STRUCTURE magazine | September 2014

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

September 2014 Concrete

Special Section 22 nd NCSEA

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FEATURES Full Metal Jacket – Part 3

36

By D. Matthew Stuart, P.E., S.E., SECB and Richard H. Antoine III, P.E., S.E. The final installment of this three-part series discusses the impact of the findings of a soil investigation and repairs that were required in the building in addition to the column jackets.

CONTENTS September 2014

COLUMNS 7 Editorial SELC

NCSEA 2014 Conference Section

38 Special Section

The National Council of Structural Engineers Associations will host its 22nd Annual Conference at the Astor Crowne Plaza Hotel in New Orleans September 17th through the 20th. Read about the conference, the extensive program, and vendor information in the Special Conference Section… and plan to attend this exciting event!

Tilt-Up Pushes the Height Envelope on a Six-Story Office Building in Texas

43

By Jeff Griffin, Ph.D., P.E. and Mitch Bloomquist Cutting edge techniques employed for a six-story office building near Houston prove that tilt-up is appropriate for high quality buildings and distinguished architectural design.

The Use of Tilt-Up Concrete for Anti-Terrorism Force Protection

46

By Thomas P. Heffernan, P.E., Brian M. Barna, P.E. and Mark P. Gardner, P.E.

STRUCTURE

®

Tilt-up construction offers a sound approach to anti-terrorism force protection at a time when facilities have never had a more complex set of protective needs.

DEPARTMENTS

Special Section

22 ND NCSEA

ON

Annual Conference

New Orleans, Louisiana

THE

COVER

A Joint Publication of NCSEA | CASE | SEI

The Sector Gate Monolith houses the primary gate east of New Orleans, which allows closure of the Gulf Intracoastal Waterway (GIWW) during storm surges. It is 380 feet long by 160 feet wide, and 50 feet from top to pile cap. It has a 150-foot-wide by 42-foot-tall opening for navigation that can be closed in 30 minutes or less. Ben C. Gerwick, Inc. was awarded an Outstanding Project Award for the design of the Monolith in the 2013 NCSEA Excellence in Structural Engineering Awards Program. This cover is in recognition of the NCSEA Annual Conference in New Orleans this month.

September 2014 Concrete

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.

54 Professional Issues Deferred Submittals – Part 3

By Dean D. Brown, S.E.

The Ladder of Invention

By Jon A. Schmidt, P.E., SECB

10 Structural Forensics Introducing and Using CRSI’s New “Treatise”

By Meghan Elliott, P.E.

15 Building Blocks High-Strength Concrete Comes of Age

By Cary Kopczynski, P.E., S.E.

18 Codes and Standards ACI 562

By Keith Kesner, Ph.D., P.E., S.E. Kevin Conroy, P.E., S.E. and Lawrence F. Kahn, Ph.D., P.E.

22 Structural Rehabilitation FRCM Systems

By Antonio De Luca, Ph.D. and Gustavo Tumialan, Ph.D., P.E.

26 Insights Advances in Steel Plate Shear Walls

By Jeffrey W. Berman, Ph.D.

30 Construction Issues Developing a Temporary Bracing Plan for Tilt-Up Panels

By Matt Bell, P.E.

Concrete Gravity Members

Couldn’t Care Less

By Matthew R. Rechtien, P.E., Esq.

61 CASE Business Practices What is the Value of Your Idea?

By John Dal Pino, S.E.

67 Spotlight Reaching for the Sky

By Chris Ramseyer, Ph.D., P.E. and Hans Butzer

74 Structural Forum How Code Complexity Harms Our Profession – Part 2

By Craig M. DeFriez, P.E., S.E.

5

9 InFocus

34 Engineer’s Notebook

57 Legal Perspectives

STRUCTURE magazine

By Randall P. Bernhardt, P.E., S.E.

September 2014

By Jerod G. Johnson, Ph.D., S.E.

50 Historic Structures Isaiah Rogers

By David Guise

IN EVERY ISSUE 8 Advertiser Index 63 Resource Guide (Anchoring) 68 NCSEA News 70 SEI Structural Columns 72 CASE in Point

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STR_7-13

Editorial

new trends, new techniques and current industry issues SELC

By Randall P. Bernhardt, P.E., S.E.

V

olunteer professional organizations occupy a significant role in the business, education, regulation and licensure of structural engineering. These groups provide a positive influence from the professionals’ vantage on the laws, integrity and quality of our careers and act as stewards for the profession.

Over the years, several organizations focusing on structural engineering have addressed separately the many issues surrounding the practice.

There are four main groups representing structural engineering in the United States: the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE), the National Council of Structural Engineers Associations (NCSEA), the Structural Engineering Certification Board (SECB), and the Council of American Structural Engineers (CASE) of the American Council of Engineering Companies (ACEC). Each organization has a slightly different focus on structural engineering arising from needs within the profession.

They have many commonalities in vision and passion. One of these common issues is structural engineering licensure.

A few visionaries in the profession conceived the idea to form a coalition to improve coordination and collaboration on issues pertaining to structural engineering licensure. It was thought that rather than running over each other in pursuing a common goal, combining the efforts of the four organizations can provide the greatest benefit to the profession. A cord of three strands, or in this case four strands, cannot be easily broken.

The Structural Engineering Licensure Coalition (SELC) was formed

by SEI, NCSEA, SECB and CASE in 2012 to champion the cause of structural engineering licensure and to build a consensus among all stakeholders. The mission of SELC is to serve as a united voice for the structural engineering profession, for the promotion of structural engineering licensure nationwide.

SELC has adopted the following positions: 1) SELC endorses the Model Law Structural Engineer (MLSE) standard developed by the National Council of Examiners for Engineering and Surveying (NCEES) in accordance with the American National Standards Institute (ANSI) consensus process as establishing the minimum set of qualifications for a licensed Structural Engineer (S.E.).

2) SELC advocates that jurisdictions require S.E. licensure for anyone who provides structural engineering services for designated structures. SELC recommends that each licensing board adopt rules to define appropriate thresholds for these structures.

3) SELC recognizes that, when S.E. licensure is enacted in each jurisdiction, it is important to ensure that an equitable transition process, as defined by the licensing board, is available for any individual who has been practicing structural engineering as a licensed Professional Engineer (P.E.).

4) SELC encourages all jurisdictions to incorporate these provisions into their current engineering licensure laws, adapting them to their unique individual situations. SELC supports the modification of existing P.E. statutes and regulations to implement S.E. licensure as a post-P.E. credential.

The SELC is led by a steering committee comprised of two members of each organization, one of the members being in a board position of that organization. There are two face-to-face meetings each year and several teleconferences to coordinate action toward the goals of the Coalition.

The goals of SELC include the following: STRUCTURE magazine

1) Develop supporting rationale for structural engineering licensure. This includes developing case studies and other supporting documentation.

2) Communicate the need and rationale for structural engineering licensure in all jurisdictions. Articles in journals, presentations and the recently launched website (www.selicensure.org) all contribute to this goal.

3) Enhance the visibility of structural engineering licensure on the national level. This includes communicating with other professional groups such as National Society of Professional Engineers (NSPE) and the National Council of Examiners for Engineering and Surveying (NCEES).

SELC recognizes the vital role that professional licensure plays in protecting the public, and unanimously affirms that the licensure of structural engineers is a critical aspect of fulfilling this responsibility.

SELC envisions a future with structural engineering licensure in every jurisdiction, thereby improving the health, safety, and welfare of the public as required by our professional charge.

Structural engineering licensure is already established in many parts of the United States. The American National Standards Institute (ANSI) consensus standard for structural engineering licensure and the nationally adopted structural engineering examination administered

by NCEES form a solid foundation on which to base the support and mechanisms necessary to initiate structural engineering licensure in all jurisdictions. By endorsing the MLSE and the ANSI standard, SELC believes in promoting common standards in all jurisdictions for structural engineering education, experience, and licensure.

For example, a key component of structural engineering licensure is the NCEES 16-hour structural examination. The 16-hour structural examination is an improvement over the NCEES 8-hour exam required by many jurisdictions and, as such, is a key differentiator for determining levels of minimal competency. The NCEES 8-hour examination for the structural engineering discipline consists of 80 multiple choice questions covering the broad spectrum of disciplines within civil engineering, with a focus of less than 40 of those 80 questions on structural engineering. When the 16-hour exam was developed, it was determined that the 80 multiple choice questions alone would not be sufficient to cover the essential items required for a minimally competent structural engineer, even if all of the questions were focused on structural engineering. The 16-hour exam includes 80 multiple choice questions, but also 8 hours of essay questions, all focused on structural engineering, that serve to test not only knowledge, but also judgment. This examination raises the bar for structural engineering and, as such, improves the level of competency serving the public.

SELC is taking action toward accomplishment of these goals and, in the process, strengthening our voice and improving the standing of structural engineering across the country. With collaboration between the different organizations and a strengthened focus on what is most important, our world will be safer and we, as structural engineers, will continue to provide a firm foundation and secure framework within which the world functions.▪ Randall P. Bernhardt, P.E., S.E. (rpbernhardt@esi-mo.com), is a Senior Structural Engineering Consultant in the St. Louis office of the forensic engineering firm of Engineering Systems Inc.

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September 2014

Advertiser index

PleAse suPPort these Advertisers

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Integrated Engineering Software, Inc..... 56 Integrity Software, Inc. .......................... 62 ITW Red Head ..................................... 25 KPFF ...................................................... 8 LNA Solutions ...................................... 58 PT-Structures ........................................ 62 Powers Fasteners, Inc. ........................ 2, 65 QuakeWrap ........................................... 21 Quikrete ................................................ 49 RISA Technologies ................................ 76 S-Frame Software, Inc. ............................ 4

Editorial board Chair

Jon A. Schmidt, P.E., SECB

A Joint PublicAtion of ncSEA | cASE | SEi AdvErtiSing Account MAnAgEr

Burns & McDonnell, Kansas City, MO chair@structuremag.org

Charles F. Minor & Associates, Inc.

Craig E. Barnes, P.E., SECB

Brian W. Miller Davis, CA

Chuck Minor

John A. Dal Pino, S.E.

Evans Mountzouris, P.E.

847-854-1666 sales@STRUCTUREmag.org

CBI Consulting, Inc., Boston, MA

Degenkolb Engineers, San Francisco, CA

Mark W. Holmberg, P.E.

The DiSalvo Engineering Group, Ridgefield, CT

Greg Schindler, P.E., S.E.

Heath & Lineback Engineers, Inc., Marietta, GA

KPFF Consulting Engineers, Seattle, WA

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

Stephen P. Schneider, Ph.D., P.E., S.E.

Roger A. LaBoube, Ph.D., P.E.

John “Buddy” Showalter, P.E.

Khatri International Inc., Pasadena, CA

CCFSS, Rolla, MO

Brian J. Leshko, P.E.

HDR Engineering, Inc., Pittsburgh, PA

BergerABAM, Vancouver, WA

American Wood Council, Leesburg, VA

Amy Trygestad, P.E.

Chase Engineering, LLC, New Prague, MN

LAX CENTRAL TERMINAL IMPROVEMENTS, LOS ANGELES, CA PHOTO BY: ELON SCHOENHOLZ

EditoriAl StAff Executive Editor Jeanne Vogelzang, JD, CAE

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Editor

Christine M. Sloat, P.E.

publisher@STRUCTUREmag.org

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Nikki Alger

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Rob Fullmer

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September 2014

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infocus

new trends, new techniques and current industry issues The Ladder of Invention

By Jon A. Schmidt, P.E., SECB

R

egular readers of this column know that more often than not it addresses some aspect of the relationship between philosophy and engineering. It should thus be no surprise that I am eager to discuss a recent book called Philosophy and Engineering: Reflections on Practice, Principles and Process, edited

by Diane P. Michelfelder, Natasha McCarthy, and David E. Goldberg, and published by Springer. In fact, I had the privilege of contributing chapter 9 on “Engineering as Willing” based on many of my past writings in this space, including the March 2010 installment of the same name. However, I will not be covering that subject matter this month.

Instead, I want to highlight chapter 27 by M. H. Abolkheir, which has the somewhat unwieldy title, “The Methodological Ladder of Industrialized Inventions: A Description-Based and Explanation-Enhanced Prescriptive Model.” The author calls himself “an industrial inventor who is a firm believer in the unique opportunities which are present in applying the abstract tools of philosophy to the examination of industrialised inventions.” Substituting “structural engineer” for “industrial inventor” and “engineering practice” for “industrialised inventions” results in a characterization that I would readily apply to myself.

Since groundbreaking inventions are commonly understood to result from “flashes of insight” that seem to come out of nowhere, conventional wisdom says that they cannot be reliably anticipated, let alone intentionally fostered. Abolkheir challenges this assumption by identifying a series of “specific statement-generating phases through which epistemically (predictively) successful industrialised inventions evolve”: 1) Epistemic Trigger – The inventor notices an “intriguing causal relation” in the form of either a technological problem (a known and desirable effect for which a cause is sought) or a technological opportunity (a known cause for which a desirable effect is sought).

2) Novel Domain – Most people assign the Epistemic Trigger to a particular area of knowledge and practice by default, but the inventor perceives it as also belonging to a different one.

3) Inventive Hypothesis – The inventor proposes a solution to or exploitation of the Epistemic Trigger that falls within the Novel Domain; i.e., a potential cause of the known and desirable effect, or a potential desirable effect of the known cause.

4) Technological Bundle – The inventor determines a combination of “Confirmed Technological Principles” (CTPs), data-supported instrumental rules and procedures, whose implementation makes the Inventive Hypothesis work.

5) Industrial Design – The inventor refines the Technological Bundle by adding more CTPs to accommodate socioeconomic requirements, such as “choice of materials, mass-producibility, cost, safety, user-friendliness, environmental impact, aesthetics, etc.”

Each phase terminates with the emergence of a corresponding statement: 1) There is a technological problem E or opportunity C. 2) Problem E or opportunity C belongs to domain X. 3) Within domain X, problem E might be solved by cause Cx, or opportunity C might be exploited to produce effect Ex. 4) To bring about effect E or Ex using cause Cx or C, implement the technological bundle consisting of CTP1 …

CTPn, where “n” is the number of CTPs necessary to satisfy technical requirements.

STRUCTURE magazine

5) To achieve an industrial design that incorporates effect E or Ex using cause Cx or C, implement the technological bundle consisting of CTP1 … CTPn+p, where “p” is the number of CTPs necessary to satisfy socio-economic requirements.

The critical “cognitive leap” typically occurs during the second or third phase – perhaps even as a combination of the two – but considerable creativity is frequently also essential in the later phases. Abolkheir asserts that this overall pattern is consistent regardless of whether the inventor is a single person or a team, whether the phases last for a few moments or many years, and whether the transitions between them occur as the result of systematic effort or happy coincidence.

He offers three illustrative examples: • While working on radar components at Raytheon, Percy Spencer noticed that a chocolate bar in his pocket had melted.

He recognized that high-frequency electromagnetic waves could be utilized in the domain of food preparation, leading eventually to the development of the microwave oven.

• While working in the spray-equipment industry, James Dyson noticed that the bag in his vacuum cleaner at home got clogged almost immediately upon use. He recognized that the centrifugal force used to separate powder in one domain could be adapted to separate dirt in another, leading eventually to the development of the cyclonic vacuum cleaner.

• While working in a laboratory, Alexander Fleming noticed that the penicillum mold inhibited the growth of bacteria cultures.

He recognized that this could have applications in the domain of pharmaceuticals, leading eventually to the development (by others) of therapeutic antibiotics.

Besides providing a roadmap for successful inventions, Abolkheir’s model also explains why some fail to materialize in what might appear to be favorable circumstances. Radar engineers prior to Spencer never took an interest in the heating effect of microwaves (Epistemic Trigger), despite “reports of partially burnt birds at the bottom of radar installations.” Vacuum cleaner manufacturers prior to Dyson concentrated on improving filter bags, never widening their focus to include other means of separation (Novel Domain). Although he possessed considerable scientific understanding of antibacterial mold, Fleming himself was never able to formulate a viable treatment (Technological Bundle).

In summary, Abolkheir believes that his “methodological ladder” specifies the conditions that are “individually necessary and jointly sufficient” for carrying out the process of invention from start to finish. Interestingly, he concludes the chapter with a plea that readers “use it with care and employ it only to good ends,” evidently recognizing that inventors – like engineers – need practical judgment to guide their applications of technical rationality.▪ Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri. He chairs the STRUCTURE magazine Editorial Board and the SEI Engineering Philosophy Committee, and shares occasional thoughts at twitter.com/JonAlanSchmidt.

9

September 2014

Structural ForenSicS investigating structures and their components

E

arlier this year, the Concrete Reinforcing Steel Institute (CRSI) published A Comprehensive and Invaluable Treatise on all Forms of Steel Reinforcement Employed in the Design and Construction of Reinforced Concrete of Long Ago. The majority of the book is an extensive catalogue of no less than 47 different types of steel reinforcing bars (four of which fall under the category of “Miscellaneous”), seven types of welded wire fabric, 22 systems of beam and girder reinforcement, 12 systems of column reinforcement, 11 slab systems and six bridge systems.

The supporting sections of the book, including a brief history of early concrete mix design as well as historic ASTM bar specifications, are secondary compared to the bar descriptions and images. Appendices are similar compendiums of reinforcing steel illustrations; for example, Appendix E contains 31 patent drawings, extending from Thaddeus Hyatt’s revolutionary pavement reinforcing issued in 1878 to latecomer J.T. Simpson’s visually interesting “deformed bar” of 1922. Appendix F contains images of over 30 early advertisements.

Appendix G paraphrases the “Alphabetical List of the 144 Foreign Systems of Reinforced Concrete Construction, with the Addresses of the Inventor or Owner of Each System, and a Concise Description of Its Special Features” from Reinforced Concrete in Europe by A. L. Colby in 1909.

This new resource for structural engineers fits into, but is distinctly different from, the expanding collection of reference materials that have been produced by professional organizations.

First, it builds on and replaces CRSI’s earlier publications: its initial reference, Evaluation of Reinforcing Steel Systems in Old Concrete Structures (1981), and its abridged version as Engineering Data Report No. 48, Evaluation of Reinforcing Bars in Old Concrete Structures (2001). These focused on summaries of industry trends in terms of material strength, specifications, and general availability of materials. This new publication is similar in function and potential use to the American Institute of Steel Construction’s (AISC) Design Guide 15, AISC Rehabilitation and Retrofit Guide: A Reference for Historic Shapes and Specifications.

The need for this type of reference is a result of the convergence of several trends in the history and contemporary practice of structural engineering. First, there was an explosive development of reinforced concrete technology in the United States during the approximate time period from 1890 to 1920. This proliferation of new products coincided with a rise in demand for industrial buildings, but preceded the formal

Introducing and Using CRSI’s New “Treatise” Vintage Steel Reinforcement in Concrete Structures

By Meghan Elliott, P.E., Associate AIA

Meghan Elliott, P.E., Associate AIA (elliott@pvnworks.com), is the founder and a principal at Preservation Design Works (PVN), a historic preservation consulting firm in Minneapolis, Minnesota.

codification of the newly available material. The rise of manufacturing, and the associated need for warehousing to accommodate product distribution, brought higher floor loads and the desire for bigger buildings. Likewise, fire and conflagration drove owners to seek “fireproof ” construction, which concrete was able to provide.

Now, about 100 years later, many of these buildings are being repurposed and retrofitted for reuse, a trend driven in part by state and federal tax credits for historic rehabilitation. Today’s structural consultants are practicing at the confluence of two trends, each at opposite ends of the century, which converge on a general deficit of understanding and available information. Students of engineering and historic preservation, as well as researchers in the small but growing field of construction history, may also find useful information and references in the book.

Researching Reinforced Concrete Developing enough understanding of an early concrete structure to analyze it for reuse can require a substantial amount of research, unless assumptions are made – potentially at the ultimate expense of the project, or loss of historic material. Certainly, knowledge of early reinforced concrete does not replace investigation, analysis, or engineering judgment; but effectively planning and implementing a search for supporting and relevant sources of information may result in the difference between a cost-effective and a cost-prohibitive project approach.

These sources can very generally be thought of in two categories: primary and secondary. Primary sources are those that are typically contemporary to the topic and representative of the query: patents, advertisements, earlier building codes, and historic newspaper or trade articles about a particular engineer, product, or analytical method (Figure 1). Secondary sources are used to establish the context, and place the question within the broader research and academic understanding of the topic. Secondary sources typically include current books, journal articles, literature reviews, or even textbooks. Both types of sources are typically needed to understand a building structure.

While the CRSI publication might initially be considered a secondary source, especially given the authors’ choice of the word “treatise,” it may be more successfully used as a collection of reprinted primary sources.

A small but growing collection of secondary sources is available to understand early reinforced concrete. Some recent publications include Donald Friedman’s Historical Building Construction: Design, Materials & Technology (2010), Amy Slaton’s Reinforced Concrete and the Modernization of American Building, 1900-1930 (2001), and Andrew Saint’s Architect and Engineer:

10 September 2014

Figure 1. An example of a primary resource for researching concrete, the William B. Hough Company advertisement for “M/B Special Open Hearth Bars” lists the buildings in which the product was used.

Image from Cement Age, December, 1911, and digitized by Google Books.

A Study in Sibling Rivalry (2007). These books can be supplemented by earlier analyses of concrete history, such as articles and books

by Carl W. Condit, a good example of which is “The First Reinforced Concrete Skyscraper: The Ingalls Building in Cincinnati and Its Place in Structural History” (1968), published in the journal Technology and Culture.

Other secondary sources are too numerous to list here, but include journal articles and trade publications, like the Association for Preservation Technology’s (APT) Bulletin and the journal or proceedings of the American Concrete Institute (ACI).

Early Reinforced Concrete The early history of reinforced concrete in the United States is very different from that of other structural materials. The infancy of modern structural analysis, combined with the new availability of concrete materials and perhaps even the innovation and shameless salesmanship on the part of structural engineers and builders, led to a proliferation of proprietary products, supported by vague or sometimes non-existent analytical methods, and a wide variety of reinforced concrete systems – from individual bar types and accessories (like formwork products) to nearly complete building systems of slabs, beams, and columns.

Friedman compares the acceptance and growth of the concrete industry to that of steel, and attributes the differences to several

key factors. First, structural steel had a head start of several decades. For example, wroughtiron use as structural framing began before the 1870s, and the basics of steel framing were in place before 1900. The use of reinforced concrete for buildings, on the other hand, was mostly a post-1900 trend.

Not coincidentally, structural engineers as a separate consulting practice and resource for architects were rapidly evolving at the same time: the introduction of reinforced concrete as a building material coincided with a new professional field of structural engineering.

According to Friedman, the use of steel framing was not an analytical leap from traditional wood building methods. Builders and architects could easily make a rational switch from a stick of wood to a stick of steel: while steel was a substantially stronger material, it followed the same beam theory and acted the same in bending and compression.

Concrete, on the other hand, required an analytical shift to integrate the new system into buildings, from a system of pieces to monolithic construction and the interaction of two distinct materials. Engineers and builders were thus using the material before it was understood. Many of the proprietary products appear as an attempt to rationalize what was already being built through experimentation and intuition.

The evolution of reinforced concrete design in the United States was driven by a small group of entrepreneurial individuals, as compared to the relatively consistent and nationwide acceptance and distribution of steel framing products. As a result, regional differences occurred, as well as leaps in the distribution of different products and systems. While there were earlier contributions

by William Ward and Thaddeus Hyatt, the momentum of innovation in reinforced concrete in the US began with Ernest Ransome.

From his practice in San Francisco, he introduced two important concepts that would remain fundamental to reinforced concrete design and construction: slabs and beams cast together monolithically, and deformed reinforcement. Most early products in concrete can be demonstrated to meet one or both of Ransome’s tenets – monolithic behavior and adhesion of concrete with steel through mechanical interaction. Ransome’s own patented steel reinforcement is easily recognized by its twisted square shape (Figure 2).

