STRUCTURE magazine | April 2013 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

April 2013 Concrete Special Section: Steel Sector Looking Good

SEI Structures Congress Pittsburgh, Pennsylvania May 2 – 4

W. Gene Corley 1935 – 2013

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CONTENTS

FEATURES

April 2013

A Worthy Wager

By Jim O. Swenson, P.E., S.E. and Jason Black, P.E., S.E. Federal Center South Building 1202 is a state-of-the-art, high performance office space for the Seattle District Headquarters of the United States Army Corps of Engineers This showcase High Performance Green Building project included many innovative design features, the top of which was perhaps the largest use of a composite concrete and timber floor system in the United States.

SFPUC Headquarters Building

By Leo Panian, S.E. and Nick Bucci, S.E. The San Francisco Public Utilities Commission’s innovative headquarters set a new standard for high-performance structures when it opened in June 2012. The building is a showcase for a host of leading-edge sustainable design elements. The design of the structural system made key contributions in achieving this distinction.

Gene Corley

Steel Sector Looking Good By Larry Kahaner

STRUCTURE

With the U.S. economy improving slowly, and global economies booming in certain regions, those in the steel sector are optimistic about what lies ahead. The software industry is seeing improvements in sales, and the steel/construction industry backs up the optimism.

SEI Structures Congress Pittsburgh, Pennsylvania May 2 – 4

ON W. Gene Corley 1935 – 2013

THE

COVER

A Joint Publication of NCSEA | CASE | SEI

On March 1st, we learned of the passing of W. Gene Corley. In this photo, Dr. Corley investigates a piece of steel at the World Trade Center site. STRUCTURE magazine has never in its history put an individual’s picture on its cover. The death of Gene Corley warrants this occasion (Page 34). April 2013 Concrete

Like A Flight of Geese By John A. Mercer, P.E., SECB

9 Historic Structures

The Kahn System of Reinforced Concrete By Ryan Salmon, EIT and Meghan Elliott, P.E., Associate AIA

12 Engineer’s Notebook

Simplified Methods in Reinforced Concrete Design By Jerod G. Johnson, Ph.D., S.E.

14 Practical Solutions

Creating an Opening in Existing Floors

18 Technology

Using Software to Control Anchor Design By Marshall P. Carman, P.E., S.E.

23 Outside the Box

Space Structures Reach Siberia By Denis Gerasimov

47 Special Section

Steel Sector Looking Good

7 Editorial

By Dominick R. Pilla, P.E., C.E., S.E. and Xiaoli Tong, P.E.

On March 1st, the structural engineering community was saddened by the news of the passing of Dr. Gene Corley after a brief battle with cancer. A recognized industry leader, Dr. Corley was at the forefront of the structural engineering profession, and the development of building codes and standards.

Special Section:

COLUMNS

IN EVERY ISSUE 8 Advertiser Index

36 InSights Bridge Fatigue By Y. Edward Zhou, Ph.D., P.E.

38 Legal Perspectives

Can I Just Cross Out The Words “Payment In Full”? By Gail S. Kelley, P.E.

40 Education Issues

Socrates, How Is Engineering Knowledge Attained?

56 Resource Guide (Engineered Wood Products)

By Erik Anders Nelson, P.E., S.E.

42 Great Achievements Othmar H. Ammann

60 NCSEA News 62 SEI Structural Columns 64 CASE in Point

By Frank Griggs, Jr., P.E., P.L.S.

59 Spotlight

Crystal Bridges Museum of American Art By Craig Schwitter, P.E. and Cristobal Correa, P.E.

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.

STRUCTURE magazine

DEPARTMENTS

April 2013

66 Structural Forum

Consequences of the Gendered Culture of Engineering By Lara K. Schubert, P.E.

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Editorial

Like new trends, A new Flight techniques ofand Geese current industry issues By John A. Mercer, P.E., SECB

population growth to a projected 9 billion people, a shift in primary global languages putting Chinese and Arabic on top, pushing English lower on the list, the need to maximize resource utilization, and realities of nature, e.g. global warming. A take away from Glenn’s presentation is, “will you be relevant in the future”? Ben Nelson of Martin & Martin spoke about Establishing a Successful Structural Engineering Training Program. This was followed by two presentations by Jon Stigliano, Top 10 Keys to Managing Multiple Deadlines & Expectations, and 8 Actions to Get People Goal Directed, Self-Motivated and Engaged in the Relentless Pursuit of Excellence. NCSEA’s excellent program is just a taste of the upcoming ACEC 2013 Annual Convention and Legislative Summit in Washington DC, April 21-24. If you were excited by speakers at the NCSEA Leadership Forum, you will be totally inspired by the ACEC Convention. They have one day of round tables based on firm size addressing HR, M&A, Finance, Legal, and other issues, and three days of nationally acclaimed speakers on a multitude of relevant business issues. This year’s convention will feature Geoff Colvin, Fortune speaking on “Outpacing Business Trends” and Chuck Todd from NBC News will talk about “Battleground Politics.” I would encourage you to consider attending. (www.acec.org/conferences/annual-13/index.cfm) Structural engineers are best equipped to provide vision, insight, and innovation into the problems our nation faces going forward. As trusted advisors, our honesty and integrity, lacking in so many other professions, gives structural engineers a solid foundation from which to launch a regime of initiatives to make significant contributions to society. We each have the opportunity to make a significant contribution to sustainability of our infrastructure, our resources, and mankind. It is in our culture to do so. As my swan song editorial, I would like to express my appreciation to everyone that made it possible for me to Chair CASE for the past 3 years. I would like to thank the leadership and staff of ACEC/ CASE, NCSEA, and ASCE/SEI for their willingness to cooperate and coordinate the activities of the three organizations. I have been a proponent of participative membership in one or more of our 3 organizations. I envision the three Organizations like a 3-legged stool, CASE/NCSEA/SEI = Best Business Practice & Risk Management/Technical Practice/Technical Codes, providing a stable foundation for the future practice of structural engineering. I will now drop back in the flight with honks of encouragement to our incoming CASE Chair, Andy Rauch.▪

a member benefit

structurE

am sure you have seen a gaggle of geese flying in a “V” formation. The lead goose creates an “aerodynamic draft” for the other geese in the flight enabling them to fly farther. He expends his energy fighting headwinds to create the draft while the other geese in the flight honk, encouraging the lead goose along their journey. From time to time the lead goose will fall back into the “V” and honk to encourage another goose taking the lead position. As the soon to be Past Chair of CASE, I will be dropping back into the flight, to honk encouragement for our new Chair, Andy Rauch of BKBM from Minneapolis, MN. Andy will become CASE Chair for 2013-2015 at the conclusion of the ACEC Annual Convention the end of this month. CASE is all about the business of the structural engineering and Andy is going to be a great leader. CASE recently held its Winter Planning Meeting preceding the NCSEA Leadership Forum in Tucson. AZ. A round table discussion kicked off the CASE meeting, with several discussion topics including: reduction in cost of professional liability insurance, design-build issues, social media and the use within firms. One participant expressed how great it was to “be able to sit among fellow structural engineers and openly discuss internal business issues and challenges.” The following day, CASE held its committee meetings to continue developing, updating, and improving CASE products supporting Best Business Practices and Risk Management Enhancement for CASE firm members. Watch for new and updated publications later this year from CASE. As one of the 57 attendees of NCSEA’s two day Winter Leadership Forum, I had the privilege to hear the guest speakers make presentations on the following topics: Kelly Riggs discussed Winning Business in a Losing Economy. Kelly’s take away is that we all look alike to the buyer and will likely be selected on price instead of capability or quality of service. He discussed strategies that we can use to overcome the price mentality. Scott Braley’s presentation was entitled Key Financial Indicators for Leading Your Firm to Success. One take away was, profits will depend more on productivity than on support from the economy. Kelly returned kicking off the afternoon with Coaching for Leaders: Transforming Potential into Performance. One quote I wrote down was, “you can’t be efficient with people, you can be effective with people”. Glenn Bell, CEO of Simpson Gumpertz & Heger, kicked off day two of the Winter Leadership Forum with a presentation Developing the Next Generation STRUCTURAL of Structural Engineers looking ENGINEERING INSTITUTE towards the future out to 2050. The forthcoming challenges for US engineers will include global

STRUCTURE magazine

John A. Mercer, P.E., SECB (Engineer@minot.com), is the president of Mercer Engineering, PC, in Minot, North Dakota. He currently serves as Chair of the Council of American Structural Engineers (CASE) and is a CASE representative on STRUCTURE’s Editorial Board.

April 2013

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American Concrete Institute ................. 37 Applied Bolting Technology .................. 52 AZZ Galvanizing .................................. 39 Canadian Wood Council ....................... 57 Computers & Structures, Inc. ............... 68 CSC Inc. ............................................... 49 CTP Inc. ............................................... 29 CTS Cement Manufacturing Corp........ 13 Design Data .......................................... 46 Enercalc, Inc. .......................................... 3 Engineering International Inc................ 19

ESAB Welding and Cutting Products .... 55 Foundation Performance Association..... 44 Fyfe ....................................................... 43 Gerdau .................................................. 22 GT STRUDL........................................ 51 Hilti, Inc. .............................................. 45 Integrated Engineering Software, Inc..... 50 ITW TrusSteel & BCG Hardware ... 15, 54 ITW Red Head ..................................... 58 JMC Steel Group .................................... 6 KPFF Consulting Engineers .................... 8

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STRUCTURE® (Volume 20, Number 4). ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/yr student; $90/yr Canada; $125/yr foreign. For change of address or duplicate copies, contact your member organization(s). Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be

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STRUCTURE magazine

April 2013

Historic structures significant structures of the past

Figure 1: Illustration of cross-sectional and perspective views of the Kahn reinforcement bar, along with a diagram of the theoretical “truss action”.

t the time of this writing, a vacant former bakery is standing for a few more days at the corner of Fifth Street North and Seventh Avenue North, just outside of the official boundary of the local and national historic Warehouse District of Minneapolis, Minnesota. The building is typical of others in the area: a one- to three-story utilitarian structure with little architectural ornamentation and several additions. The hodgepodge of construction styles is reflected by the variety of structural systems found within, including load-bearing masonry walls, cast iron columns, and framing of heavy timber, structural steel and reinforced concrete; the building is a dictionary of historic construction techniques. It is a familiar scene in many urban industrial areas: declining industries leave behind a decaying infrastructure and abandoned buildings. For years this bakery has stood with boarded windows, roof leaks, squatters, and active plundering of any metals of value. However, a recent urban revitalization has brought redevelopment interest to many of the buildings nearby. The Warehouse District is notable for its representation of the growth of industry in Minneapolis, which was supported by the early arrival of the railroads. The initial construction in the area was from the mid-19th century to support the local milling industry – first lumber, and then flour. By 1902, the connection of major railroad lines brought industries such as wholesaling and manufacturing; Minneapolis eventually became the center of distribution for America’s farm machinery. Growth in the District reached its peak around 1930, and then declined along with the rest of the American economy. Concurrently, several changes in interstate shipping legislation allowed for independence from the railroads that had been so critical to the growth of the economy in Minneapolis. The District remained relatively unchanged between 1930 and 1990, which left many of the original historic structures intact, albeit untended.

A recent survey of the area identified buildings that are potentially historic. A low-rise structure without any prominent architectural features, a series of mismatched additions, and a leaking roof might typically be dismissed. However, a 1909 building permit card for the bakery noted that the “fireproof Kahn concrete tile system” was used in the building’s early construction. Furthermore, the bakery is purportedly the site of the invention of “sliced bread” and other innovations in the baking industry. Thus, when a proposal for a new apartment building suggested demolition of the bakery, the Minneapolis Heritage Preservation Commission was charged with making the decision as to whether to allow it: could the use of the Kahn system be significant enough to merit saving it? Furthermore, how important is “sliced bread” anyway? An engineering condition assessment was ordered to determine the structural integrity of the building, and the importance of sliced bread was left to the opinion of the Commission. The “Kahn System” was invented by Julius Kahn, who filed a patent for it on December 11, 1902. Julius was the brother of the more well-known Albert Kahn, a nationally prominent architect based in Detroit who is best known for the factories he designed for automotive companies such as Packard and Ford in the early 20th century. Albert incorporated his brother’s patented reinforcement into many of the buildings he designed. Meanwhile, Julius formed the Trussed Concrete Steel Company, also based in Detroit, to manufacture, market, and provide structural engineering services for his proprietary system. It serves as the structure for buildings throughout the country, such as the Engineering Building (1904) at the University of Michigan and the Blenheim Hotel (1906) in Atlantic City, New Jersey. At that time, reinforced concrete was inherently experimental as engineers and builders worked

STRUCTURE magazine

The Kahn System of Reinforced Concrete

Why it Almost Mattered By Ryan Salmon, EIT and Meghan Elliott, P.E., Associate AIA

Ryan Salmon, EIT (salmon@pvnworks.com), is a project associate and Meghan Elliott, P.E., Associate AIA (elliott@pvnworks.com), is the founder and owner at Preservation Design Works, LLC, a consulting and project management firm in Minneapolis, Minnesota that specializes in the preservation and redevelopment of historic buildings.

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

the longitudinal reinforcement. While the lack of testing standards and documentation from that time leaves some questions today about the validity of the tests, the intention of the testing was clear: to demonstrate the strength of the product, to create confidence in the product for contractors and building code officials, and to promote a proprietary reinforcing method. Kahn’s reinforcing system drew both attention and criticism from contemporary practitioners. In particular, C.A.P. Turner, a nationally prominent engineer based in Minneapolis, vehemently objected to Kahn’s system in his 1909 book, Concrete-Steel Construction:

Figure 2: Illustration of Kahn’s reinforcement as installed in floors, beams and columns.

to understand how to design and construct safe and efficient structures from the material. Numerous patented systems were developed, such as Ernest Ransome’s twisted steel reinforcement and Claude (C.A.P.) Turner’s “mushroom system” of flat-slab floor construction using smooth round rods. Kahn’s reinforcement system was unique: it consisted of visually distinctive rolled diamond-shaped bars with flat-plate flanges (or “wings”) that were sliced and bent up at regular intervals at approximately 45 degrees from the longitudinal axis of the reinforcement. Kahn rationalized that concrete members constructed with his reinforcement, particularly beams, would act in bending as a Pratt or Warren truss, with the diagonal wings and longitudinal bars serving as tension members and the concrete serving as vertical (or diagonal) compression members (Figure 1 , page 9 ). The diagonal wings were also theorized as shear reinforcement. The system was incorporated into reinforced concrete beams, joists and – in early examples – columns (Figure 2 ). Joists were typically installed with a hollow clay tile block system that consisted of rows of blocks laid with a three- to four-inch space between. Kahn-style reinforcement was placed into the voids between the blocks, which were subsequently filled with concrete (Figure 3). The hollow clay tile blocks were left in place,

which resulted in a smooth underside suitable for finishing with plaster. The bakery used the hollow clay tile joist construction method for the floor in the 1909 addition. A publication by the Trussed Concrete Steel Company claimed that the system offered 20-30% greater capacity compared to “beams reinforced with horizontal rods and loose stirrups with the same area of reinforcement.” These claims were based on tests performed in 1907 at the University of Wisconsin on simply supported beams. According to the test report provided in the Trussed Concrete Steel Company publication, the beams with “loose stirrups” failed due to slippage of the rods and concrete shear near the supports. In contrast, the Kahn-reinforced beams were claimed to fail in flexure near the center (Figure 4 ). A review today of the test data shows that the test beams with “loose stirrups” were constructed with smooth longitudinal bars and U-shaped shear reinforcement spaced at intervals of at least three-quarters of the depth of

Figure 3: Cross-section of hollow clay tile joist floor system.

Figure 4: Load test of a Kahn System beam to failure.

STRUCTURE magazine

April 2013

In theory the Kahn bar is supposed to act with the concrete after the manner of a Warren Truss, and proof of this theory as advanced by the advocates of this type of reinforcement, reminds one of the story of the friendly discussion between two lawyers, in which the question came up as to who was recognized as the most prominent attorney in the place. “I am of course,” said the first. “How can you prove it?” asked his friend. “Why, I do not need to prove it, I am willing to admit it,” replied the first. Thus the advocate of this type of reinforcement apparently advances similarly convincing proof that the bar acts in the manner claimed. Turner also pointed out that because of how the bar was manufactured, the “wings” at the ends of the bars were shorter. He noted that shear stresses were greatest at the ends of a simply supported beam, where the Kahn System provided the least amount of shear reinforcement. Turner further critiqued it for not providing continuous longitudinal reinforcement for the beams at the columns, which created a potentially catastrophic and brittle failure mechanism; in contrast,

System. Reports published by the Joint Committee on Standard Specifications for Concrete and Reinforced Concrete in 1908, 1912, 1916 and 1924 provided specifications and guidelines for the design and construction of nonproprietary reinforced concrete structures. As concrete reinforcement became standardized into the form most commonly used today, the Trussed Concrete Steel Company broadened its market into products such as concrete pan joist formwork Figure 5: Test panel constructed with the Kahn System loaded to 4,000 and steel window frames, and psf with iron ingots for the Nichols, Dean and Gregg Warehouse Building shortened its name to the in St. Paul, Minnesota (demolished 1990). Truscon Steel Company in the 1920s. In 1935, it became a subsidiary of the Republic Turner and several other engineers at the Steel Corporation. The company no longer time promoted a configuration of continu- exists today. ous longitudinal reinforcing over the top of The pending demolition of the bakery the columns. Another shortcoming was that presented many questions about both as the length of the “wings” increased, the the structural and historic integrity of spacing of the “wings” also increased, which the building. From a structural perspeceffectively imposed an upper limit on the tive, the consulting engineering company shear strength of a beam of fixed depth. (Minneapolis-based Meyer Borgman The Kahn System was involved in at Johnson) was required to determine least two catastrophic building failures. In whether the building, and especially the November 1906, the Bixby Hotel in Long Kahn System, was adequate to support curBeach, California partially collapsed during rent and proposed floor loads. A partial construction. Engineers investigating the collapse in the area of the Kahn reinforcecollapse of the hotel concluded that pre- ment, coupled with the known inadequacies mature removal of formwork and shoring of the reinforcing and significant corrowas the cause. Two weeks later, the Eastman sion after years of water intrusion, led to Kodak Building in Rochester, New York the conclusion that the floor system likely collapsed during construction. Investigators lacked sufficient strength to support any found numerous flaws in the quality of the code-mandated loads in its current conwork. They found a large amount of wood dition. Repair of the system was deemed debris and sawdust in the concrete, as well cost-prohibitive and invasive. as improperly placed reinforcement in many The historic integrity and significance of the locations. Both investigations concluded that system is less clear than an engineering comthe collapses were not due to faulty design or parison of demand versus capacity: did the flaws in the Kahn-style reinforcement; rather, bakery building, and specifically the Kahn they were the result of poor workmanship. reinforcing, represent an important part of Ultimately, increasing standardization of construction history in the Twin Cities of St. concrete reinforcement systems and greater Paul and Minneapolis? There are a few other understanding of reinforced concrete behavior remaining buildings in the area that incorled to the decline of numerous proprietary porated the Kahn System. The “Northwest” methods of reinforcement, including the Kahn branch office of the Trussed Concrete Steel

Company designed the structure for the Minnesota State Fair Grandstand, as well as the Lowry Building in St. Paul. A description of the Kahn System in Cement Age, a trade journal of the time, mentioned that the nine-story, 450,000-square-foot Farwell, Ozmum, Kirk & Co. warehouse in St. Paul was built in 1906 with a reinforced concrete structure using the Kahn System throughout. The warehouse was designed to carry 500 psf, and was load-tested after construction to 1,500 psf by piling pig iron eight feet high in a floor bay. It currently serves as the East Building of the Ramsey County Government Center. The Nichols, Dean, and Gregg Company Warehouse in St. Paul was constructed in 1906, and was claimed to be the “strongest in the world” by the architect and contractor. Although the veracity of this claim is unknown, it was certainly a strong building as proven by load testing (Figure 5 ). Other buildings may have used the system, but documentation of the reinforcement type is not available. Kahn’s type of reinforcement is one of dozens of novel patented systems available at the beginning of the 20th century. The Kahn system exemplifies the intensive innovation, entrepreneurship, and experimentation seen in reinforced concrete construction during this period. Perhaps it is not coincidental that the inventive engineers commonly named their proprietary systems after themselves, and actively marketed their technology through testing programs, technical treatises, and paid advertising. Many of these systems have been lost to demolition, neglect, or simple lack of documentation. As engineers and historians, we ask what role engineering and construction history should play in the field of historic preservation. What lessons can we learn from these systems and this period of time? How did these engineers and their inventions influence concrete construction today? The demolition of the building was ultimately approved. The Kahn system, and the original home of sliced bread, will no longer be in Minneapolis.▪ All graphics from the Kahn System of Reinforced Concrete or Kahn System Standards publications.

