STRUCTURE magazine | November 2017

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

November 2017 Steel/Cold-Formed Steel Inside: Poly International Plaza, Beijing

Salesforce Transit Center, San Francisco Pelli Clarke Pelli Architects with Thornton Tomaseƫ and Schlaich Bergermann Partner

Pinnacle Engineering Consolidates Software Packages and Increases Productivity requirements. Working in Tekla Structural Designer, engineers don’t have to waste time switching between multiple software packages. Regardless of complexity, they can design all members and consider the overall 3D building design in one seamless process.

Easy to Use, Intuitive Interface The intuitive interface, combined with the support and training provided by Trimble made the switch to Tekla Structural Designer seamless. “It was easy to get on board with Tekla Structural Designer because it’s very intuitive,” said Ping.

Pinnacle Engineering Inc. is a structural engineering firm that provides winning services across a wide variety of project types including commercial, healthcare, workplace, institutional and educational. Founded in 1996, the firm’s focus on high quality and cost-effective structural solutions have been the foundation of its strong customer relationships with architects, developers, owners and general contractors.

One Interface, One Model Unlike traditional analysis software, Tekla Structural Designer can be used to create physical, information-rich models that contain all the intelligence needed to fully automate design and manage project changes. The result? Faster, more accurate design.

Before Tekla Structural Designer, Pinnacle relied on software that required its engineers to switch back and forth between multiple modules to make changes. This was eating up valuable time and increasing the potential for costly errors. “Tekla Structural Designer gave us the ability to design graphically in 3D, as opposed to being stuck in a two-dimensional world where we were constantly flipping back and forth between modules,” said Ping.

Whether working on large-scale or small-scale projects, Pinnacle’s engineers push the limits on structural design and rather than tell clients what isn’t possible, leverage the most innovative structural solutions available to turn design concepts into reality. This focus on cost-effective design and innovation is what led the firm to adopting Trimble’s Tekla Structural Designer.

Like so many other firms in the U.S., the team at Pinnacle was using a structural design software package that has been on the market for several years but hasn’t improved in a long time and as a result, lacks capabilities and has significant limitations. For Pinnacle, the desire to find a replacement was amplified when they became aware of the greater benefits, increased usability and rich features provided by Tekla Structural Designer. Tekla Structural Designer’s potential for greater flexibility combined with its ability to analyze and design buildings more efficiently motivated Pinnacle to make a change. “At the end of the day, you expect every structural analysis package out there to do the engineering correctly, so it really comes down to the interface and how efficiently the software can accomplish what you need,” said Kip Ping, president of Pinnacle Engineering.

TRANSFORMING THE WAY THE WORLD WORKS

“Other software packages can do the engineering fine, but the ease with which you model and the ability to understand the output in other software packages is severely lacking.”

After Pinnacle got up and running with Tekla Structural Designer, its engineers began to push the envelope and use it for more complex structures.

With Tekla Structural Designer, they could optimize multi-material buildings in a fraction of the time.

“Tekla Structural Designer has made a significant impact on our workflow,” said Ping. “The ability to model with complexity, all in one software package, saves us from paying the price of going to a finite element package where we wouldn’t get a lot of the automated features like automated bracing of members and stability checks, which are calculations that before Tekla Structural Designer, we would have to do by hand.”

Collaborative Design

“The interface and usability drew us to Tekla Structural Designer. It’s easy to use, but still provides the flexibility and sophisticated features that allow us to be more productive and get the job done in less time.”

“Before Tekla Structural Designer, we would use one frame module to create settings for a beam and then use a different module to create settings for another beam, all without the ability to see what was happening in the rest of the model. When we switched to Tekla Structural Designer, we instantly had the ability to work in a 3D model and draw columns and beams in one software. It was so much easier to visualize and quickly make changes to the model. This was a game changer.” From scheme to detailed design, one single model can contain all structural analysis and design

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties including technicians, fabricators and architects.

Engineers can integrate the physical design model seamlessly with Tekla Structures or Autodesk® Revit®, and round-trip without compromising vital design data. “Because we are creating a single model, with one data set, exporting the Tekla Structural Designer model and sharing it with architects and other stakeholders during the design process has been extremely easy,” said Ping. “It allows us to collaborate without friction and instantly understand the impact of any changes so we can make informed decisions and ultimately, deliver the best result possible to our client.”

Want to Evaluate Tekla Structural Designer? tekla.com/TryTekla

CONTENTS 34 POLY INTERNATIONAL PLAZA, BEIJING

Cover Feature

By Neville Mathias, P.E., S.E., Mark Sarkisian, P.E., S.E., and Rupa Garai, P.E., S.E. Curved site boundaries gave rise to the curved, relatively non-directional forms of the new and iconic structures in the growing business district of Dawangjing. These curves, coupled with cultural inspirations, gave rise to a building which integrated form, function, structure, building systems, and sustainable design.

Features 30 HOLLYWOOD CASINO JAMUL

38 PRESERVING NAVY HISTORY WITH DESIGN-BUILD

By Gregory P. Luth, Ph.D., S.E. and John D. Osteraas, Ph.D., P.E. Unconventional construction sequences, an innovative lateral force resisting system, and High Definition BIM are just a few of the unique features related to this three-story entertainment facility.

By Mark Hirschi, S.E. and Frank K. Humay, Ph.D., S.E. Challenges encountered during the re-purposing and upgrade of a 1930s era Navy building that survived the bombing of Pearl Harbor in 1941, were met head-on by a strong design-build team.

Columns and Departments

PROFESSIONAL LIABILITY

STRUCTURAL PRACTICES

22 Balcony Issues in High-Rise Buildings

54 Digital Stamping

By David A. Ericksen, Esq.

By Dan Eschenasy, P.E. SPOTLIGHT

EDITORIAL

7 Continuing Up the Ladder, One Rung at a Time

59 The Petersen Automotive Museum Façade

STRUCTURAL TESTING

26 Building on the Past

By Jeff Denton, P.E., S.E.

By Williston “Bill” Warren IV, P.E., S.E., SECB

By Andrew Geister, P.E.

CODES AND STANDARDS

STRUCTURAL SUSTAINABILITY

10 Cold-Formed Steel Framing Standards

42 Envision – The Future of Sustainable Infrastructure

By Roger LaBoube, Ph.D., P.E., Helen Chen,

By Evan Sheesley, S.E. and

Ph.D., P.E., and Jay Larson, P.E.

Amanda Schweickert, P.E.

HISTORIC STRUCTURES

STRUCTURAL DESIGN

14 Origins of Fire-Resistance Ratings for Steel Assemblies

46 Dunlap's Creek Arch Bridge (1839)

By Frank Griggs, Jr., D.Eng., P.E.

By Charles J. Carter S.E., P.E., Ph.D. PROFESSIONAL ISSUES OUTSIDE THE BOX

18 Second-Order Innovation

By Michael Gray, Ph.D., P.Eng.

51 Work-Life Balance, Flexibility Benefits, and Caregiving

By Angie Sommer, S.E. and Natalie Tse, S.E.

STRUCTURE magazine

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November 2017

STRUCTURAL FORUM

66 Who Hijacked My Plan Review?

By David Pierson, S.E.

IN EVERY ISSUE 8 Advertiser Index 56 Resource Guide – Software Updates 60 NCSEA News 62 SEI Structural Columns 64 CASE in Point Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement

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

Editorial

new trends, new techniques and current industry issues

Continuing Up the Ladder, One Rung at a Time

By Williston “Bill” Warren IV, P.E., S.E., SECB, F.SEAOC, NCSEA President

S

uccess is gratifying. We all strive for it on a daily basis in our professional and personal lives. When we achieve it, we should celebrate because it does not come often enough. One obstacle that accompanies success is that it then raises the bar for the next endeavor; we must reach the next rung on the ladder to meet even higher expectations.

It is with this challenge in mind that I take on my new role as President of the National Council of Structural Engineers Associations (NCSEA) for 2017-2018.

Having previously been President of NCSEA’s largest Member Organization, the Structural Engineers Association of California (SEAOC), I am familiar with the demands placed on non-profits by their members and volunteers. Our goal at NCSEA for this next year is to meet those demands and exceed expectations as we continue to thrive on the positive momentum that this organization has been building over the last several years.

The focus during my term as President will be concentrated in the following areas: • Outreach and advocacy to all those influenced and affected by structural engineering; • Increasing NCSEA’s partnerships with the state SEAs, as well as related organizations; • Taking the annual Structural Engineering Summit to an even higher level; and, • Demonstrating our love of our profession and its value to the general community.

Examining these areas one by one, plenty of opportunities exist for NCSEA and the SEA membership to continue succeeding together. To achieve this, we all must take part.

Regarding outreach and advocacy, many of our state SEAs have experienced success in connecting with the media, architects, building officials, and government officials. NCSEA must build on this success and lend its national voice to the effort to help all those affected by our practice of structural engineering begin to understand the value that our profession brings to society. The general public routinely uses the buildings and other structures that we design without a second thought, and rightly so. Raising awareness of the structural engineer’s contributions to society’s safety, health, and welfare will allow our profession to receive the recognition that it deserves.

