STRUCTURE magazine | February 2013 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

February 2013 Steel/Cold-Formed Steel NCSEA Winter Leadership Forum Tucson, Arizona March 7 & 8

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CONTENTS

Features 18

Rehabilitation of Historic Holmes Street Bridge

February 2013

By Robert E. Mateega, P.E.

The Minnesota Department of Transportation identified the Holmes Street Bridge as one of 24 bridges in Minnesota to preserve, once funding became available. The project team faced many challenges. The first was the need to complete the inspection, analysis and rehabilitation report, and plan approvals in a short six months. The next challenge was to identify engineering solutions that would meet safety and maintenance requirements, while preserving the historic features of the bridge.

Translucent Dome for Argentine Soccer Stadium Matthys Levy, P.E.

The design of the roof of the recently completed La Plata football stadium presented some unique engineering challenges. Instead of having a continuous oval perimeter, the plan of La Plata is based on two circles 279 feet in diameter whose centers are separated by 157 feet. The requirement for natural ventilation resulted in the need for openings at the two peaks. Finally, a compression ring around the arena was conceived of and built as a triangular steel truss.

Queen Richmond Centre West By Carlos de Oliveira, M.A.Sc., P.Eng, Michael Gray, Ph.D. and Jeffrey Stephenson, P.Eng

The fact that the 11- story Queen Richmond Centre West tower springs from above both existing buildings makes Phase One of this development a truly unique structure. Critical to the realization of the design from both a structural and architectural perspective is the use of elegantly shaped 31,500-pound cast steel nodes in the architecturally exposed structural steel framework supporting the building.

7 Editorial Opportunities Abound

By Barry Arnold, S.E., SECB

8 Just the FAQs Changing Masonry Standards

10 Structural Design Design of Cold-Formed Steel Nonstructural Members

By Roger LaBoube, Ph.D, P.E., Helen Chen, Ph.D, P.E. and Jay Larson, P.E.

14 Building Blocks Using Structural Insulated Panels on Non-Residential Structures By Thomas A. Moore, P.E.

Departments 30 InSights Project Delivery Systems By Stacy Bartoletti, S.E.

35 Spotlight 8 Spruce Street – Beekman Tower Silvian Marcus, P.E. and Susan Erdelyi Hamos, P.E.

on the Cover The design of the roof of the recently completed La Plata football stadium represents a serendipitous merging of two concepts: the award winning competition entry by the architect, Roberto Ferreira, and the Tenstar Dome™ structure originally developed by Weidlinger Associates for the Georgia Dome. This shows an aerial view of the completed stadium; notice the figure-eightshaped opening at the top. This design is highlighted in a feature article on page 22. ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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42 Structural Forum The Invisible Gendered Culture of Engineering By Lara K. Schubert, P.E.

In every Issue 6 Advertiser Index 9 Noteworthy 33 Resource Guide (Bridge) 36 NCSEA News 38 SEI Structural Columns 40 CASE in Point

CEU’s. Membership is $96/yr; this can equate to CEU’s as little as $8/CEU. www.foundationperformance.org

STRUCTURE magazine

February 2013

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

Advertiser index

PleAse suPPort these Advertisers

Computers & Structures, Inc. ............... 44 CSC, Inc. ................................................ 3 CTS Cement Manufacturing Corp........ 33 Design Data .......................................... 21 Engineering International, Inc............... 15 ESAB Welding and Cutting Products .... 25 Foundation Performance Association....... 5

Fyfe ....................................................... 11 GT STRUDL........................................ 32 Integrated Engineering Software, Inc..... 19 ITW TrusSteel & BCG Hardware ..... 9, 13 KPFF Consulting Engineers .................... 6 LNA Solutions ...................................... 34 New Millennium Building Systems ....... 29

editorial Board Chair

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

Brian W. Miller

CBI Consulting, Inc., Boston, MA

Mark W. Holmberg, P.E. Dilip Khatri, Ph.D., S.E.

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

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. BergerABAM, Vancouver, WA

Brian J. Leshko, P.E.

John “Buddy” Showalter, P.E.

John A. Mercer, P.E.

Amy Trygestad, P.E.

American Wood Council, Leesburg, VA

Chase Engineering, LLC, New Prague, MN

UNIVERSITY OF WASHINGTON MOLECULAR ENGINEERING BUILDING, SEATTLE, WA / PHOTO BY BENJAMIN BENSCHNEIDER

Mercer Engineering, PC, Minot, ND

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Evans Mountzouris, P.E.

The DiSalvo Ericson Group, Ridgefield, CT

HDR Engineering, Inc., Pittsburgh, PA

Chuck Minor

Dick Railton

Eastern Sales 847-854-1666

Western Sales 951-587-2982

sales@STRUCTUREmag.org

Davis, CA

Heath & Lineback Engineers, Inc., Marietta, GA

CCFSS, Rolla, MO

Advertising Account MAnAger Interactive Sales Associates

Jon A. Schmidt, P.E., SECB

Craig E. Barnes, P.E., SECB

Powers Fasteners, Inc. .............................. 2 RISA Technologies ................................ 43 S-Frame Software, Inc. ............................ 4 Simpson Strong-Tie......................... 17, 31 Soilstructure.com .................................... 5 Struware, Inc. ........................................ 27

editoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE

execdir@ncsea.com

Editor

Christine M. Sloat, P.E.

publisher@STRUCTUREmag.org

Associate Editor Graphic Designer Web Developer

Nikki Alger

publisher@STRUCTUREmag.org

Rob Fullmer

graphics@STRUCTUREmag.org

William Radig

webmaster@STRUCTUREmag.org

STRUCTURE® (Volume 20, Number 2). 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

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STRUCTURE magazine

February 2013

editorial

Opportunities new trends, new techniquesAbound and current industry issues By Barry Arnold, S.E., SECB

unique and diverse educational opportunities offers beneficial information ranging from how to design structures to how to effectively manage your business. On my way home from the 2012 NCSEA Winter Institute, I was reading a newly purchased copy of NCSEA’s Guide to the Design of Diaphragms, Chords and Collectors (a very valuable tool to have in your library). Another attendee questioned why, with over 20 years of design experience, I was reading the design guide. I explained, “I know how I design diaphragms and chords. Now I want to know how this author designs them.” My education was and still is continuing. Ed Allen, a respected structural engineer who retired 15 years ago, attends his membership meetings and participates in other seminars regularly. When asked why he continues to be involved, he stated, “How else am I going to keep up with all the changes that take place.” Ed’s education is continuing. The educational process is a career and often times a life-long process. The sage Leonardo De Vinci was reported to have said, at eighty-seven years of age, “I’m still learning.” That attitude of continuously wanting to educate himself explains why he was productive and valued throughout his career and life. In favor of educating ourselves continually, Earl Nightingale notes: “The biggest mistake that you can make is to believe that you are working for somebody else. Job security is gone. The driving force of a career must come from the individual. Remember: Jobs are owned by the company, you own your career!” Embracing the educational opportunities that surround us is vital to a successful career. An investment in your continued education is an investment in yourself and your future. If you are interested in exploring your potential and expanding your horizons, if you are interested in improving your business, if your saw has become dull and of limited use and is in need of a good sharpening, come join me and many of your peers at the NCSEA Winter Leadership Forum. The format of the NCSEA Winter Institute was changed to a Winter Leadership Forum because NCSEA saw a need for structural engineers to pull together and talk about how they can all benefit by sharing the secrets of success, something that has become of greater importance with the current economy. Attendees will have an opportunity to discuss the current economy and devise strategies for succeeding in it. The attendees will also be able to share ideas with a variety of experienced professionals about charting a course for success in the future. As a leader, your time is valuable; but so is your future. Investing in the Winter Leadership Forum is an investment in a brighter future.▪

a member benefit

structure

any superb opportunities are available to assist structural engineers in improving their skills, expanding their understanding, and increasing their efficiency and level of success. One problem our profession faces today is that too few engineers take advantage of these opportunities, and instead choose to languish in mediocrity. An education is expensive in terms of both money spent and time expended. A wise professor told me at graduation that: “The worst was over in the fact that there would be no more homework or exams.” With all due respect, my beloved professor was very wrong. I received a great education; however, I quickly learned that in college I only acquired about 10% of the knowledge I needed to survive and thrive as a practicing structural engineer. In addition, I continuously worked on ‘homework’ problems on every project and was regularly confronted with weekly examinations in the form of project deadlines. While interviewing, one potential employer stated, “We don’t expect you to know everything, but we do expect you to have a solid grasp of the basic ideas behind structural design, have the ability to rationally reason through a problem, and most important, be willing to start and embrace the next phase of your education.” He was echoing the wise observation of Ralph Waldo Emerson when he stated, “The things taught in colleges and schools are not an education, but a means of education.” In short, we should all be perpetual students and never stop seeking educational opportunities. The end of our formal education is the beginning of an educational process that should continue throughout our professional career. Having spent so much time and money on both a formal education and getting an on-the-job education, it seems wise to want to supplement those with a regular and broad exposure to the latest methods, ideas, practices, code changes, and theory. Steven Covey, when describing the Habits of Highly Effective People, referred to this part of the educational process as “Sharpening the Saw.” The need to regularly sharpen the saw is mandated in our Code of Ethics and required by law in most states. In addition to the programs offered by the SEAs, educational opportunities are also offered by NCSEA, CASE, and SEI to assist the design professional in acquiring necessary skills and knowledge. NCSEA offers an Annual Conference and a Winter Leadership Forum (see page 36 for announcement), CASE/ACEC provides a fall and spring conference, and SEI supports the profession with its STRUCTURAL Structures Congress. Each of ENGINEERING these organizations also offers INSTITUTE a variety of useful publications and webinars; and, each of these STRUCTURE magazine

Barry Arnold, S.E., SECB (barrya@arwengineers.com), is a Vice President at ARW Engineers in Ogden, Utah. He is a Past President of the Structural Engineers Association of Utah (SEAU), serves as the SEAU Delegate to NCSEA, and is the NCSEA Treasurer and a member of the NCSEA Licensing Committee.

February 2013

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

Question: Recent changes were made to ASTM C90 related to the minimum web requirements for loadbearing concrete masonry units (CMU). What, if any, impact do these changes have on the design of concrete masonry assemblies?

Answer For the vast majority of loadbearing concrete masonry construction, there is little difference in the resulting design methodologies or assumptions when using CMU meeting the new ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units. However, there are some nuances that structural engineers should be cognizant of if opting to specify alternative unit configurations now permitted under the new ASTM C90 standard. The Table summarizes the new minimum unit configuration requirements contained in ASTM C90. Compared to historical versions of this standard, the minimum web thickness for all unit sizes is now 0.75 inches where previously it varied from 0.75 inches to 1.125 inches, depending upon the nominal thickness of the unit. Additionally, the equivalent web thickness (which is the summation of the thickness of each web in a unit normalized per unit length) has been replaced with a normalized web area, which cannot be less than 6.5 in.2/ft2 for all units. The drawback of the historical equivalent web thickness requirement was that it did not capture possible variations in the height of the web, which is commonly reduced or notched for various reasons. The normalized web area

Changing Masonry Standards Answer provided by Jason Thompson, Vice President of Engineering for the National Concrete Masonry Association. Mr. Thompson is responsible for overseeing the technical activities, services, and research for the Association. He is also a Fellow of the Masonry Society.

sets a minimum value for the web to connect the face shells of a unit. It is important to stress that the revisions to ASTM C90 do not require unit configurations to be changed; instead, they permit more flexibility in unit configuration to meet evolving market-driven demands. Any unit configuration that met historical ASTM C90 requirements will continue to comply with contemporary versions of this standard. Of primary importance to structural engineers, new unit configurations used in reinforced and grouted construction will still be structurally modeled and designed as they have been in the past, taking into account the appropriate section properties to reflect the cells containing grout and reinforcement. However, for unreinforced/ungrouted masonry, the thinner webs permitted under the latest ASTM C90 standard can impact the resulting section properties of the assembly, and therefore the resulting assembly design strength. Since unreinforced, loadbearing masonry construction is rarely used any longer in the United States, these change will have little effect structurally. However, for those engineers still designing with unreinforced masonry, such structural impacts should be considered. So why change the iconic configuration of the concrete masonry unit? The short answer is that this change has already occurred in the marketplace, resulting in unit configurations such as H-Block, bond beam units, lintel units, and multi-purpose units that have evolved to meet specific project needs. Depending upon one’s perspective, these changes to ASTM C90 offer several potential benefits, including reducing unit weight (reducing structural dead load and increased construction productivity) as well as substantially increasing the thermal R-value of concrete masonry construction.

New ASTM C90 Requirements for Loadbearing Concrete Masonry Units.

