STRUCTURE magazine | September 2013

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

September 2013 Concrete

Special Section

21

ST NCSEA Annual Conference Atlanta, Georgia

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FEATURES 34 Special Section

NCSEA 2013 Conference Section The National Council of Structural Engineers Associations will host its 21st Annual Conference at the Weston Buckhead Hotel in Atlanta on September 18th through the 21st. Read about the conference, the extensive program and vendor information in this Special Conference Section… and plan to attend this exciting event!

The Pennsylvania State Capitol

38

By R. Scott Silvester, P.E., Christina T. Parker, P.E. and Niklas W. Vigener, P.E. Monumental historic masonry structures are complex structural systems whose behavior can be difficult to quantify using simple analytical methods. The solution often requires rigorous investigations, and then the combination of classical analysis techniques with sophisticated modern tools to assess performance.

Read how the Pennsylvania State Capitol Building was assessed using finite element techniques.

Wolf Girders – A Function Driven Solution

42

By John A. Lobo, P.E., S.E. and David A. Burrows, P.E. For the nearly 5-mile long Sky Train™ project at the Phoenix Sky Harbor International Airport, airport officials elected to execute the project through a Construction-Manager-At-Risk (CMAR), selected early in the design process. The CMAR provided crucial input regarding optimum choices for different sections of the system, in particular, the precast open-box girders for a majority of the elevated guideway.

Best Presentation and Best Poster

By John “Buddy” Showalter, P.E.

2013 Structures Congress

50 Business Practices

66 Structural Forum

Delegated Design

A Remarkable Profession!

By Stan R. Caldwell, P.E., SECB

STRUCTURE

Special Section

21ST NCSEA Annual Conference

A Joint Publication of NCSEA | CASE | SEI

Atlanta, Georgia

September 2013 Concrete

ON

THE

COVER

Student Opportunities at SEI

By Donna Friis, P.E.

9 InFocus Virtuous Engineering

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

11 Lessons Learned Repairs to Prestressed Strands in Double-Tee Stems

By Luis F. Estenssoro, Ph.D., S.E., P.E.

15 Construction Issues Acceptance Test Reports of Ready Mixed Concrete

By Colin Lobo, Ph.D., P.E.

18 Structural Forensics Prescription for Repair

By D. Matthew Stuart, P.E., S.E., SECB, and Ross E. Stuart, P.E., S.E.

20 Structural Sustainability LCT ONE

By Nabih Tahan

24 Building Blocks

29 Professional Issues Bridging the Gap between Climate Change Science and Structural Engineering Practice

By Richard N. Wright, Ph.D., P.E., Bilal M. Ayyub, Ph.D., P.E. and Franklin T. Lombardo, Ph.D.

Continuing Education

The Georgia Aquarium is the world’s largest, with more than 10 million gallons of water and more aquatic life than any other aquarium. Uzun & Case Engineers provided the structural design for the main aquarium, which opened November 2005 and for the Dolphin Exhibit expansion, which opened in April 2011. NCSEA is hosting its Annual Conference in Atlanta this month. (See the Special Conference Section on page 34.)

Photo by Robb Helfrick (Helfrick Photography).

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement

by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

7 Editorial

46 Education Issues

®

By the CASE Guidelines Committee

COLUMNS

By Jason Blankenship, P.E.

59 Spotlight

New Wood Materials

September 2013

High-Strength Welded Wire Reinforcement in Tilt-Up Construction

DEPARTMENTS 32 InSights

CONTENTS

4

September 2013

By D. Matthew Stuart, P.E., S.E., SECB

IN EVERY ISSUE 8 Advertiser Index 56 Resource Guide (Anchoring) 60 NCSEA News 62 SEI Structural Columns 64 CASE in Point

Cathedral of Christ The Light Architect & Structural Engineer: Skidmore, Owings & Merrill

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Editorial

Student Opportunities at SEI new trends, new techniques and current industry issues

By Donna Friis, P.E., F.SEI, M. ASCE

S

EI is pleased to highlight two new opportunities for students: Student Membership Grade and Graduate Student Chapters.

A joint effort of the Membership Committee and the Local Activities Division (LAD) – one of the four SEI divisions responsible for growing and supporting the local activities – students interested in pursuing careers in structural engineering are encouraged to join SEI. Student members of ASCE, who enjoy membership without the requirement of dues, may also elect to join SEI at no additional cost. This is as simple as selecting SEI as a free Institute upon joining ASCE. Student members receive all of ASCE and SEI student benefits, including opportunities for networking with more than 20,000 SEI members and participating on SEI committees. Additionally, SEI offers many opportunities for students including the Student Structural Design Competition, the O.H. Ammann Research Fellowship, and the Student and Young Professional Program at Structures Congress.

Most recently, graduate students at any college or university who are ASCE/SEI student members are encouraged to form an SEI Graduate Student Chapter (GSC) to further reap member benefits. GSCs enhance the education of students who are preparing to become structural engineering professionals, and engage SEI student members in SEI for a successful transition from college to career. Graduate Student Chapters organize and manage visiting speakers, prospective student events, field trips, participate in SEI, perform outreach activities, and more. Participation in a GSC can help members connect with their peers and broaden their view of what it means to be a structural engineering professional.

This year, SEI welcomed the formation of its first three Graduate Student Chapters: Virginia Tech, the University of West Virginia, and the University of Texas at Arlington.

The first official SEI GSC was founded in January 2013 at Virginia Tech (SEI-VT). Chaired by William Collins and Faculty Advisor Roberto Leon, Ph.D., the mission of the SEI-VT is to develop the leadership skills and enhance the education of students who are preparing to become structural engineering professionals. SEI-VT will engage student members in SEI to encourage active, continuous membership and involvement throughout their professional lives.

The new SEI GSC at West Virginia University (SEI-WVU) is chaired

by Daniel Estep and Faculty Advisor Udaya Halabe, Ph.D. By encouraging interaction between SEI student members and professional members, and providing opportunities for professional and educational development, SEI-WVU will facilitate a successful college to career transition and encourage its members to engage in SEI activities both at WVU and at the national level throughout their professional career.

The mission of SEI GSC at University of Texas at Arlington (SEIUTA) – chaired by Istiaque Hasan and Faculty Advisor Nur Yazdani, Ph.D. – is to create a platform for the structural engineering graduate students at UT Arlington in order to facilitate knowledge sharing and professional networking among the students and the local/national structural engineering community.

In addition to the benefits of networking and education at the local level, SEI supports its GSCs in the following ways: • Chapter announcements published on SEI website and in SEI Update • Quarterly teleconferences to learn from and collaborate with other SEI Chapters • Funded participation in the SEI Local Leadership Conference

STRUCTURE magazine

• Membership in the SEI Graduate Student Chapter Leadership Council • One complimentary ASCE Continuing Education webinar sponsored by the SEI Endowment Fund (maximum value $250) • SEI outreach supplies • Use of SEI name and branding • A 2-foot x 5-foot vinyl banner with chapter’s logo As a GSC, funding for faculty advisor and graduate student chair is provided to attend the annual SEI Local Leadership Conference – an annual meeting of all SEI Chapter and Structural Technical Group chairs. Members participate in the SEI Local Leadership Conference to learn about new initiatives, share insights and best practices, participate in technical tours and training, and to network. This year’s SEI Local Leadership Conference is planned in conjunction with the ASCE Texas Centennial, September 11-12. It will include a day-long leadership training session and a technical tour of the Cowboys Stadium. To learn more about the ASCE Texas Centennial Conference visit www.ASCE.org/SEI. The Graduate Student Chapter Leadership Council (GSCLC) is an entity within the Local Activities Division that will add oversight and program development guidance to the GSCs. Membership in the GSCLC includes each chapter’s student chair and faculty advisor along with an LAD appointed chair. The first chair of the GSCLC is Caleb Cheng L. Hing, Ph.D., P.E. Becoming an SEI Graduate Student Chapter is easy, and includes the following steps: • Request permission from your local University and submit a letter of support from the sponsoring Department Chair.

• Complete the Sample MOU with your local University signature authorizing creation of an SEI Graduate Student Chapter.

• Submit SEI GSC Application online.

SEI believes that today’s students are the future of our profession. SEI would like to invite students with an interest in structural engineering to join us, at no cost, to learn about SEI and what it can offer your professional growth. Learn more about student opportunities at www.ASCE.org/SEI.▪ Donna Friis, P.E., F.SEI, M. ASCE, is a Principal Structural Engineer with CDM Smith Inc. Ms. Friis is in the inaugural class of SEI Fellows and the first female to be elected to the SEI Board of Governors. She is an associate member of the ASCE 7 Main Committee and a voting member of the ASCE 7 Wind Committee.

Donna is Chair of the Membership Committee and the SEI Fellow Review Committee.

7

September 2013

Advertiser index

PleAse suPPort these Advertisers

American Concrete Institute ................. 10 AZZ Galvanizing .................................. 57 Computers & Structures, Inc. ............... 68 Construction Specialties .......................... 5 CTP Inc. ............................................... 25 CTS Cement Manufacturing Corp........ 51 Engineering International, Inc............... 41 Ecospan Composite Floor System ......... 17 Enercalc, Inc. .......................................... 3 Foundation Performance Association..... 48 Fyfe ....................................................... 47 Heckmann Building Products, Inc. ....... 56

Hilti North America .............................. 33 Hohmann & Barnard, Inc. .................... 14 ICC....................................................... 28 Integrated Engineering Software, Inc..... 43 ITW Red Head ..................................... 45 KPFF Consulting Engineers .................. 44 NCEES ................................................. 53 Polyguard Products, Inc......................... 27 Powers Fasteners, Inc. .............................. 2 PT&C Forensic Consulting Serv., P.A. .. 31 QuakeWrap ........................................... 52 QUIKRETE ......................................... 58

Editorial Board Jon A. Schmidt, P.E., SECB

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

AdvErtising Account MAnAgEr Chuck Minor

Dick Railton

Eastern Sales 847-854-1666

Western Sales 951-587-2982

sales@STRUCTUREmag.org

Brian W. Miller

CBI Consulting, Inc., Boston, MA

Mark W. Holmberg, P.E.

Interactive Sales Associates

Chair

Craig E. Barnes, P.E., SECB

RISA Technologies ................................ 67 Structural Engineers Assoc. of Illinois .... 42 Simpson Strong-Tie............................... 13 Soil and Materials Engineers, Inc............. 8 Structural Engineers, Inc. ...................... 39 StructurePoint ....................................... 54 Struware, Inc. ........................................ 49 USP Structural Connectors ..................... 6 Williams Form Engineering .................. 26 Wood Products Council ........................ 23

Davis, CA

Evans Mountzouris, P.E.

Heath & Lineback Engineers, Inc., Marietta, GA

The DiSalvo Ericson Group, Ridgefield, CT

Dilip Khatri, Ph.D., S.E.

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

EditoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE

execdir@ncsea.com

Khatri International Inc., Pasadena, CA

KPFF Consulting Engineers, Seattle, WA

Roger A. LaBoube, Ph.D., P.E.

Stephen P. Schneider, Ph.D., P.E., S.E.

Brian J. Leshko, P.E.

John “Buddy” Showalter, P.E.

Associate Editor

Amy Trygestad, P.E.

Graphic Designer

CCFSS, Rolla, MO

HDR Engineering, Inc., Pittsburgh, PA

John A. Mercer, P.E.

Mercer Engineering, PC, Minot, ND

Editor

Christine M. Sloat, P.E.

publisher@STRUCTUREmag.org

BergerABAM, Vancouver, WA

American Wood Council, Leesburg, VA

Chase Engineering, LLC, New Prague, MN

Web Developer

Erratum The author of the San Diego Central Library article (STRUCTURE, July 2013) has been notified of a correction. Rob Wellington Quigley Architects and Tucker Sadler Architects, a Joint Venture are the architects of record. The online version of this article has been updated.

Civil/Structural Engineer SME is seeking a Civil/Structural Engineer with 10+ years structural engineering experience related to building condition evaluation, structural rehabilitation, and design of restoration strategies to fill a position in our Plymouth, Michigan office. Must have a BS or MS in Civil Engineering, professional registration and experience in structural steel, reinforced concrete and masonry design. Ability to prepare contract documents for rehabilitation projects required. Experience with parking decks, plazas, roofs, and other structures preferred. Candidate must have excellent oral and written communication skills. Occasional travel required. SME supports clients at every stage of development and ownership, from site acquisition, design and construction, to maintenance, restoration and redevelopment. We are an employee-owned firm with a successful 49-year history of providing consulting in the geosciences, materials, and the environment. SME provides excellent opportunities for professional development in a flexible and friendly work environment. Our benefits package includes: medical, life, disability income, and long-term care insurance; 401(k) and Profit Sharing programs; and generous performance bonus and paid time off (PTO) programs. For immediate consideration, email resume and cover letter, including salary requirements, to Keith Toro, P.E.: toro@sme-usa.com.

SME is an Equal Opportunity Employer.

STRUCTURE magazine

8

September 2013

Nikki Alger

publisher@STRUCTUREmag.org

Rob Fullmer

graphics@STRUCTUREmag.org

William Radig

webmaster@STRUCTUREmag.org

STRUCTURE® (Volume 20, 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 $65/yr domestic; $35/yr student; $90/yr Canada; $125/yr foreign. For change of address or duplicate copies, contact your member organization(s). Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board.

STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be

reproduced in whole or in part without the written permission of the publisher.

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A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 P-608-524-1397 F-608-524-4432 Visit STRUCTURE magazine publisher@STRUCTUREmag.org

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inFocus

Virtuous Engineering new trends, new techniques and current industry issues

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

H

The “Why” of Engineering: Eudaimonia Third, engineers fulfill “The Proper Purpose of Engineering” (January 2013), which is to enhance the material well-being of all people, by achieving “The Internal Goods of Engineering” (March 2013): safety, sustainability, and efficiency.

It takes a deliberate decision and ongoing resolve to do this faithThe “What” of Engineering: Praxis fully. Engineers must prioritize it over not only their own immediate First, “The Social Nature of Engineering” (November 2012) is such interests, but also the external goods that are valued by those who that engineers engage in a combined human performance in which typically make the major decisions and ultimately pay the bills. The they play a particular societal role: the assessment, management, and prospective reward is the opportunity to escape, at least partially, the communication of risk. “social captivity” that renders engineering Virtuous Engineers assert their responsibility Engineers must convince others to hire largely instrumental, subject to exploitafor engaging in a combined human performance or retain them, and then ascertain and tion by managers and clients (“The Social attempt to satisfy their expectations for Captivity of Engineering,” May 2010). that involves the exercise of practical judgment each assignment. Furthermore, research As a step in this direction, engineers to enhance the material well-being of all people has repeatedly indicated that engineers can pursue their most fundamental by achieving safety, sustainability and efficiency across all disciplines, career stages, and aims – protecting people and preserving while exhibiting objectivity, care and honesty types of employers spend the majority of property, improving environments and their time at work interacting with others. conserving resources, and performing in assessing, managing and communicating risk.

Engineering is thus always a collaborafunctions while minimizing costs – for tive endeavor, assembling expertise that is distributed among multiple their own sake, rather than merely as means to a separate end. When participants; someone whose technical activities are self-motivated and merged, they constitute an overall notion of quality that engineers seek solitary is more accurately labeled as an inventor. to incorporate into everything that emerges from their efforts. Erik Engineers are the decision-makers in situations where members of Nelson hinted at this when he wrote that “design is inherently goalless” the general public are usually the potential harm-bearers, even when because the precise outcome is unknown during the process of creating they are also supposed to benefit in some way. The latter take it for it (“A Structural Engineer’s Manifesto for Growth – Part 1,” April 2012). granted that engineering design adequately accounts for all of the applicable hazards, and thus ascribe to engineers the obligation to Conclusion mitigate them. Embracing this responsibility entails not only recognizing these uncertainties and dealing with them appropriately, but Uniting all of these ideas in an arrangement that states what engialso calling attention to – preferably beforehand –any residual risk neers do, how they do it, and why it matters in broad terms, and associated with an engineered product or project. then presents the details in the reverse order, results in a concise yet comprehensive summary of our unique and vital contribution to The “How” of Engineering: Phronesis human flourishing (see box). This formulation is not meant to replace Second, engineers are able to exercise “The Intellectual Virtue of the extensive codes of ethics that engineering organizations have Engineering” (July 2013), which is practical judgment – i.e., engineer- developed over the years. Instead, it complements them by offering ing judgment – while exhibiting “The Moral Virtues of Engineering” an aspirational vision of what it means for engineers to demonstrate (May 2013): objectivity, care, and honesty. genuine integrity: your practice IS your ethics!

Engineers routinely confront difficulties and predicaments, rather It also addresses two common and related complaints within the engithan well-structured problems that have deterministic solutions neering profession – that people do not really understand and appreciate (“Engineering as Willing,” March 2010; “The Rationality of Practice,” what we do, and that our social and political influence is not what it could September 2012). Learning theories, rules, and maxims – i.e., heu- or should be. I believe that conscientiously living as virtuous ristics (“The Engineering Method,” March 2006; “Heuristics and engineers, as described here, would improve our collective Judgment,” May 2006) and design procedures (“The Nature of Theory status and enable us to assume a more prominent position and Design,” May 2009) – provides a necessary and solid foundation. of leadership in our technologically advanced culture.▪ However, it is only through experience that someone can develop the skill to discern quickly what is important in a specific set of cirJon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is cumstances, and then select a suitable way forward (“The Nature of an associate structural engineer at Burns & McDonnell in Kansas Competence,” March 2012; “Virtue as a Skill,” May 2012).

City, Missouri. He chairs the STRUCTURE magazine Editorial Risk assessment requires objectively evaluating the likelihood and severity Board and the SEI Engineering Philosophy Committee, and shares of possible threats and identifying alternatives for reducing one or both occasional thoughts at twitter.com/JonAlanSchmidt. of these parameters. Risk management requires carefully deliberating over multiple viable options and choosing one that rightly balances caution and Join the Movement! ambition on behalf of all those who may be affected. Risk communica- For more information and to collaborate on further development tion requires honestly acknowledging the dangers that cannot reasonably and implementation of the ideas outlined in this column, please visit be eliminated and informing everyone who needs to be aware of them. www.VirtuousEngineers.org. aving laid down a lot of philosophical groundwork in this space over the last couple of years, I am finally ready to attempt to pull it all together. I will do so under three headings that correspond to the central concepts in Aristotle’s approach to virtue ethics.

STRUCTURE magazine

9

September 2013

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A

Lessons Learned

new repair method was implemented to restore the structural integrity of precast double-tee stems that have lost their prestressing strands due to physical damage or corrosion. The repair method is intended for strands that are closely spaced, where currently available strand splices cannot be used without modification. Pressure jackets are used to splay the wire strands apart and align them with splices in order to re-stress the strand to the original pre-load.

problems and solutions encountered by practicing structural engineers

Background Prestressed concrete double-tee beams are precompressed with wire strands embedded in their stems. The size and number of strands in each stem varies depending on the original design requirements, and are often harped to make more efficient use of the strands and concrete cross-section. Harping consists of sloping the strands so that they start at each end of a stem at a vertical spacing of 2 inches (or more), and are brought closer together at harp points. During manufacturing, hold-downs in the stressing beds are used to react against the vertical component of the force created by the change in strand angle.

In service, the prestressed strands can be damaged physically or by corrosion. Typically, significant flexural cracking and deflections are signs that the strands are damaged and the structural capacity of the member has been compromised. Several repair methods have been used to restore the structural capacity of damaged stems. These include external post-tensioning and installation of steel channels. External posttensioning typically requires the installation of a pair of steel or concrete brackets (across the stem) on both sides of the crack, and tendons or rods that are subsequently post-tensioned at the brackets. For the steel channel method, a pair of steel channels is bolted across the stem. Each method has structural design and construction challenges that would be unique to the particular structural repair.

Investigation and Findings Over the past few years, the author investigated two precast parking garages in which each had developed a flexural crack in a stem of a doubletee at the harped point. The first garage was a 1974 structure with normal weight concrete double-tees. The bolted steel channel option, installed in 2009, worked well for this particular stem. The second garage was a 1971 structure with lightweight concrete double-tees.

In the 1971 structure, the main findings at the damaged stem included a crack that developed near midspan of an 86-foot long, 24 LDT double-tee. The crack measured about ¼ inches wide

Figure 1.

at the bottom and gradually narrowed to zero near the stemto-flange intersection.

Deflections were not noticeable, most likely because the loads of the damaged stem were being distributed to its sister stem and adjacent double-tees. The damaged stem still had its bottom strand, as described below.

An exploratory opening at the crack was made (Figure 1). It revealed that: 1) the crack developed at the harped point, 2) six strands were used, the top five strands were harped, and the bottom was straight, 3) the top five strands were positioned adjacent to each other vertically, 4) stress corrosion had caused total loss of steel area of the top five strands and the bottom strand developed minor surface corrosion, 5) the vertical steel strut used to maintain the position of the stretched strands at the harped point during manufacturing had been removed and mortar grout placed in the void, 6) no supplemental steel was present in this region of the stem, and 7) signs of cracking and corrosion were not observed beyond the crack.

The prestressed strands were ½-inch diameter strands with a likely 270-ksi ultimate tensile strength. Thus, each strand can carry tension loads in the order of about 30 kips. The concrete stems were nominal 4 inches wide and 22 inches tall.