In terms of partnerships, NCSEA will continue to grow its relationships with state SEAs and national organizations like the Applied Technology Council (ATC) and the International Code Council (ICC). With the limited resources (especially time) available to STRUCTURE magazine

everyone today, the last thing NCSEA wants to do is duplicate the efforts of others or reinvent the wheel when a perfectly good solution already exists. Thanks to its 44 Member Organizations across the country, NCSEA is uniquely positioned to help facilitate the distribution of successful ideas and products from one city, state, or region to another, ensuring that the best of the best is being utilized by the structural engineering profession nationwide. This could include white papers, webinars, publications, education speakers, and ideas on running a more effective state SEA. If I have missed anything, please let NCSEA know.

In the ultimate drive to reach the next rung of the ladder, NCSEA already is looking forward to the 2018 Structural Engineering Summit on October 24 – 27 in Chicago. Having just completed the enormously successful 2017 event in Washington, D.C. – with a record attendance of more than 500, including 59 exhibitors – the focus is squarely planted on next year. The goal is to increase attendance further, as well as foster a continued celebration of the structural engineering profession. Conferences like the NCSEA Summit provide invaluable face-to-face networking opportunities that spark creativity, collaboration, and concrete accomplishments in a world so focused on and enamored with the virtual.

Ultimately, next year’s Summit should be a cherry on the top of a year in which I want all structural engineers to take a step back and admire the profession to which we have devoted our lives. Our dedication to the public’ safety, health, and welfare is at the core of every calculation that we complete, every drawing that we seal, and all construction that we observe.

When structural engineers serve as first and second responders to hurricanes, earthquakes, and other disasters, we should all be proud. While our profession may be full of introverts, the time is now to proclaim our virtues to ourselves and to our families, friends, and anyone else who will listen. It is critical to love what you do every day, so why not tell everyone about your love?

I look forward to serving our profession and, most importantly, our citizenry throughout my tenure as NCSEA President. Taking the next step will require all of us participating in the effort, so find your role, and please carry it out. Thank you for the opportunity.▪ Williston “Bill” Warren IV is President, SESOL, Inc., Newport Beach, CA.

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November 2017

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Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA

November 2017, Volume 24, Number 11 ISSN 1536-4283. Publications Agreement No. 40675118.

STRUCTURE® is owned and published by the National Council of Structural Engineers Associations with a known office of publication of 645 N. Michigan Ave, Suite 540, Chicago, Illinois 60611. Structure is published in cooperation with CASE and SEI monthly. The publication is distributed as a benefit of membership to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/yr student; $90/yr Canada; $60/yr Canadian student; $125/yr foreign; $90/yr foreign student. Application to Mail at Periodical Postage Prices is Pending at Chicago and at additional Mailing offices.

POSTMASTER: Send address changes to: STRUCTURE, 645 N. Michigan Ave, Suite 540, Chicago, Illinois, 60611. For members of NCSEA, SEI and CASE, email subscriptions@structuremag.org with address changes. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, Publisher, or the STRUCTURE Editorial Board.

STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

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Codes and standards updates and discussions related to codes and standards

F

rom 2001 to 2012, the AISI Committee on Framing Standards developed nine different framing standards to cover specific aspects of cold-formed steel framing. Six of these standards addressed the design of structural elements, such as general provisions, wall studs, floor joists, trusses, headers, and shear walls. The other standards addressed such topics as a code of standard practice, the definition of standard product, and prescriptive design for residential applications. But, why

Cold-Formed Steel Framing Standards Updated for 2018 IBC

By Roger LaBoube, Ph.D., P.E., Helen Chen, Ph.D., P.E., LEED AP BD+C, and Jay Larson, P.E., F.ASCE Roger LaBoube 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 the American Iron and Steel Institute’s Committee on Specifications and Committee on Framing Standards.

He also served on STRUCTURE’s Editorial Board. Roger may be reached at laboube@mst.edu.

Helen Chen 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 W. Larson is Managing Director of the AISI Construction Technical Program, which includes AISI’s building code and standards development functions. He serves as secretary of the AISI Standards Council, which oversees the ANSIaccredited standards development activities of AISI. Jay may be contacted at jlarson@steel.org.

would AISI develop six discrete framing standards as opposed to one design manual? This has been an often asked question by framing design engineers. The simple reason is, it was easier to develop small single-topic documents versus a more comprehensive multi-topic document.

But, in 2015, these six AISI cold-formed steel framing standards, AISI S200, S210, S211, S212, S213, and S214 (references 1 to 6), were consolidated into a comprehensive multi-topic standard, North American Standard for Cold-Formed Steel Structural Framing, AISI S240. This new standard includes design provisions for wall systems, floor and roof systems, lateral force-resisting systems, as well as truss and header assemblies.

It should be noted that the newly developed and updated AISI framing standards refer to AISI S100-12 (10), not AISI S100-16, due to

the sequencing of the documents in the standard development schedule.

This article focuses on AISI S240 which applies to cold-formed steel structural members subject to gravity loading, wind loading, and seismic loading, except when specific seismic detailing is required. For nonstructural member design, AISI S220 governs the design (see STRUCTURE, February 2013) and when specific seismic detailing is required, AISI S400, North American Standard for Seismic Design of Cold-Formed Steel Structural Systems, is the applicable framing design standard.

Additionally, the North American Standard for Cold-Formed Steel Framing – Product Data, AISI S201, provides criteria for standardized products, AISI S202 serves as the industry code of standard practice, and AISI S230 provides a prescriptive method for one- and two-family dwellings. These cold-formed steel framing standards are available as free downloads at www.aisistandards.org.

The new AISI S240 standard has six topical chapters and two appendices. Within each topical area, the design considerations are sequentially ordered such that the document’s format serves as a pseudo flow chart that defines required design considerations (Table 1) as an aid for the design engineer.

Also, for ease of use, S240 contains a section reference table between the S240 provisions and the previous provisions (Table 2).

Chapter A, General This chapter contains general requirements as previously included in AISI S200. It outlines the scope, which is for design and installation of

Table 1. Format defines design considerations.

B2 Floor and Ceiling Framing ................................................................................................... 19 B2.1 Scope ........................................................................................................................ 19 B2.2 Floor Joist Design ....................................................................................................... 19 B2.2.1 Bending ............................................................................................................. 19 B2.2.1.1 Lateral-Torsional Buckling.......................................................................... 19 B2.2.1.2 Distortional Buckling ................................................................................. 19 B2.2.2 Shear .................................................................................................................. 19 B2.2.3 Web Crippling ................................................................................................... 20 B2.2.4 Bending and Shear ............................................................................................. 20 B2.2.5 Bending and Web Crippling............................................................................... 20 B2.3 Ceiling Joist Design .......................................................................................................... 20 B2.3.1 Tension .................................................................................................................... 20 B2.3.2 Compression ............................................................................................................ 20 B2.3.2.1 Yielding, Flexural, Flexural-Torsional and Torsional Buckling.......................... 20 B2.3.2.2 Distortional Buckling ...................................................................................... 20 B2.3.3 Bending ................................................................................................................... 20 B2.3.3.1 Lateral-Torsional Buckling .............................................................................. 20 B2.3.3.2 Distortional Buckling ...................................................................................... 21 B2.3.4 Shear........................................................................................................................ 21 B2.3.5 Web Crippling ......................................................................................................... 21 B2.3.6 Axial Load and Bending ........................................................................................... 21 B2.3.7 Bending and Shear ................................................................................................... 21 B2.3.8 Bending and Web Crippling .................................................................................... 21

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Table 2. Section reference table S240 and previous standard.

AISI S240 Section B2 B2.1 B2.2 B2.2.1 B2.2.1.1 B2.2.1.2 B2.2.2 B2.2.3 B2.2.4 B2.2.5 B2.3 B2.3.1 B2.3.2 B2.3.2.1 B2.3.2.2 B2.3.3

Title Floor and Ceiling Framing Scope Floor Joist Design Bending Lateral-Torsional Buckling Distortional Buckling Shear Web Crippling Bending and Shear Bending and Web Crippling Ceiling Joist Design Tension Compression Yielding, Flexural, Flexural-Torsional and Torsional Buckling Distortional Buckling Bending

cold-formed steel framing of a) floor and roof systems, b) structural walls, c) shear walls, strap braced walls, and diaphragms to resist in-plane lateral loads, and d) trusses for loadcarrying purposes in buildings. The chapter also includes: • Definitions for terms used in the standard • List of materials applicable to the framing members

Source Standard new (editorial) new (editorial) new (editorial) new (editorial) S210 new S210 S210 S210 S210 new (editorial) S210 new (editorial) S210

Section n/a n/a n/a n/a B1.2.1 n/a B1.2.2 B1.2.3 B1.2.4 B1.2.5 n/a B1.3.1 n/a B1.3.1

new new (editorial)

n/a n/a

• Corrosion protection requirements • Framing products • Reference documents The previous design standards limited their application to framing members having a maximum base steel thickness to 118 mils (0.1180 inches or 2.997 mm). This limitation has been eliminated from AISI S240; however, it should be remembered that 118 ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

www.buysuperstud.com/DeflectionClips or call 800.477.7883 US Patent 6213679; other patents pending

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mils is still the maximum thickness of standard products in the United States and 97 mils (0.0966 inches or 2.454 mm) is still the maximum thickness of standard products in Canada.

ASTM C955 has historically stipulated manufacturing tolerances for cold-formed steel structural framing members. These tolerances were replicated in AISI S200 in 2012 and are now included in AISI S240.

In 2012, the manufacturing tolerance values were extended to the flange width and stiffening lip length.

