STRUCTURE magazine | July 2014

A Joint Publication of NCSEA | CASE | SEI

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FEATURES 21 Special Section

Companies Doing their Part to Mitigate Earthquakes’ Effects

By Larry Kahaner

Although no two earthquakes are exactly the same – geographically or otherwise – increases in planning and code enforcement helped to lower this year’s quake death toll in Chile, according to government officials. Read how many companies also are involved in earthquake mitigation through products and services.

CONTENTS July 2014

COLUMNS 5 Editorial Is a Storm Brewing and What Should We Do About It?

By Andrew Rauch, P.E., S.E.

7 InFocus

Full Metal Jacket – Part 1

26

By D. Matthew Stuart, P.E., S.E., SECB and Richard H. Antoine III, P.E., S.E.

Virtue Ethics, Judgment, and Engineering

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

As land that can be developed has become more difficult to find, particularly in densely populated urban cities, owners and developers have increasingly turned to existing facilities to convert for new uses. First in a three-part series, this article discusses the investigation and subsequent repair of an existing timber-framed, multi-story building that is over one hundred years old.

8 Codes & Standards Insights into Wind Loads for Low-Rise Buildings

By W. Lee Shoemaker, P.E., Ph.D.

12 Structural Performance Challenges in the Blast Design of Cold-formed Steel Stud Walls

By Inna Tasmaly

DEPARTMENTS 38 Professional Issues

18 Historic Structures The Eiffel Tower at 125 Years

By Roumen V. Mladjov, S.E.

50 Structural Forum

Deferred Submittals – Part 1

How Code Complexity Harms Our Profession – Part 1

By Dean D. Brown, S.E.

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

43 Spotlight

By Erleen Hatfield, P.E. and Alan Erickson, P.E.

34 Code Updates Design of Fire-Resistive Exposed Wood Members

By Bradford Douglas, P.E. and Jason Smart, P.E.

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A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

Changes to ACI 318 for Tilt-Up Wall Panels

By James R. Baty II

Engineering a National Memorial

July 2014 Wind

31 Just the FAQs

ON

THE

37 Engineer’s Notebook

COVER

Typical boundary layer wind tunnel facility with scale model of a low-rise building in the foreground, with grid of pressure taps. Terrain roughness is simulated with blocks on the floor of the wind tunnel. Courtesy of the University of Western Ontario Boundary Layer Wind Tunnel Laboratory. See article on page 8.

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

4

July 2014

Full-Height Blocking – What Is Your Position?

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

IN EVERY ISSUE 6 Advertiser Index 40 Resource Guide (Concrete) 44 NCSEA News 46 SEI Structural Columns 48 CASE in Point

Editorial

Is a Storm Brewing and What Should new trends, new techniques and current industry issues We Do About It?

By Andrew Rauch, P.E., S.E., CASE Chair

H

aving completed the first year of my term as CASE chair, it has been a privilege to be introduced to, and get to know, so many committed engineering professionals who are working very hard for the betterment of the profession. As part of my duties, I attended both the ASCE/ SEI Structures Congress and ACEC Spring Convention in April.

I was able to hear very interesting keynote speakers and take in several great sessions at both conferences The speakers at the CASE Convocation breakfast at the Structures Congress caught my attention, and together with several other articles, the topic has remained in my mind for the past few weeks. Mr. Stephen Long of the Nature Conservatory and Mr. Frank Lowenstein of the New England Forestry Foundation spoke about the need for changes in engineering approaches to risks due to climate and disasters. They presented recently released information showing measured, not projected, changes in weather severity due to climate change. This data showed that the intensity of storms has increased in the recent past. The telling graphic for me was the superposition of a previous plot of storm intensity vs. frequency. The previous bell curve has not only shifted towards greater intensity, but has flattened as well. This combination has greatly increased the frequency of events that exceed what previously would have been considered a rarely occurring event Whether by coincidence or heightened awareness, several other similar articles have caught my eye in the past few weeks. A coalition of design and building associations, including ACEC, ASCE, AIA, AGC and ASHRAE has issued a joint statement on resilience recognizing that “natural and manmade hazards pose an increasing threat to the safety of the public and the vitality of our nation”.

This statement calls for, among other things, research, education and advocacy to improve the resiliency of our nation’s buildings, communities, and infrastructure. Recognizing the economic cost of responding to and rebuilding from these hazards and disasters increased resiliency will improve the economic competitiveness of our country.

The recently released NIST report on the Joplin tornado contained several recommendations of relevance to the structural engineering community. This report recommend the development of performance-based standards for resistance to tornadic events. These standards are proposed to be similar to those for seismic events with different performance levels such as operational, repairable occupancy, life safety, and collapse prevention. These objectives would vary depending on the building occupancy type and the severity of a tornado. For example, a building in risk category III per ASCE 7-10 would be expected to meet the repairable occupancy standard for EF-1 through EF-3, the life safety standard for EF-4, and the collapse prevention standard for EF-5. This report also recommends the installation of storm shelters in new and existing schools, office buildings, residential buildings, and other structures.

The last article reported that an insurance company was suing several communities in the Chicago area for not adequately foreseeing the effects of climate change and taking steps necessary to STRUCTURE magazine

Should disaster resiliency become part of national design standards?

Should tornado resistant design have the same level of importance as seismic design? increase infrastructure capacity to accommodate heavier rainfall.

This suit should serve as a warning to us in the design profession.

While these government entities are likely to win this suit based on sovereign immunity, how long will it be before they turn to the engineering community saying that the project designers should have had similar foresight?

As this information has tumbled around in my head, it has led me to ask a few questions. Should disaster resiliency become part of national design standards? Design for tornadoes has long been considered excessive because tornadoes affect such a small area at any given time. Earthquakes have the potential for widespread damage but occur relatively infrequently. Conversely, tornadoes occur rather frequently but the damage is not as widespread. If the number of people killed or injured by tornadoes were compared to the number killed or injured by an earthquake, would that show that tornado resistant design should have the same level of importance as seismic design? In the interim, are we fulfilling our obligation to protect the public health, safety, and welfare by designing to the status quo or should we be encouraging our clients to include resistance to tornadic events in the design of their structures?

Finally, on a completely unrelated note, I would like to extend congratulations to Dave Oxley and the rest of the ACEC/MN staff along with the numerous volunteers who spent countless hours securing the passage of an indemnification bill for the State of Minnesota. This legislation makes clauses that require design professionals to indemnify others, for anything other than their own negligence, unenforceable in the State of Minnesota.

It also requires that Minnesota be the venue for contracts for the improvement of real property in the state to prevent skirting the indemnity provisions by changing the venue for the project to another state. This is a great example of what the advocacy of ACEC and its state member organizations can do for firms of all sizes and all disciplines.▪ Andrew Rauch, P.E., S.E., is a principal with BKBM Engineers in Minneapolis, MN. He is the current chair of the CASE Executive Committee. He can be reached at arauch@bkbm.com.

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July 2014

Advertiser index

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Editorial Board Chair

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

John A. Dal Pino, S.E.

Evans Mountzouris, P.E.

The DiSalvo Engineering Group, Ridgefield, CT

Mark W. Holmberg, P.E.

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

Heath & Lineback Engineers, Inc., Marietta, GA

KPFF Consulting Engineers, Seattle, WA

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Simpson Strong-Tie................... 11, 28–29 Soc. of Naval Arch. & Marine Eng. ....... 41 Structural Engineers, Inc. ...................... 40 Structural Technologies ......................... 15 Struware, Inc. ........................................ 16 Subsurface Constructors, Inc. ................ 42 Taylor Devices, Inc. ............................... 24 USP Structural Connectors ................... 19 Wood Advisory Services, Inc. ................ 32

BergerABAM, Vancouver, WA

John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA

Amy Trygestad, P.E.

Chase Engineering, LLC, New Prague, MN

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STRUCTURE ® (Volume 21, Number 7). ISSN 1536-4283.

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6

July 2014

inFocus

Virtue new trends, new Ethics, techniques Judgment, and current industryand issues Engineering

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

V

irtue ethics has been around for at least 2,500 years, and the classic work about it will always be Aristotle’s Nicomachean Ethics. However, contemporary proponents must address a wide range of additional issues and objections that have come up over the intervening centuries, including those raised by modern alternative approaches like deontology and consequentialism (“Rethinking Engineering Ethics,” November 2010). Furthermore, there are now multiple strands of virtue ethics, each with its own unique aspects (“Engineering Ethics as Virtue Ethics,” May 2011); some of them are obvious, but others can be quite subtle.

One recent and comprehensive attempt to ground and defend an Aristotelian form of virtue ethics, as well as a corresponding theory of the virtues, is a 2009 book by philosopher Daniel C. Russell: Practical Intelligence and the Virtues, published by Oxford University Press. Russell does not actually construct a complete virtue ethical system; instead, he explores a number of criteria that one would need to satisfy in order to be viable, and then contends that only what he calls “hard virtue ethics” can fit the bill. As his title suggests, an essential feature is practical intelligence – what the ancient Greeks called phronesis, which I typically translate as practical judgment (“Knowledge, Rationality, and Judgment,” July 2012).

Russell tackles head-on two of the most common and difficult challenges to virtue ethics, acknowledging that it must ultimately be established as both normatively and empirically adequate. In other words, it has to provide a satisfactory account of what makes an action right, and it needs to be consistent with the latest and most widely held scientific findings about human psychology. The book argues – convincingly, I think – that hard virtue ethics satisfies these two fundamental requirements.

What primarily distinguishes all types of virtue ethics from the alternatives is, “roughly, that right action is defined in terms of the virtues, but not vice versa.” This is often summarized by saying that the right thing to do in any given scenario is whatever the virtuous person would do. The chief role of practical judgment is specificatory – deliberating and ultimately deciding what constitutes acting virtuously in a particular concrete situation; in other words, ascertaining what Aristotle called “the mean,” that which “is ‘fitting’ or ‘appropriate’ to the circumstances at hand.” Each virtue has distinct “targets” at which it aims, and phronesis is necessary in order to hit these targets reliably – including the coordination of multiple virtues and their different targets, which may at times appear to be in conflict with each other.

Some claim that this sets the bar too high, since there is clearly no such thing as a single person in the real world who fully possesses all of the virtues. In fact, Russell acknowledges that no single person fully possesses even one of the virtues; most notably, practical judgment itself. He addresses this by describing virtue as “a vague satis concept,” invoking the Latin word for “enough”; there are degrees of having it, as well as a sense in which it is not necessary to have it fully in order to have it legitimately. To be virtuous, it is sufficient

STRUCTURE magazine

to be virtuous enough, and to have phronesis, it is sufficient to have phronesis enough; but there is no definite boundary in either case.

The fully virtuous person is thus an idealized model, “a standard by which scales of virtuousness are calibrated.”

Of course, engineers deal routinely with vague satis concepts – although that term is probably unfamiliar – and idealized models.

For example, structures do not have to be fully strong, whatever that would mean; they simply must be strong enough. As Hardy Cross famously put it, “Strength is essential, but otherwise unnecessary.”

More generally, engineered projects and products need not be fully safe, sustainable, and efficient (“The Internal Goods of Engineering, March 2013), whatever that would mean; they simply must be safe, sustainable, and efficient enough. Practical judgment – i.e., engineering judgment (“The Intellectual Virtue of Engineering,” July 2013) – is necessary in order to convert these indeterminate ends into determinate ones for any particular case, and to select the features that must be included or may be excluded from an engineering model accordingly.

What about the second criterion for a successful virtue ethics approach? The current paradigm in social psychology is situationism, which holds that contextual variables are far more significant for determining people’s behavior than any allegedly enduring dispositions. At first, this seems like a direct contradiction of the concept of virtues as traditionally understood. On the contrary, Russell explains how situationism is not merely compatible with hard virtue ethics, but actually favorable to it. Personality is now recognized as “one’s tendency to behave for certain sorts of reasons,” rather than just “in certain observable ways,” and the virtues are precisely “practically intelligent forms of responsiveness to reasons.” The kinds of reasons that are associated with various virtues serve as the basis for individuating and relating them.

Each virtue is thus “a bundle of cognitive-affective processes by which one seeks the right goals, attends to the right features of situations, and so on, and adjusts one’s actions accordingly.” For example, someone who characteristically exhibits generosity is properly responsive to the reasons there are to be generous. Likewise, engineers who characteristically exhibit objectivity, care, and honesty (“The Moral Virtues of Engineering,” May 2013) are properly responsive – both intellectually and emotionally (“Risk and Virtue Ethics,” January 2014) – to the reasons there are to be objective, caring, and honest. Perhaps the most significant of these is the public’s tacit reliance on all engineers to assess, manage, and communicate risks on their behalf.▪ Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri. He chairs the STRUCTURE magazine Editorial Board and the SEI Engineering Philosophy Committee, and shares occasional thoughts at twitter.com/JonAlanSchmidt.

7

July 2014

Codes and standards updates and discussions related to codes and standards

T

he wind load provisions in ASCE 7 can seem overly complicated and confusing. One common criticism is that more than one method is permitted to compute the main wind force resisting system (MWFRS) loads for rigid low-rise buildings (≤ 60 feet high), and that this can produce different results. This article discusses the key research and the development of these different MWFRS wind load methods, and draws heavily from the archives of the Metal Building Manufacturers Association (MBMA) – a key player in sponsoring research that has led to the understanding and codification of wind loads on low-rise buildings.

The reader will have a better perspective on why having two methods is not an indictment of the standard, but an outgrowth of credible, yet different research efforts.

Historical Background For decades, wind engineers have understood wind-structure interaction, and can thereby effectively determine specific wind loads on any structure, no matter how complex, using wind tunnel methods. The task of trying to interpret the extensive database of wind tunnel results to codify wind loads for generic buildings is much more difficult, especially when trying to envelope loads for buildings of all heights.

Dr. Alan Davenport, of the University of Western Ontario, made significant contributions to early codification efforts. His philosophy was expressed as follows: “In formulating code specifications, the intent is usually to provide the designer with loads to ensure a minimum level of safety against damage and collapse consistent with socially acceptable rates of failure. Acceptability, in the end, is often traceable back to historical practice rather than being rigorously quantifiable, notwithstanding the considerable efforts expended to rationalize the process. Within this context, the precision of code specifications must be balanced with the advantages of simplicity; conservatism must be balanced with the need for economic design; and reality must be the final judge.”

