportation Officials (AASHTO), and it is intended to identify the structures targeted by this new regulation.▪

BOOKCASE

book reviews and news

STEEL – From Mine to Mill, the Metal that Made America

By Barry Arnold, P.E., S.E., SECB

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teel is the foundational material that gave rise to our modern civilization. From its use as piles in deep foundations; as reinforcing bars and anchor rods embedded in concrete and masonry structures; as structural shapes used as beams, columns, and braces; as bolts and light-gauge connectors in wood construction; and as light-gauge steel studs – steel is an essential and important part of our history and the modern built environment. Without steel, transportation via trains and automobiles would not exist and travel by water would be limited to small wooden vessels insignificant in size compared to the colossal steel-hull cargo vessels that transverse the oceans daily by the thousands. Without steel, bridge spans would be limited and notable bridges like the Golden Gate Bridge, Sydney Harbour Bridge, and the Brooklyn Bridge would not exist in elegant splendor like they do today. Skyscrapers, or structures of any significant height, would only exist in engineers’ dreams and imaginations if it was not for steel.

Brooke C. Stoddard has written an exceptional book that highlights the captivating history of steel and its use to create industries, generate wealth, and build nations. STEEL – From Mine to Mill, the Metal that made America is a fascinating and riveting read. Stoddard tells the story of steel from its assumed earliest discovery as iron meteorite fragments by man’s earliest ancestors to the mined and processed material we depend on in every facet of our daily lives. STEEL is a well-written and engaging history that covers centuries of experimentation, refinement, and improvement that resulted in the material we use today. Although an inanimate material, steel comes alive in this inviting and enthralling book.

Stoddard does more than just write about the history of steel; he takes you on a well-researched adventure that highlights the material and the people that produce it. Not limited to just chronicling the distant past, STEEL contains modern historical information including methods of transportation and production. In the last chapter, you will learn about the reasons behind ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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the decline of the steel industry in America and the influx of foreign steel.

Processes and procedures are written about with authenticity and accuracy because Stoddard rode in the trucks, cargo ships, and trains that transported the ore and he spent time in the factories talking to the people that produce the finished product. He captured the experience with great accuracy – enough to make the reader feel that they are participating in the same, vividly-described experiences with the author.

STEEL is a must read for any structural engineer. I found it a delightful book, a useful reference volume, and a welcome addition to my engineering library.▪ Barry Arnold (barrya@arwengineers.com) is a Vice President at ARW Engineers in Ogden, Utah. He chairs the STRUCTURE magazine Editorial Board and is the Immediate Past President of NCSEA and a member of the NCSEA Structural Licensure Committee.

award winners and outstanding projects

Spotlight

170 Amsterdam

By Mukesh M. Parikh, P.E. DeSimone Consulting Engineers was an Award Winner for the 170 Amsterdam project in the 2015 NCSEA Annual Excellence in Structural Engineering Awards program (Category – New Buildings $30M to $100M).

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ocated on a long narrow site on the Upper West Side of Manhattan, 170 Amsterdam, a $75 million project, provides the benefits of floor to ceiling windows without compromising energy efficiency. Because the project is in New York City, soil conditions are very favorable for high-rise construction. Shallow spread footings bearing on rock were used to support all columns and walls. In some locations on the site, the rock profile drops substantially; therefore, caissons with pile caps were also utilized in lieu of shallow footings. Foundation walls run to bedrock, where they have a minimum of 2-foot sockets. Portions of the foundation walls along the north and south faces of the building lie on spread footings with rock anchors and they have buttresses carrying tension forces.

A 6-inch slab on grade was used for most of the cellar and a 12-inch pressure slab was used on the west side.

The entire lateral system for 170 Amsterdam is located on the exterior of the structure due to its diagrid design. The fundamental advantages of the diagrid system, and its root appeal for architects, are simple enough. A series of triangular components, whether steel, reinforced concrete, or wood, combine gravity and lateral loads into one.

This combination allowed for an efficient design as lateral members are subject to tension and uplift forces. Allowing members to take gravity loads acting in the opposite direction greatly reduces tension and uplift.

The reduction, in turn, makes a substantial impact on the size and reinforcement of the columns.

To accurately analyze the load distribution through all members, the lateral analysis was performed using a complete three-dimensional model of the structure.

