STRUCTURE magazine | March 2015

March 2015 Seismic

A Joint Publication of NCSEA | CASE | SEI

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March 2015 38

Feature

Power of the ring editorial

7 Partnerships: New and ongoing

By Jennifer Goupil, P.E. iNFoCuS

9 Narrative and engineering

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

By Cawsie Jijina, P.E., SECB and J. Benjamin Alper, P.E., S.E. The Forum in Inglewood, California, is an arena with a cable-suspended structure. With music acts requiring heavier gear than the structure was originally designed for, there was not enough reserve capacity to support these shows. As part of the retrofit of the Forum, owners wanted to increase the load capacity of the roof by 300 percent.

HiStoriC StruCtureS

33 gustav lindenthal’s little Hell gate rail Bridge

By Alice Oviatt-Lawrence StruCtural SuStaiNaBility

55 environmental declarations and Structures

By Emily Lorenz, P.E.

leSSoNS learNed

10 earthquake damage to Cylindrical Steel tanks

By Erica C. Fischer, P.E., Judy Liu, Ph.D. and

eduCatioN iSSueS

56 Problem-Based learning in earthquake engineering Courses

Amit H. Varma, Ph.D.

By Jeena Rachel Jayamon

StruCtural deSigN

eNgiNeer’S NoteBook

14 understanding Seismic design through a Musical analogy

By Ramon Gilsanz, P.E., S.E. and Petr Vancura StruCtural FailureS

20 reflections on the 2014 South Napa earthquake

By John A. Dal Pino, S.E. StruCtural PerForMaNCe

25 learning from Structural Success rather than Failures

By Sissy Nikolaou, Ph.D., P.E. and Ramon Gilsanz, P.E., S.E.

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Feature

Constructible Criticism

By Andy Kizzee, P.E. The worldwide priority for earthquakeresistant construction is often dismissing the importance of solutions and techniques that are familiar to local builders, particularly in developing regions. Innovations in earthquake-resistant construction must be feasible to understand and implement.

47

58 extreme torsional irregularity

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

60 Qui What?

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

Feature

Steel and Cold-Formed Steel Construction

By Larry Kahaner New products and services from the steel and cold-formed steel industry continue to meet changing demands.

CaSe BuSiNeSS PraCtiCeS

StruCtural ForuM

62 Contract Writing for young PMs – Part 2

74 acceptable Collapse?

By Reid Zimmerman, P.E.

By Kate Stanton, P.E. SPotligHt

67 east Station Plaza – danseurs (dancers)

By John Sumnicht, S.E., Ronald Mayes, Ph.D. and Nicholas G. Wetzel, S.E., CPEng

On the cover The historic, Art Deco U.S. Post Office on Franklin Street in downtown Napa was damaged in the South Napa earthquake. The building was built in 1933 with funding from the Public Works Administration and designed by architect William H. Corlett. See more on the South Napa Earthquake in the Structural Failures article on page 20.

STRUCTURE magazine

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iN every iSSue 8 Advertiser Index 64 Resource Guide (Software Updates) 68 NCSEA News 70 SEI Structural Columns 72 CASE in Point 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.

March 2015

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Editorial

Partnerships: New and Ongoing new trends, new techniques and current industry issues

By Jennifer Goupil, P.E., F.SEI, M.ASCE

Y

NCSEA and SEI partner in more ways than one to strengthen outreach to students and educators, but one understated effort involves creating the NCSEA-SEI “Make Your Mark” poster each year. The NCSEA Advocacy Committee and the SEI Public Relations Committee jointly develop the poster and its message, along with distribution efforts to encourage students to pursue a career in structural engineering. The poster is available online from both organizations.

Collaboration on common topics is also embedded in many committees; for example, the Joint SEI-CASE Committee on BIM endeavors to remain current with developments as well as to disseminate information about BIM. Additionally, since business and professional practices are central to all member services, the SEI Business and Professional Activities Division Executive Committee includes a representative from CASE and a liaison from NCSEA. Distinctive opportunities abound in all of our professional organizations, but often partnerships create unique events that serve the profession. The ongoing partnership between CASE and SEI to include the CASE Spring Risk Management Convocation as part of the annual SEI Structures Congress is unparalleled. CASE provides a forum to improve the quality of structural engineering through enhancement of business practices. Access to these focused and specialized sessions are provided for all technical program registrants at the Structures Congress. The Convocation kicks off with a poignant plenary breakfast, followed by a full day’s track of technical sessions. Learn more about the CASE Spring Risk Management Convocation and this year’s Structures Congress at www.structuresccongress.org.

Finally, the unprecedented SEI partnership with the ASCE GeoInstitute for the 2016 Geotechnical & Structural Engineering Congress will provide structural engineers with unmatched education and networking opportunities with colleagues within and across disciplines. Learn more at www.geo-structures.org and note that the call for submissions to be considered for the technical program is currently open through April 7, 2015. It is important to realize that this event is developing as a new, joint event that will combine the best of both Institutes’ annual conferences – including the CASE Risk Management Convocation – and that there is no separate Structures Congress planned for 2016.

While this highlights many unique and specific partnerships among your professional societies, there are many others that exist. Success in all of these endeavors depends upon member leadership and participation, as well as staff support and cooperation. I am joined by many with a message of thanks for these successful partnerships, as it is evident to me that the new and ongoing efforts are the result of a lot of hard work, yet the benefits to our profession are unrivaled.▪

a member benefit

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our professional organizations always work hard for you, but often the groups work together for even greater impact by expressing a unified voice, strengthening an existing program’s effectiveness, or providing unique opportunities not otherwise available. New programs are announced with excitement and celebration, but then often go on to serve the profession silently, without follow-up reports on successes. I would like to discuss several unique partnerships so that you are aware, or can become re-acquainted, with these successful efforts.

There are two strong examples underway that unify many voices within the profession of structural engineering. The Structural Standards Coordination Council (SSCC) is comprised of U.S. standards development organizations (SDOs) and allied parties including ASCE/SEI, ACI, AISC, AISI, AWC, TMS, and NCSEA. The mission of the SSCC is to provide an organized mechanism for planning and coordinating the development schedules of structural standards maintained by U.S. SDOs for the benefit of public safety, health, and welfare, as well as for the benefit of structural engineering practice. This group has been meeting for many years informally, but formally organized into the SSCC in 2013. It currently meets twice per year and is working towards a coordinated suite of structural standards to be adopted into the 2018 cycle of the ICC codes.

In addition, all of the national professional organizations representing structural engineers – SEI, NCSEA, SECB, CASE – have come together to form the Structural Engineering Licensure Coalition (SELC). The SELC has been meeting since 2012 to champion the cause of structural engineering licensure and to build a consensus among all stakeholders. SELC has collected and developed resources and will be making presentations at the Structures Congress in April, as well as participating at the NCEES Annual Meeting in August, to advance its mission. SELC meets twice per year at the SEI Structures Congress in the spring and at the NCSEA Structural Engineering Summit in the fall, as well as via quarterly teleconferences; learn more about SELC at www.selicensure.org.

To bolster professional pursuit of structural licensure, the Structural Engineering Certification Board (SECB) has created an opportunity for members of SEI and NCSEA to encourage more members to obtain SECB certification. Part of SECB’s mission is to promote structural engineering licensure in all jurisdictions by providing a common national certification.

STRUCTURAL The partnerships with SEI and ENGINEERING INSTITUTE NCSEA serve to strengthen the program’s effectiveness; learn more at www.secertboard.org.

STRUCTURE magazine

Jennifer Goupil, P.E., F.SEI, M.ASCE (jgoupil@asce.org), is senior manager of engineering at the Structural Engineering Institute of ASCE.

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March 2015

Advertiser index

PlEasE suPPort thEsE advErtIsErs

Albina Co., Inc...................................... 48 American Concrete Institute ................. 32 Bentley Systems, Inc. ............................. 54 CADRE Analytic .................................. 61 Canadian Wood Council ....................... 65 Cast ConneX......................................... 49 Construction Specialties ........................ 41 Design Data. ......................................... 53 Enercalc, Inc. .......................................... 3 Engineering Ministries International ..... 44 Hayward Baker, Inc. .............................. 27 Hohmann & Barnard, Inc ..................... 19 ICC....................................................... 59 Independence Tube ............................... 17 Integrity Software, Inc. .............. 16, 30, 50 Integrated Engineering Software, Inc..... 24 Intergraph CADWorx & Analysis Sol.... 52 KPFF Consulting Engineers .................... 8 Lindapter .............................................. 51

LNA Solutions ...................................... 63 NCEES ................................................. 45 New Millennium Building Systems ....... 13 PT-Structures ........................................ 26 RISA Technologies ................................ 76 S-Frame Software, Inc. ............................ 4 SidePlate Systems, Inc. .......................... 46 Simpson Strong-Tie........................... 2, 31 Star Seismic ........................................... 57 The Steel Network, Inc. ......................... 75 Structural Engineers, Inc. ...................... 50 Structural Technologies ......................... 35 StructurePoint ....................................... 37 Struware, Inc. ........................................ 50 Taylor Devices, Inc. ............................... 11 Tekla ....................................................... 6 Williams Form Engineering .................. 21 Wood Advisory Services, Inc. ................ 61

Erratum The author of the Lessons Learned column in the February 2015 issue of STRUCTURE® magazine discovered an error after the article went to print. On page 10, “Preparation of Deposition Questions”, Item 9a should read: a. Originally approved in 2005.

The online version of this article has been revised to reflect the change. The author and STRUCTURE magazine apologize for any inconvenience.

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Advertising Account MAnAger InteractIve SaleS aSSocIateS sales@Structuremag.org Eastern Sales chuck Minor 847-854-1666 Western Sales Jerry Preston 480-396-9585

editoriAL stAFF Executive Editor Jeanne vogelzang, JD, cae execdir@ncsea.com Editor christine M. Sloat, P.e. publisher@Structuremag.org Associate Editor nikki alger publisher@Structuremag.org Graphic Designer rob Fullmer graphics@Structuremag.org Web Developer William radig webmaster@Structuremag.org

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 roger a. laBoube, Ph.D., P.e. ccFSS, rolla, Mo Brian J. leshko, P.e.

HDr engineering, Inc., Pittsburgh, Pa Brian W. Miller Davis, ca

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Seattle Tacoma Lacey Portland Eugene Sacramento San Francisco Walnut Creek Los Angeles Long Beach Pasadena Irvine San Diego Boise Phoenix St. Louis Chicago New York KPFF is an Equal Opportunity Employer. www.kpff.com

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March 2015

evans Mountzouris, P.e. the DiSalvo engineering Group, ridgefield, ct Greg Schindler, P.e., S.e.

KPFF consulting engineers, Seattle, Wa Stephen P. Schneider, Ph.D., P.e., S.e.

BergeraBaM, vancouver, Wa John “Buddy” Showalter, P.e. american Wood council, leesburg, va amy trygestad, P.e. chase engineering, llc, new Prague, Mn 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 March 2015, Volume 22, Number 3 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.

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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

Narrative and Engineering new trends, new techniques and current industry issues

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

The second chapter of psychologist Jerome Bruner’s 1986 book, Actual Minds, Possible Worlds, begins as follows:

There are echoes here of Bernard Lonergan’s cognitional theory (“How We Know and What It Means,” September 2009), the model of skill acquisition developed by Hubert and Stuart Dreyfus (“The Nature of Competence,” March 2012), and Joseph Dunne’s discussion of “The Rationality of Practice” (September 2012). Again, though, those authors wrote in the paradigmatic mode, while stories obviously belong mainly to the narrative mode. What explanatory stories do engineers know that “fit” our candidate-experience, thus turning it into actual experience – the kind that is essential for developing practical judgment?

Finally, “Stories are central to life,” asserts author and educator Roger Rosenblatt in his 2011 book, Unless It Moves the Human Heart: The Craft and Art of Writing.

There are two modes of cognitive functioning … each providing distinctive ways of ordering experience, of constructing reality.

The two (though complementary) are irreducible to one another.

Efforts to reduce one mode to the other or to ignore one at the expense of the other inevitably fail to capture the rich diversity of thought. (p. 11) Bruner calls the first mode “paradigmatic” or “logico-scientific.” Its objective is truth, and its chief function is to acquire knowledge: it seeks empirical discovery guided by principled hypotheses, and favors tight analyses that appeal to logic and verification. It is top-down, theorydriven, categorical, general, abstract, context-independent, ahistorical, and consistent. Its subject matter is the physical realm, and the most primitive and irreducible element with which it deals is causation.

Bruner calls the second mode “narrative.” Its objective is verisimilitude or plausibility, and its chief function is to impart meaning: it seeks universal understanding grounded in personal experience, and favors inspiring accounts that appeal to aesthetics and intuition.

It is bottom-up, action-oriented, interpretive, particular, concrete, context-sensitive, temporal, and often paradoxical, even contradictory.

Its subject matter is the psychical realm, and the most primitive and irreducible element with which it deals is intention.

These distinctions should sound familiar to long-time readers of this column. They closely resemble Steven Goldman’s contrast of the Principle of Sufficient Reason, which Western culture has embraced since the time of Plato and the Sophists, and “The Principle of Insufficient Reason” (May 2008), which better reflects the nature of our profession. In other words, they align with the demarcation between science as knowing and “Engineering as Willing” (March 2010). They also loosely parallel the ancient Greek concepts of episteme/techne vs. phronesis (“Knowledge, Rationality, and Judgment,” July 2012).

I suspect that most engineers (and philosophers) are like me – more comfortable operating in the first mode than the second. After all, an essay like this one primarily engages the paradigmatic mode; likewise for pretty much everything else that has appeared in this space over the years, not to mention the vast majority of other articles in STRUCTURE magazine and similar industry publications. What new insights could we gain about ourselves and our practice by deliberately applying the narrative mode instead?

In his 2010 book, Letting Stories Breathe: A Socio-Narratology, sociologist Arthur W. Frank suggests, “Stories work as people’s selection/ evaluation guidance system” (p. 46). Rather than functioning as rules,

They’re everywhere: in the law, where a prosecutor tells one story and the defense tells another, and the jury decides which it prefers … In medicine, a patient tells a doctor the story of his ailment, how he felt on this day or that, and the doctor tells the patient the story of the therapy, how he will feel this day and that, until, one hopes, the story will have a happy ending.

Politics? He who tells the best story wins … (pp. 18-19) As is usually the case when these kinds of examples are given, engineering is not mentioned; and a common complaint among us is that, in comparison with these three professions, there is a dearth of popular entertainment featuring engineers in significant roles. Is this because stories are somehow not central to what we do and how we do it? Or does it rather indicate that we are not telling our stories often enough or well enough for them to resonate with other people?

Literary theorists have attempted to identify the basic elements of successful stories. According to Bruner, “One view has it that lifelike narratives start with a canonical or ‘legitimate’ steady state, which is breached, resulting in a crisis, which is terminated by a redress, with recurrence of the cycle an open possibility.” (p. 16) Alternatively, “Kenneth Burke argues that ‘story stuff’ involves characters in action with intentions or goals in settings using particular means.” (p. 20) Bruner himself considers it sufficient that the story “contains a plight into which characters have fallen as a result of intentions that have gone awry … And it requires an uneven distribution of underlying consciousness among the characters with respect to the plight.” (p. 21) If engineers ever manage to gain greater prestige in society and influence on public policy, I suspect that it will be because we have learned to construct and communicate compelling narratives that conform to these kinds of patterns. For better or for worse, a good story can often be more persuasive than a sound argument.▪

Stories are better imagined … as a tacit system of associations that makes particular aspects of the world seem worth attending to and suggests default evaluations of what is selected … [This system] processes a large proportion of what might be called candidate-experience: what happens to a person that, if attended to, becomes that person’s experience. Candidate-experience becomes experience because it fits stories people know. (p. 47) STRUCTURE magazine

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.

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Lessons Learned problems and solutions encountered by practicing structural engineers (a) Figure 1. (a) Movement of tanks, (b) Close up measurement of movement.

O

n August 24, 2014, a magnitude 6.0 earthquake occurred northwest of American Canyon, California. The earthquake was located between two faults: the West Napa Fault and the CarnerosFranklin Fault near the north shore of the San Pablo Bay. Structural damage was most severe in the downtown Napa region, where a number of unreinforced masonry (URM) buildings were located. Damage to residential building construction was also observed surrounding the downtown region, and became less severe farther away from town. Damage to vineyards and wine storage facilities was focused mainly on damage to stainless steel storage and fermentation tanks, and damage to the wine storage barrels due to racks collapsing.

This article focuses on the cylindrical steel tank damage observed at wineries after the Napa Valley earthquake. The tank damage discussed in this article was not unique to the Napa Valley Earthquake. This type of damage has been documented after previous earthquakes around the world. Large-scale testing and numerical models have been developed to demonstrate the behavior of cylindrical steel fluid-filled tanks during earthquakes. Although damage to cylindrical steel tanks from earthquakes has been well documented, and research has demonstrated better anchorage systems may improve the seismic performance, it seems the design and construction of these tanks used in the wine industry has not advanced with these known improvements.

Discussions with selected wineries in Napa after the earthquake demonstrated that the performance objectives of the steel tanks in the wine industry differs from those in other industries that use cylindrical fluid-filled steel tanks (water, oil, chemical). Wineries experienced buckling of the tank walls, anchorage failures, and racking of the tanks against one another. However, this type

Earthquake Damage to Cylindrical Steel Tanks

By Erica C. Fischer, P.E., Judy Liu, Ph.D. and Amit H. Varma, Ph.D. Erica C. Fischer, P.E., is currently a doctoral candidate in Civil Engineering at Purdue University investigating the robustness of simple connections in fire. Erica can be reached at fischere@purdue.edu.

Dr. Judy Liu is an Associate Professor in structural engineering at Purdue University’s Lyles School of Civil Engineering. Dr. Liu can be reached at jliu@purdue.edu.

Dr. Amit H. Varma is a Professor and University Faculty Scholar in Purdue University’s Lyles School of Civil Engineering. He is the Chair of the SEI/ACI Composite Construction Committee and member of the AISC Committee of Specifications. Dr Varma can be reached at ahvarma@purdue.edu.

10 March 2015

(b) of damage was not unique to the Napa Valley Earthquake. This damage has been exhibited in previous earthquakes in California and around the world: the 1977 San Juan earthquake, 1980 Greenville-Mt. Diablo earthquake, 1984 MorganHill earthquake, 1989 Loma Prieta earthquake, 2003 San-Simeon earthquake, 2010 Maule earthquake, and the 2013 Marlborough earthquake.

Documentation of damage after each of these earthquakes demonstrates that buckling of steel tank walls and anchorage failure occurred in tanks that were full with fluid and anchored to the ground.

The February 2010 Maule Earthquake affected a region in which 70% of the wine production of Chile takes place. The ground motion measured during the earthquake was about 0.35g, and damage fell mostly in three categories: (1) damage to steel fermentation tanks, (2) wine storage barrels falling off their racks, and (3) spilled unprocessed wine.

Stainless steel tanks can be either leg supported, or continuously supported with a flat base.

Damage was observed to both of tank-types. The legged supported stainless steel (LSSS) tanks are used often to ferment and store small volumes of high quality wine. These tanks are usually between 350 to 1765 cubic feet (10 to 50m3) in capacity. The damage to the LSSS tanks as a result of the Maule Earthquake included buckling of the supporting legs caused by axial resultant forces from the overturning moment, and movement of the tank resulting in the tank falling off of the supporting concrete base when the LSSS tanks were not anchored to the concrete base.

Buckling of LSSS tanks was not observed after the Napa Valley Earthquake; however, movement of unanchored LSSS tanks was documented.

During the Maule Earthquake, LSSS tanks that had enough room to move and were unanchored performed better than the anchored legged tanks.

Figure 2. Damage to fermentation tanks. Examples ofTAY24253 buckling of BraceYrslfStrctrMag.qxd steel tank wall at base.

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However, when the tank moved, there was damage to the piping systems. Movement of the tanks was observed up to 8 inches (20cm), which is consistent with the movement of the tanks observed during the Napa Valley Earthquake and shown in Figures 1a & b.

Those tanks that are continuously supported with a flat bottom are typically larger storage and fermentation tanks, and are called flat bottom tanks. The flat bottom tanks are also anchored to concrete slabs. Damage to these tanks observed after the 2010 Maule Earthquake included anchorage failure and buckling of the stainless steel tank wall. Anchorage failures were caused by insufficient edge distance, insufficient number of anchors, corrosion of the anchors, insufficient effective anchorage length, inadequate resistance of the concrete foundation surrounding the anchor, and lack of proper steel reinforcement surrounding the anchor. Anchorage failure typically occurred in conjunction with the diamond buckling shape failure of the steel tank walls. The steel tank walls buckled in two ways: (1) diamond shape buckling, and (2) “elephant foot” failure. The diamond shape buckling failure was more common in tall, slender tanks, whereas the “elephant foot” failure could be observed in the squat tanks that were full of liquid.

The damage that was observed during the Napa Valley Earthquake was mainly the diamond shape buckling failure of the stainless steel wall in conjunction with anchorage failure of the tanks to the concrete base and is shown in Figure 2.

Another common failure that was observed after the 2010 Maule Earthquake was failure at the connection of the piping to the tanks. This type of failure occurred when the tank shifted or rocked during the earthquake, and because of the racking of the piping system against the wall of the tanks during the earthquake. Both conditions were observed after the Napa Valley Earthquake as well. Buckling of tank

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walls at the top courses occurred during the Maule earthquake due to the suction effect when there was rapid loss of liquid inside of the tank. This did not occur in tanks without a roof, as no suction effect occurred. This type of observed damage could have been prevented if a relief valve had been present.

The 1977 San Juan earthquake was a magnitude 7.4 earthquake located 50 miles (80km) north-east of downtown San Juan.

The observed tank damage included buckling of steel tank walls and anchorage failure at the connection of the tanks to the concrete base.

All of the tanks examined demonstrated “elephant foot” tank wall bulging. This damage was observed at the first course from the bottom of the tank, or just above the joint from the first to the second course of the tank.

Anchorage failure was observed in all of the tanks as well. Rehabilitation efforts occurred after the earthquake for these anchorage failures, and this included strengthening of the existing anchorage system in addition to reducing the amount of liquid in each tank.

Four of the tanks having severe tank wall buckling fully collapsed during to the earthquake. In addition to the tank shell bulging, some of the tanks exhibited weld rupture at the joint of the bottom course with the angular plate used as part of the anchorage system.

This caused loss of liquid inside of the tank.

The tank damage observed during the 1977 San Juan earthquake is the same as the damage documented through the 2014 Napa Valley earthquake, as well as the 2010 Maule earthquake. Anchorage failure is a common type of damage observed in all of the previous earthquakes where reconnaissance teams examined the tanks. This type of failure was also documented by the news after the 2013 Marlborough earthquake in New Zealand.

“The tanks are bolted to the slabs with earthquake bolts and the bolts did what they were designed to do. They stretched, and in some cases broke, but that’s what they are design to do – they kept the tanks upright”.

– The National Business Review NZ Winegrowers chief executive Philip Gregan The anchor bolts are not meant to dissipate the energy from the earthquake, but rather prevent the tank from rocking off the foundation. The above quote demonstrates that the anchor bolts served their purpose during the earthquake, but with unintended damage. Previous research and developed analytical procedures would allow engineers to design tanks to prevent this behavior.

