STRUCTURE magazine | February 2016

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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February 2016 Steel/Cold-Formed Steel NCSEA Winter Leadership Forum San Diego, CA March 10 & 11

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February 2016 28

FEATURE

Sliding Roof Design

By Dilip Khatri, Ph.D., S.E.

30 EDITORIAL

7 In Pursuit of Better

By Brian Dekker, P.E., S.E.

30

FEATURE

CODES AND STANDARDS

24 Special Inspections for Wood Construction – Part 2

By David P. Tyree, P.E.,

STRUCTURAL QUALITY

8 QC/QA Provisions for Cold-Formed Steel Structural Framing

By Jeffrey M. Klaiman, P.E., Bonnie E. Manley, P.E. and

Michelle Kam-Biron P.E, S.E.

34

FEATURE

HISTORIC STRUCTURES

47 Quebec Bridge – Part 3

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

By Jay S. Idriss, P.E., Jack Fritz, P.E. and Jon A. Schmidt, P.E., SECB STRUCTURAL SUSTAINABILITY

16 Sustainable Bridge-Building Practices

By Douglas R. Davis, P.E. BUILDING BLOCKS

20 Electroslag Welding: From Shop to Field

By Janice J. Chambers, Ph.D., S.E. and Brett R. Manning, S.E.

Marriott Marquis Renovation

By Virginia Mosquera, Ph.D., P.E.

CODE UPDATES STRUCTURAL PERFORMANCE

By Gerard M. Nieblas, S.E., Peter J. Maranian, S.E. and Jeff Lubberts, P.E.

James B. Smith, P.E. and

Jay W. Larson, P.E.

12 Dynamic Analysis of Insulated Metal Panels for Blast Effects

Crowning Achievement

53 New SDI Diaphragm Design Manual

By Thomas Sputo, Ph.D., P.E., S.E.

38

FEATURE

“The 951” in Downtown Boise

INSIGHTS

54 ACI Publications on Formwork

By David W. Johnston, P.E., Ph.D. SPOTLIGHT

59 Modular Challenges and Solutions: The Stack

By Janis B. Vacca, P.E.

By Wilson Antoniuk, P.E.

43

FEATURE

The Carey Building Vertical Expansion

By Joseph E. Caza III, P.E. and Michael Palmer, Ph.D., P.E.

STRUCTURAL FORUM

66 The Engineering Way of Thinking: An Analysis

By William M. Bulleit, Ph.D., P.E.

On the cover This all-wood structure is four stories with 74,500 square feet. The design included numerous engineering challenges. The building is kinked at an angle of 21 degrees in the middle of the structure, and the second floor is at a different angle from the first, just to name a few. See the feature article on page 38.

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.

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IN EVERY ISSUE 6 Advertiser Index 56 Resource Guide (Bridge) 60 NCSEA News 62 SEI Structural Columns 64 CASE in Point

February 2016

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

Albina Co. Inc....................................... 23 American Concrete Institute ................. 33 Applied Science International, LLC....... 67 Bluebeam Software, Inc. .......................... 4 Clark Dietrich Building Systems ........... 27 Dayton Superior Corporation ............... 25 Design Data .......................................... 52 Dlubal Software, Inc. ............................ 45 Hardy Frame ......................................... 57 Independence Tube Corporation ............. 2 Integrated Engineering Software, Inc..... 46 ICC – Evaluation Service ...................... 50 ITT Enidine, Inc. .................................. 39 KPFF Consulting Engineers .................... 6 Legacy Building Solutions ..................... 42

LNA Solutions ...................................... 53 MMFX Steel Corporation of America ... 21 NCSEA ................................................. 11 New Millennium Building Systems ....... 15 RISA Technologies ................................ 68 SidePlate Systems, Inc. .......................... 58 Simpson Strong-Tie......................... 19, 37 Steel Deck Institute ............................... 22 Structural Technologies ......................... 51 StructurePoint ....................................... 55 Struware, Inc. ........................................ 36 Super Stud Building Products, Inc......... 41 Trimble ................................................... 3 Wood Products Council ........................ 49

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ADVERTISING ACCOUNT MANAGER INTERACTIVE SALES ASSOCIATES sales@STRUCTUREmag.org Eastern Sales Chuck Minor 847-854-1666 Western Sales Jerry Preston 480-396-9585

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

Did You Know?

EDITORIAL BOARD Chair Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@structuremag.org

As part of the Structural Engineering community, STRUCTURE encourages you to comment on articles!

John A. Dal Pino, S.E. Degenkolb Engineers, San Francisco, CA Mark W. Holmberg, P.E. Heath & Lineback Engineers, Inc., Marietta, GA

All STRUCTURE articles are posted to the website (www.STRUCTUREmag.org). Scroll to the end of the article to post a comment. Authors are encouraged to reply to your comments when applicable.

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 Jessica Mandrick, P.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY

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Merit Award: Campus Housing, Residential Architect. 2011 Merit Award: Best Mid-Rise Apartment Project (4 to 6 stories), Gold Nugget Awards Program. 2011 Certified LEED Silver

Brian W. Miller Davis, CA Mike Mota, Ph.D., P.E. CRSI, Williamstown, NJ 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

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February 2016

February 2016, Volume 23, Number 2 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.

For change of address or duplicate copies, contact your member organization(s) or email subscriptions@STRUCTUREmag.org. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board.

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.

Editorial

new trends, new techniques and current industry issues In Pursuit of Better

By Brian Dekker, P.E., S.E., LEED AP, NCSEA President

I

’d like to wish you a Belated Happy New Year! If you’re anything like me, you’re still trying to break the habit of writing 2015 on checks instead of 2016; however, I think 2016 is finally starting to come easier and the year itself is picking up some momentum.

Construction spending is at its highest level since the Great Recession, and most design firms are seeing a relatively steady increase in work.

Continued growth will depend on a variety of factors, most of which are outside the control of structural engineers. There’s not much we can do, for example, about Federal Reserve rates, gasoline prices, unemployment rates, GDP, or government policies. There are plenty of ways, however, that we can continue to grow on a personal level and within our firms.

Personally, I like setting goals for the year, similar to New Year’s resolutions, even if I don’t actually start them on January 1. Although 92% of Americans fail to accomplish their New Year’s resolutions, I think that might be because most New Year’s resolutions relate to personal improvement. We all want to become a better version of ourselves. That could mean losing weight, getting organized, spending less money, saving more money, eating healthy, quitting smoking, or learning something new. I think the best way to improve your own life, however, is to first concentrate on improving the lives of those around you. Zig Ziglar said it well, “You can have everything in life you want if you will just help enough other people get what they want.” It’s sad that relatively few New Year’s resolutions seek to improve other people’s lives.

So my question for you is this: What if there was a way to improve yourself and others at the same time? If you’re a leader in your firm, the 2016 NCSEA Winter Leadership Forum (WLF) can help you do exactly that.

Professional success is a critical factor in people’s lives. As a leader in your firm, you have a major influence on the way that people feel about their jobs. Are you using your influence to help others in your firm succeed? At the WLF on Thursday, Staci Ketay Rotman, Attorney with Franczek Radelet P.C., will teach us a variety of ways to not only improve policies and procedures in the workplace, but also help employees feel more comfortable there. Staci will explain the legal aspects of how to hire the best candidates, how to prevent discrimination and harassment in the workplace, how to discipline problem employees, and how to make employee handbooks work for you, not against you. In brief, her session will enlighten you on how to make your employees more comfortable with your expectations of them while minimizing your risks of litigation. Have your questions ready. She is up for the challenge!

Maintaining a stable business is essential to helping employees reach their goals. The success of our businesses hinges on the projects we pursue, the risks we take, and the ways that we deal with problems.

Dale Munhall, Architect with Leo A Daly, postulates that the root cause of projects ending badly is usually a lack of actual teamwork among the owner, designers, and contractors, the seeds of which were sown by poor-quality contractual decisions made at the earliest stages of development. Dale will host an interactive workshop to address project delivery methods, QBS, and examples of successes and failures.

STRUCTURE magazine

At the WLF on Friday, Dan Bradshaw, with Benchmark Insurance Agency, and Craig Coburn, Attorney with Richards Brandt Miller Nelson, will teach us how to better identify, evaluate, and manage professional liability risk before it becomes reality. Their session will be followed by a claims management session, moderated by John Tawresey, retired VP & CFO of KPFF, addressing what happens when risk becomes reality and your firm is presented with a professional liability claim. What should you do or not do? John will host an interactive discussion of three actual lawsuits – with the engineers that were sued and the attorneys that represented them. You will leave with lots of great advice to bring back to the office. With this new knowledge, you can improve your firm, for the benefit of all employees.

Last but not least, the Coronado Island Marriot Resort & Spa has got to be one of the best places to spend a few days working on your New Year’s resolutions. The WLF will be on March 10 and 11, but our hotel discount runs from March 5 to 15. Take some extra time and enjoy the view of the San Diego skyline, take a walk on the white sandy beaches, take the trolley through Old Town, play a round of golf, take a whale watching cruise, check out the museums and gardens at Balboa Park, and finish your night in the historic Gaslamp Quarter. Visit www.ncsea.com and click on ‘Meetings’ for more information about the Winter Leadership Forum. Go to www.coronadovisitorcenter.com and www.sandiego.org for more information about the extracurricular activities.

I wish the best for you in 2016. I encourage you to set some New Year’s resolutions – to improve yourself, to strengthen your firm, and to help other people.▪ Brian M. Dekker is President of Sound Structures, Inc., a structural engineering firm near Chicago. He is Chair of NCSEA’s Advocacy Committee and can be reached at brian@soundstructures.net.

7

February 2016

Structural Quality issues and discussions on Quality Assurance and Quality Control

“The whole is greater than the sum of its parts” is an often-used phrase. Commonly attributed to Aristotle, these words ring especially true when examining the recent evolution of the AISI standards. Ten years ago, the AISI standards were compartmentalized into discrete packages on such topics as: general provisions, header design, truss design, structural wall stud design, floor and roof system design, and lateral force resisting system design.

Today, the landscape is much different for coldformed steel light frame construction. Over the past several years, the AISI Committee on Framing Standards (COFS), with oversight from the AISI Standards Council, has worked hard to develop a “whole” document to cover the structural design of cold-formed steel framing. Released at the end of 2015, AISI S240, North American Standard for Cold-Formed Steel Structural Framing, represents more than the sum of the individual parts. In fact, one aspect is the brand-new chapter addressing the topic of quality control (QC) and quality assurance (QA). This article explores the new standard, with special focus on these new QC and QA provisions.

QC/QA Provisions for Cold-Formed Steel Structural Framing

By Jeffrey M. Klaiman, P.E., Bonnie E. Manley, P.E., F.SEI and Jay W. Larson, P.E., F.ASCE

The online version of this article includes an overview of the AISI Committee Process. Please visit www.STRUCTUREmag.org.

New Provisions With the ever increasing size and height of coldformed steel light frame buildings along with the consolidation of the AISI standards into the new AISI S240, the AISI Standards Council seized the opportunity to institute minimum QC and QA requirements. These new requirements are contained within AISI S240, Chapter D. Table 1 shows the outline for AISI S240.

In 2013, the AISI Standards Council assigned the development of the new QC and QA provisions for cold-formed steel structural framing to the Standard Practices Subcommittee of the Committee on Framing Standards (COFS).

Shortly afterwards, an AISI task group was formed and efforts to write the provisions began in earnest. Rather than reinvent the wheel, the AISI provisions were patterned after similar requirements adopted by the American Institute for Steel Construction in the Specification for Structural Steel Buildings (AISC 360-10 Chapter N) and the Steel Deck Institute in the Standard for Quality Control and Quality Assurance for Installation of Steel Deck (SDI QA/QC-2011). The AISI task group also considered recommendations from a recent ICC code change proposal for the International Building Code (IBC) authored by the National Council of Structural Engineers Associations (NCSEA) – ICC S145-12. While the proposal was not approved for the 2015 edition of the IBC, many of the requirements seemed

8

February 2016

Table 1. AISI S240 outline.

A. General A1. Scope A2. Definitions A3. Material A4. Corrosion Protection A5. Products A6. Reference Documents B. Design B1. General B2. Floor & Ceiling Framing B3. Wall Framing B4. Roof Framing B5. Lateral Force Resisting Systems C. Installation C1. General C2. Material Condition C3. Structural Framing C4. Connections C5. Miscellaneous D. Quality Control & Quality Assurance D1. General D2. QC Programs D3. QC Documents D4. QA Agency Documents D5. Inspection Personnel D6. Inspection Tasks D7. Nonconforming Material & Workmanship E. Trusses E1. General E2. Truss Responsibilities E3. Loading E4. Truss Design E5. Quality Criterial for Steel Trusses E6. Truss Installation E7 Test-Based Design F. Testing F1. General F2. Truss Components & Assemblies relevant given today’s larger cold-formed steel framed buildings.

Similar to the AISC and SDI standards, the AISI S240 Chapter D provisions define key terms, establish responsibilities, and set requirements for the following: QC programs, QC and QA documents, inspection personnel, inspection tasks, and nonconforming material and workmanship.

AISI S240 defines the two key terms as: Quality Control (QC): Controls and inspections implemented by the component manufacturer or installer to confirm that the material provided and work performed meet the requirements of the approved construction documents and referenced standards Quality Assurance (QA): Monitoring and inspection tasks performed by a registered design professional, firm or approved agency other than the component manufacturer or installer

Table 2. Material verification tasks prior to assembly or installation.

Task

1

QC

QA

A

Verify compliance of cold-formed steel structural members: – Product identification (Section A5.5)

Perform

Perform

B

Verify compliance of connectors

Perform

Perform

C

Document acceptance or rejection of cold-formed steel structural members and connectors

Not Required1

Perform

Documentation tasks for quality control should be as defined by the applicable quality control program of the component manufacturer or installer.

to ensure that the material provided and work performed by the component manufacturer and installer meet the requirements of the approved construction documents and referenced standards. QA includes those tasks designated “special inspection” by the applicable building code.

Quality control is the responsibility of each contractor, subcontractor and installer on the project for their respective scope of work.

Depending on requirements specified by the local jurisdiction, the model building code, or the contract between the contractor and the owner or registered design professionals, the general contractor may also be responsible for hiring the QA inspector for the project.

AISI S240 Chapter D establishes the minimum QC and QA requirements for material control and installation for cold-formed steel light-frame construction. In the standard, material control refers to the general oversight of the materials by the component manufacturer and installer and involves procedures for storage, release and movement of materials. Throughout the manufacturing and construction processes, materials must be identified and protected from degradation.

Nonconforming items also need to be identified and segregated. Additionally, minimum observation and inspection tasks deemed necessary to ensure quality construction are spelled out within the chapter. However, the scope states that the QC and QA provisions do not apply to the following: cold-formed steel nonstructural members; the manufacture of cold-formed steel structural members, connectors or hold-downs other than material control; the manufacture of mechanical fasteners or welding consumables; or QC or QA for other materials and methods of construction.

Similar to the AISC and SDI QC and QA provisions, AISI S240 Chapter D provides easy to use tables that itemize the specific QC and QA tasks to be performed prior to, during and after such activities as: material verification prior to assembly and installation; welding; mechanical fastening; and special provisions for lateral force resisting systems.

As an example, Table 2 shows Table D6.5-1 from AISI S240.

Within the AISI S240 Chapter D tables, QC and QA tasks are prescribed as “observe”, “perform”, or “not required”. While different than the IBC Chapter 17 requirements for special inspection, this approach is similar to the AISC and the SDI QC and QA requirements. Observe means that items are to be inspected on an intermittent basis, and operations that do not interfere with the ability to perform inspection of these items need not be delayed pending these inspections. The frequency of observations must be adequate to confirm that the work has been performed in accordance with the approved construction documents. On the other hand, perform indicates critical tasks that are to be executed prior to final acceptance for each item or element. For the listed tasks, the inspector is required to prepare reports or other written documentation indicating whether the work has been performed in accordance with the approved construction documents.

Example Application As illustrated in Figure 1, a general contractor is building a small, 3-story cold-formed steel framed multi-family residential building (Risk Category II) located in an area with low basic

wind speeds (< 115 mph, per ASCE 7-10) and falling into seismic design category B (per ASCE 7-10). The primary structure is composed of cold-formed steel framed walls supporting cold-formed steel framed floor joists and roof trusses. The lateral stability of the structure is provided by cold-formed steel framed strap braced walls.

As outlined above, the contractor is designated as the “installer” in this example and is responsible for the QC portion of the requirements of AISI S240, Chapter D. In this project, there is a subcontractor specifically assigned for construction of the cold-formed steel framing, and the general contractor has delegated the QC responsibility to them.

Based on the contract, the owner has taken responsibility for hiring the QA inspector for all aspects of the work and has specified the frequency of observations needed to confirm that the work has been performed in accordance with the approved documents.

According to AISI S240 Chapter D, all wall and floor framing material must be verified by both the QC and QA inspector both before and after installation. This is to ensure that the material supplied and installed is the correct product and in acceptable condition.

Mechanical fastening must also be reviewed by both inspectors, but only on a periodic basis prior to installation. After installation, all connections must be reviewed and verified for conformance with the approved construction documents.

For this example building, the strap braced walls are connected by mechanical fasteners and post-installed concrete anchors. Per AISI S240, Section D6.9, special documentation for welding and fastener procedures is required. Lateral force resisting systems must be continuously reviewed during installation. Screw connections in shear walls must only be periodically reviewed during and

Figure 1. 3-story cold-formed steel framed multi-family residential building.

STRUCTURE magazine

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February 2016

Why “Quality Control and Quality Assurance” instead of “Special Inspection”?

The IBC currently specifies “Special Inspections” in Chapter 17; yet, the steel industry, as a whole, has embraced the concept of “Quality Control and Quality Assurance” – why the break with convention?

Figure 2. Nonconforming gap between structural stud and track.

after installation, but each and every postinstalled concrete anchor must be verified after installation.

The roof trusses in this example building are most likely pre-engineered and pre-manufactured, meaning that the component manufacturer performs their own in-house QC during the fabrication of these assemblies.

However, the installed placement, anchorage, bridging and bracing, as well as any mechanisms needed for transfer of lateral forces between the roof and walls systems, must be inspected during installation.

If any of the inspections uncover materials or workmanship that is not in conformance with the approved construction documents, then the building may be subject to additional inspections. For instance, Figure 2 shows a gap between the structural stud and track that exceeds the limits of AISI S240 Chapter C. This nonconformance must be brought to the immediate attention of the contractor and the installer, and brought into conformance or made suitable for its intended purpose as determined by the registered design professional.

Conclusions Today’s cold-formed steel light frame buildings are being built taller and larger than ever before. To keep up with the ever expanding market, the AISI Standards Council requested that the COFS develop a comprehensive structural standard with QC and QA provisions similar to those developed and maintained by both AISC and SDI. The new AISI S240, Chapter D was available for adoption and use in December 2015.