Minimum Face Shells and Web Requirements A Webs Nominal Width (W) of Units, in. (mm)

Face Shell Thickness (tts), min. in. (mm)B,C

3 (76.2) and 4 (102) 6 (152) 8 (203) and greater

Web ThicknessC (tw), min. in. (mm)

Normalized Web Area (A nw ), min. in.2/ft2 (mm2/m2)D

3/4 (19)

6.5 (45,140)

1 (25)

3/4 (19)

6.5 (45,140)

11/4 (32)

3/4 (19)

6.5 (45,140)

Average of measurements on a minimum of 3 units when measured as described in Test Methods C140. When this standard is used for units having split surfaces, a maximum of 10% of the split surface is permitted to have thickness less than those shown, but not less than 3/4 in. (19.1 mm). When the units are to be solid grouted, the 10% limit does not apply and Footnote C establishes a thickness requirement for the entire faceshell. C When the units are to be solid grouted, minimum face shell and web thickness shall be not less than 5/8 in. (16 mm). D Minimum normalized web area does not apply to the portion of the unit to be filled with grout. The length of that portion shall be deducted from the overall length of the unit for the calculation of the minimum web cross-sectional area. B

February 2013

news and information

ike Mota, Ph.D., P.E., F. ASCE is stepping down as a member of the STRUCTURE® magazine Editorial Board. Mike joined the Editorial Board in the spring of 2008 as a concrete industry representative. He is the Atlantic Region Manager for the Concrete Reinforcing Steel Institute (CRSI). Mike is an Adjunct at Drexel University and is an active member of several ACI and ASCE committees and serves on the Board of Directors of the Concrete Industry Board of New York City/NYC ACI. Jon Schmidt, Chair of the STRUCTURE magazine Editorial Board, had this to say on Mike’s departure: “Mike has been a valuable member of the Editorial Board for the last five years. I wish him well as he continues to serve CRSI and the structural engineering profession.” Regarding his tenure on the Board, Mike commented, “I would like to take this opportunity to say farewell to the fellow members of the Editorial Board of STRUCTURE magazine and to thank my employer (CRSI) for the opportunity afforded to me to volunteer during the past five years. This time has been

extremely gratifying both personally and professionally. I am pleased that Amy Trygestad of Chase Engineering has accepted to represent the concrete industry on the Editorial Board. The Board will be well served and the Concrete industry well represented. I will continue doing what I do best which is to provide technical assistance to structural engineers on all areas of reinforced concrete design and construction.” Amy M. R. Trygestad, P.E. will replace Mr. Mota. Ms. Trygestad manages her own structural engineering consulting firm near Minneapolis, Minnesota. She is a licensed Professional Engineer with over 17 years of experience in the structural design and construction industry. Her experience has touched many facets of the engineering and construction industry, including engineering consulting, program management, concrete subcontracting, ready-mixed concrete production, and strategic marketing and technical enhancement of concrete construction. She previously worked for the Portland Cement Association as their Building and Special Structure’s Regional Engineering Manager for the Central United States. ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

February 2013

Noteworthy

Mike Mota, Ph.D., P.E., F.ASCE

Amy M. R. Trygestad, P.E.

Her area of expertise is post-tensioned concrete design and construction, and she actively serves on the American Concrete Institute committees for Parking Structures, Prestressed Concrete, Reinforced Slabs, and Formwork. Jon Schmidt said this about Ms. Trygestad’s appointment: “I am pleased to welcome Amy to the Editorial Board. She is well-positioned to serve as an outstanding representative of the concrete industry and provide useful content for our readers.” Please join the STRUCTURE magazine Editorial Board in welcoming Amy Trygestad.

Structural DeSign design issues for structural engineers

ost typical nonstructural partitions are specified and constructed in accordance with the industry or manufacturers’ design tables and would not require additional, formal engineering input on a project-by-project basis. The manufacturers’ design tables are based on engineering principles and tests. However, there are projects where the requirements are outside the limits of the manufacturers’ design tables. The North American Standard for Cold-Formed Steel Framing – Nonstructural Members (AISI S220) was developed in 2011 by the AISI Committee on Framing Standards to help clearly delineate and eliminate confusion between the engineering principles and requirements for cold-formed steel structural members and nonstructural members. As such, provisions formerly in North American Standard for Cold-Formed Steel Framing – General Provisions (AISI S200) for material, corrosion protection, base steel thickness, product designators, manufacturing tolerances, product identification, member design, member condition, installation, connections, and miscellaneous for nonstructural members were moved to AISI S220. However, use of the more stringent requirements for structural members that are in AISI S200 for nonstructural members should be permitted, since these should demonstrate at least equivalent performance for the intended use to those specified in AISI S220. AISI S220 recognizes that the consequence of failure for a nonstructural member is less severe than for a structural member and, consequently, permits a lower reliability for nonstructural members.

Design of Cold-Formed Steel Nonstructural Members By Roger LaBoube, Ph.D, P.E., Helen Chen, Ph.D, P.E., LEED AP-BD+C and Jay Larson, P.E., F. ASCE

What is a Nonstructural Member?

Acknowledgements: The authors express their appreciation to the members of the AISI Committee on Framing Standards and its Nonstructural Task Group for their support and cooperation during the development of AISI S220.

The previous standards when defining a nonstructural member are focused on wall assemblies, as defined in the following descriptions. ASTM C645 Standard for Nonstructural Steel Framing Members A member in a steel framed wall system which is limited to a transverse (out-ofplane) nominal load of not more than 10 lb/ft2 (0.48 kPa), a superimposed nominal axial load, exclusive of sheathing materials, of not more than 100 lb/ft (1.46 kN/m), or a superimposed nominal axial load of not more than 200 lbs (0.89 kN). AISI S100 [CSA S136], North American Specification for the Design of Cold-Formed Steel Structural Members, 2007 Edition with Supplement 1

10 February 2013

An interior partition wall stud in a composite steel framed interior wall system with sheathing attached to both flanges and that is limited to a transverse (out-of-plane) nominal load of not more than 10 lb/ft2 (0.48 kPa), a superimposed nominal axial load, exclusive of sheathing materials, of not more than 100 lb/ft (1.46 kN/m), or a superimposed nominal axial load of not more than 200 lbs (0.89 kN). AISI S200, North American Standard for Cold-Formed Steel Framing – General Provisions, 2007 Edition A member in a steel framed system which is limited to a transverse(out-of-plane) load of not more than 10 lb/ft2 (0.48kPa), a superimposed axial load, exclusive of sheathing materials, of not more than 100 lb/ft (1.46 kN/m), or a superimposed axial load of not more than 200 lbs (0.89 kN). However, the nonstructural profile is often used in interior fascia and ceiling construction. Also, burying numeric requirements in a definition was considered poor standards’ writing. During the development of AISI S220 and companion 2012 revision of AISI S200, the definition of nonstructural member was generalized to include other nonstructural members such as those used in interior fascia and ceiling construction: Nonstructural Member. A member in a steelframed system that is not a part of the gravity load resisting system, lateral force resisting system or building envelope. The numeric load limitations were retained and moved to the Scope section of AISI S220. However, it is important to note that the nonstructural member definition now applies to broader applications.

Design Approaches Historically, the nonstructural wall assembly has been load tested in accordance with ICC-ES AC86 to define the strength and stiffness of the cold-formed steel wall stud acting within a composite assembly that included the gypsum wallboard. Load tables presented the design capacity of the composite wall assembly, which were based on a safety factor of 1.5. Although the composite wall assembly offered economic advantages, design conditions also often required the nonstructural member to be designed acting non-composite with the sheathing material. Examples of non-composite design conditions are ceiling framing, interior fascia framing, or partition walls with sheathing on one side only. Historically, assemblies using the non-composite assembly design approach were designed neglecting the composite-action contribution of the attached sheathings based on the design provisions of AISI S100. Thus, a safety factor of 1.67 for a bending member or 1.8 for an axial loaded member was imposed.

AISI S220 has addressed the inconsistency in the safety factors for composite and noncomposite assemblies. AISI S220 recognizes that the consequence of failure for a nonstructural member is less than for a structural member and, consequently, permits a lower safety factor or greater phi factor for nonstructural members.

Equivalent Thickness Sections

Non-composite Assemblies A non-composite assembly is defined as an application wherein the design that neglects the contribution of the attached sheathing to either the strength or stiffness. AISI S220 provides the following options when designing a non-composite assembly:

Member Design Because nonstructural members typically are relatively thin, they often do not meet the various dimensional (i.e., slenderness) limitations prescribed by Section B1 of AISI S100. Thus, the provisions of Chapters B and C are often not directly applicable. To facilitate design of the nonstructural member sections both meeting and not STRUCTURE magazine

“(i) Design using Chapters A through E of AISI S100 [CSA S136] with: ΩN = 0.9 Ω φN = 1.1 φ where Ω = Safety factor per relevant section of AISI S100 [CSA S136] φ = Resistance factor per relevant section of AISI S100 [CSA S136]” To employ the above provision, the crosssection profile must meet all dimensional and ductility limitations imposed by AISI S100. continued on next page

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Historically ASTM C645, Table 2, has stipulated minimum section properties for the nonstructural member. Included was the design property, Mn/Ω, and the minimum base steel thickness. ASTM C645 Section 4.3 stated: “Members shall be manufactured from steel having a minimum thickness, individual measurement of 0.0179 inches before application of protective coating.” The minimum base steel thickness was given, which was based on meeting the width-to-thickness ratios of Chapter B of AISI S100. However, ASTM C645 Section 9.2 permitted nonstructural profiles to have thickness values less than 0.0179 inches: “Members that can show third party testing in accordance with ICC-ES-AC86 and conform to the limiting heights tables in Specification C754 need not meet the minimum thickness limitation set forth in Section 4.3 or the minimum section properties set forth in 8.1” The minimum section properties in Section 8.1, for example Mn/Ω as listed in Table 2, were computed using AISI S100 with Fy of 33 ksi. To achieve more economical design solutions, manufacturers have developed proprietary cross sections that are thinner than 0.0179 inches, but have achieved the Mn /Ω required by ASTM C645 by using higher yield strength materials. These proprietary cross sections have been labeled equivalent thickness, i.e. EQ, sections. They possess the requisite Mn/Ω but are thinner than 0.0179 inches. For this reason, AISI S220 does not include a minimum thickness requirement.

meeting the Section B1 requirements, the following provisions have been adopted into AISI S220 for both the non-composite and composite assembly applications.

February 2013

The traditional nonstructural 35/8-inch depth C-section wall stud having a thickness equal to or greater than 0.0179 inches could utilize this provision. Traditionally, a 10 percent reduction in the omega factor or a 10 percent increase in the phi factor has been permitted for the composite wall assemblies. This reduction or amplification factor has been extended to the nonstructural assembly in AISI S220. For a section not meeting either the dimensional limitations of AISI S100 Section B1 or ductility limitations of AISI S100 Section A1.2, physical tests or rational analysis is to be employed. Thus, AISI S220 requires the following when tests alone are utilized to define the member’s strength: “(ii) Chapter F of AISI S100 [CSA S136] with: β0 = 1.6 where β0 = Target Reliability Index in accordance with Section F1.1(b) of AISI S100 [CSA S136] Ω = Safety factor per Section F1.2 of AISI S100 [CSA S136] φ = Resistance factor per Section F1.1(b) of AISI S100 [CSA S136]” It is noteworthy that the above provision will result in an omega of approximately 1.5 or a phi factor of approximately 1.0. Thus a safety factor consistent with the traditional safety factor used for a composite wall assembly is achieved. For a section not meeting either the dimensional or ductility limitations of AISI S100 and rational analysis per Section A1.2, the safety factor, Ω, is 2.0 and the φ is 0.8. However, if tests are used to validate the rational analysis, AISI S220 permits the following: “If Section A1.2(b) of AISI S100 [CSA S136] is utilized then supplementary tests are permitted to be performed and Chapter F of AISI S100 [CSA S136] is permitted to be employed for determination of Ω or φ, with Pm replaced by Ptest/Pcompute and β0 in accordance with the provisions above. In the use of AISI S100 [CSA S136] Chapter F, the professional factor, P, shall be the test-to-predicted ratio where the prediction is that of the rational engineering analysis method selected, Pm is the mean of P and VP, the coefficient of variation of P. At least three tests shall be conducted.” Composite Assembly A composite assembly is as a wall stud application wherein the design reflects the contribution of the attached sheathing to either the strength or stiffness of the wall stud.

AISI S220 provides the following guidance when designing a composite assembly: “(b) Composite Assembly Design – Assemblies using a composite assembly design approach shall be designed based on the tests undertaken and evaluated in accordance with Chapter F of this standard.” For cold-formed steel nonstructural members in interior nonload bearing wall assemblies, ICC-ES AC86, Acceptance Criteria for ColdFormed Steel Framing Members – Interior Nonload-Bearing Wall Assemblies, is generally an approved test method.

applied. The rational analysis determines that Mn = 3.26 inch-kips, based on the engineering judgment that the equations in AISI S100, Chapter B and Section C3.1.1 can be used. The safety factor and phi factor are computed using AISI S220 Section B1(a)(ii). Test

Mtest (inch-kips)

Mtest/Mn

2.90

0.89

2.99

0.92

2.95

0.90

Average

Connection Design Connection design is in accordance with AISI S100 [CSA S136] or testing in accordance with Section F1 of AISI S100 [CSA S136]. Additional design guidance is provided in Chapter D of AISI S220 regarding screw installation, stripped screws, spacing and edge distance of screws and attachment of gypsum board. The standard does not mention the penetration test for screws, i.e. the procedure for evaluating the member’s ability to pull the head of a screw below the surface of gypsum sheathing, which is addressed by ASTM C645 Section 10. Therefore, building code provisions continue to require compliance with ASTM C645 Section 10.