Anchorage failures occurred after the 2014 Napa Valley earthquake, mainly in tanks that were full. Figure 3 demonstrates some

(a)

(b)

Figure 3. Anchorage failure of fermentation tanks (a) corroded anchor used to attach flat bottom tank to concrete base, (b) anchor failure at edge of concrete base support.

examples of anchorage failures observed after the Napa Valley earthquake. Figure 3a shows a corroded anchor, Figure 3b shows an anchor that failed due to insufficient anchorage length and edge distance.

In addition to movement of legged tanks, buckling of the steel tank wall, and anchorage failures after the 2014 Napa Valley earthquake, there was also damage to the top of the steel tanks. This was not due to the suction effect as seen during the 2010 Maule earthquake, rather due to the pounding of catwalk systems against the tank walls. Figure 4 demonstrates an example of this pounding.

The catwalk in this portion of the warehouse had been removed because it was damaged; however, the denting of the tank at the top is seen.

The base shear and overturning moment have two components: convective, and impulsive. When the liquid inside of the tank moves in unison with the tank, the resulting stresses are the impulsive component. The sloshing of liquid inside of the tank against the tank walls causes the convective component. The impulsive component controls during the shorter periods, whereas the convective component controls during the long periods of seismic excitation. For a majority of tanks (0.3 < H/r < 3, where H is the liquid height within the tank and r is the tank radius), the first convective and first impulsive modes of vibration generally account for 85 to 98% of the total liquid mass in the tank. For tall tanks (H/r > 1), the remaining liquid mass vibrates at higher impulsive periods, and for squat tanks (H/r 1) the remaining liquid mass vibrates at higher convective periods.

The first simplified models developed took both the impulsive and convective dynamic contributions into account. However, the first models developed assumed only horizontal ground movement. This research determined there is a portion of the liquid in the tank that moves in a long period, while the remainder of the liquid moves rigidly with the tank walls.

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The liquid that moves with the tank wall (impulsive) moves with the same acceleration as the ground during an earthquake. The convective (translatory, sloshing) behavior is a result of the impulsive pressures. The impulse period is the major contributor to the base shear and overturning moment of the tank during an earthquake. However, these first models assumed the tank walls were rigid and did not deform during their own motion. This assumption caused unconservative base shear and overturning moment predictions using these simplified models.

Simplified models produced based upon the work performed by Housner and Jacobsen demonstrated the tank walls will deform and cause the impulse motion to be larger than originally determined. The flexibility of the tank walls can cause the impulsive motion to be greater than the ground acceleration.

These models have shown that the liquid inside the tank and the flexibility of the tank walls can amplify the base shear and overturning moments during an earthquake. In addition, the models have demonstrated that rigid or flexible foundations can significantly affect the dynamic response of these tanks.

These models have shown the maximum allowable compressive stresses reported in codes should be reevaluated to take into account vertical compressive forces and the combination of vertical compressive stress, hoop stress, and bending stress to prevent yielding of the tank walls.

These models were compared with experiments performed on cylindrical fluid-filled tanks. These tests highlighted the need for further investigation into anchorage design for anchored tanks during an earthquake, and thicker tank walls. The damage to the tanks observed during the experiments was consistent with damage viewed in previous earthquakes.

After the 2010 Maule Earthquake, the simplified method presented by Malhotra et al. [16] was used to determine the allowable stress for the damage steel tank walls [11]. The tanks that

were examined after the earthquake were used as examples, and calculations were performed to understand if allowable stress using a simplified model would have predicted failure in the tank walls. These results demonstrated that those tanks that exhibited tank wall buckling during the 2010 Maule Earthquake exceeded the allowable stress in the tank wall using the Malhotra et al. simplified model.

Analytical modeling on base isolation systems has progressed for the application to LNG tanks. These systems significantly reduce the seismic base shear and overturning moment of the tanks by 60 to 80% FEM modeling was compared with simplified methods with good agreement for preliminary design. These research projects highlight the need for similar projects for liquid-filled cylindrical tanks for the wine industry. LNG tanks are double-walled tanks with the outside wall typically post-tensioned concrete, as compared to the single-walled steel tanks used in the wine industry.

While the simplified methods of analysis provide tools for engineers to evaluate the base shear and overturning moments of fluid-filled cylindrical steel tanks during seismic events, these methods of analysis are for the elastic response analysis. Many vineyards are located in regions of strong ground motion (i.e. Chile,

Figure 4. Denting of steel tank due to pounding of tank against catwalk.

California, New Zealand). The forces obtained from the elastic response analysis are very large and reduced by factors up to 3 to obtain design forces for the tanks. Previous earthquakes and experimental research has demonstrated that fluid-filled cylindrical steel tanks will respond with non-linear behavior and sustain damage during a strong seismic event. However, there currently are no methods of analysis for nonlinear behavior of these tanks. Therefore it is very difficult to predict and quantify the damage that will be sustained by these tanks during an earthquake with strong ground shaking. The

engineering community has demonstrated the benefits of implementing relevant research results when applicable to LNG tanks and petroleum filled tanks. There is a great need for practical non-linear analysis methods for the design of fluid-filled cylindrical steel tanks.

This research needs to conform to the expected performance objectives of the vineyards.▪ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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12/23/14 3:50 PM

Structural DeSign design issues for structural engineers

Understanding Seismic Design through a Musical Analogy

By Ramon Gilsanz, P.E., S.E., F.SEI, M.ASCE and Petr Vancura Ramon Gilsanz, P.E., S.E., F.SEI, M.ASCE, of Gilsanz Murray Steficek LLP, has participated on several post-disaster investigative teams, travelling to Greece in February 2014, to Virginia in August 2011, and to Chile after the Maule earthquake of February 2010. Ramon may be reached at ramon.gilsanz@gmsllp.com.

Petr Vancura is Director of Communications with Gilsanz Murray Steficek LLP. Petr may be reached at petr.vancura@gmsllp.com.

Figure 1. Analogy: The ground exerts seismic forces upon a building following particular spectral acceleration, not unlike a musician playing an instrument according to a given score.

S

eismologists, earthquake engineers and seismic code experts understand the science of earth that moves and the structures built on it, but many of the concepts involved may be too abstract for architects, builders and the public.

This article offers an analogy to help explain seismic design and presents three different construction techniques used in Chile, Japan and the United States that counter an earthquake’s effects.

Earthquake  Music The ground exerts seismic forces upon a building following a particular spectral acceleration, like a musician playing an instrument according to a given score. In both cases, there are several elements that determine how energy is transferred, and describe how it is felt.

Earthquake  Music Soil  Musician Seismic Spectrum  Score Building  Instrument Building’s Response  Sound Building’s Occupants  Audience Event’s Social Context  Concert Hall

acceleration) and time (length of the piece). In the same way, ground-waves ”play” a building with varying frequency content, magnitude, acceleration and shaking duration. Both instrument and building either absorb or resonate the energies received based on their structure.

Different musicians play an instrument differently – musicians have different temperaments, hold their instruments differently and play with greater or lesser force. Different soils similarly “play” upon structures in varying ways.

Solid rock provides a strong foundation for a building. This dense medium also carries seismic energy at high speeds and over great distances. For example, granite, with densities generally ranging between 2.5 – 2.7 grams per cubic centimeters (g/cm3) or 155-170 pounds per cubic foot (lbs/ft3), carries compressive-dilating P-waves at up to 6,000 meters per second (m/s) or 19,700 feet per second (ft/s), and shearing S-waves at up to 3,300 m/s (10,800 ft/s) (Bourbié 1987). These speeds are a function of the material’s elastic properties: the incompressibility modulus (k) and the rigidity modulus (μ).

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

The musician engages her instrument just as the ground engages a building’s foundation (Figure 1). She plays her instrument based on a score composed of a variety of musical pitches (frequencies), dynamics (loudness), tempo (velocity/

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Figure 2. Liquefaction damage to New Zealand highways during the 2011 Christchurch Earthquake.

Courtesy of NZ Raw, 2011.

Figure 4. A ”composition” of waves over time.

Represented (from top) on east-west, north-south, up-down axes. Courtesy of Ota Kulhanek, 1990.

Figure 3. Soil liquefaction at Cherrapunji cemetery, 1897.

Sand, on the other hand, being far less dense at approximately 1.5 g/cm3 (95 lbs/ ft3) and having lower elastic moduli, may carry the P and S waves at only 400 and 100 m/s (1,300 and 300 ft/s) respectively. This medium will therefore quickly dissipate an earthquake’s momentum; but, at low densities and high water saturation, it is susceptible to “liquefaction” or displacement from beneath the building whereby, under certain vibrations, sandy soils act as a liquid (Figure 2). A first-hand account of the 1897 earthquake in Assam, India by Captain A. A. Howell illustrates this phenomenon: Several posts have sunk from a few inches to a foot deeper into the earth, causing the floor to buckle and the roof to sag.

Many, too, are out of the perpendicular.

At the point each post enters the ground, a cup-shaped depression, from one to six inches in depth and diameter, has been worn round it as though the post had been given a circular movement... Many houses sank into the ground bodily, the roof alone being visible... Several villages were, and still are, partly submerged (Oldham, 1899) (Figure 3).

Clay and silt act like a bowl of jelly, reverberating the seismic waves received from deeper and more rigid strata. The softer soil amplifies the shaking by a factor of four or more, depending on the wave frequency and the thickness of the layer of alluvium (Bolt, 1993). Subsequently, within the softer material, seismic energy may get trapped by reflection and refraction of these waves. This effect is similar to the trapping of sound waves in a concert hall where the sound energy echoes back and forth from the walls.

In such cases, the phase of each component wave is critical, since when waves are in phase, the energy is compounded.

Seismic Spectrum  Score A musical composition is defined by the loudness, pitch and tempo of its note, and can be represented graphically as a score. A specific earthquake can also be represented graphically – seismologists do this with seismograms, while engineers use spectral acceleration models.

An earthquake is defined by its magnitude (loudness or energy it releases), frequency content (pitch), and acceleration (tempo).

The waves of ground motion develop and change over distance as a result of geological properties and elasticities of the component soil materials, as well as the waves’ reflection and refraction. These waves reach the earth’s surface in different locations, at different times, then join together to produce a “composition” of P waves, S waves, Love waves, and Rayleigh waves that can be transcribed by seismographs (Figure 4).

Because P waves travel fastest of the four wave types, they arrive at a location prior

Types of Seismic Waves All elastic bodies, including geological media, carry two types of waves outward from the source of an impact – in this case, the epicenter of an earthquake. We identify these as primary (P waves) and secondary (S waves). P waves resonate through compression and dilation of (pushes and pulls within) the medium, the same way that sound waves travel through the air. Soils, unlike gasses or liquids, also transmit S waves that twist and shear the medium.

These waves move the particles of the material transversely (either vertically or horizontally) to the direction of the wave’s propagation. These motions are more similar to the behavior of light waves. P waves always travel faster than S waves.

When P and S waves reach the earth’s surface, or planar boundaries between geological strata, additional types of surface waves are generated. These waves behave comparably to sound that travels along the surface of a dome’s interior. Love waves are Figure 5. one type of S wave whereby surface particles shear only along the horizontal plane, perpendicular to the direction of propagation. Another type of surface wave is called Rayleigh, which causes surface particles to move forward, up, backward and down, in the direction of propagation, similar to ripples in a pond (Figure 5).

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to surface waves, which tend to be more destructive. P waves thus serve as a kind of early-warning system in advance of subsequent, more severe shaking. This resembles the traditional structure of a classical symphonic score – four movements, where the first, a fast-tempo Sonata Allegro, foretells what is to come.

Building  Instrument

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A musical instrument and a building both resonate, but while a musical instrument is designed to resonate music, a building is engineered to do the opposite – to stifle reverberation. The seismic engineer employs mathematical techniques to understand a structure’s “harmonics” with ground movements. Every building has its own natural frequency that depends on different factors, including its height and the lengths of structural members that comprise its frame. A xylophone’s resonators (the tube-like parts) each reverberate to their natural frequency, according to their length and stiffness in a similar way.

A building’s Seismic Response is the equivalent of an instrument’s signature sound. Some types of music naturally sound better on certain types of instruments. In the 1985 Mexico City Earthquake, the oscillation of the deepsoil lake bed caused significant damage to mid-rise concrete buildings having natural frequencies similar to the soil, whereas both stiffer and more flexible buildings were damaged less (Stone, 1987).

Apart from resonance, a musical instrument’s quality can be measured by three attributes: tonal range, ease by which pitches are carried through its body, and toughness, known as the modulus of resilience (Ur), which describes a material’s ability to absorb energy. These three attributes are also the focus of three different

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Figure 6. Concrete construction in Talca, Chile. Courtesy of GMS.

approaches engineers take to mitigate the impacts of an earthquake. The seismic engineer’s goal is to ensure that the “instrument” can resist an aggressive “player.”

Three Design Approaches Chilean seismic design practice focuses on strength with the goal of immediate re-occupancy. Buildings in Chile are designed with redundant shear walls so as to survive the quake. It is common for buildings in these seismic regions to have walls comprise 2% of the floor area (compared to only 0.5% in the US) (Figure 6 ). Masonry and concrete are brittle materials, yet have a high capacity to carry compression stresses. With proper reinforcement, they also possess the required tensile strength. For concrete and masonry structures, the shear strength must exceed the flexural strength to ensure that inelastic shear deformations do not occur because such deterioration of stiffness and strength could lead to failure (Paulay, 1992).

This strategy, however, significantly constrains architectural design and induces non-structural damage (of fixtures, egress, utilities) as the building moves rigidly with the movement of the earth; the building’s contents get severely shaken. In music, maracas have very strong, rigid shells. When shaken, the shell remains intact, but its internal pellets (contents within the maraca) are severely agitated.

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Alternative seismic design approaches contend that excessive strength is not essential, or even necessarily desirable, focusing less on “resistance” of large seismic forces, and more on the “evasion” of them.

Japanese seismic design practice effectively attempts to construct an “unplayable instrument” by disassociating the structure from the earth’s movements using base isolators.

Seismic isolation is a passive structural vibration control technology that lengthens a building’s fundamental period of vibration in order to dissipate, disperse and absorb dynamic loads. Base isolators are composed of structural elements that collectively decouple a superstructure from its substructure that rests on shaking ground (Figure 7, page 18).

These must provide both flexibility at the base of the structure in the horizontal direction and damping elements to restrict the amplitude. Additional flexibility, however, results in large relative displacement across the flexible mount. These displacements are controlled by introducing additional absorption at the isolation level. Mechanical energy dissipaters are used to provide rigidity under low lateral loads, such as wind, by virtue of their high initial elastic stiffness (Islam, 2011).

Many different types of isolator constructions exist, including elastomeric bearings, sliding bearings, springs, rollers and sleeved piles.

One drawback of this approach is its high development cost. continued on page 18

Figure 7. Building seismic base isolators. Courtesy of Wiki: Marshelec.

In our musical analogy, a flautist may exhale as hard as she likes, but the flute will not play a note if it is detached from her lips.

The United States looks to energy dissipation through plastic deformations of the structure as a more cost-effective approach toward minimizing loss of life due to collapse during an earthquake. Buildings are designed to remain intact enough to allow for safe egress, while at the same time fail at pre-determined weakened frame locations and allow for possible remediation.

Electrical musical instruments are similarly designed with fuses that will blow if overloaded rather than electrocute the player.

In steel structures, frames are proportioned and beam sections are locally weakened in such a way that the required plastic deformation of the frame may be accommodated through the development of plastic hinges at desired locations within the girder spans.

Beam-column connections are designed to force development of the plastic hinge away from the column face. When a sufficient number of plastic hinges develop, the entire frame can deform laterally in a plastic manner (Figure 8). This behavior significantly dissipates energy (FEMA-350). In wood-framed buildings, the energy dissipation is almost entirely due to nail bending.

The downside of this strategy is that, after a seismic event, the building is substantially damaged and the cost of repairing buckled or yielded structural members and connections may be on par with the cost of demolishing and replacing the structure.

Similarly, a cello is designed so that during fierce play, the strings (which are easy to replace) will dissipate energy by breaking, rather than failure of the instrument.

To put this damage into perspective, engineers forecast probabilities of failure during a Maximum Considered Earthquake (MCE).

Under these conditions, there is a 10% chance of collapse and 45% chance of damage to a

building. Therefore, 45% of the time, the building is expected to remain functional.

The probability of a seismic event occurring in excess of the MCE is only 2% in 50 years (FEMA P-695). However, “it really is the probability of structural failure with resultant casualties that is of concern, and the geographical distribution of that probability is not necessarily the same as the distribution of the probability of exceeding some ground motion,” (ATC 3-06).

The ASCE 7 seismic design provisions have therefore been amended to instead account for “risk-targeted” ground motion (MCER), representing (i) a 1% in 50-year probability of collapse, and (ii) a 10% risk of collapse given MCER occurring at a particular site. “The 1% in 50-year collapse risk objective is the result of integrating the hazard function (which is different for each site) and the derivative of the hypothetical collapse fragility defined by the 10% conditional probability” (NIST, 2012).

Building’s Occupants  Audience / Event’s Social Context  Concert Hall Different audience members may have different interpretations of the music, resulting in varying subsequent critiques of the same performance. The “intensity” of an earthquake, a qualitative concept, depends on its perceptibility (i.e. where and how the earthquake is felt), and its destructivity (i.e. what damage ensues). The Modified Mercalli Earthquake Intensity Scale is used in this regard to classify seismic activity into twelve classes ranging from “(1) Not felt except by a very few under especially favorable circumstances,” to “(12) Damage total; waves seen on the ground” (Krynine, 1957). The occupants of a building

Figure 8. Local weakening of the beam section at the desired location for plastic hinge formation.

Courtesy of GMS.

feel a seismic event and interpret it within the context of society the way that music is “felt” as an audience perceives it within a concert hall.

Such dichotomies in social context and public perception of earthquakes date back to the Enlightenment era. In his 1756 Poem on Natural Law, the philosopher Voltaire laments the devastation caused by the Lisbon earthquake of 1755, using the disaster as a vehicle to attack an erstwhile optimism (that by divine provenance, “whatever is, is right”) (Dynes 105). In response, Rousseau contends that disaster is a social construction, defined by existing cultural norms and that whether an event is considered a disaster depends on who is affected: You might have wished … that the quake had occurred in the middle of a wilderness rather than in Lisbon … but we do not speak of them, because they do not cause any harm to the Gentlemen of the cities, the only men of whom we take account.

Should it be … that nature ought to be subjected to our laws, and that in order to interdict an earthquake, we have only to build a city there? (Masters, 1992)

Figure 9. Post-earthquake conflagration in San Francisco, 1906.

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In the same correspondence, Rousseau suggests that we, ourselves, are the causes of our own problems.

Without departing from your subject of Lisbon, admit, for example, that nature did not construct twenty thousand houses of six to seven stories there, and that if the inhabitants of this great city had been more equally spread out and more lightly lodged, the damage would have been much less and perhaps of no account.

Rousseau’s discussion was perhaps the first attempt to conceptualize what is now known as “vulnerability.” From the Age of Enlightenment onward, modern disasters are usually considered primarily technological failures.

Conclusion In a symphony, there are many different instruments involved, some more critical than others depending on the musical piece.

For example, a composition might involve a trumpet solo, without which, the performance would seem empty and incomplete.

Each city, like a symphony, is different and each has its different components (like instruments), some more exposed than others (like solos within a composition).

Neither city nor orchestration functions as a sum of independent components, but rather as a complex, integrated system consisting of interdependent parts.

Individual buildings within an area are different; they are constructed differently and serve functions of varying importance to the city. Engineers focus on building performance in particular, but it is important to recognize that the buildings are only one part of a much larger system. While a building may be engineered as earthquake-resistant, society may incorrectly assume the structure is “earthquake-proof,” which it is not given the probabilities of damage described above.

Therefore, in addition to life-safety, to account for economic and functional consequences of a seismic event, a conceptual framework is being developed by the Applied Technology Council that defines two new hypothetical levels of earthquake intensity: risk-based functional level (FLER) and risk-based service level (SLER) ground motions (Kircher, ATC-84).

Life-safety, operational down-time (when the building cannot be used) and repair costs (to allow reoccupancy), though not always quantifiable, are at the forefront of an engineer’s priorities during the design of a building. However, structural damage is not the only effect of an earthquake. The wake

of an earthquake may carry with it tsunamis, fires, and risks to security, transportation, sanitation and, in some areas, nuclear hazards.

It has been estimated that structural failure resulted in only 3-5% of the 3,000+ deaths and $350M damage caused by San Francisco’s 1906 earthquake (Tobriner, 2006 ). A conflagration followed, lasting about three days, and destroying 2,831 acres. The property damage was estimated to be at least four-fifths of the property value of the city. Actual collapses during the earthquake were mainly confined to flimsy, framed structures (Reed, 1906 ).

In fact, a report by the National Board of Fire Underwriters from the year prior to the earthquake recognized the hazard: In view of the exceptionally large areas, great heights, numerous unprotected openings, highly combustible nature of the buildings, almost total lack of sprinklers... and comparatively narrow streets, the potential hazard is severe... In fact, San Francisco has violated all underwriting traditions and precedent by not burning up (NBFU, 1905) (Figure 9).▪ Special thanks to Verónica Cedillos, Dan Eschenasy and Ayse Hortacsu for their valuable insights on the subject.

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Structural FailureS investigating failures, along with their consequences and resolutions

I

n the wee hours of August 24, 2014 (3:20 am to be precise), most of the Bay Area was awakened by a 6.0 magnitude earthquake that lasted a lot longer than those sudden, one or two second jolts that happen from time to time and that residents have become accustomed to, if one can actually get used to such things. Most people probably thought, “Is this the big one?” When the ground shaking didn’t get any stronger and eventually stopped after 10 or 15 seconds, many thought “wow that was a big one, somewhere.” Those engineers with client responsibilities checked the USGS website to find out where “somewhere” actually was and then, if required, responded to the earthquake impacted area. Most people said a thankful prayer and rolled over and Figure 1. EQ response spectra (with assistance from PEER). went back to sleep.

As much as California engineers study and safe building and will survive future earthquakes. design for major earthquakes, most have never The highly variable nature of seismic ground personally experienced motions and the location of individual buildings a large earthquake since relative to the fault rupture location make this an they occur so infrequently. unrealistic expectation. Second: if a building is The largest earthquake in designed to the building code, it won’t be damNorthern California in aged. That simply isn’t true. recent memory was the 1989 Loma Prieta earthSeismic Ground Motions quake. That was 25 years ago – anyone younger than 35 probably has no This 6.0 magnitude earthquake, at least by significant memory of the event and the actual California standards, would be considered ground shaking. Depending on where one hap- moderate to strong and therefore the area of pened to be, the shaking might not have made strong ground shaking was somewhat smaller much of an impression since the epicenter was than one might think. The peak ground accelabout 80 miles from San Francisco and the eration was in the 0.3g to 0.4g range, with a damage, while very significant in total, was highly maximum (geometric mean) spectral accellocalized. Before Loma Prieta, the previous “large” eration of about 1g (Figure 1). A generation earthquake was in 1906. If you live in the Los ago, an earthquake of this size was the stanAngeles area, major earthquakes occurred in 1971 dard Uniform Building Code (UBC) “Zone and 1994, also a long time ago by most standards. 4” event. Today, this earthquake, in terms of The significant size of the South Napa earth- acceleration, is approximately 30% lower than quake gives a reason to re-learn valuable lessons the current design basis earthquake for Napa from the past that have been forgotten, and and much of coastal California, including the prepare for the next one by incorporating the inland portions of southern California, except best current knowledge. It is best not to rush to for areas very near active faults. So this event judgment and develop a host of conceptual code could be considered as a likely event throughout change provisions to address observed damage. It California and something we should be ready is better to let things settle out and reflect on the for almost anywhere and at any time. most significant issues that might require a change This earthquake and the damage it produced can in public policy, including the building code. also serve as a lesson for people living in other This article discusses the seismic ground motions parts of the country where an earthquake of this from the South Napa earthquake and its effect on size is much closer to the design basis earthquake select commercial, historic, residential and indus- for which new buildings are being designed using trial facilities. Reports suggest that the earthquake ASCE 7-10, Minimum Design Loads for Buildings caused about $400 million in property damages in and Other Structures. This would include extreme a small area with a population of about 137,000 coastal Oregon, coastal Washington including the (Napa County, 2010 census).

