STRUCTURE magazine | September 2016 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

INSIDE… 2016 STRUCTURAL ENGINEERING EDUCATION SURVEY

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STRUCTURE

September 2016

47 EDITORIAL

7 How You Can Help ICC Adoption of ASCE 7-16

STRUCTURAL REHABILITATION

34 Life before ICRI By Donald Kearney

By Ronald O. Hamburger, S.E., SECB LESSONS LEARNED INFOCUS

9 Bridging the Ethical Chasm By Barry Arnold, P.E., S.E., SECB

57 Considerations for Above Grade Residential Garages

INSIGHTS

61 Decrypting Cold-Formed Steel Connection Design By Randy Daudet, P.E., S.E.

Philipp R. Grosser, Ph.D. OUTSIDE THE BOX STRUCTURAL TESTING

18 Ground Penetrating Radar for Use on Concrete Structures

63 The Logic of Ingenuity – Part 1 By Jon A. Schmidt, P.E., SECB

By Charles Bransby-Zachary and Gina Crevello

SPOTLIGHT

67 Grove at Grand Bay STRUCTURAL SUSTAINABILITY

22 Environmental Impacts of Fire By Erica C. Fischer, Ph.D., P.E. and

By Vincent DeSimone, P.E.,

26 Confinement of Special Reinforced Concrete Moment Frame Columns By S. K. Ghosh, Ph.D. HISTORIC STRUCTURES

30 Brooklyn Bridge – Part 1 By Frank Griggs, Jr., D.Eng., P.E.

By James Case, P.E.

10 2016 NCSEA Structural Engineering Curriculum Survey 38 NCSEA 2016 Summit Special Section

and Abdul Mohammad, P.E.

47 Tornado Shelters in Schools

STRUCTURAL FORUM

By Benchmark H. Harris, P.E., S.E.

Luis Ramirez, P.E., SECB

Amit H. Varma, Ph.D. CODE UPDATES

42 STEALTH… the engineering of art FEATURES

STRUCTURAL SYSTEMS

By Richard T. Morgan, P.E. and

COVER STORY

By Douglas Gadow, P.E., S.E. and Jeremy Gavelin, EIT

14 Code Provisions for Cast-in-Place Anchor Channel Systems

74 The Ethics and Politics of Resilience By David Pierson, S.E.

IN EVERY ISSUE 8 Advertiser Index 65 Resource Guide (Anchoring) 68 NCSEA News 70 SEI Structural Columns 72 CASE in Point

On the cover This 35-foot tall, 65,000-pound thin shell concrete structure is the creation of Tristan Al Haddad of Formations Studio along with Jim Case of Uzun + Case Structural Engineers for the Promenade office tower in Atlanta, GA. See Feature article on page 42.

STRUCTURE magazine

51 Performance-Based Design of 111 Main in Salt Lake City By Mark Sarkisian, S.E., Peter Lee, S.E., Alvin Tsui, S.E. and Lachezar Handzhiyski, S.E.

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

September 2016

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Editorial

How You Can Help ICC Adoption new trends, new techniques and current industry issues of ASCE 7-16 By Ronald O. Hamburger, S.E., SECB

lease assist us in supporting the I-Code adoption of ASCE 7-16 and opposing the attempt to block the update to the 2016 edition of ASCE 7 Minimum Design Loads & Associated Criteria for Buildings and Other Structures for the International Building Code (IBC), International Residential Code (IRC), and International Existing Building Code (IEBC).

coefficients at eaves, edges, and ridge lines, as well as increase the width of these zones for low-slope roofs. However, in most regions, this is balanced by a reduction in mapped wind speeds, resulting in no net design increase for roofs and substantial reductions in main wind force resisting systems. Net pressure increases are primarily limited to coastal hurricane zones within 600 feet of the shoreline (Exposure D). Both research and empirical evidence indicate that increase is warranted. Beyond the wind coefficient issues, NAHB also opposed the update to ASCE 7-16 over concern that seismic design requirements in some portions of the country increase with the new standard. ASCE 7-16 may increase seismic design requirements for some sites and some buildings because of the adoption of new maps, and because of a change in site class coefficients. A review of 34 cities in areas of high seismicity indicates that, in most cases, the changes are typically less than +/-20%. In fact, in two-thirds of these cities the changes are less than +/-10%, and on average the new standard will result in a slight decrease in ground motion relative to the ASCE 7-10 maps. As with the wind maps, significant reductions occur in Southern California. An increase does occur in the region surrounding Las Vegas, Nevada, and the basis for the increase was developed and supported by the Nevada Bureau of Mines and Geology. The new site class coefficients have a small effect on short period buildings of most interest to home builders but can result in significant increase in base shear coefficients for tall buildings with long periods located on Class D or E sites. ASCE 7-16 requires site-specific spectra for such buildings, which has been common practice for many years. While concern over increased construction costs is understandable, it is also important to recognize the significant improvements in ASCE 7-16 including the following: • New wind speed maps that result in reduced wind speeds for much of the country and clarify the special wind study zones; • New regional snow data generated by state Structural Engineers Associations in Colorado, Oregon, New Hampshire, Washington and other mountainous states, that is now directly referenced and eliminates many, older sitespecific Case Study zones; • Entirely new chapter with tsunami design provisions.

Background At the April International Code Council (ICC) Structural Committee Hearings in Louisville, KY, a coalition lead by the American Roofing Manufacturers Association (ARMA) and the National Association of Home Builders (NAHB), opposed the adoption to the 2016 edition of ASCE 7. The coalition put forward a successful assembly motion that will result in an automatic public comment at the ICC Final Action Hearings in October. This public comment will move to modify proposal ADM-94 that, among other actions, administratively adopts ASCE 7-16 in place of ASCE 7-10. The public comment will move to retain ASCE 7-10 instead of ASCE 7-16, and, if successful, will create a significant problem for structural engineers and building officials as well as the ICC.

Why Help is Needed The updated 2016 Edition of ASCE 7-16 includes new seismic, snow and wind hazard maps, and site coefficients which have been coordinated with the 2018 IBC. If the 2016 Edition is not approved, the 2018 IBC will have an uncoordinated and confusing mixture of requirements: some based on ASCE 7-10 and some on ASCE 7-16. This will create significant enforcement problems for building officials and general confusion for anyone attempting to follow and use the code.

How to Help The next step in the code adoption process will occur at the Public Comment Hearings, in Kansas City in October, when ICC Governmental Members will vote yea or nay on this and other public comments. We urge ICC Governmental Members to vote against the public comment to the ADM-94 challenging adoption of ASCE 7-16. We also urge engineers who know building officials and other ICC Governmental Members to contact them and urge them to vote against this public comment opposing the adoption of the ASCE 7-16, and support adoption of the 2016 Edition of ASCE 7.

Take Action Now Contact building officials and other ICC Governmental Members and urge them to vote against this public comment opposing the adoption of the ASCE 7-16 and support adoption of the 2016 Edition of ASCE 7.▪

Technical Issues

Ronald O. Hamburger is a Senior Principal at Simpson Gumpertz & Heger in San Francisco. He presently chairs the ASCE 7 Committee. If you have comments, contact SEI at sei@asce.org.

ARMA launched this challenge over concerns that ASCE 7-16 wind pressure coefficients for low-slope roofs “substantially” increase wind pressure design requirements for buildings 60 feet or less in height. Indeed, ASCE 7-16 does modify and increase the wind pressure

STRUCTURE magazine

September 2016

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

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Should We Adjust Curriculum Recommendations? Does the recommended National Council of Structural Engineers Associations (NCSEA) Structural Engineering Curriculum need an update? Is a matrix methods course still necessary? Should structural analysis courses de-emphasize “hand” calculation methods to allow more time for students to analyze structures using computer programs? Should the recommended curriculum include design courses for other materials such as cold-formed steel? Do we recommend an appropriate number of courses, too many, or not enough? These are only a few of the questions that the NCSEA Basic Education Committee (BEC) has considered over the past 14 years. A group of concerned practitioners was the impetus behind the development of the recommended curriculum, and the practitioner will again be the motivation behind any changes. The NCSEA BEC requests your participation in the NCSEA Structural Engineering Curriculum Practitioner Survey to assist in determining if we are making the curriculum recommendations necessary to begin a successful career as a Structural Engineer. Please go to www.surveymonkey.com/r/NCSEAcurriculum to participate in the practitioner survey. (See the Education article on page 10 for a review of the recommended structural engineering courses oﬀered at schools based on a recent curriculum survey.)

SECB Education Certificate

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 jvogelzang@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 Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@structuremag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA 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 Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY Brian W. Miller Davis, CA Mike Mota, Ph.D., P.E. CRSI, Williamstown, NJ Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT

NCSEA and the Structural Engineering Certification Board (SECB) monitor practitioner needs through contact with structural engineers, schools and universities providing instruction for structural engineers, and professional organizations in order to monitor practitioner needs. For several years, a sub-committee of NCSEA members and SECB certificate holders have been working with schools and universities in the preparation of a program that can be used by schools, students, and industry to recognize those students who, over time, find a greater interest in structural engineering than what is provided in a broad-based civil engineering program. The result of this effort is the SECB Education Certificate, a two-part certificate intended to encourage students to acquire the academic credentials practitioners feel necessary for a successful career in structural engineering. The SECB Education Certificate program is now available to students and universities to recognize the academic fulfillment. All schools interested in learning more about the education certificate program and its implementation, should contact Craig E. Barnes, P.E., SECB at cbarnes@cbiconsultinginc.com. ERRATUM In the August 2016 Software Advertorial by Larry Kahaner, the company ASDIP Structural Software’s website address was inadvertently listed wrong. The correct web address is www.asdipsoft.com. STRUCTURE magazine

STRUCTURE

September 2016

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 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 September 2016, Volume 23, Number 9 ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact your member organization(s) or email subscriptions@STRUCTUREmag.org. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

InFocus

Bridging new trends, new techniques the Ethical and currentChasm industry issues By Barry Arnold, P.E., S.E., SECB

s our Code of Ethics relevant today, or has its strength faded with time? Is our Code of Ethics a powerful tool to assist and guide the engineer in being a professional and in making good and right decisions, or is it outdated dogma? Recently, an engineer with animated gestures and passion in his voice proclaimed, “We, as professionals, are duty bound and morally obligated to understand, live by, and enforce the Code of Ethics.” With equal commitment, another engineer stated “The Code of Ethics is an outdated albatross that hangs around the neck of the profession and limits opportunities.” A third engineer provided a different perspective, “This rift has now grown into a chasm of sorts. A divide that will be difficult to fill or bridge so the profession can join together on common ground.” He concluded by saying, “The Code of Ethics feels, to some, like a dog without a bark or bite. Obedience is considered optional because the worst that can happen for a violation, in most cases, is for the engineer to be removed from the professional organization.” Although I understand all three perspectives, I align myself with the first engineer. The Code of Ethics is a powerful document that reminds me of my obligations to my fellow engineers, to the profession, and most importantly, to society. The etymology of the word “professional” provides the foundation for this belief, and the definition provides the passion and commitment. The etymology and historical meaning of the term “professional” is from Middle English, from profes, adjective, having professed one’s vows from Anglo-French; from Late Latin professus, from Latin, past participle of profitēri to profess, confess, from pro- before + fatēri to acknowledge; in other senses, from Latin professus, past participle. Thus, as people became more and more specialized in their trade, they began to ‘profess’ their skill to others, and ‘vow’ to perform their trade to the highest known standard. With a reputation to uphold, trusted workers of a society who have a specific trade are considered professionals. (Wikipedia, italics added) A professional is a member of a profession or any person who earns their living from a specified professional activity. The term also describes the standards of education and training that prepare members of the profession with the particular knowledge and skills necessary to perform their specific role within that profession. In addition, most professionals are subject to strict codes of conduct, enshrining rigorous ethical and moral obligations. Professional standards of practice and ethics for a particular field are typically agreed upon and maintained through widely recognized professional associations… Some definitions of “professional” limit this term to those professions that serve some important aspect of public interest and the general good of society. (Wikipedia, italics added). Even though the term professional has been hijacked and misused by occupations claiming to be professionals, for those practicing in true professions (those serving some important aspect of public interest

STRUCTURE magazine

and the general good of society), the requirement is clear. Professional standards of practice and ethics are agreed upon and maintained by our professional associations. The Code of Ethics sets the standard for the engineering profession. The Code of Ethics applies to all engineers, not just those who belong to an engineering association. The Code of Ethics is a valuable resource, and provides and defines our professional duties, obligations, and responsibilities to each other and the profession; but it is also much more. It can be viewed as a type of agreement with society that engineers will conduct themselves like professionals. A hint that this is so can be found in The Fundamental Principles of both NCSEA’s and ASCE’s Code of Ethics. They are similar in requiring that: Engineers uphold and advance the integrity, honor, and dignity of the engineering profession by: 1) using their knowledge and skill for the enhancement of human welfare and the environment; 2) being honest and impartial and serving with fidelity the public, their employers and clients; 3) striving to increase the competence and prestige of the engineering profession; and 4) supporting the professional and technical societies of their disciplines. Although the Fundamental Principles can be, and often are, read as an agreement between professional engineers (engineers agreeing to a universal standard of conduct), they can also be read and understood to be the professional engineer’s contract with society. The Fundamental Principles inform society regarding what they can expect from the profession and define the areas the profession will promote, magnify, and defend. In a sense, the Fundamental Principles justify to society why engineers should be considered professionals. I believe that without the Code of Ethics – our agreement with society – engineers could become an albatross hanging around society’s neck. Without this agreement – without having these standards defined and enforced – engineering could become a pseudo-profession. Society has placed their trust in the engineering profession, and we should reciprocate by abiding by the standards of our profession – the Code of Ethics. Is the Code of Ethics worn out, or are they the standards upon which a strong profession is built, as well as the foundation for a successful career? What are your thoughts? What does the Code of Ethics mean to you? Would you like to share your ideas? The discussion continues at www.STRUCTUREmag.org.▪ Barry Arnold (barrya@arwengineers.com) is a Vice President at ARW Engineers in Ogden, Utah. He chairs the STRUCTURE magazine Editorial Board and is the Immediate Past President of NCSEA and a member of the NCSEA Structural Licensure Committee.

September 2016

2016 NCSEA Structural Engineering Curriculum Survey By Brent Perkins, P.E., S.E., NCSEA Basic Education Committee Chair

he National Council of Structural Engineers Associations (NCSEA) is pleased to present the results of the 2016 NCSEA Structural Engineering Curriculum Survey. The survey is a triennial review of the recommended NCSEA Structural Engineering Curriculum at over 250 engineering schools throughout the country that offer educational opportunities for students desiring to become professional civil/structural engineers. Since 2002, the NCSEA has promoted the recommended NCSEA Structural Engineering Curriculum as the core subject matter deemed necessary by the profession for a sound educational background in structural engineering. The recommended curriculum consists of the following twelve courses: Structural Analysis 1, Structural Analysis 2, Matrix Methods, Steel Design 1, Steel Design 2, Concrete Design 1, Concrete Design 2 (Prestressed and Post-tensioned), Timber Design, Masonry Design, Dynamic Behavior of Structures, Foundation Design/Soil Mechanics, and Technical Writing.

Percent of Engineering Schools that Oﬀer the Indicated Number of Recommended Courses 9%

16%

10%

11 Courses 10 Courses

14%

13%

9 Courses 8 Courses

16%

7 Courses 6 Courses 5 Courses or Less

Figure 1.

Percent of Engineering Schools that Oﬀer the Indicated Recommended Course

The Survey Process The NCSEA Basic Education Committee (BEC) began the process of planning for the 2016 Curriculum Survey soon after the results of the previous survey were published in the August 2013 Edition of STRUCTURE magazine. The list of schools that were contacted for participation in this year’s survey was first verified by reviewing all engineering programs accredited by ABET as Civil Engineering, Architectural Engineering, Structural Engineering, Civil Engineering Technology, Architectural Engineering Technology, and other similar related programs. There were 251 ABET-accredited engineering schools and 47 ABET-accredited engineering technology schools invited for survey participation. After confirming schools for survey participation, the NCSEA BEC members verified existing or provided new, contact information for a professor/instructor at each of the schools to be surveyed. The school’s professor/instructor contact was usually selected because they serve as chair of their department, or they taught structural engineering related courses. The survey was developed by the NCSEA BEC and deployed in three phases to improve the response rate. Phase 1 of the survey was delivered to each contact via email, with the participant given the option to complete an online survey or to download and complete a downloadable PDF form. Phase 2 was a paper survey that was mailed to the contacts that did not respond to the Phase 1 participation request. The Phase 2 paper survey provided the option for the participant to provide responses using the online survey or for the paper survey to be completed and returned via mail, email, or facsimile. Phase 3 was conducted by the NCSEA BEC and its representatives using the internet to research the engineering schools that did not respond to Phase 1 or 2. It involved studying the school’s website to determine the courses offered. Phase 3 was not utilized for the engineering technology schools that did not respond to Phase 1 or 2. After Phase 3 of the survey was completed, and before publication of the results, the NCSEA BEC emailed each Phase 3 engineering school to provide STRUCTURE magazine

12 Courses

100

100 100 90 80 70 60 50 40 30 20 10 0

100

84 63

Figure 2.

Reasons Why Timber Design is Not Oﬀered

19%

25%

Lack of Student Demand

14% 14%

Lack of School Support Lack of Timber Research Funding Lack of Timber Design Professors

17%

11%

Imposed Unit Restriction Other

Figure 3.

SECB Education Certificate See Page 8 for exciting news regarding recognition of student fulfillment of the SECB structural engineering curricula. September 2016

them with one final opportunity to review the survey results and report any corrections prior to publication.

Reasons Why Masonry Design is Not Oﬀered

The Survey Results The NCSEA BEC considers the school-reported response to the survey successful, as 118 of 251 engineering schools self-responded to the survey by participating in Phase 1 or 2, for a response rate of over 45 percent. There were 16 engineering technology programs that also self-responded to the survey, and we appreciate their participation even though these results are not included here. The enclosed list indicates the number of recommended courses that are offered at each school. Schools that participated in Phase 1 or 2 of the survey are shown in bold text. Schools that did not directly participate in Phase 1 or 2, but were part of the BEC Phase 3 research, are also included. The percent of engineering schools that offer the indicated number of recommended courses is shown in Figure 1. The percent of engineering schools that offer each of the recommended courses is provided in Figure 2. Past survey results have indicated that Timber and Masonry Design courses are not taught at nearly the same frequency as Steel and Concrete Design courses. The 2016 NCSEA Structural Engineering Curriculum Survey included additional questions as to why Timber and Masonry Design courses are not being offered in an effort to better understand the challenges schools face in offering these courses. Figure 3 records the survey participant’s response to why a Timber Design course is not offered at their school. Likewise, Figure 4 indicates the survey participant’s response to why a Masonry Design course is not offered. The survey also asked survey participants if their school offered

School

Recommended Courses Offered Alabama A&M University 6 Arizona State University 9 Arkansas State University 6 Auburn University 12 Boise State University 8 Bradley University 9 Brigham Young University 11 Brigham Young University – Idaho 11 Brown University 7 Bucknell University 10 California Baptist University 6 California Institute of Technology 6 California Polytechnic State University – San Louis Obispo 12 California State Polytechnic University – Pomona 8 California State University – Chico 6 California State University – Fresno 12 California State University – Fullerton 9 California State University – Long Beach 12 California State University – Los Angeles 10 California State University – Northridge 6 California State University – Sacramento 11 Carnegie Mellon 6 Caribbean University 9 Carroll College 8

14%

25%

14% 15% 22%

Lack of School Support Lack of Masonry Research Funding Lack of Masonry Design Professors Imposed Unit Restriction Other

Figure 4.

any form of special acknowledgment for a student that concentrates in structural engineering. The special structural engineering acknowledgment results are presented in Figure 5 (page 13). The wealth of information collected as part of the survey process prevents publication of all results in this article. Further survey results, including a listing of the recommended courses offered at each school, and if the school offers any post-graduation acknowledgement of a concentration in structural engineering, is available in the electronic version of STRUCTURE magazine at www.STRUCTUREmag.org. Later this year, the NCSEA BEC intends to make all of the survey results, including a listing of additional structural engineering courses offered at each school, available on the NCSEA website at www.ncsea.com. continued on next page

Case Western Reserve University Catholic University of America Central Connecticut State University Christian Brothers University Clarkson University Clemson University Cleveland State University College of New Jersey Colorado School of Mines Colorado State University Columbia University Cornell University Drexel University Duke University Embry-Riddle Aeronautical University – Daytona Beach Florida A&M University/Florida State University Florida Atlantic University Florida Gulf Coast University Florida Institute of Technology Florida International University George Mason University George Washington University Georgia Institute of Technology Georgia Southern University Gonzaga University Howard University

STRUCTURE magazine

10%

Lack of Student Demand

8 8 7 6 12 12 10 9 11 11 12 11 7 8 8 9 9 6 7 9 10 11 10 7 11 7

September 2016

Idaho State University Illinois Institute of Technology Indiana University – Purdue University Fort Wayne Iowa State University Jackson State University Johns Hopkins University Kansas State University Lafayette College Lamar University Lawrence Technological University Lehigh University Lipscomb University Louisiana State University Louisiana Tech University Loyola Marymount University Manhattan College Marquette University Massachusetts Institute of Technology Merrimack College Messiah College Michigan State University Michigan Technological University Milwaukee School of Engineering Minnesota State University – Mankato Mississippi State University Missouri University of Science and Technology

10 8 5 9 9 9 12 11 7 12 9 6 10 10 6 9 8 9 8 8 9 10 12 7 11 12

Montana State University Morgan State University New Jersey Institute of Technology New Mexico Institute of Mining & Technology New Mexico State University North Carolina A&T State University North Carolina State University North Dakota State University Northeastern University Northern Arizona University Northwestern University Norwich University Ohio Northern University Ohio State University Ohio University Oklahoma State University Old Dominion University Oregon Institute of Technology Oregon State University Pennsylvania State University Pennsylvania State University – Harrisburg Polytechnic University of Puerto Rico Portland State University Prairie View A&M University Princeton University Purdue University Purdue University Northwest Rensselaer Polytechnic Institute Rice University Roger Williams University Rose-Hulman Institute of Technology Rowan University Rutgers Saint Louis University Saint Martin’s University San Diego State University San Francisco State University San Jose State University Santa Clara University Seattle University South Dakota School of Mines and Technology South Dakota State University Southern Illinois University – Carbondale Southern Illinois University – Edwardsville Southern Methodist University Southern University and Agricultural and Mechanical College Stanford University Stevens Institute of Technology Swarthmore College Syracuse University Temple University Tennessee State University Tennessee Technological University Texas A&M University – College Station Texas A&M University – Kingsville Texas Tech University The Citadel

10 6 5 10 9 12 11 10 10 7 8 9 4 10 12 11 11 8 12 12 9 10 12 7 8 12 6 11 9 7 10 11 12 9 8 7 8 5 12 10 10 9 6 12 9 6 5 10 3 10 11 6 10 7 9 11 12

The City College of New York The Cooper Union Trine University Tufts University Turabo University United States Air Force Academy United States Coast Guard Academy United States Military Academy University at Buffalo (SUNY) University of Akron University of Alabama University of Alabama – Huntsville University of Alaska – Anchorage University of Alaska – Fairbanks University of Arizona University of Arkansas University of Arkansas – Little Rock University of California – Berkeley University of California – Davis University of California – Irvine University of California – Los Angeles University of California – San Diego University of Central Florida University of Cincinnati University of Colorado University of Colorado – Denver University of Connecticut University of Dayton University of Delaware University of Detroit Mercy University of Evansville University of Florida University of Georgia University of Hartford University of Hawaii – Manoa University of Houston University of Idaho University of Illinois – Chicago University of Illinois – Urbana Champaign University of Iowa University of Kansas University of Kentucky University of Louisiana – Lafayette University of Louisville University of Maine University of Maryland University of Massachusetts – Amherst University of Massachusetts – Dartmouth University of Massachusetts – Lowell University of Memphis University of Miami University of Michigan University of Minnesota University of Minnesota – Duluth University of Mississippi University of Missouri – Columbia University of Missouri – Kansas City University of Mount Union University of Nebraska

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9 10 10 7 8 8 7 10 9 9 12 6 11 10 12 5 5 11 9 11 10 12 8 12 12 7 10 12 9 9 7 12 10 4 10 6 11 11 10 7 12 12 8 10 11 6 10 7 11 9 11 11 12 12 8 8 9 4 11

September 2016

University of Nevada – Las Vegas University of Nevada – Reno University of New Hampshire University of New Haven University of New Mexico University of New Orleans University of North Carolina – Charlotte University of North Dakota University of North Florida University of Notre Dame University of Oklahoma University of Pittsburgh University of Portland University of Puerto Rico – Mayaguez Campus University of Rhode Island University of South Alabama University of South Carolina University of South Florida University of Southern California University of Southern Indiana University of Tennessee – Chattanooga University of Tennessee – Knoxville University of Tennessee – Martin University of Texas – Arlington University of Texas – Austin University of Texas – El Paso University of Texas – Rio Grande Valley University of Texas – San Antonio University of Texas – Tyler University of the District of Columbia University of the Pacific University of Toledo University of Utah University of Vermont University of Virginia University of Washington University of Wisconsin – Madison University of Wisconsin – Milwaukee University of Wisconsin – Platteville University of Wyoming Utah State University Valparaiso University Vanderbilt University Villanova University Virginia Military Institute Virginia Tech Walla Walla University Washington State University Wayne State University West Texas A&M West Virginia University West Virginia University Institute of Technology Western Kentucky University Western Michigan University Widener University Worcester Polytechnic Institute Youngstown State University

10 9 12 5 9 11 12 8 7 5 10 8 5 7 11 10 10 12 11 6 6 6 7 9 12 5 8 9 10 8 5 6 11 9 9 12 8 11 7 12 11 8 8 8 9 11 8 12 11 10 8 7 9 9 5 10 9

Structural Engineering Acknowledgment

Application of the Survey The results of the 2016 NCSEA Structural Engineering Curriculum Survey can be utilized in a multitude of different ways by high school students, college students, colleges, and businesses. For instance, prospective structural engineering high school students and their parents can use the survey to evaluate the breadth or number of recommended structural engineering courses offered by a school. However, it is important to note that the quantity of recommended structural engineering courses offered by a school should be only one of many factors utilized in determining a student’s plans. College students might use the survey to aid in locating a school that offers a distance learning course they are unable to obtain at the school they are attending. Colleges can use the survey results as part of their evaluation process when comparing their course offerings to their counterparts. Businesses can utilize the survey results as part of their employee hiring process by becoming more familiar with the course offerings of a job applicant’s alma mater. The NCSEA BEC appreciates the efforts of the over 130 dedicated educators that participated in the 2016 NCSEA Structural Engineering Curriculum Survey. The survey would not be possible without their participation. Questions or comments on the 2016 NCSEA Structural Engineering Curriculum Survey are encouraged and should be directed to education@ncsea.com.