Today, MBMA does not promulgate loading recommendations because the ASCE 7 standard and International Building Code (IBC) are adequate and are developed in consensus processes in which MBMA participates. However, when MBMA was formed in 1956, the members developed a Recommended Design Practices Manual that included specific wind load recommendations. The building codes varied considerably with regard to wind loads. MBMA evaluated all of the existing source documents and decided to base their wind load recommendations on a Navy publication. This decision was reached because the Navy publication

Insights into Wind Loads for Low-Rise Buildings

By W. Lee Shoemaker, P.E., Ph.D., F. SEI

W. Lee Shoemaker, P.E., Ph.D., F. SEI, is the MBMA Director of Research and Engineering. He has been involved in the ASCE 7 Wind Load Subcommittee and ASCE 7 Main Committee for the past 20 years. Lee may be contacted at lshoemaker@thomasamc.com.

8

July 2014

Early MBMA publications contained recommended wind loads.

was based on recent extensive wind tunnel testing and experience with actual buildings under load, and was considered the best available research and knowledge of wind loads. However, all of the available data on low-rise buildings was based on uniform flow wind tunnel testing that did not take into account the boundary layer wind effects.

In 1963, MBMA published a Primer on wind loads to try to clarify some of the confusion that existed regarding application of wind loads. This became a very useful and explanatory reference.

It is interesting to note that, in this reference, it is stated: “several methods are in use for computing the forces exerted on buildings by wind. On low buildings, say 50 feet or less in height, the wind forces for a specific set of conditions, obtained by using different methods of computing them, will vary on the average from 15 to 20%. It is not unusual to find this difference as much as 300% on buildings of certain proportions.” So, this dilemma has existed long before ASCE 7.

An update to ANSI A58.1 (which became ASCE 7 in 1988) was published in 1972. The wind loads in this ANSI document, which were primarily based on data and practices for taller buildings, was much more complex than the other available methods and produced significantly different wind loads for low-rise buildings. In 1974, when the U.S. model building codes indicated interest in adopting ANSI A58.1, MBMA decided to sponsor wind load research aimed at settling the differences in the various standards. The two leading researchers with the world’s best boundary layer wind tunnel programs at the time were Dr. Jack Cermak of Colorado State University and Dr. Alan Davenport of the University of Western Ontario. Ultimately, it was decided that the University of Western Ontario (UWO) was the best match in that UWO was engaged in some related research on low-rise structures.

UWO Research and the Envelope Method The Envelope Method (Chapter 28) in ASCE 7-10 was born out of the UWO research that began in 1974. The UWO research stretched over several years, in four phases, with the work centering on

various low-rise building wind tunnel models to evaluate the influence of many parameters.

This pioneering work launched the first comprehensive investigation of wind action on low-rise buildings, which recognized both the importance of boundary layer flow and the action of turbulence. Dr. Davenport, Dr. David Surry, and graduate student Ted Stathopoulos introduced several techniques that were innovative in their efforts to codify the wind tunnel model results.

One of these techniques was pneumatic averaging, used to convert several wind tunnel model pressure measurements to an instantaneous average by feeding many tubes into one manifold. With this technique, they were able to define loads in terms of tributary area, such as point loads, purlin loads, and bay loads. This innovative idea enabled wind tunnel measurements to capture tributary area phenomena decades before electronic pressure scanning would simplify the task.

Another novel approach that was utilized in this research was the determination of time varying integrated “generalized” loads for the total horizontal and vertical uplift forces on bays and for the bending moments in frames.

This was done through computer integration of sets of instantaneous loads weighted by the respective influence lines. Pressure tap values were multiplied by influence coefficients to produce integrated bay loads for such effects as total uplift, horizontal thrust, bending moment at the knee, and bending moment at the ridge for both rigid frames and three-hinged frames.

This generalized load method was a real breakthrough in trying to codify all of the wind tunnel data to determine the appropriate pressure distributions on the building envelope that would result in the maximum forces and reactions to govern the structural design. This method, with its separation of MWFRS and component and cladding (C & C) loads, was accepted into the 1980 National Building Code of Canada and the 1981 MBMA Manual.

The UWO MWFRS method for low-rise buildings was not initially accepted into ANSI A58.1; primarily, some felt the wind loads were only applicable to buildings with moment frames, i.e. metal buildings, since several of the structural actions monitored were based on this structural configuration. The UWO pressure coefficients were unfortunately mischaracterized as “frame coefficients” or “pseudo pressure coefficients”, which affected their acceptance. However, after the initial series of wind tunnel tests,

which included rigid frame influence lines for bending moments at sections to determine these larger scale wind actions, the sensitivity of the results to the assumption of different structural influence lines was also examined in considerable detail. This showed that the results were insensitive to the particular influence lines chosen, and merely reflected the pattern of the contributing tributary areas.

The UWO recommendations for C&C loads were less controversial and were accepted into the 1982 edition of ANSI A58.1 for buildings less than or equal to 60 feet in height. There was one piece of the UWO recommendation that was not initially accepted into ANSI A58.1, which was to set the design pressures to 80 percent of the maximum pressures instead of enveloping the maxima for all roof types, load actions, etc.

The UWO recommendations for MWFRS were accepted into the three U.S. model codes over the next several years. The Standard Building Code was the first to adopt the wind loads as an alternate procedure in the 1982 edition. The National Building Code first adopted the low-rise provisions in their 1987 edition and the Uniform Building Code adopted a very limited modified version of the provisions in their 1988 edition.

ASCE 7 first introduced the UWO MWFRS loads for low-rise buildings in the 1995 edition, after more debate over whether these loads should apply to all low-rise buildings or just to buildings with moment frames. Interestingly, the initial proposal, which went all the way to public ballot, was for this alternate method to apply to “special low-rise buildings”, which were defined as buildings with (1) a mean roof height ≤ 60 feet, (2) mean roof height not exceeding the least horizontal dimension, and (3) consists of a single story moment resisting frame in one principal direction and a moment resisting frame or braced frame in the other principal direction.

To help settle this debate, the wood industry sponsored additional research at UWO that evaluated two structural systems: (1) a threehinge moment resisting frame in one direction

STRUCTURE magazine

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July 2014

Directional Method (All-Heights) The directional method (Chapter 27) in ASCE 7-10 for computing the MWFRS loads applies to buildings of all heights. This method is essentially the same as when it first appeared in ANSI A58.1-1982. The 1982 commentary indicates that it was based on the Australian standard of 1973 and on confirmation of the values by wind-tunnel tests conducted at Colorado State University (CSU). The CSU tests were done on 15 wind tunnel models representing various aspect ratios but only two building heights were used (208 feet and 415 feet). The height to width ratio is of most significance with respect to the aerodynamics when considering high-rise buildings (height > width) and low-rise buildings (height < width). The CSU tests examined only two models in which the height equaled the width, while the other models had a height

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U.S. Code Adoption of UWO Method

Typical UWO wind tunnel model used in more recent NIST research. Courtesy of UWO Boundary Layer Wind Tunnel.

and wind bracing in the other, and (2) shear walls and trussed roof. This study concluded that the MWFRS envelope method is equally applicable to both systems and therefore should apply to all low-rise buildings. This was then accepted into ASCE 7-95 and the “special lowrise buildings” alternate method became the “low-rise building” alternate method.

The envelope method in ASCE 7 has suffered from too many attempts to clarify how the pressure coefficients are to be applied.

Numerous figures have been presented over the years (some of them wrong) and, in the author’s opinion, these have given an impression that the method is overly complicated.

The Canadian Code depicts the method in the same original treatment, with just two figures for primarily transverse or longitudinal wind. The notion that an engineer using ASCE 7 cannot understand that the wind has to be considered to blow from any direction and must be shown this in a series of figures is worrisome.

that was 2 to 8 times the building width. There was a change to the directional method roof pressure coefficients in ASCE 7-95 based on additional Australian research, although the commentary has always been very sparse with regard to the origins of the directional method and subsequent modifications.

The directional method has always been more readily accepted since it was based on a more conventional wind tunnel technique where maximum pressures are measured on the building surfaces. It was also very desirable to have a method that purportedly applied to buildings of all heights. However, given the lack of calibration of this method to low-rise buildings, coupled with our knowledge of how the wind field around low-rise buildings is more sensitive to things like roof slope than high-rise buildings, it would be advised to scrutinize this method closer with regard to applicability to low-rise buildings.

For example, the directional method does not recognize a well-known phenomenon in that the ends and edges of low-rise buildings attract the largest loads. These regions require more attention in design than the interior regions, as discovered in the UWO research and included with the envelope method.

More Recent UWO Research UWO conducted new wind tunnel studies in the early 2000s on low-rise building models with significantly more pressure taps, as part of a project primarily funded by NIST, to develop an aerodynamic database. This project benefited from advances in wind tunnel technology and data measurement that were not available during the work conducted three decades earlier at UWO. Similar data manipulation was used to evaluate the same key structural actions to make comparisons to the low-rise MWFRS methods in ASCE 7-02, the 1995 Canadian Code, the 1991 Eurocode, and the 2002 Australian Code.

These comparisons are not straightforward, as overestimations and underestimations to the latest wind tunnel data are noted in all of these codes thereby underscoring the fundamental issue that there are significant differences. Unfortunately, this study did not make comparisons to the directional method, which would have been much more informative with regard to the differences in ASCE 7.

However, several findings are germane to the discussion. The ASCE 7 envelope method was more divergent with the new wind tunnel data with increasing building height. This study pointed out that the original UWO data was based on models with a maximum height of 32 feet, and was extrapolated to the code

UWO wind tunnel showing model and upstream simulation of terrain roughness. Courtesy of UWO Boundary Layer Wind Tunnel.

definition of a low building (60 feet) and with the mean height of the building is less than the least horizontal dimension. This would indicate that studies based on low-rise models, such as the envelope method, need to be cautiously applied to buildings of greater height. By this same reasoning, the directional method based on higher buildings may be overestimating loads when applied to lower buildings; however, more research is needed to establish this.

Another finding was that the ASCE 7 envelope method more closely matched the new wind tunnel data when evaluating interior zones of the building but underestimated the peak pressure coefficients in the end zones.

As previously mentioned, the directional method does not distinguish between end zone and interior zones, and this new study validates that this phenomenon is significant and should be included for low-rise buildings.

Summary The two analytical methods for computing MWFRS wind loads in ASCE 7, i.e. the directional method in Chapter 27 that applies to all heights and the envelope method in Chapter 28 that applies to buildings with a mean roof height less than or equal to 60 feet, were verified in different wind tunnel studies.

Simplified versions of these two methods were introduced in ASCE 7-98 (envelope method applied to low-rise diaphragm buildings) and ASCE 7-10 (directional method applied to buildings ≤ 160 feet). The directional method was only calibrated for models greater than 200 feet high and with flat roofs when it was introduced. It has always been assumed to apply to buildings of all heights and all roof slopes. The envelope method was based on a wind tunnel study with models up to 32 feet high with various roof slopes and has only

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been permitted for low-rise buildings less than 60 feet high.

The fact that the envelope method was developed using influence lines to capture key structural actions, including reactions and moments in a building with moment frames, has been proven through additional studies and in documented field performance to be a reliable method for determining wind loads for low-rise buildings. The topic of the two MWFRS methods that are applicable to low-rise buildings was recently debated during the review of a proposal to revise ASCE 7.

The ASCE Wind Load Subcommittee proposal was to relocate the envelope method to an Appendix in ASCE 7-16. The envelope method would have been referenced as one of the methods that was permitted, but it was felt by some that there should only be one method applicable to buildings of all heights in the body of the standard. As of the writing of this article, that proposal did not pass the Main Committee, but the Commentary that accompanied the proposal provided the following insight, “The MWFRS Envelope Procedure was developed for low-rise buildings based on an extensive research program.

It is considered a more appropriate method for determining structural actions for applicable building shapes.”

The choice of which method to use for low-rise buildings may be based more on familiarity than on knowledge of the basis for the methods. The two MWFRS methods will produce different results. This should not be surprising or alarming to engineers in that there are many similar examples of alternative methods available in the codes and standards. The directional method is an acceptable choice for low-rise buildings, but engineers should be aware that the envelope method may be the more appropriate choice.▪

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Structural Performance performance issues relative to extreme events

Figure 1. Project’s site and building layout.

B

alancing blast load design and research with project requirements can be challenging. A simple renovation, like one including window replacement, may seem straightforward especially when seismic rehabilitation is not a concern, but on a West Coast US Military Base it is anything but. Accurately incorporating blast research with what is known about the construction of an existing building is the focus of this article.

The spotlight project is the renovation of four aircraft hangars at a Washington State military base. Two of the four hangars were originally constructed in the 1960s, one in the early 1950s, and one earlier, in the 1940s. Funding for brand-new hangars was not available, but the hangars had many inadequacies that needed to be addressed.

For this reason, the A/E team was tasked with the design of the renovation of architectural, mechanical, electrical, security, and structural components that could prolong the life of the buildings and ensure they meet the mission requirements of present and future users.

Challenges in the Blast Design of Cold-Formed Steel Stud Walls

By Inna Tasmaly

Inna Tasmaly is a structural engineer for the Buildings and Transit group for BergerABAM in Federal Way, WA. Most of her experience involves projects for the Navy and the United States Army Corps of Engineers. You may contact her at inna.tasmaly@abam.com.

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

Blast Requirements Requirements for blast protection design on military bases are governed by the Department of Defense (DoD). Criteria for various security related measures are provided by the Unified Facilities Criteria (UFC), administered by the United States Army Corps of Engineers, Naval Facilities Engineering Command, and the Office of the Air Force Civil Engineer.

DoD Minimum Antiterrorism Standards for Buildings, UFC 4-010-01, February 2012, is only required on existing buildings “when triggered” (Section 1-8.2). The replacement cost was not exceeded by more than 50% which would normally trigger a blast upgrade. However, the

12 July 2014

four hangars triggered the requirement of this standard with the Window, Glazing, and Glazed Door Replacement portion of the project. As required, Appendix B Standards 10 and 12 were used for the blast design.

Blast Loading Characteristics about the environment in which the threat exists are key to blast protective design loading determination.

Accessibility and Proximity of Threat As the four hangars are on a base with a controlled perimeter, per Section 2-4.7 of UFC 4-010-01, the restricted accessibility to the site permits application of a lower blast load. On this project, the proximity of threat varied by hangar and was governed by the distance to the parking lot. This is known as standoff distance. Figure 1 illustrates the building location relative to the parking lot. Figure 2 shows an example of a parking lot adjacent to one of the hangars. Three standoff distances are referenced in the UFC: conventional construction standoff distance (CCSD), minimum standoff distances, and actual standoff distance. If the building meets the requirements of the conventional construction of the UFC and the CCSD distance requirements, then no further analysis is required (Figure 3). These buildings had neither of these and, per the UFC, required dynamic analysis.