In addition to Ransome, Carl Condit attributes the understanding and development of reinforced concrete behavior to the importation of the Monier-Wayss system to the US from Germany. While applied to many types of concrete structures, the theory was to

STRUCTURE magazine

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September 2014

Figure 2. Excerpt of Ernest Ransome’s patent for twisted square reinforcement. The M/B Bar of Figure 1 uses a similar method for mechanical adhesion of the concrete to the steel. Digitized by Google Patents.

strengthen the concrete with steel rods located to take the tensile stresses. In all cases, the steel reinforcement was placed in two directions and tied with wires, the rods in one direction designated as carrying rods and those in the other as distributing rods. For slabs poured continuously over supports, the rods were placed at the top of the slab; i.e., the correct reinforcing pattern for continuity.

In practice, the expansion of the use of monolithic concrete in the US was substantially instigated by several engineers and builders. In addition to Ransome, other early innovators included Claude Allen Porter (C.A.P.) Turner practicing in Minneapolis, Kahn’s Trussed Concrete Steel Company of Detroit, the Ferro-Concrete Construction Company of Cincinnati, and the Condron Company of Chicago. These early engineerentrepreneurs developed a variety of systems between 1890 and 1920. The systems rationalized their inventors’ uses, understanding, and promotion of different advantages of reinforced concrete.

For example, Turner singularly focused on the monolithic nature of concrete, and criticized his peers for imitating the earlier simple systems of wood and steel. He conceptualized his patented Mushroom Flat Slab floor system, distinguished by its unique four-way

Figure 4. Illustration of cross sectional and perspective views of the Kahn reinforcement bar, along with a diagram of the theoretical “truss action.”

Figure 3. Excerpt of C.A.P. Turner’s patent for a 4-way system of slab reinforcement using smooth round bars. Digitized by Google Patents.

reinforcing and flared column capitals, as a series of flat slab cantilevers over the columns (“Deconstructing Bridge 92297,” STRUCTURE magazine, January 2014).

The slab reinforcing plans quickly illustrate the concept, and demise, of the system with its lack of reinforcing at the center of the slab span (Figure 3).

One of Turner’s competitors, particularly for industrial construction in the Midwest, was Julius Kahn who developed his Kahn System of reinforcing for beams, girders and columns (“The Kahn System of Reinforced Concrete,” STRUCTURE magazine, April 2013). Kahn conceptualized the behavior of concrete as a truss. His unique bar that formed the basis for all of his concrete construction, including columns, consisted of a longitudinal core with steel flanges that could be bent up to form the tension diagonals of the truss (Figure 4).

Similarly, the visual illustration of the system demonstrates its concept and shortcoming: a deeper beam necessitates wider flange spacing.

The truss concept also promotes a simply supported end condition at the beams.

Another system that was used during this period of innovation, and the one that is closest to our current conventions, is the Akme System of the Condron Company in Chicago.

This system, generally consisting of belts of two-way reinforcing at the slab and columns, was constructed with or without column capitals and drop panels. While there were other proprietary systems, as documented in the

CRSI resource, there is little documentation as to the prevalence and distribution of these systems. Without promotion, and ultimately adoption in building construction, these systems were entrepreneurial dead ends.

Ransome’s second contribution – the use of deformed steel reinforcement and the analysis of its adhesion with concrete – was similar in development to the proliferation of monolithic concrete systems. Ransome argued, and proved through testing, that deformed reinforcement achieved greater adhesion with concrete compared to smooth reinforcement, resulting in greater overall strength. The many types of patented bars were based on achieving mechanical adhesion with the concrete. There were even trademarked twisted square bars that were referred to as “Ransome-style” bars.

Turner disagreed with Ransome, and promoted the use of smooth round bars that, as he speculated, allowed the concrete to slip as it cured. Likewise, Kahn’s Trussed Concrete Company used different types of Kahn bars, like the Kahn Trussed bar and the Kahn Cup Bars. They also produced Rib Bars and Square Rib Bars. Several types of bars were produced by Carnegie Steel in Pittsburgh, Pennsylvania, including Columbian Bars (also known as Hanger Bars), Corrugated Bars, Elcannes Bars, Golding Monolith Bars, Havemeyer Bars, Herringbone Bars, Jenks Bars, Kahn Cup Bars, Kahn Trussed Bars, Lug Bars, Monotype Bars, Ransome Bars, Round Rib Bars, Scofield Bars, Slant Rib Bars, Square Rib Bars, Thacher Undulated Bars, U Bars, and Wing Bars.

Conclusion In the introduction to the new CRSI book, Matthew Stuart points out two of the challenges of researching historic reinforced concrete: it is very difficult to research something, like a type of reinforcing, if you do not know its name; and it is even more difficult to research something if you cannot

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even see it, as is the case with reinforcement concealed in a slab. Often, engineers are asked to make conclusions about the structural integrity of reinforced concrete with both of these unknowns.

The new CRSI resource helps to alleviate some of the difficulty of researching a type of reinforcing by providing a visual resource with extensive patent images, advertisements, and an Appendix of photographs of a 1979 Smithsonian exhibit to help give names to some of the bars and systems encountered in the field. However, secondary sources are also needed to give more context and potential information. CRSI’s Vintage Steel Reinforcement in Concrete Structures offers remarkable documentation of reinforced concrete products and systems that will hopefully stimulate additional exploration of this topic.

It would be desirable to know, for example, which of the many concrete products and systems were most popular, and whether certain products have patterns of local or regional distribution and use. Future researchers should also assess the factors and forces that influenced the standardization of reinforced concrete building. Were the concrete products and system we know today determined to be the “best,” and if so, by whom, and according to what definitions or parameters?

Additional research and publication will be necessary to determine how factors like the cost of labor, ease of assembly, marketing, and the influence of professional associations shaped the trajectory of reinforced concrete technology. In the meantime, a small but growing body of secondary sources provides some clues as to which systems succeeded and those that may never have been built, the potential modes of failure or shortcomings with respect to current building codes, and potentially the analytical methods that may or may not support the continued use of the building.▪

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s recently as 25 to 30 years ago, the steadily increasing availability of concrete with compressive strengths above 6,000 psi had the industry’s rapt attention. Back then, in many regions, strengths this high were considered revolutionary. Some people even questioned the need.

Fast forward to 2014, and designers are specifying strengths of 10,000 psi, 12,000 psi and higher.

A new 42-story residential tower in downtown Seattle is one of the first in the country to use 15,000 psi concrete in its columns, reflective of the recent advances in concrete materials technology. Used effectively, this “super concrete” allows smaller columns, shorter and thinner shear walls, and reductions in other structural elements. This results in additional interior real estate. And, when this concrete is paired with modern highproduction formwork and the advanced pumping technologies now available, the sky is quite literally the limit.

Concrete Advancements Concrete has been used as a building material for thousands of years and has played a role in the construction of some of the world’s most prominent structures. For example, the Pantheon in Rome – its unreinforced cast-in-place concrete dome completed in 126 AD – still stands today.

The icon’s longevity underscores the superiority of its design and construction. In fact, one wonders if the structure could be improved upon if rebuilt today. Since that time, however, concrete’s use

has been extended upward into towers of nearly 2,000 feet in height, and it is for these structures that high-strength concrete has found a home.

Concrete strength started trending upward in the last century when high-range water reducers began gaining prominence. Until the 1950s and 1960s, concrete suppliers struggled to create stronger concrete without sacrificing workability.

It was well known that concrete’s strength could be increased through a reduction in water content, but, without a way of preserving workability, the side effect of excessive water reduction was an extremely low-slump material that was nearly impossible to place. When material scientists began developing more effective chemical water reducers, however, the problems associated with stiff, low slump concrete began to disappear.

“Superplasticizers” such as “Mighty 150” and others hit the market and quickly became popular, gaining mainstream use by the 1980s. These new high-range chemical water reducers allowed the creation of concrete with both higher strength and adequate workability. Research and development into superplasticizers saw a steep climb during this time, simultaneous with increased R&D associated with the use of cement replacements such as fly ash, silica fume, and blast furnace slag. The result was the development of the modern high-strength concretes in use today.

As concrete strengths have increased, forming systems and pumping technology have also made significant gains, allowing structural engineers and architects to consider concrete for use in buildings that would previously have been designed using other materials. Concrete forming systems that were formerly “hand set” have largely been replaced by well engineered components that can be assembled and disassembled quickly, allowing higher field productivity and faster construction. Pumping technology has also advanced, eliminating the need for bucketing on even the highest of structures. Concrete for the Burj Khalifa (formerly the Burj Dubai) in the United Arab Emirates, in fact, was pumped to a height of almost 2,000 feet, at which point structural steel continued upward to complete the 163 story, 2,722 foot structure. The Burj Khalifa was completed in January 2010.

updates and information on structural materials

High-Strength Concrete Comes of Age

Concrete Columns The 42-story Premiere on Pine residential tower, in downtown Seattle, is one of the first in the country to use 15,000 psi concrete in its columns, reflective of the recent advances in concrete materials technology. It is scheduled for completion in April of 2015. Courtesy of Soundview Aerial Photography.

Building Blocks

Today, high-strength concrete has found its niche primarily in the columns of high-rise towers. Just a few decades ago, many designers believed that concrete was inappropriate for tall buildings, since the then lower strength mixes available would require column sizes of prohibitive proportions. continued on next page

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New Technologies Push Strengths to New Heights

By Cary Kopczynski, P.E., S.E., FACI

Cary Kopczynski, P.E., S.E., FACI, is Senior Principal and CEO of Cary Kopczynski & Company (CKC), a structural engineering firm based in Bellevue, Washington. Mr. Kopczynski is a member of ACI Committee 318 which writes the concrete building code, and serves on ACI’s Board of Directors. He also chairs the Technical Advisory Board of the Post-Tensioning Institute, is a member of Committee DC-20, and serves on PTI’s Board of Directors. Mr. Kopczynski is a Fellow of both PTI and ACI, and an Honorary Member of the Wire Reinforcement Institute. He may be reached at caryk@ckcps.com.

The Challenges of High-Strength Concrete

These two 400-foot, side-by-side residential towers are expected to break ground in Los Angeles by the end of this year, becoming the tallest reinforced concrete buildings ever built in that city. High-strength concrete is expected to be used in these building’s columns. Courtesy of Harley Ellis Devereaux.

These excessive column sizes would interfere with floor layouts and monopolize valuable leasable space. Now, with higher strengths more widely available, column sizes can be reduced and often remain constant for a building’s full height, with the concrete strength decreasing at higher levels of the structure. With standardized column sizes and fewer changes over a building’s height, formwork costs drop and schedule impacts are minimized.

One of the tallest new residential towers in downtown Seattle, Premiere on Pine, is a 42-story concrete structure that uses 15,000 psi column concrete at the base, reducing to 8,000 psi at the upper levels. Structural designers decided to amp up the column strength to take advantage of concrete’s efficiencies and maximize the available leasable space. Scheduled for completion in April of 2015, Premiere on Pine took maximum advantage of the high strength concrete available in the Seattle market.

Columns sizes of 24 inches x 30 inches and 20 inches x 42 inches are constant nearly to the structure’s top, which maximized formwork reuse and helped maintain the rapid construction pace. Column sizes for buildings of this height are commonly 20% to 40% larger. Premiere on Pine’s smaller columns increased net rentable square footage when compared to competing towers.

Seattle isn’t the only city breaking records for its construction of high-rise concrete buildings.

Two 400-foot, side-by-side residential towers are expected to break ground in Los Angeles by the end of this year, becoming the tallest reinforced concrete structures ever built in that city. High-strength concrete is expected to be used in these building’s columns as well.

The use of high-strength column concrete comes with its share of challenges. Since it doesn’t make financial sense to pour floor slabs with a similarly high strength mix – 4,000 to 6,000 psi is typically sufficient for slabs and other flexural elements – transferring column loads through lower strength floor plates can be difficult.

If the slab confinement requirements of ACI 318 are met, column concrete strength can exceed the slab concrete by as By holding back all but several inches of slab concrete much as 2.5 times, and a blended strength from the column perimeter when the slab is poured, is used for the column’s design. If not, an opening is available for the high-strength column however, there are several ways to retain concrete to pass through from above. This procedure a high-strength column’s integrity as it replaces the “puddling” option, which can sometimes be difficult to execute. Courtesy of Cary Kopczynski & Co. passes through a floor plate.

One is to increase the slab strength at the slab/column intersection by “puddling” high-strength concrete into the column area. The high-strength concrete is poured immediately before the lower-strength floor slab so that the two concretes can be intermixed and the possibility of a cold joint eliminated. While this technique is workable in theory, it can be difficult to execute in the field. It requires precise timing of concrete deliveries and a skilled field crew to ensure that cold joints do not occur.

A less common, but often more effective approach, is to hold back all but several inches of slab concrete from the column perimeter when the slab is poured, leaving an opening for the high-strength column concrete to pass through from above. This eliminates the need to puddle concrete and ensures the integrity of the column. With this approach, shear-friction rebar is typically added through the joint to supplement the strength of the connection.

While high-strength concrete is an obvious choice for columns in tall towers, it also serves a purpose in shearwall and rigid frame construction in these same buildings. Both the strength and the stiffness of shearwalls and frames are increased; and, since lateral systems are often drift controlled, the added stiffness is highly beneficial. On the 450-foot tall expansion of Lincoln Square in Bellevue, Washington, for example, designers specified 14,000 psi for strength, but also specified an elastic modulus of 5,700 ksi to control drift, a major challenge in the design of tall buildings.

Different Markets, Different Concrete The upper strength limit for concrete in a given region is largely aggregate dependent.

Some regions have access to better aggregate than others and, as a result, are able to produce higher strength concrete. Chicago and Seattle, for example, have local access to quarries that produce granite aggregate, a relatively non-porous igneous rock that is exceptionally suitable for concrete. Granite is hard and dimensionally stable. It absorbs minimal water, unlike soft limestone or other sedimentary rock found in some other markets, like Los Angeles, Texas and Florida. Such

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aggregate also tends to be more porous and angular, increasing the required water quantity and making the production of higher strengths more challenging.

Historically, geography has limited the type of concrete used in a given location since transporting aggregate great distances tends to be too costly to make financial sense.

The volume of column concrete used on a high-rise project is relatively small, however, compared to the overall project’s concrete needs. Thus, some structural engineers are specifying high-strength column concrete even if the necessary aggregate isn’t locally available, opting to sacrifice material savings for gains in productivity and additional interior square footage.

While high-strength concrete’s use is growing, lower-strength concrete still does the lion’s share of the work in concrete construction. The majority of buildings constructed in the U.S. are small enough that high-strength concrete isn’t warranted.

Further, many structural elements such as floor slabs and foundations don’t benefit significantly from the higher-strength material. Nevertheless, as the use of concrete increases and buildings go ever taller, the demand for high-strength concrete is likely to continue growing.▪

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Codes and standards updates and discussions related to codes and standards

ACI 562 Requirements for Evaluation, Repair and Rehabilitation of Concrete Buildings

By Keith Kesner, Ph.D., P.E., S.E. Kevin Conroy, P.E., S.E. and Lawrence F. Kahn, Ph.D., P.E.

Keith Kesner, Ph.D., P.E., S.E., is a structural engineer in the New York office of Whitlock Dalrymple Poston and Associates, Inc. and is the current chair of ACI Committee 562.

Kevin Conroy, P.E., S.E., is a structural engineer at Raths, Raths & Johnson, Inc. in Willowbrook, Illinois and is the current secretary of ACI Committee 562.

Lawrence F. Kahn, Ph.D., P.E., is a professor of structural engineering at Georgia Institute of Technology and was the chair of ACI Committee 562 during the development of ACI 562-13.

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t is estimated that the concrete repair industry in the United States generates between 18 and 25 billion dollars per year in construction spending. Unfortunately, repairs that do not perform as intended, either due to poor design or execution, require “repairs to the repairs”, which form a substantial component of the total figure. Seeing a lack of minimum standards, several organizations believed the concrete repair industry would benefit from a repair standard that would assist engineers, improve the concrete repair process, and reduce the extent of “repairs to the repairs.” After several years of development, the American Concrete Institute (ACI) published its first repair standard, Code Requirements for Evaluation, Repair and Rehabilitation of Concrete Buildings (ACI 562-13) in 2013. ACI 562-13 became (Figure 1) the first material-specific standard for the repair of existing concrete buildings, the first performance-based standard developed by ACI, and the first standard developed to work with the International Existing Building Code (IEBC). In areas that have not adopted an existing building code, ACI 562 can function as a stand-alone document providing guidance to structural engineers who perform evaluations of existing concrete structures and develop structural concrete repair designs.

Background For new concrete structures, the International Building Code (IBC) and ACI 318 Building Code Requirements for Structural Concrete, provide the design professional with minimum requirements for strength, serviceability and durability. At some point a building will require repairs or rehabilitation. Design professionals, owners and contractors involved with the existing structure are then faced with the challenges of damaged or deteriorated members, possible hidden deterioration, or construction defects.

The lack of a material-specific repair standard for existing concrete structures has allowed for variations in concrete repair practice, inconsistent levels of reliability of repaired structures, and placed a burden on building code officials that must approve repair construction documents based upon a lack of specific requirements. In the absence of any guidance, decisions have often defaulted to requiring a repaired structure to satisfy all criteria of a code designed to address new buildings, like ACI 318, which can result in overly costly repairs and even in decisions to demolish and rebuild entire buildings.

The IEBC and IBC Chapter 34 require repair of significant structural damage and, in some cases,

Figure 1. New ACI 562-13 repair code.

require structural improvements as well. Except for seismic elements, for which the codes cite ASCE 31 and ASCE 41, the I-codes do not contain specific requirements for the evaluation of damage and design of repairs for concrete structures.

Seeing a void in the industry and a desire to improve the practice, ACI Strategic Development Council along with the International Concrete Repair Institute (ICRI) and other organizations developed Vision 2020 in 2006, a strategic plan for the concrete repair, protection, and strengthening industry. One of their specific goals was the creation of a repair/rehabilitation code which would: 1) establish evaluation, design, materials and construction practices, 2) raise the level of repair and durability performance, 3) establish clear responsibilities between owners, designers and constructors, and 4) provide building officials with means to evaluate rehabilitation design.

It has been estimated that 50 percent of repairs are not performing satisfactorily due to errors in design, construction and/or material selection [REMR and BRE]. Vision 2020 concluded that minimum code requirements would ensure that all designers engaged in evaluation, repair, and strengthening would work from a consistent and defined level of expectations. As more professionals become engaged in repair and rehabilitation design, the need for minimum code requirements is of increased importance to assure life safety and repair performance. Overall, clearly defined and uniform code standards would lead to increased quality of structural rehabilitation leading to decisions to repair and sustain existing structures rather than to demolish and replace them with new structures.

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ACI took the lead in pursuing this goal, forming Committee 562, Evaluation, Repair and Rehabilitation of Concrete Buildings, to develop the repair/rehabilitation code.

A total of 31 members, comprised of engineers, contractors and manufacturers from across the United States and Canada were appointed and spent 7 years developing the document titled Code Requirements for Evaluation, Repair and Rehabilitation of Concrete Buildings (ACI 562-13).

Code Applicability IEBC and ACI 562-13 define an “existing building” as a building for which a certificate of occupancy has been issued, or when no certificate exists, a building that is complete and permitted for use.

Where adopted, IEBC classifies the repair or alteration of the existing building and it specifies code requirements for the project. One of the code requirements delineates whether the repair needs to satisfy code requirements for new buildings, or whether building code requirements at the time of a building’s original construction may be used. ACI 562-13 details that selection process and the specific requirements for structural concrete.

Key Provisions of ACI 562 The use of ACI 562 is described in the following sections. The first step in the process is the determination of a design basis code for the repairs, which is the design code that the repaired structure will satisfy. The design basis code is likely an older, locally adopted (state or city) code, possibly using an older edition of the IBC or IEBC. Other special codes for existing or historic buildings might also apply. After the design basis code is established, the remaining steps

Evaluation Criteria for Existing Structures Evaluation of existing structures is based upon the in-situ properties of the structure, accounting for deterioration and as-built

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Code Philosophy ACI 562’s goal was to establish minimum life safety requirements for rehabilitated structures while providing a sustainable and economic alternative to demolition and replacement. At the start of the standard’s development process, it was recognized that a tremendous variety of existing concrete buildings are in use, and that those buildings were constructed under a variety of building codes and exhibit a myriad of structural problems. Due to the wide scope of repair and rehabilitation issues, the committee concluded that a “onesize-fits-all” prescriptive standard was impractical, and that a performancebased standard would be better and allow the design professional more flexibility.

Performance-based requirements provide the design professional with minimum performance requirements to yield a safe and satisfactory repair in lieu of providing a set of “do it this way” requirements.

This performance-based approach allows for use of engineering judgment and encourages creative solutions for repair design, provided it still complies with code requirements.

in the process include evaluation of the structure, design of repairs, construction requirements including quality assurance testing, and development of maintenance recommendations for the owner’s future reference for the repaired structure.

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Durability Requirements

Figure 2. Corrosion damage in tunnel section.

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member dimensions. The commentary to ACI 562 provides guidance and references that describe how to evaluate existing structures. When existing materials appear in good condition and design drawings and other information about the original construction are not available, ACI 562-13 allows historic material properties, such as concrete compressive strength and the yield strength of reinforcing steel, to be used in analyses. ACI 562-13 encourages testing to determine material properties by specifying the use of higher strength reduction factors when existing material properties and structural geometry are confirmed. While testing to verify material properties is not required, nor imposes extra effort on the part of the owner, the testing may provide a more economical solution for the repair design.

Another optional strategy for verifying the strength of an existing structure is to perform in-situ load testing which can be useful particularly on older structures with obsolete structural systems. ACI 562-13 specifies the use of recently developed AC1 437-13 e rat bo nce a l l e co peri p ex velo de end att rn lea are sh eet m n joi

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Code Requirements for Load Testing of Existing Concrete Structures, which was specifically developed for existing structures and includes acceptance criteria based upon monotonic and cyclic test results, and provides for lower load ratings based upon load testing results.

Design of Structural Repairs The design of structural repairs using ACI 562-13 is based upon standard concepts of structural concrete behaviour and the design basis code, which is typically the version of ACI 318 used for the original design. The standard’s provisions are not new to the design professional and require many of the same items as traditional design: repaired structures shall have design strengths at least equal to the required strength based upon factored loads and members have adequate stiffness to prevent serviceability problems.

In addition to the traditional topics, provisions have been included for items that are unique to repair design such as bond of repair materials to substrates, detailing of repairs, and consideration of the interaction between repaired and non-repaired portions of a structure. The overall theme of the provisions is to direct the repair design professional to consider the behavior of the structure at all times during the repair process which, if ignored, can lead to failures of the repair.

Another addition to the standard is permitting fiber reinforced polymer (FRP) materials in repair. ACI 562-13 incorporated the FRP design standard (ACI 440.6) along with a section dedicated to ensure that FRP is properly integrated into the existing structure.

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Satisfying strength requirements is just one step towards long-term performance of a repaired structure. Improving the durability of repairs and repaired structures is a key goal of ACI 562, since the high rate of repair failure is partially due to repairs lacking adequate durability.

Durability in repaired structures is complicated as it requires consideration of many conditions outside of the repair area, such as structure use and exposure. Additionally, the service life of both the repair area and the repaired structure need to be taken into account. One example would be failure of concrete adjacent to a repair (Figure 2) due to the anodic ring effect, which is when reinforcing steel in the adjacent original material corrodes due to differing environments.

To avoid such conditions, ACI 562 requires the designer to consider the durability of the repaired area, interaction of the repaired area with the original structure, and the overall system durability at the start of the repair process. The standard’s provisions also direct the repair designer to consider the impact of cracks, corrosion and moisture transmission on the durability of repairs, which are major mechanisms that impact the repair’s performance. Like the other sections, ACI 562-13’s commentary provides discussion and references on how to design and detail durable repairs.

Another major contributor to premature failure of repairs is the lack of ongoing maintenance, such as repairing damaged coatings or aged sealants. While the repair design professional has no control over when and if maintenance is performed, ACI 562-13 dictates that maintenance requirements be provided to the owner so that the owner is aware of maintenance needs for specific repair materials and systems.

Construction The construction provisions in ACI 562 were developed to help ensure the stability of both the existing construction and the repairs during the construction phase. These provisions recognize that the repair process, particularly the removal of materials, can have detrimental effects on the structure. Such changes include increases in the unbraced length of a member, removal of confining materials (Figure 3), and altered load paths in the structural system which can create localized unintended overstresses in unrepaired members. The standard specifically requires repair documents to define shoring

and bracing requirements during all phases of the repair, if required. ACI 562-13 does not require that the repair engineer-of-record design the shoring or bracing elements; however, it does require that shoring and bracing be designed by an engineer.