Chapter B, Design This chapter contains design provisions for cold-formed steel framing members and assemblies, as previously included in AISI S210, S211, S212, and S213.

For curtain wall systems, the standard now permits the use of the bracing combination of sheathing attached to one side of the wall stud and discrete bracing for the other flange (Figure 1, page 12). The discrete braces are limited to not greater than 8 feet (2.44 meters) on center.

Built-up sections continue to be evaluated in accordance with Section D1 of AISI S100 [CSA S136]. However, AISI S240 now incorporates an exception for a built-up axial load bearing section comprised of two studs

We Va

α

1/2We

T

h 1/2We

α W Figure 1. Sheathing and discrete bracing.

Figure 2. Effective strip method model for steel-sheet sheathing.

oriented back-to-back forming an I-shaped cross-section. The exception applies where the built-up section is seated properly in a track, and the top and bottom end bearing detail of the studs consists of a steel or concrete support with adequate strength and stiffness to preclude relative end slip of the two builtup stud sections. For such applications, the compliance with the following onerous fastener end connection provision of AISI S100 Section D1.2(b) is not required: The ends of a built-up compression member are connected by a weld having a length not less than the maximum width of the member or by connectors spaced longitudinally not more than 4 diameters apart for a distance equal to 1.5 times the maximum width of the member.

This new exception provides for a more economical built-up member, as is often used as a jamb stud or shear wall boundary member.

For roof or floor diaphragms with a maximum aspect ratio of 4:1, framed with cold-formed steel and covered with nonsteel sheathings, the in-plane nominal shear strength can be determined by tests in accordance with ASTM E455. The use of ASTM E455 results in higher nominal shear strength values as compared with the cantilever test method historically used for steel deck diaphragms. The test results are to be calibrated in accordance with AISI S100 using the statistical values given in AISI S240 Section B5.4.5.

Beneficial for the design engineer is a new Effective Strip Method that enables the calculation of the nominal in-plane shear wall strength

for Type I shear walls (Figure 2). The method assumes a sheathing strip carries the lateral load via tension field action. This computational method is applicable for walls sheathed with steel sheet. This method provides an alternative approach to determine the shear wall strength, especially for those that are outside the limitations of the tested systems. The effective strip method is permitted to be used within the following range of parameters: a) Designation thickness of stud, track, and stud blocking: 33 mils (0.838 mm) to 54 mils (1.37 mm). b) Designation thickness of steel sheet sheathing: 18 mils (0.457 mm) to 33 mils (0.838 mm). c) Screw spacing at panel edges: 2 inches (50.8 mm) to 6 inches (152 mm). d) Height-to-width aspect ratio (h:w): 1:1 to 4:1. e) Sheathing screw shall be minimum No. 8. f ) Yield stress of steel sheet sheathing shall not be greater than 50 ksi (345 MPa).

Chapter C, Installation This chapter provides installation requirements previously contained in the various framing standards.

Chapter D, Quality Control, and Quality Assurance This newly developed chapter provides minimum requirements for quality control and quality assurance for material control and installation for cold-formed steel light-frame construction. Minimum observation and

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inspection tasks deemed necessary to ensure quality cold-formed steel light-frame construction are specified. The February 2016 issue of STRUCTURE contains a comprehensive discussion of Chapter D. Chapter E, Trusses This chapter contains design, manufacturing quality criteria, and installation requirements for cold-formed steel trusses as previously included in AISI S214.

Chapter F, Testing This new chapter lists applicable AISI test standards for cold-formed steel framing members, connections, and systems.

Appendix 1, Continuously Braced Design for Distortional Buckling Resistance This appendix contains requirements for the determination of the rotational stiffness that structural sheathing provides to framing members to facilitate the design for distortional buckling.

Appendix 2, Test Methods for Truss Components and Assemblies The truss component structural performance load test and full-scale truss confirmatory test methods, previously included in AISI S214, are provided in this appendix.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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Structural DeSign design issues for structural engineers

R

ecent developments in prescriptive fire resistance design resulted in the introduction and advancement of UL Design D982. A principal advantage of this UL design is that it provides the same fire protection thickness requirements for 2-hour assembly ratings regardless of whether the classification is restrained or unrestrained.

For other UL Designs, Section 703.2.3 in the 2015 International Building Code (IBC) requires that the qualification of construction for the restrained classification, in accordance with ASTM E119 or ANSI/UL 263, is the purview of the registered design professional (RDP) for the acceptance of the building official. Restrained construction is required to be identified in the construction documents.

Accordingly, it is worth repeating the basis upon which the RDP and building official can comply with this requirement. An abbreviated excerpt of the seminal journal paper by Gewain and Troup that provides this basis follows. It is entirely based on information in that paper and used here with the permission of AISC; omitted information is symbolized by ellipses (…) and [text in brackets] in this article. Please refer to the original paper for all referenced figures and images. The full paper is available at www.aisc.org/ULclarity.

Origins of Fire-Resistance Ratings for Steel Assemblies

By Charles J. Carter S.E., P.E., Ph.D. Charles J. Carter is President of the American Institute of Steel Construction, where he has worked since 1991.

“Restrained Fire Resistance Ratings in Structural Steel Buildings”

by Richard G. Gewain and Emile W.J. Troup

[This paper provides a basis for] proper application of restrained and unrestrained fire resistance ratings for steel beam floor and roof assemblies. …[It enables] architects and engineers to satisfy code provisions requiring justification where fire resistance for steel beam floor and roof systems are based on restrained assembly ratings.

Background ASTM E119 Standard Fire Test Building code requirements for structural fire protection are based on laboratory tests conducted in accordance with the Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E119 (also designated NFPA 251 and UL 263) (ASTM, 1970). …For typical steel and concrete structural systems, the behavior of specimens, in an ASTM E119 fire test, do not reflect the behavior of floor and roof constructions that are exposed to uncontrolled fire in real buildings. … …[Floor] slabs in real buildings are continuous over interior beams and girders, although this continuity has not been explicitly considered in the structural design. Beam/girder/column connections range from simple shear to full moment connections, and framing member size

The original Gewain/ Troup article was published in Engineering Journal, American Institute of Steel Construction, 2001, Vol. 38, pp. 78-89.

View of Cardington Test Building during fire exposure.

14 November 2017

Schematic of NBS (NIST) test building.

and geometry vary significantly depending on structural system and building size and layout. Even for relatively simple structural systems, realistically simulating the restraint, continuity, and redundancy present in actual buildings is extremely difficult to achieve in a laboratory fire test assembly. In addition, the size and intensity of a real uncontrolled fire and the loads superimposed on a floor system during that exposure are variables not investigated during an ASTM E119 fire test. Many factors influence the intensity and duration of an uncontrolled fire and the likelihood of full design loads occurring simultaneously with peak fire temperatures is minimal.

It is clear that the ASTM E119 Standard Fire Test was developed as a comparative and not a predictive test. In effect, the Standard Fire Test is used to evaluate the relative performance (fire endurance) of different construction assemblies under controlled laboratory conditions.

UL Fire Resistance Ratings …[Structural] connections are rarely included as part of the test assemblies. Beams in fire tests are generally supported on shelf angles with shims driven between the ends of the beam and the test frame, resulting in a highly restrained condition. Concrete slabs are poured tightly against the test frame although some shrinkage typically occurs during curing. Aside from the degree to which restraint occurs as beams and slabs are heated, these support conditions do not accurately model the structural continuity and boundary conditions of typical floor construction. …Ever since UL included the stiffness characteristics of the restraining test furnace frames in the introductory section of its Fire Resistance Directory, this criterion

has sometimes been misapplied (Ioannides and Mehta, 1997). …These stiffness values have been used to suggest that they should be the minimum stiffnesses of the steel frame into which steel beams and girders are connected to columns in actual buildings. [This] is not the case (Bletzacker, 1966; Chiappetta, Longinow, and Stepanek, 1972; Bresler and Iding, 1982; Gewain, 1982a; Gewain, 1982b; UL, 1984; Bresler, Iding, and Dawsin, 1988).

Current Building Code Requirements [Additional review of historic building codes is available in the full paper.]

International Building Code [The] International Building Code… includes wording… that evidence of a restrained condition satisfactory to the building official must be furnished by a registered design professional. …The IBC essentially requires the design professional to designate whether fire resistive floors, roofs, and beams are restrained or unrestrained. …

Synopsis of Fire Research and Analysis Early Fire Tests and Analysis of Floor Systems: 1965 – 1966 [Fire] research on the effect of restraint was conducted… (Bletzacker, 1966)… to determine the factors that had produced years of excellent field experience in actual fires, with fire protection thicknesses on steel beams based upon ASTM E119 fire tests and restrained rating criteria. …This research program studied:

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1) Connection methods for supporting protected steel beams in the ASTM E119 test furnace – including free-toexpand supports (“unrestrained”), simple double angles, and fully welded end plates (“restrained”) (see Figure 3 [in the paper]); 2) The effect of the concrete slab with ends restrained by the furnace frame; 3) The effect of design and construction – including non-composite action between beam and slab, partial composite action, and fully composite action; 4) Comparisons of beam performance – unrestrained expansion and end rotation vs. restrained expansion and end rotation, through the application of various levels of axial thrust and end moment; and 5) The effect of applied vertical load on the resulting working stresses.

[Further description of these tests is available in the full paper.]