Illustrative Examples Using fictitious test data for Mtest /Mn, the intent of the following example problems is to illustrate the application of Section B1of AISI S220. The examples illustrate the application of the various non-composite assembly design provisions. Given: 362S125-152 Design thickness = 0.016 inch (0.0152 inch/0.95 per AISI S100 Section A2.4) Fy = 50 ksi Inside bend radius = 0.030 inch Edge stiffener = ¼ inch Mn = 3.26 inch-kips computed per AISI S100, Chapter B and Section C3.1.1 (Note: This calculation ignores the fact that the width-to-thickness ratios violate Section B1.) (a) Example 1 [Rational Analysis with Supplementary Tests] – Using AISI S220 Section B1(a)(ii). For this situation, the design cannot be performed by AISI S100 Chapters B through E because the widthto-thickness ratios violate Section B1. Thus, AISI S100 Section A1.2(b), rational analysis along with supplementary tests is

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February 2013

0.90

Std Dev. COV

0.0153 0.0170

Based on the Mtest/Mn ratio, with Mn computed using AISI S100 Chapters B and C as a rational analysis results in an average 10% over estimation of the cross-section moment capacity. Thus, using AISI S100 as the rational analysis and based on the test results, the design moment capacity is the value determined by rational analysis; i.e., 3.26 inch-kips, with the following: Ω = 1.68 φ = 0.96 The Ω and φ were computed using Chapter F of S100 with β0 = 1.6 (b) Example 2 [Rational Analysis with Supplementary Tests]–Using AISI S220 Section B1(a)(ii). For this situation, the design cannot be performed in by AISI S100 Chapters B through E because the width-to-thickness ratios violate Section B1. Thus, AISI S100 Section A1.2(b), rational analysis along with supplementary tests is applied. The rational analysis determines that Mn = 2.93 inch-kips , based on the engineering judgment that the equations in AISI S100, Chapter B and Section C3.1.1 result in an average 10% over estimation of the cross-section moment capacity. The safety factor and phi factor are computed using AISI S220 Section B1(a)(ii). Test

Mtest (inch-kips)

Mtest/Mn

2.90

0.99

2.99

1.02

2.95

1.01

Average

1.006

Std Dev.

0.0153

COV

0.0152

Because supplementary tests were performed in combination with using Chapter B and Section C3.1.1, a reasonable rational analysis,

the design moment capacity is the value determined by rational analysis; i.e., 2.93 inch-kips (0.331 kN-m), with the following: Ω = 1.50 φ = 1.07 The Ω and φ were computed using Chapter F of S100 with β0 = 1.6 (c) Example 3 [Rational Analysis without Supplementary Tests] – Not using AISI S220 Section B1(a)(ii). For this situation, the design cannot be performed by AISI S100 Chapters B through E because the width-to-thickness ratios violate Section B1. Thus, AISI S100 Section A1.2(b) is being applied without supplementary tests. The safety factor and phi factor are defined by AISI S100 Section A1.2(b). Because supplementary tests were not performed and a rational analysis using AISI S100 Chapter B and Section C3.1.1 had been adopted, Mn = 3.26 inch-kips and the following factors, per Section A1.2(b) of S100 would apply: Ω = 2.0 φ = 0.80 (d) Example 4 [Tests without Rational Analysis]–Using AISI S220 Section B1(a)(ii). For this situation the design cannot be performed in by AISI

S100 Chapters B through E because the width-to-thickness ratios violate Section B1. Thus, AISI Section A1.2(a) is being applied. The safety factor and resistance factor are computed using AISI S100 Chapter F. Test

Mtest (inch-kips)

2.90

2.99

2.95

Average

2.95

Std Dev. COV

0.0451 0.0153

The design value is the average tested value of 3.29 inch-kips with the following: Ω = 1.51 φ = 1.06 The Ω and φ were computed using Chapter F of S100 with β0 = 1.6

Conclusion AISI S220, North American Standard for Cold-Formed Steel Framing – Nonstructural Members, was developed in 2011. It clearly delineates and eliminates confusion between ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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February 2013

the requirements for cold-formed steel structural members and nonstructural members. It provides a level playing field for cold-formed steel manufacturers to develop new, efficient products for nonstructural applications.▪ Roger LaBoube, Ph.D, P.E. is Curator’s Teaching Professor Emeritus of Civil Engineering and Director of the Wei-Wen Yu Center for Cold-Formed Steel Structures at the Missouri University of Technology. Roger is active in several professional organizations and societies. He also serves on STRUCTURE’s Editorial Board. Roger can be reached at laboube@mst.edu. Helen Chen, Ph.D, P.E., LEED AP-BD+C is manager of the Construction Standards Development of the American Iron and Steel Institute. She is directly involved in the development and update of AISI construction standards. Helen may be reached at hchen@steel.org. Jay Larson, P.E., F. ASCE is Managing Director of the Construction Technical Program of the American Iron and Steel Institute. Jay serves on numerous Boards and Committees related to Cold-Formed Steel structures and Specifications. Jay can be reached at jlarson@steel.org.

Building Blocks updates and information on structural materials

tructural Insulated Panels (SIPs) have historically been used more for residential construction than for non-residential construction. However, SIPs are gaining popularity in the commercial arena, especially for school construction. There are several schools throughout the country that have incorporated SIPs. One such school is Silvis Middle School in Silvis (East Moline), IL. This 52,600 square-foot facility was designed with SIP roof panels over metal bar joists, steel beams, and steel columns. SIPs were also used for the exterior walls, creating a full SIP building envelope. It is often assumed that SIP construction is more expensive than other construction methods. However, one of the reasons that SIPs were selected as the method of construction for the Silvis Middle School project was because they were the least expensive of the options that were being considered for the exterior walls.

Using Structural Insulated Panels on Non-Residential Structures A Case Study By Thomas A. Moore, P.E., LEED AP

Thomas A. Moore, P.E., LEED AP is Project Manager at Steven Schaefer Associates, Inc., Consulting Structural Engineers in Cincinnati, OH. Thomas also serves on the Board of Directors and as the Educational Committee Chair for the Structural Insulated Panel Association (SIPA). He can be reached at tam@ssastructural.com. In addition, companies and individuals can be contacted through the member directory that is available on the SIPA website at www.sips.org.

The Role of the SIP Engineer

Structural Insulated Panels are a pre-engineered building component, similar to pre-engineered wood trusses. SIP manufacturers produce SIP shop drawings, which are then reviewed by the project design team. On non-residential projects (and some residential projects), these shop drawings must be stamped by a PE licensed in the state where the project occurs. The SIP engineer reviews panel thicknesses, panel spans, connections, etc. The main difference between SIPs and wood trusses is that SIP span charts and load tables are typically based on testing, rather than material properties and calculations. Most SIP manufacturers have a code listing through ICC or an independent testing company. The manufacturer’s code listing will typically include an axial load table for wall panels and transverse load tables that would apply to wall, floor, and roof panels. There is also usually a shear wall capacity indicated, which is sometimes referred to as a “racking shear” capacity. The role of the SIP engineer is to compare the code-required design loads to the allowable loads in the code listing. Adjustments are then made, as required, to insure that the structure can resist the required design loads. Like any other pre-engineered system, there is a line between what is designed by the specialty engineer and what is designed by the engineer of record. This line can become blurred at times, especially on a project where the architect and/ or engineer of record are not familiar with structural insulated panels. It is important to identify the scope of work of the specialty engineer (SIP

14 February 2013

SIP wall panels go up first, followed by the roof panels, providing a strong, well-insulated building enclosure.

engineer) up front, in order to avoid overlap or gaps in the structural design on the project. Ideally, the SIP engineer would only be responsible for the component loads that apply directly to the SIP panels, and not to the global loads that apply to the building as a whole. However, some of these global loads (like shear wall loads) might be calculated by the engineer of record and given to the SIP engineer to check against the capacity of the SIPs.

A Diaphragm is a Diaphragm is a Diaphragm One structural element that is present on most buildings is a diaphragm. SIP structures are no different. Every SIP roof will act as a roof diaphragm. The challenge is that most SIP manufacturers do not have specific allowable diaphragm values indicated in their code listing. The main reason for this is that they have not had specific ASTM diaphragm testing performed on their panels. The allowable “racking shear” values indicated in some manufacturers’ literature are often used when checking both shear walls and diaphragms. This is a valid approach, but it’s not quite as simple as just comparing the numbers. All shear walls and diaphragms have chord forces that must be accounted for in the design, and this applies to SIP structures too. Fortunately, most SIP shear walls have continuous wood studs embedded in the ends of the panels, and they serve as the chords at the ends of shear walls. Hold down anchors are attached to the bottom of those studs to resist overturning forces, where applicable. The top and bottom plates of each shear wall will also serve as chord elements, and those plates need to be able to resist the chord forces as well. Roof diaphragms are typically much larger than shear walls, which can be a blessing and a curse. The benefit is that diaphragm forces are resisted along the full length of the perimeter walls or

Figure 2.

Figure 1.

other lateral force resisting elements. The challenge is that the wood 2x members that are embedded in the edges of the roof panels will not be continuous, making it necessary to check/design the joints for the chord forces. In addition, attachment of the diaphragm to the structure below must be designed just like any other diaphragm. On the Silvis Middle School

project, the SIP manufacturer was required to have diaphragm testing performed on their panels in order to satisfy the project design team. As a result, diaphragm test reports were available, which included specific edge conditions that were used during the testing process. See Figures 1 and 2 for details of the edge conditions that applied to the perimeter

Figure 3.

of the roof diaphragms on that project. These sections were taken from the diaphragm test reports, and they were included as part of the SIP shop drawings for the project. Section 3-3 shows metal straps being used to transfer tension chord forces across a joint in the 2x members embedded in the perimeter of the roof panels. If the roof diaphragm had consisted of metal roof deck over steel framing, the roof diaphragm forces would have been compared to allowable diaphragm capacities published in the metal deck manufacturer’s literature. Those allowable diaphragm capacities would fluctuate, depending on the spacing between fasteners at the edges of the deck. Metal deck diaphragms have a higher capacity when they are attached to the structure more frequently, and when they have more fasteners at the joints between sheets. SIP roof diaphragms are no different. The diaphragm testing was performed on SIP roof panels with edge and joint fasteners spaced at 6, 4, and 2 inches on-center. The results indicated that SIP diaphragms have higher capacities when the fasteners are spaced closer together. Therefore, the general concept of designing a SIP diaphragm is really no different than designing diaphragms of other materials. The Structural Insulated Panel Association (SIPA) has purchased the

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220

Structural Design Spreadsheets

diaphragm test results from the SIP manufacturer for the Silvis Middle School project, and those results will be made available to other SIP manufacturers that are SIPA members. This will go a long way toward allowing the use of SIPs on other non-residential projects, particularly by SIP manufacturers that have previously never had diaphragm test reports that they could use.

Do the Details Match the Design Intent? On the Silvis Middle School project, the SIP roof panels were supported by steel bar joists and steel beams. The lateral force resisting system for the building consisted of a combination of steel braced frames and steel moment frames. Design engineers asked if the SIP wall panels were intended to take axial load from the roof panels, and were told that they were not. They also asked if the wall panels were intended to act as shear walls, and were told that they were not. The wall panels were intended to resist transverse wind loads only, and they were not to be designed for any other loads. On the project drawings, the SIP roof panels were shown being attached directly to the top of the SIP walls, which were located immediately adjacent to the perimeter line of framing. Since the bottom of the roof panels were shown in direct contact with the top of the wall panels, the steel framing could not deflect without imposing axial load into the wall panels. In addition, the direct attachment of the roof panels to the wall panels would not allow the steel moment frames to “drift” without imposing shear load into the wall panels. Since the details were not consistent with the design intent, the design engineers suggested changes to the detailing. In order for the steel roof framing to deflect without applying load to the top of the wall panels, a 2-inch gap was created between the top of the wall panels and the bottom of the roof panels. This gap was then filled with compressible foam to complete the building envelope (Figures 3 and 4 , page 15 ). Allowing the steel moment frames to drift without applying shear loads to the wall panels was a much more challenging task. The tricky part was that the wall panels still had to resist transverse wind loads, but they could not be directly attached to the roof panels. The solution was to provide a slotted connection that would allow movement in the direction parallel to the wall, but that would resist movement in the direction perpendicular to the wall. Since the perimeter

Figure 5.

Figure 6.

line of steel framing was adjacent to the wall panels, this connection had to be made at the bottom of the steel beams, for accessibility reasons. The connection could not be made at the top of the beams, because there was no access to the fastener once the walls were in place (Figures 5 and 6 ).

Conclusions Structural Insulated Panels (SIPs) can be used on non-residential structures, as well as residential structures. Many of the design challenges that designers face when designing with SIPs are no different than

STRUCTURE magazine

February 2013

when designing with other materials. The general concepts of structural design still apply when designing with SIPs – complete load paths, applied loads must not exceed allowable loads, detailing must be consistent with design intent, etc. SIP manufacturers and SIP engineers typically have a lot of experience and knowledge with regards to designing and building with SIPs. Design teams should not be afraid to tap into that knowledge and experience.▪ This article was previously published in the Wood Design Focus, Spring 2012. It is reprinted with permission.

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Rehabilitation of Historic Holmes Street Bridge By Robert E. Mateega, P.E.

Historic Holmes Street Bridge.

ridges across the country are deteriorating or becoming functionally obsolete. Therefore, Departments of Transportation (DOTs) across the country have to identify and save historic bridges, thereby streamlining the replacement of non-historic bridges. The Minnesota Department of Transportation (MnDOT) identified the Holmes Street Bridge (Bridge No. 4175), commonly referred to as the Shakopee Truss Bridge, as one of 24 bridges in Minnesota to preserve once funding became available. For the Holmes Street Bridge, funding became available with passage of the American Recovery and Reinvestment Act (ARRA) of 2009. The project team of HDR as the Bridge Engineer and Mead & Hunt as the Project Historian faced many challenges. The first was the need to complete not only the inspection, analysis and rehabilitation report in six months, but also receive approval on final rehabilitation plans and specifications from MnDOT, the State Historic Preservation Office (SHPO) and the Federal Highway Administration (FHWA). A similar project would normally take 12 to 18 months. The next challenge was to identify engineering solutions that would meet safety and maintenance requirements, while preserving the historic features of the bridge. The inspection and analysis revealed the bridge to be in generally poor condition, with severe to critical deterioration in various steel and concrete members. Innovative design solutions that preserved the historical significance of the bridge included replacement of the existing ornamental railing in-kind with a safety modification, installation of replica lighting, replacement of some truss members and steel overhang brackets with shop fabricated members using rivets, and rehabilitation of concrete components using unique renovation techniques.