To facilitate their use, the QC and QA provisions for cold-formed steel structural framing, as well as the rest of the suite of AISI design and installation standards, are available as a free electronic download at www.aisistandards.org.▪

The development of QC and QA for the steel industry can be traced back to the publication of FEMA 353, Recommended Specifications and Quality Assurance Guidelines for Steel Moment Frame Construction for Seismic Applications, as part of the Program to Reduce the Earthquake Hazards of Steel Moment-Frame Structures (SAC Joint Venture) in 2000. At the time, it was noted that there were significant variations in the application of special inspection to structural steel moment frames. Over the course of the project, it became clear that achieving good quality construction in conformance with the approved construction documents involved a number of parties, including, but not limited to, fabricators, erectors and engineers. So, the report recommended using the terms “quality control” and “quality assurance” to begin delineating the different roles needed in the process. Those roles then became codified in the 2005 edition of AISC 341, Seismic Provisions for Structural Steel Buildings, which was first adopted by the 2006 edition of the IBC. From there, the AISC Committee on Specification (COS) chose to develop a coordinated and complete set of QC/QA provisions for structural steel in AISC 360-10, Chapter N. As Charlie Carter, Vice President and Chief Structural Engineer with the American Institute of Steel Construction stated in his presentation on “Quality Control and Assurance in AISC 360-10” at the 2010 North American Steel Construction Conference, “we were either [going to be] the first buffalo to the cliff or the pioneers.”

Why “Observe” and “Perform”?

The IBC currently uses “periodic” and “continuous” to describe the frequency of special inspections in Chapter 17; yet the steel industry, as a whole, uses “observe” and “perform” with explicit lists of tasks to describe the needed inspections – why?

When developing the QC/QA provisions for AISC 341-05, the AISC COS found that the terms “periodic” and “continuous” were vague and often led to different interpretations, depending upon the individual parties involved. Consequently, the structural steel industry settled on the term “observe” to describe inspections that are done intermittently. Their frequency is dependent upon the specific task, the particular needs of the project, and the contractor involved. The term “perform” is meant to apply to critical inspections that must be done prior to final acceptance of the item. Ultimately, the steel industry believes that this more uniform approach to inspection leads to better quality construction.

Jeffrey M. Klaiman, P.E., is a Principal at ADTEK Engineers, Inc. He chairs the AISI COFS Standard Practices Subcommittee and chaired the AISI task group that drafted Chapter D of AISI S240. He is President of the Mid-Atlantic Steel Framing Alliance and past President of the Cold-Formed Steel Engineers Institute. He may be contacted at jklaiman@adtekengineers.com.

Bonnie E. Manley, P.E., F.SEI, is Regional Director, Construction Codes and Standards, at AISI. She served as a codes and standards consultant to the AISI task group that drafted Chapter D of AISI S240. She serves on numerous industry and professional organizations, including the NCSEA Committee on Special Inspection and Quality Assurance (Industry Representative). She may be contacted at bmanley@steel.org.

Jay W. Larson, P.E., F.ASCE, is Managing Director of the AISI Construction Technical Program, which includes AISI’s longstanding and effective building code and standards development functions. He served as secretary of the AISI task group that drafted Chapter D of AISI S240. He provides service and leadership to numerous industry and professional organizations. He may be contacted at jlarson@steel.org.

STRUCTURE magazine

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February 2016

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Structural Performance performance issues relative to extreme events

I

nsulated metal panels can provide a costeffective exterior cladding solution for a multitude of projects. However, the same mechanical characteristics that enhance the panels’ flexural rigidity and provide weight savings also result in nonlinear response to loading. This is of particular interest in blast-resistant design, where components are often required to deform well beyond conventional serviceability limits.

In insulated metal panel products typically specified for exterior cladding applications, the interior and exterior panel faces are separated by a material such as mineral wool, polyisocyanurate foam, or other medium (Figure 1), which has two primary functions: serving as an insulation barrier to achieve a desired R-value; and increasing the moment of inertia, and thereby the flexural rigidity, without significantly increasing weight.

There are drawbacks, however, to this component geometry. A lightweight and relatively weak interior insulation material – commonly used foam has an ultimate shear stress on the order of fvc = 30 psi – does not allow for the assumption of plane crosssections remaining plane. Consequently, shear deflection cannot be neglected as in traditional bending analysis. Furthermore, the thin steel face sheets are prone to buckling prior to tension yielding of the full cross-section.

Nevertheless, with such an efficient cross-section geometry and insulation as an added bonus, this type of cladding solution is attractive to project engineers desiring weight and cost savings. Its proliferation has resulted in its specification on a variety of projects, and it has now found a common place among exterior walls systems designed for blast resistance. This article summarizes laboratory tests and simplified analytical methods that provide a fairly accurate methodology framework for the evaluation of these panels by structural engineers with blast-resistant design experience.

Dynamic Analysis of Insulated Metal Panels for Blast Effects

By Jay S. Idriss, P.E., M.ASCE, Jack Fritz, P.E., M.ASCE and Jon A. Schmidt, P.E., SECB, BSCP, M.ASCE

Jay S. Idriss (jidriss@BakerRisk. com) is a senior engineer on the Protective Structures Team at Baker Engineering and Risk Consultants, Inc., in San Antonio, Texas.

Jack Fritz (jfritz@centria.com) is a structural engineer at Centria, a major wall and roof system manufacturer with headquarters in Moon Township, Pennsylvania.

Jon A. Schmidt (jschmid@ burnsmcd.com) is an associate structural engineer and antiterrorism/blast consultant at Burns & McDonnell in Kansas City, Missouri.

Figure 2. Equivalent spring-mass SDOF system.

12 February 2016

Figure 1. Typical insulated metal panel cross-section geometry. Courtesy of Centria Formawall.

Blast Resistant Component Analysis Components specified for blast resistance are often assessed using a nonlinear dynamic singledegree-of-freedom (SDOF) methodology. The dynamic response of structural components to applied blast loads is determined by modeling them as simple SDOF systems (Figure 2).

Structural components such as walls, windows, beams, doors, and panels will deform and respond dynamically when loaded with a blast pressure history p(t).

The SDOF model for each component is constructed using its dynamic structural properties – resistance function R(x), damping c, and mass m – so that the model will theoretically exhibit the same displacement history x(t) as the point of maximum deflection in the actual component. This displacement history is obtained with numerical integration techniques using a computer algorithm to solve the equation of motion of the SDOF system at discrete time steps.

For insulated metal panels, analytical resistance functions for use in SDOF modeling have typically been created by computing the gross elastic (and sometimes plastic) section properties and treating the components as beams, assuming that

14 Test 1 - 46" (F-S) Test 3 - 58" (F-S) Test 5 - 32" (F-S) Test 5 - 44" (F-F) Test 6 - 92" (S-S)

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Figure 3. Static panel laboratory tests at Wilfred E. Baker Test Facility.

the full section yields and contributes to the moment capacity of the panel. The problem with this approach is that shear deformation and buckling are likely to occur during the panel response, such that traditional SDOF panel models routinely under-predict the response.

The derivation of an exact analytical function to model the relationship between the static resistance and deflection of an insulated metal panel is not trivial, as the function must take into account foam shear deformation and steel buckling modes, which occur at various phases of component response. Laboratory testing provides a practical way to derive such a function empirically and at full scale.

Centria commissioned Baker Engineering and Risk Consultants (BakerRisk) to obtain the necessary data using its Formawall Dimension Series (3-inch T Series) product, and subsequently to develop a methodology for blast analysis and associated appropriate analytical response limits.

Experimental Approach BakerRisk performed static tests in an apparatus similar to the one outlined in ASTM

F2247-11, Standard Test Method for Metal Doors Used in Blast Resistant Applications (Equivalent Static Load Method). Bladders within the rigid box are designed to take the shape of the confined space within the apparatus, with the test specimen forming one side of the space. The apparatus uses a similar support fixture and test frame as that used for dynamic tests in the same facility’s shock tube. The series of six tests subjected a variety of panel span configurations to increasing static load until failure, characterized as support disengagement. The collected data served as the basis for empirical resistance functions (Figure 3).

The response of an insulated metal panel can be characterized in several phases (Figure 4). The panels remain elastic and bonded throughout the cross-section under small displacements – less than one degree of support rotation when loaded statically – but the foam material then exhibits cracking and loss of composite action begins, followed by complete separation or delamination from the steel skins. As the stress increases in the steel skins, buckling occurs in the compressive skin. At this point, the foam cross-section near the supports is likely to be crushed.

Figure 4. Panel cross-section annotated with panel response phase descriptions.

STRUCTURE magazine

Secondary hinges then form in the panel skins, with membrane response occurring soon after, leading to eventual failure by support disengagement.

Analytical Approach In blast analysis and design, SDOF methods are commonly used for their simplicity, solution speed, and reasonably accurate results. In many cases, the so-called first peak response is desired when evaluating a component’s response to a blast load. A bilinear resistance function captures the initial “elastic” stiffness, while closely approximating the yield point at which the panel sections fail due to steel skin buckling or internal foam shear crushing.

For common support conditions, BakerRisk derived and validated a methodology to determine key parameters of the bilinear resistance-deflection function; namely, the equivalent elastic stiffness Ke, the peak resistance Rmax, the equivalent elastic deflection xe, and the ultimate deflection xmax.

The equivalent elastic stiffness is approximated by bisecting the resistance curves associated with the panel shear stiffness and bending stiffness. This average stiffness term

Figure 5. Shock tube at Wilfred E. Baker Test Facility.

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February 2016

Insulated metal panel response categories.

Response Level

Response Description

Support Rotation Limit (deg)

Superficial

Possible partial internal component delamination with little to no damage evident upon exterior visual inspection

2

Low

Partial shear cracking and delamination of internal foam with no steel buckling

5

Medium

Minor steel buckling with minor permanent deflection

10

High

Steel buckling and significant permanent deflection

15

Blowout

Disengagement from support(s)

Varies – Dependent upon Support Bearing and Connection Capacities excluding those that were pre-damaged from repeated testing. Loading these models with the measured pressure-time histories from the dynamic tests enabled comparison of the test data with the predicted response of the developed model, as well as the traditional gross section property model commonly used in the USACE SBEDS software program (Figure 7). Note that traditional analytical methods significantly under-predict response, primarily due to overestimation of the initial “elastic” panel stiffness.

Design Example

Figure 6. Response examples, left to right: superficial and low, medium, and high.

is expressed mathematically as Ke = 2/(1/Kv+1/ Kb). The computation of the shear stiffness parameter Kv = 8hcGc /L2 (where hc is the thickness of the foam core, Gc is the shear modulus of the foam (on the order of 300 psi), and L is the clear span length) reflects the shear deformations that occur due to damage of the inner foam layer of the panels, not typically observed or accounted for in general beam theory as previously mentioned. The bending stiffness parameter is computed as Kb = CkEsIs /L4 (where Ck is 76.8 for single (pinnedpinned) spans, 185 for end (pinned-fixed) spans, and 384 for intermediate (fixed-fixed) spans; Es is the elastic modulus of the steel (typically 29,000,000 psi); Is = (hp3–hc3)/12 is the moment of inertia of the gross steel section; and hp is the overall panel thickness).

The peak panel resistance is approximated by the insulated metal panel’s shear resistance or bending resistance, whichever is greater. The shear resistance is computed as Ry = Crv hc fvc /L (where Crv is 2 for single and intermediate spans, or 1.6 for end spans). It is important to note that the bending resistance R b = CrbIs σcr /hpL2 depends on the buckling stress of the steel panel section, which is approximated by σcr = 0.753√EcGcEs (where Crb is 16 for single and end spans, or 24 for intermediate spans, and Ec is the elastic modulus of the foam (on the order of 500 psi).

Once Ke and Rmax have been computed, xe = Rmax/Ke. The ultimate deflection is associated

with support disengagement, and thus only applies to single and end spans. It is approximated as xmax = √0.75(bs /2)(L+bs /2) (where bs is the width of the support).

Dynamic Shock Tube Testing and Analysis BakerRisk performed blast testing on insulated metal panels using a shock tube (Figure 5) to validate the simplified analysis approach.

There were ten such tests on six specimens, including retests of panels exhibiting lower damage levels in order to maximize the amount of data gathered in the program. Observed specimen response ranged from superficial to high damage (Figure 6). The Table provides qualitative descriptions, along with quantitative support rotation limits established from the results of the test program. Note that these limits are higher than those published for “metal panels” in commonly used guidelines from the US Army Corps of Engineers (USACE) Protective Design Center and in ASCE/SEI Standard 59-11, Blast Protection of Buildings. This is because those published values are derived for bare corrugated components dependent upon the tension membrane reaction capacity of connections and supporting members.

The analytical methodology developed from static testing enabled the creation of SDOF models of the dynamic test specimens,

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February 2016

Consider a project where a 2.75-inch-thick insulated metal panel with 26-gage (0.019inch) interior and exterior steel skins must be evaluated for blast resistance for an end span of 5 feet clear between supports that are 3 inches wide. The section properties are hp = 2.75 inches, hc = 2.75 – 2(0.019) = 2.712 inches, and Is = [(2.75)3 – (2.712)3]/12 = 0.071 in4/in.

Shear stiffness Kv = 8(2.712)(300)/ (60)2 = 1.8 psi/in, bending stiffness Kb = 185(29,000,000)(0.071)/(60)4 = 29 psi/ in, and equivalent elastic stiffness Ke = 2/ (1/1.8 + 1/29) = 3.4 psi/in. Shear resistance Rv = 1.6(2.712)(30)/60 = 2.2 psi, buckling stress σcr = 0.753√(500)(300)(29,000,000) = 12,000 psi, bending resistance Rb = 16(0.071) (12,000)/[2.75(60)2] = 1.4 psi, and thus peak resistance Rmax = 2.2 psi. Equivalent elastic deflection xe = 2.2/3.4 = 0.65 inch, and ultimate deflection xmax = √0.75(3/2)(60+3/2) = 8.3 inches. For foam with a density of 2.6 pcf and steel with a density of 490 pcf, weight w = (2.6)(2.712)/(12)3 + (490)(2)(0.019)/ (12)3 = 0.015 psi. Converting units, the mass for SDOF dynamic analysis is m = (0.015) (1,000)2/32.2/12 = 39 psi-ms2/in.

A structural engineer can use these parameters (Ke, Rmax, m) and the appropriate load and mass factors (KL and KM) in suitable dynamic analysis software – such as the General SDOF Program module of SBEDS – to calculate the peak panel deflection under

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Deflection (in)

any blast loading, convert it to the corresponding support rotation based on straight segments between hinge locations, and evaluate this against the limits in the Table. The acceptable response level is usually dictated by the required level of protection, with the panel treated as a secondary structural element. The maximum deflection must also be less than the ultimate deflection for panel disengagement (xmax). Response of the panel in rebound – as well as rebound connection capacities – may need to be evaluated, as well, depending upon the applied load and specific project requirements.

Test Data BakerRisk SDOF Model SBEDS SDOF Model

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Insulated metal panels are a common and cost-effective solution for exterior cladding, but their unique structural characteristics must be taken into account when analyzing their performance under high-magnitude dynamic loading, such as that produced by an explosion. This article provides the structural engineering community with a validated methodology for carrying out SDOF analysis of these products for blast effects, including typical material properties and appropriate response limits.▪

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Figure 7. Response comparisons for 72-inch spans (top) and 40-inch spans (bottom).

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Structural

SuStainability sustainability and preservation as they pertain to structural engineering

MCEO estimates that $51,000 was saved on superstructure costs by using repurposed steel beams.

C

ounty engineers face a daunting balancing act when it comes to keeping their roads and bridges in service. Today’s transportation needs are much more demanding than what the current infrastructure can handle.

This is especially true when it comes to repairing or replacing bridges. Most of the bridge inventory in state and local jurisdictions is classified as short span, less than 140 feet in length. Here’s where the balancing act comes in – on one side of the scale is the safety of the people who travel across the bridges. On the other side of the scale is a very tight budget that makes it necessary to prioritize which bridges get fixed, and how quickly. Throw into that mix the increased demand for using sustainable products and strict environmental guidelines when federal funding is involved, and the county engineer must make some tough choices. Since safety is always the priority, it takes some creative thinking and innovative solutions to meet the ever-increasing public demand for efficient roadways.

The team at the Muskingum County Engineers Office (MCEO) in Zanesville, Ohio has come up with an effective sustainable solution for building

Sustainable BridgeBuilding Practices Repurposing Steel to Replace Short Span Bridges

By Douglas R. Davis, P.E., P.S.

Douglas R. Davis is a County Engineer in Muskingum County, Ohio. He can be reached at davis.mceo@rrohio.com.

more cost-effective short span bridges. MCEO selects steel for many of its short span bridges and, whenever possible, uses repurposed steel beams removed from bridges taken out of service. The Green Valley Road Bridge near Zanesville is a good example of this plan in action.

The original Green Valley Road Bridge, built in 1951, was a 52-foot span painted-steel pony truss with reinforced concrete deck.It was replaced due to its poor condition, a 10-ton load limit, and the need for a structure that would allow crane access to construct a bridge project and a new electric transmission line downstream.

The new bridge was fabricated with repurposed W33x141 beams salvaged from a previous bridge replacement in the county. The beams were cut to length, cleaned of previous attachments, and mocked up on skew at the county’s facility. Two rows of bolted diagonal cross-frames were fabricated from angle members that were connected to web stiffeners welded to the beams. Upon completion of fabrication, the structure was disassembled, abrasive-blasted, primed and painted.

Completed in 2014, the new Green Valley Road Bridge is 52 feet long and 20 feet wide with five beam lines, four feet on center, covered with a nine-inch-thick composite reinforced concrete deck on a 10-degree skew installed on rehabilitated concrete and masonry abutments. It is the county’s fifth bridge to be replaced with repurposed steel beams. MCEO estimates that $51,000 was saved in superstructure costs by using repurposed beams versus new beams for this project.

Requirements for Repurposing Steel Beams

The Green Valley Road Bridge is the fifth structure to be replaced with repurposed steel beams in Muskingum County.

16 February 2016

MCEO chooses repurposed steel when the span length, beam size and hydraulic opening allow.

The challenge in using recycled or repurposed beams is finding beams that are long enough and shallow enough to carry the required load for the span. Beam sizing may require several iterations to find the right application and is impacted by

the span, spacing, loading, required vertical clearance, water opening (if over water), beam self-weight, and steel strength.

The first step in the selection process is determining if the beam can carry the load. The age and strength of the salvaged beam must be considered when evaluating applications.

The age of the steel can provide clues to the steel’s strength; however, lab testing of beam samples should be used if no other information (such as record drawings or invoices) is available. A deeper/taller beam may be required for the same span if a weaker grade of steel is encountered. A few other selection requirements must then be verified, such as if the span is over a road, can traffic pass under the bridge? If the span is over water, can flow resulting from storms clear the bridge without flooding the way?

Saving Costs While Being Sustainable

Repurposed bridges in Muskingum County, Ohio Location

Span

Beam Size

Source

Availability of Steel Beams Many large beams can be found on the state and federal systems. MCEO prefers to obtain them before they are cut into short lengths so they can be used for crossings that require deep beam sections. Most salvaged beams can be purchased for scrap steel price. It is ideal if the state has a salvage program because if the

Cost Savings

1

North Branch 38 feet Road

4-W33x130

Pleasant Valley Road

2015

$40,000

2

Green Valley Road

51 feet

5-W33x141

Pleasant Valley Road

2014

$51,000

3

Rural Dale Road

55 feet

6-W33x141

Pleasant Valley Road

2005

$55,000

23 feet

6-W12x79

Stock

2012

$20,000

4

Richey Road

5

Clay Pike Road

53 feet

4-W30-116 2-W27x102

Stock

2007

$52,000

6

Goosecreek Road

16 feet

5-W14x48

Scrap $0.20/lb

2014

$5,000

7

Bush Hill Road

28 feet

5-W14x48

Scrap $0.20/lb

2014

$7,000

TOTAL SAVINGS

The beams for the Green Valley Road Bridge were selected from MCEO’s most successful salvage project – the 2005 repurposing of a 326-foot-long, three-beam line, five-span bridge on Pleasant Valley Road. From the Pleasant Valley Road Bridge, MCEO salvaged three W33x130, 33 ksi beams, approximately 48 feet long; and 12 W33X141, 33 ksi beams, approximately 60 feet long. In addition to the Green Valley Road Bridge, these beams were used to construct a 55-foot long x 24-footwide bridge on Rural Dale Road in 2005 and a 38-foot-long x 16-foot-wide bridge on North Branch Road in 2015 – essentially constructing three new bridges from one source.