[This project] showed that... simple beamto-column shear connections in typical steel-framed construction [will] provide fire endurance equal to or greater than that measured when testing very highly restrained test specimens in a massive ASTM furnace test frame… It was observed that even these typical shear connections provide rotational and axial restraint for the beam due to interaction with the concrete floor slab and the inherent stiffness of columns.

[Information on fire modeling can be found in the full paper.]

Large Scale Building Fire Test: 1981 [This test] structure had a footprint of 32 [feet] × 40 [feet] and was 20 [feet] high (see Figure 4 [in the paper]). The frame was sized to represent a floor at mid-height of a 20-story office building and was fabricated of hot rolled structural steel sections fastened to columns with high-strength bolts. The floor slab at the second-floor level was subjected to a design live load of 80 lb/ft2 and consisted of normal weight concrete on a steel deck. During each of the tests, one 16 [-foot] × 20 [-foot] × 10 [-foot-high] bay of the test frame was exposed to fire and the structural steel and metal deck protected with spray-applied fire protection material, ½[-inch] thick. The assembly used a W12×22 beam framing into a W12×22 spandrel and W12×30 girder and was based upon UL Design No. N805 (UL, 2001), because of its similarity to the construction details being tested (see Figure 5 [in the paper]).

Both ASTM E119 fire exposures and ventilation controlled fires (freeburn, using wood pallets as the fuel) representing exposures expected in an office occupancy were used.

Temperature measurements were recorded during and after the tests through the slab

Beam in Cardington Tests after reaching temperature in excess of 1,600°F.

thickness, along the beam profile, on the columns in the test bay, and within the fire compartment. Vertical deflections were measured across the exposed portion of the floor slab and horizontal deflections were measured along the columns and spandrel beams of the test bay and in the fire compartment. …The data from all three tests showed that the structural framing had equal or better fire resistance than a single beam in the ASTM E119 fire test protected in accordance with the restrained rating criteria. The guidelines in Appendix X3 of ASTM E119 for restrained beams were confirmed by these results.

Underwriters Laboratories, Inc. Fire Tests: 1983 – 1984 [These tests] investigated the similarities and differences during UL 263 (ASTM, E119) fire tests in the performance of restrained steel beams with different end conditions (UL, 1984). The end conditions investigated were: 1) Beams restrained in the UL test frame in the traditional manner, by placing steel shims between the ends of the beams and the test frame; and 2) Beams placed in the test frame using typical field bolted clip angle connections (see Figure 7 [in the paper]). Results of these fire tests, based on Table 1 in the UL test report, are summarized in Table 1 [in the paper]. In evaluating the test data from these fire tests and other tests, the UL report concluded the following: There does not appear to be significant differences in the fire resistance performance of restrained beams that are shimmed against the test frame as compared to restrained beams that are bolted to clip angles in the manner described in this report. Thus, this test confirmed that beams with bolted connections should be considered as restrained beams.

Computer Modeling of the 1965 OSU/AISI Fire Tests: 1988 [Further modeling and analysis were performed considering] two components of end restraint in realistic steel-framed buildings: 1) Rotational restraint, provided by simple bolted connections; and 2) Axial restraint, due to column restraints, floor slabs, and adjoining construction.

Rotational Restraint The minimum restraint condition used… was a connection generally considered as a pinned or simple shear connection by designers: a 3-bolt single plate framing connection.

Figure 9 [in the paper] shows the results of the… analysis and the results of corresponding unrestrained and fully restrained beams.

Figure 10 [in the paper] illustrates that the end moments due to the bolted end connections reduce mid-span moments and stresses at all stages of the fire test. More highly restraining connectors were not studied since a minimum-sized bolted end connection gave essentially restrained-based fire endurance.

Based on these results, [it was concluded] that a minimum amount of rotational restraint (no axial restraint considered) provided by simple shear connections produces a fire endurance that approximates that of the identical floor system assembly but with fully fixed, moment-resisting connections.

Axial Restraint The… study for axial stiffness and its effect on fire endurance involved a W12×27 beamslab assembly from the OSU tests, framed into a single W14×43 column. The column was assumed fixed one story above and one story below. Restraint due to both weak-axis

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and strong axis orientation of the column (the latter about ten times stiffer) were studied. The conclusion reached… was that axial restraint in the absence of rotational restraint does not increase fire endurance over that of minimal rotational restraint alone (see Figure 11 [in the paper]).

It should be noted that, although the component of restraint to the axial growth of beams provided by column stiffness can increase fire endurance of the floor or roof system, excessive restraint can cause buckling of beam flanges or damage to connections.

Contrarily, very flexible columns theoretically could be subjected to significant horizontal deflections at the floor or roof level during heating or cooling. However, there are no known cases of actual uncontrolled fires in which any of these effects have impaired the performance or fire endurance of protected structural steel framing.

Combined Axial and Rotational Restraint Results from analysis of combined axial and rotational restraint (weak-axis column orientation) are shown in Figure 12 [in the paper] and compared with unrestrained and fully restrained connections. Again, the conclusion drawn… was that, if minimal rotational restraint is provided by standard shear connections at the ends of the beam, restrained-based fire endurance is achieved even if there is little or no contribution from axial restraint. Steel framing in both interior and exterior bays will behave as restrained assemblies as long as the connectors are attached to columns or other members to develop some degree of rotational restraint, typically achieved with standard shear connections.

Other Findings [This study also] validated the practical classification of restrained construction for structural steel in ASTM E119, Table X3.1.

[It] also noted other practical factors that further support this conclusion, such as: continuity and redundancy; lower load levels during actual fires; and, composite action between steel and concrete. …

Recent Studies and Fire Tests The authors have included the following remarks about several recent studies that reinforce the [points made in the paper].

Cardington Fire Tests: 1995 – 1996 [These] tests were conducted on an eightstory, steel-framed office building at the Cardington Laboratory of the Building

Ioannides and Mehta: 1997 An analytical study on restrained/unrestrained fire ratings used the measured temperatures at various locations along the depth of the beam and slab to determine nominal flexural strength and capacity of a beam during the ASTM fire test (Ioannides and Mehta, 1997). The authors offered an analytical procedure, using an assumed time-temperature history for the particular assembly and beam rating coupled with the known properties of the steel at various elevated temperatures, to calculate the nominal flexural strength of the beam. They also provided methods to increase the nominal flexural strength (if needed) by accounting for the effects of rotational restraint (due to connections and slab reinforcement) and thrust restraint. Their study showed that, considering the combination of factors that occur in real buildings during real fires, steel beams, protected with spray-applied fire protection material thicknesses for restrained beams, can have sufficient load-carrying capacity without even counting on any restraint.

An Extreme Fire Event Experience from intense, uncontrolled fires in unsprinklered structural steel high-rise buildings with spray-applied fire protection during the past few decades is limited.

However, these few events have borne out the ability of steel and concrete floor systems to mobilize the surrounding structural elements and prevent collapse under the most

intense of fire exposures. Perhaps the most dramatic example of steel’s fire endurance occurred in a high-rise fire in an East Coast city in 1991 – probably the most intense high-rise fire ever experienced in the United States (Klem, 1991). The fire was reported to have caused a complete burnout of eight upper stories over an 18-hour period, being halted at the 30th floor by sprinklers that were being retrofitted into the building from the top floor downward. Although there was considerable distress to steel floor assemblies (originally fire protected based upon a restrained rating classification), there were no reported floor collapses. Dexter and Lu (Dexter and Lu, 2000) later studied the effects of high temperatures and horizontal expansion/contraction and rotation of floor beams on the restraining columns.

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Conclusions 1) The unrestrained assembly fire resistance rating for structural steel beam floor and roof systems, based on ASTM E119 temperature criteria only, has no relevance to the behavior of these systems under uncontrolled fires in real buildings.

2) The fire endurance of structural steel beam floor and roof construction under uncontrolled fire is enhanced by the interaction of the beams with the other structural elements and constructions that are integral with or surround the exposed assembly.

3) All steel beam connections to other structural steel members exhibit both axial and rotational restraint.

4) The least stiff connection typically used for steel framed construction (such as a three-bolt single plate connection) is adequate to develop restrained performance. Conclusions drawn from the fire research and computer modeling that have been performed by various agencies, including Underwriters Laboratories, Inc., support the conclusion that a restrained assembly classification and fire protection design is most appropriate for steel beam floor and roof assemblies, and verify the guidance contained in ASTM E119 …Appendix X3.

5) The performance of structural steel beam and concrete floor systems exposed to uncontrolled fires observed during the research and analysis studies conducted during the past 25 years largely explains the excellent performance of these systems during severe fire exposures in unsprinklered, modern high-rise buildings.▪

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Research Establishment in the United Kingdom (Newman, 1999) (see Figure 13 [in the paper]). …The structure was five bays long (148 [feet]) by 3 bays wide (69 [feet]) by 108 [feet-high], and beams in most of the tests were designed as simply-supported acting compositely with a concrete slab cast on metal deck. Columns were protected up to the underside of the floor slab and the beams, deck and floor slab in this unsprinklered building were unprotected.

Although the test program included one test on a restrained beam assembly on the seventh floor, it was noted that restraint as a variable in fire tests is largely unheard of in Europe. During this restrained assembly test, the maximum beam temperature reached was about 1,650°F and the maximum deflection was about 10 [inches] (see Figure 14 [in the paper]). Although distress was noted in the bottom flange of the beam and at the connections (during cooling), the floor assembly continued to support its applied load at the conclusion of the test (see Figure 15 [in the paper]).