Bridge Description The Holmes Street Bridge, built as a highway bridge in 1927, provided access across the Minnesota River for the city of Shakopee and points west to the Twin Cities Metro Area. Listed in the National Register of Historic Places (National Register) as a rare example of a deck-truss bridge in Minnesota, the Holmes Street Bridge is a 645-foot long STRUCTURE magazine

bridge with an out-to-out width of 42.4 feet. The superstructure consists of two 30-foot long cast-in-place reinforced concrete deck girder south approach spans, four 125-foot long riveted steel deck truss main spans, and two 30-foot long cast-in-place reinforced concrete deck girder north approach spans. The truss spans consist of three parallel riveted steel Warren trusses with verticals. The bridge deck consists of a 30-foot wide roadway and two 6-foot wide raised cantilever sidewalks. The substructure consists of a U-shaped reinforced concrete South Abutment, two reinforced concrete south approach piers with four arched openings, three reinforced concrete river piers with two recessed arches on each side, two reinforced concrete north approach piers with four arched openings, and a U-shaped reinforced concrete North Abutment that features a stairway on the east side. In order for a property to be historic, it has to have characterdefining features which are prominent or distinctive aspects, qualities, or characteristics that contribute significantly to its physical character. Features may include materials, engineering design, and structural and decorative details. The Shakopee Truss Bridge has two character-defining features which were defined as follows in the MnDOT Historic Bridge Management Plan for Bridge No. 4175 (June 2006): • Feature 1, Deck-truss design and construction. The Shakopee Truss Bridge is a rare example of a deck truss bridge in Minnesota. This feature includes the four main spans, each of which has three riveted, steel trusses designed in a Warrenwith-verticals configuration. • Feature 2, Classical Revival architectural details. Because of its urban location as a gateway to downtown Shakopee, the Shakopee Truss Bridge was designed with Classical Revival stylistic elements. This feature includes recessed panels in the concrete river piers (Piers 3-5), open-arched concrete piers in the approach spans (Piers 1-2 and 6-7), recessed panels on the abutments, ornamental metal railings on the approach spans and main spans, concrete parapet railings on the abutments, and stairways adjacent to the north abutment.

February 2013

In-Depth Inspection and Analysis The project team performed an in-depth inspection of the bridge from within arm’s length of each member. Access to inspect the bridge truss members was provided from an Under Bridge Inspection Vehicle (UBIV) with a 60-foot reach. The in-depth inspection revealed delaminating and spalling concrete members; severely corroded ornamental railing members; severely corroded sections of stringers, floor beams and overhang brackets; severely corroded truss members; gusset plate section loss; pack rust; and frozen bearings. Most of the deterioration of the steel members was located in areas that were exposed to moisture, namely the exterior trusses on either side of the bridge and areas adjacent to the open joint at the end of each truss span. LARSA and STAAD 2D truss models were created to determine the forces in the various truss members. Prior to the project, it was determined that, following rehabilitation, the bridge would be reopened as a pedestrian and bicycle bridge with vehicles using a new bridge constructed downstream. Therefore, the bridge deck was analyzed using the controlling load case between an 85 psf pedestrian live load or an American Association of State Highway and Transportation Officials (AASHTO) standard H-10 Design Truck which consists of 4 kip front axles and 16 kip rear axles separated by 14 feet. The raised sidewalk was analyzed using only the 85 psf pedestrian live load. A special load case consisting of the UBIV was also considered, as this would be the vehicle used to inspect the bridge. The analysis followed the AASHTO Manual for Bridge Evaluation and the MnDOT LRFD Bridge Design Manual. The analysis models coupled with spreadsheets developed by the project team to analyze gusset plates, and information from the

Deteriorated truss members and gusset plates prior to repair.

in-depth inspection, revealed which portions of the bridge needed to be repaired or replaced. This included gusset plates, floor beams, stringers, overhang brackets, and truss members; the raised concrete sidewalks; the roadway deck; expansion joints; bearing pins; the ornamental metal railing; and concrete surfaces.

Repair Recommendations and Innovative Solutions As the bridge was historic, the project team had to ensure that the rehabilitation plans on this eight-span concrete girder and steel deck

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truss structure complied with Section 106 of the National Historic Preservation Act, and followed guidelines in the National Park Service Preservation Brief 15, Preservation of Historic Concrete. Additionally, the project could have no adverse effects on the historic resource as determined by MnDOT, SHPO and FHWA. To streamline the process of determining the appropriate treatment methods for the extensive concrete repairs, the project team developed a repair matrix that distinguished treatments based on location and public visibility. For example, the team determined that concrete areas not visible, such as river pier areas, could be repaired with standard MnDOT construction techniques. Areas clearly visible to the public, including abutments and parapets, required historic repair techniques to ensure conformance with historic surfaces, and were included in the detailed project specific specifications. The specifications included requirements that the repaired concrete match the adjacent existing concrete in terms of finish, texture, surface detail and color. The contractor was required to provide a minimum of 3 samples, at least 12 inches by 12 inches in size, to demonstrate that they could match the adjacent existing concrete. The matrix clarified and expedited the appropriate treatments for both plan development and communication with the contractor. An additional repair matrix was developed to address the repair and/ or replacement of deteriorated steel truss members. Rivets are a key feature of historic truss members, but few contractors today are able to install rivets in the field. When 30 steel sidewalk overhang brackets and six bottom chord members in highly visible areas were severely deteriorated and required replacement, the project team specified that the new members be shop-fabricated with rivets. Historic railing typically presents design challenges due to noncompliance with current safety standards. The original metal ornamental railing was no exception. Not only did the railing openings not meet current MnDOT or AASHTO standards, but multiple sections exhibited critical deterioration. The project team looked at six different options ranging from reuse to replication to redesign, but based on issues of deterioration, cost and safety, the team chose to replicate the original railings with minor modifications, while refurbishing original castiron newel posts. AASHTO standards require that openings between members of pedestrian railing shall not allow a 6-inch sphere to pass through the lower 27 inches of the railing and an 8-inch sphere should not pass through openings above 27 inches. MnDOT standards, which are more stringent than AASHTO, require that openings between members shall not allow a 4-inch sphere to pass through the lower 27 inches, and a 6-inch sphere should not pass through any opening above 27 inches. The original railing allowed a 6-inch sphere to pass through openings both below and above 27 inches. Therefore, MnDOT issued a design exception for the project, whereby the MnDOT requirements for the openings in a pedestrian railing were waived in favor of the AASHTO requirements. The replica railing was able to meet AASHTO opening requirements by the addition of a 3/16-inch steel stainless steel cable, which prevented a 6-inch sphere from passing through the lower 27 inches of the railing. It was determined that the addition of the stainless steel cable was less intrusive on the character-defining feature, than changing the dimensions of the railing to meet today’s design standards. To reduce cost, the team recommended button-head bolts with acorn-style nuts replicate the 1,200-plus rivet connections of the original railing. Another innovation related to historic truss members was a solution to prevent future deterioration, most of which was due to drainage runoff from the deck drains and open joints at each truss end. Hydraulic analysis showed that the deck drains could be eliminated, and the open joints could be replaced with strip seal expansion joints. STRUCTURE magazine

Shop-fabricated bottom chord truss member with rivets.

This was a simple and ingenious solution to damaging deck drainage runoff and the subsequent corrosion of steel truss members.

Construction and Lessons Learned Construction of the rehabilitation project was performed by Edward Kraemer and Sons as the prime contractor. For concrete repairs, the contractor used shotcrete with subsequent surface treatment, employing color stain and microabrasive blasting for surface texture and graffiti removal on highly visible historic areas. This was the first time the technique was used by MnDOT for this purpose or permitted by the SHPO for historic concrete repair. The contractor also successfully prepared test panels for on-site product demonstrations for MnDOT and SHPO, and now these methods are approved and provide practical solutions to historic concrete repair challenges for future projects. One of the lessons learned on the project was to pay close attention to member removal and the location of rivets with heads on only one side. Removal of bottom chord members was very challenging since the gusset plates at the bearing points were remaining in-place; some of the rivets in the gusset plate at the bearing point only had a head on one side and therefore could not be replaced. The contractor was able to remove the bottom chord member by removing rivets with heads on both sides, and prying the member out. The project benefited from having repairs priced per type, e.g. stringer repair or truss member repair. Given the old age of the bridge, additional areas requiring repair were identified when portions of the bridge were removed. Since repairs had been priced by type, which included means and methods, the compensation of additional repair items was straight forward, without having to determine the additional cost of installing and carrying out the repair.

Conclusion Rehabilitation of the historic Holmes Street Bridge preserved an elegant 84-year old structure for future generations of pedestrians and bicyclists. Innovative, collaborative engineering design preserved or restored historic materials and features, including ornamental railing, riveted bridge components and concrete detailing. The Holmes Street Bridge rehabilitation, stands as a creative model for similar projects in communities throughout Minnesota and the United States.▪

Robert E. Mateega, P.E. (robert.mateega@hdrinc.com), is a Senior Bridge Engineer at HDR Engineering Inc., in Minneapolis, Minnesota. February 2013

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Translucent Dome for Argentine Soccer Stadium Matthys Levy, P.E.

Figure 1: Aerial view of completed stadium showing figure-eight-shaped opening.

he design of the roof of the recently completed La Plata football stadium represents a serendipitous merging of two concepts: the award winning competition entry by the architect, Roberto Ferreira, and the Tenstar Dome™ structure originally developed by Weidlinger Associates for the Georgia Dome. Compared to the Georgia Dome, however, the La Plata project presented some unique engineering challenges. Instead of having a continuous oval perimeter, the plan of La Plata is based on two circles 279 feet (85 meters) in diameter whose centers are separated by 157 feet (48 meters), resulting in a configuration that looks like a MasterCard® symbol (Figure 1). Furthermore, the requirement for natural ventilation resulted in the need for openings at the two peaks, 222 feet (67.6 meters) above the playing field, defined by the center of the two circles and protected from rain by umbrellas, affectionately called “sombreros.” Finally, a compression ring around the arena, instead of being built of concrete as at the Georgia Dome, was conceived of and built as a triangular steel truss, partly to introduce lightness in what is a very massive structure, to encourage free airflow in this naturally ventilated dome, and to provide space for two levels of skyboxes and control booths. The 53,000-seat soccer stadium in La Plata, Argentina, opened in 2003, lacking its signature twin-peaked fabric dome, and reopened to great fanfare on February 17, 2011, after completion of its roof structure, which was two thirds covered. Construction of the first phase of the project started in 1998, resulting in the completion of the playing field somewhat below original grade and an earth berm on which was poured a concrete seating bowl, crowned by the trussed steel compression ring. The material for the roof, including the fabric and cables for the Tenstar Dome, was also purchased at that time and placed in storage when Argentina faced a financial crisis in 2000. For the next 11 years, the stadium, with its trussed compression ring in place, stood waiting for construction of the roof.

The trussed compression ring (Figure 2) consists of steel pipes with diameters of 42 inches (1,066 millimeters) for the top chord, 36 inches (914 millimeters) for the posts, and 28 inches (711 millimeters) and 18 inches (457 millimeters) for the diagonals. The vertical posts of this truss form a colonnaded gallery at the back of the stands and sit on baseplates anchored to the foundation which consists of concrete pile caps at the top of the berm, with concrete piles that extend down to virgin soil. Concrete grade beams tie the pile caps together and act essentially as the bottom chord of the trussed compression ring. Since the compression ring must carry both gravity loads from the roof and wind loads acting against the roof surfaces, lateral resistance is required between the ring and the foundations. The roof structure is also subject to thermal stresses due to temperature variations resulting from restraining the ring at the foundation. These were analyzed and were found to be acceptable if one post on each side of the kink (where the two circles meet) was radially released. This was accomplished with guided Teflon® bearings that permit radial displacement but not circumferential movement. Framing for the skyboxes and control

STRUCTURE magazine

Figure 2: Interior view of compression ring.

February 2013

Figure 3: Interior view during construction, showing catwalk on bottom hoop cable and ridge cables at top nodes.