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STRUCTURE magazine

April 2013

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

f you are like me, you emerged from your collegiate experience with a broad array of fundamental tools in structural design that, hopefully, armed you adequately for your chosen career. I recall finishing my bachelor’s degree and having a skill set that, in retrospect, might be described as “barely sufficient”. With this statement, I do not mean to diminish the quality of my education, nor the dedication or expertise of excellent professors. I simply mean that a four-year college experience laced with a generous dose of liberal arts education requirements barely compares to the experience and learning that take place in actual practice. Among the skills that I gained as an undergraduate were the basics of reinforced concrete design, including beams and columns. I eventually came to understand that the concepts that pertain to these elements also permeate nearly every aspect of reinforced concrete design, from footings to shear walls. I have also come to understand that, like many other materials, there are simplified approaches for reinforced concrete design. Although they should not become the final basis of design, they can serve as effective tools to corroborate more detailed calculations or to estimate geometries, sizes and proportions as part of a preliminary or schematic design. This article seeks to address and elaborate upon a few of the simplified methods commonly used for reinforced concrete. First, consider the familiar As~Mu/4d approach that is commonly used in the design of reinforced concrete beams. Quite simply, the required area of steel is approximately equal to the factored moment (in kip-feet) divided by 4d, where d is the effective depth from the extreme compression fiber to the centroid of the tensile reinforcement (in inches). When sizing a beam, it is advisable to start with the ACI provisions for span-to-depth ratios. You may recall that for a simply supported beam having a total height (h) not less than span/16, deflection calculations may be omitted. This is good precedent for beginning a beam design. As for the width, good proportioning of sizes will often show that widths between one-half and two-thirds of the depth are often appropriate. Regarding the reinforcement, contemporary texts offer elaborate approaches for determining how much steel to use, and computers can make the trial-and-error process relatively quick and painless. Examination of the basic equations,

Simplified Methods in Reinforced Concrete Design By Jerod G. Johnson, Ph.D., S.E.

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 SEAU Newsletter (Fall 2012). It is reprinted with permission.

a = A s fy /0.85f 'c b and Mn = As fy (d-a/2),

12 April 2013

Figure 1.

shows that a second-order polynomial can be developed for which the required area of steel (As ) can be solved by substituting Mu for Mn. The problem is that this is tedious and yields an exact result that is not necessarily pragmatic considering the discrete bar sizes available. This is why the As~Mu/4d method is so useful. This equation is not typically found in modern concrete design textbooks, yet it is perhaps one of the most prolific approximations within structural engineering. Does it have a rational basis? One would assume that it must, because it always seems to work, provided that the beam dimensions are reasonable. If we make the simple yet rational approximation that the internal lever arm between tensile and compressive resultants in a concrete beam is equal to 90% of the effective depth (d ), then the (d-a/2) component of the “exact” equation above simply becomes 0.9d (Figure 1). Assuming fy = 60 ksi since this is almost always the case, we now have a simple equation for approximate nominal flexural capacity:

Mn = As(60 ksi)(0.9d ) Now, substitute Mu for Mn and convert from units of kip-feet to kip-inches by multiplying Mu by 12. Next, assign  = 0.9, which is usually the case unless reinforcing ratios become extremely high or the beam is unusually shallow, and we get the result: As 

Mu Mu(12) = 0.9(60)(0.9d ) 4.05d

Hence the long-held approximation does have a rational basis. What about column axial/flexural design? A knee-jerk reaction for many might be to open up a spreadsheet or some other automated tool. Before doing this, we might ask the following: What are the two most descriptive points on an interaction diagram? I believe that they are the points intersecting the x and y axes; in other words, the moment capacity when there is no axial load, and the axial capacity when there is no moment. Knowing what interaction curves will likely develop with respect to these points can be instructive.

CONSTRUCTION CEMENT

FA S T ER Figure 2.

Pn ≈ 0.65(0.80)(0.85f 'c A g+fy As) ≈ 0.44f 'c A g + 0.52f y A s

calculations, rather than the dozens or perhaps hundreds of calculations necessary to develop the complete interaction curve. The approximate interaction curve is established using the aforementioned calculations as a basis and then superimposing what may be deemed a “standard” interaction curve shape, scaled to match the two previously determined points. This curve should not be used where a high degree of accuracy is needed. For instance, if a point representing simultaneous bending and axial loads (Mu , Pu) falls directly on the approximate curve, more refined calculations or a more conservative design should be considered. Upon validating a simplified method such as this, it becomes possible to adapt it to other design scenarios. In particular, in-plane flexural design of concrete shear walls can be particularly tedious. While redundancy precludes elaborating upon a simplified method for concrete shear wall flexural design, it is sufficient to say that most concrete shear walls are not loaded anywhere near their peak axial capacities. In fact, axial loads on shear walls are often so low that they can simply be characterized as vertical beams. Considering the typical interaction curve, it is no stretch to rationalize that accounting for axial load will likely increase flexural capacity, at least to a point. In that sense, simplified methods (like Mu /4d ) to determine approximate areas of boundary element steel can be useful and are likely to be conservative.▪

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Applying the parameters of our 18-inch square column yields Pn ~ 720 kips. I now have two points on the interaction diagram that I can use to make an educated guess of the interaction diagram shape, which can be compared with the interaction diagram based on the provisions of ACI 318 (Figure 2). Although there are some differences, the approach yields a speculative but conservative interaction curve that is reasonably close to the “actual” curve. This was achieved with only two fundamental

This article is intended for structural engineering practitioners and other design professionals seeking to expand their repertoire of fundamental skills and tools. The suggested techniques and simplified methods are derived from general principles of concrete design and relevant ACI code provisions. These procedures should not be used for final structural design, but may serve well as preliminary estimates or for verification of final design. Assurance of code compliance remains the responsibility of the Structural Engineer of Record.

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April 2013

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So, how can we estimate these points without a bunch of tedious calculations? Start by looking at the moment capacity under zero axial load (i.e., the column behaves like a beam). If reinforcing ratios are relatively low (1% to 3%), then it stands to reason that bars in compression or near the neutral axis probably do not contribute much to flexural capacity. Consider an 18-inch square column with f 'c = 4,000 psi and eight #7 vertical bars (about 1.5% steel) in a standard 3x3 pattern and 2.5 inches of cover to bar center. At zero axial load, the compression zone becomes relatively small, such that the neutral axis lies relatively close to the extreme compression fiber. Drawing upon this logic, we can conclude that the centroid of tensile forces for the reinforcement at the opposite side of the column is typically about two-thirds of the column thickness (h), which would be 12 inches in this example. Using this as the effective depth results in an approximate flexural capacity of 142 kip-feet. Note that this process may be done in reverse with the Mu /4d approach when starting from scratch. Next, consider the axial capacity. We start by examining the column cross-section. We need to sum the capacity of the concrete and the steel; for simplicity, ignore the area of concrete replaced by the reinforcement since this is only 1% to 3% of the gross concrete area. Since the column is tied, we will use  = 0.65. Adapting the ACI column equation to these ideas yields:

STRONGER MORE DURABLE

Practical SolutionS solutions for the practicing structural engineer

Typical floor construction types.

t is not unusual to create an opening in existing floors during building renovations and alterations. A new opening may be used for stairs, an elevator shaft, a duct penetration, skylights, etc. In order to execute a feasible modification and maintain the existing building’s structural stability, a qualified structural engineer should be involved during the initial planning phase. With varied knowledge of floor construction types and extensive experience in structural evaluation and strengthening, the structural engineer can present valuable suggestions regarding the selection of opening locations, construction feasibility and possible strengthening options. This article presents a typical procedure to create openings in existing floors, and discusses some practical issues.

Creating an Opening in Existing Floors From Planning to Completion By Dominick R. Pilla, P.E., C.E., S.E., RA and Xiaoli Tong, P.E.

Dominick R. Pilla, P.E., C.E., S.E., R.A., owns and operates Dominick R. Pilla Associates, P.C. In addition, Mr. Pilla is an associate professor at the Bernard & Anne Spitzer School of Architecture at City College of New York. He can be reached at dominick@drpilla.com. Xiaoli Tong, P.E., is an Engineer with DRPILLA. Prior to joining DRPILLA, Mr. Tong gained most of his professional experience while working in a prominent national research institute on building technology in China. He can be reached at xiaolit@drpilla.com.

Planning of an Opening Where to make an opening in a floor sounds very simple – just put it where it should be – but this is true only for new construction, when all kinds of openings can be accommodated using various structural design methods. However, it is a very different situation to create a new opening in an existing floor where construction is constrained by surrounding elements that are part of structural systems. An improper location of the opening may lead to a large amount of renovation work, making the project uneconomical and perhaps even rendering it impossible to develop a feasible structural solution. A good plan for an opening is half the battle; the first and primary rule of thumb is to avoid locating the opening across major existing building elements – i.e., girders, columns and walls – to limit the affected zone, in regard to altering the structural continuity of the building. Due to the many possible types of construction that may be encountered – such as a masonry arch floor, a steel-wire catenary floor, and modern beam/plate floor types that consist of wood or light gauge steel joists, steel beams, precast concrete planks, cast-in-place concrete slabs, etc. – a thorough understanding of the existing building type and floor system must be obtained. A review

14 April 2013

of existing construction documents, if available, will provide basic information; however, physical inspections and probes are essential to determine as-built conditions. Based on the findings of a comprehensive study of the floor system, the location of the openings can be adjusted and finalized.

Evaluation of Existing Structures Once the opening is located, relevant existing floor structures must be carefully assessed. The proposed opening may affect existing floor structures in one or all of the following ways: (1) the design live load is increased at the new stair landing area, thereby overloading adjacent portions of the floor; (2) the original structural design assumptions (e.g., continuous beam, arch action, etc.) will not be satisfied after the opening is made; (3) in the case of a T-beam, the flange is partially or completely removed at the opening side, thereby reducing flexural resistance and stiffness; and (4) structural capacities are undermined when floor reinforcement is eliminated or cut off when creating an opening in a concrete slab. Actual effects on any existing floor structures are dependent on its construction type. Masonry arch floor construction, made of hollow tiles or terra cotta, was very popular for buildings constructed from the late 1800s to early 1900s. The segmental masonry pieces work together, and span between adjacent steel beams by using arch action with tie rods to resist the tension thrust. Once some segments are removed for an opening, the corresponding arch action will be lost. The remaining pieces will not be stable and should be removed. If a tie rod is to be cut off, it may be necessary to install a new steel beam beforehand, unless field conditions suggest that the required tension thrust is properly resolved by the stability of the adjacent spans or bays. Steel wire catenary floor construction became popular in 1910 and disappeared gradually after World War II. The steel wires are draped and continuous over steel beams so that gravity loads are sustained by the tension in the suspended wires, which are encased in cinder concrete mainly for the purpose of fire protection. When an opening is to be made in this system, it is inevitable that some wires will need to be cut, which will disrupt the continuity and stability of the system. In order

Finite element analysis of a two-way slab with opening. Effects of an opening to existing concrete slab.

to stabilize the floor at adjacent spans, proper anchorage of the cut wires must be designed. For floors consisting of joists or floor beams, an opening can usually be framed simply by installing new transfer beams, which form the perimeter of the new opening. These transfer beams can support the floor joists/ beams at the opening, and distribute design loads to adjacent girders, columns and walls. Evaluation of the existing structures under new loading conditions is straightforward but essential. An opening in precast plank floors can be framed by the installation of steel headers. The new members will redistribute the design

loads to adjacent planks in accordance with the guidelines presented in the PCI Design Manual, and the relevant planks should be evaluated for design loads per the renovation plan in addition to the distributed loads from the header. Moreover, the remaining parts of planks with proposed openings must be reassessed to determine whether the development length of the residual strands, from the cut edge to the point of maximum required moment, is still valid for the full specified tensile strength. Otherwise, the residual flexural resistance should be adjusted. A reinforced concrete slab may be treated as either a one-way slab or a two-way slab ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

April 2013

based on the aspect ratio of the length in the long direction to the width in the short direction. A one-way slab is considered when an aspect ratio of at least two is realized. A one-way slab will function like a beam in the short direction, continuously spanning over supports such as T-beams or walls. However, continuity will be interrupted at the proposed opening and the slab’s required design moments at adjacent spans will be increased. In addition, the T-beam’s flange will be partially or completely removed at the opening side, weakening the T-beam’s design strength and stiffness and perhaps even inducing torsion effects. continued on next page.

New transfer beams around the opening.

Externally bonded/bolted steel plates method.

A two-way slab is considered when an aspect ratio of less than two is realized. It supports the design loads in both directions on its column strips and middle strips simultaneously. When an opening is to be made, part of the slab’s column strip and/or middle strip is removed, and relevant reinforcement is cut off. To calculate the required moment capacity after creation of the opening, the equivalent frame method specified in ACI 318 is still applicable as long as the assumptions are satisfied. However, a finite element analysis is a better way to find relatively more accurate solutions to the design moments and maximum deflections concerned. In a finite element model, at least two adjacent floor spans around the opening must be considered. Load-bearing walls and additional spans of the floor slab may be simplified as proper boundary conditions. To calculate the residual flexural resistance, the actual amount and placement of steel reinforcement in the slab must be investigated and verified by using non-destructive test instruments such as ground penetration radar. By comparing the required design moment to the residual flexural resistance, it can be determined if strengthening of the slab due to the opening is necessary. It should be noted that if an opening is located completely within the “slab” portion of a two-way slab–i.e., not located across column strips – then the resulting opening may not require reinforcement.

Strengthening Design Options An efficient strengthening method is to install new transfer beams to frame an opening. The

new beams will take design loads on residual floor structures around the opening and distribute the loads to adjacent existing girders, columns or walls. The new beams can often be framed flush with existing floor structures and totally hidden inside finish ceilings. Due to its simplicity and efficiency, the transfer beam is generally the first choice to strengthen an opening whenever possible. However, for certain floor construction types like concrete slabs, new transfer beams cannot be framed flush, but must instead be installed underneath the slab to connect with adjacent existing columns or girders. When floor headroom and aesthetic appearance are of paramount concern, externally bonded or bolted plate methods may be employed. For this popular and economical strengthening approach, the steel plates are considered to be tension reinforcement placed on the surfaces of concrete slabs. The plates are sized based on the required design moments under superimposed loads. The bonding agent (e.g., epoxy resin) and anchor bolts provide the surface shear stresses needed for composite action between the plates and the concrete. When it is necessary to strengthen the slab in both directions, the intersection of steel plates must be properly detailed. Some practical solutions include encasing the steel plate in one direction into the concrete slab or pre-welding the steel plates in both directions at the intersection points.

Peer Review and Construction Prior to making a new opening in an existing building, a construction permit is often required, for which an independent structural

Ground penetration radar image of slab reinforcement.

STRUCTURE magazine

April 2013

peer review is mandatory per the building code. If possible, the building’s original structural engineer of record, who has the greatest knowledge of the existing structural design, is the most appropriate design professional to serve as the peer reviewer. The peer review involves confirming the renovation design criteria, attesting to the general completeness of the construction documents, and verifying the new design in accordance with building codes and relevant industry standards. All comments by the peer review must be answered and manifested in the final construction documents. The construction itself begins with shoring installation to support all interim design loads during construction. The shoring often simply consists of 2x stud walls around the proposed opening. It may be omitted if floor structures are to be properly strengthened, as per the design, prior to making the opening. An overcut should be prohibited; marking opening edges and drilling holes at the corners is good practice to prevent this. Diamond blade saws are commonly used to cut existing floors. After the opening is made, fire protection should be applied on new steel members either by spray or as part of a rated ceiling assembly.

Summary Each building is unique, and there is no one universal method by which to create openings in every building type. In this article, we have discussed basic principles that should be respected when considering a proposed opening. There will arise many deviations when facing actual projects. A structural engineer, with appropriate knowledge and experience, will be required to coordinate thoroughly with the owner, architect and other relevant parties in order to evaluate and implement an appropriate and economical proposal, design and construction for a new floor opening.▪

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Technology information and updates on the impact of technology on structural engineering

oncrete Capacity Design (CCD) has been a code methodology for anchor design since it was introduced directly into section 1913 of the 2000 International Building Code (IBC). It was initially a strength design option and was limited to cast-in-place anchors only. The CCD method provided better predictions of concrete breakout strengths than the previously common 45-degree cone method. The new provisions also clearly identified specific limit states, which may not have been apparent in older design tables. The scope of the provisions expanded when they appeared in Appendix D of ACI 318-02, which standardized the analysis methodology for postinstalled anchors. Improved accuracy came at a cost. One of the advantages of the CCD method was that it used a simpler rectangular area, rather than overlapping circular cone areas. Unfortunately, over the past decade, a few paragraphs of text and an allowable stress design table have turned into the 48 pages of provisions and commentary that now reside in Appendix D of ACI 318-11. Fortunately, there are several software applications that can assist with the heavy lifting of anchor design. However, each application has its own default set of assumptions, features, and limitations. It is incumbent upon the designer to be aware of these and work within the capabilities of each software application. Different applications can provide significantly different results for what may appear to be the same input parameters. Seven different software applications are discussed below (see table), and are broken into the following three categories. 1) Proprietary Anchor Manufacturer Software a. Hilti PROFIS Anchor (Version 2.3.3) b.Powers Design Assist® (Version 2.1.4762.17678) c. Simpson Strong-Tie® Anchor Selector™ (Version 4.11.0.0) 2) Third-Party Anchor Software a. Quick Anchor by SK Ghosh Associates (Version 2.0.4) b.DS Anchor by Dimensional Solutions (Version 5.0.0) 3) Integrated Base Plate Design Software a. RISABase by RISA Technologies (Version 2.1) b.RAM Connection V8i Standalone by Bentley® Systems (Version 8.0) Each vendor filled out a survey describing the assumptions and analysis methodology that its software used for various limit states, and identified its software’s features. In addition to the survey, example problems were run comparing

Using Software to Control Anchor Design By Marshall P. Carman, P.E., S.E.

Marshall P. Carman, P.E., S.E. (mpc@ssastructural.com), is a project manager at Steven Schaefer Associates, Inc., Consulting Structural Engineers in Cincinnati, Ohio.

18 April 2013

the results with the survey responses (see sidebar, Example Problems, page 21). All of the applications typically provided the same results for anchor groups subjected to concentrically applied tension, but results varied for anchor groups subjected to a bending moment or to shear.

Shear in Anchor Rod for Base Plates with Grout Pad or Stand-Off If anchors rods are used to resist shear forces from a base plate, they may also be subject to flexure. Because of this, shear lugs, embedded columns, or other alternatives are likely better options for transferring shear unless the loads are small. Where shear is transferred through the anchor rods in lightly loaded connections, oversized holes to accommodate erection tolerances prevent predictable shear transfer through the anchors. In this case, shear can be transferred to the anchor rods via plate washers welded to the top of the base plate. This will result in a moment arm at least as long as the base plate thickness. Furthermore, some flexure could be induced into the anchor rods for any base plates with a standoff condition, with or without grout. ACI 318 Appendix D does not explicitly contain provisions for considering flexural forces in anchor rods. Any reduction in capacity due to stand-off is limited to the provisions in section D.6.1.3, which require that the shear capacity of the anchor rods be multiplied by 0.8 when used with a built-up grout pad. Other publications, which are not referenced by the IBC, have a more thorough treatment of this condition. AISC Steel Design Guide 1, Base Plate and Anchor Rod Design, Second Edition, provides a design example in section 4.11 considering flexure in anchor rods for base plates with oversized holes. Section 4.2.2.4 of Annex C of ETAG 001, Guideline for European Technical Approval of Metal Anchors for Use in Concrete, provides more detailed requirements for considering flexure in anchor rods for base plates with grout or a clear stand-off. None of the software applications currently use the AISC methodology. Most of them only consider the 0.8 reduction factor as required by ACI 318 Appendix D. Hilti PROFIS Anchor and Powers Design Assist consider the ETAG methodology by default. This results in a significant difference in anchor shear capacities between software applications, especially where smalldiameter anchors or thick grout pads are used. In Example Problem #1, the capacity differed by a factor greater than five between applications that considered flexure and those that did not. The detailed output in both Hilti PROFIS Anchor and Powers Design Assist provides a capacity that does not consider flexure due to the stand-off or

Cay2

HSS 4x4x1/4 COLUMN

0' - 8"

Cay1

1/2" x 12" x 12" BASE PLATE ON 1 1/2" GROUT PAD w/ (4) 1/2" DIAMETER ANCHOR RODS (F1554 GR 36 w STD HEX HED), EMBED = 6".