Quality Assurance General building codes contain special inspection requirements for testing of concrete materials in new construction, and these requirements typically include a number of concrete tests based on the volume of concrete placed. Using these inspection requirements for repair construction is not realistic, as a very limited amount of materials testing would be performed since repair construction is often completed in smaller increments. While ACI 562-13 does not mandate additional testing beyond these requirements, it leaves the testing and inspection requirements to the discretion of the design professional. As with any project, the design professional has the ability to specify additional testing if it is warranted for unique conditions. ACI 562-13’s commentary provides a listing of items that the design professional can include as part of a quality assurance program.

Figure 3. Buckled reinforcing steel bar.

Impact of ACI 562 Use of the ACI 562-13 standard will provide designers consistent code requirements for repair of structures, and building code officials a means to examine repair documents for permitting. Most importantly, ACI 562-13 provides a minimum

level of life safety for repaired buildings, along with setting a standard of care for structural repair.▪ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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Structural rehabilitation renovation and restoration of existing structures

FRCM Systems The Second Generation of Externally-Bonded Composite Systems for Strengthening of Concrete and Masonry Structures

By Antonio De Luca, Ph.D. and Gustavo Tumialan, Ph.D., P.E. Antonio De Luca, Ph.D., is a Structural Engineer at Simpson, Gumpertz & Heger, Inc. Antonio may be reached at ADeluca@sgh.com.

Gustavo Tumialan, Ph.D., P.E., is Senior Project Manager at Simpson, Gumpertz & Heger, Inc. Gustavo may be reached at GTumialan@sgh.com.

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fter overcoming the initial growing pains (insufficient experience, track record, and knowledge overshadowed by overzealous euphoria with “magic” material capabilities), externally-bonded fiber reinforced polymer (FRP) systems have become one of the preferred technologies for repair and strengthening of concrete and masonry structures in the United States. FRP systems have features such as high tensile strength, light weight, relative ease of installation, and resistance to corrosion, which make them attractive to the repair industry.

However, FRP also has limitations, which can preclude their use in some applications. For instance, high temperatures compromise the efficiency of FRP systems, FRP applications are limited on moist surfaces or at low temperatures, and FRP systems typically act as a vapor barrier.

These drawbacks are all related to the epoxy matrix used to embed and bond the fibers. Thus, substituting the epoxy matrix with a cementitious matrix appeared to be the most reasonable solution to improve the overall performance of externally-bonded composite systems. This new generation of composite systems is known as fabric reinforced cementitious matrix (FRCM). FRCM developed as an evolution of ferrocement, where the mortar matrix is reinforced with open meshes of continuous dry fibers. In the literature, FRCM is also known as Textile Reinforced Concrete (TRC), or Textile Reinforced Mortar (TRM).

The first use of TRC and TRM was reported in Europe in the late 1990s in new construction applications such as permanent formworks elements, facades, tanks and containment.

Constituent Materials

fiber filaments. However, the open structure of the fabric meshes provides higher matrix-reinforcement interface area which is needed to achieve the composite action between the matrix and the reinforcing system. Typically, the mesh openings do not exceed 0.75 inches. The rovings are typically coated with resin to improve the bond to the mortar matrix, enhance the long-term durability and improve the load transfer among the roving filaments. The fabric meshes are typically made of carbon, alkali-resistant glass, basalt, polymeric fibers (such as Polyparaphenylene benzobisoxazole, PBO), or hybrid systems.

The function of the matrix is to encapsulate and protect the fibers, and transfer stresses from the concrete or masonry substrate to the fibers.

Stress transfer is accomplished through bonding between the substrate and the matrix, and the mechanical interlock between the fabric and the matrix. The composition of the cementitious matrix is very important and crucial for the performance of the FRCM system. The mortar should be non-shrinkable and workable, to be easily applied with a trowel and to penetrate the fabric mesh openings, and viscous to apply on vertical surfaces. In addition, the mortar rate of workability loss should be low to allow for multiple layers of reinforcement.

Both hydraulic and non-hydraulic cements can be used. Finely graded sands (grain size smaller than 0.02 inch) help improve the workability of the fresh mix and the impregnation of the fabric mesh. The water-to-mortar ratio by weight typically ranges between 15% and 25%. The mortar mix can include chopped fibers to reduce the plastic shrinkage cracking. Organic compounds can also be used to control the hardening rate and the workability of the fresh mix, to improve the bond to the fabric mesh, and to enhance the mechanical properties. Their content is generally limited to be less than 5% by weight of cement to obtain a fire-proof matrix.

FRCM systems consist of fibers embedded in a cementitious matrix. The function of the fibers is to carry tensile stresses. In FRCM composite systems, the fiber sheets or fabrics that are typically used in FRP are replaced with open fabric meshes in which the rovings are assembled in at least two directions (generally orthogonal) by means of weaving, knitting, tufting, or braiding. “Closed” fiber fabrics are not suitable because the cementitious matrix cannot penetrate and impregnate the

The performance of FRCM systems is highly dependent on their tensile strength and bond strength. The FRCM tensile behavior can be differentiated in three phases (Figure 1). In the first phase, the load is carried primarily by the cementitious matrix until cracking. In the second phase, the matrix undergoes a multicracking process resulting in transfer of stresses from the reinforcing fabric to the matrix, with some

The FRCM System

Mechanical Properties

Table 1. Typical filament properties of commercially available fabrics (ACI 549-13).

Fiber filament properties

Fiber types AR-Glass

Basalt

Carbon

PBO

180

380

550

852

Modulus of elasticity, ksi

10,500

12,500

33,800

39,600

Ultimate tensile strain

0.018

0.030

0.016

0.025

Ultimate tensile strength, ksi

22 September 2014

Figure 1. FRCM stress – strain diagram.

Figure 2. Typical pull-off failure mode. Courtesy of the University of Miami.

debonding at the fabric-matrix interface.

At the third phase, the composite system behaves almost linearly until failure occurs due to the progressive rupture of the roving fiber filaments and debonding of the fabric from the matrix. In this phase, the load is carried almost exclusively by the fabric. The modulus of elasticity is influenced by the fiber volume content.

As a comparison, FRP has a single-phase linear elastic tensile behavior until failure. The ultimate tensile strain in FRP is limited by the ultimate strain of the fibers.

The tensile properties of FRCM cannot be generalized, and each system should be evaluated individually. However, the tensile failure generally occurs at a strain level of approximately 50% of the ultimate tensile strain of the fiber filament. Table 1 provides a summary of the mechanical properties of several commercially available fabrics.

The bond strength of FRCM to the substrate material is difficult to quantify as it depends on the type of fibers, fiber sizing, mesh layout, composition of the matrix, substrate properties, and quality of the surface preparation. Unlike FRP, the FRCM fibers are not impregnated; therefore, pull-off tests on concrete substrates typically show the fracture failure within the fabric reinforcement or at the fabric-matrix interface (Figure 2).

results of durability testing is still limited.

However, based on available tests, FRCM is expected to overcome some of the issues that are typically found in FRP because the cementitious matrix performs better than the polymeric matrix in moist and chemically aggressive environments. Moreover, research studies have proven the longevity of alkali-resistant (AR) glass fiber within the cementitious matrix.

Applications in Structural Strengthening FRCM systems are a viable option for flexural and shear strengthening of concrete and masonry members. In general, the strength increases in reinforced concrete beams or slabs, and unreinforced masonry walls strengthened with FRCM systems are comparable to those of similar elements strengthened with FRP. However, their overall behavior is slightly different. In the case of FRP-strengthened elements, failure is typically due to the debonding from the concrete or masonry substrate. This type of brittle failure does not generally occur with FRCMstrengthened elements, where less brittle “unzipping” failures typically occur due to progressive slippage of the fibers within the

FRCM systems offer better performance under elevated temperatures, humidity, and ultraviolet radiation than FRP systems. In contrast to FRP, FRCM is inherently noncombustible and can be used unprotected.

Combined with their noncombustibility and nontoxic characteristics, FRCM systems are a good option for strengthening when resistance to high temperatures is required.

Durability FRCM for structural strengthening applications is a relatively new material. The

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Figure 3. Slippage of the fabric within the cementitious matrix in proximity of a flexural crack in concrete beam. Courtesy of the University of Miami.

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September 2014

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Physical Properties

cementitious matrix or delamination at the fiber-matrix interface. Fiber slippage across a flexural or shear crack is caused by the gradual loss of bond between the fibers and the matrix and/or by the gradual rupture of the fibers (Figure 3). Fiber delamination generally occurs when multiple layers of FRCM reinforcement are used and is preceded by large fiber slip (Figure 4, page 24).

FRCM systems can also be used to provide confinement to concrete columns to increase their axial strength. The effectiveness of FRCM is highly dependent on the number of confining layers and the tensile strength of the cementitious matrix, which determines whether the behavior is controlled by delamination of the fabric within the matrix or fiber rupture. At this time, limited research is available to assess the feasibility of FRCM systems for seismic retrofitting of columns.

In the case of masonry strengthening, FRCM systems can be used on concrete and clay masonry walls. Cementitious matrices of FRCM are more compatible with masonry substrates. Masonry elements are many times subject to continued exposure to moisture migrating through the wall thickness.

Polymeric matrices of FRPs can act as thermohygrometric barriers which can cause moisture to remain trapped within the masonry and

Figure 4. Delamination of the fabric within the cementitious matrix. Courtesy of the University of Miami.

lead to debonding of the strengthening material. The porosity and vapor permeability of cementitious matrices of FRCMs are similar to the masonry substrate and moisture does not become trapped within the masonry substrate. Figure 5 illustrates the strengthening with FRCM of the masonry arches of a church in Italy.

ACI 549 Design Guidelines Earlier this year, the American Concrete Institute (ACI) published ACI 549.4R13 – Guide to Design and Construction of Externally Bonded FRCM Systems for Repair and Strengthening Concrete and Masonry Structures, a document developed by Committee 549. For design purposes, the ACI 549 Guide idealizes the FRCM tensile stress-strain curve as bilinear with a bend-over point (or transition point) corresponding to the intersection obtained by continuing the initial and secondary linear segments of the response curve (Figure 1). The initial linear segment of the curve corresponds to the FRCM uncracked linear elastic behavior and it is characterized by the uncracked tensile modulus of elasticity. The second linear segment, which corresponds to the FRCM cracked linear elastic behavior, is characterized by the cracked tensile modulus of elasticity.

The design approach for flexure and shear strengthening considers an effective usable strain of FRCM, which represents a strain limit that globally accounts for the loss of bond. ACI 549 identifies three different types of bond failures: cohesive, when the failure occurs in the substrate material; adhesive, when the failure occurs at the interface between the FRCM and the substrate material; and, adhesive, when the failure is within the FRCM at the interface between the reinforcing fabric and the matrix. The first two types of failure are also observed in FRP, while the third failure is specific to FRCM. Depending on the amount of FRCM, this limit is typically in the range of 50 to 70% for concrete, and 30 to 40% for masonry.

Once the effective strain is defined, the design procedure of FRCM strengthening is similar to the design procedure using FRP.

The ACI 549 design guide recommends that the FRCM system manufacturer perform tests meeting the acceptance criteria (AC434-13) established by the International Code Council Evaluation Services (ICC-ES) to obtain the mechanical, physical, and durability properties to be used in design. The qualification test plan defined by AC434-13 includes the definition of the following: matrix drying shrinkage, matrix void content, tensile properties, bond strength, interlaminar shear strength, long-term properties, and freezing and thawing resistance. A material system that has been evaluated according to these acceptance criteria and has received a product research report from ICC-ES can be accepted by code officials as building code compliant.

Construction FRCM systems are installed using the hand layup method. The surface preparation requires surface roughening and leveling, and moistening to achieve the saturated surface dry condition. Surface preparation of masonry substrates typically does not require roughening. The installation procedure is simple.

Mixing and application of the cementitious matrix is similar to conventional hand-applied repair mortars used in concrete repairs. First, a thin layer of cementitious matrix (in the range of 0.2-inch thick) is uniformly applied (troweled- or sprayed-applied) on the substrate, then the fabric mesh is pressed into the matrix. Finally, a second thin layer of cementitious matrix is applied on top of the mesh. Multiple layers of mesh can be applied following the same procedure.

The cementitious matrix in the first mesh layers does not need to be fully cured in order to apply subsequent layers. Primers, fillers, and/or protective coatings may be required for some substrates or types of matrices.

Temperature at the time of installation can affect the cementitious matrix. Thus, high temperatures (in the range of 95-130°F) may reduce the workability, while low temperatures (in the range of 39-43°F) may slow down setting considerably.

Final Thoughts FRCM systems are currently being introduced in the structural repair and rehabilitation industry as a new, effective strengthening technology. Due to their superior performance at high temperatures, better compatibility with the substrate, and improved durability, FRCM systems are a good alternative to FRP systems. It is expected that the use of FRCM systems to strengthen existing concrete and masonry structures will become a common tool for design professionals and contractors with the availability of the ACI 549 design guide.▪

Figure 5. Strengthening of masonry arches using Carbon-FRCM. Courtesy of Ruredil S.p.A.

STRUCTURE magazine

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September 2014

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InSIghtS new trends, new techniques and current industry issues

S

teel plate shear wall (SPSW) technology is advancing, making more wide-spread implementation of seismic force resisting systems possible. These stiff and ductile systems have had years of research that has demonstrated their excellent seismic performance, explored various details and configurations, and resulted in the design provisions in ANSI/AISC 341-10, where they are denoted special plate shear walls. The key principal for design is that yielding is expected in the web plates, at the beams ends and at the column bases.

SPSW ductility is superior to braced frame and even moment frame systems. Figure 1 shows the base shear versus story drift behavior for a well-detailed SPSW (Li et al. 2014) and a concentrically braced frame detailed to provide better ductility than a modern special concentrically braced frame (Roeder et al. 2011). Both are results from two-story, nearly full-scale tests with somewhat different base shear capacities.

Admittedly, the SPSW strength would have to be increased to make a direct comparison; however, it is clear that the SPSW has superior ductility, retaining a larger percentage of its peak strength to significantly larger drifts. The maximum drift of nearly 5% for the SPSW is more than could be expected for many moment frame systems as well.

Advances in Steel Plate Shear Walls

By Jeffrey W. Berman, Ph.D.

Recent Advances in SPSWs

Jeffrey W. Berman, Ph.D., is Thomas & Marilyn Nielsen Associate Professor of Structural Engineering and Mechanics at the University of Washington, Seattle. Jeffrey may be reached at jwberman@uw.edu.

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

Recently, important advances in SPSW design and behavior have been made and are described below. Note that many other considerations for design, including the use of reduced beam section beam-to-column connections, perforated web plates, and horizontal struts for tall first stories, were described along with general SPSW deign methods in AISC Design Guide 20 (Sabelli and Bruneau 2006).

Figure 1. Large-scale SPSW and SCBF test specimens and hysteretic behavior. Courtesy of K.C. Tsai and NEESHub.

Tension Field Action & Web Plate Modeling Experimental and computational studies on inelastic tension field action have recently demonstrated that the angle of inclination of the web plate tension field changes as the web plate undergoes plastic strain. Web plate yielding and significant plastic strain is expected in design level earthquake events when maximum demands will be imposed on the surrounding beams and columns. Therefore, it makes sense that numerical models used for design of SPSWs should use the angle of inclination after yielding. Equation F5-4 in ANSI/AISC 341-10 was derived using elastic strain energy and is a good approximation of the inclination angle after web plate elastic buckling but prior to yielding.

Figure 2 shows the migration of the inclination angle with increasing story drift from experiments and numerical simulation where the angle approaches 45°. This result has been supported by other tests and analyses (Webster et al., 2014) and a 45° angle is proposed for seismic design.

Figure 2. Web plate inelastic tension field action test setup and angle of inclination migration with increasing drift.

26 September 2014

Figure 3. New web plate material models for truss elements in strip modeling of SPSW.

Figure 4. Coupled SPSW test at the University of Illinois. Courtesy of Daniel Borello.

Similar tests and analyses on web plates within a pin-connected boundary frame have improved the understanding of the inelastic cyclic response of web plates. This understanding has led to the development of a phenomenological material model that can represent the complex web plate behavior as shown in Figure 3 (Webster 2013). This material model can be used in simple strip models of SPSWs and will soon be available as a material option in OpenSEES. This advance provides an efficient way to model the nonlinear behavior of SPSWs.

performance (Dowden and Bruneau, 2014), and two-story full-scale proof-of-concept tests as in Figure 5 (Clayton et al., 2014).

Improved Efficiency in SPSW Column Design One of the critical factors limiting the implementation of SPSWs is the large column sizes required to resist the combined axial and flexural demands from overturning, frame action and web plate forces. Recent research

by Li et al. (2014a and 2014b) has developed recommendations for design that allow the formation of the column plastic hinges, not at the base as previously recommended, but at a height of ¼ to 1/3 of the story height above the base where the moment is typically maximum in the compression column. This reduces flexural demands significantly and does not impact performance of the system as long as the column does not form a plastic hinge at the top of the first story. In full-scale two-story tests, Li et al. (2014b) found that a 20% reduction in column weight could be achieved with no impact on performance.

weight savings when two individual walls are coupled and show, through nonlinear analysis, that they have excellent seismic performance.

Recently completed large-scale tests on two coupled steel plate shear wall systems as shown in Figure 4 confirmed the numerical analysis results and validity of the design procedure (Borello 2014).

Self-Centering SPSWs Minimizing residual drift and ensuring simple post-earthquake repair strategies is a current focus of much earthquake engineering research. In this context, recent research has implemented self-centering steel moment frame technology in steel plate shear walls. The system, illustrated in Figure 5, utilizes post-tensioned beam-tocolumn connections to provide recentering after earthquakes and web plate tension field action to provide stiffness and energy dissipation. Recent research on these systems has included the development of performancebased design recommendations (Clayton et al., 2012), large-scale subassemblage tests to explore design parameters (Clayton et al., 2013), shake table tests on systems with different connections to demonstrate system

Conclusions and Future Challenges SPSWs remain an under-utilized lateral force resisting system despite their excellent seismic performance. Some of the recent advances described here are helping to solve this problem and also push the technology further. A better understanding of inelastic web plate behavior is making the system more efficient to design and analyze, alternative approaches for column design have resulted in reduced required sizes, advances in coupled steel plate shear wall design now provide a solution for building cores, and systems with self-centering provide a solution for applications where minimizing postearthquake downtime is critical. Additional innovation is necessary from practicing engineers, fabricators and erectors to develop fabrication and construction techniques that help improve efficiency. Such advances would increase SPSW implementation which, considering its excellent performance, should be a priority for the industry.▪

Coupled SPSWs Coupled SPSWs offer designers the flexibility to use SPSW systems in cores of taller buildings but there has been little guidance on design methods, steel coupling beam detailing, and general behavior until recently.

Borello and Fahnestock (2013) describe design concepts for coupled SPSWs, recommend target values for the degree of coupling (ratio of the overturning moment resisted by the individual walls to the total overturning moment), demonstrate significant steel

Figure 5. Self-centering SPSW schematic and full-scale test specimen.

STRUCTURE magazine

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September 2014

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ConstruCtion issues discussion of construction issues and techniques

A

completed tilt-up structure relies upon connections to the roof and floor diaphragms to transfer lateral loads to a lateral force-resisting system, such as shear walls or bracing. During construction, however, temporary wall bracing is needed to resist lateral forces. The most significant lateral force that most panels will experience is wind loading.

Having adequate temporary bracing of tiltup panels is imperative for jobsite safety. The Occupational Safety and Health Administration (OSHA) requires that tilt-up concrete panels be temporarily braced to prevent panels from overturning or collapsing during the construction of a tilt-up structure (Title 29, Code of Federal Regulations, Standard 1926.704). However, OSHA does not specify how to prevent tilt-up wall panels from overturning or collapsing.

Bracing must be carefully engineered to resist all reasonably expected wind loads, just as panels are engineered to resist in-service loads and lifting stresses; the placement of braces and the materials used to resist the brace forces cannot be improvised. To assist in the structural design of temporary bracing, the Tilt-Up Concrete Association (TCA) provides a guide known as the TCA Guideline for Temporary Wind Bracing of Tilt-Up Concrete Panels during Construction.

The guideline defines parameters by which the bracing scheme should be designed.

There are a number of ways to provide resistance to the forces transmitted through tilt-up braces during the construction period, such as

Developing a Temporary Bracing Plan for Tilt-Up Panels

By Matt Bell, P.E.

Matt Bell, P.E., is a project manager and structural engineer at LJB and is on the TCA Board of Directors. He can be reached at mbell@LJBinc.com. For more, visit www.tilt-up.org.

The panel erection crew winding the temporary braces for final plumbing of the wall panel during erection.

Wall panel temporary braces attached to the inside face of wall prior to panel erection.

poured concrete “deadmen” (or footings), helical ground anchors (HGAs) or using a permanent slab-on grade.

HGAs are manufactured steel foundation elements that consist of a solid steel square bar shaft with one or more steel helical plates welded onto the shaft at predetermined spacing. They are placed directly into the foundation soil and are connected to the typical wall panel pipe braces using an alternate connector. They are installed in the ground at the same angle as the wall braces that attach to them. HGA design is typically done by the anchor manufacturer, who reviews the soil conditions at each project site and then bases the required soil embedment length for their anchors upon these soil conditions. HGAs essentially work as screws and must be installed to a certain torque to attain the loads from the steel braces and transfer them into the ground for both tension (pullout) and compression (bearing) resistance to wind loads.

Utilizing a slab-on-grade for bracing is common and typically is the most efficient and cost-effective form of bracing. However, until recently, neither OSHA nor the TCA guideline assigned responsibility for designing the slab-on-grade for construction loads due to tilt-up wall bracing. Most of the time, the slab-on-grade is only designed for service loads, without consideration of construction loads due to panel braces.

Because of the sequencing of wall panel shop drawing generation and lifting and bracing design (which is often done by a wall panel specialty engineer hired by the tilt-up contractor), it is also common for the brace loads to be determined after construction has already begun, when it is too late to design the floor slabs appropriately.

For this reason, in early 2014, the TCA released a supplementary statement intended to assign responsibility for the structural design for bracing and ensure that this design happened closer to the beginning of a project, as follows: The Owner’s designated representative for construction shall be responsible for assigning a qualified firm to review the floor slab capacity for the bracing of the tilt-up panels

30 September 2014

in accordance to the latest edition of the TCA bracing guidelines.

In addition to increasing jobsite safety, a well-sequenced and well-executed erection process improves the cost-effectiveness of tiltup construction. Temporary wind-braces are an integral part of this erection process.

What Constitutes a Wind Load?

The recommendations established by the TCA do not address loss of property, but are set according to the limits of life safety considerations. The guideline is based on Risk Category I structures, defined as “Buildings and other structures that represent a low risk to human life in the event of failure.” This category was selected because the guideline is strictly limited to structures that are under construction.

The guideline also does not address high wind events, such as tornadoes and hurricanes. It is expected that a construction field office would have the site cleared of personnel when excessive wind speed is imminent.

Specific recommendations contained within the guideline have evolved over time, alongside the evolution of tilt-up design itself. As panels have gotten taller and panel shapes more sophisticated, the guide moved away from a blanket recommendation that was intended only for small, uniform panels and toward an analytical process based upon ASCE/SEI Standard 37- 02, Design Loads On Structures During Construction. The current version of the guideline tabulates wind forces for tilt-up panels as tall as 100 feet.

The panel erection crew using pry bars to position the panel into the proper location on the footing.

While 37-02 forms the basis for design recommendations, the TCA guideline now uses wind speed set forth by updates in the ASCE 7-10 provisions. These provisions identify a design wind speed of 105 mph for Class I structures in most areas of the United States, based upon historical wind speed data. However, the guideline recommends that the 105 mph wind speed be multiplied by a factor of 0.80 (which is permitted by the ASCE for projects whose duration is six weeks to one year), resulting in a wind speed of 84 mph for calculating brace loads. Areas of the country that are frequently exposed to wind speeds above 105 mph are identified in the ASCE’s Basic Wind Speed map as “Special Wind Regions.” These zones require a higher construction period design wind speed than normal.

