STRUCTURE magazine | May 2015 by structuremag

May 2015 Masonry

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May 2015 26

Feature

thermal Mass Solutions By Bob Habian, AIA The Jess S. Jackson Sustainable Winery building (JSWB) project team set out to design a Net Zero Energy, LEED Platinum building at the University of California, Davis. Concrete masonry not only saved the day, but it opened the door for engineers to take a more active role in energy optimization at the earliest stages of the project.

26 editorial

7 Slow engineering? By Ed Quesenberry, P.E., S.E.

education iSSueS

32 Masonry Preservation education By Lindsay M. Hofgartner, Ing.

inFocuS

9 the Virtues of ignorance By Jon A. Schmidt, P.E., SECB leSSonS learned

10 Brick Beams

HiStoric StructureS

39 Whipple double intersection cast and Wrought iron truss By Frank Griggs, Jr., D. Eng., P.E.

By David T. Biggs, P.E., S.E. SPotligHt Structural ForenSicS

14 evaluating existing and Historic Stone arch Bridges By Carlo Citto, P.E. and

43 P750 Helicopter Maintenance Hangar By Gene O. Brown, P.E. and Min S. Koo, P.E.

David B. Woodham, P.E. Structural ForuM Structural deSign

21 Special reinforced Masonry Walls

50 of course Structural engineering education is Sustainable

By Gregory R. Kingsley, Ph.D., P.E.,

By Charles W. Dolan, P.E.,

PEng, P. Benson Shing, Ph.D. and

S.E., Ph.D.

10 in eVery iSSue 8 Advertiser Index 8 InBox 30 Noteworthy 34 Resource Guide (Steel/CFS) 44 NCSEA News 46 SEI Structural Columns 48 CASE in Point

Thomas Gangel, P.E. inSigHtS

24 Fastening Steel deck By Thomas Sputo, Ph.D., P.E., S.E., SECB

On the cover Six-span, railroad stone arch bridge constructed in 1907 over Conemaugh River, Pennsylvania. It was later replaced by a new steel truss bridge when the railroad was realigned due to construction of the Conemaugh River Dam. Read more in the Structural Forensics article on page 14.

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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.

May 2015

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Editorial

Slow Engineering? new trends, new techniques and current industry issues By Ed Quesenberry, P.E., S.E.

expectations for us to be able to do more work in less time, and for less money, greeting us daily when we sit down at our desks. So, is it time for a Slow Engineering movement? Effects of Honore’s “road runner culture” on the practice of Structural Engineering may be seen by some to be positive and beneficial. For instance, being able to multi-task is a vital attribute to have as an engineer. Being spawned out of a high speed culture, our multi-tasking skills have been honed and serve us well in our professional lives. However, lurking in the shadows of our “road runner” workplaces, there are risks and tangible detriments that a high speed existence carries. On a personal level, we may face health issues or burn out when our bodies and minds simply cannot keep up the pace anymore. Likewise, our profession may suffer from the effects of speed in the long term if we do not take some steps to slow down soon. The most obvious part of our profession that is increasingly at risk at the hands of speed is the accuracy of our work. QA/QC programs are increasingly difficult to implement due to the schedule and fee pressures today’s projects impart. In addition, to meet shrinking design budgets, young engineers are being put in charge of designs that are at or beyond the limits of their professional development, opening the doors for oversights, errors and omissions. Lastly, increasingly complex code provisions are stumbling blocks as we race to get our documents assembled, and are often overlooked or outright ignored. Another pillar of our profession that is on shaky, speedaholic ground is creativity. As we try to find ways to do more with less, we resort to tried and true solutions to building problems rather than innovating leaner, more cost-effective ones. As engineers, we are professionally obligated to ensure the safety of the public through providing accurate, code-compliant, costeffective designs. If speed is being allowed to degrade our ability to fulfill this obligation, is it time to make a change? Because this Slow Movement concept is so new to me, I do not pretend to know exactly how to go about slowing down. However, I am now trying to find ways both at home and at work to drop the intensity a bit. The jury is out as to whether or not I will be successful, but I figure that I can only benefit from this effort, so there is no reason not to try. I recommend that all of you take a 20 minute break from your busy, but hopefully not frenetic, lives to watch Honore’s video (www.ted.com/talks/carl_honore_praises_slowness) and reflect on his message using your life as the lens. If enough of you buy into the concept, Structural Engineers could be on the ground floor of a Slow Engineering movement, and the world will be a safer, happier and more relaxed place as a result.▪

a member benefit

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n a recent flight to an NCSEA Board Meeting, I decided to detach a bit and surfed the in-flight entertainment selections on the seat back screen in front of me. A TED Talk titled In Praise of Slowness caught my attention because my brain seemed to be craving a break from mulling over drag strut connections and Board agendas. For those of you who are not familiar, TED is a non-profit organization that promotes the sharing of ideas through brief, thought-provoking talks given by people from all different industries, cultures and backgrounds. This particular talk was given by Carl Honore, a Canadian journalist who has been following and writing about various so-called “Slow Movements” around the world. I had heard of the Slow Food movement before but, being from Portland, I thought it was just another hug-your-chicken scheme and of no relevance to my personal or professional life. However, Mr. Honore informed me that the Slow Movements that started in Europe have progressed well beyond food and lifestyle focuses, and have spread into the workplace in many countries as well. The premise of the Slow Movement is to curb the effects of the fast-paced, frenetic lifestyle most of us lead today by finding ways to slow down. In places where the Slow Movement has taken hold, the results are apparently astounding. According to Honore, Western Culture is “...losing sight of the toll speed takes” and that the Slow Movement has proven that “…by slowing down at the right moments, people do everything better.” Perhaps the impact of this video on me was heightened because, when I boarded the plane, I was still buzzing from my harried pre-flight routine of responding to emails using one hand, while handling my grande Starbucks and pumpkin bread with the other. Mr. Honore’s message was like a glass of water in the desert for me and, ever since I heard it, I have been thinking a lot about how I might slow down my own life and if our profession or the built environment might benefit from us engineers stepping off the treadmill occasionally. I know I am not alone in my hectic everyday life because I see evidence of it everywhere. Speed has consumed our younger generation who, at a very young age, become technology junkies and demand that life be as fast as the 4G network their phones are on. As Honore aptly puts it, for today’s youth, “…even instant gratification takes too long.” Speed dominates our higher education system, which seems to be more focused on minimizing the time it takes for students to earn their degree rather than on preparing them for their professional lives. Fast food chains tap into the need for speed, popping up all over the world as fueling stations for STRUCTURAL the full-throttle set. This same ENGINEERING demand for speed permeates INSTITUTE the structural engineering profession, with the ever-increasing STRUCTURE magazine

Ed Quesenberry, P.E., S.E., is the founding Principal of Equilibrium Engineers LLC and serves on the NCSEA Board of Directors. He can be reached at edq@equilibriumllc.com.

May 2015

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EDITORIAL BOARD Chair Jon A. Schmidt, P.E., SECB Burns & McDonnell, Kansas City, MO chair@structuremag.org Craig E. Barnes, P.E., SECB CBI Consulting, Inc., Boston, MA John A. Dal Pino, S.E. Degenkolb Engineers, San Francisco, CA Mark W. Holmberg, P.E. Heath & Lineback Engineers, Inc., Marietta, GA Dilip Khatri, Ph.D., S.E. Khatri International Inc., Pasadena, CA

letters to the editor

Roger A. LaBoube, Ph.D., P.E. CCFSS, Rolla, MO

Congratulations on the “harmony” of this edition and the “symphony” of the 4 articles beginning with Jon Schmidt’s Narrative and Engineering, continuing with Ramon Gilsanz and Petr Vancura’s Understanding Seismic Design through a Musical Analogy, then Reflections on the 2014 South Napa Earthquake by John A. Dal Pino and finally by the thoughtful Acceptable Collapse by Reid Zimmerman. Together, they made the art of Structural Engineering as it is in practice more easily appreciated and understood.

Brian J. Leshko, P.E. HDR Engineering, Inc., Pittsburgh, PA Brian W. Miller Davis, CA Mike Mota, Ph.D., P.E. CRSI, Williamstown, NJ Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT

Peter A. Culley, S.E. Tiburon, CA peter@culleys.com

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John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org May 2015, Volume 22, Number 5 ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact your member organization(s) or email subscriptions@STRUCTUREmag.org. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

InFocus

The new trends, Virtues new techniques of Ignorance and current industry issues By Jon A. Schmidt, P.E., SECB

y title this month comes from a collection of essays that resulted from a June 2004 meeting in Matfield Green, Kansas, which is a small town in the Flint Hills – one of my favorite landscapes – roughly a two-hour drive from my home. Edited by Bill Vitek and Wes Jackson, The University Press of Kentucky published it in 2008 with the subtitle, Complexity, Sustainability, and the Limits of Knowledge. The SEI Engineering Philosophy Committee was intrigued by the book’s provocative name and decided to read and discuss it together. What follows are some of my own reflections. The overall premise is that the scientific revolution prompted by the development of modern philosophy, most notably by Descartes and Bacon, was (and still is) driven by a KnowledgeBased Worldview (KBW). Charles Marsh actually traces it all the way back to the ancient Greeks and suggests that, in retrospect, Isocrates (a leading Sophist) had it right, while Socrates, Plato, and Aristotle (the “true” philosophers) all had it wrong – much like the assessment of Steven L. Goldman regarding the inferior status of engineering in Western culture (“The Principle of Insufficient Reason,” May 2008). The editors’ introduction describes KBW as “the merger of techne (the everyday knowledge gained by experience and repetition with little regard for how and why) and episteme (the knowledge that comes from the rational pursuit of causes and first principles)” (p. 2). Of course, I call these technical rationality and theoretical knowledge, respectively; and conspicuous by its absence is phronesis or practical judgment (“Virtuous Engineering,” September 2013). Anna L. Peterson wrote the only chapter specifically about ethics, classifying consequentialism and deontology – which she calls “rule-based ethics” – as “knowledge-based ethics” and criticizing them accordingly. Aristotelian virtue ethics, in particular as revived by Alasdair MacIntyre (“Rethinking Engineering Ethics,” November 2010), is one of her examples of “ignorance-based ethics” because of “its insistence that moral judgment need not wait for full knowledge and … the admission that ethics always entails uncertainty” (p. 130). Each of the other chapters likewise argues, in its own way, for an alternative Ignorance-Based Worldview (IBW) and explores what it might look like. As the various authors are careful to clarify, what they advocate is not so much ignorance itself, but admission of the degree to which ignorance is an unavoidable aspect of the human condition; that is, we must acknowledge the limits of our knowledge. Even so, Robert Root-Bernstein notes that “you have to know what you do expect before you can be surprised by what you didn’t expect … You have to be prepared to recognize your ignorance if you are to benefit from it.” As Vitek summarized, “If knowledge is a tool, ignorance is a perspective.” What beneficial insights might such a perspective provide? One recurring implication is avoiding the hubris that all too often has accompanied our supposed mastery of nature. Wendell Berry calls this “arrogant ignorance” and goes on to identify several other

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kinds – inherent ignorance, historical ignorance, willful ignorance, materialist ignorance, moral ignorance, confident ignorance, fearful ignorance, for-profit ignorance, and for-power ignorance. Paul G. Heltne narrows it down to just two: imposed ignorance and humble ignorance. The former is operating whenever we “are made to feel that it would be foolish to ask questions about derived conclusions or about basic assumptions.” By contrast, the latter is “filled often with the joy of discovery and wonder at what is discovered.” In other words, as summarized by Peter G. Brown, “Ignorance is another name for humility, humility before the mysteries of life and the universe.” This extends even to our most sophisticated scientific and philosophical pursuits: “Since theories and concepts are always simplifications of reality, they will never be as complex as reality itself.” Two different chapters go so far as to state, “The greatest single achievement of science in this most scientifically productive of centuries [the 20th] is the discovery that we are profoundly ignorant. We know very little about nature and we understand even less.” Ironically, they cite two different sources for this quote – Lewis Thomas and Ann Kerwin – suggesting ignorance in at least one case of its true origin. Craig Holdredge develops this notion further, observing “one fundamental bias that infects modern Western culture: the strong propensity to take abstract conceptual frameworks more seriously than full-blooded experience.” He recommends that we “open up our perceptual field by trying to put the conceptual element in the background,” thus “acknowledging our ignorance and maintaining … intellectual modesty,” which “demands changing not only the content of our concepts but also their form or style.” This is difficult because the tendency to abstract – to think in terms of simplified models – is ingrained into us throughout the educational process, such that we rarely even realize that we are engaging in it. As is often the case, I will conclude by asking: What does this have to do with engineering? I would say that engineers are explicitly trained to affirm our ignorance and take it into account. In fact, we do so routinely – although we usually call it uncertainty, rather than ignorance. As I have said (and written) many times, the most important thing for any engineer to know is what he or she does not know. One version of my favorite summary of our profession (“The Definition of Structural Engineering,” January 2009) says that we should practice it “in such a way that the public at large has no reason to suspect the extent of our ignorance”; however, we most certainly need to be very well aware of it ourselves.▪ 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.