48" x ??" x 12" CONCRETE FOOTING (3000 PSI NWC)

Cax1 0' - 8"

Cax2

grout pad, but that value is not included in the final interaction equations or the typical results shown on the screen.

Concrete Breakout in Shear for Loads Perpendicular to an Edge

Concrete Breakout in Shear for Loads Parallel to an Edge Per section 6.2.1.c of ACI 318 Appendix D, the breakout capacity for a shear load parallel to an edge is equal to two times the capacity of a fictitious load perpendicular to the edge. While the commentary provides potential breakout cases for loads perpendicular to an edge, there is no corresponding commentary regarding concrete breakout in shear for loads parallel to an edge. Powers Design Assist and Hilti PROFIS Anchor both use the anchor row nearest to the edge to determine the breakout area. Hilti PROFIS Anchor compares this capacity to the shear demand on the entire anchor group, which is consistent with how the software considers shear perpendicular to an edge (Case 3). By contrast, Powers Design Assist treats shear parallel to an edge differently than it treats shear perpendicular to an edge, comparing the breakout capacity to the proportional shear demand on the anchor row nearest to the edge (Case 1).

STRUCTURE magazine

April 2013

Consideration of Base Plate and Distribution of Axial Forces to Anchors When an anchor group is subject to an eccentric tension load or applied moment, how the software models or considers the base plate will affect the resulting tension force in the anchors. DS Anchor and Quick Anchor do not consider a base plate at all. In DS Anchor, if a moment is applied to an anchor group, the software will distribute tension and compression loads to the anchors based upon the section modulus of the bolt group. In Quick Anchor, the anchor bolts are not assumed to take any compression, so the designer has to model only the anchors subject to tension and determine the resultant tension force on the anchor group outside of the software. Generally, the force distribution assumed by DS Anchor will be conservative, but if the designer is concerned that the difference between the base plate bearing method and the anchor rod section modulus method is significant, then the approach required by Quick Anchor could be applied to a DS Anchor model as well. The other software applications consider base plate bearing to resist compression and

220

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Commentary section RD.6.2.1 of ACI 318-11 describes three potential cases for evaluating concrete breakout perpendicular to an edge for a group of anchors with multiple rows. Case 1 assumes that the critical breakout is based upon the front anchors and their projected area, and evaluates it against the shear load proportional to that row. Case 2 permits the breakout area to be based upon the rear anchors, but evaluates the capacity against the total shear on the anchor group. Case 3 assumes that the breakout area is based upon the front anchors and evaluates the capacity against the total shear on the anchor group. Case 3 could conservatively be applied to all situations, but is only referenced for specific anchor spacing and edge distance conditions. Since this information is in the commentary, it is not actually part of the code itself. It is therefore the responsibility of the designer to determine the appropriate breakout behavior for each situation. However, the default breakout area varies between programs. For example, Hilti PROFIS Anchor and Powers Design Assist always use Case 3, which will provide a significantly lower capacity than applications using Case 1 or Case 2. In Example Problem 2, the difference between these two assumptions was a factor of two. The designer has control over the breakout areas in some of the software applications. Simpson Strong-Tie Anchor Selector allows

the designer to select a check box to “Apply entire shear load at front row for breakout” in order to force the use of Case 3. The stated rationale for this is that, due to the potential annular space between the rod and the baseplate, it is possible that the baseplate will engage only the front row of anchors and transfer the entire shear load to it prior to making contact with the rear row. Both Hilti PROFIS Anchor and Powers Design Assist allow the designer to select from anchor group templates that have slotted holes to prevent the application of shear to specific anchors. DS Anchor allows the designer to select which specific anchors take shear or tension.

Where anchors are located near a narrow section of a slab or wall, the provisions of section D.6.2.4 of ACI 318 may result in a significant reduction in the allowable breakout area in the perpendicular direction, such that the parallel breakout case no long controls. Software applications that allow the user to enter an infinite edge distance will apply this provision differently than applications that consider a large but finite edge distance. In Example Problem #1a, concrete breakout shear capacities differed by a factor greater than three.

distribute tension to the anchors accordingly. However, their results differ slightly, depending on how they model the base plate. Most of the applications treat the base plate as rigid, but RISABase considers the stiffness of the base plate, so changing the thickness will result in a different load distribution. This analysis methodology will identify the effects of prying action for thin base plates subject to uplift, which can result in a higher tension demand.

RAM Connection allows the user to choose whether to consider strain compatibility, and whether compressive bearing stress is distributed in a rectangular or triangular pattern. Each of these choices can affect the tension force indicated for the anchors.

Custom Anchor Layouts Most of the applications are limited to rectangular or preselected anchor layouts. Hilti PROFIS

Anchor, DS Anchor, and RAM Connection permit custom anchor layouts. This can be helpful when analyzing circular patterns, or asymmetric patterns subject to a moment or eccentric load. However, analyzing a custom anchor bolt pattern may provide unexpected results for shear breakout limit states. The concrete breakout cases described in commentary section RD.6.2.1 of ACI 318 are set up for rows or columns of anchors orthogonal to the concrete edge. Anchors that

Anchor Design Software Comparison. Proprietary Anchor Manufacturer Software

CIP Anchor Type Grout Bed

Governing Code

Post-Installed Anchor Type

Anchor Patterns

Breakout Edge Distance

Pullout Bearing Area

Headed “Bolt”

Flexure in Rod

Powers Design Assist

Simpson Strong-Tie Anchor Selector

Dimensional Solutions DS Anchor

S.K. Ghosh Associates Inc. Quick Anchor

RAM Connection

RISABase

ACI 318 D6.3.1

X ETAG 001 Annex C

ETAG 001 Annex C

ACI 318 D6.3.1

ACI 318-02

ACI 318-05

Custom Database

Custom

N/A

ACI 318-08

ACI 318-11

X X

Adhesive

Hilti

Powers + Custom

Undercut

Hilti

Powers + Custom

Custom Database

Custom

N/A

Expansion

Hilti

Powers + Custom

Custom Database

Custom

N/A

Concrete Screw

Hilti

Powers + Custom

Custom Database

Custom

N/A

Rectangular/Predefined

Custom/Asymmetric

Perpendicular – Rigid

Case 2

N/A

Parallel – Rigid

Case 2

X N/A

Case 2

Cases 1&2

Case 2

N/A

Case 2

Case 1

Cases 1&2

Case 2

Cases 1&2

Case 1

Cases 1&2

Perpendicular

Case 3

Cases 1&2 or 3

Parallel

Case 3

Case 1

Standard Hex Nut

Heavy Hex Nut

Square Nut

Heavy Square Nut

Custom Input / Plate Washer Miscellaneous Features

Integrated Base Plate Design Software

Hilti PROFIS Anchor L or J “Bolt” Welded Headed Studs

Third-Party Anchor Software

Lightweight Concrete

ACI 318-11 Only

X***

PAB Anchors

Custom/ User Input

Multiple Load Combinations

* Post-installed mechanical anchors only ** Does not evaluate anchor groups with asymmetric layout *** Sand-lightweight concrete only

STRUCTURE magazine

April 2013

N/A

are not perfectly equidistant from an edge are considered different rows. Anchor software that assumes Case 3 for breakout behavior, such as Hilti PROFIS Anchor, provides the unexpected result of significantly decreasing the shear breakout capacity of an anchor group when a single anchor is moved away from the row nearest the edge. With one less anchor in this row, the breakout area of the row nearest to the edge is reduced, but the software still assumes the full shear on the anchor group is resisted by this row, so the demand/capacity ratio increases. Anchor software that assumes Case 1 or Case 2 behavior, such as RAM Connection, provides the opposite but equally unexpected result. If a single anchor is moved slightly towards the edge, the group breakout capacity may actually increase. Similar to the above example, the breakout area of the front row is still reduced, but the shear demand on this anchor may be reduced even more. The software is no longer subtracting the overlapping breakout areas of individual anchors, because they are not technically located in the same row.

Analysis of Third-Party or Generic Anchors

Other Features The applications have several other different features and limitations. Some can handle multiple load combinations, while others

Code: Concrete Strength: Cracked Concrete: Concrete Thickness: Grout Pad: Anchor Type:

ACI 318-08 3,000 psi, Normal Weight Yes 12 inches 1½ inches ½-inch Dia ASTM F 1554 Gr 36 (Std Hex Head), Embed = 6 inches Anchor Spacing: 8 inches in square pattern, unless noted otherwise Anchors Welded: No Ductility: Assumed No Ductility in Connection Supplemental Reinf: No Anchor Reinf: No Edge Reinf: No Baseplate: ½ inch x 12 inches x 1 foot 0 inches Column Profile: HSS 4x4x1/4 Example Problem 1: Shear Parallel to Edge with Grout Pad/Small Edge Distance Edge Distance: Cax1 = 5 inches, Cax2 = 35 inches, Cay1 = 20 inches, Cay2 = 20 inches Applied Load: Vy = 3,000 pounds, T = 3,000 pounds, All Seismic Load (SDC C+) Example Problem 1a: Shear Parallel to Edge with Grout Pad/Large Edge Distance Edge Distance: Cax1 = 5 inches, Cax2 = 35 inches, Cay1 = 300 inches (or infinite), Cay2 = 300 inches (or infinite) Applied Load: Vy = 3,000 pounds, T = 3,000 pounds, All Seismic Load (SDC C+) Example Problem 2: Shear Perpendicular to Edge with Grout Pad/Symmetric Edge Distance: Cax1 = 5 inches, Cax2 = 35 inches Cay1 = 20inches, Cay2 = 20 inches, C Applied Load: Vx = -1,500 pounds, T = 3,000 pounds, All Seismic Load (SDC C+) Example Problem 3: Shear Perpendicular to Edge with Grout Pad/Asymmetric Anchor Spacing: 1 anchor moved 1/4 inch out of near row Edge Distance: Cax1 = 5 inches, Cax2 = 35 inches Cay1 = 20 inches, Cay2 = 20 inches, C Applied Load: Vx = -1,500 pounds, T = 3,000 pounds, All Seismic Load (SDC C+) are limited to a single load case. Some do not include reduction factors for lightweight concrete, while others do. Some incorporate baseplate design, include headed studs for embed plate design, or permit custom bearing areas for cast-in-place anchors with plate washers. If an application is missing a feature, some hand calculations in the margins can usually fill in the missing information. In addition, the software vendors are constantly updating and improving their software. What may seem like a missing feature in one application today may be added in the near future. In conclusion, it is very important to be aware of the assumptions that are being made by the software, be familiar with the output, and recognize that

STRUCTURE magazine

April 2013

when switching between applications, results may vary – even though both may very well be correct.▪

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An engineer may design for a specific postinstalled anchor, but a contractor may submit a request for substitution to use an alternate product. If the designer uses software from a different vendor to analyze the substitute anchor, it may be difficult to determine if the results are different because the anchors are different, or simply because the software’s assumptions are different. Powers Design Assist and Quick Anchor both allow the designer to enter parameters for a generic or third-party post-installed anchor. While this requires manually entering anchor properties each time, it allows for comparison between anchor products while keeping all other modeling assumptions the same. DS Anchor allows the user to create a database of post installed anchors, which can be referenced from any subsequent model. The engineer is responsible for maintaining the third-party anchor data and ensuring that it is being applied appropriately, in accordance with the corresponding Evaluation Report.

Example Problems

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Outside the BOx highlighting the out-of-theordinary within the realm of structural engineering

Figure 1: Flower bud.

nine-story glass building, shaped like a flower bud, is being built in the young scientific and industrial center of Siberia, Novosibirsk (Figure 1). In such a harsh weather environment – where during five cold days in January the temperature can drop down to -39 degrees (C), and the difference between the day and night temperatures in March can reach 30 degrees (C) (from -15degrees to +15 degrees (C)) – such a building may seem to be very risky and unexpected. Nevertheless, the designers deliberately chose the natural and transparent shape of a flower bud to challenge and confront the Siberian winter. This structure is directly connected to an existing rectangular building, creating a significant contrast with the unopened petals. The foundation and framework are built from reinforced concrete. The facade is fully captured by a cylindrical node system, a single-layer structure in the triangular geometry of the surface. Supporting elements are directly connected to the structure. The nodes are shaped aluminum tubes, and regions for rod assemblies are milled on the cylindrical nodes (Figure 2). The configuration of the node is defined by three parameters (Figure 3 , page 24): • the angle between the tangent plane and the surface (α); • the angle of rotation (β); and • the screw angle for the desired edge (γ). The windows are heat strengthened glass units with both panes made of laminated glass. The most important point of the design was not to play too much with biological form associations, and to prevent naturalization so that people will get only a hint of the floral form. To emphasize the shape of the bud, the designers focused on the faces of the petals, which were difficult to design, calculate and make landfall with a negative angle. An additional challenge was relating the curvilinear outlines of the concrete-iron overlaps with the curvature of the shells. continued on next page

Space Structures Reach Siberia

Figure 2: Node connections as viewed from the outside and inside.

STRUCTURE magazine

By Denis Gerasimov

Denis Gerasimov is the founder of SPACESTRUCTURE in Novosibirsk, Russia. He can be reached at 2147409@ngs.ru, or visit http://spacestructure.ru.

Figure 3: Angular parameters of each node element.

Another important decision was how to combine the elements of the shell; i.e., whether to use welding or bolting. The designers chose bolted connections, because visually they are more clear and linear. The main difficulty encountered during the project installation was not having a proper construction site, which hindered mechanization and made it impractical to mount large assembled elements. As a result, installers had to work with climbing equipment, using winches and hoists (Figure 4). Initially there was a permit for a threestory building, which was almost completely designed and built. During its construction, a ten-story building permit was obtained. Needless to say, it was difficult to adjust the project accordingly, strengthening the foundation and columns and maintaining the architectural idea without dismantling the erected frame. Planning and coordination of the project took place within the existing Russian framework of procedures and standards for design and construction. Some of the difficulties were associated with gaining approval from various government departments. The main concern was structural and fire safety.

Designing the reinforced concrete frame in SCAD software (Figure 5 ), which is used a lot in Russia, helped the team to avoid questions and comments on that aspect of the project. On the other hand, the space frame facade represents a completely new product and therefore needed special tests for durability and fire resistance. Structure CAD (SCAD) is a computer program for structural analysis that uses the finite element method to determine the stress-strain state of the structure under static and dynamic effects, and also performs certain aspects of the design of structural elements. The software is based on a system of complex functional units connected by a single information environment. The project is created by verbally describing the design scheme in the input language. The import process then converts this representation into the internal format, which can also be converted back into text. The geometry of the design model can be formed with the help of AutoCAD. ANSYS is another computer tool for solving engineering problems and carrying out the calculation process (CAE-tools). This software was designed to optimize the

Figure 5: Computer models of the structure.

STRUCTURE magazine

April 2013

Figure 4: Installing elements by working with climbing equipment.

development of the early stages of design, reduce the cost of production and the development cycle of new products, and minimize the number of field tests. It performs simulation using the finite element method and facilitates solving all kinds of problems from various areas of physics, including structural, thermal, hydrodynamic, and electromagnetic mechanics, as well as combinations thereof. Finally, ADVANCE STEEL provides parametric three-dimensional modeling of steel structures and provides tasks for a 5-axis CNC machine to manufacture components. It is a powerful, easy-to-use tool based on Building Information Modeling (BIM) technology. The program automates the entire process of creating working drawings, specification sheets according to Government Standards, and CNC data. This improved the quality of the drawings, reducing the risk of errors. The main lessons from the design and construction of the flower bud will be learned later, after the building has been operating for some time, and will be linked to the climatic conditions of Siberia – not just winter’s cold, but also summer’s heat. However, from one standpoint, the experiment is already a success: the entire process used only local labor, without the involvement of outside contractors, and its features and overall aesthetic are promising to serve as a new beginning in the architecture of the Siberian city.▪

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Code Listed

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In the SpecS On the JOb At YOur ServIce™

A Worthy Wager Innovation at Federal Center South By Jim O. Swenson, P.E., S.E. and Jason Black, P.E., S.E.

The Commons. Courtesy of Benjamin Benschneider.

ederal Center South Building 1202 is a state-of-the-art, high performance office space for the Seattle District Headquarters of the United States Army Corps of Engineers (USACE). KPFF Consulting Engineers provided both civil and structural engineering services, from the design competition phase through to completion of this showcase High Performance Green Building project. Top among the many innovative design features that the project boasts is perhaps the largest use of a composite concrete and timber floor system in the United States. Composite concrete and wood floors were not part of the original design concept but ultimately became critical to achieving the project goals. This is that story.

conference rooms and shared facilities. The design called for a beautifully finished, exposed, concrete floor that could also be used to encapsulate and hide some building system elements such as conduit. A concrete floor also had the advantage of being highly durable and low maintenance, and could be used as a structural diaphragm to transmit lateral forces to concrete shear walls. There was also a strong desire that the structure of the Commons feature the salvaged timber. The final architectural/structural floor solution in the Commons consisted of 4 inches of concrete over salvaged 2x6 timber decking supported by 8x16 wood beams spanning an average of 22 feet. This framing system was accepted by the GSA and was the basis for the pricing submitted by the design-build team.

Design-Build Competition

Discovery after Deconstruction

In 2009, the General Services Administration (GSA) solicited designbuild proposals for a high performance office building for the USACE at the Federal Center South campus along the Duwamish Waterway in Seattle, Washington. Led by Sellen Construction and ZGF Architects, LLP, the team won the design-build competition in March 2010. Integral to the winning design was the concept of reclaiming heavy timber framing from the existing 1940’s warehouse on the proposed building site, and incorporating it into a significant portion of the new facility.

After deconstruction of the existing warehouse, a comprehensive timber inventory was developed by the GR Plume Company, the

TEMPORARY SUPPORT, TO ALLOW CONC PLACEMENT

The Commons One of the more striking spaces in the building is the centrally located atrium, or the “Commons,” which includes a gathering place, STRUCTURE magazine

4" REINFORCED CONCRETE SLAB 5' WIDE TEST ASSEMBLY

Test assembly diagram.

April 2013

CUSTOM LAG BOLT

2x RECLAIMED TIMBER DECKING

8" x 16" RECLAIMED BEAM

Beam #3 test just prior to failure.

Deconstruction of the warehouse. Courtesy of Charles Lozner.

timber fabricator. This led to the unfortunate discovery that not enough salvaged timber was recovered to completely frame the Commons if the beams were spaced at 4 feet on-center, the calculated spacing using the National Design Specification for Wood (NDS) for conventional non-composite timber beams. A creative solution was required to save the design concept.

hole diameters with a single plunge; a smaller one for the threaded portion and a larger one for the smooth shank. This streamlined the amount of labor required to drill all the lag screw holes and install the lags. Now all that was needed was to put the assembly to the test.

Test Procedure

Defining a Solution KPFF proposed completing the Commons using only the reclaimed timber from the old warehouse by increasing the beam spacing to 5 feet oc. and using composite construction. This innovative approach eliminated the need for non-salvaged timber and retained the character desired by the architect. This was important because the intent was to expose all the framing and it would be difficult to match the aesthetic of the on-site salvaged timber with new wood pieces. Although unproven, the team believed that using composite beams was a gamble worth taking, and one that seemed achievable within the schedule and budget. The GSA and USACE were approached about the idea, with the caveat that they would be able to review and approve both the design and testing procedures. Approval was obtained to proceed.