Figure 4: Attachment of cables to post.

booths was set into and hung from the 42.6-foot (13 meters) high and 29.5-foot (9 meters) wide trussed compression ring. The vertical posts were shop fabricated with gusset plates to catch diagonal and radial tubes. At the top of each post, a gusset plate was provided to engage the socket of the cable dome’s radial cables and fitted with holes through which temporary construction cables could be connected. Since the circumferential top chord pipe is always in compression, flanged, bolted connections were installed at the top of the posts. The truss diagonals are either bolted or pinned to the joint weldments. The top of the posts form the spring line for the dome, which consists of the triangulated ridgenet of cables characteristic of a Tenstar Dome. A series of three tension hoops step inward and upward from this inner top chord of the truss. Cables sloping down from the top of the posts hold the first of these hoops. From the node formed by the intersection of these sloping cables and the first tension hoop, a rigid vertical post, called a “flying post,” rises to the first line of ridgenet nodes. From those nodes, diagonal cables slope down to the second tension ring, which supports a second series of posts. This sequence is repeated until reaching the top of the third ring, at which point another series of cables converges at the center of each peak. Catwalks are attached to each hoop cable, and bridges interconnect the catwalks for access to the lighting and sound systems and rigging for special events (Figure 3). Because of the kink at the center of the stadium that results from the reentrant perimeter, the members along the centerline are subject to compression rather than tension and are therefore pipes rather than cables. This introduced a complication in the erection of the dome and the need for added temporary towers. It also necessitated a field modification to the nodes at the top of the posts in the region of the kink to permit both radial and transverse rotation. The nodes at the top and bottom of each of the flying posts are unique weldments that have to accommodate the continuous tension hoop cables and diagonal cables, as well as attach to the post itself (Figure 4 ). The hoop cables that continue through the node sit in a slot formed by steel bars welded to a steel plate. They are clamped down with a second plate that is bolted to the first, creating a friction clamp. Since as many as four 3.9-inch (98-millimeter) cables are used in the first hoop, the resulting welded steel node assemblies are very large, with overall dimensions of 6.6 feet (2 meters) x 6.6 feet (2 meters) x 3.3 feet (1 meter) and weighing as much as 2 tons. The top weldment, with gusset plates for ridge cables and diagonal

cables, is rigidly attached to the post, while the bottom weldment is pinned, permitting radial rotation. The Tenstar Dome is a tensegrity system that is defined as a “spatial network in a state of self stress.” The system acts like a truss in which the bottom chord is interrupted and follows the line of hoop cables around to the opposite side of the arena. The system is truly three-dimensional rather than planar, and therefore benefits from the triangularization of the structural elements. This improves loadcarrying capability and permits the unconventional geometry of structures such as La Plata. To prevent cables from becoming slack under load, the system has to be prestressed, resulting in an extremely rigid structure. Instead of providing a means of adjusting the tension in each cable, in a Tenstar Dome such as La Plata, lengths are fixed based on the final configuration of the dome and the level of prestressing needed. This implies that the system remains slack until the last cable or post is installed, and therefore impacts the erection system. Two temporary towers were built to erect the roof structure, one at the center of each of the two peaks (Figure 5 ). Jacking cables from these towers were run through sheave blocks (pulley devices) at each node of the assembled hoops, laid out on the ground, and run through another set of sheave blocks at the top of the ring, which were in turn connected back down to the hoops. This arrangement lifted the hoop simultaneously upward and outward into its final position, where

STRUCTURE magazine

Figure 5: Temporary erection tower.

February 2013

Figure 6: Installation of fabric cover over cable network.

it could be connected to the diagonal cables. To create the kink, a temporary cable was stretched across the stadium, connecting the two sides of the hoop cable. The vertical posts were then lifted into place and attached to the nodes in the hoop cable. Afterwards, the ridge cables were attached to the top of the posts. This same procedure was followed to the center of each peak. During the erection of the rigid members comprising the elements across the kink at the centerline of the stadium, secondary temporary towers supported the arch structure. Also, since the compression ring tends to move inward when the cable net is installed prior to the completion of the arch structure, a telescoping vertical member was provided at the center of the arch and was jacked once the structure was completely assembled, in order to move the ring back out to its final location. Once the cable network was complete, the fabric covering was installed (Figure 6 ). The special fabric used on this project is a hightranslucency Teflon-coated fiberglass that was developed to provide sufficient natural light for growing the turf. Although studies demonstrated the fabric’s effectiveness, the owners were concerned about the damage to the turf that would occur when the arena is used for special event such as concerts. Therefore, it was decided to pave the playing area and to use palletized grass panels that could be stored outside the stadium when not needed for soccer games. This solution helped make La Plata Stadium a truly multipurpose arena. This phase of the roof construction extended the fabric only to the second hoop, leaving a figure-eight hole in the center of the stadium. (Figure 7 ). However, the Tenstar cable dome structure is currently complete, and when the balance of the fabric and its two sombreros are added, the architect’s original conception will finally be realized. The construction of the La Plata dome recognizes the adaptability of the Tenstar concept to complicated shapes that can be built in stages to meet owners’ financing constraints. Variants of this concept are currently on the drawing boards, including a retractable roof that rides on top of the cable dome, providing a lightweight, aesthetically pleasing yet economical solution for covered arenas.▪

Figure 7: Interior view of completed roof.

Matthys Levy, P.E. is chairman emeritus of Weidlinger Associates, Inc., and former director of its Building Design Group. Levy is the recipient of numerous professional awards. He is also the author of many popular books on structures and climate effects, including the classic Why Buildings Fall Down.

STRUCTURE magazine

The Team Engineer: Weidlinger Associates, Inc., New York, NY Architect: Roberto Ferreira, Arquitectos, Barcelona, Spain Roof Contractor: Birdair, Inc., Buffalo, NY Steel fabricator: Astillero Rio Santiago, Ensenada, Argentina Cable supplier: Wire Rope, Montreal, Canada Software: LARSA and MCM/BLD3D

Materials Cables: 500 tons Steel compression ring: 3,000 tons Skyboxes: 1,000 tons Posts, Arch pipes, Central pentagons: 800 tons Weldments, catwalks: 600 tons UltraLUX fabric: 29,300 square meters (315,268 square feet) and 27 tons

February 2013

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Queen Richmond Centre West Composite Cast Steel Nodes Suspend 11-Story Office Building above Two Heritage Structures By Carlos de Oliveira, M.A.Sc., P.Eng, Michael Gray, Ph.D. and Jeffrey Stephenson, P.Eng

lthough the Queen Richmond Centre West (Figure 1) in Toronto offers a brilliant example of adaptive re-use through its integration of two existing heritage buildings into the construction of a new 11-story office building, it’s the fact that the 11-story tower springs from above both existing buildings that makes Phase One of this development a truly unique structure. Critical to the realization of the design from both a structural and architectural perspective is the use of elegantly shaped 31,500pound cast steel nodes in the architecturally exposed structural steel framework supporting the building. In 2010, Allied Properties REIT commissioned Dermot Sweeny of Sweeny Sterling Finlayson &Co Architects (&Co) to design a landmark mixed-use development in Toronto’s entertainment district. &Co engaged Stephenson Engineering and, given the positioning of the two existing heritage structures on the site, presented the structural engineering firm with the challenge of suspending the office building above the two existing structures. This configuration would thus form a large L-shaped, glass-enclosed atrium with direct access from streets to the east and south of the complex as well as to a mid-block public lane to the north. &Co’s desire to offer tenants office space with clean, unobstructed ceilings led to their specification of a raised floor system for building services and ultimately drove their selection of an exposed reinforced concrete structural system for the 11-story tower – not the least-weight structure to suspend by any means. Stephenson Engineering’s early structural concepts for the support of the tower focused on the use of a mega-column and beam system which formed a moment frame assemblage capable of carrying the substantial gravity and lateral forces from the tower above. In addition to the considerable magnitude of the forces, also driving the size of these structural elements was the 70-foot clear height between street level and the underside of the tower. Although this structural scheme was capable of supporting the proposed tower, &Co challenged Stephenson to develop a more elegant concept. The Stephenson Engineering team held an internal design charette which, working with &Co, led to the development of the unique “delta frame” concept that was ultimately employed in the design and construction of the building. Essentially, each delta frame is an hourglass space frame configuration formed from two stacked rectangular-based space frame pyramids – the top pyramid being inverted such that the apex of both pyramids meet at a central point in space. With three such delta frames arranged within the complex’s L-shaped atrium and tied together with a diaphragm at their tops, the unbraced length of each of the inclined mega columns is reduced. Aligning each of the corners of the upper pyramids directly beneath tower columns above provides a direct load path for gravity loading. The three delta frames also form a major part of the lateral system – the only other effectual lateral support through the atrium space is provided by a single reinforced concrete stair and elevator core which descends down from the tower above. This concept immediately became the preferred solution by both the architect and the owner alike and became the focal point for all imagery surrounding the project (Figures 2 and 3). STRUCTURE magazine

Figure 1: This rendering shows the site from the south-east corner of Peter Street and Richmond Street. Courtesy of Sweeny Sterling Finlayson &Co Architects Inc. and Allied Properties REIT.

Figure 2: Rendering of the atrium from the Peter Street entrance, directly beneath one of the delta frame structures. Courtesy of Sweeny Sterling Finlayson &Co Architects Inc. and Allied Properties REIT.

The next challenge was the design of the members comprising the delta frames. To achieve the strength and stiffness required to support the office tower, the round tubular steel members of the delta frame needed to be 1000 mm (393/8 inches) in outer diameter and, since steel tubes of that diameter are not readily available in wall thicknesses greater than 50 mm (2 inches), the steel legs had to also be concrete filled such that their composite strength and stiffness could be relied upon to carry the massive forces involved. The central kernel point of the three delta frames – the joint where the four legs of the lower pyramidal frame meet the four incoming legs from above – also presented a unique engineering and fabrication

February 2013

Figure 4: Rapid prototype of the cast steel node at 1:20 scale. Courtesy of Cast ConneX Corporation. Figure 3: REVIT model view from outside of the Richmond Street entrance. Courtesy of Stephenson Engineering Ltd.

STRUCTURE magazine

February 2013

Figure 5: Rapid prototype of a full delta frame at 1:100 scale. Courtesy of Sweeny Sterling Finlayson &Co Architects Inc. and Allied Properties REIT.

the alternative geometry, delicately blending adjacent tubular extrusions together using variable radii, the resulting surface expression was of vertically continuous delta frame members. Rapid prototyping (Figures 4 and 5 ) was used to model two full delta frame assemblies – one featuring each node type – and the alternative nodal geometry was immediately identified as the preferred solution by the architectural team. Although shaping of the exterior of the node was primarily driven by aesthetics, shaping of the interior of the node was driven entirely by structural requirements and casting constraints. Since the legs of the delta frame were to be concrete filled, the supplier employed a cellular interior design which provides for the vertical continuity of the concrete fill within the legs of the delta frame members directly through the four independent chambers of the node. In so doing, concrete could be pumped from the bottom of each delta frame leg continuously

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challenge. From an architectural perspective, concentric framing resulted in the least visually obtrusive support structure; however, the complex, overlapping field-welded central junction could not be reliably fabricated. Hence a nodal approach was required, where the central intersection junction would be fabricated separately with the incoming members to be connected to the node in the field. To accommodate weld fabrication of the node itself – to provide weld access, reduce joint overlaps, and to reduce the need for internal stiffening – the tubular members had to be spread apart from one another, which in turn introduced significant eccentricity in the framing and necessitated the use of an 8-inch thick central plate at the “waist” of the node to tie all of the tubular elements together. The eccentricity in the framing imparted additional bending demand on the already heavily loaded delta frame members. More concerning, however, was that the lateral stiffness of each of the delta frames was significantly reduced with this approach, as counteracting forces passing through the node had to be transmitted through the central plate in shear and bending rather than directly through to the diagonally opposite lower leg as would be the case with a very stiff or fully concentric node. ETABS analyses showed that the stiffness of the node significantly affected the distribution of lateral forces between each of the delta frames and the other elements of the lateral system. The architectural team raised concern as well, as the central node had ballooned to twice its originally intended size, with the splaying of the legs of the delta frame being somewhat unsightly and the horizontal band produced by the central plate being quite far from what was originally envisioned.

During this time, the construction manager and builder for the project, Eastern Construction, reached out to local steel fabricators to discuss the construction of the delta frame structures. The design team simultaneously contacted Cast ConneX, as Stephenson wanted to investigate whether the use of a cast steel node would better address the complex structural and architectural requirements for the delta frames. After some initial discussions, Cast ConneX was engaged by Eastern Construction to conduct a feasibility study, and carried out a preliminary volumetric optimization of the node and prepared a detailed costing for their design-build services. Satisfied that casting the nodes provided significant advantages and value over a conventionally fabricated node – improved strength, stiffness, and reliability and vastly improved aesthetics – Allied Properties engaged Cast ConneX via Eastern Construction to engineer, detail, and supply 3 identical cast steel nodes for the project. Simultaneously, local steel fabricator and erector Walters Inc. was engaged to provide design-assist services with respect to the rest of the structural steel framing on the project. Having already carried out a course volumetric optimization to identify the most economical overall dimensions for the node, Cast ConneX worked closely with &Co Architects on the node’s exterior shaping using 3-dimensional solid modelling software. When asked to contour nodes such as these, the automatic reaction is to maximize the size of transitional radii such that all surfaces are blended together. However, the supplier prepared two exterior geometry options: one where all transitional radii were maximized and an alternative where only the curvature in the vertical direction was maximized. Focused on

Figures 6 & 7: Finite element analysis – equivalent stress results for a load case. Courtesy of Cast ConneX Corporation.