All internal columns, walls, and slabs were modeled to ensure exterior columns captured the impacts of gravity forces. Seismic and wind loads calculated from ASCE7-05 and the 2008 New York City Building Code were applied to the finite element model along the principal axes of the structure.

Building drifts could then be evaluated to ensure they met ASCE 7 allowable story drift based on occupancy.

Both the interior and exterior columns of the building carry most of the gravity loads.

There are 18 interior rectangular columns for the first 14 floors, which become eight (8) at the building setback. The exterior columns are all 24-inch diameter architectural concrete which take both gravity and lateral loads. As the exterior columns slope and intersect to create the lateral diagrid, special attention was required at the connecting locations. Columns could not be congested with steel, as the crowding would cause constructability issues. The structural team opted to use 100 ksi MMFX reinforcement in the lower columns which allowed the use of six (6) #11 bars to be sufficient. At intersection points, two columns become one with a maximum of 4.1% steel.

The intersections of the concrete structure rise to the top of the building at different heights, giving the appearance of a façade in motion while also allowing for the reuse of prefabricated fiberglass formwork with the concrete cycle. The continuity and efficiency of the system allow for a lighter and stiffer building that utilizes less material than a traditional high-rise.

The use of a flat plate slab system allows for ease of constructability for formwork and concrete placement. Slabs all use 8000 psi concrete and vary from 8 to 12 inches throughout the superstructure. Transfer beams were introduced at the 14th floor, where the setback occurs, to pick up new exterior columns on the west side.

The diagrid sat 4 inches from the façade and required a smooth finish since it was completely visible from all angles. Creating mockups assisted all the teams in visualizing constructability issues beforehand. The concrete used to create the exoskeleton is the result of a specialized mix that gives the material the appearance of limestone.

The formwork for the round, crossed column shapes involved an intricate fiberglass system with multiple units that were

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tightly connected to achieve maximum re-use and economy.

The form system and the reinforcing were designed so a pump-placing tube could be inserted into the crossed shapes, which achieved a smooth and consistent surface without blemishes or discoloration. Using a small aggregate mix, placing concrete into the blind areas of the formwork required no vibration. The concrete mix was a dense, high fluid self-consolidating mix using gray cement and slag to achieve a light gray finish and meet LEED standards.

The successful implementation of the concrete exoskeleton, which minimizes internal supports, liberates interior space and provides greater flexibility for systems installations, made 170 Amsterdam Avenue an exceptional project that will influence structural design on a local and global level.▪ Mukesh M. Parikh is a Managing Principal in the New York office of DeSimone Consulting Engineers. Mr. Parikh specializes in the design of concrete and steel structures. He can be reached at Mukesh.parikh@de-simone.com.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

What Happened to Chapter 34?

Structural Provisions in the International Existing Building Code When your state adopts the 2015 International Building Code (IBC), it will probably also adopt the 2015 International Existing Building Code (IEBC). That’s because the 2015 IBC has replaced the rules governing additions, alterations, repairs, etc. that used to be in Chapter 34 with a pointer to the IEBC. Is this a problem? No, but it might lead to some confusion and to more inconsistency from state to state, because the IEBC allows the user to pick one of two “methods” to follow – either the Prescriptive method, which matches the old IBC Chapter 34, or the Work Area method, which takes a more nuanced approach to non-conforming conditions in existing buildings. (There’s a third Performance method, but it’s rarely used on projects with structural issues.)

As the IEBC is adopted, some states might allow both methods.

Others might make the leap and adopt only the Work Area method. Still others (California, for example) might stick with the older Prescriptive method only.

NCSEA’s Position

The multiple methods were intended, back in 2006, to provide flexibility to users as they transitioned to the new Work Area method. Unfortunately, what was intended as a flexible code with options is now seen as a confusing code ripe for gaming. If both methods are allowed, owners and designers are implicitly encouraged to just select the cheaper option. If a state keeps things simple by adopting only one method, any intended flexibility is lost, and the Work Area method never gets tried.

Eventually, we expect the Prescriptive method to fade away.

Meanwhile, it is NCSEA’s position that there is no longer any reason for the structural provisions of the IEBC’s two main methods to differ at all. So, for the 2015 and 2018 editions, our Existing Buildings Subcommittee has worked to make the structural provisions of the IEBC’s Prescriptive and Work Area methods identical.