Type and Size of Threat The explosive weight is the equivalent weight of TNT used to describe an explosive threat. It is defined in the UFC 4-010-01 as Type I, II, or III based on the building classification and the Level of Protection (LOP) for the project. The actual value for the explosive weight is specified in UFC 4-010-02 DoD Minimum Antiterrorism Standoff Distances for Buildings. This document is For Official Use Only and, although the actual weight is used in design, all reports and final calculations must keep the explosive weight confidential.

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Figure 2. Parking.

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Figure 3. Parking and roadway control for existing buildings – controlled perimeter.

Contractors that require the actual value must provide documentation of US Citizenship and obtain them from the contracting officer on their project.

General Loading on Hangars Figure 1 illustrates the close proximity of the parking spaces to the adjacent hangars. This layout produced excessive blast demand for windows and subsequently the existing structural members during analysis. Parking spaces are in high demand at this busy military base and direction from the Corps of Engineers project manager was to protect parking.

Therefore, mitigating blast by reducing proximity to parking was initially not an option.

Dynamic analysis of windows and structural members on each of the four hangars was completed for the actual standoff distances.

After involving a window supplier, standoff on Hangar A had to be increased from 20 to 30 feet to reduce costs associated with blast resistant windows. The removal of 2 parking stalls was recommended for Hangar A in order to increase the actual standoff distance from 20 feet to 30 feet.

Multiple parking locations within range of each building were considered for determining reflective and incidental pressures for each elevation of the hangar that had windows. For window design, the actual standoff distance and applicable explosive weight was

provided for the window manufacturer to use during construction. A peak pressure impulse, per ASTM F2247, was provided on the drawings for the door manufacturer to estimate blast pressure loads.

The closest blast threat was at Hangar A and resulted in maximum fully reflective blast pressure for any wall framing. The north elevation of Hangar D had the largest standoff distance, where the computed peak incidental pressure was approximately three times the ASCE 7 static wind load pressures. This resulted in the lowest loading for any of the new wall framing. An angle of incidence is the angle between the surface and the direction of the shock wave propagation. Because the building is normal to almost any point from where the blast threat can come from, the angle of incidence was assumed to be zero. Using the angle of incidence may have reduced the blast load in a few select locations, but was not considered since the cost to detail varying conditions was not efficient for design nor for construction.

Blast clearing, another parameter used in dynamic analysis, “…occurs due to pressure discontinuities at the edges of surfaces that develop when the blast wave impacts a surface… this can result in a quicker dissipation of the blast wave in higher pressure areas.” [USACE PDC-TR 06-08] This was ignored because the length of the building adjacent to the parking lot and

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Figure 4. Deflection head and vertical slip details for CFS stud.

the height is large enough that the dissipation of energy is not likely. Assuming no clearing is conservative.

Blast Design As mentioned, the UFC 4-101-01 directs the designer to use specific methods for dynamic analysis on a variety of structural system

solutions. The Protective Design Center (PDC) of the Army Corps of Engineers provides support for the blast protection of military facilities and maintains the recommended tools for dynamic analysis and design, including Single-Degree-of-Freedom Blast Effects Design Spreadsheets, or simply SBEDS. Because of the extreme event, the SBEDS design philosophy uses the full strength of

Figure 5. Typical high blast pressure wall.

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the structural element to sustain the blast pressures. Computed dynamic behavior and output reactions are nonlinear. To ensure satisfactory dynamic behavior, the inelastic response is limited, resulting in response criteria of a maximum allowable support rotation Ɵ and ductility ratio μ for every structural element. The maximum limits of Ɵ and μ are recommended values provided by the PDC in

TR 06-08 Single Degree of Freedom Structural Response Limits for Antiterrorism Design based on the required Level of Protection (LOP) for the building and the type of component (primary, secondary, nonstructural). In this project, a ductility ratio limit of 2 was needed for metal studs, while 3 was the ductility ratio limit for existing columns in the structure.

SBEDS has a cold-formed steel (CFS) and structural steel library with complete, commercially available, stud and steel shapes.

Input for SBEDS includes span length, spacing or tributary width, material properties, section properties, blast load parameters, and response criteria.

Cold-formed Steel Stud Wall Detailing

High-level Blast Pressure HSS framing was needed because the CFS studs could not span the full height individually (Figure 5). Because Hangar D is an historical building, the client wanted to maintain opening size and location during glazing replacement, therefore, HSS was oriented primarily horizontally. Hangars B, C, and D have an architectural precast panel on the first floor that the architect wanted to avoid cutting, so these hangars also required horizontal HSS framing. This permitted the use of CFS by reducing the span length of the CFS framing.

The horizontal HSS was, in most cases, framed into a vertical HSS to carry loads into the diaphragm. At a few locations, where doors interrupted the framing, this was not feasible and existing W6 columns had to be evaluated

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The hangars each consist of a two story attached office with a clerestory above which opens to the hangar bay. The original façade of Hangar D consists of corrugated metal siding while Hangars A, B, and C have corrugated metal siding with precast concrete panels along the bottom half of the first floor and at the ends of the buildings.

The primary objective was to distribute wall loading into the diaphragm and allow for the building mass to react against the blast loading. Two types of CFS framing were needed on this project. For high blast pressures, Hollow Structural Section (HSS) shapes were utilized to transfer blast loads from the CFS framing to the structure. Low-level blast pressure lent itself to CFS studs for the entire wall.

Deflection head and vertical slip details were used to avoid superimposed dead and live load axial demand on CFS studs (Figure 4). This detailing was complicated but allowed for a lighter-weight system. This general connection-type was available in SBEDS.

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for blast load, axial load, and reduced ductility acceptance criteria. The W6 column could only resist the blast loading from a tributary width of approximately 5 feet, and therefore could not be used to resist the load from the full wall.

The CFS studs framed to the underside of the spandrel beam. In most cases, this spandrel was a light weight beam not capable of resisting lateral loading from the reaction of the studs. New braces were designed to carry the load to the diaphragm by way of a cover plate. The cover plate was needed to enhance the gravity capacity, but primarily it was needed to distribute the lateral blast demand to the new bracing elements (Figure 6 ). Additional consideration had to be made when designing connections, since welding to older steel can sometimes be problematic.

Bolting was specified wherever possible.

Low-level Blast Pressure

Figure 6. Bottom flange bracing detail.

CFS studs framing the full-height of wall (Figure 7) were utilized where blast pressures were low enough. Built-up sections, up to four S and T shapes, were needed at window and door jambs to transfer the reactions from the glazing. This required careful input and special evaluation to use SBEDS. Bracing was required similar to the walls with HSS framing to distribute load to the metal roof deck and/or wood diaphragms (Figure 8). The design was primarily controlled by the capacity of the existing diaphragms.

It was unclear if research was available on performance of connection details, and some assumptions had to be made for the input based on our specific type of connections.

Conclusion

Figure 7. Typical lightly loaded wall.

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Building renovations can often be challenging and solutions are atypical. A balance has to be made between the goals of the project, what the code requires, what’s best for the client, and your desire to want to tear down the building and start over. In a blast design project, the process can be enriched with the following lessons learned:

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Figure 8. Brace at lightly loaded wall.

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July 2014

1) Always determine what the blast requirements may be during the preliminary stages of a project.

Verify blast threat proximity, requirements, and project parameters to ensure that your client knows the level of effort required.

2) Involve a window manufacturer with knowledge of blast design for glazing during the early stages of your project. Your glazing (i.e. glazing type, thickness, panes) and blast criteria may change based on input from a glazing specialist. The glazing type can also drastically change the loads carried through to the rest of the structure.

3) Determine the façade on your project including possible historical requirements to maintain existing aspects, and assess blast threat and develop demands for each unique façade on the project (Figure 9 ).

4) Group demands into framing types, detailing needs, and typical CFS framing to minimize design and construction effort. Also, review the original construction documents to understand structural conditions and load paths for the building early in the project timeline.▪

Figure 9. Historical Hangar D BIM model.

Figure 10. Hangar D. Historically significant structure construction, date unknown.

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Historic structures significant structures of the past

M

arch 31, 2014 marked the 125th anniversary of the inauguration of the Eiffel Tower. Erected in 1889 on Champs de Mars in Paris for the Fourth World Exposition, the Eiffel Tower became famous even before its opening.

This technical achievement became a symbol of Paris and all France. Humans, who for millennia tried to achieve more than those who came before, did not succeed for more than 4,500 years to exceed the height of the pyramids in Egypt. The tallest spires of Gothic cathedrals barely stand higher than the Great Pyramid in Giza, but then the Eiffel Tower reached into the sky, twice as tall.

Today it is the most visited monument in the world; every year, more than six million people pay tribute to the old “iron lady.” The tower, subject to so much controversy during its planning and construction, is now one of the planet’s most famous structures.

It is normal to ask what makes this tower so popular. While it is easy to understand the admiration caused by an edifice 300.5 meters (984 feet) tall near the end of the 19th century, it is more difficult to explain why this old iron lattice structure still has such a strong effect, even though buildings have already reached heights above 800 meters (2,625 feet). If, at its completion 125 years ago, the tower was a sensation, why – even in the age of electronics, satellites, and people walking on the moon – does it still have such a strong effect on us? It cannot be mere skill that has transformed it from a technical achievement to a masterpiece of human effort.

Standing at the base of the tower and looking upward at its elegant lines reaching the sky, one feels proud to be a human being. Perhaps this is the main reason – the Eiffel Tower symbolizes the eternal human striving toward new heights, as the first monument built not to the gods or to an emperor, but to ourselves and to our unlimited human possibilities.

This creation is a result of the development and achievement of metallurgical and construction technologies, experience gained from many bold and complicated structures, and challenges and competitions between engineers, architects, companies and nations. The Eiffel Tower is the materialized symbol of progress during the Industrial Revolution of the 19th century. In the 1870s and 1880s, the favorable conditions for such technical achievements were building fast: • Significant advancement of the industry; • Development of construction materials, techniques and technologies; • Competitions on World Expositions; • Better structural engineering knowledge and experience;

The Eiffel Tower at 125 Years The Symbols of Progress Do Not Have an Age

By Roumen V. Mladjov, S.E.

Roumen V. Mladjov, S.E. (rmladjov@louieintl.com), is a Senior Associate with Louie International in San Francisco, California.

18 July 2014

• A new Universal (World) exposition planned for 1889 in Paris, and strong desire in France to recapture her previous glory; and • The right man for accomplishing a super task – Alexandre Gustave Eiffel.

Alexandre Gustave Eiffel was born 1832 in Dijon, France. He graduated from L’Ecole Centrale des Arts et Manufactures in 1855 as a chemical engineer.

After one year with Nepveu & Cie, a railway construction company, he started working in 1857 as an engineer for the railway company Pauvel & Cie, where he became chief of the construction office.

In 1866, Eiffel established his own company – Eiffel et Cie from 1868, later Compagnie des Etablissements Eiffel from 1879 – with which he designed and built railways, bridges and structures in Europe, Africa, South America and Asia.

Eiffel built with his team more than a hundred significant bridges and other structures, gaining a lot of practical experience and establishing his reputation as someone with the greatest structural skills of all his contemporary engineers. Parts of his work are two remarkable bridges that are considered as the general rehearsal for his highest achievement, the Eiffel Tower: • Maria Pia Bridge, built in 1877 over the Duoro River in Porto, Portugal, with a 160-meter (525-foot) span; and • Garabit Viaduct, built in 1884 over the Truyere River, France, with a 165-meter (541-foot) span.

Among other well-known projects, Eiffel was also the engineer for the support frame structure of the Statue of Liberty in New York City, Le Palais

movement of the eighteenth century and by the Revolution of 1789, to which this monument will be built as an expression of France’s gratitude.”

Eiffel encouraged multiple uses of the tower beyond its original entertainment purpose.

He himself used it for research on wind forces and velocity, meteorological observations and air resistance on falling bodies; his cabinet can still be seen on the third level near the top.

The tower was used for transmitting radio signals from 1898, and as a military radio post in 1903; it transmitted the first public radio

program in 1925, and has been used more recently for television broadcasting.

The Eiffel Tower remains unique in shape; its pure, exposed forms are elegant and slender, simultaneously providing a feeling of strength and stability. This combined expression of strength and lightness is characteristic of the few truly great structures in the world, and the Eiffel Tower definitely belongs to this group.

After 125 years, the Eiffel Tower remains an example of excellent engineering, and a great contribution to the art of structural engineering.

There is still a lot to learn from the old iron lady.▪

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des Machines for the 1878 Paris Universal Exposition, the Bon Marché department store in Paris, the iron framing for the cathedral of Notre-Dame and a revolving cupola for the Nice Observatory. Eiffel’s goal was always to build structures that were lighter, cheaper, and stronger at the same time.

In 1886, an open competition was announced for the centerpiece of the Exposition Universal in Paris, and all entries had to include a study for a 300-meter (984-foot) metal tower on Champs de Mars. The exposition was organized to show that “the law of progress is immortal, just as progress itself is infinite.”

After winning the competition, Eiffel’s company was awarded the design and construction of the tower. Eiffel was assisted in the project by his leading engineers, Maurice Koechlin and Emile Nouguier, and the architect Stephen Sauvestre.

The tower structure is built with 7,300 tons of wrought iron. Eiffel’s design office needed 5,330 drawings for the tower and its 18,038 elements, which were connected with 2.5 million rivets. Horse-drawn carts transported preassembled parts of the structure from the company workshop near Paris to the site. Up to 120 workers on the site and 330 in the workshop were involved with fabrication and erection.

The construction started on January 28, 1887 and was completed after two years, two months, and three days on March 31, 1889. The height of the tower when completed in 1889 was 300.65 meters (986 feet). The tower base is a square, 125 meters (410 feet) per side. In 1957, an antenna was added, which brought the total height to 320.75 meters (1,052 feet).

In 2000, the tower’s height reached 324 meters (1,063 feet) after the installation of another antenna.

The elegant lines of the tower are purely functional, as the hyperbolic shape of the legs is driven by a design for optimal resistance to wind loads. As David P. Billington states, “The Eiffel Tower’s shape expresses visually the engineer’s ideal for resisting the forces of wind.” This approach to tall structure design was developed by Eiffel during his bridge-building in the Massif Central of France, characterized by very strong winds.

The tall piers of the Garabit Viaduct were designed on the same principle.