Repurposing can save more than 80 percent of the cost of purchasing new beams while extending the life of a steel beam. At the end of the beam’s extended life, it can be recycled again and again into new steel products.

MCEO saved $51,000 with the Green Valley Road Bridge and $40,000 with the North Branch Road Bridge. If not for the salvaged steel, the county would not have been able to replace the North Branch Road Bridge, but instead would have been forced to close it due to its condition and the lack of available funding to purchase new beams.

Year Replaced

$230,000

Bridge owners can typically construct short span steel bridges with on-hand tools and equipment using local work crews, saving significant project costs.

beams are taken off of a locally owned bridge that is being replaced with federal dollars and the state does not have a salvage program, then the county must pay for salvaged materials worth more than $5,000 in value. Ohio is considering the development of a salvage program to address this issue.

MCEO purchases excess inventoried beams from a local fabricator for reduced costs and rescues beams from the local iron recycling/scrap iron yard. The strong relationships forged over the years with local business owners enables MCEO to purchase beams that are designated as excess stock or slated for recycling.

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Additionally, MCEO maintains a detailed inventory of existing bridges as part of its repurposing plan. The inventory includes the number, size, length, approximate age and condition of beams available in the yard and throughout the entire existing bridge inventory. MCEO then evaluates the hydraulics for each bridge replacement location to determine the required maximum depth of a repurposed steel beam. When the span length and required vertical clearance under the bridge have been determined, the repurposed beams can be matched for future bridge replacement locations. continued on next page

What’s Involved When Using Federal Funding for Local Bridge Projects?

Recycled steel provides superior durability with minimal impact to the environment.

Steel = Time and Cost Efficiencies in Design and Construction Approximately 60 percent of Muskingum County’s 409 bridges are constructed with steel. There are 42 steel truss bridges (one built in 1913), three steel girder bridges, 186 steel beam bridges and 19 buried steel structures (corrugated plate/pipe).

In addition to its recycling/repurposing advantages, MCEO prefers steel because it provides these cost-saving and time-saving benefits: • Steel is readily available to MCEO as a construction material.

• It offers ease of handling, repairability and a uniform fabrication process by MCEO personnel or a local fabricator.

• It is ideal when using local crews.

Many of the bridges in Muskingum County are over 50 years old. Several of those were built by county crews that set the steel beams with county equipment (no large cranes required, saving significant costs) and repair them with welding or bolting. Many of MCEO’s concrete structures are unrepairable or more costly to repair once they begin to fail due to spalling and reinforcement deterioration.

• Steel facilitates ease of load rating. A steel beam bridge can be load rated simply by determining the steel section size and amount of section loss. A concrete structure is more difficult to load rate due to the lack of design drawings showing the amount and location of reinforcement in the structure.

County engineers do not have enough local funds to properly maintain their infrastructure.

As a result, they seek federal dollars, which brings with it federal environmental requirements and oversight by the U.S. Fish and Wildlife Service (USFWS), the U.S. Army Corps of Engineers (USACE), and the U.S. Environmental Protection Agency (USEPA).

Federally endangered and threatened species (such as bats) limit tree cutting from April through September, which can delay the start of projects. Waterways with over 10 square miles of drainage area may be habitat for freshwater mussels which require, at a minimum, a mussel survey. If mussels are located, then relocation and a check-up to determine their health one year after relocation are required. Small percidae fish (known as darters) spawn in the spring and can delay in-water work until after July 1st. Bald eagle nests can result in restrictions to work around nesting areas and may impact project limits.

Work in the waterway falls under the oversight of the U.S. Army Corps of Engineers.

Depending on the size, quality and designation as a scenic waterway, permits may need to be obtained to protect water quality and to place fill material in the waterway.

The most common USACE permit is required when there is a need for the removal or placement of fill, and is related to section 404 of the Clean Water Act (commonly referred to as a 404 permit). Depending on the length of the waterway to be disturbed, requirements to obtain an individual permit or a general permit will apply. A general permit is straightforward and requires an application and design showing the volume of material to be removed or placed. For a fairly common project requiring only placement of rock channel protection, it can take up to three months to obtain a permit. The application for this permit typically takes 3-6 hours to submit and usually results in a few requests from the USACE for clarification and information before it is issued. An individual permit can take up to a year or more depending on the magnitude of the impact.

The Clean Water Act also applies to construction storm water discharges. Projects over one acre in size require a permit and a plan to prevent the release of sediment-laden water from the site. These permits are issued by the state EPA or equivalent.

Most bridge projects are located within the flood plain of a waterway and require coordination and a permit for floodplain management under the Federal Emergency Management Agency’s (FEMA) National Flood Insurance Program. The goal of this review is to prevent an increase in the 100-year flood elevation upstream and downstream of the bridge.

While securing federal funding is important for rebuilding critical local infrastructure, it can create significant design and construction delays for local jurisdictions.

• Because of steel’s efficiencies in construction and installation, there is a shorter time required for road closures.

Training Opportunities and Design Tools Available at No Charge County engineers are accustomed to meeting challenging demands with creative solutions.

Repurposing steel beams is an effective method for MCEO, and Muskingum County will be using repurposed steel well into the future.

MCEO has benefited from several helpful training tools for constructing short span steel bridges that are available free of charge from the Short Span Steel Bridge Alliance (SSSBA). These tools include complimentary workshops for county engineers, Departments of Transportation (DOT) personnel, design firms and road supervisors that can be scheduled through each state’s

STRUCTURE magazine

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February 2016

Local Technical Assistance Program/Tribal Technical Assistance Program Centers.

Conducted by bridge engineers, the halfday or full-day format covers design tools, case studies, accelerated bridge construction options, practical and cost-effective fabrication, buried steel bridges, recent innovations in protective coatings, and more. Topics can be tailored to the needs and interests of the local agencies. For more information, visit www.shortpsansteelbridges.org.

A free web-based design tool developed by the SSSBA provides customized short span steel bridge designs. eSPAN140 delivers preliminary design solutions for individual projects, and the contact information for companies and people who can deliver the bridge. After the user inputs a minimum of three project parameters, a PDF document of steel solutions is delivered within seconds.

Since 2012, approximately 2,000 preliminary designs have been generated. More information is available at www.espan140.com.▪

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Building Blocks updates and information on structural materials

T

he technological advances in electroslag welding have facilitated its progression from manually fusing vessel joints filled with scrap metal to automatic field-welding of thick steel joints in high rise buildings and long span bridges. The latest version of electroslag welding, ESW-NG (the NG stands for narrow gap – about ¾ inch), is currently accepted by AASHTO for welding common types of bridge steels and is included in the bridge welding code (AWS D1.5: 2010 with interim revisions). This welding method has also satisfied criteria for AISC-defined Demand Critical Welds. A task group is working toward inclusion of ESW-NG welding into the AWS D1.8 Structural Welding Code – Seismic Supplement.

An ESW-NG weld consists of coalesced alloycored wire, base metal, and a consumable wire guide. The production of a sound weld requires about one inch of molten slag floating atop a molten weld pool, a motorized flux dispenser, a wire feeder, a water circulator, and a welding power supply. Either a constant potential DC or a square wave AC welding power supply is well suited for the ESW-NG welding process.

Containment of the molten weld and slag pools is provided by a sump, run-off tabs, water-cooled copper welding shoes or metal containment plates, and sealant. Welding shoes are detailed for optimal heat transfer and joint orientation.

ESW-NG welds are generally single-pass, made in the vertical position, have a deposition rate of about 1 inch per minute, and do not require pre-heat. Defects typically associated with a weld pass, such as slag inclusion and porosity, are very atypical of ESW-NG welds.

Electroslag Welding: From Shop to Field

By Janice J. Chambers, Ph.D., S.E. and Brett R. Manning, S.E.

Janice J. Chambers is an associate professor of structural engineering at the University of Utah. She may be reached at janice.chambers@utah.edu.

Brett R. Manning is a vice president at Schuff Steel. He may be reached at brett.manning@schuff.com.

1888 patented welding process resembling electroslag welding used scrap metal as filler material.

is channeling are melted. Metal guides must not make contact with the walls of the joint, which would cause an electric short-circuit.

The Linde Division of Union Carbide (Linde) and the Hobart Brothers Company (Hobart) were issued patents that focused on round guide (“guide tube”) profiles. Linde developed a fluxcoated consumable guide tube. The coating insulated the guide from the walls of the joint.

Using Linde’s process, the guide tube’s flux liquefaction was unpredictable and the slag pool depth was difficult to manage. A single-wire stationary guide within an ESW weld cavity could create a weld of reasonably uniform properties in joints of up to approximately 2 inches (50 mm) thick. To ensure an even deposition of weld metal across thicker joints, Hobart developed a method of oscillating consumable guides. This method incorporated insulating rings, which prevented electric short-circuiting. An experienced welding operator added flux according to the sounds emitted from the weld pool. Flux

Process and Development of Electroslag Welding An initial arc is necessary to commence the ESW welding process. The arc is soon extinguish by predeposited flux. Electric current passing through the slag pool creates a molten resistor that is heated to approximately 3500°F. Hence, ESW is considered to be resistance welding.

Advancements made in ESW to achieve the superior physical properties of ESW-NG focused on electrode chemistry, wire guides, flux maintenance, welding shoe architecture, management of heat transfer during the welding process, and automation.

ESW Wire Guides and Flux Maintenance During the ESW welding process, wire must be guided into the weld cavity. Consumable metal guides replaced non-consumable guides early in the evolution of ESW. As an ESW weld progresses vertically, a stationary wire guide and the wire it

20 February 2016

Modern electroslag welding: ESW-NG.

Cross-section of an ESW-NG joint during fabrication and isometric of the contained joint.

was added when the operator heard the weld excessively arcing. If the weld became too quiet, too much flux had been added.

Round guides evolved into flat guides housed with channels for feeding one to multiple wires. These guides eliminated the need for oscillating guides and opened the door for narrowing the welding gap of conventional ESW, from approximately 1.25 inches (32 mm) to ¾ inch (19 mm) used in ESW-NG.

Box column diaphragm ESW-NG welding.

Contemporary ESW-NG incorporates automatic wire feeding and flux dispensing. The wire feed rate is synchronized with guide consumption. About ½ of the required starting flux is added to the welding sump before the commencement of welding. The balance of the starting flux is gradually added during the first minute of welding. As welding progresses vertically, traces of flux plate the walls of the welding shoes. Automatic flux dispensers maintain a constant-depth slag pool by

monitoring variations in electric current and potential. Flux addition is generally very small and constant. The required amount of flux is about 0.2 ounces (5.5 g) per minute.

Welding Shoes and Management of Heat Transfer Side containment has always been used to construct an ESW weld. When possible, ESW-NG welding shoes are constructed of copper, which has very high thermal

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February 2016

a flexible enter section that allows the welding shoe to fit snugly against misaligned plates.

There are also welding shoes for welding plates of different thickness and a welding shoe for welding T-joints. Welding shoes have also been designed for oblique-angled joints.

Electroslag Welding in the Shop

Stiffener plate topology for ESW-NG welding that does not required 180 degree rotation of the girder.

Wire guides pass through pre-fabricated slots in web.

Shop-Welding of Stiffener, Continuity, and Base Plates The joint formed by a stiffener, continuity, or a base plate and a flange of a wide-flange shape is a T-joint. As welds increase in thickness, so does the expense of typical arc welding processes, because these welds must be made in multiple passes and require preheat.

Currently, three stiffener plate configurations are available to ESW-NG welding. The traditional option requires a 180 degree rotation of the girder after completion of welding the first stiffener plate. By fabricating beveled slots entirely or partially through the web of the girder, the need to rotate the girder during stiffener plate welding is eliminated.

These slots also have the added advantage of relieving residual stresses existing in rolled shapes near their fillet “k” area.

Column stiffener plates were welded with the traditional ESW process in Northern and Southern California buildings prior to 1980. The October 17, 1989 Loma Prieta and January 17, 1994 Northridge earthquakes

Mock-up of instrumented column flange splice.

Traditional horizontal FCAW column splices can be rapidly welded at 45 degrees using ESW-NG.

provided real-world comparisons of all of the welding processes used to fabricate steel structures in California. Not one failure or crack propagation was discovered in any of the ESW welds inspected.

Box Columns Fabrication The welding of diaphragm plates to the interior walls of box columns using arc welding methods is labor-intensive, particularly welding the final of the four welds needed to attach these plates. With the introduction of ESW’s “key-hole” welding method, this process was made simpler. Holes are cut through two parallel box column plates in line with the centerline of the seam weld gap, where a sump and run-off tabs are installed. A wire guide is inserted to commence the ESW welding process. The vertical rate of rise required to produce a sound keyhole weld is about 1 inch per minute (26 mm/minute). Today, not just the final, but all diaphragm welds of box columns may be quickly made using ESW-NG.

Taking ESW-NG to the Field Rarely was conventional ESW seen at the site of a major structural engineering project.

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conductivity – allowing rapid heat transfer from the base metal. Additional heat retardation is provided by coolant, typically water, that circulates through the channeled body of welding shoes. ESW-NG copper welding shoes are fabricated from solid 1-inch (25 mm) thick copper plate. The finished products are at least 4 inches (100 mm) wide and 12 to 18 inches (300 mm – 450 mm) long.

Although rapid heat transfer from the base metal is desirable, if heat escapes from the molten flux and weld pools too rapidly, the weld cross-section will be of exaggerated barrel-shape, or worse, incomplete fusion at the weld corners can occur. The architecture of ESW-NG welding shoes promotes complete and uniform fusion of the weld and base metals across its width. A tri-part welding shoe (Tri-part Shoe) incorporates several features that enable complete fusion at the weld’s corners. A version of the Tri-part Shoe, the Tri-part Articulated (Flex) Shoe, has

ESW-NG welds thick plates and cross-sectional elements [from about 1 inch (25 mm) to 6 inches (150 mm) in thickness] much more efficiently than traditional multi-pass arc welding processes such as flux-cored arc welding. However, ESW-NG requires the force of gravity and more instrumentation than conventional arc-welding processes found in the field. Hence, ESW-NG welding has seldom been seen at a construction site, until recently.

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ESW-NG was recently used to weld BRB gusset plates to plates embedded in the concrete core of the Wilshire Grand Hotel in downtown Los Angeles.

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One notable ESW field application occurred during the construction of the New Orleans, Louisiana Mercedes-Benz Superdome, circa 1975. With the immergence of ESW-NG, electroslag welding is now a highly-competitive option for welding thick steel joints in the field.

East Span, San Francisco – Oakland Bay Bridge Tower

welding heavy column flange splices of large W-shapes, since joints oriented 45-50 degrees from vertical can be successfully welded with ESW-NG. It takes 30 hours or more to splice a heavy-column using FCAW. In comparison, it takes about 30 minutes or less to weld both flanges of any thickness material using ESW-NG.

Conclusion

thick plates in a steel fabrication shop.

It can economically weld stiffener, continuity, and base plates to the flanges of steel shapes, and attach diaphragms to the inside walls of box columns. Modern technological advances in ESW, embodied in ESW-NG, has also expanded its role to the construction site of a major high-rise building and bridge construction. ESW-NG is proving itself to be the most cost-effective choice at many connections, for the reliable production of thick welds in steel bridges and buildings.▪

The first ESW-NG field-welding occurred during the construction of the East span of the Electroslag welding may no longer be San Francisco/Oakland Bay Bridge (complete considered as simply one option to splice early in 2014), the world’s longest selfanchored suspension (SAS) bridge. The base of its single tower consists of twenty (20), 33-foot (10 m) long ESW-NG welds that join steel plates, up to four inches (100 mm) in thickness. Five uniquely oriented joints required custom welding -Angle -Flat Bar -Square Bar -Wide Flange -Channel -Square Tubing-Tee -Rectangular Tubing -Round Tube & Pipe -Round Bar -Rail -Plate shoes. Thirty-six-foot (11 m) long guides channeled two 3⁄32-inch (2.4 mm) diameter alloy-cored wires into the molten slag and weld pools as three shoes on each side of the joint were leap-frogged in unison ahead of the pools. The ESW-NG welds were completed in 60 days. Less than 5% of the total length of the welds required repairs. Weld defects were generally due to variations (on the shallow side) in the optimal slag pool depth.

STRUCTURAL STEEL BENDING EXPERTS

The tallest skyscraper in California, The Wilshire Grand Hotel, is under construction in downtown Los Angeles. Its lateral force resisting system consists of a concrete core, buckling-restrained outrigger braces (BRBs), and perimeter belt trusses. ESW-NG welds joined gusset plates for Lower Outrigger BRBs to the structure. These BRB ESW-NG joints are approximately 12 feet high x 2.75 inches thick (3.6 m x 7 cm). ESW-NG welds up to 49 inches (149 cm) long and 5 inches (15 cm) thick also joined the flanges of the chord and diagonal members of the Lower Belt truss to the face of box columns.

This issue contains an article on the Wilshire Grand and two prior issues (December 2014 and August 2015) of STRUCTURE tracked construction of the Wilshire Grand.

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February 2016

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The Wilshire Grand Hotel, Los Angeles, California

Codes and standards updates and discussions related to codes and standards

T

his article is the conclusion of a twopart series which discusses special inspection provisions for wood construction found in Chapter 17 of the International Building Code (IBC). Although the IBC is in use or adopted in 50 states, the District of Columbia, Guam, Northern Marianas Islands, New York City, the U.S. Virgin Islands, and Puerto Rico, each state and jurisdiction may not adopt the same edition of the code and/or make amendments to the code. Included are examples of special inspection provisions from California, Washington, and Wisconsin based on the 2012 IBC. The previous article (Part 1, STRUCTURE, January 2016) provided an overview of the special inspection provisions for wood construction found in the 2015 IBC.

State of California Prior to adopting the IBC as a model code, the 2001 California Building Code (CBC) used the 1997 Uniform Building Code as a model code.

Special inspection for wood construction was only required for prefabricated structural elements and not for seismic and wind force resisting systems and components.

However, structural observation was required for buildings in seismic zones 3 and 4. It wasn’t until the 2007 CBC that California transitioned to the 2006 IBC as the model code. The 2007 CBC was the first edition that included provisions for special inspection of seismic and wind force resisting systems and components.

Special Inspections for Wood Construction Part 2

By David P. Tyree, P.E., C.B.O., James B. Smith, P.E., and Michelle Kam-Biron P.E, S.E.

California Agencies, Boards, Commissions and Departments David P. Tyree is the Central Regional Manager, James B. Smith is the Midwest Regional Manager, and Michelle KamBiron is the Director of Education at the American Wood Council, Washington, DC.