Design While allowed by the current Uniform Building Code, a specific design methodology is not provided for composite concrete-timber beams by the National Design Specification® (NDS®), ACI 318, or 2009 International Building Code (IBC). This meant that testing would be required as an undefined system per IBC 1604.7. Interestingly, the Eurocode has a method for designing composite concrete-timber elements. In fact, several techniques for achieving composite action are used in Europe, often driven by a need to retrofit very old timber buildings. KPFF’s approach for achieving composite action was to use lag screws as the connectors between the wood and the concrete. To control the number of lag screws required on each timber beam, lag screws were custom fabricated that contained a longer section of un-threaded bolt length than a standard lag. This custom lag led to an innovative fabrication method by the GR Plume Company, which developed a drill bit that drilled two different

The team initially chose 3 full-size, representative beams from the salvaged timber for full scale testing. It was acknowledged that 3 samples would not necessarily represent a significant statistical data set, and that the result of each test sample would ultimately have to be taken on its own merits. Then a decision would have to be made as to whether to proceed with construction using composite beams. KPFF developed a test procedure in accordance with IBC section 1715. The procedure addressed the physical test setup, the load increments (concrete eco-blocks), the order and location of how the load increments would be applied, what kind of data would be collected, how the beams would be instrumented, and what the criteria for success and failure would be. It was also critical that all aspects of the test assemblies replicate the eventual in-place construction as close as reasonably possible. The onsite testing was conducted in an area of the warehouse that had previously been used for heavy manufacturing. KPFF performed finite element modeling to evaluate the existing slab and foundations below where the testing would occur. The analysis demonstrated that the testing would not be affected by deflections of the existing floor and foundation system. Another issue was how to pour the concrete slabs for each test beam. The actual building construction would involve single span wood decking spanning between the beams. In order to produce a flat surface for the bottom form of the concrete, but still ensure a direct connection between the slab and the beams, small notches were cut into the top of the beams to create seats for deck bearing. This kept the top of decking relatively flush with the top of the beams and allowed direct contact between the slab and the beams. Since the test slabs would need to include only half of a span on each side of a beam, the edges of the concrete were supported by short “pony walls”. It was critical to repeatedly cut down these walls to shorten them after the initial concrete set to ensure they were not shoring up the composite slabs during the curing process. These walls remained as a safety measure during test loading. continued on next page

STRUCTURE magazine

April 2013

Commons interior. Composite floor above. Courtesy of Benjamin Benschneider.

Initial Beam Testing Before installing the decking, lag screws, reinforcement, and slabs, it was decided to try and obtain modulus of elasticity (E) values for the bare beams. A test was performed to load a beam with a single load increment, measure the deflection and back-calculate a value of E. Additionally, vibration testing was performed to establish the natural frequency and back-calculate an E value using the vibration response. This testing indicated an average E of 2,500 ksi, compared to the NDS design value of 1,600 ksi. Taking the time to establish this true value of E would prove to be a very useful decision. After the composite test beams were constructed, the slabs were allowed to cure for 28 to 30 days, with 12 to 14 deflection measurements taken to evaluate creep over the cure time. The amount of measured creep for the 3 beams ranged from about 3/16 to ¼ inch, showing very little spread between them. Sellen constructed the test beams, support frames, and loaded the beams during testing. KPFF instrumented the beams and took measurements during the tests. GSA and USACE were kept aware of the testing process and were invited to attend.

Final Testing With the test specimens cured and in place, it was time to try to break things! The test process required that each composite beam hold twice the design live load (2x80 psf ) for 24 hours and then be able to recover 75% of the measured deflection within 24 hours of being unloaded. The first beam passed this test with flying colors, as did the other two. In fact, one beam recovered 91% of its measured deflection from this portion of the test. None of the three exhibited any physical signs of distress from this initial loading phase. STRUCTURE magazine

Aerial of completed project.

After conducting the required test for twice the live load on each specimen, each beam was tested with the intent of failing it. For beam #1, concrete eco-blocks (weighing 1750 pounds each) were placed until the beam was carrying 38,500 pounds of blocks, or more than 400% of the design live load. This was unexpected. Additionally, there were no visible signs of distress at that point. It was decided to stop at that load and let it sit fully loaded for 24 hours. No visible signs of distress were observed after 24 hours. For beam #2, concrete blocks were stacked on the assembly until 56,000 pounds of load was present, more than 600% of the design live load. At this point there were safety concerns because the entire slab-beam “T” section was beginning to rotate; loading was stopped in order to avoid the whole assembly toppling over. No visible signs of failure or distress were observed then, or after the blocks were removed. The deflection gages had maxed out with a value of 1.285 inches at around 550% of design live load. Due to the experiences with beams #1 and #2, the loading procedure for beam #3 was altered to use larger eco-blocks for the initial loading course to allow more weight to be stacked with a lower center of gravity. At just over 500% of the design live load, a small crack was

April 2013

detected around a knot at about a third point in the beam span. At about 650% of design live load, the crack lengthened and a series of cracking sounds were heard. Finally, at 61,250 pounds of load, it was decided that it wasn’t safe to load the beam any further. About 10 minutes after this last load increment was placed, the wood beam failed in flexure with a sudden, loud crack!

Composite Action

Building Data: Size: Three-story, 209,000 SF building Reclaimed heavy timber and decking in Commons: 300,000 BF Targeting LEED Gold

Team:

All three of the test specimens supported significantly more than the required load with no signs of distress. There was no question that the system had adequate capacity, but how much composite action was achieved? After analyzing the deflection results, it was estimated that the amount of composite action achieved probably ranges from 60% to 80%, depending the value of “E” used in the calculation. It is likely closer to the lower end of this range, which is consistent with results from testing in Europe for systems with lag screws. If higher composite action is required, then a different technique should be used to develop the composite action. In our case, it was enough.

Summary Federal Center South Building 1202 is a definitive statement that visionary architecture, innovative engineering and design/build delivery methods can produce world class architecture worthy of celebration. Creative problem solving, a willingness to take risks, and a high degree of trust within the design build team all combined to allow the delivery of a world class facility with a truly innovative concrete and timber composite floor system.▪

Owner: General Services Administration (GSA) Tenant: United States Army Corps of Engineers (USACE) Seattle District Structural & Civil Engineer: KPFF Consulting Engineers Contractor: Sellen Construction Timber Fabricator: GR Plume Architect: ZGF Architects, LLP

Funding:

American Recovery and Reinvestment Act (ARRA)

Jim O. Swenson, P.E., S.E., is an Associate and project manager with KPFF Consulting Engineers. He was the lead engineer for the design and testing of the composite beam system used on Federal Center South 1202. Jim can be reached at JimS@kpff.com. Jason P. Black, P.E., S.E., is a Structural Principal with KPFF Seattle. Jason can be reached at Jason.Black@kpff.com.

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STRUCTURE magazine

April 2013

SFPUC Headquarters Building An Innovative High Performance Structure By Leo Panian, S.E. and Nick Bucci, S.E.

he San Francisco Public Utilities Commission’s (SFPUC) new headquarters in San Francisco, California, set a new standard for high-performance structures when it opened in June 2012. The building, slated for LEED Platinum certification, is a showcase for a host of leading-edge sustainable design elements, making it one of the greenest office buildings in the nation. In this case, the design of the structural system, including its post-tensioned concrete shear walls and construction materials, made key contributions in achieving this distinction. The structural design followed a simple strategy of creating a highly durable and resilient structure that could be built with significantly reduced environmental impact, for a cost that was comparable to a more conventional design. In seismic country, the key to durability and resilience is designing a structure that is able to withstand a major earthquake with minimal damage. As a provider of lifeline infrastructure, the SFPUC was keen to ensure that the new facility could be easily repaired and reoccupied immediately after a large earthquake. This meant designing to a higher standard of seismic performance, which would limit structural deformations during a major shock and allowing the building to return to its original plumb position, protecting the building, occupants, contents and its systems. An innovative approach using post-tensioned concrete shear walls with composite link beams was applied to cost effectively satisfy the ambitious seismic criteria. The high-performance seismic design of the SFPUC was based on a two-tiered criteria, which required that the structure would meet 1.0% maximum interstory drift under the design basis earthquake (DBE), corresponding to a return period of 475 years, and 1.5% maximum drift under the maximum considered earthquake (MCE), corresponding to a 2,500-year return period. Moreover, the structural system has the ability to recenter the building, resulting in negligible residual deformations. In comparison, a similar building designed to conventional standards would be allowed a maximum drift of 2.0% under the DBE, with no limit on residual drift. Major non-structural components, including the exterior cladding and the mechanical, electrical, and plumbing equipment of the building were designed to

Figure 2: Schematic view of underside of floor framing and core walls.

Figure 1: Completed SFPUC building.

Figure 3: Isometric view of core walls.

STRUCTURE magazine

April 2013

Figure 4: Schematic cutaway view of the structural system.

Figure 5: Mat foundation reinforcing with curved saddle for post-tensioning of the vertical post-tensioning cables.

remain substantially free from damage during the DBE event. The exterior cladding system was explicitly designed to remain damage-free at the DBE event and operable with limited damage at the MCE event. The thirteen-story structure extends almost 200 feet above grade and comprises roughly 277,500 square feet (Figure 1 ). The structural system consists of a framing system of post-tensioned concrete slabs and beams supported on concrete columns and concrete core walls. The core walls, located at each end of the building, provide the building’s lateral resistance (Figure 2 ). The floor plan consists of an asymmetrical column-grid arrangement with long spans (nearly 41 feet) in the transverse direction of the building and short spans (20 feet) in the longitudinal direction (Figure 2 ). With this arrangement, a flat-plate slab solution would be impractical and inefficient. The structural engineers devised an efficient framing solution consisting of shallow transverse post-tensioned beams and one-way longitudinal post-tensioned slabs. The beams are typically 36 inches wide and 16 inches deep, and the slabs 6 inches thick. The two concrete core shear walls are founded on a 10-foot-thick mat foundation atop micropiles embedded 65 feet below. This combination of mat foundation and micropiles are intended to resist the seismic overturning load (Figure 3 ). The micropiles are approximately 10 inches in overall diameter and consist of a continuous 2.5-inch diameter high-strength threaded rod that is inserted into the drilled shaft and then pressure grouted, creating piles capable of achieving

high tension and compression strengths. While micropiles have traditionally been used in retrofit and transportation applications, there are several advantages to using micropiles for new construction. Their small diameter allows for a higher concentration of strength and stiffness per area, and the piles can be field tested, which allows for a more efficient design. For seismic resistance, the building uses an innovative system of self-centering concrete core shear Figure 7: Hydraulic stressing jack walls and composite link beams being placed over the vertical post(Figure 4 ). The shear wall design tensioning tendons. consists of conventional bonded reinforcing and vertical unbonded post-tensioning (PT) cables. At each core wall, the vertical post-tensioning tendons extend from the top of the core wall down through a saddle within the mat foundation (Figure 5 ) and back up to the top of the wall. Each of the two core walls contains eight tendon bundles that are about 400 feet long. Each bundle comprises up to 28 continuous 0.6-inch diameter strands. The vertical post-tensioning helps to provide the strength and elasticity needed to recenter the structure. Additionally, the vertical post-tensioning tendons allow for a reduction of approximately 50% in the quantity of the vertical bonded mild-steel reinforcing in the walls. This reduces labor costs and minimizes wall congestion. The cables are post-installed through corrugated steel ducts that are installed in the walls (Figure 6 ) and stressed at the top of the structure with a hydraulic jack (Figure 7 ). During a seismic event, the mild-steel reinforcing bars yield to dissipate energy, much like the behavior of a conventional concrete shear wall. However, the unbonded tendons remain elastic to provide a positive restoring force that recenters the structure. The walls are proportioned so that the overall flexural strength attributable to post-tensioning alone is approximately 50% of the total flexural strength of the wall. It is critical that the walls are detailed to maintain sufficient ductility and good hysteretic behavior under the high compressive strains and repeated load reversals. This is even more important for a PT shear wall, where the PT imposes additional compressive force on the wall. In order to ensure adequate compressive strength at the wall boundary zones, the walls were constructed of high strength concrete designed to reach a compressive strength of

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STRUCTURE magazine

April 2013

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Figure 9: Rendering of the composite link beam and shear-wall reinforcing.

Figure 8: Typical shear-wall cross section.

8,000 psi at 90 days. Additionally, special care was taken while detailing the boundary zones by adding extra confining reinforcing to extend the strain capacity of the concrete at ultimate loading. Nonlinear response history analysis was used to predict forces in critical elements, eliminate non-ductile failure modes, and ensure stable flexural mechanisms. The walls are heavily reinforced at the plastic hinge zone and first several levels of the structure. A typical wall cross section at the plastic hinge zone is shown in Figure 8. The wall consists of #10 vertical bars at both the boundary areas and at the distributed field reinforcing, with #9 horizontal shear reinforcing. At the boundary zones and areas of high compression force, the walls are confined with #5 cross ties and stirrups. In order to expedite onsite construction speed, the boundary reinforcing cages were preassembled with the stirrups installed. The horizontal reinforcing bars were lapped outside of the boundary zone to allow for easier field installation and T-heads were used to limit the congestion. The composite link beams are another innovation incorporated into the structural design (Figure 9 ). The core walls enclose some of the building’s elevators, stairs, and mechanical shaft. The door openings into the core create coupling beams formed over the doorways. Traditionally, coupling beams are heavily reinforced, often with diagonal reinforcing, which makes them difficult to construct. For this building, the composite coupling beams were formed with a 3/8-inch thick steel jacket that was designed as both a stay-in-place formwork and beam reinforcing. The link beams are 30 inches wide and vary from 20 to 36 inches deep (Figure 10). The external steel jacket alters the behavior of the link beam in a fundamental way. Under cyclical seismic loading, the steel jacket forces a single flexural crack to form at the face of the wall, rather than allowing the distributed cracking that would be expected in a plastic hinge region of a conventional beam. Furthermore, the steel jacket relieves the compressive strains on the concrete and allows for a more ductile response with less degradation in strength and stiffness. These effects required several specialized design considerations. The longitudinal reinforcing bars in the link beams were debonded from the surrounding concrete with waxed sleeves at the joint between the steel jacket and the concrete core wall to allow an adequate plastic strain length, to prevent premature tensile fracture. In addition, embedded steel brackets were provided to mechanically restrain the link beam, ensuring a direct, reliable transfer of shear at the interface with the walls. The external steel jacket eliminates the cracking and spalling damage that would otherwise be expected with a conventional coupling beam, thus minimizing the need for extensive post-earthquake repairs. STRUCTURE magazine

Figure 10: Link beam steel jacket.

As the SFPUC was designed to achieve LEED platinum status, it was important for the team to address the environmental impact of the concrete. Through a collaborative partnership between Tipping Mar, the general contractor, and the concrete supplier, custom low-cement concrete mixtures were developed that were shown to reduce the carbon footprint of the material by 50% overall. The high-strength green-concrete mixes were tailored for each application, and specified the replacement of Portland cement by up to 70% using a combination of slag and flyash. The SFPUC headquarters project embodies the spirit of the institution it serves. It represents a significant advancement in how office buildings are designed and built. In this spirit, Integrated Project Delivery (IPD) was selected for the design and construction of the building. This delivery method allows for a collaborative relationship between the owner/ developer (SFPUC and SF DPW), the contractor, and designers, whereby the risks and rewards are shared. This building’s design and construction is a demonstration and guiding example of how leading-edge technologies and innovations can come together to fulfill an ambitious civic vision of sustainability.▪ The building was designed through the collaboration of KMD Architects and Stevens and Associates Architects, with Tipping Mar and SOHA Engineers performing the structural engineering design. Webcor Builders was the general contractor and Central Concrete was the concrete supplier for the project. San Francisco’s Department of Public Works was responsible for managing the project.

Leo Panian, S.E., is a principal at Tipping Mar, Berkeley, California, and served as associate-in-charge on the SFPUC headquarters project. Leo may be reached at Leo.Panian@tippingmar.com. Nick Bucci, S.E., is a project manager at Tipping Mar and served as project manager on the SFPUC headquarters project. Nick may be reached at Nick.Bucci@tippingmar.com. All graphics courtesy of Tipping Mar. April 2013

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W. Gene Corley The Structural Engineering Community Mourns the Loss of an Innovative Leader

n March 1st, the structural engineering community was saddened by the news of the passing of Dr. Gene Corley after a brief battle with cancer. At age 77, Dr. Corley had accomplished much in his career, but was most notably known for his investigation of the collapse of the World Trade Center towers after the terrorist attack on September 11, 2001. A recognized industry leader, Gene was at the forefront of the structural engineering profession, and the development of building codes and standards. W. Gene Corley was born in in 1935, the son of the late Clarence W. and Mary Douthit Corley of Shelbyville, Illinois. Gene was influenced from a young age by his father, a contractor who built single-family homes, shopping malls and grocery stores. In an interview with Dr. Corley by the Chicago Tribune in 2001, Gene mentioned that “I was on building sites even before I was big enough to crawl.” He graduated from Shelbyville High School in 1954 and went to study architecture, but didn’t think he could draw well enough. An early indicator of his dedication to the field of structural engineering was his commitment to his education, receiving a Bachelor of Science Degree in Civil Engineering (1958), and a Masters (1960) and Doctorate in Structural Engineering (1961), all from the University of Illinois. Upon completion of his Ph.D., he served as a commissioned officer in the U.S. Army. During this period, Dr. Corley was a research and development coordinator with the U.S. Army Corps of Engineers at Fort Belvoir, Virginia. His duties included bridge design, acceptance testing of mobile floating assault bridge equipment, design of tank launched bridges and fatigue testing of bridges fabricated from high strength steel, aircraft aluminum and titanium alloys. In the 1960s, Gene turned down a job with NASA working on the lunar rover program, and took a position at the Portland Cement Association (PCA), a nonprofit that represents cement companies. According to Gene, “After I finished my Ph.D at the University of Illinois, I spent three years in the military. At the end of that, I interviewed all over the state. I had some fantastic opportunities at that time. It was a really good time for engineers to look for work. I actually had offers for more money to do other things, but I felt that the offer from the Portland Cement Association was exactly in line with what I’d been trained to do, and was my best opportunity...” As demand for consulting grew, the research and development laboratory for PCA was eventually spun off as a for-profit company, expanding into other building materials and engineering issues and offering engineering, testing, and consulting services. First known as Construction Technology Laboratories, the firm changed its name to CTLGroup in 2005 to reflect the fact that it provided both laboratory services and engineering consulting services. When CTLGroup first became an independent subsidiary, it expanded its scope of services beyond concrete and modified its structures laboratory to incorporate the testing of steel structures. While serving in successively more responsible positions, Dr. Corley was directly involved in the development of improved design procedures for structural concrete, concrete pavement, railroads and structures subjected to fire loads. In addition, he served on earthquake STRUCTURE magazine

damage investigation teams, carried out investigations of damaged or deteriorated structures and developed repair procedures for numerous buildings and bridges. Gene served as an expert advisor during the investigation and trial resulting from the 1993 fatal fire at the Branch Davidian complex in Waco, Texas. In 1995, Dr. Corley led the investigation of the structural performance of the Alfred P. Murrah Federal Building in Oklahoma City, following the bombing there. He served as the head of the Building Performance Assessment Team (BPAT) which involved the American Society of Civil Engineers, as well as representatives from the Federal Emergency Management Agency (FEMA), the United States Army Corps of Engineers, the General Services Administration, and the National Institute of Standards and Technology. Commenting on how his career evolved, Gene highlighted the emergence of “forensic” engineering. “…there definitely have been big changes. One of the changes is that at the time I was hired as a development engineer for the PCA laboratories, the science of construction forensic work really didn’t exist. There were very few people doing anything like that at the time. When I started with PCA, I was doing work to develop new design concepts and better ways to use concrete. Really most of my work dealt with ways to develop more economical and safer high-rise buildings. That’s what I started doing. Then, as I progressed in my experience, I was put in charge of all engineering uses of concrete … as time went along, I started getting hired as a consultant on jobs where people either wanted to

April 2013

do things that were unusual -that hadn’t been done before -or they had tried to do something and had run into trouble and needed help in finding a solution to the problem. That led into the investigation of more and more troubled structures and eventually into the investigation of collapses -finally, of major collapses and major problems with structures of all types.” Dr. Corley built his reputation as one of the world’s experts on structures damaged by natural and manmade disasters as he investigated some of the most notable building failures in recent U.S. history, earning him the label of the “preeminent expert on building collapse investigations and building codes” by the American Society of Civil Engineers (ASCE). As the nation and the world watched coverage of the September 11, 2001 attack on the World Trade Center’s (WTC) twin towers, the following fires, and the eventual collapse of the World Trade Center Towers, the engineering community immediately began to ask questions: How were the towers able to withstand the enormous impact of a 767 without collapsing? Could anything be done to make the buildings survive longer in the ensuing fires? To help answer these questions, the American Society of Civil Engineers/Structural Engineering Institute and FEMA joined together to study the performance of collapsed and damaged buildings, and asked Dr. Corley to lead the team. With the cooperation of nearly a dozen other societies and organizations, this team of 23 Structural and Fire Protection Engineers completed their work on May 1, 2002. Gene would describe the methodologies and findings of the WTC investigation in later interviews. “There are usually two parts to any investigation like that. The early investigation needs to be done rapidly and with whatever resources are available at that point, and from that first investigation, recommendations can be made for, in some cases, further investigations, and for whatever can be done differently, such as changes in building codes… we had to find out what happened at the WTC, to preserve evidence of what had happened, and to recommend what additional work, if any, needed to be done.” “We found one piece of steel across the street from Tower 1 and by reading the numbers on it, we could identify that it was from the area above where the aircraft went in, and where there was fire in Tower 1. The building it was imbedded in had no fire in it. By looking at the piece of steel, we could see that on one end, it showed no indication of fire, and that end was in a position low enough to be below the fire, but the other end was smoke-coated and had fire damage. This showed something very important, and that was that at the time it was in the fire there was no fireproofing on that piece of steel. That was important in bringing us to the conclusion which the National Institute of Standards and Technology (NIST) came to also, i.e., that when the planes hit the buildings, they knocked off fire proofing from the steel and that left the steel more vulnerable to fire after impact.” W. Gene Corley authored hundreds of technical papers and books, and frequently lectured on the subjects of prevention of failures, effects of earthquakes and design and repair of structures. Dr. Corley was passionate about codes and standards that affect structures, and chaired ACI Committee 318 for six years as the committee developed the 1995 Building Code Requirements for Structural Concrete. He also served on several other national and international committees that prepared recommendations for structural design and for design of earthquake resistant buildings and bridges. His professional activities resulted in his receiving numerous national and regional awards. Dr. Corley served in leadership roles for several professional organizations, both national and international, including the National Council of Structural Engineers Associations STRUCTURE magazine