Seattle area, and the areas around New Madrid, There are two common misconceptions that Missouri and Charleston, South Carolina. In always seem to arise after an event of this nature these areas, a 6.0 magnitude earthquake will be a that should be dismissed. First: if a building sur- much less frequent occurrence than in California, vived undamaged in past earthquakes, it must be a but they will eventually occur.

Reflections on the 2014 South Napa Earthquake

By John A. Dal Pino, S.E.

John A. Dal Pino, S.E., is a Senior Principal at Degenkolb Engineers in San Francisco, CA, and a member of STRUCTURE’s Editorial Board. John may be reached at jdalpino@degenkolb.com.

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Figure 2. Damaged URM building.

Figure 3. Damaged, retrofitted URM building.

Historic Buildings Downtown Napa has a number of historic unreinforced masonry structures (URM) dating back to the late 1800s and early 1900s when commercial development of the area first occurred. URM buildings typically have brick or stone masonry exterior walls with wood framed floors and roofs. The ends of the floor and roof joists bear in pockets in the walls and derive their vertical support there.

In the oldest buildings, there was often no mechanical connection between the wood and the masonry, while in later vintage structures,

there are nominal steel anchor rods, often referred to as government anchors (as in “the government made me do it”) that connect the walls and floors/roofs. Past earthquakes, even moderate ones, have shown URM structures to be one of the most dangerous classes of buildings because they are prone to partial or total collapse. When the walls pull away from the floors, the floors fall and the walls crumble.

Like many other California communities, the City of Napa has a URM ordinance which it adopted in 2006. It gave property owners two years to survey and assess their buildings and develop a plan for mitigating the seismic ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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risk, albeit to a less prescriptive standard than for other existing buildings but with the same life-safety goal. Another year was allotted to perform the construction work. In theory, by 2009, the hazard posed by URMs should have been greatly reduced. Many buildings were retrofitted, but many were not because either the building owner lacked the financial resources or because they believed their building was safe despite what the experts said.

The spotty performance of URM buildings in the South Napa earthquake (Figure 2), even those buildings that had been retrofitted (Figure 3), reconfirmed perceptions

Figure 4. Toppled wine barrels.

about the hazards these buildings pose to the public. The earthquake damage showed that some of the un-strengthened buildings really did need to be strengthened, but it also showed that many buildings that had been strengthened sustained serious, life threatening damage.

In many communities, URM buildings showcase community history, provide a visual link to the past, and offer interesting architectural spaces for restaurants, shops, offices and the like. Since it is apparently almost impossible to fully eliminate all risks from URMs, communities need to reconsider what ought to be done with these buildings. Many are protected historical structures, so they can’t exactly tear them all down in the interest of seismic safety. The Napa experience would suggest that improvements need to be made in terms of safety, but that raising the standard too much will result in the strengthening becoming overly costly and visually destroying what makes URM buildings interesting in the first place.

An alternative is to publically acknowledge that even strengthened URMs are significantly more dangerous than most other buildings and leave it at that. While that might be the right policy for the risk from infrequent earthquakes, it may be one the public finds troubling given the serious lifesafety consequences.

steel) and stacked wooden barrels (Figure 4 ). Wine industry sources place the damage at approximately $80 million. Given the extreme weight of the stacked barrels, toppling barrels also caused significant damage to the structural framing in some lightframed buildings, and nearly created lateral and vertical instabilities that would have resulted in structural collapse.

It will be left to other observers to discuss whether the tanks were strong enough and whether they were anchored properly to prevent damage, and to opine as to whether it is prudent to stack wine barrels from floor to ceiling. The more interesting question is how does one address the seismic safety of an industrial facility where not everything can be braced or anchored?

A bit of background in winery operations: Once the wine is placed in the barrels for aging, the barrels need to be stored. To save floor

Industrial Buildings Napa is not an industrial town in the classic sense, but it does have a significant, world class agricultural wine industry, with all of the grape processing and wine storage and bottling infrastructure that goes with it. The wineries sustained a significant amount of damage to their wine storage tanks (mainly modern thin-walled stainless

Figure 5. Exterior wall separation/gap.

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space, they are stacked high and wineries fill up the entire warehouse with minimal wasted aisle space. But they also need to be accessed regularly for a year or two while the wine matures, after which the barrels are emptied and the wine placed in bottles for sale. During this two year handling period, the barrels are unstacked and restacked on a more or less continuous basis in a process of topping up to eliminate unwanted air space, and rotating to shift the sediments. Getting to the barrels in the back means one needs to move the barrels in the front first (kind of like retrieving something from the back of your closet). It is not practical to anchor the barrels down as one would do with a fixed piece of equipment or a tank.

Other industries face similar problems with stacked pallets of merchandise or raw materials. A tall stack represents an obvious seismic falling hazard to workers below, but since the materials are “on the move” so to speak, what can be done to improve safety?

Given the constraints, if there were a practical solution, the industry would already be doing it. There may be a better and safer way to stack the barrels, but even then, the risk probably can’t be completely eliminated since fixed anchorage isn’t really practical. How about an early warning system? Wouldn’t it be beneficial to know that an earthquake was about to occur, even with just a few seconds warning? This idea isn’t as far-fetched as it sounds. The Seismological Laboratory at the University of California, Berkeley and the San Francisco Bay Area Rapid Transit District (BART) are researching such an early warning system and received some positive indications about its effectiveness during the South Napa earthquake. BART received notification of

Figure 6. Residential cripple wall failure.

the earthquake moments before the ground motions reached their system 50 miles to the south. Had the BART trains been running (they weren’t at 3:20 am), train operators could have started to slow the trains to protect passengers. In a winery, 15 seconds warning would give the workers a chance to move to dedicated safe locations away from the greatest hazards near the barrel storage.

Another idea would be to prevent the ground shaking from getting to the stacked material in the first place. Base isolation has become an accepted, somewhat routine method for protecting high value property. In a warehouse environment, it would certainly be possible to create an isolated double slab with simple ball and cone isolators. This approach is used to protect data centers located in high seismic regions.

The similarity with the wine industry is that the computers in data centers need to move around, aren’t easily anchored and are susceptible to internal damage from intense shaking.

drift, resulting in damage to the connections that stabilize the wall and attach it to the steel structure (Figure 5).

Besides the damage, the more important issue is the design coordination of the architectural and structural systems, whether designed by the architect or by a third-party specialty structural engineer working for the contractor. In California, cladding receives extensive review and scrutiny by the State on hospital projects, but less so on commercial buildings, where the responsibility for proper design and construction rests almost exclusively with the design professionals. In the interest of public safety, clear and continuous communication and coordination is required between all parties, with each taking responsibility for their assigned roles and tasks. It is critical that the parties resist the temptation to limit their involvement in the process, thereby shifting design responsibility to others.

Residential Buildings

Commercial Buildings Most of the commercial buildings, except the historic masonry structures and some other older buildings, performed reasonably well. This should not be surprising, since the ground motions were lower than those of the current building code design basis earthquake.

One of the more interesting damage observations, from an AE industry perspective, involved the incompatibility between the lateral movement of the structure and the non-structural cladding in a modern threestory steel frame building. In this building, the cladding consisted of a balloon-framed metal stud and stucco exterior wall. The structure laterally deflected more than the stiff cladding and the cladding connections could tolerate, due to the lack of horizontal seismic jointing to accommodate inter-story

The observed damage was similar to that seen in past earthquakes. Older homes fall off their foundations (Figure 6 ), masonry chimneys fall over or suffer significant damage, and internal contents fall. For engineers, there was no mystery about what was going to happen.

What engineers ought to be doing is figuring out how to prevent the damage in the first place, given the importance of a safe, dependable housing stock.

Wood frame homes, except those founded on a concrete slab-on-grade, are classic soft-story buildings with rigid superstructures above open crawl spaces. The retrofit techniques necessary are well known and widely available.

The Association of Bay Area Governments (ABAG) has a wonderful collection of information for homeowners, and their engineer and contractor, to use.

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March 2015

The real question is why haven’t more homes been retrofitted? Is it apathy, ignorance of the issue, or a lack of financing?

Probably some combination of the three.

What is needed is a financing program, coupled with incentives and education. The City of Berkeley has a model program that helps homeowners finance the purchase and installation of rooftop solar panels, repaid through their property taxes. In California, many homeowners are house rich and cash poor, so this approach to earthquake retrofit seems like an avenue communities ought to explore.

One of the more significant, and avoidable, reported injuries in the earthquake was to a teenager who was hurt while sleeping in front of the living room fire place when the facia stone fell on him. Masonry chimneys, given their significant mass, are not really compatible with wood frame construction.

Is the house anchored to the chimney or is the chimney anchored to the house? The best approach to protecting life safety is to eliminate the hazard in the first place. Newer homes don’t have brick chimneys, but rather metal fire boxes and stainless steel flues in wood framed enclosures. Masonry chimneys ought to be demolished and replaced in older homes.

News reports indicated that, surprisingly, most of the residential injuries were cuts from broken glass. Not from windows, but from glassware on the floor, mainly in the kitchen. People were awakened by the earthquake, got up in a dark house (the electricity was out) and walked into the kitchen to see what had happened. They stepped on broken glass and cut their feet, resulting in many emergency room visits.

Just like the stacked wine barrels, it is not practical to anchor plates and glassware that are used daily. Let’s face it, some risks need to be accepted, but having a flashlight and a pair of shoes or slippers available before investigating in the dark is a lesson worth learning.

Summary The South Napa Earthquake provided a valuable reminder to engineers and the public of what they should expect from time to time when they live in earthquake country.

The same could be said for the tornados in the midwest and south, and hurricanes in the southeast coastal areas. These events are going to happen regularly. There is no denying that. Resilience and readiness is superior to response and repair. So we might as well get prepared for them!▪

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wo major earthquakes hit the Cephalonia Island of Greece on January 26th and February 3rd of 2014, with magnitudes of M = 6.0 and 6.1. For comparison, the recent South Napa earthquake of August 24, 2014 had M = 6.0 (EERI, 2014) and the Northridge earthquake of 1994, which has been used in development of seismic codes, had M = 6.7 (NCEER, 1994). An extensive United States (U.S.) reconnaissance mission was mobilized as a collaborative effort of the Geotechnical Extreme Events Reconnaissance (GEER) Association (supported by the National Science Foundation), the Earthquake Engineering Research Institute (EERI) and the Applied Technology Council (ATC). The U.S. reconnaissance team worked together with the Greek earthquake engineering community in a multidisciplinary international team. The GEER/EERI/ATC issued a report of their findings in 2014 and their authors’ input to this article is gratefully recognized.

The reconnaissance team documented the postearthquake condition of several two and three story reinforced concrete (RC) structures that were designed according to the local seismic code.

These structures are located in close proximity, some as close as 150 feet (50 m), to strong motion accelerometer stations that recorded some of the strongest sequences of ground motions known in Europe. The documentation includes photographs, observations, and as-built drawings with design calculations. These structures exhibited surprisingly good structural behavior for the level of shaking they experienced, which changed the focus to observations of resilient structural performance instead of failures, as is usually done in other earthquake studies. This paved the way to a new generation of reconnaissance.

This article attempts to explain the resilient behavior of the local type of construction that (a)

sustained significantly higher accelerations than their design accelerations with minimal structural damage, some non-structural effects, and no loss of life or significant injuries. One of the documented RC structures was modeled and analyzed using actual recorded ground motions. The results provide some hypotheses of the factors that may have contributed to the observed behavior, which will hopefully enhance our understanding of seismic resiliency of short RC buildings.

Structural Performance performance issues relative to extreme events

Seismic Background and 2014 Events Cephalonia is located in the Ionian Sea at western Greece, on one of the most tectonically active features of Europe: the Hellenic Trench, with ongoing subduction of the African Plate beneath the Aegean Sea and Eurasian Plates (Figure 1). In addition, the island is crisscrossed in different directions by various types of faults (normal, reverse and strike-slip).

Due to its tectonic environment, Cephalonia has a remarkable seismic history which can be traced back to antiquity, with documentation of the strongest historical events since the 15th century AD available in a book by Papazachos & Papazachou (2003).

In recent history, the sequence of destructive shocks of 1953 is of significant importance, as it led to the development of the first Greek Seismic Code in 1959. The largest event had a magnitude M = 7.2 and caused serious damage in all of the Ionian islands with complete destruction of Cephalonia, Zante and Ithaca, including collapse of 27,659 out of 33,300 houses and 455 fatalities. continued on next page (b)

Learning from Structural Success rather than Failures

Figure 1. (a) Location of Cephalonia Island of Greece. Hellenic Trench tectonic feature of the Mediterranean Sea (Papaoioannou et al., 2006); (b) Epicenters of 1st M6.0, 1/26/14 event (green star) and 2 nd M6.1, 2/3/14 event (red star). Squares show selected EPPO-ITSAK strong motion stations.

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By Sissy Nikolaou, Ph.D., P.E., Ramon Gilsanz, P.E., S.E., F.SEI, Dimitrios Iliadelis, P.E., Menzer Pehlivan, Ph.D., Akbar Mahvashmohammadi, Sanaz Saadat, Ph.D., Marina Moretti, Ph.D., Anastasios Sextos, Ph.D. and Panos Tsopelas, Ph.D.

Sissy Nikolaou, Ph.D., P.E., is senior associate of Mueser Rutledge Consulting Engineers (MRCE) in New York City (NYC). She is President of the NY-NE Chapter of EERI, advisory member of GEER and leader of the reconnaissance mission for this article. Dr. Nikolaou may be reached at snikolaou@mrce.com.

Ramon Gilsanz, P.E., S.E., F.SEI, is a founder of Gilsanz Murray Steficek (GMS). Mr. Gilsanz has participated on several post-disaster investigative including the NYC building assessments post-hurricane Sandy and post 9-11, including the WTC7 collapse analysis.

Mr. Gilsanz may be reached at ramon.gilsanz@gmsllp.com.

Figure 2. Comparison of response spectra for rock, stiff, and soft soil conditions for: Cephalonia Island, Greece based on EC-8 (black lines) and Portland, Oregon based on MCE of IBC-2009 (blue lines). Both cities have equivalent rock short period acceleration Ss = 0.9 g (or PGA = 0.36 g).

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A similar sequential pattern was repeated in 2014 with two main events on January 26 (M = 6.0) and February 3 (M = 6.1).

Buildings in the epicentral region experienced Peak Ground Accelerations (PGA) up to 0.75g and Spectral Accelerations (SA) around 2.5g short structural periods (T) between 0.2 and 0.3 seconds. Most of the structural damage occurred during the second event in the Paliki peninsula, Figure 1b (page 25), since many structures had already suffered damage during the first event. Strong motion station locations and their recordings were available by the Institute of Engineering Seismology & Earthquake Engineering (EPPO-ITSAK, 2014) and the National Observatory of Athens, Institute of Geodynamics (NOA-IG, 2014). Stations at the capital, Argostoli (ARG2), and towns of Lixouri (LXR1), Chavriata (CHV1), and Aghia Thekli (AGT1) by EPPO-ITSAK are shown in Figure 1b.

Figure 3. Comparison of elastic code (EC-8 and EAK) response spectra for various ground types with spectra of recorded motions from the 2 nd event.

Design Codes and Recorded Motions The first Greek seismic code of 1959 was supplemented in 1985, and a next generation of seismic codes took effect in 1995. This code was modified in 2000 to include the European pre-Standard – ENV provisions (predecessor of Eurocode), and was finalized with the name EAK (Greek Seismic Code). In 2012, the provisions of Eurocode (EC-8) were enforced in conjunction with the occasionally more stringent EAK. Based on the EC-8 code, Cephalonia falls on the highest seismic zone of Europe, with a PGA of 0.36 g on rock. Figure 2 presents EC-8 code spectra for different site conditions, generally constructed in a similar manner to the International Building Code (IBC).

A U.S. city with an equivalent seismicity to Cephalonia is Portland, Oregon with a Maximum Considered Earthquake (MCE) PGA = 0.36 g or a short-period Spectral Acceleration of Ss = 0.9 g in rock class B (IBC2009, based on the American Society of Civil Engineers’ ASCE 7-05). For comparison of EC-8 and IBC-2009 based code spectra, MCE Spectral Acceleration values for rock, stiff soils, and soft soils are shown in Figure 2 for the two cities. Generally, the SA values are similar between the two codes except for soft soils where the EC-8 code is significantly more conservative than the IBC equivalent around structural periods shorter than 0.8 seconds.

Ground Motion Recordings The second event produced the highest ground motions, shown as acceleration response spectra compared to EC-8 code’s STRUCTURE magazine

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elastic spectra in Figure 3. The high ground motion amplitudes can be partially attributed to local site effects, directivity of shaking, and the pronounced irregular topography throughout the island.

Recorded SA values generally far exceeded code-based values, especially between periods ranging from 0.2 to 0.3 seconds, which correspond to the empirically expected period range of the majority of the building stock for two and three story RC buildings. These recorded SA values peaked at 3 g in the town of Chavriata and 1.5 g in the town of Lixouri, exceeding the maximum elastic code values by a factor of 1.25 to 2.5. Depending on the design Response Modification Factor (R), the recorded SAs could have resulted in actual seismic loads higher than the design values by an astounding factor of 2.5 to up to 8.5 (for R between 2 and 3.5).

Structural Observations Overall, the building stock of Cephalonia is relatively new since most of the island was rebuilt after the 1953 events to meet the 1959 and later seismic codes. The close-knit family social structure of Cephalonia has created a tradition of building and expanding homes over the span of many decades. Several generations of a single family typically live together in the same house, which they expand vertically and laterally as their families grow.

This results in buildings that have portions built decades apart under different codes and structural systems.

The predominant (residential and commercial) building type is well constructed, up to three stories in height, with a mix of continued on page 28

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b) The reconnaissance information included design documentation and visual inspections. The owner provided us with design drawings and calculations that had been submitted to the local Department of Buildings, as it is a tradition for Greek owners to keep copies of these documents. c) Acceleration time histories were available for analysis.

Modeling Figure 4. Typical confined masonry construction in Greece, with the infill masonry having concrete beams around openings, dowelled into the concrete structure (left). Characteristics of typical hollow clay bricks used for infill (right), after Xalkis Bricks (2015).

reinforced concrete, masonry infill, and wood roofs. The infill masonry has concrete beams around openings, dowelled into the concrete structure. Hollow clay bricks in one or two vertical rows, with insulation material in between, are used for infill. A typical construction example and properties of a typical hollow brick are given in Figure 4.

This practice is different from typical confined masonry (Meli, 2011) or regular infill masonry construction, as it is lighter due to the holes in the infill bricks and stiffer due to the thick RC structural frame. These low rise buildings behaved well during the 2014 earthquakes, at the most, suffering minor damage at the brick infill walls, which, in some cases, were separated from the RC frame. Most of the significant structural damage occurred in older masonry buildings that did not have this type of construction (GEER/EERI/ATC, 2014).

the town of Chavriata, which recorded very high accelerations (Figure 3). Shown in Figure 5, the ground floor of the structure is a coffee shop and the rest has residential occupancy.

This structure was chosen because: a) Its behavior was good despite its close proximity to CHV1. No major damage was identified other than some bottles falling off the shelves and some dislocated clay roof tiles, which is indicative of minimal or non-existent nonlinear behavior.

The geometry of the Havdata structure, approximately 23 feet x 23 feet (7 m x 7 m) in plan, was approximated based on available drawings and photographs. However, the design documentation that was provided was found to be incomplete. Assumptions were made for the thickness of the concrete beams, and the strength and composition of the infill. The assumed member sizes, floor and roof dead loads and seismic weight, calculated per ASCE 7, are given in Table 1. The live load was taken as 40 psf (2 kPa) and 20 psf (1 kPa) for the floors and roof, respectively. The seismic weight includes dead load and perimeter wall loads. The perimeter walls were assumed to be a layer of thick hollow bricks with properties indicated in Tables 1 and 2. The bricks are 2.5 inches x 5 inches x

Case Study of Reinforced Concrete Havdata Building A two (to three) story RC structure in the town of Havdata next to an old masonry structure that completely collapsed was selected as the case study. The building was built in 1995 in accordance with the EAK code. It is located about 1.2 miles (2 km) north of the strong motion station CHV1 in

Figure 5. Havdata structure located 1.2 miles (2 km) north of CHV1 station sustained no significant structural damage while masonry building next to it collapsed completely. Copies of design drawings (right).

Table 1. Member sizes, loads, and seismic mass parameters used in modeling.

Member Concrete Slab

Section (inch) 4

Dead Load (DL) Floor

(psf )

Roof

Seismic Weight (psf )

Floor

(kips)

Concrete Slab

50

Wood Frame

15

1

86.5

Beam

12 x 16

Beam

35

Clay tile

10

2

82

Column

40 x 12

Column

43

Insulation

8.5

3

18

2.5 x 5 x 7.5

FaÇade

25

Total, Roof DL

33.5

Floor finish

5

Hollow brick wall

Total, Floor DL STRUCTURE magazine

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Table 2. Structural dynamic analyses. Varying parameters assumptions and summary of results.

CaSe

Input Ground Motion

1 2 3 4

Rock from deconvolution

5

8 9

Thickness tw (inch) 1.58 3.15

Elastic Modulus Ew (ksi) 1,000

Surface recorded at CHV1

10

1.58 3.15

Structural Period (seconds)

Maximum Roof Displacement

1st Mode 2nd Mode X-X T1 T2 X (inch) 0.14

0.10

-0.20

1st Story Drift

Sheer Stress

Y-Y Y (inch)

X-X ∆ X (inch)

Y-Y ∆Y (inch)

1st story walls, average τ (psi)

-0.09

0.10

0.04

200

3,000

0.10

0.07

-0.08

0.03

0.04

0.01

190

1,000

0.11

0.08

-0.11

0.04

0.06

0.02

100

3,000

0.08

0.05

-0.04

0.02

0.02

0.01

100

0.31

0.26

-1.48

1.16

0.56

0.51

–

1,000

0.14

0.10

-0.33

-0.14

0.16

0.06

310

3,000

0.10

0.07

-0.12

0.05

0.06

0.02

290

No Wall

6 7

Infill Wall Parameters

1,000

0.11

0.08

-0.19

0.06

0.10

0.03

160

3,000

0.08

0.05

-0.06

0.04

0.03

0.01

160

0.31

0.26

-2.58

2.06

0.98

0.90

–

No Wall

7.5 inches (60 mm x 120 mm x 190 mm) with a weight of 3 pounds (1.3 kg) for each brick. An effective thickness of 1.58 inches (40 mm) was assumed and the wall dead load over the façade area was taken equal to 20 psf (1 kPa). Based on the above information, a linear elastic finite element 3-D SAP2000 model was created, as shown in Figure 6a. For modeling, the beams were connected to the center of the columns and a rigid body diaphragm was assigned to nodes at each floor. The infill walls were modeled as shell elements.