Although this article is based on the 2015 IBC, California has yet to adopt the 2015 IBC as its model code and is in the process of developing California Amendments, which will eventually become the 2016 CBC. The CBC is part of the California Code of Regulations, Title 24, also referred to as the California Building Standards Code, and is published in its entirety every three years by order of the California legislature. The California legislature delegated authority to various state agencies, boards, commissions and departments to create building regulations to implement the state’s statutes. A city, county, or city and county may establish more restrictive building standards reasonably necessary because of local climatic, geological, or topographical conditions. The current 2013 CBC and California Residential Code (CRC) use the 2012 IBC and 2012 International Residential Code (IRC) as its model codes.

Chapter 17, Structural Tests and Special Inspections, includes amendments from adopting

24 February 2016

Special inspection provisions for construction are found in Chapter 17 of the International Building Code (IBC).

state agencies, including: California Building Standards Commission (State owned buildings, including University and State College buildings and all buildings not otherwise regulated by other state agencies), Department of Housing and Community Development (HCD) 1 & 2 (hotels, motels, apartments, dwellings and permanent buildings within mobile home parks), and Office of Statewide Health Planning and Development (OSHPD) 2 & 3 (skilled nursing facilities & clinics). Chapter 17, Structural Tests and Special Inspections, also includes amendments from adopting state agencies, including: Division of the State Architect-Structural Safety (public schools), Division of the State Architect-Structural Safety/ Community Colleges (community colleges) and OSHPD 1 & 4 (acute-care hospitals and correctional treatment centers). However, there are no significant California Amendments for wood in Chapter 17A. Significant California Amendments to IBC Chapter 17 What follows are several significant amendments to IBC Chapter 17: OSHPD 2: 1704.2.3 Statement of Special Inspection provision requires special inspections for conventional light-frame construction of Section 2308. HCD 1: 1704.2.4 Report requirements references provisions for the construction and inspection of factory-built housing.

OSHPD 2: 1705.5.3 Manufactured trusses and assemblies expands the scope of inspection for manufactured trusses and assemblies, and does not limit this to trusses with a clear span greater than or equal to 60 feet. Continuous inspection and a report are required for lumber species, grades, and moisture content; type of glue, temperature, and gluing procedure; type of metal members and metal plate connectors; and workmanship.

City of Los Angeles The City of Los Angeles (COLA), Los Angeles Municipal Code (LAMC) Sixth Edition, Chapter IX Building Regulations, Article 1 Buildings, is the Los Angeles Building Code (LABC). The LABC adopts by reference portions of the 2013 CBC and 2012 IBC and is amended by Ordinance Number 182850.

COLA Special Inspection

COLA Structural Observation COLA section 91.1704.5. Structural Observations clarifies that the registered design professional in responsible charge for the structural design may perform structural observations and he/she may delegate responsibility for structural observations to another registered design professional. Also included are requirements for the owner or owner’s representative to coordinate a preconstruction meeting with the engineer or architect responsible for the structural design, structural observer, contractor, affected subcontractors, and deputy inspectors. The structural observer is to preside over the meeting. The purpose of the meeting is to identify the major structural elements and connections that affect the vertical and lateral load systems of the structure, and to review scheduling of the required observations.

The LABC exempts one-story wood framed Group R-3 and Group U Occupancies less than 2000 square feet in area from structural observation that are not in Risk Category III or IV, provided the adjacent grade is not steeper than 1 unit vertical in 10 units

State of Washington The Washington Association of Building Officials (WABO) developed a Special Inspection Registration Program to create a uniform method of determining qualifications of special inspection agencies and special inspectors. The voluntary registration program is designed to provide a means of documenting special inspection and testing qualifications, and competency in various types of work cited in the IBC. The current list of special inspection categories includes: • Reinforced Concrete (RC) • Prestressed Concrete (PC) • Shotcrete (SC) • Structural Masonry (SM) • Structural Steel and Bolting (SSB) • Structural Welding (SW) • Spray-applied Fire-resistive Materials (FP) • Lateral Wood (LW) • Cold-Formed Steel Framing (CF) • Proprietary Anchors (PA) For the purposes of this article, the focus will be on the Lateral Wood category.

Development of the Lateral Wood Special Inspection (LWSI) registration program was initiated by WABO a decade ago. The first version employed the special inspection requirements in Chapter 17 of the 2003 IBC. This program was a natural addition to WABO’s existing Special Inspection Registration Program (SIRP) which already met other code-mandated needs for special inspections. Since that time, LWSI materials have been updated as new editions of the code are adopted. Washington currently adopts and modifies the 2012 edition of the IBC. Because critical details in the lateral force resisting framing of wood buildings are beyond the normal scope of conventional framing inspections, this program specifically targets critical building components in multi-story wood buildings that must be properly installed to withstand seismic and high-wind events.

The program aids in increasing the uniformity and quality of inspection procedures, and establishes inspector credentials. The developmental committee, consisting of code officials, engineers, and architects,

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Significant amendments in the LABC, including 91.1704.2 Special Inspections, require a Registered Deputy Inspector (RDI) rather than just an approved agency as stated in the CBC. In addition, the RDI shall demonstrate competence to the satisfaction of the Superintendent of Building rather than to the building official. Per Division 2 Definitions and Abbreviations of the LABC, the Superintendent of Building is the General Manager of the Department of Building and Safety of the City of Los Angeles or a duly authorized representative. COLA has a certification/license requirement for RDIs as required by the Chapter for structural wood.

Additional sections provide extensive requirements beyond the ICB or CBC; however, there are no specific changes related to the inspection process.

There are no LABC amendments to subsection IBC or CBC subsection 1705.5 Wood Construction of Section 1705 Required Verification and Inspection.

horizontal (10% sloped), and assigned to Seismic Design Category A through D. The City of Los Angeles’ website contains an extensive library of Building and Safety Forms such as Registered Deputy Building Inspectors Certificate of Compliance, Structural Observation Report Form, Architects or Engineers Certificate of Compliance, Deputy Correction Notice, etc for use, as applicable, by the design professional.

provided tools to assist in the facilitation of the program and to outline the responsibilities of the LWSI inspector. Those responsibilities include: General • Authority to carry out requirements of the enforcing jurisdiction.

• Notify the jurisdiction about the type of inspection in accordance with jurisdiction requirements.

• Present for continuous inspection during execution of all work for which the special inspector has been engaged.

• Verify that the local jurisdiction inspectors have approved the conditions at the site when required.

• Submit periodic written and verbal progress reports to the local jurisdiction as required.

• Notify the contractor when discrepancies occur.

• Notify the building official of uncorrected discrepancies.

• Verify that structural plan changes are properly documented, and approved by the enforcing jurisdiction.

• Maintain records of work inspected, including discrepancies and actions taken.

• Submit final compliance reports.

Technical • Identify lateral force resisting systems for conformance, including shear walls, diaphragms, chords, sub-diaphragms, hold-downs, connectors, and drag struts.

• Verify placement of plates, shear walls, diaphragms, squash blocks, hold-downs, strapping, beams, and columns.

• Verify stud spacing, blocking, panel material and orientation, nail size and spacing, anchor bolt spacing, location, strap-size and location, and use of glue.

Material Identification • Verify wood species and grade, dimensions, sheathing material, and engineered lumber applications.

• Verify fasteners, including nails, staples, screws, and bolts for size, type, grade, and location.

• Verify hardware, including holddowns, straps, ties, rods, nuts, anchors, engineered systems, and prefabricated panel size types and location. Verifying that the hardware specified on the plans has been installed. Reviewing and verifying manufacturer installation procedures.

Workmanship • Verify the proper use of materials, including appropriate cutting, notching, nailing, and member alignment.

• Verify material condition, including member damage, shipping, handling, weather impacts, and hardware.

• Verify any associated testing that should occur including pullout tests for epoxied anchor bolts.

• Review plans for associated general requirements and details for foundations, connections, beams and columns, shear walls, and diaphragms.

Through this program, local building jurisdictions can easily ascertain and approve credentials of prospective special inspectors. The program also oversees and certifies quality control agencies where inspectors are employed.

State of Wisconsin Wisconsin has had a state-wide commercial building code since their Safe Place Statutes were first put in place in 1913. The ensuing Wisconsin Commercial Building Code (WCBC) was developed and went into effect in 1914. Although the use of model codes was being considered in the late 1970s, it was not until 1998 that the State of Wisconsin began the rulemaking process that would consider the then proposed I-Codes for adoption as the state-wide WCBC. Early editions of the WCBC aligned the plan review arm of enforcement with a few of the larger cities that had building inspection departments and with the State agency assigned stewardship of the Safe Place Statutes. Inspections were conducted by those larger cities and the State agency staff. State law placed the greatest responsibility for safe places on the owner, and safe construction of those buildings on supervision by architects or engineers. Understanding the limited role that building departments were expected to take in the requirement for providing a safe place, the Administration section of the WCBC included language to reinforce that it is the responsibility of the owner and architect.

By 1976, the WCBC added language to clarify the Wisconsin design professional’s responsibility to ensure that all commercial buildings over 50,000 cubic feet total volume were constructed in accordance with the design plans and comply with the WCBC. The WCBC requirements for a supervising professional cover all aspects of the code.

Registered architects and professional engineers functioning as supervising professionals can hire specialists to monitor/inspect special aspects of a project that are deemed critical.

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The WCBC only included specifics associated with pile foundations and protection of adjoining property (underpinning). At the time the model code provisions associated with Special Inspections were being considered in 1999, it was determined that the methodology in place in Wisconsin corresponded to and in some ways exceeded the provisions for Special Inspection that existed in Chapter 17 of the 2000 International Building Code. Accordingly, the entirety of IBC Chapter 17 was removed from state-wide adoption.

Shortly after the first adoption, it was recognized that there were many provisions within Chapter 17 that would be advantageous to users of the code while not conflicting with the state’s Supervising Professional methodology. Accordingly, when the 2006 edition of the IBC was adopted in 2008, the important provisions for in-situ load testing and preconstruction load testing were included.

Wisconsin currently adopts and modifies the 2009 IBC by only specifying requirements in IBC sections 1711 (Design Strengths of Materials), 1712 (Alternative Test Procedure), 1713 (Test Safe Load), 1714 (In-situ Load Tests), 1715 (Preconstruction Load Tests) and 1716 (Material and Test Standards). The provisions normally associated with special inspections elsewhere in the United States are currently excluded.

Even though the original intent was to allow local municipalities the option to adopt the excluded provisions, the changes made within 2013 Act 270 established the WCBC as a uniform code. Accordingly, the administrative rules that create the WCBC will have to be changed in order to use the Special Inspection program outlined in IBC Chapter 17 or allow programs as implemented in the States of California and Washington. The State of Wisconsin is currently in the middle of their process to evaluate the 2015 edition of the IBC for adoption as the statewide uniform commercial building code.

Conclusion Each state and jurisdiction can make amendments to the code. Chapter 17 of the IBC dealing with special inspections is not immune from this practice. This article provides perspectives from the states of California, Washington, Wisconsin, and the City of Los Angeles regarding special inspection provisions for wood construction. Structural engineers play an important role in the special inspection process, and all owners and design professionals should be aware of the importance of special inspection in providing a safe, code-compliant building.▪

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SLIDING ROOF DESIGN Frida Restaurant in Torrance, California

By Dilip Khatri, Ph.D., S.E.

Figure 1. Architectural rendering of front corner elevation of Frida Restaurant.

O

ne of the most satisfying aspects of being a structural engineer is to see your project constructed. Even more satisfying is knowing you contributed to making something unique, creative, and aesthetically pleasing to society.

Inspiration and gratification are rare in any professional endeavor, and the author is pleased to be part of the team that has made this project a reality. The Frida Restaurant definitely brings home that feeling of accomplishment, as the Structural Engineer (SE) staff have worked tirelessly with the Architect, Tag Front Design, to meet the design challenges. As this article is written in November 2015, the contractor is completing the final phase of this restaurant for its Grand Opening

by December 15, 2015, and by time of publication the restaurant will be serving customers at the Fashion Mall Plaza in Torrance, California.

Why is everyone so excited and proud of this retail project? Several reasons come to mind, but one striking feature of this architecturalengineered design is the roof structure. It is designed to “slide open and closed” similar to a convertible rooftop on a car. Figures 1 through 5 provide illustrations on the creative design concept from the Architect.

The roof has perimeter skylights that allow natural light to illuminate the interior areas to create a warm spatial effect, which enhances the dining

experience. Perimeter skylights that run the entire length of the roof diaphragm (on both sides) create diaphragm shear transfer issues, which posed structural engineering design challenges. The client wanted an interior space that was “free of columns” and had full opening on all sides, with glass and other architectural features. This eliminated the possible use of a standard shear wall system. An interior bar design is “suspended” from the ceiling with no visible support from the floor (Figure 2). Tag Front designed an open floor plan that is free of visible column supports, but follows no standard grid. Specifically, the floor plan does not follow a standard rectilinear grid system with columns at even spacing. The support system is irregular, and with certain columns taking loading with eccentricity/torsional components to the lateral beams.

Figure 2. Interior rendering showing the hanging bar design.

Figure 3. Interior views showing full glass openings with no shear walls.

STRUCTURE magazine

Structural Design Solutions The selection for the lateral force resisting system (LFRS) was steel moment frames with hollow structural steel tube (HSS) columns and tube beams in both directions, connected with ordinary moment frame connections. The HSS columns provided equal moment capacity along both axes, which allowed the design to be balanced efficiently, due to

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Figure 4. 3D isometric showing sliding roof over garden area.

Figure 5. Interior rendering with open space and no column interference.

the irregular grid layout. Certain column locations are positioned with eccentric loading from the roof support and/or beam locations, which required extra design effort to make them work. Foundation design utilized spread footings with base moment connections through a pedestal design interconnected with grade beams. Seismic considerations were important, as the site is classified Seismic Design Category “D”.

Fortunately, no liquefaction or unusual soil conditions were present.

The sliding roof design created additional dead load demand on the structure, which resulted in 16-inch square HSS sections that carry beam spans of up to 20 feet, in order to meet the Architect/Owner criteria of an open floor plan. The additional dead load also resulted in large footings and grade beams because the base moments were high, due to the large loads (when compared to typical single story retail buildings) and long spans of the supporting beams. Lateral drift was critical in the stiffness design of the LFRS to reduce any possible impact to the adjacent mall structure.

On the interior, the open floor design is further enhanced by the unique bar design, which is suspended from the ceiling. This consists of structural tubes welded together and “hangs” from a ceiling beam with no support from the foundation. A lateral analysis of the Bar support structure had to prove that the drift did not exceed certain limits so as to endanger the occupants from flying bottles. Similar to the bar, the fire place is designed within a fully-suspended wall with no direct support from the foundation. A steel support beam with a specially fabricated plate cross section was designed to serve this purpose.

Collaboration with the Architect, Owner, and Contractor Tight time frames, short turnarounds, and a critical schedule all characterize the stress level on this project. Structural engineering design is never done in a vacuum, and the SE team collaborated very closely with Tag Front Design and the Contractor to work out the details.

During construction there are always change orders, RFIs, and designconstruction issues that must be addressed promptly, sometimes leading to heated “discussions”, but at the end of the day the problems must be solved. The author must admit, even after 33 years in the profession, we are always perpetual students of structural engineering. Every project brings new lessons that hopefully make us sharper engineers for the next project. The Frida project definitely taught new solutions to old problems and reemphasized the team relationship with the Owner, Architect, and Contractor. Perhaps the most important contribution that SEs can make to this working relationship is to be available and open to new ideas. Often, our initial reaction when we see the Architect’s concept is to rethink our proposal! However, a project like this is too delicious of a challenge. Be grateful for the experience.

The author discovered that collaboration is not just about being a good engineer, but being open to other people’s ideas and suggestions.▪

Retractable Roof Design This project’s most unique feature is the retractable/sliding roof design, which allows the owner to cover the patio seating area, depending on the weather conditions. The sliding roof is elevated approximately four feet above the rest of the roof plane, which creates some challenges for diaphragm shear transfer and produces torsional bending moments on the supporting beams. The roof structure is supported on two rail beams (i.e., two structural tubes) on both sides, which then transfer the load to vertical tube columns resting on the roof diaphragm beams. Seismic loads do not govern, but the wind loads are substantially higher than the dead loads. The analysis encompassed the use of torsional load transfer with vertical tubes to support the sliding roof through an elevated steel moment frame on top of the building moment frame system. Certainly this is one of the most unique designs the author has worked on in recent years.

Because of timing issues and tight schedules, the sliding roof has to be installed after the restaurant’s opening date in December 2015 and will be completed in the first quarter of 2016.

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Dilip Khatri, Ph.D., S.E., is the Principal of Khatri International Inc. and Khatri Construction Company located in Pasadena, California. He has served as an expert witness for several construction-law firms and as an insurance/forensic investigator of structural failures. He serves as a member of STRUCTURE’s Editorial Board and may be reached at dkhatri@aol.com.

All photos courtesy of Tag Front Design.

Project Team Structural Engineer: Khatri International Inc., Pasadena, CA Owner: Frida Restaurant, Beverly Hills, CA Architect: Tag Front Design, West Hollywood, CA Contractor: Ck2d Construction Roof Manufacturer: Rollamatic Roofs, Inc. Roof Structural Design: Ficcadenti, Waggoner, & Castle

February 2016

CROWNING ACHIEVEMEN

By Gerard M. Nieblas, S.E., LEED AP, Peter J. Maranian, S.E. and Jeff Lubberts, P.E.

T

he crowning achievement on the Wilshire Grand project will be the Crown Sail and Spire that set atop the roof of the building. By any measure the crown sail and spire are a building unto themselves.

Typically, engineers place structures over rigid bases that are 10x stiffer than the structure above. This allows the structure to be designed as if on a rigid base. With the Wilshire Grand project, engineers set a stiff structure on top of a flexible one. This resulted in a sail and spire with very high seismic design requirements from upper mode effects produced by the supporting 73-story building.

Project Description The Wilshire Grand Project is approximately 2,000,000 square feet with 900 hotel rooms, 400,000 square feet of office space and 45,000 square feet of retail space. The 5 level subterranean parking covers the entire site and will accommodate 1,100 vehicles. The structure will have a rooftop pool with ocean views, pressurized double decker elevators, an architectural roof top sail and a 300-foot tall architectural spire.

The Tower structure is 73 stories, with the lower floors comprised of office space and the upper 40 floors as hotel rooms. The lateral system for the building is a concrete core wall with concrete-filled steel box columns and structural steel framing outside the footprint of the core. The lateral system of the Tower is extremely slender. In the transverse building direction the core wall is 30 feet wide and nearly 1,000 feet tall.

Along the height of the structure there are buckling restrained braced frames to reduce the overturning demands of the core wall on the mat foundation, and to stiffen the structure for transverse wind and seismic drift.

Sail and Spire with KAL logo. Courtesy of AC Martin.

Sail Structural System The base of the sail is founded on the 73rd floor with the sky bar and reflective pool. The sail houses the uppermost elevators and elevator machine room along with the tactical approach, building maintenance unit (BMU) #1 on the 75th level, BMU #2 on the 76th level, and catwalks for access to LED lighting.

Base of sail with DYWIDAG connectors anchors. Courtesy of Schuff Steel.

Lounge at 73 rd floor. Courtesy of AC Martin.

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Artist rendering of Sail and Spire. Courtesy of AC Martin.

Top connection of spire to sail. Courtesy of Schuff Steel.

The structural system for the sail is a three dimensional space truss.