Outside the BOx highlighting the out-of-theordinary within the realm of structural engineering

S

teel casting is considered an innovative, leading-edge technology when used in the design of building structures. However, there are several notable North American buildings that used steel castings that have been in service for over a decade. As steel castings become more commonly used in building design, innovative applications of this technology are emerging.

Increasingly, structural engineers are turning to the freedom of geometry and material capabilities offered by casting manufacturing to solve tough structural challenges. This article presents three examples of this “second-order” innovation.

Designer Materials When designers think of steel castings, they often first think of beautiful, organically-shaped connection nodes like those used in the Transbay Transit Center in San Francisco. In this type of application, castings are selected because they offer the geometric freedom that can provide performance advantages over conventionally-fabricated details. The material used for typical cast structural nodes is usually very similar to that of conventional structural steel. However, designers of some of the world’s tallest building structures are now turning that convention upside-down.

One novel casting technology for heavily loaded multi-directional connection nodes, such as those found in transfer or outrigger levels of high-rise towers and other heavy structures, provides simple geometry with complex, engineered material.

Often, heavily loaded multi-directional nodes are

Second-Order Innovation

By Michael Gray, Ph.D., P.Eng.

fabricated with heavy plates laminated together, combined with complex fabrication. One challenge in using heavy steel plates in this way is that, once the plates exceed 2.5 inches in thickness, the achievable yield strength is typically less than 50 ksi. If the connected members are of a 50 ksi material and loaded close to their capacity, this strength mismatch can pose a significant challenge. Heavy plates can also exhibit centerline shrinkage which makes them susceptible to lamellar tearing when loaded normal to the plane of the plate.

This new technology consists of rectangularly shaped castings manufactured with a steel grade that provides minimum yield strengths of 50 ksi through cross sections up to approximately 48 inches by 48 inches, while remaining weldable via conventional means. This can only be achieved through careful control of alloy elements in the block material, combined with an engineered hot working and heat treatment to promote grain refinement. Structural attachments can be welded to the faces of the blocks to create hybrid cast/fabricated nodes that are easily installed in the field.

The solid rectangular block easily accommodates the flow of forces through the node. Thus far, the largest (by weight) rectangular block in use is a 30-inch x 32-inch x 103-inch block utilized in a new steel high-rise in New York. NY.

Form Finding Optimization As has occurred in many other fields of practice, digital design has opened the door to exciting new geometric forms in structural engineering.

The next revolution in computer-assisted design is quite possibly topology optimization. Topology optimization is the use of numerical analysis to

Michael Gray is Executive Vice President of Cast Connex. Michael has designed steel castings for numerous projects across North America. He can be reached at m.gray@castconnex.com.

Figure 1. Cast nodes in the architecturally exposed steel frames at the Transbay Transit Center. Courtesy of Transbay Joint Powers Authority.

18 November 2017

(a)

Figure 2. Machined high strength cast steel rectangular block for highly-stressed multi-directional connection nodes.

(b)

(c)

Figure 4. a) Typical wide flange beam used in a common mechanical structure; b) and c) analysis results and preliminary casting designs from topology optimizations with two unique design spaces.

The original design was a stiffened wide flange section weighing 1950 pounds. The first optimization was conducted using a design space of 127 x 15 x 30 inches. The optimization included minimum thickness constraints which are determined based on the thickness limitations of the casting process. As such, the resulting design weighed 3,430 pounds and resulted in a geometric form that was awkward and inefficient. As with other iterative designs, the input parameters were adjusted to modify the converged solution. The design space was decreased to 127 x 15 x 22.5 inches to develop a second optimized solution that was more readily castable and made better use of the material. Somewhat counterintuitively, reducing the available depth enables more efficient use of Figure 3. High strength cast steel rectangular block installed cast material, because the minimum in a high-rise in New York City. Courtesy of Juan Estevez, required material thickness is better Tishman Construction. utilized. As such, the resulting design optimize material use and form within a attained by reducing the design space weighed defined design space and for a specific set of 1,555-pounds, which is an approximate boundary conditions. The nearly free-form 20% reduction in weight compared with geometry achievable via the casting process the current beam. The resulting geometric is well suited to design that is informed by form was used to create a castable geometry topology optimization. that is currently being explored as a practical One example of the optimization was used replacement for the wide flange beam in the to develop a cast steel component that would mechanical structures studied. replace a wide flange section used in large mechanical structures in the oil industry.

Product Hacks This particular beam element is subjected to three-point bending, including out-of- Another use of steel castings is to use standard plane loading considerations. Provided connector products outside of their original with loading and geometric constraints, intended design. One case study of a “prodthis exploratory design effort was a perfect uct hack” is in the new elementary school opportunity to use topology optimization to in Grand Prairie, Alberta. The design of this develop a preliminary geometry. The series of school included several inclined timber coldrawings in Figure 4 illustrates the geometry umns that support an over-hanging roof and of the original part (Figure 4a) and the two are located on the exterior of the building. optimized solutions (Figures 4b and 4c).

Originally, the designers at Stantec desired STRUCTURE magazine

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a custom cast steel connection for the ends of the columns. However, schedule compression would not accommodate the lead time required for a custom casting, which is approximately 18 to 22 weeks. The team developed an innovative solution that would support an aggressive construction schedule while still providing the smooth geometric form that was the original driver for the desire to specify castings. Innovative detailing enabled the use of standardized cast steel connectors, intended for circular hollow sections, as timber end connectors. These standardized cast steel connectors were fitted with a knife plate that would slot into the ends of 12-inch diameter timber columns and connect using three through-bolts per end. The ends of the timber columns were tapered to match the taper of the cast connector, creating a pleasing aesthetic.

Another potential product hack is a new application for anti-seismic, cast steel yielding connections in truss moment frames.

These cast steel yielding connections dissipate seismic energy via flexural yielding of several parallel cast steel yielding fingers. Cast steel yielding connections were developed to enhance the ductility of vertical braced frames, but the connectors can be used at the end of any axially loaded member to provide fully symmetric yielding. One innovative application of this connector that is currently under exploration is their use in the seismic retrofit of deficient truss moment frames.

Ideally, truss moment frames dissipate seismic energy by yielding under vertical shear, which is achieved by axial yielding of diagonal web members and shear yielding of chord members in the central portion of the truss.

Unfortunately, many older truss moment frames were not designed with ductility in mind and thus are unable to dissipate seismic energy in the desired manner. It has been proposed that one possible solution to increase

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Figure 6. Sloped wood columns support an over-hanging roof in Grand Prairie, Alberta. Courtesy of Stantec.

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Figure 7. Standard cast steel connectors typically used in structural steel were “hacked” as timber end connectors. Courtesy of Stantec.

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ductility in such a system is to replace select web members of deficient trusses with cast steel yielding connections.

Since the depth of truss moment frames is usually much less than a typical story (AISC 341-16 limits the depth of trusses in new Special Truss Moment Frames to 6 feet or less), the diagonal web members of the truss are generally much shorter than conventional STRUCTURE magazine

CD17070_Clips_Structure_ThirdPg_VertAd_June17.indd 15/11/17 11:58 AM

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braces. The use of cast steel yielding connections in the retrofit of a deficient truss moment frame is appealing because, unlike axial yielding elements, the deformation capacity of these devices are not linked to the length of the connected member. A cast steel yielding connection can provide the ductility of a full story brace in a structural element much shorter than a typical story.

The retrofit scheme is developed by modeling a truss with cast steel yielding connections included in critical members. The appropriate size of the connector is selected for strength. Then the calculated drifts must be checked to ensure that the connector has adequate stiffness and displacement capacity and that the expected over-strength associated with the peak connector deformation is allowable from a capacity design approach. The envisioned retrofits involve fully replacing the critical web members with new elastic member and cast steel yielding connections. This concept is under consideration from multiple building owners but has yet to be implemented.

The innovative nature of steel castings enables increasingly creative applications for this technology. Engineers are using the freedom of material and geometry achievable with steel castings as a new tool to solve increasingly unique structural challenges.▪

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Structural PracticeS practical knowledge beyond the textbook

A

ccording to the Epidemiology of Balcony Fall-Related Injuries, United States, 1990-2006 (American Journal of Emergency Medicine, 2011 February 29), there were 86,500 fall cases (including 8 fatalities) over the period studied. This estimate was based upon injuries requiring emergency medical treatment, and it reports that 5,600 cases involved structural failures. The information available did not allow the study’s authors to assess whether the structural failures were due to overload or to defective floors or railings.

To differentiate between balconies and decks, the 2006 International Building Code defines an exterior balcony as “an exterior floor projecting from and supported by a structure without additional supports” and defines an exterior deck as “an exterior floor system supported on at least two opposing sides by an adjoining structure and/or posts, piers, or other independent supports.” It is likely that the paper’s authors were not aware of the difference and had included falls from decks in some of their statistics. Nevertheless, the numbers are worrisome.

Balcony Issues in High-Rise Buildings

By Dan Eschenasy, P.E., F.SEI, SECB

Dan Eschenasy is the New York City Buildings Department Chief Structural Engineer. He is an Honorary Member of SEAoNY and a member of the ASCE Structural Assessment of Buildings Committee.

Recent stories in the local press might have created the impression that fatal accidents involve mostly wood balconies, but reports from the United Kingdom, Netherlands, Australia, and Brazil describe cases involving concrete balconies.