(a)

(b)

Input Ground Motions The recorded ground motions from the CHV1 station during the second event were used for the dynamic time history analyses. These motions were recorded on reported stiff soil conditions and depict spectral accelerations that reach 2.4 to 2.7 g in both horizontal directions for short structural periods (less than 0.4 s). In addition to the soil-recorded motions and considering the overall geology around the Havdata house, bedrock ground motions were derived to examine the response to direct bedrock input. The derivation was made by filtering out the soil effects in the CHV1 records using a linear elastic deconvolution, which is an analytical procedure that produces a rock outcrop motion based on recorded ground surface motion. For the soil properties, the generalized sedimentary profile of interchangeable layers of weathered marls, limestone, and sandstone were used, presented in the 2014 GEER/EERI/ ATC report for this area.

Specifically, the deconvolution analysis was performed for a 230-foot (70-meter) thick soil column having a linearly increasing shear wave velocity with a mean value of 1,500 ft/s (500 m/s). The resulting rock motions were found to

Figure 6. (a) Finite element linear elastic model of Havdata structure. (b) Distribution of maximum shear stress in infill walls (psi).

be lower by an approximate factor of 2 in the short period range (0.2 and 0.4 seconds). Figure 7 (page 30) summarizes deconvolution analysis and plots the predicted rock motions. Both rock and surface motions were rotated to the two orthogonal X-X and Y-Y directions of the building, for use as input in the structural model, assuming the X-X structural model axis has an angle of 45o with the North-South direction.

Dynamic Analyses In an effort to simulate the observed behavior, the team performed five analyses varying the effective element thickness tw and the modulus of elasticity Ew of the infill walls. Specifically, the five sets of parameters used are: 1) tw = 1.58 inches (40 mm), Ew = 1,000 kips per square inch (ksi) (7,000 MPa)

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2) tw = 1.58 inches (40 mm), Ew = 3,000 ksi (21,000 MPa) 3) tw = 3.15 inches (80 mm), Ew = 1,000 ksi (7,000 MPa) 4) tw = 3.15 inches (80 mm), Ew = 3,000 ksi (21, MPa) 5) No infill wall in the model The results are summarized in Table 2, where Cases 1 to 5 were analyzed with the reduced rock motions and Cases 6 to 10 were analyzed with the recorded surface motions. The first (T1) and second (T2) structural modes of the building range from 0.08 to 0.14 seconds and 0.05 to 0.1 seconds, respectively. When the infill wall was removed from the model, the periods elongated accordingly to 0.31 and 0.26 seconds. The maxima of roof displacement, first story drift, and average shear stresses

along the first story walls are also shown on Table 2, with plots of shear stresses in the model plotted on Figure 6b (page 29).

Analyses considering thicker, heavier walls did not produce results significantly different than those in Table 2.

These preliminary results show that the building is stiff with short periods, and therefore, it shakes like a rigid body with small drift, which agree with the observations. While the results are reduced when the rock motions are applied instead of the soil motions, the stresses in the brick walls with clay units still exceeded the allowable levels, which are between 50 psi and 100 psi (International Masonry Institute, 1998) under both applied motions. Since no damage in the infill was observed, additional investigations on the infill material, the concrete construction, and a better understanding of the in-situ subsurface conditions and topography are needed to successfully replicate the observed behavior.

Conclusions

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– A sequence of strong earthquakes during January and February of 2014 in Cephalonia, Greece produced some of the highest ground motions ever recorded in Europe, reaching 2.5 g in the short period range between 0.2 and 0.3 seconds. Details are presented in GEER/EERI/ATC (2014).

– The typical modern local construction method is a modified confined lightweight masonry system with reinforced concrete moment frames, brick infill walls with hollow clay tiles, and roofs with wood frames. These short (two and three story) structures behaved essentially elastic with no serious visible structural damage and reacted more like rigid bodies with very short periods. The stiffening effect made the structures

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Figure 7. Ground motions at: (i) ground surface as recorded in the CHV1 station at the 2nd event (top) and (ii) rock at the Havdata building site (bottom), following deconvolution analysis of the generalized profile (left).

experience the peak ground acceleration, which was 70% smaller than the spectral accelerations in short periods.

– A case of a non-damaged structure in close proximity to a strong motion station was selected for analysis. Since no damage was observed, a linear dynamic time history analysis method was selected. Modeling was feasible since the team had visually inspected the structure, and obtained partial design and drawing documentation. To simulate local site conditions, the available recorded time histories were deconvoluted from the ground surface to the structure’s bedrock using a generalized soil profile.

– The analyses were varied parametrically to account for the uncertainty in the elastic modulus and the effective thickness of the infill wall. Results demonstrated very low periods of about 0.1 second and confirmed the observations that inferred small drifts and displacements during the events. The model predicted shear stresses in the infill material which would have caused damage that was not observed. Hence, this type of robust construction behaved better than expected.

– The Greek method of confined masonry is an inexpensive way for building RC structures with only 20% of the overall construction cost attributed to the structure.

The observed and well documented good behavior of several structures of Cephalonia should be studied further, including pertinent testing of the infill material and its interaction with the RC frame, and in-situ testing to better define the site-specific ground motions. This method may be beneficial in other countries of high seismicity

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March 2015

and similar weather. This design approach of shortening the structural period should ensure that the structure does not move in the inelastic range, which would elongate its period and attract significantly higher seismic forces.

In closing, the 2014 Cephalonia events allowed the reconnaissance team to focus on collecting data of resilient performance in addition to failures, paving the way to a new generation of reconnaissance that will hopefully lead to better understanding of resiliency after strong earthquakes.▪ The author’s gratefully acknowledge the support of GEER and NSF, EERI, and ATC for the reconnaissance mission to Cephalonia and the contribution of our Greek and U.S. collaborators that co-authored the GEER/EERI/ATC (2014) report.

The online version of this article contains detailed references and bios for the additional authors. Please visit www.STRUCTURemag.org.

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N

ear the flagship Hell Gate Bridge (STRUCTURE, October 2013), and crossing a former inlet between Wards and Randalls Islands, stands Gustav Lindenthal’s still-in-service 1915 Little Hell Gate Bridge; four unique skewed-deck truss spans of reverse parabolic bowstring arches. They are visually striking, sited as they are above flat land and below miles of high plate-girder viaducts. The total length between centers of the abutments is 1153.5 feet. Four-rail tracks operate on the 60-foot wide deck (Figure 1).

The War Department at that time regulated waterways and, as this arm of the East River was only a few feet deep and would not carry maritime traffic, it granted approvals in 1906 and 1912 for piers in the inlet and the use of falsework for the construction.

Later, landfill from the Triborough Bridge project (Ammann, 1937) entirely filled the inlet.

Timber and Masonry for the Piers The Portland cement concrete piers bear at four tons per square foot on foundations of hard strata, typically mica schist, encountered at a shallow depth of about 12-15 feet below mean low water. Henry Seaman, consulting engineer for the masonry on the project, described the process of the foundation and pier construction. Executed by the McClintic-Marshall Construction Company, piles were first driven into the river bottom to support the timber falsework of square posts and longitudinal bracing members.

Next, for the piers near Little Hell Gate, heavy-timber crib open-cofferdams were built, and the area within leveled and dried. Concrete for the foundation of the piers was poured into forms set within the dams.

Granite veneer covers the 12 vertical feet between mean high and low tide levels to protect the concrete piers from wear due to rapid current. The timber for the trestle, posts, and longitudinal bracing of the falsework was longleaf yellow pine.

And a great deal of it. The project used 360,000 board feet of heavy timber for falsework construction for each span. In discussions after completion of the project, some engineers suggested that floating the truss arches into place might have been more economical and efficient.

Historic structures significant structures of the past

Figure 1. Flanked by viaduct spans, the century-old, still in service, distinctive Little Hell Gate Bridge reverse bowstring arch-spans suspend; with the Hell Gate and Triborough Bridges beyond. HAER NY 12116, Weinstein, Photographer, 1996.

Formwork consisted of two-inch thick, shiplap timber sheeting under four by eight-inch studs, held with wales and then bolted end-toend for tensioning against leakage. The river pier shaft forms were barrel-hooped.

On Randalls Island, concrete was mixed on-site in a hopper below ground level to facilitate measuring, placed from derricks on platforms into buckets, and then transferred to the site; but on Wards Island, the concrete was placed by the relatively new practice of chuting.

The concrete was conveyed to hoisting buckets up to a guy wire-supported 215-foot high, freestanding timber tower – the highest erected to date – and chuted to the end point. The completed piers are slightly battered at 1:15 and are 110 feet above mean high water, with 25-foot diameters at the water line.

The piers have horizontal and vertical steel reinforcing, at the time a comparatively recent and internationally little-understood technology, still based largely on trial and error. After 1900, several universities, the American Society of Civil Engineers, the Bureau of Standards, and the American Railway Engineering and Maintenance of Way (AREMA), among others, combined efforts to share the many emerging independent scientific laboratory analyses’

Gustav Lindenthal’s Little Hell Gate Rail Bridge

Figure 2. Lindenthal office drawing, Little Hell Gate Bridge, plan and elevation. The center skewed piers originally aligned with the inlet current. Two tracks load each truss. Transactions of ASCE, v. 82: 1918.

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New York City

By Alice Oviatt-Lawrence

Alice Oviatt-Lawrence is principal of Preservation Enterprises, an international architectural-engineering research and historic-building analysis organization. She serves on the SEAoNY Publications Committee and may be reached at StrucBridge@aol.co.uk.

Figure 3. Lindenthal office detail, transverse section drawing. Sway-frames transfer lateral loads from the bottom chord via stiff diagonals to a heavy & rigid lateral system in plane with the top chord truss. Transactions of ASCE, v. 82: 1918.

methods and test results, to understand and standardize the structural properties of bonded steel bars and concrete.

equilibrium, being 15 feet below the support points of the abutments and piers, contributes to the overall stability and rigidity of the structure under dead and live loading.

There are fixed bearings in the end spans at the abutments, whereas the center three skewed piers have moveable 24-inch high cast steel rocker bearings as reactions to onesided loading. At the center pier, there is an expansion joint of about six inches. Secondary stresses are relatively large in the end panels.

McClintic-Marshall Construction Co. also handled the manufacturing and erection of all the steel for the trusses. Steel gantry travelers erected 11,250 tons of steel. Bents supported the material track at the top chord level, from which the truss members were lifted from below the track by the traveler.

After the bottom chords were assembled and laid on adjustable camber blocking, the posts, diagonals and top chords were set in-place by gantry traveler. Total costs of the project were $990,000 (Figure 5).

The Floor

The Superstructure The lightweight, simple, riveted web trusses are of lightweight Class A open-hearth structural steel. The reverse bow-string (under) deck trusses are constructed of 50-foot high parabolic and parallel arches, set 52 feet apart.

The bottom tension chord is comprised of between ten to thirteen pinned eye-bars – the largest size forged to date, each at 38 feet long, 16 inches wide by about two inches thick, and connected by 16 inch-diameter pins tightly covered with cast-iron caps. Twenty-one of the 1,900 tons of annealed structural steel full-size eye-bars were tested before construction, with results of an average elastic limit of 36,500 pounds per square inch (psi) and an ultimate tensile strength of 61,800 psi.

The truss structural steel is slightly higher at 66,000 psi, and has a yield point of 35,000 psi (Figures 2, page 34 and 3).

There are no transverse supports at the bottom chords. Instead, stiff diagonal sway frames connected to each vertical web member angle up from the bottom chord, transferring wind loads up to a rigid and extraheavy wind and vibration truss in plane with the top chord (Figure 4). The angles and joints connecting the uniform-sized truss members of the reverse bowstring arches are geometrically aligned, so as to equalize and distribute the dead loads.

The partially shaded below-deck truss arches experience less equally-distributed exposure to thermal expansion and contraction than would above-deck metal arches. The center of

For the track floor, a timber floor of treated ties and a reinforced flat slab design were each initially considered, then rejected; for the first, due to the high contemporary cost of timber, and for the latter due to the design team’s cautiousness in depending upon reinforcement to any great extent to resist an assumed axle loading of 70,000 psi plus a 200 percent impact. While the aforementioned

Figure 4. The Buttressed Barrel-Vault Arch at end pier 53, view to the north. The round river-piers and reverse arch spans stand and suspend beyond.

Stiff steel sway frame diagonals provide lateral bracing. Concrete cracks, and white alkaliaggregate reaction deposits are active. Many tree roots stress shallow foundations.

standardization studies were ongoing, there remained some distrust, specifically in the reliability and durability of the bonding between the steel and concrete to resist the stresses.

Instead, the floor is a solid ballasted type.

A skeleton framework of eight-inch I-beams spaced at fifteen inches on center are placed across two stringers laid over one-eighth inch thick steel sheets per track. Five-eighths

Figure 5. Detail, Little Hell Gate Reverse Bowstring Truss Bridge, 1915. Lower tension chord of eye-bars, with a view up to the deck, illustrating an array of structural steel truss members. Except for the eye-bars’ 16-inch diameter pins, the bridge is riveted to exacting specifications, at the high cost of 25 cents each.

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inch tie-rods, spaced ten inches apart, are fixed near the bottom of the I-beams. Three inches below the top, more reinforcing bars are placed longitudinally within the ten-inch thick concrete-encasement, or ballast-surrounded “tray”, poured flush to the bottom surface of the framework. There are embedded four-inch diameter vertically-aligned drain pipes. A two-inch thick timber plank walkway rests on the ends of the I-beams, between each track. The concrete is smooth troweled – one part Portland cement, two parts well-graded sand, and four parts of broken limestone (75 percent three-quarter inch stone and 25 percent screened as per the 1911 AREMA guidelines). Tests in 1915 revealed a compressive strength of 3,500 psi at 28 days. There is a less than 1.8 in 12 transverse slope, with no waterproofing materials.

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The three circular-in-section, skewed doublecolumn river piers positioned between the squared abutment end piers are oriented longitudinally parallel to the inlet water flow, spaced about 296.5 feet apart. As the average spacing of all the other piers in the several miles-long viaduct spans are mostly in the 80+ foot range, the contrasting, large increase in spacing of the Little Hell Gate Bridge spans draws direct visual attention to the unique bridge. In addition, Lindenthal included simple end towers to further highlight the bridge.

Gustav Lindenthal considered the Little Hell Gate Bridge significant. The design elements, for example, of repeating various arch schemes throughout the project’s length, punctuated at nodes by outstanding bridges that made advancements in engineering, express aesthetic sensitivity along with structural purpose. Lindenthal intended his bridges to contrast with the many ubiquitous utilitarian truss rail bridges. The end towers, by architect Henry Hornbostel, are hollow, contain interior staircases, and include special crossbeams to carry the contact wires for the early electrification system. The end towers are diminutive as compared to the towers of the nearby Hell Gate Bridge, and therefore do not compete.

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Figure 6. East face, pier 54. Permeable, centuryold weathered concrete surface with exposed, large-sized aggregate which appears to have settled at the time of the pour. Note the one-part Portland cement to one-to-two parts fine-aggregate mortar slushing-edge between the horizontal pour layers.

AREMA 1911 Specifications, in use at the time, stated that a uniform distribution of materials shall be obtained with the use of a straight slicing shovel after each pour.

and density of the steel. Readings reflecting off the steel via nondestructive, timed electrical waves in the 0.1 to 25 MHz range were then compared with control data. The tests revealed that the loading and all material capacities were in excess of both historic and current AREMA rating capacities. The century-old cast iron cap-covered structural steel truss joint pins showed no cracking.

Concrete surfaces, observed in an October 2014 site trip, exhibited weathering, spalling, cracking, and incipient rust stains, especially at the Little Hell Gate end piers.

Much of the original dense concrete protective exterior surface layer (Figure 6 ) is eroded, exposing the interior to destructive alternating wet-dry cycles. Moisture is clearly penetrating the masonry via gravity and wind forces, surface tension, and capillary action. In addition, alkalis in the Portland cement, used in the concrete mix, are reacting with siliceous or carbonate elements in the aggregate. The chemical reaction develops new compounds as gelatinous white alkali within the masonry, which then expands through the masonry to harden on the exterior surfaces. While Portland cement was generally in use by c. 1890, its uniformity and alkali content varied considerably. The reaction phenomenon would be researched after c.

1916, when widespread reports of concrete

deterioration emerged. The research continued into the 1950s, at which time the exact science behind the reaction was still little understood (Figures 7 and 8).

Cracks and strength-loss result from masonry-mass volume changes. At each end pier there is a continuous vertical crack leading all the way down on both faces of the re-entrant spandrel walls and cornices, and following through the vertex (center) of the six-foot deep barrel-vaulted arch-intrados (soffit), reflecting some displacement of the heavy masonry structural elements.

Through-cracks have developed near the springing points in the same manner as at the vertex. Hinges have formed where the lines of thrust converge within the archstructure boundaries. Three hinges produce a statically determinate structure with changing equilibrium and shifting thrust moving increasingly horizontally through the hinging points. Internal and external degradations develop instability and eventual overloading of the structure.

The eradication of the Little Hell Gate inlet in 1930s mitigated some of the bridge’s environmental hazards – such as continued exposures to corrosion-causing salty estuarial waters, and scouring at the piers – and contributed in part to the bridge’s low maintenance record. At the time, advancements occurred in paint technology, which indicated that applying a slightly alkaline paint and providing positive electrolytic action via added sulfate of lead, or zinc oxide mixed with linseed oil, was most protective. Lindenthal

Figure 8. Cylindrical-vault abutment sidewall, end pier 53. Detail of active and desiccated white alkali deposits from reactions between inherent chemicals in the cement and aggregate, thermal effects, polluted air, and moisture. Note the resulting pattern-cracking below the arch springing. Increasing permeability of the mass and incipient oxidation of reinforcement are contributing to the cracking.

knew this, as he used these types of paints on his other metal bridges as far back as 1883.

The bridge was painted in 1939 and 1995, with only minor repairs to the steel in 1992.

The metal truss is nearly free of rust. The Centennial of this historic and significant project is in 2015.▪

Figure 7. South face end pier 49. Vertical and horizontal popout-cracking, with ongoing severe spalling and alkali-aggregate reaction evident. New compounds from the reaction expand inside the masonry mass; the resulting localized pressure-zones result in microfracturing and spalling of the structure, here seen in the re-entrant spandrel-wall below the cornice. Cracks are oriented parallel to the bars. Volume changes and strength-loss of the masonry-mass are in progress.

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Figure 1. The exterior of the Forum.

T

Power of the Ring

By Cawsie Jijina, P.E., SECB and J. Benjamin Alper, P.E., S.E.

he Forum in Inglewood, California (also known as the Fabulous Forum) is an arena with a cable-suspended structure – not unlike a suspension bridge. There are 40 columns positioned equally on a 404-foot diameter circle that taper into precast concrete arches which support the 70-foot high compression ring. Forty cables, each 3 inches in diameter, one from each column, are strung from these columns to a central tension ring. The entire roof structure sits on the cables. The inward force (pull) from the cables is countered by the giant compression ring, which, at the time it was designed, was the largest compression ring in America. In its original design, one hundred percent of the heavy lifting is done by the cables (Figure 1).

Designed and built in the early 1960s, the Forum’s structural design favored economy of construction with little concern of future expansion. But music acts today are bringing in heavier and heavier gear – video boards, lighting, LED arrays, speaker banks, rigging – and they want to suspend it all from the roof/ceiling rather than build their own structures. The Forum’s roof cables simply did not have enough reserve capacity to support these shows. To further complicate the design, the rigging consultants recommended the addition of a tension grid system to cover almost a third of the cable area under the roof. In a tension grid system, individually framed panels with tensioned wires create a walking surface where riggers can easily walk and drop motorized cables and chains from the primary structure above to support the lights and sounds below. This would further increase the demand on the existing roof structure.

One Ring to Push Them The typical demands for increased loading capacity when you retrofit a building are on the order of 20 or perhaps even 50 percent – but the Forum’s owners wanted to increase the load capacity of the roof by around 300 percent. The capacity needed could not be obtained with conventional reinforcement design techniques. A completely out of the box, innovative solution was needed. Inspiration was found in the giant cathedrals of ancient Europe. They are all domed structures, which always have a compression ring at the top in the form of an oculus. They also have a tension ring around the perimeter to resist the dome’s natural tendency to flatten out. In a dome, all forces radiate outwards.

At the Forum, the roles are reversed. The compression ring is on the perimeter, and the tension ring is at the center, at a slightly lower elevation. Contrary to a domed structure, in this arena all forces move in a direction opposite to a domed structure. This is not a STRUCTURE magazine

compression structure, but a pure tension structure. The ring outside is being pulled inwards because the sag of the cables causes all forces to radiate inward.

The engineering logic was to create a modern-day version of a dome and marry a new compression structure to the existing tension structure (Figure 2). ). It would relieve the forces on the existing exterior perimeter ring, and generate the extra capacity. A hybrid structure like this had never been designed before – this would be the only structure of its type in the world that had both a tension ring and a compression ring at its center.

Figure 2. Initial structural concept sketch.

Data Collection Accurate design requires precise knowledge of the existing structure.

As the cables act in a non-linear manner, simple structural analysis methods do not generate accurate results. Possessing the original structural drawings without having the sequencing of the cable erection and jacking, and the original pre-tensioning magnitude, was insufficient to accurately model the structure. As the original sequencing and jacking forces of the cable structure were not available, further investigation was necessary. Knowledge of the exact cable location in its current state, and an inventory of the existing loads supported by the cable along with the precise amount of force currently in the cable was required to accurately model the structure in absence of the original sequencing. Measuring the cable locations in space was easily achieved with a 3D laser scan of the ceiling. This provided information on the location coordinates of all cables for the entire roof. Finding the existing force in the cable was more complicated, requiring a ‘lift off’ test of the cable. The ends of the existing cables were concrete encased at the completion of installation. During the ‘lift off’ test, the concrete encasement was chipped away, exposing the end wedge fitting of the existing cable. A jack with a custom threaded and fabricated pin was used to engage the cable end. The cable end

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Figure 4. Steel compression ring while being setup for welding on the arena floor.

the new ring was raised into position. The new domed structural framing was then loosely connected to the new Compression Ring and the entire system was allowed to gently settle so that the forces could re-distribute themselves (Figure 5).

One Ring to Tie the Two and Bind Them Once the new structure settled into equilibrium and all elevations were recorded, the jacks went to work again and raised the new system a precisely calculated amount. The goal was to balance the compression forces from the new structure racing towards the outer perimeter ring with the tension forces from the existing structure racing away from the outer perimeter ring so that the perimeter ring became the binding element. The old tension system was integrated with the new compression system utilizing twenty radial trusses, resulting in a structure dubbed by many of the concert riggers as the ‘best rig on the west coast.’