17% 7%

Diploma or Transcript Acknowledgment Structural Engineering Certiﬁcate No Special Acknowledgment

74%

Unknown

Figure 5.

Brent Perkins, P.E., S.E., is a Project Engineer with Dudley Williams and Associates, P.A. in Wichita, KS. He can be reached at bperkins@dwase.com.

Your Opinion Counts! See page 8 for an invitation to structural engineering practitioners to voice their opinions on the appropriateness of the NCSEA Structural Engineering Recommended Curriculum in today’s environment. We encourage you to become a part of the discussion.

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RECORDS “An NCEES Record makes it fast, easy, and convenient to apply for additional P.E. licenses in other states.” Alexander Zuendt, P.E. Zuendt Engineering Record holder since 2011

National Council of Examiners for Engineering and Surveying® P.O. Box 1686, Clemson, S.C. 29633 864.654.6824

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September 2016

Structural SyStemS discussion and advances related to structural and component systems

nchor channel systems are cast into a concrete member. They are used to attach both structural and nonstructural components. Attachment of nonstructural components, such as curtain wall, is a typical anchor channel system application. Traditionally, anchor channel systems have been designed using manufacturer’s data and allowable stress design. Anchor channel systems can now receive recognition under the International Building Code (IBC) for design with strength design provisions. The International Code Council Evaluation Service (ICC-ES) has developed the Acceptance Criteria for Anchor Channels in Concrete Elements (AC232) to qualify anchor channel systems, and to design these systems using the provisions given in AC232 and in the anchoring-to-concrete provisions provided in the American Concrete Institute (ACI) publication Building Code Requirements for Structural Concrete (ACI 318).

Code Provisions for Cast-in-Place Anchor Channel Systems By Richard T. Morgan, P.E. and Philipp R. Grosser, Ph.D.

Richard T. Morgan is the Manager for software and Literature in the Technical Marketing Department of Hilti North America. He is responsible for PROFIS Anchor and PROFIS Rebar software. He can be reached at richard.morgan@hilti.com.

History of Anchor Channel Design

Anchor channels have been in use for over 100 years. An anchor channel is part of an overall system consisting of the fixture being attached, T-bolts, a steel channel and anchor elements. T-bolts attach the fixture to the channel via the channel lips. The forces acting on the fixture are transferred through the channel into the concrete via the anchor elements. Figure 1 illustrates curtain wall attachment using an anchor channel system. AC232 was developed to qualify anchor channel systems for recognition under the IBC, and to utilize anchoring-to-concrete strength design provisions for anchor channel system design. AC232 test programs establish the structural performance of anchor channel systems to resist static loads, wind loads, and seismic loads. The design of anchor channel systems is not within the current scope of ACI 318.

However, AC232 Section 3.0 Design Requirements provides amendments to the ACI 318 anchoringto-concrete provisions that permit the design of anchor channel systems as if they were included in ACI 318 anchoring-to-concrete provisions. Anchor channel systems satisfying the AC232 test programs may receive recognition under the IBC via an ICC-ES Evaluation Service Report (ESR). The ESR is based on the design provisions given in Section 3.0 of AC232.

Development of AC232 AC232 was first approved by the ICC-ES Evaluation Committee in October 2010. The original purpose of AC232 was to provide provisions for the qualification and design of anchor channel systems to resist tension loads and shear loads acting perpendicular to the longitudinal axis of the channel in normal weight concrete elements. Anchor channel systems satisfying these provisions can now receive recognition under the IBC via an ESR. The original AC232 provisions were based on European provisions for qualification and design with adoptions based on the anchoring-to-concrete provisions in ACI 318. A task group was formed by the Concrete and Masonry Anchor Manufacturers Association (CAMA) to support further development of AC232. The task group, designated “Task Group AC232”, is comprised of manufacturers of anchor channel systems as well as representatives from academia, regulatory bodies, testing laboratories and professional and technical associations. The efforts of Task Group AC232 have resulted in several improvements and additions to the original AC232 provisions. Design provisions for shear load acting in the direction of the longitudinal channel axis were not originally included into AC232 due to insufficient research defining qualification and design for this condition. Therefore, one of the initial efforts for Task Group AC232 was to propose and develop design provisions for the qualification

Philipp R. Grosser is the Head of Technology and Engineering for Cast-in Systems with the Hilti Corporation in Schaan, Liechtenstein. He is also Chair of the CAMA Task Group AC232. He can be reached at philipp.grosser@hilti.com.

Figure 1. Anchor channel system.

14 September 2016

Influence of RED T-bolt

Influence of BLUE T-bolt

1.0

A’1 Na2

lin

A’2

Na1

lin

1 A’1

Influence of BOTH T-bolts

1.0

Na1

lin

A’2 l2

Na1 + Na1

Na2

Na2 + Na2

lin

Figure 2. Anchor channel system triangular load distribution.

and design of anchor channel systems when the applied shear load acts in the direction of the longitudinal channel axis. Another significant effort of the task group was to develop provisions for the qualification and design of anchor channel systems in structures assigned to Seismic Design Category C, D, E or F. Anchor channel system design in structures assigned to Seismic Design Category A and B is considered a “non-seismic” design application in AC232. These extensions to AC232 were approved by the ICC-ES Evaluation Committee in February 2015. Next, Task Group AC232 proposed additional design provisions for the transfer of shear load acting in the direction of the longitudinal channel axis. These provisions, which include testing and evaluation for locking channel bolts in combination with non-serrated channels, and for serrated channels in combination with matching serrated channel bolts, were subsequently added to AC232 in June 2015.

Finally, in October 2015, the ICC-ES Evaluation Committee approved Task Group AC232 modifications permitting the use of anchor channel systems in all-lightweight and sand-lightweight concrete. All of these changes result in AC232 now providing a complete framework for anchor channel system recognition under the IBC.

Design using AC232 Loads acting on a fixture must be transferred through the anchor channel into the concrete via the T-bolts and the anchor elements. T-bolt loads result from the applied loads acting on the fixture. Loads acting on the T-bolts are transferred through the anchor channel into the anchor elements. AC232 permits calculation of the load distribution on anchor elements using either an elastic analysis, that takes into account the elastic support by anchors and the partial restraint of the channel ends by concrete

Figure 3. Anchor channel system failure modes.

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September 2016

compression stresses, or using a triangular load analysis. Use of the triangular load analysis to determine the loads acting on each anchor element is described in this article. Before the loads acting on each anchor element can be determined, the loads acting on the T-bolts must be determined. Assuming the fixture is rigid, a linear elastic stress/strain analysis can be used to calculate the tension and shear loads acting on each T-bolt. Next, the load acting on each anchor element resulting from the load acting on each T-bolt must be calculated. If a triangular load analysis is used, each T-bolt load can be assumed to have an influence on each of the anchor elements within a given distance from the T-bolt. The magnitude of a T-bolt load on an anchor element will be proportionate to the distance of the anchor element from that T-bolt. If the anchor channel system consists of more than one T-bolt, a linear superimposition of each T-bolt load on each anchor element must be made to determine the total load on each anchor element. Anchor channel system strength design calculations are based on the most unfavorably loaded anchor element, and the concrete geometry associated with this element. Figure 2 illustrates how the triangular load distribution is used to determine the loads acting on each anchor element for a tension loaded anchor channel. Strength design requires a calculated nominal tension strength (Nn) or nominal shear strength (Vn) to be multiplied by a strength reduction factor (φ-factor) to obtain a design strength (φNn or φVn). Design strengths correspond to

Figure 4. Anchor channel system load transfer.

possible failure modes. The design strength must be greater than or equal to the corresponding factored tension load (Nua) or factored shear load (Vua). Anchor channel system design strengths must be calculated for each anchor element and checked against the factored load acting on that element. φ-factors corresponding to steel and concrete failure modes for a particular anchor channel system are reported in the ESR. Figure 3 (page 15)illustrates possible failure modes for anchor channel systems. AC232 permits the use of anchor reinforcement to preclude concrete breakout failure in tension or shear. Bars designed as anchor reinforcement must be developed on both sides of the potential concrete breakout surface. AC232 also permits the use of supplementary reinforcement to provide additional concrete breakout capacity in tension or shear. Concrete breakout failure is not precluded when supplementary reinforcement is used because supplementary reinforcement is not specifically designed for development on both sides of the potential concrete breakout surface. Anchor channel system design in structures assigned to Seismic Design Category A and B is considered a static design application in AC232. Design strengths for static tension correspond to tension steel and concrete failure modes. Design strengths for static shear correspond to shear steel failure modes and to concrete failure modes based on whether the shear load acts perpendicular to the channel axis or in the longitudinal direction of the channel axis. Static steel nominal strengths for a particular anchor channel system are reported in the ESR. Nominal concrete strengths for static tension and static shear must be calculated using the static provisions

defined in AC232 Section 3.0, and also reported in the anchor channel system ESR. Anchor channel system design in structures assigned to Seismic Design Category C, D, E and F is considered a seismic design application in AC232. Design strengths for seismic tension correspond to tension steel and concrete failure modes. Design strengths for seismic shear correspond to shear steel failure and to concrete failure based on shear load acting either perpendicular to the channel axis or in the longitudinal direction of the channel axis. Nominal steel strengths for seismic tension and seismic shear will be reported in the ESR. Nominal concrete strengths for seismic tension and seismic shear must be calculated using the seismic provisions defined in AC232 Section 3.0, and also reported in the anchor channel system ESR. Shear load acting on the anchor channel system must be considered regarding whether it acts perpendicular to the longitudinal channel axis or in the direction of the longitudinal channel axis. Load acting perpendicular to the channel axis is primarily transferred into the concrete via the side of the channel. Only a small portion of the load is transferred into the concrete via the anchor elements; however, AC232 provisions conservatively assume only the anchor elements are effective in transferring shear load into the concrete. When the shear load acts perpendicular to the longitudinal channel axis, concrete breakout and concrete pryout are calculated using AC232 provisions, which are also reported in the anchor channel system ESR. When the applied shear load acts in the direction of the longitudinal channel axis, only the anchor elements are assumed to be effective in transferring this load into the concrete. ACI

STRUCTURE magazine

September 2016

318 anchoring-to-concrete provisions are used to calculate concrete breakout for this condition. Pryout is calculated using AC232 provisions, which are also reported in the anchor channel system ESR. Refer to a particular anchor channel system ESR for additional information. Figure 4 illustrates the assumed load transfer for anchor channel systems. If the calculated design strengths for each failure mode being considered are greater than or equal to the corresponding factored load for that failure mode, the anchor channel system design is satisfied pending a combined load interaction check. If tension and shear loads act on the anchor channel system, the combined tension and shear interaction for each failure mode must be satisfied. Reference AC232 Part D.7.4, Section 17.6.4 (ACI 31814) for specific interaction equations, which can be summarized as follows: • tension and shear interaction for steel failure of the T-bolt • tension and shear interaction for steel failure of the connection between the anchor element and the channel • tension and shear interaction for steel failure due to point of load application on the channel lip (channel lip failure or flexural failure of the channel) • tension and shear interaction for concrete failure (pullout, concrete breakout or side-face blowout in tension, and concrete breakout or pryout in shear)

Future Provisions for AC232 Although the anchor elements of an anchor channel system can be considered cast-in headed studs, AC232 design provisions to calculate nominal concrete breakout strength in shear lead to more conservative results compared to results obtained using ACI 318 anchoring-to-concrete provisions for cast-in headed studs. There are several reasons why AC232 design provisions deviate from the provisions given in ACI 318: • Research on anchor channels located close to a fixed edge and loaded in shear is limited; therefore, AC232 provisions to calculate concrete breakout strength in shear are based on simplifications • Shear load acting perpendicular to the longitudinal channel axis is primarily transferred into the concrete via compression stresses between the side of the channel and the concrete. Only a small portion of this load is transferred into the concrete via the anchor elements. However, for reasons of simplicity, AC232 assumes shear load is acting perpendicular to the longitudinal channel

Summary The International Code Council Evaluation Service (ICC-ES) Acceptance Criteria for Anchor Channels in Concrete Elements (AC232) establishes requirements for anchor channel systems to be recognized under the International Building Code (IBC). AC232 permits qualification and design of anchor channel systems in normal weight and lightweight concrete to resist static loads, wind loads, and seismic loads. AC232 design provisions are considered amendments to ACI 318 anchoring-to-concrete provisions. Recognition of anchor channel system compliance is provided by an ICC-ES Evaluation Report (ESR).▪

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axis is transferred into the concrete exclusively by the anchor elements. • The AC232 triangular load distribution method results in higher loads on the anchor elements compared to ACI 318, which assumes a uniform load distribution • AC232 and ACI 318 use different models to calculate the effectiveness of anchor reinforcement in the concrete Since anchor channel systems are a type of cast-in-place anchor, AC232 improvements are needed to permit a design that more effectively utilizes ACI 318 anchoring-toconcrete provisions. CAMA Task Group AC232 is working to develop AC232 provisions that better represent the load-bearing behavior of anchor channel systems. The long-term plan is to include anchor channel systems within the scope of ACI 318 anchoring-to-concrete provisions. AC232 currently limits anchor channel configurations to those produced from steel, with at least two anchor elements attached to the back of the channel profile. Anchor channels made of other materials, such as aluminum, is a future possibility. Only anchor channel configurations with I-shaped anchors or round-headed anchors are within the current scope of AC232. Anchor channel configurations that include reinforcing bars are often used for face-of- slab and corner applications; however, provisions for testing and design of these configurations are not included in the current scope of AC232. Additional research is required before these configurations can be included within the scope of AC232. The current scope of AC232 limits anchor channel system embedment depths to a minimum value that precludes installation in very thin concrete members (e.g. concrete over metal deck). Additional research is needed to understand the load-bearing behavior of anchor channel systems for this application, thereby permitting design and installation at shallower embedment depths.

Structural teSting issues and advances related to structural testing

on-destructive Testing (NDT) plays a critical role in the understanding of existing structures. Investigative techniques available offer practical, efficient, and cost-effective solutions to obtaining information on quality, construction, and performance that may be otherwise hidden to the naked eye. The use of NDT tools vastly reduces the need for exposing embedded structure through probing, and assists in making more informed decisions when samples or probes must be performed. Technology and products develop rapidly in many industries. The Information Technology (IT) and Automotive industries are good examples of this phenomenon, where high global demand drives the availability of funds for research and development. As a result, advancements in products and new technology are quick to emerge. The development of NDT test equipment, however, has not been so rapid to develop since its introduction. In 1950, The Schmidt Hammer, also known as “Swiss Hammer,” became the world’s first patented nondestructive testing method for concrete. The use of Ground Penetrating Radar (GPR) (Figure 1) did not gather much momentum as a mainstream inspection technique until the 1980s and 90s. Contrary to the IT and Automotive industries, the demand for concrete inspection products and associated technology has typically been restricted to a limited number of professionals and inspection firms with a foothold in the field of NDT. Firms seeing a limited global demand for these products did not allocate significant budgets for equipment purchase, and allocated even less budget for employing specialist investigators to collect and analyze data. This left the NDT world waiting extended periods for new generations of equipment to develop.

Ground Penetrating Radar for Use on Concrete Structures By Charles Bransby-Zachary, BSc MRICS, and Gina Crevello, MSc, PA Charles Bransby-Zachary is a Partner at Echem Consultants LLC. Mr. Bransby-Zachary is a member of the International Association for Preservation Technology [APT], a Board Member of the Association for Preservation Technology North East Chapter (APTNE) and a Professional Member of the Royal Institute of Chartered Surveyors [RICS]. He may be reached at cbz@e2chem.com. Gina Crevello is a Principal and Founder of Echem Consultants LLC. Ms. Crevello is on the Board of Directors for the Association of Preservation Technology and is active with the National Association of Corrosion Engineers and the International Concrete Repair Institute. She may be contacted at gcrevello@e2chem.com. The online version of this article contains references. Please visit www.STRUCTUREmag.org.

Figure 2. SIR8 GSSI GPR equipment – approximate year 1999. Courtesy of GSSI and Echem Consultants LLC.

Over the last ten years, significant advancements have been made in the development of NDT technology that now allow for detailed and accurate inspection of concrete. There are numerous pieces of equipment and test methods which allow for an extensive understanding of a structure with limited material removal. Despite the rapid advances that have occurred over the past 10 years, this article explores some of the significant advances that have happened in the last 20 years in the development of GPR equipment for its use in NDT inspection of concrete. It briefly discusses how the GPR technology works, what improvements have been made to the units and what the most current equipment is now capable of achieving. Figures 2, 3 and 4 show how far GPR equipment has come in the last two decades.

NDT of Concrete Structures

By the late 1980s and early 1990s, the only technique capable of scanning through concrete and providing imaging data suitable for determining the structure’s arrangement was Ground Penetrating Radar (GPR). Ideally, this method was combined with rudimentary metal detectors. Even the combined use of these two techniques was somewhat unreliable regarding their functional operation and the quality of data output. One positive factor during this time was that only a few firms provided these services. The reduced number of companies meant that operators and data analysts were typically well trained, with practical experience. However, since the equipment was still quite unreliable, even unpredictable, and the data was of poor resolution, interpretation mistakes were inevitable. This did some damage to the industry as a whole, often creating a feeling of skepticism about the technology and also about those who purported to be experts in their field. Figure 1. Modern GPR equipment, raw data, and corroding steel reinforcement. Courtesy of Echem Consultants LLC.

18 September 2016

What can it provide?

Figure 3. SIR4000 GSSI GPR equipment – 2016. Courtesy of GSSI and Echem Consultants LLC.

This meant that traditional methods of inspection, such as probing, were heavily relied upon, for a significant period, to answer questions about the arrangement and condition of concrete (mass & reinforced). In the past 20 years, GPR equipment has advanced from being unreliable and malodorous (due to significant carbon dust ejections in early equipment) to one which is now more reliable and accurate.

Ground Penetrating Radar What is it? Ground Penetrating Radar (GPR) is an imaging technique that uses wide-band sinusoidal electromagnetic waves to produce high-resolution images of the subsurface materials, typically from zero to approximately 33 feet (10 meters) in depth. GPR is an effective tool for subsurface inspection and quality control on engineering construction projects. The survey method is rapid, nondestructive and noninvasive. (Yelf, R.)

When combined with the use of other methods of inspection, such as magnetics and acoustics, GPR remains the most commonly used and reliable technique to assess a concrete structure. Interpretation of GPR data commonly helps to confirm the following main questions asked of a concrete structure: • Concrete component thickness and reinforcement cover thickness (including variations from the original design) • Existence, spacing, arrangement, and depth to embedded reinforcement • Existence of other features such as prestressing cables, embedded conduits, and pipes Condition information can also be recovered using GPR, including the determination of: • Existence, location, and severity of voiding and honeycombing within the concrete • Existence and location of delamination /separation parallel to the concrete surface • Relative moisture content (laboratory testing still required for accurate measurement) It is important to remember that condition information is most accurately achieved when combined with other inspection techniques such as half-cell potential, linear polarization resistance (LPR), moisture meters, infrared thermography, and ultrasonics. No one technique can provide all the answers, especially if the problem is reinforcement corrosion. (Watt, David S.) How does GPR work? An electromagnetic pulse of energy is sent into the structure under investigation. When

Figure 4. Bridge Inspection Unit with single antennae. Courtesy of GSSI and Echem Consultants LLC.

the pulse passes from one material type to another, the pulse wave velocity changes. This shift in wave velocity at the boundary between material types causes energy to be reflected back to the receiver and provides a record of the interface. Both the transmitted and received signals are waves. The system utilizes the principle that radio waves travel at different velocities through different materials. Since the velocity is dependent upon the electrical characteristics of that material, the change in that electrical difference can be recorded by the impulse radar. (Daniels, D. J.) Data Interpretation Radar data, in its analog form, is comprised of a series of sinusoidal lines that require skillful interpretation to provide meaningful results. The simplest items to understand in a typical section of data scan are metallic inclusions

Figure 5. Left: Early GPR data; approximate year 1987. Right: GPR data; approximate year 2015. Courtesy of ACSESS Digital Library and Echem Consultants LLC.

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September 2016

Corrosion Extent

Moisture Extent Figure 6. Multi-array Bridge Inspection Unit in operation scanning bridge deck arrangement and condition. Courtesy of Echem Consultants LLC.