The sail is approximately 100 feet tall and has a structural steel weight of about 900 tons, with a plan area of about 5,000 square feet.

The lateral forces from the Maximum Considered Earthquake (MCE) are 4.25G in the North-South direction and 5G in the east-west direction. These seismic forces induce uplifts on the wide flange columns as much as 3,800 kips. These high seismic demands are a result of higher mode effects from the supporting tower. These column bases were anchored with what are normally used as rock anchors (DYWIDAGs). These columns have 8 (150ksi), 2½-inch (2.8-inch OD) anchors embedded into the concrete 14 feet.

One of the many design challenges for the support of the sail were the effects of long term creep and shrinkage of the concrete core wall.

Portions of the sail are supported directly off the concrete core wall and the edges of the sail extend over the structural steel framing.

Over the next 100 years, the concrete core wall will creep and shrink approximately 2 inches more than the elastic shortening of the steel columns. The sail columns at the edges of the steel framing are designed with a 5-inch gap between the bottom of the column and the floor (that would normally support the column). This gap is necessary to keep these columns from pushing down on the steel framing from concrete creep, concrete shrinkage and MCE deflections.

of the spire is a light beacon. It is a tapered stainless steel circular section with perforated holes.

Long term creep and shrinkage of the concrete core wall created support problems for the spire. The lateral restraint of the spire on the 75th level has large steel pins with hinges to allow the sail structure to move downward with creep and shrinkage from the supporting core wall below. From transverse MCE loads, the maximum horizontal reaction is 660 kips per pin. All of the vertical loads of the spire are supported on the 73rd level.

The spire will be erected in 40 sections and bolted together. The bottom sections of the spire are joined together with 144 11/8-inch A490 bolts.

The spire will be subject to wind loading over many, many years.

To compensate for fatigue over the life of the structure, wind stresses were limited to 10ksi for the 50 year wind event. Ancillary welds to the spire for ladders and maintenance were also prohibited to prevent any adverse effects from welding. All ancillary attachments to the spire will be in drilled and tapped holes with rounded edges. The rounded edges reduce stress concentrations and allow for a more uniform layer of galvanization.

After galvanization, the welds will be peened to relieve residual tensile stresses. The process of peening induces residual compressive stresses in the peened surface. These surface compressive stresses provide better resistance to metal fatigue and to corrosion.

Spire

The total height of the spire is 300 feet. The spire is supported vertically off the 72nd floor and is restrained horizontally from wind and seismic forces at the 75th level in the sail. The spire cantilevers 217 feet, with an 83-foot backspan.

The spire tapers along its height. At the base, the spire is 6½ feet in diameter and 3.33 feet in diameter at the top. The uppermost 17 feet BIM/Revit model of Sail and Spire.

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BMU’s There are two building maintenance units housed in the sail. BMU #1 is on the 75th level and BMU #2 is on the 76th level. Each of these BMUs fold outward and telescope upward to clear the sail and maintain the exterior of the structure below. continued on next page

Plan views of BMUs. Courtesy of Skyrider/GinD.

Hinged connection of spire to sail. Courtesy of Schuff Steel.

The building maintenance units for the structure are massive. Their dead weights are approximately 128,000 pounds each. When considering the earthquake response of the BMUs on the sail, they place a 6G demand (700 kip singular reaction) on the sail from 1.5MCE. The BMU arms extend approximately 100 feet to reach the longitudinal edges of the structure. These BMUs need to accommodate a sloping curtainwall. On the north face of the structure, the building skin (and structural columns) slopes 6 feet horizontally in three floors.

On the west face of the structure, the building slopes over 45 feet horizontally along its height. On the east face, the upper portions of the structure extend out past the lower cantilevered portions below.

The BMUs have to, in effect, reach under an overhang.

Section of BMU. Courtesy of Skyrider/GinD.

Conclusion The Crown Sail and Spire will be the crowning achievement of the Wilshire Grand Project. This will be the tallest building west of the Mississippi. Outside of New York and Chicago, it will be the tallest building in the United States. This building will redefine the skyline of Los Angeles. With its elegant sail atop the structure, it will be the only building in Los Angeles without a flat top roof.▪

Plan at BMU. Courtesy of Skyrider/GinD.

Gerard M. Nieblas, S.E., LEED AP, is President of Brandow & Johnston Inc. Peter J. Maranian, S.E., is a Principal and Jeff Lubberts, P.E., is a Project Manager at Brandow & Johnston.

Gerard may be reached at gnieblas@bjsce.com.

Project Team Structural Engineers of Record: Brandow & Johnston Inc. Owner: Hanjin Group Architect: AC Martin Inc. General Contractor: Turner Construction Structural Consultant for Performance Based Design: Thornton Tomasetti STRUCTURE magazine

BMU extended at Tower.

Courtesy of Skyrider/GinD.

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Marriott Marquis Renovation

By Virginia Mosquera, Ph.D., P.E.

Supporting world’s largest LED billboard installation at the crossroads of the world required quick coordination and immediate solutions to conflicts.

T

he iconic Marriott Marquis hotel, located at the center of Times Square, was recently renovated to display the world’s largest high-definition LED billboard (Figure 1).

At five stories tall, this gigantic screen spans the entire width of the building (a full city block, from West 45th Street to West 46th Street on Broadway), wrapping partway around its sides. The renovation also included converting the two underground parking levels and first two above grade-levels to prime double-height retail spaces, the remodeling of back-of-theater rooms, and the creation of new rooftop space offering coveted views of the New Year’s Eve ball dropping.

Figure 1. Marriott Marquis building featuring the world’s largest high definition LED sign.

Project Background In 1985, as part of the revitalization of Times Square, the Marriott Marquis Hotel, designed by the Architect John Portman, opened.

The 574-foot-tall hotel is one of the largest in Manhattan, with 49 floors, 1,946 rooms, a 1,500-seat theater, more than 100,000 square feet of event space, and a revolving roof top restaurant.

The structural engineer, Weidlinger Associates, Inc. (now Thornton Tomasetti), used structural steel framing composed of built-up columns, rolled wide flange columns, and rolled wide flange beams supporting the metal-deck with concrete topping floor system. The hotel features a large atrium with 12 elevators around a concrete core.

Standard steel trusses were used at selected locations. Steel Vierendeel trusses were used throughout the building to allow for desirable long spans without having open-rooms interrupted with cross-members.

Since the time the Marriot Marquis opened, Times Square has blossomed into one of the most visited tourist attractions in the world, becoming a commercial center filled with signage, theaters, and stores.

Vornado Realty Trust, which owns multiple retail properties throughout New York City, signed a lease to redevelop the retail space at the Marriott Marquis and install the largest, most technologically advanced LED sign in order to display advertisements in the heart of Times Square. They hired H3 Hardy Collaboration Architecture as the architect; Weidlinger Associates as the structural engineer; and Turner for construction management.

LED Sign Support To support the 25,740-square-foot LED sign load at the perimeter of the building, the structural engineer had to provide connection

Figure 2. Broadway framing.

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Figure 3. Vierendeel truss.

Figure 4. Installation of LED sign.

points for the various existing conditions around the building, and assess and reinforce the existing steel-framed structure for the new additional load of the LED screen and its back-up structure.

The original building façade consisted of precast panels attached to the perimeter steel beams. Some openings through the panels had already been created to support light signage around the building.

Since each of these openings are costly, connection points to the existing framing were minimized and, where possible, connections from previous signage and existing openings in the precast façade were used.

On the north and south faces of the LED sign, corresponding to the 45th and 46th Street facades, the building columns are set back about 8 feet from the façade and cantilever beams extend from these columns to support the existing façade. The support of the new screen was created by extending the cantilever beams. In the instances when the cantilever beams were found not to have the additional capacity required to support the new loading, the beams were reinforced using top and bottom steel plates.

The LED screen is five stories tall and is located between levels 3 and 8. The supporting framing for the sign along Broadway was divided into three sections (Figure 2). On the north and south sections, the existing façade was set-back from the property line; at these two areas, the hotel requested open-terraces overlooking Times Square to be constructed on the 8th floor. On the south side, moment frames were constructed along the property line that provided support to both the LED sign and the south terrace. On the north side, a combination of new framing along the property line and framing cantilevering out of existing columns was used.

For economy, existing connections and precast openings were also used on the north and south sides of the Broadway facade. In the middle section, above level 6, the existing façade protruded and had to be demolished to install and support the LED sign. The framing in the middle portion of the Broadway façade consisted of hangers suspended from the floors above, and did not have the capacity to support the new load; therefore, the existing structure in this area could not be used. To accommodate the absence of connection points on this portion of the façade and satisfy the stringent limitations on the deflections of members supporting the LED screen, a vierendeel truss was used (Figure 3). The truss spans 57 feet horizontally and has vertical supports only at the existing columns at level 3. It is connected horizontally at only a few discrete points within its 75-foot height to reduce displacement produced by wind loads. The vierendeel truss was selected

as the most efficient solution to span the distances between the supports, creating a structure that was robust for both the vertical load and the wind load.

The LED screen consists of approximately 6- by 8-foot interlocking panels that connect to a secondary or back-up structure connected to the supporting structure described previously. The supporting structure had to be designed for the deflection limits required to accommodate the LED screen; however, it was also very important in the design to control the relative deflections at different support points within the width and height of the screen to avoid having issues during and after the installation of the screen panels. For this reason, sandbags with the same weight as the LED screens were stacked on the back-up structure of the LED sign, allowing for adjustments to be made before the installation of the LED screen and resulting in a successful procedure (Figure 4).

STRUCTURE magazine

Interior Work Achieving the developer’s intent to create ample top-quality retail spaces required the conversion of both underground parking levels and the first two above-ground levels into double-height spaces. To accomplish this, the cellar level and second floor were demolished, making the foundation wall and columns supporting the 44-story tower span twice their original design height (Figure 5, page 36).

Both the columns and the foundation walls had to be reinforced; the column reinforcing consisted of plates welded to the column flanges, while the additional demand on the foundation wall was resolved by building a steel frame adjacent to the wall. This provided a mid-span support for the wall to bear on the dry-packed horizontal steel members of the frame.

An important aspect of this work was to devise a sequencing scheme for the reinforcement of the columns and foundation wall that allowed for the demolition of the floor level and also ensured the safety of the structure at all stages. Different types of reinforcing options were evaluated. The main two factors that determined the column reinforcing used were that plating would cause minimum space intrusion and guarantee the stability of structure at all construction stages. The existing columns had the strong-axis capacity to span the two levels, however the weak-axis capacity was insufficient; therefore, the demolition and reinforcing scheme chosen consisted of initially demolishing only the deck and beams bracing the column on its strong axis, then providing

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Figure 5. New double story space with reinforced columns.

the flange plate reinforcing. Once the reinforcement was installed, the increased column section would have sufficient axial capacity in the weak axis to allow for proceeding to demolish the beams that were bracing the columns on the weak axis.

That reinforcing scheme was typical at the two basement levels.

Some of the columns on the first two levels above grade also had to be reinforced to allow for double height spaces. These columns were very critical to the structure as they were part of both a vierendeel truss lateral system for the building in one direction and a bracing system used for gravity in the other direction. The moment connected beam of the Vierendeel needed to be removed to allow for an open space.

Since these columns were critical to the building, plating sequencing needed special care. Plates on each side of the beam were temporarily installed on the column to provide the required axial capacity. After the beam removal, a plate centered on the column flange was installed that would not protrude as much from the column as the temporary side plates (Figure 6).

The structural interior work also included the floor demolition and design of new beams and reinforcing of existing beams to support stairs, as well as framing evaluation for infill loading at multiple locations in the building. The engineer also devised reinforcement solutions to meet head-height requirements, reducing the depth of a number of beams by as much as 1 foot.

Additional Challenges

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Fortunately, the original architectural and structural drawings were available, which helped the design process significantly. However, as in all renovation projects, some conditions in the field are different

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Figure 6. Column reinforcing.

or not exactly as shown on the existing drawings. In some cases, electrical or architectural equipment was found to impede the construction of structural members as intended in the design phase, and changes to the design had to be made on multiple occasions to accommodate the existing conditions. Conditions found in the field made the work more cumbersome and challenging, requiring non-typical solutions. One example is a beam on the terrace floor that could not be connected to the existing framing adjacent to it due to conflicts. A member cantilevering out from an existing moment frame six feet away had to be used to support the edge of the beam, instead of the simple shear connection that would have been typically required.

Besides the conditions found in the field, construction deadlines were also a big constraint, especially for the construction related to the LED sign, which had to be finished and running for a holiday completion deadline. For the swift progress and completion of the project, quick coordination among all team members and immediate solutions to conflicts during erection were necessary. The project’s success was due to the efforts of all parties involved in the design and construction phases to realize the owner’s vision.▪

CMU or Tilt-up Concrete Walls Analyze solid walls for out of plane loading and panel legs next to or between openings by automatically calculating loads to the wall leg from vertical and horizontal loads at the opening. ($75.00 ea)

Virginia Mosquera, Ph.D., P.E., is a Senior Project Engineer at Thornton Tomasetti in New York City. Virginia may be reached at VMosquera@ThorntonTomasetti.com.

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STRUCTURE magazine

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February 2016

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“The 951” in Downtown Boise All wood. Mid-rise. Mixed use.

By Wilson Antoniuk, P.E. The 951 is kinked at a radius of 21 degrees in the middle of the structure. Courtesy of Phil McClain.

B

oise, Idaho has been on numerous “Best of …” lists. This includes number four of “Best Cities to Live In” by Livability. com, number three for “Best River Town in America” by Outside Magazine, “The Best Cities for Men” by Men’s Health Magazine, and the lists go on. To capitalize on this trending city, developer and design architect Glenn Levie conceptualized and developed “The 951” building just steps from the epicenter of downtown Boise. His vision for the structure was to accommodate a unique land layout with a mixed-use space – all under one roof.

The all-wood structure is four stories with 74,500 square feet. The first level is 4,100 square feet designed for retail space, with the remainder dedicated to 68 apartments on the upper floors. Seven of the apartments are two-story units that combine a street-level workspace – sometimes called live/work units – with private stairs leading to the living quarters above.

The building design was unique and new for the Boise landscape, and one that included numerous engineering challenges along the way. Levie’s architectural vision for the structure had to make use of a land lot that curves with the street. The building is kinked at an angle of 21 degrees in the middle of the structure. The second floor is at a different angle from the first, and the main floor has a clerestory with two stories of open space above.

According to AHJ Engineers’ project manager Craig Brasher, the design was further complicated by the first floor needing open area to fit commercial retail space and the upper floors being residential space. Different space usage created a unique design and structural challenge, as first floor walls do not align with the walls above.

Furthermore, the apartments had window openings and jogged walls for patios – each floor has different wall jogs, some exterior patios over living space, some patios are cantilevered. The structural complexities of The 951 were varying and unique. To facilitate the projects’ success, General Contractor Steed Construction got their team together with the project engineer and suppliers to vet potential problems early and establish transparent lines of communication.

STRUCTURE magazine

7x7 laminated veneer lumber and laminated strand lumber columns are set in place.

7/16 inch OSB wall sheathing wraps the structure.

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Wood Construction Was an Easy Decision One of the first hurdles was to determine the construction material. The typical construction approach would be for a “concrete podium” design where the main level utilizes concrete walls with the second floor consisting of a suspended concrete slab, and then the floors above would be wood construction. Because of the architectural vision and plans that included the jogged window openings, the concrete podiums just didn’t make sense. There was a need for continuity of materials between all the floors, which wood construction could accomplish.

The use of wood was a good solution since it is an economical and renewable resource, and there is regional subcontractor familiarity in working with wood that equates to labor savings during construction.

In selecting the wood manufacturer, Brasher based his decision on the following capabilities: ability to manage multiple shop drawings and details, package and deliver laminated veneer lumber (LVL) and I-joist products based on the scheduled construction timeframe, and deliver a complete package. The complexities of the project needed the expertise of a wood manufacturer capable of field support and the organizational depth to problem solve unexpected issues.

I-joists between the first and second floors. Courtesy of Steed Construction.

Structural Design Challenges, So Many Unique Situations The main level of The 951 was designed for different usage than that of the upper floors. The main floor required open, flexible space to attract commercial tenants. And remember, the second, third and fourth floors were designed for apartment usage. The result is that vertical loads needed to be concentrated into beams and transferred

I-joists bearing at an exterior wall and a laminated veneer lumber header over a window opening.

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Carbon Summary Carbon Summary Results

Project N

V V

Results

C C

Laminated veneer lumber joists at 16 inches on-center support three stories of bearing walls above.

O

C

O

O

C

O

Volume of wood products used: 880 cubic meters (31070 cubic ft) of lumber and sheathing U.S. andofCanadian forests used: grow this much wood in: Volume wood products 3 minutes 880 cubic meters (31070 cubic ft) of lumber and sheathing Carbon in the wood:grow this much wood in: U.S. andstored Canadian forests 794 metric tons of carbon dioxide 3 minutes Avoidedstored greenhouse emissions: Carbon in the gas wood: 1688metric metrictons tonsofofcarbon carbondioxide dioxide 794 Total potential carbongas benefit: Avoided greenhouse emissions: 2482 metric tons of carbon dioxide 1688 Total potential carbon benefit:

Equivalent to: 2482 metric tons of carbon dioxide

Carbon Summary

474to: cars off the road for a year Equivalent

Energy operate a home 474 carstooff the road for a for year211 years

Results

Engineered wood packages are delivered to the jobsite based on the construction schedule.

V

Project Name: Thea 951 Energy to operate home for 211 years Date: November 19, 2015

Volume of wood products used:

880 cubic meters (31070 cubic ft) of lumber and sheathing to columns. Lateral loads were also concentrated into beams and Results from this tool are estimates of average wood volumes only. transferred via theU.S. diaphragm to the offset walls below. and Canadian forests grow this much wood in: Detailed life cycle assessments (LCA) are required to accurately The lateral loads added up to hold down forces of more than 27,000 3 minutes determine a building's carbon footprint. Please refer to the pounds and shear wall forces greater than 1,000 plf. These values References and Notes' for assumptions and other information required double hold downs forinthe LVL columns and sheathing Carbon stored the2.0E wood: on each side of many walls.

Th e vertical load values required customrelated to the calculations.

794 metric tons of carbon dioxide fabricated base plates for the 2.0E LVL columns to avoid crushing wood sill plates. Th e holdgreenhouse down anchor bolts were embedded into Avoided gas emissions: As an all-wood structure, The 951 contains: C O O the footings due to high forces baseddioxide on the ACI Appendix D 1688 metric tonsand of carbon • 230,300 board feet of dimensional lumber to frame the walls calculations. The footings provided the concrete area necessary where • 5,800 sheets of OSB, including wall and roof sheathing, and Totalwas potential carbon benefit: the foundation wall too narrow to comply with Appendix D. floor decking 2482 metric of into carbon The hold down anchor bolts tons going thedioxide footings required special • 31,200 lineal feet of I-joists, of various depths and series contractor layout instructions for field placement.

3

C

• 4,650 ft of engineered wood products including LVL, PSL and glulam Using the Wood Works Carbon Calculator, the amount of wood used in the structure is input and the output details environmental impacts.

Equivalent to: Live/Work Spaces Create

Unique Fire-Rating Requirements 474 cars off the road for a year

Fire-safe construction for The 951 was complicated due to the mixed usage of the structure. The Type V-A construction required a onehour fire rated floor/ceiling assembly for most of the structure. The Energy to operate a home for 211 years design team and building owner also wanted to create a floor and ceiling assembly that satisfied the IIC/STC/Vibration rating criteria that was economical and easy to build.