May 2015

Lessons Learned problems and solutions encountered by practicing structural engineers

Brick Beams After 30 Years, a Friary Project continues to Provide Valuable Lessons By David T. Biggs, P.E., S.E., Dist.M.ASCE, Hon.TMS, F. SEI, FACI

David T. Biggs, P.E., S.E., Dist.M.ASCE, Hon.TMS, F. SEI, FACI, is a principal of Biggs Consulting Engineering, Saratoga Springs, NY. He received The Masonry Society’s 2013 Paul Haller Structural Design Award and serves on TMS 402/602. He has served on the Boards of ASCE, SEI and TMS. David can be reached at biggsconsulting@att.net.

n 1981, a young architect and the author were tasked with designing a friary at Siena College in upstate New York. The friary is a residence for the Franciscan Friars who are administrators, professors and staff members at the college. The building (Figure 1) includes two residential wings and a large entrance and common area. Structurally, the residential wings use cold-formed metal framing as bearing and shear walls with bar joists and metal roof deck framing to create a gable shape. The wings are one-story with double loaded corridors; one wing has a partial basement. The common area has two stories framed in structural steel framing and bar joists. The lower level aligns with the partial basement of one wing. The architect’s conceptual design included a cavity wall with exterior brick veneer and interior brick veneer. The design team discussed options for emphasizing the masonry, since one of his design goals was to disguise the cold-formed metal and steel framing. This led to the use of brick beams throughout the building so that there would be no exposed steel framing over the openings. The more conventional approach would use exposed steel plates and angles above the openings, but they would not provide the aesthetic desired. This article is a look back at the design and construction of over 50 brick beams that became an architectural highlight of the building. These brick beams were built with simple construction techniques that are as valid today as they were in the 1980s. A key point here is that elegant and sophisticated masonry buildings need not be complicated to design or construct.

Types of Brick Beams Three types of brick beams were developed for the building. In each case, the beams fulfilled a

Figure 1. East entrance into common area (2014).

10 May 2015

Figure 2. Interior brick beam.

structural and an aesthetic purpose. One type was an interior beam that crossed the corridors of the residence wings. The second was an interior beam used in conjunction with steel framing. The third was an exterior beam used in conjunction with steel framing and the exterior cavity wall. Interior Brick Beam This beam type was the simplest of all three to construct (Figure 2 ). The three-wythe beam supports its self-weight and a knee wall of coldformed metal framing that is above the ceiling. There are two of these beams at intervals along the corridors at entries to the residence rooms. The flexural reinforcement for the beam is placed in a grouted core (Figure 3a). The depth did not require shear reinforcement; the #2 stirrups are used to position the flexural reinforcement. Figure 3b shows a cross-section when wider beams are needed. The formwork was simply bottom forms of plywood sheathing on 2 x wood joists spanning across the corridor (Figure 3a). The brick beam was constructed on the sheathing. Once the masonry design strength was reached, the formwork was removed and the bottom mortar joints were raked out and pointed with fresh mortar to provide a finished appearance.

Figure 3a. Three-wythe interior brick beam.

Figure 3b. Wide interior brick beam.

The design methodology in 1981 used allowable stress design (ASD) procedures. While still applicable today, the current code (TMS 402, Building Code Requirements for Masonry Structures) now allows Strength Design to be used as well. There are many publications (such as the Masonry Designers Guide from The Masonry Society, www.MasonrySociety.org) that illustrate the design steps using either ASD or Strength. The reinforced masonry beam carries all the dead load of its self-weight and the superimposed loads from above. For this project, all of the beams were sitebuilt. Today, prefabricating these beams and setting them in place to speed up construction could also be considered. Movement joints at each are necessary unless the supporting walls are short, as in this project.

framing and the walls above; floor beams carry floor dead loads. Superimposed dead and live loads are distributed to both the steel framing and brick beams. The brick beam solution for this condition in the 1980s was to provide a suspended brick beam from the steel framing (Figure 6) using stirrup hangers. The underside of the beam is all brick, similar to the interior brick beams previously described. Today, structural engineers might be tempted to use a patented system of steel hangers and embedded plates to create the hung beam. While those systems work very well, the procedure presented here is simple, straightforward and less expensive. The brick beam is not just hung weight from the steel beam; it is a structural element. The brick beam must carry load that is related to the construction sequence.

Interior Brick Beam with Steel Framing

a. Construction

Many of the large openings required structural steel for the primary framing. However, the desire was still to have exposed brick beams (Figure 4). In Figure 5, there are encased steel columns and steel beams. The steel framing was used for the floor and roof framing since there was insufficient depth available for brick beams alone to support the loads. The steel beams support roof dead loads, self-weight of the

As with conventional steel-framed construction, the steel framing was installed first along with the metal deck for the floor and roof. For the floors, the concrete was placed; for the roof, the roofing system was installed. As seen in Figure 6, there is a welded steel plate at the underside of the steel beam. It is intended to support the brick veneer at the level of the steel beam and above. In many projects, that plate is visible, and completes

Figure 4. Interior openings with masonry beams.

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the underside of the beam and the opening. For this project, the plate is not visible because the brick beam encases the bottom of the steel framing. The brick was installed in two stages. For the first stage, the brick veneer was constructed above the steel plate to maximize the dead load on the steel beam. For the second stage, the brick beam was constructed below the steel plate. One brick at the underside of the steel plate was left out at intervals to provide access for grouting the cavity of the brick beam. The access bricks were installed last. Because this design was used on the interior, no weeps, flashing or insulation were needed. The joint at the steel plate was mortared. b. Load Distribution Stage 1: The construction sequence dictates the design of the brick beam. Each steel beam first supports various dead loads (wDL Steel) that include its own self-weight (wbeam), the floor framing and metal deck (wframing), the remaining floor and roof dead load (wDL) and all the masonry wall above the steel plate (wbrick above). wDL Steel = ∑ (wbeam + wframing + wDL + wbrick above) Stage 2: The brick beam was constructed aided by stirrup hangers from the steel

Figure 6. Interior brick beam with steel framing.

Figure 5. Interior openings with steel framing.

May 2015

Figure 8. Exterior brick beam with steel framing. Figure 7. Exterior brick beams.

ws = wLL x (EsIs)/(EsIs+EbbIbb) wbb = wLL x (EbbIbb)/(EsIs+EbbIbb), or wbb = wLL – ws Therefore, load sharing means the brick beam does not have to support all of wLL and results in the shallowest possible brick beam. c. Design The steel framing is designed in accordance with AISC provisions; the total load supported is wDL Steel + ws. Load factors should be applied to these service loads if Load Factor design methods are used. Using the masonry code (TMS 402), the deflection of the steel beam should be limited to l/600 because it supports masonry. In the 1980s, the code-allowable beam deflection was also limited to a maximum of 0.3 inches. That requirement has subsequently been deleted for reinforced masonry beams. Today’s structural engineer should still consider total deflection, so as not to cause cracking. For the design of the brick beam, the total load is wbb = wLL – ws.

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plate. The hangers were installed during Stage 1 along with the upper brick veneer. The brick beam was formed on the bottom, similar to the interior brick beam previously described, and the reinforcement, ties, brick and grout were placed. Once masonry cured, the bottom forms were removed and the weight of the brick beam (wDL Brick beam) was distributed between the steel beam and the brick beam. The sharing is a result of the hangers from the steel plate into the brick beam that ensure equal deflections of the two structural members. Any superimposed dead load or live load on the steel framing (wSuperimposed) is also shared with the brick beam. Therefore, the added load on the combined steel beam and brick beam (wLL) is represented by: wLL = wDL Brick beam + wSuperimposed. Also, wLL = ws + wbb where ws is the proportion of load wLL assigned to the steel beam and wbb is the proportion of wLL assigned to the brick beam based upon consistent deflections. Knowing that the steel beam deflection is proportional to ws/EsIs and the brick beam is proportional to wbb/EbbIbb and that these are equal, it is possible to solve for ws and wbb.

Figure 9. Interior of exterior wall beam.

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May 2015

Brick beam design in the 1980s used only ASD. Today, the structural engineer can use ASD or Strength Design provisions. The d distance for design is as shown in Figure 6. The effective beam width includes the brick and the grout. In addition to determining the flexural and shear reinforcement in Figure 6, the brick beam requires some additional detailing. Single leg Z-anchors are used with cored brick to improve the bond with the grouted portion of the beam. Exterior Brick Beam with Steel Framing The construction sequence and design of the exterior brick beams match the methodology described for the interior brick beam with steel framing and the finished appearance (Figure 7). The primary difference is with the construction of the cold-formed metal framed wall (Figure 8). The original construction had batt insulation within the cold-formed framing, and flashing and weeps within the cavity. By modern standards, rigid insulation in the exterior cavity would be preferable, as seen in Figure 8. In addition, an air and moisture

Figure 10. Aesthetic brick beam.

Figure 11. Brick beams at entry.

barrier as well as proper flashing and weeps are all required, but not shown. Figure 9 shows the interior surface of the exterior brick beam, and a sealant joint at the bed joint with the steel plate is visible (arrow). Sealant joints were only installed in bed joints for the beams in the exterior walls, but mortar could have been used due to the composite nature of the steel beam and brick beam interaction.

time. Figure 7 shows relatively few joints. By today’s standards, joints full height on the jambs of large openings would likely be used.

Summary

Remember the young architect? He’s Tom Birdsey, AIA, NCARB, LEED AP, now the President and CEO of EYP Architecture and Engineering, one of the top design firms in the US and internationally. Looks like making good masonry decisions early in one’s career can lead to great things!▪

Overall, the brick beams on this project have performed well for over 30 years and Acknowledgements still provide a wonderful aesthetic for the building (Figures 10 and 11). Once a meth- Owner: Siena College, Loudonville, NY odology for load-sharing was developed, Fr. Mark G. Reamer, Guardian, St. Lessons Learned the design and construction procedures Bernadine of Siena Friary 1) After more than 30 years, the were simple and easy to implement. Given Mark Frost, Assistant Vice President for performance of the brick beams has another opportunity today, the author Facilities Management been very good. The interior beams would include the brick beams in a similar Structural Engineer of 1980s project: Ryan are in excellent shape and have manner and incorporate the latest technolBiggs/Clark Davis, Clifton Park, NY required no maintenance. A couple ogy for the cavity wall construction for the 1 10/04/2015 16:01 Page 1 of the exterior beams have had minor ArmathermAd_5x3_5"_Layout exterior walls. cracks and some repointing repairs. This is very impressive when considering life cycle costs. 2) Many engineers will remember ™ the development of cavity walls with cold-formed metal framing Thermal bridging solutions in the 1970s and 1980s. Air to improve building and moisture barriers were envelope performance… not developed, and insulation Prevent thermal bridging at placement and sheathing masonry shelf angle connections selection were not exactly what using Armatherm™ FRR thermal would be done today. Therefore, break material and thermal break should problems occur with the washers. wall system in the future, they Improve the effective R value will likely be attributed to the of masonry walls by 50% 1980s cavity wall construction and decrease Heat loss at and not the brick beams. structural connection points. 3) A primary lesson learned is that the placement of movement joints in veneers is very important and that Armadillo NV LLC sales@armadillonvinc.com our understanding of proper 800.580.3984 www.armadillonvinc.com placement has improved over

Armatherm

May 2015

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STRUCTURE magazine

Structural ForenSicS investigating structures and their components

tone is one of the oldest construction materials used by man, as well as the longest lasting building material available. Whether stone structures were built to provide shelters, aid agriculture, or provide a passage over an obstacle such as a river, a valley, etc., they have made a significant contribution in shaping the cultural landscape of countries around the world. In the United States, many examples of stone arch bridges can be found, still accomplishing their original function of bridging streams and rivers. Many people recognize the need to preserve these historic structures, as they are part of the history and heritage of many local communities. This goal should be balanced with the need for safe roadways and bridges. The preservation and rehabilitation of historic stone arches involves many steps and parties. This article focuses on the structural evaluation and assessment aspects of the preservation. From the design professional side, a successful outcome starts with the structural engineer recognizing that, even though these structures were not designed to perform under modern traffic loads, they can still perform well due to their inherent strength and durability.

Evaluating Existing and Historic Stone Arch Bridges By Carlo Citto, P.E. and David B. Woodham, P.E.

Historical background

Carlo Citto, P.E., is a structural engineer at Atkinson-Noland & Associates. He can be reached at ccitto@ana-usa.com.

Compared to other countries with a long tradition in masonry construction, the inventory of masonry arch bridges in the United Stated is rather small. According to the 2013 National Bridge Inventory (NBI) there are 1699 masonry bridges in the U.S., of which nearly 93% are on roads other than the National Highway System. These bridges are typically on lower volume road

Masonry bridge construction over time in the U.S. Construction of new masonry bridges dropped off dramatically at the beginning of the 20 th century and essentially stopped at the outset of World War II.

systems that are not eligible for federal funding. Detailed records for masonry railroad bridges are not as readily available, but it seems likely that there are at least as many masonry railroad bridges in service as the NBI reports for roads. Of the current NBI masonry bridges in service, 50% were built prior to the end of 1910: half of the masonry bridges in use are more than 100 years old. This compares with 1% of the in-service concrete bridges, 4% of the in-service steel bridges, and 3.5% of the in-service wood/ timber bridges having been constructed before 1910. It is clear that most masonry bridges have exceeded their intended service life. As a result, many masonry arch bridges have functional issues including inadequate width, non-compliant guardrails, etc. but remain in service due to their critical location, cost of replacement, community involvement or historic designation. The majority of the existing masonry bridges are concentrated in the northeastern part of the country where European settlers, who brought the technical skills required for the construction

David B. Woodham, P.E., is vice president at Atkinson-Noland & Associates. He can be reached at dwoodham@ana-usa.com.

Six-span, railroad stone arch bridge constructed in 1907 over Conemaugh River, Pennsylvania. It was later replaced by a new steel truss bridge when the railroad was realigned due to construction of the Conemaugh River Dam.

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Longitudinal crack below spandrel wall, at junction with barrel vault.