Repairs to Prestressed Strands in Double-Tee Stems

By Luis F. Estenssoro, Ph.D., S.E., P.E.

Luis F. Estenssoro, Ph.D., S.E., P.E., is a Principal with Infrastructure Consultants, Engineers LLC in Englewood, CA. He may be reached at lfestenssoro@gmail.com.

Pressure Jacket A stressing device was designed to restore the prestressing forces directly to the original strands.

It is intended for situations where the prestressed strands are so close to each other that available re-stressing splices cannot be used without some modification. The stressing device uses two

STRUCTURE magazine

11

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

pressure jackets such that strand splices can be used.

For this case, Grabb-It strand splices (G-I strand splice) were used to re-stress the strands.

A G-I strand splice is a specialty “comealong” device, manufactured specifically for prestressing strands (refer to manufacturer literature). It grabs the ends of strands with anchors and standard prestressing wedges, and then pulls the strands together by torqueing on a long, double-handed threaded nut. A torque wrench is used to torque the nut, thus tensioning the strands. Concrete has to be excavated to expose the free ends of the strand, install the splice, and apply the proper torque.

The manufacture’s calibration table is used to determine the torque-tension relationship.

The splice is intended to be installed in line with the strand (aligned, not offset). These splices have been tried in repairs of bundled post-tensioned tendons where the splices were not aligned with the tendons. Difficulties were experienced achieving torque values, most likely because the splice deformed at high torque values. Thus, it was determined for this case that the splices should be aligned with the tendons.

The challenge in this project was that the failed strands were close together, and the G-I splices could not be installed properly to apply high tension loads. In order to install the splices, have room for the torque wrench, and align the splices, the strands needed to be separated (splayed). The pressure jacket shown in Figure 2 does that. At one end it receives the strands at their original position and at the other end it separates them enough to install the splices in line with the strands, and have room for the torque wrench. Within the pressure jacket, the strands need to have DT w/cracked, corroded cables

Figure 3.

smooth transition curves (no kinks). A mirror pressure jacket is needed on the opposite side of the strand splices.

If the strands were to be tensioned, they would straighten and would be damaged due to the sharp angles caused by separating the strands in this fashion. To avoid this, the jackets are filled with flowable concrete mortar by pumping grout into the jackets and letting it cure. As the strands are tensioned, internal pressures are developed because the strands still want to straighten, but the grout resists these forces. The internal pressures are resisted by the steel pressure jacket – hence the name.

The internal pressures can be calculated using equations for curved tendons.

The pressure jacket consists of a carbon steel tube with injection and breathing ports, two end plates with holes to match the strands at one end and separate them at the other end, and grout. The end plate holes include stainless steel protection sleeves to: 1) isolate the prestressing steel from the carbon steel and thus inhibit galvanic corrosion, and 2) 5 – G-I cable splices

A

B

Pressure jacket 5-½"ф cables 3" +/2"

C 1'-10

A-A A

4"

B

C

Undamaged cable

S.S. Sleeves typ.

1" 4"

B-B

4"

C-C

Figure 2: Pressure jacket – repair details.

6-½"ф pipe with end 1ф's Vent

10"

Compression Block & Final Build-up

STRUCTURE magazine

Grout Injection Port

Pressure Jacket

12

September 2013

inhibit damage between the strands and end plates. Grabb-It strand splices are used to tension the strands.

Stressing Sequence The installation of the pressure jackets and the strand splices required excavating the lower portion of the stem (Figure 3). Re-stressing five strands to a total load of 150 kips required that the bottom section of the augmented stem be cast and cured while the strand splices were still accessible (Figure 2). After the strands were tensioned, the splice pocket was filled with grout.

Other Applications Modifications to the pressure jacket described here can be made for repairing post-tensioned tendons that are bundled together and need to be separated in order to install re-stressing devices, and other conditions.

Conclusion A repair option is presented to address damaged prestressed strands and post-tensioned tendons in concrete. The main concept was the development of a pressure jacket able to splay strands so that they are aligned for the proper use of strand splices. The repair procedure restores the tension forces directly back to the original strands.▪

Acknowledgments The author acknowledges Ms. Jennifer Black and Mr. Joe Shelly of C. B. Richard Ellis for allowing this information to be released.

The design of the pressure jacket method started at the author’s previous employer.

Restruction Corporation, a specialty concrete repair contractor located in Sedalia, Colorado, performed the repair work.

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T

he process of testing concrete and quality assurance criteria for ready mixed concrete delivered to projects are reasonably well established. The owner or the owner’s representative hires an independent testing and/or inspection agency to perform quality assurance functions during the construction of the Work. Industry standards provide requirements for the following: • qualification of testing agencies and testing technicians performing tests at the jobsite and in the laboratory • frequency of testing • standardized procedures for obtaining samples and performing tests • acceptance criteria for fresh and hardened concrete tests • referee testing and criteria when test results fail to meet the acceptance criteria Industry standards require that the concrete supplier maintains a quality control plan. Quality control on the part of a ready mixed concrete supplier constitutes proactive actions that ensure that quality of the product is maintained; consistency of product characteristics is assured between loads and for the duration of the project; and steps are taken to avoid the delivery of non-conforming product. Quality control constitutes management of materials used for concrete, the concrete mixtures being produced, and the production process. Certification of production facilities, such as that administered by the National Ready Mixed Concrete Association (NRMCA), provides some assurance that the concrete plants and delivery vehicles comply, at a minimum, with industry standards.

The Need With regards to strength requirements, the concrete supplier should be able to respond to situations when strength test results are trending towards potential non-compliance. Prior to a project, the supplier is required to use a complete test record from previous projects as a basis for establishing their concrete mixture proportions and properties for new Work, and to provide this documentation in a submittal to the engineer of record.

To ensure that this occurs, it is essential that the concrete supplier be provided ALL reports of acceptance tests performed by third-party testing agencies on the concrete mixtures delivered during the a project. These test reports should be provided in a timely manner so that strength test and other data can be charted and proactive action can be taken to ensure that specified requirements for concrete, especially strength, are not violated.

Figure 1 (page 16) illustrates a chart of the individual strength test results plotted along with the specified strength and the ACI 318 acceptance criteria for these data. The overall average of the

complete strength test record is also plotted. The overall average can be plotted for smaller sets of strength tests to observe a change in the average strength during different periods. Figure 2 (page 16) plots the running average of 3 consecutive strength tests relative to the specified strength. The running average of 3 tests should not fall below the specified strength. More involved quality control charting processes, such as cusum (cumulative sum) charts are also used to gain an early indication of a decreasing trend of test results. Some of these are discussed in ACI 214R, Guide to Evaluation of Strength Test Results of Concrete.

When low strength problems occur, considerable time and money is expended to evaluate the cause and to take corrective actions. It is thereby beneficial to all parties to minimize the risk of low strength concrete. From the perspective of the engineer of record, he/she is assured that characteristics of concrete are consistent with the needs of the project, corrective action can be taken when a decreasing trend is observed and before there is a non-conformance with the project specifications, and dispute resolution and the associated project delays and increased cost can be avoided.

Why is the distribution of test reports an issue?

Some testing agencies do not provide test reports to concrete suppliers because they believe these reports should only go to the entity that contracted with them for the testing services. Some testing agencies believe that distribution of test reports to several entities increases their cost, although this concern should be less of an issue with the widespread availability of electronic communications. Some testing agencies only provide failing strength test results to concrete suppliers to notify them that a problem exists.

Clearly this is undesirable because, if all previous tests were provided to the concrete supplier, a trend or anomaly may have been observed and a failing test result could have likely been avoided.

Many concrete producers have established relationships with local testing agencies to ensure that test reports of all tests performed on their concrete are distributed to them. With the ease of web-based test reporting systems, the distribution of test reports is streamlined and can be readily accessed by pertinent project team members.

ConstruCtion issues discussion of construction issues and techniques

Acceptance Test Reports of Ready Mixed Concrete Who Should Get Them?

By Colin Lobo, Ph.D., P.E.

Colin Lobo, Ph.D., P.E, is Senior Vice President of Engineering at the National Ready Mixed Concrete Association. He is a member of ACI Committees 318 and 301 on Structural Concrete Building Code and Specifications for Structural Concrete, respectively. He is also an active member of ASTM Committee C09 on Concrete and Aggregates. Colin may be reached at clobo@nrmca.org.

Revisions to ACI 318 Important revisions were approved in the ACI 318-11 Building Code Requirements for Structural Concrete to address issues related to testing of concrete and reporting of results. Section 5.6.1 of ACI 318-11 has been revised to address distribution of test results. The following is the excerpt from the Code: continued on next page

STRUCTURE magazine

15

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

Running Average of 3 Consecutive Tests

Chart of Strength Test Results 4000

Overall Average

Compressive Strength, psi

Compressive Strength, psi

4000

3600

3200

Specified Strength, ƒć

2800

2400

2000

(ƒ´c - 500) psi

3600 3200 2800

2000 0

5

10

15

Test Number

20

25

0

5

15

20

25

Figure 2: Running average of 3 consecutive test results relative to the specified strength.

that can negatively impact the service life of concrete structures.

The contractor or other owner’s representative should ensure that the distribution list of test reports includes the entities listed in ACI 318. ACI Committee 311 publishes ACI 311.6, Specification for Ready Mixed Concrete Testing Services that can be used by the owner as part of the contract for testing and inspection on projects. One of the mandatory checklist items that is required to be addressed to make this a complete specification is to state the agency’s responsibility for submittal of reports to include timelines, methods of delivery, and the distribution list. The distribution list defined in the contract with the testing agency should include the concrete supplier and all the other parties listed in ACI 318-11. Details about the acceptance testing and distribution of test results should be addressed in a concrete pre-construction conference. Details on acceptance testing that includes proper distribution of test reports, time constraints, and the distribution list should be discussed with the involvement of the engineer of record, general contractor, the concrete contractor, the concrete supplier and the testing agency.

A comprehensive checklist covering various aspects of construction and testing is published by the National Ready Mixed Concrete Association and the American Society for Concrete Contractors. Include the importance of the concrete pre-construction conference and incorporation the proper report distribution and transmission method into the conference agenda. ACI Committee 132 on Responsibility in Concrete Construction is finalizing their document that defines this important process.

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Test Number

Figure 1: Monitoring strength test results relative to strength acceptance criteria.

All reports of acceptance tests shall be provided to the licensed design professional, contractor, concrete producer, and, when requested, to the owner and the building official.

The following is the discussion in the Commentary to this Code provision: The Code requires testing reports to be distributed to the parties responsible for the design, construction, and approval of the work. Such distribution of test reports should be indicated in contracts for inspection and testing services. Prompt distribution of testing reports allows for timely identification of either compliance or the need for corrective action. A complete record of testing allows the concrete producer to reliably establish the required average strength fcr' for future work.

This commentary highlights the fact that distribution of test results is important not only to the current project, but also to quantify the level of quality control of the concrete supplier, which is measured by the standard deviation of strength test results. While a component of this variability is attributed to testing, a measure of standard deviation allows for continuous improvement and facilitates better optimization and reliability of concrete mixture proportions for future projects. A complete test record from past projects is required for use as the basis of a submittal for future work. Optimization of concrete mixtures for the specified performance will avoid significant overdesign for strength. The benefits include reducing the potential for cracking of concrete associated with thermal effects, drying shrinkage and some types of chemical-related distress

Specified Strength, ƒ´c

2400

16

September 2013

ACI 318-11 includes another revision regarding testing that now requires testing agencies to comply with ASTM C1077, Standard Practice for Agencies Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Testing Agency Evaluation. This has been a requirement in ACI 301, Specification for Structural Concrete, and ASTM C94, Specification for Ready Mixed Concrete, but is now also an ACI 318 Code requirement. ASTM C1077 establishes quality systems for testing agencies, requiring labs to have periodic inspections of their procedures and equipment, verifies qualifications of testing technicians and requires laboratories to participate in proficiency sample testing. Proficiency sample testing allows labs to compare their results to those of other labs when the same material is tested. The validation that a laboratory complies with ASTM C1077 is obtained through an accreditation program provided by several national and local entities; however, ACI 318 does not require the testing agency to be accredited. ACI 311.6 goes this extra step to require testing agencies to be accredited and lists acceptable testing agency accreditation programs.

Conclusion It is imperative that information obtained from third-party evaluation of any product be provided to the manufacturer. This is not only of interest to the manufacturer, but it also serves the interest of the user of the product. Timely distribution of test results to all impacted parties will ensure that quality is maintained and will save time, money and prevent delays in project schedules.▪

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Structural ForenSicS investigating structures and their components

A

s a part of Pennoni’s on-call contract with an existing client, the Philadelphia structural division investigated and developed repair bid documents for an existing, three-level, 1,200-space precast concrete parking garage during the last quarter of 2012.

Due to the extent of ongoing deterioration at the facility, a portion was already closed to vehicular traffic prior to the start of the investigation, prompting expedited completion of the services and deliverables provided to the client.

In order to determine the extent and cause of the deterioration and develop recommendations for repairs, Pennoni’s team performed a thorough visual and tactile condition assessment of the garage, along with extensive material testing. The scope also included a large concrete retaining wall on the south side of the facility, five connected stair towers and two pedestrian bridges, all of which exhibited deterioration. The owner also made available existing drawings and previous reports of investigations for review.

Material testing performed included water-soluble chloride content tests and petrographic analysis of concrete cores taken from various critical locations throughout the structure. The purpose of the material testing was to aid in the identification of the underlying causes of the observed deterioration.

Prescription for Repair The Triage, Life Support and Subsequent Euthanasia of an Existing Precast Parking Garage – Part 1

By D. Matthew Stuart, P.E., S.E., F. ASCE, F.SEI, SECB, MgtEng and Ross E. Stuart, P.E., S.E.

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

Ross E. Stuart, P.E., S.E. (RStuart@Pennoni.com), is a project engineer at Pennoni Associates in Philadelphia, Pennsylvania.

Description of Existing Structure The existing garage was initially constructed in 1992, and consisted of two framed levels of precast and cast-in-place concrete construction.

Overall, the parking garage was approximately 345,000 square feet in size and configured as shown in Figure 1. The ground level consisted of a concrete slab on grade with concrete retaining walls along the inner ramp. The upper framed levels consisted of two similar but different construction types, which were built at two different time periods. The original construction consisted of 16-inch-deep precast, prestressed double tees, which spanned between 36-inch-deep precast, prestressed inverted “T” girders.

Prior to the investigation, the majority of the double tee bearing conditions had been supplemented with post-installed galvanized steel brackets attached to the supporting girders as a part of previous repair work at the garage. The girders were supported in U-shaped slots formed in precast inverted L-shaped (at exterior locations) and T-shaped (at interior locations) concrete columns and haunches, which were filled with site-cast concrete to create a semi-monolithic connection between the girder and column haunch.

The second construction type consisted of 24-inch-deep precast, prestressed double tees supported by 36-inch-deep cast-in-place,

Figure 1: Typical parking garage plan.

post-tensioned inverted “T” girders. The posttensioned girders were cast monolithically with the columns, creating rigid portal frames at each girder line. The existing drawings did not indicate whether the post-tensioning system consisted of sheathed (unbonded) monostrand tendons or banded, ducted and grouted (bonded) tendons.

For both methods of construction, the girders spanned parallel to the lines of radius extending from the center origin point of the semicircular garage. The precast double tees spanned along the chords and were therefore parallel to the direction of the traffic aisles. In addition, an approximately 2-inch-thick, field-cast concrete topping was placed over all elevated garage wearing surfaces. A liquid membrane with embedded sand aggregate had also been applied over all of the framed levels (drive aisle and parking stalls) in 2010.

Observations Pennoni prepared thorough and comprehensive documentation of all observed and investigated deficiencies. Although there was a wide range of varied types of deterioration, the most significant area of concern involved the precast and prestressed inverted “T” concrete girders that supported the 16-inch-deep double tees. The deterioration associated with these members included: 1) Random cracking, as well as cracking associated with reinforcement corrosion.

In general, the cracks were horizontal, parallel to the span, and located at the column/girder “hinge” interface, and also near the top of the girder web.

2) Spalls and subsurface delaminations in the presence of corroded reinforcement. These were generally located on the bottom of the girders and typically involved the entire soffit width, extending for several feet along the entire beam. Other minor

18 September 2013

Figure 3: Corroded and failed prestressing strands at precast girder.

Figure 2: Spalling due to deteriorated strands at precast girder.

spalls were located at the column/ girder “hinge” interface, at the top web and at other random locations on the sides of the girders.

3) Three bays of framing on the third level were blockaded from vehicular traffic due to extremely severe spalls and corrosion of the bottom prestressing strands of the three girders that supported these areas (Figures 2 and 3). The deterioration of the prestressing strands varied from severe to complete loss of section at this location.

The girders supporting the second level generally exhibited fewer deficiencies than those supporting the third level. The cast-in-place, post-tensioned concrete inverted “T” girders that supported the 24-inch-deep precast double tees exhibited very few deficiencies.

However, some minor spalls and corroded reinforcement were evident at isolated locations (Figure 4).

Material Testing Results In addition to the visual observations and physical sounding of the parking structure, Pennoni obtained drilled powder and concrete core samples from six areas of the garage for the purposes of further laboratory analysis, as described in the Table. The team selected these locations based on their proximity to observed deterioration and the material tests performed as a part of the previous reports.

The drilled powder samples were used to conduct water soluble chloride tests and obtained from a depth of approximately ½ inch to 1 inch at each location. Core samples PAI-4 and PAI-5 were taken through the composite section of the 2-inch topping and 2-inch double tee flange, resulting in two powder samples but only one core sample. All of the open core holes were filled with high-strength grout after the sample had been removed.

Petrographic analysis indicated that the concrete contained some entrained air at all locations, although the amount of air voids

Material Testing Results Summary Table Percent Chloride

Depth of

Side of prestressed, precast inverted T-girder

1.515%

0.1-inch

Level 3

Side of prestressed, precast inverted T-girder

1.045%

0.4 to 0.6-inch

PAI-3

Level 3

Side of cast-in-place posttensioned inverted T-girder

1.345%

0.1 to 0.2-inch

PAI-4A

Level 3

Cast-in-place topping

0.595%

0.1 to 0.2-inch

PAI-4B

Level 3

Prestressed, precast TT flange

0.065%

N/A

PAI-5A

Level 3

Cast-in-place topping

0.07%

0.4 to 0.7-inch

PAI-5B

Level 3

Prestressed, precast TT flange

0.075%

N/A

Level 2

Side of prestressed, precast inverted T-girder

0.97%

0.2 to 0.4-inch

Sample No.

Location

PAI-1

Level 3

PAI-2

PAI-6

Description

(by weight of cement) Carbonization

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September 2013

Figure 4: Rust staining due to internal corrosion of post-tensioned girder reinforcing.

precluded the establishment of a percentage of entrainment. The aggregates consisted of natural sand fine aggregate and crushed angular coarse aggregate. The distribution of aggregates appeared good in all cores with no signs of segregation, except core PAI-#1 where there was a lack of intermediate sizes.

The concrete paste was moderately hard with some unhydrated particles in all cores. Core samples PAI-1, PAI-2 and PAI-3 had some water voids, while the remaining cores had many water voids, with some larger in relative size. No cracks were observed in any of the cores except at a cold joint between the topping and double tee flange.

Conclusion By conducting a thorough site condition assessment, Pennoni was able to document the type and extent of deterioration present in the existing parking structure, and identify its potential sources via the use of appropriate material sampling and testing.

Parts 2 through 4 of this series of articles will include analysis of the observations and material testing, discussion of a service life analysis, conclusions, and recommendations for the temporary repair, stabilization and ultimate replacement of the garage.▪

Structural

SuStainability sustainability and preservation as they pertain to structural engineering

LCT ONE Case Study of an Eight-Story Timber Office Building

By Nabih Tahan, AIA

Nabih Taban, AIA, is an international architect, passive house consultant and VP of Business Development for the Cree GmbH Buildings. He can be reached at nabih.tahan@creebuildings.com.

The online version of this article contains numerous website links for reference. Please visit www.STRUCTUREmag.org.

T

he challenges facing today’s global construction industry are tremendous. As the global population becomes increasingly urbanized, the construction industry is expanding to accommodate urban residential needs. The World Health Organization estimates that, by 2030, six out of every ten people will live in a city, and by 2050, this proportion will increase to seven out of ten people.

That means, in less than two decades, 60 percent of the world population will live in urban centers.

It is estimated the global construction industry will simultaneously expand by 70 percent to $12 trillion by 2020 to keep pace. This realization has policy makers increasingly concerned about the environmental impact of the predicted global urban building boom.

Currently, the construction industry is responsible for using roughly 40 percent of the world’s total energy, CO2, and resources, as well as contributing to a similar magnitude of global waste production. Keeping in mind growing population and environmental concerns, a fresh perspective to urban architecture, that is both sustainable and efficient, is gaining ground. Today’s new outlook turns to wood in an effort to build greener.

The use of wood for tall building construction is not a novel idea. In fact, the five-story Horyu-ji pagoda in Japan is over 1500 years old. Engineered wood provides equal structural strength and fire protection, as well as lower environmental impact, lower embodied energy, and lighter foundation requirements than comparable concrete and steel construction. Today, 10-story buildings comprised almost entirely out of engineered wood, like glued laminated timber (glulam) and cross-laminated timber (CLT), are being constructed, and could likely reach up to 30-stories in the future.