Changes in the 2015 IEBC

To make the methods match, the following upgrade triggers from the Work Area method have been added to the Prescriptive method: • Seismic bracing of unreinforced masonry parapets is required when an alteration replaces 25 percent of the roof in an area of moderate or high seismicity (Section 403.5).

• Wind upgrade of diaphragms and related load path elements is required when an alteration replaces 50 percent of the roof in a high wind area (Section 403.8).

The following new provisions were added to both methods: • A lateral evaluation (and possible retrofit) is required when an essential facility in an area of very high seismicity (Seismic Design Category F) undergoes a major alteration (Sections 403.4.1 and 907.4.3).

• Seismic bracing of unreinforced masonry parapets and installation of roof-to-wall anchors is required in an area of moderate or high seismicity when the building undergoes a major alteration, regardless of the scope of roof replacement (Sections 403.6, 403.7, 907.4.5, and 907.4.6).

Even with these changes, however, the 2015 Prescriptive and Work Area structural provisions still have a few substantial differences. At code hearings last April, NCSEA proposals to reconcile the methods were tentatively approved for the 2018 IEBC, but in the 2015 edition, there are still the differences shown in the table below.

David Bonowitz, S.E. chairs the Existing Buildings Subcommittee of NCSEA’s Code Advisory Committee. Committee members representing NCSEA Members Organizations are listed at www.ncsea.com/ committees/existingbuildings/.

Condition

2015 Prescriptive Provision

2015 Work Area Provision

Alteration, lateral loads

Requires check with IBC-level seismic loads.

(Section 403.4)

Allows check with reduced seismic loads.

(Section 807.5)

Major alteration, seismic design category F

Requires seismic check only. (Section 403.4.1)

Requires seismic and wind check.

(Section 907.4.3)

Major alteration, rigid wall – flexible diaphragm buildings in moderate or high seismicity

Requires roof-to-wall anchors for unreinforced masonry buildings only. (Section 403.6)

Requires roof-to-wall anchors for buildings with unreinforced masonry, reinforced masonry, or concrete walls (tilt-ups). (Section 907.4.5)

Major alteration with substantial structural alteration

No requirement

Requires lateral system check.

(Section 907.4.2)

Change of occupancy

Requires seismic check only, when risk category changes. (Section 407.4)

Requires seismic, wind, and snow checks when risk category changes; live load check in affected areas; check of access to risk category IV buildings. (Sections 1007.1, 1007.2, 1007.3.2)

Change of occupancy, seismic check

Allows exception for 1. Equivalence to new structure, 2. Change to risk category III in area of low seismicity. (Section 407.4)

Allows exception for 1. Equivalence considering reduced seismic loads, 2. Small area subject to change of occupancy. Also allows use of Appendix A1 for change to RC III. (Section 1007.3.1)

Historic buildings

Exempts historic buildings from any structural work. (Section 408.1)

Requires all structural work, same as for nonhistoric building. (Section 1206.1)

Relocated buildings

Requires relocated building to meet all structural requirements for new buildings.

(Section 409.1)

Allows exceptions for small changes in wind, snow, and seismic loads due to relocation.

(Sections 1302.3, 1302.4, 1302.5)

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Have your Project Recognized at the 2016 NCSEA Summit!

Call for Entries – Excellence Awards The NCSEA Excellence in Structural Engineering Awards annually highlights some of the best examples of structural engineering ingenuity throughout the world. Structural engineers and structural engineering firms are encouraged to enter this year’s program. Projects will be judged on innovative design, engineering achievement and creativity.

Up to three awards will be presented in seven categories.

Eligible projects must be substantially complete between January 1, 2013 and December 31, 2015. Entries are due Tuesday, July 12, 2016.

Awards will be presented in September at the NCSEA Structural Engineering Summit in Orlando. Winning projects will be featured in future issues of STRUCTURE magazine. For award program rules, project eligibility and entry forms, see the Call for Entries on the Awards page of the NCSEA website at www.ncsea.com.

Applications must be approved by the MO prior to submitting.

Requests may be submitted for any program that is consistent with NCSEA’s mission. Requests will not be accepted, however, for political contributions or for reimbursement of lobbying expenses. Applications must clearly define who or what group is to receive the funds, the amount requested and what the funds will be used for, how it advances the NCSEA Mission Statement, and how it can be leveraged with other funding. Matching contributions from a Member Organization are encouraged, but not required.

For more information on the Program and the application, visit www.ncsea.com.