To solve the problem, the manufacturer suggested a change in the I-joist size and on-center spacing. The change in design plans would achieve the required fire rating and eliminate the need for two layers of gypsum board in the ceiling assembly. The revised plans required redesigning the second, third and fourth-level floor systems to a 24-inch on-center spacing of joists, in addition to increasing the STRUCTURE magazine

joist flange to 1.5 x 3.5 inches – as compared to a 16-inch on-center with a 2.5-inch flange.

These changes met the one-hour fire rating along with reducing the overall number of I-joists, hangers, and blocking required, thus also reducing the labor needed for installation. This is an excellent example of how framing intelligently can help keep material and labor costs down. The new I-joist on-center spacing provided the additional benefit of the larger joist cavities, which helped meet the acoustical criteria.

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Date:

Project N Results fr Date: Detailed

determin Results fr Referenc Detailed related to determin

Referenc

related to

With a four-story structure, a two-hour fire rating was required at the stairwells and elevator shafts. The two layers of gypsum board used to achieve this rating required unique I-joist hangers to perforate through the gypsum board and attach to the supporting LVL beams or walls. Once difficult to source, these hangers are becoming more common with the increased use of wood for mid-rise construction.

The structural complexities of The 951 were varying and unique because of the awkward land layout, mixed-use space, and architectural vision. The engineering, construction, and wood manufacturer stakeholders communicated early and often to leverage each party’s expertise in solving the structural challenges. The result is a beautiful asset to Boise’s urban and contemporary live/work space that is sure to be one of Boise’s best.▪ From Boise, Idaho, Wilson Antoniuk, P.E., is a Technical Representative with RedBuilt™ LLC. Wilson can be contacted at WAntoniuk@redbuilt.com.

Project Team Structural Engineer: AHJ Engineers, Boise, Idaho Developer and Design Architects: Levie Development Group, LLC, Encino, California General Contractor: Steed Construction, Eagle, Idaho Engineered Wood Manufacturer: RedBuilt, Boise, Idaho A clerestory balcony offers unique curb-side aesthetics.

Courtesy of Phil McClain.

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STRUCTURE magazine

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February 2016

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Figure 1a. Carey Building Southeast elevation during steel erection.

Courtesy of Gary Hodges Photography.

Figure 1b. Carey Building REVIT rendering of Southeast elevation.

Rendering courtesy of John Snyder Architects.

THE CAREY BUILDING VERTICAL EXPANSION

By Joseph E. Caza III, P.E. and Michael Palmer, Ph.D., P.E.

A

22,000-square-foot vertical expansion is currently under forces, creating excessive building drift. To maintain the total drift construction at the existing Carey Building located at level to less than L/500, the design required a series of steel braced 314-320 East State Street, Ithaca, NY. The mixed-use frames to pass though the core of the existing and new building building, owned by Travis/Hyde Properties of Ithaca, is (Figure 2). The “overbuild” columns are located directly over the being expanded to accommodate new commercial space and residential existing reinforced concrete columns. To ensure a successful design, apartments while maintaining the current first floor retail space. The the existing structure required an extensive structural analysis to expansion involves the addition of five stories stacked above an existing locate building elements that needed to be bolstered to support the two-story reinforced concrete structure originally constructed in 1922. additional gravity and lateral loads.

The expansion will increase the building height from 27 feet 2 inches The first phase of the project was to analyze and reinforce the existing to a height of 81 feet above finished grade. The unique design sup- foundation. Based on initial field investigations, the original foundaports the entire addition on the existing structure by locating the five tion was recognized to be composed of shallow caissons, possibly hand story frame directly over the existing concrete dug. Discovered during construction were columns (Figure 1a and 1b). An important three existing foundation types: strap footfacet of the project was the need to have the ings at the West wall columns, shallow caisson retail space on the first floor remain occupied foundations, and typical spread footings. The and open for business throughout the project. methodology used for the existing foundation The expansion or “overbuild” is composed of redesign, to ensure sufficient bearing capaca steel superstructure with 5½-inch lightweight ity and to mitigate unwanted settlement, was concrete floor slabs on 2-inch composite steel to ensure that the existing foundation did deck. The lightweight concrete system was not support any additional load. The founchosen to create a 2-hour barrier between dation loads increased from a typical load of floors without fireproofing the steel floor deck.

180 kips to a maximum total new foundaThe structure’s lateral restraint is provided by tion load of 360 kips. The decision was made a hybrid lateral force resisting system. The to support this additional load on the new concrete and masonry elevator shaft located foundation elements. The new design requires towards the North East corner of the structure the enlargement of the existing foundations provides the primary lateral restraint. Due to with reinforced concrete “footing extensions” the eccentric position of the shaft, which was doweled into the existing foundations (Figure required to provide the client’s prospective 3 and 4, page 44). tenants open assembly space at multiple floors, A primary concern was the amount of the applied lateral forces do not coincide with reinforcing in the existing foundations. The the center of rigidity of the shear wall system. Figure 2. Center core braced frame existing footing depths vary from 18 and 26 The consequence is additional lateral torsional at basement level. inches; therefore, the only reliable method of STRUCTURE magazine

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determining the size and location of existing footing reinforcing was by destructive testing. In lieu of extensive destructive field tests, the existing footings were treated as plain concrete when designing the footing extensions. With the assistance of a reinforced concrete collar used to supplement existing column reinforcement at the basement level, most of the footing extensions do not require an additional reinforced concrete “cap” over the existing footings. A concrete cap was required at one braced frame foundation (Figure 5). The additional concrete cap self-weight also serves to completely mitigate foundation uplift at this location.

The second phase of the project was to reinforce the existing concrete columns. Ground Penetrating Radar (GPR) testing was successfully performed on each existing column, along with selective destructive visual inspections at each level, to evaluate the existing column reinforcing. The tests proved essential, as no reinforcing was detected in the lower portion of the basement level columns. To support an additional five-story steel structure, the columns were strengthened with a reinforced concrete collar. The collar consists of a 1-foot 4-inch reinforced concrete band wrapping the existing column (Figure 6). The original redesign called for a less intrusive stepped collar, but the as-built collar was found to be more constructible and still allowed for acceptable storage space. The reinforcement within the collar provides the much needed confinement of the existing concrete columns. The collar is also helpful to reduce the moment arm between the center of the existing assumed plain concrete footing and the new footing extensions.

The third phase of the project was the placement of the elevator shaft foundation. The foundation was designed with the assistance of underground engineering specialist Brierley Associates, headquartered in Syracuse, NY. The elevator shaft is constructed of 12-inch cast-inplace reinforced concrete up to the new third floor level and 12-inch reinforced masonry to the roof level. As a primary component of the lateral force resisting system, not only is the elevator shaft tasked with providing gravity support for the adjacent framing, but also with resisting wind and seismic event forces. With an aspect ratio of nearly 8V:1H, bending controls the shaft design. Also, the slender elevator shaft walls introduce significant uplift forces to the foundation.

To resist the uplift, (8) 8-inch diameter micro-piles were uniformly spaced around the elevator shaft foundation and socketed 25 feet

Figure 4. Footing extension reinforcing at existing caisson foundation.

Figure 3. Footing extension reinforcing typical detail.

into bedrock located 30 feet below grade. Problematic to the design was how to transfer the uplift forces between the elevator shaft shear walls and the micro piles. The solution was to weld a series of ½-inch shear studs to the micro piles and extend the pile shaft directly into the elevator foundation walls, thereby lapping the pile casing with the foundation wall vertical reinforcing. The micro-piles also served a critical function during excavation for the elevator pit and pile cap.

The elevator shaft is located within 2 feet of an existing column and in close proximity to the earth retaining exterior basement wall. The 8-foot deep excavation necessary for the elevator foundation would undermine both soil bearing elements. A plan was devised to create a support of excavation (SOE) system using the micro pile casings that would extend up to the basement floor elevation and become cast into the foundation wall (Figure 7). The SOE utilizes a typical soldier pile and lagging scheme, with the micro piles serving as the soldier piles. Six-inch WT standoffs were welded to the outside of

Figure 5. Braced frame uplift resisting mat footing.

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Figure 6. Existing column concrete collar reinforcing.

the soldier piles to create a void space between the lagging and the micro pile casing. The void space permitted concrete to flow between the lagging and the casing, completely casting the micro pile into the elevator shaft foundation wall.

For the Structural Engineer, the design and development of a vertical expansion over an existing structure is a unique opportunity to preserve and reuse the original building’s form and function, while creating new space for a more comprehensive use of the building site.▪ Joseph E. Caza III, P.E. (jec@elwynpalmer.com) is a Professional Engineer and Associate with Elwyn & Palmer Consulting Engineers, PLLC of Ithaca, NY. Michael Palmer, Ph.D., P.E. (mcp@elwynpalmer.com) is a Partner with Elwyn and Palmer Consulting Engineers, PLLC of Ithaca, NY.

Project Team Structural Engineer: Elwyn & Palmer Consulting Engineers, PLLC Owner: Travis/Hyde Properties, Ithaca, NY Geotechnical Engineer: Elwyn & Palmer Consulting Engineers, PLLC Foundation Design: Elwyn & Palmer Consulting Engineers, PLLC with Brierley Associates Architect: John Snyder Architects, Ithaca, NY General Contractor: Lechase Construction, Rochester, NY

Figure 7. Aerial view of micro pile support of excavation at new elevator shaft.

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Historic structures significant structures of the past Final plan of trusses.

T

he newly accepted design of the Quebec Bridge maintained the 1,800foot main span with straight upper and lower chords on the anchor and cantilever spans. All of the parts, especially the lower compression chords, were much larger than the Phoenix Bridge/Cooper design.

Instead of building the suspended span out from the ends of the two cantilever arms, they decided to build it off site and lift it into place. The suspended span was built starting in May 1916 at Victoria Cove, approximately three miles below the bridge, and was finished in July. The plan was to float it under the bridge and lift it into place, hanging it from suspenders attached to the ends of the cantilever arms. The span, with its length of 650 feet and weight over 5,000 tons, was floated into place on September 11 and connected to the lifting jacks. What happened next, if it hadn’t happened would not be believed, but the Quebec curse reappeared. The official report of the Board of Engineers, which now had H.

P. Borden as a member, described the series of events on that fateful day.

“Preparations for floating were completed about September 1, 1916, but the range of tides, at this date, were not suitable. It was felt by the contractor, however, that several days could be spent to advantage in drilling their engineers and men in the various operations and in making a final inspection of the equipment and appliances. The next series of high tides occurred on September 11, and, weather conditions being favourable, the span was floated at 3:40 a.m. and by 4:40 a.m. it was being towed out into the river. Four small tugs and one large tug were attached to the downstream side, with two small tugs upstream. As the tide was running strong, the tugs had little to do but guide the span on its trip up the river. At 6:35 a.m. the span reached the bridge site and at 7:40 a.m. the lifting hangers at all four corners had been

Quebec Bridge Part 3

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.

Parts 1 and 2 of this article can be found in the December 2015 and January 2016 issues of STRUCTURE magazine. Visit www.STRUCTUREmag.org to read digital versions.

New lower chord at pier, Modjeski, Monsarrat, Schnieder (l to r).

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Suspended span collapsing into the St. Lawrence River.

Quebec Bridge 2008.

connected. At 8:50 a.m. the jacks began lifting, and during the third lift of two feet the scows floated clear, leaving the span suspended about 20 feet above the water. After another lift of two feet, work was stopped to allow the men a period of rest and breakfast.

Up to this point the entire operation of floating the span and connecting it to the lifting hangers had worked exactly according to schedule. Nothing occurred that had not been foreseen and provided for. There was no wind, and every condition was favourable. As the work remaining to be done was simply a repetition of mechanical operations which had already been successfully performed, it was felt that most difficult part of the work had been satisfactorily accomplished.

At 10:30 a.m. jacking operations were resumed and one more lift made. The pins had been inserted connecting the lifting links to the fixed jacking girders, thus transferring the load directly to the cantilever trusses. The load on the jacks had been released and they were being lowered for another lift when, at 10:50 a.m., a sharp report was heard and the span was seen to slide off its end supports into the river.”

Unlike the first failure where there were few eyewitnesses to the collapse, this time the press, photographers and officials of the government and the Board were on hand to witness the failure. Engineering News reported “many prominent engineers from the United States and Canada were on the suspended span when the lifting operations began. At the intermission in the jacking operations, they came ashore.

That saved their lives...” They also reported that “both cantilever arms of the structure were thronged with many prominent engineers who had come to see the crowning achievement of the Quebec Bridge’s history.” The first reports of the failure came to Engineering News just before they went to press for their September 14 issue. Based upon limited information, they wrote: “The engineering world was amazed when the

south cantilever of this great bridge fell nine years ago; but words are inadequate to express its sensations at the news that again this great bridge enterprise has suffered an unprecedented disaster.”

Thirteen men were killed this time, with fourteen injured. Once again an intensive investigation into the cause of the accident was launched. It was clear to all that the truss had fallen off of the southwest supporting girder. The designers had used cruciform steel castings at each corner to provide for movements about two perpendicular axes.

The investigating team was confident that this was the sole cause of the failure; but, to leave no stone unturned, they investigated three other possible failure mechanisms.

The most significant was that of a “failure of the suspended span through some error of design.” Their conclusion was that the failure was indeed due solely to a failure of the casting. The ends of the cantilever spans had deflected seven and one half inches when they were subjected to the load of the suspended span. When the span dropped, the arms were seen “to spring violently upward, setting up severe vibrations and oscillations.” A thorough examination of the structure showed “no evidence of injury or distortion of any kind.” The engineering journals of the world wondered if it would be possible to “raise this span from the bottom of the river, in water about 200 feet deep?” No one had any thought that the span could be reused, but they were discussing reclaiming the truss for its scrap value. The Engineer, London wrote “the span has in all probability fallen more or less in position; and if it is found on inspection to be indeed worth saving, it is not impossible that the arms of the cantilevers may serve as cranes to raise it from the bottom.” This suggestion was not followed, and the span still rests at the bottom of the river.

On September 13, 1916, the St. Lawrence Bridge Company accepted full responsibility for the failure and took “immediate steps to replace the span.” The bridge company was in the process of tooling up to make shells for the war effort, but still had enough of the original equipment available to fabricate a

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new truss which followed the same lines as the previous span with the exception that more nickel steel was included in the upper lateral bracing system. Carnegie Steel was able to fit in the rolling of the new steel for the span even though it to was actively involved in the war effort. The Board and the Bridge Company decided that the entire lifting apparatus would have to be rebuilt due to excessive deformations of the lifting links occasioned by the fall.

Work on the new suspended span got under way at Sillery on June 4, 1917, with the span being completed on August 27. It was floated into place on September 17 or just over one year after the failure. This time, however, the erectors were even more careful than they were previously and had modified the end supports for the truss. The new device did away with the necessity for the second pin, which was responsible for the cruciform type of bearing originally used. The span was jacked and lifted into place over the next three days, with the final pins connecting the permanent suspension bars to the centre span being driven at 4 p.m., Thursday, Sept. 20, 1917.

The Engineering News-Record which had just been formed by the merging of Engineering News and Engineering Record reported the moment as follows: “The seventy-fifth lift followed immediately, and locomotive cranes were run out to all four corners with pin-driving cages and pins. At the end of the stroke, at 3:25, the first of eight pins was driven. The clearances were perfect, and each long pin slipped through its eye bars with a few taps from a short rail swung by about ten men. Every ringing blow of the rails stirred the onlookers. And when at 4 o’clock the last foreman shouted, “Right, here!” all restraint among workers and watchers was lost. The crane whistles on the bridge picked up the men’s cheers and the river boats passed the signal down to the City of Quebec, where (by the Mayor’s proclamation) every whistle and bell and automobile horn was turned loose, and flags and buntings were thrown to the breeze everywhere, for Quebec realized that its dream of thirty years had come true.” continued on page 51

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The Engineer, London wrote “one of the greatest, if not the greatest, feat of bridge engineering the world has ever seen was brought to a successful conclusion, on Thursday, September 20, 1917 at 4:01 p.m., when the 10-inch pin connecting the two sections of the Quebec Bridge to the ends of the cantilever arms were driven.” The Canadian Engineer proclaimed “Canadian Engineering Has Triumphed at Quebec.”

The dedication of the bridge by the Prince of Wales was similar to that of the Firth of Forth Bridge 29 years earlier. This time, however, no one was knighted, as the project had been from its new start in 1908 a team effort. The main players were Ralph Modjeski who had been a member of the Board from the beginning, C. C. Schneider who had a connection with the bridge from 1907 when he was a consultant to the Royal Commission to his death in early 1916, and C. N. Monsarrat who was chief engineer for over eight years.

The engineers, fabricators, and erectors of the St. Lawrence Bridge Company under the leadership of Phelps Johnson had built a bridge with a quality of workmanship unmatched in its day.

The bridge was the product of American and Canadian engineering and bridge fabrication. It still carries railroad and highway traffic across the river. The lessons learned were hard ones, but never again would all the responsibility of a major project be placed on the shoulders of one, or even two men, but would be team projects with all members of the team working towards a successful completion. Checking at all stages of construction is now standard practice.

Having men on the site during construction, with the authority to act, sadly lacking at Quebec, is also now standard practice.

While it is still not possible to test full size compression members such as were designed at Quebec, we are able to test large members and through experience have designed many large compression members for bridges and buildings. As the result of the failure, the United States Congress authorized the construction of a $1,750,000 testing machine designed by A. H. Emery for the United States Bureau of Standards and installed it at the Watertown Arsenal.

The bridge, with its 1,800-foot main span, was the longest span bridge in the world for many years and still is the longest span cantilever bridge in the world. In 1987, it was designated an International Historic Civil Engineering Landmark by the American and Canadian Societies of Civil Engineering.▪

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code developments and announcements

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By Thomas Sputo, Ph.D., P.E., S.E.

4) 5)

6)

7)

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DIAPHRAGM DESIGN

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8) Since the Second Edition, the strength of concrete filled steel deck diaphragms has been the sum of the strength of the deck, controlled by the fasteners and the concrete fill. AISI S310 and DDM04 place an upper limit on the contribution of the fasteners to 25% of the total diaphragm strength.

For more information on the 4th Edition Diaphragm Design Manual, visit the SDI website at www.sdi.org.▪ Thomas Sputo is the Technical Director of the Steel Deck Institute and a Consulting Engineer with the Gainesville, Florida firm of Sputo and Lammert Engineering, LLC, tsputo50@gmail.com.

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he Steel Deck Institute (SDI) has released the new and long awaited 4th Edition of the Diaphragm Design Manual (DDM04). This new edition complies with the requirements of the new ANSI/AISI S310-13 North American Standard for the Design of Profiled Steel Diaphragm Panels.

At 408 pages, the 4th Edition is larger than its predecessor and will be an invaluable resource to structural designers.

The First Edition of the DDM, published in 1980, was authored by Dr. Larry Luttrell, P.E., the Technical Advisor to the SDI. The diaphragm design method developed by Dr. Luttrell was based on a rational analytical model of the deck panels and the support and sidelap fasteners, which was substantiated by extensive testing. The Second Edition of the DDM, published in 1995, added a design method and design tables for floor deck diaphragms. A Third Edition was published in 2004. The new Fourth Edition is also authored by Dr. Luttrell, with the assistance of John Mattingly, P.E., SDI Technical Consultant; Walter Schultz, P.E., SDI Diaphragm Committee Chair, and Dr. Thomas Sputo, P.E., S.E., SDI Technical Director.