(NCSEA), the Structural Engineers Association of Illinois (SEAOI), the Illinois Structural Engineering Board (ISEB), the National Council of Examiners for Engineering and Surveying (NCEES), and the ASCE/SEI Technical Council on Forensic Engineering. Notably, Gene was instrumental in the formation of NCSEA. As a past president and leader of SEAOI, he, along with Jim Cagley, Paul Fratessa (deceased), and a few others, founded NCSEA in 1993. Gene served on the first Board of Directors and was the fourth NCSEA President, from 1996-1997. During his presidency, the organization recapitalized, moved its offices, and hired a new executive director. Gene loaned his talents and prestige to the upstart organization and was instrumental in its success. He was passionate regarding the role of structural engineers in the protection of the public. Dr. Corley also strongly supported licensing of structural engineers. “The structural engineer is the only one always responsible for life safety,’’ said Corley. “To provide life safety takes a level of knowledge in structural engineering. It is not enough to know civil engineering.” “Gene’s legacy in the structural engineering profession is unparalleled. He was an innovative thought leader who consistently contributed generous amounts of his time and knowledge to the profession,” said Jeffrey L. Garrett, Ph.D., S.E., CTLGroup President & CEO. Dr. Corley’s interest in the structural engineering profession was demonstrated daily by his tireless efforts in helping state structural engineering associations, giving technical presentations and seminars, and teaching examination review courses. He didn’t leave a list of monumental structures for the world to remember him by; and there are no bridges or high rise buildings associated with his name. Gene left something much more significant. He left a legacy of service to the profession of structural engineering, along with a reputation of integrity, astounding knowledge, and class. Gene Corley is survived by his wife of 53 years, Lynd, three children (Anne, Bob, and Scott) and nine grandchildren. Please join NCSEA, SEI, CASE and STRUCTURE magazine in sending condolences to Dr. Corley’s family.▪

Quotes attributed to Dr. Corley were taken from an interview conducted by Laurence W. Johnson of the Skokie Public Library in 2011, transcripts of numerous committee meetings, and general comments recorded in the press. April 2013

InSIghtS

new trends, new techniques and current industry issues

Bridge Fatigue By Y. Edward Zhou, Ph.D., P.E., M. ASCE

atigue specifications for the design of new, and evaluation of existing, highway bridges are provided by AASHTO in the LRFD Bridge Design Specifications (LRFD) and the Manual for Bridge Evaluation (MBE), respectively. Recently published NCHRP Report 721 Fatigue Evaluation of Steel Bridges contains the latest developments in fatigue evaluation of existing bridges. Steel fatigue refers to localized damages caused by cyclic stresses of nominal magnitudes well below the static yield strength of the steel. Fatigue damage on steel bridges has been categorized as either load-induced or distortion-induced. Load-induced fatigue is due to the primary in-plane stresses in the steel plates that comprise bridge member cross-sections. The stresses for load induced fatigue can be directly correlated with the bridge live load using conventional design theories, and are typically calculated and checked in the fatigue design or evaluation process. Distortion-induced fatigue is due to secondary stresses in the steel plates that comprise bridge members. These stresses, which are typically caused by out-of-plane forces, can only be calculated with refined methods of analysis or measured by strain gages, far beyond the scope of a conventional bridge design or evaluation. AASHTO fatigue specifications classify commonly used steel bridge details into fatigue Categories A, B, B', C, C', D, E and E' based on their fatigue characteristics. The “S-N curves”, where S is the stress range of a constant amplitude cyclic loading and N is the number of cycles to a fatigue failure, define a lower-bound fatigue resistance for each of the categories. The S-N curves also contain a constant-amplitude fatigue threshold (CAFT) for each fatigue category. No fatigue damage is assumed to occur if the stress range from a constant-amplitude loading is below the CAFT. For the evaluation of existing riveted bridges, AASHTO provides additional information for fatigue classification. The MBE suggests that the base metal at net sections of riveted connections of existing bridges be evaluated as Category C fatigue detail instead

of Category D as specified in the LRFD for the design of new bridges, to account for the internal redundancy of riveted members. NCHRP Report 721 provides further guidelines for the fatigue resistance of tack welds and riveted connections. Tack welds are common in old riveted steel structures, and their fatigue strength has not been welldefined in previous specifications. It was suggested that tack welds of normal conditions be evaluated as a Category C fatigue detail, as opposed to Category E for “base metal for intermittent fillet welds” as defined in previous AASHTO specifications. It was also suggested that for riveted members of poor physical condition, such as with missing rivets or indications of punched holes, Category D should be used. One of the most important issues in bridge fatigue life assessment is to determine the variable-amplitude stress range spectrum, or histogram, that the fatigue detail is subjected to, and an effective stress range that can properly represent the entire histogram for equivalent fatigue damage. The AASHTO MBE allows alternative methods for estimating load-induced stress ranges for fatigue life assessment. These methods include: simplified analysis and the LRFD fatigue truck loading; simplified analysis and truck weight from weigh-in-motion study; refined analysis and the LRFD fatigue truck loading; refined analysis and truck weight from weigh-in-motion study; and lastly, field-measured strains under actual loads. The MBE provides different load factors for estimating the effective stress range using these methods. NCHRP Report 721 introduced a Multiple Presence Factor for adjusting the calculated effective stress range based on the AASHTO single-lane fatigue loading to account for the simultaneous presence of trucks in multiple lanes based on weigh-in-motion data. Evaluation of load-induced fatigue includes the infinite fatigue life check and finite fatigue life estimate. Only bridge details that fail the infinite life check are subject to the more complex finite life assessment. The fatigue life of a fatigue-susceptible detail is infinite if all the stress ranges the detail

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experiences throughout its service life are less than the constant amplitude fatigue threshold (CAFT). NCHRP Report 721 clarified the infinite life check and recommended that (Δf )max (maximum stress range expected at the fatigue-prone detail) be taken as 2.0(Δf )eff (effective stress range due to variable amplitude bridge loading) for calculated stress range due to a fatigue truck determined by a truck survey or weigh-in-motion study, or the larger value of two times field measured effective stress range or the field measured maximum stress range, unless another suitable value is justified. NCHRP Report 721 also provided several refinements to finite fatigue life assessment, including: (1) adding an Evaluation 2 fatigue life level; (2) providing a closed form solution for the total finite fatigue life using an estimated traffic growth rate and the present (ADTT)SL (average number of trucks per day in a single lane); (3) introduction of Fatigue Serviceability Index for measuring the performance of a structural detail with respect to its overall fatigue resistance; and (4) providing recommended actions for varying calculated values of the fatigue serviceability index. The general procedure for evaluating load-induced fatigue should begin with the simplest stress-range estimate allowed by AASHTO. If the detail passes the infinite life check, no further refinement is required. However, if the initial analysis suggests that the detail does not have infinite fatigue life, a refined procedure should be considered. Engineering experience has demonstrated that field strain measurement can most accurately determine live load-induced stress ranges of variable amplitude.▪ Y. Edward Zhou, Ph.D., P.E., M. ASCE, is the National Practice Leader – Bridge Instrumentation & Evaluation of URS Corporation, and is based in Germantown, Maryland. He is a past chairman of ASCE Committee on Fatigue and Fracture. Edward may be reached at ed.zhou@urs.com.

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LEGAL PERSPECTIVES

discussion of legal issues of interest to structural engineers

Can I Just Cross Out The Words “Payment In Full”? By Gail S. Kelley, P.E.

isputes over payment are seldom pleasant. They can be particularly unpleasant when a client claims that the work was in some way deficient or less than what was required by its contract, and refuses to pay the full amount of the contract. If the amount in question is large and the claim is unjustified, it may be worth taking legal action. Unless the client can prove that the work was less than what was contracted for, refusal to pay the contract price constitutes a material breach of contract.

L L U F T IN

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Negotiating a Reduction in the Contract Amount If the amount in question is not large, it may make more sense to negotiate a reduction in the contract price. The legal term for this is accord and satisfaction. The agreement on the amount owed is the accord; payment of this amount is the satisfaction. The legal basis for the accord is that because the client allegedly did not receive what it bargained for, it does not actually owe the contract amount. The amount owed is thus considered unliquidated, which means that it cannot be determined from the contract. The doctrine of accord and satisfaction evolved from common law principles that encourage parties to settle a disputed debt without judicial intervention. The client must believe, in good faith, that the work done was in some way less than what was contracted for; it cannot simply refuse to pay in order to reduce the contract amount. The client is considered a debtor since it owes some amount of money for the work done. The party that did the work is considered a creditor. The accord is a second contract between the parties; as such, it should specify not only the amount that will be paid, but also when the payment will be made, and any other relevant payment terms. The accord does not replace the original contract, but the original contract is suspended until the payment is made. When the payment is made, both the original contract and the accord are discharged. If the payment is not made, there is no satisfaction and the creditor can take legal action based on either the original contract or the accord.

Receiving a Check for Less than the Contract Amount Sometimes, there is no negotiation on the amount of the reduction, the client simply sends a check for less than the amount of the contract and writes a notation such as “payment in full” on the face of the check or the accompanying voucher. The creditor’s rights in such a situation require a little more discussion. Historically, this was simply considered an accord and satisfaction. As long as the check or voucher made it clear that the check was intended to be full payment, the creditor, by cashing the check, was deemed to have agreed to the amount. The creditor could not avoid the accord by crossing out the payment-in-full language. Similarly, it could not avoid the accord by adding “Cashed under protest” or “Cashed with reservation of rights” to its endorsement. In some cases, the creditor may have been forced to cash the check in order to pay its own bills. Nevertheless, courts generally held that the creditor had accepted the accord, even in cases of extreme financial hardship. The only way the creditor could avoid the accord was by either returning or destroying the check.

Changes in the Uniform Commercial Code In the 1970s, however, a new version of the Uniform Commercial Code (UCC) was published. The UCC is a model code

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whose goal is to harmonize the law related to sales and financial transactions between the diﬀerent states. Like other model codes such as the International Building Code, the UCC does not become the law in any state until it is adopted by that state. A state may adopt all or part of a model code, or may adopt it with amendments that modify or add sections. The new version of the UCC included a section (§1-207) which stated that if a party accepted performance with an explicit reservation of rights, it did not prejudice the rights reserved. The new version of the UCC also included a section that allowed a creditor who had cashed a full payment check to “undo” the satisfaction by returning the money within 90 days. Although the UCC strictly applies only to the sale of goods, several states have extended its provisions to transactions involving services. In addition, some states have held that UCC provisions apply to services when payment is by check, because such a payment would fall within the UCC provisions on Negotiable Instruments. After adoption of the new version of the UCC, courts in several states held that if the recipient of a full payment check made it clear that the check was being cashed under protest, the recipient did not lose its rights to sue for the balance owed. Words such as “without prejudice” or “under protest” (so-called words of protest) on the back of the check were suﬃcient to preserve the recipient’s rights.

Return to the Common Law Accord and Satisfaction These rulings were widely challenged, though, and in all states except New York, were subsequently overturned on appeal. By and large, the appeals courts held that UCC §1-207 was not meant to supersede the common law accord and satisfaction. UCC §1-207 was subsequently renumbered to §1-308 and revised to make it clear that it did not apply to an accord and satisfaction. Reservation of rights under the UCC is now limited to situations where a party agrees to accept the other party’s performance, even though the performance is not in accordance with contractual requirements. As an example, a party might agree to accept delivery of defective items because they could not obtain replacement items in time. If the party made it clear that they were reserving their rights, they would probably be entitled to an adjustment in the contract price, unless the contract explicitly stated that acceptance waived all rights to an adjustment. The amount of the adjustment would be based on the party’s “damages” – in other words, any costs the party had incurred because the items were defective.

Current Holdings on Accord and Satisfaction Although there have not been any reported cases recently, New York courts apparently still allow the recipient of a full payment check to reserve its rights even though it has cashed the check. In addition, a few states allow a creditor to undo a satisfaction by returning whatever money was received within 90 days. Nevertheless, public policy supports certainty in business transactions; if a creditor cashes a check marked “payment in full,” courts in most states will hold that the entire debt is discharged. One exception is if the debtor intentionally misrepresented its entitlement

to a reduction in the amount of its debt. Intentional misrepresentation is fraud; any time a party is induced to enter into a contract by fraud, the contract (in this case the accord) can be voided, even if it has already been satisfied.▪ Gail S. Kelley, P.E., is a LEED Accredited Professional as well as a licensed attorney in Maryland and the District of Columbia. Ms. Kelley is the author of Construction Law: An Introduction for Engineers, Architects, and Contractors, published in 2012 by John Wiley & Sons. Ms. Kelley can be reached at Gail.Kelley.Esq@gmail.com.

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Education issuEs

core requirements and lifelong learning for structural engineers

Socrates, How Is Engineering Knowledge Attained? By Erik Anders Nelson, P.E., S.E.

ould Socrates help us understand how structural engineering knowledge is attained? We know from his actions, and through Plato’s writings, that he is clearly able to help us understand the importance of a liberal education. How does this translate to engineering education? For Socrates, education within any classroom needs to foster freedom and inquiry. He is someone who literally lost his life in defense of the spirit of inquiry (read the Apology or Crito). The most telling dialog of Socrates on the importance of inquiry is Plato’s Meno. It is where we find Socrates asking fundamental questions about learning itself and the method of attaining knowledge. The following text was written by Plato in 380 B.C.E. and translated by Benjamin Jowett. I am going to borrow and edit heavily the entire dialog (even replace words) because I think this is exactly the type of conversation that should take place in all of our classrooms. Not only does it teach us the importance of the Socratic method of inquiry, it also can also help us as educators. Meno. Can you tell me, Socrates, whether structural engineering is acquired by theory or by practice; or if neither, then whether it comes to man through testing nature, or in what other way? Socrates. Oh Meno, you have far too good an opinion of me, if you think that I can answer your question. For I literally do not know what structural engineering is, and much less how it is acquired. I confess with shame that I know literally nothing about engineering. Meno. And how will you enquire, Socrates, into that which you do not know? How do we learn something of which we have no knowledge? Soc. I will tell you how: All enquiry and all learning is but recollection. We do not learn, we recollect. Meno. What do you mean by saying that we do not learn, and that what we call learning is only a process of recollection? Can you teach me how this is? Soc. I told you, Meno, and now you ask whether I can teach you, when I am saying that there is no teaching, but only recollection; and thus you imagine that you will involve me in a contradiction!

Meno. Indeed, Socrates, I protest that I had no such intention. I only asked the question from habit; but if you can prove to me that what you say is true, I wish that you would. Soc. It will be no easy matter, but I will try to please you to the utmost of my power. Suppose that you call one of your numerous uneducated slaves, that I may demonstrate on him that the question of learning is recollection. We will have to get to what structural engineering is another day – and concentrate on how one knows things. I will, however, use the area of a column as an example – something I am sure is used by the structural engineer. Meno. Certainly. Come hither, boy. Soc. Tell me, boy, do you know a figure like this section of a column? Is it not a square? Boy. Yes, I do. It is a square. Soc. And you know that a square figure has these four lines equal? Boy. Certainly. Soc. And these lines which I have drawn through the middle of the square are also equal?

Boy. Clearly, Socrates, it will be double the length of the side, so each side will be four. Soc. Do you observe, Meno, that I am not teaching the boy anything, but only asking him questions; and now he fancies that he knows how long the side of the column is necessary in order to produce a column of eight square feet; does he not? And does he really know? Meno. Certainly not. Soc. Observe him while he recalls the steps in regular order. (To the Boy.) Tell me, boy, do you assert that double the area comes from doubling the side? Boy. Yes Soc. But does not this line become doubled if we add another such line here? Boy. Certainly. Soc. And are there not these four divisions in the figure, each of which is equal to the figure of four feet? Boy. True. Soc. And four times is not double is it? Boy. No, indeed. It is four times as much.

Boy. Yes. Soc. A square may be of any size? So a column may be of any size? Boy. Certainly. Soc. And if one side of the column be of two feet, and the other side be of two feet, how much area will the whole column be? Let me explain: if in one direction the column was of two feet, and in other direction of one foot, the whole would be of two feet taken once? Boy. Yes. So two by two would be four square feet. Soc. Good. And might there not be another square column with an area twice as large as this? And what is the area of that doubled column? Boy. Eight square feet of course. Soc. Correct. And now try and tell me what is the length each side if the area of the square column is eight?

Sixteen! Oh no – that column is huge! Soc. So, what side length would give you a space of eight square feet? Is not a space of eight, half the size of sixteen? Boy. Certainly. Soc. Then the line which forms the side of eight square feet ought to be more than this line of two feet, and less than the other of four feet? Boy. It ought. Soc. Try and see if you can tell me how much it will be.

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Boy. Three feet. Soc. And how much are three times three feet? Boy. I am counting and I am close but nine is not eight. So I was wrong again! Soc. But from what length of line would give you eight square feet? Tell me exactly; and if you would rather not reckon, try and show me the line. Boy. Indeed, Socrates, I do not know. Soc. Do you see, Meno, what advances he has made in his power of recollection? He did not know at first, and he does not know now, what is the side of a column of eight square feet: but then he thought that he knew, and answered confidently as if he knew, and had no difficulty; now he has a difficulty, and neither knows nor fancies that he knows. Meno. True. Soc. Is he not better off in knowing his ignorance? If we have made him doubt, and given him the “torpedo’s shock,” have we done him any harm? We have certainly, as would seem, assisted him in some degree to the discovery of the truth; and now he will wish to remedy his ignorance, but then he would have been ready to tell all the world again and again that double the area should have a double side. He would have lived his entire life with false knowledge – and this is just area stuff, I have not even discussed column buckling! Meno. True. Soc. But do you suppose that he would ever have enquired into or learned what he fancied that he knew, though he was really ignorant of it, until he had fallen into perplexity under the idea that he did not know, and had desired to know? Meno. I think not, Socrates. Soc. Mark now the farther development. I shall only ask him, and not teach him, and he shall share the enquiry with me: and do you watch and see if you find me telling or explaining anything to him, instead of eliciting his opinion. Tell me, boy, is not this a square of four feet which I have drawn? Boy. Yes. Soc. And how many times larger is this space than this other? Boy. Four times. Soc. But it ought to have been twice only, as you will remember. And does not this line, reaching from corner to corner, bisect each of these spaces? Boy. Yes. Soc. And how many spaces are there in each section?

Boy. Two, since there are two triangles and one square. Soc. And four is how many times two? Boy. Twice, two times two is four. Soc. And from what line do you get this figure? Boy. From this. Soc. That is, from the line which extends from corner to corner of the figure of four square feet? Boy. Yes. Soc. And that is the line which the learned call the diagonal. And if this is the proper name, then you, boy, are prepared to affirm that in order to double the area of the column, you would square the diagonal?

Boy. Certainly, Socrates. Soc. What do you say of him, Meno? Were not all these answers given out of his own head? Meno. Yes, they were all his own. Soc. And yet, as we were just now saying, he did not know? Meno. True. Soc. But still he had in him those notions of his – had he not? Meno. Yes. Soc. Then he who does not know may still have true notions of that which he does not know? Without any one teaching him, he will recover his knowledge for himself, if he is only asked questions? And this spontaneous recovery of knowledge in him is recollection? Meno. True. Soc. And this knowledge which he now has must he not either have acquired or always possessed? Meno. Yes. Soc. And if there have been always true thoughts in him, both at the time when he was and was not a man, which only need to be awakened into knowledge by putting questions to him, his soul must have always possessed this knowledge, for he always either was or was not a man? Meno. I feel, somehow, that I like what you are saying. Soc. And, Meno, I like what I am saying. Then, as we are agreed that a man should enquire about that which he does not know; that is a theme upon which I am ready to fight, in word and deed, to the utmost of my power.