Two-span, stone arch bridge constructed in the late 1880s over Cottonwood Creek in Colorado Springs, Colorado. It served as a railroad bridge until the early 1960s when the tracks were abandoned. It was reopened to vehicular traffic in 2012 after a restoration project.

of the arches, first arrived. Location and technological innovation affected their spread as well. Higher concentrations are found where construction material (i.e. stone) was readily available. Since the first bridges were built in the early colonial years, American engineers had a relatively short timeframe to implement the design and construction of stone arch bridges before the advance of alternative materials, such as iron, steel, and reinforced concrete, made stone obsolete. Still, engineers had a preference for stone when performance and durability were more important than cost and efficiency. Masonry arches were the primary choice for railroad bridges well into the early twentieth century, where the need to carry heavy train loads was met by the excellent structural capacity of the stone arch. Dry-laid construction was likely used for most of the early bridges, when the available mortar in the U.S. was not suitable for this type of construction. Lime mortar was common in masonry construction until late-nineteenth century, before the spread of hydraulic cements. Because of its low compressive strength, slow hardening, and tendency to dissolve in a harsh environment, lime mortar was not well-suited for stone arch bridges. Considering also its self-draining feature, dry-laid masonry was somewhat superior to wet-laid, or mortared, masonry in the early age of stone bridges. With the introduction of better performing mortars, the wet-laid construction typology took over and allowed engineers to design larger and more durable bridges. Most of these dry-laid early bridges

have been lost, and the majority of the stone arch bridge inventory in the U.S. comprises mortared masonry.

Stone spalling and deterioration due to freeze/thaw.

Evaluation and Assessment Design professionals play a key role in the preservation of stone arch bridges. The crucial question the structural engineer is often called to answer is: “What is the capacity of the existing bridge?” Defining the load carrying capacity of stone arches is a challenging task. There is not a widely accepted analysis procedure among the engineering community, and structural engineers approaching this problem face a set of challenges that starts with the lack of information on how the bridge was constructed. Typically, construction documents, such as plans and specifications showing geometry and materials used in the construction, don’t exist. The analysis itself is complicated by a number of unknown factors including the contribution of spandrel walls to the stiffness of the arch barrel, interaction of the barrel with the fill, fill properties, and the effects of material degradation or cracking in the barrel. Further, material properties are unknown unless a significant effort is expended to test the compressive strength, tensile strength, and elastic modulus of the masonry assemblage. Fill properties are rarely investigated. The first step towards a successful structural assessment is the field investigation of the bridge. Significant properties to investigate are the overall geometry, thickness of the arch barrel, and materials used in the construction.

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May 2015

Large longitudinal cracks at stone arch intrados.

Of great importance is the assessment of damage in the existing structure that could impact the capacity of the bridge. Common distresses include stone deterioration, mortar weathering, cracking in the arch barrel and spandrel wall, and displaced stone units. Efflorescence at the underside of the arch barrel is an indication of insufficient drainage within the arch. The trapped moisture has the potential for material damage in cold climates due to freeze/thaw cycles. Nondestructive Evaluation (NDE) techniques can provide valuable information to support the analysis of masonry arch bridges. Microwave radar, also referred to as Surface Penetrating Radar (SPR), can be successfully used to determine the arch thickness and investigate the integrity of the barrel vault. Details about voids within the masonry, loss

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of cross-section, the configuration of the fill, and the presence of anomalies or utilities buried in the fill can be obtained with low-frequency microwave radar. Infrared thermography can provide information on moisture profiles in the masonry leading to diagnosis of the extent of damage caused by excessive moisture or saturated freeze/thaw conditions. Stone and mortar samples can be collected and tested for mechanical properties and mortar composition. A live load test is also a valuable tool for the evaluation and rating of stone arch bridges. The structure can be directly rated to a particular live load in what is generally called “proof testing”. This approach runs the potential for inelastic responses and the possibility of imparting damage to the structure if the bridge is required to function under a very heavy vehicle. From an investigative standpoint, a “diagnostic” approach is preferred. The diagnostic method uses a vehicle load well below the maximum capacity of the structure but still capable of generating a significant live load response in the bridge. The structure is instrumented using surface-mounted strain transducers and Linear Variable Differential Transformer (LVDT) displacement sensors. The sensors are concentrated at key locations, such as the arch mid-span (crown) and quarter-points. The data collected during the test is generally used to calibrate a finite element model of the structure that can then be used to develop accurate load ratings for a large variety of vehicle classes. Another key aspect of the live load test is the use of a slow-moving vehicle that allows for a complete response history, or “influence line,” to be collected. All of the steps described above are taken to improve the confidence level in the evaluation of the load carrying capacity of the bridge. Engineers who have confidence in their information are less likely to make overly conservative assumptions. Software and ConSulting

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Typical live load test instrumentation layout, with LVDT sensors and strain transducers installed on the underside of the arch barrel.

Analysis and Load Rating Stone arch bridges can be analyzed using different analysis techniques. The most common are: semi-empirical methods such as the MEXE method; plastic limit analysis methods (three hinge and rigid block); and, the Finite Element (FE) or Discrete Element (DE) methods. Semi-empirical methods are conservative in nature and should only be used as screening tools. Limit analysis methods provide a more refined analysis and are appropriate for most structures. The FE method is suitable for all structures, including problems involving complex geometry or load conditions and evaluation of various strengthening options. Modeling of distress conditions, such as material deterioration, spandrel wall separation, and longitudinal cracks is also possible. This, however, results in very complex models that are difficult to validate and, as such, should only be performed by experienced engineers. The American Association of State Highway and Transportation Officials (AASHTO) Manual for Bridge Evaluation (MBE) addresses the load rating of unreinforced masonry arch bridges and, according to the MBE, masonry arch bridges are evaluated at the Inventory Level only. The intent of rating at the Inventory Level is to determine the live load at which the structure can be safely used for an indefinite period of time, that is, without damaging the structure. The AASHTO rating procedure also requires the

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May 2015

load-carrying capacity to be evaluated using the Allowable Stress (AS) method based on limiting the tensile and compressive stresses that develop in extreme fibers under a combination of axial and bending forces. An axial force-bending moment interaction diagram is typically used to accomplish this task. Failure modes due to instability should also be investigated. Allowable inventory compressive stresses for different types of masonry construction are provided in the MBE. Yet, no allowable tensile stress values are provided, and there is a lack of direction in the manual on how to evaluate this property. Some researchers (Boothby et al. 2004) have recommended that tensile strength up to 5% of the compressive strength may be assigned to masonry, depending on the condition of the bridge. Recognizing that masonry can carry some levels of tension stresses, the rating factors can be substantially improved. However, engineering judgment is required in selecting an appropriate value if material testing is not performed. The MBE describes the interaction diagram approach under the section addressing the rating of concrete components subjected to compression and bending. Following this approach, the capacity of a stone arch crosssection is defined by the intersection between a capacity line, which accounts for the internal forces produced by the live load, and the interaction diagram. The axial force and bending moment capacities are then used to calculate the rating factor. Focusing on the FE method, continued on page 18

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arguably the most common approach due to the large number of commercial software available, different modeling schemes can be adopted for the analysis and computation of axial and bending forces required for the bridge rating. Common options include: frame analysis, two- and three-dimensional models, and linear versus nonlinear material formulations. A two-dimensional approach requires less modeling and computational effort but some assumptions on the load dispersion through the fill and in the arch are needed, which may result in a conservative rating. More realistic load and stress distributions may be obtained with a threedimensional model, with the potential for an improved load rating. In a linear analysis, both soil and masonry are allowed to carry tension. This assumption may lead to erroneous predictions of the stress levels in the bridge, especially for moving loads approaching the ultimate capacity of the arch. Nonlinear material formulations can be implemented to provide a more accurate prediction of the stress levels and, ultimately, rating factors. The shortcomings are the higher computational cost and the complex calibration of the nonlinear material parameters. The challenge for the structural engineer is to find an acceptable balance between computational cost and accuracy of the results when selecting the most appropriate analysis tool. Load test results allow for validation of the analysis method in light of the many material unknowns, material interactions and assumptions inherent in the analysis. Several factors should be taken into consideration, such as the historic importance of the bridge,

Stress distribution in barrel vaults and spandrel walls.

its current and future use, the complexity of the structure, and the current condition of the structure.

Repair, Strengthening, and Maintenance Repairs usually involve localized mortar repointing and replacement of deteriorated stone. Often the new stone can be sourced locally, and brought in and shaped as necessary to achieve an appearance matching the original stone. For partial stone replacement, the new stone should be keyed into the existing with bond stone header and/or stainless steel ties. A properly functioning drainage plan is important to mitigate the risk of material deterioration in the arch barrel. Spandrel

wall cracks (i.e. separation) can be repaired by installation of tie bars to mechanically connect the wall to the arch barrel. Spandrel walls can also be mechanically connected together with transverse tie bars. Key to the longevity of the bridge is a long-term maintenance program. The structural capacity of an existing arch bridge can be improved in several ways. A new structural slab can be built immediately under the roadway to spread the vehicular loads to a larger arch section. “Saddling” consists of placing a new, cast-in-place or pre-cast, reinforced concrete arch immediately above the existing arch. In both cases, however, it is difficult to maintain traffic on the bridge during construction, especially on narrow bridges. Cementitious grout can be injected into cracks and voids to restore the structural integrity of the arch barrel. Corrugated steel plates, shotcrete, and FRP can be installed to the intrados, but these approaches may not always be appropriate for historic bridges.

Conclusions

Grouted anchors used to connect a cracked (i.e. separated) spandrel wall to the arch barrel.

STRUCTURE magazine

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Stone masonry arch bridges have successfully served the transportation needs of local communities for more than three centuries, and are now part of the history and heritage of this country. However, many of the existing bridges have exceeded their intended service life and have functional or structural issues, yet remain in service due to their critical location, cost of replacement, community involvement or historic designation. From the structural engineer’s standpoint, understanding the appropriate evaluation methods, analysis techniques, and repair and strengthening options is critical to the preservation and rehabilitation of stone masonry arch bridges.▪

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nder the National Earthquake Hazards Reduction Program (NEHRP) and the stewardship of the National Institute of Standards and Technology (NIST), the Applied Technology Council (ATC) and the Consortium of Universities for Research in Earthquake Engineering (CUREE) have jointly prepared an excellent series of ten succinct and practical seismic design guides for practicing engineers, available for free online at www.nehrp.gov/library/techbriefs.htm. Among the most recent additions is a guide entitled Seismic Design of Special Reinforced Masonry Shear Walls, A Guide for Practicing Engineers (referred to here as the Guide). The objective of the Guide is to synthesize model building code requirements and leading practitioner-recognized techniques, some of which may be forward-looking in recognition of on-going code development processes. The Guide recognizes a fundamental challenge unique to masonry design. Other construction materials allow the structural designer to locate and size structural elements to achieve the desired or needed behavior, and the building is then constructed around these structural elements. Masonry, in contrast, serves simultaneously as architecture (defining a building’s external or internal appearance as well as its internal functional program), enclosure (defining a building’s external envelope), and structure (resisting vertical and lateral loads). The structural designer does not get to choose the configuration of these wall elements; instead, the other design factors dictate their locations and proportions. Thus, the structural designer must work with the elements that configure the space – must play with the cards that are dealt, in a manner of speaking. The designer must be able to anticipate the expected behavior of those elements so that he or she can adapt the design and detail each element appropriately to resist all required loading combinations to meet the intent of the code for stiffness, strength, and ductility. This is true for structural walls in all seismic design categories, but can be particularly challenging for special walls, because the expected level of ductility implied by the “special” designation simply may not be available. To this end, the Guide focuses narrowly on the design of one classification of walls for one loading case: Special Reinforced Masonry Shear Walls subjected to in-plane seismic and gravity loads. Within this classification, it distinguishes between two fundamental types: • Walls whose behavior is dominated by flexure, with reliable ductility and inelastic displacement capacity. These are flexuredominated walls.

• Walls whose behavior, often for reasons beyond the control of the structural designer, are dominated by shear, with limited ductility capacity. These are sheardominated walls. With this as a continuing theme, the Guide then explores a number of important design issues affecting special walls, including: • The use of different design methodologies permitted by the codes, including a brief introduction to new provisions for limit design. • The effect of different plan configurations of walls on their expected behavior. • The behavior of coupled walls and perforated walls. • The influence of wall aspect ratio and axial loads. • Guidance on the use of different analytical tools for masonry. • The importance of maximum reinforcement limits to design. • The influence of lap splices on behavior. • The use of boundary elements. • Detailing and constructability issues. • Design process flow chart. • What to do when shear dominated behavior is unavoidable. This article touches on a few of these issues.

Structural DeSign design issues for structural engineers

Special Reinforced Masonry Walls

When Masonry Shear Walls are Special The International Building Code (IBC 2012) requires the use of special reinforced masonry walls whenever masonry structural walls are used to resist seismic forces in new buildings assigned to Seismic Design Category D, E, or F. The design force levels are specified in Minimum Design Loads for Buildings and Other Structures (ASCE 7), and the design procedures and detailing requirements are addressed in the 2013 edition of Building Code Requirements for Masonry Structures (TMS 402). In ASCE 7, special walls are assigned the highest response modification factor, R, of any of the masonry shear wall types. For bearing wall systems R = 5; for building frame systems, R = 5.5. Inherent in the use of an R factor of 5 or more is the presumption of ductile behavior, associated with the development of plastic hinges with stable inelastic rotation capacity. The particular challenge of masonry seismic design addressed in the Guide is that the designer cannot presume that following the prescriptive requirements of TMS 402 will necessarily ensure the ductile, flexure-dominated behavior assumed in the determination of the design seismic loads. continued on next page

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NEHRP Technical Brief for Designers By Gregory R. Kingsley, Ph.D., P.E., PEng, P. Benson Shing, Ph.D. and Thomas Gangel, P.E. Gregory R. Kingsley, Ph.D., P.E., PEng, is the President and CEO of KL&A Inc., Structural Engineers and Builders in Golden, Colorado. P. Benson Shing, Ph.D., is a professor of Structural Engineering at the University of California, San Diego. He is a member of the Seismic Subcommittee and the Flexure, Axial Load, and Shear Subcommittee of TMS 402 on Building Code Requirements for Masonry Structures. Thomas Gangel, P.E., is a Principal at Wallace Engineering Structural and Civil Consultants out of Tulsa, Oklahoma. He has been an active member of the TMS 402/ACI 530/ ASCE 5 Masonry Standards Joint Committee since 1993.