Figure 3. Lift off testing at cable ends.

was then slowly pulled until the end cap of the cable wedge lifted off the compression ring, thereby transferring the entire load from the cable into the calibrated jack (Figure 3). At that one instantaneous moment in time when the cable moves, the point of equilibrium shifts and the existing cable force is determined. This procedure was repeated multiple times. Once all data was collected, it was then input into Severud’s own custom created software, where the output quickly converged, giving the final results.

One Ring to Gather Them Severud’s design concept envisioned that a new structure would be created within the volume of the existing roof and be seamlessly merged with the existing structure in the same curved roof plane, taking advantage of the subtle curve of the roof (used for drainage). A compression ring was then introduced, like an oculus in a cathedral, except it was fashioned out of steel to bring the entire compression structure together. The new structure, in combination with the existing structure, does all the heaving lifting. The cables continue to support the roof as well as take up any unbalanced rigging loads.

Getting the new compression ring into position required careful planning. No mobile crane could just lift this ring up above the perimeter of the roof, reach more than 240 feet from the edge of the promenade at the perimeter of the arena to the center, and then gently lower this massive ring. Severud elected to design the new Compression Ring such that it could be raised up to the roof from the arena floor. That meant that the new compression ring had to slide up through the center opening of the existing Tension Ring to its final top-chord position. That dictated the 19-foot diameter of the ring. Compression forces dictated the 2.5-inch plate thickness (Figure 4 ). False-work was erected, a hydraulic lift was placed, and STRUCTURE magazine

Rock Concerts, Performance Events, Seismic Events and Asymmetric Loadings The Forum sits approximately four miles from a seismic fault line.

It is in a zone of high seismic activity. It is also a perfectly symmetric structural design. The ideal seismic design is one where the center of mass is coincident with the center of resistance, resulting in a perfect balance of forces during a high seismic event. However, the majority of the concert and performance events are not “In the Round” (centered in the arena) but are “End Stage” events resulting in an asymmetric loading on the structure. The effect is negligible during a routine event but when hanging 300,000+ pounds asymmetrically, it poses a further challenge. The designers had to make

Figure 5. Steel compression ring being lifted into place at top. Steel tension ring is in view at the bottom.

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sure throughout the building’s renovation that the building’s center of mass stayed the same, and that the total mass did not increase beyond a set percentage. If an element was added or removed, it had to be balanced out with a similar operation on the other side.

It was also necessary to compensate for the addition and removal of loads that were strictly event-dependent. Structural Engineers value redundancy. But performance artistes never conform (that is why they are artists!). The design of the Forum required the study of every possible concert configuration from past concerts and, working with the rigging consultant, potential future concerts. The arena was then re-structured to absorb all of these possible scenarios.

Proof of the structure’s performance capability came in August 2014 when the MTV Video Music Awards Event was staged in the arena (Figure 6). A total of 300,000 pounds of equipment, speaker banks, video walls, graphics boards, LED banks, moving catwalks, etc. was hung from this innovative structural system. 300,000 pounds, hanging about 65 feet off center, on a 404-foot clear span caused this tensioncompression structure to deflect a total of 17/8-inch. A very good day in the office.

The authors would like to thank Manny Morden, P.E., S.E. for his invaluable efforts on this project.▪

Figure 6. Steel compression ring at the top of the structure to create the dome.

Cawsie Jijina, P.E., SECB, is a Principal at Severud Associates. He can be reached at CJijina@severud.com.

J. Benjamin Alper, P.E., S.E., is an Associate at Severud Associates.

He can be reached at JAlper@severud.com.

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Owner:

Project Team

The Madison Square Garden Company Consultants: Severud Associates: Structural Engineer of Record Brisbin Brook Beynon Architects: Architect of Record ME Engineers: MEP Engineer of Record Clark Construction Company: General Contractor Gafcon: CM/Owner’s Representative Ed Kish Rigging: Rigging Consultant Beck Steel: Steel Fabricator Bragg Steel: Steel Erector IA Stage (Skydeck): Tension Grid Fabricator March 2015

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ConstruCtible CritiCism Mitigating SeiSMic HazardS witH realiStic recoMMendationS

By Andy Kizzee, P.E.

T

he global structural engineering community is making earthquake-resistant construction a priority worldwide.

Much of this effort comes from countries where the research is performed and leading codes are written. Care is being taken to ensure that globally promoted seismic retrofit and reconstruction solutions use materials and techniques that are familiar to local builders. Innovations in earthquake-resistant construction in the developing world must be at a scale that is feasible for the owners and builders not only to understand, but also to implement.

A recent Engineering Ministries International (EMI) project in north India provides a good illustration of this principle. The client in question had just completed construction of a new primary school. The rectangular building, opening onto a large courtyard, was designed and constructed prior to EMI involvement. The school was originally intended to have two stories, but the client had not built a structure of this scale before, and neither had the local builder.

Construction did not go well, and the local builder was replaced prior to the placement of the first floor slab. The lack of a professional design, coupled with an inexperienced contractor, resulted in subpar construction. As the client came to the realization that the building would likely be unable to support the originally planned second story, he asked the EMI team – on-site to design new buildings for the expanding school campus – to offer an opinion.

The EMI team inspected the building and reviewed photos taken during construction. It was quickly confirmed that not only should a second story not be added, but the school was already vulnerable to collapse in the event of a strong earthquake. The first contractor formed and placed the roof-level beams separately from the slab and located them nearly 10 inches too low, then laid three courses of brick to make up the difference prior to forming and placing the roof slab. While unorthodox, this method is stable under gravity loading.

However, if earthquake shaking were to cause the three brick courses to crack and be displaced, the reinforced concrete roof slab would STRUCTURE magazine

Retrofit detail at interior wall.

only be supported at the corners by the columns. This could cause punching shear failure and potentially collapse.

Structural engineers must be aware of their responsibility to inform clients and/or the public of such a hazard, and then make recommendations to mitigate it. If the goal of the recommendations – in this case, seismic retrofit of an existing school building – is to reduce the hazard, then they must be realistic to undertake. An extensive retrofit design that improves life safety does not reduce the hazard at all if it is never actually constructed.

In a country with a fully developed building code enforcement system, this recently completed school building would likely not be allowed to be occupied until the structural safety issues were fully remediated. Third-party engineers would be hired, and new reinforced concrete shear walls with large footings would be designed

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Roof beams poured independently from the slab.

and installed in many locations throughout the building. The system would be designed according to thoroughly researched and legally enforced building codes. In the event of an earthquake, the stiff shear walls would attract most of the lateral forces, and the building would not be in danger of collapse.

If such a fully-designed solution were to be recommended for this remote school in India, however, little good would come of it.

Although technically effective, such a solution would likely be deemed too costly and too disruptive to be installed, and the building would remain in its vulnerable state.

To reduce the hazard, a seismic retrofit scheme must be relevant to local construction practices and realistic for the owner undertake. It also must be communicated in a culturally sensitive and appropriate way in order to maintain a good relationship with the client and to be able to continue supporting its mission.

One way to do this is, whenever possible, to use references from local or regional sources. In India, the Building Materials & Technology Promotion Council (BMTPC), in coordination with many leading earthquake engineering research institutions, has assembled many of the internationally proven details and techniques for earthquakeresistant construction and published them in Hindi, modified for use with regional building types. The school principal, while fluent in both Hindi and English, was excited to receive copies of these materials to distribute to his contractor and other local builders.

With these considerations in mind, EMI’s recommendations in this case were as follows: Recommendation #1 – A non-technical solution to mitigate a technical problem Develop an earthquake drill for students and teachers.

All schools have various safety drills: fire, tornado, security lockdown, etc. Schools in seismic zones should have earthquake drills so that students know how to react. In many countries of the world, students are taught to “Drop Cover & Hold” to protect themselves from falling objects. For this school, the architectural layout of the classrooms is such that it makes more sense for the students to exit STRUCTURE magazine

Roof slab supported by column and bricks.

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the classroom as quickly as possible and gather in the courtyard away from the building.

Recommendation #2 – Technical solutions that can realistically be implemented Undertake a relatively minor modification to the building.

Removing the plaster from the three courses of brick between the roof beam and roof slab will facilitate the installation of welded wire mesh beneath a fresh layer of plaster. The mesh will be anchored to the beam below and slab above, and also tied together on both sides of the wall. This will allow the slab to remain supported by the bricks for a longer duration during sustained earthquake shaking.

For structural engineers operating in places of the world without fully developed code enforcement systems, it is vital to recommend seismic retrofits that will actually be implemented. This principle applies not only to technical solutions, but also to any behavioral or human interaction changes that are suggested. For this client, although the risks due to strong ground motions may not be completely eliminated, these realistic recommendations will substantially reduce risk and allow EMI to continue providing technical advice as the school expands in the future.▪ Andy Kizzee, P.E. (akizzee@emi2.org), is a structural engineer and disaster response coordinator for the Engineering Ministries International (EMI) office in New Delhi, India. EMI provides architectural and engineering design services for Christian ministries worldwide (www.emiworld.org).

The issue was discovered only by viewing the construction photos as the plaster concealed the slab support condition.

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March 2015

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Steel and Cold-Formed Steel Construction Firms Roll Out New Products and Services

By Larry Kahaner

C

ompanies involved in steel and cold-formed steel construction are bringing new products and services to the market to meet the changing demands of their customers.

At SidePlate Systems, Inc. (www.sideplate.com), Jason Hoover, Industry Outreach Executive, says that the new SidePlate field-bolted connection has been gaining traction across the United States. “We use this on wind-governed or low-seismic jobs in regions where field bolting is preferred over welding. SidePlate moment frames are more efficient than conventional construction, so our designs have always saved tonnage, but recently there’s been a greater push from our clients on speed of construction. Our field-bolted connection saves a huge amount of time in the field, so that’s a big part of its appeal.”

Hoover notes that the Strongsville, Ohio, company’s first project done with the SidePlate field-bolted connection was a smaller medical office building in North Carolina. “The erector estimated a 21 day schedule, and he finished in only 7.5 days. Everyone involved was thrilled with that.

“Similarly, we have an office building project in St. Louis where an erector told me that he didn’t like the SidePlate field-bolted connections because the job was going too fast. He said to me: ‘Normally I would have spent all day welding that joint, but with this I’m done in about an hour. We’re going to be off this job weeks early, and now I’ve got to find more work for my guys.’ He did add that he understands why it’s good for the General Contractor and the Owner, though.

This is the type of ‘negative’ feedback we like to hear.”

Hoover adds: “We continue to fight misconceptions that SidePlate is simply another 1:1 connection option or that we manufacture something. The reality is that our designs improve the entire lateral system, and the connections themselves are built by any steel fabricator. Our staff includes twenty-one structural engineers, but we partner with the entire project team, from the structural engineer of record to fabricators and erectors, to ensure everything goes smoothly.”

Amber Freund, Vice President, Operations at RISA Technologies (www.risa.com) in Foothill Ranch, California, would like SEs to know that interoperability continues to be a big priority for design projects. “RISA’s integration with both Revit and Tekla are being used by engineers on both large and small projects,” she says. As for new offerings she notes: “RISA-3D is a comprehensive cold-formed steel analysis and design software which allows you to model using any of the SSMA shapes, as well as custom shapes. In the recent release of RISA-3D version 13, the Cold-Formed Steel code for the AISI 2012, CSA 2012 and CANCERO 2012 was added. This update also included the design and code checks for back-to-back Cees and Tracks. These compressive checks were also improved to consider the user controlled unbraced lengths for torque.”

STRUCTURE magazine

In conclusion, Freund says that RISA’s business is growing. “We are continuing to add new products and features to RISA software. We are encouraged to hear more engineers starting new projects, which is a good sign of economic recovery (or at least the start of it).” (See ad on page 76.)

Brian Smith, President & CEO of Albina Pipe Bending Co., Inc. (www.albinaco.com) says that his company’s culture fosters a continuous improvement concept when approaching its services. “We are constantly looking to improve the services we provide,” he says of the 3rd generation company based in Tualatin, Oregon. This year, 2015, will mark their 76th year in business. “We have found it best to always define expectations with customers. Doing this is not always easy, but certainly something we pride ourselves on. We run an internally designed and programmed computer program. This program is all inclusive to every aspect of our business and customer service. The most recent advancements implemented to our software are related to scheduling. Our software will factor in variables to help project a completion date as well as a ready to ship date for every job in our shop.”

Smith adds: “To also help with customer service we are frequently updating our website. Some recent improvements allow customers to order certain parts online, as well as see customer-specific pricing online. Furthermore, we have also posted a virtual tour and videos highlighting many areas and processes in our facility.”

Albina provides bent and fabricated items to a number of different end users, Smith says. “We are able to bend a wide range of materials – pipe, tube, plate, square/rectangular and all forms of structural steel – as well as a wide range of sizes from the very small to the very large. In conjunction with our diversification, we adhere to very strict quality and scheduling standards providing customers with what they expect, when they expect it. With our diversified range of materials, and determined efforts to provide the highest quality products, we have been able to weather the economic downturn seen over the last six years. We have been able to come out stronger than when we were going into the recession.”

Also attributable to Albina’s growth and continued success is their focus on capital expenditures. “We are methodically investing in new equipment, tooling and technology to either replace aged equipment or add to our already vast equipment inventory. Capital expenditures have greatly helped Albina stay in front of the curve and remain a leader in the bending industry,” Smith concludes. (See ad on page 48).

At Lindapter USA, (www.lindapterusa.com) headquartered in Bradford, England, Marketing Manager Wayne Golden is highlighting one of his company’s latest developments. “Lindapter, the inventor of the original Girder Clamp and Hollo-Bolt, has developed the Type AAF, a new High Slip Resistance (HSR) clamp for connecting

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steel sections. This product offers adjustability, anti-corrosion protection and high load capacities, even in low temperature environments,” he says.

“Lindapter’s flagship product is the latest addition to its HSR family of clamps designed for high-load requirements including frictional, tensile and combined load applications.

The clamp features an innovative two-part design that self-adjusts to suit a range of flange thicknesses, allowing contractors to use a single product type for multiple connection requirements. Typical applications include connecting steel-framed roofs, pipe supports and mechanical handling equipment, while specialist applications include the renovation of bridges and offshore platforms.”

Golden says the new product is manufactured from SG iron with specific low temperature properties so the Type AAF provides resistance in cold environments where impact strength is important. “Durability also extends to corrosion protection as the product is supplied with a hot dip galvanized coating as standard. Engineers can be confident that they are specifying a safe and reliable connection, as load capacities have been verified by independent testing.”

In conclusion, Golden says: “Compared to conventional methods such as drilling or welding, the Type AAF can be installed in minutes without the need for hot work permits, reducing construction time and labor costs. For additional convenience during installation, Direct Tension Indicators (DTIs) can be used to ensure that the correct tension is applied to the fasteners.” (See ad on page 51).

Carlos de Oliveira, CEO at Cast Connex Corporation (www.castconnex.com), is particularly proud that at the 2014 SEAOC Convention in Indian Wells, California, a project utilizing the Cast Connex High Strength Connectors (HSCs) was nominated for an Excellence in Structural Engineering Award. “This particular application was a 43-foot tall support platform at an oil refinery in Richmond, California. The lateral force resisting system of the platform was designed as a Special Concentrically Braced Frame; the brace members were circular hollow structural sections and the bracing connections utilized Cast Connex High Strength Connectors.”

The project had unique challenges, “A particular challenge on this project was the time and sequence required to erect the new platform, as the platform was located in the middle of an active refinery. For this client, every day of disruption is very expensive.

The High Strength Connectors, which have also been employed in other structures in this facility because they are a very economical seismic brace connection solution, were selected because they enable rapid installation. In the Excellence in Structural Engineering Award application poster, the structural engineer of record from Jacobs stated that the HSCs were selected ‘for ease in erection and smooth flow of forces.’

“High Strength Connectors are designed to be connected to the brace member via a shop-performed complete joint penetration weld around the entire circumference of the section. The completed continued on page 50

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innovative components for inspired designs

braces are then shipped to the construction site, where they are installed via double shear bolted connections to traditional gusset plates.

This double shear bolted configuration eliminates field welding of the brace connections and the associated special inspection of those welds, while using a minimal number of pretensioned high strength bolts. From an erection standpoint, the HSC is one of the most efficient bracing connections available, due to erection speed and savings in inspections. Further, given that field welding can be delayed due to weather conditions which would not prohibit bolting, use of the connectors also reduces risk to the construction schedule.”

Cold-formed steel stud walls are emerging as a new and attractive option for blast resistant design due to the combination of high strength and ductility that enable them to absorb and dissipate blast energy through large deformation and yielding, according to Nabil Rahman, Director of Engineering and R&D, The Steel Network, Inc., (www.steelnetwork.com) headquartered in Durham, North Carolina. “However, in order to achieve the required energy absorption of steel stud walls requires special attention to the stud-to-track and bridging connection details, which has remained an active area of research and development for The Steel Network, Inc. (TSN) and Applied Science International, LLC (ASI).”

Rahman notes: “While much of the existing literature on the topic has described specialized ideal boundaries to ensure that the full tensile membrane response of the studs would be achieved prior to connection failure, the study of commercially-available connections and bridging was lacking. This prompted TSN and ASI to sponsor a series of three open-area blast tests with the University of North Carolina – Charlotte (UNCC) to examine the blast performance of 6-inch cold-formed steel stud wall panels comprised of its BuckleBridge single piece bridging system and VertiClip SL600 head-of-wall connector.

“The blast loads applied to the specimens had maximum reflected impulses and peak reflected pressures that were consistently greater than UFC 3-340-02’s design values. Measured ductility limits in the experiment met the limits established by the U.S. Army Corps of Engineers Protective Design Center, which suggests ductility limits between 2 and 5 for cold-formed steel studs. These limits correspond to component damage levels of hazardous failure and

blowout respectively, and could be viewed as being somewhat conservative based on the results of these exploratory and limited tests.

TSN‘s VertiClip SL600 head-of-wall connection and the BuckleBridge single piece bridging system not only kept the wall intact, but also allowed the studs to develop their end rotation and flexural ductility.” (See ad on page 75.)

Design Data (www.sds2.com) of Lincoln, Nebraska, is eager for SEs to learn about its new products. “SDS/2 v. 2015 is Design Data’s newest product that brings major advancements to connection design for steel,” says Strategic Sales Manager Michelle McCarty. “Now engineers can lock in specific variables for connection design and receive immediate feedback through limit states tables and calculations that update on-the-fly. This gives engineers full control over every aspect of the connection and immediate feedback for their design.

“SDS/2 v. 2015 also has the recently-added functionality to create CNC files for cold formed steel shapes, allowing users to send DSTV files to the shop to help automate fabrication operations, like copes and holes placed on cold-formed shapes,” says McCarthy.”

She says that the company has noticed more engineering companies considering adding steel detailing to their offerings.

“Engineering groups are seeing real benefits to including steel detailing as a part of their deliverable, as it reduces RFIs and can decrease timelines, not to mention adding to their bottom lines.

Challenges that come along with launching a detailing department include finding the right staff and adjusting your company’s established work process to view detailing as an extension of the engineering process. However, the ability to offer a complete package with fabrication drawings as a part of the deliverable presents more opportunity for profit,” McCarthy says. (See ad on page 53).

The 2014 Acquisition of GT STRUDL, (www.intergraph.com) by Intergraph Process, Power & Marine, Huntsville, Alabama, part of Hexagon, has paid immediate dividends with program enhancement releases in 2014 and two more planned for 2015, according to Leroy Emkin, Executive Technical Director. “The highlights are the unique bi-directional capability of frame members and finite elements with GT STRUDL CAD Modeler, incorporation of network licensing through the SmartPlant License Manager (SPLM), Tekla Structures

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interface updated, offshore improvements, and the upcoming GT Menu Graphical Interface update.”

He adds that 2014 had provided a rebirth for GT STRUDL through Intergraph’s successful CADWorx & Analysis University Express Global tour (375 attendees), webinars productions (1183 registered attendees), product newsletters, and the creation of the Link-In GT STRUDL Technical User Forum. Says Emkin: “Through this outreach, upcoming development items were identified to complement our Rigorous Response Spectrum Seismic Analysis and the consequences of Nonlinear Geometric Analysis, the need for new/ additional design codes, automatic wind/seismic load generators, and an evolving ‘State of the Art’ integration & interoperability with other Intergraph solutions.

“Combing Intergraph’s resources with GT STRUDL’s global network of dealers, trainers, and support staff enables us to deliver an optimized and efficient work process for the following: faster designs with more accurate results produced in hours, not days or weeks; less assumptions leading to safer structure and equipment designs; cost savings realized by evaluating complete systems instead of individual components, and the ability for teams to collaborate and share the same 3D Model to avoid redesign and construction delay cost,” concludes Emkin. (See ad on page 52).

Raoul Karp, Vice President of Structural and BrIM Products at Bentley Systems, Incorporated (www.bentley.com) based in Exton, Pennsylvania, says that conditions worldwide have improved with a dramatic increase in construction over the preceding few years.

“While some engineering firms have indicated a difficulty in finding qualified hires, others have expressed a hesitation to increase the size of staff because, while there is plenty of work right now, the future is unclear. As a result, engineers at many firms are working longer hours

to make up for the manpower shortage. A solution to that problem is to empower engineers to work more productively. To that end, Bentley Systems, Inc. is now offering the new Structural Enterprise License. At little more than the cost of an individual major product license, this license includes STAAD.Pro, STAAD Foundation and all RAM Products including RAM Structural System and RAM Concept. This provides the engineer with the tools that are right for the task at hand. Furthermore, the interoperability capabilities between these programs, as well as with other products outside Bentley from Autodesk, Trimble and others, enable engineers to perform their tasks more quickly and efficiently.”

Karp adds: “Several new versions of these products have recently been or will soon be released with powerful new features to meet the demands of domestic and foreign markets, including: STAAD.Pro with AISC 341 Seismic Provisions, global code updates including Canadian and Indian codes, and soon to be introduced major enhancement to the Powerful Input Editor. On RAM Structural System updates include the design of CoreBrace Buckling Restrained Braces and the Canadian concrete and steel code, and RAM Connection with Eurocode 3, provide a big step up in user productivity and enabling fast consideration of design alternatives.” (See ad on page 54).

Simpson Strong-Tie (www.strongtie.com) of Pleasanton, California, has three new innovative, cost-reducing utility clips for cold-formed steel construction: the SFC steel framing connector, the SJC steel joist connector and the SSC steel stud connector, according to Randy Daudet, Cold-Formed Steel Industry manager. “New features include pre-punched holes for anchoring to steel or concrete, and intuitive fastener hole patterns to satisfy the structural needs of engineers and simplify installation for contractors. We also recently introduced MSSC kneewall connectors that are designed to work in tandem with

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EW N PRODUCT

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Simpson Strong-Tie BP1/2-3 bearing plates to provide solutions for moment-resisting kneewall applications.”

Daudet says that key features of these new utility clips include: • Clips fit the open side of the stud without having to add track.

This adds versatility to the line, and reduces material and labor for contractors.

• Clips are easy to specify via our standard round (min) and triangle (max) tabulated loads. Also, versatility is ensured for non-standard designs via square holes that allow engineers to calculate their own screw pattern.

“In addition,” says Daudet, “we just launched the LSUBH bridging connector that offers a lower-cost option to our popular SUBHMSUBH u-channel bridging connectors. The LSUBH connector provides all the installation benefits of the SUBH/MSUBH connectors, and is suitable for many wind-bearing and load-bearing situations where the load demand is light to moderate.