NCSEA Webinars

July 28, 2016 Communication Between the Structural Engineer & Masonry Contractor

July 12, 2016 Rehabilitation of Timber Structures

June 2016

Don’t delay in securing your hotel reservation for NCSEA’s 2016 NCSEA Structural Engineering Summit!

The Summit will be held at Disney’s Contemporary Resort, which is just a short monorail ride, water-launch trip or walk to the Magic Kingdom Park. Hotel reservations are accessible through a link online at NCSEA’s website.

Register now for the best discounts and secure your hotel room, as we expect a sell-out.

The Summit will feature a slate of terrific educational sessions and social functions. More information can be found at www.ncsea.com.

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Register today at www.ncsea.com!

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Summit Hotel Rooms over 60% reserved

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Disney’s Contemporary Resort September 14th-17th

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July 19, 2016 Design Considerations for Mid-Rise Structures

More detailed information on the webinars and a registration link can be found at www.ncsea.com. Subscriptions are available!

1.5 hours of continuing education. Approved for CE credit in all 50 states through the NCSEA Diamond Review Program. www.ncsea.com.

2016 Structural Engineering Summit

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NCSEA is pleased, for the second year, to offer NCSEA Member Organizations the opportunity to apply for the NCSEA Grant Program. Deadline for applications is August 15.

This program has been developed to assist Member Organizations in growing and promoting their organization and the structural engineering field, in accordance with our new Mission Statement: NCSEA advances the practice of structural engineering by representing and strengthening its Member Organizations. Five grants were awarded in 2015, the first year of the program.

Any NCSEA Member Organization or member(s) of a Member Organization is eligible to submit an application.

STRUCTU

NCSEA Grants Program Process Open

June 21, 2016 Introduction to Structural Fire Engineering

News from the National Council of Structural Engineers Associations

At the NCSEA Structural Engineering Summit, special awards are given to NCSEA members who have provided outstanding service and commitment to the association and to the structural engineering field.

The NCSEA Service Award is presented to an individual who has worked for the betterment of NCSEA to a degree that is beyond the norm for volunteerism. The award is given to someone who has made a clear and indisputable contribution to the organization and to the profession. Board members are not eligible.

The Robert Cornforth Award is presented to an individual for exceptional dedication and exemplary service to the organization and to the profession. The award is named for Robert Cornforth, a founding member of NCSEA and treasurer on its first Board of Directors, and a member of OSEA. Nominations must be submitted by NCSEA Member Organizations.

The Susan M. Frey NCSEA Educator Award is presented to an individual who has a genuine interest in, and extraordinary talent for, effective instruction for practicing structural engineers.

The award was established to honor the memory of Sue Frey, one of NCSEA’s finest educators.

The nomination form for these awards is available at www.ncsea.com, and the deadline date for nominations is July 6. Nominations are requested for all awards; however, awards are based on worthy recipients and may not be awarded each year.

A nomination form can be found at www.ncsea.com/awards.

NCSEA News

Nominations Open for Special Awards

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CALL FOR PROPOSALS NOW OPEN

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

2017 STRUCTURES CONGRESS April 6 – 8, 2017, Denver, Colorado Now accepting individual papers and complete session proposals for consideration.

Structures Congress 2017 is a forum to advance the art, science, and practice of structural engineering. The SEI National Technical Program Committee (NTPC) is seeking proposals for complete sessions and abstracts for individual papers to be presented at Structures Congress 2017.

Criteria used by the NTPC to review and evaluate the proposals include – but are not limited to – the following: • Technical Content • Presentation Quality • Applicability to the audience, i.e., what the audience will take away from the presentation To submit a proposal for consideration at Structures Congress 2017, visit www.structurescongress.org. The conference website will have detailed information and step by step power points to assist you.

Abstracts and Session Proposals should focus on topics and subtopics consistent with the list to the right. A complete list of sub-topics is available at www.structurescongress.org.

SEI encourages submissions from practitioners, educators, researchers, structural engineers, bridge and building designers, firm owners, codes and standards developers, and others. Final papers are optional but strongly encouraged.

The due date for abstract and session proposals is June 2, 2016. Visit the congress website, www.structurescongress.org, to submit your proposals.