Figure 1: The eight-story LCT ONE in Dornbirn, Austria was erected in just eight days.

A strong example of tall wood buildings is the LCT ONE in Austria, built in 2012, by Cree GmbH which is the parent company of Cree Buildings in North America (Figures 1 and 2). The system is an eight-story, timber-based, sustainable building that was constructed to demonstrate how the global building industry could reverse the environmental impact of today’s construction trends.

This flexible, high-performance, prefabricated construction system meets all technical and economical requirements of modern real estate markets. Built to Passive House standards (established by the Passive House Institute in Germany), its construction is predominantly based on the renewable resource of wood with additional emphasis placed on resource and energy efficiency. The Passive House standard is one of the most stringent energy standards in the world, and is focused solely on reducing energy consumption of a building. Cree’s LCT ONE demonstrates to the building industry that a modern systematic approach to construction can

Figure 2: The LCT ONE is one of the tallest office buildings in the world with exposed structural timber.

20 September 2013

Figure 3: The Cree GmbH building system consists of glulam posts supporting hybrid wood/ concrete floor slabs (core not shown for clarity).

Figure 4: After all the walls are installed, the floor slabs, which were fabricated with a hole in each corner, slide over the pins in the glulam posts.

apply new timber technologies and industrial processes to concurrently guarantee improved building performance and reduced environmental impact.

Sustainability-minded structural engineering firms not only analyze the structural properties of products they specify, but they also consider the environmental impact and energy performance of their buildings. The embodied energy of products plays a major role in determining the environmental performance of a building and, for wood, the embodied energy is quite low. Additionally, without considering thermal bridges, the detailing of structural members could lead to building heat loss, lower energy performance, and increased operational costs. Through a collaborative effort between architects, engineers, builders, and product manufacturers, the LifeCycle Tower system was created to resolve not only structural problems but environmental, social, and economic issues as well.

percent while shortening construction times by 50 percent. Additionally, when considering the embodied energy to produce wood, as well as the “end of life” potential to generate energy from the wood, a timber building would use 39 percent fewer resources during its lifetime.

Learning from advances in the automobile and computer industries, the effort produced an industrial, systemized process for buildings.

Product development considered the entire life cycle of buildings, including their resource extraction, material production, construction, operation, demolition, and recycling.

Additionally, the system integrates the building’s design and planning, off-site production and on-site assembly, initial and future uses, and eventual dismantling and recycling of its structure. The “core and shell” approach provides a structural system and enclosure of a tall, large-volume wood building.

Founded on Research

Construction for the LCT ONE started in September of 2011, in Dornbirn, Austria and was finished within a year. It is an eight-story building with a footprint of approximately 40 feet by 80 feet. Built to Passive House standards, the building has received a pre-certificate for the Gold designation from DGNB, the German Sustainable Building Council, and the highest level of standard from its Austrian counterpart, ÖGNI. Additionally, it is expected to receive Platinum LEED certification by the US Green Building Council.

The Cree Buildings wood building system consists of a central core, posts and hybrid slabs (Figure 3). The core, where the elevators, stairs, wet rooms and chases are located, is the stiffening element of the building. While wood is the optimal choice material for the

In 2009, before building the LCT ONE, Cree GmbH conducted joint research between its parent company (Rhomberg Bau), the Berlin office of the global engineering firm Arup, and renowned Austrian architect Herman Kaufmann, an internationally recognized, award winning architect specializing in timber design and construction. Focused on life cycle assessment and performance, the research team aimed to resolve the environmental, design, and construction issues involved in modern building structures. After careful examination, the research team concluded that, when compared to a reinforced concrete building, a 20-story high-performance timber building could reduce CO2 emissions by 90

8 Stories in Wood

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September 2013

core, concrete and steel can also be used. To expedite the building approval process of LCT ONE, concrete was used.

On the exterior of the building, about 30 feet away from the core, the exterior walls are installed (Figure 4 ). The walls consist of load bearing glulam posts, which are spaced approximately 10 feet apart, and a curtain wall building enclosure attached to the exterior of the posts. The curtain wall does not carry any loads and can be made out of any material, although wood is preferred as a renewable resource. The types of windows, insulation, water, air and vapor barriers, exterior finishes and other layers are designed through the collaboration of the architect, engineers and wall manufacturers and take into consideration the climate, orientation and energy performance standard demanded by the client.

The floor system is made out of hybrid wood/concrete slabs which are approximately 30 feet long and 10 feet wide. The glulam posts support the exterior end of the slabs.

The interior side of the slab is supported by the core. Compared to a monolithic system of all concrete or all wood, the hybrid approach takes advantage of each material’s individual properties to meet the structural, fire, acoustic and thermal requirements while simultaneously employing the least amount of resources and energy.

Structurally, glulam posts support the gravity loads. The lateral forces are transferred from the posts to the slabs through a hinged connection (Figure 5, page 22). The slabs are connected to each other to form a diaphragm.

The forces are then transferred from the slab to the core and down to the foundation.

Similarly, the mechanical, electrical, plumbing and fire protection systems can be integrated within the “core and shell” and optimized

Figure 5: This cross-section of the floor and post assembly was adapted to meet the seismic requirements of the San Francisco region.

according to the building orientation and building enclosure. These systems can be prefabricated and are easily accessible between the wood members in the hybrid slabs.

For the construction process, while the foundation and core of LCT ONE were being built on site, the wall components were prefabricated in a carpentry shop and the hybrid slabs in a precast concrete facility. Once the core was finished, on-site assembly of the wall and slabs began. It took five carpenters only eight days to assemble eight floors, as is demonstrated by a time-lapse video developed

by Cree GmbH.

Saving Time and Resources with Prefabricated Construction Austria has a long history of prefabricating high-performance building components out of wood. Heavy timber, or engineered lumber, which is available worldwide, is commonly used for the load-bearing elements as it is a stable material that will not shrink and twist.

Besides improving the structural stability, controlled shrinkage makes it possible to optimize building energy efficiency due to decreased air infiltration.

The prefabrication design process for the walls began with CAD software and CNC machinery to cut the timber to very tight tolerances. All wood members, including studs, were comprised of engineered lumber. The wall panels were produced horizontally, on tables by assembling the framing members, installing the insulation between studs and the sheathing on the outside. After completing the wall panels, they were tilted up to install the windows. To complete the walls, every joint, including those surrounding the windows, were taped airtight with high-performance tape.

To produce the slabs, the timber was ordered from a lumber manufacturer who cut the members to the required tolerances and

attached the necessary metal connectors.

The beams were then transported to a precast concrete manufacturer who placed the wood elements in metal forms, added metal reinforcement, and poured the concrete. For each form, this process was repeated daily. The advantage of this system is that it allows the concrete to cure off-site and prevents moisture from being introduced into the building. The prefabricated slabs are assembled quickly on site (averaging 8 minutes per slab) to very tight tolerances (Figure 6 ).

Once the building envelope was complete, blower door tests were conducted in two stages. This was done to ensure that the air sealing work was effective, guarantee the performance of the building envelope, and certify that LCT ONE met the Passive House standard. First, after the wall installation was complete, a random test, which excluded the core, was performed on two floors that resulted in 0.35 air changes per hour at 50 Pascal. Before commissioning the LCT ONE, a second blower door test was performed on the entire building including the core. This test revealed 0.55 air changes per hour at 50 Pascal, which met the Passive House standard, thus highlighting LCT ONE’s reduced energy consumption and ecological footprint.

Fire and Seismic To adapt the LCT system to North American building regulations, CREE Buildings has worked with Arup’s San Francisco office.

Their objective has been to design within the existing height and area code limitations, and demonstrate their innovative building system to the California and North American building industry. The buildings would be defined as heavy timber (HT) for height and story limitation.

During fires, steel buildings can collapse abruptly once high temperatures are reached.

Conversely, wood burns predictably at a constant rate of approximately 1.5 inches per hour. Therefore, the size of a wood structural member can be increased accordingly for fire protection. This additional thickness is referred to as the charring layer of timber.

The combination of oversized wood beams, metal connectors and reinforcement, and a specially designed concrete mix, resulted in successfully passing a two-hour fire test for the slabs as an integrated unit.

For the seismic design, Cree Buildings and Arup also developed a comprehensive seismic system, with robust ties between all the structural elements, to provide stability under large displacements. Under lateral

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September 2013

Figure 6: Due to the large, prefabricated components of the Cree Buildings system, only five carpenters were required to assemble the entire building envelope and floor slabs (detail by Arup).

movement, the exterior glulam columnconnections are designed to maintain local stability, but the columns are not part of the lateral force resisting system. Instead, the central core provides the primary lateral stability. Moreover, robust connections bind the hybrid slab modules together to distribute lateral loads to the core.

Conclusion Currently, the building industry continues to rely heavily on manual on-site labor and labor-intensive processes, which often result in low productivity, waste and the use of antiquated technology. In turn, the building industry has made limited progress in terms of industrialization and modern manufacturing processes, while other industries have considerably advanced.

Developing more systems like the LCT ONE “shell and core” example, offers a flexible design solution, where high-performance can be achieved, with minimal resource allocation.

The LCT ONE offers a window into the potential for new and innovative sustainable building solutions for the future growth of the world’s cities. Based on the premise that the building industry does not have to automatically rely exclusively on concrete and steel for urban buildings, the LCT ONE system demonstrates that there is an opportunity to substitute timber for many applications, and the option for the building industry to be even more sustainable.▪

Building Blocks updates and information on structural materials

High-Strength Welded Wire Reinforcement in Tilt-Up Construction

By Jason Blankenship, P.E.

Jason Blankenship, P.E. (jblankenship@needhamassoc. com), is a structural engineer with Needham & Associates, Inc. in Lenexa, Kansas, a consulting engineering firm that is heavily involved in the tilt-up design industry.

For more information on WWR applications, visit the Wire Reinforcement Institute website (www.wirereinforcementinstitute.org).

A number of publications, design guides, and design tools are available.

These panels were reinforced using a single uniform mat of WWR throughout, with tied rebar cages (two mats of rebar) added at jamb strips. Courtesy of Lithko Contracting, Inc.

H

igh-strength welded wire reinforcement (WWR) mats offer a viable alternative to traditional tied rebar mats in tilt-up concrete panels. Using WWR can result in an overall decrease in reinforcing steel tonnage for the project, and allows much faster placement. Both of these factors can improve the project schedule and budget. However, there are critical differences in the panel design that must be considered.

WWR is manufactured using stock coils of colddrawn steel wire, either smooth or deformed, which is then fabricated into sheets capable of being shipped. Individual transverse wires are dropped in place along the length of the continuous longitudinal wires and welded at each crossing. The process is highly automated, resulting in accurate and predictable spacing of wires, which can be customized as needed for individual project requirements. After fabrication, sheets can be bent into nearly any shape, including tied column cages. These are frequently required in tilt-up construction for narrow strips adjacent to openings where placement of traditional rebar is especially difficult and time-consuming.

WWR is available in several grades of steel, as covered under ATSM A1064 (smooth fY, MIN = 65 ksi, deformed fY, MIN = 70 ksi). Deformed wire with fY = 80 ksi is commonly specified and readily available. In some cases, the use of higherstrength reinforcement can reduce the overall area of steel required, resulting in greater efficiency and decreased quantities.

There are two primary issues with high-strength WWR substitution that impact the panel design.

First, with higher reinforcing steel strength comes proportionally higher strain in the concrete. For heavily reinforced panels, this can result in a section that is not tension-controlled, violating one of the primary criteria of tilt-up panel design under ACI slender wall provisions. It is therefore critical to reduce the area of steel to maintain the same strain relationship within the design section.

Using this reduction is common when a contractor or rebar supplier proposes WWR substitution for rebar, but should always be verified by the engineer prior to approval. Some suppliers may propose a direct one-for-one substitution based on area of steel only. At first glance, this may appear to include “bonus strength,” but it is not appropriate for slender wall design.

The second issue pertains to second-order (P-Δ) effects, which have a significant impact on slender wall design. Using a proportional ASfY (rebar) = ASfY (WWR) substitution may resolve issue #1 above, but the lower steel area also reduces the cracked-section moment of inertia for the concrete panel (ACI 318-11, Eq. 14-7). In turn, the deflection (ΔU) due to second-order moments increases, reducing the overall flexural capacity of the panel (Eq. 14-4, 14-5). In such cases, either greater steel area or increased concrete strength is necessary. This effect is especially apparent in panels with a single mat of reinforcement centered in the panel depth. Panels with two reinforcing mats have a greater effective section depth, which typically limits P-Δ effects to a manageable level where a steel area reduction is achievable.

24 September 2013

When designing with WWR, it is possible to provide a more accurate quantity of reinforcement than with traditional rebar. In an effort to keep the bar size and spacing simple and practical, greater amounts of steel are frequently provided than truly necessary for the design (e.g., using #5 @ 6 inches instead of #5 @ 7.5 inches). With the greater variety

of wire diameters that are readily available, and more accurate spacing control with shop-fabricated WWR sheets, it is possible to design panel reinforcement much closer to the true area of steel necessary (D9 @ 4.5 inches is just as easy as D20 [#4 bar] @ 6 inches). On a large project, this savings in steel tonnage can be significant.

PANEL #1: (Single Mat) Panel Criteria: Panel span = 31 feet, 0 inches Thickness = 7¼ inches, single mat centered DL = 500 plf, WL = 20 psf ΔMAX = h/150 = 2.48 inches Material Properties: f'C = 4,000 psi fY = 60 ksi (mild steel rebar) fY = 80 ksi (WWR) Rebar Option: AS,VERT = 0.44 in2/ft (use #6 @ 12 inches) AS,HORIZ = 0.174 in2/ft (use #4 @ 12 inches) Steel strain = 0.0101 MU = 82.6 kip-in/ft ϕMN = 83.3 kip-in/ft Actual steel weight = 2.17 psf

WWR Option: AS,VERT = 0.39 in2/ft (use D20 @ 6 inches) AS,HORIZ = 0.174 in2/ft (use D9 @ 6 inches) Steel strain = 0.0083 MU = 95.1 kip-in/ft ϕMN = 95.4 kip-in/ft Actual steel weight = 1.97 psf Designing the section using 80 ksi WWR, the required reinforcement reduces slightly.

Note that a direct ASfY substitution for WWR would provide 0.33 in2/ft and an equivalent ϕMn = 83.3 kip-in/ft, but the required moment capacity increases due to the reduced cracked-section moment of inertia. Overall panel steel area decreases slightly due to the additional wire size and spacing options.

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September 2013

For double-mat panels with reinforcement at each face, horizontal bars are often kept at a tighter spacing than what would otherwise be required by code to control shrinkage cracking (18 inches maximum per ACI 318; 15 inches maximum per National Building Code of Canada). Bar sizes are driven somewhat by handling concerns; often #3 bars are avoided.

This can result in horizontal steel significantly greater than the minimum specified by ACI. Using WWR, wires with a smaller diameter and closer spacing can provide more uniform crack control using less steel area. Wire sizes need not be limited due to handling concerns since each intersection is welded, providing inherent stability during transportation and construction.

One particularly interesting application of WWR for tilt-up construction is at narrow panel strips adjacent to doors. Manufacturing and warehouse facilities frequently have relatively tall load-bearing panels with narrow jamb strips at dock doors, as illustrated in the Figure. These jamb strips frequently require tied column cages, which are cumbersome and time-consuming to fabricate from rebar in the field. In most cases, a WWR cage can achieve the same design intent while incorporating both the vertical reinforcing and ties into a single shop-fabricated assembly. Jamb cages can be dropped straight from the truck

PANEL #2: (Double Mat) Panel Criteria: Same as Panel #1, except reinforced at each face

AS,HORIZ = 0.174 in2/ft (use D6 @ 8 inches EF) Steel strain = 0.0314 MU = 67.5 kip-in/ft ϕMN = 68.1 kip-in/ft Actual steel weight = 1.84 psf

Rebar Option: AS,VERT = 0.205 in2/ft EF (use #4 @ 12 inches EF) AS,HORIZ = 0.174 in2/ft (use #4 @ 18 inches EF) Steel strain = 0.0337 MU = 62.4 kip-in/ft ϕMN = 62.4 kip-in/ft Actual steel weight = 2.23 psf

For the double mat panel, the reduction in actual steel area using WWR is significant (17.5% less). Because the horizontal wires for WWR can be smaller in diameter and more closely spaced, the same (or better) crack control can be accomplished using less steel. A portion of these savings (10%) occurs simply due to the increase from 60 to 80 ksi steel.

WWR Option: AS,VERT = 0.17 in2/ft EF (use D12 @ 8 inches EF)

PANEL #3: (Typical Dock Door Jamb Strip, Double Mat) Panel Criteria: Same as Panel #2, but jamb strip width = 2 feet, 3-inches Rebar Option: AS,VERT = 0.58 in2/ft EF (use #6 @ 9 inches EF) AS,HORIZ = 0.174 in2/ft (use #3 closed ties @ 6 inches) Actual steel weight = 5.50 psf

WWR Option: AS,VERT = 0.48 in2/ft EF (use D16 @ 4 inches EF) AS,HORIZ = 0.174 in2/ft (use D5 @ 6 inches EF) Actual steel weight = 3.94 psf For jamb strips, the WWR sheet can be bent into a closed cage, including both the vertical reinforcing and horizontal ties.

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September 2013

into the form, rather than spending valuable hours field-tying them. Through the use of smaller-diameter wire “ties,” bend radii can be minimized (wire = 2*db vs. rebar = 4-6*db), permitting a double mat of reinforcing in a panel thickness that otherwise could be too congested. Using smaller wires can also provide better confinement, with less risk of segregation during concrete placement.

For illustration purposes, consider the following tilt-up panel designs, using ACI 318-11 section 14.8 slender wall provisions.

For simplicity, a single load combination (D+W) is considered.

Conclusion When properly designed, the use of WWR can improve the economy and performance of a tilt-up project. For engineers, specifying WWR can result in a more accurate reinforcement design with better confinement and control of shrinkage cracking. For contractors, the use of WWR can simplify installation and result in significant labor and schedule savings. Material savings for single mat panels are typically minor, but are more significant for double mat panels.

Involvement of the tilt-up engineer is always critical to ensure that the WWR utilized is appropriate for slender wall design.▪

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Professional issues issues affecting the structural engineering profession

Figure 1: U.S. Average Temperature Projections (draft NCA 2013).

W

eather, climate and extreme events are key considerations in structural engineering design and practice. Weather is defined as “the state of the atmosphere with respect to wind, temperature, cloudiness, moisture, pressure, etc.” (NWS, 2013). Weather generally refers to short-term variations on the order of minutes to about 15 days (NSIDC, 2012). Climate, on the other hand, “is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years” (IPCC, 2007). An extreme event is a weather event that is rare at a particular place and time of year (IPCC, 2007). For instance, at Washington Reagan National Airport on June 25 (Washington Post June 26, 2013), the normal high temperature is 87°F (climate), the high in 2013 was 93°F (weather) and the record high was 100°F in 1997 (extreme event).

Scientists have reached a consensus that weather, climate and extreme events of the past generally will not be representative of those of the future.

Moreover, climate science is not able precisely to forecast the climate, weather and extreme events of future decades. This poses a challenge to structural engineers whose design standards are based on the assumptions of stationary climate, weather and extreme events as observed in the past. The Committee on Adaptation to a Changing Climate (CACC) of the American Society of Civil Engineers (ASCE) is addressing this in its white paper, Bridging the Gap between Climate Change Science and Civil Engineering Practice (ASCE 2013). The purpose of this article is to alert structural engineers to this challenge,

inform them of the guidance available from the white paper, and invite their participation in the profession’s response to the challenge.

Bridging the Gap between Climate Change Science and Structural Engineering Practice

Current Climate Science The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for the assessment of climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts. The Table (page 30) shows the recent, qualitative IPCC assessment, based on observations and global climate models, of future weather and extreme events relevant to structural engineering design (IPCC 2012).

The U.S. Global Change Research Program (USGCRP) involves thirteen federal agencies and is led in the White House Office of Science and Technology Policy. USGCRP is preparing a National Climate Assessment (NCA), which will be issued in 2014; a draft has been available since January 2013 (NCA 2013). The draft NCA was prepared by the National Climate Assessment and Development Advisory Committee involving over 240 authors, including climate and social scientists and engineers. It has chapters on urban systems, infrastructure and vulnerability, U.S. regions, mitigation and adaptation.

Figure 1, U.S. Average Temperature Projections, taken from the draft NCA, illustrates both the

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By Richard N. Wright, Ph.D., P.E., Dist.M.ASCE, NAE, Bilal M. Ayyub, Ph.D., P.E., F. ASCE and Franklin T. Lombardo, Ph.D., M. ASCE

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

potential significance of climate change for structural engineering and why climate science cannot now quantitatively forecast future climate, weather and extreme events.

The solid line for the 20th century shows an increasing trend, amounting to about 2°F for the century, with the observed variations from the trend as large as 2° F. The projections for the 21st century are derived from global climate models that consider a variety

of scenarios for economic development and control of greenhouse gas emissions (Moss et al. 2010). The lowest curve is based on greenhouse gas concentrations peaking at 490 ppm carbon dioxide (CO2) equivalent and then declining; it leads to an additional 2°F increase in U.S. average temperature in the 21st century. The highest curve is based on emissions continuing to produce greenhouse gas concentration of 1,370 ppm CO2

equivalent in 2100; it leads to an additional 9°F increase. The historical trend of atmospheric CO2 is shown in Figure 2. The CO2 data (red curve) for Mauna Loa, measured as the mole fraction in dry air, constitute the longest record of direct measurements of CO2 in the atmosphere. The black curve represents the seasonally corrected data.