Figure 8: One of the cast nodes after having just been removed from the heat treatment oven. Courtesy of Bradken Inc.

through to the top of the 70-foot tall delta frame. This also provides for continuity of the steel-concrete composite action into the node itself. Cast ConneX provided Stephenson Engineering with guidance on their proper simulation of the node in their ETABS building model, ensuring that eccentricities, fixities, and stiffness assumptions at the node were appropriately modeled. Stephenson then used their updated ETABS model to pass loading information back to the supplier for their engineering design and analysis of the node itself, using 3-dimensional solid modelling and finite element analysis (FEA). Cast ConneX’s numerical model (Figures 6 and 7 ) consisted of both frame and solid elements, the latter being used to model the cast steel node and tubular hollow section stubs extending beyond the ends of the node’s nozzles. The frame members were tied to the distal ends of the finite element meshed tubular stubs in all degrees of freedom using a coupling constraint. Structural loading was applied to the top of the delta frame in the analysis model. Loading was provided by Stephenson Engineering as output from their ETABS model of the entire building structure. Factored forces were provided for the three unique delta frame support structures for 124 load combinations each. To eliminate the potential for input errors and to automate the exhaustive 372 cases to be analyzed, the loading was read from the electronic ETABS output files provided by Stephenson and written directly into the FEA software application by proprietary software developed by the fabricator. The analysis process was iterative, with several incremental changes being made to optimize the cast node’s internal shaping and with all analyses being re-run. The supplier prepared all casting specifications, prepared and sealed an engineering report on their node design, produced and sealed casting shop drawings, coordinated all casting manufacturing and machining, and delivered the finished castings to Walters. Cast ConneX selected Bradken’s Atchison, Kansas facility to cast the three 31,500-pound nodes (Figures 8 and 9 ). To address the lead time requirements for the production of the cast nodes, Eastern Construction authorized the casting manufacturing well in advance of releasing the remainder of the structural steel work scope. Walters’ design-assist services in relation to the cast node focused on the detailing of the welded joints between the casting’s nozzles and the incoming tubular steel jackets of the composite delta frame members, where they were able to significantly reduce the cost of field welding. Walters’ analysis showed that combined bearing and partial joint penetration welds would be sufficient to transfer the predominately compressive stresses at the joints, rather than employing complete joint penetration welds which would have required more than 4-times the weld volume. Additionally, Walters’ welding engineer reviewed Cast ConneX’s cast steel grade selection, and prepared and oversaw the qualification of the welding procedure specifications for the welds between the cast and rolled steels.

This project provides a brilliant example of how best to leverage steel castings to enable the realization of an iconic building. The owner and design team’s open mindedness to consider alternative design and procurement methods was the key to the complete integration of the cast nodes into the design – meeting &Co Architects Figure 9: One of the nodes ready to ship to inspirational design intent, the machine shop. Courtesy of Bradken Inc. achieving a truly remarkable structural feat, and simultaneously improving constructability. Cast ConneX is often asked when casting a connection makes sense from a purely economic perspective. When the design team carried out their original feasibility and costing study for this project, a direct comparison was made between the costs to cast and to fabricate the nodes. This direct comparison of manufacturing costs alone showed the cast nodes to be somewhat more expensive. However, this supposed cost premium was likely covered several times over through the improvement of the structural effectiveness of the delta frames (particularly through their significantly improved ability to resist lateral loading which reduced structural demand on other elements of the lateral force resisting system), the simplification of the construction and concrete filling of the delta frame members, and – less quantifiably but perhaps most importantly from the Owner’s perspective – in the realization of a truly iconic design. A model of urban intensification and a shining example of sustainable construction with a target to attain LEED® Gold certification, this development will create an all new state-of-the-art office building commencing 70 feet above street level and offer a lobby and retail complex in the building’s soaring atrium that extends the public realm into a controlled environment. Construction of the building is ongoing, with tentative completion in 2014.▪

STRUCTURE magazine

Carlos de Oliveira, M.A.Sc., P.Eng is president and principal structural engineer at Cast ConneX Corporation. Carlos is widely recognized as a foremost expert in the design and use of steel castings in building construction. Carlos may be reached at carlos@castconnex.com. An inventor of yielding connectors for high ductility non-buckling braced frames and a co-founder of the company, Michael Gray, Ph.D. is the vice-president of advanced technologies at Cast ConneX Corporation. Michael may be reached at m.gray@castconnex.com. Jeff Stephenson, P.Eng is Managing Principal at Stephenson Engineering in Toronto, ON. Jeff may be reached at jstephenson@stephenson-eng.com. February 2013

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Project Delivery Systems Risks Associated with the Alternatives By Stacy Bartoletti, S.E. The information contained in this article is derived from an internal committee at Degenkolb Engineers. The author wishes to acknowledge the work of that committee and thank them for their efforts summarized here.

s an industry we are seeing alternatives to the traditional Design-Bid-Build (DBB) delivery methods grow in prominence. Two of these are Integrated Project Delivery (IPD) and Design Build (DB). IPD is relatively new, while DB has been around for a long time. In both cases, the Structural Engineer (SE) needs to be aware of different risks that can arise.

Integrated Project Delivery There are certain characteristics present in most IPD projects that introduce legal risks not normally present on DBB projects. IPD projects call for a team-based, heavily collaborative approach to performance and a means by which team members share in the project’s success or lack thereof. This has the potential to blur lines of responsibility. On a DBB project, the responsibilities of the SE are usually separate and distinct from those of other team members. The IPD project model attempts to change the dynamic from multi-team performance to a single-team focus. IPD projects are structured to require early and frequent collaboration among team members. This could heighten the risk of assuming responsibility for mistakes made by other parties who receive such input. For example, if the SE offers advice to a contractor related to means and methods, is the SE thereby assuming responsibility for any associated mistakes? While this concern is significant in theory, as IPD appears to be currently playing out, the frequent collaboration that is a hallmark of IPD projects does not appear to be resulting in a blurring of the disciplines. In practice, each party’s work is not so blended with another’s that it becomes impossible to determine who did what. Most legal disputes involving the SE relate to complaints brought by project team members. The risks associated with claims asserted by another team member are not viewed to be any greater in an IPD process. However, there is a real possibility of being dragged into a legal action brought by a party unrelated to

the design under the argument that a single entity is responsible for the suffered damages and that each team member is jointly and severally responsible for the resulting harm. While IPD may be thought of as being on the cutting edge of today’s design processes, professional liability insurance is very much rooted in tradition. By and large, insurance has not evolved as a result of alternative project delivery; rather, professional liability insurance remains rooted in making sure that the clear delineation of duties is preserved. Thus, insurance coverage may be difficult to discern for actions that were the result of collaboration among several team members. It is not all doom and gloom when it comes to IPD and legal risks. In fact, there are a lot of things to like in a true IPD project. In order to encourage creativity and information sharing, and to reduce the likelihood of defensive engineering and construction, most IPD contracts will contain liability waivers that reduce or eliminate the ability of project team members (including the owner) to sue one another. Even in the absence of favorable contractual language, contractor-related claims alleging design defects will likely be severely curtailed given the opportunity of the contractor to participate in the design development portion of the project.

Design-Build DB is when one entity, the design-builder, contracts with the project owner to provide both design and construction services. On most projects, the general contractor is the design-builder and the SE is a subconsultant, either directly to the general contractor or to the architect. Most legal risks to the SE in such an arrangement will likely arise as a result of the general contractor’s inability or unwillingness to recognize that the very same contract language that may be perfectly acceptable to a contractor will not be acceptable to an engineer. If the general contractor enters into a ‘standard’ construction contract with the owner, and then attempts to flow down the

STRUCTURE magazine

February 2013

same or similar provisions, the SE will likely face the prospect of assuming uninsurable risk. Potential problem areas include the standard of care, indemnification, and liquidated damages. Standard of Care: Contractors often promise, via contract, that their work will be free of defects and mistakes. A primary reason why contractors agree to such language is that, should they fall short of this perfection threshold, their commercial general liability insurance will cover their shortcomings. However, if the SE were to promise perfection and fail to achieve it, professional liability insurance would only provide coverage to the extent of the SE’s negligence. Indemnification: Similarly, whereas the general contractor will most likely be covered by insurance for signing on to an indemnification clause not limited to the extent of their negligence, this is not the case for the SE. Liquidated Damages: It is not unusual for a contractor to agree to pay a pre-determined dollar amount for each day a project’s substantial completion is delayed beyond a certain date. This may be appropriate for contractors who control the job site and receive the lion’s share of compensation associated with the project; again, this is not the case for the SE. Another potential legal risk associated with a contractor-led DB project involves structural observation. Traditionally, the SE is charged with observing and reporting the contractor’s defective work to the owner. This check and balance is designed to enlist the SE in watching out for the interests of the owner. However, in a DB project, the SE works for the contractor, creating a potential conflict of interest.

Conclusion Alternative project delivery presents different and, in some cases, heightened legal risks when compared to the traditional DBB model. This does not mean that these projects should always be avoided; it just means that additional up-front consideration should be given in the SE’s go/no-go decision-making process. While some of the risks can be avoided by appropriate contractual terms, the most important mitigation tip is to choose projects and team members wisely.▪ Stacy Bartoletti, S.E. is the President and CEO of Degenkolb Engineers in San Francisco, California. He is a member of the CASE Executive Committee and chairs the CASE Tool Kit Committee. He can be reached at sbartoletti@degenkolb.com.

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S-FRAME Software Inc.

Description: An easy-to-use structural modeling and analysis

CTS Cement Manufacturing Corp.

Phone: 800-929-3030 Web: www.ctscement.com Product: Rapid Set® Low-P™ Cement and Type-K Cement Shrinkage Compensating Concrete

Description: Complete bridge deck overlays faster with Rapid Set Low-P cement. Better quality, lasting performance and a lower in-place cost. Type-K Cement Shrinkage-Compensating Concrete has been used in over 800 bridge decks with reduced permeability, excellent durability, virtually no cracks and increased concrete life cycle.

Pile Dynamics, Inc.

Phone: 216-831-6131 Web: www.pile.com/pdi Product: Pile Driving Analyzer

Description: The PDA is the most widely employed system for Dynamic Load Testing in the world. It can assess the capacity of multiple drilled shafts, cast-in-place, continuous flight auger, bored or driven piles in a single day.

Wheeler Phone: 800-328-3986 Web: www.wheeler-con.com Product: Prefabricated Bridge Kits

Description: Uniquely qualified in the design and fabrication of recreation and vehicular bridges for parks, trails and roadways. Utilizing steel, timber or FRP construction, Wheeler manufactures bridges of enduring beauty and durability. Knowledgeable project advice, quality products and attention to customer service.

Williams Form Engineering Corp. Phone: 616-866-0815 Web: www.williamsform.com Product: Post Tension Systems

Description: 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 85 years.

STRUCTURE magazine

February 2013

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Description: Software for 4D construction phase analysis of any segmentally constructed bridge. Calculates timedependent behavior of concrete, tendons, and stays. Particularly well suited for balanced cantilever and spliced girder bridges. Handles geometry, camber, and stress control during construction and reports service load design values.

Phone: 203-421-4800 Web: www.s-frame.com Product: S-FRAME® Analysis

environment for bridges, frames, trusses, office and residential highrises, industrial buildings, plate/shell structures, and cable structures for seismic analysis, staged construction, slab design, Direct Analysis Method, linear and nonlinear static and time history analyses, moving load analysis, buckling load evaluation and more.

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award winners and outstanding projects

Spotlight

8 Spruce Street – Beekman Tower By Silvian Marcus, P.E., F. ASCE and Susan Erdelyi Hamos, P.E. WSP Cantor Seinuk was an Award winner for the 8 Spruce Street – Beekman Tower project in the 2012 NCSEA Annual Excellence in Structural Engineering Awards Program (Category – New Buildings over $100M).

hen it opened in 2011, the 870-foot, 76-story iconic Beekman Tower, designed by renowned architect Frank Gehry, became New York City’s tallest residential tower. Located just south of the Brooklyn Bridge, the 1.1 million square feet mixed-use building is redefining the skyline of Downtown Manhattan. The tower, offering 903 high-end residential units, luxury amenities and unobstructed 360 degree panoramic views sits above a 100-foot tall, 6-story podium that comprises a new 100,000 square foot public school and a 21,000 square foot ambulatory care center for New York Downtown Hospital. The building’s main aesthetic is its undulating, asymmetrical steel curtain wall. The sculptural façade is comprised of stainless steel and glass panels and gives the building a sense of movement. Mr. Gehry’s “Bernini folds” conceal a multitude of challenges successfully met through the implementation of innovative structural engineering solutions. Beekman Tower is a reinforced concrete building. The structure is composed of castin-place, concrete flat plate floors supported by reinforced concrete columns and shear walls. The 5- to 6-foot deep mat foundation is supported on 18-inch diameter concrete encased steel piles and also various capacity drilled caissons adjacent to an MTA subway tunnel. The lateral wind and seismic resisting system is composed of reinforced concrete shear walls surrounding the building’s core. For increased system efficiency, outrigger walls are introduced at mechanical floor levels 6, 38 and 76. The outrigger walls engage the perimeter columns, augmenting the lateral system substantially. These concrete walls were carefully located to minimize the impact of the mechanical equipment functions. The fact that all the shear walls are centralized around the core, with no walls dissecting the typical residential floors, provided the architect/developer great design opportunities unobstructed by the structural elements. The outriggers and their associated belt wall system play a vital role in reducing the building drift as well as the base moments due to lateral forces. These elements helped reduce the thickness of the shear walls and ensured

an extremely efficient system. In addition, in order to further provide adequate lateral stiffness and minimize architectural impact, high strength concrete of over 12,000 psi was specified for the shear walls and columns, whereas the specification for slab concrete ranged from 5,000 to 8,600 psi. The outrigger walls were also used as transfer structures for the exterior columns. The building stacking changes at the outrigger floors, and most of the exterior column pickups are undertaken by the outriggers to maintain efficiency of internal space. A further unique challenge of axial shortening had to be met. Studies were performed and over-pour values were specified for casting the columns in order to mitigate the effect of differential axial shortening between the core walls and the columns; not just for the final construction condition, but also for the construction sequencing stages. The structural challenge of accommodating the undulating façade, as well as the differing apartment layouts, was met by ‘walking’ the columns at several locations and levels. No tower floor plates are alike and slab edges are in different planes on every floor; however, in order to simplify the formwork, columns were designed and constructed to stay in the same plane for about every eight to twelve floors. At the ‘change’ levels, the columns broaden or ‘walk’ to encompass the column location above and below. This strategy, apart from avoiding the use of transfer beams, also avoided the need to slope the columns, which would have required more complicated and laborious formwork. The strategy provided the added benefit of maintaining a streamlined construction rhythm. In addition, 3-dimensional CAD detailing was undertaken to design the formwork for the undulating slab edges and maintain the sculptured edge detail of the concrete floors. The process was supplemented by independent x, y, z–coordinate surveying using the Total Station system. The rectilinear podium is clad in terracottacolored masonry. Its design was carefully and closely coordinated with the school architects (Swanke Hayden Connell) in order to ensure an optimum layout, considering that the school was supporting the 72 stories above.