Eiffel was well aware that his new structure would be more than just a tower: “…it would symbolize not only the art of the modern engineer, but also the century of Industry and Science in which we are living, and for which the way was prepared by the great scientific

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Companies Doing their Part to MITIGATE EARTHQUAKES’ EFFECTS

By Larry Kahaner

T

he 8.2 magnitude earthquake that hit Chile in April, along with the resulting tsunami, killed six people; two of them succumbed to heart attacks. Contrast this to the February, 2010, 8.8 magnitude earthquake in which 500 Chileans died. Although no two earthquakes are exactly the same – geographically or otherwise – increases in planning and code enforcement helped to lower this year’s quake death toll, according to government officials.

“They’re a seismically active region of the world and they are very good at implementing their building codes similar to California,” John Bellini, a Denver-based geophysicist at the U.S. Geological Survey told CNN. “Because of that, you would see less damage than in other places that have poorer building codes... that’s probably one of the reasons there haven’t been as many casualties as there could have been from a magnitude earthquake of this size.”

Chilean President Michelle Bachelet, said: “This is a great example to all of us that when we work together in an adequate manner, and we when we follow the plans that have been established in the region, we work well.”

Many companies also are involved in earthquake mitigation through products and services. The Fyfe Company, along with their construction arm, Fibrwrap Construction, both part of Aegion Corporation (www.aegion.com) headquartered in St. Louis, Missouri, has a broad reach of business, serving public sector, private sector and utilities.

Renee Hernandez, Director, Sales & Marketing, Fyfe/Fibrwrap, says: “At this time, the industry’s main area of growth is in the private sector, specifically for multi-use building, gypsum residential, parking structures, and commercial buildings that require a change of use or strengthening solution. The West Coast, primarily California, has a broader acceptance for the TYFO and Fibrwrap systems. The development possibilities are wide open in the East Coast, with aged architecture and endless strengthening possibilities. FYFE/Fibrwrap has offices near the major cities to support the growth and establish partnerships with progressive construction experts.”

Hernandez adds: “Fyfe/Fibrwrap enhances the structural capacity of existing structural elements by providing additional strengthening, rehabilitation and repair (including seismic retrofit), pipe rehabilitation, structural preservation, comprehensive force protection, blast mitigation, corrosion related repair and rehabilitation, additional loading and environmental protection.”

STRUCTURE magazine

The company works with customers that require strengthening or rehabilitation including structures, infrastructure and facilities. They work in industrial facilities, waterfront structures, government facilities, transportation infrastructure, high rise buildings, gypsum homes and parking structures. “Our customer base expands throughout the progression of the project, starting with the engineers, architects and owners while also partnering with the general contractor and designbuild firm. We provide sustainable solutions to all sectors within the construction industry,” says Hernandez.

Victor Reyes, Division Director, Fyfe says that he would like SEs to know about TYFO Composite Anchors. “The TYFO Composite Anchors expand the uses of the TYFO Composite Systems. By working concurrently with the TYFO Composite Systems, the Composite Anchors allow the Composite Systems to not only transfer forces into existing systems, such as slab, column and beams, but also through obstructions such as drag forces on the top of a slab with a wall in the way.” He says that for specific applications, it was necessary to increase the allowable design stress of FRP composite systems for shear strengthening for beam and wall applications under static and seismic loads. “This was achieved through the creation of the TYFO Composite Anchors, which are made of the same material as the TYFO Composite Systems. Both large-scale and small-scale testing has shown that using the same material provides continuity and allows the Composite Systems to achieve higher design stresses for both static and seismic loads. From these tests it was shown that the use of the TYFO Composite Anchors not only transfers loads from the Composite System into the structural system, but also contributes to the structural system to continue to behave as a ductile system under seismic loads.” (See ad on page 22.)

Taylor Devices (www.taylordevices.com) in North Tonawanda, New York, manufactures damping devices for absorbing dynamic energy to protect building and bridge structures from earthquakes and unwanted wind vibrations, according to Craig Winters, a Seismic Products Sales Manager. He says that customers range from engineers to contractors to owners of any infrastructure.

“Taylor Devices is currently involved in research for the use of these uniquely adaptable devices for smaller wood-frame structures and houses,” says Winters. Taylor dampers were tested on a fullscale, 4-story wood building at the University of California at San

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July 2014

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Diego. The house was strengthened with better connections in its frame members; a light steel moment frame and wood shear walls on the upper floors were added. Nine small fluid dampers were installed on the first floor only. The dampers were built into 4- x 8-foot modular panels and driven via Taylor Devices’ patented Toggle Brace Systems. “The results so far have been excellent, even though the dampers are small and only placed on the first floor.”

Two short videos about the tests that Winters recommends watching can be found at www.youtube.com/watch?v=0O6DZ3dqh3c and www.youtube.com/watch?v=25hCATGKSbI. Adds Winters: “SEs should understand that these are not new devices.

They are simply an adaptation of our existing, patented toggle brace technology into a new use, for building structures previously not

STRUCTURE magazine

considered candidates for our technology. It was always thought that wood-frame structures were too light and not ‘tied-together’ well enough to benefit from the advantageous use of our Fluid Viscous Dampers. This has changed with the new research, and the patented toggle brace mechanisms for these applications…. Owners of existing infrastructure seem to be leaning towards performance improvement using low-cost structural improvements to their existing structures, which can easily be accommodated with the use of Taylor dampers and technology.” (See ad on page 24.)

At SidePlate Systems (www.sideplate.com) in Laguna Hills, California, the latest news is that the company’s connections are now listed as prequalified moment connections in the ANSI/AISC 358-10 standard. “This followed a thorough examination by AISC’s Connection Prequalification Review Panel (CPRP) over two years,” says Jason Hoover, Industry Outreach Executive, Eastern Regional Business Manager.

“SidePlate’s prequalifications go beyond those of other moment connections. These include HSS beams, biaxial connections, and the deepest allowable moment frame beams (W40). The ANSI/AISC 358-10 Commentary also provides the history and evolution of SidePlate connections that will be helpful for engineers looking for more background.”

He notes that SidePlate connections have been prequalified by ICC-ES, DoD, OSHPD, DSA and other agencies for many years, but having AISC’s approval is the ‘gold standard.’ “More jurisdictions are starting to reference this AISC prequalification, so we felt it would give engineers more confidence and make their lives easier without having to worry about additional reviews and approvals.”

Hoover says that healthcare construction has been SidePlate’s biggest sector historically, along with commercial, institutional, and government buildings.

“Specifically, we work directly with structural engineers during design phase, then with the fabricator, erector, and contractor during construction.” He adds: “Our business is strong, and our customers seem to be getting busier as well. In particular, the West Coast has picked up quite a bit versus 2013, but the difficult winter has slowed down many projects in the Midwest and the eastern United States.

Healthcare is steady, and we’re starting to see more commercial office building projects starting up.”

Hoover would like to clear up some false impressions about SidePlate. “There are still misconceptions that we manufacture a product, but we are a specialty design firm and our connections are built by the project’s steel fabricator. The other big misconception is that a SidePlate connection is simply a 1:1 comparison with continued on page 24

22

July 2014

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other types of connections. Our connection stiffness changes the entire lateral system, so lighter member sizes can be used and it’s a holistic improvement on the structure.”

DECON (www.deconusa.com) is the original North American manufacturer of STUDRAILS and has recently become a subsidiary of JORDAHL GmbH, which for more than 100 years has manufactured high quality connection and reinforcement products for use in the international construction industry, according to Frank Metelmann, President of JORDAHL. “We supply two market leading use in both public and commercial building projects including highbrands, DECON punching shear concrete reinforcement products and rise buildings, offices, hospitals, schools, transportation structures, JORDAHL anchor channels for structural and architectural concrete and stadiums.” connections. Our products are globally recognized for quality and Metelmann says that the company’s customers span the entire buildTAY24253 BraceYrslfStrctrMag.qxd 9/3/09 10:09 AM for Pageing 1 industry. “Both STUDRAILS and JORDAHL anchor channels engineering excellence, and are widely specifi ed internationally are specified by structural engineers.

STUDRAILS are typically purchased by general contractors or concrete subcontractors. This can also be true for Y O U B U I L D I T. JORDAHL anchor channels, but they W E ’ L L P R O T E C T I T. are very versatile in their application and are very often also purchased by curtain wall contractors, architectural metal contractors, elevator companies, steelwork contractors, and precast concrete Stand firm. Don’t settle for less than the seismic protection manufacturers.” of Taylor Fluid Viscous Dampers. As a world leader in As for new offerings, Metelmann outthe science of shock isolation, we are the team you lines three of them. First is JORDAHL want between your structure and the undeniable forces anchor channels which have new design of nature. Others agree. Taylor Fluid Viscous Dampers software. JORDAHL EXPERT softare currently providing earthquake, wind, and motion ware is the first anchor channel software based on the International Building Code protection on more than 240 buildings and bridges.

(IBC), and the International Residential From the historic Los Angeles City Hall to Mexico’s Code (IRC), and ICC-ES AC 232, he Torre Mayor and the new Shin-Yokohama High-speed says. Second are BIM files for the range Train Station in Japan, owners, architects, engineers, of JORDAHL anchor channels. The BIM and contractors trust the proven files enable modeling of these products technology of Taylor Devices’ using the Revit platform. Third is the Fluid Viscous Dampers. new IAPMO Uniform ES Report. “The new IAPMO Uniform ES Report for JORDAHL anchor channels is the first independent performance and quality assurance evaluation report for anchor channel products in North America,” says Metelmann. “These offerings were based on a perceived requirement from structural designers and code officials to provide independently verified standards of design and quality assurance into the anchor channel market. We see BIM as a continuing evolution of building design and are pleased to also enable Taylor Devices’ Fluid Viscous Dampers give you the seismic protection the easy inclusion of anchor you need and the architectural freedom you want. channels into building planning using this medium.”▪

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FULL METAL JACKET Part 1: Evacuation

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

Figure 1.

T

his article, which will be presented in three parts, discusses the investigation and subsequent repair of an existing timber-framed, multi-story building that is over one hundred years old. The investigation initially resulted in the need to evacuate the occupied building, which allowed for the innovative repair of severely deteriorated timber columns by encapsulating the wood within replacement steel columns that essentially jacketed and abandoned the original wood members in place.

As land that can be developed has become more difficult to find, particularly in densely populated urban cities, owners and developers have increasingly turned to existing facilities to convert for new uses.

These older buildings typically exhibit structural deterioration due to lack of maintenance and exposure over time that must be addressed in order to ensure the safe adaptive reuse of the facility. Assessing and developing repairs for the deteriorated conditions of older vintage structures can be challenging due to the lack of drawings and antiquated methods of construction that are typically encountered.

Pennoni Associates Inc. was recently involved with a condition assessment of six structures that fall in the above category as a part of a loan default acquisition by a property management client. The historic property was part of a mill complex that was likely constructed in the late 1800s to early 1900s, and had been converted into a mixed-use facility including residential apartments and commercial and industrial spaces within the last 15 to 20 years. The buildings were constructed with masonry stone and brick, as well as timber, concrete, and steel framing. Given the age of the facility, the structures were in relatively good condition. However, there were several major concerns that were identified as needing further investigation, including exploratory demolition that was beyond the scope of the original agreement with the client. All of the observations and recommendations were documented in a report submitted to the client.

A few months after submission of the report, the client requested further investigation of one of the major items of concern, because observations by the first floor tenant indicated that the columns appeared to be moving. The affected building was a five-story (including a full basement) rubble stone masonry wall structure. The portion of the building that was exhibiting structural distress was framed with STRUCTURE magazine

Figure 2.

heavy timber beams spaced at approximately 8 feet on center that spanned perpendicular to the longitudinal axis of the building. The beams were supported by timber columns located at the approximate midpoint of the transverse dimension of the facility, for a maximum clear span of approximately 22 feet. Wood decking spanned between beams, which interrupted the columns at each floor; however, the beams were spliced with a keyed scarf joint with beveled cuts at the centerline of the columns. In addition, a timber corbel or pillow beam was located below the beam and on top of the column below. This connection is illustrated in Figure 1.

Although it could not be confirmed visually, it was assumed that mortise and tenon joints had been used between the lower column and the corbel, the corbel and the beam splice, and the beam and the column above. This method of construction was used on all of the framed floors and roof; however, at the first floor, the beams were interrupted by the basement column, which extend up to the top of the first floor, where there was a connection to the bottom of the column above. There did not appear to be a connection between the first floor beams and the face of the columns, but the beams were supported by full-height 3x12 timber plates that were through-bolted to the sides of the columns directly beneath the beams. The first floor of the building included a concrete slab that was cast on top of the timber floor decking; however, at the other floors, it could not be confirmed if a similar concrete topping had been placed due to the presence of the existing floor finishes.

The occupancy of the building was divided into a combination of residential, commercial, and industrial spaces. The first (ground) floor of the building housed a glass-blowing shop with large kilns and a commercial kitchen. The glass-blowing operation also used a portion of the basement below. The second floor of the building was not occupied,

26

July 2014

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

Richard H. Antoine III, P.E., S.E. (RAntoine@Pennoni.com), is a Project Engineer at Pennoni Associates in Philadelphia, Pennsylvania.

Figure 3.

UNIVERSITY VILLAGE, SEATTLE, WA

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but it had been previously used by a plastic manufacturing company.

The third and fourth floors of the building were divided into individual residential apartment units. Due to the heavy loads associated with the first floor kilns, timber posts and masonry piers had been installed in the basement in addition to the main building columns, to distribute the first floor loading to the basement slab on grade.

The deleterious structural conditions included two primary issues. The first condition included extensive previous insect infestation damage observed in the basement at several of the timber columns, beams and decking. The second condition involved visible vertical settlement of several of the columns due to what appeared to be almost a complete loss of section at the base of the columns in the basement (Figure 2).

It was unclear whether the loss of section was due to insect damage, deterioration due to exposure of the base of the column below the slab on grade to moisture, or both. The non-uniform vertical deflection of the columns had also resulted in the horizontal rotation and out-ofplane movement of the corbel and beams that were supported by the top of the column just below the second floor (Figure 3).

The extent of section loss at the bases of several of the timber columns below the basement slab on grade was extensive, and in some cases appeared to have resulted in little to no end bearing of the column on top of the footing. At these same locations, it appeared that the 3x12 side plates that were through-bolted on each side of the columns were supporting not only the first floor beams, but also the building column above. The bases of the 3x12s rested on the slab on grade immediately adjacent to the edge of the hole in the slab that had been previously occupied by the deteriorated building column base. In addition, these same 3x12s exhibited significant insect damage and moisture-related deterioration. This condition appeared to be very precarious and in danger of immediate collapse.