Greenhouse gas emissions in the 21st century will depend upon worldwide private and public

Extreme Events from IPCC(2012).

Physical Impact

Observed Changes

Projected Changes

Temperature

Very likely decrease in number of unusually cold days and nights at the global scale. Very likely increase in number of unusually warm days and nights at the global scale. Medium confidence in increase in length or number of warm spells or heat waves in many (but not all) regions. Low or medium confidence in trends in temperature extremes in some subregions due either to lack of observations or varying signal within subregions.

Virtually certain decrease in frequency and magnitude of unusually cold days and nights at the global scale. Virtually certain increase in frequency and magnitude of unusually warm days and nights at the global scale. Very likely increase in length, frequency, and/or intensity of warm spells or heat waves over most land areas.

Precipitation

Likely statistically significant increases in the number of heavy precipitation events (e.g., 95th percentile) in more regions than those with statistically significant decreases, but strong regional and subregional variations in the trends.

Likely increase in frequency of heavy precipitation events or increase in proportion of total rainfall from heavy falls over many areas of the globe, in particular in the high latitudes and tropical regions, and in winter in the northern mid-latitudes.

Winds

Low confidence in trends due to insufficient evidence.

Low confidence in projections of extreme winds (with the exception of wind extremes associated with tropical cyclones).

Tropical Cyclones

Low confidence that any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities.

Likely decrease or no change in frequency of tropical cyclones. Likely increase in mean maximum wind speed, but possibly not in all basins. Likely increase in heavy rainfall associated with tropical cyclones.

Likely poleward shift in extratropical cyclones. Low confidence in regional changes in intensity.

Likely impacts on regional cyclone activity but low confidence in detailed regional projections due to only partial representation of relevant processes in current models.

Medium confidence in a reduction in the numbers of midlatitude storms.

Droughts

Medium confidence that some regions of the world have experienced more intense and longer droughts, in particular in southern Europe and West Africa, but opposite trends also exist.

Medium confidence in projected increase in duration and intensity of droughts in some regions of the world, including southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa. Overall low confidence elsewhere because of insufficient agreement of projections.

Floods

Limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at regional scale. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes. High confidence in trend toward earlier occurrence of spring peak river flows in snowmelt- and glacier-fed rivers.

Low confidence in global projections of changes in flood magnitude and frequency because of insufficient evidence.

Medium confidence (based on physical reasoning) that projected increases in heavy precipitation would contribute to rain-generated local flooding in some catchments or regions. Very likely earlier spring peak flows in snowmeltand glacier-fed rivers.

Extratropical Cyclones

Very likely that mean sea level rise will contribute to upward

Extreme Sea trends in extreme coastal high water levels. High confidence Likely increase in extreme coastal high water worldwide related to that locations currently experiencing coastal erosion and Level and Coastal increases in mean sea level in the late 20th century. inundation will continue to do so due to increasing sea level, Impacts in the absence of changes in other contributing factors.

Other Impacts (Landslides and Cold Regions)

Low confidence in global trends in large landslides in some regions. Likely increased thawing of permafrost with likely resultant physical impacts.

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High confidence that changes in heavy precipitation will affect landslides in some regions. High confidence that changes in heat waves, glacial retreat, and/or permafrost degradation will affect high mountain phenomena such as slope instabilities, mass movements, and glacial lake outburst floods.

September 2013

policy decisions and actions, which are unpredictable, but can be represented by scenarios such as those used in preparing Figure 1.

What Can Engineers Do? The purpose of the ASCE Committee on Adaptation to a Changing Climate (CACC) is to identify and communicate the technical requirements and civil engineering challenges for adaptation to climate change. Based on the results obtained, response activities may be planned in the Technical Activities Divisions, Technical Councils, Institutes, and other elements of ASCE. These activities may include recommendations for initiatives related to: • climate change and its effect on the safety, health and welfare of the public as it interfaces with civil engineering infrastructure; and • appropriate standards, loading criteria, and evaluation and design procedures for the built and natural environment, and related research and monitoring needs.

The purposes of the CACC white paper Bridging the Gap between Climate Change Science and Civil Engineering Practice (ASCE 2013) include the following: • Fostering understanding and transparency of analytical methods necessary to update and describe climate, weather and extreme events for planning and engineering design of the built and natural environments.

• Identifying (and evaluating) methods to assess impacts and vulnerabilities caused by changing climate conditions on the built and natural environments.

• Promoting development and communication of best practices in civil engineering for addressing uncertainties associated with changing conditions, including climate, weather, extreme events, and the nature and extent of the built and natural environments.

Engineers can join in research with climate and weather scientists to develop integrated models for climate, weather and extreme events (National Academies 2012), which, combined with observations, can give probabilistic guidance for the conditions

for which structures should be designed, constructed, operated and maintained.

Before such research is conducted and its results are incorporated into structural standards – a process that may take a decade or more – the question arises of what structural engineers can do to comply with the most fundamental canon in the ASCE Code of Ethics: “Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable Figure 2: Atmospheric CO2 at Mauna Loa Observatory development in the performance (www.esrl.noaa.gov/gmd/ccgg/trends/). of their professional duties.”

There is useful guidance in the concept of “long life, loose fit, low energy” magazine and other media. They will as expressed by Alex Gordon, president of ultimately guide the evolution of structhe Royal Institute of British Architects tural standards and practices. Engineering (Gordon 1972): research, in collaboration with climate and • Long life contributes to sustainability social scientists, can improve both obserand reduction of greenhouse gas vations of climate/weather/extremes and emissions through conservation of modeling to provide a probabilistic undermaterials and energy required for standing of the changing nature of hazards, removal and replacement. Long life risks and benefits as bases for appropriately can be promoted by siting to avoid evolving engineering standards.▪ susceptibility to flooding and wildfires, and using structural systems and details that are inherently resistant to extremes Richard N. Wright, Ph.D., of temperature, wind and precipitation.

P.E., Dist.M.ASCE, NAE However, shorter service lives, where (richard.n.wright@verizon.net), is economical, will provide opportunities the retired director of the Building and to account for better knowledge of Fire Research Laboratory at the National climate/weather/extremes in design of Institute of Standards and Technology future replacements.

(NIST) in Montgomery Village, Maryland.

• Loose fit means making structures Bilal M. Ayyub, Ph.D., P.E., F. ASCE adaptable to conditions that could (ba@umd.edu), is a professor of civil and not be foreseen during the original environmental engineering and the director design – a quality already widely of the Center for Technology and Systems exemplified by older structures in Management at the University of Maryland useful service today. in College Park (www.ctsm.umd.edu).

• Low energy, including the embodied energy in original construction Franklin T. Lombardo, Ph.D., M .ASCE and the operating energy over the (lombaf@rpi.edu), is a research assistant structure’s service life, provides both professor of civil and environmental economic benefits and reductions in engineering at Rensselaer Polytechnic the greenhouse gas emissions driving Institute in Troy, New York. climate change.

Engineers can and should share their insights in adapting to climate change with case studies published in STRUCTURE® ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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September 2013

InSIghtS

new trends, new techniques and current industry issues

New Wood Materials Cross Laminated Timber (CLT)

By John “Buddy” Showalter, P.E.

C

ross Laminated Timber (CLT) is a flexible building system suitable for use in all assembly types (e.g., walls, floors, and roofs). Made from industrial dried lumber stacked together at right angles and glued over their entire surface, it is an exceptionally strong product that retains its static strength and shape, and allows transfer of loads on all sides. Panels are prefabricated based on the project design, and arrive at the job site with windows and doors pre-cut. Although size varies by manufacturer, they can be as large as 54.1 x 9.7 x 1.6 feet and include 3, 5, 7, or more layers.

Common connections for CLT assemblies include wall-to-foundation, wall-to-wall (straight or junction), floor-to-floor, wallto-floor, and wall-to-roof. Panels may be connected to each other with half-lapped, single or double splines made from engineered wood products, while metal brackets, holddowns, and plates are used to transfer forces.

Mechanical fasteners may be dowel-type (e.g., nails, screws, glulam rivets, dowels, bolts) or bearing-type (e.g., split rings, shear plates).

CLT assemblies excel in terms of fire protection because, like heavy timber, they char at a rate that is slow and predictable, maintaining their strength and giving occupants more time to leave the building. CLT structures also tend to not to have as many concealed spaces within floor and wall assemblies, which reduces the risk that a fire will spread. The American Wood Council (AWC) conducted a successful ASTM E119 fire resistance test on a CLT wall last year at NGC Testing Services in Buffalo, NY. The wall, consisting of a 5-ply CLT (approximately 67/8 inches thick), was covered on each side with a single layer of 5/8-inch Type X gypsum wallboard. The wall was loaded to the maximum load attainable by the NGC Testing Service equipment.

The test specimen lasted 3 hours, 5 minutes, and 57 seconds (03:05:57). www.awc.org/ Code-Officials/2012-IBC-Challenges/NGCCLT-Report.pdf In terms of seismic performance, wood buildings perform well because they’re lighter and have more repetition and ductility than structures built with other materials, which make them effective at resisting lateral and uplift forces. To illustrate this, the Trees and

The American Wood Council (AWC) conducted a successful ASTM E119 fire resistance test on a CLT wall last year at NGC Testing Services in Buffalo, NY.

Timber Research Institute of Italy tested a full-scale seven-story CLT building on the world’s largest shake table, in Japan, with excellent results. Even when subjected to severe earthquake simulation (magnitude of 7.2 and acceleration of 0.8 to 1.2 g), the structure showed no residual deformation.

The maximum inter-story drift was 1.5 inches and the maximum lateral deformation at the top of the building was just 11.3 inches.

Recently, an AWC code change to expand the use of CLT into the heavy timber construction classification (Type IV) was approved for incorporation in the 2015 International Building Code (IBC). The change will allow more options for CLT use in non-residential buildings. In addition to the Type IV classification, a new product standard, ANSI/APA PRG 320-2011 Standard for PerformanceRated Cross-Laminated Timber, will be referenced in the 2015 IBC. Until the 2015 IBC is published and adopted, building officials are approving designs using the alternate materials and methods provision of the code.

Additionally, Skidmore Owings & Merrill LLP (SOM) recently released the Timber Tower Research Project, an initiative sponsored by the Softwood Lumber Board (SLB), to establish the structural viability of a 42-story-tall prototypical mass timber framed building. The new prototype is a hybrid system that uses the most efficient structural combination of mass timber (including CLT), concrete, and steel to reduce the carbon footprint of the resulting design by between 60

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September 2013

and 75 percent when compared to the concrete benchmark.

As with all wood products, the benefits of CLT include the fact that it comes from a renewable and sustainable resource. Wood also has a low carbon footprint by continuing to store carbon absorbed during a tree’s growing cycle, and avoiding greenhouse gas emissions that are often the result of using other building products that require large amounts of fossil fuels to manufacture. In fact, the architect of a CLT apartment building in the UK estimated that, between the carbon stored in the panels and emissions avoided by not using concrete, he kept about 300 metric tons of carbon out of the atmosphere. The CLT building was also estimated to weigh four times less than its concrete counterpart, which reduced transportation costs, allowed the design team to reduce the foundation by 70 percent, and eliminated the need for a tower crane during construction.

It took four carpenters just nine weeks to erect nine stories – and the entire construction process was reduced from 72 weeks to 49.

Leading wood organizations have collaborated to publish a new CLT Handbook which can be downloaded at www.masstimber.com.

Printed copies are available at www.awc.org.▪ John “Buddy” Showalter, P.E., is Vice President of Technology Transfer at the American Wood Council and a member of STRUCTURE magazine’s Editorial Board.

He can be reached at bshowalter@awc.org.

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21st Annual Conference

September 18-21, 2013

Westin Buckhead Hotel, Atlanta, Georgia

Wednesday — September 18 8:00 – 12:00

10:15 – 10:30

NCSEA Board Meeting

General Engineering SELC SI/QA Committee Wind Committee SECB Board Meeting Advocacy Committee Basic Education Committee CAC Steering Committee Publications Structural Licensure Young Member Group Support

11:00 – 8:30 noon – 1:00

3:00 – 5:00 Tutorial: The AISC Direct Analysis Method Leroy Emkin, Ph.D, P.E., F. ASCE, GA Tech Dr. Emkin will demonstrate the Method and the impact on structural engineering workflow.

Dr. Emkin is a consultant on cost effective use/misuse and engineering ethics of using computers in structural engineering practice.

5:30 – 6:30 6:30 – 8:30

Young Engineers Reception Structural Engineering Certification Board (SECB) Reception

Thursday — September 19 7:00 – 8:00 8:00 – 8:15

Breakfast Welcome and Introduction

Trade Show open Lunch on the Trade Show floor

Concurrent Sessions 1:00 – 2:15 A) ACI 550: Guide to Emulating Cast-in-Place Detailing for Seismic Design of Precast Concrete Structures Harry Gleich, P.E., FACI, FPCI, Chairman of ACI-ASCE 550, Metromont Corporation Harry will discuss ways to design precast structures for seismic.

B) The Analysis of Offset Diaphragms and Shear Walls Terry Malone, P.E., S.E., WoodWorks The presentation covers analyzing horizontally offset diaphragms, and in-plane and out-of-plane offset shear walls.

Terry Malone is a licensed structural engineer, and is the author of “The Analysis of Irregular Shaped Structures: Diaphragms and Shear Walls”.

2:15 – 2:45 Refreshment Break in Exhibit Hall

8:15 – 9:15 Keynote Address: The Philosophy of Design: The Structural Engineer’s Role in Creating New Architecture Bill Baker, P.E., SECB, F. ASCE, FIStructE, Structural & Civil Engineering Partner, Skidmore, Owings & Merrill. His best known contribution has been to develop the “buttressed core” structural system for the Burj Khalifa, the world’s tallest manmade structure.

9:15 – 10:15 DoD Minimum Antiterrorism Standards for Buildings Jon Schmidt, P.E., SECB, M. ASCE, Burns & McDonnell Jon Schmidt will present an overview of the latest edition of Department of Defense (DoD) Unified Facilities Criteria.

Jon Schmidt is an associate structural engineer and the Director of Antiterrorism Services at Burns & McDonnell, nationally recognized in the field of building design to mitigate terrorist attacks and intentional threats.

STRUCTURE magazine

Refreshment Break

10:30 – noon ASCE 41-13: Seismic Evaluation and Retrofit of Existing Buildings Robert Pekelnicky, P.E., S.E., LEED AP, M. ASCE, Degenkolb Engineers The presentation summarizes the new ASCE 41-13 standard, a combination of ASCE 31-03 and 41-06.

Bob Pekelnicky is a recognized leader in the field of earthquake engineering.

Committee Meetings 8:00 – 1:00 9:00 – 12:00 11:00 – 1:00 10:00 – 12:00 12:00 – 5:00 1:00 – 5:00 1:00 – 5:00 1:00 – 5:00 1:00 – 5:00 1:00 – 5:00 2:00 – 5:00

www.ncsea.com

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Concurrent Sessions 2:45 – 3:45 A) Connections: The Last Bastion of Rational Design Bill Thornton, Ph.D., P.E., NAE, Cives Corp The session will focus on the effects of mainframe design on connections, bolt and weld choices, analysis assumptions and reality, and the Lower Bound Theorem of Limit Analysis.

Dr. Thornton is Corporate Consultant and Vice-President for Cives Engineering Corporation. He was elected to the National Academy of Engineering in 2013 and currently serves as a member of technical committees of AISC, ASCE, and RCSC. He was also chairman of the AISC Committee on Manuals for 26 years.

Visit www.atlanta.net for more information on our host city.

September 2013

B) Load Generators: What Exactly is My Software Doing? Sam Rubenzer, P.E., S.E., FORSE Consulting In using a structural analysis and design software package, structural engineers need to know what sections of the code are used for load generators in common software packages.

Sam Rubenzer worked for Bentley Systems, training structural engineers on STAAD.pro and each of the RAM structural engineering software programs and, in 2010, founded FORSE Consulting.

3:45 – 4:45 A) UMinn. Northrop Auditorium RenovationUnderpinning & Micropile Foundation Case Study Greg Greenlee, P.E., Engineering Partners Intl.

This session will discuss how a multi-phased underpinning and micropile foundations construction sequence was used within the confines of the building envelope.

Greg Greenlee has 19 years of experience in structural building design; specialty foundation design, temporary shoring and earth retention design; and building code and standard development.

B) The Structural Curtainwall John Tawresey, S.E., KPFF Consulting Engineers This presentation will use project examples of curtainwall systems to clarify and classify curtainwall structural criteria in the building codes, industry standards, and architects’ typical specifications.

John Tawresey has 40 years of curtain wall design experience, including materials of glass/aluminum, thin stone, precast concrete, brick, ceramic tile, EIFS, stucco, and various metals (steel and aluminum).

5:30 – 6:30

President’s Reception for Member Organization Delegates Welcome Reception with Exhibitors

6:30 – 8:30

Concurrent Sessions 8:00 – 10:00 Member Organization Reports 8:00 – 10:00 Vendor Product Presentations Software CSC Strand7 Valmont Nemetschek

10:00 – 10:30 10:30 – 3:30

Refreshment Break in Exhibit Hall Member Organization Executive Director Meeting

Non-Software New Millenium AZZ Side Plate Foundation Tech.

1:30 – 2:45 Guide to the Design of Building Systems for Serviceability in Accordance with the 2012 IBC and ASCE/SEI 7-10 (Part 1) Kurt Swensson, Ph.D, P.E., LEED AP, KSi Structural Engineers The author of the new Guide to the Design of Building Systems for Serviceability in Accordance with the 2012 IBC and ASCE/SEI 7-10 will present practical information and design examples to evaluate the serviceability performance of buildings in accordance with the requirements of the 2012 IBC and referenced standards.

Dr. Swensson has over 25 years of experience designing structure for buildings throughout the U.S. He is founder and president of KSi Structural Engineers which has designed building structures in 41 states and Puerto Rico.

2:45 – 3:15

Refreshment Break

3:15 – 5:00

Guide to the Design of Building Systems for Serviceability in Accordance with the 2012 IBC and ASCE/SEI 7-10 (Part 2) Kurt Swensson

Saturday — September 21

10:30 – noon Practical Design of Complex Stability Bracing Configurations Donald White, Ph.D, Georgia Tech This presentation discusses a general approach based on AISC Appendix 6, but using a practical computational tool to address attributes not captured by the Appendix 6 design equations.

STRUCTURE magazine

Trade Show Exhibitor Meeting Lunch (exhibits close at 1:00)

Awards Reception (Formal attire encouraged) Banquet and Awards Presentation NCSEA will be announcing the 2013 Excellence in Structural Engineering Awards at the Awards Banquet. Awards will be given in eight categories, with one project in each category named the Outstanding Project. Categories for 2013 are: • New Buildings under $10 Million • New Buildings $10 Million to $30 Million • New Buildings $30 Million to $100 Million • New Buildings over $100 Million • New Bridge and Transportation Structures • International Structures • Forensic/Renovation/Retrofit/Rehabilitation Structures • Other Structures

Continental Breakfast Trade Show open

8:00 – 8:20 8:30 – 8:50 9:00 – 9:20 9:30 – 9:50

10:45 – 11:15 noon – 1:00

6:00 – 7:00 7:00 – 10:00

Friday — September 20 7:00 – 8:00 7:00 – 1:00

A professor at the Georgia Institute of Technology School of Civil and Environmental Engineering (CEE), Don White’s research covers design and behavior of steel and composite steel-concrete structures as well as computational mechanics, methods of nonlinear analysis and applications to design.

7:00 – 8:00 8:00 – noon 12:30 – 2:00

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Continental Breakfast NCSEA Annual Business Meeting Board of Directors Meeting

Register online at www.ncsea.com

September 2013

21st Annual Conference

September 18-21, 2013 Denotes NCSEA membership

Westin Buckhead Hotel, Atlanta, Georgia

www.ncsea.com

(xx) Booth number

American Concrete Institute (30)

Nucor Vulcraft Group/Ecospan (7)

www.concrete.org

www.ecospan-usa.com

www.aisc.org

www.powers.com

www.atlastube.com

www.sideplate.com

www.azzgalv.com

www.strongtie.com

www.bekaert.com

www.starseismic.net

www.bentley.com

www.steeljoist.org

www.herculesbolt.com

www.beaufort-analysis.com

www.castconnex.com

www.uspconnectors.com

www.cscworld.com

www.valmont.com

www.sds2.com

www.vector-corrosion.com

American Institute of Steel Construction (31)

Powers Fasteners (38)

Atlas Tube (23)

Side Plate Systems (4)

AZZ Galvanizing (19)

Simpson Strong Tie (2)

Bekaert (33)

Star Seismic (20)

Bentley Systems (26)

Steel Joist Institute (13)

Blind Bolt (32)

Strand 7 (14)

Cast Connex Corporation (5)

USP Connectors, Hardy Frames (42)

CSC Inc. (36)

Valmont (1)

Design Data (34)

Vector Corrosion Tech (18)

Euclid Chemical (15) www.euclidchemical.com

Fabreeka International Inc. (35)

BAR

www.fabreeka.com

9

47

48

49

50

8

www.foundationtechnologies.com

12

Foundation Technologies (21)

43

44

45

46

Fyfe Co. (29)

www.gtstrudl.gatech.edu

Available

7

Hayward Baker (37)

39

40

41

42

35

36

37

38

14

Reserved

GTSTRUDL (16)

13

www.fyfeco.com

www.haywardbaker.com

Hilti (43)

6

us.hilti.com

Holcim Inc (39) www.holcim.us

5

33

34

www.itwredhead.com

27

28

29

30

23

24

25

26

19

20

21

22

Lindapter USA (27) www.lindapterusa.com

3

Nemetschek Scia (3) www.nemetschek-scia.com

2

New Millenium Building Systems (17) www.newmill.com

Nucor Vulcraft Group (6)

1

www.vulcraft.com

STRUCTURE magazine

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September 2013

18

17

32

16

31

ITW Commercial Construction-N. America (22)

15

www.iccsafe.org

4

FOOD STATION

International Code Council (8)

Registration

Conference Hotel

Full conference registration includes: • • • • • • •

The Westin Buckhead is the host hotel for the NCSEA Annual Conference. Guests can indulge in world-class shopping at the adjacent Lenox Mall and Phipps Plaza, or access myriad dining options in minutes.