This new Fourth Edition improves the earlier 3rd Edition in several ways.

1) The Manual complies with the analysis and design methods contained within the AISI S310 Standard. The AISI S310 Standard puts the design method of the first three editions of the Diaphragm Design Manual into a building code enforceable standard. The resistance and safety factors are the same as those in the Third Edition (DDM03).

2) The Manual contains 26 design examples illustrating the design and analysis of steel deck diaphragms, both roof and floor deck. This is an increase over the previous edition which contained 16 examples.

3) New examples include calculation of deflections of non-symmetric diaphragms, diaphragms with open areas, and perforated and acoustical deck. Additional examples also

show the calculation of diaphragm strength and stiffness using the AISI S310 provisions.

Examples include expanded discussion of the interaction of wind uplift with diaphragm strength.

Fasteners included in the Manual include generic welds and mechanical fasteners in accordance with the strength and flexibility provisions of AISI S310, but also include fastener strengths calculated in accordance with the previous DDM provisions, and proprietary screws and power actuated fasteners. The use of the previous DDM provisions and proprietary fasteners are permitted by AISI S310 as alternate fasteners with performance substantiated by testing.

Diaphragm load tables are separated into two sections; calculated using the generic AISI S310 weld and screw provisions, and calculated using the previous edition DDM fastener equations and proprietary fasteners.

The same resistance and safety factors apply to both methods.

The diaphragm buckling strength limit has been updated based on further testing and analysis by the AISI Diaphragm Subcommittee.

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new trends, new techniques and current industry issues

ACI Publications on Formwork

By David W. Johnston, P.E., Ph.D., FACI, F.ASCE, NAC Formed Concrete Surface Categories Category Concrete surface finish with

A

CI has published three documents that will assist in selecting, designing, and specifying formwork systems for concrete structures. The first of these releases was a new document intended to provide a means of better communicating the desired formed surface finish and quality between the engineer/architect and the contractor. The most recent releases are revisions of documents that have been staples in the formwork community for years.

ACI 347.3R-13, Guide to Formed Concrete Surfaces, is an entirely new document released in spring 2014 by ACI Committee 347, Formwork for Concrete. Chapters within ACI 347.3R describe formed surfaces, basics of layout and design, specification, construction, and evaluation of formed surfaces.

The document’s primary function is to provide a detailed method for classifying formed concrete surfaces. Four levels of quality, called Concrete Surface Categories (CSC), are classified based on the visibility of the completed surface as well as the importance of its visual appearance (see Table). For each CSC, qualities such as texture, surface void ratio, color uniformity, surface irregularities, and treatments of construction joints are defined. The guide also discusses phases of construction relating to concrete surfaces, from planning, selection of materials, and construction and repair procedures through the acceptance of a concrete surface. Ultimately, ACI 347.3R13 can help the project owner, design team, contractor, formwork supplier, concrete supplier, and all other parties involved in the construction process in reaching a specific understanding of how a desired as-cast concrete surface can be defined and produced.

ACI 347R-14, Guide to Formwork for Concrete, presents the recommendations of ACI Committee 347, based on changes that have accumulated in the 10 years since the previous edition was published in 2004.

By providing guidance regarding contract documents, selection of formwork, and use of formwork, the document serves as a reference for design architects and engineers, formwork engineers, and contractors.

For easy reference, the document lists items that should be indicated in the contract documents by the engineer/architect. Examples include materials and accessories; finishes; design, inspection, and approval responsibilities; and any

Description

Basic requirements

CSC1

Concrete surfaces in areas with low visibility or of limited importance with regard to formed concrete surface requirements, used or covered with subsequent finish materials.

Normal requirements

CSC2

Concrete surfaces where visual appearance is of moderate importance.

CSC3

Concrete surfaces that are in public view or where appearance is important, such as exterior or interior exposed building elements.

CSC4

Concrete surfaces where the exposed concrete is a prominent feature of the completed structure or visual appearance is important.

Special requirements

requirements that would restrict the selection, design, or layout of the formwork. ACI 347R-14 also contains recommendations for the formwork engineer that will design the formwork and select the components. The recommendations cover topics such as loads, factors of safety, and shoring and bracing. The design recommendations for concrete lateral pressure have been revised to a tabular presentation for a more direct understanding, and the provisions for wind load magnitudes and minimums have been clarified. The chapter on materials has been revised to reflect the changes in many material design specifications and standards used in formwork.

Additional information that can be helpful for all parties includes chapters on architectural concrete, special structures, and special construction methods. These have been generally revised to reflect current practice.

ACI SP-4 Formwork for Concrete, 8th edition, was released in October, 2014. Formwork for Concrete has been and continues to be a cooperative effort supported by individuals, companies, public agencies, and industry and professional associations. In large measure, this is due to the groundwork laid and respect for Formwork for Concrete garnered through the pioneering efforts of the late Mary K. Hurd, the previous author of SP-4.

As a member and past Chair of ACI Committee 347, the author was tasked to revise and update for the new edition. The eighth edition, as all previous editions, follows the most recent guidelines established by ACI Committee 347 and documented in the committee report, now ACI 347R-14, which is reprinted in full in the appendix. This new edition of Formwork for Concrete considers the updated lateral pressure and other provisions now provided by ACI 347R. Expanded coverage is provided in SP-4 for wind loads on formwork specialized from ASCE/SEI

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7-10 as modified by ASCE/SEI 37-14. Analysis of the shoring and reshoring process for multistory buildings, and evaluation of concrete and structure strength to withstand shoring loads, has been expanded in a new chapter. Design of formwork has been divided into two chapters, one focusing on bending, shear, and deflection of wall, slab, and column formwork members, and a second focusing on shoring and bracing members. Bridge formwork considerations have been moved into a separate chapter. A new chapter summarizing the recommendations of ACI 347.3R on specifying and evaluating formed concrete surfaces has been added.

This edition also reflects changes in wood design recommendations of the AWC NDS-2012 with 2013 addendum, and introduces load and resistance factor design (LRFD) for wood formwork members in addition to the primary coverage based on allowable stress design (ASD) procedures. The recent recommendations of other ACI committees have also been considered in the manual revisions and some related OSHA provisions have been extracted for convenient reference in the appendix. The extensive glossary of terms has been updated to reflect the latest changes in ACI 347R and ACI Concrete Terminology.

Revising and bringing an iconic document up-to-date included reference to the latest design standards, design methods, procedures, products, and both revised and new worked examples.

Nearly 500 modern color photographs were selected to enable the eighth edition of Formwork for Concrete to be the first edition in full color.▪ David Johnston is the Edward I. Weisiger Distinguished Professor Emeritus in Construction Engineering at North Carolina State University. He is active in the technical committees of ACI and ASCE. David can be reached at johnston@ncsu.edu.

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Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: IES VisualAnalysis Description: You may not need the longest span, like Golden Gate or Roman arch. Just analyze your footbridge plan; then celebrate as people march for engineers of local fame: designers of a gorgeous frame.

MDX Software

Phone: 573-446-3221 Email: sales@mdxsoftware.com Web: www.mdxsoftware.com Product: MDX Software Curved & Straight Steel Bridge Design & Rating Description: Used by many top design firms and DOTs to design and rate steel girder bridges for compliance with AASHTO Specifications: 7th Edition LRFD Bridge Design Specifications, 2nd Edition Manual for Bridge Evaluation (LRFR), and 17th Edition AASHTO Standard Specification for Allowable Stress Design and Load Factor Design.

Opti-Mate, Inc.

Phone: 610-530-9031 Email: optimate@enter.net Web: www.opti-mate.com Product: Bridge Engineering Software Description: For steel, prestressed concrete or reinforced concrete bridges using Merlin Dash, horizontally curved steel I-girder or box girders using Descus I or Descus II, truss bridges using TRAP and the SABRE software for sign structures.

All Resource Guide forms for the 2016 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

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POSTEN Engineering Systems

Phone: 510-275-4750 Email: sales@postensoft.com Web: www.postensoft.com Product: POSTEN X Description: The most efficient & comprehensive post-tensioned concrete software in the world that, unlike other software, not only automatically designs the tendons, drapes, as well as columns, but also produces highly efficient, cost saving, sustainable designs with automatic documentation of material savings for LEED. The others simply analyze – POSTEN DESIGNS.

S-FRAME Software

Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: S-FRAME Analysis with Integrated Concrete and Steel Design Description: A trusted industry leader for over 35 year provides a structural analysis and design environment with fully integrated steel, concrete and foundation design and optimization tools. Versatile enough for linear and advanced non-linear analysis, commercial and industrial structures, international design constraints, and integration with BIM and CAD links.

Product: S-FOUNDATION Description: Quickly design, analyze and detail your structure’s foundations with S-FOUNDATION, a complete foundation management solution. Run as a stand-alone application, or utilize powerful roundtripping integration links for a detailed soil-structure interaction study. Automatically creates and manages the meshed foundation model and Includes powerful import/export 3rd party links.

Simpson Strong-Tie

Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Simpson Strong-Tie® Anchor Products Description: A wide range of anchoring and fastening products for concrete and masonry applications, including code-listed solutions, coldformed steel connectors, direct fastening systems, general purpose anchors and fasteners, restoration products, carbide drill bits and accessories. For more information or to download the 2016 Anchor Systems catalog, visit the website.

Product: Simpson Strong-Tie® FX-70® Structural Repair and Protection System Description: Many bridges are constructed with steel pipe and H-piles that deteriorate over time. The FX70 system makes in-place repair of piles possible and practical. By eliminating the need to dewater repair sites or take structures out of service, FX-70 drastically reduces the overall cost of restoring deteriorating or damaged structures.

Standards Design Group, Inc.

Phone: 800-366-5585 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Wind Loads on Structures 4 Description: Performs computations in ASCE 7-10, Chapters 26-31; also ASCE 7-98, 02, 05, Section 6.

Computes wind loads by analytical method rather than the simplified method, provides basic wind speeds from a built-in version of the wind speed, allows the user to enter wind speed. WLS4 has numerous specialty calculators.

Trimble

Phone: 770-426-5105 Email: kristine.plemmons@tekla.com Web: www.tekla.com Product: Tekla Structures Description: Increase productivity through higher automation of fabrication and 4D project management.

Extensive range of steel profiles including elliptical and tubular, and individual connection details with welds and bolts. Drawings and reports automatically generated from the constructible 3D model.

Wheeler Bridge Phone: 952-929-7854 Email: dclemens@wheeler1982.com Web: www.wheeler-con.com Product: Recreation and Vehicle Bridges Description: Producing bridge solutions to both public and private infrastructures. Utilizing steel and timber construction, Wheeler manufactures vehicle and recreation bridges of enduring beauty and durability.

Knowledgeable project advice, quality products and attention to customer service.

Strand7 Pty Ltd

Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: An advanced, general purpose, FEA system used worldwide by engineers, designers, and analysts for a wide range of structural analysis applications. It comprises preprocessing, solvers (linear and nonlinear static and dynamic capabilities) and postprocessing. Features include staged construction, a Moving Load module and quasi-static solver for shrinkage and creep/ relaxation problems.

StructurePoint

Product: spMats Description: Used for analysis, design and investigation of commercial building foundations, and industrial mats and slabs on grade. It incorporates a sophisticated FEM Solver increasing capacity and substantially speeding up solutions for large and complex models.

IMAGINE THE DESIGN POSSIBILITIES WITH HARDY FRAME ®

Large windows, bold expansive spaces flooded with natural light. The Hardy Frame® Shear Wall System makes it possible.

Hardy Frame® with it’s high shear values and very narrow widths, provides architects and engineers with the most versatile options in contemporary design.

As part of MiTek’s complete range of structural products, the Hardy Frame® Shear Wall System, along with USP Structural Connectors® and the Z4 Tie-Down System can offer you stronger integrated structural solutions System, as well as greater design opportunities.

Contact us today and let us create the right solutions for you. Hardyframe.com/solutions.

800 754.3030.

StruM.I.S LLC

Phone: 610-280- 9840 Email: sales@strumis.com Web: www.strumis.com Product: StruM.I.S – Steel Fabrication Software Description: StruM.I.S and its various global offices has been providing best practices software solutions to the steel industry for nearly 30 years. A team of more than 100 people and 24 developers ensure StruM.I.S software meets the latest and future requirements of the industry and its leaders.

©2016 MiTek, All Rights Reserved

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Phone: 847-966-4357 Email: info@StructurePoint.org Web: www.structurepoint.org Product: spColumn Description: Used for design of shear walls, bridge piers as well as typical framing elements in buildings and structures. It is developed for the design and investigation of reinforced concrete sections subject to combined axial and flexural loads.

NO WELDING. NO WAITING. New SidePlate ® Bolted Special Moment Frame Introducing SidePlate® Bolted™ Special Moment Frame (SMF), our latest innovation that excels in high-seismic construction. This field-bolted connection allows anyone to fabricate and install, requiring less steel, less labor and no delays for weather or welding inspections. Working as an extension of your design team, SidePlate optimizes structural steel buildings to help you finish on time and under budget. Find out how you can build even more value into your seismic projects.

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award winners and outstanding projects

Spotlight

Modular Challenges and Solutions: The Stack

By Janis B. Vacca, P.E., LEED AP

The Harman Group, Inc. was an Outstanding Award Winner for The Stack project in the 2015 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings $10M to $30M).

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s with any novel idea for construction, the key is to not be constrained by the conventional. This can be difficult for engineers.

Take The Stack, a 38,000 square foot, sevenstory, 28-unit modular apartment building, the first built in New York City. The elegance of the design was in its simplicity. The innovation and challenge of the project was to take basic building materials, utilize them to their maximum efficiency and adapt them for use in modular construction. The project required fabrication, shipping and assembly of 56 modules. Module dimensions and weight were controlled by shipping and crane constraints.

Key architectural features that added to the construction challenge were differing geometries on each floor, with balconies, terraces, stained polished concrete floors and cantilevered “boxes”, creating a complex puzzle to be assembled quickly and correctly in the field.

Additionally, key to leasing success was designing the modules with an attractive ceiling height.

Modules for the 1, 2 and 3 bedroom units were constructed off-site at DeLuxe Building Systems in Berwick, Pennsylvania, and were transported to Inwood, a neighborhood at the northern tip of Manhattan. They were then stacked atop a steel-framed podium level.

The modules were approximately 12 feet wide. Floors were framed with 4½-inch thick slabs-on-metal-deck spanning between 10-inch deep “band rail” channels. The channels spanned between rectangular HSS post columns varying in size from HSS 3x3 to HSS 6x3. The 3-inch dimension on the tubes was critical to minimize the dimensional impact of the double walls. All of the structure was fire rated, with inspection and certification occurring in the plant with stickers placed on the boxes prior to shipment.

Lateral loads were typically resisted with cross-strap braced frames located within the walls of the modules. The typical gap between the boxes was 2 inches to allow for tolerances.

With modular construction, critical loads can sometimes be the transportation loads.

If the boxes are not rigid enough, interior finishes can crack. The boxes incorporate the floor framing and ceiling framing for rigidity.

With a shipping height limit just above 11 feet, it is a challenge to ship the boxes and attain a ceiling height as close to 9 feet as possible. For The Stack, the ceiling steel framing was limited to 4 inches in depth to maximize the ceiling height.

Deluxe Building Systems used an old World War II warehouse to build the boxes in assembly line fashion. Their plant included a concrete batch plant, continuing to add to quality control without consideration of weather effects. Staining and polishing the concrete proved a challenge, particularly with matching seams.

The field built ground level steel framed construction was also included in Deluxe’s scope. Shop fabricated “tree columns” were used to support both sides of the boxes. The “tree columns” were erected and connected to girders at the end of these columns to create moment frames, with the boxes sitting directly on the steel. Access was required through the boxes to handle the significant lateral loads being translated to the base building.

The Developer, Jeffrey M. Brown, was committed to building the development using modular methods. As with any innovation, challenges were in translating common contiguous features through the modular box joints. With The Stack, there were no common corridors and easily accessed vertical shafts. Modular construction relies on horizontal translation of MEP systems to common vertical shafts. It also relies on corridors to make ugly box to box structural connections. Since this was not feasible for The Stack, interior block-outs in finishes were required to not only connect the boxes, but connect MEP systems.

Close communication between the designers and manufacturing personnel was continuous throughout design. All framing and details were coordinated and reviewed with the module manufacturer to confirm that the design was configured in accordance with the capabilities and preferences of the factory personnel.

Connection details between the modules were developed such that the boxes could be lowered into place onto alignment pins, and then be bolted or welded in place. Timing was

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Courtesy of Gluck+.

important to minimize potential for water infiltration during construction. Temporary roofs were included to minimize this potential.

The 56 modules were erected in nineteen days with a single crane and crew of 14 workers.

Main stream modular building construction is still feeling its way. As field labor costs rise, determining the best way to build offsite and erect onsite remains a challenge. It is key that all personnel understand the limitations of the construction method. Team members familiar with modular construction are important for success. Early planning is required, with an understanding of financial goals and construction logistics. As with traditional construction, it is necessary to minimize the field construction to put the boxes together.

The modular design and construction methods used for The Stack incorporate high quality design and materials into a swift and streamlined process, resulting in an elegant residential building built with maximum efficiency. The lessons learned from this project will further refine the modular design and construction process.▪ Janis B. Vacca is a Vice President and Principal at The Harman Group. She is a member of numerous professional organizations, including the American Society of Civil Engineers, the American Concrete Institute and the Delaware Valley Association of Structural Engineers. Janis may be reached at jvacca@harmangroup.com.

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Each year the NCSEA Publications Committee leads, edits, reviews, and sometimes even authors design guides on a variety of topics of interest to our structural engineering community. This year has been no different.

The end of summer 2015 release titled Guide to the Design of Common Irregularities in Buildings, 2012/2015 IBC and ASCE/SEI 7-10 (Prasad et al.) fully explains how and why building irregularities impact structural design and provides detailed examples of how to appropriately analyze and design lateral force-resisting elements for various types of irregular buildings located in Seismic Design Category (SDC) B and D. The book references the 2012 IBC and ASCE/ SEI 7-10, and references material standards from the 2012 IBC by section number. It is also applicable to the later versions of these standards and the 2015 IBC. Four detailed design examples include an overview of applicable irregularities, a discussion of appropriate analysis and design requirements, determination of key lateral force-resisting system demands, and design of select example elements contained in the building’s load path.

In conjunction with the release of the irregular buildings publication, NCSEA is

also offering a live course. The course provides an overview of the book material and includes approximately 25 percent new material not included in the actual publication to help the engineer better understand the fundamental theory behind the practical example problems, and to verify approaches used with hand calculations and simple computer modeling results.

The 4-hour NCSEA Diamond approved course can be provided as a stand-alone course or as part of an arranged program such as an NCSEA Member Organization meeting. All attendees receive one copy of the new guide.

The committee has completed its final technical review of a second publication, a relatively shorter guide on the design of glazing as a structural element.

The purpose of this design guide is to provide the structural engineer with sufficient background knowledge and current methods to determine the specification of glass elements in buildings. It is aimed at structural engineers who are experienced in designing building structures and elements using traditional materials but with little to no experience in using glass to transfer forces. A publication date of spring 2016 is expected.