The evaluation team immediately notified the building owner that the structure was not safe for occupancy and should be evacuated. The owner obtained a second opinion from another local structural engineering firm, which agreed with the assessment and encouraged the owner to evacuate the building immediately due to the unsafe condition of the structure. As a result, the owner contacted the local building officials, who assisted in evacuating the building of all third- and fourth-floor residents, as well as the first-floor tenants.

Part 2 of this article will discuss the nature of the deterioration observed and the solutions considered for the repair of the deteriorated columns associated with the referenced building.▪

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July 2014

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Just the FAQs questions we made up about ... CONCRETE

Placement of concrete to the tilt-up panel forms is followed by vibration, screeding and floating for desired finish.

Courtesy of Concrete Strategies, St. Louis, MO.

A

change is coming this year to the familiar ACI 318, Building Code Requirements for Structural Concrete, published by the American Concrete Institute. The existing format of ACI 318 dates back to the 1960s, and feedback from code users in recent years has made it clear that a modernized version is necessary. Especially for rapidly evolving parts of the industry, such as tilt-up construction, the new code should ensure greater overall consistency and accuracy.

But what exactly will be different? Here James Baty, technical director for the Tilt-Up Concrete Association, answers a few questions about the revised code.

Q: Why are we hearing so much about ACI 318 right now?

Answer ACI 318 is published in successive threeyear cycles, and ACI 318-14 is being released

Prepared for concrete placement, the tilt-up panel forms permit visible inspection of all structural reinforcement required by the engineer of record and panel engineer.

Courtesy of Panattoni Construction, Sacramento, CA.

soon. The reason why so much publicity surrounds this particular version is that the code has been completely reorganized. A herculean task for any document, but especially so for a code document with references and relationships connected from cover to cover.

Changes to ACI 318 for Tilt-Up Wall Panels

Q: Why was such a major overhaul necessary?

Answer The purpose of the reorganization was to distill the complex relationships of physical behaviors in materials and forces into compartmentalized design elements of a building. In real-world scenarios, once the overall structural system for a building has been determined, a designer considers the structure one piece at a time. Therefore, the code that directs the design – based on the behavior of any one of these elements – should maintain a logical focus for the designer. The existing 318 layout forces the designer to traverse an entire document to reference a variety of behaviors and sub-parts. In other words, a designer should be able to design a concrete column with information contained in one location within the code and be able to follow that design step-by-step in a logical progression. It is ineffective to have to design for one force and then go somewhere else in the code book to do a reference check on a separate analysis.

Q: Can you give an example, specific to tilt-up, of how the previous version was cumbersome to use?

Answer Tilt-up wall panels, primarily those used as load-bearing structures, are designed based on an analysis of not only the moments from applied loads, but also secondary moments due to the P-∆ effect. In order to proceed with the design of a common tilt-up wall panel spanning from roof to floor with no intermediate bracing, ACI 318 was first applied through Section 14.8 to determine the strength requirements. Based on these results, the designer then needed to check Section 9.3 and 10.3 for tension-controlled flexural members.

Once the applied loads were determined, the

STRUCTURE magazine

31

By James R. Baty II

James R. Baty II (jbaty@tilt-up.org), is technical director for the Tilt-Up Concrete Association (TCA). He is currently the secretary and a voting member for the ACI 551–Tilt-Up Concrete Committee, serves as chair for ACI 332–Residential Concrete Committee and is a voting member of ACI 306–Cold Weather Concrete, ACI C650–Tilt-Up Certification, and the newly forming Residential Foundation Technician Certification committee.

Tilt-up panels are easily designed to accommodate large openings while maintaining performance of the perimeter structure. Courtesy of Panattoni Construction, Sacramento, CA.

designer then used Section 9.2 to determine the controlling load combination. Once the vertical steel was determined, the designer headed back to Chapter 10 to check for the tie requirements around the vertical steel, and did a check against Chapter 21 for determining whether the panel would behave like a column or a beam. The behavior between panels and resistance to sliding or overturning forces were checked in Section 16.5, and the shear resistance in Chapters 11 and 21. All of this took place before connections were detailed in Appendix D. Of course, this is a simplification of the procedure, but it does demonstrate how well a designer must know ACI 318, as well as why there are some very good design guidance documents that have been produced in the last five years.

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Q: Can you give an example, specific to tilt-up, of a construction detail or process that has a more streamlined layout in ACI 318-14?

Answer As presented by ACI staff engineers during the past several months, the new organization ensures each chapter will contain all requirements for a given building element.

For example, there was a “Walls” chapter in ACI 318-11; however, it did not contain all

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of the requirements for walls. The designer had to read the requirements in the “Walls” chapter and understand how they modified the core behavior-based chapters (7 through 12) in order to meet the code. If the wall was precast or tilt-up concrete, the designer would also have to read Chapters 16 and 18 and understand how those requirements further modified Chapters 7 through 12 and 14.

ACI 318-14 now has all of the information needed for walls in one chapter. An example of this simplification is the minimum reinforcement required for a wall. In ACI 318-11, the designer would have had to read Sections 11.9.8, 14.2.7, 14.3.1, 14.3.2, 14.3.3, 16.4.1, 16.4.2, 18.11.2.1, and 18.11.2.3 to have a complete understanding of the minimum reinforcement requirement. In ACI 318-14, all of these requirements have been moved to one location in an easy-to-understand table (11.6.1). The table is read from the left starting with the type of wall. Then the designer applies the conditions and limits as they move across the table to the answer on the right.

Q: Will the new code help increase the use of tilt-up concrete?

Answer I do expect this new code organization to simplify the design process so that a broader cross-section of engineers feels comfortable with the design procedure for tilt-up buildings. It should eliminate some of the frustration that can come with a complicated method of design. Certainly, it should also aid in the general response of design to condition rather than evidencing excessive design parameters for conservative engineers that do not have as strong a command of the intimate behaviors.

Q: Will the new code be helpful as an educational resource?

Answer Absolutely. This, perhaps, is one of the revision’s most important aspects. There is no denying that talented and experienced engineers leading the industry have complete confidence in the use of and design response to the current code(s). However, tomorrow’s building is already in the hands of the next generation(s) of talent, and therefore a document with more efficient design procedures and methodologies will only quicken their command of the medium and increase the level of their creativity for great and effective solutions.

Q: One benefit of ACI 318-14 is that the new structure is expected to be easier to expand upon in the future. Is this particularly important to a rapidly evolving part of the construction industry, such as tilt-up?

STRUCTURE magazine

32

July 2014

Tilt-up panels, as the structural envelope, are secured with temporary bracing until all structural connections are completed.

Answer Unequivocally, yes. The hardest part of updating a complex code is ensuring that a change in one section does not conflict or constrain the design intent in a later step. By maintaining an efficient focus on the design requirements and procedures for a given element, desired or needed changes can be more easily tracked through the process without losing sight of the net result.

Q: Can you explain how ACI 318-14 will help ensure that buildings meet code requirements?

Answer Perhaps the biggest impact that 318-14 will have on the general industry is ensuring that key elements of a design are not overlooked. The nature of a code is to ensure the effectiveness of an element for long-term serviceability and performance.

Missing an important section for performance, behavior or a check means that, at some point, the design element may be conservatively designed and therefore less economical than it otherwise may have been. It also means that there could be a critical error in the potential behavior, perhaps caught by a specialty engineer or an experienced contractor resulting in change orders or having other ramifications. A code that provides more consistency – as well as assurance that all features of the design process are identified and easily referenced in logical succession – will only improve the relationship of that element to the meticulous code requirements that have been developed.

Q: When can we expect 318-14 to come out?

Answer Although there is never an official publication date for an industry document such as this, every indication from ACI is that it will be available for order in the late fourth quarter of 2014. The public is expected to see a review period this summer.▪

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Code Updates code developments and announcements

T

he model building codes in the U.S. cover virtually every safety-related topic associated with construction of buildings. Fire-related issues comprise a surprisingly large portion of the model codes. Designing for fire safety is a complex and multifaceted issue. Discussion in this article is limited to design of exposed wood members.

Additional information on building code requirements for wood can be found in the American Wood Council’s (AWC) Code Conforming Wood Design documents available for free download at www.awc.org.

Fire Design of Exposed Wood Members The fire resistance of exposed wood members, including lumber, glued laminated timber, and structural composite lumber (SCL), may be calculated using provisions of Chapter 16 of AWC’s National Design Specification® (NDS®) for Wood Construction. This allowable stress design approach is referenced in 2012 International Building Code (IBC) Section 722.1. The design procedure allows calculation of the capacity of exposed wood members using basic wood engineering mechanics. Actual mechanical and physical properties of the wood are used, and member capacity is directly calculated for a given period of time – up to 2 hours. Section properties are computed assuming an effective char rate, βeff, at a given time, t. Reductions of strength and stiffness of wood directly adjacent to the char layer are addressed by accelerating the char rate by 20 percent. Average member strength properties are approximated from existing accepted procedures used to calculate design properties. Finally, wood members are designed using accepted engineering procedures found in NDS for allowable stress design. Note, the design procedures presented in NDS Chapter 16 are not intended to be used for design and retrofit of a The fire resistance of structure after a fire event. exposed wood members, The 2012 and earlier verincluding lumber, glued sions of the International laminated timber, and Building Code (2012 structural composite IBC 722.6.3) have also lumber (SCL), may contained an empirical be calculated per IBC Section 722.1. calculation method for

Design of Fire-Resistive Exposed Wood Members

By Bradford Douglas, P.E. and Jason Smart, P.E.

Brad Douglas, P.E. (bdouglas@ awc.org), is Vice President of Engineering and Jason Smart, P.E. (jsmart@awc.org), is Manager of Engineering Technology with the American Wood Council.

34 July 2014

The calculation procedure for fireresistance of exposed wood members is found in Chapter 16 of AWC’s National Design Specification (NDS) for Wood Construction.

estimating the structural fire resistance of wood beams and columns exposed to a standard fire exposure for up to 1 hour. However, this empirical method has been deleted in the 2015 IBC in favor of the provisions contained within NDS Chapter 16, which are much broader in application and leave less room for design error.

Basis for NDS Chapter 16 Approach AWC’s Technical Report No. 10 (TR 10), Calculating the Fire Resistance of Exposed Wood Members, contains full details of the NDS method as well as design examples, and is available for free download at www.awc.org. TR 10 was recently revised to incorporate the following: • A new section that supports the use of the design method with smaller dimension sizes associated with lumber joist floor assemblies; • Revised design examples to match the 2012 NDS; • Revised design tables in Appendix A, which allows more accurate calculation of fire resistance of columns with any slenderness ratio, eliminates tabulation of very special cases that can be misapplied (i.e., deleted beams that are exposed on 4-sides that are assumed to be fully-braced throughout the fire rating, columns that are only exposed on 3-sides but are assumed to be unbraced, and tension members that do not resist flexure due to member dead load), and more in-depth discussion of how the tables were developed; and • A new Appendix B that calculates the fire resistance of single-span lumber joists for any design stress ratio when joists are exposed on 3-sides and braced on the top edge.

For beams and columns stressed in one principal direction, simplifications can be made which allow the creation of load ratio tables.

These load ratio tables can be used to determine the structural design load ratio at which the member has sufficient capacity for a given fire resistance time. Tables in DCA 2 give load ratios corresponding to 1-hour, 1½-hour and 2-hour fire resistance ratings for specified member dimensions. All tabulated load ratios apply to standard reference conditions where the load duration factor, wet service factor, and temperature factor equal 1.0 (CD=1.0; CM=1.0; Ct=1.0). For more complex calculations where stress interactions must be considered, or where standard reference conditions do not apply, designers should use the provisions outlined in TR 10, along with the appropriate NDS provisions.

AWC’s Technical Report No. 10 (TR 10): Calculating the Fire Resistance of Exposed Wood Members, contains full details of the NDS method as well as design examples, and is available for free download at www.awc.org.

Design of Fire-Resistive Exposed Wood Members (DCA2) replaces the empirical design equations in the 2012 IBC with simplified design information developed in accordance with the NDS for exposed wood members, and is available for free download at www.awc.org.

Conclusion

Simplified Approach AWC’s Design for Code Acceptance 2 (DCA 2): Design of Fire-Resistive Exposed Wood Members has been revised to replace the empirical design equations currently in the 2012 IBC with simplified design information developed in accordance with the code-approved NDS fire design procedure for exposed wood members. The tables and examples have been rewritten for consistency with the approach outlined in the 2012 NDS and TR 10.

Designers, regulators, and fire officials throughout the country recognize the superior fire resistance demonstrated by structural wood beams and columns in actual fires. Structural fire design provisions have been incorporated in Chapter 16 of the NDS, which is referenced in Section 722.1 of the 2012 IBC as a method of calculating fire resistance of exposed wood members. A comprehensive discussion of this mechanics-based design procedure can be found in Technical Report No. 10, while DCA 2 provides a simplified description of this code-approved fire design procedure for exposed wood members. Both documents, available for free download at www.awc.org, provide simple design tables, connection details, and other design information to facilitate fire design of exposed wood members.▪

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NCEES will be at the NCSEA Annual Conference, September 17—20.

Are you planning to take the SE exam?

NCEES Exam Development Engineer Jason Gamble, P.E., will be on hand to answer all your SE exam questions.

We’ll also be giving away free copies of the NCEES Structural Engineering Sample Questions and Solutions. It’s the only practice exam that’s created by the experts who develop the actual exam.

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STRUCTURE magazine

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July 2014

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mong the many code provisions which may be characterized as ambiguous, few seem as pervasive as the issue of full-height blocking for either wood or coldformed steel construction. Opinions regarding the need for full-height blocking widely varying, and it seems that even the purpose of full-height blocking is subject to debate. To some, the term “rollover” blocking is used, reflecting the concept that it prevents rolling over of trusses or rafters.

Others call it “seismic” blocking, clearly denoting its purpose with respect to an earthquake threat.

No doubt the term “hurricane” blocking reflects a similar concept.

Although these purposes hold similarities, one could argue that “rollover” blocking need not necessarily match the depth of the trusses or rafters to which it abuts. After all, such blocking may clearly prevent “rolling” failure without being contacted intimately by the deck above. Plus, keeping the height of blocking less than the depth of the abutting truss provides needed ventilation for the attic cavity. However, arguments in favor of full-height blocking, even shaped blocking to accommodate deck slope, stem from clearly defined code provisions that relate to developing a continuous and reliable load path for lateral forces.

Interestingly, the full-height blocking concept has a code basis in International Residential Code (IRC) items R602.10.6.2(2) and R804.3.8(2,3).