Reserve your room online at www.ncsea.com for the $169 group rate.

Three breakfasts Two lunches Three receptions Refreshment breaks Trade show access All educational sessions & resources Awards Banquet

Special Offers!

Engineers 35 years of age or younger pay only $550 for complete registration, which also includes special Young Engineer activities.

Transportation to Hotel

First-Time Attendees to the NCSEA Annual Conference pay only $600.

The hotel is accessible by train 50 minutes from the Atlanta airport.

The Westin Buckhead hotel is located just one block from the Buckhead Metro stop along the Red Line.

REGISTER TODAY!

All NCSEA conference events take place at The Westin Buckhead Hotel.

Car Rental & Airfare Discounts

Reservation information is available at www.ncsea.com.

The 2013 NCSEA Annual Conference has partnered with Avis to provide rental cars at a discounted rate. If you wish to reserve a car please contact Todd Alexander at 800-525-7537 Ext. 35003 or the Meetings and Convention Department at 800-525-7537 to receive the best rate possible. Please mention AWD# G028164 when you call. If you wish to reserve a car online, visit Avis.com and use the discount code AWD# G028164.

Sponsors NCSEA extends its appreciation to the sponsors of the NCSEA Annual Conference.

NCSEA has partnered with American Airlines for discounted airfare for the NCSEA Annual Conference. The NCSEA discount code is: A9893BP. This number goes into the Promo Code box when buying online tickets at www.aa.com, and will give a 5% discount.

Passengers may also call 800-433-1790.

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STRUCTURE magazine

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September 2013

Pennsylvania

The

STaTe CaPiTol

By R. Scott Silvester, P.E., Christina T. Parker, P.E. and Niklas W. Vigener, P.E.

Evaluating the Structural Performance of Unreinforced Monumental Masonry Structures

Figure 1: Pennsylvania State Capitol Building.

E

ven when they are intact, monumental historic masonry structures – including structural systems such as towers, domes, arches, tunnels, buttresses, and vaults – are complex structural systems whose behavior is difficult to quantify using only simple analytical methods. Some of the parameters that complicate the analysis approach are the indeterminate behavior of large interconnected systems, intractable boundary conditions, the variability of materials, direction-dependent strength properties of masonry, and deterioration. When cracks occur, structural behavior changes as displacements take place, and loads are redistributed throughout the structure.

Frequently, conditions such as moisture intrusion or cracking, movement, and deterioration of mortar, brick, stone, or terra cotta prompt an evaluation of the structure to understand the causes, as well as the implications that include diminution in structural integrity and prognosis for future performance. This often prompts structural engineers to opine on whether a deteriorated masonry structure is safe.

Figure 2: Central dome structure. Detail from drawing A-6: Restoration of the Peristyle Deck

by Perfido Weiskopf Wagstaff & Goettel dated 2008 with annotations by SGH.

The solution to this problem often requires structural engineers to engage in rigorous investigations to reveal the construction and condition of a structure, and then to combine classical analysis techniques that explore the design intent with sophisticated modern tools to assess performance with distress. When properly executed, finite element computer programs, which engineers commonly apply to analyses of structures with known configurations and properties, can model the behavior of complex masonry structures with uncertain properties. The model must be carefully developed to strike a balance between model complexity, level of confidence in the structure being modeled, and the need to achieve meaningful results. Although modeling results can be informative, they should be considered one constituent of a carefully planned engineering study to evaluate a historic structure’s condition and performance.

The Pennsylvania State Capitol Building (Figure 1) in Harrisburg, Pennsylvania, constructed circa 1906, is an example of a monumental masonry structure assessed using finite element techniques. The Capitol

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structure has complicated geometries with an upper drum and colonnaded peristyle, lower drum, and four supporting vaulted arches with intersecting pendentives (Figures 2 and 3). This unreinforced load-bearing masonry construction supports a truss framed dome, a colonnaded lantern, and a statue above. The lower drum contains a circumferential arched tunnel below the peristyle deck.

During work associated with restoration of the peristyle deck (Figure 4 ) to address leakage below the dome structure, the restoration team noted cracking and moisture-related deterioration of the brick and granite masonry drum below the deck. The State of Pennsylvania’s Office of General Services, concerned about this distress, commissioned an engineering study to evaluate the structural performance of the brick masonry of the lower drum, including consideration of the observed masonry deterioration and cracks.

Configuration Part of the challenge in analyzing monumental unreinforced masonry structures is

Figure 3: Computer enhanced image identifying components of central dome structure.

understanding and adequately modeling the structural configuration and the materials of construction. Engineers often are hampered by the lack of drawings, and by access to assess materials and construction deep inside thick structural elements.

Thick masonry construction often contains a combination of exterior stone and interior brick. There may be voids inside massive construction that appears solid from the outside.

When reliable drawings are not available, the engineer must use prudent investigation and judgment to identify critical features of the structural system. In the case of the Capitol assessment, exploratory openings, drilled cores, and masonry removals for ongoing waterproofing repairs revealed that the typical

Figure 4: Peristyle deck above the lower drum.

wall construction consists of regularly coursed interior brick, making up the greatest portion of the wall thicknesses, and exterior granite ashlar. Stone and brick are interconnected with stone header courses that primarily occur at counterbalanced stone cornices that extend into the brick masonry backup. In their archives, the State maintains original building drawings that provide additional information about the thick masonry construction, not revealed by limited openings and removals (Figure 5).

Materials

a single stone type such as granite can vary in material properties depending on its composition and origin.

Tensile strength of historic masonry depends primarily on mortar properties and its constituents (cement, lime, and sand). The tensile strength of mortar often is assumed to be low, and generally should be considered zero for soft mortars.

In an effort to thoroughly assess the Capitol, the study team extracted brick masonry prisms for laboratory flexural and compressive strength testing to determine tensile strength, compressive strength, and stiffness properties.

FLOORVIBE v2.10

Figure 5: Tunnel Section. Detail from drawing A79: Elevation inside of dome from balcony steel trusses by Huston dated 1903. Courtesy of Joseph M. Huston.

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Masonry, the material, is strong in compression Varying and Changing and weak in tension. Shear strength often is a Conditions function of the level of compression and the direction of force application. Therefore, unre- Masonry deteriorates over time, impacting the inforced masonry structures primarily achieve overall strength and performance of the structheir strength through a combination of com- ture. This deterioration usually impacts stress pression and shear resistance, and structural levels in masonry structures and, in some cases, mass and configuration usually determine the can impact load paths. The type and extent magnitude of compression. However, masonry of deterioration of masonry/mortar can vary structures rarely are constructed to completely throughout a single structure and is dependent avoid tensile stresses, so tensile strength – low on a variety of factors, including quality of though it often is – usually plays a role in load resistance. Hence, understanding both compressive and tensile strengths of NEW VERSION RELEASED masonry is important for understanding structural performance, and potentially the overall stability.

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Figure 7: Deteriorated masonry behind granite ashlar cladding at exterior of lower drum.

Figure 6: Crack survey in tunnel of lower drum.

materials, initial construction quality, location, exposure, and maintenance program.

Cracks in brick masonry result from tensile stresses and/or shear stresses. Sources of these stresses include, but are not limited to, restraint of volume change, lateral thrusts from structural configurations, superimposed loads, and differential building settlement.

Volume change can be driven by irreversible expansion (i.e., brick growth) and cyclical expansion and contraction due to seasonal and daily temperature and moisture fluctuations.

The location, orientation, and extent of cracked or deteriorated masonry must be understood to evaluate whether the structural performance of the component and overall gravity and lateral-load-resisting systems are negatively impacted. The progression of masonry deterioration over time can lead to load redistributions, which can contribute to additional cracking and distress and further load redistribution. Masonry walls may lean, and arches/domes may flatten from lateral thrust, yet still maintain overall stability. The assessment of the extent of impact caused by deterioration and cracks requires structural evaluation with careful consideration of geometry, material properties, structural conditions, and analysis approaches.

Conditions in the Capitol The Capitol did not have readily visible signs of global displacements, but had localized

downward displacement and cracking of granite peristyle pavers below colonnades.

The arch of the circumferential tunnel had a continuous crack at its crown and transverse cracks below the colonnades (Figure 6 ).

Longitudinal cracks near the intersection of the exterior wall and tunnel floor were also observed. The systemic nature of longitudinal cracks appeared to relate to the outward thrust of the tunnel arch. The repetitive nature of the transverse cracks appeared more likely caused by the intrinsic stress pattern derived from the complicated, indeterminate configuration of the dome structure – perhaps a combination of flexural stresses from superimposed colonnades and hoop stresses. No cracks were found that were consistent with cracking due to differential settlement.

The Capitol structure had washed out mortar and deteriorated brick masonry behind granite ashlar cladding (Figure 7 ). Some delaminated masonry in the circumferential tunnel was associated with corrosion of embedded metal pipes.

These conditions required further analysis to understand the significance of the masonry deterioration and distress.

Modeling Approach Several finite element modeling methods are available to evaluate structural responses in monumental masonry construction with consideration to variety of geometry, material properties, and boundary conditions.

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Certain techniques allow modeling of the construction material as elastic or inelastic, and geometry as linear or nonlinear. Further, analysis can examine behavior in either two or three dimensions. Depending on the method and the level of detail required, the input can become quite exhaustive, the actual model run time can be extensive, and the results can become difficult to validate. The level of sophistication of the model needs to be balanced with the level of certainty about the structural configuration and materials, and the level of precision necessary to resolve performance issues.

To find a balance between model complexity and meaningful results for evaluation of the Capitol structure, a phased approach to developing a final three dimensional finite-element model was used. Initially, an independent model of the steel framed dome structure was created to compute reactions to superimpose on the masonry structure. For the masonry construction, two-dimensional models of certain components were created to conduct sensitivity analysis of a wide range of material, geometry, and boundary assumptions to estimate the effect on the model results. For instance, changes in stiffness of the granite masonry exterior, which represents a small portion of the masonry thickness, had little effect on the overall model behavior, and representative properties from published data were able to be used. Also, investigators identified an optimal element mesh size and a meaningful approach to representing cracked masonry by providing disconnects between model elements, and deteriorated masonry was simulated using zero-stiffness finite elements.

Figure 9: Radial tensile stress in lower drum.

Figure 8: Finite element model of upper drum/lower drum/arches.

Once assumptions for geometry, material, and boundary conditions were established based on the two-dimensional models, a partial threedimensional linear elastic model of half the axisymmetric structure was prepared, applying symmetry boundary conditions to represent the rest of the structure (Figure 8). Since obvious signs of settlement issues on the building were not evident, fixed boundary conditions were used at the bottom of the masonry arches.

Iterative analyses was used to evaluate deterioration and distress. The analysis started by modeling the structure without cracks or deterioration. Then cracks were introduced at areas with concentrated tensile stresses to see how the condition redistributes forces in the structure. A process of lengthening cracks was repeated, which redistributed forces until the masonry tensile stresses were well below the tensile capacities. The stresses, deflections, and stability of the structure were then reviewed. A similar iterative approach was used to evaluate the effect deterioration has on the structure.

Results

Conclusions • Load paths of monumental masonry structures are inherently complicated.

These complications are caused by initial highly indeterminate construction geometries and the fact that actual load paths evolve due to load redistribution in response to deterioration, distress, and movement.

Therefore, these load paths cannot easily be resolved with classical hand calculation approaches.

• Finite element modeling can be a powerful tool to help the investigator evaluate load paths and structural performance of a monumental masonry structure. The work at the Pennsylvania Capitol showed that the results of finite element modeling correlate well with actual performance.

• The success of the finite element modeling depends on the diligent construction of the model and its boundary conditions, and the amount and quality of actual building performance data, such as material properties derived by testing.

• As with any analytical technique, the results of the finite element model must be carefully augmented by, and

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scrutinized against, the results of other approaches. Finite element analysis is but one of several techniques, the most important of which is the investigator’s own engineering judgment, that must be deployed in the evaluation of monumental masonry structures.

The authors acknowledge the support of the State of Pennsylvania’s Department of General Services, the architecture firm of Perfido Weiskopf Wagstaff & Goettel, and the partners of Simpson Gumpertz & Heger.▪ R. Scott Silvester, P.E., is a Senior Project Manager at Simpson Gumpertz & Heger (SGH) in the Structures Group.

Christina T. Parker, P.E., is a Senior Staff – II at SGH in the Building Technology Group.

Niklas W. Vigener, P.E., is a Senior Principal at SGH in the Building Technology Group.

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The results of the analysis correlated well with the observed conditions of the masonry construction. Under gravity loads, the model showed tensile stresses that exceed tested capacities where there were cracks in the actual brick masonry (Figure 9). The results of the iterative analysis demonstrated redistribution of tensile and compressive stresses with reasonable magnitudes and continuity of load path through the masonry of the lower drum, even with cracks and deterioration. Consequently, the cracking and deterioration were not cause for concern about the structural integrity of the lower drum. Finite element analyses raised confidence levels in this conclusion.

Continued masonry deterioration and propagation of masonry cracks can increase

the stresses in the remaining competent masonry, cause further deformations of the lower drum, and increase the width of the circumferential cracks in the crown of the tunnel. Since moisture likely contributed to existing deterioration, it was prudent to continue a planned program of masonry repairs to protect the structure from moisture intrusion along with recommending future monitoring.

Wolf Girders – A Function Driven Solution The First Precast Open Box Girders for Phoenix and Arizona

By John A. Lobo, P.E., S.E. and David A. Burrows, P.E., LEED AP BD+C This is the second in a series of articles about the components of the new PHX Sky Train™ in Phoenix, Arizona.

Part 1 of the series was published in the July 2013 issue of STRUCTURE magazine, and Part 3 will appear in an upcoming issue.

PHX Sky Train route map.

T

he initial 2-mile stage of the nearly 5-mile long PHX Sky Train™ opened on April 8th, 2013. The Sky Train is a planned automated transit system that will link the terminals of Phoenix Sky Harbor International Airport (PSHIA) and the economy parking lots at the east and west end of the airport with the consolidated rental car facility and the valley’s Light Rail system. The system provides a fast, safe, convenient, and more sustainable transportation link that will serve an expected 2.5 million passengers a year and provide the springboard for future growth.

Currently operating, Stage 1 is approximately 2 miles long, with over 1.5 miles elevated, including three stations. Stage 1A, which is under construction, is expected to become operational in early 2015, and extends the system by another ¾ mile to a fourth station. The elevated guideways comprise a variety of structure types, from steel girders to cast-in-place post-tensioned box girders to precast prestressed concrete girders. This mix was dictated primarily by constructability and cost considerations. The Airport elected to execute this project through a Construction-Manager-At-Risk (CMAR) who was selected early in the design process and provided crucial input to the facilities design team regarding optimum choices for different sections of the system. The precast open-box girders for a majority of the elevated guideway is one of the most visible examples of a design choice influenced by the input received from the CMAR. This article discusses the process behind selection and evolution of the open-box girder used in the guideway.

STRUCTURE magazine

From Cast-In-Place to Precast Cast-in-place (CIP) post-tensioned box girders are a common and popular choice for bridges in Phoenix and across Arizona, and were a natural initial choice for the elevated guideway. The CIP box girder is well suited to the curved alignment of the train and the typical span lengths under consideration, and all local contractors are experienced in construction procedures. This structure type was chosen in the 30% design documents used in selection of the CMAR. The CMAR suggested that precast concrete girders might be better suited to construction within the airport, with advantages in cost, time of construction and reduced congestion due to elimination of falsework and cited the success of a precast girder system in a similar airport train system they had recently completed. They brought this suggested change to both the designer and owner for further discussions. The owner liked the potential cost and time savings, but preferred the clean shape of the CIP box girder to the more angular appearance of the standard precast I-girder alternative typically used in Arizona. The CMAR’s previous project used a combination of two different shaped precast girders in conjunction. The precast Texas U54 box girder was placed in the more visible location, partially shielding the AASHTO Type IV girder. However, the Texas standard box girder is not used in Arizona, and local precasters had no experience in their construction nor the forms or infrastructure required.

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The changes and modification of the U-beam concept as design progressed.

The elevated guideway under construction, showing erection of the U-beams.

Selecting and Optimizing the Shape

www.iesweb.com

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The CMAR facilitated a meeting between the designer and a local precaster to discuss options. The cost of using standard box girders from another state was obviously high. Discussions therefore focused on the advantages and disadvantages of paired girder types versus a system of all AASHTO I-girders, either all Type IVs or Type Vs. The mixed girder type was the most expensive, with additional cost premiums because of the limited quantities of each type of girder. However the project had been approved and presented in numerous public meetings using the trapezoidal box girder shape, and the owner was reluctant to abandon the agreed upon structure in favor of an exclusively I-girder system. Given the general consensus against a mixed girder system and the need to retain a trapezoidal box girder look, the designer suggested The completed elevated guideway in service. the obvious next step – to adopt a system of precast open box girders, with an additional question of whether it would be more economical two of them beneath the seventeen foot wide deck. The designer to adopt a standard Texas girder or a simpler shape. This question was looked at using a narrower version of the U54 by removing a one discussed in a meeting with a local precaster, facilitated by the CMAR, foot width from the bottom flange, to match the width established and the designer decided, with the agreement of both the owner and in design of the rabbit-ears girder. This effort was not carried further CMAR, to design a simple trapezoidal precast concrete box girder that would be easy and economical to build locally.

The design started with the simplest trapezoidal shape, but that shape was quickly abandoned. The lack of a top flange shifted the centroid of the girder Structural Software Designed for Your Success excessively towards the bottom, and it was extremely difficult, if not impossible, to provide sufficient prestressing force to * Easy to Learn resist service conditions without dam* Analyze Anything aging the girder during the prestressing * Design for: process and erection. This established the + Steel need for top flanges and the “rabbit ears” + Wood option followed, with greater success. Top + Concrete width of the section was driven by the + Aluminum minimum width of the guideway deck, + Cold-Formed and depth of the section and thickness of * Friendly Support the flanges was optimized though iteration. While Arizona has not used precast trapezoidal box girders and has no standard shape, there are several states that have standardized these types of girders, including Colorado, Florida and Texas, with the Texas “tub-girders” being perhaps the most widely known. The design team decided to look at the possibility of using Free 30-Day Trial the standard Texas shape as an alternative to an all new customized shape. However, IES, Inc. | 519 E Babcock St. Bozeman MT 59715 the team found that the standard Texas 800-707-0816 | info@iesweb.com U-54 beam was a little too wide to fit

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since the capacity of the modified beam restricted the Wolf AASHTO AASHTO Texas span lengths to 80 feet or less. Also, any cost savings Girder Girder Type IV Type V U-54 Tub from use of a standard shape would be lost if the forms had to be permanently modified.

Weight plf 1,099 822 1,055 1,167 The designers noted the details of the Texas U54 beam Depth in 60 54 63 54 and decided to incorporate some of the details into the 2 1,055 789 1,013 1,120 Cross-sectional area in final custom shape, thus creating the final version of the girder that was subsequently nicknamed the “Wolf Moment of Inertia 260,730 521,180 403,020 in4 466,415 girder”, an internal joke on the name of this designer that was not adopted officially on the project. A key Performance in Service detail adopted from standardized sections was the chamfers in the top flange that facilitate stripping of the forms without damaging While the design used some standard geometry from Texas tub girders, the concrete girder. The designers also drew on existing knowledge the difference in depth and width of the Wolf girder precluded use of in standardized open girders when detailing mild steel reinforcement, existing forms. US Concrete Precast Group, who won the contract to skewed ends and spacing of internal diaphragms. provide the 11,000 linear feet of Stage 1 girders, opted to use a custom built girder form. The self-stressing form provided the reaction to the prestress jacking force, eliminating the need for bulkheads. In the case Comparison with AASHTO I-Girders of Stage 1A, the precaster, TPAC, used custom built conventional metal The Wolf girder is comparable to AASHTO Type IV and Type V forms. The Wolf girder used only straight strands, with debonding at girders, as seen in the Table. the ends to control initial stresses, and hence both precasters did not The Wolf girder is about 25% heavier than an AASHTO Type IV require hold-downs or a structural slab beneath the girder. but offers approximately 50% more capacity, for an overall 25% better The casting and stressing of the girders was largely incident free. In the strength to weight capacity. AASHTO Type V girders are approxi- case of Stage 1 girders, the precaster used a high workability mix that mately 15% more efficient than Wolf girders. However the alignment facilitated placement of concrete. For Stage 1A, the project team allowed and column arrangement dictated by existing ground conditions did the use of Self Consolidating Concrete that had been recently approved not allow for optimum span arrangement, and the Type V girders for bridge girders by the Arizona Department of Transportation. In both did not provide a saving over the Wolf girder. A preliminary estimate cases the result was a high quality surface finish with minimal blemishes. showed that that the elevated guideway would contain 19,000 LF At this time, the Stage 1 girders have been in service for approxiof Type IV girders or 15,000 LF of Type V girders, but only 11,000 mately 3 months, in addition to the period of systems testing, and LF of Wolf girders. have performed extremely well. Stage 1A girders were erected late in 2012 and the deck was cast earlier this year, with no notable problems reported VERNONIA K–12 SCHOOL, VERNONIA, OR / PHOTO BY: LINCOLN BARBOUR in construction or performance.