The panel erection crew using an extendable level to check plumb of the wall panel.

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Bracing Basics Brace manufacturers typically publish design manuals, making it easy to select the proper brace size and capacity for a broad range of wall panel heights. Installation guidelines, proper orientation and limitations are also typically published by the manufacturers within the manuals. A minimum of two braces per panel should be used; however, depending on the panel geometry, more braces may be required.

Not only are braces used to resist wind loads on each panel, they are used during erection to plumb the wall panels. Tilt-up panel braces have threaded ends that allow for winding to shorten or lengthen the brace, and thus pull the top of the wall panel inward or push it outward for final plumbing.

Some braces may require a sub-support system of knee, lateral and end bracing to increase their strength against a buckling failure. However, to simplify installation, it is typically preferred to utilize larger/stronger braces or more braces at a closer spacing in lieu of using a knee bracing system. In some circumstances, the anchorage of the brace to the slab or wall panel, rather than the capacity of the brace itself, will control the maximum brace spacing.

Braces may be attached to the panels before or after erection. However, when panels are cast inside face up and the braces will be attached to a resisting system on the inside of the building (such as the slab-on-grade), the preferred method is to attach the braces to the panel before lifting to increase erection productivity. In this case, the braces are placed just under the roof diaphragm so that, when the roof installation is complete, the braces can be removed and the floors below can be installed. In multi-story buildings more

Erected wall panels braced to the slab on grade.

than 3 stories tall, it is often more efficient to brace to the outside of the building to prevent delays in erection on the inside of the building. Otherwise, sequencing of steel erection, floor pours, and stability requirements must be carefully planned with the consent of the structural engineer(s).

On panels where braces must be attached after the panel is erected due to job site conditions, it is common for workers using ladders or aerial lifts to attach the braces to the panel while it is being held in the vertical position by the crane and bearing on the casting surface. In this scenario, it is common to install helical ground anchors or concrete deadmen around the outside perimeter of the building prior to wall panel erection.

Slab Design The type and location of floor slab joints, slab thickness, reinforcing, leave-out strips and concrete strength should be considered when determining if the floor slab is an adequate anchorage for the brace loads.

Additionally, minimum concrete thickness for adequate anchor embedment should be a consideration when specifying the slab thickness. Thickened strips of slab, centered about where the braces will land, may be preferred in lieu of thickening the entire floor slab for wall panel temporary bracing.

When designing the slab on grade for brace loads, one must determine the wall brace component forces (horizontal/sliding and vertical/uplift) from the design wind load applied to the braced wall panels. The portion of the slab that is being relied upon to resist the brace forces must be heavy enough to resist both sliding and uplift from the brace forces. When a thickened slab is utilized, soil passive pressure may also be considered in resisting sliding.

Engineering judgment should be used when considering the portion of slab to account for in resisting brace loads. Sliding forces may be resisted by all slab areas between the wall panel and the brace anchorage to the slab; however, for uplift a smaller strip of slab should be accounted for and floor joints should be a consideration in what that strip width can be.

Bracing Connections For connection of panel braces to the wall panel, coil inserts are usually cast into the wall panels. These coil inserts are manufactured with a plastic void plug to prevent concrete infiltration within the coil. This plug can easily be removed with pliers, after the panel has been cast, to accept a compatible ¾-inch diameter coil bolt.

Anchors used for attachment of the base of the braces can also be coil bolts attached to coil inserts cast into the floor slab, though it is often more efficient to use ¾-inch diameter concrete expansion anchors so that the braces

can simply be attached where they land at the base. When using concrete expansion anchors, it is important to select an anchor that is easily removable after use so that only easily patchable holes are left in the floor.

Typical tilt-up brace expansion anchors utilize an insert which is left in the concrete.

The anchor itself can be unscrewed from the insert. Concrete screw anchors (usually ¾-inch diameter) are also common for tilt-up brace anchorage. These anchors are threaded to engage the concrete rather than utilizing an expandable insert to engage the concrete.

Anchors are an engineered product.

Manufacturer’s information offers useful guidance for placement in the panels as well as for jobsite practices that allow the maintenance of safe working loads and safety factors.

Bracing Sequencing Bracing represents an additional element in the tilt-up process which needs to be carefully positioned and sequenced. When not planned adequately, braces can interfere with crane movement, lifting and even the placement of other braces. Brace planning efforts must consider crane access as well as each panel’s casting bed location and lifting sequence.

Braces located at interior corners also need particular attention; the panel that will be erected first needs to have its bracing placed high enough that perpendicularly placed bracing can be maneuvered comfortably below it. Openings or leave-outs in the floor slab often present problems requiring braces to be angled slightly. When floor slab openings or leave-outs are excessive, the panels should be braced to HGAs or deadmen. In corners, it is possible to brace diagonally to the adjacent orthogonal panel, if the orthogonal panel is braced adequately to stand alone until the adjacent panel is erected and braced.

For More Information Final brace design forces should be calculated using equations set forth in ASCE 7-10 and the appropriate factors for the project. The TCA guideline includes detailed information on calculating brace forces and loads that will dictate design.

As tilt-up structures evolve away from their big-box predecessors and into architecturally unique buildings, the individualized design of temporary bracing systems becomes more important. Well-designed bracing not only helps maintain the cost and scheduling efficiencies that tilt-up is known for – it makes for a safer jobsite, as well.▪ Wall panel erection in progress.

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September 2014

On-Demand Webinars Now Available from ACI On-demand webinars are accessible anywhere you have an Internet connection. Gain insight as industry experts explain a code, design method, or concept—then successfully complete a short quiz to earn your continuing education credit.

• Anchorage to Concrete (five session series) • Guide to Decorative Concrete Topics: Introduction, Tension and Shear Design, Designs with Combined Tension and Shear, Installer Certification and Anchoring Specifications, Design Examples Each session is 0.15 Continuing Education Units (1.5 PDH); Price: $75 nonmember/$60 member

• The Reorganized ACI 318-14: Benefits, Rationale, and Availability • Testing Reinforced Concrete Structural Elements under Slowly Applied Simulated Seismic Loads

• Guide to Design and Construction of Exter- • Tolerance Compatibility in Concrete nally Bonded Fabric-Reinforced CementiConstruction tious Matrix (FRCM) Systems for Repair and • Internal Curing: Curing Concrete from the Strengthening Concrete Structures Inside Out • Certified Adhesive Anchor Installers • Tolerance Compatibility in Concrete ✓ 318-11 Requires them Construction ✓ ICC-ES Product Reports Require them ✓ DO YOU?

• ACI 332: A Contractor-Friendly Concrete Code

Each session is 0.1 Continuing Education Units (1 PDH); Price: $30 nonmember/$24 member

To check out these webinars and our live monthly offerings visit ACIeLearning.org

RESOURCES FOR SUCCESS FROM ACI! +1.248.848.3800  www.concrete.org

Coming to a Code near you!

EnginEEr’s notEbook aids for the structural engineer’s toolbox

T

he title of this article may seem like a trivial question, but it deals with an issue that in large measure might be overlooked. At first glance, one might think, “Of course not; gravity columns are designed for gravity, so why would I need to address the seismic provisions in Chapter 21 of ACI 318-11?” The answer is a simple matter of deformation compatibility, which ASCE 7-10 addresses for Seismic Design Categories (SDC) D through F in Section 12.12.5. It clearly lists reinforced concrete frame members not part of the lateral-force-resisting system as an exception, with a deferral to ACI 318-11 Section 21.11 – ASCE 7-10 Errata No. 2 corrects this reference to ACI 318-11 Section 21.13 – which is titled, “Members not designated as part of the seismicforce-resisting system”.

We can appreciate that gravity-load-carrying members are inextricably linked to the lateralforce-resisting system. Though not specifically designed to provide lateral stiffness, the performance and behavior of such elements can be significantly

Concrete Gravity Members Do ACI Seismic Provisions Apply?

altered in a seismic event. Hence, we must deal with deformation compatibility issues and ductility requirements for reinforced concrete gravity columns during a seismic event, in accordance with ACI 318-11 Section 21.13.

How do we know when it is required to incorporate the ACI seismic provisions for gravity members? In general terms that match the ACI code language, gravity members are those “not designated as part of the seismic-force-resisting system in structures assigned to SDC D, E, and F” mentioned in section 21.13.1 of ACI 318. The same section of ACI indicates that members not explicitly checked may just be designed using the ACI 21.13.4 provisions, which may be onerous.

It is interesting to note that earlier versions of ACI 318 Chapter 21 qualified members requiring such attention in “regions of high seismic risk,” which led to some ambiguity and confusion, especially for structures seemingly on that threshold. Currently, ACI uses the more direct Seismic Design Category language.

ACI 318-11 Section 21.13.3 addresses induced moments and shears under design displacements (δu), which are taken as the magnified

Are induced moments and shears under design displacement (δu) less than the moment and shear strength of the member?

By Jerod G. Johnson, Ph.D., S.E. Condition A

Jerod G. Johnson, Ph.D., S.E. (jjohnson@reaveley.com), is a principal with Reaveley Engineers + Associates in Salt Lake City, Utah.

A similar article was published in the Structural Engineers Association-Utah (SEAU) Monthly Newsletter (February, 2006). Content is reprinted with permission.

Condition B

21.13.3.1 – If Pu < Ag f 'c /10; 21.5.2.1 controls: Min. reinforcement per Ch. 10 ρmax = 0.025 transverse spacing ≤ d/2 full length

Yes

No

21.13.3.2 – If Pu < Ag f 'c /10; 21.6.3.1 – 0.01 ≤ ρ < 0.06 21.6.4.2 – Hoops per 7.10.4 Crosstie spacing (hx) ≤ 14 inches 21.6.5.1 – Ve forces may be determined from Mpr (maximum probable moment).

21.6.5.2 – Ve may need to be taken as zero.

Use so for full length, so shall not exceed 6 longitudinal bar diameters or 6 inches. so = 4 + (14 – hx)/3

21.13.3.3 – If Pu > 0.35Po ; 21.13.3.2 – (above) 21.6.4.7 – Provisions for additional transverse reinforcement.

ACI Provisions for gravity members in SDC D, E, or F.

34 September 2014

21.13.4.1 – Materials Shall Satisfy: 21.1.4.2 – f'c ≥ 3000psi 21.1.4.3 – f'c ≥ 5000psi (LW) 21.1.5.2 – Grade A706 (unless qualified) 21.1.5.4 – fy/max = 100,000psi (for calcs) 21.1.5.5 – fy and fyt < 60ksi (11.4.2) 21.1.6 – (mechanical splices) 21.1.7.1 – (welded splices)

21.13.4.2 – If Pu ≤ Ag f 'c : 21.5.2.1 – Min. reinforcement per Ch. 10. ρmax = 0.025 21.5.4 – Ve shall be determined from Mpr. transverse spacing ≤ d/2 full length.

21.13.4.3 – If Pu > Ag f 'c : 21.6.3.1 – 0.01 ≤ ρ < 0.06 21.6.3.2 – 6 bars min with circular hoops 21.6.3.4 – Splicing provisions 21.6.4 – Transverse reinforcement provisions 21.6.5 – Shear strength provisions 21.7.3.1 – Transverse joint provisions

displacements using the appropriate Cd factor multiplied by the elastic displacements using pseudo-static elastic analysis methods. ACI 318-11 Chapter 21 identifies two conditions for seismic detailing of gravity members, which are distinguished by the strength trigger and, for convenience, are hereafter referenced as Conditions A and B. Condition A pertains when induced moments and shears due to displacements, δu, combined with the effects of gravity moments and shears, do not surpass the strength of the column.

In such cases, the provisions of Sections 21.13.3.1 through 21.13.3.3 must be satisfied, and the more critical load combination of (1.2D+1.0L+0.2S ) or 0.9D must be used.

The factor for live load (L) may be reduced to 0.5 in accordance with standard provisions of the Strength Design Load Combinations. For Condition B, induced moments and shears surpass member strengths and greater ductility detailing is in order, since the analysis predicts that the member will yield. Section 21.13.4 thus controls.

The Figure provides a flow chart indicating the ACI 318-11 Chapter 21 provisions that may be applicable. It contains the referenced code provisions and very brief descriptions

thereof – an abbreviated summary due to limitations of space and the complexity of the code, but it does provide the appropriate direction. Essentially, these provisions provide triggers based on the levels of axial, bending and shear load that increase the need for seismic detailing – in many cases the same detailing as that required for members of the lateral-force-resisting system.

The ACI seismic provisions that are applicable to members not proportioned to resist lateral forces – i.e., gravity members – are complex and can significantly alter the minimum requirements. Among the triggered detailing requirements are increased longitudinal reinforcement, volumetric determination of ties and stirrups, ties and stirrups along the entire member lengths, cross tie requirements, and a generalized decrease in tie/stirrup spacing. A simple example of this is column ties. The ACI 318-11 Chapter 7 provisions for tie spacing are quite simple: 16 vertical bar diameters, 48 tie diameters, or the least column dimension. However, the Chapter 21 provisions are far more complex and may require a much tighter tie spacing, typically not more than 6 inches.

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September 2014

Why such onerous provisions? Reconnaissance efforts and other learning experiences from recent earthquakes have shown time and time again that reinforced concrete can demonstrate excellent ductility when it is appropriately reinforced. The ACI 318-11 Chapter 21 provisions provide a logical and rational approach for determining whether gravity members are at risk, and to what extent their reinforcements should approach the ductile detailing provisions normally applied to members that are part of the lateral-force-resisting system. It really should not be surprising to find that the transverse reinforcement of a gravity column might not be too different from that of a moment frame column.

Another worthy note is that these provisions are driven by drift of the structure, which only makes sense. Following this, we should expect that more flexible lateral systems, such as concrete moment frames, will likely have greater densities of transverse reinforcement in gravity members than their stiffer counterparts, such as shear walls – a fact often overlooked when considering the pros and cons of different lateral systems.▪

FULL METAL JACKET Part 3: Foundation Revisions

By D. Matthew Stuart, P.E., S.E., F. ASCE, F.SEI, SECB, MgtEng and Richard H. Antoine III, P.E., S.E.

T

he subject building is an existing timber-framed, multistory structure that is over one hundred years old. Previous installments of this article have discussed the investigation and resulting need to evacuate the occupants, the nature of the deterioration observed, and the solutions considered for repair of the deteriorated columns. This final part will discuss the impact of the findings of a soil investigation that resulted in the need to develop alternate foundation solutions for the support of the steel jacket column support, and repairs that were required in the building in addition to the column jackets.

Shortly after the repair design was approved by the owner and peer-reviewed by another structural engineering firm, a twofoot-square test pit was created in the basement slab on grade so that geotechnical engineers could confirm the slab thickness and allowable soil capacity assumptions made during the design and analysis phase of the project. This investigation determined that the slab was not six inches thick, and was instead cast in two separate layers for a total of approximately 4½ inches on average, typically 3 inches with a 1½-inch topping. It also determined that the soils in the test pit were extremely soft and filled with slag, and that there were extensive voids underneath the slab that extended several feet in multiple directions. The presence of the voids was attributed to the soil getting washed away by what appeared to be water that was flowing beneath the slab. The presence of water was also consistent with the deterioration of the timber columns below the slab on grade that could be attributed to moisture, rather than insect infestation.

As a result of these findings, it was necessary to abandon the slab on grade as a method of supporting the steel jacket and grillage. Three alternate foundation options were eventually considered: helical piles, compaction grouting under the slab, and conventional spread footings.

The use of conventional spread footings was deemed impractical due

Figure 2.

STRUCTURE magazine

Figure 1.

to the amount of soil that would need to be removed and the adverse impact of excavating several large holes in the basement, which had limited vertical head room. In addition, an evaluation of the soil identified the presence of hazardous materials that would have to be remediated as a part of any excavation.

The use of compaction grouting was also deemed impractical because of the expense and difficulty of ensuring that all of the slab voids had been properly filled and the required depth of grout penetration into the upper layer of soft soil had been achieved. Ultimately, helical piles (Figure 1) were chosen as the preferred foundation option for four reasons: 1) The rig used to install the piles could fit within the confines of the basement.

2) The capacity of the piles could be easily determined on site, based on the torque achieved during drilling.

3) The original steel grillage design only needed to be modified slightly to accept the piles, which in turn did not alter the fabrication of the previously approved steel jacket and channel base assembly.

4) The cost of the helical piles was less than the other foundation options.

In order to modify the original steel channel grillage design to accommodate four symmetrically placed piles at each column, HSS steel members were introduced to transfer the reaction of the steel jacket channel bases. The only concern with the pile foundations was the possibility of adverse effects from the vibrations that might be induced from the installation process on the deteriorated columns. In order to mitigate these concerns, the following precautions were employed prior to installing the piles.

First, temporary shoring of the columns from the underside of the second floor pillow beams to the basement slab on grade took a portion of the load off the main columns during the construction phase. Second, the steel column jackets, channel bases and HSS grillage had to be erected and in place at each column prior to the installation of the helical piles. The purpose of this precautionary measure was to provide some means of mitigating the unexpected failure of a column by arresting a collapse via the installed steel jacket and grillage sitting on top of the existing slab on grade.

In addition, at the locations where the temporary shoring could not be installed due to the obstruction of a kiln, four of the eight steel “underpinning” rods had to be installed at the top of the

36

September 2014

Figure 3.

Figure 4.

jacket (Figure 2). The purpose of this last precautionary measure was to provide some redundancy via partial support of the column by the rods and steel grillage support on top of the existing slab on grade. There were no unexpected problems encountered during the installation of the steel jackets or piles, even though epoxy injection repairs were required at several columns (Figure 3). However, at a few locations, the top of rock was encountered at a shallow depth, which did not allow for the installation of the piles to the required minimum soil depth. As a result, the piles were installed to refusal, then encased in a subgrade concrete pier of a diameter that provided adequate contact area at the top of rock to support the imposed column load.

The purpose of the steel column jacket solution was simply to stabilize the building in place, and not attempt to jack the structure back up to its original floor and roof elevations that existed before the column deterioration and settlement began (Figure 4). A similar approach was also taken for the repair of the horizontally distorted column, corbel and beam connection at the second floor. The fix used at the second-floor connection involved installing a stiffened steel side plate on each face of the joint that straddled the timber beam, pillow beam and top of the first-floor column. The side plates were attached to the wood framing via lag bolts, rather than through bolts. Although there may have been hidden mortise and tenon joints connecting each of the three individual timber members together at the joint, the steel side plates effectively stiffened and stabilized the connection.

Spanning between the steel side plates, HSS steel members were installed to brace each beam/corbel/column connection and prevent any additional out-of-plane rotation or movement of the joint (Figure 5 ). The HSS bracing was installed between all of the affected column/beam connections, and extended to an adjacent masonry wall at one end of the glass-blowing room and to a steel column and beam at an adjoining room next to the kiln room.

Where the HSS brace was attached to the steel column and beam, the second-floor diaphragm, which was positively attached to the top of the steel framing, was available to resist lateral loads imposed on the line of HSS bracing due to any additional horizontal movement that might occur at the existing distorted column/beam connection. As a result, the existing connections were secured in place, and therefore capable of providing continued structural support of the second-floor framing and bracing of the top of the first-floor column.

STRUCTURE magazine

Figure 5.

The final remaining repairs associated with the project included minor epoxy injection and/or replacement of some badly damaged timber decking and floor beams. A portion of the credit for the successful implementation of this project can be attributed to the involvement of the contractor, PULLMAN/Shared Systems Technology, Inc. The contractor was selected for this project based on the evaluation team’s previous successful experience with Pullman’s level of workmanship and expertise on similar restoration and emergency shoring projects.▪

37

D. Matthew Stuart, P.E., S.E., F. ASCE, F.SEI, SECB, MgtEng (MStuart@Pennoni.com), is the Structural Division Manager at Pennoni Associates Inc. in Philadelphia, Pennsylvania.

Richard H. Antoine III, P.E., S.E. (richard.antoineiii@jacobs.com), was a project engineer at Pennoni Associates Inc. and is now with Jacobs in Philadelphia, Pennsylvania.

Parts 1 and 2 of this series were published in STRUCTURE magazine in the July 2014 and August 2014 issues.

September 2014

2014 Annual Conference September 17–20 Astor Crowne Plaza Hotel New Orleans, LA Wednesday, September 17 8:00 – 5:00 8:00 – 12:00 5:30 – 6:30 6:30 – 8:30

Committee Meetings NCSEA Board of Directors meeting Young Engineer Reception SECB Reception

Thursday, September 18 8:00 a.m.

Welcome & Introduction

8:15 – 9:45 Keynote: Prepare Your Practice – Why Your Strategic Plan is Doomed to Fail Kelly Riggs, President, Vmax Performance Group Unfortunately, most strategic plans are doomed to fail. Find out why, and find out how to develop a strategic plan that drives your company to its best performance.

Kelly Riggs is a business performance coach, founder of The Business LockerRoom, and a speaker and performance coach in the areas of sales, management leadership, and strategic planning.

9:45 – 10:45 Prepare for the Future – Where Codes & Standards are Heading NCSEA Code Advisory Committee The leaders of NCSEA’s Code Advisory Committee will conduct a lively, interactive discussion, providing insight into the continuing evolution of the codes and standards.

Moderator: Thomas DiBlasi, P.E., SECB, Chair, NCSEA Code Advisory Committee, DiBlasi Associates Panelists: Donald Scott, S.E., PCS Structural Solutions Kevin S. Moore, S.E., P.E., SECB, SG&H Inc. David Bonowitz, S.E. Williston Warren, IV, S.E., SESOL, Inc. 11:00 – 12:00 Prepare for the Unthinkable – Designing Buildings for Tornadoes Bill Coulbourne, P.E., Director of Wind & Flood Hazard Mitigation, Applied Technology Council The presentation will cover tornado research topics, design methods using ASCE 7-10 with needed modifications to account for tornado wind structures, and some examples on how to apply these concepts to building design.

Bill Coulbourne, P.E., SECB, is Director of Wind & Flood Hazard Mitigation for the Applied Technology Council and has been involved in investigations for every major hurricane, flood, and many tornadoes for the last 20 years. He serves on the ASCE 7 Wind Load Task Committee, the NCSEA Wind Load Committee, and the ASCE 24 Flood-Resistant Design and Construction Standard.

Register today at www.ncsea.com!

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38

Concurrent Sessions 1:00 – 2:15 A. ACI 562 Building Code for Repair of Existing Concrete Structures Keith Kesner, Ph.D., P.E., S.E., Senior Associate, WDP & Associates The presentation will provide an understanding of how the ACI 562 code was developed, motivation for development, and how the ACI 562 code will impact concrete repair practice.

Keith Kesner, Ph.D., P.E., S.E., is a Senior Associate at WDP & Associates and is the current chair of ACI Committee 562 “Evaluation Repair and Rehabilitation of Existing Buildings”, which has developed a code for repair of existing concrete buildings.

B. Wind Engineering Beyond the Code Roy Denoon, Ph.D., CPP Wind Engineering Consultants Wind loading codes and standards are designed to provide reasonably reliable design for the majority of buildings and structures but they don’t cover unusual forms or, often, wind sensitive components. This presentation will examine code limitations and present examples of under-designed structures and components, as well as describe alternative design approaches.

Dr. Roy Denoon is a Vice President of CPP Wind Engineering and Air Quality Consultants and has conducted wind tunnel testing and field measurements on many notable projects throughout the world, including two Olympic stadiums and the world’s tallest building, Burj Khalifa.

Concurrent Sessions

3:00 – 4:00

A. 2012 National Design Specification for Wood Construction Overview Michelle Kam-Biron, P.E., S.E., SECB, M.ASCE, Director of Education, American Wood Council This session will provide an overview of changes in the 2012 American Wood Council’s National Design Specification (NDS) for Wood Construction (ANSI/ AF&PA NDS) and Supplement.

Michelle Kam-Biron, P.E., S.E., SECB, is Director of Education for the American Wood Council, providing continuing educational resources related to structural wood for architects, engineers, and code officials.

B. Three Diverse Adaptive Reuse/Renovations Bill Bast, P.E., S.E., SECB, Principal, Thornton Tomasetti Three case studies of recent renovation or adaptive re-use projects will be presented, ranging from a building facade over-clad to adaptive re-uses of 1920’s buildings in Chicago.