Questions? Contact Debbie Smith dsmith@asce.org or 703-295-6095

Major Topics Blast and Impact Loading and Response of Structures Bridges and Transportation Structures Buildings Business and Professional Practice Education Forensic Natural Disasters Nonbuilding and Special Structures Nonstructural Systems and Components Research Sharing Claim Experiences

Errata SEI posts up-to-date errata information for our publications at www.asce.org/SEI. Click on “Publications” on our menu, and select “Errata.” If you have any errata that you would like to submit, please email it to Jon Esslinger at jesslinger@asce.org.

Tsunami Resilient Design Provisions to be Included in ASCE 7-16

SEI Welcomes New Sustaining Organization Member Schnabel Foundation

The ASCE/SEI 7 Standards Committee has approved a new Chapter 6 for Tsunami Loads and Effects for the 2016 edition of the ASCE 7 Standard, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. Chapter 6 in ASCE 7-16 provides the first comprehensive tsunami design provisions in the world and represents the state of the art tsunami design knowledge presented in enforceable code language. These new provisions, five years in the making, are a unified set of analysis and design methodologies that are consistent with probabilistic hazard analysis, tsunami physics, and structural reliability analysis. They apply to the states of Alaska, Washington, Oregon, California, and Hawaii for the design of critical and essential facilities located in mapped tsunami design zones.

Schnabel Foundation Company is SEI’s newest Sustaining Organization Member.

We hope you will join them, Hayward Baker, International Code Council, Simpson Strong-Tie, and Geopier Foundations, Inc., in support of SEI. Being a Sustaining Organization Member will raise recognition for your organization with decision makers in the structural engineering community year-round, and show your leadership and support for SEI in their goal to advance and serve the structural engineering profession. Demonstrate your commitment and increase your organization’s visibility with more than 25,000 SEI members and at SEI conferences through www.asce.org/SEI, the monthly SEI Update e-newsletter, and STRUCTURE magazine. Learn more at www.asce.org/SEI-Sustaining-Org-Membership.

Questions? Contact Suzanne Fisher sfisher@asce.org.

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International Workshop on Disaster Resilience

Engineers are innovators – we are using new technology, building sustainably and shaping projects that meet tomorrow’s challenges. What are the innovative projects or new ways that infrastructure is being planned, built or funded in your area? Be a part of identifying the next #GameChangers that will shape the future. ASCE’s Committee for America’s Infrastructure invites you to submit projects that are changing the infrastructure game to the #GameChangers project. To submit, share the name of the project and a link to tell us more about where it is from and why it is a #GameChanger at http://ascegamechangers.org.

The SEI Disaster Resilience of Structures, Infrastructures, and Communities Committee is participating in organizing the 1st International Workshop on Disaster Resilience, September 20 – 22, 2016 in Torino, Italy. The program includes two days of sessions at the magnificent Hall of Honor in 16th century Valentino’s Castle. An additional day of sessions and visits will be held in the Joint Research Centre in Ispra, which includes the Elsa Lab and Crisis Management Center. Learn more on the workshop website at www.workshop-torino2016.resiltronics.org.

Local Activities New Orleans Chapter

The SEI Philadelphia Chapter has been very active with a full slate of activities over the past year that have benefited their local members. Monthly technical dinners gave members up-to-date information about local bridge and infrastructure projects, and updates on new wind load provisions. Also, the chapter reached out to engineering students at local universities. Learn more on the SEI News web page.

The SEI New Orleans Chapter is participating in a wide range of activities this year. Recent events provided their members with valuable enrichment. These include seminars that presented technical content and outreach to local students to encourage interest in engineering. Learn more on the SEI News web page.

Colorado Chapter To complement the technical meetings that the Colorado Chapter holds every other month, the section planned a tour of a local steel fabricator. In March, a group of SEI members toured Central Denver Ironworks (CDI), a steel fabricator located in Downtown Denver. The chapter is looking forward to another tour later this year. Contact the chapter at sei.colorado.chapter@gmail.com to learn more about their activities and become involved.

St. Louis Chapter On March 18, the SEI St. Louis Chapter went on a tour of the construction of the Campus Renewal Project taking shape at the Barnes-Jewish Hospital north campus and the St. Louis Children’s Hospital expansion. The Campus Renewal Project is a long-term project to transform Washington University Medical Center (WUMC) through new construction and renovations.

The campus is vast and includes Barnes-Jewish Hospital, St. Louis Children’s Hospital and Washington University School of Medicine. Campus Renewal encompasses the three institutions with an overall focus on improving the patient and family experience from both a clinical and campus perspective.