The Wolf Girder, the first major use of a precast open box girder in Arizona, was developed to meet a specific need on the Sky Train project and has performed as well as expected, blending structural efficiency and stability with an aesthetically pleasing form. This girder will be used not only on the upcoming Stage 2 of the Sky Train, but having proved its worth will hopefully be adopted for local projects in Phoenix and elsewhere in Arizona.▪ John A. Lobo, P.E., S.E., is a senior bridge engineer at HDR, Denver, CO. He was lead designer for the precast portion of the elevated guideway and a member of the Sky Train fixed facilities design team for 10 years. He can be reached at John.Lobo@hdrinc.com.

WINNER OF THE

2012 AIA PORTLAND PEOPLE’S CHOICE AWARD

Seattle • Tacoma • Lacey • Portland • Eugene • Sacramento • San Francisco • Walnut Creek • Los Angeles • Long Beach • Pasadena • Irvine • San Diego • Boise • Phoenix • St. Louis • Chicago • New York

David A. Burrows, P.E., LEED AP BD+C, is a senior structural engineer at Gannett Fleming, Phoenix, Arizona.

He was the lead engineer for the design of the Taxiway R crossing. David can be reached at dburrows@gfnet.com.

All photos courtesy of Gannett Fleming, Inc.

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Education issuEs discussion of core requirements and continuing education issues

A

lthough continuing education is known by a number of different acronyms, – CEU (Continuing Education Unit), PDH (Professional Development Hour), CPC (Continuing Professional Competency), CPD (Continuing Professional Development) and CE (Continuing Education) – the purpose of requiring licensed professionals to obtain it is the same: to assure an engineer’s ongoing competency in order to safeguard the life, health, property and welfare of the public.

CPC requirements for engineers are established by each state licensing board, and can also be found in the National Council of Examiners for Engineering and Surveying (NCEES) Model Law/ Rules and CPC Guidelines. It should be noted that 0.1 CEU = 1.0 PDH; however, some CE certifying entities define 1.0 PDH as a minimum of 50 minutes of contact time during a one-hour CE activity. In addition, none of the state boards indicate whether the time required to take a test

Continuing Education Understanding CE Requirements for Professional Structural Engineers

By D. Matthew Stuart, P.E., S.E., F. ASCE, F.SEI, SECB, MgtEng

Licensing Board Survey The following discussion is intended to help summarize the pertinent results of a survey that the author conducted, as a part of the development of this article, of the licensing boards relative to what kinds of CE activities are acceptable or unacceptable, and reasons why a CE course or activity is typically rejected. More details are included with the online version of this article at www.STRUCTUREmag.org.

Typical Acceptable CE Activities:

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

associated with a CE activity should be included, but the International Association for Continuing Education and Training (IACET) does allow inclusion of the test time in the CEU calculation.

To some structural engineers, the effort required to acquire and maintain a CE record in order to obtain and renew their professional licenses seems like a complete waste of time. Others recognize the value of CE as a critical part of professional licensing and career development. The author’s personal opinion is that CE is a crucial part of his ongoing professional competency. Nevertheless,

Although acceptance criteria may vary, the primary objective of CE is the same from state to state: to maintain, improve or expand the skills and knowledge relevant to the licensee’s field of practice. Generally speaking, all state boards accept courses in ethics; technical subject matter; topics that contribute to the health, safety and welfare of the public; and laws and regulations pertaining to engineering practice. A majority of state boards will also accept courses in project management, dispute resolution, and contract administration. Some state boards may accept courses in accounting, leadership, business or office management, or personal improvement.

Typical Unacceptable CE Activities: In general, an activity is unacceptable to any state board if it is not relevant to either the professional skills or scientific knowledge related to the practice of engineering. Unacceptable activities include taking part in sightseeing tours, participating in general business meetings, attending a

product demonstration show, or taking courses unrelated to the profession. Examples of unacceptable course topics include, but are not limited to, marketing, estate or financial planning, insurance, and real estate. Some state boards also do not accept courses in accounting, leadership, business or office management, or personal improvement. Self-study credits are usually not acceptable unless there is a quiz administered by a third party.

Reasons Why a CE Course or Activity is Rejected: CE courses or activities are typically rejected only during an audit. Typical reasons that a board will use as a basis for rejection include: • Courses offered by a non-approved sponsor when pre-approval is required.

• The subject matter is not related to the profession.

• The subject matter is not deemed to contribute substantially to the practice of engineering.

• Repetitive attendance of a course or activity.

• The date of the course or activity did not occur within the registration period.

• Inadequate documentation; e.g., the certificate is provided in a foreign language or no certificate of completion is provided.

• Unverifiable attendance or participation.

• Incomplete courses or activities.

• Self-study hours without proper documentation.

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between each state can make it challenging for engineers licensed in multiple states to acquire and document PDHs that serve to comply with all of the states in which they are licensed. Most states also do not require that you obtain the necessary CE upon your initial registration, or at the first renewal following the initial licensure. However, this waiver does not necessarily apply to comity, reciprocity or reinstatement applications.

Another variable that exists between the states is the ease with which the licensee can document PDHs. Some states merely require that

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you check a box that attests to your fulfillment of the CE requirements, while other states (e.g.

West Virginia) necessitate the cumbersome and time-consuming documentation of all CE via detailed online entry forms that are not very user-friendly. It should also be noted that the minimum period of time that PDH records must be retained varies from state to state, although the typical period is two to four renewal cycles (normally three to six years).

An interesting trend in continuing education requirements is the growth of “correspondence”type CE courses, which include the use of

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there have been some CE opportunities in which he has participated, including preapproved material, where the value of the time spent to sit through the session was questioned because of the poor quality of the presentation and/or its content.

The fact remains that since CE was first mandated by the Iowa board in the 1970s, additional state Boards have adopted provisions in their licensing laws such that now approximately 72% of jurisdictions currently require it. It is therefore very likely that most, if not all, of the state boards will eventually adopt CE requirements. In addition, it is the author’s understanding that there has been an increasing interest in establishing consistency between the many different CE requirements by the state board delegates that are involved directly with NCEES. Although a majority of the state boards already mandate continuing education, requirements vary considerably from state to state. These variations include provisions for a minimum number of PDHs in mandatory topics (such as ethics), a minimum number of live PDHs, the total number of PDHs required per renewal period, and whether or not courses/providers must be pre-approved.

A survey of all of the U.S. state and territory boards, conducted as a part of the development of this article (see Licensing Board sidebar), indicates that currently a total of 39 states have CE requirements, only seven of which (Florida, Indiana, Louisiana, Maryland, New Jersey, New York and North Carolina) pre-approve CE providers or courses.

Some states are also very liberal with what is considered a CE activity. New Mexico, for example, allows subscription to a technical journal or trade publication for the first 12 months of the biennium reporting period to count as 1.0 PDH. Similar to CE rules in a number of Canadian provinces, a few states also allow for a portion of an engineer’s work experience to count toward the CE requirements. Many states allow participation in a professional society to count as a CE activity; however, a number of these same states require that the participation include either membership in a committee or a position as an officer in the organization.

It is not necessary to obtain separate and distinct PDHs for each state in which you are licensed, so it is possible to claim the same PDHs for a number of different license renewals. However, the variation in CE requirements

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Continuing Education Organizations The following is a list of organizations/entities that are involved in the CE process for engineers in one way or another. A description of the group’s capabilities and relationship to CE for engineers is also provided.

AIA CES The mission of the American Institute of Architects (AIA) Continuing Education System (CES) is to assist its members in satisfying the professional learning requirements of the many state and territorial licensing boards for architects.

However, many professional engineers also participate in AIA CES opportunities under the assumption that professional engineering boards will likewise accept the activity. Similar to engineering licensing boards, the state architectural licensing board requirements for CE vary; however, AIA is currently working with the National Council of Architectural Registration Boards (NCARB) to standardize them.

The continuing education requirements for AIA members are listed below.

1) Complete 18 hours of Mandatory Continuing Education (MCE) or Learning Units (LU) each year by December 31st.

2) 12 of the 18 hours must be related to HSW (Health, Safety & Welfare) topics.

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magazine articles and online courses as a source of PDHs. Currently, the NCEES CPC Guidelines, under the section titled Other Course and CPC Activities, indicates that a “correspondence” course is allowed as long as there is evidence of achievement and completion of a final graded exam; “self-study” activities are not allowed.

At the time that NCEES was involved with

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3) As of 2013, at least 8 of the 12 HSW hours must be related to sustainable design.

4) HSW credits must be completed by taking qualifying courses from a registered AIA CES provider only.

5) HSW credits must be reported directly by AIA CES registered providers.

In addition, the AIA CES pre-approves CE courses and providers, provides a list of available courses, and provides a recordkeeping service. “Self-reporting” CE activities are not administered by an AIA CES provider, but are eligible for LU credit.

Self-reporting CE provides an avenue for AIA members to log credits outside of the AIA CES on their transcripts.

The International Association for Continuing Education and Training (IACET) is a nonprofit organization that promotes quality in the field of CE. IACET is responsible for the development, implementation and maintenance of the ANSI/IACET Standard for continuing education and training. This

standard is organized around research-based practices that have been proven effective in addressing individual, organizational and/or social needs.

In 1968, a group of individuals concerned about the lack of recordkeeping for continuing education and training activities – who came from academia, professional associations, business, health professions and government – formed a national task force.

In 1970, they created the CEU, defined as equal to ten contact hours of participation in an organized continuing education experience that was responsibly sponsored and provided adequate direction and qualified instruction.

A CEU can include the time required to complete a quiz, but does not include nonworking lunch or personal breaks.

IACET currently accredits over 500 continuing education and training providers across all industries. The IACET standard has ten categories that a provider must satisfy including the requirement that records be maintained for at least seven years. While IACET accredited Authorized Providers are only formally recognized by the New York and Florida licensing boards, they are also accepted by every state.

the Registered Continuing Education Program (RCEP, see Continuing Education sidebar), “self-study” was defined as an asynchronous or “flat” activity in which the time spent could not be controlled.

NCEES did not allow “self-study” courses because of the assumed difficulty that the state boards would have in evaluating PDH credits for activities where there was no method to regulate the amount of time a professional participated. However, a subsequent survey of the licensing boards that the author conducted in 2006 concerning the acceptance of “flat” asynchronous distance learning (ADL) determined that only one state (New Hampshire), of the 19 boards that replied, specifically did not accept this type of CE. (A copy of this survey is available with the online version of this article at www.STRUCTUREmag.org.)

The RCEP, which is now administered by the American Council of Engineering Companies (ACEC), allows ADL “selfpaced” activities, but they must first be tested via a pilot program by at least

ten professionals in order to determine the number of PDHs to be granted. However, the RCEP restricts from the ADL application process those CE providers that only offer traditional self-study, non-interactive courses.

IACET also allows “self-paced” programs by providers that can satisfy all ten categories of its ANSI-accredited standard. Similar to the RCEP provisions, this includes the establishment of a standard number of CEUs for the course via a pilot program by selecting a representative sample audience of five to ten participants to complete the event. The time spent by each member of the sample is then totaled and averaged to determine the number of CEUs for the course.

As the number of states requiring CE has increased, so has the number of entities providing opportunities to obtain it. Sources of CE for engineers include a wide range of providers from online universities and colleges to more traditional sources such as material and product venders and suppliers. The preferred venues for CE activities have also shifted from lengthy live seminars offered in just a few

IACET

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myLearning

NSPE

The American Society of Civil Engineers (ASCE) myLearning system (www.asce. org/Continuing-Education/myLearning/) is available to members as a part of their regular dues. The myLearning system provides a searchable catalog of ASCE’s CE courses, online testing and grading, online PDH certificates, and PDH recordkeeping and transcript services. To pass a quiz, one must answer at least 70% of the questions correctly. There are several reasons why ASCE has its own myLearning system and also supports the RCEP program. First, myLearning has a number of capabilities that the RCEP system does not offer, including the ability to take automatically graded tests online. Second, myLearning assures that ASCE is in compliance with and remains a member in good standing of IACET. Maintaining ASCE’s IACET Authorized Provider accreditation is important, as it helps to assure that the CEUs and PDHs awarded by ASCE are accepted by state licensing boards that have a continuing education requirement.

Third, the RCEP provides ASCE members with the ability to search courses offered by other societies and organizations in addition to ASCE if they are not able to find topics in myLearning.

The National Society of Professional Engineers (NSPE) provides an online list of CE providers who follow the NCEES Model Law/Rules and CPC Guidelines (www.nspe.org/Education/index.html).

The website also provides a list of available webinars and on-demand courses, as well as a summary of the CE and licensure requirements for each jurisdiction. NSPE requires that each participant in a session take and pass a quiz to receive credit. To pass a quiz, one must answer at least 70% of the questions correctly. Records of all quiz results are maintained and available for inquiries from individuals or states; however, individuals are not able to access their records directly.

NSPE is not affiliated with IACET. The most popular NSPE courses involve ethics.

NCEES Other than its initial involvement with the RCEP and the development of its Model Law/Rules and CPC Guidelines, NCEES has no direct involvement with CE for engineers and currently only provides links to the state licensing boards on its website for additional information (ncees.org/licensing-boards/).

The Practicing Institute of Engineering, Inc. (www.practicinginstitute.org/) evaluates and approves CE providers and courses for the New York State Board only; however, a number of other state boards accept New York approved CE opportunities. PIE does not use the NCEES Model Law/Rules and CPC Guidelines, and instead follows New York laws as the basis for evaluating CE opportunities. PIE does not maintain records for individuals; instead, each engineer is responsible for maintaining his/her own PDH log.

RCEP The Registered Continuing Education Program, which is now administered by ACEC with the support of ASCE, was originally developed by NCEES in conjunction with ACEC. The RCEP (www.rcep.net/) is a registry of CE providers who follow

Acknowledgements The author would like to thank the following individuals for contributing to this article: Sara Meier, CAE, Executive Director, IACET Marie D. Ternieden, Ed.D. Vice President, Business Resources and Education, RCEP John Huang, Ph.D, PE, LEED AP, PDHonline/PDHcenter John A. Casazza, CAE, Aff.M.ASCE, Managing Director, Continuing Education, ASCE

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SECB To the best of the author’s knowledge, other than the ACEC MgtEng Certification, SECB is the only professional organization outside of the state boards that requires PDHs as a part of its certification process (www.secertboard.org/recertification.htm).

All electronic, web-based continuing education credits for SECB can only be obtained from pre-approved providers associated with 17 professional organizations. Rather than using the NCEES Model Law/Rules and CPC Guidelines, the SECB PDH requirements were developed based upon what the members of the Board of Directors believed were appropriate for structural engineers because of a concern that state boards do not scrutinize the content of CE adequately. Other than providing carryover PDHs as a part of the form that must be filled out for the recertification process, SECB does not provide a recordkeeping service for its members. The website provides a listing of CE and licensure requirements for each jurisdiction. SECB is not affiliated with IACET.

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major cities to shorter and more convenient distance learning, such as webinars that are offered to individuals or groups of participants at multiple office locations. The corresponding cost of CE activities has also broadened, when you compare the expense of university programs to free “lunch and learn” presentations by material and/or product venders, and all day, long-distance seminars vs. shorter online webinars.

The bottom line is that there are a lot of CE opportunities to choose from, some of which are good and some not so good. Licensed engineers must therefore be very discerning when selecting a topic and/or provider in addition to evaluating the cost.▪

PIE

the NCEES Model Law/Rules and CPC Guidelines. The website provides links to registered providers and a master calendar of scheduled and on-demand educational activities. In order for an RCEP provider’s quiz to be passed, the minimum number of questions that must be answered correctly is 70%. The RCEP also provides recordkeeping of CE certificates of completion, transcripts, and career documents, which can be made available to state licensing boards. Although PDHs are automatically uploaded into the user’s record by the provider, the user can also upload logs from other CE activities. In addition, the website provides a listing of CE and licensure requirements for each jurisdiction. The RCEP is not affiliated with IACET.

Business Practices

business issues

Delegated Design It is All about Communication By the CASE Guidelines Committee

P

roject design and delivery systems have become more and more complex. The days when the Structural Engineer of Record (SEOR) designed all aspects of a project in a straightforward design-bid-build environment are becoming few and far between. Today, with the pressures on construction cost, design fees, and design and construction schedules, SEORs are looking to do more for less fee and in less time, while also delivering superior service. So, in addition to delegating the responsibility for the design for secondary structural elements (such as stairs, cladding, elevator rails, etc.), SEORs are also delegating the responsibility for the design of many primary structural elements (such as steel joists, metal deck, precast concrete slabs and beams, etc. in addition to traditional connection design) to a Specialty Structural Engineer (SSE). All of these elements introduce additional structural engineers into the process and, given concurrent changes in the design and delivery systems (design-build, designassist, integrated project delivery, etc.), it is not surprising that project participants have differing opinions as to what is the “design” and who has the ultimate responsibility for it.

In such environments, the SEOR’s relationship with the SSE may be tested and strained and may become confrontational, particularly if the process is not managed well or if the motive of the SEOR for delegating is less than altruistic. Obviously, this is not the desired SEOR/ SSE relationship; the project will be better served with an atmosphere of trust, openness, understanding and cooperation. The owner, contractor, subcontractor and design team will all benefit from a non-controversial attitude with appreciation and acceptance of each other’s knowledge, expertise and experience.

Communication There are three keys to this or any relationship, and they are not new. They are communication, communication and more communication that is clear, concise and non-compromising.

The first step is the proper delegation of design responsibility and a well-defined scope of services within the SEOR’s initial engagement on the project. The Owner and the SEOR need to

…it is not surprising that project participants have differing opinions as to what is the “design” and who has the ultimate responsibility for it. agree to what will be designed by the SEOR and what aspects of the project will be designed by SSEs. It continues with concept development, the preparation of the specifications and construction documents, and is followed by pre-bid and pre-construction conferences. However, the process is not complete until the SSE’s submittals have been reviewed by the SEOR to confirm that the SSE’s interpretation of the design criteria is appropriate and acceptable, and the totality of the work is coordinated and complete.

Primary and Secondary Structural Elements The issue that has most complicated the relationship between the SEOR and SSE has been the recent trend of including primary structural elements in the process. Design delegation of secondary structural items such as stairs, handrails, davits, and elevator support rails and beams, has been accepted for some time; their design is governed by time tested industry standards and practices. However, the delegation of the design for primary structural elements such as light gage trusses, wood trusses, structural precast concrete panels, post-tension concrete members, metal deck, and structural steel connection design has established the necessity for the SEOR to fully define the loading, design criteria and performance standards for each primary structural element to enable the SSE/subcontractor to properly develop their design/proposal.

While the secondary systems are important to the functionality of the completed structure, the primary systems have unique needs associated with structural stability and coordination requirements of code compliance and public safety. Therein lies the rub. The SEOR’s delegation of the design of primary structural elements to an SSE requires project specific loading, design and acceptance criteria, and a comprehensive understanding of how the

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entire, sometimes unique, structural system is to perform while secondary elements may be acceptable as more standardized “off-theshelf ” type items. As a possible rule of thumb, to develop a base line for what information is needed by the SSE, the SEOR needs to ask the question “what would I need if I had to design it myself?” More often than not, the SEOR probably does not spend as much time thinking about the “to be delegated” items, as he believes that the responsibility has passed on to the SSE and they are now someone else’s concern. This is definitely the wrong attitude to have, since the responsibility for the entire project still lies with the SEOR. If various SSEs design less than adequate systems based on poorly drafted or considered design and performance criteria, the result will be a poor project with many design and construction problems. In a worst case scenario, the SEOR will wish that he had just designed the delegated systems in-house.

As an example of possible pitfalls, roof systems like steel joists, light gage trusses and wood trusses may require special loading as necessary for snow drift, mechanical units, solar panels, roof drain piping, seismic bracing, and sprinkler piping. The snow drift and roof drain piping loading are definable and should be shown on the contract documents. On the other hand, mechanical units loading and size may not be known until a mechanical subcontractor has been selected and requires the SSE to coordinate with the general contractor.

Seismic bracing loads will be provided to the SSE by another SSE who was selected to design anchorage and bracing for piping and equipment. Sprinkler piping is even less defined than the mechanical units. Many times, the only information known about the sprinkler system is the location of the water line entering the building. Again, the layout and loading from the sprinkler is known after the sprinkler subcontractor is selected and the system is designed

Standards But let’s go beyond the not so straightforward issue of developing specific design and performance criteria. How is the delegated design going to be achieved and what standards are going to be followed? There are many important issues to consider: • Do you understand the industry code of standard practice for the element being delegated? Does it even exist? Is it insurable?