Bill Bast, P.E., S.E., SECB, is a principal in Thorton Tomasetti’s Chicago office and a past president of NCSEA. He focuses on building projects that involve renewal or forensic structural engineering services.

September 2014

Concurrent Sessions

4:00 – 5:00

A. AISI Standard & Tech Notes Vincent E. Sagan, Chairman, P.E., Cold-Formed Steel Engineers Institute This presentation will summarize and discuss the CFSEI Tech Notes, which aid structural engineers in the application of design specifications and standards, and explore design issues and challenges that are unique to cold-formed steel structures.

Vincent E. Sagan is an Associate Principal with Wiss, Janney, Elstner Associates, Inc. (WJE). He serves on the AISI Committee on Specifications for the Design of Cold-Formed Steel Structural Members and is the Past Chairman of the CFSEI Executive Committee.

B. High Roller Observation Wheel Jason Krolicki, ARUP San Francisco The Las Vegas High Roller is the world’s largest observation wheel at 550 feet tall and has a maximum capacity of 1120 passengers during each 30 minute rotation. This session will discuss the challenges structural engineers face in designing complex movable structures and the necessary considerations for passenger experience.

Jason Krolicki is an Associate Principal, leads ARUP’s structural group in San Francisco, and was the project manager for the design of the High Roller.

6:30 – 8:30

Welcome Reception on Trade Show floor

Friday, September 19 8:00 – 10:00 8:00 – 10:00

Member Organization Reports Vendor Product Presentations

10:30 – 12:00 Student to Teacher – Gaining Competency after the University A panel discussion led by the NCSEA Young Member Group Support Committee Panelists from EIs to Senior Structural Engineers will highlight common techniques to advance technical abilities from student to competent structural engineer and will discuss the different methods utilized by present-day EIs, as well as methods to remain technically relevant, in this interactive session.

The NCSEA Young Member Group Support Committee helps Young Engineers form, maintain, and grow NCSEA MO Young Member Groups in their area.

Moderator: Heather Anesta, P.E., ME, Stantec Consulting Inc. Panelists: Barry Arnold, P.E., S.E., MS, Vice President, ARW Structural Jami Lorenz, P.E., Partner, BCE Structural Jim Malley, P.E., S.E., MS, Senior Principal, Degenkolb Eng. Emily Guglielmo, P.E., S.E., MS, Martin/Martin, Inc. Ellen Kuo, P.E., MS, SMMA Jera Schlotthauer, EIT, MS, Matin/Martin, Inc. James Newhall, EIT, CTSAZ Sofia Zamora, EIT, CBI Consulting 1:00

Trade Show closes

1:00 – 1:45 The Most Common Errors in Wind Design & How to Avoid Them Emily Guglielmo, S.E., Associate, Martin/Martin This session will help the practicing engineer correctly apply the current wind load provisions of ASCE 7. It will include STRUCTURE magazine

discussion of commonly misunderstood and misapplied sections of the code, ideas for simplifying wind load analysis, and the future of the wind load provisions.

Emily Guglielmo is an Associate with Martin/Martin, Inc, San Francisco Bay Area, and was honored with the BD+C 40 Under 40 Award (2013) and Structural Engineer Rising Stars Award (2013). She was also an ENR 20 Under 40 recipient in 2014.

1:45 – 2:30 The Most Common Errors in Seismic Design & How to Avoid Them Thomas F. Heausler, P.E., S.E., Heausler Structural Engineers The presentation will identify the most common errors in seismic design and calculations, and it will demonstrate the proper application of Codes and Standards to avoid errors and misapplications. Low seismic risk design categories and the surprisingly-numerous seismic provisions which apply, as well as the requirements unique to high seismic risk design categories only, will be discussed.

Thomas F. Heausler, P.E., S.E., of Heausler Structural Engineers, has 33 years of experience in Structural and Seismic engineering. He is a voting member of ASCE 7 Seismic Provisions (since 2006), and serves on the NCSEA Seismic Code Advisory Committee.

3:00 – 4:00 Practical HSS Design with the Latest Codes & Standards Kim Olson, P.E., Technical Advisor, Steel Tube Institute & Structural Engineer, FORSE Consulting From bamboo to TS to HSS, hollow structural section evolution will be discussed along with the corresponding research which resulted in these changes. A discussion of design and construction challenges will sort out the misconceptions and present methods for addressing the remaining challenges.

Kim Olson, P.E., is a Structural Engineer at FORSE Consulting. As a technical advisor to the HSS Committee of The Steel Tube Institute, Kim works to educate architects and engineers on HSS. 4:00 – 5:00 Practical Steel Connection Software Design Using 2010 AISC Standard Steve Ashton, P.E., SECB, Principal, Ashton Engineering & Detailing, SDS/2 Engineering Representative for Design Data The session will feature effective procedures and time-saving tips for reviewing software-generated connection designs, common pitfalls and how to avoid them.

Steven Ashton, P.E., SECB, Principal, Ashton Engineering & Detailing and SDS/2 Engineering representative for Design Data, has over 23 years of experience in structural engineering consulting and software development/ promotion, and as a Senior Engineer with AISC. 6:00 – 7:00 7:00 – 10:00

Awards Reception (formal attire encouraged) NCSEA Banquet & Awards Presentation,

featuring the NCSEA Excellence in Structural Engineering Awards and the NCSEA Special Awards

Saturday, September 20 8:00 – 12:00 12:30 – 2:00

39

NCSEA Annual Business Meeting NCSEA Board of Directors Meeting

September 2014

2014 Annual Conference September 17–20 Astor Crowne Plaza Hotel New Orleans, LA (xx) Booth number

Denotes NCSEA membership

(55) AISC

(45) Nemetschek Scia

www.aisc.org

www.Nemetschek-Scia.com

www.concrete.org/

www.NEWMILL.com

www.atlastube.com

www.powers.com

www.azzgalv.com

www.sideplate.com

www.bekaert.com/building

www.strongtie.com

www.blindbolt.com

www.steeljoist.org

www.castconnex.com

www.steeltubeinstitue.org

www.abchance.com

www.strand7.com

www.cfsei.org

www.cscworld.com

www.sds2.com

www.usg.com

www.ecospan-usa.com

www.vector-corrosion.com

www.euclidchemical.com

www.vulcraft.com

(47) New Millennium Building Systems

(52) American Concrete Institute

(54) Powers Fasteners

(21) Atlas Tube (38) AZZ Galvanizing

(39) Side Plate Systems

(42) Bekaert

(37) Simpson Strong Tie

(57) Blind Bolt

(35) Steel Joist Institute

(32) Cast Connex Corporation

(41) Steel Tube Institute

(43) Chance Civil Construction

(60) Strand7 PTY LTD

(30) Cold-Formed Steel Engineers Institute

(22) TEKLA/CSC Inc

(59) Design Data

(17) USG

(20) Ecospan

(48) Vector Corrosion Technologies

(31) Euclid Chemical

(19) Vulcraft

(53) Fabreeka International INC

Sponsors

www.fabreeka.com

(40) Five Star Products, Inc

NCSEA extends its appreciation to the sponsors of the NCSEA Annual Conference.

www.fivestarproducts.com

(44) Headed Reinforcement Corp

Platinum

www.hrc-usa.com

(51) Hilti

www.us.hilti.com/engineering

(58) Holcim Inc www.holcim.us

(34) Independence Tube Corporation

Gold

www.independencetube.com

(46) International Code Council www.iccsafe.org

(49) ITW Red Head, Ramset and Buildex www.itwredhead.com

(33) ITW Trussteel

Silver

www.trussteel.com

(36) Lindapter

www.lindapterusa.com

Copper

(18) LNA Solutions www.lnasolutions.com

(56) MiTek, USP, Hardy Frame-ZoneFour www.uspconnectors.com

Contributing

(50) NCEES

Sound Structures, Inc

www.NCEES.org

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September 2014

Registration

Full conference registration includes: • • • • • • •

Three breakfasts Two lunches Three receptions Refreshment breaks Trade show access All educational sessions & resources Awards Banquet

Conference Hotel

The Astor Crowne Plaza New Orleans, at the “Gateway to the French Quarter,” is located where Canal Street meets Bourbon Street. Enjoy 4-diamond accommodations, sophisticated meeting space, and southern hospitality combined with personalized service.

Reserve your room online at www.ncsea.com for the $145 group rate. Contact NCSEA if the hotel is sold out.

Special Offers!

Engineers 35 years of age or younger pay only $250 for complete registration, which also includes special Young Engineer activities.

First-Time Attendees to the NCSEA Annual Conference pay only $600.

Transportation to Hotel The hotel is accessible by shuttle from the Louis Armstrong New Orleans Airport, for $20 one way or $38 round trip. Shuttle service can be booked by visiting www.airportshuttleneworleans.com.

Airfare Discounts NCSEA has partnered with American Airlines for discounted airfare for the NCSEA Annual Conference. The NCSEA discount code is: 3494BS. This number goes into the Promo Code box when buying online tickets at www.aa.com, and will give a 5% discount. Passengers may also call 800-433-1790.

REGISTER TODAY!

All NCSEA conference events take place at The Astor Crowne Plaza Hotel.

Reservation information is available at www.ncsea.com.

Join us in New Orleans!

Reserved

Available

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September 2014

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Tilt-Up Pushes the Height Envelope on a Six-Story Office Building in Texas

By Jeff Griffin, Ph.D., P.E., P.M.P. and Mitch Bloomquist

Southwest corner. Courtesy of Powers Brown Architecture.

E

ngineering advancements can have a major impact on the end design of buildings, improving their aesthetics and therefore their marketability. Cutting edge techniques employed for a six-story tilt-up speculative office building near Houston prove that advancements in the field of tilt-up concrete construction are having a positive impact on real estate profitability.

When it comes to commercial real estate, having a “Class A” label can greatly increase the rents that a property can command. The Building Owners and Managers Association (BOMA), an international organization that manages measurement standards for buildings, defines Class A properties as the “most prestigious buildings competing for premier office users with rents above average for the area. Buildings have high quality standard finishes, state of the art systems, exceptional accessibility and a definite market presence.” Furthermore, the architecture of a Class A building has to be a cut above the utilitarian ‘box.’

The Sierra Pines II building represents Phase 2 of the Reserve at Sierra Pines project. It is situated on a four-acre site within The

Woodlands, one of America’s first master-planned communities.

Located in suburban Houston, Texas, The Woodlands covers 28,000 acres and includes 7,000 acres of protected green space, making it a highly marketable location.

Before it could qualify as a Class A property, however, Sierra Pines II had to achieve architectural distinction. To do so economically, tilt-up concrete construction was selected. Once seen as a method suitable only for warehouses and other lower-end structures, tilt-up has proven itself as appropriate for high quality buildings and distinguished architectural design. At six stories, Sierra Pines II will be the tallest building constructed with load-bearing tilt-up concrete in Texas.

Defying ‘The Box’ The 154,213-square-foot Sierra Pines II building is vertical in its proportions, which differentiates it from many tilt-up projects. Potential tenants within The Woodlands market typically do not require the large footprint office buildings of the recent past, and the 25,000 square-foot floor plates of Sierra Pines II make for better views and provide more daylight for the building’s occupants. Rising property values also play into the equation; as the cost of land increases, building higher makes more and more sense.

Four + Two

Phase 2 east side formed panels. Courtesy of E.E. Reed Construction, L.P.

STRUCTURE magazine

The building’s six-story walls are composed of a lower four-story panel measuring 58 feet 11 inches tall with a two-story panel measuring 31 feet 2 inches in height stacked on top. While the 90+ foot tall elevation could theoretically have been engineered utilizing single panels, site constraints, namely the available casting area, restricted the height of the panels. continued on next page

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The four-story panels were cast on the building slab and adjacent casting beds, strategically located to preserve the soaring pine trees that make the site so attractive. Once the four-story panels were lifted into place, the two-story panels were cast. While two different casting sequences are not as efficient as one, this approach delivered several advantages for this project. First, it allowed for a relatively slender six-story tilt-up building to be constructed on a very tight site. Dividing the wall panels into two sections gave the designers the ability to reduce the thickness of the two-story panels. The lower four-story panels are 14 inches thick while the upper two-story panels are only 7½ inches thick.

The major architectural advantage, which ended up having a dramatic effect on the rhythm of the façade, was the ability to shift the panel joints so that the panels are not aligned vertically from the bottom of the building to the top. This allowed the entire fenestration pattern to shift, breaking down the scale of the building. The shift in panel joints had structural implications as well. The load path is disrupted at the shift, creating highly concentrated vertical and lateral loads over openings in the lower four-story panel.

These loads are transferred into the fourth story headers through a series of embeds with weld plate connections, then on to the vertical panel legs by reinforcement designed to handle the shear and flexure resulting from this load transfer. The design takes into account the rigidity of the beam and column elements in

Overall building perspective looking at the east face as viewed from the parking garage.

Courtesy of Big 4 Steel Services, L.P.

the panel; as a result, shear stirrups and ties are incorporated into the panel in addition to the normal vertical and horizontal reinforcement.

Finally, the shift in joint location allowed for a quick erection process because there were fewer alignment challenges.

By separating the panel legs with openings instead of having them side by side, the legs appear much thinner and lighter. The panel joint itself is broken by the openings at each level, further eliminating the perception of a large panel.

Building the Tallest Load-Bearing Tilt-Up in Texas

Erection of the upper panels on the northwest corner. Courtesy of Big 4 Steel Services, L.P.

Due to soil conditions, it was necessary to extend foundation bearing more than 6 feet below finished grade. To keep the panels from growing any taller, thereby saving casting space, a 5-foot tall poured-in-place concrete stem wall extends from the top of the footing to 1 foot below the finished floor.

Welded plate connections, similar to those used between the lower and upper panels, connect the four-story panels to the concrete stem wall.

For a variety of structural reasons, welded plate panel-to-panel connections are utilized throughout the structure in lieu of grouted sleeve connections or simple plate connections with expansion anchors. At many locations, panel joints occur above openings, creating cantilevers. The most dramatic joints occur at the ends of the building, where multi-story openings wrap the corners of the building.

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The cantilevered header elements form a mitered corner condition. The panels are connected at the corner to stabilize the somewhat delicate arms of the panel and connected on the other side of the panel to reduce overturning forces in the plane of the wall. The building is designed to withstand 110 mph three-second gusts per the requirements of the 2009 International Building Code (IBC) using ASCE 7-05 for the wind design. While greater than most inland locations, this wind load is typical for the region and contributed to the need to connect panels to one another across the panel joints.

Tilt-up panels, because of their composition and size, often provide the necessary lateral stability for the building as shear walls. However, because of the larger wind loads, an architectural mechanical screen on the roof, numerous large openings and the slender aspect ratio of the building, diagonal steel bracing is incorporated at two interior column lines.

The main entrance panel presented several engineering challenges. The upturned “U” shaped panel is 58 feet 11 inches tall and almost 40 feet wide, with a four-story tall (54 feet 11 inches) 30-foot wide opening.

On the outside edges of the panel, small, cantilevered fingers extend out to form half of the adjacent panel openings at each floor.

The 14-inch thick panel is designed with integral 16-inch returns along the large center opening for added rigidity. According to the contractor, this panel was the most difficult to tilt.

Erection of the upper panels on the east face as viewed from the northeast corner. Courtesy of Big 4 Steel Services, L.P.

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Once designed, innovative thinking on the construction side furthered the project’s success. For example, the project had originally been engineered using the 2012 TCA Guideline for Temporary Wind Bracing of Tilt-Up Concrete Panels during Construction to utilize three 52-foot tall braces per lower panel. By switching to higher-strength braces, and helical ground anchors to take full advantage of the capacity of those braces, it was possible to eliminate one brace per panel, or 33 percent of the braces.

In addition to reducing the number of braces per panel, the team was able to reduce the length of the braces from 52 feet to 42 feet.

With the original three-brace configuration and the location of openings within the panels, taller braces were required to get above the openings. With only two braces per panel, they could be located between openings at a lower elevation. This presented additional savings on freighting. On a very tight site with panels braced to the exterior, this also meant additional room around the perimeter because the shorter braces could be anchored closer to the structure. Once the concrete slabs of the second through fifth floor were in place, these braces were even removed prior to erecting the upper panels, thereby freeing up the room necessary for the panel erection crane to traverse the perimeter of the building.

As tilt-up construction pushes the height envelope across the nation, office buildings are likely to be among the earliest adopters in terms of building type. For now, six stories is the typical ‘limit’ for which load-bearing tilt-up construction is specified, mostly due to the limitations of equipment and bracing. For taller buildings, conventional construction using tilt-up construction as cladding panels offers an economical solution.

Taller buildings will be possible as the design and construction communities continue to experiment with stacked panel projects, developing more effective bracing arrangements and stacking configurations.▪ Jeff Griffin, Ph.D., P.E., P.M.P., is a Principal and Senior Project Manager with LJB Inc. He has particular expertise in the design of structures built with site cast tilt-up concrete wall panels. He can be reached at jgriffin@ljbinc.com.

Mitch Bloomquist serves as Managing Director for the Tilt-Up Concrete Association (TCA), the international nonprofit trade association for the global tilt-up concrete construction industry. He can be reached at mbloomquist@tilt-up.org.

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Getting the underground utilities in place early was critical to the process. Because of the tight site, the vast majority of space surrounding the building was needed for casting beds and braces during construction. Both underground utilities and helical brace anchors had to be placed strategically to avoid conflicts.

The project was divided along its east/west axis for the purpose of construction sequencing. Concrete placement for the south half of floors two through five was a focus for the team as this allowed for the removal of the braces along the south of the building, thereby relieving site congestion. With these floors constructed, crews were able to begin interior framing and worked to rough-in the vast majority of the mechanical, electrical and plumbing on the south side while concrete placement on the north half continued. The internal core steel structure for floors five and six was also in place before the upper panels were lifted into place.

Construction started at the end of September 2013 and the building will be turned over to the developer in August 2014.

mpleted in

Building co

2013.

Aerial view of steel erection in progress.

The Use of Tilt-Up Concrete for Anti-Terrorism Force Protection

By Thomas P. Heffernan, P.E., LEED AP BD+C, Brian M. Barna, P.E., LEED AP BD+C and Mark P. Gardner, P.E.

D

epartment of Defense (DoD) facilities have never had a more complex set of protective needs than they do today. Following the Sept. 11, 2001 attacks, the DoD published its Unified Facilities Criteria (UFC) 4-010-01, DoD Minimum Anti-Terrorism Standards for Buildings.

In 2013, this document was updated to its current version. UFC 4-010-01 identifies what reasonable precautions can be taken – for a reasonable cost – on buildings owned, leased, privatized or otherwise occupied, managed or controlled by or for the DoD. It also prescribes methods for achieving the desired level of protection. The document indicates that it is most cost effective to address anti-terrorism force protection (AT/FP) during design and early construction, rather than to retrofit facilities. Tilt-up construction offers one sound approach to accommodating AT/ FP from the outset of building design.

Reasonable Protection Because it would be impractical to provide a level of protection that would guard against every possible situation, UFC 4-010-01 standards seek to minimize the likelihood of mass casualties in the event of an unforeseen terrorist attack. Table 2-1, Levels of Protection – New and Existing Buildings outlines the varying levels of protection and the potential building damage/performance associated with each level. The table also presents resultant potential injury. A secondary document, UFC 4-023-03, Design of Buildings to Resist Progressive Collapse, sets design criteria to prevent disproportionate collapse of structures with three or more stories. The goal of UFC 4-023-03 is to produce structural systems that limit the effects of localized failure and prevent the spread of damage from element to element. The required design level of resistance to progressive collapse is determined by the building’s Occupancy Category (OC) in accordance with UFC 4-023-03 Table 2-2, Occupancy Categories and Design Requirements.

A Maryland Facility Provides a Proving Ground Tilt-up concrete, long recognized as a quick and economical building method, is now being proven as a means of achieving high levels of blast force protection and progressive collapse resistance. A fourstory building constructed in 2013 in Maryland near the nation’s pre-eminent center for information, intelligence and cyber security provided a test case for the AT/FP abilities of tilt-up design.

The building was built on a speculative basis, which is not common for an AT/FP structure because of the increased upfront costs. The tilt-up design achieved cost savings that made it feasible for the developer to include AT/FP in the initial design, thus improving the building’s marketability to government or federal contractor user groups. This building is part of a larger campus of buildings with similar performance capabilities.

The building was built as a joint venture between Konterra Realty and Boston Properties, and is a product of extensive, ongoing research conducted by Hinman Consulting Engineers, Powers Brown Architecture, Cardno Haynes Whaley and Harvey-Cleary Builders. This group developed a research case study in 2011 in

Panel leg reinforcement. Additional stirrups at first floor for ELR requirements.

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which the design of an existing office building was modified to determine whether it was feasible to apply the UFC requirements for blast and progressive collapse resistance at a medium level of protection. At this level of protection, the building would potentially experience minor, economically repairable damage resulting from an attack of given magnitude. The outcome of that study confirmed that tilt-up design could be used to achieve force protection for blast and progressive collapse resistance without perimeter columns. The research suggested that the premium for a tilt-up building incorporating medium level of protection was expected to be around $15 per square foot more than conventional construction methods without these capabilities.

Working through the Details To apply the UFC 4-010-01 criteria to the design of the Maryland building, building elements were analyzed individually to check their ability to withstand an air-blast load as determined by the design basis threat at the appropriate standoff distance. (Standoff distance is the distance maintained between a building and the potential location for an explosive detonation). The site was intentionally designed with constraints to maximize standoff distance, which is the most effective way to protect a structure from an exterior explosive threat.

The project was classified as OC III, which includes both an Alternate Path (AP) requirement and an Enhanced Local Resistance (ELR) requirement to resist progressive collapse. The AP method is described in the document as often being the most practical approach for load-bearing wall structures. Essentially, this method requires the structure immediately adjacent to a damaged area to be able to transfer loads around the affected area down to the foundation, thereby isolating the failure and avoiding the spread of damage. ELR requires that the shear capacity of each first floor wall and its connections to the building diaphragms exceed each wall’s flexural capacity to prevent a brittle-type failure from an extreme event at the lowest structural level.

The Maryland building consists of 32 four-story tilt-up concrete panels, typically 30 feet wide and 64 feet tall. The tallest panel is 68 feet tall and weighs 125 tons. The minimum panel structural thickness was determined to be 11 inches for blast and progressive collapse resistance. The typical overall panel thickness was increased to 15 inches to allow the panel legs to maintain this minimum structural thickness behind a continuous window strip with 4-inch deep mullions that wraps around the entire building perimeter at the fourth floor. This continuous window strip gives the appearance of a ribbon window from the exterior, enhancing the aesthetic appeal of the building and masking the tilt-wall nature of the structure.

The foundation system consists of shallow spread footings supporting interior columns and a continuous wall footing at the perimeter supporting the wall panels. In addition to in-service gravity and lateral loads, the perimeter footing was designed for construction loads and progressive collapse loads. For construction loads, the footing was designed for the case when the panel weight is concentrated at bearing channels at each end, rather than the more uniform distribution of panel loads after grouting under the panel. For progressive collapse loads, the footing was designed to take additional load locally from redistribution of building loads if any panel leg was removed in a progressive collapse scenario.

AT/FP requirements influenced the structural design in many ways. The progressive collapse requirement was a factor influencing STRUCTURE magazine

Erection of corner panel with strongbacks.

the decision to use full-height panels with a 30 foot module for the panel width. Limiting panel joints limited instances of discontinuity that needed to be bridged with large steel connections.

Dowels cast into the wall panels at the first floor were designed to resist tension from a blast force that would result in the panel pulling away from the building in a rebound response during a blast event. Similarly, the connections of continuous deck edge angles to embedded plates in the wall panels at each elevated floor were designed to resist out-of-plane panel loads caused by blast forces.

Beams are connected to plates embedded in the tilt-wall panels by double-angle shear connections with horizontally-slotted holes for construction tolerance and thermal expansion. Kickers at each panel leg at each floor just above the window head also help to tie the panels back to the diaphragm to distribute the blast loads and meet progressive collapse requirements. Due to the load bearing nature of the wall, the wall systems are designed to remain elastic when subjected to the blast loading. The analysis was performed via Hinman’s developed software BAM®.