STRUCTURE magazine

West Virginia University Graduate Student Chapter The SEI Graduate Student Chapter at West Virginia University was recently named as the SEI 2016 Graduate Student Chapter of the Year. This award has motivated chapter members to become more involved in their campus and the local community.

The chapter has hosted or participated in numerous events over the past few months including a student open house, a guest lecture, and a joint fundraiser with the ASCE student chapter.

Learn more on the SEI News web page.

Get Involved in SEI Local Activities Join your local SEI Chapter, Graduate Student Chapter, or Structural Technical Groups (STG) to connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area. If there is not an SEI Chapter or STG in your area, talk with your ASCE Section/ Branch leaders about the simple steps to form an SEI Chapter.

Visit the SEI website at www.asce.org/SEI and look for Local Activities Division (LAD) Committees.

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The Newsletter of the Structural Engineering Institute of ASCE

Philadelphia Chapter

Structural Columns

Share Innovative Projects & Trends Changing the Industry

The Newsletter of the Council of American Structural Engineers

CASE Heads to Chicago This Summer CASE Summer Planning Meeting August 3 – 4, 2016; Chicago, IL

Join us for the following sessions/speakers:

The CASE Summer Planning Meeting will again be scheduled for August 3 – 4 in Chicago, IL. A popular feature of the planning meeting is a roundtable discussion on topics relating to the business of Structural Engineering, facilitated by the CASE Executive Committee members. Topics have included the Business of BIM, using social media within your firm, Peer Review, and Special Inspections. Attendees to this session will earn 2.0 PDHs. Please contact CASE Executive Director Heather Talbert (htalbert@acec.org) if you are interested in attending this roundtable or have any suggested topics for the roundtable.

CASE Risk Management Seminar August 4 – 5, 2016; Chicago, IL This summer, for the first time in 9 years, CASE will put on the industry’s only seminar dedicated solely to improving your firm’s business practices and risk management strategies. Come and join us and learn to Manage Risk for High Stakes Success in Chicago on August 4 – 5 for training and collaboration with industry leaders and project managers from firms of all sizes, intended to improve your structural engineering practice.

Immerse yourself in topics designed to help engineers learn better ways of reducing areas of risk and liability on projects while learning about tools that are available to implement better practices immediately in your firm.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Thursday, August 4 6:00 pm – 8:00 pm – Dinner with Speaker World Trade Center: Then & Now Ahmad Rahimian, Ph.D., P.E., S.E., F.ASCE USA Director of Building Structures Friday – August 5 7:45 am – 9:00 am – Breakfast with Speaker Brian Stewart, Attorney at Law, Collins, Collins, Muir & Stewart, LLP 9:00 am – 9:15 am Break 9:15 am – 10:30 am – Session 1 Professional Negligence (Karen Erger, Eric Singer) 10:30 am – 10:45 am Break 10:45 am – 12:00 pm–Session 2 How to Succeed without Risking it All! (Panel of Experts) 12:00 pm – 1:15 pm Lunch 1:30 pm – 2:45 pm – Session 3 Secrets to Communicating Technical Topics to NonTechnical Audiences (Shelley Row) 2:45 pm – 3:00 pm Break 3:00 pm – 4:15 pm – Session 4 Recapping New Risk Management Concepts Moderator: Brian Stewart, Collins, Collins, Muir & Stewart, LLP 4:15 pm – 4:30 pm Wrap-up / Adjourn This new CASE Convocation Seminar is geared towards Owners, Principals, Project Managers, and Risk Managers. If you are concerned with risk management, new trends, and profitability, you cannot afford to miss this event! Join us August 4 – 5 in Chicago for the updated CASE Risk Management Convocation!

To register for this event, go to www.acec.org/coalitions.

CASE in Point

CASE Risk Management Tools Available Foundation 7 Compensation – Prepare and Negotiate Fees that Allow for Quality and Profit

as project engineers and project managers often ask the question – “How do we decide on fees?” This tool may be a useful primer for these employees and lead to a further discussion with firm management on the firm’s fee development strategies.

Tool 7-1 Client Evaluation

Foundation 8 Contracts – Identify Onerous Contract Language

Do you know who your best clients are? Do you know where you should be focusing your marketing and sales efforts to maximize the financial performance of your firm? You may be surprised.