• If you don’t like what is in the code of standard practice, you have the opportunity to change it via the contract documents. Do you know what needs to be changed? Does your understanding of the code enable you to be certain that a particular change does not impact other aspects of the code?

• Is the SEOR responsible for specifying and also verifying the qualifications and experience of the SSE? • Is there a means to ensure that the SSE has interpreted the SEOR’s requirements properly during the bidding stage?

• Who is responsible for the coordination and/or compatibility of the primary structure (designed by the SEOR) with the delegated design portion (designed by SSE)?

• How are the material quantities, details and loadings of the delegated design portion being accounted for in the final design by the SEOR? • Who is responsible for the final product? Again, communication plays a key role.

• What is the impact of the elements designed by the SSE on the primary structural system?

• Must SEOR review the results of the SSE’s design to establish compliance with the governing codes and specifications?

Triple Protection Against Corrosion Increase Corrosion Resistance

Selecting the SSE After the scope of work, including the project specific loading, design and acceptance criteria, is defined, the next step is the selection of the subcontractor. To ensure the contractor’s SSE is knowledgeable and experienced in the design of the designated elements, the SEOR should establish in the contract documents the minimum qualifications and experience of the SSE. One might say that the subcontractor that is retaining the SSE should be responsible for his selection, and ultimately the subcontractor will have to live with the designs prepared by his SSE. However, a poor selection, possibly the low bidder, may lead to not just the subcontractor having issues but the total design and construction team having to live with the poor results, extensive rework or modifications and the possibility of litigation.

The possibility of litigation leads to the question – does the SSE have liability insurance and, if so, how much? Is it sufficient based on the nature of the element and its importance in the strength and integrity of the overall structure? It is important to note that being a licensed Professional Engineer or licensed Structural Engineer does not mean that he or she has the knowledge and experience to perform the design services needed.

It is imperative that the SEOR’s contract documents adequately define the SSE’s qualifications and experience requirements.

Use in areas susceptible to corrosion and chloride

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Increase the life expectancy of metals, steel and rebar

Limits on Delegation What about the material that has not been designed and is to be designed after the bids have been taken? If the bids or proposal to do the work establish qualifications to these unknown quantities, this can lead to controversy. Again, establishing the complete scope,

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by his SSE. The fundamental issue with these unknowns is whether the SSE is aware they exist so that he is not blindsided after or during his design effort. The owner will not be happy to be drawn into a war between the SEOR and the contractor and a small army of SSEs. As another example, the Steel Joist Institute (SJI) 2010 Code of Standard Practice for Steel Joists and Joist Girders states that the SEOR shall “calculate and provide the magnitude and location of ALL JOIST and JOIST GIRDER LOADS”. The term “ALL” implies a level of completeness that might not be achievable by the SEOR. There will probably be some unknowns that the SEOR will need to make the SSE aware of, and there are loadings that will require his coordination with other trades.

This SJI Code also identifies five (5) options that are to be used to specify joist design loads.

The SEOR shall use one of the five options to allow: • The estimator to price the joists; • The joist manufacturer to design the joists properly; or • The owner to obtain the most economical joists.

These issues of properly estimating the cost, properly developing the design and providing the economics for the Owner seem to be creditable goals for the relationship of the SEOR and the SSE.

definition and responsibility of the work to be performed by the SSE is the principal duty of the SEOR. While the construction documents, drawings and specifications are the primary tools, the pre-bid and pre-construction conferences can be useful in clarification and confirmation that the project requirements are understood.

The 2010 AISC Code of Standard Practice (COSP, AISC 303-10) includes a codification of an undefined and uncontrolled but widely employed industry practice that had existed since the 1960s. Section 3.1.2 defines the connection design or selection process, identifies the loading and connection information that must be supplied by the SEOR and SSE, and addresses any project or design concept specific issues or restraints that are to be considered.

The COSP has designated delegated steel connection design as Option (3). This option is to be noted “In the structural design drawings or specifications, the connection shall be designated to be designed by a licensed professional engineer working for the fabricator”. The COSP establishes the information needed by the SSE and emphasizes needs for conferences, pre-submittals and proper review and approval by the SEOR. The CASE Guidelines Committee has recently published a white paper on this facet of

delegated design in A Review and Commentary of the American Institute of Steel Construction 2010 Code of Standard Practice for Steel Buildings and Bridges. Incorporated in this new document are examples of Pre- Bid and Pre-Construction Conferences agendas.

The ability to delegate design elements may also be limited by local building codes, regulations, and professional licensure requirements.

When developing standard language for inclusion in contracts, the SEOR should review these requirements before attempting to delegate design responsibilities. A local jurisdiction may have specific code language requiring the SEOR to design items which are not normally included in the SEOR’s basic services. On those occasions, the SEOR should address those secondary items, modify the contract documents accordingly and include the design of these elements in his basic services and not delegate the design of such elements.

Summary In summary, it is important to view delegated design as a way to achieve the best possible project result for the owner given the project constraints on fee, schedule and quality. It is obviously a complicated process that requires

considerable knowledge and skill in order to achieve success. Communication is the key, and it starts at the very beginning of the project. It requires that the SEOR continually thinks about what will be needed by the SSE, how best to specify the requirements of the design, how to define the process and how the interaction of other designers is going to work, and who can and cannot be an SSE. It is much easier to discuss concerns and issues as the project is developing during the design phase or in the pre-bid/pre-construction meetings, than it is to correct the problems after the fact. You are part of a team, and part of the process, so be proactive within your discipline and promote efforts to coordinate. Insist on two-way communication with an open mind to ensure the best understanding possible to those interpreting your design and intent.▪ The goal of The Council of American Structural Engineers (CASE) is to promote excellence in structural engineering business practices and risk management. The information presented in this article was developed by CASE members who volunteer their time and expertise to advance the structural engineering profession.

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Thanks to you & SEAOI for offering it via the Web.”

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Anchoring guide American Wood Council

Phone: 202-463-2766 Web: www.awc.org Product: ANSI/AF&PA SDPWS-2008 Description: Special Design Provisions for Wind and Seismic standard with Commentary; covers materials, design, and construction of wood members, fasteners, and assemblies to resist wind and seismic forces.

CSC

Phone: 877-710-2053 Web: www.cscworld.com Product: Tedds Description: Automating your everyday structural designs, Tedds broad library includes anchor bolt design per ACI 318 Appendix D. The calculation includes comprehensive checks for tensile and shear failure of anchors and is available as part of a free trial at the website.

Product: Fastrak Description: Software for designing structural steel buildings using a single model, also provides an integrated design of anchor bolts.

All Resource Guides and Updates for the 2014 Editorial Calendars are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

Anchor Bolts, Concrete, Façade, Geotechnical, Masonry, Post-Tensioning, Reinforcing and Utility Anchors, and General Hardware & Ties

CTP

Phone: 219-878-1427 Web: www.ctpanchors.com Product: Concealed Masonry and Stone Panel Description: Non-corrosive restoration anchors used to re-anchor masonry facades to various building materials.

Decon® USA Inc.

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

Gripple Inc.

Phone: 630-406-0600 Web: www.gripple.com Product: Gripple Spider Description: A cast-in-place insert/hanger solution for concrete ceilings, the Spider is installed prior to the concrete pour. From the ground, a special Swivel Toggle cable hanger inserts into the Spider and locks in place to provide a secure hanging point for ductwork or other suspended services. Sold in a ready-to-use kit.

Halfen USA

Phone: 800-423-9140 Web: www.halfenusa.com Product: Anchor Channels Description: Halfen Anchor Channels are typically hot dipped galvanized with welded I-anchors. They are foam filled to keep concrete out of the channel cavity while the concrete is poured and vibrated. A t-bolt is used for attachment. There is no welding or drilling required onsite.

Hayward Baker

Phone: 800-456-6548 Web: www.haywardbaker.com Product: Anchors – Ground or Rock Description: Hayward Baker Inc., provides permanent, temporary, and removable ground and rock anchors for support of excavations, permanent resistance of hydrostatic uplift forces on bottom slabs, and resistance of windinduced uplift forces. Hayward Baker also provides the full range of geotechnical construction services.

Heckmann Building Products, Inc.

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Hohmann & Barnard

Phone: 631-234-0600 Web: www.h-b.com Product: Sharktooth Insert Description: An adjustable anchor for Precast, Relief Angles and Partition Top applications with working loads up to 8,000 lb/ft.

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Product: Thermal 2-Seal Wing Nut Tie Description: Features a Polymer Coated Steel Wing that is encapsulated in UL-94 Plastic to reduce thermal transfer through rigid insulation and wallboard.

ITW Commercial Construction, North America

Phone: 630-825-7900 Web: www.itwredhead.com Product: Epcon S7 Description: Epcon S7 is the new fast cure, all weather code approved Red Head adhesive! This hybrid adhesive has the ability to work fast with the strength and reliability of an epoxy. Formulated and code approved for use in water saturated, submerged and damp holes (ICC-ES ESR 2308).

Powers Fasteners

Phone: 985-807-6666 Web: www.powers.com Product: Post-installed Concrete Anchors Description: IBC Listed/Compliant Anchors: Powers-Stud+ SD1/SD2 wedge anchors – PE1000+ / AC100+Gold adhesive anchors – Self Tapping Concrete Screws – Vertigo & Snake overhead anchors – Atomic Undercut anchors

RISA Technologies

Phone: 949-951-5815 Web: www.risa.com Product: RISABase Description: When accuracy counts, RISABase delivers. RISABase uses an automated finite element solution to provide exact bearing pressures, plate stresses, and anchor bolt pull out capacities, eliminating the guess work of hand methods. Define bi-axial loads and eccentric column locations. Choose from several connection types and specify custom bolt locations.

Simpson Strong-Tie

Phone: 925-560-9000 Web: www.strongtie.com Product: Mech. Anchors, Adhesives & Design Software Description: Innovative, code-listed anchors and fasteners, including Titen HD® screw anchor, StrongBolt® 2 wedge anchor and SET-XP® and AT-XP adhesives. New 3D Anchor Designer™ software has 42 pre-loaded anchor configurations.

USP Structural Connectors

Phone: 952-898-8772 Web: www.uspconnectors.com Product: USP Structural Connectors Description: Since 1954, USP Structural Connectors (a division of Mitek) has become the world’s leading manufacturer of code approved, structural connectors and innovative software solutions. USP’s 4000+ products are engineered, manufactured and tested to withstand Mother Nature, and are backed by our professional engineering and technical support teams and international sales.

Williams Form Engineering Corp.

Phone: 616-866-0815 Web: www.williamsform.com Product: Anchor Systems Description: Williams Form has been providing threaded steel bars and accessories for rock anchors, soil anchors, high capacity concrete anchors, micro piles, tie rods, tie backs, strand anchors, hollow bar anchors, post tensioning systems, and concrete forming hardware systems in the construction industry for over 90 years.

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SPOTLIGHT

award winners and outstanding projects

Best Presentation and Best Poster 2013 Structures Congress Each year attendees at the ASCE/SEI Structures Congress recognize excellent technical session presentations and posters through the “Best of the Best” program. By casting ballots available to all attendee, a Best Presentation and Best Poster are chosen. In addition, there is a drawing to award one of these voters a Kindle Fire. The votes are collected and tallied by the SEI Public Relations Committee. The winners were announced at the Closing Plenary Session on Saturday, May 4, 2013. The lead authors of the Best Presentation and Best Poster each receive complimentary registration for Structures Congress 2014, taking place April 3-5, 2014 in Boston, Massachusetts.

measures, and for the acceleration of insurance claims. Mr. Burns is a member of the Board of Directors and the managing principal of Thornton Tomasetti, a US based firm he has been with since 1995. He has over 30 years of experience designing structures as well as investigating and renovating existing buildings.

Best Presentation

Best Poster

This year’s winner for best presentation was Construction Defect Case Studies – What Engineers Should Know, a panel presentation moderated by Mr. Joseph Burns, P.E., S.E., F. ASCE, of Thornton Tomasetti, an engineering firm which maintains offices across North America and around the globe.

This panel discussion of construction defects and how they should be mitigated was of particular interest to the attendees that conduct work in this area. Mr. Burns highlighted the presentations by Steve Dennis and Duke Wellington, given during this session, as well as the support provided to the development of the presentations by Dan Cuoco. The important elements of this session, highlighted in the votes received from conference participants, included the suggestion that firms consider adding a clause in their contract language requiring the parties to agree on a neutral expert in the event of disputes between the various parties. While arranging for an independent review of work that is planned is a standard practice prior to the initiation of a project, consideration of a neutral party to assist should a difference of opinion arise during the course of a project might not always be included in the development of a contract.

This is a simple but profound change in the implementation of a project that could provide assurance of continued communication and a successful completion should differences of opinion arise during the course of a project. This suggestion was judged by the positive feedback received to be a practical tool that could be incorporated within a building project to help in the resolution of problems or differences of opinion during the course of a project.

A second item from the session was a message for those who, as a part of their professional career, serve as expert witnesses or who hope to serve in an expert capacity in court cases as a part of Joseph Burns, P.E., their future career. The S.E., F. ASCE panel’s recommendation was that you should encourage your professional peers to provide expert witness work only as an adjunct to their design work.

This is because providing only forensic work could distort the practical and efficient ways to resolve a problem. A balance of forensic work and design work was recommended.

Engineers participate in the annual SEI structures congress for a variety of reasons.

Gaining insight through practical observations provided by a panel of experts in this year’s session on construction defect studies is a good example of the knowledge that can be taken away from this conference, and the other technical conferences and webinars prepared by ASCE/SEI. The Structures Congress attendees appreciated the insights provided by Mr. Burns that could assist firms in resolving disputes that might arise and achieving successful completed projects. The attendees acknowledged through their votes that the profession needs professional development in this niche area, and they made this point clear by selecting this session as the 2013 ASCE SEI Structures Congress Best of the Best Presentation.

Joseph Burns, P.E., S.E., F. ASCE, has a background in the evaluation of structural failures to determine safety and remediation

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The Best Poster winner is Collapse Behavior of Steel Columns under Lateral Loading by Julie Fogarty and Sherif El-Tawil, Ph.D., P.E., F. SEI, F. ASCE. The effect of local buckling due to lateral loading on the axial capacity of steel columns was investigated in this poster using detailed finite models. An overview of past research addressing column failure under seismic loading was presented to characterize the current state of knowledge.

Preliminary simulation results indicated that flange local buckling due to lateral loading could significantly reduce the axial resistance of steel moment frame columns.

Some of the motivation for this examination was the observation that local flange buckling may play a critical role in promoting progressive collapse during seismic events. In addition, previously published analyses often do not consider inclusion of local flange buckling, although it has been seen in experimental setups.

Julie Fogarty is a graduate student at the University of Michigan, Sherif El-Tawil, Ph.D., P.E., F. SEI, F. ASCE, is a professor and associate chair of the Department of Civil and Environmental Engineering at the University of Michigan.▪ Collapse Behavior of Steel Columns under Lateral Loading J. Fogarty1 and S. El-Tawil2 1 2

Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109; email: jefogart@umich.edu PhD, PE, FASCE, Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109; email: eltawil@umich.edu

MODEL SETUP

ABSTRACT The effect of local buckling due to lateral loading on the axial capacity of steel columns is investigated using detailed finite element models. An overview of past research addressing column failure under seismic loading is presented to characterize the current state of knowledge. Preliminary simulation results indicate that flange local buckling due to lateral loading could significantly reduce the axial resistance of steel moment frame columns.

MOTIVATION • Several researchers have noted local flange buckling may play a critical role in promoting progressive collapse during seismic events.

• Inclusion of local flange buckling has not been present in the majority of published analytical and numerical seismic analyses even though the phenomenon has been seen in experimental setups (Krishnan and Muto 2012, Lamarche and Tremblay 2011, Suita et al. 2007, Suita et al. 2008).

• Prior work by the authors using computational and analytical methods indicated that any interruption of the load path due to local damage can lead to a significant decrease in axial resistance of steel columns.

RESULTS

Boundary and Loading Conditions • W24x176 column chosen due to a) use as a moment frame column in a National Institute of Standards and Technology seismically designed building and b) satisfies requirements for highly ductile members specified in ANSI/AISC 341-10.

• ANSI/AISC 341-10 Chapter D general member ratio limits as shown in Table 1 are not well developed.

• Force-controlled axial load/force-controlled lateral load scheme chosen as best representation of loading condition at the system level.

• Fixed-fixed and fixed-pinned columns investigated to represent extremes of actual boundary condition in system.

Lateral motion in direction of arrow and vertical motion permitted. Arrow indicates direction of applied lateral load.

• W24x176 column was altered to evaluate the effect of b/t ratio, h/tw ratio, and aspect ratio • ANSI/AISC 341-10 Chapter D ratio limits were assessed

Figure 3. Geometry affected by changing various parameters.

No translation or rotation allowed at base of column.

Figure 2. Finite element model with boundary conditions.

RESULTS Parametric Study Figure 4. Deformed shapes for a) fixed-fixed column and b)fixedpinned column under 10% axial load post failure.

CONCLUSION Preliminary studies indicate that a column which meets the seismic design guidelines for a highly ductile member may not be able to acheive 4% lateral drift ratio under high axial loads. However, it should be noted that the results presented here are based on the study of columns in isolation that use idealized boundary conditions and are not part of a moment frame system. The implications shown through this preliminary study need to be further investigated before they can be completely justified. The authors are currently expanding their studies to include more column cross-sections typically utilized in seismically designed buildings as well as the effects of the system on column behavior.

ACKNOWLEDGEMENTS Figure 1. Prior work showing the significant decrease in axial resistance for a W14x120 steel column under a) different locations and amounts of damage along the length of the column and b) various amounts of flange damage within the cross-section.

Figure 5. Parametric study investigating the effect of the a) b/t ratio, b) h/tw ratio, and c) aspect ratio of the W24x176 column

This material is partly based upon work supported by the National Science Foundation (NSF) Graduate Student Research Fellowship under Grant No. DGE 0718128. The work was also supported by the University of Michigan and US NSF grant CMMI-0928547. Any opinions, findings, conclusions, and recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the sponsors.

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News form the National Council of Structural Engineers Associations

Celebrating

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The 2013 NCSEA Special Awards Honorees

The following awards will be presented at the Awards Banquet on September 20 during the 2013 NCSEA Annual Conference in Atlanta. For more information on the Annual Conference, see pages 34-37.

The James M. Delahay Award Alan G. Steinle, P.E. 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.

Alan Steinle is Vice President of Structural Engineering at VanDemark & Lynch, Inc., a Wilmington, Delaware Civil/Surveying firm. Alan received his BSCE from the University of Delaware in 1970, served on active duty as an Army Corps of Engineers Officer, was the Port Engineer at the Port of Wilmington, Delaware, a project manager with a steel fabrication/erection company, and a structural engineer for a local consulting firm. In 1993, he founded Steinle Construction Engineers, Inc., which was acquired by VanDemark & Lynch in 2011. Alan has been a member of the Delaware Architectural Accessibility Board, a National Director of ACEC, President of ACEC Delaware, and a member of the CASE Contracts Committee. He is Past Chairman of, and currently an ACEC Delegate to, the Engineers Joint Contract Documents Committee. Alan is an International Code Council member and has been the NCSEA representative to the International Residential Code (IRC) Development Committee since 2006. He recently participated in the IRC Development Hearings in Dallas for the 2015 IRC.

The NCSEA Service Award Greg Schindler, 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.

Greg Schindler is an Associate at KPFF Consulting Engineers in Seattle. He has been involved with NCSEA from its inception and attended its formative meeting in Denver in 1992 as a representative of the Board of Directors of SEAW. Since then, Greg has been actively involved in many aspects of NCSEA, including serving for several years as Chair of the NCSEA Awards Program. He served on the NCSEA Board of Directors from 1997 to 2002 and was President from 2000-2001. Currently, he is a member of the Editorial Board of STRUCTURE Magazine, is on the NCSEA Code Advisory Subcommittee on Quality Assurance and Special Inspection, and represents NCSEA on the Board of Directors of the Building Seismic Safety Council. He is also a former board member and Past President of SEAW, Seattle Chapter, where he has served on several committees and served as chair of the SEAW structural refresher course and as an instructor in the ATC-20 training course. In 2001, he was honored as the SEAW Seattle Chapter Structural Engineer of the Year.

The Susan M. Frey NCSEA Educator Award Susan M. Frey, P.E., S.E. NCSEA is pleased to announce the creation of a “Susan M. Frey NCSEA Educator Award”, established to honor the memory of one of NCSEA’s finest instructors, who passed away in May, 2013. NCSEA posthumously recognizes Sue Frey as the inaugural winner, in recognition of her genuine interest in, and extraordinary talent for, effective instruction for practicing structural engineers. Subsequent winners of this award will present a special webinar to NCSEA members at a deeply discounted cost, as a continuing legacy to Sue Frey.

Sue Frey spent her entire career at CH2M HILL and also served as an adjunct professor in the civil engineering department at Oregon State University beginning in 1995. Sue contributed countless volunteer hours to NCSEA, actively participating in the Licensure and Continuing Education Committees. She was instrumental in the development of the NCSEA-Kaplan Structural Examination Review Course and taught the masonry and exam strategies portions of the Course to stellar reviews. Sue was also a frequent presenter at NCSEA seminars and webinars.