STRUCTURE magazine

February 2013

Developer: Forest City Ratner.

Larger clear spans of up to 35 feet with 10to 12-inch flat plate floors were utilized to accommodate the school and hospital architectural layouts compared to the shorter spans using 8-inch flat plate floors within the residential spaces above. The site is tightly bound on all sides by a hospital, a university, two landmark historic buildings and a subway tunnel. Construction logistics met these challenges by continuously having two concrete trucks available in the building’s west plaza (which was designed to carry their loads) for continuous pouring. The construction team managed to keep to a 2-day cycle at the highest floors by pumping concrete all the way to the top of the building. Foundation work started in October 2006 and work on the superstructure began in April 2008. The building topped out in November 2009. The project came in under budget and on schedule in spite of a 3 month work hiatus related to the recent recession. The Public School opened in September 2011, and residential leasing and occupancy began in February 2011. The fast-track construction of this unique and iconic building is testament to the overall team’s efficient design and construction planning.▪ Silvian Marcus, P.E., F. ASCE is the Chairman at WSP Cantor Seinuk. Mr. Marcus was the Principal-in-Charge for the project. Susan Erdelyi Hamos, P.E. is a Vice President at WSP Cantor Seinuk. Ms Hamos was the Project Manager for the project.

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2012 – 2013 NCSEA Membership

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Partnering Organizations

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NCSEA News

News form the National Council of Structural Engineers Associations

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CASE Washington, DC

SEI (Structural Engineering Institute of ASCE) Reston, VA

Associate Members AISC Chicago, IL American Wood Council Leesburg, VA Bentley Systems, Inc Carlsbad, CA Fabreeka International, Inc. Stoughton, MA

Insurance Institute for Business & Home Safety Tampa, FL International Code Council Birmingham, AL Metal Building Manufacturers Association Cleveland, OH

NCSEA recognizes and thanks its Partnering Organizations and the following companies, organizations, and individual structural engineers, for their Associate, Affiliate and Sustaining memberships in 2012-2013. For information about becoming an Associate, Affiliate or Sustaining member, contact Susan Cross at 312.649.4600, ext. 204. Schuff Steel Company Phoenix, AZ Simpson Strong-Tie Pleasanton, CA USP Structural Connectors Burnsville, MN

Affiliate Members AZZ Galvanizing Services Joliet, IL

DECON USA, Inc. Beaufort, SC

Red Seat Software Grapevine, TX

Bekaert Marietta, GA

Dwyer Companies West Chester, OH

RISA Technologies Foothill Ranch, CA

Cast Connex Corporation Toronto, Ontario

Fibrwrap Construction, Inc. San Diego, CA

SE Solutions, LLC Holland, MI

Cold-Formed Steel Engineers Institute (CFSEI) Washington, DC

Hilti, Inc. Tulsa, OK

SidePlate Systems, Inc. Laguna Hills, CA

Construction Tie Products, Inc. Michigan City, IN

ITW Commercial Construction – Ramset, Red Head & Buildex Addison, IL

Steel Joist Institute Myrtle Beach, SC

CSC Inc. Chicago, IL

Powers Fasteners Brewster, NY

Strand7 Beaufort, NC Vector Corrosion Technologies Wesley Chapel, FL

Sustaining Members Andersen Bjornstad Kane Jacobs, Inc Seattle, WA Barrish, Pelham & Associates, Inc. Sacramento, CA Barter & Associates, Inc. Mobile, AL Bennett & Pless, Inc. Atlanta, GA Burns & McDonnell Kansas City, MO Cartwright Engineers Logan, UT Construction Technology Laboratories Skokie, IL Cowen Associates Consulting Structural Engineers Natick, MA Criser Troutman Tanner Consulting Engineers Wilmington, NC STRUCTURE

DCI Engineers Seattle, WA Degenkolb Engineers San Francisco, CA DiBlasi Associates, P.C. Monroe, CT Dominick R. Pilla Associates Nyack, NY Dunbar, Milby, Williams, Pittman & Vaughan Richmond, VA Engineering Solutions, LLC Oklahoma City, OK Gilsanz Murray Steficek, LLP New York, NY Kevcor, Inc. Westport, CT LBYD, Inc. Birmingham, AL magazine

February 2013

Martin/Martin, Inc. Lakewood, CO Ruby & Associates, Inc. Farmington Hills, MI Simpson, Gumpertz & Heger, Inc. San Francisco, CA Structural Engineers Group, Inc. Jacksonville, FL TGRWA, LLC Chicago, IL The Harman Group, Inc. King of Prussia, PA The Haskell Company Jacksonville, FL Thornton Tomasetti Chicago, IL United Structural Systems Ltd., Inc. Lancaster, KY Wheaton & Sprague Engineering, Inc. Stow, OH

March 7-8 • Westin La Paloma Resort • Tucson, Arizona

Game-Changing Strategies for the New Economy

Visit www.ncsea.com for reasons why Chris Poland, Bill Thornton, Barry Arnold and Bill Warren will all be at the NCSEA Winter Leadership Forum in Tucson!

Sessions: Developing the Next Generation of Structural Engineers Glenn Bell, senior principal & CEO, Simpson Gumpertz & Heger Key Financial Indicators for Leading your Firm to Success Scott Braley, FAIA FRSA, Braley Consulting & Training Establishing a Successful Structural Engineering Training Program Ben Nelson, PE, SECB, Martin/Martin Hard Choices in a Soft Economy: 4 Mistakes you Can’t Afford to Make Kelly Riggs, Vmax Performance Group Coaching for Leadership: Transforming Potential into Performance Kelly Riggs, Vmax Performance Group Top 10 Keys to Managing Multiple Deadlines & Expectations Jon Stigliano, Strategic Solutions Group 8 Actions to Get People Goal-Directed, Self-Motivated, and Engaged in the Relentless Pursuit of Excellence Jon Stigliano, Strategic Solutions Group

News from the National Council of Structural Engineers Associations

The NCSEA Winter Leadership Forum will gather together leading structural engineers in an energetic and engaging environment focused on leadership, networking and game-changing strategies for the new economy. The Forum will be beneficial for professionals who seek to enhance their businesses, management skills and effectiveness within the context of their firm and individual performance. It is ideal for anyone with current or anticipated management responsibilities, ranging from principal to senior- and mid-level management, to people expecting to take on leadership roles. Attendees will participate in two days of invaluable sessions, roundtables, and networking time. This event will explore the mindset and skills necessary to be a transformative leader, as well as how to best align your role with your company’s needs.

At the NCSEA Winter Leadership Forum, share business ideas, successes and failures, with other structural engineering principals and benefit from the experiences of others.

NCSEA News

NCSEA Winter Leadership Forum

SEAMass forms Young Members Group

February Webinars February 7, 2013: Assessing and Dealing with Geotechnical Risk, A Structural Engineer’s Dream or Nightmare – Dennis Beohm February 12, 2013: Wind Series #2 ASCE 7-10: Components & Cladding Wind Load Provisions for Walls and Roofs – John Hutton & Michael Stenstrom February 26, 2013: Wind Series #3 Component & Cladding Wind Loads for Building Appurtenances, Open Buildings, and Other Structures – Tom DiBlasi & Bob Paullus

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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.

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There are a number of NCSEA Member Organizations throughout the country that have formed, or are forming, Young Member Groups. NCSEA now has a Young Member Group Support Committee that is charged with helping to form and promote Young Member Groups within Member Organizations. The committee is chaired by Tom Grogan and has developed a manual together with materials to assist Member organizations in forming, marketing and managing their Young Member Group. These materials are available on the Young Member Group page of the NCSEA website.

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The Structural Engineers Association of Massachusetts (SEAMass) formed a Young Members Group, which held its first meeting in December. The SEAMass Young Member Group is chaired by Ellen Kuo, P.E., LEED AP BD+C, of Symmes Maini & McKee Associates, Ellen Kuo and Sofia Zamora, EIT, of Weston & Sampson Engineers. The group was formed to guide and support young engineers in their transition between school and industrial practice while developing a structural profession. “We formed the group in October, and our first meeting was successful with a great turnSofia Zamora out,” stated Kuo. “Since then, we have received numerous inquiries about becoming a part of the group from young engineers in Massachusetts, Rhode Island, Connecticut and New Hampshire, and from students in local universities. We are providing a platform for young members to exchange structural knowledge, and to share lessons learned from past and ongoing projects. We plan to shape our members into more valuable structural engineers and to further educate them to grow and advance in their career.” The group plans educational sessions, field trips, and PE “Teach-Ins”. The first Teach-In was held in January, led by Craig Barnes, P.E. In February, the group will hold a combined social event with the Boston Society of Civil Engineers Section Young Member Group, along with a Teach-In by Mike Berry, P.E.

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Structures 2013 Congress Technical Sessions

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Thursday, May 2, 2013 Track

Innovative Engineering

Reinforced Concrete

Seismic

Extreme Loading

Research

Track Chair Brian McElhatten

Cynthia Duncan

Charles Roeder

William Jacobs, V

Colby Swan

8:00 AM – 9:30 AM

IE100 Innovative Engineering 1: Case Studies of Successful Projects

SE100 Seismic Retrofit and Enhancement 1

RC100 New Developments for Analysis and Design of Structural Concrete BeamColumn Connections

EL100 Tornado-Resilient Communities Reducing Losses to Buildings

RA100 Emerging Steel Framing Systems Towards Damage Resistant Seismic Design and Rehabilitation

10:00 AM – 11:30 AM

IE110 Innovative Engineering II: Case Studies of Successful Projects

SE110 Seismic Retrofit and Enhancement 2

RC110 Two-Way SlabsCurrent Design and Construction Issues

EL110 Extreme Loads on Cold-Formed Steel Framing -Analysis and Design for Earthquake, Blast and Fire

RA110 Structural Control and Vibration Mitigation

11:45 AM – 1:45 PM Opening Plenary Luncheon and Awards Program 2:00 PM – 3:30 PM

IE120 High-Rise/Tall Buildings Topics

SE120 Case Studies Using Nonlinear Dynamic Analysis

RC120 Bringing Reinforcing Bar Anchorage into the 21st Century

EL120 Natural Disasters and Extreme Loading

RA120 Student Structural Design Competition

4:00 PM – 5:30 PM

IE130 Response of Tall Buildings to Fire

SE130 Collapse Assessment of Conventional and High-Performance Structures Designed in Seismic Regions

RC130 Unconventional Reinforced Concrete Columns

EL130 Design of HighRisk Buildings Against Disproportionate Collapse

RA130 Seismic Input and Structural Modeling

Friday May 3, 2013 7:00 AM – 8:15 AM CASE Breakfast Track

Masonry and Wood

Seismic

Steel Topics

Special Building Topics

Research

Track Chair Brian McElhatten

Cynthia Duncan

Charles Roeder

William Jacobs, V

Colby Swan

8:30 AM – 10:00 AM

SE200 Seismic Analysis and Performance Based Design

SL200 Stainless Steel Design

SB200 Floor Vibrations Serviceability

RA200 Infrastructure Resilience to Natural Disasters

SE210 Proposed Seismic Performance Framework for Design of New Buildings

SL210 Stability Analysis and Design: Theory is Practical

SB210 Structural Optimization in Framed Buildings-Spanning from Theory to Practice

RA210 Risk -Based Decision Making for Infrastructure Systems

MW200 Using Hybrid Masonry to Brace SteelFramed Buildings

10:30 AM – MW210 Advances in Masonry Testing 12:00 PM and Design

12:00 PM – 1:30 PM Buffet Lunch in Exhibit Hall 1:30 PM – 3:00 PM

MW220 Advances in the Design and Analysis of Wood Building Systems

SE220 Supplemental Damping Systems

SL220 Introduction to the 2nd Edition of AISC Seismic Design Manual

SB220 Fire Loading: Modeling Techniques and Building Response

RA220 Strengthening and Restoration Using Composite Materials

3:30 PM – 5:00 PM

MW230 Advances in Wood Testing and Design

SE230 Floor Diaphragms: Behavior and Design

SL230 Design Innovations for Steel Braced Frames and Steel Plate Shear Walls

SB230 Advances in Reinforced Concrete Testing and Design

RA230 Pittsburgh Research-in-Progress

Saturday May 4, 2013 Track

Seismic Innovation

Seismic Testing and Evaluation

Sustainable Building Systems

Sustainability in Structures

Research

Track Chair Brian McElhatten

Cynthia Duncan

Charles Roeder

William Jacobs, V

Colby Swan

8:30 AM – 10:00 AM

ST300 Advanced Testing Methods in Earthquake Engineering Research

SS300 Green Giants: Tall and Sustainable

SA300 Sustainable Systems and Materials

RA300 Testing of Novel Structural Concepts

ST310 Application of Experimental Techniques for System-Level Seismic Evaluation of Structures

SS310 Aesthetics of Sustainable Structures

SA310 Taking Measure of Structural Thermal Breaks

RA310 Computational Modeling of Nonlinear Structural Performance

SI300 Innovations in Seismic Braced Frames

10:30 AM – SI310 Innovations in Seismic Steel 12:00 PM Moment Frames

For more information about the Structures 2013 Congress, including Registration and Housing visit our website at www.structurescongress.org. STRUCTURE magazine