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In other words, we should want our students to acquire the freedom that allows them to acknowledge the one certainty in life: “Indeed, Socrates, I do not know.” Recognition of that certainty – we are all ignorant – is the pathway to learning. Then learning things will belong to them, instead of just repeating things that belong to others (memorization of facts, test-taking, etc). Future engineers need to process the tools resulting from a liberal education to help us listen and read attentively and deeply, to express ourselves intelligibly and precisely, to measure and question the world, and to seek truth. This will help us become lifelong learners. Another useful result is that it will make us better at understanding the highly technical and theoretical aspects of engineering, too. This may also assist us in deciding difficult questions, such as: Is it a good idea to teach a class that is new, like “Sustainability in Civil Structures” or the highly technical “Advanced Matrix Analysis,” and replace classes that reinforce the basics? There are only so many hours in the current curriculum, so this is important. However, we know that regardless of which class we may add – and consequently which class we remove – every class needs to foster enquiry. We need to resist cramming students’ heads with more and more knowledge (so-called), whether it is more mathematics, new theory based on a particular research agenda, or trends in the marketplace. This may numb the minds of our future engineers. Teaching should be about assisting the student in discovery – i.e., a liberal education – not supplying information or listing the latest facts. We do not want engineers who merely regurgitate what they have been taught and what they have memorized. We want them to struggle, and to engage the world and people in meaningful ways. We want engineers with a spirit of inquiry and love of learning that will last a lifetime. So even if we add courses that submit to trends in the marketplace or wrongly decide that our students need more mathematics, we had better make sure that Socrates joins every class.▪ Erik Anders Nelson, P.E., S.E. (ean@structuresworkshop.com), is owner of Structures Workshop, Inc. in Providence, RI and teaches at the Rhode Island School of Design and Massachusetts Institute of Technology. Please visit and comment on his engineering blog at www.structuresworkshop.com/blog.

Great achievements

notable structural engineers

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

mmann was born on March 26, 1879, in Schaffhausen, Switzerland, the home of the famous 18th century Grubenman wooden bridge. His family was of moderate means with his father in manufacturing and his mother in hat making. At an early age he showed an aptitude for mathematics and began studying for a civil engineering degree at the Polytechnikum in Zürich, Switzerland. He graduated in 1902. The college, now named the Swiss Federal Institute of Technology, was founded in 1854 and was one of the leading schools of science and engineering at that time. He studied under Wilhelm Ritter who visited the United States in 1893 to observe engineering works and described them in his lectures. After graduating, Ammann worked on railroad layout and in 190304 he worked in Frankfurt, Germany on reinforced concrete structures. In 1904, Othmar came to the United States for what he thought would be a few years to work on the major projects he had heard about while in college. He fortunately found a position with the Union Bridge Company under Charles Macdonald and his engineer Joseph Mayer. The company was building some of the major bridges in the country, such as Macdonald’s proposal for a 2,400-foot span cantilever railroad bridge across the Hudson River. With mentors like Mayer and Macdonald, Ammann quickly learned the U.S. methods of building bridges fast and inexpensively. He then moved to Harrisburg, Pennsylvania for a short time to work with the Pennsylvania Steel Company under Frederick Kunz. Then Othmar worked with Gustav Lindenthal as Consulting Engineer to the Department of Bridges in New York City. The Pennsylvania Steel Company was in the process of building the Queensboro (Blackwell’s Island) Bridge at the time. Amman briefly returned to Switzerland to marry Lilly Selma Wehrli and then returned to Harrisburg. He spent a short time at McClintic/Marshall followed by a stint with Ralph Modjeski in Chicago working on bridges for the Oregon Trunk Railroad, including a 340-foot span arch bridge over the Columbia River. He assisted C. C. Schneider in writing a report on the collapse of the Quebec Cantilever Bridge.

As a result of the Quebec failure, Kunz and Ammann wrote a report confirming the safety of the Queensboro Bridge and its design. Between 1909 and 1912, Ammann worked with the newly formed firm, Kunz & Schneider Consulting Engineers, in Philadelphia, Pennsylvania. One of their major projects was an arch bridge across the Reversing Falls at St. John, New Brunswick. In 1912, he was hired by Gustav Lindenthal as his chief assistant on the design of the Hell Gate Arch Bridge. Lindenthal was selected as Chief Engineer for the New York Connecting Railroad, which included the Hell Gate Bridge, as well as Chief Engineer for a bridge across the Hudson River. The Hell Gate Bridge was the longest span arch bridge in the world at the time, and Ammann was in charge of its design and construction, with David B. Steinman as his assistant. The threat of war in Switzerland resulted in Ammann returning to his homeland as an Army Lieutenant in the summer of 1914. Lindenthal advanced Steinman to Ammann’s position. The threatened war did not occur, and Ammann returned to his position and Steinman was demoted. The shift resulted in a bitter rivalry between the two men until Ammann’s death. Lindenthal proposed a bridge across the Hudson River as early as 1885. Due to financing and other concerns, it never got past a groundbreaking in 1895. In 1920 he, with Ammann’s design help, proposed a huge bridge at 57th Street for railroads, motor vehicles and rapid transit costing in excess of $100,000,000. Financing was slow, and Lindenthal and Ammann, with Steinman’s help, designed the Sciotoville Continuous Truss bridge across the Ohio River. It was the longest span truss bridge in the country at the time (1922). Lindenthal sent Ammann to Portland, Oregon where he

Hell Gate Bridge, Lindenthal and Ammann.

STRUCTURE magazine

April 2013

had received a contract to design three bridges across the Willamette River. The Ross Island Bridge was a cantilever, the Burnside Bridge was a truss Othmar H. Ammann. bridge with bascule span and the Sellwood Bridge a continuous truss. Each bridge was unique. Designed in 1922 to 1923, they were built between 1925 and 1926. In 1923, when Ammann returned to the New York office of Lindenthal, work was proceeding on the Hudson River Bridge. There were growing concerns that the bridge was too large and the approaches would take too much land and cost too much. Lindenthal, however, was convinced that a bridge of this size and at this location was absolutely necessary. Ammann went to Lindenthal suggesting that a smaller bridge aimed primarily at automobiles and located farther up the river would receive the necessary support from the city and states. Lindenthal accused Ammann of “timidity and shortsightedness”, and that he was “looking ahead for 1,000 years.” On March 23, 1923 Ammann left Lindenthal and set up his own office in New York City. He worked primarily on his own design for the Hudson River Bridge with no client to pay the bills. It would be at 179th Street between Fort Lee (New Jersey) and Fort Washington (New York), have a span of 3,500 feet and carry eight lanes of automobile and truck traffic. It would be built for under $40,000,000. He first proposed his design at a meeting of the Connecticut Society of Civil Engineers on February 19, 1824 and sent his plan to Governor Silzer of New Jersey. Silzer sent Ammann’s drawings and proposal to the press, including The Engineering Record that published them with a small drawing and brief description in the January 3, 1924 issue. The article mentioned the drawings were by Ammann, and the bridge was estimated to cost $30,000,000 and would connect with the Washington Arch Bridge over the Harlem River to provide “direct access to the Bronx Borough and to highways leading to New England without entering New York’s intensive traffic area.” With

until 1951. This was followed by a survey of the Brooklyn Bridge in 1941. He reported the bridge was in excellent condition. He was appointed chairman of a three man commission, with Theodore VanKarman and Glenn Woodruff, to report on the failure of the Tacoma Narrows Suspension bridge, designed by Leon Moisseff, which fell November 7, 1940 shortly after it opened. They found the long slender deck, designed using the deflection theory, was susceptible to aerodynamic forces that led to the

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Verrazano Narrows Bridge.

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the support of New Jersey and New York, Ammann’s design was accepted and placed under the Port Authority of New York with Ammann designated as Chief Bridge Engineer for the Authority. The bridge was built between 1927 and 1931, and opened October 24, 1931. At the same time he was designing the George Washington Bridge, Ammann was also designing the Bayonne Arch Bridge over the Kill Van Kull leading to Staten Island. It was then the longest span arch bridge in the world (1,652 feet). He also supervised construction of two bridges across the Arthur Kill, the Goethals and Outerbridge, both of which were designed by J. A. L. Waddell. In 1923, Othmar was appointed Chief Engineer of the Triborough Bridge Authority under the legendary Robert Moses. Moses planned a major project consisting of a 1,380-foot span suspension bridge over the East River, 1,600 feet of truss bridge, a 770-foot long lift bridge and 3½ miles of viaduct. The project was built between 1934 and 1936. This was followed by the BronxWhitestone Bridge. It was a 2,300-foot span suspension bridge and opened in 1939 in time for the New York Worlds Fair. While designing these bridges, Ammann maintained his position with the New York Port Authority. At the same time, he was one of the consultants to Joseph B. Strauss on the design and construction of the Golden Gate Bridge in San Francisco. Strauss also consulted with Ammann on his George Washington and Bayonne Bridges. The Golden Gate Bridge, with its 4,200-foot span, surpassed the George Washington Bridge by 700 feet to become the longest suspension bridge in the world at the time. It opened in 1937. He also consulted with one of his early mentors, Ralph Modjeski, on his Benjamin Franklin (originally the Delaware River) Suspension Bridge across the Delaware River that opened up July 1, 1926. Its 1,750 foot span was the longest in the United States at the time. In 1939, Ammann resigned from the Port Authority and set up a partnership with C. C. Combs, a well-known landscape architect. Highway work made up most of their efforts in the first years. Their first bridge work was a pedestrian lift bridge to Ward’s Island in the East River. Ammann called this his “Little Green Bridge”. It had a lift span of 312 feet. Due to financing, it did not open

April 2013

George Washington Bridge 1931 to Present, Single deck shown.

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observed oscillation. With this information, Ammann stiffened his Bronx-Whitestone Bridge in 1946. In 1947, the partnership of Ammann and Combs came to an end, and Ammann formed a new company, Ammann & Whitney Consulting Engineers. Whitney was a well known expert on reinforced concrete. Much of their work came from Ammann’s New York contacts. In 1956, Moses hired the firm to design the Throgs Neck suspension bridge across the East River. The span was 1,800 feet, and it opened January 11, 1961. In 1957, Othmar was called back to his first bridge, the George Washington, to add the lower deck that he had provided for back in the late 1920s. It was added between 1958 and 1961, without stopping traffic on the original bridge. He was asked to serve on a panel of engineers in 1947, with his long time competitor David Steinman, on the Mackinac Bridge connecting the upper and lower peninsulas of Michigan. In 1951, the

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commission rejected a tunnel but determined a bridge was feasible. The earlier design by Modjeski and Masters was rejected, and a new design was sought. Initially Ammann was selected by the Board, but his fee was considered excessive and the contract was given to Steinman. The culmination of his bridge career came when he was selected to design the Verrazano Narrows Bridge between Brooklyn and Staten Island. David B. Steinman also planned a bridge he called the Liberty Bridge at the site as early as 1926. Ammann started his design in 1948. Due to financing, he did not start work until the mid 1950s. The span of the bridge would be 4,260 feet, surpassing the Golden Gate Bridge by 60 feet. Its upper deck opened November 24, 1961 and its lower deck June 28, 1968. When the Verrazano Narrows Bridge opened, Ammann was 80 years old. At its dedication, the Mayor of the City stated the bridge was “a structure of breathtaking beauty and super engineering.” Throughout his career, Ammann had as a guiding philosophy, “Economics and utility are not the engineers only concerns. He must temper his practicality with aesthetic sensitivity. His structures should please the eye. In fact, an engineer designing a bridge is justified in making a more expensive design for beauty’s sake alone. After all, many people will have to look at the bridge for the rest of their lives. Few of us appreciate eyesores, even if we should save a little money in building them.” The story of Ammann and his New York Bridges is told in Six Bridges, The Legacy of Othmar H. Ammann by Darl Rastorfer. Ammann died September 23, 1965 at the age of 86

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April 2013

with the New York Times calling him “one of the great bridge builders of this century.” He had won many accolades over the years, but his most significant was the National Medal of Science granted him by President Lyndon Johnson in 1964. He was the first civil engineer to be honored in this way; he was awarded the honor under the classification of Behavioral and Social Sciences. His citation stated, “For a half century of distinguished leadership in the design of great bridges which combine beauty and utility with bold engineering concept and method...” Edward Cohen, a long time associate with Ammann & Whitney, wrote, “The outstanding characteristic of Ammann’s design is simplicity; he was the enemy of the ornate, the complicated, the extravagant, the ponderous.” His image lives on in a bronze bust that was unveiled in the George Washington Bridge Bus Station in 1962, coinciding with the dedication of its lower level. It is passed by thousands every day, but few know the story of the man behind Six Bridges of New York City.▪ Dr. Griggs specializes in the restoration of historic bridges, having restored many 19th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an independent Consulting Engineer. Dr. Griggs can be reached at fgriggs@nycap.rr.com.

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Steel Sector Looking Good Software Industry Provides Design Barometer and Steel Construction Industry Backs Up Projections By Larry Kahaner

teady improvement seems to be the sentiment most often expressed by company officials involved in the business of steel construction. With the United States economy improving slowly but surely and the global economies booming in certain regions, those in the steel sector are optimistic about what lies ahead for 2013. “From my conversations with people in the industry, things are turning in the right direction. There are areas that are doing better than others, but the worst of the economic downturn appears to be behind us,” says Michelle McCarthy, Strategic Sales Manager for software developer Design Data (www.sds2.com) of Lincoln, Nebraska. Others concur. “We continue to see improvement in the number of projects in construction. Although I don’t see the ‘boom’ of five years ago, we are definitely seeing a steady increase in projects and are even seeing older projects being resurrected,” notes Amber Freund, Director of Marketing at RISA Technologies (www.risa.com), in Foothill Ranch, California. Adds Michael Brooks, President of Enercalc, Inc. (www.enercalc.com) of Corona del Mar, California, “Since last June we’ve noticed a surge in activity, meaning there is lots of design work ‘on the boards’. Users are staying current with their software maintenance, and new sales of full systems have increased. After 30 years of observing economic cycles, we believe you will see construction starts looking strong in mid-2013.” Companies are continuing to upgrade products, keeping them current with new standards and customers’ demands. For example, Design Data has been in business for more than 30 years and its DS/2 software solutions provide automatic detailing, connection design, engineering information, and other data for the steel industry’s fabrication, detailing and engineering sectors. “The release of SDS/2 v7.3 not only introduced an enhanced version of our core product to the market, it also served as the launch of a new suite of solutions designed to serve the needs of all members of the construction team,” says McCarthy. “Of particular interest

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“From my conversations with people in the industry, things are turning in the right direction. There are areas that are doing better than others, but the worst of the economic downturn appears to be behind us.” to structural engineers are SDS/2 Connect, SDS/2 Engineering, SDS/2 Approval and SDS/2 Viewer. SDS/2 Connect is an add-in for Autodesk Revit Structure that gives engineers access to the powerful connection design of SDS/2 within their own Revit model. Engineers can design and apply steel connections in Revit that are backed by long-hand design calculations and provide a higher level of detail for the model,” she says. “SDS/2 Engineering, SDS/2 Approval and SDS/2 Viewer all work in the native SDS/2 model environment, but are segmented according to the user’s role. SDS/2 Engineering is a structural analysis software that allows users to design and size structural members, calculate loads on the structure like wind loads or transfer forces, and still includes the ability to design connections. Because SDS/2 Engineering works in the SDS/2 native environment, this same model can be opened by the detailer, reducing the time spent duplicating model input. “With SDS/2 Approval, approving engineers can view the model, design calculations and drawings, giving easy access to vital information while eliminating the need to flip through hundreds of pages of paper documents. The free SDS/2 Viewer can be used by anyone who wants to view the project’s progress. SDS/2 Viewer provides engineers with an easy method to get an overall view of the steel on the project, even if they are not taking part in the model approval process,” McCarthy says. continued on next page

April 2013

RISA has added features to its software, too. Says Freund: “Retaining wall design was added to RISAFoundation last year, and we are excited about this new feature. The interface is easy to use and allows engineers to quickly input their soil and wall properties. This feature is fully integrated with RISA-3D so your wall or column reactions can be transferred to RISAFoundation to design your retaining walls, mat slabs, pile caps or other foundation elements. It allows you to go back and forth during your design process and these model changes are automatically updated between the two programs.” She adds that the company is proud of reaching its 25th anniversary last year, saying: “RISAFoundation has had the ability to design all other foundation types so retaining walls completes this program. Whether an engineer is designing one retaining wall or an entire building foundation system, RISAFoundation can handle all of the different foundation elements. We have had a number of new versions released this year that include many new features such as 64-bit versions of all of our programs which enables users to run even larger models than before.” (See ad on page 67.)

nother company celebrating an anniversary, its 30th year in business, is Enercalc where Brooks notes, “We’re also celebrating our sixth major release of our structural engineering software system. We tailor the software to the common yet complex component calculations for low to mid-rise buildings…the most common structures anywhere. We’re a group of experienced structural engineers and have a large and long term, yet constantly growing, user base.” He says that the company has released its steel modules now conforming to AISC 360-710. Enercalc also added to its series of loading development modules with more wind, seismic and snow calculators. The new Project Load Group Builder provides a way to list and tabulate individual contributions of gravity loads for a project. “Providing a tool to assist the engineer in the calculation of loads frees the engineer to apply his or her time on higher and better uses such as economizing the structure, proportioning LFRS frames to bring lateral drift under control, or coming up with creative solutions to meet the needs of the owner and/or the architect. It also offers the engineer an independent check on their input used to develop loads in other programs,” Brooks says. “Our users provided feedback indicating that these were areas that cost them a great deal of time, or that require the development and maintenance of spreadsheets and other tools. All of this becomes a distraction and an inefficiency to our users… keeping them from adding the greatest value to products by functioning at their highest and best use.” (See ad on page 3.)

ur products undergo constant enhancement and improvement to stay current with the ever-changing requirements of the structural engineering profession,” says Rob Tovani, Director of Verification, Validation, and Training at Computers & Structures, Inc. (www.csiberkeley.com) headquartered in Berkeley, California. The company has four specific products: ETABS, SAP2000 CSiBridge, and SAFE. “ETABS is a building program, just like Bridge is a bridge program, and SAFE is a concrete floor and foundation program. SAP2000 is a general analysis program,” he says. “Now we’re going to be releasing a product that enhances the way we do detailing, so that engineers will be able to first analyze, then design, and have a whole set of drawings produced for steel and concrete buildings. It’s an enhancement to our existing

programs. We actually have a version of this which has been released in our SAFE program, but we’re enhancing all of our programs to have this feature.” As for the overall market, Tovani notes: “We have four products for different sectors, so it seems there’s always some energetic activity somewhere in the world… I’ve talked to some engineering firms who are slowing down, and that does trickle over into software purchases. People weren’t making purchases of software a while back, but now have to get current again. So, our software sales remain brisk.” (See ad on page 68.)

-Frame Software (www.s-frame.com) in Guilford, Connecticut announced the release of S-FRAME Structural Office R11 this year, according to CEO Marinos Stylianou. “This marks one of the most extensive releases ever delivered by S-FRAME Software. It contains significant updates and new functionality to the complete product line of S-FRAME Analysis, S-STEEL Design, S-PAD Design, S-CONCRETE Design, S-LINE Design & S-CALC plus two brand new products S-VIEW and S-FOUNDATION.” He adds: “R11 includes important new functionality and many enhancements designed to improve our client’s user experience and to address their need to innovate and improve their productivity: full integration of analysis and steel design, addition of three new advanced analysis types, increased solver performance and accuracy, new nonlinear material models, an across-the-board new licensing system, two revamped BIM links for Revit and Tekla, updates to several design codes and the addition of new ones, ability to customize the programs based on language, and a host of other new features and enhancements. In addition, we introduced two brand new products, S-VIEW for structural model viewing, sharing, and validating and S-FOUNDATION for foundation analysis and design.” Stylianou says the company saw strong growth in 2012 and he expects to see considerable business growth in North America and Asia. “We also believe that Europe will offer some opportunities that we plan to evaluate with localized R11 products.” (See ad on page 4.)

ccording to Stuart Broome, Vice President of Chicago-based CSC, Inc. (www.cscworld.com), the company specializes in developing code-based structural design solutions. “This means that rather than adding design post processors on a frame analysis program, we build our software from the ground up around the requirements of a design code (such as AISC360 in the case of Fastrak).” Broome adds: “We have just launched our latest version – Tedds 2013 (Tedds is a structural calculations software). Up to twice as fast as its predecessor, Tedds 2013 includes a new, fully integrated 2D frame analysis application as well as many new and enhanced calculations to both U.S. and Canadian design codes. Tedds 2013 is also compatible with Microsoft Word 2013.” Fastrak is a steel building design software alongside CSC’s Integrator. As an Autodesk Structural Industry Partner, the company has launched CSC’s Integrator. “Available as part of Fastrak, this unique and free software enables structural engineers to synchronize models between Autodesk Revit Structure and Fastrak. It is an industry-leading solution making two-way integration with Revit Structure easy, highlighting any amendment made during the synchronization process, thus enabling engineers to react to changes quickly and reduce the risk of errors,” says Broome. continued on page 50

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April 2013

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Martin/Martin gains the competitive edge with Tedds Patrick McManus, Technical Director, explains how Martin/Martin saved time, improved consistency and enhanced quality control by standardizing on structural calculation software, Tedds.