Figure 1. Elevations of typical masonry walls.

Figure 2. Conceptual illustration of the influence of shearspan ratio, axial load, and ratio of vertical to horizontal reinforcement on wall behavior.

Design Principles for Special Masonry Shear Walls Shear Wall Configurations in Buildings

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Masonry shear walls can have a variety of plan configurations. Most reinforced masonry codes and design guides focus on single, planar walls. Intersecting walls often create flanged configurations in T, L, I, C, or box shapes that can significantly affect the behavior. Typical walls also vary in elevation configuration, several of which are shown in Figure 1. Ultimately, the behavior of these different configurations is related to the collective behavior of multiple wall elements, each with its own aspect ratio, axial load, and reinforcement. These issues are discussed in detail in the Guide.

Design Methodologies TMS 402 offers both Allowable Stress Design and Strength Design approaches. In the Guide, the primary emphasis is on Strength Design because TMS 402 addresses ductility requirements relevant to special walls more explicitly in that method. The Guide also provides a brief introduction to Limit Design, which is included in a new Appendix C to the 2013 edition of TMS 402. Flexure- versus Shear-dominated Walls Flexure-dominated elements are generally ductile. Shear-dominated elements are generally brittle, with failure characterized by diagonal shear cracks. Examples of each from laboratory tests are shown in the Guide. The implicit goal of TMS 402 is that special masonry shear walls be flexure-dominated and ductile. The code indirectly encourages designs that meet this goal through prescriptive requirements for distribution of reinforcement, limitations on bar diameters, maximum reinforcement restrictions, and other provisions. Figure 2 illustrates the factors that lead to shear dominated behavior in a qualitative way. The Guide provides a more quantitative illustration of the influence of aspect ratio, axial load, and ratio of vertical to horizontal reinforcement on behavior. Maximum Vertical Reinforcement Requirements The requirements of TMS 402 §9.3.3.5 for strength design are intended to limit the

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amount of vertical reinforcement in shear walls to ensure that they exhibit ductile flexural behavior under seismic forces. The various limits of reinforcement stipulated in TMS 402 §9.3.3.5.1 through §9.3.3.5.4 are directly related to the respective ductility levels expected of ordinary, intermediate, and special walls. In the design of special walls, it can be challenging to meet design requirements that limit the total amount of vertical reinforcement in special walls: the maximum permissible reinforcement percentage is much less for special walls than for ordinary walls, and it decreases further as the design axial force increases. These are all discussed in the Guide, together with discussion of special cases when maximum reinforcement requirements do not apply (e.g. for squat walls with Mu/(Vudv) < 1.0). The maximum reinforcement provisions may also be waived when certain provisions associated with boundary element reinforcement are satisfied. Perforated Walls and the Limit Design Method Perforated walls (Figures 1b, 1c, and 1d ) can be particularly challenging because wall elements between openings normally have low shear-span to depth ratios, and may have high axial loads as well; they are therefore vulnerable to shear-dominated behavior. Appendix C (Limit Design) of TMS 402 provides an alternative way of designing special walls that is particularly beneficial for perforated walls, and addresses behavior modes explicitly.

Limit Design can be applied to individual lines of resistance in structures that are otherwise designed according to the strength design requirements of Chapter 9. It allows the structural designer to explicitly take into account the anticipated plastic mechanism of the wall system, to control the aspect ratios and reinforcement of wall elements to achieve the best behavior possible, and to detail the elements in accordance with the resulting flexure- or shear-dominated behavior. To determine the required design strengths of each wall segment, Limit Design requires plastic limit analysis, which is also discussed in the Guide.

Design Guidance

(Biggs Consulting Engineering), and Steve Dill, (KPFF Consulting Engineers) for being an especially active and engaged review panel.

Acknowledgements

Dedication

The authors are grateful for the leadership and direction provided by Jon Heintz (ATC), Robert Reitherman (CUREE) and Steven McCabe (NIST). Particular thanks to Richard Klingner (Professor Emeritus, University of Texas, Austin), David Biggs

This article is respectfully dedicated to the memory of Professor M.J.N. Priestley whose visionary work over many decades provided much of the foundation for the design principles discussed in the Guide.

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Following detailed discussion of behavior, the Guide offers clear guidance for the designer regarding both analysis and design of special reinforced masonry walls with simple and complex wall configurations. A flow chart provides a step by step presentation of the process. This includes consideration of out-of-plane loading, moisture change, and thermal effects in tandem with design for inplane shear forces and axial loads in accordance with TMS 402. Ultimately, the designer is encouraged to take additional steps to establish whether the special wall is flexure-dominated (the implicit code intent for special walls) or shear-dominated (the unfortunate but unavoidable result of some architectural wall configurations). When a wall is shear-dominated, options are presented to achieve flexure dominated behavior, or, if that is not possible, to design for shear dominated behavior in a responsible way using a capacity design approach, and recognizing the reduced ductility of these wall elements. The designer should note that when sheardominated masonry walls are designed with the understanding that they will attract forces larger than those consistent with a response modification factor, R, diaphragms and their connections must resist those larger forces as well.

for seismic design of masonry. Reinforced masonry has unique challenges, and this short guide should make those challenges a bit more understandable for all.▪

InSIghtS new trends, new techniques and current industry issues

teel floor or roof deck is only as good as its fastening. Whether it is the performance of the product as a diaphragm to transfer wind or seismic forces, resisting wind uplift, acting as a concrete form, providing bracing to beams or joists, or providing a safe working platform during construction, proper fastening makes the deck do its job.

What Choices Do I Have for Fastening Deck? Traditionally, deck has been installed using welds for fastening to supports and button punches or welds for joining side-laps. However, over the past 30 years, mechanical fasteners such as screws, power actuated fasteners, and proprietary sidelap crimping devices have proven to be viable alternatives. When welding, it is essential that the finished weld penetrate into the supporting beam or joist, and that the puddle engage the deck on the weld perimeter. The complete welding process usually requires 3 to 6 seconds, or perhaps longer on multiple deck thicknesses or thicker deck. This process requires a welder who is qualified to make these specific welds. Per AWS D1.3 Structural Welding Code – Sheet Steel, arc spot welds can be made through multiple thicknesses of steel deck, as long as the total base metal (bare steel) thickness of the deck does not exceed 0.15 inches. Screws can be used for both fastening to supporting members and for fastening sidelaps. Typically #10 screws are used for sidelap attachment, and larger #12 or #14 screws are used for support fasteners. The drill points on these screws vary in length depending on the total thickness of the steel to be connected. Screws are installed using torque controlled drills which allow for proper installation without overdriving and stripping the screw. Several manufacturers have developed “stand up” drilling equipment. Power actuated fasteners (or PAF’s) look similar to short nails that are driven into the supporting structure using either pneumatic pressure or powder cartridges. The driving process allows the fastener to penetrate the steel deck layer and fuses the fastener shank to the base steel supports. The force used for driving the PAF is varied depending upon the steel strength and thickness. Proper driving is ensured by following the manufacturer’s instructions, setting the power regulation on the installation tools, making trial fastenings and visual identification of the fastener head and washer conditions. These fasteners cannot be used for sidelap connections.

Fastening Steel Deck By Thomas Sputo, Ph.D., P.E., S.E., SECB

Thomas Sputo, Ph.D., P.E., S.E., SECB, is the Technical Director of the Steel Deck Institute, and a consulting structural engineer with the Gainesville, FL firm of Sputo and Lammert Engineering, LLC.

24 May 2015

Welds, screws and PAF’s can be combined; for instance, welds used for support connections and screws for sidelap connections, or in combination as part of a zoned steel deck diaphragm.

How Should I Choose a Fastening Method? Generally, arc spot welded support connections are stronger and less flexible than mechanically connected support connections for both shear and uplift if the welding procedure is done properly. This may lead to needing a less dense fastening pattern for the deck, but there are pros-and-cons to be considered for each method. • Welding is a comparatively slower process and requires a higher level of skill. Inspection requirements are more time consuming also, when compared to many mechanical fasteners. • Some screws and all power actuated fasteners are proprietary products with strengths and flexibilities unique to that product; therefore they cannot be generically specified. For deck sidelap connections, welded sidelaps are again stronger and generate less flexible diaphragm performance than screwed or button punched sidelaps, but the weld between the two layers of sheet steel at the side-lap can be difficult. While welded sidelap connections of 22 gage deck are permitted, their use is not recommended. Some proprietary crimped sidelaps have strength and stiffness equal to welds.

How Can I Fasten Deck More Economically? On larger structures, consider zoning your roof deck connection design and select the fastening pattern to match the uplift and diaphragm demand which will vary across the floor or roof. Another way to provide for an economic yet well performing deck installation is to provide the deck erector with options. Installer preferences can vary regionally and should be considered. One way to accomplish this is to provide a fastening design that meets diaphragm and uplift requirements using generic welds and/or screws, and allow the deck installer to provide an engineered proprietary alternate connection method which meets strength and stiffness requirements. In order for the installer to provide an alternate, design requirements including zoned uplift (for roofs) and diaphragm strength demand needs to be provided. The loads need to be indicated as either ASD or LRFD, and noted if they are due to wind or seismic loading. Even if an alternate design is not permitted, this is important information to provide on the drawings.

What Should I Consider When the Deck is Loaded by Wind? Anytime that deck fasteners are subject to both wind uplift and in-plane shear when loaded as a diaphragm, the combined tension and shear forces on the fasteners must be considered using interaction equations. A key point to remember is that if the shearwalls or other shear collectors are at the edges of the roof, this will combine the highest in-plane shear demand with the highest wind uplift pressures at the edge zones. The 2013 SDI Roof Deck Design Manual provides guidance on how to combine these forces.

How Can I Provide for Quality in the Fastening? The SDI has developed the ANSI/SDI QA/ QC-2011 Standard for Quality Control and Quality Assurance for Installation of Steel Deck which provides requirements for steel deck installation quality (including fastening) in a mandatory format that can be used for inspection purposes. This Standard is incorporated by reference in Chapter 17 of the 2015 International Building Code, and is

Power actuated fastening. Courtesy of Pneutek, Inc.

available for free download from the SDI website (www.sdi.org). It is highly recommended that designers require compliance with the quality procedures in the standard

through incorporation of the Standard in project specifications, even when special inspections are not required.▪

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May 2015

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A Net Zero Energy Strategy with Structural Implications (and Opportunities) By Bob Habian, AIA Figure 1. Partial height thermal mass walls connected to passive ducts for night time cooling. Courtesy of Guttmann & Blaevoet Consulting Engineers.

he Jess S. Jackson Sustainable Winery building (JSWB) project team, led by Siegel and Strain Architects, set out to design a Net Zero Energy, LEED Platinum building, at the University of California, Davis, where summer temperatures exceed one hundred degrees on a regular basis. Concrete masonry, as seen in Figure 1, not only saved the day, but it opened the door for IDA Structural Engineers of Oakland, CA to take a more active role in energy optimization at the earliest stages of a project.

climates like Davis, California, where there are high diurnal swings from hot to cold in a 24-hour period, exposed interior thermal mass, in the form of concrete masonry, can radically decrease the overall energy consumption. As shown in Figure 3, interior comfort is achieved using two primary strategies, time lag and damping. Insulation by itself can only achieve time lag. Thermal mass, however, contributes to both time lag and damping. Achieving the proper balance of both is the shortest path to achieving internal comfort.

Energy Management is Mandatory

Framed Structures Lack Sufﬁcient Mass

The production of energy is the leading contributor to carbon footprint and climate change and, in the U.S., the Building Sector consumes more energy than any other sector (Figure 2). In response, a number of stricter energy code requirements are being enforced across all building types. The cost of energy is rising and is a matter of growing concern for building owners. The JSWB project team set out to not only reduce their energy consumption, but together decided to reach a level of Net Zero Energy (NZE), in which the total energy consumed is offset by renewable energy production on site. The most important factor in achieving NZE is reducing the overall energy consumption to the lowest possible level.

The building industry in the Western U.S. has shown a long-standing preference for framed, insulated, low-mass buildings that shake and don’t fall down in earthquakes. A common belief in the west is that heavy mass buildings perform poorly in seismic conditions. Most often, the building failures referenced are unreinforced or poorly constructed. In addition, the historic abundance of wood has influenced our appetite for low mass, framed solutions. As a result, we traditionally rely on a combination of insulation and air handling systems to achieve interior comfort. To that end, most project participants believe the architect and the mechanical engineer are the only ones needing to be at the table to determine an optimal comfort strategy. As conventionally framed designs move in the direction of increased interior exposed The Basics of Thermal Mass thermal mass, the structural engineer becomes a Figure 2. U.S. energy use by sector. The goal of every building design is to achieve inter- Data source: US Energy Information necessary participant in the discussion. nal comfort regardless of outside temperatures. In Administration (2012). STRUCTURE magazine

May 2015

Figure 3. Time lag and thermal damping.