“At Simpson Strong-Tie, we listen to our customers and develop new products that are designed and tested to meet their needs,” adds Daudet. “Engineers and contractors are moving away from field cut clip angles in favor of pre-punched pre-engineered solutions.

Contractors save time and money by not having to cut and pre-drill clips. Designers prefer pre-punched pre-engineered solutions because it’s easier for contractors to install clips according to plan and control installation quality.”

Simpson Strong-Tie also released a new software program for cold-formed steel Designers that automates product selection and complicated design provisions of AISI, and offers more robust design tools for users, Daudet notes. “CFS Designer software is the new version of LGBEAMER, a software program that for years has been one of the industry’s most widely used CFS member design tools. With

CFS Designer, engineers enjoy the key benefits of LGBEAMER, and also have access to connection design and a more powerful software platform. The new version maintains the useful design tools that automate common CFS systems such as wall openings, shearwalls, floor joists, and rafters, but with an upgraded user interface that makes input faster and more intuitive. The software allows the design of multiple engineering models within the same job file, and supports connection design for specific Simpson Strong-Tie curtain wall and bridging connectors like the SUBH u-channel bridging connector, and the SCB by-pass slide clip.” (See ads on pages 2 and 31).▪

ADVERTISING OPPORTUNITIES Be a part of upcoming

SPECIAL ADVERTORIALS in 2015.

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introDucing the

HoW/2

Design ConneCtions with SDS/2

SerieS by SDS/2

true connection DeSign, not SimpLy connection veriFicAtion SDS/2 is the only system that provides true connection design — for individual members, as well as all interacting members in a structural joint.

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FuLL Joint AnALySiS Instead of choosing a connection from a library, SDS/2 designs the connection for you, based on parameters that you establish at the beginning of a project.

All connections SDS/2 automatically designs will comply with the connection design code standards the user chooses.

learn more Want to see how simple it really is to design connections in SDS/2? Scan the QR code to watch SDS/2’s connection design in action.

SDS/2 provides long-hand calculations of all designed connections, which simplifies the verification process. Scan the QR code to view an example of SDS/2’s automatically generated calculation design reports.

cLASh prevention SDS/2 checks for interaction with other connections within a common joint. That means adjusting connections for shared bolts, checking driving clearances for bolts, sharing, adjusting and moving gusset and shear plates when required, and assuring erectablity of all members. All adjusted connections are automatically verified based on selected design criteria.

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Visit www.bentley.com/Structural to learn more! © 2014 Bentley Systems, Incorporated. Bentley, the “B” Bentley logo, ProjectWise and MicroStation are either registered or unregistered trademarks or service marks of Bentley Systems, Incorporated or one of its direct or indirect wholly owned subsidiaries. Other brands and product names are trademarks of their respective owners.

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sustainability and preservation as they pertain to structural engineering

Structural SuStainability

Environmental Declarations and Structures

By Emily Lorenz, P.E., LEED AP BD+C

T

he U.S. Green Building Council (USGBC) continues to drive market transformation related to green building. Most recently, this is evidenced by the increase in the number of manufacturers and trade associations that have undertaken development of product category rules (PCRs) and environmental product declarations (EPDs) in response to a new credit in LEED v4. This article discusses the status of PCRs and EPDs in the concrete industry and how they can be used by structural engineers.

Influence of LEED The LEED v4 Materials and Resources Credit: Building Product Disclosure and Optimization – Environmental Product Declarations “reward[s] project teams for selecting products from manufacturers who have verified improved environmental lifecycle impacts.” One of the options requires the use of 20 permanently installed products that have a: • Product-specific declaration, • Industry-wide (generic) environmental product declaration (EPD), • Product-specific Type III EPD, or • Declaration from a USGBC-approved program.

This credit rewards points to projects that use products, such as concrete, that have an EPD, but it doesn’t require specific values or thresholds on environmental impacts.

This has led the concrete industry, among others, to develop PCRs and EPDs. In November 2012, the Carbon Leadership Forum (CLF) at the University of Washington released a U.S.-specific PCR for concrete, which was revised in December 2013. In February 2013, the World Business Council for Sustainable Development (WBCSD) also announced the development of a PCR for unreinforced concrete. Other concrete-related industry PCRs that have been published recently include: • Slag cement, (August 2014), • Portland, blended hydraulic, masonry, mortar, and plastic (stucco) cements (September 2014), and • Manufactured concrete and concrete masonry products (December 2014).

These PCRs have been used to develop EPDs for concrete-related industries. While several individual companies have published EPDs for individual concrete-related products, a comprehensive report on the environmental impacts of concrete was published by the National Ready-Mixed Concrete Association (NRMCA) in October 2014. NRMCA’s Industry-Wide (IW) Environmental Product Declaration (EPD) and Benchmark (Industry Average) Report discloses average environmental impacts for concrete. These data are for concretes of varying strengths, uses, and mixture proportions.

Role in Structures Most balanced studies show that there isn’t much difference among the environmental impacts of structural materials over the life of a structure. This is good news to structural engineers, who often have factors other than environmental impact (cost, availability, timing) affecting the choice in structural materials. So how can structural engineers use EPDs in practice?

Though the temptation to compare the environmental impact of different structural materials using EPDs might be there, the ISO documents explicitly forbid it. EPDs may only be compared if products are evaluated using the same PCR (see sidebar), and in the whole-building context. If the decision to use concrete has already been made for a project, EPDs of different concretes (that use the same PCR) can be used to determine the optimum mixture to reduce environmental impact and

achieve the performance attributes that are desired for the project.

EPDs may also be used to reevaluate the performance requirements that are set for the concrete in certain applications. Perhaps the slower strength gain of a high-fly-ash concrete can be accommodated on certain parts of the structure, like the foundation.

Knowledge is Power Though environmental impacts don’t yet have the same influence over design decisions as cost and schedule, structural engineers do have the ability to reduce environmental impacts with an increased knowledge gained from EPDs. And because structural materials are typically a large portion of the structure (by weight if not volume), structural engineers may have more influence over reducing environmental impacts of buildings than they realize.▪ Emily Lorenz, P.E., LEED AP BD+C, is an independent consultant in the areas of LCA, EPDs, PCRs, green building, and sustainability. She can be reached at emilyblorenz@gmail.com or through her website at www.SevgenConsulting.com.

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

What are PCRs and EPDs? Environmental product declarations (EPDs) are Type III environmental labels according to International Organization for Standardization [ISO] 14025. For a given functional or declared unit, EPDs list the environmental impacts for a product. It is important to note that these labels only list environmental impacts; they do not rank the environmental impact of a product.

Product category rules (PCRs) set the rules for how a life-cycle assessment (LCA) is performed. The LCA is the analysis that is performed to determine the environmental impacts for a given product category (such as unreinforced concrete). This ensures consistency in procedures and interpretation of commonly used LCA standards. A PCR also establishes what information is reported in an EPD (such as environmental impact categories and other information), and how that information is formatted. This ensures consistency in reporting.

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Education issuEs

core requirements and lifelong learning for structural engineers

Problem-Based Learning in Earthquake Engineering Courses Incorporating a Case Study

By Jeena Rachel Jayamon

A

problem-based learning case study is developed and can be incorporated as part of seismic design or earthquake engineering courses.

In many universities, these courses are already part of the graduate course curriculum for students majoring in structural engineering.

This is an advanced course and requires a strong background in structural analysis and dynamics of structures.

Through the proposed assignment, students will learn to select and process appropriate ground motions for use in seismic design; apply different analysis methods; select and design an appropriate structural system to resist earthquake loadings; and use required codes of practice for design and detailing. This article is intended to continue discussions among academic and industry professionals about the potential skills acquired through the assignment, and gather opinions about additional features that can be included to help students acquire more knowledge related to topics in earthquake engineering.

Course Curriculum The proposed problem-based assignment described below can be part of a graduate level class on Topics in Earthquake Engineering. This course is designed to provide strong understanding of the fundamentals of earthquake engineering built on knowledge in structural dynamics and seismic hazard analysis (the basis of which are already covered in other courses). Through this course, students will learn to select and process appropriate ground motions for use in seismic design; select and design an appropriate structural system to resist earthquake loadings; use required codes of practice for design and detailing of the structural system; and, apply different dynamic or equivalent static analysis methods to check the safety of the system. Another part of this course is devoted to introducing different methods and practices for seismic performance assessment of new and existing buildings. The proposed problem-based assignment is mostly worked for the first part of the course curriculum to design a lateral load resisting system to protect buildings against earthquake hazards.

Objective of the Case Study The main objective of this assignment is to help students learn about the design of buildings and infrastructure facilities to resist ground motions generated from natural earthquake and other seismic hazards. The student community can apply the lessons they learned about ground motion selection/scaling and the design as well as detailing of various lateral load resisting systems, in this specific assignment. During lectures, the instructor will introduce and give sufficient guidance for using different seismic codes and reference manuals. And through the assignment, the student community will practice the use of appropriate seismic design codes and manuals in the design and detailing of a given structural system.

Specific Topic of Consideration Company ‘X’ located in Texas wants to build a new office in California. As Texas is a low seismically active area, the office is not designed to resist earthquakes. Now that they are building their new office in California, which is located in a high seismically active zone, the officials want to know about the various means and measures in which they could build a safe office building. The owners of the company approached you (or your office) and would like to get a set of building designs for constructing a new office building in Los Angeles. They want you to produce required drawings and designs to be supplied to a construction company, and would also

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like to know how this new design is sufficient to ensure appropriate safety to the building.

As a structural engineer, you are ethically committed to describe to the client the various potential seismic threats and supplementary methods you have included in the design to resist these hazards.

Steps Involved in Solving the Case Stage 1 • Once the building site location is finalized, use various tools to find different site-specific details that might be used throughout the design process.

• With the site details, use appropriate ground motion selection and scaling strategies to develop the ground motions for use in design.

Stage 2 • With the results from Stage 1, select a suitable lateral load resisting system for use in the building to resist lateral earthquake loads. You are free to choose any standard available load resisting system or design a new system. In either way, you have to judge the rationale behind the selection of the typical system. If you are proposing a new system, you have to supply enough information to substantiate that the system is equivalent, or better than, other codecomplaint systems.

Stage 3 • Model the trial design of the building in a suitable structural analysis program and verify the accuracy of the model.

• Apply appropriate structural analysis methods and find the required results for use in the design of the building system.

• Check if the lateral load resisting system satisfies the requirements of seismic design guidelines for strength and serviceability limits.

• Iterate the current design to produce more economical design solutions.

• Evaluate the system to determine if various performance levels and objectives (from an immediate occupancy of the building to life safety when subjected to a probable earthquake event) are met.

load resisting system and analyzing it to ensure the applicability at a particular site should be collectively completed by different members in the group.

Students Final Submittals Each group needs to submit two reports – a mid-term and final. The mid-term project should have all information about the various site-specific details that are investigated and how the group arrived at the selection of the specific structural system. The final report should be focused on the specific design details of the selected system and how this system satisfies the desired protection that may result from an expected seismic hazard.

Each member should turn in a cover letter to indicate the specific tasks they have completed as part of the project team.

Project Working Groups

Assessment of Students’ Submissions

Since the project involves a variety of tasks that can be performed in parallel, students are allowed to work in groups of 3 or 4 members. The various tasks involved in developing the design of a structural lateral

Each group submission will be judged on the basis of the following criteria.

• Accurate evaluation of seismic load to be applied in the building system. (10%)

• Correct analytical structural modeling and analysis. (10%) • How well the strength, safety and serviceability requirements are satisfied in the final design. (50%) • Is the design efficient and practical to construct? (10%) • Are the designs innovative and creative? (10%) • Oral presentation and submission of reports. (10%)▪ Jeena Rachel Jayamon is a PhD student in the department of Civil and Environmental Engineering at Virginia Tech. She finished her undergraduate degree in Civil Engineering from the National Institute of Technology Calicut (NIT Calicut, India) and holds a masters degree in Structural Engineering from Virginia Tech. Jeena is an active student member of ASCE and EERI chapters, and also serves as the Vice-President of the SEI graduate student chapter at Virginia Tech. Jeena can be reached at jeenarj@vt.edu.

Input on this topic is encouraged.

Please forward comments/suggestions to publisher@STRUCTUREmag.org.

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EnginEEr’s notEbook

aids for the structural engineer’s toolbox

Extreme Torsional Irregularity

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

A

mong categorizations of seismic behavior that have been adopted in modern codes is extreme torsional irregularity. Torsional irregularity is not an unfamiliar concept, having been expressed in codes in various forms for decades. It is an issue that engineers have learned to deal with, particularly in seismically active areas. Extreme torsional irregularity, however, is a somewhat newer concept and subset within the larger issue of torsional behavior. It is something that can greatly limit and restrict flexibility in choosing seismic force-resisting systems and configurations.

Recent codes have defined torsional irregularity as the condition where the maximum story drift, including accidental torsion, at one end of the structure transverse to an axis is more than 1.2 times the average of the story drifts at the two ends of the structure. A little pencil work will show this means that if one end of a rectangular structure drifts more than 1.5 times the other end, torsional irregularity is said to exist. For the newer category of extreme torsional irregularity, the calculation steps are fundamentally the same, but this designation is assigned to structures where the maximum story drift, including accidental torsion, at one end of the structure transverse to an axis is more than 1.4 times the average of the story drifts at the two ends of the structure. Again, in simple terms, this means that if one end of a rectangular structure drifts in excess of 2.33 times the other end, extreme torsional irregularity is said to exist.

What difference does this make in design?

Today’s sophisticated analysis software is capable of handling any degree of torsion. As far as basic analysis goes, there is fundamentally no difference between “regular” torsional irregularity and extreme torsional irregularity. The major difference is found in structures assigned to Seismic Design Category (SDC) E or F. To put it simply, section 12.3.3 of ASCE 7-10 states that structures assigned to SDC E or F having horizontal irregularity Type 1b of Table 12.3-1 (extreme torsional irregularity) “shall not be permitted”. In other words, any structure assigned to SDC E or F is not allowed to have extreme torsional irregularity, and thus the design must be changed accordingly. Assignment of SDC E or F occurs for structures with long-period

Extreme torsional irregularity is something that can greatly limit and restrict flexibility in choosing seismic force-resisting systems and configurations. spectral accelerations (S1) of 0.75g or greater.

This pertains to a great many sites in heavily populated regions of moderate to high seismicity. Under the current code, designers of projects within these areas must be aware of the extreme torsional irregularity issue and design buildings accordingly.

Recent changes to long-period spectral accelerations resulted in diminished values for many regions across the country. This made a tremendous impact on seismic design in regions of moderate to high seismicity, which were plagued with a 0.75g “trigger boundary” for S1. For a time, this code provision meant limitations on permissible behaviors regarding the torsional issue as mentioned previously.

Engineers had less latitude and were forced to help clients understand the limitations of geometries that were once compliant, but had become problematic because of issues such as torsion.

In the ever-evolving field of seismic design, only time will tell what direction future spectral acceleration maps will go. Those designing structures in regions where the long-period spectral acceleration response is near 0.75g should maintain a keen awareness of changes to these criteria, as this issue holds major implications, including the assignment of the SDC and associated limitations regarding certain irregularities.

An issue of discussion that many engineers have raised regarding the classification of torsional irregularity is the fact that the methodology does not address the magnitude of relative story drifts. Using values derived from the fundamental rectangular model mentioned previously, if one end of a rectangular structure drifts 0.8 inches and the other end drifts 1.2 inches, the average drift is 1.0 inch, and since the maximum drift is at least 1.2 times the average drift, the structure is said to have torsional irregularity. For the same model, if one end of the structure

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drifts 0.6 inches and the other end drifts 1.4 inches, the average again is 1.0 inch, but the structure is now said to have extreme torsional irregularity since the maximum drift is at least 1.4 times the average.

Next, consider a similar structure with a lateral force-resisting system consisting of concrete shear walls. Perhaps the drifts are 0.08 inches at one end and 0.12 inches at the other end, for an average of 0.10 inches.

Although the deflections are miniscule, the structure is nonetheless classified has having torsional irregularity. Likewise, for drifts of 0.06 inches at one end and 0.14 inches at the other, the maximum drift divided by the average is 1.4 and the structure has an extreme torsional irregularity, forbidden for SDC E or F. Thus story drifts may be almost immeasurably small, yet the irregularities are still said to exist.

Granted, torsional irregularity is meant to reflect a broad behavioral issue encompassing not only drift, but distribution of forces. In this case, magnitudes of forces and baseline strengths of systems may be the controlling design concern, relegating drifts to the “non-governing” category. However, magnitudes of drifts play a major role in the serviceability of nonstructural systems, and stability assessment of both structural and nonstructural systems. Clearly, smaller drifts carry reduced consequences, and larger drifts carry increased consequences.▪ Jerod G. Johnson, Ph.D., S.E. (jjohnson@reaveley.com), is a principal with Reaveley Engineers + Associates in Salt Lake City, Utah.

A similar article was published in the Structural Engineers Association-Utah (SEAU) Monthly Newsletter (November, 2004). Content is reprinted with permission.

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LegaL PersPectives

discussion of legal issues of interest to structural engineers

Qui What?

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

Q

ui tam. Don’t know the phrase?

You should. It is short for qui tam pro domino rege quam pro se ipso in hac parte sequitur, Latin for “who as well for the king as for himself sues in this matter.” Qui tam lawsuits are, according to Black’s Law Dictionary, lawsuits brought under a law “that allows a private person to sue for a penalty, part of which the government or some specified public institution will receive.”

Qui tam cases are a notable feature of the regulation of public contracting, which, given the amount of public contracting directed towards construction, makes them a prominent aspect of the construction business.

If the Latin name were not giveaway enough, the roots of qui tam actions extend back to the English common law writ of the same name, by which a private individual who assisted a prosecution could receive all or part of any penalty imposed. Qui tam actions originated in 13th century, Norman-ruled England, as a mechanism to further enforce the King’s laws.

Historical Context of the False Claims Act Whatever may be said of the writ’s continuing vitality in the United Kingdom, it is alive and well in the United States, despite its advanced age. Indeed, the first qui tam statute enacted by this federal government, the eponymous “Lincoln Law,” or False Claims Act, became law in 1863.

Just as future President Grant was poised to maneuver against fortress Vicksburg to solve one problem facing the federal government, then President Lincoln was maneuvering in Congress to solve another: endemic fraud in the explosion of federal contracting arising from the war effort, when the government was too overextended to combat it.

The False Claims Act Today: Liability Although certainly not alone, the False Claims Act is an enduring tool to combat government fraud. Since 1986, when strengthened

during the defense build-up to address contractor price gouging, the Act has helped recover tens of billions of taxpayer funds.

(See e.g. www.dodig.mil/sar/index.html.)

Congress most recently revamped it in 2009 with the passage of the Fraud Enforcement Recovery Act of 2009. The False Claims Act’s current manifestation is codified at 31 U.S.C. 3729, et seq.

The False Claims Act: Liability The Act outlaws a broad swath of fraudulent conduct in federal contracting, including – and most important for the construction context – fraud in seeking payment on federal projects. It covers, and makes liable, anyone who “knowingly” (31 U.S.C. 3729(a)(1)): 1) “presents … a false or fraudulent claim for payment or approval;” 2) “makes, [or] uses … a false record or statement material to a false or fraudulent claim;” or 3) conspires to do the same “is liable to the [federal g]overnment.”

How liable? Liable for “a civil penalty of not less than $5,000 and no more than $10,000, as adjusted” for inflation, “plus 3 times the amount of damages,” i.e., the amount of the fraud, sustained by the government because of the act of that person, plus “the costs of a civil action brought to recover any such penalty or damages.” (31 U.S.C. 3729(a)(1) and (3); but see (a)(2) (providing for reduced liability in certain circumstances.) The availability of costs – including attorney fees – make qui tam lawsuits popular among the legal profession: plaintiffs need not have their own funds to afford a lawyer.

The breadth of these provisions is, like the devil in the details, here, in the definitions of the key words. Key words are defined broadly.

Under the Act, a person acts “knowing[ly]” if, “with respect to information” he or she “acts in deliberate ignorance” or “reckless disregard” “of the truth or falsity of the information.”

(31 U.S.C. 3729(b)(1).) There is no need for “proof of [any] specific intent to defraud.” (31 U.S.C. 3729(b)(1).)

The False Claims Act’s enactment was, according to legend, instigated by unscrupulous contractors who sold the Union Army decrepit horses and mules in poor health, defective arms, and spoiled food and other provisions.

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Further, while excluding claims for individual wages, salaries and certain “income subsid[ies],” the Act gives “claim” a similarly broad definition. (31 U.S.C. 3729(b)(2)(B).)

A “claim” is a “request … for money … that … is presented to … the United States; or is made to a contractor … if the money is to be spent or used on the [federal g]overnment’s behalf or to advance a [g]overment program or interest, and if the … [g]overment … provides or has provided any portion of the money or property requested or demanded … or will reimburse such contractor, grantee, or other recipient for any portion of the money or property which is requested …” (31 U.S.C. 3729(b)(2).)

The bottom line is that anyone involved in false billing on a federal construction project, no matter how far removed from the federal funds, runs the risk of False Claims Act liability. From the contractor who “front-loads” his or her payment schedule, to the design professional who knowingly passes it along. The situations are easy to imagine. The most common is a government contractor, or a subcontractor, submits an invoice for payment before it is due. Another is a subcontractor that submits an invoice for payment based on an incorrect representation that the work complies with specifications or contract requirements. Finally, still a third situation is a contractor who submits an invoice that fails to provide the government, or a downstream contractor or subcontractor, with legitimate credits for offsets. Nor is the liability here limited to the companies involved. Individuals can face individual liability for their individual actions.

The False Claims Act: Enforcement Of course, the signature aspect of the Act – what makes it a qui tam law – is its enforcement mechanisms. It’s the original “whistleblower” statute.

In addition to authorizing the Attorney General to sue violators, 31 U.S.C. 3730(a), the Act deputizes pretty much everyone else to do the same, providing that they “may bring a civil action for a violation of ” the Act “for the person and for the” federal government.”

percent of the proceeds of the action or settlement of the claim, depending upon the extent to which the person substantially contributed to the prosecution of the action,” plus “an amount for reasonable expenses … plus reasonable attorneys’ fees and costs.” (31 U.S.C. 3730(d)(1).) If the federal government does not proceed, the relator “shall receive an amount which the court decides is reasonable for collecting the civil penalty and damages,” which “shall not be less than 25 percent and not more than 30 percent of the proceeds of the action” plus “reasonable expenses … plus reasonable attorneys’ fees and costs.” (31 U.S.C. 3730(d)(2).)

In the latter case, where the government balks, however, there is risk. “If the [federal g]overnment does not proceed with the action and the person bringing the action conducts the action, the court may award to the defendant its reasonable attorneys’ fees and expenses if the defendant prevails in the action and the court finds that the claim of the person bringing the action was clearly frivolous, clearly vexatious, or brought primarily for purposes of harassment.” (31 U.S.C. 3730(d)(4).)

The False Claims Act: Other Provisions As a “whistleblower” statute, the Act not only incentivizes, but insulates relators, barring discrimination against them because of their lawful acts, including “in the terms and conditions of employment …” (31 U.S.C. 3730(h).)

Finally, to prevent relators from climbing onto the “gravy train,” the Act bars relators from becoming qui tam plaintiffs once the government has sued, or once the claim is public knowledge, unless the relator qualifies as the “original source.”