Figure 7. Multi-array Bridge Inspection Unit contour plot data presentation. Courtesy of ACSESS Digital Library and Echem Consultants LLC.

such as reinforcement bars, dowels, pipes, and pre-stressing tendons. Their successful identification, however, can still require an experienced eye, as data response and data resolution can change dramatically from material to material so that a drilled hole or a piece of aggregate high, in iron for example, could be mistaken for a metal inclusion. Experience with and knowledge of the equipment is crucial to successful data interpretation.

allows for scanning through asphalt and other masonry types, such as brick and stone pavers; however, it was specifically developed with structural health assessments in mind. This system is comprised of multiple antenna frequencies, instead of using the traditional individually mounted antenna set up, for data collection. The antenna array can provide a highly detailed 3D underground tomography of the mapped surface. This greater detail enables a more accurate diagnosis of a structure’s thickness, reinforcement placement, retained moisture, and levels of deterioration, most commonly associated with moisture or delaminations. As with all NDT techniques, the use of this equipment must be combined with additional investigation techniques to corroborate the data and verify the results. The design of the system allows for rapid, accurate, high-resolution data to be collected at speeds of up to 12 miles per hour. When comparing this data to vehicle-mounted aircoupled (not in contact with the surface) GPR arrays, which gather data at higher speeds, the resolution is far more defined. This is due to intimate contact with the surface and a high density of data (Figure 6). Data is collected in plan and section up to two feet in depth. Typical data presentation is stitched together to provide maps of the areas tested and associated conditions. The integrated software correlates propagation velocity and attenuation to areas of risk. Maps of concrete cover and moisture are generated (Figure 7). Section details can be extracted from any data point on the plan; therefore, where the moisture or degradation is highlighted, the section can be reviewed for visual affirmation of the condition. This high level of detailed data allows the team to go back to areas of risk and confirm their condition. This makes interpretation and decision making for repair strategies much easier for projects involving bridges, roads, parking garages, tunnels, warehouses, and many other concrete slab applications.

Data Resolution On a positive note, data resolution has improved significantly over the past 20 years. Radar data in the 1990s was burnt onto thermal paper using electrically driven belts; as a result, the printers threw out carbon dust and the data was often smudged and of poor quality. Today, radar data is much cleaner and clearer and is digitally recorded for computer use. A comparison of data resolution is shown in Figure 5 (page 19). To generate three-dimensional (3D) maps with traditional antennae heads, the surface of the concrete requires multiple passes on a grid pattern in both X and Y coordinates. There are bridge inspection units on three wheel carts that make data collection for smaller bridge decks faster; however, the time required for multiple passes and subsequent data processing makes the process somewhat time-consuming.

Modern Mapping of Conditions One of the most recently developed pieces of GPR equipment emerging in today’s market is the multi-array (fitted with multiple antennae) bridge inspection unit (BIU). Although typically linked to bridge inspections, this device can map the arrangement and condition of any horizontal structure, providing specific information on reinforcement cover depth, delamination, voiding, and relative moisture content. Its use does not have to be limited to concrete either. The technology

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September 2016

Summary The use of non-destructive testing equipment and its development for the assessment of concrete structures has gathered positive momentum over the past two decades. The benefits of using the technology have been embraced by a great many in the construction industry. It is now much better understood and is relied upon by owners and project teams to understand their structures better, while vastly reducing the need to damage them through exposure or probing. GPR bar mapping devices have now become so reliable and user-friendly that they are no longer only exclusively used by NDT companies. Mobile GPR units are used to map bar positions, and can do so accurately. Bridge deck inspection units are rapidly changing, and improving, at a time when the United States’ infrastructure rating is at its lowest. The need to understand critical conditions from the scanned surface, in a nondestructive manner, is becoming ever more vital. It is now feasible to achieve complex data mapping with available GPR technology. This includes additional reinforcement layers, complex construction arrangements, increased moisture content, evidence of voids, or reinforcement corrosion conditions. The speed of response, the detailed data collection, and the advances in software are leading to a better understanding of existing conditions. As the technology continues to be enhanced, the resulting data from surveys and studies are being correlated with other NDT methods. This helps to define patterns in deterioration and associated GPR responses. Programs created by the Federal Highway Administration (FHWA), such as the Strategic Highway Research Program 2 (SHRP2), are highlighting the best methods for rapid collection. It is presumed that these technologies will continue to develop and become even more accurate in the future.▪

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Structural

SuStainability sustainability and preservation as they pertain to structural engineering

ire is an extreme loading condition that must be considered in the design of buildings. Upon initial ignition, building fires are typically small, localized and dealt with efficiently by active protection systems, such as sprinklers. In certain situations, where there is adequate fuel, ventilation, and lack (or failure) of active protection systems, the compartment fire may flashover and develop into an extreme fire loading scenario. During such design fire scenarios, the gravity loading on the structure does not change significantly, but the structural properties (elastic modulus, yield strength, and failure strength) of the steel and concrete materials decrease dramatically. In addition, thermal deformations and movements due to the expansion of structural members, and the restraints by the surrounding (cooler) system impose large force demands. This behavior is different from other natural or man-made disasters where the material properties of the structural elements remain constant while the imposed loading increases. Researchers and engineers in the field of extreme loading on structures (i.e. earthquake, hurricane, tsunami) are developing performance-based design approaches as an alternative to the current prescriptive methodologies. This shift in engineering design allows building owners to specify the additional performance objectives the design team should target. These performance objectives are not only for the structural and non-structural performance of the building, but also include environmental impacts throughout the life of the building. Climate change has made building owners and design team contributors cognizant of the carbon emissions and embodied energy of a typical building. Popular sustainability metrics (i.e. LEED) aim to reduce carbon in buildings through decreasing quantities of material. More recently, LEED developed three pilot credits to incorporate planning for and reducing vulnerabilities towards natural disasters such as earthquakes, tsunami, wildfire, floods, and hurricanes. Structural fire engineering research typically focuses on life safety, property loss, and continuity of business; however, the fire event can have significant impact on the natural environment as well. In addition to the carbon emission of the fire itself, a fire can have non-carbon contamination of the air, water supply, and soils. The fire plume contains contaminants from the contents of the building. Many new building products are made from synthetic plastics and polymers, which are more flammable than their natural predecessors and release harmful agents during

Environmental Impacts of Fire By Erica C. Fischer, Ph.D., P.E. and Amit H. Varma, Ph.D.

Erica C. Fischer is a member of the ASCE/SEI Sustainability Committee and Chair of the Disaster Resilience Working Group. She is also an active member of the ASCE/SEI Fire Protection Committee. She works as a Design Engineer at Degenkolb Engineers in Seattle, WA. Dr. Fischer can be reached at efischer@degenkolb.com. Amit H. Varma is a Professor and University Faculty Scholar at Purdue University’s Lyles School of Civil Engineering. He is a member of the AISC Committee of Specifications and Chair of AISC Task Committee 8 on Fire. He is also the Chair of the SEI/ACI Committee of Composite Construction. Dr. Varma can be reached at ahvarma@purdue.edu.

a fire. Contamination of the soil and water can occur from the products of combustion in the fire plume. Lastly, contamination of the water supply in an area can occur as a result of runoff from fire suppression methods (i.e. sprinklers, firefighting techniques) which can contain toxic byproducts of the fire.

Sustainability Within the sustainability framework, there are two measures for the contribution of buildings to climate change and impacts on the environment. One such measure is life cycle assessment (LCA), which is a standardized methodology for comparing environmental impacts of developing, using, and disposing of a product or a service. Another measure is the cumulative energy demand (CED). The CED is the energy consumed during a product’s life cycle. The result of this evaluation is called the “embodied energy” of a product or a service. Commercially available software such as Athena Impact Estimator (Athena Sustainable Materials Institute) includes the embodied energy of a building in the output when the user can input the operating fuel consumption. The topic of sustainability as it relates to structural fire engineering has two parts: (i) reduction in embodied carbon and energy of a building by optimizing the use of fire protection systems and construction materials to achieve the required fire resistance rating of a building, while minimizing the impact of fire on the building and surrounding area, and (ii) reducing the ecological impact of fires through environmental impact assessment, site planning, and strategic storage of chemicals. Both of these objectives align with the goals and objectives of many sustainable metric programs (i.e. LEED); however, fire is not considered a potential hazard on buildings by these metrics. Buildings around the world require sprinkler systems above certain occupancies and floor area via applicable codes. To improve the fire resistance of a structure, building owners can increase the fire protection of the building. Fire protection comes in two forms: active and passive. Active fire protection is in the form of building sprinklers, and passive fire protection is in the form of fire protection on individual structural members (i.e. spray-applied fire protection, intumescent paint). To increase both the passive and active fire protection in a building, additional material is required, and therefore additional carbon emissions and embodied energy is added to a building. While the upfront carbon may be higher in a building with an increased fire resistance rating, the potential for replacement of components is lower. Therefore, if a fire does occur within a building, there are less elements that would need to be replaced afterwards. This is one potential vantage point

22 September 2016

of addressing sustainability and structural fire engineering – from a material quantity standpoint. Building fires have environmental impacts that effect the air, water, and soil quality of a region. Current sustainable design methodologies aim to reduce the CO2 emissions of buildings by reducing material quantity and embodied carbon of the materials themselves through strategic construction choices. However, during a fire, this reduction in carbon may be negated due to the additional carbon emitted into the environment Sandoz chemical warehouse fire. through combustion of building contents. Environmental impact assessment Previous Fires and (EIA) of a fire to the surrounding area must Their Impacts be considered during an LCA evaluation. Typically, this assessment is performed for a Fires have a large impact on the environment project without the consideration of a disas- due to the transmission of harmful chemiter. Similar to an LCA evaluation, evaluating cals through combustion of the contents of a the impact of a structure on the surround- building. Previous fires highlight the signifiing environment during a potential hazard cant impact fires have on the environment or is critical to understanding the impact of the the impact fire-fighting techniques can have structure and its contents on the built and to surrounding areas. Other countries (i.e. natural environment. In the case of a fire, New Zealand) have developed agencies to this means identifying potential hazards in plan and manage ecological disasters resulting the environment that could result from an from fire-water runoff. For brevity, only a few unexpected fire event. fire events be discussed within this article:

(1) Sandoz chemical warehouse fire in Basel, Switzerland (1986), and (2) Sherwin Williams paint factory in Ohio, USA (1987). Sandoz Chemical Warehouse in Basel, Switzerland – November 1986 The Sandoz chemical warehouse in Basel, Switzerland stored insecticides, fungicides, and chemical dyes. The fire was too large to extinguish with foam; therefore, water was used from the Rhine river. Fire fighters used approximately 105 gallons (400L) per second of water to extinguish the fire over several hours. Residents of the area were instructed to keep windows and doors closed due to the smell of the burning building’s contents and potential for air pollution. The water used to extinguish the Sandoz chemical warehouse fire resulted in large quantities of storm water drainage into the Rhine river. The quantity of fire-water runoff into the Rhine river was not exceptionally large; however, due to the nature of the toxins burning within the building, all aquatic life was destroyed in the vicinity as well as several miles downriver (125 miles or 200km). The aquatic life in the Rhine river was affected for over ten years after the fire. continued on next page

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The lasting effect of toxic chemicals in the Rhine river surrounding the Basel area was not only due to the individual toxic chemicals (1351 metric tons of chemicals, 987 of which were agrichemicals), but also due to the harmful effect of the combination of chemicals, more harmful than the individual chemicals themselves. Long-term effects of the fire-water runoff included contamination of the ground water 46 feet (14 meters) below grade due to seepage of chemicals into the soil. Air contamination was minimal despite a smell in the town due to the Sulphur-based chemicals burning. The resulting ecological damage caused by the Sandoz chemical fire was the product of poor placement of a chemical facility, and poor emergency planning when considering potential hazards. A facility with ecologically hazardous materials was located near a major water-way, highly reactive and incompatible chemicals were stored close to one another, the sprinkler systems were inadequate for controlling a fire, and no methodologies were developed to control potential water runoff in the case of a fire. Sherwin Williams Paint Factory in Ohio, USA – June 1987 The Sherwin Williams paint factory in Ohio stored approximately 1.5 million gallons of paint. The paint factory was constructed on top of aquifers that provided water to wells for over 130,000 people in the area. During the fire, the fire department considered the effects of extinguishing the fire with water that would then seep into the ground and potentially contaminate the aquifer versus the potential air contamination from the combustion of the contents of the factory. The resulting ecological damage from the Sandoz chemical fire was taken into consideration when the firefighters were making their decision. The Sherwin Williams paint factory had a working sprinkler system with a diesel fire pump. The fire pump was located in a separate building and had a capacity of 2,500 gallons per minute (gpm). The pump had fire department connections for additional capacity. These connections were located on the warehouse side of the detached building. The sprinklers were activated by the fire, and triggered the call for the fire department. The fire chief made a decision for the fire fighters not to hook up to the fire pump due to concerns for the safety of the fire fighters and exposure to high heat and potentially dangerous conditions. The sprinkler system controlled the fire in the office area of the building; however, this had little impact on the remainder of the building fire due to the wide spread burning

and height of the flames. Early on, the fire department saw the water runoff due to the sprinkler system activation and a broken sprinkler pipe. Because of the fire chief ’s concern for water runoff entering into the city’s water supply, the fire fighters were directed to only apply water in areas where runoff could be monitored on paved areas. Local water experts, and state air and water pollution experts, were on the scene during the first day of the fire. The consultation they provided to the fire department considered the tradeoff between air pollution and water pollution. The fire was contained within 12 hours of starting. There was a small amount of fire-water runoff contamination in the Miami river; however, it was addressed quickly and effectively. The management of the Sherwin Williams paint factory fire showed how careful and strategic risk management can be effective. Considerations were made regarding the characteristics of the chemicals and contents burning, proximity to water supply sources, air versus water pollution, ability to control run-off, and short term versus long term hazards due to the fire. These considerations resulted in a successful hazard mitigation procedure for the fire.

Environmental Impact of Fire There are short term and long term environmental impacts of fire. The short term impacts are experienced by the affected community immediately following the fire event; however, the affected and neighboring communities may not be aware of the pending long term impacts of fires. There are a large variety of hazardous agents that are released during a fire. These hazards include: general pollutants/indicators, metals, particulates, polycyclic aromatic hydrocarbons (PAHs), chlorinate dioxins and furans, brominated dioxins and furans, polychlorinated biphenyls and polyfluorinated compounds. In order to perform an EIA and understand the short and long term effects these hazards have on the environment, engineers and researchers must understand the origin of these hazards (what building components or products release these hazards during combustion) and how these hazards impact the water, air, and soils in the area of a fire. The exposure duration (i.e. duration of fire) will have an effect on the impact these hazards will have on the environment. Short term fire effects include the impact to the local environment within the fire plume zone and the water runoff zone. The short term effects are concentrated in the local area/

STRUCTURE magazine

September 2016

vicinity of the fire and immediate surrounding areas. Short term hazards can include nitrogen oxides, sulphur oxides, some metals, halogenated acids (HX) and particulates. These short term effects may be easier to mitigate and prevent escalation of. The long term effects of fires are impacts that are not immediately felt or recognized. These effects are more likely to impact the water supply and soils in the area of the fire. The list of hazards that result from long term effects can be extensive. The smoke plume created from the fire is the largest contributor to potential air contamination. Emissions include inorganic gases, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and dioxins. The quantity of these emissions is not necessarily in a harmful quantity to the average population; however, it can be quite dangerous for the at-risk population. Firefighters and automatic sprinklers use water and other extinguishing agents to prevent the fire from spreading. Runoff resulting from the large quantities of water used should be treated prior to the water entering and disrupting nearby water ways. PAHs, VOCs, hydrocarbons, dioxins, metals, ammonia, and other suspended solids can be expected to be in the run-off. In addition, any products on-site in a building or warehouse will be present in the fire effluent. During the Sandoz chemical fire, chemicals in the factory were present in the runoff that entered the Rhine river. Effects on soil occur much later after the fire than the effects on the air and water supplies. In addition to any products on-site in a building or warehouse, the long-term exposure impacts on the soils are PAHs, dioxins, furans, and metals. The dioxins emissions from a fire are about the same as the dioxins emissions from traffic or municipal waste combustion.

Fire-LCA A comprehensive fire LCA tool developed by the SP Fire Testing Laboratory in Sweden is available for commercial use. Fire-LCA is similar to typical LCA tools used by the industry (i.e. Athena). The difference is that there are modules to account for the effect of a fire during the life-time of a structure. These modules recognize the extent of the damaged area, the fire extinguishment and replacement of damaged components. While Fire-LCA is a comprehensive evaluation of the life cycle assessment of a building and the environmental impacts the building would have with a potential fire, the program can be difficult to use. Fire-LCA considers the potential for each material to combust, which

requires the consideration of a number of different input fires. This program requires the cooperation of industry providers of building materials to evaluate the post-fire impact on the surrounding environment. In Europe, manufacturers are required to release the information containing the composition of the materials; however, in the United States, the LCA evaluation results include a large range of impacts due in most part to the proprietary nature of building material composition. The commercially available software in the U.S. makes it easier to use Fire-LCA; however, it is still a very complicated and involved process.

the material quantity and reduction in emissions standpoints. Excluding one or the other is neglecting to evaluate the full life cycle impacts of a structure that is subjected to a fire within its life time. Researchers have summarized the work to date on the environmental impact reduction of fires. Future work in this field should include continuing to develop an LCA tool that allows for the environmental impacts of a fire to be evaluated both on a local and global scale. To develop this tool, detailed information regarding the composition of building materials must be

available. A commercially available, simplistic approach to performing a fire LCA in conjunction with a performance-based design guideline for fire would provide structural engineers with the tools to consider fire as a potential hazard that can fit into a sustainability metric.▪ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

Conclusion and Future Work

STRUCTURE magazine

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Hazard mitigation and sustainable design have developed independent of one another. As such, popular sustainable design metrics provide large benefits to the reduction of materials without consideration of the impacts those reductions have on the disaster resilience of structures. These metrics also place large emphasis on the reduction of CO2 emissions and embodied energy in the selection of building materials. However, previous fires have shown that the effluents released during a fire can negate the reductions in carbon and energy used in the planning and construction process. LEED recently release three new pilot credits which incorporate planning for, designing for, and considering the after math of disasters such as tsunamis, hurricanes, floods, earthquakes, and wildfires. However, building fires were not included in these credits. The case studies referenced in this article demonstrate that building fires should be considered in an initial hazards assessment of a building site. Emergency planning for a potential fire, especially for buildings containing toxic chemicals, can decrease the potential impact on the ecological and environmental surroundings of a building. Structural engineers have the ability to design buildings for enhanced resiliency to fires through consideration of buildingspecific fires rather than prescriptive fire protection design. Consideration of the contents of a building is critical when determining the fire resistance rating of the structure. This approach aligns with a performance-based design for fire. Sustainability and hazard mitigation of fires must be approached from both

September 2016

Code Updates code developments and announcements

he American Concrete Institute (ACI) published the Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14) in the Fall of 2014. ACI 318-14 has been adopted by reference into the 2015 International Building Code (IBC). There are very significant organizational as well as technical changes between ACI 318-11 and ACI 318-14. A two-part article on the changes was published in the April and May 2016 issues of STRUCTURE magazine. A follow-up article on one of the most significant technical changes – the seismic design provisions for special (meaning specially detailed) shear walls – was published in the July 2016 issue. This is the last follow-up article on another critical change in the requirements for the confinement of columns in special moment frames of reinforced concrete.

Introduction to the Changes The ability of the concrete core of a reinforced concrete column to sustain compressive strains tends to increase with confinement pressure. Compressive strains caused by lateral deformation are additive to the strains caused by the axial load. It follows that confinement reinforcement should be increased with the axial load to ensure consistent lateral deformation capacity. The dependence of the amount of required confinement on the magnitude of the axial load imposed on a column has been recognized by some codes from other countries (such as Canada’s CSA A23.3-14 and New Zealand’s NZS 3101-06) but was not reflected in ACI 318 through its 2011 edition. The ability of confining steel to maintain core concrete integrity and increase deformation capacity

Confinement of Special Reinforced Concrete Moment Frame Columns Requirements of ACI 318-14 By S. K. Ghosh, Ph.D.

S. K. Ghosh (skghoshinc@ gmail.com) is President, S. K. Ghosh Associates Inc., Palatine, IL and Aliso Viejo, CA. He is a long-standing member of ACI Committee 318, Structural Concrete Building Code, and its Subcommittee H, Seismic Provisions.

The online version of this article includes a key to notations and detailed references. Please visit www.STRUCTUREmag.org.

is also related to the layout of the transverse and longitudinal reinforcement. Longitudinal reinforcement that is well distributed and laterally supported around the perimeter of a column core provides more effective confinement than a cage with larger, widely spaced longitudinal bars. Confinement effectiveness is a key parameter in determining the behavior of confined concrete (Mander et al. 1988) and has been incorporated in the CSA A23.3-14 equation for column confinement. ACI 318, through its 2011 edition, did not explicitly account for confinement effectiveness in determining the required amount of confinement. It instead assumed the same confinement effectiveness independent of how the reinforcement is distributed. Given the above, confinement requirements for columns of special moment frames (Section 18.7.5, Figure 1), with high axial load (Pu > 0.3Ag f'c) or high concrete compressive strength (f 'c > 10,000 psi) are significantly different in ACI 318-14. The following excerpt from Sheikh et al. explains why high-strength concrete columns are grouped with highly axially loaded columns: “For the same amount of tie steel, the flexural ductility of HSC [High Strength Concrete] columns was significantly less than that of comparable NSC [Normal Strength Concrete] specimens tested under similar P/f'c Ag values. For the same percentage of the confining steel required by the ACI Building Code, NSC columns displayed better ductility than comparable HSC columns tested under similar P/f'c Ag. However, for the same level of axial load measured as a fraction of Po (the ultimate axial load capacity), HSC and NSC columns behaved similarly in terms of energy-absorption characteristics when the amount of tie steel in the columns was in proportion to the unconfined concrete strength. Conversely, the amount of confining steel required for a

Figure 1. Confinement of rectangular column of special moment frame.

26 September 2016

Table 1. (ACI 318-14 Table 18.7.5.4). Confinement of high-strength or highly-axially-loaded rectangular column of special moment frame.

Figure 2. Confinement of high-strength or highlyaxially-loaded rectangular column of special moment frame.

certain column performance appears to be proportional to the concrete strength as long as the applied axial load is measured in terms of Po rather than P/f'c Ag.” The discussion below is about confinement over the length lo, the region of potential plastic hinging. One important new requirement is as follows: 18.7.5.2 – Transverse reinforcement shall be in accordance with (a) through (f ) Where Pu > 0.3Ag f 'c or f'c > 10,000 psi in columns with rectilinear hoops, every longitudinal bar or bundle of bars around the perimeter of the column core shall have lateral support provided by the corner of a hoop or by a seismic hook, and the value of hx shall not exceed 8 in. (Figure 2). Pu shall be the largest value in compression consistent with factored load combinations including E. The change from prior practice is that instead of every other longitudinal bar having to be supported by a corner of a tie or a crosstie, every longitudinal bar will have to be supported when either the axial load on a column is high, or the compressive strength of the column concrete is high. Also, the hooks at

both ends of a crosstie need to be 135-deg. As importantly or perhaps more importantly, the center-to-center spacing between laterally supported bars is restricted to a short 8 inches. In the absence of high-strength concrete or high axial loading, the maximum spacing goes up to 14 inches. In ACI 318-11 and prior editions, the 14-inch limitation used to apply to the center-to-center spacing between legs of hoops and crossties. The other new requirement is in the following section: 18.7.5.4 – Amount of transverse reinforcement shall be in accordance with Table 18.7.5.4 (reproduced here as Table 1). The concrete strength factor, kf , and confinement effectiveness factor, kn, are calculated by (a) and (b). kf =

f 'c + 0.6 ≥ 1.0 25,000

(18.7.5.4a)

kn =

nl nl – 2

(18.7.5.4b)

Where nl is the number of longitudinal bars or bar bundles around the perimeter of a column core with rectilinear hoops that are laterally supported by the corner of hoops or by seismic hooks. See Tables 2 and 3 for

Table 2. Values of concrete strength factor, kf .

values of kf and kn, respectively, calculated by the above formulas.

Impact of Changed Confinement Requirements As is seen above, for columns that are made of concrete with specified compressive strength, f'c, exceeding 10,000 psi and/or are subject to factored axial force, Pu, exceeding 0.3Ag f'c (Ag = gross cross-sectional area), the required confinement over regions of potential plastic hinging (typically at the two ends) is now a function of the axial force. The impact of the changed requirements is assessed in Table 4 (page 28). Bars larger than No. 6 in size are not very practical for use as transverse reinforcement. Also, the ensemble of one hoop and crossties in two orthogonal directions has a thickness of 2¼ inches for No. 6 bar size, which translates into a 1¾-inch clear spacing for a 4-inch center-to-center spacing. Thus, Table 4 shows the limitations on sustainable axial load as the specified compressive strength goes beyond 6 ksi. The limitations have become significantly more severe under ACI 318-14. It should be noted that ACI 318 does not allow Pu to exceed 0.8 (accidental eccentricity factor) x 0.65 (φ for columns

Table 3. Values of confinement effectiveness factor, kn .