Lightweight concrete on metal decking was chosen as the floor system at each level to reduce the weight of the structure, thereby contributing to the reduction of progressive collapse load. Due to pressures from blast loads, the roof structure consists entirely of wide flange steel beams instead of an open-web steel joist system, as would be more typical for conventional construction. Beams were spaced at 10 feet on center, similar to the floor beams at

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Erected panels from the building interior. Embedded plates at each panel joint will be connected for progressive collapse resistance.

intermediate levels. Therefore, a 3-inch deep steel deck was used to accommodate the longer span between supports.

Lightweight concrete mixes were used for the panels to reduce weight and enable the panels to be erected with an economical crane.

Embedded plates in the panels have reduced capacity in lightweight concrete per ACI Appendix D. Therefore, to keep the sizes of embedded plates manageable, 6,000-psi concrete was used for the tilt-up panels to increase the capacity of the connections to meet blast and progressive collapse loads.

Perhaps the most unique elements of the design are the panel-topanel connections at each panel joint, which are designed to allow loads to redistribute in a progressive collapse scenario while still permitting in-plane movement of the panels under service conditions.

Traditionally, tilt-up panels are not connected to one another except, perhaps, at the corners of a building. In older tilt-up structures, where connecting panels was more common, concrete shrinkage and basic thermal movement often caused these connections to either fail or damage the concrete wall. Because of the Alternate Path requirement for this project, the design team utilized large plates spanning across panel joints and connected to embedded plates in each panel to tie the structure together. There are four embedded plates on each side of each panel. The large embedded plates, each up to 5 feet tall and 18 inches wide with up to 20 headed studs, weighed on average 300 pounds and had to be set by mobile crane.

The panel connections alternated between a connection plate welded to the embedded plates on each side of the joint and a connection plate welded to the embedded plate on one side of the joint, and fastened with a bolted slip connection on the other side of the joint.

This alternating pattern continued around the building, allowing for in-plane movement of the panels.

There were approximately 1,370 embeds in 32 panels, not including the window anchor blast embeds for 208 openings. In addition to the weight of some of the embeds, the density of the steel reinforcement made setting difficult. Many panels required more than 14,000 pounds of rebar to be placed, with total panel weights exceeding 248,000 pounds. The size and weight of the panels, combined with the number of large openings and deep depressions, called for unique lifting and bracing engineering strategies. Full-height double-stacked strongbacks were used to erect the panels where necessary; the strongbacks utilized the existing reinforcement in the panels and reduced the need for additional reinforcement, helping to keep costs to a minimum.

STRUCTURE magazine

Panel exterior face with temporary braces during construction.

Conclusions The numerous challenges faced on this project were overcome by collaboration, planning and persistence. This structure serves as a testament to the versatility, economy and strength of tilt-up as a building system, and its ability to meet the diverse needs of a wide array of building requirements. It also provides conclusive evidence that, in the post-9-11 era, tilt-up offers a valuable advantage in terms of AT/FP design.▪

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Thomas P. Heffernan, P.E., LEED AP BD+C, is a Senior Vice President at Cardno Haynes Whaley in Reston, VA. He can be reached at tom.heffernan@cardno.com.

Brian M. Barna, P.E., LEED AP BD+C, is a Senior Associate at Cardno Haynes Whaley in Reston, VA. He can be reached at brian.barna@cardno.com.

Mark P. Gardner, P.E., is a Managing Engineer at Hinman Consulting Engineers, Inc. in Alexandria, VA. He can be reached at mgardner@hce.com.

September 2014

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Historic structures significant structures of the past

Isaiah Rogers Tubular Bridges and Boston’s Mechanics’ Fairs

By David Guise

B

etween September 20th and October 2nd of 1841, an estimated eighty thousand people visited the Third Charitable Mechanic Association Exhibition held in Boston’s Faneuil Hall and Quincy Market.

They crowded the halls, admired the exhibits, and walked through Isaiah Rogers’ amazing 70-foot span, ten-foot diameter tubular bridge of intersecting helixes that connected the second floors of the two buildings. The bridge, one of the highlights of the exhibit, was widely acclaimed and awarded a gold medal.

Later that year, Rogers obtained a patent for his unique invention. In 1850, as architect for the Burnet House Hotel in Cincinnati, he used this same configuration to build a bridge across the hotel’s open courtyard.

No documentation has come to light that anyone other than Isaiah Rogers ventured to build a bridge of this design. While intriguing to look at, it would be extremely difficult to construct, and its complexity rendered it beyond the capability of any contemporary engineer to calculate the sizes of its various members in relation to a specific span and load.

Rogers’ bridge took its place in the Fair’s ongoing tradition, started in 1837, of erecting, and then dismantling after the fair closed, a unique temporary bridge to connect the two exhibit buildings.

The Sixth Charitable Mechanic Association Fair, held in 1850, featured a most unusual, irrational, bridge configuration as the connection between

David Guise retired after 40 years of private practice as principal of his architectural firm and is Professor Emeritus at City College of New York. He can be reached at davidguise@myfairpoint.net.

Isaiah Roger’s 1841 patent drawing; Library of Congress Patent Office.

Faneuil Hall and Quincy Market. It was designed

by Henry Lanergan, who had patented his invention earlier that year. No document has come to light indicating that either Lanergan, or anyone else, ever built another bridge to this design.

Given the occasion, Rogers and Lanergan seized the opportunity presented to them, and turned their ideas into realities. Contemporary builders trusted the simpler proven configurations available to them at the time, and saw no advantage in emulating either Rogers’ or Lanergan’s trusses as both were costly and difficult to construct. Thus, the only known examples of these two designs are the ones their inventors built.

As part of the Fourth Mechanics’ Fair, held in 1844, a father and son team introduced their now well-known Pratt truss design to bridge the space between the two Fair structures. The engineering logic and simplicity of constructing a Pratt truss was recognized at once, and later, in its more efficient steel form, it became the most commonly used mid-span truss configuration in America.

Wrought-Iron Tubular Bridges

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

Henry Lanergan’s 1850 patent drawing; Library of Congress Patent Office.

The underlying concept of building a tubular bridge is inherently rational, although the form proved to be economically unfeasible. More straightforward examples with simpler configurations than intersecting helixes would be built.

Suspension bridges had proved to be too flexible to carry trains, and iron tubes seemed to present an answer in that they would deflect less and be more resistant to horizontal wind loads. Their excessive weight and cost ultimately made them

50 September 2014

1850 Britannia wrought-iron tubular bridge over the Menai Straight. Courtesy of Los Angeles County Museum of Art.

non-competitive compared to steel trusses.

Perhaps the best known tubular iron crossing is the railroad bridge completed in 1850 over the Menai Straits in western England. It was a rectangular wrought-iron tube built by Robert Stephenson, son of the locomotive engineer George Stephenson. Trains traveled inside the tube, as did the pedestrians in Rogers’ cylindrical tube.

The two center spans of the Britannia Bridge are each 460 feet long, with the two end spans 230 feet each. The overall length of the crossing, including the entry towers, is 1,511 feet.

Although to the naked eye the tubes appear

to have a constant cross section, the overall height of the tubes gradually increases from 22 feet 9 inches at the abutments to 30 feet at the mid-river tower. The tube sections are all riveted together forming one continuous hollow girder from abutment to abutment.

The maximum bending moment for a continuous beam is at the mid-span support, and is the engineering reason for a deeper tube at that point.

The lack of ventilation in solid tube railroad bridges made the journey through them extremely unpleasant, as the soot from the locomotives had no outlet other than at the ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Berkeley Wise’s 1902 Gobbins Path Bridge.

ends of the tube. There are stories of gentlemen taking clean shirts with them in order to change after passing through the Menai tubular bridge.

Many articles credit Great Britain as the birthplace of the Tubular Bridge and the 400-foot span Conway Bridge, also built by Stephenson and completed in1848, as the first example. However, Rogers’ 1841 tubular bridge preceded it by seven years, and the Menai Bridge by nine. continued on next page

Original Victoria Bridge over the Saint Lawrence River, completed in 1859. Illustrated London News, Feb. 19, 1859.

Neither Stephenson, nor his contemporaries, could accurately calculate the load capacity of their tubes. They initially thought the tube would be excessively deflected by the coal hauling trains and had designed iron suspension chains to help support it. In the process of trial and error testing of the tube for deflection, they realized that the suspension chains were not necessary. However, the towers from which the chains were to be hung had already been built, which explains their strange presence.

Built as part of Canada’s Grand Trunk Railroad, the1859 Victoria Bridge over the Saint Lawrence River was the most important tubular bridge in the Western Hemisphere, and acclaimed by some at that time as the 8th wonder of the world. The overall bridge length between abutments is 6,600 feet. All of its parts were made in England and riveted together at the construction site. There are twenty four, 242-foot spans, and a main ship channel span of 330 feet. Trusses would ultimately prove to be far more economical than tubes. When the bridge was upgraded in 1897-8 to accommodate vehicle traffic in addition to carrying trains, the tubes were replaced by trusses.

that is visually reminiscent of the timber one Rogers erected 169 years earlier for Boston’s Mechanics’ Fair. This steel, 115-foot 6-inch clear span bridge solved the problem of providing daylight in a tubular design. It provides pedestrian access over the railroad tracks at the La Roche-sur-Yon train station in France.

Bridges are an indispensable part of our environment. Building them will always be an evolving undertaking. In engineering parlance, the “best” design for a given situation is usually taken to mean the one that can carry the required live load (people, vehicles, trains) across a given distance using the least amount of material. However, engineering knowledge, availability of materials, and the skill levels of workmen are ever changing commodities. Tschumi’s bridge was no more “practical” than Rogers’. Lanergan’s was almost silly. It is a shame we no longer have those wonderful fairs that permitted inventors to display their ideas. Tschumi’s and Wise’s examples have taught us that impractical can still be frivolous fun, that there are a few circumstances where “practical” need not always be the highest criteria.

Apparently there is an innate fascination with the concept of a bridge one moves through, rather than over.

Tubular bridges constitute a small side-bar in the long history of bridge building. They ultimately turned out to be an inefficient design.

The story of their evolution and demise as vehicle and/or railroad bridges provides an example of the engineering community’s willingness to try new forms when the current ones fail, to recognize changing requirements, to adopt the use of new materials, and to abandon old ideas.

Acknowledgements If Sara Wermiel had not passed on an inquiry as to whether anyone had ever built a tubular bridge to Isaiah Rogers’ patent, this article would never have been written.

Henry Scannell at Boston’s Public Library located newspaper articles verifying the construction of Rogers’ Boston and Cincinnati bridges. James Stewart, Frank Griggs and Sara Wermiel read early drafts and helped to improve the manuscript.▪

20th and 21st Century Examples of Pedestrian Tubular Bridges Perhaps the most dramatic tubular bridge is an elliptical one built by Berkeley Wise in 1902 as part of Gobbins Path, a terrifying ocean-edge tourist walk in Ireland. Traversing through it had to be a thrilling experience.

Structurally, it has much in common with a Pratt truss; it is a tubular bridge more by shape, than by engineering design.

In 2010, Bernard Tschumi, an architect best known for the “follies” he designed for a Paris park in the 1980s, collaborated with Hugh Dutton to design a cylindrical tubular truss

Tschumi-Dutton’s 2010 steel upgrade of Rogers’ 1841 timber design. Courtesy of Bernard Tschumi architects, Christian Richters, photographer.

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Professional issues

issues affecting the structural engineering profession

Deferred Submittals Part 3: When is Final…Final?

By Dean D. Brown, S.E.

O

n the subject of deferred submittals, let us touch on an issue relating to when an engineered design (containing a deferred submittal) is considered final. Virtually every building department requires an engineered set of plans to be stamped by the EOR as a condition of granting a building permit.

This is often before any deferred submittal documents have been finalized and reviewed by the EOR and submitted to the building official for approval.

Using the Survey State (mentioned in Part 2 of this series) as an example, the Rules of Professional Practice (for professional engineers) stipulate that (regarding the use of a seal), “The seal, signature and date shall be placed on all final specifications, land surveys, reports, plats, drawings, plans, design information and calculations, whenever presented to a client or any public or government agency. Any such document presented to a client or public or government agency that is not final and does not contain a seal, signature and date shall be clearly marked as ‘draft’, ‘not for construction’ or with similar words to distinguish the document from a final document.” (emphasis added) One could ask the State Board of Professional Engineers (The Board), how final does FINAL need to be before an engineered plan (containing a deferred submittal) is sealed? If there is no guarantee that a building official is going to properly enforce the routing of a deferred document, how final does an engineered plan need to be before a seal is used? It could be argued that upon initial application for building permit, the engineered plans are only a work-in-progress and need further information (from the deferred submittals) to complete. The statute establishes the condition that a ‘draft’ document cannot be final AND cannot contain a seal. There is no interim classification. If he/she chooses not to stamp, no building permit will be issued. If he/she stamps, then technically it could be argued that the engineer is violating the Rules of Professional Practice (at least in this state). There is no middle ground allowed. This concern was flagged to the State Board’s attention and they responded that it was a mute issue (i.e.,

So when is final…Final? At time of building permit…or when the EOR receives all complete deferred documents…or has participated in construction observation of the project? it was not an issue other engineers in that state were voicing).

Compare, then, which states other than the Survey State are indicating regarding the use of a seal (emphasis added): • Utah – “Any final plan, specification, and report of a building or structure erected in this state shall bear the seal of a professional engineer or a professional structural engineer…”.

• Missouri – “Plans, specifications, estimates, plats, reports, surveys, and other documents…shall be sealed and dated unless clearly designated preliminary or incomplete. If the plan is not completed, the phrase, ‘Preliminary, not for construction, recording purposes or implementation’ or similar language or phrase…” “It shall be a disclaimer and notice to others that the plans are not complete.”

• Nevada – “…all engineering plans, specifications, reports or other documents that are submitted to obtain permits, are released for construction or are issued as formal or final documents to clients, public authorities or third party must bear…’the seal and signature of the engineer.’”

• Illinois – “The use of a professional engineer’s seal on technical submissions constitutes a representation by the professional engineer that the work has been prepared by or under the personal supervision of the professional engineer or developed in conjunction with the use of accepted engineering standards.

The use of the seal further represents that the work has been prepared and administered in accordance with the standard of reasonable professional skill and diligence.”

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• California – “All civil (including structural and geotechnical) engineering plans, calculations, specifications (hereinafter referred to as ‘documents’)…shall be prepared by, under the responsible charge of, a licensed civil engineer and shall include his or her name and license number. Interim documents shall include a notation as to the intended purpose of the document, such as ‘preliminary,’ ‘not for construction,’ ‘for plan check only,’ or ‘for review only.’ All civil engineering plans and specifications that are permitted or are to be released for construction shall bear the signature and seal or stamp of the licensee and the date of signing and sealing or stamping. All final civil engineering calculations and reports shall bear the signature and seal stamp of the license, and the date of signing and sealing or stamping.”

Notice that Illinois does not use the word ‘Final’, and California uses the term ‘Interim’, inferring that the document is a work-inprogress. So, is there something unique about the practice of engineering in these two states?

In regards to what is being discussed, the answer is no.

Back to the Survey State, the author initially proposed revised language (on the use of a seal) to a state senator, suggesting the following, “Plans, specifications, estimates, plats, reports, surveys, and other documents or instruments shall be signed, sealed and dated unless clearly designated preliminary or incomplete. If the plan is not completed, the phrase, ‘Preliminary, not for construction, recording purposes or implementation’ or similar language or phrase shall be placed in an obvious location so that it is readily

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found, easily read and not obscured by other markings. It shall be a disclaimer and notice to others that the plans are not complete.”

The state senator indicated that the suggested change had to be turned over to the Board for involvement.

When proposed to the engineering board, they in turn responded with the following, “It was not the Board’s function to shepherd your bill through the legislature, or educate you on the legislative process.” They then continued, “The Board …has not heard any concern from others on this matter and does not share your concern. The Board does not have the inclination to adopt your proposal, nor does it see the need to change (state) law as currently written… (and) does not agree with your proposed change.” Furthermore, they indicated that they would oppose such change to legislation if proposed, but gave no reason as to why.

It’s interesting to note that this same state board issued an earlier newsletter to the engineering community at large, soliciting recommendations on what could be done to better the practice of structural engineering.

This state’s responsible charge statute includes language that says, “…‘Responsible Charge’ means the control and direction of engineering work…” The author asks, other than the use of his or her seal, what influence of control does an EOR have regarding their responsible charge? Is not the ‘control and direction’ of an engineer’s work directly impacted by a Building Official in this regard?

So when is final…Final? At time of building permit…or when the EOR receives all complete deferred documents…or has participated in construction observation of the project? When should an EOR’s role on a project be deemed complete? To what degree does document finality correlate to an engineer’s “completeness” of responsible charge?

That is a matter for further debate.

In conclusion, in this age of integration, engineers need to be better at protecting their interests. They do this by controlling when and how their seal is used. There also should be better consensus among all states regarding the use of the stamp, especially considering the complexities of deferred design and submittals.▪

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discussion of legal issues of interest to structural engineers

LegaL PersPectives

Couldn’t Care Less Part 2: A Malpractice Primer for Structural Engineers

By Matthew R. Rechtien, P.E., Esq.

P

art 1 of this series (STRUCTURE, June 2014) built the foundation for understanding structural engineering malpractice. We explained concepts like liability and claims, generally, and tort liability specifically. On top of that foundation, we erected the framework, examining the basic elements of structural engineering malpractice, starting with the concept of duty.

In this article, we complete our project by examining the final three elements of structural engineering malpractice: breach, damages and causation. We then close out this subject by exploring some common defenses to malpractice liability.

Breach The second element of a structural engineering malpractice claim is its simplest: breach.

Simple because breach is defined by the first element, duty. A structural engineer commits a breach when they do not meet their duties.

Proving a duty requires proof of what the engineer should have done; proving a breach is as simple as establishing that the engineer did not do it.

Damages Where a man has but one remedy to come at his right, if he loses that he loses his right. Holt, CJ, Ashby v White (1703), 2 Raym 954.

It is a vain thing to imagine a right without a remedy; for want of right and want of remedy are reciprocal. Id. This brings us to the third element of any malpractice claim: damages. Without damages, what Black’s Law Dictionary defines as “[m]oney claimed by, or ordered to be paid to, a person as compensation for a loss or injury,” there is no malpractice liability. An engineer is not typically liable in malpractice for careless practice that causes no harm.

Although the “loss or injury” necessary to

trigger liability is often physical (e.g., death or a broken leg), it need not always be. It could be a sagging floor, drooping cladding, or objectionable movement.

There are numerous kinds of damages: punitive, liquidated, consequential, etc.

When we talk about malpractice, however, the damages for which the structural engineer may be liable are generally compensatory damages: damages sufficient in amount to indemnify the injured person for the loss suffered. Put differently, the focus of a malpractice claim is generally to make the injured person “whole.” This is an admittedly fuzzy concept when applied to broken legs and the like, which no doubt explains at least part of the public curiosity over verdicts in personal injury cases like the McDonald’s hot coffee case.

Compensatory damages are a fuzzy concept applied to non-economic damages, too. If an owner is stuck with a floor that vibrates, how can that injury be measured? How can he or she be made “whole?” The law employs two general approaches. One measures diminution in value: how much less is the owner’s building worth because of the malpractice, the vibrating floor. The other measures the cost of repair, i.e., the cost to fix the problem.

Jurisdictions vary in their preference for one approach over another. Some jurisdictions employ both, the proper approach depending on the factual circumstances. Thus, for example, although one jurisdiction may favor the cost of repair measure, it may opt for the diminution measure where the engineer’s defect needs no fixing, and where fixing it would require the wasteful destruction of good work.

Determining the proper approach or measure under the law can be tricky business, and often the subject of expert testimony.

Finally, the element of compensatory damages raises the related subject of “betterment,” the idea that compensatory damages should compensate, but not overcompensate. Thus, if an engineer commits malpractice by specifying a 5-inch floor where 7 was needed, the engineer may be liable for the rework, but the owner is not entitled to the additional 2 inches they never purchased in the first place.

The law will not permit the owner to profit from the malpractice.

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Causation I am by no means sure that if a man kept a tiger, and lightning broke his chain, and he got loose and did mischief, that the man who kept him would not be liable. Bramwell, B, Nichols v Marsland (1875), L R 10 Ex 260.

We now come to causation, the trickiest element of all. A malpractice claim (and the resulting liability) requires that the engineer’s breach caused the injury at issue.

Great minds since Aristotle – who in Metaphysics stated one definition of a cause as “the result of whose presence something comes into being” – have struggled with understanding causation. Yet, causation is the soul of liability: the idea that a person should only be responsible for the consequences of their own actions, the harms they cause, is deeply rooted in American jurisprudence. Nevertheless, to say that a person is liable for all consequences of their actions goes too far. The world is interconnected; one thing leads to another. Any injury is the result of countless actions. This is the “butterfly effect,” a concept that meteorologist Edward Lorenz planted in the public consciousness when he observed: “one flap of a seagull’s wings could change the course of weather forever.” The law also recognizes that a person should not necessarily be responsible for every consequence of his actions. From these two basic rules, arise the two forms of causation that are essential to any malpractice claim.

The first kind of causation, causation in fact, arises from the rule that a person should only be responsible for the consequences of their own actions. This kind of causation is captured by the jargon that often precedes it: sine qua non, literally, “without which it cannot be.” Lawyers often refer to this as a “but for” test. But for the malpractice, would the injury have happened?

Causation in fact asks whether the malpractice was necessary (if not necessarily sufficient) for the injury to occur. If the injury would have happened regardless of the engineer’s breach, then there is no claim. If for example, a motorist is distracted upon viewing a sagging steel beam and as a result collides with a stop sign, then the

malpractice of the beam’s designer is a cause in fact of the motorist’s resulting injuries.

However, would it be fair to hold the beam’s designer responsible for the motorist’s injuries?

Most would say no, which is why the law also requires legal causation, or proximate cause.

Proximate cause captures the notion that some consequences of negligent acts are too remote, too difficult to foresee, to give rise to liability.

Minor v Zidell Trust, a 1980 case before the Oklahoma Supreme Court, furnishes a good example of the limits of proximate cause in the structural engineering context. There the Court held that even though an engineer had negligently designed the curb in a parking garage, and but for that design, an unconscious motorist would not have been able to drive over it and suffer injury, “[s]uch an event was so extraordinary that it was unforeseeable in law” and there was no proximate cause and no liability.

Proximate cause relates to another key legal concept: intervening events (i.e., causes) may relieve the negligent engineer of liability. In a 1986 case, the Ohio Supreme Court (in Cincinnati Riverfront Coliseum, Inc v McNulty Co) held that although a structural engineer’s design was defective, material deviations from it during construction were a significant enough cause of the injury to relieve the engineer of liability. It found that the deviations broke the causal connection between the design and the injury.

Defenses Finally, no discussion of malpractice would be complete without mention of “affirmative defenses.” These are like claims: they are a set of facts that, if established, negate an

otherwise established claim. In other words, even if a plaintiff can prove malpractice, by proving that he or she suffered an injury caused (proximately and in fact) by an engineer’s breach of their professional duties, the engineer may be able to prove other facts to defeat that claim. As Black’s Law Dictionary puts it, an affirmative defense is “new facts and arguments that, if true, will defeat the plaintiff’s … claim, even if all [its] allegations are true.”

There are a great many recognized affirmative defenses to malpractice claims: common law, contractual and statutory. Here, we mention two of the most common: 1) statute of limitations and repose, and 2) comparative or contributory negligence.

As to the former, in Michigan, for example, MCL 600.5839(1) provides that “[n]o person may maintain any action to recover damages for any injury … arising out of the defective and unsafe condition of an improvement to real property against any state licensed … professional engineer … more than 6 years after the time of occupancy of the completed improvement …”

This statute of repose puts a limit on the time that a plaintiff may wait before suing.

If the plaintiff exceeds that limit, his or her claim, even if otherwise valid, is barred and will be dismissed. Similar statutes exist in various other jurisdictions.