Conclusion Whether or not a structural engineer ever encounters a qui tam action, given the increasing prevalence of government money in the construction industry, and the pervasive reach of qui tam laws like the False Claims Act, it is simply not a prudent choice to remain oblivious.▪ Matthew R. Rechtien, P.E., Esq., (MRechtien@BodmanLaw.com), is an attorney in Bodman PLC’s Ann Arbor, Michigan, where he specializes in construction law, commercial litigation, and insurance law. Prior to becoming a lawyer, he practiced structural engineering in Texas for five years.

Those interested in further reading on the subject may consider reading False Claims in Construction Contracts: Federal, State and Local, Charles M. Sink and Krista Lee Pages, Editors, ABA Publishing, 2007.

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State Qui Tam Laws While Mr. Lincoln’s law is the original, and most commonly litigated, qui tam statute, it’s hardly alone. Not only are there other federal qui tam statutes, but many states have adopted analogous statutes of varying scopes.

Indeed, as of the publication date, more than 25 states have false claims acts of some sort, though many are narrowly focused on, for example, healthcare claims.

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

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(31 U.S.C. 3730(b)(1).) Such persons are “relators,” and, as an exception to the general rule, need not have been personally harmed to have standing to sue.

When relators sue, they sue “in the name of the” federal government; from that point forward, their claims “may be dismissed only if the court and the Attorney General give written consent to the dismissal and their reasons for consenting.” (31 U.S.C. 3730(b)(1).)

Qui tam actions under the Act proceed in one of two ways: conducted by the government, or conducted by the relator. Indeed, on filing of a qui tam complaint, the Act obliges the relator to serve the federal government with a copy of the complaint and all “material evidence and information the person possesses.” (31 U.S.C. 3730(b)(2).)

The Act also provides that the filing is to “remain under seal for at least 60 days, and shall not be served on the defendant until the court so orders.” (31 U.S.C. 3730(b) (2).) This allows the federal government to decide whether to take over the case. The federal government may during the 60-day period “proceed with the action, in which case the action shall be conducted by the Government” or “notify the court that it declines to take over the action, in which case the person bringing the action shall have the right to conduct the action.” (31 U.S.C. 3730(b)(4).)

The relator’s rights vary depending on the government’s choice. If the government proceeds, “it shall have the primary responsibility for prosecuting the action.” (31 U.S.C. 3730(c).) The relator may continue at that point as a party to the case, but subject to significant constraints: overruled by the government’s actions, but generally entitled to a hearing or other process. (31 U.S.C. 3730(c)(2).) If the federal government does not proceed, “the person who initiated the action shall have the right to conduct the action,” subject to the federal government’s right to be served with the papers filed in the action, and its potential right to intervene later “upon a showing of good cause.” (31 U.S.C. 3730(c)(3).)

Why take on the headache of being a relator? The Act incentivizes the very deputies it appoints. Even if the government proceeds, the relator “shall [generally] … receive at least 15 percent but not more than 25

CASE BuSinESS PrACtiCES

business issues

Contract Writing for Young PMs Part 2

By Kate Stanton, P.E.

T

his article is the second in a series from CASE to help structural engineering firms become more profitable by using contracts effectively, focusing on how a young project manager can write and use contracts to achieve more successful projects.

In the hands of a young project manager (or any manager), a well-written contract is a valuable resource. A well-written contract can reduce uncertainties in scope, perform double-duty as a project work plan (including manpower breakdowns if scope is itemized into different tasks), start communications with the client off on a good path, and make identification of additional services-worthy items more clear. Conversely, a poorly written contract can result in wasted time, effort, and profits while playing the “is this or isn’t this in my scope” game and potentially result in an unhappy client who isn’t getting what he/ she paid (or thought he/she paid) for. With this in mind, let’s take a look at how to write and use contracts to gain the most benefit.

Use Established Contract Resources In the first article of this series (December 2014), standard contracts, including those published by the American Institute of Architects (AIA) and the Council of American Structural Engineers (CASE) were discussed.

Use them! These gems contain a wealth of industry-accepted, lawyer-vetted clauses.

They have been written to cover all of the bases. (Seriously, if left on your own, would you have thought to consider all sixty-six scope of services items that are listed in CASE Document 6, Commentary on AIA Document C401 ‘Standard Form of Agreement Between Architect and Consultant’? Doubtful!)

Moreover, your clients are likely to be familiar with these documents and may be more inclined to accept the standard contract terms without a fuss. Keep in mind, however, that AIA documents are written with terms that are favorable to architects, sometimes at the detriment of engineers. Modifications of the standard contract may be necessary.

If your firm has contract templates that have been developed in-house, these will likely

Words of Wisdom for Young Engineers Writing Contracts As a young engineer, you have probably worked on projects where you were paired with other young clients/consultants (since we tend to work on jobs that fit our limited experience levels). Rather than stumbling along with a “deaf leading the blind” type of relationship, I like to rely on a well-written contract to clearly lay out expectations; and I use my contract throughout the course of the project to stay aligned with my project scope.

– Kate Stanton, Project Manager with Schaefer I learned the hard way about the importance of writing a solid contract while working on a renovation project in which I did not write the contract or study it closely prior to beginning the work. Our contract vaguely stated that we would “update our drawings as required during the course of the project”. There were multiple changes by our client and existing conditions discoveries during construction that required design and drawing changes. The majority of these changes would have been worthy of additional services had the original contract language allowed me to pursue those.

– Travis McCoy, Project Manager with Schaefer When I was president of the firm, I wanted project managers that impressed the client so much that when the client had another project, he/she would call that project manager directly instead of me. If the project manager had reached this level of trust with his/her clients and developed other business skills such as preparing proposals and contracts, they were the ones promoted to more responsible positions in the firm.

– Steve Schaefer, Founder and Chairman of Schaefer address issues unique to your firm. The author’s firm’s contract database includes pre-written appendices to pick and choose from, a veritable list of “I-got-burnt-by-thatonce-and-I-won’t-get-burnt-again” clauses developed over years of working with repeat clients and on repeat project types. As a young project manager, leaning on in-house contract resources is a great way to write contracts that align with your company’s level of service and that protect your company’s best interests.

Be as Specific as Possible with Your Scope Breaking the project down into an itemized list of smaller tasks has many benefits. The list will provide clarity to both you and your client regarding what has been included in the scope, making it easier to identify items that have inadvertently been left off. Taking this scope list and estimating the time required for each task is a good way to calculate the minimum fee for negotiating with your client.

This is much more accurate than looking at the project as a whole and throwing a

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number out. Divide and conquer! Itemizing also comes in handy as the list can perform double-duty as a project work plan. With tasks and time requirements clearly stated at the onset of project work, it will be easier to stay on schedule and within budget during the project.

Establishing the basis of your contract is also important. Include a list of all drawings (and issue dates) and correspondence used when determining contract scope and fee. Follow up on any verbal correspondence with email documentation that can be added to the project file. This way, when a pre-fabricated awning shown on the basis-of-scope/fee drawings develops into a compound-curved canopy that cantilevers over a driveway, you will be able to address this scope change with your client and discuss additional services.

State Assumptions, Limitations, and Exclusions In the land of unicorns and healthy bacon, our clients give us all of the information that

we need upfront and project changes don’t happen. Unfortunately, this land does not exist. As our industry continues to push the envelope on expedited project schedules and design-build collaborations, we are often faced with providing a contract based on limited or incomplete information. Without knowing what the project will actually evolve into, writing an appropriate contract scope and calculating an adequate project fee is a daunting task and warrants careful communication with your client. If you are a sub-consultant, ask him/her how they are handling project uncertainties when developing their contract with their client, and tell them that the uncertainties (if not explicitly excluded) force you into a higher fee to cover the costs of potential unknowns. Solicit feedback from a more senior project manager in your office – you will want to make sure that your contract handles this situation in the same manner that similar past projects have, and that your contract doesn’t make your firm susceptible to undesirable risks.

Writing contracts for renovation and expansion projects can also be tricky. Your scope should state any assumptions (for example, “fee is based on having existing drawings”), limitations (“field investigation of

existing structure does not include material strength testing” or “unforeseen foundation conditions may require additional engineering services beyond those that you have requested”), and exclusions (“fee does not include design of temporary shoring and/ or lateral bracing required during renovation”). As is often the case, stating what is not in your scope is just as important as stating what is in your scope. Of course, you will have to strike a balance between an exhaustive list of exclusions against the client’s perception that you are backing them into a corner and will inundate them later with additional service requests.

Reap the Benefits of a Well-Written Contract Let your well-written contract benefit you throughout the course of the project. Now that you’ve written a rock-solid contract, be sure to use it to your advantage. Using a contract’s itemized task breakdown as your project work plan was mentioned previously, but the benefits of a well-written contract do not end there.

When it acts as the first formal communication between you and your client, a

well-written contract can establish you as a project manager with solid communication skills who understands both the priorities of the project and the value that you bring to the project team. Use the contract scope and fee during a kick-off meeting with other in-house engineers and detailers to divvy out project responsibilities and budgets. The contract will also become a valuable reference when scope creep and project changes threaten to derail project schedule and profits – you can point to the well-written project scope and more easily argue your case for additional time to complete work and/or additional service fees.

All in all, a well-written contract can be a valuable tool to increase project efficiencies, client satisfaction, and overall project success. Young project managers who approach contract writing with the same care and consideration they allot to their engineering calculations will reap the benefits.▪ Kate Stanton, P.E., is a project manager and company stockholder at Schaefer, a 60 person structural engineering firm with offices in Cincinnati and Columbus, Ohio. Kate can be reached at kate.stanton@schaefer-inc.com.

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Product: RAM Structural System Description: The RAM Structural System is the only fully integrated engineering software with complete building analysis, design, and drafting for both steel and concrete structures.

CADRE Analytic Phone: 425-392-4309 Email: cadresales@cadreanalytic.com Web: www.cadreanalytic.com Product: CADRE Geo Description: Geodesic design application for generating a wide variety of geodesic and spherical structures for CAD or FFA applications. Output are clean DXF files suitable for structural analysis applications. Produces detail design data for domes such as hub and panel layouts, dimensions, dihedral angles, volume and surface area.

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.

Decon USA Phone: 707-996-5954 Email: frank@deconusa.com Web: www.deconusa.com Product: Jordahl Anchor Channels Description: Software provides a user-friendly and safe calculation for anchoring in concrete with JTA anchor channels. Features a technical and economical optimization of the design for each individual connection. 3D graphics are easy to use and allow a fast and clear input of all data.

Product: Studrails® Description: A free design software for Studrails called STDESIGN 3.1. The software can be downloaded from the website and complies to ACI 318, ACI 421.1 and CSA A 23.3. PC based and excellent for efficient and verifiable output on punching shear reinforcement.

Design Data Phone: 402-441-4000 Email: doug@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.

ENERCALC, Inc.

ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: www.enercalc.com Product: Structural Engineering Library Version 6 Description: The big news is the CLOUD. The Structural Engineering Library is now available for Cloud usage. No more installing, control codes, activating, file shuffling, or updating.

Projects files can be moved to/from Cloud SQL. Monthly rates available. Cloud is included for active MSP users.

IES, Inc. Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis, ShapeBuilder, VisualFoundation Description: Try IES structural tools today!

Download a free-trial or watch a training video to get a jump start. Decide which product will meet your needs with the ‘Compare Products’ page. For 20 years, IES products sell themselves: Find out why, and then solve your next problem in minutes. continued on page 66

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Software UpdateS

news and information from software vendors

Nemetschek Scia

Standards Design Group, Inc.

StructurePoint

Phone: 410-290-5114 Email: dmonagan@scia-online.com Web: www.nemetschek-scia.com Product: Scia Design Forms Description: Integrate custom checks into your FEA workflow. Scia Design Forms makes it easy to script custom calculations that can run as standalone checks or link to Scia Engineer’s FEA workflow. Writing your own checks inside your FEA software is a real game changer. Try it for free!

Phone: 800-366-5585 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Wind Loads on Structures 4 Description: Performs computations in ASCE 7-10, Chapters 26-31 also ASCE 7-98, 02, 05, Section 6 and computes wind loads by analytical method rather than the simplified method, provides basic wind speeds from a built-in version of the wind speed, allows the user to enter wind speed.

Numerous specialty calculators.

Phone: 847-966-4357 Email: info@structurepoint.org Web: www.StructurePoint.org Product: Reinforced Concrete Design Software Description: spColumn for shear walls, bridge piers as well as typical framing elements in buildings and structures; spMats for commercial building foundations and industrial mats and slabs on grade; spSlab for reinforced concrete floor systems; spWall for cast-in-place reinforced concrete walls, tilt-up walls, ICF walls, and precast architectural and load-bearing panels.

Strand7 Pty Ltd

Struware, LLC

Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: An advanced, general purpose, FEA system used worldwide by engineers and analysts for a wide range of structural analysis applications. Strand7 can be used as a standalone system, or with Windows applications such as CAD software. It comprises preprocessing, solvers (linear and nonlinear static and dynamic) and postprocessing.

Phone: 904-302-6724 Email: email@struware.com Web: www.struware.com Product: Struware Code Search Description: Imagine getting all pertinent wind, seismic, snow, live and dead loads for your building in just minutes. Program simplifies ASCE 7 & IBC by catching the buts, ifs, insteads, footnotes and hidden items that most people miss. Demo on the website. Current users: a new update is available for download.

StrucSoft Solutions

Phone: 770-426-5105 Email: Info.us@tekla.com Web: www.tekla.com Product: Tedds Description: Perform 2D frame analysis; access a large range of automated structural and civil calculations to US codes and speed up daily structural calculations.

Product: Scia Engineer Description: New for 2015. Scia Engineer offers an easy way to plug structural analysis and design into today’s BIM workflows. Tackle larger projects with advanced non-linear and dynamic analysis.

Plug into BIM with IFC, and bi-directional links to Revit, Tekla, and others. Free demo!

Powers Fasteners Phone: 845-230-7533 Email: Mark.Ziegler@sbdinc.com Web: www.powers.com Product: Powers Design Assist Description: Anchor design software now includes the ACI 318-11 code provisions. Download or update your version to version 2.2 today, to take advantage of the most current code standard.

Product: Powers Submittal Generator Description: PSG is a new submittal and substitution online tool that helps contractors create submittal packages in just a few steps and allows them to include all applicable code reports and technical details with a few clicks.

Contact us for a free demonstration!

Simpson Strong-Tie Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: CFS Designer™ Software Description: With CFS Designer software, coldformed steel Designers can design CFS beamcolumn members according to AISI specifications and analyze complex beam loading and span conditions. It allows the design of multiple engineering models within the same job file, and supports connection design for specific Simpson Strong-Tie curtain wall and bridging connectors.

Product: Strong Frame® Moment Frame Selector Software Description: The Strong Frame Moment Frame Selector Software (for U.S. and Canada) helps engineers select an ordinary or special moment frame based on given geometry and loading. With only minimum input geometries, the software narrows down available stock frames to a handful of possible solutions, or provides a possible customized solution.

Phone: 514-731-0008 Email: info@strucsoftsolutions.com Web: www.strucsoftsolutions.com Product: Metal Wood Framer Description: A template-based and rule-driven extension to Autodesk® Revit® for framing.

Empowers users to automate the modeling, clash detection & manufacturing of light gauge steel and wood framing including shop drawings, cut lists, BOM, optional CNC output & more.

Structural Engineers Inc. FLOORVIBE

Phone: 540-731-3330 Email: tmmurray@floorvibe.com Web: www.FloorVibe.com Product: FloorVibe v2.20 Description: Analyze floor vibrations due to walking and rhythmic activities and for floors supporting sensitive equipment. Version 2.20 includes recommendations in the just released SJI Technical Digest 5 “Vibration of Steel JoistConcrete Slab Floors”, as well as, the AISC Design Guide 11 “Floor Vibrations due to Human Activity”.

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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Tekla, Inc.

Product: Tekla Structures Description: Create and transfer constructible models throughout the design lifecycle. From concept to completion, Tekla Structures allows you to create accurate and information-rich models that reduce RFIs and enable structural engineers proven additional services. Models are used for drawing production, material take offs and collaboration with disciplines like architects, consultants, fabricators and contractors.

WoodWorks Software Phone: 800-844-1275 Email: sales@woodworks-software.com Web: www.woodworks-software.com Product: WoodWorks Design Office Suite Description: Conforms to IBC 2012, ASCE7-10, NDS 2012, SDPWS 2008; SHEARWALLS: designs perforated and segmented shearwalls; generates loads; rigid and flexible diaphragm distribution methods.

SIZER: designs beams, columns, studs, joists up to 6 stories; automatic load patterning.

CONNECTIONS: Wood to: wood, steel or concrete. Canadian version available.

award winners and outstanding projects

Spotlight

East Station Plaza – Danseurs (Dancers)

By John Sumnicht, S.E., Ronald Mayes, Ph.D. and Nicholas G. Wetzel, S.E., CPEng Simpson Gumpertz & Heger Inc. was an Outstanding Award Winner for the East Station Plaza – Danseurs (Dancers) project in the 2014 NCSEA Annual Excellence in Structural Engineering awards program (Category – Other Structures).

U

nion City, California wanted to develop a civic plaza to the east of the Union City BART station.

Although money was tight due to the economic downturn, the City allocated local grant funding for the plaza upgrades.

The architect for the project, Boris Dramov, FAIA, of ROMA Design Group, envisioned a centerpiece for the plaza – a terraced fountain with three bronze sculptured “Danseurs” – on platforms positioned within the fountain.

The sculptures were fabricated in France, and for a time, were displayed in the plaza on the north side of the Louvre in Paris. Union City officials, in conjunction with the architect identified the sculptures and the City purchased them before the design of the fountain commenced. At a pre-proposal meeting, Boris expressed a concern about the seismic performance of the sculptures. As shown by the photo, his concerns were well founded.

Each sculpture is approximately 16 feet (5 m) tall, weighs approximately 4,000 pounds (1,800 kg), and is very slender. The ankles of the sculptures are only approximately 6 inches in diameter. In addition, the Hayward fault is only 0.6 miles (1 km) northeast of the site. At the first sign of shaking, the sculptures would be severely damaged or possibly collapse if a conventional approach to the anchoring the sculptures was used.

John Sumnicht, principal-in-charge, suggested mounting the sculptures on base isolated platforms to address this challenge.

The concept of an isolated platform is similar to that used in base isolated buildings – put the object on a suspension with springs and shocks to reduce the lateral forces on the object – but on a smaller scale. This was the only scheme that had a chance of protecting the sculptures without obtrusive and objectionable external bracing.

John Meyer and Ron Mayes, both with Simpson Gumpertz & Heger, Inc. (SGH), first proposed isolated floors a number of years ago when they were working for a biotech company on how to protect high value equipment or product from damage during strong ground shaking. They proposed mounting

the high-value equipment and product on isolated floors. They worked with Dynamic Isolation Systems (DIS) to develop an early prototype utilizing small platforms with a rubber isolator and dampers. DIS took the concept and developed a system that relies on springs and cables.

The isolation system used for the sculptures utilizes cross-linear bearings and a bi-directional spring unit that acts as the energy dissipation element and the spring.

The hysteretic behavior of the spring unit is unconventional, with bilinear and different ascending and descending branches. The stiffness of the three branches (K1, K2, and Kr) is a function of the spring stiffness, and each can be adjusted to optimize the desired isolator behavior.

The program, Design Ground Motion Library, developed by AMEX Geomatrix Consultants, Inc., was used to develop the ground motions. The ground motions were then scaled to the response spectrum for the East Union Plaza site.

An analytical model of a sculpture on top of the isolation floor was developed using SAP2000.

The sculptures and steel platform were modeled as linear elastic elements, and the spring unit was modeled with non-linear elements that followed the force-deformation response.

In evaluating the seismic performance of the sculptures, the accelerations that the sculpture would experience and the stresses that would develop in the ankles of the sculptures were of paramount concern. For the Design Earthquake (DE) event, the average acceleration of the seven time histories at the center of mass of the sculpture, if the sculptures were rigidly attached, is 1.30g. When evaluating the stresses in the ankles, the average demand-tocapacity ratio (DCR) for a rigidly attached sculpture is 4.95. The DCR is an indicator of the ductility demand or inelastic deformation that will occur at the ankle location resulting in a rotation of the statue from the vertical position. If the sculptures are rigidly attached to the base, it is clear that a hinge would form at the base of the sculptures resulting in collapse during moderate to strong ground shaking.

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With the isolated platform, for the DE event, the average displacement of the seven time histories is 20 inches, the average acceleration is reduced to 0.2g, and the average DCR for the stress in the ankles is reduced to 1.04. With a DCR of 1.04, little to no damage of the sculpture during a DE ground shaking is expected.

The isolation platforms were beautifully incorporated into the fountain by placing them on stone-clad pedestals, artfully arranged in the fountain. In addition, the platforms are clad in stone and bronze to transition seamlessly from the pedestals to the statues.

Through the use of isolated platforms SGH was able to provide the architect and City an elegant solution to protecting their civic sculptures from earthquake damage. The total construction cost for the project was approximately $5,700,000.▪ John F. Sumnicht, S.E., is a Senior Principal with Simpson Gumpertz & Heger Inc. John can be reached at JFSumnicht@sgh.com.

Ronald L. Mayes, Ph.D., is a Staff Consultant with Simpson Gumpertz & Heger Inc. Ronald can be reached at RLMayes@sgh.com.

Nicholas G. Wetzel, S.E., CPEng, specializes in the design of new structures, seismic evaluation of buildings, seismic rehabilitation of existing structures, and investigation of structural failures.

GINEERS

March 24, 2015 The Correlation Between Soil Bearing Capacity & Modulus of Subgrade Reaction Apurba Tribedi, C.E., Director of Product Management at Bentley Systems Inc.

2015 NCSEA Excellence in Structural Engineering Awards Highlighting the best examples of structural engineering ingenuity throughout the world Eight categories: • New Buildings under $10M • New Buildings $10M to $30M

March 31, 2015 AWC’s 2015 Special Design Provisions for Wind and Seismic – Overview & Changes from Previous Editions Michelle Kam-Biron, P.E., S.E., SECB, M.ASCE, Director of Education for the American Wood Council April 14, 2015 Quality Assurance For the Structural Engineer Edward Westerman, P.E., S.E., Director of Structural Engineering with Clark Nexsen

• New Buildings $30M to $100M • New Buildings over $100M • International Structures • Renovation/Retrofit Structures

April 28, May 5 & May 12, 2015 Coming in April and May, Jon Schmidt’s 3-part series on blast: Design Criteria/ Structural Elements/Glazing Systems.

Jon A. Schmidt, P.E., SECB, BSCP, Director of Antiterrorism Services at Burns & McDonnell

• Other Structures • New Bridges/Transportation Structures

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More information and entry form at www.ncsea.com

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Entries are due Monday, July 20, 2015, and awards will be presented at the NCSEA Structural Engineering Summit on October 2nd in Las Vegas.

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Eligible projects must be substantially complete between January 1, 2012 and December 31, 2014.

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News form the National Council of Structural Engineers Associations

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NCSEA Webinars

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CALL FOR ENTRIES

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Diamond Reviewed

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.

visit www.ncsea.com for more information

Join us in Las Vegas for the new

NCSEA News

2015 StructuraL EnginEEring Summit Red Rock Resort, September 30 – October 3 2015 marks the 1st NCSEA Structural Engineering “Summit”. The Summit is the new title for NCSEA’s Annual Conference, which draws together the best in the structural engineering field. If you are a structural engineer or a company providing products and services to structural engineers, this is the meeting you don’t want to miss!