Specified compressive strength of concrete, f 'c

Concrete strength factor, kf

No. of laterally supported longitudinal perimeter bars, nl

Confinement effectiveness factor, kn

10,000

1.0

2.00

12,500

1.1

1.50

15,000

1.2

1.33

17,500

1.3

1.25

20,000

1.4

1.20

22,500

1.5

1.17

25,000

1.6

1.14

1.13

1.11

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September 2016

Table 4. Impact of the changed confinement requirements of ACI 318-14 for the regions of potential plastic hinging of special moment frame columns.

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with discrete transverse reinforcement) x Po = 0.525 Po, where Po = Ag f'c + Ast (fy – f'c) So, 0.5 f'c A g is an extremely high axial load level, which is unlikely to be encountered in special moment frame columns. Also, if one needs to go beyond the range of factored axial loads and concrete strengths that can be accommodated with No. 6 transverse reinforcement at a reasonable spacing, the most effective solution is to switch to transverse reinforcement with yield strength, fyt, higher than 60 ksi. ACI 318 allows fyt to be up to 100 ksi.

Conclusions This article discusses the modified ACI 318-14 confinement requirements for columns of special moment frames. It is shown

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that the modified requirements have a significant impact on columns that are highly axially loaded (Pu > 0.3Ag f'c) or made of highstrength concrete (f'c > 10,000 psi) or both.▪

Acknowledgments Grateful acknowledgments are due to Pro Dasgupta and Ali Hajihashemi of S. K. Ghosh Associates Inc. for their considerable help with the paper.

Portions of this article were originally published in the PCI Journal (March/ April 2016), and this extended version is reprinted with permission.

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Historic structures significant structures of the past

John A. Roebling’s vision of the Brooklyn Bridge 1867.

T Brooklyn Bridge Part 1 By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S.

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

he Brooklyn Bridge, across the East River in New York City, is perhaps the most recognized bridge in the United States. As a result of David McCullough’s book The Great Bridge and Ken Burns’ American Stories – Brooklyn Bridge series, many engineers know some of the backstories of the bridge. Don Sayenga’s book, Washington Roebling’s Father, also clarified which Roebling, John or Washington, built the Bridge. Part 1 starts with the earliest plans for a bridge and runs up to John Roebling’s death in 1869 before the onset of construction. In the 19th century, Manhattan and Brooklyn were the first and third largest cities in the United States, separated only by the East River, which varied in width along its length. Some of the earliest proposed bridge locations were across Blackwell’s Island, well above the centers of population where the island separated the river into two channels. Proposals were made as early as 1804 to cross the river at that point. Graves, in 1837, and John A. Roebling, in 1856, made following proposals. Farther to the south, closer to the centers of population, Thomas Pope proposed his Flying Pendant wooden bridge in 1809, followed by a suspension bridge by Julius Adams in 1864 and another suspension bridge by John A. Roebling in 1867. Roebling had been looking at a bridge at the Fulton Ferry for many years, starting in 1852 when, as the story goes, he and his son Washington were stuck on a ferry in an ice jam. He wrote a letter to Abram Hewitt, a New York City leader, about his plan for a bridge. Hewitt forwarded the letter to the Journal of Commerce for publication. His plan was for a 1,600-foot span with a vertical clearance of 130 feet with ornate towers. In March 1860, he had completed his Niagara Railroad Bridge and started his 1,057foot span Covington and Cincinnati Bridge (STRUCTURE, May 2016) across the Ohio

River. It was then that the Architects and Mechanics Journal wrote an article questioning if a long suspension bridge was even possible in Brooklyn. Roebling responded with a lengthy letter supporting his proposal, entitled Bridging the East River. He wrote, “A few years ago I was requested by some prominent citizens of New York and Brooklyn, to investigate this project and to state my views in a general way. Those views were published in the Journal of Commerce. They have been undergoing, since, a further review and scrutiny.” He made three main points. The first being that only a suspension bridge or a tunnel would keep the harbor free for ship traffic. The second that trains of cars propelled by wire-operated ropes and stationary engines were necessary to move a half million people daily across the bridge. Moreover, finally, “the merits of the enterprise as a good first rate investment must be undoubted, else no private capital can be enlisted. As to the corporations of Brooklyn and New York undertaking the job, no such hope need be entertained in our time. Nor is it desirable to add to the complication and corruption of the governmental machinery of these cities. There would be no objections to a subscription by either corporation, but the enterprise to be successful must be conducted by individuals.” By 1864, while still working on the Covington & Cincinnati Bridge, he wrote an article for Engineering Magazine in London. It was under the heading Proposed American Suspension Bridge: I propose to start in the vicinity of the Park of the city of New York, at an elevation of about 80 feet above tide, thence ascending about 125 feet, to the centre of the East River (having a clear elevation of 180 feet), thence descending towards the heights of Brooklyn, and landing within sight of the City Hall… The superstructure of this magnificent bridge would thus form an arch about two miles long, clearing the water of the east River in one sweep of 1,600 feet to 1,800 feet span, and extending over the houses of both cities….My plan provides two floors similar to the Niagara

30 September 2016

of the profession. He was strongly pressed for the place by incorporators and outsiders. Objection was made, however, that he had never built a large structure of this kind, and it was deemed advisable to secure, if possible, the services of someone experienced in the construction of great suspension bridges, particularly as the public were beginning to doubt the possibility of building the bridge in consequence of the natural and mechanical difficulties to be overcome. It was known to some of the incorporators that John A. Roebling, then residing in Trenton, N. J. has had large experience in works of the character of the proposed to be built.” Kingsley approached Roebling in Trenton, and Roebling agreed to take on the role of Chief Engineer provided he was also appointed to supervise the construction of the bridge and not just prepare the plans. He was awarded a contract dated May 23, 1867, for $8,000 per year and told to begin work immediately, with the understanding that Kingsley would pick up the initial costs while financing of the bridge was initiated. On or about the time he was approached by Kingsley, he modified his deck design once again to provide for a central walkway by separating the two center cables, with the walkway or promenade just above the adjacent railway and carriageway.

Later in May, as he was beginning to put together his report, he maintained the pedestrian way in the middle of the bridge but raised it, evidently to give the pedestrians a better view of the river. His six (6) lines of equal depth trussing were apparently fixed in his thinking at this time, but he widened his outer carriageways. He knew the success of his project was having a firm foundation for his masonry towers and anchorages. He sent Washington to Europe on a belated honeymoon and also to study what the Europeans were using for bridge foundations, especially pneumatic caissons and their use of steel in their bridges. Washington graduated from Rensselaer Polytechnic Institute in Troy, New York in 1857. He then worked on Roebling’s Allegheny River Bridge in Pittsburg, after which he enlisted in the Union Army in which he served for over three years, resigning with the rank of Lieutenant Colonel. He had married Emily Warren, the sister of General G. K. Warren, his commanding officer, and worked on finishing the Covington & Cincinnati Bridge that opened on January 1, 1867, staying on for another few months finishing up the project. While Washington was away, John worked on the preliminary plans for the bridge with Wilhelm Hildenbrand and Griefenberg, both

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Bridge, the upper floor for railway conveyance, the lower one for promiscuous travel on foot, horseback or carriage. The entrance of the upper or railway floor will be next to the City Halls of New York and Brooklyn and may be kept independent of the entrance to the lower floors, which may be located nearer to the river. There will be sidewalks on both floors, and these will become favorite resorts for those who want take exercise in the open air. The great majority of passengers will of course, use the cars on the upper floor. My experience and long familiarity with the working of inclines enables me to devise such plans as will render this portion of the structure and its operation, perfectly successful. The materials of construction will be principally granite and iron, the latter placed so that it can be readily preserved by painting. The rigidity of the superstructure will be as great as that of a tubular bridge. Iron trusses of great depth, connecting both floors, together with effective over-floor stays, and the great weight of the structure itself and inherent rigidity of the cables will provide ample stiffness. He kept working on different deck layouts, starting with the Niagara double deck plan as well as a single level deck with two tracks down the middle flanked by roadways. In late 1866, William Kingsley, a well-known Brooklyn contractor, was convinced that a bridge was possible and decided to visit the home of Henry Murphy, a New York State Senator, about supporting legislation to authorize the creation of a corporation to build and operate a toll bridge across the river. On January 25, 1867, Murphy, good to his word, submitted the proposal to the legislature. The act was approved on April 16, 1867, as Chapter 399 of the 19th Session. It was entitled “An Act to incorporate the New York Bridge Company, for the purpose of constructing and maintaining a bridge over the East River, between the cities of New York and Brooklyn.” The capital stock was fixed at $5,000,000 in shares of $100 each. The bridge was to be completed on or before June 1870 and was to provide a clearance of 130 feet over the East River so as not to obstruct river traffic. One month after the Company was formed, The Brooklyn Daily Eagle, May 24, 1883 wrote, “The managers came to the point where it was necessary to appoint a chief engineer to complete the plans and build the bridge. Among those earliest suggested for the position was Julius W. Adams, who was regarded as a brilliant and talented member

German immigrants. By September 1, 1867, of 1,600 feet span, 135 feet elevation, he had completed his preliminary plans and across the East River, in accordance with written a 48-page report. On September 7, the plans proposed by Mr. Roebling, he gave an oral report to the Board. The and that such structure will have all the Report, like all of Roebling’s writings, was strength, stability, safety and durability well written and thorough. He ended with, that should attend the permanent conAs a great work of art, and as a successful nection by a bridge of the cities of New specimen of advanced Bridge engineerYork and Brooklyn. With this expression of 1867 plan with elevated walkway and two cross beam designs. our professional judgment we could, and ing, this structure will forever testify to the energy, enterprise and wealth of that perhaps should, close this report. community, which shall secure its erection. hands out. Brooklyn approved the purchasing It was not until June 21, 1869, that General He still hadn’t decided on a foundation as of 30,000 shares on December 22, 1868, and A. A. Humphries of the Corps of Engineers Washington had not returned from Europe New York City purchased 15,000 shares two informed Murphy and the Bridge Company with his suggestions. On September 10, the days later. Private individuals, including Tweed’s of the findings of his Board of Engineers. Brooklyn Eagle published an extensive sum- 560 shares for which he paid nothing, held the He had four conditions, the first of which mary of the report in which Roebling gave an remaining 5,000 shares. had the most impact on the design of the estimated cost of $6,675,357. It said: In early January 1869, Roebling, sensing that bridge. It was “… the centre of the main span We devote a very considerable portion of our momentum was growing for the bridge, sug- shall, under no conditions of temperature or space today to the report of Mr. Roebling, gested to the Board that they appoint a Board load, be less than one hundred and thirty-five the engineer of the proposed bridge across of Consulting Engineers to review his plans. feet in the clear above mean high water of the East River designed to secure to these The Board approved of this, believing that con- spring tides, as established by the United State two great centres of population ample firmation and approval by some of the leading Coast Survey.” The other conditions dealt and uninterrupted communication. The engineers of the country would bolster public with the sizes of structural members, stating report will attract great interest, for it confidence in the bridge. The Board consisted that no member shall be reduced below the may be accepted as the first practical step of seven (7) prominent engineers: Horatio Allen, sizes given, no part of the foundations of towards the realization of one of the most Chairman, Benjamin H. Latrobe, William J. the piers shall project beyond the existing remarkable enterprises of our time, and McAlpine, John Serrell, James Kirkwood, J. pier lines, and “no guy or stays shall ever be inaugurating a new era in the history of Dutton Steel and Julius Adams. The fledgling attached to the main span of the bridge which Brooklyn…. Mr. Roebling discusses in American Society of Civil Engineers had been shall hang below the bottom chords thereof.” his report seven questions. The people of reconstituted in 1868 after a period of inactiv- Humphries wanted the higher clearance as Brooklyn and New York are mainly interity of 10 years, and four of its early presidents the busy Brooklyn Navy Yard was just north ested in three of them were Kirkwood, McAlpine, Allen, and Adams. of the bridge site. This clearance was greater Is a Bridge necessary? The committee started meeting in March than Roebling thought necessary, but the Can it be built? 1869, with both John and Washington in Company was forced to submit to it. Will it pay? attendance, reviewing the plans and listening Things were looking up for Roebling and the They agreed with Roebling that the answer to John’s description of his report and design. Company and, in June, Washington was at to all three questions was yes, quoting from To give a better understanding of the plans, the bridge performing the survey that would his report and adding thoughts of their own. especially as this bridge would have almost a be used during construction of the bridge. They concluded: 40% increase in span length and be a much Using triangulation methods, they measured But the project will pay? As an investmore heavily loaded bridge with an 85-foot a base line and the required angles to arrive ment, it will receive encouragement from wide deck, Roebling suggested they make a at the final centerline of the bridge from City capitalist everywhere. Brooklyn herself can grand tour of his bridges in Pittsburg, Niagara, Hall, New York to City Hall, Brooklyn. When afford to build. Nothing is more certain and Cincinnati. In Pittsburg, on April 15, he these spikes were set, and the lines marked on than that she cannot afford not to. We showed them his Smithfield Street Bridge over buildings, it was the first actual work on the refer our readers to Mr. Roebling’s report the Monongahela River built in 1845-46 and ground since the borings were taken in 1867. with great pleasure. his Allegheny Bridge constructed in 1860. Later that month, John came up from Trenton The Committee on Plans and Surveys approved They then moved to Cincinnati on April 17 to either help in the survey, or to check the the Report, with the understanding that some to view his 1,057-foot long bridge with a deck work Washington and his crew had done. On things were still not fixed but that they could be width of 35 feet, then the longest suspension Monday, June 28, John was standing on some addressed during the next phase of design. Later bridge in the world. This was followed, several guide piling, called the rack, leading to the in October, the full Board met and accepted days later, by a trip to Niagara to view his Fulton Ferry slot when a ferry hit against the the recommendation of the committee for the 820-foot span double deck railroad/carriage/ piling and a string piece moved causing his foot “immediate commencement of the work.” This pedestrian bridge (STRUCTURE, June 2016) to be crushed between the timbers or piling. would be the last meeting for over a year as the over the Niagara Gorge. This bridge was fin- The doctors recommended amputating his Board was to have great difficulty in interesting ished in 1855 and, after 12 years of service, crushed toes. Roebling consented but insisted many people in the value of its stock. Funding was performing at a high level. that it be done without anesthesia. After that, was a problem. Much of 1868 was taken up in The Board of Engineers submitted their Roebling followed his own advice and used a getting the Cities of New York and Brooklyn to report in June 1869, fully supporting water drip therapy. This was unsuccessful. After take stock in a private bridge building company. Roebling’s plans writing, two weeks tetanus set in followed by lockjaw, The infamous Boss Tweed and his colleagues That it is beyond doubt entirely practiand he died on July 22nd. The Chief Engineer in Tammany Hall of New York City had their cable to erect a steel wire suspension bridge was dead. What would happen to the Bridge?▪ STRUCTURE magazine

September 2016

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Structural rehabilitation

This is the second in a two-part article on repairing aging, normally reinforced, concrete garage structures existing in aggressive weather environments. Part 1: The Designer’s Perspective was published in the April 2016 issue of STRUCTURE® magazine.

renovation and restoration of existing structures

The Contractor’s Perspective

Life before ICRI By Donald Kearney

Don Kearney is a founding Principal of Contracting Specialists Inc. (CSI) with offices in Boston, DC and Pompano Florida. Don is a chartered member of the Institution of Engineers of Ireland (CEng MIEI) and the Institution of European Engineers (Eur Ing) and can be reached at dkearney@ contractingspecialists.com.

Over the last 30 years, the author worked in the concrete restoration industry as an engineer, owner’s representative and, for the past 20 years, on the contracting side. In that time, these experiences provided valuable perspectives of all sides of this issue, but more importantly a true appreciation of the practicalities that need to be considered in the field of concrete restoration. Many of the earliest garages constructed in the first part of the twentieth century are no longer in existence, having been demolished due to age or re-development activities or even transformed into office space over the years. A few have survived without extensive remodeling or remediation; and these garages offer a glimpse, like a museum, into the history of the concrete repair industry in its innovations, failings and successes over the course of time. Repairs performed using gypcrete, drypack, early bag mixes, epoxy mortar and even polyurethane base coat (extended with sand) are still evident today. Too often, people jump to conclusions as to the failure of a material or application technique without investigating the true causes. There is not a single material, nor application process, in use today that has not endured failures. In these cases, a systematic analysis of all materials and processes is required to determine the root cause. Many organizations, specifically the American Concrete Institute (ACI) and International Concrete Repair Institute (ICRI), have devoted significant amounts of time and resources in preparing guidelines for good practices and procedures for the concrete repair industry. These guidelines should be referenced and consulted with any concrete repair project.

Bid and Pre-Construction Specialty contractors in the field of concrete repairs generally get introduced to a project at the budget or subsequent bid phase. Design engineers will at times seek a contractor’s assistance with project budgets or help with phasing of complex garages. Time allocated to the bid process is limited, dependent upon the size and complexity of the projects, as this is a non-compensatory task. Engineers who have spent weeks and possibly

months on the design assume that contractors have spent a similar amount of time in preparing their bid. With a bid period of generally two weeks, allotted time can be measured in hours or, at maximum, days. When bidding a project, the restrictions imposed can be as important as, and at times of greater significance than, the work itself. Phasing, work hours, traffic control, site logistics, and schedule can have significant impacts on the price. The owner and their consultant have a variety of contract types at their disposal for bidding purposes. Unit Price Contract The Unit Price contract is the most common form of contract adopted by the experienced consultant. Site soundings, testing and sometimes exploratory demolition provide the consultant with sufficient information to develop a detailed scope and bid quantities. A well-defined scope and working parameters will generally provide very competitive bids from experienced contractors. This is the contract form primarily recommended by ICRI and forms the basis for their technical bulletin Guide for Methods of Measurement and Contract Types for Concrete Repair Work. Time and Material Time and Materials contracts are best suited to emergency work, where the consultant has not been afforded the time to perform due diligence and develop a proper scope of work. Lump Sum Lump Sum contracts are rarely used in the concrete repair industry, as the work scope cannot be fully established and the potential for latent conditions makes this a very risky proposition for a prospective contractor. In the event that an experienced contractor is presented with this situation, a large contingency is generally incorporated which in turn is bad for the owner. The alternates of an aggressive or underbid proposal from the contractor will quickly result in dissatisfaction among all parties. The Players As with any contract, a successful outcome is heavily dependent upon all parties working closely together and the owner obtaining a successful end product, while at the same time the contractor makes a fair market value profit. Owners typically want a quick start to their garage repair projects, so the pre-construction process (which includes permitting, submittals, schedules and phasing plans) needs to be expedited. The contractor also needs to review the documents, drawings and details carefully, and issue any RFIs where they foresee problems or conflicts.

34 September 2016

Construction Upon capture of the garage project and the first work phase, it is critical that the contractor mark out all repair areas in conjunction with the Engineer of Record (EOR). This allows for more accurately sequenced and scheduled work. Of equal importance is to establish what the deteriorated areas are exhibiting and to see whether alterations in approach to the specified repairs are required. Too often, inexperienced engineers adhere strictly to the specification as opposed to using it as a guide. A lack of experience and recognition of varying conditions can result in a poor repair strategy. The use of boiler plate specifications, not specific to the job at hand, can also be problematic. The author has seen specifications where a clause has been inserted restricting demolition hammers to 12 pounds. The impracticality of this is akin to cutting your lawn with scissors. In both cases it can be done, but the cost and time impacts are prohibitive.

Identifying Repair Areas Sounding and demarcation of defective areas of concrete are generally performed by chain

Congested reinforcing over a beam after demolition.

drag, with more precise soundings performed with a hand held hammer. Markings are generally located approximately 6 inches beyond the delaminated edge to ensure that the extent of unsound concrete and any suspect areas are captured in the repair. The first dilemma often faced by the EOR is curtailing the quantities while still ensuring that sufficient concrete is being removed to achieve a durable repair. Patches should follow a regular shape and acute ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

September 2016

angles should be avoided. Many times concrete demolition is not permitted beyond the corroded length of the bar in an effort to minimize quantities, but this may result in development of accelerated deterioration at the new bond line (often referred to as the halo effect). Too often, a review of concrete repairs previously undertaken in a garage indicates deterioration of areas just beyond, and sometimes extending back into, recently installed patches. continued on next page

Demolition For most contractors, it is both preferable and more efficient to sawcut in advance of the main demolition. Care needs to be exercised with this approach, as nicking or cutting of the embedded reinforcement can cause additional problems and the need for additional repairs in the form of supplemental reinforcement. Although the intent at the time of construction was to provide a minimum of 1 to 1½ inches of concrete cover, deficiencies in cover have in many instances initiated the problems being observed. Therefore, spot checks on the depth of reinforcement are critical if this procedure is adopted. If the cover to the reinforcement is predominantly less than ¾ inches, then the EOR will have to be satisfied with a perimeter cut of less depth than specified. All floor demolition is different, and production can vary significantly depending on the type of equipment utilized, the strength of the existing concrete and the density of embedded reinforcement. Generally the restriction for demolition of suspended floor slabs is 30 pound hammers. Different types of chisels for the pneumatic equipment will also be utilized to determine best results. The EOR also needs to evaluate the existing reinforcing for loss of section to determine whether supplemental bars are required or, alternatively, whether any of the existing damaged reinforcement is redundant and can be removed without replacement. Hydro-demolition of concrete has found a place in the industry but, like many other means and methods, it is suited to certain projects and is constrained in many instances because of logistical issues. There is no doubt that hydro-demolition produces a better surface profile and cleans the bars of contaminants. However, water containment, treatment, clean up and protection of fixtures, along with price, can make it uneconomical unless large areas are available at one time.

Horizontal Deck Repairs Once the repair areas have been demolished and fine chipped, the process for final preparation in advance of placement can begin. The approach to this can vary significantly depending upon the area being repaired. This is where the EOR may have to vary their thought process and look at what produces the best repair considering constructability and site conditions. In the instance of small horizontal repairs, the process of surface preparation by water blasting, mechanical grinding or sand

blasting is straightforward. The bars are primed soon afterward and the area subsequently patched with either a modified bag mix, or ready mix depending upon the economics of the situation. Where large areas are being prepared, and particularly where there are large amounts of reinforcement, a different approach, at times, needs to be considered. Cleaning of rust from the bars followed by washing of repair areas can lead to rusting of the reinforcement before the opportunity exists to prime the bars – a process specified by many engineers. The requirement to prime bars with a zinc rich or epoxy primer, where the manufacturer requires the removal of all oxidation, is not at all times feasible on a construction site given that moisture in the environment or a final cleaning with water will immediately start the rusting process. Priming of bars that have started the corrosion process will lead to rust bleed or spotting. An evaluation by an inspector following ACI 301 Specifications for Structural Concrete will in many instances result in a failed inspection, as the guideline states that “When concrete is placed, all reinforcement shall be free of materials deleterious to bond.” In a paper distributed by the Aberdeen Group, titled How Clean Must Rebar Be?, it was found that contaminants such as rust form release agents. Even motor oil, applied to reinforcing, had little effect on bond strength. Therefore, more consideration is being given to providing a more protective long term environment for the reinforcement in the form of sacrificial anodes or the addition of a corrosion inhibitor to the mix in lieu of bar priming. With any concrete placement, adhering to the contractor’s pre-inspection list and procedures is essential to ensure that the placement is performed correctly. Large placements can appear somewhat chaotic, but there are certain items that require particular attention in order to achieve a successful end product. In the case of a ready mix placement, trucks must be scheduled at correct intervals. Each load must be checked for both air and slump to ensure compliance with the mix design. Areas must be pre-wetted to a saturatedsurface-dry (SSD) condition and a bonding agent or a slurry coat applied to the substrate in advance of the placement. Vibration and compaction is often achieved through the use of a vibrating screed, as conventional vibrators in a shallow patch area can often result in segregation. Hand finishing of the edges is also critical as this is traditionally a weak point in the repairs and, even with the greatest

STRUCTURE magazine

September 2016

care, hairline cracking at this interface is likely to occur. In many cases, the EOR calls for these perimeters to be routed and sealed with a urethane sealant, irrespective of whether a topical coating is being applied to the finished surface. Wet cure requirements are often substituted by the use of a curing compound. However, wet curing is more advantageous when the repair area is subject to sunlight and heat.