“At Martin/Martin we work on a variety of commercial projects and specialize in arena and stadium work, defensive design and construction services. To meet the requirements of such demanding and differing projects we historically used software packages from multiple vendors. This was difficult to manage as each software package had its own interface and approached engineering problems differently. No single engineer knew every product in-depth, which created problems with quality control, consistency, and it impacted project scheduling. What we really needed was a single software package that could reliably and accurately do everything we needed.” “Tedds was our ideal solution because it provided an extensive library of calculations and created transparent output with detailed equations. It also reduced the need to perform calculations by hand, which had been very time consuming.

“Tedds has an extensive calculation library and produces transparent output with detailed equations.”

Tedds also offered us the capability to write our own calculations which has been invaluable. It works within the Microsoft Word interface, enabling us to develop custom tools that allow us to efficiently handle complicated problems that have not been well addressed by other software developers. This has given us a competitive advantage and we see great potential to take this further.”

“We have been able to write our own calculations in Tedds.” “Since standardizing on Tedds we have decreased our number of vendors, which has saved time for our information technology teams and our engineers speak to fewer technical support teams.

“Tedds is fast and intuitive and is used by all our engineers.” Tedds is really easy to use so it has become a staple tool for all our engineers, who now use the Tedds library daily for our quick component calculations. We have also standardized our output which immediately improved our consistency and quality control.

“Tedds has helped us to meet aggressive project demands and deliver a high quality service to our clients.” Without Tedds, calculations would have taken considerably longer to develop and verify, with less transparent output. Tedds is flexible, it’s regularly updated and the size of the library means we can quickly respond to the changing needs of our clients.” CSC thanks Martin/Martin for its contribution to this case study.

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lso upgrading their software is IES, Inc. (www.iesweb.com) in Bozeman, Montana. Engineer and Developer Terry Kubat says: “We are regularly upgrading our products, like VisualAnalysis and ShapeBuilder to meet customer needs by adding new features or just by simplifying existing tasks. Structural engineering is a demanding profession that requires the use of sophisticated tools, but that does not mean engineers should be forced to decipher complicated software. If we have done our job, then we will have fast tools that get the right answers. And, if we have done our job well then even when engineers make mistakes the software will catch those problems and clearly communicate it back to the customer – automatically. “ IES prides itself on listening to customers and using what they say to improve their products. “We know that engineers are overworked and have little time to evaluate new tools. Our web site offers very brief introductory videos to make it easy to find out what a product does and how it works. Once they are ready to try a product, it takes less than five minutes to get it downloaded and running,” says Kubat.

lthough computers and software are vital to engineering, Leroy Emkin, Founder and Co-Director of the CASE Center (CASEC) in Atlanta (www.gtstrudl.gatech.edu), says that SEs must be “in control of the engineering analysis and design process, with a clear understanding of the characteristics and facilities of the computational tools used for that design. Those computational tools cannot be simple and highly automated ‘black boxes’ working in the

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way programmers have chosen them to work, rather than in the way engineers intend them to work.” He adds: “This can only be achieved by providing the engineer with control over software processing, and by having complete and extensive user documentation. CASEC is committed to the development of structural engineering software that engages qualified, knowledgeable, and experienced structural engineers in the modeling, analysis, and design process. We provide structural engineers with a variety of powerful command, menu, and GUI tools that allow them to implement analysis and design strategies developed by the engineer for solving simple to complex structural modeling, analysis, and design problems.” According to Emkin, the success of GT STRUDL – its Structural Design & Analysis software programs – is demonstrated by its widespread use in the nuclear power and nuclear defense industries of the United States and other countries.”GTSTRUDL development fully conforms to the rigorous ASME and NRC quality assurance and quality control regulations and guidelines. GTSTRUDL’s verification and validation procedures include more than 4,100 test problems ranging from relatively simple textbook academic problems to highly complex and very large structural models of actual heavy industry structures.”

ompanies on the hardware side of the steel sector are busy as well. “Our international business is booming, and the U.S. seem to be picking up, indicating a slow but steady climb out of the funk of 2008,” says Chris Curven, Vice President, Field Bolting Specialist at Applied Bolting Technology (www.appliedbolting.com) in Bellows Falls, Vermont. Applied Bolting Technology designs and manufacturers Direct Tension Indicators (DTIs) used predominantly in structural bolting applications. They are designed Your Success to guarantee that bolts are installed to the specified tension, regardless of the torque required to get there, says Curven. “Our DTIs and Squirter DTIs conform to ASTM standards, and can be used in accordance with the RCSC and AASHTO specifications.” Curven notes: “The Squirter DTIs have revolutionized the bolt-up process in structural applications. They have the added feature of providing a visual indication when the desired tension is achieved. They make bolt installation and inspection easier and more accurate. In large structural projects, bolting can consume over half of the total labor expense. Improving accuracy and efficiency translates into huge savings. We’ve heard numbers as high as 20 percent.” He says that Applied Bolting provides training to engineers and iron workers. “We travel all over the world to inform designers about the benefits of using DTIs, and showing first-time users how to use them properly,” Curven says. (See ad on page 52.) continued on page 52

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ducation is also an important part of the agenda at JMC Steel Group (www.jmcsteelgroup.com) in Chicago, says Senior Sales Engineer Brad Fletcher. “We’ve done a number of things along that front. That’s my main purpose for going out and talking to people. We educate people about our company, as well as about the product and the industry itself.” In order to help SEs understand more about hollow steel structures, JMC has developed a video series which can be viewed on their website. “We debuted a number of the videos during our Steel Day event last fall, and the immediate feedback from that crowd was very positive.” He says that the industry has grown in the past 10 to 15 years and with that growth has come many more available sizes. “We met and exceeded our goals last year of what we wanted to do and so we set the bars a little higher this year. We’re promoting a jumbo-size range as well, so that’s definitely something to show off. “ In January, the company also launched an online forum called the Atlas Connection that allows engineers to join a secure community and ask questions of HSS experts inside and outside of the company. “It’s a way to create a dialogue or a conversation about HSS and the issues surrounding HSS, so we’re pretty excited about that. The feedback for that has been really great.” (See ad on page 6.)

“Even though we are large, we listen to our customers to ensure we are continuously improving, not only ourselves but our working partnerships as well. We may have the largest range of steel joist and deck products in the nation and produce more of it than anyone else, but it is for naught if both our customers and ourselves aren’t successful while doing it; that is a partnership. This mutual respect is just part of why we’ve been taking care of our customers for more than a half century,” he says. Mauk notes two products that he would like SEs to know about. First is Ecospan, a Proprietary Composite Floor System that has been around for several years and is starting to find its place in today’s economy. “Our lightweight, mechanically fastened Ecospan system with our proprietary Shearflex composite fasteners have really made a lot of progress in areas like hotels, dormitories, multi-family residential, and mezzanines that increase floor space in already existing warehouses.” Second is NuBIM Vulcraft, a plug-ins for Tekla, SDS/2 and Revit. “Vulcraft is continuing to provide value-added tools based on listening to our customers. These BIM tools are assisting the AEC community in specifying our products and providing easier communication methods for fabricators. While this is still an ever-changing area, we believe we must commit time and resources to utilize these tools to communicate more effectively with our customers.” ialogue is also an important goal at Vulcraft/Verco Group Mauk adds: “The last few years have been a challenge not only (www.nucor.com), according to T.J. Mauk, Manager of for our customers, but for individual American families, difficult New Product & Market Development in Norfolk, Nebraska. for American companies and difficult for the United States of structure 1-2 april 13:show 2/28/13 10:59 AM Page 1 continued on page 54

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machine’s handles are built to be used with mechanical hoisting. From the external body, to the visual display, to the internal design, Warrior is meant to be used in the most demanding environments.”▪

n the welding side of the steel sector, officials at the ESAB Group, Inc. (www.esab.com) in Hanover, Pennsylvania, would like SEs to learn about Warrior, which they call the next generation of welding technology. Greg Stauffer, Vice President for Sales Support and Standard Equipment, ESAB North America, says: “Warrior is an inverter-based power source for MIG, flux-cored, stick, and TIG welding. It’s also for arc gouging. Warrior delivers up to 500 amps and is designed for heavy-duty use in rugged environments.” Stauffer says that fabricators want versatile equipment that can consistently perform in dirty work environments. “Of course, in this economic climate, everyone needs tools that return value on the investment. Warrior delivers value not only with price, but it uses less energy than other machines, making it cost effective. It is also one of ESAB’s user-friendliest machines, which makes it easy for novice welders to use. The simplicity of Warrior means users aren’t losing time on the learning curve.” He adds: “Our customers also don’t want to lose time when machines are down for repair. Warrior is durable and designed to perform consistently in harsh work environments. It is designed to work with generators, and the

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STRUCTURE magazine

April 2013

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ENGINEERED WOOD PRODUCTS GUIDE a definitive listing of wood product manufacturers and their product lines WoodWorks Software

Associations American Wood Council

Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org Product: 2012 NDS Wood Design Package Description: The 2012 NDS, 2012 NDS Supplement: Design Values for Wood Construction, 2008 Special Design Provisions for Wind and Seismic (SDPWS), and ASD/LRFD Manual set is available for purchase at our website.

APA – The Engineered Wood Association

Phone: 253-565-6600 Email: help@apawood.org Web: www.apawood.org Product: APA Description: APA focuses on helping the industry create structural wood products of exceptional strength, versatility and reliability. Nearly 500 publications, extensive research and technical reports, free CAD details, comprehensive market studies and more.

Connectors Simpson Strong-Tie ®

Wood Structural Panels

Phone: 800-844-1275 Email: sales@woodworks-software.com Web: www.woodworks-software.com Product: WoodWorks® Design Office Description: SHEARWALLS: designs perforated and segmented shearwalls; generates loads; rigid and flexible diaphragm distribution methods. SIZER: designs beams, columns, studs, joists up to 6 spans; automatic load patterning. CONNECTIONS: Wood to: wood, steel or concrete. Canadian version available.

Engineered Lumber Phone: 949-951-5815 Email: info@risatech.com Web: www.risa.com Product: RISA-3D Description: RISAFloor and RISA-3D form the premiere software package for wood design. Create 3D models of your entire structure and get full design of wood walls (with and without openings), flexible wood diaphragms, dimension lumber, glulams, parallams, LVL’s, joists and more. Custom databases for species, hold-downs-and panel nailing offer total flexibility.

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Phone: 800-844-8281 Email: marty.hawkins@trimjoist.com Web: www.trimjoist.com Product: TrimJoist Description: The marriage of an open web floor truss and a wood ‘I’ Joist, bringing the best features of each together to form an adjustable floor joist. TrimJoist is produced in 2-foot increments ranging from 4 to 30 feet and in depths of 11⅞, 14, 16 and 18 inches.

USP Structural Connectors

Phone: 952-898-8772 Email: Info@uspconnectors.com Web: www.uspconnectors.com Product: USP Structural Connectors Description: The world’s leading manufacturer of code approved, structural connectors and innovative software solutions. Engineered, manufactured and tested to withstand Mother Nature and are backed by engineering and technical support teams. All Resource Guides and Updates for the 2013 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

Phone: 800-275-7086 Email: info@pbssips.com Email: www.premiersips.com/bc Product: Premier SIPs Description: SIPs have been evaluated for performance in demanding structural situations, including under high winds, earthquakes and snow loads. Exceptionally strong in racking diaphragm shear capacities. Create tight, well-insulated building envelopes for superior energy efficiency.

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Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Connectors for Engineered Wood Description: Offer unmatched quality and are backed by our uncompromising commitment to customer service. You can count on Simpson Strong-Tie to work closely with contractors, specifiers and code officials to deliver innovative, code-listed solutions. Our full line of EWP connector products includes I-Joist hangers and structural composite lumber connectors.

Phone: 877-900-3111 Email: timberlinx@rogers.com Web: www.timberlinx.com Product: Timberlinx Description: Embedded Steel Connections with Defined Engineered Values.

Insulfoam

Phone: 608-403-4197 Email: steve.winistorfer@tecotested.com Web: www.tecotested.com Product: Certification and Testing Description: Third-party certification and testing agency for structural wood panels, engineered wood products, and structural adhesives. Visit our website to learn more about TECO and its services.

Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Wood Strong-Wall® Shearwall Description: Can be installed around window and door openings, on garage wing walls, interior walls or other locations where increased lateral resistance is required. Wood Strong-Wall panels can reduce the amount of wall space required for shearwalls, allowing for more windows and doors in house designs.

Wheeler

Phone: 800-328-3986 Email: info@wheeler-con.com Web: www.wheeler-con.com Product: Panel Lam Bridges Description: Wheeler designs and supplies treated timber bridge kits for recreation and vehicular applications.

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Phone: 888-453-8358 Email: wood@weyerhaeuser.com Web: www.woodbywy.com Product: Trus Joist® TJI® Joists with Flak Jacket™ Protection Description: A simple, cost-effective way to achieve one-hour floor/ceiling assemblies. Provide one-hour fire-rated assembly with only a single gypsum layer and no mineral wool in multi-family buildings. Also help meet 2012 IRC R501.3 fire-protection requirements in single-family homes.

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award winners and outstanding projects

Spotlight

Crystal Bridges Museum of American Art By Craig Schwitter, P.E. and Cristobal Correa, P.E. Buro Happold Consulting Engineers, PC was an Outstanding Award Winner for the Crystal Bridges Museum of American Art project in the 2012 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings over $100 Million)

rystal Bridges Museum of Art is an iconic museum inspired by the local Arkansas landscape and the exotic suspension bridges of Bhutan. The 201,000-square foot museum is a complex of eight buildings located in Bentonville, Arkansas. Designed by Safdie Architects, each of the eight buildings, although individually unique, relate to each other through a unified palette of concrete, wood, copper and glass. There are five “land” structures that nestle into the hillsides and three “water” structures that create a circular promenade on the site. The land buildings are set in the sloped hillsides of the creek ravine. Where there is only soil under the buildings, drilled piers provide vertical support. Lateral loads are taken back through floor diaphragms and distributed to grade beam-supported minipiles farther up the slope that are inserted into rock sound limestone. The sizes of the grade beams are typically 30 feet deep with widths varying from 30 to 64 inches to accommodate the minipile geometries. The drilled pier diameters range from 2 to 3.5 feet, with rock embedment depths of 3 to 18 feet. The reinforcement included number 8 bar reinforcements with number 4 spiral ties. The lower levels of the land buildings are concrete frames that feature either beams or flat slabs that span 20 to 30 feet and are column supported. The upper-level columns and retaining walls are spanned by curved laminated timber beams (glulams), 10.5 x 31 inches in cross section. The building roofs are made of locally sourced glulam beams with alternating strips of copper cladding and glazed skylights. The bridge buildings notable because of their hanging arch forms, represented a real engineering challenge. Their bases form concrete weir structures that serve as the floors and, in the case of the two spanning buildings, also control the streamflow to create the signature museum ponds. The roofs of these buildings are a series of nonrepeating glulam arches, each of which has a

unique inner and outer radius. Each arch is broken into three segments and tapers at the ends, varying in cross section from 10 x 32 inches to 10 x 24 inches. These arches rest on pairs of 4-inch diameter stainless steel cables strung between heavy concrete abutments that support the roofs. The roofs and floors are connected by external steel facade mullions that both support the facades and impart additional stability to the roofs under live loads. The glulams are connected to each other by a series of T-shaped steel purlins, 5 x15 inches in cross section, located atop the glulam beams. Since the number of purlins is constant throughout the cross section, as the bridge roofs become wider, the spacing between the purlins gradually changes. This provides the T-shaped purlins with both a vertical and a horizontal inclination with respect to the glulams. The engineers also used smaller, secondary timber purlins to divide the roof into opaque and skylighted areas. These secondary purlins have ¾-inch cross bracing that provides the roof plane with a structural diaphragm. The roofs are based on catenary shapes that are created by the deflection of the cables. The structures are designed so that the cables carry all of the dead load. Once the dead loads of the roofs were installed, the cables deflected and attained their final geometries. The facade mullions were then added, connecting the glulam beams directly to the ground. This created stiffer load paths that carried any additional live loads from the roofs. The mullions supplement the horizontal diaphragm of the roofs and provide lateral stability under wind and seismic loading. The bridges are suspended from abutments at either end; these abutments rest on mat foundations that utilize shear keys and are located directly on rock. Rock anchors were installed along the rear portions of the

STRUCTURE magazine

April 2013

abutments and sleeved through the abutments. Once the concrete for the abutments was placed, the anchors were pretensioned in order to resist the cable pull loads. The foundations of the peninsula-like Great Hall building are slightly different in that there is only one abutment. The cable structure is tied to rock anchors inserted into the pond for added stability. The design of typical and repeatable details that could effectively be used with the complex geometry of the roof was one of the principal challenges of this project. One of these is the visible connection between the cables and the glulams at the typical ball joint castings. The detail functioned as a universal joint within the degree of movement defined by the geometry of the Great Hall, which presented the most challenging conditions of all of the bridge buildings. The repeatable detail could accommodate the number of variations that would occur as each glulam advanced along the cable. Crystal Bridges, with its complex geometries, would not have been possible were it not for a high level of collaboration between the design team, contactors, and the owner, and the use of BIM and digital fabrication technologies in order to ensure that the complex geometries specified could be designed and built.▪ Craig Schwitter, P.E., is a Partner and Principal at Buro Happold. Craig can be reached at craig.schwitter@burohappold.com. Cristobal Correa, P.E., is an Associate Principal at Buro Happold. Cristobal can be reached at cristobal.correa@burohappold.com.

GINEERS

Repair of Construction Defects – Every Project Has Them David Flax, Euclid Chemical Company There are construction defects on almost every job, unless it is a very small job or unless the owner is extremely fortunate. The list of likely defects includes cracks, spalls, rock pockets, delaminations, chips, gouges, rained on slabs, uneven slabs, etc. On a typical job, repairs may have to be done to slabs, or vertically, or overhead. This presentation will discuss identifying the defects, repair material selection, repair methods, surface preparation, bonding, curing, etc. In some cases it will be important for the repairs to be aesthetic as well as functional and we will cover how to accomplish that.

April 25, 2013

UR CT RU TIN N CO

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NCSEA

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Designing Connections to HSS – Introduction to Moment and Truss Connections Brad Fletcher, S.E., Atlas Tube Known for its strength and aesthetic appeal, the usage and popularity of hollow structural sections (HSS) continues to grow. Whether HSS is used as a primary structural support or as an architectural element, it is the designer’s responsibility to select and specify the type of connections that will be used. This webinar will provide engineers with an introduction to two of the most commonly-used types of connections for hollow structural sections. Topics covered will include key considerations in the design of moment and truss connections, review of resources available to assist designers, cost factors, and more.

Diamond Reviewed

NCSEA News

NCSEA Signs New Agreement with SECB

April 9, 2013

News form the National Council of Structural Engineers Associations

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Requirements Change for SECB Certification

April NCSEA Webinars

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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. Register at www.ncsea.com.

In Memoriam

Dr. W. Gene Corley, NCSEA President, 1996 –1997

Gene Corley, left, receiving the 1999 NCSEA Service Award from NCSEA Board President Emile Troup.