In the past ten years in New York City (NYC), there were several serious structural balcony related accidents, some involving balconies from relatively recent construction. Balcony accidents may refer to events where occupants fall or where pedestrians

are hit by falling debris. One can distinguish three modes of balcony failure – failure of the cantilevered slab, local deterioration of the cantilevered surface, and failure of the railings. This article discusses failures of balconies that were investigated as a result of accidents or were described in reports prepared in compliance with the NYC mandated periodic inspection of façades.

Exterior Balconies in NYC Apartment Buildings In NYC, before World War II, balconies were erected almost exclusively as components of exterior fire escapes. A substantial number still exist, but their condition is not discussed here as they are rarely present on buildings taller than six stories. It is worth mentioning that some wrought iron fire escapes dating from the 1910s are still looking fine.

In the early decades of the last century, it was not uncommon to decorate façades with decorative terracotta Juliet balconies (i.e., balconets). They were only meant to give the visual illusion of a balcony and their width did not allow any use by tenants. In many cases, the terracotta balusters of these balconets had cracked or became loose and had to be repaired or removed. A serious accident occurred in 2008 when a significant portion of such a balconet collapsed (Figure 1), as the corrosion of the embedded steel outriggers caused the cracking of the terracotta floor. That building façade had been subject to a recent periodic inspection, but the prescribed repair consisted only of patching cracks in the terracotta. Similar terracotta problems led some building owners to remove the balconets, to the desperation of architectural preservationists.

In the early 1950s, balconies started to be built as a special amenity for high-end apartments, but

Figure 1. Collapse terracotta balconet.

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Table 1. 2007-2017 façade incidents – buildings 6 stories and above.

YEARS

Less 50

50 to 75

75 to 100

Over 100

Total

Balcony

7

7

1

1

16

Balcony Railing

6

1

1

8

Cornice

2

7

17

30

56

PARAPET

5

38

26

26

95

Window/Glass

13

4

5

4

26

No. Buildings

4,598

3,562

8,281

4,803

21,244

Grand Total

33

56

50

62

201

soon after they were included in the design of middle-class developments. By that time, the typical structure of the NYC high-rise apartment building was the “concrete flat slab” and, as a consequence, the typical balcony has since been a concrete cantilever, usually not wider than 4 or 5 feet. The 1960s were marked by a massive effort of replacing slums with new apartment buildings. The large projects were made possible by federal government financing. The balcony became a common feature of high-rise apartment buildings especially as a result of specific financial incentives that favored apartments with balconies. Compared with the entire NYC building stock, the high-rise structures built in the last 50 years can be categorized as recent construction, constructed using engineered materials and engineering principles that are not much different from those used today.

The New York City Buildings Department Emergency Operations Center (EOC) dispatches inspectors when notified of major façade incidents. The inspectors’ initial reports are recorded in a database. The principal sources of notifications for these major incidents are the city’s emergency response personnel (e.g., fire or police). In general, these are notifications of accidents that have just occurred or seem imminent. The data includes almost all major incidents, but also

Figure 2. Balcony collapse after shore removal.

many events where façade failures might not have resulted in injuries. The database contains only a subset of the population of façade failures, as a good number of minor façade failures do not reach the EOC. As a result, an analysis can only allow inferences as to the type and trends of façade deterioration.

The data in Table 1 is an extract from the façade incidents recorded from 2007 up to 2017. The data was filtered to exclude incidents not relevant to this article (walls, ornaments, appurtenances).

Incidents involving buildings with less than 6 stories were not counted and, as a result, all balconies, except for two, were concrete.

Periodic façade inspections are required only for buildings over 6 stories, so a good number of incidents counted in the table had occurred in buildings that were not subject to these periodic façade inspections.

There are too many variables involved to perform an accurate, in-depth statistical analysis, but a simple examination of the numbers reveals that balconies constitute a majority of incidents. This should be no surprise – a defective façade component is at a higher risk of falling when it is present on a protruding element. (In addition to gravity, a lateral force is required to displace a section that has a support below.)

In the author’s opinion, it is significant that the number of balcony incidents exceeds parapet incidents for buildings erected over the past 50 years, the period when balconies became a common building feature. There are some essential similarities – both parapets and balconies are exterior, unheated structures, exposed to the elements (changes in temperature, rain, and wind).

They differ in constituent material (concrete vs. brick) and some exposure conditions – balconies are exposed to standing water

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and parapets are exposed to higher wind pressures. The significance of the comparison resides in the fact that, historically, parapets have been a major source of accidents.

Structural Performance of the Cantilever Structure Live loads specific to balconies and railings were introduced in the NYC Building Code of 1968. While the live load in the American Society of Civil Engineer’s ASCE 7, Minimum Design Loads for Buildings and Other Structures, has varied depending upon the edition, the NYC regulations have been constant in specifying 150% of the load of the adjoining occupied area. It is interesting to note that there is some evidence that, although an NYC apartment with a balcony commands a higher price, the actual owner’s use of balconies is very minimal. As a result, there is limited information on the performance of balconies under live load.

There might have been some cases of excessive deflection; but, according to the author’s observations over the past fifteen years, there has been no report of the collapse of a concrete slab balcony due to live load.

A balcony is a non-redundant structure; design or construction errors cannot hide as the cantilever does not have the advantage afforded by multiple load paths nor the added capacity allowed by stress redistribution. Some published reports on balcony failures elsewhere mentioned overloading.

However, in the cases investigated, the author determined that the failure of the concrete structure was mostly due to improper placement of the reinforcing (Figure 2).

Improper placement of reinforcement may be the result of negligent construction execution or insufficient detailing. Architectural details require the top of the balcony slab to be slightly lower than the interior floor to prevent rain driven water or snow from penetrating into apartments. The design and details need to recognize the drop and also the need for a larger concrete cover dictated by the weather exposure. Missing or misplaced reinforcement may lead to the collapse of the balcony under its own weight. We have seen this occurring immediately after the removal of re-shores (Figure 2). For cases of misplaced reinforcing bars, it is conceivable that the tensile capacity of the unreinforced concrete is sufficient to sustain the dead-weight stresses, but a failure can occur later under occupant load.

Insufficient reinforcement may also result in excessive balcony deflections. Such deflections or creep are likely to change the intended

Probably the most common surface failure is the spalling that occurs to the outside corner due to corrosion of the railing post (Figure 4).

Galvanic corrosion may occur even at the base of aluminum posts when they are in contact with steel reinforcing bars. Patching cracked concrete can provide relief for five to ten years, but ultimately the corroded reinforcement and the deteriorated concrete have to be replaced (Figure 5). While the engineering principles of the repair/replacement of concrete are simple, the execution is sometimes very expensive due to the difficulty of working from hanging scaffolds. By now, most of the balconies erected in the 1960s have had their edges repaired or reconstructed.

In 2010, a young man fell from a 24th-floor balcony. The department’s investigation determined that the fall had occurred through the opening created by the failure of the metal panel underneath the handrail. It was found that the original installation for balcony railings met the code strength requirements, but it was flawed as it did not restrain an upward movement of the panel. As a result of the lack of restraint, some minor upward pull on the panel (under minor loads, not necessarily specified in the code) could bend the panel into a potentially dangerous position that could become permanent. The inspectors observed several permanently deformed panels at other floors (Figure 6).

The collapse was possible only because of a flaw in the design – lack of vertical restraint at the panel ends. Calculations demonstrated that, if the restraint was present, the collapse would not have occurred.

Following the accident, a citywide search identified six other high-rise apartment buildings with balconies having the same insufficient panel connection details. These balconies were vacated until the repairs were performed. The 2014 New York City

Building Code contains an added requirement for the design of components; “a concentrated upward load of 50 pounds (0.22 kN) applied at the most critical location”.

(2014 New York City Building Code, Section 1607.7.1.2). A separate analysis of several periodic façade inspection reports revealed that inspectors were mainly concerned with danger to pedestrians below and less with the structural reliability of the railings. The department notified the industry of the problem and ordered supplemental inspections specifically focused on the condition of railings of balconies, setbacks, and terraces. Common defects observed included: 1) rusted pickets, 2) displaced or detached rails, 3) guard rail assemblies easily displaced under a slight force, 4) open cracks around pitch-pockets of railing posts, 5) deterioration of end railing attachments to walls, and 6) loose connections. The safety of railings is strongly impacted by the deterioration or degradation of the concrete at the balcony’s edge, as discussed above.

According to the data in Table 1, failures of railings, balconies, and glass seem to be more predominant in newer construction. This might be due to the effect of newer trends in architectural design, as well as the time delay it takes for building codes to adapt to and regulate newer systems. According to the Expert Panel on Glass Panels in Balcony Guards Report – 2012 (Ontario Ministry of Housing), the leading causes of failure include deficiencies in railing installation, impact-related incidences, and nickel sulfide impurities in glass.

A detailed technical discussion of glass in balcony railings is beyond the scope of this article, but the few cases of glass failures in balcony railings match the Expert Panel findings.

In 2010, a moderate intensity wind microburst collapsed a 10-foot by 30-foot full height glass enclosure on a 52nd-floor balcony (Figure 7). In its fall, the glass destroyed the skylight roof of a ground floor public

Figure 5. Edge balcony during repair.

Figure 6. Panel not permanently secured.

Failure of Railings Figure 3. Crack along balcony edge.

path of rainwater collection or possibly forcedeformation of the railing installation.