Overhead and Vertical Repairs Traditionally, hand applied repair mortars have been used for vertical and overhead repairs. There are many inherent problems with achieving a good durable repair using this method. Generally, application is limited to 2-inch lifts. Proper substrate preparation is critical and scratching of the surface between lifts without disturbing the material at the bond line is difficult, unless performed by an experienced mechanic with the proper tools. Also, a congested reinforcing configuration makes full compaction and encapsulation of the reinforcing difficult. Recently, and particularly on large extensive repair areas, shotcrete, either wet or dry, has become very popular. However, successful application is heavily dependent upon the material selected, equipment being used and, of prime importance, the experience of the nozzle person. To introduce and maintain quality control, the nozzle person must obtain separate certifications for overhead and vertical application processes. Form and pump has become common in recent years, particularly with the advent of materials extended with pea stone that have low shrinkage and high slump characteristics. This is certainly the desired process as a monolithic repair is obtained. With form and pump, critical items to be aware and vigilant of include pre-wetting prior to placement, durable formwork capable of withstanding the required pressure, and vibration of the forms to ensure compaction without causing segregation. With enclosed forms, care needs to be exercised to remove trapped air – otherwise voids will occur and can significantly impact the integrity of the repair.

Future The future of the concrete repair industry will see a more mechanized approach for demolition and material placements. A greater emphasis will be placed on how to provide long term protection for embedded reinforcement, as corrosion is the primary cause for concrete deterioration.▪

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2016 Structural Engineering Summit

Disney’s Contemporary Resort · Lake Buena Vista, FL · September 14th-17th

STAY CONNECTED BY USING THE HASHTAG #NCSEASummit

Wednesday, September 14 8:00 – 5:00 8:00 – 12:00 4:30 – 5:30

NCSEA Committee Meetings NCSEA Board of Directors Meeting Reception hosted by NCSEA Young Member Group, featuring recognition of the Summit

12:15 – 1:30 Lunch on the Trade Show Floor Concurrent Sessions 1:30 – 2:45 A) SEAOC Structural/Seismic Design Manual

Ryan Kersting, S.E., Doug Thompson, S.E., SECB, and members of the SEAOC Seismic Committee SEAOC is now in the process of updating the SEAOC Structural/Seismic Design Manual to reflect the requirements of the 2015 IBC. This presentation will focus on Volumes 1 and 2, providing a blend of a general overview and presentation of select details of design.

Scholarship recipients and the presentation of the Young Member Chapter of the Year award. All attendees welcome!

6:00 shuttle service

Gala Evening at the Orlando Art Museum sponsored by Computers & Structures, Inc.

B) Strut and Tie Design: What They Didn’t Teach You in School

Thursday, September 15 7:00 – 8:00 7:00 – 8:00 8:00 – 8:15

Breakfast Delegate Interaction Breakfast Welcome 8:15 – 9:30 Keynote: Structural Engineering for Walt Disney Theme Parks Kent Estes, S.E., Ph.D., Walt Disney Imagineering The presentation will provide a glimpse into the process of designing Disney theme parks, with a specific focus on structural engineering. It will discuss Disney’s unique construction practices, local building infrastructure, and building codes, as well as the varying soil conditions and mitigation measures.

Kent Estes has 40 years of structural engineering experience, with over 30 of those in Disney theme parks on three continents in the architectural and engineering arm of The Walt Disney Company, Walt Disney Imagineering. He has just moved back from China, where he served as the Design Manager for the Main Entry area of Shanghai Disney for a team of designers, architects and engineers, and was the Lead Structural Engineer for the park, hiring and overseeing a team of local Chinese structural engineers. He has worked on a total of eight theme parks from beginning of design through to construction.

9:45 – 11:00 ASCE 7-16 Wind: How it Aﬀects the Practicing Engineer

Don Scott, P.E., S.E., F.SEI, F.ASCE, Vice President/ Director of Engineering, PCS Structural Solutions Attendees will gain an understanding of the most important changes to ASCE 7-16 wind load provisions and how they impact design. They will learn how to use ASCE 7-16, while avoiding costly errors due to a lack of understanding of the changes. Don Scott serves as Chair of the ASCE 7 Wind Load Subcommittee and the NCSEA Wind Engineering Committee, and has given numerous presentations on US wind load provisions throughout his career.

11:00 – 12:15 Wind Loads on Non-Building Structures for the Practicing Engineer Emily Guglielmo, P.E., S.E., F.SEI, Principal,

Concurrent Sessions 3:15 – 4:30 A) 2015 IBC, ASCE 7-10 and SDPWS Seismic Provisions for Wood Construction

Michelle Kam Biron, P.E., S.E., SECB, Education Director, American Wood Council This presentation highlights 2015 IBC, 2010 Minimum Design Loads for Buildings and Other Structures (ASCE 7-10) and the 2015 SDPWS requirements applicable to the seismic design of wood structures. Michelle Kam Biron is Director of Education for the American Wood Council (AWC) where she oversees and develops continuing educational resources related to structural wood for architects, engineers, and code officials.

B) New ACI Standards & the Repair of Existing Concrete Structures

Chuck Larosche, P.E., Principal, Wiss Janney Elstner & Associates ACI has recently published ACI 562-16 - “Code Requirements for Assessment, Repair and Rehabilitation of Existing Concrete Structures” and will soon publish ACI 563 - “Specifications for Concrete Repair”. The presentation will include specific case-study examples on use of the new standards. Chuck Larosche has experience in structural design, investigation, and evaluation of existing structures and materials, and he has combined his construction background with his knowledge of material behavior in existing structures in the area of masonry, concrete, and steel evaluation.

6:00 – 8:00

Welcome Reception on Trade Show Floor

Friday, September 16

Martin/Martin, Inc. The session will discuss ASCE 7 wind load provisions for non-building structures, including equipment, walls, signs and towers, and how to correctly apply them through examples. An in-depth exploration for engineering commonly encountered situations that are not directly addressed in the code will follow. Emily Guglielmo is a principal of the Martin/Martin, San Francisco office, and currently serves as an NCSEA Board Member and member of the NCSEA Wind Engineering Committee.

STRUCTURE magazine

Thomas Mendez, S.E., Structural Engineer, WSP | Parsons Brinckerhoﬀ This presentation will focus on discussing the ACI-318 building code strut-and-tie requirements and reviewing some of the real-world examples. Thomas Mendez is a Structural Engineer for WSP | Parsons Brinckerhoff, specializing in the design of tall and super-tall high rise buildings.

7:00 – 8:00 8:00 – 9:35 8:00 – 9:35

Attendee breakfast on Trade Show floor NCSEA Delegate Collaboration Session Vendor Product Presentations

Don’t forget to download the 2016 Summit App! September 2016

Concurrent Sessions 10:00 – 11:15 A) Presenting TMS 402-13, The Masonry Design Standard

B) Florida SE Licensure: How the Bill was Created and Almost Became Law

Edwin Huston, P.E., S.E., Principal, Smith & Huston, Consulting Engineers The Masonry Society is now the sole developer of the Masonry Standard, and the 2013 edition has been adopted by the 2015 IBC, The session will review some of the significant changes from TMS 402-11/ ACI 530-13//ASCE 5-11. Ed Huston is a former President of the Board of Directors of NCSEA & current chair of the Code Advisory Committee – General Requirements Subcommittee. He serves on the main committee & the Flexural, Axial & Shear subcommittees of TMS 402.

B) Becoming a Trusted Advisor: Communication and Selling Skills for Structural Engineers

Annie Kao, P.E., Senior Field Engineer, Simpson Strong-Tie By understanding the customer’s needs, a successful sales person can turn into a trusted advisor, an integral part of the client’s team. This presentation will go over the basics of sales and how structural engineers can use these techniques every day to achieve greater client satisfaction and elevate their perceived value. Annie Kao is a senior field engineer for Simpson Strong-Tie, where she connects and educates engineers, architects, building officials, and contractors on design and product solutions for wood, concrete, steel, and masonry construction in the Southwest region of the U.S.

Concurrent Sessions 11:15 – 12:30 A) Great (and Horrible) Masonry Design Practice

Donald Harvey, P.E., Associate Vice President, Atkinson-Noland & Associates This presentation will touch on some of the most common detailing and design snags in modern masonry and provide guidance on how to design masonry structures that are durable, beautiful, and constructible. The presentation will also highlight a few very recent changes to masonry codes and standards that could have a significant (positive) impact on your design. Donald Harvey has authored several papers relating to nondestructive evaluation of structures, masonry material testing, and evaluation methods for existing buildings, and he serves on several ASTM committees related to masonry.

B) Has THIS Ever Happened to You?

NCSEA Young Member Group Committee, moderated by Jera Schlotthauer, EIT, chair This session will consist of an array of technical and nontechnical presentations gathered from young engineers. Presentations will be delivered using the short, fast-paced and automated PechaKucha format which limits presenters to an allotted amount of time and number of slides. A Q & A will follow. The NCSEA Young Member Group Support Committee (YMGSC) facilitates the formation, growth and success of NCSEA Member Organization Young Member Groups through collaboration, support and outreach in an effort to transition students and young engineers into successful, professional engineers and future leaders of the Structural Engineering Profession.

12:30 – 1:30 Lunch Concurrent Sessions 1:45 – 3:00 A) So you Want to Delegate Connection DesignHow to Do It Right

Kirk Harman, P.E., S.E., SECB, President, The Harman Group AISC adopted delegation of structural steel connection design by structural engineers to the steel fabricator, in the 2010 Code of Standard Practice. The variability in this practice is significant from coast to coast. Wherever a structural engineer’s documents fall in this range of practice, it is important to know what the AISC Code of Standard Practice says and how it can be implemented into the documentation of a project. Kirk Harman serves on the AISC Committee on the Code of Standard Practice. He is currently Chair of the Task Group on BIM and served as Chair of the Task Group on Quality in Steel Construction.

STRUCTURE magazine

Tom Grogan, P.E., S.E., FSEA and The Haskell Company This presentation will discuss the process FSEA went through to attempt to obtain SE Licensure in Florida, including the process for writing the bill, selection of representatives and senator, committee presentations, the vote and bill reconcilation, governor’s veto and follow-up meeting. Tom Grogan is the Chief Structural Engineer/Director of Quality for The Haskell Company. He is Vice President/Incoming President of the NCSEA Board of Directors, a member of the Structural Licensure Committee, and the NCSEA alternate representative to the Structural Engineering Licensure Coalition’s steering committee.

Concurrent Sessions 3:30 – 4:45 A) Upcoming Changes to AISC 341 - Seismic Provisions for Structural Steel Buildings

Jim Malley, S.E., Senior Principal, Degenkolb Engineers Balloting has completed to update AISC 341-10 for the 2016 edition that will be incorporated with ASCE 7-16 and AISC 360-16 into the 2018 IBC. The document will have significant technical modifications including new material specifications, use of steel braced diaphragms, new column splice details, changes to BRBF provisions, requirements for SCBF gusset plate welds, application of demands on columns that participate in intersecting frames and a number of other items. In addition, significant new provisions related to the seismic design of multitier braced frames will be provided. This presentation will summarize the changes proposed for the 2016 edition of the AISC Seismic Provisions. Jim Malley has over 30 years of experience in the seismic design, evaluation and rehabilitation of building structures, and was responsible for the analytical and testing investigations performed as part of the SAC Steel Project in response to the Northridge earthquake damage. He is a member of the AISC Specifications Committee and the Chair of the AISC Seismic Subcommittee, the AWS Subcommittee on Seismic Welding Issues, and a member of the Board of Directors of EERI and the Applied Technology Council. He is a past president of NCSEA and received the James A. Delahay award in 2014.

B) Top 10 Useful Lessons for Structural Engineers

Lawrence Novak, S.E., F.ACI, F.SEI, LEED AP, Director of Structural Engineering, Portland Cement Association Typically much is written and presented about outstanding projects in our profession. Rarely do we talk about the philosophy behind the design … even rarer do we take two steps back and delve into the important life lessons which can be gleaned from a career in structural engineering. What do we really do and what does the world expect of us? Prior to joining Portland Cement Association, Larry Novak was an Associate Partner with Skidmore, Owings & Merrill where he served as the lead structural engineer for the Burj Khalifa, the world’s tallest building. He serves on the ACI 318 Code committee, the ACI 130 committee on Sustainability of Concrete and has served as Director on the governing board for SEAOI, TCA and the Illinois Engineering Hall of Fame.

6:00-7:00

Awards Reception (formal attire encouraged but not required)

7:00

NCSEA Banquet & Awards Presentation, featuring the NCSEA Excellence in Structural Engineering Awards & the NCSEA Special Awards

Saturday, September 17 7:00-8:00 8:00-12:00 12:30-2:30

Breakfast NCSEA Annual Business Meeting NCSEA Board of Directors Meeting

September 2016

Thank You to Our 2016 Exhibitors Trade Show Hours: Thursday, September 15th —9:30 a.m. to 3:30 p.m. & 6:00-8:00 p.m. Friday, September 16th — 7 a.m. to 12:30 p.m. Denotes NCSEA membership

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Exhibitor list as of 8/8/16 For a current list please visit www.ncsea.com.

September 2016

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New Millennium Bldg Systems www.newmill.com Nucor www.nucor.com Powers Fasteners www.powers.com RISA Technologies www.risa.com SCIA a Nemetschek Company www.scia.net SECB www.secb.org SidePlate Systems, Inc www.sideplate.com Simpson Strong Tie www.strongtie.com Steel Deck Institue www.sdi.org Steel Joist Institute www.steeljoist.org Steel Tube Institute www.steeltubeinstitute.org Strand7 Pty Ltd www.strand7.com Trimble www.tekla.com USG www.usg.com/structural Vector Corrosion www.vector-corrosion.com available sponsorship location reserved

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AISC www.aisc.org Alpine ITW www.trussteel.com American Concrete Institute www.concrete.org Armatherm armadillonvinc.com Atlas Tube www.atlastube.com AZZ Galvanizing www.azzgalvanizing.com BASF Corporation www.master-builders-solutions.basf.us Blind Bolt www.blindbolt.com Cast Connex Corporation www.castconnex.com CLP Systems www.clp-systems.com Dlubal Software, Inc www.dlubal.com Euclid Chemical www.euclidchemical.com Fabreeka International www.fabreeka.com Geopier Foundation www.geopier.com Hayward Baker www.haywardbaker.com Headed Reinforcement www.hrc-usa.com Hilti www.us.hilti.com Hubbell Power Systems, Inc. www.abchance.com ICC-ES www.iccsafe.org ITW Red Head www.itwredhead.com LafargeHolcim www.holcim.us Lindapter www.lindapterusa.com Meadow Burke LLC www.meadowburke.com Menard USA www.menardgroupusa.com MiTek USA/MiTek Builder Prod. www.mitekbuilderproducts.com

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Registration

Full conference registration includes: • 17 educational sessions & resources on 2 tracks, geared toward the practicing structural engineer • Wednesday evening receptions • Thursday’s Reception on the Trade Show Floor • All breakfasts, lunches & refreshment breaks • Access to the NCSEA Trade Show • NCSEA Awards Banquet, featuring the Excellence in Structural Engineering Awards and NCSEA Special Awards

Conference Hotel

The Summit will be held at Disney’s Contemporary Resort, which is just a short monorail ride, waterlaunch trip or walk to the Magic Kingdom Park. It oﬀers breathtaking views of Cinderella Castle, Bay Lake or the Orlando skyline and features oversized guest rooms that include complimentary Wi-Fi. Hotel reservations are accessible through a link on NCSEA’s website.

Disney’s Magical Express Service

Take the hassle out of arrival with Disney’s Magical Express Service! This complimentary service provides transportation for you and your bags from Orlando International Airport (MCO) to your Disney Resort Hotel, then back again at the end of your stay. Luggage is delivered right to your Resort room. To book, call 407-827-6777 or visit the special NCSEA Disney microsite.

There will be plenty of opportunities to network with structural engineers from across the country at the sessions and these special events:

• Young Engineer Reception • Gala Evening Event at the Orlando Art Museum, sponsored by Computers & Structures, Inc. • Opening Trade Show Reception

Special Offers!

Extra Magic Hours

Each day, one of the Walt Disney World® Theme Parks opens one hour early or remains open up to two hours after regular closing time for Disney Resort Guests. This is a great way to maximize the value of your Disney Theme Park Tickets based on your schedule. (Valid Theme

Engineers 35 years of age or younger pay only $350 for complete registration, which also includes special Young Engineer activities. First-Time Attendees to the NCSEA Structural Engineering Summit pay only $600.

Park admission and Walt Disney World® Resort ID required.)

STRUCTURE magazine

September 2016

Stealth THE ENGINEERING OF ART By James Case, P.E.

hat do you do when a client approaches you with an entirely unique structural challenge? That was the structural engineering dilemma presented to Uzun + Case by artist Tristan Al Haddad of Formations Studio who proposed a 35-foot tall, 65,000-pound thin shell concrete sculpture for the Promenade office tower in Atlanta. The first engineering question was “Why concrete – there are many synthetic materials well suited to the creation of amorphous forms?” To which the artist responded, “I want to do something with concrete that has never been done before, to create something that is simultaneously delicate and solid, something that shows the hand of its creator.” And so the journey began. Fortunately, this seemingly free-form structure had been conceived utilizing computer-generated geometry and principles of structural behavior. In fact, Stealth is an assemblage of hyperbolic paraboloid shell elements. The use of hyperbolic paraboloid thin shell concrete forms was popularized by engineers such as Felix Candela and Heinz Isler in the 1950s and 1960s. The shells for Stealth are not uniform in thickness but curve in cross-section, leaving thinner edges and a thicker midsection. This creates the illusion of a thin profile throughout.

Stealth.

Structural Analysis Work began by analyzing the structure with the finite element program SAP, using a mesh generated by Formations Studio and rectilinear shell elements of varying thicknesses to simulate the sculpture’s elliptical cross section. A centerline mesh was exported from the parametric modeling program Rhino and imported into SAP using the DXF format. The mesh was created by the artist using parameters specified by Uzun + Case. The varying thickness of the cross section was approximated by zones of constant thickness which stepped at their intersections with one another. The sharing of electronic information greatly expedited the analysis process. Both service and ultimate stresses/forces were considered. The service level results were based upon a 10-year return period and used to calculate crack widths and deflections. The ultimate level forces were based upon a 700-year return period and used for strength design. ASCE 7-10 ultimate wind speeds correspond to approximately a 7% probability of exceedance in 50 years (Annual Exceedance Probability = 0.00143; MRI = 700 years). A combination of wind and gravity forces controlled the design of the structure. Seismic forces were not critical. Reinforcement for crack control was calculated first, followed by an ultimate strength check. The analysis results indicated that the upper portion of the sculpture behaved like a shell with relatively low stresses, necessitating a maximum thickness of only 7 inches. It was reinforced with a mat of #5 reinforcing bars at 4-inch on center each way. The lower portion of the sculpture was controlled by bending, necessitating an increase in thickness to 14 inches. The high bending stresses are resisted by (2) #7 reinforcing bars at 4-inch on center vertically with #5 horizontal ties at 4-inch on center. The accurate bending of the vertical bars to fit within the exacting forms was a

Stress diagram.

STRUCTURE magazine

September 2016

Leg to mat foundation connection detail.

Several options were considered for the design of the formwork system, including a solid system of ¾-inch plywood layers. Ultimately, to minimize material usage, a two-way structural rib system was chosen. It consisted of ¾-inch plywood ribs skinned with three layers of ¼-inch marine grade plywood, providing the flexibility to form the synclastic and anticlastic double curvatures required by the sculpture.The digital modeling, indexing, and CNC routing of the formwork was a monumental effort given that each of the 183 pieces of formwork for the sculpture was unique. The rebar at the base was treated similarly with CNC cut templates made for each bar to enable accurate bending. The bars and formwork for each section were transported to the site as a complete assembly. continued on next page

Upper portion cross section top. Lower portion cross section bottom.

major challenge, which was executed in house by Formations Studio. The use of double #7s instead of #9 bars was based upon the studio’s limited bar bending capabilities. Base supports consisted of four pinned nodes at each of the two legs. The position of the supports corresponded to the centroid of vertical reinforcing bar groups which connected the legs to the mat foundation below. The mat foundation is 12 feet x 15 feet x 16 inches thick, reinforced with #7@12 bottom and #6@12 top. The SAFE computer program was used to analyze and design this element based upon an allowable soil bearing pressure of 2000 PSF. Crack control and durability were priALL NEW GUIDE! mary design parameters. The structure was designed not to crack, except at the base where crack widths were limited to avoid durability concerns. Five (5) pounds per cubic yard of Forta Ferro fibers were added to control cracking and improve durability at thin cross sections. Cracking was evaluated using the computer program Response 2000 based on the reinforcement and combined bending, axial, and shear forces at each section. Crack widths were limited to 0.2 mm in general but to avoid excessive thickness at the base of the sculpture crack widths of 0.33 mm were allowed.

Design smarter Guides Webinars eLearning Online Tools Technical Notes Reference Material

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Formwork and Reinforcement Fabrication Due to the complex and exacting nature of the structure, formwork and reinforcing steel fabrication was performed in the artist’s studio. STRUCTURE magazine

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Concrete design aids on demand:

manufacturing process, the formwork fit-up was excellent. The foot and ankle rebar was fabricated at the Formations Studio facility. All other reinforcement for the sculpture was bent on site. Much effort was made to ensure that the specified 1½-inch rebar clearances were maintained. Uzun + Case inspected all rebar before concrete placement. All concrete was placed via a line pump system. Concrete arrived with an integral color, Formwork. but a second color, ‘Carbon’, was added at the job site. Concrete spread averaged 24 inches. All concrete was vibrated for proper consolidation using a small head and motor assembly. Form removal was tedious due to the curvature of the sculpture. Finally, Formations Studio painstakingly shaped and polished the surface to achieve the glass-like finish. The sculpture was shaped with a steel cup wheel and wet polished using a diamond pad system utilizing increasing fineness from 50 grit to 3000 grit. Finally, the structure was coated with a lithium polysilicate penetrating densifier/ sealer (Pentra-Sil by Convergent Concrete Technologies).

Structural Monitoring and Performance

Base reinforcing.

Concrete Mixture Initial studies for the structure considered steel fiber reinforced ultrahigh performance concrete. This proved impractical due to the high flexural stresses at the sculpture base and the need to create continuity at construction joints. A 5000 PSI conventionally reinforced concrete design was selected. The final mixture was developed with the assistance of Thomas Concrete Technical Services Laboratory. The mix design required 5000 psi and very high flowability to achieve the very thin profile details at the edge of the structure. Liquid integral color dosages were provided by Increte. Since aggregates make up such a significant portion of the mixture, and therefore greatly affected color, numerous lab batches were produced to look at local granite aggregates, imported black granites, and slags and finally the chosen material, a blue/black Georgia limestone. Seventy-six (76) ounce per cubic yard of SIKA ViscoCrete 2100 high range water reducer was used for dispersion, strength, and rheological properties.