Finding the Right Balance of Thermal Mass and Insulation After initially attempting to achieve NZE with a traditional metal Figure 4. JSWB – temperature comparison. Courtesy of Chien Si Harriman. frame building, in combination with an exterior skin of insulated metal panels, and a high degree of interior batt insulation, (R-59.6 in the walls and R-76 in the ceiling), the JSWB team determined that an insulation-only approach was simply not adequate to achieve NZE. And even though the exposed concrete slab did provide a fair amount of interior thermal mass, it did not offer quite enough to make a difference. The mechanical engineer, Guttmann & Blaevoet, of Sacramento, California, along with their in-house thermal mass expert, engaged a strategy of trying to achieve a classic balance of time lag (due to insulation), and temperature damping (due to thermal mass). After numerous rounds of modeling, the optimal blend of exterior insulation and interior, exposed thermal mass, was achieved simply by adding a partial height, solid grouted masonry wall, that was neither load bearing nor attached to the building envelope. This wall, in combination with the exposed concrete slab, achieved enough of a mass effect to allow the team to completely eliminate any need for a traditional air-handling unit for heating and cooling. – Chien Si Harriman, Guttmann & Blaevoet The results of the modeling are shown in Figure 4. With exterior summer temperatures approaching 110 degrees, the interior holds structural engineer explored various configurations of the masonry and to a steady range of 70 to 73 degrees. determined that a partial height wall with modest footing requirements was a more cost-effective placement than other options requiring So What Does NZE Mean larger footings. Additionally, it was the structural engineer that had to address how the overall system would function, the result of which for Structural Engineers? was that the structural envelope would remain unattached from the OPPORTUNITY! Concrete masonry as a thermal mass component concrete masonry. Together, the architect, mechanical engineer and for energy optimization is a relatively misunderstood material to many structural engineer designed an ideal solution for reducing the overall mechanical engineers and architects alike. The proper integration of energy requirement. concrete masonry requires a careful review of the structural implicaOn average, in the U.S., existing buildings account for 97% of the tions, particularly with respect to footings and connections to other building stock, with only 3% being newly constructed, annually. In structural elements in the overall project. And given the load bearing the western U.S., the majority of existing buildings are framed, insucapacity and shear resistance of concrete masonry, there are many lated, and low mass, most of which could benefit from the addition more options available today to integrate interior exposed thermal of interior exposed thermal mass. So rather than simply competing mass into the overall structural design. for work on new construction, structural engineers have a tremenOn this project, the structural engineer played an important role in dous opportunity to participate in the retrofit of existing buildings. determining the most cost-effective placement and configuration of And while most “energy retrofit” projects focus on high efficiency the concrete masonry. The mechanical engineer undertook a specific air handling systems, there is clearly a greater opportunity to reduce effort to determine the proper amount of surface area and volume of or even eliminate mechanical systems through the proper balance of masonry that would have the most impact on the energy model. The insulation and interior exposed thermal mass. continued on next page

“By adding just a small amount of concrete masonry to the interior of the building, we were able to eliminate the active mechanical heating and cooling system”

STRUCTURE magazine

May 2015

And There is an Even Simpler Solution Integral-insulated CMU, also called Hi-R H block, as manufactured under license by Basalite Concrete Products LLC, is an innovation in the masonry industry that combines the best of traditional concrete masonry with an outboard insulation and interior exposed thermal mass solution (Figure 5). This system, when used as a load bearing, exterior envelope solution, integrates the best elements for energy optimization in a single-wythe, solid-grouted barrier wall. A trend toward thermal mass solutions will allow structural engineers to become early adopters of NZE strategies and to position themselves for significant project opportunities in new and retrofit construction, now and for years to come.▪

JSBW Project Team Owner: University of California, Davis Structural Engineer of Record: IDA Structural Engineers, Inc., Oakland, CA Builder: Pankow Builders, Oakland, CA Architect: Siegel & Strain Architects, Emeryville, CA MEP Engineer and Energy Modeler: Guttmann & Blaevoet Consulting Engineers, Sacramento, CA Concrete Block Producer: Basalite Concrete Products LLC, Dixon, CA

Figure 5. Hi-R H Integral Insulation CMU. Courtesy of Concrete Products Group.

Bob Habian, AIA, is a California licensed architect and leads Masonry Market Development for Basalite Concrete Products LLC in Dixon, California. He may be reached at bob.habian@paccoast.com.

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STRUCTURE magazine

May 2015

Powerful calculations,

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Noteworthy

news and information

Amy M. R. Trygestad Retires from STRUCTURE’s Editorial Board

my M. R. Trygestad, P.E., is stepping down as a member of the STRUCTURE magazine Editorial Board. Amy joined the Editorial Board in February of 2013 as a concrete industry representative. Amy is President and principal engineer for Chase Engineering in Minnesota. Chase Engineering is the local structural engineering partner with Thornton Tomasetti for the new 65,000+ seat Minnesota Multi-Purpose Stadium, currently under construction. Ms. Trygestad is an active member of the American Concrete Institute, serving on several ACI committees and as secretary of both 423–Prestressed Concrete and 421–Reinforced Concrete Slabs. Regarding her tenure on the Board, Amy commented, “I would like to express my sincerest gratitude for the opportunity to serve on the Editorial Board of STRUCTURE magazine. It has been a pleasure and privilege to work with contributing authors, fellow board members, and publishing staff to help produce this great industry publication.”

Returning to the Board, Mike Mota, Ph.D., P.E., F.ASCE, F.ACI, is the Vice President of Engineering for the Concrete Reinforcing Steel Institute (CRSI). Mike is responsible for the Engineering Department and oversees the development of all technical publications and standards. Mike is an active member of several ACI and ASCE committees, including ACI 318 and 318 sub B and sub R. He’s Chair of ACI Committee 314 on Simplified Design of Concrete Buildings, and he serves on the Board of Directors of the Concrete Industry Board of New York City/NYC ACI Chapter. Jon Schmidt, P.E., SECB, Chair of the STRUCTURE magazine Editorial Board, had this to say: “I was sorry to see Mike go, and am very happy to have him back. I appreciate Amy’s contributions during the time in between, and wish her all the best.” Please join the STRUCTURE magazine Editorial Board in welcoming back Mike Mota!

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STRUCTURE magazine

May 2015

NEW CODE REFERENCES AVAILABLE!

2015

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Education issuEs discussion of core requirements and continuing education issues

magine studying historic restoration while surrounded by historic structures and conservation experts in a city with over two thousand years of history. Is there any better way to learn?

Europe Bound While finishing up my undergraduate degree, I began researching graduate programs. I had a strong interest in historic preservation and rehabilitation, and wanted to pursue further education in this subject area. I looked at many programs offered in North America, but they were mainly geared towards architects. As an engineer, I wanted to find a program that had a focus on structural stability and analysis of historic structures, as well as aesthetics and material preservation. When restoring a historic structure, it is important to understand the structural system and how it was built in order to ensure its stability for future generations. The North American programs in restoration do not offer this type of focus; they are architecturally oriented. While interviewing for an engineering post-graduate position at a university in Canada, a professor told me about the Advanced Masters in Structural Analysis of Monuments and Historical Constructions (SAHC) program. After researching the program further, I knew I had found the perfect match for my interests and engineering background.

Masonry Preservation Education A Look Inside the Advanced Masters in Structural Analysis of Monuments and Historical Constructions By Lindsay M. Hofgartner, Ing.

Lindsay M. Hofgartner, Ing., is a Design Engineer at Ryan Biggs | Clark Davis Engineering & Surveying, P.C. (formerly Ryan-Biggs Associates), in Skaneateles Falls, NY where she works on many of the firms historic preservation, masonry restoration, and forensic engineering projects. She can be reached at LHofgartner@ryanbiggs.com.

The SAHC Masters Program The SAHC masters program is a one-year Master of Science program on the engineering

of conservation of structures, with a focus on architectural heritage. It consists of both coursework and a dissertation. Coursework is concentrated in two countries each year, and dissertation work is divided between all involved institutions. The academic institutions involved in the program are the University of Minho, Portugal, Czech Technical University in Prague, Czech Republic, the University of Padova, Italy, the Technical University of Catalonia, Spain, and the Institute of Theoretical and Applied Mechanics, Czech Republic. The coursework consists of six units including History of Construction and of Conservation, Structural Analysis Techniques, Seismic Behaviour and Structural Dynamics, Inspection and Diagnosis, Repairing and Strengthening Techniques, Restoration and Conservation of Materials, and an Integrated Project. It is an international program that is taught in English. In my 2012 graduating class, there were students from Australia, Canada, France, Greece, India, Italy, Mexico, Peru, Portugal, Serbia, Spain, South Korea, Turkey, and U.S.. Professors from all over Europe and the world came to give us lectures on their areas of expertise. I performed my coursework at the Czech Technical University in Prague with thirteen other students. Prague (Figure 1) is a beautiful and architecturally rich city with buildings that date back almost a thousand years. I worked with Professor Maria Rosa Valluzzi and Professor Claudio Modena during my dissertation at the University of Padova. The title of my dissertation thesis was Kinematic Analysis and Intervention Design of a Complex Building Aggregate in Villa Santa Lucia degli Abruzzi in L’Aquila Province. The thesis was a study of the seismic vulnerability of a historic masonry building in a province of Italy that has high seismic hazard. The research

Figure 1. Prague is often called the City of a Hundred Spires.

32 May 2015

Figure 2. Class photo at Valtice Chateau, Czech Republic.

focused on the collapse mechanisms of the building and various intervention techniques to prevent failure in future earthquakes. I recently published a paper and presented on this same topic at the 9th International Masonry Conference in Guimarães, Portugal. The SAHC masters program was a very enriching experience for me. It was a great opportunity to study in a different country with people from all over the world. My professors and classmates taught me a lot about engineering and conservation practices in their home countries. I built many strong friendships with my classmates and learned about their different cultures. It was incredible to study historic conservation in a place like Europe, where there are historic masonry buildings at every turn. The coursework material came to life during our field trips to historic structures around the Czech Republic and Italy. Figure 2 is a class photo taken during a field trip to Valtice Chateau in the region of Southern Moravia in the Czech Republic. The courses focused on conservation from a structural and material degradation point of view. They were academically rigorous and very interesting. One of my favorite courses was History of Construction and of Conservation. In this course, we explored the different restoration strategies throughout history, learned about historic construction and design techniques, and discussed damage mechanisms for masonry and timber structures. In Figure 3, I am completing a building evaluation in the attic of the Church of Our Lady Victorious in Prague for one of the class assignments. I also especially enjoyed the Restoration and Conservation of Materials course. In this course, we learned about the material properties of historic masonry and

other common building materials, how they degrade, and how they can be restored. There were also many lab experiments as part of this course, with lots of hands-on experience. As part of the Integrated Project course, I studied the structural stabilization and moisture remediation of a historic monastery, as well as the damage mechanisms of a medieval stone arch, seen in Figure 4.

Bringing My Knowledge Back Across the Atlantic Since graduating from the SAHC masters program, I have worked at Ryan Biggs | Clark Davis Engineering & Surveying, P.C. (formerly RyanBiggs Associates), a consulting firm in New York State specializing in structural engineering, civil engineering and surveying. I specialize in structural restoration services including nondestructive testing, building investigations, masonry restoration, timber rehabilitation, and renovations of historic structures. The knowledge and experience I gained from the SAHC program has been incredibly useful. The analysis, inspection, diagnosis, and non-destructive testing techniques I learned while overseas have been particularly relevant to my work.

Figure 4. Medieval Stone Arch in Prague.

STRUCTURE magazine

May 2015

Figure 3. Investigating the roof structure of Church of Our Lady Victorious, Prague.

North America has a rich architectural history and many historic structures. Although they are not as old as many of the structures in Europe and other parts of the world, they played a significant part in our history and should be preserved for future generations. In order to preserve these structures, engineers must understand historic construction techniques, materials, and structural systems in order to design suitable restoration and rehabilitation strategies. The SAHC masters program provides a wealth of information that we can use in North America to preserve our historic structures and keep the past alive. I would recommend the SAHC masters program to all engineers who are interested in historic restoration and rehabilitation. It is a beneficial program for both those who have recently finished their undergraduate degrees, and those who have been practicing engineering but would like to become more specialized in historic structures. The program is geared towards those with engineering backgrounds. However, architects with technical backgrounds will also find this program worthwhile. The SAHC masters program is very unique and provides an incredible opportunity to travel, to study with engineering students from all over the world, and to learn from a diverse group of experts from leading European universities in the field of conservation. It is an excellent program and I highly recommend it. For more information about the SAHC masters program, please visit www.msc-sahc.org/.▪

Steel/Cold-Formed Steel ProduCtS Guide a definitive listing of steel/cold-formed steel product manufacturers/distributors and their product lines Suppliers Aegis Metal Framing Phone: 314-851-2200 Email: answers@aegismetalframing.com Web: www.aegismetalframing.com Product: Ultra-Span®, Steel Engine, Aegis Design Description: A division of MiTek®; the leading provider of pre-fabricated cold-formed steel truss and panel systems, and services for commercial, institutional and residential construction. Aegis provides a complete line of cold formed steel framing (also known as light gauge steel framing) including the UltraSpan truss system and WallSolutions™ prefabricated panels.

Albina Co., Inc. Phone: 866-252-4628 Email: info@albinaco.com Web: www.albinaco.com Product: Curved and Rolled Steel Description: Produce virtually any metal component that needs to bend or curve. Impeccable reputation in the steel bending and fabrication industry, for producing difficult and unusual parts. Pipe, tube, structural steel, plate and specialty bending and rolling for structural, architectural, industrial, manufacturing, ornamental and recreational applications.

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Phone: 800-580-3984 Email: sales@armadillonvinc.com Web: www.armadillonvinc.com Product: Armatherm Description: Provides thermal bridging solutions to improve building envelope performance. Armatherm thermal break material prevents cold bridging in structural steel connections including shear and moment connections, masonry shelf angles, cladding and curtain walls. Thermal modeling and structural design available as part of your design-build team.

Phone: 800-754-3030 Email: dlopp@mii.com Web: www.hardyframe.com Product: Hardy Frame® Panels, Brace Frames and Special Moment Frames Description: Hardy Frames, a MiTek® Builder Product, manufactures pre-assembled shear wall systems. HFXSeries Panels and Brace Frames are fabricated with CFS in wood and steel stud heights; custom heights are available. HF Special Moment Frames are the first preassembled SMF and features the AISC CPRP Certified SidePlate® moment connections.

CAST CONNEX Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Innovative Connection Solutions Description: The leading supplier of cast steel components for use in the design and construction of building and bridge structures. Universal Pin Connectors™ and Architectural Tapers™ bring off-theshelf simplicity and reliability to AESS, while custom designed components enable unparalleled opportunity for creativity in design.