Local Deterioration The NYC periodic façade inspection law has included some condition assessments of balconies since its promulgation in 1980. The reports, prepared in conjunction with periodic inspections, provide useful information on the ways concrete balconies deteriorate. The symptoms of failures described are typical for weather exposed concrete (concrete spalling, cracking, rust of reinforcement, and related consequences). The condition is most likely made worse by the exposure of both faces to weather. Because they may allow rainwater accumulation or stagnation, balconies are more likely to deteriorate when compared with the vertical surfaces of the façade of the same building. Architectural coverings and even carpets may influence the rate of decay.

The deterioration is more prevalent along the outside edges of the balcony (Figure 3).

Figure 4. Concrete spall at corner post.

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space. The collapsed occurred when the interior space was depressurized by a window being opened inside the apartment. In another case, a wind-borne wicker chair, left unattached on a 45thfloor penthouse terrace, hit and broke a glass panel, injuring five pedestrians below. A 42-story building on Fifth Ave had repeated balcony railing breakage.

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In 2014, a tenant sat on top of the railing of a 16-story balcony. A bolt connecting the rail to the wall sheared and the tenant fell. Of course, this was not a normal or expected use of the railing. According to the data in the Epidemiology of Balcony Fall-Related Injuries, only 1 in 15 falls are due to engineering or material failure. One should not draw much confidence from such a ratio since a fall from a high-rise balcony will be a fatal fall. A balcony allows occupants to be close to the building’s leading edge. People’s behavior is not always as predicted by engineering standards.

Engineers and architects should exercise the utmost prudence when designing and constructing balconies and associated railings and parapets.▪

Structural teSting issues and advances related to structural testing

D

esign professionals rely on numbers.

Some of the most important numbers represent the design loads on a structure during an event with a certain probability of occurring, and the resistance of the structure given its geometry, material properties, and connections. In a new structure, these quantities are generally known, specified, and listed on project documents. Design loads are determined by building codes and jurisdiction.

Material properties are specified by the designer and verified through testing.

However, when you are dealing with a century-old masonry building for which no design documents are available and multiple modifications have been made over its lifetime, how can critical values such as material properties be determined?

Figure 1. Laboratory flexural bond testing apparatus.

Investigation and Testing Investigation and testing of the actual structure give the designer the most accurate values on which to base their design. Methods include removing samples from the structure for testing in a laboratory, testing materials in place, and fully nondestructive techniques.

Building on the Past Determining Existing Masonry Structural Properties

By Andrew E. Geister, P.E.

Andrew E. Geister is an Engineer with Atkinson-Noland & Associates, Inc. in Boulder, Colorado. He is a member of multiple committees in The Masonry Society.

Assembly Testing

Figure 2. Field adaptation of bond wrench testing.

The Building Code Requirements for Masonry Structures TMS 402-13/ACI530-13/ASCE5-13 (TMS 402) permits testing of masonry prisms removed from structures for verifying in-place strength. Masonry prisms can be removed from the existing structure and tested in the laboratory.

However, it is critical to take special care during the removal and transportation process in order to keep the assembly intact and as similar to its in-place condition as possible.

Selection, removal, and transportation of prisms should follow the procedure of ASTM C1532, Standard Practice for Selection, Removal, and Shipment of Manufactured Masonry Units and Masonry Specimens from Existing Construction.

Samples should be representative of the structure as a whole or should represent the specific location or physical condition, such as weather exposure or degree of deterioration, for which properties are to be measured. Prism specimens are commonly removed from an existing wall using a series of cuts with a diamond blade power saw. Typically, the first cut is made along the bottom surface of the prism, and shims are inserted into the open joint to support the prism’s weight while cuts are made on the top and sides. Prisms need to be confined and secured before transporting, which can be done using straps, clamps, or through-bolted top and bottom plates.

If prisms are shipped, they need to be packed with adequate padding to protect them from damage.

The most common tests performed on masonry prisms removed from existing construction

include compressive strength per ASTM C1314 and flexural bond strength per ASTM C1072. To accurately determine the compressive strength of the prism, the ASTM C1314 standard is explicit in describing height to thickness ratios and other parameters.

Masonry flexural bond strength is tested using an apparatus known as a bond wrench (Figure 1), which clamps on and applies torque to the top unit of a prism until the bond between the unit and the rest of the prism fails.

In-Place Testing of Masonry As an alternative to removing and transporting masonry prisms to a laboratory for testing, in-place (in situ) methods exist for evaluating masonry compressive strength, stiffness, and flexural bond strength. Masonry compressive strength and stiffness are measured in place following ASTM C1197, Standard Test Method for In Situ Measurement of Masonry Deformability Properties Using the Flatjack Method. In this test, hydraulic bladders known as Flatjacks are inserted into slots cut in mortar joints above and below the section of masonry to be tested – typically five courses between Flatjacks. The Flatjacks are then pressurized to induce compressive stress on the masonry while surface strain is measured, either manually using dial gauges or electronically using linear variable differential transformers (LVDTs).

The resulting test data can be used to generate a stress-strain curve for the masonry in place. If

26 November 2017

Figure 3. Typical masonry deformability test configuration using Flatjacks and LVDTs.

Figure 4. Shear test following Method B (left), Method C (right).

compressive failure of the masonry occurs during the test, then compressive strength can be measured directly. If failure does not occur during the test, masonry compressive strength can be estimated using established correlations to the measured stiffness.

Masonry shear testing can be performed in-place by three distinct methods described in ASTM C1531, Standard Test Methods for In Situ Measurement of Masonry Mortar Joint Shear Strength Index. Method A involves using Flatjacks above and below the unit to be tested to apply a known compressive stress while measuring the force required to push the unit horizontally into an adjacent head joint previously cleared of mortar. The Flatjack-controlled compressive stress can be incrementally increased while measuring the force needed to move the unit at each increment to determine the coefficient of friction between mortar and units. Method B involves the use of a hydraulic ram to move the test unit horizontally, similar to Method A. However, instead of controlling the compressive stress on the test unit, the investigator or designer must estimate and subtract the acting overburden loads from tested values. Method C is similar to Method B, except that a specially-sized Flatjack inserted into an evacuated head joint is used to apply the lateral force. The advantage to

Method C is that the only material removal required is two mortar head joints, minimizing repairs after testing.

One method of masonry sample removal involves drilling to remove core samples.

International Existing Building Code (IEBC) – A106.3.3.2 permits tensile splitting tests conducted on 8-inch diameter cores for qualifying masonry quality, as an alternative to shear tests. Core removal may also be useful to facilitate visual observation of wall section properties and construction quality. For multiwythe grouted brick construction, the shear bond strength of a grouted collar joint between two brick wythes may be evaluated following the method of California Test 644. While this test is sometimes also applied to grouted CMU construction, variability and inaccuracy may result from the presence of cross webs and the tapered profile of face shells.

Component Materials Testing In some cases, removal of intact prisms may not be possible due to appearance, deterioration, or loss of integrity. Individual units may be removed from carefully selected locations throughout the structure and evaluated for properties like compressive strength and absorption for the purpose of selecting compatible replacement and repair materials.

Masonry units removed from the structure

may also be used to construct prisms in the laboratory to simulate original masonry for testing. Information about the original mortar is also needed to construct prisms that behave similarly to the original structure. An alternate to prism testing, the unit strength method is a means to verify the compressive strength of new masonry construction by determining the compressive strength of units and mortar type. From these two components, a conservative compressive strength for the assembly can be determined using a table that correlates assembly compressive strength with masonry unit compressive strength and mortar type.

Tabulated f'm values are based on data for modern masonry units and are not intended for use with historic masonry construction.

Mortar Analysis, Characterization (Chemical, Petrography) Determining mortar type can be useful to facilitate the unit strength method or comparison to published design values. More commonly, however, mortar analysis is performed so that repair and replacement mortar can be specified that is compatible with the original. There are a number of different analysis methods, many of which involve digesting the binder paste using acids. Further analysis methods are performed to determine binder to aggregate

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Figure 5. Masonry anchor tension test configuration.

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ratio, and chemical composition to help identify binder type.

Component Testing – Anchors The capacity of attachments to existing masonry may be verified through testing following the requirements of ASTM E488 – 96 (2003), Test Methods for Strength of Anchors in Concrete and Masonry Elements. Anchors may be tested in tension or shear, depending on their application in the structure. ASTM E488 requires that anchor strength is calculated as the average of at least five anchors.

ASTM E488 only includes failure mechanisms that involve rupture or breaking of elements. For example, failure includes anchor pullout, fracturing of the substrate, or anchor yielding. E488 does not include any limitations on the displacement of the anchor as failure criteria. However, in historic masonry structures, anchors often exhibit very large deflections/displacements before any catastrophic failure and these large displacements often govern the design of the anchors.

Anchor displacement criteria are described in Section A107 of the IEBC and the Uniform Building Code (UBC) Standard 21-7 (Test of Anchors in Unreinforced Masonry Walls) as a measure of successful anchor performance.

UBC 21-7 specifies that, when testing retrofit anchors in masonry, the test load shall be reported at a relative movement of ⅛-inch, measured between the anchor and the adjacent masonry surface.

In historic masonry structures, anchors tend to exhibit relatively large displacements without catastrophic failure. In some cases, anchors can be tested to very high loads without brittle or inelastic behavior, but the displacements become very large (at or near the capacity of the test apparatus). Therefore, it may be appropriate to apply a displacement criterion to anchors in masonry for this type of structure.