Another common defense is comparative negligence or fault. Black’s Law Dictionary defines comparative negligence as the “principle that reduces a plaintiff’s recover proportionally to the plaintiff’s degree of fault in causing the damage, rather than barring recovery completely.” Many states

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have codified this principle. Michigan, again as an example, enacted this defense in MCL 600.2959, which provides that: “[i] n an action based on tort or another legal theory seeking damages for personal injury, property damage, or wrongful death, the court shall reduce the damages by the percentage of comparative fault of the person upon whose injury or death the damages are based …” Bottom line: under this statute and others like it, a plaintiff’s recovery will be reduced by the extent to which their own carelessness contributes to their injury. The same statute further provides that if “that person’s percentage of fault is greater than the aggregate fault of the other person or persons … the court shall reduce economic damages by the percentage of comparative fault of the person upon whose injury or death the damages are based … and noneconomic damages shall not be awarded.” This means that if the plaintiff is more than 50% responsible, then not only are their damages reduced accordingly, but noneconomic damages, i.e., “pain and suffering” damages, are no longer available.

Conclusion This ends our malpractice primer for structural engineers. Taken together, both parts of this primer provide a structural engineer with an intellectual framework for understanding malpractice claims, as well as an explanation of the essential building blocks of these claims. The primer also identifies some of the more typical but tricky issues that arise in malpractice disputes. While not an exhaustive treatment of the subject, these articles should, however, give the reader at least working fluency in the subject.▪ Matthew R. Rechtien, P.E., Esq., (MRechtien@BodmanLaw.com), is an attorney in Bodman PLC’s in Ann Arbor Michigan, where he specializes in construction law, commercial litigation, and insurance law. Prior to becoming a lawyer, he practiced structural engineering in Texas for five years.

Disclaimer: The information and statements contained in this article are for information purposes only and are not legal or other professional advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances. This article contains general information and may not reflect current legal developments, verdicts or settlements; it does not create an attorney-client relationship.

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CASE BuSinESS PrACtiCES

What is the Value of Your Idea?

By John Dal Pino, S.E.

W

hat is the value of your idea?

No, not what is the value of your ideas to people in society in terms of the benefits they enjoy by safely crossing the river, or riding out the storm protected in the building you designed, but what is the monetary value of your ideas to your client? Put another way, how much profit do you think should accrue to you and your firm as a result of your dedication, creativity and hard work from a business relationship with another party who will rightfully exploit your ideas to the fullest extent possible for their own benefit? I know many engineers who are very uncomfortable discussing profit, thinking it to be unseemly and frankly not something “professionals” should openly discuss or be concerned with.

Right? Are you one of them?

Despite what many professionals might like the state of the business world to be, profit is an absolute necessity to maintain a healthy and thriving business. Healthy firms need investment capital for new equipment and infrastructure, monies to compensate investors, and capital for ownership transitions and finally, the inevitable, retirement. But even if you view business from a more socialistic, egalitarian perch, despite voluminous theory to the contrary, history has shown that profit from success is necessary.

So when there is money to be made, it is incumbent on engineers to make as much money as possible to feed the many entities hungry for profit within our firms. Of course, we have our professional reputations to maintain, but one can suggest that engineers often argue against themselves in negotiations. Rather than stake out a position that will ultimately lead them to a fee, scope and terms “in the middle” of possible outcomes, they start much too close to their desired end point and then spend most of the negotiation on their own side of the field, rather than near the opponents end zone, to use a football analogy.

Engineers have long wished to charge their clients for the value that they believe their services have created for the client. Except for a few engineers, who have exceptional knowledge, practice in niche markets, or possess special skills or use proprietary technologies, turning such desires into a sustainable reality

in a competitive environment has been elusive, much like the search for the holy-grail or the fountain of youth.

Traditional cost-based methods of compensation, such as lump-sum (based on a percentage of construction cost or a percentage of the total A/E fee) or hourly rate for a fixed number of hours (using client-approved overhead and profit), just don’t offer much opportunity to capture some of the value up for grabs. These methods have evolved from the common understanding by purchasers of engineering services (some might say a common misunderstanding, reinforced by the actions of engineers themselves) that all engineers are equally competent technically, have the same educational backgrounds and experience, and provide the same services in following the building code.

The value of the end product to the owner or user is rarely if ever part of the fee discussion or negotiation. In fact it is probably very difficult for the engineer to determine the true “value” of the services provided to the client, and even if the value is known, it would be difficult to use in establishing value-based compensation in a competitive environment, since market forces drive prices lower. Engineers are not unique in the situation in which they find themselves. Many service providers in similarly competitive industries (doctors, lawyers, plumbers, auto mechanics to name just a few), where the buyers of services have good access to information regarding the cost of doing business and can shop around before buying, are faced with the same situation.

So, to borrow a phrase, what is to be done?

Engineers need to consider re-designing their businesses with the goal of identifying and providing value to the customer in terms that the customer understands, priced using an incentive-based compensation scheme, in conjunction with a competitive lump sum fee for basic services.

Of course, basic engineering services, yielding drawings and specifications and priced using common industry practices, will always exist. However some engineering services can have a very significant effect on the client’s planning and investment decisions, and thus are of extreme value. It is critical that the engineer have a strong understanding of the clients business to quickly zero in on the most important value added services contained in

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his proposal. The key is to recognize these services early on, and then take care not to “give away” these services by including them as a normal part of basic project services priced using the traditional compensation methods. Not to diminish the importance of coordinated and complete construction documents based on excellent engineering, but the greatest influence that an engineer can have on the ultimate success of a project often occurs at the earliest stages of planning, when the broadest decisions having the most impact are made, and during construction, when the contractor is “on the clock.”

Examples of where structural engineers can significantly contribute to the success of a project in the pre-design phase are: • Building site location, orientation and massing • Simplification of construction methods yielding reduced construction schedules • Foundation systems, particularly on difficult sites • System selection and constructability, resulting in more efficient use of materials • Initial costs versus long-term costs • Ease of repair after catastrophic events • Interpretation of codes, standards and regulations • Setting of the design schedule Opportunities once the design process is complete include: • Time through plan review • Avoidance of delays in the construction schedule • Minimizing the cost of change orders • Minimizing the number of RFIs during construction • Involvement in construction means and methods In this incentive-based arrangement, the engineer would be rewarded for superior advice and counsel, innovation, schedule control, and construction cost control, all of which create value for the client. It will not be for every project or client, and the engineer will not receive any additional compensation unless he identifies and negotiates such work in his proposal and is able to effectively communicate why this compensation is in the interests of both the engineer and the owner. The engineer

will need to approach the client with a different mind-set, starting first with a discussion of the scope of value, well in advance of a scope of work, if such a scope is required at all.

In each service area targeted for incentive compensation, a benchmark target for a “typical job” would need to be established before the start of the project, with incentive-based compensation linked to the savings or value achieved in each area. A very aggressive engineer with a greater appetite and tolerance for risk might be willing to create a deduct amount for targets not met, and a potential larger add amount for targets met in excess.

The success of this approach will depend on finding the right clients (typically experienced and knowledgeable ones) that understand that they only get so much from the market price of basic services and that there must be ways to do better. Of course the engineer will need to do a good job of marketing and effective communication too, with facts correlated to metrics that the owner understands to back up their argument. Other team members, including the architect, may need to join in the effort, since it may be difficult to incentive-price services to the owner without a team approach. The key

is to develop a continuous dialogue between engineer and client that focuses on issues and results and culminates in an arrangement or framework for compensation focusing on winwin results, rather than a dialogue that always returns to a detailed examination of work scope, hours, hourly rates, overhead costs, etc.

Some engineers have wrongly assumed that value-based compensation is nothing more than charging a higher lump sum fee for basic services under certain conditions or situations.

Perhaps they suspect that the client is not in a position to be too price sensitive, or has few other options. Some engineers also think that due to their perceived technical competence alone, or perhaps due to their “reputation” in the engineering community, they should be able to charge a value-based fee because the buildings they design are better buildings, without facts to back up the claim. These engineers are correct in that the ability to extract more fee on these bases is part of value-based compensation, but is actually only a very small part, with a limited upside and a potentially significant downside, if a valued client suspects they are being taken advantage of. In the long run, the market will adjust and eliminate such increased fees. The

best applications of value-based compensation lie elsewhere and create potential win-win situations for clients and engineers alike.

Perhaps the most valuable thing we can do for our profession is to start a serious dialogue about value-based compensation, what it means and doesn’t mean, and how to effectively achieve it so that a paradigm shift for the industry can begin. The Council of American Structural Engineers (CASE) is the premiere organization for promoting excellence in structural engineering business practices and risk management, and CASE member firms volunteer their time, experience, and expertise to develop guidelines, tools and publications to assist our profession in improving business practices. If you desire to improve the structural engineering profession and are interested in contributing to the advancement of your profession, contact CASE, an ACEC Coalition.▪ John Dal Pino, S.E., is a Senior Principal in the San Francisco office of Degenkolb Engineers. John is a member of STRUCTURE’s Editorial Board and can be reached at jdalpino@degenkolb.com.

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Phone: 816-896-4266 Email: pschmidt@halfenusa.com Web: www.halfenusa.com Product: Halfen Anchor Channel Description: Halfen is a global leader in design and manufacturing of anchor systems for concrete. Hot rolled anchor channels for edge or top of slab transfer high loads while also providing field adjustability.

Custom anchors are available for special corners and thin slab conditions.

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Hardy Frame

Phone: 800-754-3030 Email: dlopp@mii.com Web: www.hardyframe.com Product: Hardy Frame Shear Walls Description: Hardy Frame now offers pre-engineered anchorage solutions that drastically reduce the large pad footings that can be associated with pre-fabricated Shear Wall Panels; standard details are available for inclusion with plan submittals.

Heckmann Building Products, Inc.

Phone: 800-621-4140 Email: info@heckmannanchors.com Web: www.heckmannanchors.com Product: Pos-I-Tie® ThermalClip® Description: This new break-through in masonry construction adds thermal-break technology to the Original Pos-I-Tie Veneer Anchoring System!

Dramatically decrease the amount of thermal conductivity from exterior walls to the backup. The high strength proprietary composite resin has a very high UL 94 V-0 fire rating.

Hilti, Inc.

Phone: 800-879-8000 Email: us-sales@hilti.com Web: www.us.Hilti.com Product: Hilti Mechanical and Adhesive Anchors Description: Hilti Mechanical Anchors including HDA, Kwik Bolt-TZ and Kwik HUS-EZ. Hilti Adhesive Anchors including HY-150 MAX-SD and RE 500-SD.

Hubbell Power Systems, Inc. – CHANCE

Phone: 855-477-2121 Email: civilconstruction@hubbell.com Web: www.abchance.com Product: Helical Anchors Description: A helical anchor/pile is a segmented deep foundation system with helical bearing plates welded to a central steel shaft. Load is transferred from the shaft to the soil through these bearing plates.

IES, Inc.

Phone: 800-707-0816 Email: sales@iesweb.com Web: www.iesweb.com Product: IES VisualAnalysis Description: VisualAnalysis offers ACI Anchor Design checks with the base plate design feature included in VAConnect. Use VisualAnalysis for a wide variety of analysis and design projects. It is simple, productive and versatile.

Integrity Software, Inc.

Phone: 512-372-8991 Email: sales@softwaremetering.com Web: www.softwaremetering.com Product: SofTrack Description: Saves money by accurately controlling usage all Bentley® applications. SofTrack’s solution is unique because it tracks usage by the Bentley Product ID code(s) activated during application usage including those activated by MDL applications.

Version and Feature Strings set by the Municipal License Administrator are also tracked.

continued on next page

ANCHORING GUIDE

Anchor Bolts, Concrete, Façade, Geotechnical, Masonry, Post-Tensioning, Reinforcing and Utility Anchors, and General Hardware & Ties

ITW Red Head

Powers Fasteners

Kelken Construction Systems

Product: Powers Design Assist (PDA) Anchor Software Description: Enables users to input technical data into a dynamic model environment to specify anchors.

PDA-360 is a FREE online version of our popular anchor design software. Powerful calculations with fast, detailed results. Works with any popular internet browser or mobile device.

Phone: 630-848-5611 Email: marketing@itwccna.com Web: www.itw-redhead.com Product: C6+ High Strength Structural Epoxy Description: The new Epcon C6+, high strength structural epoxy, delivers 35% higher average bond strength and has the highest tension performance in submerged applications based on side-by-side pull tests. Recent testing indicates it can deliver more than a 27% improvement in bond strength than the next highest-rated brand.

Phone: 732-416-6730 Email: dick@kelken.com Web: www.kelken.com Product: Keligrout Anchor Systems Description: Structural high strength polyester anchoring system.

Malcolm Drilling Co., Inc.

Phone: 985-807-6666 Email: kirk.reimer@sbdinc.com Web: www.powers.com Product: Mechanical and Adhesive Anchoring Description: Approved Mechanical Anchors including SD1, SD2, SD4, SD6, PowerBolt+, WedgeBolt+, Snake, Vertigo+, and Atomic Undercut. Powers Adhesive Anchors - Pure110+, PE1000, and AC100.

RISA Technologies

Phone: 253-395-3300 Email: jstarcevich@malcolmdrilling.com Web: www.malcolmdrilling.com Product: Geotechnical Construction Description: Malcolm Drilling, the premier geotechnical specialty contractor in the United States, constructing deep foundations and earth retention systems, including permanent ground anchors, tieback & tiedown anchors, soilnailing, Ground Improvement, and construction dewatering.

Phone: 949-951-5815 Email: info@risa.com Web: www.risa.com Product: RISABase Description: When accuracy counts, RISABase delivers. RISABase uses an automated finite element solution to provide exact bearing pressures, plate stresses, and anchor bolt pull out capacities, eliminating the guess work of hand methods. Define bi-axial loads and eccentric column locations.

Choose from several connection types and specify custom bolt locations.

All Resource Guides and Updates for the 2015 Editorial Calendars are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

S-FRAME Software Inc.

Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: S-FOUNDATION Description: Quickly design, analyze and detail your structure’s foundations with a complete foundation management solution. Run as a stand-alone application, or utilize S-FRAME Analysis’ powerful 2-way integration links for a detailed soil-structure interaction study. S-FOUNDATION automatically manages the meshed foundation model and includes powerful Revit and Tekla BIM links.

Product: S-CONCRETE Description: Displays instantaneous results as you optimize, and design reinforced concrete walls, beams and columns or automates your workflow by checking thousands of concrete section designs in one run. With comprehensive ACI1 318-11 design code support, S-CONCRETE produces detailed reports that include clause references, intermediate results and diagrams.

Simpson Strong-Tie

Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: AT-XP®, SET-XP® and ET-HP® Description: These anchoring adhesives have been tested in accordance with updated requirements of ICC-ES AC308 for IBC 2012 recognition, and submitted to code body agencies as mandated.

Qualified for threaded rod/rebar in cracked/uncracked concrete and masonry applications. Our Anchor Designer™ software supports post-installed adhesive and mechanical anchor solutions.

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2014 Annual Trade Show in Print The definitive buyers’ guide for the practicing structural engineer Get your submissions in soon for this year’s issue! Visit www.STRUCTUREmag.org.

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Does Your Firm Understand The 2012 Building Code Requirements For Concrete Anchoring?

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ANCHORING GUIDE Standards Design Group, Inc.

Phone: 800-366-5585 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Window Glass Design 5 Description: WGD5 performs all required calculations to design window glass according to ASTM E 1300-09. WGD5 also performs window glass design using ASTM E 1300 02/03/04, ASTM E 1300-98/00 and ASTM E 1300-94. GANA endorses WGD5 as best tool available in designing window glass to resist wind and long-term loadings.

Strand7 Pty Ltd

Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: An advanced FEA system used worldwide by engineers for a wide range of structural analysis applications. It comprises preprocessing, a complete set of solvers and post processing. It includes a range of material models suitable for the analysis of soil allowing for simulations of the complete soil/ structure system.

Anchor Bolts, Concrete, Façade, Geotechnical, Masonry, Post-Tensioning, Reinforcing and Utility Anchors, and General Hardware & Ties

Tekla

Phone: 770-426-5105 Email: info.us@tekla.com Web: www.tekla.com Product: Fastrak Description: Software for designing structural steel buildings using a single model, also provides an integrated design of anchor bolts.

Product: Tedds Description: Automating your everyday structural designs, Tedds’ broad library includes anchor bolt design per ACI 318 Appendix D. The calculation includes comprehensive checks for tensile and shear failure of anchors and is available as part of a free trial on the website.

Timberlinx

Phone: 877-900-3111 Email: timberlinx@rogers.com Web: www.timberlinx.com Product: Timberlinx Description: A connection tube, inserted equally in both members of the joint and linked by two expanding cross pins. Wood/wood, wood/concrete, wood/steel connectors.

USP Structural Connectors

Phone: 952-898-8702 Email: sbell@mii.com Web: www.uspconnectors.com Product: USP Epoxy Solutions Description: Offering five epoxies, with applications from heavy-industrial/commercial to household DIY projects: CIA-GEL 7000-C™ is for seismic/high wind, cracked concrete; CIA-GEL 7000™ is for masonry and fully grouted CMUs; CIA-EA™ is for fast-cure all-weather anchoring; CIA-GEL 6000-GP™ is a general purpose quickcure; Miracle Bond™ is for DIY household projects.

Williams Form Engineering Corp.

Phone: 616-866-0815 Email: williams@williamsform.com Web: www.williamsform.com Product: Anchor Systems Description: Williams Form Engineering Corporation has been providing threaded steel bars and accessories for rock anchors, soil anchors, high capacity concrete anchors, micro piles, tie rods, tie backs, strand anchors, hollow bar anchors, post tensioning systems, and concrete forming hardware systems in the construction industry for over 90 years.

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award winners and outstanding projects

Spotlight

Reaching for the Sky

By Chris Ramseyer, Ph.D., P.E. and Hans Butzer, AIA, LEED AP SXL was an Award Winner for the SkyDance Bridge project in the 2013 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Bridges & Transportation Structures).

M

ayor Cornett described this project as a competition to design a pedestrian bridge of iconic status to serve as a symbol of Oklahoma City. The $6.8M design would literally and figuratively bridge the north and south portions of a new city park, and connect the past with the future of Oklahoma City to travelers of I-40 (formerly Route 66). The result is SkyDance Bridge, a 380-foot-long pedestrian bridge and 197-foot-tall sculpture that spans Interstate 40 near Harvey Avenue south of downtown.

The flight of the Scissor tailed Flycatcher, Oklahoma’s State Bird, perhaps best evokes the shaping forces of the Oklahoma wind.

This “skydance” of spring is a V-shaped flight drawn against the sky, marking its signature mating dance. The bird’s distinctive tail feathers demonstrate an evolved necessity to navigate swirling prairie winds. SkyDance Bridge’s soaring architecture was inspired by Oklahoma’s state bird, and reflects the cosmopolitan and vibrant qualities of Oklahoma City.

From October 2008 until June 2011, the design of the bridge evolved, continually adapting to a series of changes including: which design code to design with, changes to governing structural load criteria, dramatic changes to funding sources, a complex client consisting of local, state and federal government agencies and, as time progressed, an accelerated construction schedule.

The architectural design challenges included a true 3-dimensional design which was required due to the lack of symmetry of any element.

The 3-D design model was populated with individually unique feathers and supports that were created by an algorithm. None of the feathers, clips or supports were drawn on paper.

A totally electronic submission of drawings was required for the individually unique feathers and the individually unique support elements.

The structural design challenges included the fact that no line of symmetry exists in any of the elements. Even the wings have a slight twist or rotation along their length. The 3-D design required that the Architectural and structural

model matched not just closely, but exactly.

Accurate construction of the SkyDance structural geometry required the use of the structural engineer’s electronic files to ensure fabrication tolerances. Due to its complexity, SkyDance was modeled with two different structural engineering programs to verify the results. To make it more interesting, the bridge is designed under the AASHTO code while the SkyDance structure is designed under the International Building Code (IBC). This meant that the center pier had to meet the requirements of both codes. Due to the height and geometry of SkyDance, the center pier has a very small lateral deflection requirement. But, due to the highway alignment, this pier has a maximum width of 4 feet.

To solve this problem, a collection of drilled shafts support the pier, which was designed with post tensioning to help limit the deflections. The design of the concrete filled steel feet and the cold formed steel support elements draw upon research conducted at Oklahoma University’s (OU) Fears Structural Engineering Laboratory by Dr. Ramseyer. Aeroelastic issues (Vortex shedding, flutter, galloping and divergence) had to be addressed. Due to its location over a major highway, FHWA & the Oklahoma DOT required that the SkyDance structure be designed to meet or exceed the fatigue threshold.

The fabrication and construction challenges included the requirement that all fabrication and erection had to be completed in 156 days from the day bids were let. Jigs were required for fabrication of all elements to ensure fit up in the field.

These jigs were built using surveying equipment to a precision of 0.01 inch on elements up to 150 feet long. Two of the HSS pipe connections in the SkyDance structure were connecting 11 and 13 elements at each node. The fabricator proposed a change to this highly complex connection, which was approved by the Architects and Structural Engineers as an improvement over the earlier design. These are the cruciform “star” nodes directly over the walkway.

The core of these connections consists of solid steel, 14-inch in diameter and 14- and 16-inch thick. Due to accurate design and fabrication, no field modification of any steel element was required. 665 feathers, 1330 clips and 10,640 uniquely located holes align perfectly, with no field modifications. SkyDance was fabricated in 6 pieces (2 wings, 2 legs, 1 body and 1 tail) to minimize field welding. Only 15 welded connections needed to be made in the field

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Courtesy of Simon Hurst.

The designers were equally as concerned with crafting a comfortable urban walkway as they were with forging an iconic regional landmark. The thick wooden deck of the bridge deadens the roar of the interstate below and forms a pedestrian-scaled bird’s nest dotted with benches. Vertical notches in the wood railing provide small children with protected lookouts from which to watch cars.

The bridge design and structural engineering was performed by S-X-L. Civil engineering was performed by MKEC engineering. SXL is a collaboration of architects, engineers, university professors and designers that include 5 architects and 2 engineers: • Architects: Hans Butzer, Stan Carroll, Jeremy Gardner, Ken Fitzsimmons and David Wanzer • Engineers: Chris Ramseyer and Laurent Massenat Manhattan Road and Bridge was the general contractor. W&W Steel fabricated the structural steel and Swanda Brothers fabricated the stainless steel feathers.

The SkyDance Bridge has become an important teaching element for Professors Butzer, Carroll and Dr. Ramseyer’s. Several OU classes from both engineering and architecture visited the fabrication and job site during the construction phase. Dr. Ramseyer’s has made SkyDance a central element of his , with his engineering students studying the structural analysis, steel design and bridge engineering design aspects along with fabrication and erection issues.▪ Chris Ramseyer, Ph.D., P.E. (ramseyer@ou.edu), is an Associate Professor at the University of Oklahoma and the Director of the Donald G. Fears Structural Engineering Laboratory. He served as lead structural engineer for SkyDance Bridge.

Hans Butzer, AIA, LEED AP (butzer@ou.edu), is Director of Architecture and A. Blaine Imel, Jr. Professor, Mabrey Presidential Professor of Architecture and Urban Design at the University of Oklahoma, College of Architecture.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

The 2014 NCSEA Special Awards Honorees

The following awards will be presented at the Awards Banquet on September 19 during the 2014 NCSEA Annual Conference in New Orleans. For more information on the Annual Conference, see pages 38 – 41.

The James M. Delahay Award The James M. Delahay Award is presented at the recommendation of the NCSEA Code Advisory Committee to recognize outstanding individual contributions towards the development of building codes and standards. It is given in the spirit of its namesake, a person who made a long and lasting contribution to the code development process.

James R. Cagley, P.E., S.E. James R. Cagley is a licensed engineer in Maryland and 32 other jurisdictions, including California where he is a licensed Structural Engineer. He is a past President of the American Concrete Institute (ACI) and a past-Chairman of the ACI 318 Standard Building Code Committee. He is presently a member of the ASCE/ SEI 7 Committee “Minimum Design Loads for Buildings and Other Structures” and is past chairman of the Task Committee on Live Loads. Cagley was one of the founders and the first President of NCSEA.

James O. Malley, S.E. James O. Malley is a Senior Principal with Degenkolb Engineers, with over 30 years of experience in the seismic design, evaluation and rehabilitation of building structures. He was responsible for the analytical and testing investigations performed as part of the SAC Steel Project in response to the Northridge earthquake damage. He is Chair of AISC’s Seismic Subcommittee, was named the 2010 T.R. Higgins Lectureship Award winner, and was given the AISC Lifetime Achievement Award in 2012.