Heckmann Building Products Inc. Phone: 708-865-2403 Email: info@heckmannanchors.com Web: www.heckmannanchors.com Product: Pos-I-Tie® Brick Veneer Anchoring System Description: The Pos-I-Tie Family of Products allows worry-free attachment of Brick or Stone Veneers to Structural Steel Studs. The Barrel Screw allows lateral load transfer between the backup and the veneer without any loads affecting the sheathing. A thermal break system is available for Brick Veneers.

Decon® USA Inc.

Simpson Strong-Tie

Phone: 866-332-6687 Email: frank@deconusa.com Web: www.deconusa.com Product: Anchor Channels Description: The exclusive representative of Jordahl in North America. Hot rolled Anchor Channels are embedded in concrete and used to securely transfer high loads. Their main application is for flexible connections of glazing panels to high-rise buildings. Anchor Channels with welded-on rebar or corner pieces are available.

Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Total Solution Provider for CFS Commercial Construction Description: A total solution provider for coldformed steel (CFS) commercial construction, delivering innovative CFS connector, anchor and fastener solutions. We reduce your installed costs by designing products that minimize screw count, eliminate the need for pre-drilling and minimize tool clearance issues without compromising strength and durability.

Product: Studrails® Description: The North American standard for punching shear enhancement at slab-column connections. Studrails are produced to the specifications of ASTM A1044, ACI 318-08, and ICC ES 2494. Decon Studrails are increasingly used to reinforce against bursting stresses in banded posttension anchor zones.

Halfen USA Phone: 800-423-9140 Email: pschmidt@halfenusa.com Web: www.halfenusa.com Product: Anchor Channel Description: Halfen anchor channel and t-bolt systems are engineered to provide adjustable connections for concrete construction. The channel comes in cold rolled or hot rolled profiles. All Resource Guide forms for the 2015 Editorial Calendar are now available on the website, www.STRUCTUREmag.org.

Product: LSUBH Bridging Connector Description: Simpson Strong-Tie now offers a lowercost option to its popular SUBH line of u-channel bridging connectors for cold-formed steel construction. The new LSUBH 20-gauge bridging connector provides all of the benefits of the SUBH connector, and is suitable for many wind- and load-bearing situations with light to moderate load demand.

Taylor Devices, Inc. Phone: 716-694-0800 Email: taylordevi@aol.com Web: www.taylordevices.com Product: Seismic Dampers Description: Fluid Viscous Dampers literally soak up the energy of earthquake induced motion, preventing structural damage. Compact, yet powerful, increasing structural damping levels to as much as 50% of critical, the results being truly dramatic stress and deflection reduction, actually lowering the total cost of the structure.

continued on page 37

STRUCTURE magazine

May 2015

Strong Structures Come From Strong Designs

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Phone: 402-441-4000 Email: marnett@sds2.com Web: www.sds2connect.com Product: SDS/2 Connect Description: Enables structural engineers using Revit Structure for BIM to intelligently design steel connections and produce detailed documentation on those connections. SDS/2 Connect is the only product that enables structural engineers to design and communicate connections based on their Revit Structure design model as part of the fabrication process.

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StructurePoint Phone: 847-966-4357 Email: info@structurepoint.org Web: www.StructurePoint.org Product: Concrete Design Software Description: pcaMats-spMats: Analysis, design and investigation of concrete foundations, mats, combined footings, pile caps and slabs on grade. pcaSlabspSlab: Analysis, design and investigation of elevated reinforced concrete beams, joist, one-way, two-way and slab band systems. All Resource Guide forms for the 2015 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

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May 2015

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quire Whipple (STRUCTURE, September 2005 and December 2014) patented his bowstring truss in 1841 and built them across the Erie and other Canals and rivers. These were generally for wagons and carriages. In 1846/47, he wrote his A work on Bridge Building Consisting of two essays, The One Elementary and General, the other showing Original Plans and Practical Details for Iron and Wooden Bridges. In it he gave the first correct method of determining the load in every member of his truss by the method of joints, and even utilized a graphical method of determining these loads. He studied all the standard trusses to prove that his Bowstring Truss was the most efficient. He determined, much to his surprise, “prior to 1846, or thereabouts, I had regarded the arch formed truss as probably, if not self evidently, the most economical that could be adopted; and at about that time I undertook some investigations and computations with the expectation of being able to demonstrate such to be the fact, but on the contrary the result convinced me that the trapezoidal form, with parallel chords and diagonal members, either with or without verticals, was theoretically more economical without than with vertical members – there being shown a less amount of action (sum of maximum strains into lengths of respective long members) under a given load,” and “it was apparent that each of the three forms – the arch, and the trapezoidal with and without verticals – possessed certain practical advantages entitling each to preference in respective cases, and, no other forms or combinations presenting themselves which seemed capable of competing successfully with these, they were assumed by me as those which would be the prevailing forms which coming practice would adopt.” He also determined that the most efficient angle for his diagonals was 45º. Near the end of his first essay, he got into the use of iron bridges for railroads. He designed them for a load of 2,000 pounds per foot, using an allowable tensile strength of wrought iron of 10,000 pounds per square inch and 10,000 pounds per square inch for cast iron in compression. In his

Whipple Single Intersection Truss, from book.

second essay, he described various trusses, including his bowstring truss, which he followed with his Cancelled Truss Bridge. He wrote, “if rightly proportioned is from 5 to 10 per cent cheaper than an arched bridge of the same strength, and for railroad bridges, is generally to be preferred,” and “it is decidedly preferable when the track may be placed on a level with the top of the trusses.” He wrote, “this plan, with the single cancel as in Figure 7, is good, perhaps the best, for any span under 75.” Spans “from 70 or 80, to 160 feet stretches, should be made with double cancels, or two crossings of diagonals.” He built several short span iron bridges, single cancel and bowstring, for the Newburgh Branch of New York & Erie Railroad in the late 1840s. Even though successful, they were removed after a failure of an iron bridge by Nathaniel Rider on the Harlem River Railroad. Wendell Bollman (STRUCTURE, February 2014 and February 2006) had built several of his iron trusses for the B&O Railroad, including the Winchester & Potomac span (STRUCTURE, February 2015) of the Harper’s Ferry Bridge with a span of 124 feet. Albert Fink (STRUCTURE, May 2006) also built his Monongahela River Bridge for the B&O in 1852 with three spans of 205 feet (STRUCTURE, March 2015). Up to 1853, however, Whipple had never built one of his Double Cancelled Bridges, later called Double Intersection or Trapezoidal Bridges. It wasn’t until 1852 that he designed a bridge, on a skew of 44º, for the Vermont & Canada Railroad north of Watervliet, New York (West Troy) over the enlarged Erie Canal. Whipple himself described the bridge as follows, continued on next page

significant structures of the past

Whipple Double Intersection Cast and Wrought Iron Truss

West Troy or Vermont and Canada Railroad Bridge, note skew.

STRUCTURE magazine

Historic structures

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

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

“The bridge was built in 1852 and 1853, and put in use in the spring of the latter year. It was 150 feet in length (146 feet clear span), of the Whipple trapezoidal plan, with vertical posts and pin connections, proportioned for a maximum load of one ton per lineal foot, and contained (exclusive of beams and track stringers, which were of wood), in round numbers, 32,000 lbs. of wrought and 43,000 lbs. of cast iron, being probably the lightest iron R. R. bridge of equal span ever constructed. [Emphasis Added] The lower chord was composed of links formed of round bars 23/8 inches in diameter in the center and diminishing, according to diminution of strain towards the ends of the truss. The links were connected in pairs by cast-iron connecting blocks or pins, 18 to 20 inches in length of a square form and pierced with holes for diagonal members to pass through; these being secured and adjusted by nuts upon the ends. The block had also upon the upper side a bevel seat for the lower end of the post. The upper chords were composed of cast iron hollow cylinders, about 9 inches in diameter, ½ inch to 5/8 inch thick, and 10 feet 8 inches long; the diameter being swelled out for 3 or 4 inches from the ends, giving about one inch in thickness at the abutting surface. There was an opening in the under side at the ends, to admit the ends of the verticle and diagonal members; the former forked and having semi-circular notches in the ends of the prongs for the connecting pins to rest upon. The abutting ends of the chord cylinders also having semi-circular notches, forming when together round holes horizontally through for connecting pins. The posts (21 feet 4 inches long between centers of chords), were each composed of four hollow tapering castiron pieces, the two middle ones about 5 feet 10 inches, and the two endmost about 4 feet 6 inches long, all about 6-inch in diameter at the smaller and 7 inches to 8 inches at the larger ends. The upper most pieces being forked at the smaller ends connecting with the upper chords before explained, and having a stout flange of a square form at the other end to meet the large end of the adjacent piece. The lower end piece, the same as the upper, with the exception of having a plain square end

Whipple Double Cancelled, Intersection, Trapezoidal Truss, from book.

resting upon the seat formed, as before stated, upon the connecting block of the lower chord. The two middle pieces were alike, being forked at the smaller ends, where they met in the center of the post, thus affording an opening for the passage of the diagonals, the larger ends meeting and abutting against the flanges of the end pieces. The four pieces thus described, placed end to end were secured together by four 5/8 or ¾ inch rods (according to the relative strains of the several parts), extending from the flange of the upper to that of the lower piece, with heads at the upper end and nuts at the lower ends of the rods, and with a stretcher at the center, spreading the rods at that point to a distance of 9 inches or 10 inches from center of the post, thus stiffening and supporting the members against tendency to deflect under longitudinal compression. The stretcher was so formed as to hold the abutting rods of the middle pieces in place, and had also an opening in the center for diagonals to pass through.” The reason for making it a double intersection was that, as the span length increased, the depth of the truss had to get deeper and with a normal panel length the diagonals would have been too steep. He wrote, “Now in trusses of considerable length, and, consequently, depth, it becomes expedient, in order to avoid too great a width of panel (horizontally), or an inclination of diagonals too steep for economy of material in those members, to extend them horizontally across two or more panels, or spaces between consecutive nodes of the chords. In such cases, the truss may be called double or treble cancelated, according as the diagonals cross two or three panels.”

STRUCTURE magazine

May 2015

If he wanted to keep his truss statically determinate, his diagonals had to cross the verticals without being connected to them. This made it possible to separate the truss into two statically determinate trusses, sometimes called Pratt Trusses as the diagonals are in tension. He later built similar trusses at Utica and Boonville, New York. Many people believed the trusses were too frail to carry railroad loading. The Railroad Commissioners of New York State had James Laurie, then President of the ASCE, examine all three bridges. He concluded, “While therefore, I cannot say that the bridge is unsafe, neither can I say that it is beyond question. I certainly consider it as being of too light construction for the passage of the loads at the speeds mentioned in the law establishing the Board of Railroad Commissioners, and although these may somewhat exceed what is required in ordinary practice, it is at all times desirable to have surplus strength, and the more especially when the plan of the bridge is of a new or novel construction.” In other words they, while safe, may not have been safe enough for Laurie. When the bridge was removed in 1883, Whipple himself wrote a letter to Engineering News stating, “On disconnecting the parts of the bridge after 30 years of usage, the cast-iron portion, without exception, were found to be in a sound and perfect condition as also the wrought iron, with the exception of the rod that broke a few months before the taking down of the bridge, with a suspicious looking fracture leaving, however, sufficient stamina in the remaining parts to prevent a collapse of the structure, although the broken piece was one of a pair of the most important diagonals, and whether the result was due to the original defect of

The next man to pick up the design and improve on it was Jacob Hays Linville of the Keystone Bridge Company. He maintained Murphy’s pins and lower chord, but built the top chords and verticals with wrought iron Keystone Column shapes. He built many spans on bridges across the Ohio River, with his longest at Cincinnati with a span of 420 feet. This was followed by several bridges across the Mississippi and other rivers. George Morison picked up the design in the many bridges he built across the Missouri, Mississippi, Snake and other rivers. Over time, Morison replaced the wrought iron with steel. From the mid-1850s to about 1890, the Whipple Double Intersection Bridge was the most common truss used by railroads. Alfred P. Boller wrote, “the Whipple type (often erroneously called the Pratt) excepting for small spans, has been universally adopted throughout the country as the most economical and constructively the simplest...” The longest bridge built by George Morison was across the Ohio River at Cairo, where he used two Whipple Double Intersection through trusses with two spans of 518 feet (the longest of the type ever built), seven of 400-foot, and three deck spans of 240 feet for a total

length of steel bridge plus 38 spans of steel viaduct, making it the longest bridge in the United States at the time. Whipple, in addition to his Bowstring and Double Intersection Trusses in cast and wrought iron, also designed and built the first successful vertical lift bridge across the Erie Canal in 1874. These bridges, in addition to his books, inspired Boller to write, “Squire Whipple, who is justly entitled to be called the father of the American trapezoidal iron truss bridge, built his first iron bridge in 1840. In 1847, he published his first work on ‘Bridge Building,’ in which he gave correct rules and formulas for computing the maximum strains from fixed and moving loads, in the various members of a truss; and recommended the now common form with inclined end posts, with link bars for tension members, which finally developed into our present eye-bars and pin-connections...” and that Whipple, “the retiring and modest mathematical instrument maker who, without precedent or example, evolved the scientific basis of bridge building in America.” It was appropriate then that ASCE, after its resurrection in 1867, named Whipple its First Honorary Member.▪

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the metal, or to deterioration consequent upon usage, is not quite patent, and the case might be worthy of investigation by those interested in the further construction and use of railroad bridges containing wrought iron in like condition of exposure.” The Utica Bridge, built in 1854 with a span of 123 feet, even though taken out in a flood on St. Patrick’s Day 1865 and rebuilt shortly after using the same materials, lasted even longer. Engineering News wrote on July 18, 1891, “Its existence and capacity for useful work at the present day is creditable alike to its designer and to its builder. Even with modern engine and car loads, which are about double what they were when the bridge was designed, the maximum strain in a web member is 13,165 pounds per square inch, and the greatest strain in the lower chords is 12, 566 pounds. It was an experiment in bridge building, and aroused much discussion at the time, and was roundly condemned by some engineers; and, as was quite natural under these conditions, it was a made a little too strong for the work then to be performed and almost strong enough for the increased traffic of another and succeeding generation. But in consideration of the rapidly increasing load put upon it in the last few years, the board recommends that it be replaced by a more modern type of bridge. It should be preserved somewhere as the work of a pioneer in a type of iron bridge that has since made American bridge engineers famous.” Whipple built many others, sometimes called Whipple Patent Bridges, even though he never patented the style, for roadways throughout New York. In 1859, John W. Murphy who worked with Whipple on the Erie Canal picked up the design and replaced the cast iron junction blocks along with the lower chords with pins and links in place of Whipple loops. He built many of these for railroads in Pennsylvania, and they became known locally as MurphyWhipple Bridges. Whipple wrote, “In the year 1859, or thereabouts, he [Murphy] built a few bridges, which they were pleased to designate as Murphy-Whipple bridges, to which I made no objections, though it has perhaps been the means of disseminating false impressions. ‘Murphy-Whipple bridges,’ properly considered, simply means bridges built by Murphy upon plans and principles originated by Whipple. My relations with Mr. Murphy were most friendly, and he conceded to me all my claims to originality in the bridge question.”