This tool will help you answer those questions by analyzing the amount of work and profit for each client.

Tool 7-2 Fee Development This tool is intended to be used within a consulting firm to stimulate thought and consideration in the development of fees.

Engineers in firms that may be experiencing new responsibilities STRUCTURE magazine

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Tool 8-1 Contract Review Do you (or your legal counsel) review every contract to find onerous clauses? Do you know what they are? Do you always find them? This tool will help you find these clauses or words throughout the document.

You can purchase all CASE products at www.booksforengineers.com.

June 2016

Since its inception in 1995, the American Council of Engineering Companies’ prestigious Senior Executives Institute (SEI) has attracted public and private sector engineers and architects from firms of all sizes, locations and practice specialties. Executives – and up-and-coming executives – continue to be attracted by the Institute’s intense, highly interactive, energetic, exploratory, and challenging learning opportunities.

In the course of five separate five-day sessions over an 18-month timeframe, participants acquire new high-level skills and insights that facilitate adaptability and foster innovative systems thinking to meet the challenges of a changed A/E/C business environment.

The next SEI Class 22 meets in Washington, D.C. in September 2016 for its first session. Registration for remaining slots is available.

Executives with at least five years’ experience managing professional design programs, departments, or firms are invited to register for this unique leadership-building opportunity. As always, course size is limited, allowing faculty to give personal attention, feedback, and coaching to every participant about their skills in management, communications, and leadership.

SEI graduates say that a major benefit of the SEI experience is the relationships they build with each other during the program.

Participants learn that they are not alone in the challenges they face both personally and professionally, and every SEI class has graduated to an ongoing alumni group that meets to continue the lifelong learning process and provide support.

For more information, visit http://sei.acec.org or contact Deirdre McKenna, 202-682-4328, or dmckenna@acec.org.

On April 17-20, a record 1,400 ACEC members attended the ACEC Annual Convention in Washington, D.C., meeting with 300 Senators, Congressmen, and Capitol Hill staffers to urge passage of energy legislation, tax reform, and design-build/ procurement reforms.

500-plus attended the black-tie Engineering Excellence Awards Gala, which recognized 160+ preeminent engineering achievements from throughout the world. SFO Air Traffic Control Tower & Integrated Facility in San Francisco, CA, was honored with the 2016 Grand Conceptor Award on April 19th. The engineering work for the project was done by long-standing CASE member, Walter P Moore.

ACEC’s Annual Convention also marks the induction of a new ACEC Executive Committee. Peter Strub, Senior Vice President, TranSystems Corporation, succeeded Ralph Christie as ACEC Chairman for 2016 – 2017 at the spring meeting of the ACEC Board of Directors.

The CASE scholarship, administered by the ACEC College of Fellows, is awarded every year to a deserving student seeking a Bachelor’s degree, at a minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given $17,000 to engineering students to help pave their way to a bright future in structural engineering. CASE strives to attract the best and brightest to the structural engineering profession, and educational support is the best way we can ensure the future of our profession.

The 2016 winner, Jeffery Bloss, will graduate this fall with a Master’s Degree in Structural Engineering from the University of Kansas.

WANTED

Engineers to Lead, Direct, and Get Involved with CASE Committees!

If you are looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!)

CASE Committees. Join us to sharpen your leadership skills – promote your talent and expertise – to help guide CASE programs, services, and publications.

We have a committee ready for your service: • Risk Management Toolkit Committee: Develops and maintains documents such as business practices manuals and policies for engineers under CASE’s Ten Foundations for Risk Management.

Please submit the following information to htalbert@acec.org • Letter of interest • Brief bio (no more than two paragraphs) STRUCTURE magazine

Expectations and Requirements To apply, you should • be a current member of the Council of American Structural Engineers (CASE) • be able to attend the groups’ two face-to-face meetings per year: August, February (hotel, travel reimbursable) • be available to engage with the working group via email and conference call • have some specific experience and/or expertise to contribute to the group Thank you for your interest in contributing to your professional association!

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CASE is a part of the American Council of Engineering Companies

ACEC’s 2016 Annual Convention And The Scholarship and Legislative Summit Winner Is…

CASE in Point

A/E Industry’s Premier Leadership-Building Institute Filling Fast for September Class

Structural Forum

opinions on topics of current importance to structural engineers

Five Tips for Engineering Managers

By Stan R. Caldwell, P.E., SECB

A

fter forty-five years of experience as a structural engineering manager, including much trial and error, I have learned what works well and what does not. Based on what I have learned, I would like to offer this advice on five important topics.