Although these figures and the accompanying text address both wind and seismic forces, and the triggers that activate the need for blocking, the provisions are not entirely clear and may appear to support the concept of blocking that is not full-height. Is full-height (even shaped) blocking ever required? If so, when?

Not surprisingly, informal surveys of building officials and others charged with code interpretation regarding the full-height blocking issue in regions of high seismicity generally result in a deferral to the engineer of record. Observations of many light-framed projects demonstrate widespread variation. Many engineers of residential construction design and detail full-height blocking, but builders – due to tradition, ignorance or economy – often fail to install it according to the engineer’s intent. Lack of field observation by the engineer of record contributes to the variation seen in practice. Some engineers even vehemently support the position that fullheight blocking is rarely (if ever) needed for light-framed construction. They hold that the relatively low seismic mass, presence of interior gypsum panels, and even potential cross-grain bending of trusses and rafters all support the argument that full-height blocking is not needed. What is your position?

The variation in opinion and practice is due in no small part to the somewhat ambiguous nature

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

Full-height blocking detail consistent with FEMA 232.

of the code. Perhaps future code provisions will provide further clarity. FEMA 232, Homebuilders Guide to Earthquake Resistant Design and Construction (June 2006, available electronically at www.fema.gov), provides more definitive direction. According to Section 6.3: “Rafters and ceiling joists having depth to thickness ratios exceeding 5:1 (e.g., 2x10) need blocking at their points of bearing to prevent rotation or displacing laterally from their intended position …

However, when the nominal size of the ceiling joist or rafter is 2x10 or smaller, blocking over the exterior wall may be omitted.” FEMA 232 further states: “Although blocking may not be required for 2x10 and smaller rafters, there still must be a load path for lateral loads in the roof sheathing to reach the exterior braced walls immediately below the roof. The most direct load path is for the roof sheathing to be edge nailed to blocking between each rafter. That blocking is then nailed to the wall top plate …” The Figure is an illustration depicting this condition.

It seems clear that the best approach for defining the lateral load path from the roof diaphragm to the walls is to provide full-height blocking.

Some may argue that this is a difficult detail that serves more to elevate costs than to provide a safe structure. This is a debatable point, but not likely sufficient to overcome the base recommendation of FEMA 232.▪

Full-Height Blocking – What Is Your Position?

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

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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.

Professional issues

issues affecting the structural engineering profession

Deferred Submittals Part 1: Integrating Responsible Parties

By Dean D. Brown, S.E. Over the course of my career, I have worked in both engineering design and construction.

While I have dealt with each of the systems described above, most of my experience has been with pre-engineered wood trusses. My purpose here is not to so much discuss their design, but rather focus on the overall coordination needed during the design process, including their role as a deferred submittal. – Dean Brown

W

e are living in an age of integration. Just pick up your smart phone for a quick example. Information is increasingly becoming real time. You will hear buzzwords or buzz-phrases like interoperability, integrated project delivery, partnering, design-build, holistic, sustainable, cross-functional teams, and streamlining. The trend is to compress time and cost while increasing scope and service.

Doing more with less is the new normal in today’s professional practice. Evolution is the constant Integration affects structural engineers in common ways, perhaps in varieties not typically thought about. Many of today’s projects include proprietary products that involve specialty engineers and deferred submittals. Examples include metal-plateconnected wood trusses, cold-formed steel trusses, pre-engineered metal buildings, prestressed or post-tensioned concrete systems, and some types of curtain walls.

Use of these systems creates new complexities and requires greater coordination between design professionals and contractors. Building codes, specifications, general notes, standard contracts, and rules of professional responsibility need to reflect this practice, because engineering design is no longer performed in a bubble.

Definitions Deferred submittals are clearly defined in the 2009 International Building Code (IBC) (Section 107.3.4.2) as “portions of the design that are not submitted at the time of the (permit) application and that are to be submitted to the building official within a specified period.” Please note that this provision requires the deferred submittal to be listed on the construction documents, and many building officials also require

them to be listed on the application for a building permit.

ANSI/TPI 1-2007, a wood truss building code reference document published by the Truss Plate Institute, defines deferred submittals as “those portions of the design that are not complete at the time of the application for the Building Permit and that are to be submitted to the Building Official within a specified period in accordance with Legal Requirements.”

The California Division of the State Architect (DSA) elaborates further (www.dgs.ca.gov/ dsa/Programs/progProject/overview/ projsubmitintro.aspx): “Deferred approval does not mean that the A/E of Record may defer the design of the component to the contractor. DSA requires that the A/E of Record accept responsibility for verifying that all components (including those granted deferred approval) of the project are properly designed by appropriately licensed design professionals. The A/E of Record is also responsible for coordination of all components of the project. Finally, the A/E of Record is responsible for designing connections to the structure for all deferred approval components and verifying that all interactions (deflection compatibility, drift compatibility, vertical loads, etc.) are adequately addressed and in conformance with good engineering practices and the California Building Standards Code.”

Reasons for this hierarchy in review are best described by the wood truss industry in Appendix H of the Metal Plate Connected Wood Truss Handbook, Third Edition: “Contemporaneous preparation of the Building Structural System Design Documents (i.e., contract documents prepared by the EOR) with that of the Truss Design Drawings (i.e. prepared by the Specialty Engineer of Record (SEOR)) would allow for easier design of support and bearing conditions, temporary and

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permanent lateral and diagonal bracing, and all the anchorage needed to resist uplift, gravity and lateral forces on the structure. However, as it is often impractical or even impossible for the Truss Designer to provide input at the time the Building Structural System Documents are prepared, many engineering assumptions will need to be made in the design of the structure.

Accordingly, the Truss Design Drawings, when produced, may not exactly match with the assumptions used. For example, it is very unlikely that the calculated uplift loads will match the uplift loads developed by the Truss Designer. They should not be expected to be identical. For this reason, it is essential that the Truss Design Drawings be reviewed and approved by the Owner or the Building Designer as delegated by the Owner. It is the responsibility of the Owner or the Building Designer, as delegated, to specify appropriate uplift loads and connection requirements for use by the Contractor for all anchorage and connection requirements of the Trusses.”

Roles and Responsibilities As implied, the structural design process is iterative, requiring the EOR and SEOR to coordinate their efforts. While this is a critical step in the review process, the EOR is ultimately in responsible charge to ensure that the overall structure is safe and code-compliant. In its MasterSpec evaluations, the American Institute of Architects (AIA) writes, “Design responsibility issues continue to trouble the truss industry … [which] maintains that some design areas remain the responsibility of others.

Although truss fabricators engineer wood trusses, other related requirements, such as permanent bracing and anchoring trusses at bearing points, are not addressed.”

Especially over the last few building code cycles, the truss industry had worked hard at clarifying language on respective roles and responsibilities between the EOR, SEOR and building official. A good example in one in which the author acted as EOR and construction manager/field superintendent for the building owner.

layout (per truss manufacturer and SEOR). Girder trusses may be in different locations. Bearing points may have been adjusted. Headers may need to be redesigned. Jack trusses may be in different locations.

Permanent bracing (e.g., between the wood structure and the truss diaphragm system), other truss overbuild or piggy back locations, truss deflections, and truss supports and anchorage (e.g., for lateral and vertical loading conditions) need to be checked.

• After review of the TDD, the EOR makes revisions to the SDD, re-stamps if necessary, and indicates to the building official that the deferred submittal is in general conformance with the SDD. The updated documents are routed back to the client and/or contractor.

• The contractor, in turn, provides the updated set (both the SDD and the TDD) to the building official for approval.

• Once approval has been granted, the contractor returns the approved TDD back to the truss plant and jobsite office, and fabrication begins.

The contractor may also need to make some framing revisions based on the updates.

• Trusses are fabricated and shipped to the project site.

• The framing contractor begins the erection of the truss system and calls for appropriate inspections by the building official.

While the 2009 IBC (Section 107.3.4.2) stipulates that deferred documents are deferred designs, it also mandates the proper review of such documents by stating, “Documents for deferred submittal items shall be submitted to the registered design professional in responsible charge [EOR] who shall review them and forward them to the building official with a notation indicating that the deferred documents have been reviewed and found to be in general conformance to the design of the building.” A good engineering practice would be to cite this provision in the general notes and emphasize that erection of trusses must not occur until the EOR has reviewed the TDD.

Conclusions As with most design-bid/negotiate-build projects, the only common stakeholders

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from design through construction are the owner and the building official. Generally, architects and engineers have limited access to jobsite progress, depending on their contracts with the owner. The contractor, in turn, may or may not be involved in constructability reviews during the design phase. The owner in most cases is not a building professional, and therefore not familiar with typical industry practices for deferred document approvals. That leaves the building official, who is charged with the authority to ensure that proper routing takes place.

In this age of integration, success depends on all stakeholders acting in unison with building code standards. We need to focus more on commonalities with other building professionals, rather than differences. A previous STRUCTURE magazine article, Good Design Should Consider Poor Execution (May 2011) by Bouldin and Showalter, states, “An implicit assumption in the design of wood framed structures is that proper construction methods are followed during the implementation of these designs.” Do we as designers likewise make an implicit assumption that building officials are reviewing deferred submittals properly? Part 2 of this series, will attempt to answer that question with some of the author’s own findings.▪

Dean D. Brown, S.E. (browndean57@yahoo.com), is a Professional Structural Engineer in the state of Utah. He works as a senior structural engineer for Lauren Engineers & Constructors in Dallas, TX.

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The project was a wood-framed assisted living campus and involved pre-engineered wood trusses (ten buildings in all). While there can be (and are) many other scenarios, the following sequence is what the wood truss fabricator and the author used to get documents routed and approved.

Variations will depend on regional practices, the truss manufacturer, and even the local building official.

• The Structural Design Drawings (SDD) are submitted with P.E. stamp, date and signature to the building department as a condition of being granted a building permit.

The deferred submittals (e.g., preengineered wood trusses) are listed on the SDD and on the building permit application. Some building officials will instead require the Truss Design Drawings (TDD) as described by the 2009 IBC (Section 2303.4) to be submitted with the original application. Some truss plants, in an effort to appease the building official, will provide a ‘preliminary’ design to serve as a placeholder for the deferred final design.

• Once a review of the SDD has been satisfactorily achieved, a building permit is issued.

• The contractor installs the foundation and erects the load-bearing walls.

Concurrently, the contractor also places a purchase order for the preengineered trusses. Many truss plants subcontract the truss engineering to a third-party SEOR. As in the author’s case, the truss plant does not proceed to a final design on the trusses until a purchase order has been officially placed and jobsite conditions have been verified.

• After load-bearing walls have been framed, the truss manufacturer comes to the jobsite and performs a final measure of the wall layout to ensure field and plan dimensions coincide.

• The truss plant releases the SEOR to finalize the design and submit TDD for reviews and approval.

• A copy of the final TDD design is sealed, signed, and dated by a registered P.E. and sent to the client (i.e., the contractor). The contractor, in turn, routes a copy of the deferred submittal to the owner and/or EOR for final concurrent review.

• The EOR checks for differences between the assumed truss layout (per SDD) and the final truss

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Spotlight

Engineering a National Memorial

By Erleen Hatfield, P.E., AIA, LEED AP and Alan Erickson, P.E. Buro Happold Consulting Engineers was an Award Winner for the World Trade Center Memorial Pavilion project in the 2013 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings $30M to $100M).

T

he new National September 11 Memorial Museum Pavilion, located within the archaeological heart of the World Trade Center in New York City, opened to the public on May 21, 2014.

The 47,000 square-foot museum pavilion designed by Snøhetta architects’ New York office with associate architects, Adamson Associates, is the only above grade building on the World Trade Center memorial grounds and serves not just as an entrance to the museum below, but also provides ticketing for the museum, exhibits, and an auditorium.

Buro Happold provided structural and MEP engineering for this important, challenging and elegant structure. The pavilion is on target for LEED gold certification.

Site Complexity The complexity of designing and constructing the museum pavilion on the World Trade Center site was especially challenging. The museum pavilion is surrounded by projects that constrain it both in geometry and in structural design: the active PATH commuter rail, the memorial pools at the original locations of the twin towers, and New York City subway lines. The pavilion structure starts at plaza level and extends 4 stories above the street. Design of both the architecture and structure required collaboration with many stakeholders on the site, including the Port Authority of New York and New Jersey, the PATH station design team, the MTA, Lend Lease (general contractor for the pavilion), along with other general contractors working on site.

Gravity/Transfer Structure From a structural perspective, achieving the experience envisioned by the architects required reconciling complex constraints. The majority of the pavilion is supported over the PATH train station and tracks, while the balance is supported on the below grade museum. Careful coordination and analysis of the surrounding structural constraints was critical in identifying support points for the pavilion. When

constraints such as train track positioning, the location of the memorial pools and museum below, street locations, and emergency vehicle access were considered, limited locations for structural support were available. In addition, the long span underground PATH station was unable to accommodate any additional load from the Pavilion. Only 12 points, in addition to a reinforced concrete core at the south, were determined to be capable of supporting loads from the pavilion. Even with considerable coordination, many columns required transfer girders below plaza level to align with columns over the train tracks. The limited support points resulted in many unusual spans, with no typical conditions. This resulted in a unique steel framed structure with W36s and W40s throughout. At the building’s north edge, an additional support point was required; however, the PATH station long span structure below could not support the pavilion loads. To provide support, a 22-foot-deep, full-story steel truss cantilevered from the pavilion core walls at level 3, providing a location to hang the floors below and effectively cantilevering a portion of the pavilion structure over the PATH station. Pleased with the achievement of supporting the structure with complex constraints, Lou Mendes, Senior Vice President for Design & Construction at the 9/11 Memorial, said “The Buro Happold Structures Team overcame a unique and complex challenge of designing a project with limited structural support and lack of column space – and they did so phenomenally.”

Lateral Structure Similar constraints also created unique challenges for the lateral stability of the pavilion.

The reinforced concrete core providing lateral stability is located directly above the PATH train tracks, making transfer of lateral forces to the ground difficult. Adding further complication, the long span PATH station structure was unable to accommodate additional lateral load.

To solve this issue, the lateral load was transferred to the below grade museum. To transfer the load to the museum, the pavilion is ringed with steel and reinforced concrete composite

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drag beams connected to shear walls in the museum. To construct the pavilion shear walls over the tracks, erection trusses support the full weight of the 4 story pavilion concrete walls.