Jim has served as a member of the SEAONC and SEAOC Board of Directors and was President of SEAONC in 2000-2001 and SEAOC in 2003-2004. He was named a SEAOC Fellow in 2007 and an Honorary Member of SEAONC in 2014. He also was a member of the Board of Directors of NCSEA, serving as President in 2011, and he currently serves as a member of the Board of Directors of EERI.

The NCSEA Service Award The NCSEA Service Award is presented to an individual or individuals who have worked for the betterment of NCSEA to a degree that is beyond the norm of volunteerism. It is given to someone who has made a clear and indisputable contribution to the organization and therefore to the profession.

Susan Jorgensen, P.E. Susan Jorgensen is the President of Prairie Smoke Engineering, LLC, in Highlands Ranch, CO. She was previously Senior Structural Project Engineer, Vice President, Managing Principal, and Director of Operations for the Denver office of LEO A DALY. Before moving to Colorado to open the satellite office, she served as a lead structural engineer in the LEO A DALY Omaha office for 10 years. Prior to joining LEO A DALY in 1997, she gained structural engineering design experience working with consulting firms in Colorado, North Dakota, and South Dakota. Susan is active in NCSEA as the Chair of the Licensure Committee and is also a candidate for the NCSEA Board of Directors.

The Robert Cornforth Award This award is presented to an individual for exceptional dedication and exemplary service to a Member Organization and to the profession. Nominees are submitted to the NCSEA Board by the Member Organizations.

Dustin Cole, P.E., S.E. Dustin Cole is the Director of Engineering for NCI Building Systems, a metal building manufacturer with thirteen engineering locations across the United States and Canada. Dustin is a member of the American Society of Civil Engineers and has been active with the Oklahoma Structural Engineers Association (OSEA) for many years. Serving as OSEA’s Executive Director since 2000, Dustin has performed the duties of secretary and treasurer while providing ongoing assistance to OSEA’s officers as they prepare for monthly meetings and semiannual conferences. Dustin is licensed as a Professional Engineer in all fifty states, the District of Columbia, Puerto Rico, and five Canadian provinces including licensure as a Structural Engineer in five states. Dustin serves on the Metal Building Manufacturers Association (MBMA) Technical Committee and is currently chair of their inspection handbook task group.

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The Susan M. Frey NCSEA Educator Award is presented to an individual who has a genuine interest in, and extraordinary talent for, effective instruction for practicing structural engineers. The award was established to honor the memory of Sue Frey, one of NCSEA’s finest instructors, who passed away in May, 2013. Winners of this award will present a special webinar to NCSEA members at a deeply discounted cost, as a continuing legacy to Sue Frey.

Timothy Mays, Ph.D., P.E. Timothy Mays is President of SE/ES and an Associate Professor of Civil Engineering at The Citadel in Charleston, SC. He previously served as Executive Director of the Structural Engineers Associations of South Carolina and North Carolina and personally spearheaded the development of both organizations. Tim currently serves as NCSEA Publications Committee Chairman. He has received two national teaching awards (ASCE and NSPE) and both national (NSF) and regional (ASEE) awards for outstanding research. He is the recipient of the 2009 NCSEA Service Award and the 2008 Outstanding Young Alumni Award from Virginia Tech. Tim has been recognized for outstanding design work on high profile structures in the southeastern United States. He sits on several code writing committees, teaches courses on NCSEA publications, and has presented at NCSEA Conferences. He also instructs, and has received some of the highest instructor evaluations from students of, NCSEA’s SE Exam Review Course.

NCSEA News

The Susan M. Frey NCSEA Educator Award

NCSEA Awards Eight Young Member Scholarships to Annual Conference

Melody Tan A Structural Engineer with Murray Engineering in New York, she is a member of the Structural Engineers Association of New York and a member of their University Outreach subcommittee.

Elizabeth LaCrosse An Associate II Engineer with Wiss, Janney, Elstner Associates in Chicago, she is a member of the Structural Engineers Association of Illinois and is the co-chair of their Young Engineers Committee.

James Newhall A Structural Designer at Caruso Turley Scott in Tempe, Arizona, he is a member of the Structural Engineers Association of Arizona and a member of the NCSEA Young Member Group Support Committee.

John Leary A Structural Engineer with Bowman, Barrett & Associates in Chicago, he is a member of the Structural Engineers Association of Illinois and is an active volunteer with Engineers Without Borders.

October 16, 2014

Overview of Codes Affecting Midrise Construction & Special Design Considerations Michelle Kam-Biron, P.E., S.E., SECB, M.ASCE, Director of Education, American Wood Council

October 23, 2014

Structural Glass Andrea Hektor, P.E., S.E., Associate, KPFF, Portland, OR

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These courses will award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program. Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern. NCSEA offers three options for NCSEA webinar registration: Ala Carte, Flex-Plan, and Yearly Subscription. Visit www.ncsea.com for more information or call 312-649-4600.

ASS

More information on the NCSEA Annual Conference can be found on pages 38 – 41.

NCSEA Webinars

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Tony Nguyen A Bridge Engineering Intern at HNTB in Seattle and a graduate student, he is a member of the Structural Engineering Association of Washington and active in their Earthquake Engineers Committee and Disaster Preparedness & Response Committee.

Jera Schlotthauer A Structural Engineer, EIT II with Martin/Martin Wyoming in Cheyenne, she is a member of the Structural Engineers Association of Wyoming and a member of the NCSEA Young Member Group Support Committee.

STRUCTU

Michael Murphy An Engineer with Thornton Tomasetti in Chicago, he is a member of the Structural Engineers Association of Illinois and serves as the social media chair of their Young Engineers Committee.

News from the National Council of Structural Engineers Associations

Shaina Saporta A Senior Engineer with Arup in New York, she is a member of the Structural Engineers Association of New York.

For the third year, NCSEA awarded Young Member Scholarships for the NCSEA Annual Conference. The scholarship competition was open to any current member of an NCSEA Member Organization who was under 36 years old.

Applicants were asked to compose an essay or video answering one of three questions, as well as write a brief essay upon attending the Annual Conference. Level one scholarships were for new scholarship winners and included registration and a travel stipend. Level two was for previous winners, which included registration only. The winners of this year’s scholarships are:

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ASCE-171 ETS2015 CONFERENCE WEB/EMAIL BANNERS

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Electrical Transmission & Substation Structures Conference 2015 Call for Abstracts Closes September 10, 2014 The State-of-the-Industry Forum for Transmission and Substation Engineers • Discover Technical Knowledge • Hear Project Case Studies • Find Real-World Solutions • Watch Vendors Demonstrate Products and Services Now accepting abstracts for consideration, case studies strongly encouraged. A poster session format may also be provided.

The ASCE/SEI Electrical Transmission & Substation Structures Conference is recognized as the must-attend conference that focuses specifically on transmission line and substation

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ELECTRICAL TRANSMISSION & SUBSTATION STRUCTURES CONFERENCE 2015

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structures, and foundation construction issues. This event – for ELECTRICAL TRANSMISSION & SUBSTATION STRUCTURES utilities, suppliers, CONFERENCE 2015 contractors, and consultants – offers an ideal | setting for learning and networking.

Grid Modernization – Technical Challenges & Innovative Solutions Visit the SEI website at www.asce.org/SEI for more information and to submit your proposal. All proposals are due ELECTRICAL TRANSMISSION September 10, 2014. & SUBSTATION STRUCTURES Branson, Missouri

September 27- October 1

CONFERENCE 2015

| September 27- October 1

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Summer Special on Live Webinars

Savings on On-demand Webinar Packages

Individual members may receive the special reduced rate of $99 for any live webinars taking place through December 31, 2014.

Register at www.asce.org/Continuing-Education/Webinars/ Live-Webinars/ by September 30 to lock in the special rate.

Earn Your PDHs Online – Anytime, Anywhere

Second ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures December 10 –12, 2015 Hyatt Regency San Francisco Call for abstracts and session proposals will open in Fall of 2014.

Purchase a Package of Your Choice and Save up to 50%! ASCE’s Webinar Packages provide you the training you need in a convenient and cost-effective way. Recorded from our most popular Live Webinars, ASCE’s On-Demand Webinar Packages are presented by the best instructors in engineering. See the packages available at www.asce.org/Continuing-Education/ Distance-Learning/On-Demand-Webinar-Packages/.

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 Paul Sgambati at psgambati@asce.org.

Search for New SEI Director The American Society of Civil Engineers (ASCE) is currently searching for a Director to manage the day to day and strategic operations of ASCE’s structural engineering specialty institute, SEI, creating value added products and services, and ensuring its programs are responsive to the needs of its members and consistent with the overall mission and vision of the Institute.

Responsibilities include: managing overall operations of the institute; developing staff; establishing budgets; developing and implementing programs in conjunction with institute leadership – i.e. conferences, publications, and standards; managing technical, educational, professional activities and facilitating committee work in those areas; developing and implementing STRUCTURE magazine

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strategic plan with Board of Governors’ approval; and networking with other similarly aligned organizations and identifying opportunities to partner.

Ideal candidates will have a degree in civil engineering plus an advanced degree. An advanced degree in structural engineering is highly desirable. Candidates must possess or be able to shortly become a registered professional engineer. Ten to fifteen years’ experience in structural engineering with demonstrably increasing responsibility is required. Association management experience would be considered a plus but is not required; however, candidates are expected to be familiar with the many products and activities developed by SEI. See the ASCE website at http://asce.applicantpro.com/jobs/ for more information.

September 2014

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The O. H. Ammann Research Fellowship in Structural Engineering is awarded annually to a member or members of ASCE or SEI for the purpose of encouraging the creation of new knowledge in the field of structural design and construction. All members or applicants for membership are eligible.

Applicants will submit a description of their research, an essay about why they chose to become a structural engineer, and their academic transcripts.

This fellowship award is at least $5,000 and can be up to $10,000. The deadline for 2015 Ammann applications is | November 1, 2014.

For more information and to fill out the on-line application the SEI website at: www.asce.org/SEI. ANSMISSION & visit SUBSTATION

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ASCE is seeking members to serve on a committee for the development of a national consensus standard on estimating wind speeds in tornadoes and other windstorms. The intent of the standard is to develop standardized methods for estimating the intensity of tornadoes and other severe wind storms. Users of the standard could include, but are not limited to, wind and structural and forensic engineers, meteorologists, climatologists, forest biologists, risk analysts, emergency managers, building and infrastructure designers, and the media. The content of the standard would include improvements to the existing damagebased Enhanced Fujita (EF) scale to address known problems and limitations, and incorporation of additional methods to estimate intensity such as those based on radar measurements, treefall pattern analysis, and forensic engineering analysis, and archival of the data used for estimating wind speeds. Interested parties may submit an online standards committee application at www.asce.org/codes-standards/applicationform/. For more information, please contact James Neckel, Codes and Standards Coordinator at jneckel@asce.org.

Call for 2015 SEI/ASCE Award Nominations Nominations are being sought for the 2015 SEI and ASCE Structural Awards. The objective of the Awards program is to advance the engineering profession by emphasizing exceptionally meritorious achievement, so this is an opportunity to recognize colleagues who are worthy of this honor. Nomination deadlines begin October 1, 2014, with most deadlines falling on November 1, 2014. Visit the ASCE Awards and Honors page at www.asce.org/leadership-and-management/awards/ for more information and nomination procedures.

Geotechnical & Structural Engineering Congress 2016 February 14-17, 2016 Phoenix, AZ Start working on your abstract and session proposals early for submission this fall.

We are seeking dynamic sessions and presentations on topics addressing both Geotechnical and Structural Engineering issues. Final papers are optional and will not be peer reviewed.

Consider submitting either session proposals or single abstracts related to the topics and subtopics of interest to both professions.

A full list of topics and subtopics, and a list of GI and SEI Committees for collaboration, are on the conference website at www.asce.org/geoseicongress.

The 2016 congress will feature a total of 15 concurrent tracks: 5 tracks will be on traditional GI topics, 5 tracks on traditional SEI topics, and 5 tracks on joint topics. In addition, we will be offering interactive poster presentations within these tracks.

STRUCTURE magazine

Key Dates: Open call for abstracts and sessions – October 15, 2014 Close call for abstracts and session – April 7, 2015 (no extensions) Visit the joint conference website at www.asce.org/geoseicongress for more information.

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The Newsletter of the Structural Engineering Institute of ASCE

Students are invited to apply for valuable Society Scholarships and Society Fellowships for Fall 2015. Two scholarships uniquely serving structural engineering students are: Eugene C. Figg, Jr. Civil Engineering Scholarship and Y.C. Yang Civil Engineering Scholarship. Other opportunities for consideration are: Lawrence W. and Francis W. Cox Scholarship, John Lenard Civil Engineering Scholarship, Robert B. B. and Josephine N. Moorman Scholarship, and Samuel Fletcher Tapman ASCE Student Chapter Scholarship. Graduate students may apply for: Trent R. Dames and William W. Moore Fellowship, Freeman Fellowship, J. Waldo Smith Hydraulic Fellowship, and Arthur S. Tuttle Fellowship. Complete applications, including current transcripts, are due February 10, 2015. See the ASCE website at www.asce.org/Student-Organizations/Scholarships-andFellowships/Scholarships—-Fellowships/ for more information, or contact awards@asce.org.

New Standard for Estimating Wind Speeds in Tornadoes and Other Windstorms

Structural Columns

2015 Ammann Fellowship Call for Nominations

ELECTRICAL TRANSMISSION & SUBSTATION STRUCTURES CONFERENCE 2015

2014 CASE Best Sellers Purchase Your Copy Today!

The Newsletter of the Council of American Structural Engineers

Contract Documents #1: An Agreement for the Provision of Limited Professional Services This is a sample agreement for small projects or investigations of limited scope and time duration. It contains the essentials of a good agreement including scope of services, fee arrangement and terms and conditions. #2: An Agreement between Client and Structural Engineer of Record (SER) for Professional Services The purpose of this document is to provide a sample agreement for providing structural engineering services directly to a Client.

It is not intended to be used when the Structural Engineer of Record is the Prime Design Professional (See CASE Document 13).

This is written as an Agreement and can be reproduced on the firm’s letterhead, if desired. This Agreement is unique in that the Summary of Services is presented in matrix form as Exhibit A, and the desired scope of services can be defined by simply checking the included or not included column. A list of Terms and Conditions is included in Exhibit B. The Summary of Services matrix and Terms and Conditions are consistent with the National Practice Guidelines for the Structural Engineer of Record. #11: An Agreement between Structural Engineer of Record (SER) and Contractor for Transfer of CAD Files on Electronic Media The purpose of this document is to provide an agreement for the SER to use when transferring digital data (CAD or BIM) files to the contractor.

Traditionally, the use of reproductions of the SER’s drawings by the contractor to prepare shop drawings was not recommended

by CASE due to potential liability concerns. However, the efficiencies of production, coordination, and communication through electronic media, more specifically CAD and BIM, are undeniable and file sharing has become the industry standard.

CASE in Point

National Practice Guidelines 962: National Practice Guidelines for the Structural Engineer of Record (SER) The purpose of this document is to give firms and their employees a guide for establishing Consulting Structural Engineering Services, and to provide a basis for dealing with Clients generally and negotiating Contracts in particular. Since the Structural Engineer of Record (SER) is normally a member of a multidiscipline design team, this document describes the relationships that customarily exist between the SER and the other team members, especially the team leader. Further, this Guideline promotes an enhanced Quality of Professional Consulting Structural Engineering Services while also providing a basis for negotiating a fair and reasonable compensation.

962-D: A Guideline Addressing Coordination and Completeness of Structural Construction Documents The guidelines presented in this document will assist not only the Structural Engineer of Record (SER) but also everyone involved STRUCTURE magazine

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with building design and construction in improving the process by which the owner is provided with a successfully completed project. Their intent is to help the practicing structural engineer understand the importance of preparing coordinated and complete construction documents, and to provide guidance and direction toward achieving that goal.

These guidelines focus on the degree of completeness required in the structural construction documents (“Documents”) to achieve a “successfully completed project” and on the communication and coordination required to reach that goal. They do not attempt to encompass the details of engineering design; rather, they provide a framework for the SER to develop a quality management process.

Currently, the coordination and completeness of Documents varies substantially within the structural engineering profession and among the various professional disciplines comprising the design team. The SER’s goal should be meeting both the owner’s and the contractor’s needs by producing a complete and coordinated set of Documents. Owners and contractors generally understand that some changes to the Documents will occur, because they realize that no set of Documents is perfect. The SER must focus on completeness, coordination, constructability, and the reduction of errors in order to minimize potential changes (See also Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents).

962-G: Guidelines for Performing Project Specific Peer Reviews on Structural Projects Increasing complexity of structural design and code requirements, compressed schedules, and financial pressures are among many factors that have prompted the greater frequency of peer review of structural engineering projects. The peer review of a project by a qualified third party is intended to result in an improved project with less risk to all parties involved, including the engineer, owner, and contractor.

Many aspects of the peer review process are important to establish prior to the start of the review, in order to ensure that the desired outcome is achieved. These items include the specific goals, scope and effort, the required documentation, the qualifications and independence of the peer reviewer, the process for the resolution of differences, the schedule and the fee. The intention of these guidelines is to increase awareness of such issues, assist in establishing a framework for the review and improve the process for all interested parties.

Risk Management Toolkits 1-1: Create a Culture for Managing Risks and Preventing Claims This tool includes a story board and role playing guide to involve your staff in the risk management discussion. It also includes sample commitment statements for your firm to buy into the process.

5-1: A Guide to the Practice of Structural Engineering Intended to teach structural engineers the business of being a consulting structural engineer and things they may not have learned in college. While the target audience for this tool is September 2014

These publications, along with other CASE documents, are available for purchase at www.booksforengineers.com.

9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents The Tool Kit Committee has repackaged a previously released CASE document with upgrades and additions! A summary test and answer key have been added to the Appendix of the original document. It is recommended that engineers read this Guideline and take the test at the end of the document.

More experienced engineers should then sit down with the engineers to go over the various subjects and answer any questions. The CASE Drawing Review Checklist will be a valuable tool to take away from this experience and implement into normal office use

WANTED

CASE in Point

the young engineer with 0-3 years of experience, it also serves as a useful reminder for engineers of any age or experience.

The Guide also contains a test at the end of the document to measure how much was learned and retained. Other sections deal with getting and starting projects, schematic design, design development, construction documents, third party review, contractor selection/project pricing/delivery methods, construction administration, project accounting and billing, and professional ethics.

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

We have two committees ready for your service: • Contracts Committee: Responsible for developing and maintaining contracts to assist practicing engineers with 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.

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!

CASE Risk Management Convocation Headlines a Strong Lineup of Risk Management Sessions at ACEC Fall Conference You will not want to miss these additional important risk management sessions: Climate-Smart Engineering Approaches to Disaster Risk Stephen Long, The Nature Conservancy The CASE Convocation offers a full day of sessions on Thursday, October 23, dedicated to best-practice structural engineering: 6:30 am Addressing the Hidden Risks in Today’s Design Contracts Brian Stewart, Collins, Collins, Muir & Stewart; James Schwartz, Beazley; Rob Hughes, Ames & Gough 10:30 am The Five Commandments of A&E Risk Dan Buelow, Willis A/E 2:30 pm Managing the Emerging and Enduring Risks of Professional Practice Karen Erger, Lockton Cos. 5:30 pm ACEC/Coalition Meet and Greet For more information and to register, http://conf.acec.org/conferences/fall2014/index.cfm.

STRUCTURE magazine

Case Study – Infrastructure Funding and Other Innovations in Asset Management Mike Baker, David Evans and Associates, Inc. Engineer-Led Design-Build – Simple, Safe & Profitable Mark Friedlander, Schiff Hardin The Conference also features: • General Session addresses by business strategist Erik Wahl, political analyst Charlie Cook and FERC Commissioner Tony Clark • Member Firm CEO panels on the nation’s booming energy markets and the 2015 business outlook • CEO roundtables • Exclusive CFO and CIO tracks • Numerous ACEC coalition, council, and forum events • Earn up to 21.75 PDHs

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CASE is a part of the American Council of Engineering Companies

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.

Structural Forum

opinions on topics of current importance to structural engineers

How Code Complexity Harms Our Profession Part 2

By Craig M. DeFriez, P.E., S.E.

I

n Part 1 of this article (July 2014), I examined the wind load provisions in ASCE 7-10 to illustrate how the everincreasing complexity of code provisions has negatively impacted our profession. In this second and final installment, I would like to take a look at where we have been as a profession in recent decades, and perhaps extrapolate where we are heading if current trends continue.

When I began my career in the early 1980s, the building code was a single volume. It included most of the provisions, equations, and methodologies needed to design a building of any material type. A few other reference books were necessary, such as the AISC Steel Construction Manual, which itself was only 1 inch thick rather than rivaling the size of the Las Vegas phone book. Per the 1988 Uniform Building Code, determining the wind pressures on a building was a very straightforward and understandable process, completely described in less than 3 pages and a few simple tables, as opposed to 113 pages in 6 chapters of ASCE 7-10. The same could be said for the seismic provisions, contained in less than 20 pages and a few tables, compared to 134 pages in ASCE 7-10. Loads were developed at service levels, there were only five basic load combinations, and most design was done using allowable stresses – a method still preferred by many engineers today when given the choice.

We were able to develop design forces quickly, using a few easily understood equations. We acquired an intuitive feel for structural behavior, because the methodology for developing loads and applying them to the design of systems and components was comprehensible to the human mind. This is no longer the case, considering the dozens of codes, commentaries, guides, and manuals to which structural engineers must now refer.

Unfortunately, we have allowed academia, code committees, and regulatory agencies to seduce us with the idea that – for the sake of (alleged) accuracy in analysis, refinement in design, and greater building safety – we must sacrifice intimacy with our craft.

Reasonable accuracy in analysis and design is important, but we must maintain some perspective and balance between theory and practice. The mandates of local building departments, actual field conditions, and varying construction practices often conflict with the level of analysis and design refinement to which we now routinely subject ourselves. A lot of buildings were designed using the simpler methods of the past, and most are still in service. Computers have become valuable tools in modern engineering practice, allowing us to design more complex structures than would have been possible even a few decades ago. No one disputes the value of such technology, but when the codes and standards become so complex and the design methodologies so intricate that we become almost totally dependent on computer software – not as a tool, but as a crutch – we are a step removed from truly comprehending what we are doing.

Several years ago, my son was enrolled in a civil engineering degree program and asked my advice about specializing in structural engineering. I told him that it is a demanding profession. The volume of knowledge that he will be expected to master is extensive. The professional license to practice is difficult to obtain. It is a constant struggle to adapt to new and sometimes unintelligible changes in code provisions and design methods every few years. Occasionally, we find out that previously adopted code provisions are flawed, only to be replaced by new and even more complex provisions, with the assurance that they are now “correct.” And, sometimes they are still wrong and are again modified in the very next code cycle.

I explained to my son that he would have to become nearly totally dependent on computer software to do his job. Designing a building has become more a matter of how adept you are at using a particular vendor’s program – each with its own peculiar idiosyncrasies and nuances – than any real understanding about the behavior of the structure or what constitutes good design practice. Much of

structural design has become a black box activity; most engineers today are unwilling or unable to wade through complex and confusing equations and methodologies to do basic design work, when they can simply input a few parameters into software developed by others and get an answer. It may not always be the right answer or the best answer, but it is an answer.

The undeniable evolution of complexity in code provisions and design methodologies increases the likelihood for misinterpretation and error, which may actually diminish the accuracy in design and safety for which we are striving. Structural engineering has often been characterized as both art and science, but it is not quantum physics, and we should not behave like it is. It is the application of fundamental principles of statics and mechanics of materials combined with experience and judgment to produce buildable and reasonably safe structures.

Can we honestly say that we can still wrap our brains around all of the provisions and methodologies contained in the current building code and referenced standards? We may soon be at a tipping point, if we are not already there. Will the structural engineers of the future practice the art and science of structural design with understanding, good judgment, and competence? Or will they be relegated to serving as technicians who simply use software to design buildings without having any real understanding of what the software is doing.

My son ultimately decided to specialize in water resources and environmental engineering, and is happily employed in that field. I cannot say that I blame him.▪ Craig M. DeFriez, P.E., S.E. (cmdefriez@yahoo.com), is a consulting structural engineer living in Carson City, Nevada. During his career he has had extensive experience in plan checking, peer reviews, and code interpretation and enforcement.

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

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September 2014

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