Construction To facilitate construction, an intricate scaffolding system was designed and built around the Sculpture, and erected in lifts as the formwork for the sculpture was placed. Form delivery was sequenced to avoid damage due to prolonged weather exposure. Formwork for the entire sculpture was left in place until concrete placement was complete. The levelness, elevation, and orientation of the foundation of the sculpture were critical. The foot and ankle placement was one of the most challenging due to the unusual geometry and the large amount of reinforcement. The structure was built in four-foot lifts, with forms that were bolted together. Due to the computer controlled STRUCTURE magazine

To verify structural modeling assumptions, Uzun + Case instrumented the finished sculpture with accelerometers to measure its fundamental frequency. The measured value of 2.5 hz was within 5% of the value predicted by the eigenvalue analysis when adjusted for average actual vs. specified concrete strengths. This gave added confidence that the complex computer model had accurately captured the behavior of the structure. The finished surface was inspected and observed to be of excellent quality and free of visible cracks other than those at the ankle zones, which are of predicted width. It was satisfying to have predicted the cracking performance accurately, but the author was secretly hoping for the cracks not to appear! This demonstrates the importance of managing expectations in advance since all parties were satisfied with the resulting performance.

Collaboration Artist and engineer, working together, were able to create a concrete structure of extraordinary geometric complexity, thinness, and grace. Stealth was the result of a collaborative and respectful working relationship between artist and engineer. The artist thought like an engineer in conceiving of a form that was not only interesting and beautiful but also structurally feasible and buildable. The engineer thought like an artist in striving to make the structure not only stable but also as thin and as faithful to the artist’s vision as possible.▪

Jim Case, P.E., is a Senior Principal at Uzun + Case, LLC in Atlanta, GA. He can be reached at jcase@uzuncase.com.

September 2016

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The Concrete Authority ACI 318-14: Building Code Requirements for Structural Concrete & The Reinforced Concrete Design Handbook (Vol. 1 & 2) Organized from the designer’s perspective, the new edition of ACI 318-14 includes more tables and charts, a consistent structure for each member chapter, and fewer cross references. “The Reinforced Concrete Design Handbook” provides many design examples of various reinforced concrete members based on the design of a seven-story building.

ACI 562-16: Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures and Commentary & Guide to the Code for Assessment, Repair, and Rehabilitation of Existing Concrete Structures (Coming Soon) Based on nearly one century of content from the American Concrete Institute, the new ACI 562-16, “Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures and Commentary,” and the companion Guide combine the Institute’s historical knowledge with state-of-the-art resources on the evaluation, repair, and rehabilitation of concrete buildings. ACI 562-16 provides minimum performance requirements that address the unique nature of existing building construction, and includes requirements on all aspects of concrete repair, from conception to completion, including the basis for compliance, evaluation and analysis, design of structural repairs, durability, and construction.

www.concrete.org

TORNADO SHELTERS IN SCHOOLS Masonry Tornado Shelter Case Study: Marshall Junior High, Marshall, TX By Benchmark H. Harris, P.E., S.E., LEED AP The new Junior High School for Marshall Independent School District in Marshall, Texas.

ection 423 of the 2015 International Building Code (IBC) has a new requirement that construction for new schools and additions to existing schools (up through high school, with some limited exceptions) have tornado shelters. These shelters must comply with ICC 500-2014 ICC/NSSA Standard for the Design and Construction of Storm Shelters if the project is located in the zone where the minimum required design wind speed for a tornado shelter is 250 mph, as shown by the shaded region in the attached map. (This requirement for tornado shelters also applies to critical emergency operations such as fire, rescue and 911 call centers.) Many of the structural engineering requirements involve coordination with a Local Emergency Planning Committee, the school district, architect, civil engineer, mechanical engineer, electrical engineer, technology designer and even the interior designer. Furthermore, ICC 500-2014 requires independent peer reviewers for both structural and architectural provisions, as well as an onsite structural engineer hired by the Owner to make observations during construction as part of the quality assurance plan. All this coordination elevates the significance of the primary structural engineer’s role during the planning of the shelter, and can require a greater effort than for traditional structures. When Huckabee (an Architectural and Engineering firm) began master planning construction with Marshall Independent School District (MISD) in Marshall, Texas, they informed the district of the new IBC requirements. While the current building code in Marshall does not require tornado shelters yet, new construction will be required to have tornado shelters after the city of Marshall adopts the 2015 IBC. MISD elected to proactively have tornado shelters designed in all of the four new facilities associated with a recent bond program. The current building code in Marshall is the 2009 IBC, which only requires tornado shelters be designed using ICC 500-2008 if a part of a building is specifically designated as a tornado shelter. Therefore, these shelters were designed using the 2008 version (the first edition) of the ICC 500 standard. STRUCTURE magazine

It is important to note that there are some significant differences between the 2008 and 2014 versions of the ICC 500 standard. Both versions require standardized debris impact testing (2x4 missiles). Section 803.1 of the older version requires that doors, windows and impact-protective systems be tested at the “maximum size” listed for use. However, the new version requires these systems be tested at both the “maximum and minimum size” listed for use. The general rationale for the new, additional requirement is that smaller components can theoretically be more rigid. This rigidity means less time for energy transfer and that can equate to greater forces on parts of the system. Having specimens created and tested by a laboratory takes time and money; therefore, many component manufacturers have tested only one large size for each model and not tested small specimens yet, primarily because they have not had time to react to the new provision for minimum size testing in ICC 500-2014. The effect is that many building components need to be the same size as tested if the ICC 500-2014 standard is used, and those sizes are generally larger than is preferable for daily use of the facility. For example, ASSA/ABLOY makes a StormPro door system that would have to have 4 foot wide x 8 foot high doors rather than the smaller, standard sizes for doors. The new Marshall Junior High is under construction currently and is designed to have 121,560 square feet of floor plan area. The Marshall ISD Local Emergency Planning Committee indicated that the number of occupants required for design of the shelter is 1,400 people, which was based on Texas Education Agency requirements and the actual anticipated population (rather than what the IBC would require for fire egress, which would be much higher); and, the City of Marshall agreed with this interpretation. ICC 500 requires at least five square feet of open floor plan area for each occupant, with ten square feet for occupants in wheelchairs. Therefore, the design team recommended using the portion of the facility generally intended for locker rooms which had sufficient open area (including a long corridor), a low roof elevation (approximately 15 feet above finish floor), and concrete masonry construction for durability and low maintenance cost in the locker room environment. continued on next page

September 2016

ICC 500 requires that “lay down, rollover and collapse hazards” be considered. Because the locker room area is adjacent to a series of taller practice gymnasiums, additional loads were simulated by adding the weight per square foot of wall area for the gymnasium wall system to the weight per square foot of roof area for the gymnasium roof, and multiplying that sum by 1.5 to simulate impact as with crane loads. Designers applied this additional live load pressure over a horizontal distance from the perimeter of the shelter against the gymnasium, equal in horizontal length to the difference in elevation between the top of the gymnasium parapet to the mean roof height of the shelter. This was to simulate the gymnasium wall forming a hinge at the top of the shelter and a hinge at the roof-to-wall connection for the gymnasium, with the mechanism collapsing on top of the shelter. This method was approved by the Local Emergency Planning Committee and the district’s Independent Structural Engineering Peer Reviewer. The Tornado Shelter for the Marshall Junior High project was designed with load-bearing, reinforced concrete masonry walls with a composite steel beam and concrete slab over metal deck structural roof system. The wind pressure governed the design of the wall over the debris impact resistance criteria. The walls generally consist of fully grouted 12-inch CMU with two vertical #5 reinforcing bars (double curtain) at 16 inches on center and various patterns of horizontal reinforcement. Debris impact testing reported by Texas Tech University demonstrated that the specified masonry assembly is acceptable. Proper grouting is essential for quality masonry in tornado shelters. If voids form behind the face shells as grout shrinks, it is possible that debris impacts on the exterior face of the wall could cause the face shells on the interior face to delaminate and become projectiles within the shelter. Instead of having a mechanical ventilation system which would require back-up power for two hours, such as an emergency generator that would need to be protected from wind pressures and debris impact, a method of providing natural ventilation was specified. Atmospheric Pressure Change (APC) venting was not provided due to the adverse impact the large openings would have on the use of the space; a value of GCp = +/-0.55 was used under the exception that does not require APC venting. Providing a means for natural ventilation when the shelter is activated, but closing off this system when the building is under normal occupancy, presents numerous architectural, mechanical, electrical, and structural challenges. There are requirements for lower openings and upper openings for air circulation. Because masonry is constructed in-place by trained craftsmen, baffling chambers, such as the one shown, that have various partitions to divert the trajectories of possible debris impact (which can be much smaller than the standardized 2x4 missile) were easy to design, specify and have constructed. (Other systems, such as precast concrete, are more limited in their ability to provide customized baffling systems that work with typical architectural floor plans.) Tall parapets are not desirable because flying debris like trees can catch on them; therefore, a 2-foot maximum parapet height from top of the CMU to top of the concrete roof deck was designed. The 2-foot maximum parapet criteria provided sufficient height for detailing flashing and allowing roof slopes with a constant height top-of-wall architectural elevation. Because the location was not at the front of the building, the short parapet height was aesthetically acceptable. Baffling (to divert debris and thus slow down impact) is required for any openings in the shelter envelope greater than 3.5 square inches; therefore, roof drains were avoided by having the roof drain off of the low wall without a parapet. ICC 500 requires a quality assurance plan, addressed for this project by embedding provisions in the quality control specifications for the entire project. For the entire project, the specifications require that STRUCTURE magazine

Debris impact baffling chamber for natural ventilation.

an Independent Quality Control Agency (IQCA) perform or provide all special inspection, special testing, and structural engineering observation for the shelter according to the “Statement of Special Inspections, Testing and Observation” in Specification Section 01 4533 titled Code-Required Quality Control. The qualifications for the structural observer are that the individual be a Professional Engineer (PE) licensed in Texas and listed on the Texas Board of Professional Engineers as practicing structural engineering or be a Structural Engineer (SE) licensed in Texas. The on-site masonry inspector is required to be a certified TMS Masonry Field Testing Technician. The masonry testing technicians are required to be certified TMS Masonry Laboratory Testing Technicians.

Summary The 2015 International Building Code has a new requirement that tornado shelters be designed in all new school construction (up through high school) in over a quarter of the United States. The MISD Junior High project is an example of how ICC 500 (which was not originally written to be a mandatory requirement for schools) was applied to provide school occupants protection from tornados. Reinforced masonry was selected for its compatibility with the use of the space, considering its durability and flexibility to meet structural and performance criteria.▪

Benchmark H. Harris, P.E., S.E., LEED AP, is the Director of Engineering for Huckabee, an Architecture & Engineering firm with six offices all over Texas. He is the Chair of the The Masonry Society (TMS) Disaster Investigation Program and the recipient of the 2015 Paul Haller Award from TMS. He is currently working with the ICC 500-2014 Committee on the development of a Commentary document. Mr. Harris can be reached at bharris@huckabee-inc.com. September 2016

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Performance-Based Design of 111 Main in Salt Lake City By Mark Sarkisian, S.E., Peter Lee, S.E., Alvin Tsui, S.E. and Lachezar Handzhiyski, S.E. Courtesy of City Creek Reserve, Inc.

111 Main’s reinforced concrete core wall system provides vertical and lateral support for an innovative 25-story office tower suspended over adjacent performing arts center.

ocated in a region of high seismicity in close proximity to the active Salt Lake Segment of the Wasatch Fault Zone, the new 111 Main office tower in Salt Lake City, Utah, comprises 501,455 square feet of Class A office space. The 25-story building rises 387 feet above grade and contains a penthouse roof-level steel hat-truss system with all perimeter columns suspended to allow for air-rights overhang at adjacent performing arts center. The overall project design challenges and solutions were described in STRUCTURE magazine, June 2016. This article focuses on the two stage performance-based seismic design methods undertaken by the design team during the project design development, independent peer review, and approval process. Designed to meet the minimum requirements of the 2012 International Building Code (IBC) and ASCE 7-10 provisions, the building superstructure construction incorporates a ductile reinforced concrete core wall system that exceeds the height limit of 160 feet per ASCE 7-10 Table 12.2.1. Thus, as a non-prescriptive alternate design method permitted by IBC Section 104.11, performance-based seismic design procedures were adopted following the guidelines of the Pacific Earthquake Engineering Research Center (PEER) Tall Building Initiative Guidelines (2010). The PEER TBI guidelines require that code equivalent or better performance is demonstrated at peak Maximum Considered Earthquake (MCER, 2% in 50yr, 2475 ARP) demands. Under construction, 111 Main is scheduled to be completed in August 2016.

Two Stage Performance-Based Design In addition to the ambitious design challenge of hanging all 18 perimeter steel columns from penthouse roof trusses to allow an airrights overhang at the new 4-story performing arts center directly to the south of the tower, the project was driven by a fast-paced design and construction schedule to achieve project deadlines and commitments. During the Stage 1 procedure, final proportioning of reinforced concrete core wall design including thicknesses, openings, boundary zones, and link beams was achieved using simplified tri-directional linear response spectrum analysis and design. During the Stage 2 procedure, which included rigorous oversight by the Seismic Design Review Panel (SDRP), the team conducted tri-directional nonlinear response history analysis (NLRHA) to demonstrate that the structure design, determined in Stage 1, satisfied the performance-based inelastic design criteria of the PEER TBI guidelines. Site-Specific Response Spectra and Ground Motions Site-specific response spectra and ground motions for the Maximum Considered Earthquake (MCER) were developed per ASCE 7-10 requirements by the geotechnical engineer, URS, and the SDRP. The MCER spectrum was defined as the lesser of the deterministic and probabilistic MCER ground motions. To address the response of the hat-truss supported structure, vertical spectra was developed based on the median V/H ratios of Gϋlerce and Abrahamson, defining two sets

Figure 1. Structural systems description.

STRUCTURE magazine

September 2016

of conditioned horizontal and vertical response spectra. For the Stage 2 NLRHA procedure, two suites of seven sets of three-component ground motion time histories, spectrally scaled to the MCER spectra, were selected. Each of the seven ground motions were randomly rotated as recommended by SDRP.

Table 1. Stiffness property modifiers used in Stage 1.

Element

Basement Wall

0.20

0.12

Core Shear Wall

0.50

1.00

Structural Systems Description

Link Beam

0.15

1.00

The superstructure typical framed levels consist of WF steel composite deck and slab construction with perimeter W14 columns as shown in Figure 1. The ductile reinforced concrete shear wall core construction includes 30-inch-thick walls extending from the top of the basementlevel pile-cap foundations to the underside of the trussed penthouse at Level 25. The core walls are configured on two grid lines in the east-west direction (62 feet 6 inches) and three grid lines in a northsouth direction (42 feet 9 inches) utilizing specified self-consolidating concrete with a strength of 8,000 psi except at Level 24, below the hat-trusses, where 10,000 psi is needed. Perimeter column loads representing approximately 40% of the building gravity dead and live loads are transferred from the roof hat-trusses to the top of the core walls via six articulated spherical structural steel bearings. The core wall loads are transferred to a deep foundation system consisting of driven steel HP-piles extending to depths of 100 feet and greater below grade, with a total of 373 HP14 piles.

Level 1 Diaphragm

0.20

0.12

Tower Diaphragm

0.50

Table 2. R-Factors at MCER level used in Stage 1.

Element

Rx and Ry

Link Beam

3.5

1.0

Flexural in Shear Wall

3.5

1.0

Shear in Shear Wall

2.0

1.0

Steel Roof Truss

2.0

1.0

Steel Hanging Column

2.0

1.0

Foundation System

2.5

1.0

Table 3. Expected material properties (φ=1.0).

Stage 1: 3D Linear Analysis and Design

Material

The design team was challenged to use linear dynamic modal response spectrum analysis (MRSA) during a 10-week design development phase to finalize the proportions, design, and quantities of the ductile reinforced concrete bearing wall system. These details were needed prior to building a 3D-nonlinear analysis model to demonstrate compliance with the performance-based design PEER TBI MCER level acceptance criteria. The two-stage strategy included a Stage 1 linear MRSA and a Stage 2 nonlinear analysis verification of the Stage 1 results which would occur during the final construction document design phase. A 3-dimensional ETABS by Computers and Structures, Inc. (CSI, v2013) linear analysis model was developed for the MRSA with 5% modal damping. The structure seismic force resisting system (SFRS) was modeled and included the complete gravity and lateral structural system load path from foundations (pinned at basement level), basement walls, Level 1 diaphragm, core walls, hat-trusses, floor framing, hanging perimeter columns, and structural bearings at top of core walls below Level 25 trusses. Stiffness property modifiers were used as recommended in PEER/ATC 72-1 (2010) for the concrete lateral and gravity elements to account for cracked section

Figure 2. New and modified core wall openings to reduce stress concentration and increase ductility.

STRUCTURE magazine

Expected Strength

Reinforcing Steel in Concrete

1.17 fy

Concrete

1.3 f'c

ASTM A992/A572 Steel

1.1 Fy

properties during a seismic event as summarized in Table 1 with additional conservative assumptions made for the shear stiffness of core wall and link beam elements, as well as the lower bound stiffness for the ground level diaphragm. To estimate demands at MCER level using Stage 1 MRSA, more conservative values of ductility based system response modification R-factors were utilized for the bearing wall system than prescribed by code minimum (ASCE 7-10) requirements (R=5 at DE, 2/3 MCER). These values, as summarized in Table 2, were based on recent research summarized in NEES webinar, Performance, Analysis and Design of Flexural Concrete Walls by Lehman and Lowes (2013). The research included a 1/3 scale testing program with wall specimens detailed with varying parameters per ACI 318-11 requirements, correlated with FEMA P695 probability based collapse prediction modeling. The research concluded that R-factors for various high rise concrete wall systems to achieve 20% probability of failure at MCER was about 3.5, which is significantly lower than the ASCE 7-10 value and the shear demand in core wall should be increased by a flexural overstrength factor and dynamic amplification factor. A simplified approach was utilized for 111 Main using R=3.5 for deformation controlled actions and R=2 for force controlled actions. At MCER level demands, expected material properties and capacity reduction factor, φ=1.0, were assumed as summarized in Table 3. Since IBC 2012 and ASCE 7-10 do not explicitly address the directional combinations for vertical seismic load, the ASCE 4-98 (2000) Section 3.2-26 standard for the Seismic Analysis of Safety-Related Nuclear Structures was referenced for defining the combined horizontal and vertical seismic load combinations. Combining with PEER TBI

September 2016

(2010) Section 7.6.1, the tri-directional seismic load combinations used in Stage 1 analysis at MCER MRSA were as follows, where Lexp is the expected live load (25% of the unreduced live load): 1) 1.0D + Lexp ± 1.0Ex ± 0.4Ey ± 0.4Ez 2) 1.0D + Lexp ± 0.4Ex ± 1.0Ey ± 0.4Ez 3) 1.0D + Lexp ± 0.4Ex ± 0.4Ey ± 1.0Ez Following coordination of core wall openings with the Architecture/MEP design team, and preliminary analyses indicating high wall and link beam shear stress concentrations, the structural design team introduced additional new and modified core wall openings to reduce stress concentrations at story stiffness and strength transitions as shown in Figure 2. The additional link beams introduced by these openings significantly increased the ductility of the structure while balancing the stiffness along parallel core wall grid lines.

Therefore, the structure remains essentially elastic and satisfies the service-level immediate occupancy performance objective. Stage 2 Nonlinear Analysis Modeling The 3-D nonlinear analysis model using PERFORM-3D (CSI, v2011) is shown in Figure 3. The model included the core walls, all hanger columns and hat truss elements comprising the SFRS and load path in resisting both horizontal, and vertical seismic loads. At typical steel framing levels, masses were lumped at perimeter columns and core wall locations, with rigid diaphragms at Levels 2 to 24. The model was pinned at a basement foundation level with no soil support springs modeled at basement walls. Concrete core walls were modeled using the PERFORM-3D Inelastic Shear Wall element using two vertical steel and concrete fibers per panel zone element and four fibers per each boundary zone element. Coupling beams were modeled using five different models, depending on reinforcement arrangement and aspect ratio, utilizing both conventional and diagonally reinforced beams. Model material properties were based on most recent recommended research and testing results.

Stage 2: 3D Nonlinear Analysis and Design

With the development and design of the SFRS determined from Stage 1 linear elastic procedures, a Stage 2 nonlinear analysis procedure was used to evaluate the design using the PEER TBI procedures and Performance Studies acceptance criteria during the project construction document phase. Establishing the project specific Some significant performance studies were conducted procedures and criteria included the collaborative recin assessing the structure and model before commencommendations of the SDRP in the final verification, ing with the NLRHA to address questions posed by Figure 3. PERFORM-3D (CSI) design, and detailing of the structure. The SDRP input the SDRP. These studies included hat-truss gravity nonlinear analysis model. included additional performance checks consistent load effects on the concrete core ductility and strength, with the intent of the PEER TBI guidelines. The guidelines provide an cracking vs. yield moment core capacity, displacement-based design alternative to the prescriptive procedures for seismic design in ASCE 7 concepts assessing the distribution of vertical reinforcement ratio, and with the intent to permit the design of buildings using non-prescriptive coupling beam strength vs. core flexural strength checks over the height systems of equivalent performance that are capable of achieving the of the core wall structure. Figure 4 illustrates nonlinear core wall behavior seismic performance objectives of Occupancy Category II buildings. using a core cross section fiber model (XTRACT) in consideration of The guidelines consider the inelastic response of the structure’s global global axial-moment and moment-curvature effects demonstrating a behavior and element components using NLRHA at the MCER level substantial increase in moment strength due to additional compressive collapse prevention performance objective. The 111 Main acceptance loads from the hat-truss. Cracking vs. yield moment capacity at upper criteria included consideration of bounded basement level backstay effects, levels with low flexural reinforcement ratio was also considered. inter-story and residual drift limits, as well as consideration of force and deformation controlled element component performance in the SFRS Stage 1 & Stage 2 Summary Results at the MCER. Serviceability at the 43-year earthquake event was also considered, but spectral demands were significantly less than those from Representative summary analysis results show good correlation in the MCE spectrum reduced by the Stage 1 response modification factors. comparison of Stage 1 (MRSA) and Stage 2 (NLRHA) procedures.

Figure 4. Core wall fiber cross section analysis.

STRUCTURE magazine

September 2016

Figure 5. Summary Stage 1 & Stage 2 interstory drift demands.

While predicted MCER inelastic inter-story drift ratio demands (Figure 5) are similar, the nonlinear analysis of Stage 2 illustrates a more uniform redistribution of peak pier wall shear stresses. These global summaries, as well as additional Stage 2 results including limits on wall strains at confined and unconfined concrete, coupling beam rotations and residual drift demands, demonstrate full conformance with the project design criteria and with the performance intent of ASCE 7-10 for Occupancy Category II buildings.

two-stage methodology allowed for early coordination of the seismic force-resisting system with architecture and MEP design teams without compromising the quality of structural solution delivered in the final design. The simplified Stage 1 approach can be used in concept and schematic design of tall core wall buildings in high seismic regions to assess design feasibility quickly without the need for complex nonlinear analysis. The reader is referred to a more detailed summary of this twostage performance-based design approach in SEAOC 2015 Convention paper, by the authors, titled, Performance-Based Design of 111 Main.▪

Conclusions

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Faced with an accelerated design and construction project schedule, the SOM structural design team developed a two-stage performancebased methodology which required close collaboration with the SDRP to achieve performance objectives and meet project milestone deadlines. While utilizing a simplified Stage 1 linear MRSA procedure, the

Acknowledgments The authors gratefully acknowledge the 111 Main project sponsors led by City Creek Reserve, Inc. and Hamilton Partners for their strong support of the design team in reaching project goals and objectives. We thank the Seismic Design Review Panel led by Chair Chris Kimball, Joe Maffei, Karl Telleen and Norm Abrahamson for their constructive recommendations and collaboration. In Salt Lake City, Eric Kankainen served as structural plan reviewer. Bill Gordon was project geotechnical engineer with seismic hazards developed by Ivan Wong and Patricia Thomas at URS. We also thank Phil Miller and the team at Dunn & Associates for their valuable support in the development of the analysis and design of the deep foundation system. Mark Sarkisian, S.E., (mark. sarkisian@som.com) is Partner, Peter Lee, S.E. (peter.lee@som.com) is Associate Director, Alvin Tsui, S.E., (alvin.tsui@som.com) is Associate, and Lachezar V. Handzhiyski, P.E., (lachezar.handzhiyski@som.com) is Design Engineer, Skidmore, Owings & Merrill LLP in San Francisco, CA.