She served as President of the Structural Engineers Association of Oregon (SEAO) from 1997-1998, was honored by SEAO with a Special Merit for Lifetime Achievement Award, and was SEAO’s Delegate to NCSEA for many years. She was awarded Purdue’s Civil Engineer Alumni Achievement award in 2005 and served on Purdue’s Civil Engineering Advisory Council. Sue was an active member of The Masonry Society, The Masonry Standard Joint Committee and the American Concrete Institute.

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Allison Clark, P.E. Allison Clark is a structural engineer with Stanley D. Lindsey & Associates, Atlanta, Georgia.

She is a member of the Structural Engineers Association of Georgia (SEAoG) and their Young Member Group.

James Newhall James Newhall is a structural designer at Caruso Turley Scott, Tempe, Arizona. He is a member of the Structural Engineers Association of Arizona (SEAoA) and serves as the Central Chapter’s Young Member Group chairman.

Baby Boomers Delay Retirement – Career Bottleneck at the Top, Steven Isaacs, FMI Get the Value You Deserve Without Ruining the Relationship, Steven Isaacs Three Levels of Ownership Transition Small Firms: Brian Dekker, Sound Structures Medium-Size Firms: Don Scott, PCS Structural Solutions Large Firms: Mark Aden, DCI Engineers

March 21

Leadership is a Full-Contact Sport: Dealing with Conflict in the Workplace, Jennifer Morrow, ADR (Alternative Dispute Resolution) Systems You’ve Been Sued – Now What? What Structural Engineers Need to Know to Structure Their Defense, Kevin Sido, Hinshaw & Culberton LLP Managing the Cost of Conflict: Mediation, Arbitration or Litigation?, Jennifer Morrow and Kevin Sido Each day will also include roundtable discussions with the day’s speakers and attendees.

NCSEA Webinars September 26, 2013

The Importance of a Specification or General Structural Notes (GSN) Review David Flax, Euclid Chemical Company

Jera Schlotthauer Jera Schlotthauer is an Engineer I with Martin/ Martin Wyoming, Cheyenne, Wyoming. She is a member and alternate delegate to the newly formed Structural Engineers Association of Wyoming (SEAWY) and looks forward to developing their Young Member Group.

Erection Engineering: The Science Behind the Art Clinton Rex, Stanley D. Lindsey & Associates

October 15, 2013

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Formwork: As-Cast Surface Finishes Kim Basham, KB Engineering, LLC

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These courses will award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program.

Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern. Register at www.ncsea.com.

ASS

For more information on the NCSEA Annual Conference, including a full schedule of educational sessions, exhibitor list, conference sponsors and registration information, see pages 34-37.

October 3, 2013

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William Eric Cannon, P.E. William Cannon is a structural engineer with NAVFAC SE, Jacksonville, Florida. He is a member of the North Florida chapter of the Florida Structural Engineers Association (FSEA) and is active in their Young Member Group.

March 20

News from the National Council of Structural Engineers Associations

Travis Brackus Travis Brackus is a project engineer with BHB Consulting Engineers, Salt Lake City, Utah.

He is a member of the Structural Engineers Association of Utah (SEAU) and is assisting in the development of their Young Member Group.

Meritage Resort & Spa, Napa, California

STRUCTU

For the second year, NCSEA awarded Young Member Scholarships for the NCSEA Annual Conference. The scholarship competition was open to any current member of an NCSEA Member Organizations who was under 36 years old.

The applicants were asked to compose an essay answering one of two questions, as well as state what they expected to gain from their attendance at the conference and how they would apply it to their position.

Each scholarship covered a full registration to the conference, including special features for Young Engineers.

The winners of this year’s scholarships were:

NCSEA News

Winter Leadership Forum set for Napa March 20 -21, 2014

NCSEA awards five Young Member Scholarships to Annual Conference

COUNCI L years

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Attention Undergraduate Student Teams and Faculty Advisors

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Participate in the 2014 SEI Student Structural Design Competition Innovative projects demonstrating excellence in structural engineering are invited for submission. A written submission is judged and three finalist teams are invited to present their designs at Structures Congress 2014 in Boston, MA, April 3 – 5, 2014. The finalist teams are judged on an oral presentation during the conference, and 1st, 2nd, and 3rd place awards are determined as a combination of the written submission and oral presentation. Awards include complimentary registration to the conference (up to three student registrations and one full registration for the faculty advisor) and cash prizes: First Place: $1,000 Second Place: $500 Third Place: $250 For more info visit www.asce.org/SEI.

ASCE Week – A Continuing Education Event November 4 – 8, 2013

This event brings together our most popular face-to-face seminars in one location, and offers two special field trips for you to choose from. Earn up to 36 PDHs. Structural topics include Design for High Wind and Flood, Design of Anchors, Forensic Report Writing, Instrumentation and Monitoring, and more. Register by October 11 and save up to $800. Visit the ASCE Week webpage at www.asce.org/asceweek/ for more information.

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

Local Activities SEI Mohawk Hudson Chapter Under a special election, Timothy Schroder, P.E. was nominated as the Chair Elect for the Mohawk-Hudson SEI Chapter. Tim will be filling the Board position recently vacated

by Samantha Beaulac, EIT who relocated to New York City to take a position with Thornton Tomasetti, Inc. At the June SEI Chapter Meeting, Richard C. Wakeman, P.E. of C.T. Male Associates, Latham NY, gave a presentation on pressure grouted compaction piles and soil stabilization techniques employed on a NYC Hospital project. The program was accredited for 1 PDH.

Get Involved With Your Local SEI Chapter Join your local SEI Chapter or a Structural Technical Group (STG) to connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area.

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If there is not an SEI Chapter or STG in your area, talk with your ASCE Section/Branch leaders about the simple steps to form an SEI Chapter. Visit the SEI website at www.asce.org/sei for information on existing chapters and resources to develop new ones.

Some of the benefits of forming an SEI Chapter include: • Connect with other SEI local groups through quarterly conference calls and annual conference • Use of SEI Chapter logo branding • SEI Chapter announcements published at www.asce.org/SEI and in SEI Update • One free ASCE webinar (to $299 value) sponsored by the SEI Endowment Fund • Funding for one representative to attend the 2013 SEI Local Leadership Conference, September 11-12 in Dallas, to learn about new SEI initiatives, share best practices, participate in leadership training, a technical tour of the Dallas Cowboys Stadium, etc.

• SEI outreach supplies available upon request For more info, contact Suzanne Fisher at sfisher@asce.org.

September 2013

Seismic Design with ASCE 7-10 The 2013 California Building Code goes into effect on January 1, 2014, with seismic requirements based on ASCE 7-10.

Are you ready to start using the provisions of ASCE 7-10 for seismic design? ASCE Continuing Education is offering a daylong seminar that will cover the major changes in ASCE 7-10.

Presented by Greg Soules, P.E., S.E., F. SEI, F. ASCE, vice chair of the ASCE 7 Seismic Subcommittee, this seminar will review changes to the seismic provisions as well as: • Changes to Chapter 1 General Provisions, and Chapter 2 Load Combinations, • The new Expanded Seismic Commentary, and • Example problems illustrating design approaches.

The class will be interactive, providing discussion and exercises.

Seminar attendees will walk away with an understanding of: • The changes in ASCE 7-10 relevant to seismic design, and • How to apply seismic provisions to buildings, nonstructural components, and non-building structures.

This course brings training on ASCE standards directly to engineers at an incredible value. At $325 for members, this is a 75% reduction from similar length ASCE seminars.

Three California locations are available: San Francisco – September 23 Los Angeles – September 26 San Diego – September 27 For more information visit the SEI website at www.asce.org/SEI.

SAVE THE DATE Structures Congress 2014 April 3 - 5, 2014 Boston, Massachusetts

Active ASCE/SEI member Michel Bruneau recently received the Award for Best Second Novel from the Next Generation Indie Book Awards, and has been selected as a Literary Fiction finalist for ForeWord Reviews’ Book of the Year Award for his novel, The Emancipating Death of a Boring Engineer. In addition, Bruneau has received positive reviews from the San Francisco Book Review, the Midwest Book Review, Readers Favorites, and many others. Some of these reviews are posted on the author’s website at www.michelbruneau.com/MB-Literature.htm, together with more information on the novel. You can also read the first two chapters of the novel on the Amazon website, www.amazon.com. Bruneau is planning a third novel for publication in 2016.

O.H. Ammann Research Fellowship Applications Now Being Accepted The O. H. Ammann Research Fellowship in Structural Engineering is awarded annually to a member or members of ASCE or SEI for the purpose of encouraging the creation of new knowledge in the field of structural design and construction. All members or applicants for membership are eligible. Applicants will submit a description of their research, an essay about why they chose to become a structural engineer, and their academic transcripts. This fellowship award is at least $5,000 and can be up to $10,000. The deadline for 2014 Ammann applications is November 1, 2013.

This year SEI has developed an online application process; paper and emailed applications will no longer be accepted.

STRUCTURE magazine

Applicants will fill out an online form and submit a PDF containing parts of their application. Letters of recommendation will be uploaded on a companion site, and official transcripts need to be sent directly to SEI staff. Visit the SEI website at www.asce.org/sei for more information about the online application and to apply.

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September 2013

The Newsletter of the Structural Engineering Institute of ASCE

SEI Member’s Second Novel Receives Acclaim

Structural Columns

Prepare for the New California Building Code

2013 CASE Best Sellers Purchase Your coPY TodaY!

National Practice Guidelines

CASE in Point

The Newsletter of the Council of American Structural Engineers

962: National Practice Guidelines for the Structural Engineer of Record (SER) The purpose of this document is to give firms and their employees a guide for establishing Consulting Structural Engineering Services, and to provide a basis for dealing with Clients generally and negotiating Contracts in particular. Since the Structural Engineer of Record (SER) is normally a member of a multidiscipline design team, this document describes the relationships that customarily exist between the SER and the other team members, especially the team leader. Further, this Guideline promotes an enhanced Quality of Professional Consulting Structural Engineering Services while also providing a basis for negotiating a fair and reasonable compensation.

962-A: National Practice Guidelines for the Preparation of Structural Engineering Reports for Buildings The purpose of this document is to provide the structural engineer a guide for not only conducting conditional surveys, code reviews, special purpose investigations and related reports for buildings, but includes descriptions of the services to aid with client risk management communication issues. This Guideline is intended to promote and enhance the quality of engineering reports.

A section of this Guideline deals specifically with outlines for various reports. While it is not intended to establish a specific format for reports, it is believed there may be certain minimal information that might be contained in a report. The Appendix includes disclaimer language which identifies statements one might consider to clarify the depth of responsibility accepted by the report writer.

962-D: A Guideline Addressing Coordination and Completeness of Structural Construction Documents The guidelines presented in this document will assist not only the Structural Engineer of Record (SER) but also everyone involved with building design and construction in improving the process by which the owner is provided with a successfully completed project. Their intent is to help the practicing structural engineer understand the importance of preparing coordinated and complete construction documents and to provide guidance and direction toward achieving that goal.

These guidelines focus on the degree of completeness required in the structural construction documents (“Documents”) to achieve a “successfully completed project” and on the communication and coordination required to reach that goal. They do not attempt to encompass the details of engineering design; rather, they provide a framework for the SER to develop a quality management process.

Currently, the coordination and completeness of Documents varies substantially within the structural engineering profession and among the various professional disciplines comprising the design team. The SER’s goal should be meeting both the owner’s and the contractor’s needs by producing a complete STRUCTURE magazine

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and coordinated set of Documents. Owners and contractors generally understand that some changes to the Documents will occur, because they realize that no set of Documents is perfect. The SER must focus on completeness, coordination, constructability, and the reduction of errors in order to minimize potential changes.

Contract Documents #2: An Agreement between Client and Structural Engineer of Record (SER) for Professional Services The purpose of this document is to provide a sample agreement for providing structural engineering services directly to a Client. It is not intended to be used when the Structural Engineer of Record is the Prime Design Professional (See CASE Document 13).

This Agreement is written as an Agreement and can be reproduced on the firm’s letterhead, if desired. This Agreement is unique in that the Summary of Services is presented in matrix form as Exhibit A, and the desired scope of services can be defined by simply checking the included or not included column. A list of Terms and Conditions is included in Exhibit B. The Summary of Services matrix and Terms and Conditions are consistent with the National Practice Guidelines for the Structural Engineer of Record. #11: An Agreement between Structural Engineer of Record (SER) and Contractor for Transfer of CAD Files on Electronic Media The purpose of this document is to provide an agreement for the SER to use when transferring digital data (CAD or BIM) files to the contractor.

Traditionally the use of reproductions of the SER’s drawings by the contractor to prepare shop drawings was not recommended

by CASE due to the potential liability concerns. However, the efficiencies of production, coordination, and communication through electronic media, more specifically CAD and BIM, are undeniable and file sharing has become the industry standard. #13: Prime Contract, An Agreement between Owner and Structural Engineer of Record (SER) for Professional Services This document is to be used when the Structural Engineer serves as the Prime Design Professional. It is intended to be used for projects which are predominately structural in nature, but may require other engineering disciplines and architectural services which are more than incidental; structures such as parking garages, warehouses, light industrial buildings, sports facilities and structural renovations. It should be distinguished from CASE Document 2, which is to be used when the Structural Engineer of Record contracts directly with the Owner, but does not serve as the Prime Design Professional.

These publications, along with other CASE documents, are available for purchase at www.booksforengineers.com.

September 2013

Strong Lineup of Risk Management Sessions at ACEC Fall Conference • Greg Cohen, President/CEO, American Highway Users Alliance • Emil Frankel, Former Assistant Secretary of Transportation, now visiting scholar Bipartisan Policy Center • Kerry O’Hare, Vice President and Director of Policy, Building America’s Future • Fred Studer, Dynamics GM, Microsoft on How Technology Will Transform the Business of Engineering • CEO Roundtables • CIO and CFO Industry Sessions • Emerging Leaders Forum • 30 Industry Education Sessions offering 21.5 PDHs

Other Fall Conference Highlights include: • Mitch Daniels, Former Indiana Governor and President, Purdue University, on The Private Sector and Public Projects • CEO Panel on Trends in Private Client Methods – Commercial, Industrial, Energy • Victor Mendez, FHWA Administrator on MAP-21 and the Future of the Federal Highway Program • Expert Panel Discussion on Transportation Funding Options and Outlook

Register now at www.acec.org/conferences/fall-13/index.cfm.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

ACEC Business Insights Upcoming ACEC Online Seminars Winning the Client Interview to Win More Business

Ready/AIM/Fire: Achieving Record Sales and Profits

October 15, 1:30-3:00 pm

October 17, 1:30-3:00 pm

Learn how to hone your presentation and communication skills in The Engineered Interview: A Civil, Structured, Electrified Approach to Winning More Business. Susan Murphy of Murphy Motivation and Training will demonstrate how to leverage your unique experience and personality to increase business and form more successful relationships. For more information and to register, http://tinyurl.com/n72b2o3.

Nothing happens in a consulting engineering firm until a project is sold and the contract is signed. Until then, everyone is overhead. Ready/AIM/Fire: Achieving Record Sales and Profits teaches effective business development skills to marketers and technical professionals who come into contact with clients and potential clients. For more information and to register, http://tinyurl.com/k6zbn4m.

If You Haven’t Planned It, You Can’t Control It

How Can You Exceed My Expectations if You Don’t Know What They Are?

October 16, 1:30-3:00 pm

October 22, 1:30-3:00 pm

Taking the time to plan properly is an investment you cannot avoid – if you want to meet your goals and support your employees. In If You Haven’t Planned It, You Can’t Control It, Gary Bates, Roenker Bates Group, demonstrates the relationship between “planning” and “controlling,” maps out everything that needs planning and controlling in an engineering firm, and outlines the seven basic steps required to plan and control all facets of running a successful firm. For more information and to register, http://tinyurl.com/kt3ke4e.

The idea of seeking out regular, reliable and candid feedback from clients is simultaneously exciting and terrifying. In How Can You Exceed My Expectations if You Don’t Know What They Are?, David Stone of Stone & Company will describe how to obtain honest client feedback and what to do with it. For more information and to register, http://tinyurl.com/lg4q3x2.

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September 2013

CASE is a part of the American Council of Engineering Companies

The CASE Convocation offers a full day of sessions on Monday, October 28 dedicated to best-practice structural engineering: 10:30 am What’s Next, the Legal Aspects of Building Information Modeling, Sue Yoakum, Donovan Hatem LLP 2:15 pm Practical Insurance Advice, Brian Stewart, Collins, Collins, Muir + Stewart; Tom Bongi, Caitlin; Atha Forsberg, Marsh 4:00 pm Developing an Internal Culture to Manage a Firm’s Risk, Michael Strogoff, Strogoff Consulting 5:30 pm ACEC / Coalition Meet and Greet

CASE in Point

CASE Risk Management Convocation

Structural Forum

opinions on topics of current importance to structural engineers

A Remarkable Profession!

By Stan R. Caldwell, P.E., SECB

S

tructural engineering has been around since the first cave shortage, yet there is a growing perception that this noble profession might now be dying. What fuels this troublesome notion? Perhaps it starts in high school, where many of the brightest students are discouraged from pursuing the long, hard path to engineering. Why labor over calculus and physics, when those hours could be more productively spent learning “high tech” skills like HTML5? Those who resist this logic are often advised to pursue fields of engineering such as electrical and chemical, which are perceived to offer high initial compensation and early exposure to emerging technology.

The perception does not improve in college. Students discover that entry into the profession usually requires a master’s degree, a 4-year internship, an 8-hour fundamentals exam, and a 16-hour professional practice exam with a low passing rate. In return, they are told to expect a modest but comfortable income. Structural engineering has the distinction of being perhaps the only recognized profession that is not supported by any dedicated departments or degree programs at major universities. The dean of engineering at one large institution believes that structural engineering is obsolete. He views structural engineers as little more than math technicians who meticulously follow precise recipes to produce adequate designs.

In the workplace, many structural engineers find themselves positioned pretty low on the project “food chain.” MEP engineers typically receive higher fees in return for somewhat less effort and far less liability. Architects and civil engineers are almost always the prime professionals on building and bridge projects, respectively. They frequently select structural engineers based exclusively on price, often neglect to include them in the critical conceptual phases of their projects, and pass along as much of the liability as possible. Only a handful of states offer any type of “S.E.” license; most simply lump structural engineering with all other disciplines under a generic “P.E.” license. Meanwhile, structural design codes and regulations have evolved into a self-perpetuating industry, with each revision becoming more prescriptive, thereby allowing less opportunity for structural engineers to exercise their professional judgment.

Finally, there is the general public; they really have no clue who we are or what we do. Based on media reports, it seems obvious that buildings are designed by architects and bridges are designed by state highway engineers. I can think of just one movie featuring a structural engineer, and he turned out to be a terrorist (Tim Robbins in Arlington Road). Likewise, the only television series featuring a structural engineer highlights a criminal (Wentworth Miller in Prison Break). Compare this with virtually any other profession. The problem is not that we suffer from a poor public image, but rather that we have no image whatsoever!

Enough! The reality is that structural engineering is a wonderful profession with a bright future. In his 1929 Inauguration Address, President Herbert Hoover stated:

“Ours is a great profession. There is a fascination of watching a figment of the imagination emerge through the aid of science to a plan on paper. Then it moves to realization in stone or metal … Then it elevates the standard of living …

That is the engineer’s high privilege.”

Tremendous satisfaction can be achieved by observing the successful completion of a significant building or bridge that you have nurtured from conception. There is also considerable satisfaction derived from the service that we render to society. Ron Hamburger once wrote: “Most structural engineers, over the course of their careers, are responsible for protecting more lives than most medical doctors.”

It is a myth that structural engineering is a lousy business and structural engineers are poorly paid. Structural engineers are not prohibited from acting as the prime professional on any project, and many are seizing that opportunity. While fee pressure will never be eliminated, it can be effectively remedied by emphasizing value and striving for better clients and projects. Structural engineers normally are compensated at least as well as architects and civil engineers with comparable experience, and some become wealthy.

We provide structural engineering services by exercising considerable professional judgment, even though we do not always recognize it as such. We are continually challenged with the ever-increasing size and complexity of our structures, as well as the advanced materials and techniques used in their construction. Computers have given us incredible power to test multiple options and visualize the results without the number-crunching drudgery of years past. In fact, it might even be argued that structural engineering is fun!

What about the future? Under sustained pressure from automation, globalization, and contractor-led procurement, the role of the structural engineer is certainly not guaranteed. Will we sit quietly on the sidelines and accept whatever role society crafts for us, including possible obsolescence, or will we actively work to steer the profession toward a thriving future? All structural engineers, and especially younger structural engineers, must step beyond the workplace. One good place to start would be active involvement in your SEI or SEA chapter or state organization. Another would be service on SEI, NCSEA, CASE, or SECB committees; there are more than 100 to choose from. As Richard Weingardt often says: “The world is run by those who show up.” The time has come for structural engineers to conquer their stereotypical inhibitions and show up.▪ Stan R. Caldwell, P.E., SECB (www.stancaldwellpe.com), is a consulting structural engineer in Plano, Texas. He currently serves on the SEI Board of Governors and the SECB Board of Directors.

This column is an updated version of an editorial from the February 2001 issue of STRUCTURE magazine. The slightly refreshed message is just as timely today as it was then.

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

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September 2013