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The third NCSEA Winter Leadership Forum drew principals and leaders from a diverse group of engineering firms to Coral Gables, Florida, for thought-provoking sessions, meaningful interaction, and networking. Sessions focused on business development, retaining good relationships with your clients, banking, and organic growth versus growth by acquisition, then finished with a case study that separated the group into four Boards of Directors, to discuss whether or not to purchase another firm. Attendees enjoyed 65-degree weather, a great reception sponsored by ICC Evaluation Services, and some excellent restaurants one block away, on Miracle Mile.

Thank you to ICC Evaluation Services for being a sponsor of NCSEA’s Winter Leadership Forum.

NCSEA News

Leaders and Principals Gather for High-Level Talks and Networking in Coral Gables, Florida

News from the National Council of Structural Engineers Associations

“It was a great event. The topics were right on target and relevant. The venue was excellent. The attendees were engaged in presentations. And best of all, everyone was talking – freely and openly.”

Barry Arnold, P.E., S.E., SECB Principal, ARW President, NCSEA

Engineers from the following firms were represented at the 2015 NCSEA Winter Leadership Forum:

GINEERS

Mark D. Aden, P.E., S.E. President/CEO, DCI Engineers

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“I really enjoyed it as usual. Great group of people this year, and the banking presentation was excellent.”

OCIATI

KL&A, Inc. LV Engineers Magnusson Klemencic Associates Martin/Martin, Inc. McLaren Engineering Nayyar & Nayyar O’Donnell & Naccarato Paul J. Ford and Company PEAK Engineering, Inc. Providence Bank Reaveley Engineers + Assoc.

SMBH, Inc Sound Structures, Inc Stantec STV, Incorporated TGRWA, LLC Thornton Tomasetti TLV Holdings Wallace Engineering

ASS

ARW Engineers Ascent Group, Inc. Barter & Associates, Inc. BHB Consulting Engineers Bob Rude Structures, Inc. Bowen Engineering Corporation DCI Engineers Degenkolb Engineers Dibble Engineers Douglas Wood Associates, Inc. Equilibrium Engineers LLC Gilsanz Murray Steficek LLP Haskell HGA IBI Group Michigan, LLC International Code Council JDB Engineering, Inc. John Tawresey Consulting Joshua B. Kardon + Co.

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Registration Now Open for Structures Congress 2015 New ideas. New practices. New science.

New resources. New colleagues.

April 23 –25, 2015, Portland, Oregon

Early Bird Registration Rates Available until March 4, 2015.

The Structures Congress will feature 120 informative technical sessions, topics will include: • Buildings • Bridges • Wood • Tall Buildings • Business and Professional Practice • Natural Disaster and Resilience • Structural Steel • Wind • Blast • Masonry • And many more There will also be sessions on “Expanding the Structural Engineer’s Role in Society.” Don’t miss the CASE Spring Risk Management Convocation. Earn up to 15PDHs! Visit the congress website at www.structurescongress.org for more information and to register.

Reactivation of Blast Protection of Building Standards Committee First published in 2011, ASCE/SEI 59-11 Blast Protection of Buildings is being revised to improve current content and expand its scope. The committee that will undertake this task is being reconstituted, with the potential that the first meeting will be during the 2015 Structures Congress in Portland, Oregon. Please express your interest in membership of this committee by submitting an application on the SEI website at www.asce.org/structural-engineering/ sei-codes-and-standards-committee-application/.

IBC Student Paper Competition Entries due by March 31, 2015 The International Bridge Conference James D. Cooper student paper competition is open to college and university engineering students in the United States and worldwide. The winning paper will receive a $1,000 Fellowship, complimentary conference registration, hotel and travel allowances to attend the 32nd Annual IBC, June 7-11, 2015, in Pittsburgh, PA. Additionally, the winning paper will be considered for inclusion in the published proceedings and for presentation at the conference. Deadline is March, 31, 2015. See the IBC website at www.eswp.com/bridge/student_aid_bridge.htm for more information and to apply.

New Structural Books Available from ASCE Wind Induced Motion of Tall Buildings Wind-Induced Motion of Tall Buildings presents an overview of current research on occupant response to motion in tall buildings. This state-of-the-art report describes the physiology and psychology of the human perception of motion, and explains the factors that can be used to characterize a building’s movement. The authors summarize the results of field studies and motion simulator experiments that examine human perception of, and tolerance for, building motion. They survey the serviceability criteria adopted by international standards organizations and offer general acceptance guidelines based on peak acceleration thresholds. Finally, they identify design strategies that can mitigate wind-induced building motion through structural optimization, aerodynamics treatment, and vibration dissipation or absorption.

This report was developed by SEI’s Tall Buildings Committee.

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.

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ASCE 24-14 Flood Resistant Design and Construction Flood Resistant Design and Construction, ASCE/SEI 24-14, provides minimum requirements for design and construction of structures located in flood hazard areas and subject to building code requirements. Identification of flood prone structures is based on flood hazard maps, studies, and other public information. This standard applies to new structures, including subsequent work, and to work classified as substantial improvement of existing structures that are not historic. Standard ASCE/SEI 24-14 introduces a new concept, Flood Design Class, that bases requirements for a structure on the risk associated with unacceptable performance. This standard provides essential guidance on design and construction to structural engineers, design professionals, code officials, floodplain managers, and building owners. The standard is adopted by reference in model building codes.

This standard was prepared by SEI’s Flood Resistant Design and Construction Standards Committee.

To purchase these and other structural books visit the ASCE Bookstore at www.asce.org/bookstore/.

March 2015

You are invited to contribute to the new ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering. If you are a practicing engineer or researcher in the field of risk or uncertainty analysis in engineering systems, we ask you to consider sharing your expertise by either submitting a manuscript to the Journal or contributing as an expert reviewer. The Journal presents state-of-the-art research and best practices on risk and uncertainty related issues. Topics include but are not limited to: • Risk quantification based on hazard identification, • Scenario development and rate quantification, • Consequence assessment, • Valuations, perception, and communication, • Risk-informed decision-making, • Uncertainty analysis and modeling, • Other related areas.

Visit the ASCE website at http://ascelibrary.org/page/ajrua6/ editorialboard, to learn more.

Call to SEI Committee Chairs to Submit Proposals by June 1 The SEI Futures Fund (SEIFF) invites proposals for new initiatives in line with SEIFF strategic areas that benefit the structural engineering profession and/or SEI as a whole, and would not otherwise be funded out of SEI Division or operating funds. Review the SEIFF Case Statement and the Guidelines for FY2016 funding requests. If your SEI Division Executive Committee wishes to vet the proposal, plan to do so this spring, to meet the June 1 final proposal submission deadline. See the SEI website at www.asce.org\SEI for more information.

Call for abstract and session proposals now open until April 7, 2015

Connect | Collaborate | Build Be part of the technical program for this unique event featuring dynamic sessions and presentations on topics addressing both Geotechnical and Structural Engineering issues. Final papers are optional and will not be peer reviewed. Consider submitting either session proposals or single abstracts related to the topics and subtopics of interest to both professions.

The 2016 joint Congress will feature a total of 15 concurrent tracks: there will be tracks based on traditional GI and SEI topics, and tracks on joint topics. In addition, we will be offering interactive poster presentations within these tracks. This event will be held instead of a Structures Congress in 2016.

All proposals must be submitted by April 7, 2015 (no extensions).

Visit the joint conference website at www.Geo-Structures.org for more information and to submit your abstract.

Save The Date

Second ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures December 10-12, 2015 Hyatt Regency San Francisco www.atc-sei.org/

Local Activities Roanoke Chapter Welcome to the newly established SEI Roanoke Chapter.

SEI Roanoke Chair Patrick Williams leads the effort to bring together the local structural engineering community to raise awareness for the new SEI Roanoke Chapter, and plan activities to serve local members and the community, including the nearby SEI Graduate Student Chapter at Virginia Tech.

Oregon Chapter The Oregon ASCE Chapter has formed the new SEI Oregon Chapter. The new chapter will focus on providing greater access to information, helping members stay current on structural engineering trends, connecting with a diverse population of like-minded engineers, and becoming good stewards of the built environment. SEI Oregon will appoint board members and hold elections for officers who will serve for 2015.

STRUCTURE magazine

University of Texas at Arlington Graduate Student Chapter The Graduate Student Chapter at UT Arlington had a very productive fall. Activities included field visits to construction sites, seminars, and participating in an ASCE webinar.

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 LAD Committees.

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The Newsletter of the Structural Engineering Institute of ASCE

SEI Futures Fund Seeks Strategic Initiative Proposals for Funding Consideration

February 14–17, 2016, Phoenix, AZ

Structural Columns

ASCE-ASME Journal of Risk and Geotechnical & Structural Uncertainty in Engineering Systems Engineering Congress 2016

CASE in Point

The Newsletter of the Council of American Structural Engineers

Use of the LPTA Acquisition Procedure in Contravention of the Brooks Act

T

he Federal Acquisition Regulation (FAR) states in FAR 1.102 that “The vision for the Federal Acquisition System is to deliver on a timely basis the best value product or service to the customer, while maintaining the public’s trust and fulfilling public policy objectives.”

Over the past several years, primarily in response to reduced procurement budgets, some federal government agencies have started using with greater frequency the Lowest Price Technically Acceptable (LPTA) procedure in the acquisition of technical services, including professional architectural and engineering services in some instances, in their attempt to obtain best value.

This practice raises serious concerns in the architectural and engineering communities and appears to be in contravention of the Brooks Act, or at least the spirit thereof, which established Qualification-Based Selection (QBS) as the norm in Federal contracting for architects and engineers

What is LPTA? In 1997, LPTA was added to the FAR as a source selection process in FAR 15 – Contracting by Negotiation. FAR 15.101-2 states that “the LPTA source selection is appropriate when best value is expected to result from selection of the technically acceptable proposal with the lowest evaluated price.” In other words, the LPTA process was intended to be used in situations where paying more for a product or service was not expected to provide better/greater value to the government because all of the offerors had satisfied the minimum requirements specified, i.e. the LPTA process by definition provided the best value. Additionally, in FAR 15-101, the concept of a price-value continuum is introduced, and it is stated that the selection based on price is most appropriate “where the requirement is clearly definable and the risk of unsuccessful contract performance is minimal” and on the opposite end of the continuum, when “The less definitive the requirement, the more development work required, or the greater the performance risk, the more technical or past performance considerations may play a dominant role in source selection.”

These contrasting points draws a fair distinction for when price is the appropriate selection measure (e.g. products and commodities) and when it is not (e.g. services).

If LPTA was used to contract for services, once it is determined which offerors meet the minimum stipulated requirements in the government’s announcement (say with regard to prior project experience, staffing requirements, technical capabilities and the like), the final selection would be based solely on the lowest price. A firm with a slightly higher price than the low price, but offering vastly superior resources and capabilities, is not to be selected, based on the no better value concept.

Obviously, under this guideline for the use of LPTA, the acquisition of professional architectural and engineering services raises serious concerns in the architectural and engineering communities. Architects and engineers all know from experience that the best value to the government is really measured by the lowest total cost of a project that satisfies the government’s programmatic and life-cycle costs which, STRUCTURE magazine

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on a design and construction project, include both the cost of construction and life time ownership costs, including operations and maintenance, as well as the far smaller cost of architectural and engineering services.

As noted above, the use of LPTA is also in contravention of the acquisition regulations in FAR 36 – Construction and Architect-Engineer Contracts, Sub 36-6 – Architect-Engineer Services, which is based on Public Law 92-582, otherwise known as the Brooks Act. It would be fair to ask whether the Federal government would include an entire chapter in the FAR specifically for the acquisition of services from contractor, engineers and architects if the government really wanted LPTA to be used.

As taxpayers and citizens, some push-back by architects and engineers on the perhaps illegal, but most definitely inappropriate, use of LPTA is warranted. Design professionals never wish to speak ill of their clients, but since they are in the business of offering advice and guidance and being trusted advisors to their clients, if they believe that the procurement of the services required isn’t being done in accordance with the client’s goals and best interests, they have a duty to speak up.

The Brooks Act Concern within the AE community regarding the ability to fulfill the government’s best value goal when AE selection was based on the lowest bid (i.e. the lowest-price offeror) led to the passage of Public Law 92-582, otherwise known as the Brooks Act, 1972, as an amendment to the Federal Property and Administrative Services Act of 1949. The purpose of the Brooks Act was to establish Federal policy concerning the selection of firms and individuals to perform architectural, engineering, and related services to the Federal government. Section 904, titled Negotiations of Contracts for Architectural and Engineering Services, provides guidelines on how firms are to be selected and the order in which qualifications are evaluated: “Sec. 904.(a) The agency head shall negotiate a contract with the highest qualified firm for architectural and engineering services at compensation which the agency head determines is fair and reasonable to the Government.”

The best value selection process can be summarized in three simple steps: 1) Which firm is the most qualified? 2) Is that firm’s proposed fee fair and reasonable? 3) If yes, then proceed to a signed contract. If no, then proceed to next most qualified firm and start over. The government’s integration of the Brooks Act into the FAR for the procurement of public projects established the QBS process.

Comparisons So given the tools the government has at its disposal, the question is when should it use QBS and when should it use LPTA? The answer seems clear that when acquiring services from architects and engineers, the procedures in FAR 36.6 (QBS) are the only appropriate, and they might say legal, way.

March 2015

Recent Experiences

Conclusion

The AE industry has become aware of the use of LPTA or practices very close to LPTA in the second-phase of the two-phase Design-Build acquisition process, contained in FAR 36.3.

In the two-step process, the most qualified contractor/ designer teams are identified in phase one based on relatively low cost technical approach and qualifications submissions.

In phase two, extensive additional technical information is submitted along with expense price proposals, requiring significant design work to be performed, in order to accurately identify construction costs, per FAR 15. FAR 15 allows the contracting officer broad latitude in defining the selection criteria, i.e. whether technical factors are most important or whether pricing factors are most important in a tradeoff process along the best-value continuum. FAR 15 also allows the use of LPTA, which is the most extreme version of selection based on price importance since trade-offs are not permitted. To be consistent with the spirit and benefits of the Brooks Act, since architects and engineers are involved, phase two really ought to be solely evaluation based on additional technical factors and an interview, leading to the ranking of the most qualified firms, followed by a negotiation with the most qualified team on the price. Anything less than this subverts the entire process and changes it into a price competition amongst the qualified firms, whether it is explicitly stated or not. The most qualified firms will likely look very similar to the government (since phase one eliminated all but the most qualified teams); therefore, everyone on the design-build team will be asked to provide their lowest price so the team can submit the lowest total price in an attempt

In a response to reduced budgets and cuts in spending, some Federal agencies have resorted to the use of LPTA, or practices very close to LPTA, as a selection tool for some technical services, including architectural and engineering services covered

by FAR 36. With regard to the services of architects and engineers, this is in contravention of the Brooks Act, which was passed by Congress to ensure that architectural and engineering services are always made based on a Qualifications-Based Selection process devoid of the influences of price. It is not conceivable that the requirements for such architectural and engineering services (qualifications, skills, resources, facilities, past performance, etc.) could be written so well, and with such precision and detail, that the government agency could confirm the offeror’s minimum technical credentials and thereby base the selection on lowest price and assure that best value is obtained. Use of the QBS process benefits the project owner and the public by providing the opportunity to optimize the life-cycle costs, performance, and safety of a project by using the most qualified technical team at a point in the project when the cost of services is relatively, extremely low.

It would be fair to say that the use of LPTA, or practices very close to LPTA, would likely result in the selection of the lesser qualified professional with the lowest paid staff providing the poorest service. All fee above the minimum will be been wrung out of the offer. In the long term, this impacts innovation and design capabilities too, because firms will have insufficient funds to conduct training, study new ideas, perform research and the like. Hardly a recipe for project success or a path to achieve design excellence and best value in today’s complex world.

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to win. This is defacto low bidding for AE services, albeit amongst a short list of teams, the activity the Brooks Act sought to eliminate.

The government regularly acquires non-AE technical services that don’t clearly fall within the purview of FAR 36. This is where things get a bit sticky. But if the success of QBS in selecting architects and engineers is to serve as any lesson, a QBS procedure is most appropriate and will yield the best results when the government’s requirements are less definable or specific, are apt to change and/or grow over time, when there is the possibility of additional compensation for added innovation, etc. LPTA would seem to be applicable to the acquisition of only true commodities such as materials and products that have to be manufactured to certain industry standards such as ASTM, API, etc. This includes the ability to prototype and test.

Infrastructure projects are always unique, due to geographical location, weather conditions, soils composition, topography, location and type of utilities available, geotechnical formations, etc. The skill of the most qualified technical team to deal with known and unknown situations, and to optimally design the project the first time, is important.

The costs and time impacts of corrections, renovations, or even demolishment and reconstruction are too high for infrastructure projects, often more than the original construction. Risking this on using LPTA to save relatively small and usually non-existent savings on the cost of engineering services is questionable.

CASE in Point

Architects and engineers can point to more than a generation of successfully completed projects since the passage of the Brooks Act as evidence that QBS works and serves the interest of the government and the citizenry. Trying to develop a work-around of the Brooks Act to save a few dollars up-front, with no guarantee of saving money in total, seems misguided.

Since the cost of engineering services are so small, relative to the total construction and ownership costs for a project, any perceived savings in the cost of those services are inconsequential when compared to the impact of those services on total project costs and performance. Seeking the lowest cost of these services forces offerors to cut corners (e.g. less innovation, fewer alternatives considered, reduced level and hours of staff used, or types of equipment/tools applied).

This is not a benefit to the client/owner or the public, especially when public safety may be involved, as with most infrastructure projects.

Another drawback to using cost as a discriminator is that the scope of work becomes fixed, in order to fairly compare costs. With QBS, the scope of work is negotiated with the most qualified offeror, as part of arriving at a fair and reasonable fee for services. A better understanding of the work involved and the true needs of the client results from this process, all before signing a contract. With the fixed scope of a LPTA process, scope flaws, errors, or improvements may not be addressed until after contract award, requiring negotiations with the contractor on a sole source basis. This is not the best way to achieve true cost benefits.

Structural Forum

opinions on topics of current importance to structural engineers

Acceptable Collapse?

Thoughts on Building Seismic Performance Objectives

By Reid Zimmerman, P.E.

“D

anger. Extremely Flammable.

Fire/Explosion Hazard.” These words are printed in cautionary lettering on a little green propane tank used for my camping stove. Equally interesting, though not quite as dramatic, is the word “overbuilt” printed just above the manufacturer’s name. In context with the outcome of failure – an explosion – overbuilt seems stout, safe and ultimately reassuring.

Contrast this to the newly stated seismic performance objectives in ASCE/SEI 7-10, Minimum Design Loads for Buildings and Other Structures. In words printed for a different audience, ASCE/SEI 7-10 specifies an explicit acceptance of up to a 10% probability of partial or total collapse under Maximum Considered Earthquake (MCER) shaking.

You might be thinking to yourself, “I don’t remember that being in ASCE 7”; and if you were to consult your trusty ASCE/SEI 7-05, you would be right. But with the publication of ASCE/SEI 7-10, acceptable probabilities of collapse have been explicitly included in the commentary to Chapter 1. They are defined as a 10%, 6% and 3% acceptable probability of collapse given MCER shaking for Risk Category II, III and IV structures, respectively. The history of establishing such values dates back many years and has evolved through several FEMA publications.

A complete description is beyond the scope of this article and, frankly, should be told by someone older and wiser than myself, preferably while sitting around a campfire. What I can assure you is that (1) it was not settled on without thought, (2) it is in moderate agreement with the implicit assurances of past versions of ASCE/SEI 7, and (3) it will garner additional study in the years to come.

With the rise in popularity of statistics, everything from the outcome of the U.S. presidential election to the chance of rain in Portland, Oregon is being approached within a probabilistic framework. The acceptability of collapse for new buildings should be no different. How are we to say what is “conservative” or “safe” – or for that matter “overbuilt”

– without a point of reference? ASCE/SEI 7-10 now provides this probabilistically-based benchmark from which we can look back and, hopefully, move forward.

Let’s start with the good. We have no dramatic evidence that buildings constructed to ASCE/SEI 7-05 are especially collapse-prone in earthquakes. It should be acknowledged, though, that we do not have much data in recent years for real earthquakes producing severe shaking in the United States. Given our current knowledge, we can deem a building designed to ASCE/SEI 7-05 as generally acceptable in terms of collapse safety. It follows that, since the probability of collapse for those structures approximately matches the values found in ASCE/SEI 7-10 (confirmed by analytical studies), we are in the right ballpark for acceptable collapse probabilities.

So we know where we are, but do we know where we want to be? A 10% probability of collapse may be both consistent with the intent of the implicit provisions in ASCE/SEI 7 and attainable within the cost expectations of current building owners and developers, but is it “safe enough”? Or, even more perplexingly, could it be “too safe”? In justifying an acceptable probability of collapse, one might naively argue that the only acceptable probability of collapse is zero, but this is unattainable (even theoretically) and oversimplifies the issue. Instead, an acceptable probability of collapse would likely grow out of consideration for livability, cost-effectiveness and other concerns of modern society in balance with, but not necessarily in equal proportion to, public safety.

To attain this balance requires the input of the general public. However, with a mistaken belief in “earthquake-proof ” buildings still pervasive in society, and misunderstanding of statistics common – I admit to being guilty of this myself at times – is the general public knowledgeable enough to enter into this discussion? Some recent initiatives, such as the building rating system proposed by the U.S. Resiliency Council (www.usrc.org), reflect the belief that a system driven by the public

can succeed. While it would seemingly be undemocratic to disagree, the concern is over how to educate people so that they may make an informed decision.

Taking a step back, let’s ask ourselves why codes change at all. One’s first guess might be that they change to make buildings safer.

While I agree in principle, I believe that this is only half the story. They really change when the benefit-to-cost ratio of the revised language is favorable, or when new data implies a greater risk than previously anticipated. In the past, the benefit-to-cost ratio had to be presumed or was obvious from earthquake reconnaissance (e.g., out-of-plane anchorage of walls to diaphragms). What was missing, and what the explicit definition of acceptable probability of collapse provides, is a quantitative way of justifying future changes. I understand that not all things can be directly and quantitatively related back to collapse due to our own limitations and the uncertainty inherent in the natural world. Yet shouldn’t our goal (and our expectation) be to reduce the acceptable probability of collapse in future versions of ASCE/SEI 7? Isn’t that our duty as a profession?

As engineers, we pride ourselves on our ability to envision solutions in the presence of amazing uncertainty and randomness. Rather astoundingly, we do an impressive job of this.

However, sometimes this culture comes at the cost of permitting ourselves the freedom to ask difficult questions without immediately worrying about an answer. Is a 10% probability of collapse an acceptable target, or is it simply a product of our engineering culture – an answer to a difficult question using the only information we have? I don’t know. I wish it were as simple as being able to state that our buildings are “overbuilt,” like my little green camping stove propane tank. I think I’ll go camping.▪ Reid Zimmerman, P.E. (Reid.Zimmerman@kpff.com), is a structural design engineer at KPFF Consulting Engineers in Portland, Oregon.

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

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