STRUCTURE magazine

September 2016

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ecently, an insurance adjuster engaged one of the authors to help determine the replacement cost for vehicle damage to a residential garage. The residence is constructed on a hillside, on the downslope side of the roadway. The house is typical of many at such locations; the garage and public living spaces are at the uppermost/street level and private spaces like bedrooms are located in the story below. Below the lower story is a steeply sloped crawlspace, with walls on the downhill side that are approximately sixteen feet tall. A driveway bridge connects the road to the garage. Figure 1 presents a typical example of this type of residence. Apparently, upon returning home, the homeowner was parking in the garage and lost control of the vehicle. The vehicle drove through the rear wall and fell down to the ground behind the garage, approximately 30 feet below. The accident was fatal. Surprisingly, the adjuster estimates that he has a claim almost every month in which a vehicle has driven through the rear wall of a residential garage. Although typically, in those incidents, the vehicle drove into the adjoining residence and came to a stop. This was the only fatal incident that he observed. The adjuster asked the author to prepare a report describing a structural repair to develop a cost for the work. During the course of preparing the report, it became apparent that neither the International Residential Code (IRC) nor the International Building Code (IBC) has specific requirements for vehicle retention in residential garages.

Figure 2. Light shearwall assembly for upper level walls typically used by the authors.

Lessons Learned problems and solutions encountered by practicing structural engineers

Figure 1. Typical hillside house with upper level garage.

Code Review A review of the 2012 IBC indicates provisions for vehicle barriers in Section 1607.8.3. “Vehicle barriers for passenger vehicles shall be designed to resist a concentrated load of 6,000 pounds in accordance with Section 4.5.3 of ASCE 7” (American Society of Civil Engineers Standard Minimum Design Loads for Buildings and Other Structures). ASCE 7 specifies additional criteria on how that load is to be applied. What is not immediately obvious is in which situations the designer is required to provide such a vehicle barrier. IBC Section 406 presents occupancy-related requirements for garages and, within it, Section 406.4 provides guidance for public parking garages that includes requirements for vehicle barriers (Subsection 406.4.3). Specifically, barriers are required at ends of drive lanes or parking spaces where the vertical distance to the ground or surface below is greater than one foot. Note that Section 406 applies to both open and enclosed parking garages, suggesting that enclosing a garage is not adequate and either the wall needs to be the vehicle barrier itself or it needs to be protected by one. IBC Section 406.3 presents the different and separate requirements for private parking garages and carports. Section 406.3 has no requirement for vehicle barriers. The inclusion of vehicle barrier requirements in Section 406.4 and not in Section 406.3 suggests to the designer that it is appropriate to omit such barriers in private garages. Since most private garages are in single-family residences, duplexes or townhomes, the building may be designed according to the provisions of the IRC. The authors reviewed the 2012 IRC and found no requirement for vehicle barriers at the rear of garages. As the specific code for residential construction, the IRC provides prescriptive requirements for garage construction. Chapter 6

STRUCTURE magazine

Considerations for Above Grade Residential Garages

Lessons Learned from a Fatal Accident By Douglas Gadow, P.E., S.E. and Jeremy Gavelin, EIT

Douglas Gadow is a Senior Principal at Linchpin Structural Engineering, Inc. located in Truckee, California. He can be reached at doug@linchpinse.com. Jeremy Gavelin is a Project Engineer at Linchpin Structural Engineering. He can be reached at jeremy@linchpinse.com.

of the IRC provides prescriptive requirements for walls and includes guidance for a variety of different types of construction. Wood framed walls are typical for a residence with upper level garages. The authors found that following prescriptive wall construction provisions, a rear wall of a garage might be framed as lightly as 2x4 studs spaced 24 inches on center. Wall sole plates are fastened to floors with 16d nails spaced at 16 inches on center. The exception is for a wall that is a bracing wall panel, in which case it would have three nails every 16 inches.

nails acting in withdrawal. Considering three sheathing nails acting in withdrawal and two sole-plate-to-stud-end-grain nails acting in shear, the capacity to resist the vehicle load at the base of the wall was calculated to be approximately 2,000 pounds, and that is with a 2.0 load duration factor for impact. The assembly detailed will not provide adequate restraint for vehicle impacts – the sole-plate-to-stud connection can be expected to fail and a vehicle would not be restrained. During the author’s investigation at the residence where the tragic accident occurred, the observed failure was at the sole plate to stud connection.

Analysis

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It is apparent that conventional wall framing provides inadequate restraint to vehicle loads. The authors practice in a region that requires that all houses be engineered rather than framed according to conventional provisions. Therefore, the authors analyzed the wall construction that they would typically specify in the region for this type of house. For most residences, the walls would be framed with 2x6 studs spaced 16 inches on center, sheathed to provide lateral resistance, and generally connected according to Figure 2 ( page 57 ). When a 6,000-pound vehicle load is applied two feet above the subfloor, for an eight-foot-tall

Design Figure 3. Schematic view of vehicle retention posts within the rear wall of the garage.

wall, the reaction at the base is 4,500 pounds. An entire wall assembly was evaluated to determine its failure mechanism. ASCE 7 requires applying the vehicle load to an area no larger than 12 inches by 12 inches; therefore, the entire vehicle load is applied to a single stud. The “weak link” is the sole-to-stud nails acting in shear combined with the exterior sheathing

Despite there not being a clear code requirement to do so, and because of the significant consequences, many Owners are willing to pay the extra cost for a more robust barrier upon learning the potential risk. Most Owners are, however, not eager to have bollards about their garages taking up valuable floor space. Considering that, and the difficulty of designing bollards restrained only by the wood floor framing, integrating vehicle restraints into the rear wall of the garage is a solution. These restraints can be HSS steel posts spaced less than five feet on center – in order to prevent a vehicle from getting between them – within the wall cavity. The HSS posts connect to the roof and floor framing, and transfer the reactions from the vehicle load into the diaphragms and the lateral force resisting system. Figure 3 shows schematically how to incorporate these types of posts into the wall, floor and roof. An additional design feature involves placing a horizontal beam at the vehicle bumper level to better spread the impact load and engage multiple posts.

Conclusion

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September 2016

It appears that current codes for residential garages do not have specific requirements for vehicle barriers, and conventional construction provides little restraint for vehicle loads. For hillside homes with garage floor elevations that are well above the grade beyond the parking area, there is a potentially high consequence if a vehicle is to drive into the rear wall. A recent fatal incident, that one of the authors observed, tragically exemplifies this. Despite this, a wary designer can recognize the risk and design an easily installed and cost effective vehicle barrier in a wood-framed residence.▪

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ne of the world’s greatest unsolved mysteries of our time lies in a courtyard outside of the Central Intelligence Agency (CIA) headquarters in Langley, Virginia. It’s a sculpture called Kryptos, and although it’s been partially solved, it contains an inscription that has puzzled the most renowned cryptanalysts since being erected in 1990. Meanwhile, in another part of the DC Beltway about 15 miles to the southeast, another great mystery is being deciphered at the American and Iron Institute (AISI) headquarters. The mystery, structural behavior of cold-formed steel (CFS) clip angles, has puzzled engineers since the great George Winter helped AISI publish its first Specification in 1946. In particular, engineers have struggled with how thin-plate buckling behavior influences CFS clip angle strength under shear and compression loads. Additionally, there has been considerable debate within the AISI Specification Committee concerning anchor pull-over strength of CFS clip angles subject to tension. The primary problem has been the lack of test data to explain clip angle structural behavior. Even with modern Finite Element Analysis (FEA) tools, without test data to help establish initial deformations and boundary conditions, FEA models have proven inaccurate. Fortunately, joint funding provided by AISI, the Steel Framing Industry Association (SFIA), and the Steel Stud Manufactures Association (SSMA) has provided the much-needed testing that has culminated in AISI Research Report RP15-2, Load Bearing Clip Angle Design, that summarizes phase one of a multi-year research study. The report summarizes the structural behavior and preliminary design provisions for CFS load bearing clip angles and is based on testing that was carried out in 2014 and 2015 under the direction of Cheng Yu, Ph.D. at the University of North Texas. Yu’s team performed 33 tests for shear, 36 tests for compression, and 38 tests for pull-over due to tension. Clip angles ranged in thickness from 33 mils (20 ga.) to 97 mils (12 ga.), with leg dimensions that are common to the CFS framing industry. All of the test set-ups were designed so that clip angle failure would preclude fastener failure. For shear, it was found that clips with smaller aspect ratios (L/B<0.8) failed due to local buckling, while clips with larger aspect ratios failed due to lateral-torsional buckling. Shear test results were compared to the AISC Design Manual for coped beam flanges, but no correlation was found. Instead, a solution based on the Direct Strength Method (DSM) was employed that utilized FEA to develop a buckling coefficient for the standard critical elastic plate-buckling equation. Simplified methods were also developed to limit shear deformations to 1/8 inch. For compression, it was found that flexural buckling was the primary failure mode. Test results were compared to the

InSIghtS new trends, new techniques and current industry issues

Generic CFS Clip – with 5x5 angle.

gusset plate design provisions of AISI S214, North American Standard for Cold-Formed Steel Framing – Truss Design, and the axial compression member design provisions and web crippling design provisions of AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members, but no good agreement was found. Therefore, an alternate solution was developed that utilized column theory in conjunction with a Whitmore Section approach that yielded good agreement with test results. It was further found that using a buckling coefficient of 0.9 in the critical elastic buckling stress equation will produce conservative results. Finally, for pull-over due to tension, it was found that clip angle specimens exhibited significant deformation before pulling over the fastener heads (essentially the clip turns into a strap before pullover occurs). However, regardless of this behavior, tested pull-over strength results were essentially half of AISI S100 pull-over equation E4.4.2-1. Thanks to AISI Research Report RP15-2, there is a clearer understanding of the CFS clip angle structural behavior mysteries that have puzzled engineers for many years. However, just as the CIA’s Kryptos remains only partially solved, some aspects of clip angle behavior remain a mystery. For instance, how are the test results influenced by the fastener pattern? All of the test data to date has used a single line of symmetrically placed screws. This is something that does not occur for many practical CFS framing situations and will need additional research. Another glaring research hole is the load versus deflection behavior of clip angles under tension. As briefly mentioned above, the existing pull-over testing has demonstrated that excessive deflections can be expected before pull-over actually occurs. Obviously, most practical situations will dictate a deflection limit of something like 1/8 inch or ¼ inch, but today we don’t have the test data to develop a solution. Fortunately, AISI in conjunction with its CFS industry partners continues to fund research on CFS clip angle behavior that will answer these questions, and possibly many more.▪

STRUCTURE magazine

Decrypting Cold-Formed Steel Connection Design

By Randy Daudet, P.E., S.E.

Randy Daudet is a Product Manager with Simpson StrongTie. He is a member of the AISI Committee on Specifications and currently the Chair of the Test Based Design Subcommittee. He can be reached at rdaudet@strongtie.com.

the out-of-the-ordinary within the realm of structural engineering

The Logic of Ingenuity

The Logic of Ingenuity The process of (abductively) creating a diagrammatic representation of a problem and its proposed solution, and then (deductively) working out the necessary consequences, such that this serves as an adequate substitute for (inductively) evaluating the actual situation.

Part 1: Engineering Design By Jon A. Schmidt, P.E., SECB

Outside the BOx

his article is the first of a fourpart series, the title of which is a bit counterintuitive and perhaps even slightly misleading. Common parlance tends to identify logic with strictly deductive reasoning and ingenuity with cleverness, so the reader might be expecting me to offer a procedural algorithm that somehow guarantees an innovative outcome (“The Rationality of Practice,” September 2012). What I have in mind instead is logic in the broader sense as the norms of thought in general, and ingenuity in the narrower sense as the distinctive essence of engineering practice; after all, “ingenuity” and “engineering” have the same etymological roots (“Philosophy and Engineering,” September 2008). If the phrase sounds vaguely familiar, that may be because I used it in my last philosophical InFocus column (“Representation and Reality,” September 2015). I suggested there that the “logic of inquiry” identified by Charles Sanders Peirce as integral to science – which consists of formulating a hypothesis (abduction), explicating what follows from it (deduction), and then trying to falsify it (induction) – also serves as a “logic of ingenuity” in engineering. My goal in these follow-up pieces is to explore such a notion more fully. By doing so, I hope both to complement and to supplement what William M. Bulleit has recently written in this magazine about “The Engineering Way of Thinking” (Structural Forum, December 2015 – March 2016). Although they are structurally analogous, scientific and engineering reasoning are widely understood as pursuing very different ends (“The Principle of Insufficient Reason,” May 2008). Rather than the discovery of a universal theory with general application, an engineer is typically oriented toward the design of a particular artifact for a specific purpose. As I have said many times before, much like science is viewed as an especially systematic way of knowing, engineering may be viewed as an especially systematic way of willing (“Engineering as Willing,” March 2010). The “abductive” aspect of engineering design is imaginatively conceiving a potential artifact. Peirce noted that humans are remarkably successful at “guessing” scientific hypotheses, and argued that this reflects how our instincts and sentiments are attuned to nature through calibration over many generations. Likewise, by

gaining extensive experience of the right kind, an engineer cultivates a disposition to perceive the key attributes that are likely to make something suitable for its intended function (“The Nature of Competence,” March 2012). The “deductive” aspect of engineering design is carefully translating those characteristics of the proposed artifact into its physical requirements (“Artifacts and Functions,” September 2010). Some engineers are “hands-on” enough to fashion their own contrivances, but most instead have to explain them in detail – for example, by preparing drawings and specifications – so that someone else will be able to assemble them. The “inductive” aspect of engineering design is rigorously testing the artifact once it actually exists, in order to confirm that it performs as expected. This is fairly routine when it is feasible to manufacture prototypes, as for most engineered products; but it is rarely practicable for large engineered projects, such as buildings and bridges. In these cases, a second cycle of abductiondeduction-induction must be nested between the first two steps just outlined: engineering analysis. The “abductive” aspect is developing an idealized model of the artifact and its immediate environment (“Complicated + Complex = Wicked,” July 2015). The “deductive” aspect is processing this model in accordance with idealized assumptions; today, this is often done with the help of a computer. The “inductive” aspect is interpreting the results by comparing them with idealized rules, which are usually prescribed by industry-wide codes and standards. Peirce pointed out that the logic of inquiry in science is ordinarily self-correcting in the long run; the world will confront a persistent investigator with unpleasant surprises if a hypothesis is inconsistent with how it really operates. Unfortunately, when this happens in engineering, there tends to be a high cost – measured in dollars and/or in lives (“Remember the Hyatt,” January 2011). To avoid this, the logic of ingenuity involves the assessment of the model, rather than the artifact itself. Engineering science, including forensics (“Learning from Failures,” July 2006), provides genuinely inductive support for the overall validity of this approach by supplying and verifying the various heuristics that engineers implement in executing it (“The Engineering Method,” March 2006; “Heuristics and Judgment,” May 2006).

STRUCTURE magazine

September 2016

If the conclusion of the analysis is not acceptable, then it is necessary to revise the model – or possibly even the artifact concept – and carry out another analysis; the engineer must deem everything to be satisfactory before moving on to drafting instructions for constructing the artifact itself. Thus, representation is at the heart of what William Addis called a “design procedure” – most notably in non-prototypical engineering, where it is essential to achieving both outputs: description and justification (“The Nature of Theory and Design,” May 2009). I will close for now by calling attention to a couple of additional features of the latter task. First, Peirce strongly believed that all deductive reasoning is, in an important sense, mathematical; and all mathematical reasoning is diagrammatic. What he meant by this is that it proceeds by creating, manipulating, and observing an icon that accurately reflects the form of the significant relations among the parts of the object of interest. Hardy Cross hinted at this facet of engineering analysis when – as recounted by one of his last students at Yale University, Edward O. Pfrang – he defined a structure as “a system of connections loosely held together by members,” rather than the other way around. Second, it is crucial for the engineer – by exercising good practical judgment – to discern which relations are truly significant, and then devise a suitable icon of their form accordingly. Mete Sozen expressed a similar concern by posing a question that is well worth pondering: “Is an exact analysis of the approximate model an approximate analysis of the exact structure?” An affirmative answer is a fundamental, yet subtle – and therefore easily overlooked – presupposition of modern engineering. I will have more to say about these two points in subsequent installments.▪ Jon A. Schmidt (jschmid@burnsmcd.com) is an associate structural engineer in the Aviation & Federal Group at Burns & McDonnell in Kansas City, MO. He serves as Secretary on the NCSEA Board of Directors, chairs the SEI Engineering Philosophy Committee, and shares occasional thoughts at twitter.com/JonAlanSchmidt. Titles refer to past STRUCTURE articles; www.STRUCTUREmag.org.

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STRUCTURE magazine

September 2016

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award winners and outstanding projects

Spotlight

Grove at Grand Bay By Vincent DeSimone, P.E., FACI, F.ASCE, Hon. Ph.D., Luis Ramirez, P.E., SECB and Abdul Mohammad, P.E. DeSimone Consulting Engineers was an Outstanding Award Winner for the Grove at Grand Bay project in the 2015 NCSEA Annual Excellence in Structural Engineering Awards program (Category – New Buildings over $100M).

esigned by Bjarke Ingels Group (BIG), Grove at Grand Bay, the first truly twisting buildings in the United States, will be an iconic residential project located at the former site of the Grand Bay Hotel in Miami. Grove at Grand Bay features two towers rising 20 stories above a lush landscaped two-story podium. The two towers are low density, with 98 spacious custom homes featuring 12-foot high ceilings and 14-foot deep balconies. To capture the full panoramic views of Biscayne Bay and the Miami skyline, the architect rotated the towers incrementally along the height for a total rotation of 38 degrees. Site constraints required a square footprint for the base of the south tower. The floor plate increases in length as the building twists, maximizing the sellable area. The north tower footprint remains a constant rectangle throughout its height. When completed, these towers will be the first LEED Gold Certified residential buildings in Miami-Dade County.

Horizontal Shear Force The true twisting nature of the columns posed a number of structural challenges that demanded a fresh, innovative approach. The foremost challenge was to resist torsion generated in the tower core due to the sloping column geometry. The horizontal component of the gravity load in the columns is resolved in the slabs by transferring it to the interior core shear walls, which are the only consistently vertical structural elements in the building. Since all the columns are rotating in the same direction, additional horizontal thrust from all columns creates a large shear force in the tower cores. The magnitude of shear forces in the tower cores due to self-weight was considerably higher than that generated by the design hurricane wind loads. To minimize the total horizontal shear force transfer into the core walls, a “hat truss” was introduced at the roof. The hat truss is comprised of a series of beams cantilevered from the cores and connected to all the columns. The hat truss collects

superimposed dead load and live load, delivering the “suspended” loads directly to the core as a vertical load component. This alternate load path reduced torsional forces in the core by approximately 30 percent. The magnitude of the combined horizontal shear force from the building self-weight and the hurricane wind loads would require conventionally reinforced concrete shear walls to be 6 feet thick. To regain valuable real estate, a composite concrete shear wall and link beam system was introduced. The composite action between steel and concrete allowed a substantial wall reduction to 30 inches thick. Internal steel plates with thicknesses of up to 3.75 inches were required to achieve the overall wall thickness. Rolled steel sections replaced traditional reinforcing steel in the boundary element zones. The plates extend vertically for 15 floors, with normal reinforcing steel continuing to the roof.

to allow a 10-inch thick post-tensioned slab to span the remaining distance. This provided a 12-foot clear ceiling dimension.

Building Movement

Cost Conclusions

Building movement was another challenge, especially before the “hat truss” was installed and loaded. A linear analysis was performed, and it was determined that there was considerable horizontal displacement of the floors due to self-weight alone. Therefore, an extensive analysis was conducted to estimate the accurate building movement using a nonlinear construction sequence analysis. The tower floor plates are cambered rotationally, as much as a half-inch relative to the floor below, for 75% movement due to the building self-weight to compensate for the displacement. This allows the tower to settle back to the design coordinates just before the hat truss reaches design strength.

The South Florida residential market is currently leading the construction boom in the United States. In such a competitive environment, cookie-cutter architecture is unlikely to sell at desirable prices and developers are demanding more technically challenging and unique designs. However, there is a limit to what the market will pay and how much a developer is willing to spend. With the structural ingenuity used in the Grove at Grand Bay, the premium for a twisting architectural design was limited to an additional 18 percent above traditional construction. Without extraordinary interdisciplinary work between the entire design team, the project would not be a success.▪

Flexible Unit Layouts

Vincent DeSimone is the Founder, Chairman and Senior Principal-in-Charge of design at DeSimone Consulting Engineers.

Column-free interiors were provided to allow for maximum flexibility of the unit layouts. Resulting spans between the core and perimeter columns ranged up to 40 feet and balconies cantilevered up to 16 feet. DeSimone proposed a scheme with an 8-foot wide, 16-inch thickened slab around the core

STRUCTURE magazine

September 2016

Design Flood Elevation As is common in many coastal areas of Florida, this site is subject to flooding during tropical storm events. Portions of this site are located in a FEMA designated AE-12 flood zone. For insurance requirements, this prescribed the entire basement slab to be designed to a design flood elevation of +13.0 NGVD, resulting in a design uplift pressure of 710 pounds per square foot. Multiple-pile podium caps were replaced with a single larger pile with a cap poured monolithically with the basement slab to reduce the cost of excavation and dewatering. Additional cost savings were realized by using post-tensioning to reduce the mild steel in the slab.

Luis Ramirez is a Project Director at DeSimone Consulting Engineers. Abdul Mohammad is a Project Manager at DeSimone Consulting Engineers.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

2016 NCSEA Special Awards Honorees The following awards will be presented at the Awards Banquet on September 16th during the 2016 NCSEA Structural Engineering Summit in Orlando. For more information on the Summit, see pages 38 – 41.

James M. Delahay Award

NCSEA Service Award

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

David Bonowitz, S.E.

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

Carrie Johnson, P.E., SECB

David Bonowitz is a structural engineer and a consultant on disaster risk reduction policy. He is a graduate of Princeton University, holds a Master’s degree in Structural Engineering from U.C. Berkeley, and is a licensed California Structural Engineer. His engineering experience includes work in Indonesia, Japan, Micronesia, and Pakistan, as well as significant research following the Loma Prieta, Guam, Northridge, and Humboldt County earthquakes. From 2004-2007, he served as the first structural engineer for California’s Judicial Branch, developing design criteria and managing evaluations for California’s 500-plus court facilities. Since 2012, he has been one of the U.S. delegates to the U.S.Iran Joint Seismic Workshop. He chairs the NCSEA Existing Buildings Subcommittee of the Code Advisory Committee, which develops and coordinates building code changes on behalf of the nationwide engineering community. David was the 2004 recipient of SEAONC’s Edwin Zacher Award for Outstanding Service to the Structural Engineering Profession and the 2005 recipient of EERI Northern California’s Award for Innovation and Exemplary Practice in Earthquake Risk Reduction. In 2011 he was made a Fellow of the Structural Engineers Association of California.

Carrie Johnson serves as a principal and Chief Information Officer of Wallace Engineering Structural Consultants, Inc., a national structural and civil engineering firm headquartered in Tulsa with offices in Oklahoma City, Kansas City, Denver, Atlanta and Chicago. Carrie received her Bachelor of Architectural Engineering and Master of Architectural Engineering from Oklahoma State University and is a licensed engineer in 43 states. Her project work is concentrated in the retail industry. Carrie is a Past-President of NCSEA and has served on a number of committees within the organization. She has served as chair of the NCSEA Excellence in Structural Engineering Awards since 2003, as co-chair of the Continuing Education committee since 2010 and as chair of the NCSEA Structural Engineering Summit committee since 2015. Carrie has also served on the NCSEA Advocacy/General Public and Media Committee and is an active member of OSEA, in which she served as President twice (in 2001 and 2009) and was the OSEA delegate to NCSEA for six years.