February 2013

Business and Professional Practice

Pittsburgh Unique Structures

John Tawresey

Jonathan McHugh

Shalva Marjanishvili

Bruce Peterson

Cheng Lok Caleb Hing Greg Soules

PR100 Media Relations 101

PA100 Geologic/ Geotechnical Challenges Affecting Structural Design in Western Pennyslvania

BT100 Multi-Hazard Robustness Assessment of Building Structural Systems 1

BP100 Structural Health Monitoring of Full-Scale Bridges-1

BR100 Aesthetics of American Signature Bridges

NB100 Design and Analysis of Power Plants

PR110 Soft Skills for the Young Engineer

PA110 The Tunnels of Pittsburgh

BT110 Multi-Hazard Robustness Assessment of Building Structural Systems 2

BP110 Structural Health Monitoring of Full Scale Bridges 2

BR110 Bridge Practice and Case Studies

NB110 Art and Creativity of Structural Engineering

BR120 The Bridges of Pittsburgh

NB120 Design of Petrochemical and Other Industrial Facilities

Blast

Bridge Practice

Bridge Research & Implementation

Non Building Structures

Opening Plenary Luncheon and Awards Program PR120 Practicing Engineers Trial Design Examples

PA120 Pittsburgh’s River Structures Locks and Dams and Economic Consequences

BT120 Recent Research Advances in Disproportionate Collapse

BP120 Bridge Monitoring and Assessments

PR130 Construction Defect Case Study – What Engineers Should Know

PA130 Pittsburgh’s Professional Sports Facilities

BT130 Analysis Methods for Blast Loads

BP130 Structural Health BR130 Bridging the Monitoring Pittsburgh Area with Steel

NB130 Analysis and Modeling of Nonbuilding Structures

Business and Professional Practice

CASE

Blast

Bridge Practice

Bridge Research & Implementation

Non Structural Components

John Tawresey

Paul Mlakar

Shalva Marjanishvili

Bruce Peterson

Cheng Lok Caleb Hing John Silva

PR200 The Structural Engineering Profession from a Young Professional’s Persepective: Diversity, Challenges and Retention

CS200 The Business of BIM

BT200 Prediction of Blast Loads 1

BP200 Bridge Substructure Analysis

BR200 Unique Bridge Engineering

NS200 Full-scale Building-NCS Earthquake and Fire Test Program: A NEESLandmark Project

PR210 Capstone Programs for Structural Engineering Students: Exploration of Goals and Needs

CS210 Trends in Effective BT210 Prediction of Use of Commercial Blast Loads 2 Softwate for Building Structural Design

BP210 Bridge Analysis

BR210 Bridge Simulations and Fatigue Study

NS210 Establishment of Seismic Demand on Nonstructural Components

Buffet Lunch in Exhibit Hall PR220 What’s The Matter With Engineering

CS220 Reviewing Contractor’s Electronic Models in Lieu of Hard Copy Shop Drawings

BT220 Testing Methods for Blast Response

BP220 Bridge Seismic and Dynamic Behavior

BR220 Bridge Design

NS220 Response of Ceiling Systems, Sprinkler Piping and Nonstructural Partitions to Earthquake Loading

PR230 Lifecycle of a Structural BIM: Using the Right Tools for the Job

CS230 BIM Validation: Modeling for Downstream Success

BT230 Blast Resistant Glazing and Curtainwall

BP230 Structural Behavior

BR230 Fire Risks and Impacts to Bridges

NS230 Wind Loading on Roof Mounted Solar Systems

Business and Professional Practice

Business

Blast

Resilience

Bridge Research & Implementation

Non Building Structures

John Tawresey

Jeremy Isenberg

Shalva Marjanishvili

Sam Kiger

Cheng Lok Caleb Hing Greg Soules

PR300 BIM Beyond Design

BU300 Can Alternative Delivery Methods be the Solution to our Nation’s Infrastructure Problem?

BT300 Evaluating New Materials and Methods for Blast Protection

RR300 Structural System Resilience and Risk Mitigation Under Multiple Hazards

BR300 Performance Based Design of Bridges: Practical Applications

NB300 Foundations and Other Design Issues for Wind and Solar Towers

PR310 Structural Level of Development (LOD) in BIM, Guidelines for The Practice

BU310 Challenges for the Practice of Structural Engineering

BT310 Progressive Collapse and Structural Robustness: An International Perspective

RR310 Pittsburgh’s Green Building Legacy and Future

BR310 Assessment of The Seismic Response of Structures Crossing FaultRupture Zones

NB310 Equipment Containment Structure and Foundation Design

To view the interactive Technical Program, including all presenters and abstracts, on the SEI Website, visit www.structurescongress.org STRUCTURE magazine

February 2013

The Newsletter of the Structural Engineering Institute of ASCE

CASE Breakfast

Structural Columns

May 2– 4, 2013 – Pittsburgh, Pennsylvania

The Newsletter of the Council of American Structural Engineers

CASE Released Two New Tools CASE Tool 2-5: Insurance Management: Minimize Your Professional Liability Premium Professional liability insurance is often one of the largest overhead items in a structural engineering firm, and most insurance company applications do not provide adequate space to delineate details of your firm’s practice and to differentiate your firm from any other firm. This tool is designed as a guide to help you provide critical additional information to the underwriter to differentiate your firm from the pack.

Being adequately compensated for the effort and value added to a project by the structural engineer is an essential element of the consulting structural engineering practice. Developing fair, yet adequate fees is always a challenge. This tool is intended to be used within a consulting firm to stimulate thought and consideration in the development of fees.

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

Coalitions Corner CASE is a member of ACEC’s Coalitions, groups that provide a home for communities of practice across the engineering industry.

Join ACEC Coalitions on Twitter

CASE in Point

CASE Tool 7-2: Fee Development Methods and Key Considerations

Twitter is a great way for ACEC’s Coalition to disseminate information, start conversations, and let the world know when downtown DC is shaking from earthquakes! Follow us and get the latest from Last Word, ACEC’s weekly newsletter, updates from the Capitol on hot-button issues, education opportunities, networking opportunities, and to follow us live during conferences and events! Follow @ACECCoalitions

ACEC Annual Convention APRIL 21-24, 2013 – Washington, DC The 2013 ACEC Annual Convention will be held April 21-24, 2013 at the Grand Hyatt Hotel in downtown Washington, DC. Convention highlights will include:

STRUCTURE magazine

• Opening General Session on Outpacing Business Trends with Geoﬀ Colvin, Senior Editor-at-Large, FORTUNE • CEO Panel on Major Projects and Alternative Delivery Systems with Alan Krause, President/CEO, MWH; Garry Jandegian, President, Infrastructure and Environment, URS; Michael S. Della Rocca, Chief Executive, AECOM North America • Keynote Luncheon on Battleground Politics with Chuck Todd, Political Director and Chief White House Correspondent, NBC News • 2013 Large/Small Firm Teaming Fair • Congressional Issues Briefing • CIO and CFO Council Symposiums • 2013 Engineering Excellence Awards Gala Banquet and After Party Go to www.acec.org/conferences/annual-13/index.cfm to learn more and to register!

February 2013

The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program. We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives in educational support.

In addition, the CASE scholarship offers an excellent opportunity for your firm to recommend eligible candidates for our scholarship. If your firm already has a scholarship program, remember that potential candidates can also apply for the CASE Scholarship or any other ACEC scholarship currently available. Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. You don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

If you would like more information on the items below, please contact Ed Bajer, ebajer@acec.org.

Update: The Engineer as Municipal Advisor The law defines municipal advisor as a person or firm that provides advice to a municipal entity in connection with municipal financial products or the issuance of municipal securities. Although the proposal includes an exemption for “engineers providing engineering advice,” the SEC has proposed defining engineering advice so narrowly that traditional engineering services, such as cash-flow modeling and feasibility studies, would not be covered by the exemption. Outgoing SEC chair has indicated they may have cast their net a little wider than intended. The rule has been delayed again until September of 2013.

Electronic Transmittals

Handling a Request for Documents When You Are Not a Party to a Lawsuit Firms handle this in different ways. Some contact the requesting party and try to find out exactly what they are looking for and discuss a solution. Some notify their insurer who will sometimes cover the costs of reproduction in the name of loss prevention. If the request is overly broad, an objection can be filed with the court which could halt the process and possibly end up with a narrower request. Requests for documents have become so commonplace that some firms have developed a system that makes the production of documents as trouble-free and economical as possible. In any event, it should be handled by your attorney. It’s always possible to end up as a party to the suit.

Unverified documents that have been transmitted electronically have been questioned as to their legal standing. The sender of the documents may not know whether they might have been altered. Persons on the receiving end of these documents use them at their own risk. Depending on the firm and the situation, it can be made clear to the receiver of electronic documents, through a disclaimer reviewed by an attorney, that only signed and sealed hard copies should be considered the original documents of record.

STRUCTURE magazine

You can follow ACEC Coalitions on Twitter – @ACECCoalitions.

February 2013

CASE is a part of the American Council of Engineering Companies

CASE Business Practice Corner

CASE in Point

Donate to the CASE Scholarship Fund!

Structural Forum

opinions on topics of current importance to structural engineers

The Invisible Gendered Culture of Engineering By Lara K. Schubert, P.E.

n my first year of engineering work, my boss asked me to write for the company-wide newsletter, addressing this question: How does a woman succeed in a male-dominated field? My response was immediate: The same way as a man! This fiery piece insisted that one can choose to be affected by external pressures or can overcome them, and that women could certainly excel in the field. At the time I was responding to the idea that there are innate differences in ability between men and women, and so I did not acknowledge any significant difference in experience. After more than four years of working as a structural engineer, I decided to pursue graduate studies in the humanities. While I am still a part-time engineer, I am also a doctoral student specializing in feminist studies, an insider-outsider who can now see things that were invisible to me before. In this piece, I will elucidate the gendered culture of structural engineering. Mary Daly’s quote asserts that a status quo exists. If we simply add women and stir – or incorporate any other under-represented group – substantial changes are unlikely. But altering the gendered status quo is much more controversial. The first step is recognizing the prevailing culture. Think about your office culture and the professional organizations in which you participate: can you identify prevailing values that remain largely unspoken and invisible? When I started working, I found that I had to adjust to a whole new way of thinking and being in the world. When ways of acting and types of reasoning that are valued in a field of study or profession align with societal expectations for a particular gender, we can say that its culture is gendered. It is important to ask two things: Does this culture improve or hinder our work? Whom does it benefit and whom does it limit or exclude? My experience is not an archetype but may help to unearth systems of thought. When I entered the field of structural engineering, one challenge was the analytical approach to everything. Logic was the primary value – not just in design, but in

Real boundary living is a refusal of tokenism and absorption, and therefore it is genuinely dangerous. —Mary Daly all aspects of office life. All assertions were open to being logically challenged. At lunch, when we talked about politics or vacations or anything really, we had to have a good argument and show our colleagues that we were very smart. This was all part of the persona. To be an engineer is to be an expert in everything – not just to clients, but also to fellow engineers. This new pressure to impress was exhausting and something that I had to work hard at keeping up. Women in other predominantly male fields of science, technology, and mathematics have had similar experiences. For instance, Evelyn Fox Keller articulates a similar phenomenon from her time as a graduate student in theoretical physics at Harvard in the 1960s: “I didn’t fully understand then that in addition to the techniques of physics, they were also studying the techniques of arrogance. This peculiar inversion in the meaning of humility was simply part of the process of learning how to be a physicist. It was intrinsic to the professionalization, and what I might even call the masculinization of an intellectual discipline.” She calls this masculinization because such traits are more acceptable for males in our society. Whether or not you agree with this, it remains important to consider how different groups of people are socialized – think of people’s expectations of mothers vs. fathers, and portrayals of women and men in film and advertisements. For whom is lack of humility more socially acceptable? For whom is it more detrimental? In my own experience, the culture of structural engineering was gendered in other ways, though at the time this was largely invisible to me. When I joined a mid-sized engineering firm I was the only female engineer there. An image that sticks in my mind is my first tour of the office. As I shook hands with each engineer at his desk, I noticed that most – in my mind it was all – of them wore white-collared

button-down shirts. This may seem comical in retrospect, but it made a real impact. I resolved that to be respected by my colleagues I would wear collared, button-down shirts and did this consistently, only changing my strict self-imposed policy after transitioning to part-time. The significance of an implied internalized dress code cannot be overstated. This is an outward, visible way in which the culture is gendered. In Rosemary Tong’s book, Feminist Thought, she criticizes “articles written for women about dressing for success, making it in a man’s world, being careful not to cry in public, avoiding intimate friendships, being assertive, and playing hardball,” which are counter to the positive aspects of the abilities that women are socialized to hone, like cultivating community. This is not to suggest that all women are inclined toward “feminine” traits and all men are inclined toward “masculine” traits. While I value abilities that are expected of women, I find them difficult to cultivate. However, choosing these virtues and reflecting on our values is imperative to enhance the field of structural engineering. Rather than opening it up to women, which has already happened, the culture of the profession should be open to transformation. My next column in this space will show that this culture makes it particularly difficult for women to rise to the top. The challenge is to innovate our own professional culture. If we call into question its gendered nature and consider new ways of being structural engineers, our field might truly flourish.▪ Lara K. Schubert, P.E. (lschubert@holmesculley.com), works part-time for Holmes Culley Structural Engineers, has taught at Cal Poly Pomona, and is a PhD candidate in religion at Claremont Graduate University.

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

February 2013

STRUCTURE magazine | February 2013

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