The Tridents One of the most striking features noticed upon entrance to the Pavilion is two 80 foot tall artifacts known as the “tridents”, which originally formed the iconic outer structural support of the original towers. The tridents are housed in a full height steel and glass atrium that also extends one story below grade. The atrium steel support is a complex configuration of HSS 20x8 and 20x12 steel tubes clad with a uniform rectangular curtainwall system set at an angle. Due to their size, the tridents were installed in 2010, prior to the installation of the atrium steel. The tridents were then protected as the atrium and remainder of the pavilion were constructed.

Within the atrium, the pavilion’s freestanding grand stairs are over 30 feet tall, and the stair widens as it descends, bringing visitors within close proximity to the tridents. The stair has limited support points, creating the appearance of floating within the space. Careful consideration to performance and vibrational aspects of the hollow steel section stair was required to ensure visitor comfort as they descend and potentially pause along this feature.

Amidst the World Trade Center’s extensive and layered redevelopment, the new Memorial Museum Pavilion rises up a beacon of hope and engineering ingenuity to provide a bold, yet respectful connection between the bustling nature of the newly developed world trade center above and the memorial and museum below.▪ Erleen Hatfield, P.E., AIA, LEED AP, is a Partner and North American Structural Discipline Leader for Buro Happold. Erleen may be reached at erleen.hatfield@burohappold.com.

Alan Erickson, P.E., is a Senior Structural Engineer at Buro Happold.

Alan may be reached at alan.erickson@burohappold.com.

GINEERS

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News form the National Council of Structural Engineers Associations

NATIONAL

NCSEA Code Advisory Committee Report

By Thomas A. DiBlasi, P.E., SECB, NCSEA Code Advisory Committee Chair The Code Advisory Committee’s charge is to improve the building codes to assure safe, economical and reliable construction.

However, building codes today consist of no single document, but rather, a complex suite of documents including the model codes themselves, the ANSI consensus standards the codes adopt by reference, and a series of evaluation services reports that identify the code conformance of proprietary products of different types. The Committee’s specific activities include: 1) Monitoring the status of the building codes, their referenced standards, and evaluation service approvals, to assure that our “codes” are providing safe and economical structures without placing undue burden on structural engineers, either through unfair apportionment of professional responsibility/liability or through imposition of unclear, conflicting, or hard‐to‐ implement requirements.

2) Advocating proposals to the standards committees, to address our membership’s concerns.

3) Providing public comment on the standards associated with revisions that are not in our members’ interests.

4) Developing and submitting code change proposals to the ICC, to address issues of concern.

5) Monitoring code change proposals submitted by others, to assure that these do not violate the principles indicated in item 1 above.

6) Attending the ICC code hearings and advocating for, or submitting argument against, proposals consistent with the goals indicated in item 1 above.

7) Partnering with the ICC‐ES to improve the technical adequacy of their evaluation of acceptance criteria and product reports.

8) Providing public comment on acceptance criteria proposals, through the public hearing process, as appropriate to accomplish the goals in item 1 above.

NCSEA News

Building Codes

ICC is nearing the end of the process of developing its 2015 series of model building codes. This takes place in three groups (A, B and C), over a period of three years. Group A changes which were administered in 2012 included technical changes to structural design criteria within the International Building Code (IBC). Group B changes which were administered in 2013 included administrative adoption of updated structural standards as well as technical changes to the International Residential Code (IRC) and the International Existing Building Code (IEBC). Group C changes (administered this year) were largely limited to the International Green Construction Code and, as such, were not the focus of the CAC. The 2015 Code Development Cycle has been particularly frustrating for the CAC and other structural Standards Developing Organizations (SDOs) due to the fact that the structural Code Change Proposals for the 2015 IBC were required to be submitted in January 2012 at which time the 2012 IBC had been adopted in few (if any) jurisdictions. In an effort to address this concern, the newly-formed Structural Standards Coordination Council (comprised of ACI, AISC, AISI, ASCE/SEI, AWC, STRUCTURE magazine

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NCSEA and TMS) appealed to ICC, and ICC agreed to move the IBC structural provisions back to Group B in the upcoming 2018 Code Development Cycle.

While this has been a less active year due to the lack of structural Code Development Hearings, the work of the subcommittee continues. A brief summary of their activities is as follows: General Engineering Subcommittee, chaired by Ed Huston.

Perhaps the one bright side to the 2015 Code Development Cycle was that it allowed the General Engineering Subcommittee to focus on issues related to the IRC, since the IRC remained in Group B while the IBC structural issues were covered a year prior in Group A. In past code cycles the primary focus had been the IBC, and it is now recognized that attention should also be given to the IRC. As the IBC structural provisions and the IRC provisions will both be contained within Group B of the 2018 Code Development Cycle, the General Engineering subcommittee will be expanded by four members to provide the manpower needed to effectively address both codes, and an IRC working group will be formed.

The Existing Buildings/Structural Retrofit Subcommittee, chaired by David Bonowitz, is planning to develop a set of online Existing Buildings case studies to illustrate the concepts we have built into the I-codes over the last few cycles.

The Special Inspections/Quality Assurance Subcommittee, chaired by Kirk Harman, will be developing Code Change Proposals in an attempt to expand required Structural Observations in Chapter 17 of the 2018 IBC. The Seismic Provisions Subcommittee, chaired by Kevin Moore, has been participating in ballots being executed by the Provisions Update Committee (PUC) of the Building Seismic Safety Council (BSSC) and has been encouraging participation in this endeavor by NCSEA Member Organizations who are voting members of the PUC. The subcommittee will be assessing proposed changes to ASCE/SEI 7-16 which is currently under development. In addition, the subcommittee will be working with the Publications Committee to develop a Seismic Design Manual for Seismic Design Category C. The Wind Provisions Subcommittee, chaired by Don Scott, has been developing a section for inclusion in the IEBC to provide requirements and guidance for the upgrading of existing buildings located in high wind regions. It has also been reviewing and providing input to the work of the ASCE Wind Load Subcommittee as the wind load provisions to ASCE 7-16 are being developed.

The Evaluation Services Advisory Subcommittee, chaired by Bill Warren, is contemplating the development of a webinar to better acquaint structural engineers with the Evaluation Services process and to instill in them a better understanding of the importance of the Evaluation Services Reports and how they work in conjunction with the building code.

Tom DiBlasi, P.E., SECB, is Principal/President of DiBlasi Associates, PC, Monroe, CT, and a past president of NCSEA. July 2014

Friday, September 19

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

8:00–10:00 8:00–10:00 10:30–12:00

Thursday, September 18

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NCSEA

Diamond Reviewed

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Check out the new Subscriber Bonus for new Webinar Yearly Subscriptions at www.ncsea.com!

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

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August 5, 2014 Progressive Collapse Design Guidance & Methods of Analysis, Aldo McKay, P.E., Principal and Senior Engineer, Protection Engineering Consultants

August 26, 2014 Principles of Ground Movement Design, James Hussin, P.E., Director, Hayward Baker, Inc.

STRUCTU

July 22, 2014 DoD Minimum Antiterrorism Standards for Buildings, Jon A. Schmidt, P.E., SECB, BSCP, Director of Antiterrorism Services, Burns & McDonnell

Platinum Sponsor:

August 19, 2014 Parking Garage Repairs: Identification, Evaluation, the Process, and the Repair, David Flax, Euclid Chemical Co.

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NCSEA Webinars

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6:30–8:30

NCSEA Annual Business Meeting NCSEA Board of Directors Meeting

Visit www.ncsea.com for more details!

Registration & hotel reservations open!

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Concurrent Sessions:

8:00–12:00 12:30–2:00

ATI

4:00–5:00

Saturday, September 20

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Concurrent Sessions:

6:00–7:00 7:00–10:00

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3:00–4:00

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Concurrent Sessions:

4:00–5:00

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1:00–2:15

1:00 3:00–4:00

Member Organization Reports Vendor Product Presentations Student to Teacher – Gaining Competency after the University, a panel discussion led by the NCSEA Young Member Group Support Committee A. The Most Common Errors in Wind Design & How to Avoid Them, Emily Guglielmo, S.E., Associate, Martin/Martin B. The Most Common Errors in Seismic Design & How to Avoid Them, Tom Heausler, P.E., S.E., Heausler Structural Engineers, member of ASCE 7 Seismic Provisions Committee Trade Show closes Practical HSS Design with the Latest Codes & Standards, Kim Olson, P.E., Technical Advisor, Steel Tube Institute and Structural Engineer, FORSE Consulting Practical Steel Connection Software Design Using 2010 AISC Standard, Steve Ashton, P.E., SECB, Principal, Ashton Engineering & Detailing, SDS/2 Engineering Representative for Design Data Awards Reception (formal attire encouraged) NCSEA Banquet & Awards Presentation, featuring the NCSEA Excellence in Structural Engineering Awards and the NCSEA Special Awards

News from the National Council of Structural Engineers Associations

11:00–12:00

Concurrent Sessions:

UC

9:45–10:45

1:00–1:45

Welcome & Introduction Keynote: Prepare Your Practice – Why Your Strategic Plan is Doomed to Fail, Kelly Riggs, President, Vmax Performance Group Prepare for the Future–Where Codes & Standards are Heading, NCSEA Code Advisory Committee Prepare for the Unthinkable – Designing Buildings for Tornadoes, Bill Coulbourne, P.E., Director of Wind & Flood Hazard Mitigation, Applied Technology Council A. ACI 562 Building Code for Repair of Existing Concrete Structures, Keith Kesner, Senior Associate, WDP & Associates, Chair of ACI 562 B. Wind Engineering Beyond the Code, Roy Denoon, CPP Wind Engineering Consultants A. 2012 National Design Specification for Wood Construction Overview, Michelle Kam-Biron, P.E., S.E., SECB, M.ASCE, Director of Education, American Wood Council B. Three Diverse Adaptive Reuse/ Renovations, Bill Bast, P.E., S.E., SECB, Principal, Thornton Tomasetti A. AISI Standard & Tech Notes, Vince Sagan, Chairman, Cold-Formed Steel Engineers Institute B. High Roller Observation Wheel, Brandon Sullivan, ARUP San Francisco Welcome Reception on Trade Show floor

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8:00 a.m.

8:15 – 9:45

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8:00–5:00 8 a.m.–12 p.m.

5:30–6:30 p.m.

6:30–8:30 p.m.

NCSEA News

Wednesday, September 17

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SEI Election Announcement

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

July 31, 2014 Deadline There are ten Governor positions on the Structural Engineering Institute Board of Governors: two representatives from each of the four Divisions (Business and Professional, Codes and Standards, Local Activities, and Technical Activities), one appointed by the ASCE Board of Direction, and the most immediate and available Past President of the SEI Board.

The representatives from the Divisions each serve a four-year term. In accordance with the Structural Engineering Institute Bylaws, this year SEI is conducting an election for a Codes and Standards Activities Division (CSAD) representative and Business and Professional Activities Division (BPAD) representative on the Board of Governors. The CSAD and BPAD Executive Committees have nominated Chris D. Poland and David Cocke as their candidates, respectively. In accordance with the SEI Bylaws, each ballot provides a space for a writein vote. If you are a member of SEI, please complete and mail your ballot to the address provided. Either vote for the named candidate OR provide a write-in candidate. Because we must confirm SEI membership, only signed ballots will be accepted.

Chris D. Poland, P.E., S.E., F.SEI, M. ASCE has had a structural engineering career spanning more than 40 years that includes a wide variety of new design work, seismic analysis and strengthening of existing buildings, structural failure analysis, and historic preservation.

As an internationally recognized authority on earthquake engineering, Chris routinely participates in policychanging research and code development projects sponsored by the NSF, USGS, NIST and FEMA. Chris is the former CEO, Chairman and Senior Principal of Degenkolb Engineers where he worked for more than 40 years. He retired from the firm and started his own firm in 2014. As a passionate advocate and voice for seismic safety and resilient cities, he actively participates in the academic, ethical and social advancement of his field and lectures often. Among his many areas of professional service, Chris is the former Chair of the Congressionally-mandated Advisory Committee on Earthquake Hazards Reduction for NEHRP. He is the current Chair of the Codes and Standards Activities Division (CSAD) for the Structural Engineering Institute of ASCE and served as the Chair of the ASCE-SEI Standards Committee on Seismic Rehabilitation of Existing Structures during the standardization of ASCE 31-03, 41-06 and 41-13.

He is also currently chair of the VA Structural Safety Advisory Committee. Chris is an active advocate for earthquake resilience in his community. He is a former member of the San Francisco Chamber of Commerce, member of the Board of Directors of the San Francisco Planning and Urban Research Association, and is a member of the National Academy of Engineering. He has been the leading force behind development of the SPUR Resilient City Initiative for the City and County of San Francisco and is the Co-Chair of the San Francisco Lifelines Council.

David Cocke, S.E., F.SEI, M. ASCE, serves on the SEI Business and Professional Activities Division Executive Committee and is Past Chair of the SEI Public Relations Committee. He also serves as a member of the SEI Futures Fund Board. David founded Structural Focus in 2001 after 20 years at Degenkolb Engineers. David started with Degenkolb in San Francisco in 1981, opened and managed their new office in Los Angeles in 1995 to 2001. David is registered as a structural engineer in California, Arizona, Nevada, Colorado, Florida and several other states. His experience includes new structural design, seismic evaluation, historic preservation, and retrofit design. He has managed a variety of project types and sizes. Examples include large and small historic landmark building strengthening and repairs, new laboratory buildings, repair and retrofit of commercial buildings, large university building renovations, renovations and design of new studio production facilities, evaluations of large building inventories (industrial, high-tech and film studios), and numerous university and school renovations, additions and strengthening. David is very active in the preservation of historic buildings and has made numerous presentations regarding the reuse of existing buildings as supporting sustainability principles. David is also co-founder and Managing Director of SAFEq Institute. David is a recognized expert in building business resiliency and continuity related to disaster risks. He was an on-the-ground responder, inspecting buildings for weeks after the 1989 Loma Prieta earthquake.

David’s believes that preplanning and partnerships with cities can substantially minimize business interruption in the wake of an earthquake or other disaster. That belief was the driving idea behind the SAFEq Institute, serving as a resource for postdisaster inspections information and providing direct services to government entities.

Full Name: _____________________________________Member’s ASCE/SEI ID No:________________ (Please print) Date:______________ Signature: _______________________________________________________________

Return postmarked no later than July 31, 2014 to: SEI Board Election, 1801 Alexander Bell Dr., Reston VA 20191.