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May 2015

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award winners and outstanding projects

Spotlight

P750 Helicopter Maintenance Hangar By Gene O. Brown, P.E. and Min S. Koo, P.E. Frankfurt Short Bruza Associates was an Outstanding Award Winner for the P750 Helicopter Maintenance Hangar project in the 2014 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings $30M to $100M).

he Helicopter Maintenance Hangar was constructed at Naval Air Station North Island, the birthplace of naval aviation. Architects and structural engineers collaborated on a facility design worthy of this location, worked to control its visual scale and soften its industrial nature. Land-side points of entry utilized cast-inplace concrete structures in naval aviation themed elements to create organizational, material and spatial hierarchy. Set behind these elements, the massing of the twostory administrative portion of this facility undulated to create a softer rhythm across its 631-foot front face and created opportunities for operable windows, daylight and outdoor break areas. A curved roof profile sculpted the hangar bay’s boxy volume and provided a visual transition from the lower administrative space behind. A second curved roof feature was added over each squadron’s space and was rolled up over the hangar roof to resemble stacked waves, which further broke up the massive volume. Translucent insulated panels in the vertical zone of the trusses provide significant natural daylighting, and at night give the appearance the roof is much thinner and is hovering over the lower walls. Vertical lifting hangar doors provided a clean appearance, and columns were minimized to maintain the effect of one continuous opening across the front of the facility. Although the elevated design aesthetic immediately catches one’s eye, the structural challenges and solutions were a major

component to this project’s success. Not only did the structure have to support and compliment the architectural features, it had to meet several environmental and physical demands such as a corrosive marine environment, high seismic considerations and a site which was determined to be liquefiable. Historically, the project site was below sea level and had been reclaimed by placing fill soils to get above tide levels. A layer of liquefiable soils was identified and a Site Class of ‘F’ was assigned. Forty foot deep stone columns were constructed across the site to reinforce and densify granular soils. This provided an increase in bearing capacity, decrease in settlement and mitigation of the potential for liquefaction. After the construction of nearly one-thousand stone columns, this deep densification soil improvement program improved the Site Class to ‘D’. Structural engineers utilized buckling restrained brace technology to reduce the design seismic loads imposed on the structure, provide superior ductile and energy dissipative behavior and simplify the entire structure in general. Due to a higher behavior factor and increased fundamental period, smaller structural members could be utilized, connections were simpler and the required seismic bracing demands were reduced on all building

systems. As an added benefit, fewer expansion joints were required, thus further simplifying the structure and freeing up more functional space for the facility’s occupants. While the aforementioned technologies were highly effective solutions, the ingenuity in the design of the hangar trusses had the largest overall impact to aesthetics, building function and economy. The top chords of the truss were segmented, and purlin end connections had individual vertical adjustment to create the varying roof curves. Truss symmetry was utilized throughout, with special consideration given to the location of vertical members to control shadows visible through the translucent insulated panels. The truss bottom chords supported bridge cranes, fall arrest systems and extensive catwalks. These catwalks and platforms permitted building HVAC equipment to move into the hangar space in order to free up additional floor space for each Squadron. The 112,000 square foot helicopter maintenance facility measures 631 feet wide by 151 feet deep and is over 65 feet tall. It utilized 1,487 tons of structural steel including connections, 5359 cubic yards of concrete and achieved LEED® Gold certification. Most importantly, this new facility improves day-today readiness and mission execution through its arrangement and state-of-the-art features, but the Navy also proudly stated the facility would, “… inspire and enhance Sailors’ morale, both on-board (the Air Station) as well as those across the bay.”▪ Gene O. Brown, P.E., is a Principal at Frankfurt Short Bruza Associates (FSB) and Director of Federal Programs. Min S. Koo, P.E., is a Senior Structural Engineer at FSB. Both may be reached through FSB’s website at www.fsb-ae.com.

STRUCTURE magazine

May 2015

NCSEA is once again oﬀering scholarships for NCSEA Young Engineers to the NCSEA Structural Engineering Summit, September 30-October 3 at Red Rock Resort in Las Vegas. Scholarships will include complete registration to the Summit, which includes all educational sessions, meal functions, trade show, and the NCSEA Awards Banquet, as well as a monetary stipend that may be used for transportation and hotel costs. Qualified applicants will be under 36 years of age and a current member of an NCSEA Member Organization. Application forms, as well as information on the 2014 recipients, are available on the NCSEA website under the Awards tab. Applicants may complete a written application, which includes an essay, or a video submission, with a deadline of June 1. Young Member Scholarship winners will also be recognized at the October 2 NCSEA Awards Banquet during the Summit.

NCSEA Cornforth Award honorees

1999

2001 2003

Gene Corley Rawn Nelson Tim Slider Norm Scheel Fred Cowen Craig Cartwright Stephanie Young Ronald Hamburger Jon Schmidt Timothy Mays Edwin T. Huston Marc S. Barter Emile Troup Michael Tylk Greg Schindler Susan Jorgensen

2000 2001 2002 2004 2006 2007 2008 2009 2010 2011 2012 2013 2014

2004 2005 2009 2010 2011 2012 2014

Emile Troup Ben Baer Marc S. Barter Michael Tylk Craig Barnes David Bonneville William Holmes Robert Johnson Edwin T. Huston William L. Lavicka Ronald Milmed Dustin Cole

Susan M. Frey NCSEA Educator Award honorees 2013 2014

Sue Frey Tim Mays

The nomination form is available at www.ncsea.com. The deadline is July 20.

NCSEA Webinars May 12, 2015 Practical Design of Structures for Blast Effects: Glazing Systems Part 3 of this series will address static analysis using equivalent wind pressures and dynamic analysis using specialized software. Jon A. Schmidt, P.E., SECB, BSCP, Associate Structural Engineer and Director of Antiterrorism Services, Burns & McDonnell June 16, 2015 Safe Room Designs and Examples

This webinar will explore the current ICC 500 Standard design methodology and how proposed ASCE changes for 2016 might aﬀect the design methods and results. William Coulbourne, P.E., Director of Wind & Flood Hazard Mitigation, Applied Technology Council

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

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News form the National Council of Structural Engineers Associations

Young Member Scholarships open for NCSEA Summit

NCSEA Service Award honorees

NCSEA News

At the NCSEA Structural Engineering Summit, special awards are given to NCSEA members who have provided outstanding service and commitment to the association and to the structural engineering field. The NCSEA Service Award is presented to an individual who has worked for the betterment of NCSEA to a degree that is beyond the norm for volunteerism. The award is given to someone who has made a clear and indisputable contribution to the organization and to the profession. The Robert Cornforth Award is presented to an individual for exceptional dedication and exemplary service to the organization and to the profession. The award is named for Robert Cornforth, a founding member of NCSEA and treasurer on its first Board of Directors, a member of OSEA, and secretary of the Oklahoma State Board of Registration for Professional Engineers and Land Surveyors. Nominations for the Robert Cornforth Award must be submitted by NCSEA Member Organizations. The Susan M. Frey NCSEA Educator Award was established to honor the memory of one of NCSEA’s finest instructors. The award honors interest in, and extraordinary talent for, eﬀective instruction for practicing structural engineers. Winners of this award are asked to present a special webinar to NCSEA members at a deeply discounted cost, as a continuing legacy to Sue Frey. The nomination form for these awards is available at www. ncsea.com, and the deadline date for nominations is July 11. Nominations are requested for all awards; however, awards are based on worthy recipients and may not be awarded each year.

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Nominations open for NCSEA Special Awards

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2014 NCSEA Conference Young Member Scholarship recipients.

STRUCTURE magazine

May 2015

Non-CalOES courses 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 registrations to NCSEA webinars: Ala Carte, Flex-Plan, and Yearly Subscription. Visit www.ncsea.com for more information or call 312-649-4600.

Wood and Cold-Formed Light Steel Frame Construction – Deficiency in the IBC Special Inspections Kirk Harman, P.E., S.E., President, The Harman Group BIM and Structural Engineering Desiree Mackey, BIM Manager, Martin/Martin Building Rating, Retrofit Ordinances, and Community Resilience Panel from Structural Engineers Association of California

The NCSEA Summit will feature: • Structural Engineering Education • Trade Show • Awards Banquet, including the NCSEA Excellence in Structural Engineering Awards and the NCSEA Special Awards • Opportunities to network and meet structural engineers from across the country

NCSEA News

Educational Sessions will include:

News from the National Council of Structural Engineers Associations

Quality Assurance for Structural Engineering Firms Cliff Schwinger, P.E., Vice President & Quality Assurance Manager, The Harman Group The ASCE 7-16 Tsunami Loads & Effects Design Standard Gary Chock, President, Martin & Chock; Chair, ASCE 7 Tsunami Loads & Effects Subcommittee Working With Multiple Generations Panel Discussion with the NCSEA Young Member Group Support Committee Lateral Analysis: Right Way and Wrong Way to Do it in Structural Engineering Software Sam Rubenzer, P.E., S.E., Structural Engineer, FORSE Consulting

Concrete & CMU Elements in Bending + Compression John Tawresey, retired, KPFF Consulting Engineers Lateral Design of Buildings with Sloped Diaphragms Steven Call, P.E., S.E., Call Engineering The Decline of Engineering Judgment Jon Schmidt, P.E., SECB, Associate Structural Engineer and Director of Antiterrorism Services, Burns & McDonnell Problem Solving for Repairing Wood Structures Kimberlee McKitish, P.E., Nutec Group

The NCSEA Structural Engineering Summit will take place at the Red Rock Resort in Las Vegas. The hotel features seven restaurants, spa, a bowling alley, movie theatre, and arcade along with a casino. There is a complimentary scheduled shuttle to and from McCarran Airport and the Las Vegas Strip. A reservation link for the NCSEA group rate at the hotel, as well as a link to register for the Summit, are available at www.ncsea.com.

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Don’t Wait Register for the Summit and secure your hotel room today! Join us in Vegas!

Effective Communication: Tips for Improving Your Skills Kirsten Zeydel, S.E., President, ZO Consulting & Annie Kao, P.E., Field Engineer, Simpson Strong-Tie

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Find the Lost: 6 Steps to Improve Profits June Jewell, CPA, AEC Business Solutions

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Upcoming Changes to the Wind Loading Provisions in ASCE 7-16 Don Scott, S.E., PCS Structural Solutions; Chair, NCSEA Code Advisory Committee Wind Engineering Subcommittee

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Electrical Transmission & Substation Structures Conference 2015 RegistRation now open September 27 – October 1, 2015, Branson, Missouri Grid Modernization – Technical Challenges & Innovative Solutions

Demonstration events currently planned are:

The ASCE/SEI Electrical Transmission & Substation Structures Conference is the must-attend conference on transmission line and substation structures and foundation construction issues. This conference – for utilities, suppliers, contractors, and consultants – offers an ideal setting for learning and networking. • Discover Technical Knowledge • Hear Project Case Studies • Find Real-World Solutions • Watch Vendors Demonstrate Products and Services Enjoy On-site Demonstrations This event, sponsored by Quanta Services, will offer participants unique opportunities to witness several overhead power line construction and supplier demonstrations in a single day. Demonstrations will take place on-site adjacent to the Branson Convention Center and indoors in the Convention Center. No additional transportation will be required.

Engineers Week Field Trip to Los Angeles City Hall

• • • • • • • • • • • •

High-Voltage Scaffolding Substation Energized Pulling Zone with Suits Crux Steel-Cap Micropile Setup Rope Rescue Kits Safety Display Pallet-Mounted Display Robotic Arm B.H. Aerial Lift Truck Setup Video of Training Facility / Energized Work Vibration Demonstration Inspection Drone Demonstration Steel Pole Slip Joint / Pole Jacking Demonstration Hybrid Pole Assembly Joining Spun Concrete and Tubular Steel Poles • FRP Gin Pole Construction • And more For more information and to register, visit the conference website at www.etsconference.org.