NCSEA mourns the passing of Dr. W. Gene Corley. He was a jewel in our crown, instrumental in founding, promoting, and maintaining everything NCSEA stands for, and, especially, in making structural engineering a recognized discipline across the nation. He will be sorely missed. Jeanne Vogelzang, NCSEA Executive Director on behalf of the Board, staff & membership of NCSEA

STRUCTURE magazine

The National Council of Structural Engineers Associations (NCSEA) has signed a new partnering agreement with the Structural Engineering Certification Board (SECB). The Structural Engineering Institute (SEI) also signed a new agreement with SECB. The primary purpose of these partnering agreements is to have all structural engineering professional organizations working together and speaking with a unified voice. The agreements represent a significant new step in this direction. Specific goals include: • To promote the structural engineering profession. • To promote structural engineering licensure in all U.S. jurisdictions. • To promote meaningful continuing education for structural engineers. To encourage more NCSEA and SEI members to obtain SECB certification, SECB has enacted a two-year minimum open enrollment method for licensed professional engineers practicing structural engineering to attain certification based on experience and education. The license and/or registration must have been awarded on or before July 1, 2005 and must remain valid continuously through the time of application. The open enrollment period began January 1. In addition, SECB has reduced application fees for NCSEA and SEI members from $350 to $200. The reduced application fee will be available for a minimum period of two years and is a one-time (not annual) fee. For more details, or to view updates to the application requirements, go to www.secertboard.org/application. “The partnering agreements between SECB, NCSEA, and SEI demonstrate that there is a unified voice in the structural engineering profession,” said Greg Soules, P.E., S.E., SECB, Chair the SECB Board of Directors.

CALL FOR ENTRIES

2013 NCSEA Excellence in Structural Engineering Awards Highlighting the best examples of structural engineering ingenuity throughout the world Eight categories: • New Buildings under $10M • New Buildings $10M to $30M • New Buildings $30M to $100M • New Buildings over $100M • International Structures • Renovation/Retrofit Structures • Other Structures • New Bridges/Transportation Structures Eligible projects must be substantially complete between 1.1.10 and 12.31.12. Entries are due Friday, July 12, 2013, and awards will be presented at the NCSEA Annual Conference September 20 in Atlanta. More information and entry form at www.ncsea.com April 2013

NCSEA News

NCSEA First Winter Leadership Forum a Huge Success! The inaugural NCSEA Winter Leadership Forum is history, and the two-day event met and exceeded all expectations. Over 50 leaders and principals from a diverse group of structural engineering firms in the United States engaged in thought-provoking sessions, meaningful interaction, and networking in Tucson. Sessions included subjects like Developing the Next Generation of Structural Engineers, Key Financial Indicators for Success, Managing Multiple Deadlines and Expectations, and Establishing a Structural Engineering Training Program in Your Firm. The Forum also included an interactive Roundtable event where attendees participated and discussed a range of topics. This was the first year for the Leadership Forum, and plans are already underway for the 2014 event.

News from the National Council of Structural Engineers Associations

Don’t miss the video recap of the Winter Leadership Forum at www.ncsea.com! Engineers from the following firms were represented at the 2013 NCSEA Winter Leadership Forum: AHJ Engineers, PC Arup ARW Engineers Barter & Associates, Inc. BHB Engineers CH2MHILL Cives Corporation David E. Groblewski, P.E., Inc. DCI Engineers Degenkolb Engineers Dibble Engineers, Inc. DiBlasi Associates, P.C. Dunn Associates, Inc. Gilsanz Murray Steficek Gregory P. Luth & Assoc. (GPLA) Haskell IBI Group / Giffels, LLC Jacobs Engineering Grp Jose I. Guerra, Inc. Kiewit Power Engineers

KL&A, Inc. Martin/Martin, Inc. Mercer Engineering, PC Nayyar and Nayyar Int’l Inc. NCI Group PEAK Engineering Reaveley Engineers + Assoc. Rubinos & Mesia Engrs. Ruby+Associates, Inc. SESOL, Inc. Skidmore, Owings & Merrill Sound Structures, Inc. Stantec Steven Schaefer Assoc. TETER Architects & Engrs. TGRWA, LLC The Di Salvo Ericson Grp Thornton Tomasetti Wallace Engineering Walter P Moore Weidlinger Associates Wiss Janney Elstner Assoc.

“The Winter Leadership Forum was a nice change from the past Winter Institutes and afforded not only great learning opportunities from terrific speakers, but also a chance to meet and learn from other firm leaders from across the country.” William D. Bast, P.E., S.E. Principal, Thornton Tomasetti

NCSEA expresses its appreciation to platinum sponsor

GINEERS

STRUCTURE magazine

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

myLearning Last Chance to Register for the Structures 2013 Congress Your New PDH Tracker and Personalized Don’t miss this opportunity to attend this year’s Structures Congress. Offerings this year include: • Two Pre-Conference Seminars on Sustainability and Accelerated Bridge Construction • Eleven Tracks of Technical Sessions • Outstanding Keynote Speakers • CASE 2013 Spring Risk Management Convocation • Student Program • Young Professionals Program • Thursday Night SEI Welcome Reception • Friday Night Reception at the Heinz History Center • Comprehensive Exhibit Hall • Many Opportunities to Network • Over Sixty Committee Meetings • And Much More For more information about theStructures 2013 Congress and to register, visit www.asce.org/SEI.

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.

Hub for Continuing Education

Manage your professional development and license renewal through ASCE’s new learning management system – myLearning. Track all your PDHs/CEUs, including those from other providers; obtain certificates of completion; take program-related exams; print or save transcripts of your professional development – all in one place! Make myLearning your personalized hub for continuing education and explore the comprehensive program catalogand track your PDHs. Visit the myLearning website at www.asce.org/mylearning/ and get started today.

LOCAL ACTIVITIES The SEI Illinois Chapter hosted its 20th Biennial Lecture Series at the Union League Club of Chicago on March 6, March 20, April 3, and April 17 in 2013. These prestigious seminars featured distinguished speakers from all over North America, and attracted many talented professionals from the Chicago land area. For more information about this and other chapter activities, please see the chapter webpage at www.isasce.org/web/technical/structural.html. To get involved with the events and activities of your local SEI Chapter or Structural Technical Group (STG) http://content.seinstitute.org/committees/local.html. Local groups offer a variety of opportunities for professional development, student and community outreach, mentoring, scholarships, networking, and technical tours.

Structures Congress 2014 Call For Proposals

Be part of the cutting-edge technical program of the Structures Congress 2014 in Boston, April 3-5, 2014. The Structural Engineering Institute is now accepting session and presentation proposals for the Structures Congress 2014.

Key Dates All Abstract and Session Proposals due June 12, 2013 Notification of Acceptance September 18, 2013 All Final Papers due December 18, 2013 (extensions not possible)

Session proposals can take two forms, a traditional session with 4 papers presented, or a panel session with no papers and perhaps more audience interaction. In addition, you can submit individual abstracts that may be combined with others to form cohesive sessions. Topics will include but are not limited to: Bridges Buildings Seismic Wind and Flood Loads Sustainability Business and Professional Practice Blast and Impact Loading Nonbuilding and Special Structures Nonstructural Systems and Components

Visit the Structures Congress 2014 website for more information and submission instructions http://content.asce.org/conferences/structures2014/call.html. STRUCTURE magazine

April 2013

Two SEI Members Added to National Academy of Engineering

Brian Kukay (member of the SEI Technical Activities Division Timber Bridge Committee), along with students Logan Dunlap and Daniel Zieske of Montana Tech, are conducting a nationwide Survey of Timber Bridge Construction and Maintenance. The survey was developed with input from Sheila Duwadi of FHWA, Jim Wacker of ASCE and the Forest Products Laboratory, and Phil Pierce, Chair of the Timber Bridge Committee. The survey will determine the extent of the use of wood for vehicular bridges and to assist in resolving issues of concern that bridge owners might be experiencing. Results will be provided to the American Association of State Highway and Transportation Officials and may lead to potential further investigation and/or research. If your state would like to participate in this survey, but has yet to do so, please contact Brian Kukay at Montana Tech of the University of Montana, bkukay@mtech.edu or 406-496-4517.

Congratulations to the following SEI members for their election to the National Academy of Engineering, one of the most esteemed career honors an engineer may receive: • Gregory Deierlein, P.E., F. ASCE, civil and environmental engineering professor, Stanford University, Stanford, Calif. For development and implementation of advanced structural analysis and design techniques. • Sharon Wood, M. ASCE, professor and chair, University of Texas civil, architectural, and environmental engineering department, Austin. For design of reinforced concrete structures and associated seismic instrumentation for extreme loadings and environments. Visit the NAE website at www.nae.edu to learn more about the National Academy of Engineering.

Don’t miss the opportunity to attend and expand your professional knowledge October 10-12, 2013 in Charlotte, North Carolina. Join ASCE and industry professionals from across the globe in the “Queen City” to discover hot topics and the latest trends in Innovations in Project Financing. Visit the Annual 2013 Conference site at www.asce.org/Conferences/ASCE-143rd-Annual-Civil-Engineering-Conference to learn more about this year’s conference. Hope to see you in Charlotte.

New ASCE Structural Webinars Available SEI partners with ASCE Continuing Education to present quality live interactive webinars on useful topics in structural engineering. Several new webinars are available: Wind Design for Components and Cladding

April 4, 2013

Bill Coulbourne

Roof Failure due to Snow Loading – 2010-11 Southern New England Case Study

April 15, 2013

Michael O’Rourke

Changes to the Nonbuilding Structures Provisions in ASCE 7-10

April 17, 2013

J.G. (Greg) Soules

The Five Most Common Errors Made During Bridge Inspections

April 22, 2013

Jennifer C. Laning

Connection Solutions for Wood Framed Structures

April 29, 2013

Tom Williamson

Wind Tunnel Testing for Wind Loads on Structures

May 1, 2013

Forrest J. Masters

Evaluating Damage & Repairing Metal-Plate-Connected Wood Trusses

May 15, 2013

Jim Vogt

Seismic Assessment and Design of Pipelines

March 27, 2013

Donald Ballantyne

Webinars are live interactive learning experiences. All you need is a computer with high-speed internet access and a phone. These events feature an expert speaker on practice-oriented technical and management topics relevant to civil engineers. Pay a single site fee and provide training for an unlimited number of engineers at that site for one low fee, and no cost or lost time for travel and lodging. ASCE’s experienced instructors STRUCTURE magazine

deliver the training to your location, with minimal disruption in workflow – ideal for brown-bag lunch training. ASCE Webinars are completed in a short amount of time – generally 60 to 90 minutes – and staff can earn one or more PDHs for each Webinar. Visit the ASCE Continuing Education website for more details and to register: www.asce.org/conted.

April 2013

The Newsletter of the Structural Engineering Institute of ASCE

Save The Date – ASCE Annual 2013 Conference

Structural Columns

Timber Bridge Survey Announced

Creating a Culture of Quality

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Tool 1-1: Create a Culture for Managing Risks and Preventing Claims

CASE Tool 1-2: Developing a Culture of Quality

Inject into your firm a culture of risk management. This is the first and most comprehensive tool offered on risk management in the engineering industry. It includes a video, a story board and role playing guide to involve your staff in the risk management discussion. If you want to put your firm’s personnel on the path to good risk management habits, this is where you start.

Culture is hard to define in an organization, but it is a key part of what gives a design firm character. CASE Tool No. 1-2, Developing a Culture of Quality was developed to identify ways to drive quality into a firm’s culture. It is recognized that every firm will develop its own approach to developing a culture of quality, but following these 10 key areas offers a substantial starting point. The tool includes an attached white paper and PowerPoint presentation that can be customized to facilitate the overall discussion. You can purchase all CASE products at www.booksforengineers.com.

CASE Risk Management Convocation in Pittsburgh

Timing of ACEC Convention Opportune for Industry Advocacy

The CASE Risk Management Convocation will be held in conjunction with the Structures Congress at the Westin Convention Center in Pittsburgh, PA, May 2-4, 2013. For more information and updates go to www.seinstitute.org. The following CASE Convocation sessions are scheduled to take place on Friday, May 3:

With Congress and the Administration again locked in a budget showdown, the upcoming ACEC Annual Convention in Washington, D.C., April 21-24, will provide a unique opportunity for ACEC’s “citizen lobbyists” to urge lawmakers to advance federal infrastructure programs essential to the nation’s growth. ACEC’s lobbying effort will promote the passage of water, transportation and energy initiatives that should receive bipartisan Congressional support. The Convention also includes a wide range of expert panels, including federal agency officials discussing new business opportunities. A Teaming Fair for small and large firms will also be a highlight. For more information on the ACEC Convention, go to the following link: www.acec.org/conferences/annual-13/.

8:30 AM–10:00 AM – The Business of BIM Speaker: David Odeh, Odeh Engineers, Inc. 10:30 AM – 12 Noon – Trends in Effective Use of Commercial Software for Building Structural Design Speakers: Pedro Sifre & James Parker, Simpson, Gumpertz & Heger, Inc. 1:30 PM – 3:00 PM – Reviewing Contractor’s Electronic Models in Lieu of Hard Copy Shop Drawings Speakers: David Ruby, Ruby + Associates, Inc. 3:30 PM – 5:00 PM – BIM Validation: Modeling for Downstream Success Speakers: David Aucoin

You can follow ACEC Coalitions on Twitter – @ACECCoalitions.

Donate To The CASE Scholarship Fund! The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program. We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives in educational support. STRUCTURE magazine

In addition, the CASE scholarship offers an excellent opportunity for your firm to recommend eligible candidates for our scholarship. If your firm already has a scholarship program, remember that potential candidates can also apply for the CASE Scholarship or any other ACEC scholarship currently available. Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction and you don’t have to be an ACEC member to donate! Please contact Heather Talbert at htalbert@acec.org to donate. April 2013

Since its inception in 1995, the American Council of Engineering Companies’ prestigious Senior Executives Institute (SEI) has attracted public and private sector engineers and architects from firms of all sizes, locations and practice specialties. Executives – and up-and-coming executives – continue to be attracted by the Institute’s intense, highly interactive, energetic, exploratory, and challenging learning opportunities. In the course of five separate five-day sessions over an 18-month timeframe, participants acquire new high-level skills and insights that facilitate adaptability and foster innovative systems thinking to meet the challenges of a changed A/E/C business environment. The next SEI Class 19 meets in Washington, D.C. in September 2013 for its first session. Registration for remaining slots is available.

Executives with at least five years’ experience managing professional design programs, departments, or firms are invited to register for this unique leadership-building opportunity. As always, course size is limited, allowing faculty to give personal attention, feedback, and coaching to every participant about their skills in management, communications, and leadership. SEI graduates say that a major benefit of the SEI experience is the relationships they build with each other during the program. Participants learn that they are not alone in the challenges they face both personally and professionally, and every SEI class has graduated to an ongoing alumni group that meets to continue the lifelong learning process and provide support. For more information, visit www.acec.org/education/sei/ or contact Deirdre McKenna, dmckenna@acec.org, or 202-682-4328.

If you would like more information on the items below, please contact Ed Bajer, ebajer@acec.org.

Standard of Care: What the Judge can tell the Jury There are various “instructions” a judge can give a jury in determining the standard of care for an engineer. Below is just one used (CA) that recognizes that an unsuccessful effort does not necessarily mean a breach of the standard of care. [A professional ] is not necessarily negligent just because [his/ her] efforts are unsuccessful or [he/she] makes an error that was reasonable under the circumstances. [A professional ] is negligent only if [he/she] was not as skillful, knowledgeable, or careful as another reasonable [professional ] would have been in similar circumstances.

Recovering Payment on a Federal Project The Miller Act was created to protect sub-contractors against non-payment by the prime contractor. A design firm faced with the risk of non-payment may only rely upon the protection of STRUCTURE magazine

the Miller Act for compensation in limited circumstances. For a design firm, it depends on the nature of the services provided. If on-site services are not provided, it is clear they cannot use the Miller Act to recover payment. However, recovery under the act is possible when a designer performs on-site supervision or inspection duties in addition to “typical” design services such as the preparation of plans, details and specifications.

Gaining Mastery of the EJCDC General Conditions Construction administration calls for a thorough knowledge of the general conditions of a contract. The more complete your grasp of the details of that document, the more perfect will be your mastery of the many situations which it controls. No important decision affecting the owner’s rights should be reached without consulting the general conditions, since something in them is probably affected by it. The new 2013 version of EJCDC General Conditions will be available very shortly, if not already available from ACEC. Check the ACEC website, acec.org, for availability. Look for the 2013 edition.

April 2013

CASE is a part of the American Council of Engineering Companies

CASE Business Practice Corner

CASE in Point

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

Structural Forum

opinions on topics of current importance to structural engineers

Consequences of the Gendered Culture of Engineering By Lara K. Schubert, P.E.

n my February column, I challenged engineers to think about the culture of structural engineering. The workplace that I described is now one where about half the engineers are women, but the gendered culture of engineering is still not extinct. Challenges particular to women persist in the field. Again, I encourage you to think about the invisible culture of your own workplace and the culture of structural engineering more broadly. This follow-up piece shows how some aspects of this culture may be particularly stifling for women. In a study for the National Bureau of Economic Research, Jennifer Hunt shows that women are not only more likely to leave engineering than men, but also more likely to leave engineering than other fields. Based on my own experience and others’ work on the perceptions of women in related fields of science, technology, and mathematics, I offer some possible contributing factors for this phenomenon. With this information, engineers in management positions will be better equipped to retain women, rather than losing the expertise and talents of this population; and, female engineers might be better able to understand some of their difficulties and be more likely to believe in the possibility of change. At the beginning of my career, I knew little about day-to-day engineering. Consequently, my first year was a period of intense absorption. From close observations of other engineers, I perceived that a good engineer has sound arguments not only for design decisions but also all other assertions. This pressure to be an expert in everything meant always arguing a position rather than admitting being wrong. This demeanor comes freely for some and is cultivated by others. As I struggled to learn analysis methods and code requirements on the job, I consistently asked a senior engineer for help and wondered how others knew it all. After many months, I had an extraordinary epiphany, realizing two important truths: everyone makes mistakes and no one knows everything. This finally freed some conceptual space for me to work. If only this had been transparent at the start and inquisitiveness clearly valued over

“Self-confidence is crucial in advancing and enjoying a research career. From an early age, girls receive messages that they are not good enough to do science subjects or will be less liked if they are good at them.” — Ben Barres mastery, I would have been able to muster self-confidence much more quickly. A culture that intentionally affirms inquiry, recognizes that mistakes are unavoidable, and institutes collaboration to ensure appropriate design accordingly will free engineers to grow in their profession. Initial intimidation may be universal for inexperienced engineers, but it has a substantial impact on women who more commonly struggle with lack of self-confidence. Research sponsored by the National Science Foundation reported this challenge for women in science, technology, engineering and mathematics (STEM) fields. Girls assess their own mathematical abilities at a lower level than boys with similar achievements. This lack of self-confidence aligns with the fact that people are more likely to doubt women’s competence, intensifying the pressure that a beginning female engineer puts on herself. A New York Times article in September 2012, Bias Persists for Women of Science, confirmed yet again that both women and men tend to favor male candidates. Ben Barres wrote about perceptions based on gender in a compelling article in the July 2006 issue of Nature. Barres is a neurobiology professor at Stanford who started his career as a woman. He has a unique perspective because early in his career he went through hormone treatments to transition from female to male. Barres argues that the main factor for the gender disparity in science is social. Because people generally assume that women are worse at science, women lack the selfconfidence that more men enjoy. He cites a study showing that the bar is set higher for women scientists; it found that women applying for a research grant needed to be 2.5 times more productive than men in order to be considered equally competent. Barres’s own experience is telling. He recalls that, shortly after his sex change, a faculty member was heard to say, “Ben Barres gave

a great seminar today, but then his work is much better than his sister’s.” Barres’s “sister” was simply Ben as a woman. Clearly his work was not different, but it was assessed differently based on the gender of the researcher. While biases are not easily changed, transforming the culture of structural engineering is possible. An important step is to create a culture in which engineers can retain respect when they admit that they do not know something. Women need to feel both respected and included. Such a transformation requires selfreflection within the field itself, as well as by principals who provide intentional supportive mentoring and begin to see the unacknowledged culture of engineering with a critical lens in order to open it up. If structural engineers think about how the culture of engineering colludes with societal pressures on women (and other under-represented populations), aspects of the culture may begin to change and allow more talented female engineers not only to enter the profession, but also to stay, grow, and advance. Perhaps if I had perceived such success to be possible, I would still be a full-time engineer. While I enjoy aspects of engineering, I was not able to see the prospects for change before gaining a certain distance from the profession. I hope that what I have learned will help all engineers to see the culture of engineering and the potential for transformation. Subsequently, others who do not fit the typical model of an engineer, but have desire and skill, will choose to stay in the profession, forcing the model to change and helping the field itself to flourish.▪ Lara K. Schubert, P.E., works part-time for Holmes Culley Structural Engineers, has taught at Cal Poly Pomona, and is a PhD candidate in religion at Claremont Graduate University. She can be reached at lschubert@holmesculley.com.

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

April 2013

NASCC BOOTH 725

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STRUCTURE magazine | April 2013

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