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

Robert Paullus, Jr., P.E., SECB (awarded posthumously) Robert (Bob) Paullus, of Paullus Consulting Engineers, graduated from Christian Brothers University with a B.S. in Civil Engineering and recieved an M.S. from the University of Memphis. Bob held numerous positions during his engineering career starting with Chicago Bridge and Iron after college, and moving on to become Senior Structural Engineer for the Arkansas office of Crafton and Tull, Chief Engineer of the Memphis office of Barter & Associates, Inc., and owner of his own firm, Paullus Consultants. Bob founded and became President of the West Tennessee chapter of the Tennessee Structural Engineers Association (WTNSEA). He subsequently brought the three Tennessee STRUCTURE magazine

SEA groups together to form the Tennessee Structural Engineers Association (TNSEA). He served as TNSEA President and was honored in 2015 with the title of “Distinguished Member”. Bob was TNSEA’s first delegate to NCSEA and subsequently served as an NCSEA Board member and as NCSEA President (2008-2009). Bob served on two NCSEA Code Advisory Subcommittees (Seismic and Wind), the NCSEA SEER Committee, and the NCSEA Structural Engineering Certification Board interest committee. He was a member of the ASCE 7 Main and Seismic Subcommittees, as well as the ASCE 7 Seismic and Wind Loads subcommittees. He also served as a member of the Arkansas Fire Prevention Code Review Committee and the Tennessee Task Force One, a FEMA Urban Search and Rescue Team. September 2016

The winners of this year’s scholarships, an all-time high at eight winners from seven NCSEA Member Organizations, are shown below.

Colby Baker A Project Engineer with Ruby+Associates, Inc., Bingham Farms, Michigan, Colby is a member of the Structural Engineers Association of Michigan.

Solomon Ives A Project Manager with Kordt Engineering Group, Las Vegas, Nevada, Solomon is a member of the Structural Engineers Association of Southern Nevada.

Austin Curnutt A student at Kansas State University, Austin is a member of the Structural Engineers Association of Kansas and Missouri.

Ben Mall A Design Engineer with McNamara•Salvia Structural Engineers, Boston, Massachusetts, Ben is a member of the Structural Engineers Association of Massachusetts.

Leif Erickson A Design Engineer with KPFF Consulting Engineers, Portland, Oregon, Leif is a member of the Structural Engineers Association of Oregon.

Brian Post A Structural Engineer with Thornton Tomasetti, Boston, Massachusetts, Brian is a member of the Structural Engineers Association of Massachusetts.

Samantha Fox An Engineer with BCE Consulting Engineers, Inc., Bozeman, Montana, Samantha is a member of the Structural Engineers Association of Montana.

Charlotte Van Voast A Structural Engineer with Lopez Smolens Associates, Boulder, Colorado, Charlotte is a member of the Structural Engineers Association of Colorado.

The NCSEA Structural Engineering Summit offers discounted registration for young engineers, as well as special activities and resources, including a Young Engineers’ Reception and specialized resource sheets for each of the Summit educational sessions.

News from the National Council of Structural Engineers Associations

For the fourth year, NCSEA awarded Young Member Scholarships for the NCSEA Structural Engineering Summit. The scholarship competition was open to any current member of an NCSEA Member Organization who was under 36 years old. Applicants were asked to compose an essay or video answering one of three questions, as well as write a brief essay after attending the Summit. Scholarships included Summit registration and a travel stipend. The winners’ essays or videos can be viewed at www.ncsea.com under the Awards tab.

NCSEA News

NCSEA Awards Eight Young Member Scholarships to Summit

More information on the NCSEA Structural Engineering Summit can be found on pages 38 – 41.

NCSEA Webinars

October 6, 2016

Detailed information on the webinars and a registration link can be found at www.ncsea.com. Subscriptions that include both live and recorded webinars are available! 1.5 hours of continuing education. Approved for CE credit in all 50 states.

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Design of Advanced Composite Rehabilitation Systems – Avoiding Pitfalls and Confidently Detailing Designs The webinar will highlight the existing omissions and potential pitfalls that exist in the available design guidelines while also providing guidance on these areas of concern. Scott Arnold, P.E., Director of Engineering and Research & Development, Fyfe Company

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(this webinar will be held from 2:00-3:30 p.m. CT) Tsunami Design in ASCE 7-16: Overview of the New Provisions This webinar will feature a presentation on tsunami design, specifically the upcoming provisions in ASCE 7-16 (IBC-2018). Seth Thomas, P.E., KPFF

October 20, 2016

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Case Studies in Evaluation & Instrumentation of Existing Buildings Three separate case studies highlighting evaluation and instrumentation of existing buildings will be presented. Chuck Larosche, P.E., Stephen W. Foster, P.E., and Jeremiah D. Fasl, Ph.D., P.E., all of Winn, Janney Elstner Associates, Inc.

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

How You Can Help ICC Adoption of ASCE 7-16 ASCE 7-16 Chair Ron Hamburger, S.E., P.E., SECB, F.SEI, is asking that SEI members contact their local building officials and urge them to support adoption of the 2016 Edition of ASCE 7-16, Minimum Design Loads & Associated Criteria for Buildings and Other Structures. It is especially important for the ICC to adopt ASCE 7-16 because of the following significant changes to the standards: new wind speed maps, new regional snow data, and a new chapter on tsunami design provisions. SEI is asking building officials and other ICC Governmental Member voting

representatives to support ASCE 7-16 during the Group B Public Comment Hearings at the 2016 ICC Annual Conference, Kansas City, MO on October 19 – 25, 2016. Don’t miss Ron’s editorial on page 7 of this month’s STRUCTURE magazine. In the article, Ron gives more information on how you can help. If you are attending the 2016 ICC Annual Conference in Kansas City, you can help the adoption of ASCE 7-16 by voicing your support at the Group B – Policy Comment Hearings to support the adoption of the 2016 Edition as a reference standard.

Don’t Miss the ASCE 2016 Convention September 28 – October 1, 2016, Portland, Oregon The ASCE 2016 Convention will include thought-provoking activities such as interdisciplinary education sessions, inspiring and enlightening keynote speakers, tours, short courses and networking opportunities with potential clients and project team leads. The convention will address the things that matter to you: • State of the industry and profession • Professional development • Multi-disciplinary technical education • Natural & man-made disasters • Strategic issues / public policy • Significant projects • History & heritage

Visit the Convention website at http://asceconvention.org for more information, to download the Preliminary Program, and to register.

Keynote Presentation Video Now Available At the 2016 Geotechnical and Structural Engineering Congress in Phoenix, Robert C. Sinn, P.E., S.E., F.ACI, F.IABSE, LEED AP BD+C, F.ASCE, Principal and Building Structure Practice Leader, Thornton Tomasetti Inc.; and Alan R. Poeppel, P.E., Senior Principal, Langan Engineering and Environmental Inc. made a keynote presentation on Building the Kingdom Tower in Jeddah, Saudi Arabia. A video of that presentation is now available. The distinguished presenters shared their experiences addressing the significant technical engineering challenges of designing what will be, when completed, the new tallest building in the world. Starting with a brief overview of the architectural and master planning scheme for the tower and the surrounding

STRUCTURE magazine

developments, they then explain important aspects of the geotechnical site exploration program, piled raft foundation design and significant foundation-tower interaction studies, along with long-term settlement predictions, the completed pile load testing program, and ground seismicity studies. The presentation also discusses the development of the tower superstructure and foundation systems including historical precedents, the wind tunnel testing program, and other unique aspects of the tower structural, geotechnical, engineering design, and construction planning. These include critical technical issues such as soil structure interaction and the prediction of vertical shortening due to the long-term creep and shrinkage of the concrete frame, and behavioral characteristics of the tower under lateral and gravity loadings. View the presentation at https://youtu.be/J-44jfV_gfo. September 2016

The SEI Cold-Formed Members Committee is sponsoring the CFSEI International Cold-Formed Steel Building Student Design Competition. The goal of this competition is to push the creative bounds of structural design with light-steel framed buildings. SEI Fellow Cristopher D. Moen is chairman of this year’s program and encourages undergraduate and graduate students to enter as teams or individuals. Each team can request an engineer mentor and submissions are due March 3, 2017. For more information or to enter, visit the CFSEI website at https://cfsei.memberclicks.net/student-competition.

Errata

SAVE THE DATE Planning for Structures Congress 2017 is underway. Keynote speakers and the technical program will be finalized soon. Visit the Congress website, www.structurescongress.org, for more information.

SEI Local Activities Maryland Chapter The SEI Maryland Chapter has received a Space Public Affairs Grant that helped them develop a small shake table program that can travel to a variety of small events. In the past year, the chapter used the table for national and local science fairs, national STEM conferences, career fairs, outreach programs for young engineers, and scout meetings. Through their working relationship with a local university, groups also have the opportunity to observe a larger shake table. In May, SEI-MD assisted with a Maryland Quality Initiative (MdQI) outreach event. MdQI is a cooperative effort by Maryland’s transportation industry dedicated to continuous quality improvement in the planning, design, construction, and maintenance of Maryland’s transportation system. The chapter did 10-minute demonstrations to small groups, showing what a shake table model represents in real life and how engineers design structures to withstand earthquakes. Approximately 85 students specializing in an engineering curriculum participated. The chapter invites interested SEI members with basic knowledge of structural engineering concepts, to borrow the shake table to conduct student demonstrations. Email the chapter at sei@ascemd.org and SEI-MD will be happy to assist you. Learn more on the SEI News web page at www.asce.org/ structural-engineering/structural-engineering-news. STRUCTURE magazine

Get Involved in Local SEI Activities Join your local SEI Chapter, Graduate Student Chapter (GSC), 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 a SEI Chapter, GSC, or STG in your area, review the simple steps to form a SEI Chapter at www.asce.org/structural-engineering/sei-local-groups. Local SEI Chapters and Structural Technical Groups of the ASCE Sections/Branches serve local member structural, technical, and professional needs through a variety of innovative programs. SEI supports local SEI Chapters with opportunities for local Chairs to learn about new initiatives and best practices with other local SEI Professional Chapter and Grad Student Chapter leaders (quarterly conference call and annual funded SEI Local Leader Conference including technical tour and training). Those local structural groups that affiliate with SEI and establish local Chapters receive SEI Chapter logo/branding, complimentary webinar and banner, and more.

September 2016

The Newsletter of the Structural Engineering Institute of ASCE

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.

The SEI Global Activities Division Executive Committee is supporting the 39th Symposium of the International Association of Bridge and Structural Engineering (IABSE), September 21 – 23, 2017 in Vancouver, Canada. The symposium will focus on three major themes, Innovations in Structures, Existing Structures into the Future, and Performance Based Design. Authors are invited to submit short abstracts relating to these themes and to the overall motto “Engineering the Future.” For more information and to submit an abstract, visit the IABSE website at www.iabse.org.

Structural Columns

International Cold-Formed SEI Sponsors IABSE Steel Building Student Design Vancouver Symposium Call for papers open until October 15, 2016 Competition

CASE Risk Management Contracts Available

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE #1 — An Agreement for the Provision of Limited Professional Services This is a sample agreement for small projects or investigations of limited scope and time duration. It contains the essentials of a good agreement including scope of services, fee arrangement, and terms and conditions. CASE #2 — An Agreement between Client and Structural Engineer of Record for Professional Services This agreement form may be used when the client, e.g. owner, contractor developer, etc., wishes to retain the Structural Engineer of Record directly. The contract contains an easy to understand matrix of services that will simplify the “what’s included and what’s not” questions in negotiations with a prospective client. This agreement may also be used with a client who is an architect when the architect-owner agreement is not an AIA agreement. CASE #3 — An Agreement between Structural Engineer of Record and Consulting Design Professional for Services The Structural Engineer of Record, when serving in the role of Prime Design Professional or as a Consultant, may find it necessary to retain the services of a sub-consultant or architect. This agreement provides a form that outlines the services and requirements in a matrix so that the services of the subconsultant may be readily defined and understood. CASE #4 — An Agreement between Owner and Structural Engineer for Special Inspection Services Special Inspection services provided by a Structural Engineer are normally contracted directly by the Owner of a project during the construction phase. This agreement has a Scope of Service that directly relates to the applicable code or industry standard requirements. The Structural Engineer of Record, or another structural engineer providing these services, may use this agreement. The language for coordinating laboratory testing work is also included in this agreement. CASE #5 — An Agreement for Structural Peer Review Services A request to perform a peer review of another structural engineer’s design brings with it a different responsibility than that of the Structural Engineer of Record. The CASE #5 document addresses the responsibilities and the limitations of performing a peer review. This service is typically performed for an Owner but may be altered to provide peer review services to others. CASE #6 — Commentary on AIA Document C141 “Standard Form of Agreement between Architect and Consultant,” 1997 Edition and AIA Document C142 “Abbreviated Standard Form of Agreement between Architect and Consultant,” 2009 Edition This document provides a form letter of agreement to be used with adoption by reference to AIA Document C401. This Agreement is intended for use when the owner-architect agreement is an AIA B-series. A scope of services is included. The purpose of the commentary is to point out provisions that merit special attention. STRUCTURE magazine

CASE #6A — Commentary on AIA Document B-141 “Standard Form of Agreement between Owner and Architect with Standard Form of Architect’s Services”, 1997 Edition The purpose of this Commentary is to point out provisions which merit special attention, or which have been found to contain “pitfalls.” CASE #8 — An Agreement between Client and Specialty Structural Engineer for Professional Services When structural engineering services are provided to a contractor or a sub-contractor for work to be included in a project where you are not the Structural Engineer of Record, but you are a specialty structural engineer. Your contractual relationship differs from the norm, and the typical contract forms will not suffice. The CASE #8 document is tailored to this particular situation. CASE #9 — An Agreement between Structural Engineer of Record and Testing Laboratory The Structural Engineer of Record may be required to include testing services as a part of its agreement. If a testing laboratory must be subcontracted for this service, CASE # 9 may be used. It can also be altered for use between an Owner and a testing laboratory. You can purchase these and the other Risk Management Tools at www.acec.org/coalitions/coalition-publications.

ACEC Fall Conference Features Case Risk Management Convocation and More! On October 19 – 22, ACEC is holding its Fall Conference at The Broadmoor, Colorado Springs, CO. CASE will be holding a convocation on Thursday, October 20. Sessions include: 10:45 am Contractual Risk: Mastering Indemnity, Insurance, and the Standard of Care Speakers: Ryan Kohler, Collins, Collins, Muir + Stewart 2:00 pm Developing a Risk Management Plan for Your Firm Diane Mika, Berkeley Design Professional Underwriters 3:45 pm Balancing Project Risk and Reward: Lessons Learned from Current Professional Liability Claims Robert Hughes, Ames & Gough; Sam Muir, Collins, Collins, Muir + Stewart 5:00 pm ACEC/Coalition Meet and Greet The Conference also features: • CEO roundtables; • Exclusive CFO, CIO, Architect tracks; • Numerous ACEC coalition, council, and forum events; and • Earn up to 21 PDHs September 2016

ACEC Brings High-Level Training to Aspiring Engineers ACEC’s new Pathways to Executive Leadership program provides in-depth instruction into the intricacies of leading an A/E firm, giving participants the skills necessary to think strategically in their markets, build effective teams, and deliver great customer service. The program will span six months, beginning October 18-21, 2016 at the ACEC Fall Conference in Colorado Springs and ending April 22 – 25, 2017 at the ACEC Annual Convention in Washington D.C., and includes both onsite and online sessions. Pathways to Executive Leadership is designed for mid-career professionals with 8-12 years experience who seek to elevate their career track. It fills the gap between ACEC’s Business of Design Consulting program and the Senior Executive’s Institute. Faculty includes Geordie Aitken and Magda Dominik of the Aitken Leadership Group; Rod Hoffman and Barb Smith of S & H Consulting; and ACEC Member Firm leaders. To register for this program or get more information about the schedule, go to www.acec.org/calendar/calendar-seminar/ consulting-by-design-pathways-to-executive-leadership. STRUCTURE magazine

Programs and Communications Committee – Nils Ericson (nericson@m2structural.com) • Confirmed/finalized sessions for 2017 ASCE/SEI Structures Congress • Working on session for 2017 AISC Conference and the ACEC Annual Convention • Putting together the 2016-2017 editorial calendar for articles to Structure Magazine from CASE • Evaluating Risk Management seminar for this year and will be putting together list of topics/sessions for next year’s seminar Toolkit Committee – Brent White (brentw@arwengineers.com) • Finished update on the following current tools: • Tool 10-1 – Site Visit Cards released with the updated Site Visit Guideline document • Working on the following new tools: • Firm Handbook Guide • Project Management Training Tool • Reviewing the CASE Ten Foundations of Risk Management and updating to reflect current practice The 2017 CASE Winter Planning Meeting is scheduled for February 17 – 18 in San Diego, CA. If you are interested in attending the meeting or have any suggested topics/ideas from a firm perspective for the committees to pursue, please contact Heather Talbert at htalbert@acec.org.

Risk Management Strategies for Bottom-Line Results ACEC Fall Conference, October 19 – 22 The upcoming ACEC Fall Conference, at The Broadmoor in Colorado Springs, will feature more than 30 advanced business programs, including eight sessions focused on managing firm liability and risk: • Contractual Risk: Mastering Indemnity, Insurance, and the Standard of Care • Harnessing Technology to Reduce Errors and Disputes • Limiting Liability Risks on New Residential Development • Developing a Risk Management Plan for Your Firm • Balancing Project Risk and Reward: Lessons Learned from Current Professional Liability Claims • Public-Private Partnerships and Design-Build Opportunities/Risks for Consulting Engineers • Professional Liability Case Study Marathon • Cybersecurity: Protecting Your Firm The Conference, October 19 – 22, will also feature Colorado Governor John Hickenlooper, political analyst Stuart Rothenberg, Forbes Publisher Rich Karlgaard, Mt. Everest climber Eric Weihenmayer. Also featured will be Member Firm leaders on the M&A and water markets and smart cities, as well as CEO, CFO and CIO roundtables and Emerging Leaders and Coalition programs. For more information and/or to register www.acec.org/conferences/fall-conference-2016.

September 2016

CASE is a part of the American Council of Engineering Companies

On August 3rd and 4th, the CASE Winter Planning Meeting took place in Chicago, IL with over 30 CASE committee members and guests in attendance, making this a well-attended and productive meeting. Included in the planning meeting was a roundtable discussion lead by members of the CASE Executive Committee. During the meeting, break-out sessions were held by the CASE Contracts, Guidelines, Membership, Toolkit, and Programs & Communications Committees. Listed below are the current initiatives being developed by the committees: Contracts Committee – Ed Schweiter (ews@ssastructural.com) • Laying groundwork for next CASE Contracts Library update in 2018 by reviewing documents to see what “must have” language needs to be standard among all Terms and Conditions within the documents • Creating a matrix of which contract to use in certain situations Guidelines Committee – Kirk Haverland (khaverland@larsonengr.com) • Releasing updated Guidelines on Site Visits with the updated Tool on Site Visits • Releasing updated Guidelines for Specialty Structural Engineering • Working on the following new documents: • Commentary on ASCE-7 Wind Design Provisions • Commentary on ASCE-7 Seismic Design Provisions • Guideline on Geotech Reports Membership Committee – Stacy Bartoletti (sbartoletti@degenkolb.com) • Current CASE membership = 161 member firms (as of August 1st); working on policy for dropping members for non-payment of yearly membership fee • Working on communication summary to make sure message on meetings, publications, and sessions is getting out to the right individuals

CASE in Point

CASE Summer Planning Meeting Update

Structural Forum

opinions on topics of current importance to structural engineers

The Ethics and Politics of Resilience By David Pierson, S.E.

he concept of Structural Resilience has recently become a hot topic within the structural engineering community. With the establishment of the U.S. Resiliency Council (USRC), structural engineers may have found their version of the U.S. Green Building Council (USGBC). Perhaps, with time, USRC ratings will have significance in the same way Leadership in Energy and Environmental Design (LEED) ratings have some significance for buildings. The idea is that we should design structures to be more resilient in the face of the natural disasters to which we anticipate they will be exposed. It is proposed that we design buildings to performance objectives higher than the current code mandates. The present basis of design within the building code is, in general, based on Life Safety. Risk is a part of life, so the establishment of a proper level of risk was required. I don’t know how all decisions related to this were made, but here is where we are – most loads are based on a 50- or 100-year recurrence interval, meaning they will (statistically speaking) be exceeded once every 50 or 100 years. Seismic risk is a bit more complicated, involving seismology, geology, fragility curves, etc. But for most of the U.S., the code implies a Life Safety performance objective for a 475year event. This seems reasonable since the Constitution of the United States gives the government a role in protecting the lives of the public. Therefore, when we design and build structures that others will enter, it is proper that the government mandate that the design and construction comply with a Life-Safety objective, with risks properly considered. So, it is natural to ask – should the government impose mandates on private citizens that require higher resilience in privately owned buildings? This question cannot be answered independently of political philosophy. Because among the foremost rights given to American Citizens is the right to own and use property as they see fit, provided they don’t infringe on the rights of others.

The conflict arises in part because of the varied interpretations of the “promote the general welfare” clause in the constitution. Those with a more liberal political view argue that this clause gives wide latitude to the government to impose more regulations on property owners given larger societal concerns. Local governments essentially rely on this clause as they enforce zoning regulations, etc. within their communities. Similarly, progressives may wish to impose resilience mandates on property owners based on the “greater good” that may be realized in the event of a disaster. On the flip side, conservatives argue that free market forces should be adequate to move the construction industry towards resilience. For example, insurance companies are among the best evaluators of risk. If they price insurance commensurate with building resilience, there is a free market force at work. If the perception of risk changes such that the public demands more resilient buildings, then lease rates for those buildings will bring higher profits and building owners will move toward providing such buildings. Now, if resilience is to be sold on the free market, how ought we to approach this? Are there ethical considerations? This is where it gets a bit thorny. As educated professionals, society affords us some respect with regards to understanding risks associated with the design of buildings. We are bound, by our code of ethics, to communicate the risks to society in a truthful manner. But, as we enter into this realm of design beyond the current code, there is a new issue that we are faced with. If what we “sell” to the general public (in our attempts to persuade them to have their building designed beyond the building code) will result in additional fees and profit for ourselves, then we are in a precarious situation regarding our ability to remain objective. There are many ways to present findings when statistical probabilities are involved. Mark Twain said, “There are three kinds of lies – lies, damned lies, and statistics.” The reality is that, to make any assertion regarding

risks, many assumptions must be made. And so, various people looking at the same data might assess the uncertainties differently and arrive at different conclusions. This is where “truth” might become a bit “blurry”. Risk will always be a part of life. And so, people have different levels of tolerance for risk. Therefore, as we communicate with those whose money must be spent to increase building resiliency, we need to understand that their level of risk tolerance may be different than ours. Wealthy people might have the resources to spend more to reduce risks related to building resiliency. But that doesn’t mean they will view that as the best investment of their money. How should we respond if owners do not want to spend more money on their building? I think that if we are too invested in advocating for resilience, we might tend to overstate the risks, overstate the amount of possible future savings, and undervalue the present value of the money that must be spent. I also fear that we might decide that, since we are so smart, we must protect the general public from themselves and therefore move toward mandating resilience through government force. As we find ourselves involved in discussions regarding resilience, we must understand the repercussions of advocating for code changes that will increase building performance beyond basic life safety. If we choose to advocate for increased resilience, we must carefully consider whether or not we want it to be brought about through free market forces or government intervention. And if by government intervention, then we must acknowledge that we are advocating for some level of infringement on the rights of American citizens.▪ David Pierson is a Vice President at ARW Engineers in Ogden, Utah. He can be reached at davep@arwengineers.com.

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

September 2016

STRUCTURE magazine | September 2016

Articles inside

STRUCTURAL FORUM

SPOTLIGHT

INSIGHTS

LESSONS LEARNED

STRUCTURAL REHABILITATION

CODE UPDATES

STRUCTURAL TESTING

STRUCTURAL SUSTAINABILITY

STRUCTURAL SYSTEMS

EDITORIAL