SEI 2014 Board of Governors Election Official Ballot Business and Professional Activities Division Codes and Standards Activities Division q David Cocke q Chris D. Poland Write-in:____________________________ q Write-in:____________________________ q STRUCTURE magazine

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July 2014

Challenges & Innovative Solutions ELECTRICAL TRANSMISSION & SUBSTATION STRUCTURES CONFERENCE 2015

ELECTRICAL TRANSMISSION & SUBSTATION STRUCTURES CONFERENCE 2015 Branson, Missouri

New Edition of Seismic Evaluation | and Retrofit of Existing Buildings Standards Now Available Branson, Missouri

September 27- October 1

Structural Columns

625x352px (Institute Homepage Slideshow)

Grid Modernization – Technical Challenges & Innovative Solutions

| September 27- October 1

300x75px Banner — MIRA (approved)

Grid Modernization – Technical Challenges & Innovative Solutions 400x100px ASCE Weekly News Banner

Electrical Transmission ELECTRICAL TRANSMISSION & SUBSTATION STRUCTURES & Substation Structures CONFERENCE 2015 Conference| 2015

ELECTRICAL and TRANSMISSION & SUBSTATION Standards 41 & 31 are updated STRUCTURES CONFERENCE 2015 combined in ASCE/SEI 41-13 Branson, Missouri | September 27- October 1

Banner — MIRA (approved) This next-generation standard300x75px describes deficiency-based and systematic proBranson, Missouri September 27- October 1 cedures that use performance-based Grid Modernization – Technical Challenges & Innovativeprinciples Solutions to evaluate and retrofit existCall for Abstracts Now Open 600x100px Email Banner ing buildings to withstand the effects of earthquakes. This standard updates and The conference will provide a forum for transmission and substareplaces the previous Standard ASCE/SEI tion engineers to exchange ideas, concepts, and philosophies, 41-06, Seismic Rehabilitation of Existing while providing new engineers with the opportunity to learn Buildings, as well as Standard ASCE/SEI more about the art and science specific to transmission lines and 31-03, Seismic Evaluation of Existing Buildings. Visit the SEI structures, substation structures, and foundation engineering. website at www.asce.org/SEI or the ASCE Publications webThe Conference Steering Committee is currently accepting site at www.asce.org/bookstore to purchase your copy today. abstracts of papers to be presented in technical sessions, with case studies strongly encouraged. A poster session format may also be provided. Visit the SEI website at www.asce.org/SEI for more information and to submit your proposal.

All proposals are due September 10, 2014.

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.

Join ASCE for the inaugural International Conference on Sustainable Infrastructure 2014 in Long Beach, California November 6 – 8, 2014. Our full conference program includes short courses, special events with riveting keynote speakers, and a technical tour. It promises to be an event you will not want to miss. Visit the conference website to learn more at http://content.asce.org/conferences/icsi2014/.

Get Involved in your Local SEI Chapter Get Involved in SEI Local Activities

University of Central Florida Graduate Student Chapter The University of Central Florida (UCF) announces the establishment of their new SEI Graduate Student Chapter. This is the 5th SEI Graduate Student Chapter to be established in this ever expanding program. The UCF student chapter is open to all engineering students, graduate and undergraduate. The UCF GSC recently participated in East Central Florida SEI chapter’s annual seminar on May 16, 2014, and interacted with engineers from around the region attending the annual seminar. The student chapter is led by Doctoral student Ozan Celik and the faculty advisor is Dr. Necati Catbas.

STRUCTURE magazine

Join your local SEI Chapter, Graduate Student Chapter, or Structural Technical Groups (STG) to connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area.

If there is not an SEI Chapter or STG in your area, talk with your ASCE Section/Branch leaders about the simple steps to form an SEI Chapter. Some of the benefits of forming an SEI Chapter include: • Connect with other SEI local groups through quarterly conference calls and annual SEI Local Leadership conference • Use of SEI Chapter logo branding • SEI Chapter announcements published at www.asce.org/SEI and in SEI Update • One free ASCE webinar sponsored by the SEI Futures Fund • Funding for one representative to attend the annual SEI Local Leadership Conference to learn about new SEI initiatives, share best practices, participate in leadership training, and earn PDHs. • SEI outreach supplies available upon request Visit the SEI website at www.asce.org/SEI for more information on how to connect with your local group or to form a new SEI Chapter.

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July 2014

The Newsletter of the Structural Engineering Institute of ASCE

First International Conference on Sustainable Infrastructure

The Newsletter of the Council of American Structural Engineers

CASE in Point

Tool Box Updates CASE 962 – National Practice Guidelines for the Structural Engineer of Record The purpose of this document is to give firms and their employees a guide for establishing consulting structural engineering services, and to provide a basis for dealing with clients generally and negotiating contracts in particular. Since the Structural Engineer of Record (SER) is normally a member of a multi-discipline design team, these Guidelines describe the relationships that customarily exist between the SER and the other team members, especially the prime design professional.

Furthermore, these Guidelines seek to promote an enhanced quality of professional services while also providing a basis for negotiating fair and reasonable compensation. The Guidelines also provide clients with a better opportunity to understand and appreciate the scope of services that the structural engineer should be retained to provide.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

CASE 962A – National Practice Guidelines Addressing the Preparation of Structural Engineering Reports for Buildings The purpose of this document is to give firms who prepare structural engineering reports for condition assessments, load capacity, structural damage/failure investigations, building performance, and other special purpose investigations, a guide for preparing such reports. Firms can also use the information contained in the Guidelines to establish and describe the scope of services to be performed and to reach a contractual agreement with their client. The Guidelines are intended primarily for use in the preparation of reports for buildings.

In addition, it is intended that these Guidelines will be used to promote and enhance the quality of written engineering reports.

Clearly, written reports describing the engineer’s findings in a factual, truthful and unbiased manner will not only serve the client better, but will also benefit the engineering profession through enhancement of its image.

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

Call For Volunteers: 2014 –2015 CASE Committees WANTED: Engineers to Lead, Direct, and Get Involved with CASE Committees!

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

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

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

• Toolkit Committee: Develops and maintains documents such as business practices manuals and policies for engineers under CASE’s 10 Foundations for Risk Management.

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Expectations and Requirements To apply, you should • be a current member of the Council of American Structural Engineers (CASE) • be able to attend the groups’ two face-to-face meetings per year: August, February (hotel, travel reimbursable) • be available to engage with the working group via email and conference call • have some specific experience and/or expertise to contribute to the group Please submit the following information to htalbert@acec.org • Letter of interest • Brief bio (no more than 2 paragraphs) Thank you for your interest in contributing to your professional association!

July 2014

For 20 years, ACEC has offered the premier executive leadership course designed specifically for the A/E/C community – the ACEC Senior Executives Institute (SEI). SEI is an intensive 18-month program taught by recognized experts and instructors from The Brookings Institution, national universities and business consulting organizations. The classes meet for five separate four- or five-day sessions.

The next class, SEI Class 20, is now open for registration and will begin in September, 2014.

For more information, contact Dee McKenna, Deputy Director, ACEC Business Resources & Education Department, at dmckenna@acec.org or 202-347-7474.

Since 2009, the CASE Scholarship has helped engineering students make positive steps towards a bright future in structural engineering The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student pursuing a Master’s degree in Structural Engineering. CASE strives to attract the best and brightest to the structural engineering profession, and educational support is the best way we can ensure the future of our profession. This year we were fortunate enough to be able to award two scholarships through the generosity of CASE members: Adam Morel, will graduate with a Master’s Degree in Structural Engineering from Purdue University, West Lafayette, IN.

SAVE ThE DATE

CASE Summer Planning Meeting

James Yokoyama, will graduate with a Master’s Degree in Civil Engineering with a Structural Emphasis from the University of Hawaii-Manoa.

Upcoming ACEC Online Seminars – August Are You Fighting Fires Instead of Managing Your Employees?

Tuesday, August 12, 2014; 1:30pm to 3:00pm Eastern Every engineering or technical manager knows how important it is to be available to assist their subordinates. If they did not have the knowledge and experience to do that, probably someone else would have their position. Too often though, the manager does an inadequate job of delegating various tasks and responsibilities. This leads to the ever present problem of subordinates bringing their managers multiple “fires” for the manager to put out, or at least play a major role in extinguishing the flames.

Your employees will never realize their potential as long they can rely on you to do their firefighting for them. This webinar will explore this problem in detail and help you understand the proper methods to get out of the firefighting business.

Ten Keys to Business Continuity Planning

Wednesday, August 20, 2014; 1:30pm to 3:00pm Eastern Developing and maintaining a Business Continuity or Disaster Recovery Plan is a daunting task. All you hear is “We need to develop a Business Continuity Plan, but it’s too labor intensive.”

“Maintaining the BC takes too much time.” “We have this great Plan, but no one knows what’s in it.” Sometimes it seems like only divine intervention will help. Learn the 10 keys to developing, implementing and maintaining an effective business continuity management program.

STRUCTURE magazine

Mergers and Acquisitions, 2.0

Wednesday, July 16, 2014; 1:30pm to 3:00pm Eastern An increasing number of engineering and consulting firms are acquiring other firms, merging their firms or selling their practices. Although every transaction is different, with respect to its economic and legal terms, they all follow the same process.

Many engineers and consultants have limited experience buying or selling their firms. Understanding this M&A process is crucial for a party considering a merger-acquisition opportunity to avoid common pitfalls. In this seminar, you will learn the essentials of M&A, including tools to help you: • Value your firm • Position and package your firm for sale and attract the best buyers • Understand the M&A process, including economic and legal terms of a deal • Avoid common pitfalls to achieve a successful transaction You can register for these and other ACEC online seminars at www.acec.org/acecmainsite/education/webinars.

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July 2014

CASE is a part of the American Council of Engineering Companies

The CASE Summer Planning Meeting is scheduled for August 5-6th in Chicago, IL. The night of August 5th will feature a discussion with a representative from Willis A/E practice on risk management and contracts. Attendees to this session will also earn 2 PDHs. On August 6th, the CASE Committees will meet in person to plan out the next year. If you are interested in attending the roundtable/meeting, please contact CASE Executive Director Heather Talbert at htalbert@acec.org.

CASE in Point

20 th Senior Executives Institute CASE Announces the 2014 Class Now Open for Registration CASE Scholarship Winners

Structural Forum

opinions on topics of current importance to structural engineers

How Code Complexity Harms Our Profession Part 1

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

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n a recent Structural Forum column, A Remarkable Profession!, September 2013, Stan Caldwell pointed out some of the negative aspects of structural engineering that often prompt complaints from its practitioners. Those comments resonated with me and, I suspect, many of the more seasoned engineers who have witnessed significant changes in the profession over the past few decades. I contend that our most serious threat is not low fees, bid shopping, or lack of respect, but something self-inflicted: It is the unreasonable and unnecessary degree of complexity in building code provisions and design methodologies that poses the greatest danger to the future vitality and survival of our profession. In Part 1 of this article, I will illustrate that point by specifically examining the new ASCE 7-10 wind load provisions.

One of the significant changes is the adoption of so-called “ultimate” wind speeds similar to strength-level earthquake loads incorporated into the building code some time ago. Strength design was first introduced as a method of proportioning structural components such that no applicable limit state is exceeded when the structure is subjected to all appropriate load combinations. As originally conceived, strength design involved developing service loads that were increased by various load factors and then compared with a material-dependent limit state such as flexure or shear. We have now taken a concept related to design properties for materials, and invented pseudo design forces that do not actually exist in nature. Wind speed, a term commonly understood even by nonengineers, has now been transformed into a set of contrived velocities that have no intuitive or actual relationship with how hard the wind actually blows.

For example, under earlier codes we designed for an 85-mph maximum wind speed in my area. This seemed sensible because we often have wind gusts of 60 mph or more during severe storms. There was an intuitive and rational relationship between actual wind velocities and the design-level wind speed

that we used in our calculations. Under ASCE 7-10, we now design for ultimate wind speeds ranging from 105 to 120 mph in this area, depending on the building classification. A Risk Category II building is now designed for a 115-mph ultimate wind speed based on the new maps, which incorporate a load factor and a building risk factor. Wind speed is no longer an atmospheric phenomenon that has a real-world practical meaning, but is somehow oddly coupled to a material limit state as well as the building type. What do these parameters have to do with how fast the wind blows? The whole concept can only be rationalized through a series of mathematical gyrations – try explaining that to your contractor or owner!

ASCE has acknowledged for years that the wind load provisions are difficult to understand and apply. Even the new so-called “simplified method” is neither simple nor even coherent, since it generates pseudopressure coefficients mysteriously correlated to member forces in buildings rather than actual design pressures (whatever that may mean). Hence, if you compare the analytical (or Directional) method with the simplified method, ASCE tells us up-front that you will get different results. Is that supposed to give us confidence? ASCE seminar instructors admit that the simplified method for Components & Cladding is more difficult to use than the analytical method, so in code-speak, I guess that “simplified” in no way means easier to understand.

They also acknowledge that previous versions of the code got some things wrong – such as ASCE 7-05 wind loads being 20% conservative compared to the new ASCE 7-10 provisions. While recently watching an ASCE webinar on the new wind load provisions, the instructor made a mistake in applying the new provisions in an example that he was presenting. Even as he acknowledged his error, he jokingly warned the class how easy it is to make such mistakes – exactly my point! Given that kind of admitted fallibility, does anyone doubt there will be significant

changes to the next version of ASCE 7? The point is that when the code provisions are so transitional and complex that even the experts cannot adequately explain them, there is definitely a problem. ASCE claims that they have “improved” the wind load provisions in ASCE 7-10, but in truth, it remains a befuddling mess. If you disagree, try explaining how to use Figure 28-4.1 to someone. The ASCE webinar instructor could not do it.

To help compensate for this complexity, ASCE 7-10 provides a series of step-bystep procedures for designers to follow. This prompts the question, “Why is that necessary?” The answer is because there is nothing straightforward, intuitive, or even rational about the wind load provisions. It would seem to confirm the observation from Mr. Caldwell’s article that structural engineers are becoming “little more than math technicians who meticulously follow precise recipes to produce adequate designs.” You know who (or what) is really good at that? Computers.

Structural engineers must now heavily rely on sophisticated and expensive software to handle the bewildering maze of code-required load generation, load combinations, analysis procedures, and design methodologies. Given this current trend, it is not unreasonable to predict that computer software will soon take analysis and design out of the hands of engineers and turn it over to technicians and programmers.

In the second installment of this article, which will appear in a future issue, I will take a broader look at how design practices have changed over the past several decades and offer some additional thoughts about current trends that may affect the sustainability of our profession.▪ Craig M. DeFriez, P.E., S.E. (cmdefriez@yahoo.com), is a consulting structural engineer living in Carson City, Nevada. During his career he has had extensive experience in plan checking, peer reviews, and code interpretation and enforcement.

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

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