Swim Upstream More than one hundred years ago, master builders like Eiffel and Roebling dominated the structural engineering profession. Since then, structural engineers have gradually moved down the “food chain.” Whether self-imposed to reduce liability exposure, or shoved aside by more ambitious professionals, many structural engineers now find themselves in unfortunate circumstances. MEP engineers typically receive higher fees than structural engineers, while providing less effort and taking less risk. Architects and civil engineers are almost always the prime professionals on building and bridge projects, respectively; and they frequently select structural engineers based almost exclusively on price, often neglect to include them in the critical conceptual phases of their projects, and pass along as much of the liability exposure as possible.

The most effective remedy for this situation is to proactively steer your firm upstream.

Structural engineers are not prohibited from acting as the prime professional on any project, and some firms are seizing that opportunity. Strive to work directly for project owners whenever possible, and to earn a seat at the “big table” where the earliest and most important project decisions are made. Always remember: other parties can only maintain your inferiority with your consent.

Stay in Your Lane Most jurisdictions offer only generic P.E. licensure, which allows an engineer to practice in any area where they feel they are competent.

This practice has resulted in structures designed by civil, mechanical, and electrical engineers.

Some structural engineers also stray out-ofbounds. When an engineer practices outside

their area of competence, the results are often disastrous. I witnessed a particularly egregious example involving a mid-rise luxury condominium tower overlooking a prestigious golf course. The structural engineer on this project, the leader of a small structural design firm, also decided to act as the civil, mechanical, electrical, and plumbing engineer. He engaged a sole-practitioner architect, provided office space for him, and overruled much of the architectural design. Then he started a construction company specifically to build the project and a testing laboratory to inspect it. In addition to all of this, he served as the managing partner of the developer. As you might imagine, the project encountered multiple problems. The litigation that followed has been ongoing for six years, and the engineer, the contractor, and the developer have all declared bankruptcy.

I encourage you to be entrepreneurial, but only if you stay within your areas of competence or add new competencies through education and experience, or by acquisition.

Embrace Construction Only accept assignments that include full construction administration services. It is during construction that your risk is highest and more disputes arise there than after completion. If the construction is deficient, you will be a party to any subsequent litigation whether or not you or your staff visited the job site. Insist on being paid for site visits and regularly visit every job site to ensure that your design intent is achieved.

Structural engineers are often asked to certify the construction of their projects, and they often get themselves into trouble by doing so. You should never certify any construction unless a member of your firm provided observation of that construction. My advice is to certify only what you or your staff have personally observed and know to be fact.

Cherish Your People Few firms enjoy truly unique technology, facilities, and other resources. The only

long-term competitive edge that any firm has is its people. So hire only the best and the brightest. Place them in a professional environment with clear office policies, effective collaboration, first-rate technology, meaningful mentoring, real opportunities for training, and exposure to the profession beyond the workplace. Then challenge them with diverse projects and a bit more responsibility than you think they can handle. Correct their errors and shortcomings, but also reward their accomplishments with timely bonuses and recognition. Promote based on merit alone, and let the cream rise to the top regardless of seniority. Most important of all, listen intently to the thoughts and concerns of every person and act on what you hear.

With the right people in the right environment, your firm is sure to prosper.

Make a Profit There are many firms that never decline a project. Others gladly accept whatever fee is offered. Still others are content to work on handshake agreements without any written documentation. In doing so, they set the bar too low and damage the profession as a whole.

Although engineering managers might be reluctant to admit it, their firms exist to make a profit. You are running a business, not a practice. Accordingly, without compromising your integrity or professionalism, you should strive to make a profit on every project. Insist on written agreements that adequately define your scope, schedule, and fee. Fulfill your commitments and never hesitate to demand additional fees whenever your scope grows or additional services are requested.

Profitable firms are healthy firms, but they are maintained only through a sharp focus.▪ Stan R. Caldwell (StanCaldwellPE.com) is a consulting structural engineer in Plano, Texas. He currently serves on the SECB Board of Directors, the SELC Steering Committee, and the SEI Task Committee on Digital Presence.

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C 3 Ink, or the STRUCTURE® magazine Editorial Board.

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