With the help of a few external authors, the committee is working on quite an exhaustive design guide on foundation design for structural engineers. The publication will be titled Guide to the Design of Building Foundations in Accordance

New and Improved!

NCSEA Webinars

NCSEA is pleased to announce that its provision of live webinars, certificates, and recordings has been updated; and its recorded webinar library is now automated. Viewers can watch recorded webinars anytime of the day or night, take quizzes, and receive certificates.

In addition, changes were made that will allow NCSEA to drop the $30/ recorded webinar fee for subscribers, beginning February 1.

There is no time like the present to become a subscriber. For $995, you receive one year of live webinars (at least 20/year) and as many NCSEA online recorded webinars as you would like to watch.

February 11, 2016 Steel Curtain Walls

with the 2015 IBC and ASCE/SEI 7-10. This practical design guide will be a problem based step by step review of all major provisions contained in Chapter 18 of the 2015 IBC. Emphasis will be placed on structural provisions and interaction with geotechnical engineers. The committee is aiming for a 2016 release of this publication.

Unrelated to the foundation design guide, the committee is days away from reviewing the final draft of Guide to the Design of Shoring Systems and plans to release this publication in Summer 2016.

It will include the following examples with full connection details, specifications, and pictures: • Typical sheet pile wall applications • Cantilever steel soldier pile wall • Restrained (i.e. tiebacks) steel soldier pile wall • Soil nail wall • Deep soil cement mixed walls for excavation The Young Members Group is continuing to work with the Publications Committee on a practical-topics-for-young-engineers training guide. The group is focusing on the development of webinars first and then plans to expand the webinars into a training guide. Webinars are already being planned for 2016.

Timothy W. Mays, Ph.D., P.E. Publications Committee Chair

Chuck Knickerbocker, Curtainwall Manager, Technical Glass Products February 23, 2016 Welded Connections: the Good, the Bad, and the Ugly

Duane K. Miller, Sc.D., P.E., Lincoln Electric

March 22, 2016 IBC Chapter 17: Special Inspections and Testing

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CE credit in all 50 states through the NCSEA Diamond Review Program. www.ncsea.com.

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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

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Chris Kimball, P.E., S.E., Kimball Engineering EN

NCSEA News

News form the National Council of Structural Engineers Associations

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Publications Committee Update

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How does your firm function compared to other AE firms?

The Winter Leadership Forum is an opportunity for setting new goals. Can your firm be more effective, influential or successful in 2016 and beyond?

Don’t Be Left Out!

Managing Your Staff

Update on Employment Law – Troubleshooting – Staci Ketay Rotman, Attorney, Franczek Radelet P.C. How to achieve your business objectives while minimizing the risks of litigation. Topics include: • Hiring the Best Candidate…Lawfully!

• Properly Classifying and Paying Your Workers • Independent Contractor v. Employee • Exempt v. Nonexempt • Preventing Discrimination & Harassment in the Workplace • The Handbook: Informing Employees of Policies & Procedures • Disciplining the Problem Employee

Identify, Evaluate & Manage Risk – Dan Bradshaw, CPCU, Benchmark Insurance Agency – Craig Coburn, Attorney, Richards Brandt Miller Nelson Professional liability claims typically start with a real or perceived technical issue and evolve into a full-fledged claim because of a poor business decision. In this session, attendees will learn (or be reminded of ) how these factors combine to spawn a professional malpractice claim and gain valuable insight on how to better identify, evaluate and manage professional liability risk before it becomes reality and after it becomes a claim.

Risk becomes Reality: Claims Management

Interactive Discussion of Three Lawsuits – with the engineers that were sued and the attorneys that represented them – Seasoned (been sued) structural engineers and defense counsel; moderated by John Tawresey, S.E., retired VP & CFO, KPFF Structural engineers and defense counsel from three firms will present what happened to them when they were sued for professional negligence; and the audience will have an opportunity to predict the outcome.

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Register online and make hotel reservations now at www.ncsea.com!

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The Winter Leadership host hotel is the Coronado Island Marriott Resort & Spa, featuring a full-service spa, three heated pools and convenience to beautiful sandy beaches, shopping and restaurants at Ferry Landing. The WLF room rate is $239 with a complimentary resort fee (a $25 value).

Coronado Island, situated just across the Big Bay from downtown San Diego, is known for two famous structures, the historic Hotel del Coronado and the distinctive San Diego-Coronado Bridge. Beyond these architectural/structural marvels, the quaint island offers beautiful beaches, restaurants, galleries and unique shopping experiences. Take a ferry across the Bay to explore San Diego–stroll through Old Town and the Gaslamp District, explore the museums and gardens of Balboa Park, or go whale watching.

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Methods, Advantages & Disadvantages This interactive workshop will explore virtually every aspect of modern project delivery and the advantages and disadvantages of each method, with a deep dive into results of major studies that document what works and what doesn’t in the design and construction industry.

– Dale Munhall, Architect, Director of Construction Phase Services, Leo A Daly

Professional Liability Risk Management

News from the National Council of Structural Engineers Associations

What’s the Best Project Delivery System for You?

Sessions on Friday will test you on professional liability risk before and after it becomes reality:

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Sessions on Thursday will be interactive and focus on project and employee risks:

NCSEA News

How do you define success?

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REACH SEI MEMBERS

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

WITH SEI SUSTAINING ORGANIZATION MEMBERSHIP

Save the Date

2017 STRUCTURES CONGRESS April 6 – 8, 2017 Denver, Colorado

Increase your exposure to more than 25,000 SEI members through www.asce.org/SEI, SEI Update e-newsletter, STRUCTURE magazine, and at SEI conferences year round.

www.asce.org/SEI-Sustaining-Org-Membership

Local Activities Maryland Chapter

Get Involved in SEI Local Activities

The SEI Maryland Chapter was selected as the 2016 SEI Chapter of the Year. Their commitment to provide high quality events for membership, and significant outreach to the next generation of structural engineers, continues with a full slate of recent activities. The chapter hosted a presentation about the restoration of the Thomas J. Hatem Memorial Bridge and the T.R. Higgins Lecture at Morgan State University. They also conducted a construction tour of a new terminal connector at BWI Airport. For more details, see the full story on the SEI News page at the website.

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.

Reach SEI Members with Register for ASCE Week SEI Sustaining Organization March 14 – 18, 2016, Orlando, Florida Save up to $900 and earn up to 36 PDHs. Choose from 10 Membership seminars including structural and professional practice topics.

Join SEI as a Sustaining Organization Member to raise recognition for your organization with decision makers in the structural engineering community year-round, and to show your leadership and support for SEI 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.

We hope you will join Hayward Baker, International Code Council, and Simpson Strong-Tie in support of SEI as an SEI Sustaining Organization Member. Learn more at www.asce.org/SEI-Sustaining-Org-Membership Questions? Contact Suzanne Fisher sfisher@asce.org.

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In addition, a private Behind-the-Scenes Disney Tour, including the Utilidors, is available. Book one seminar now and save up to $350 off regular seminar prices; book two seminars and save up to $1,300 through February 19, 2016. View the schedule and register at www.asce.org/asceweek.

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.

February 2016

Building Information Modeling: Applications and Practices

On May 20, 2013, the third violent tornado in 14 years tore through Moore, Oklahoma, creating a path of destruction through dense residential areas and damaging several critical facilities. Nearly 1,100 single-family homes were leveled, and 24 people died. Moore, Oklahoma, Tornado of 2013: Performance of Schools and Critical Facilities presents the observations, findings, and recommendations of a team of structural engineers and construction specialists who assessed the structural damage to nonresidential buildings.

The team investigated the tornado’s effect on schools, a medical center, and buildings supported by long-span structural systems.

They found that the most common structural failures related to masonry and steel framing.

Topics include: • a history of significant tornado events in Moore, Oklahoma • results of damage assessments and a summary of observations for a medical center, five schools, a bowling alley, and a strip mall • a survey of building codes and relevant standards used in Moore • conclusions with recommendations The damage assessments and, more importantly, the recommendations for strengthening new and existing critical facilities will be of interest to structural engineers, architects, building owners, local officials, and code developers working to reduce the damage caused by high-wind events.

Building information modeling (BIM) has become a significant area of endeavor in the architecture, engineering, construction, and operations (AECO) industries.

The models generated from BIM are being used for analysis and design of buildings and other infrastructure. The ability to integrate schedule and cost data with the analysis and design process makes BIM a very useful tool.

Building Information Modeling contains 13 chapters, contributed by international researchers and practitioners, that present a comprehensive overview of the recent advances in the application of BIM across the AECO industry. The use of BIM is examined as a framework for structural design; in cost estimation; in adaptive cyber-physical systems; in construction progress monitoring and project management; in green building project delivery; in commissioning and facilities management; in military construction; in model assessment; and in integration with augmented reality.

Engineers, architects, contractors, building owners, facility managers, as well as researchers, will find this publication a valuable resource.

Tier 1 Checklists for Seismic Evaluation of Existing Buildings In Seismic Evaluation and Retrofit of Existing Buildings, Standard ASCE/SEI 41-13, a three-tiered process is established for seismic evaluation according to a range of building performance levels. Tier 1 evaluation focuses on identifying potential deficiencies in existing buildings based on the performance of similar buildings in past earthquakes. The systematic procedure sets forth a methodology to evaluate the entire building in a rigorous manner.

Tier 1 Checklists for Seismic Evaluation of Existing Buildings: Fillable Forms for Standard ASCE/SEI 41-13 is a complete collection of the screening checklists included in Appendix C of Standard 41-13. The evaluation checklists, covering a variety of building types and seismicity levels, are now offered as fillable PDF forms that can be completed using Adobe Acrobat Reader. The collection of 34 forms includes the summary data sheet, Life Safety and Immediate Occupancy checklists for basic configuration and 15 building types, and a nonstructural checklist. Each form contains criteria for four seismicity levels: very low, low, moderate, and high.

STRUCTURE magazine

Design of Latticed Steel Transmission Structures (10-15) This standard provides requirements for the design, fabrication, and testing of members and connections for latticed steel electrical transmission structures. Covering guyed and self-supporting structures, these requirements are applicable to hot-rolled and cold-formed steel shapes. The standard specifies the design criteria for structure components – members, connections, and guys – to resist design-factored loads at stresses approaching yielding, buckling, or fracture. This new edition, which replaces the previous Standard ASCE 10-97, presents minor changes to the design requirements and introduces new sections on redundant members, welded angles, anchor bolts with base plates on leveling nuts, and post angle member splices.

Topics include: • loading, geometry, and analysis • design of members, including compression members, tension members, and beams • design of connections, including fasteners, minimum distances, and attachment holes • detailing and fabrication • full-scale structure testing • structural members and connections used in foundations • quality assurance and quality control Standard ASCE/SEI 10-15 is a primary reference for structural engineers designing latticed steel electrical transmission structures, as well as for other engineers, inspectors, and utility officials involved in the electric power transmission industry.

Visit the ASCE Bookstore at www.asce.org/Books_Standards to purchase these and other structural books.

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The Newsletter of the Structural Engineering Institute of ASCE

Moore, Oklahoma, Tornado of 2013: Performance of Schools and Critical Facilities

Structural Columns

New Structural Publications from ASCE

CASE in Point

The Newsletter of the Council of American Structural Engineers

JUST RELEASED: Updated Sample Correspondence Letters

Donate to the CASE Scholarship Fund!

CASE has updated and released Tool 4-3: Sample Correspondence Letters, the most comprehensive CASE tool that provide sample letters aiding the firm in daily operations.

This tool was updated in 2015 to include: • A new section containing sample collection letters, including both a model lien letter and model audit inquiry letter.

• New letters about contracting directly with a geotechnical firm • New letters about job site hazards CASE Tools are developed and released with the sole purpose of ensuring CASE members manage risk and safety when engaging in structural engineering projects. We encourage you to download them and incorporate them into your business.

You can purchase this and the other Risk Management Tools at www.acec.org/bookstore.

The CASE scholarship, administered by the ACEC College of Fellows, is awarded every year to a deserving student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given over $17,000 to engineering students to help pave their way to a bright future in structural engineering.

We encourage our fellow structural engineering colleagues to support this popular and successful program. Your contribution today will help CASE and ACEC increase scholarship funds to promising students who need them most. This is an exceptional opportunity to encourage growth in the structural engineering profession and ensure that the highest caliber of students become the future of our industry.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

CASE Risk Management Tools Available Foundation 1 Culture – Create a Culture of Managing Risks & Preventing Claims Tool 1-1 Create a Culture for Managing Risks and Reducing Claims The most comprehensive CASE tool that provides sample templates and presentations that aid in creating a culture of risk management throughout the firm.

Tool 1-2 Developing a Culture of Quality This tool was developed to identify some ways to drive quality into a firm’s culture. It is recognized that every firm will develop its own approach to developing a culture of quality, but following these 10 key areas offer a substantial starting point.

The tool includes a white paper and customizable PowerPoint presentation to facilitate overall discussion.

Foundation 2 Prevention & Proactivity – Act with Preventative Techniques, Don’t Just React Tool 2-1 A Risk Evaluation Checklist Don’t overlook anything! A sample itemized list of things you should look for when evaluating a prospective project.

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Tool 2-2 Interview Guide Getting “the right people on the bus” is one of the most important things we can do to mitigate risk management and yet we never learn about interviewing skills in school. It is the second tool related to the Second Foundation of Risk Management, Prevention and Proactivity. The tool will help your firm conduct higher quality interviews and standardize the process among all your staff.

Tool 2-3 Employee Evaluation Templates This tool is intended to assist the structural engineering office in the task of evaluating employee performance. The evaluations provide a method to assess employee performance and serve as an integral part of the company’s risk management program.

Tool 2-4 Project Risk Management Plan This plan will walk you through the methodology for managing your project risks, along with a few common project risks and templates on how to record and track them.

Tool 2-5 Insurance Management: Minimize Your Professional Liability Premium This tool is designed as a guide to help you provide critical additional information to the underwriter to differentiate your firm from the pack.

You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

February 2016

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

If you’re 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.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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 Please submit the following information to htalbert@acec.org • Letter of interest • Brief bio (no more than 2 paragraphs) Thank you for your interest in contributing to your professional association!

Does your firm have an innovative idea or method of practice? Looking to get more involved on short duration projects?

We are inviting you to “share the wealth” and submit a proposal for a web seminar topic, publication, or education session you would like to see CASE present at an upcoming conference. Our forms are easy to use and you may submit your information via email. Go to www.acec.org/coalitions and click on the icon for Idea Sharing to get started.

Questions? Contact us at 202-682-4332 or email Katie Goodman at kgoodman@acec.org. We look forward to helping you put your best ideas in front of eager new faces!

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STRUCTURE magazine

65

February 2016

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The Engineering Way of Thinking: An Analysis

By William M. Bulleit, Ph.D., P.E.

I

n two previous columns (“The Engineering Way of Thinking: The Idea,” December 2015; “The Engineering Way of Thinking: The Future,” January 2016), I discussed the idea of the engineering way of thinking (EWT) and what it might bode for the future. This column is an analysis of the EWT, performed in a manner similar to how the philosopher Ludwig Wittgenstein – who received his initial education in engineering – might have gone about it. It consists of a number of statements organized in a way that I hope will lead you to a better understanding of the EWT. 1. Engineers want to make something – an artifact – or want to alter an existing artifact.

1.1. Artifacts can be objects, processes, or systems – a combination of objects and processes.

2. Making or altering artifacts means perturbing reality.

2.1. Any perturbation of reality involves uncertainty, often a significant amount of uncertainty.

2.2. Making or altering an artifact requires planning and prediction, in part to deal with uncertainty.

2.2.1. The planning and prediction for making or altering an artifact is design.

2.2.2. Design requires a will to make or alter an artifact.

3. The actual making or altering of the artifact comes after the design and is construction, fabrication, manufacture, implementation, instantiation, etc. It requires tools that are also a part of engineering.

4. The EWT involves all methods, techniques, thought processes, and so on that are used to make or alter artifacts.

4.1. The EWT also involves meta-efforts to turn the EWT back on itself. The EWT is itself an artifact.

4.2. The EWT must draw on a wide range of disciplines to allow engineers to make or alter artifacts. These include, but are not limited to, mathematics, physical science, natural science, engineering science, engineering technology, written and oral communication, philosophy, psychology, manual labor, equipment operation, trades such as welding, group dynamics,

economics, computer-aided design and drafting (CADD), building information modeling (BIM), 3D printing, and so on.

4.3. The EWT requires that engineers develop mental models based on a wide range of disciplines, and that they continually broaden those horizons.

5. The EWT draws on these disciplines using pragmatic criteria: If it looks like it might work, try it. If it works, use it.

5.1. In design, the “its” are often referred to as heuristics – things that help to make tractable the kinds of problems that are intractable from a purely mathematical or scientific viewpoint.

5.1.1. The heuristics used in design have limits. These limits may be readily apparent, or not in the least bit apparent.

5.1.2. Exceeding the limits of heuristics leads to failure, potentially catastrophic, but often non-catastrophic.

5.1.3. Failure means that the heuristic must be re-examined in light of its being falsified in some sense.

6. Normal or day-to-day engineering generally limits itself to heuristics that have not been falsified by failures, at least for the range in which they are being used, and thus are supported by the engineering community.

6.1. Normal engineering is focused on getting the job done. This part of the EWT, getting the job done, is often considered engineering proper. Getting the job done is engineering, but it is not all of engineering, and it certainly is not the EWT; it is just a part of the EWT. 6.2. Normal engineering is a heuristic within the EWT. 7. No individual engineer uses the entire EWT, any more than any individual engineer uses all available engineering technical knowledge.

7.1. The EWT encompasses all tools used presently by engineers, all tools used in the past that might be used again, and all new tools that might be used in the future.

7.2. The EWT evolves when engineers, both individually and in groups, try new, previously untested tools to make or alter existing or new artifacts.

7.2.1. New artifacts may be ones that have existed for some years, but have never

been examined by the EWT (e.g., social systems), or ones that have never before existed (e.g., quantum computers).

7.2.2. An engineer’s discipline, or even subdiscipline, should be a base camp from which to explore the peaks and valleys of the EWT. 8. Designing artifacts often requires some amount of reduction of the system to a control volume; e.g., a beam in a building or a pump in a water system.

8.1. A control volume can also be a reduced time frame. A simple example is a 50-year design life. In more complicated systems, the control volume might be determined by a prediction horizon.

8.2. A prediction horizon is the point in time at which predictions of the entire system behavior become so uncertain that they should no longer be used in design decisions. As the EWT is applied to complex systems, such as the earth’s climate and its interactions with human society, control volumes based on appropriate prediction horizons will be vital to engineering design.

9. Designing artifacts is by nature reductionist, since control volumes are necessary.

9.1. The need to be reductionist must be continually reassessed, otherwise we will miss the forest by focusing on the trees.

9.2. Using a control volume of an artifact to allow manageable analysis is a heuristic that is used in normal engineering and is widely applicable to the EWT. 10. Most, if not all, heuristics in normal engineering can be extended to counterparts in the EWT. The EWT exists at the present time in only a weak sense. In order for it to become stronger, engineers will need to think more broadly about how normal engineering can be extended into areas where it has not typically been applied before.▪ William M. Bulleit (wmbullei@mtu.edu) is a professor in the Department of Civil and Environmental Engineering at Michigan Tech in Houghton, Michigan, and the vice chair of the SEI Engineering Philosophy Committee.

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.

STRUCTURE magazine

66

February 2016