Upcoming Conferences Second ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures December 10-12, 2015 www.atc-sei.org Geotechnical & Structural Engineering Congress 2016 February 14-17, 2016 www.Geo-Structures.org

Student Competition on Cold-Formed Steel Design Three elementary schools in Los Angeles participated in a special Engineers Week program which included conducting an egg drop design challenge in the Los Angeles City Hall Rotunda. The winning student received a Lego Architecture set and each school received a Make Your Mark poster. Visit the SEI website at www.asce.org/SEI and click on News to learn more. Include the Make Your Mark poster in your efforts to inspire and encourage students to pursue structural engineering as a career. Produced by the National Council of Structural Engineers Associations (NCSEA) and SEI. Complimentary posters are available upon request to Suzanne Fisher. Be sure to include the number of posters you are requesting and where they should be sent. Visit the ASCE website at www.asce.org/pre-college_outreach/ for more resources and ideas for outreach with young students. STRUCTURE magazine

The International Student Competition on CFS Design is organized by the Cold-Formed Steel Engineers Institute and supported by ASCE-SEI Committee on Cold Formed Members. The competition is open to all full-time students at any level in any engineering school in the world. The task given to students typically focuses on coming up with an optimal design of a coldformed steel cross section for a specific design condition. The top three designs are also given monetary awards and plaques. Submissions are due by end of September 2015. Entries are judged by a panel of industry professionals and ranked according to the design’s efficiency and constructability, as well as the quality of the essay submitted with the entry. Visit the competition website at www.cfsei.org/student-competition for more information and to apply. May 2015

SEI Student Video Competition Congratulations to the University of Naples team for their winning video, The Engineering Journey. The winning video showed how structural engineers solved problems throughout history. The video premiered at the SEI booth in the Structures Congress Exhibit Hall, with the winning team in attendance all the way from Italy. Learn more at www.asce.org/structural-engineering/sei-students/.

Student Structural Design Competition The SEI Student Structural Design Competition recognizes excellence in structural engineering education at the undergraduate level. The three finalist teams for 2015 are: • UNC Charlotte for their CB&I Intake Structure Project • Vermont Tech for their Structural Design of Ashrae Research & Manufacturing Center Project • Villanova University for their Torti Bridge Project

The three teams presented their projects at a special session at the 2015 Structures Congress. Learn more at www.asce.org/ structural-engineering/sei-students/.

SEI Young Professionals Scholarship Congratulations to the recipients of the 2015 SEI Young Professional Scholarship, which helps support their participation at Structures Congress: • Kris Clemente, P.E., A.M.ASCE • David Gelder, EIT • Tyler Graybill, EIT, A.M.ASCE • Lachezar Handzhiyski, P.E., M.ASCE • Devin Jones, P.E., M.ASCE • Christina Salchow, P.E., M.ASCE • Behrouz Shafei, Ph.D., P.E., M.ASCE • Reid Strain, P.E., M.ASCE • Kyle Turner, EIT, A.M.ASCE • Marcin Wasaznik, P.E. Learn more at www.asce.org/structural-engineering/seiyoung-professionals/.

SEI New Orleans Chapter

SEI Oregon Chapter

So far in 2015, the SEI New Orleans Chapter has hosted two seminars which presented valuable technical information to their members. Three additional seminars are planned over the next few months. In addition, the chapter participated in a regional science fair as judges on structural projects, and provided volunteers for a local Mathcount contest. Visit the SEI website at www.asce.org/SEI and click on News to learn more.

SEI is pleased to announce that the ASCE Oregon board of directors have unanimously approved the establishment of a SEI local chapter. The Oregon SEI chapter is in the process of establishing a chapter board and outlining a vision with goals for the future. The chapter plans to host and participate in technical activities that aid in providing up-to-date information and training, promote best practices, mentorship to younger members, leadership and career development and training the next generation of engineers. To do this, the chapter needs members, a board of directors and a slate of officers. Members in the Oregon area who are interested can join by contacting Oregon SEI president Tom North at Thomas.north@usace.army.mil.

SEI West Coast Florida Chapter The SEI West Coast Florida Chapter was pleased to partner with the Tampa Bay Rays to offer an in-depth tour of Tropicana Field. On February 27th, the group of 38 local engineers walked on the field and in the dugouts, discussed the suspension roof system, and learned about structural related features of the building. Built in 1986 for $138 million, the “Thunderdome” was renamed Tropicana Field after an $85 million renovation in 1996. The cable-supported roof is 225 feet above second base and the capacity is 42,735. Many other fun facts were shared, including: citrus aromas pumped into the ventilation system, what it takes to host a football game, and what happens when a bird makes their way inside. The tour concluded with a Q&A session with a senior manager of Stadium Operations at Tropicana Field.

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

SEI WVU Graduate Student Chapter The SEI Graduate Student Chapter at West Virginia University recently participated in Freshman Visitation. This is an opportunity to provide information about civil engineering to freshmen students. University faculty and GSC officers gave presentations on the kinds of structures and materials, and the use of composites to repair and rehabilitate structures. Visit the SEI website at www.asce.org/SEI and click on News to learn more.

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

May 2015

The Newsletter of the Structural Engineering Institute of ASCE

Local Activities

Structural Columns

Student & Young Professional News from Structures Congress

The Newsletter of the Council of American Structural Engineers

CASE in Point

CASE Risk Management Tools Available Foundation 5 Education: Educate all of the Players in the Process Tool 5-1: A Guide to the Practice of Structural Engineering Intended to teach structural engineers the business of being a consulting structural engineer and things they may not have learned in college. While the target audience for this tool is the young engineer with 0-3 years of experience, it also serves as a useful reminder for engineers of any age or experience. The Guide also contains a test at the end of the document to measure how much was learned and retained. Other sections deal with getting and starting projects, schematic design, design development, construction documents, third party review, contractor selection/project pricing/delivery methods, construction administration, project accounting and billing, and professional ethics. Tool 5-2: Milestone Checklist for Young Engineers The tool will help your engineers understand what engineering and leadership skills are required to become a competent engineer. It will also provide managers a tool to evaluate engineering staff.

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

STRUCTURE magazine

Tool 5-3: Managing the Use of Computers and Software in the Structural Engineering Office Computers and engineering software are used in every structural engineering office. It is often a struggle to manage and supervise these tools. Software availability is in constant flux, software packages are continually updated and revised, and few software packages fully meet the needs of any office. This tool is intended to assist the structural engineering office in the task of managing computers and software. Tool 5-4: Negotiation Talking Points This tool provides an outline of items for your consideration when you are in a situation in which you are pressured to agree to lower fees. The text is subdivided into situations that are commonly experienced in our profession. This document is purely advisory and designed to assist you in your individual negotiations and business practices.

Foundation 6 Scope: Develop and Manage a Clearly Defined Scope of Services Tool 6-2: Scope of Work for Engaging Sub-Consultants This tool should be used when a structural engineer is asked by the prime consultant or owner to provide input on subconsultant selection and scope of work, or when the structural engineer is required to retain the sub-consultant directly.

May 2015

CASE Member Firms Win Grand, Honor Awards

The CASE Summer Planning Meeting is scheduled for August 6-7 in Chicago, IL, featuring a roundtable discussion on topics relating to the business of Structural Engineering, facilitated by the CASE Executive Committee members. Topics in the past have included the Business of BIM, using social media within your firm, Peer Review and Special Inspections. Attendees to this session will also earn 1.5 PDHs. Please contact CASE Executive Director Heather Talbert (htalbert@acec.org) if you are interested in attending this roundtable or have any suggested topics for the roundtable.

Congratulations go out to CASE Member firm Weidlinger Associates, Inc. of New York, NY for winning a Grand Award for its project, World Trade Center 7: Collapse Analysis and Assessment Report in New York City. The project was also a finalist for the Grand Conceptor Award awarded at the recent Engineering Excellence Awards Gala held during the ACEC Annual Convention last month. CASE Member Firms Walter P Moore and Magnusson Klemencic Associates, Inc. each won Honor Awards for their projects, Southwest University Park, El Paso, TX and the San Ysidro U.S. Land Entry Port of Entry Modernization, San Ysidro, CA, respectively.

August 6–7, 2015; Chicago, IL

CASE in Point

CASE Summer Planning Meeting

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

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

WANTED

Engineers to Lead, Direct, and Get Involved with CASE Committees! If you’re looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!) CASE Committees. Join us to sharpen your leadership skills – promote your talent and expertise – to help guide CASE programs, services, and publications. We have a committee ready for your service: • Risk Management Toolkit Committee: Develops and maintains documents such as business practices manuals and policies for engineers under CASE’s Ten Foundations for Risk Management.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

STRUCTURE magazine

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

May 2015

CASE is a part of the American Council of Engineering Companies

Since its inception in 1995, the American Council of Engineering Companies’ prestigious Senior Executives Institute (SEI) has attracted public and private sector engineers and architects from firms of all sizes, locations and practice specialties. Executives – and up-and-coming executives – continue to be attracted by the Institute’s intense, highly interactive, energetic, exploratory, and challenging learning opportunities. In the course of five separate five-day sessions over an 18-month timeframe, participants acquire new high-level skills and insights that facilitate adaptability and foster innovative systems thinking to meet the challenges of a changed A/E/C business environment. The next SEI Class 21 meets in Washington, D.C. in September 2015 for its first session. Registration for remaining slots is available. Executives with at least five years’ experience managing professional design programs, departments, or firms are invited

Structural Forum

opinions on topics of current importance to structural engineers

Of Course Structural Engineering Education is Sustainable By Charles W. Dolan, P.E., S.E., Ph.D.

awrence Bank’s article, Is Structural Engineering Education Sustainable? (STRUCTURE, February 2015), raises interesting issues and exposes the separation between education and practice. For one thing, structural engineering education is constantly evolving. The notion that today’s design is based on books from the 1950s and 1960s ignores the reality that the better texts are philosophically well-thought-out, present fundamental structural behavior, and follow with how codes and standards interpret this behavior to protect life safety. Similarly, an emphasis on mechanics, which arguably goes back centuries, provides the novice engineer with the tools and ability to assess today’s sophisticated computer programs. Any practicing engineer observing a senior design project that uses 3D building information modeling (BIM) tools will observe exceptional presentation creativity, often accompanied by a naive structural framing system. Focusing on current hot topics or tools does little for fundamental understanding. For decades, the educational community has struggled to assess the content of the engineering curriculum. Current civil engineering programs require between 128 and 132 semester hours for a bachelor’s degree. This compares to the requirement of 140 to 150 semester hours only a half century ago. Arguably, today’s students do not need six hours of drafting and descriptive geometry, or awareness of how many butts make a hogshead. By the same token, the increase in sophistication in all engineering disciplines hardly argues for a reduction in credit hours. Critical tradeoffs are required to expose the student to emerging technologies and determine which topics can appropriately be dropped. The educational and practical implications of this pressure on the curriculum are reflected in the ASCE initiatives to require additional credit hours beyond a bachelor’s degree to be eligible for professional registration. Structural engineering education then asks: Where does sustainability fit in the curriculum? A quick scan of ACI, AISC, or ASEE journals will find dozens of papers on methods to improve engineering education. Authors range from dedicated professors to past luminaries such as Fazlur Khan. ACI alone has

over 100 articles on all aspects of sustainability, ranging from materials to structures to construction. Thus sustainability is working its way through the literature to the student. A vision of aligning teaching, research and practice to focus on sustainability may be naïve and possibly misguided. For example, structural design could focus on optimization of structural framing systems to reduce material. Optimization algorithms were developed in the late 1960s and fell by the wayside because overall construction costs favored high repeatability, rather than close tracking of individual components. An alternative approach is suggested in the draft National Performance Based Design Guide (http://npbdg.wbdg.org/). One recommendation would require all building live loads to be at least 100 psf. This would allow for easy reconfiguration of the structure for new uses, thus capturing all of the embodied energy. Such an approach is diametrically opposite of an optimization strategy. The profession has yet to determine the preferred sustainability solution. In either event, the decision will not be made in the classroom. Life-cycle cost analysis and triple bottom line are often useful measures of sustainable design. The General Services Administration and large corporations have a vested interest in sustainable construction because they own the facility for the long haul; hence these measures are useful to them. A speculative developer, on the other hand, looks primarily at the short-term payback and tax depreciation, and thus may have little interest in sustainability. Structural engineers serve both kinds of clients. On a larger scale, few if any engineering programs offer courses in structural rehabilitation or use of composite materials. The former would capitalize on the extended lifespan and embodied energy of existing structures; the latter directly addresses the multitude of unreinforced masonry structures in seismically active regions. The open question is whether addition of these courses is the best use of the limited curriculum openings. The issue of providing adequate housing for the three billion people living on less than five

US dollars a day is more compelling. The effort requires clean water, transportation, and communications in addition to housing. If there is any doubt that this problem is not being addressed, you need only attend a student meeting of Engineers without Borders. Solutions abound. Research at some universities examines rapid deployment shelters for disaster areas using the Haitian earthquake as a template for what may be needed. Most importantly, students and faculty are engaged and together generating solutions to these problems. The last and perhaps most important item in keeping structural engineering education sustainable is the interaction between education, research, the practitioner, and the codes. The interplay of these four activities keeps the profession relevant. There is no leader in this effort, but it is rather a symbiotic relationship between the players. Students require several years of professional practice prior to licensure. Part of this on-the-job training addresses the above-mentioned gaps in their educational preparation. Structural failures, while few, lead to building code changes and new research initiatives. Similarly, university research into structural systems, behavior, performance, and modeling lead to innovations in design and updating codes. Initiatives at the National Science Foundation to expand hybrid and multi-scale modeling will advance the ability of the structural engineer to incorporate sustainability into a design. Sustainability will ultimately fall out where it best fits the societal interest. Thus, sustainability is evolving into the curriculum in materials, modeling, design and construction courses. In a profession where life safety and protection of the public are paramount, this interaction is constantly evolving, students and faculty are engaged and motivated, and the future is indeed very bright.▪ Charles W. Dolan, P.E., S.E., Ph.D., (CDolan@uwyo.edu), is emeritus H. T. Person professor of engineering at the University of Wyoming and a member of ACI Committee 318, Building Code for Concrete Structures. He has over 45 years of consulting engineering experience.

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

May 2015

STRUCTURE magazine | May 2015

Articles inside

Fastening Steel deck

Whipple double intersection cast and Wrought iron truss

evaluating existing and Historic Stone arch Bridges

Masonry Preservation education

Special reinforced Masonry Walls

the Virtues of ignorance

of course Structural engineering education is Sustainable

Brick Beams