Quantity of Tests In situ masonry tests are conducted to quantify mechanical properties necessary for structural capacity analysis and design of strengthening systems. The types of tests are based on ASTM test method requirements as described above, and the number of tests is based on requirements of ASCE 41, Seismic Rehabilitation of Existing Buildings. Depending on the use and expected performance of the building, the designer may choose either a “comprehensive” or “usual” level of knowledge. Additional tests give greater confidence that results represent in-place properties.

Engineers without confidence in materials and their properties are more prone to design overly

Table 1. Tests required by Standard ASCE 41-13.

Specified Design Strength Known?

Level of Testing

Number of Tests

f'm – yes

At least two tests for each different masonry compressive strength throughout the building

f'm – no

Minimum of six total tests; at least one test on each type of structural component

Usual

Eight tests minimum per building At least two tests for each wall or line of wall elements providing lateral resistance If coefficient of variation of test values exceeds 25%, number of tests shall be doubled If mean values from in situ tests are less than listed default values, the number of tests shall be doubled

Comprehensive f'm – yes

If original construction documents are available, at least three tests on each masonry class and for each three floors or 3000 square feet (278.7 m2) of wall surface

f'm – no

If original construction documents are not available, at least six tests in each masonry class and for each three floors or 3000 square feet (278.7 m2) of wall surface

Table 2. Tests required by IEBC.

Property

Number of Tests

Bed Joint Shear Strength

• At each of the top and bottom stories: at least 2 tests per each line of shear walls • At all other stories: at least 1 test per line of shear walls • Not less than one test per 1,500 square feet (139.3 m2) of wall area • Not less than 8 tests total per building

Existing Tension Anchors

• 4 per floor or 10% of total

New Tension Anchors

• Test 5% of all new tension bolts in direct tension, plus another 20% more using a torque wrench • New through bolts (with anchor plates) – no tests needed.

conservative solutions. Tables 1 and 2 summarize the recommended testing schedules for usual and comprehensive levels of knowledge based on ASCE 41-13 and the IEBC.

Conclusion Existing masonry structures can present several challenges to structural designers due to

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unknown material properties and variable construction quality. Fortunately, standard test methods exist for in-place evaluation and sampling for laboratory testing, which is effective when performed by qualified personnel. A successful, thorough evaluation program will give structural designers the information they need to be confident in their design.▪

© 2017 ClarkDietrich Building Systems

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Hollywood Casino Jamul Tree House Sequence, HD BIM, and PBEE

H

By Gregory P. Luth, Ph.D., S.E. and John D. Osteraas, Ph.D., P.E.

ollywood Casino Jamul (HC Jamul) is a three-story entertainment facility, located in Jamul, California, with approximately 200,000 square feet of gaming, restaurants, and lounges atop an eight-story, belowgrade, 1,800-space parking garage. The casino structure’s innovative steel lateral force resisting system utilizes rocking braced frames and Krawinkler fuses integrated into Vierendeel trusses to produce a performance-based seismic design. This keeps the integrity of the perimeter cantilevered gravity system protected while the lateral system is repairable after a major seismic event.

The parking garage is a post-tensioned concrete slab system built using an unconventional construction sequence. The casino steel structure construction was prioritized ahead of the garage structure underneath it, to compress the overall construction duration and accelerate the completion of the design-intensive casino interior.

A single High Definition Building Information Model (HD BIM), developed in Tekla Structures, was used from conceptual design to construction documents, and finally to shop drawings.

Construction Sequence Structural Concept The concept was first to erect the steel casino structure, supporting it on concrete stair and elevator cores and 90-foot tall steel “stilts” that would eventually become encased in the final concrete garage columns. The final columns would be founded on conventional spread footings bearing on rock.

During construction, a temporary lateral system supported the casino and provided anchorage for tension ties that braced the columns against buckling. Casino elevators and escalators would be installed with the steel. MEP, roofing, and exterior closures would be completed and theming underway when there were still months to go on the construction of the seven 550-foot by 220-foot, below grade post-tensioned concrete slabs.

STRUCTURE magazine

Contractor Selection The sequencing was established to build the casino structure first.

Then, the eight-story parking garage would be brought up while the intensive build out of the architectural theming, finishes, and MEP systems on the inside of the casino were put in place. A set of schematic design documents based on this concept was issued in October of 2013 and used to solicit proposals from three general contractors.

The ability of the contractors to collaborate with the design team in fleshing out the details of the final design, based on cost and schedule evaluations, was paramount in the selection process.

A general contractor team composed of Rudolph Libbe, an Ohiobased contractor who had previously worked with this owner and had participated in a previous HD BIM project with the design team, and C. W. Driver, a Southern California general contractor familiar with the local sub-contractor market, both embraced the concept and brought their own ideas to the interview. They were selected to team with the Jamul Indian Tribe, Penn National Gaming, and the rest of the design team to deliver the project. The contractor estimated that the proposed sequence had potential to save seven months on the schedule.

With coordination and input from the general contractor, all temporary conditions from the start of construction to completion were included in the structural design.

Excavation and Retention System The excavation varied from 90 feet deep on one end to 30 feet deep on the other. The material consisted of weathered granite bedrock that ranged with depth from soft to very hard. A soil nail wall, designed by an independent engineering firm, provided permanent support for the excavation and was eventually tied to the permanent structure so that the two worked together. Excavation commenced in early 2014 with the anticipation that the bulkhead walls would take at least one

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Figure 1. Exterior view of the completed casino. Courtesy of Marnell Architects.

year to complete; at that time, the design of the casino was still at a schematic design level.

The project scheme envisioned that, during excavation activities, the steel structure could be designed and detailed so that steel erection would commence as soon as the foundations were in place. The plan was to use steel braced frames for the “tree-house” lateral system and encase them in concrete walls within the garage construction. The excavation proceeded faster than expected through the summer of 2014; however, the casino design evolved more slowly than anticipated. A strategic decision was made to change the temporary steel lateral system to permanent concrete walls so that there would be no lag time if the excavation was completed early.

Early Wall Construction The buttress walls were constructed to a height of approximately 90 feet using shotcrete. They were designed for wind loads in the freestanding condition, and to carry seismic and wind loads for the completed casino structure without help from the garage slabs. The walls are founded on grade beams that mobilize sufficient dead load to resist overturning in temporary conditions.

In the final building, the early walls are incorporated into the overall foundation walls, stair and elevator cores, and ramps. The ramp slabs had to be constructed early to mobilize out-of-plane frame action for wind resistance in addition to temporary guy cables. The reinforcing steel was designed to be prefabricated into cages, with details such as straight dowels that could be loosely tied in the link beam cages. This

was done so that the development length of reinforcing steel could then be slid out into the columns. This level of detail was incorporated into the HD BIM model to decrease labor and increase safety.

Tree House Columns and Framing The main casino floor and the office area above were framed with 30-foot by 60-foot bays using W27x84 and W30x99 beams on 10-foot centers spanning to W30x116 girders. 16-inch square box columns were used for the temporary condition to fit within the planned 28- by 28-foot module concrete columns supporting the eight-story parking structure. These box columns would support the full weight of the Casino structure 90 feet in the air. After much discussion, it was decided to design the columns for the full dead load of the superstructure plus a 20 pound per square foot construction live load over all floor and roof areas. The columns were designed with a fixed base condition and a single level of bracing at the 7th garage floor, approximately 60 feet above the foundation.

Each column was braced by HSS6X4 tension ties at approximately 90 degrees and placed flatwise at the center of the 10-inch thick posttensioned slab. The tension ties were supported at mid-span by sag rods to the floor framing (Figures 5, 6 and 7, pages 32 and 33). The connections at the columns allowed the HSS members to be offset by one-inch vertically from each other to accommodate the slab reinforcing and post-tensioning strands in orthogonal directions so the HSS tension ties would not need to be removed. (After all this planning and design, the contractor decided that it was less effort to cut the tension ties after the slab at the 6th floor was tensioned.)

Figure 2. HD BIM model of 90-foot tall early walls.

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Figure 3. Prefabricated rebar cages and shotcrete forms for early walls.

Figure 4. View of the site during early wall construction.

The tension ties were supported on either side of the building by 10-foot-wide shop fabricated frames that spanned from the foundation to the first casino diaphragm 90 feet above. These were designed in accordance with AISC stability requirements for stiffness under theoretical loads. The diaphragm was supported for all lateral loads by the primary lateral system formed by the early walls.

All elements of the temporary system were part of the structural design, coordinated with the contractor, and included in the HD BIM.

are used to tune the pushover curve. Krawinkler fuses are steel plates with diamond-shaped cutouts that provide substantial shear strength, a predictable yield force that mobilizes both shear and flexural yield, stable hysteresis loops, and disproportionate displacement capacity.

The system configuration utilizes rather narrow braced frames that have a true pinned connection on one leg, allowing the entire frame to rotate about the base. The rotation is prevented by coupling the frame to the Vierendeel truss system at the office level above the casino.

The shear that can be carried by the Vierendeel trusses is limited by the use of fuses at the mid-height of the members. A vertical BRB is used in place of the 2nd column in the braced frame. The forces in the system are limited by the capacities of the BRB column and the Krawinkler fuses.

Performance-Based Earthquake Engineering The project is in an area of moderate seismicity, with SDS = 0.63, SD1 = 0.22, and classified as site Class B. An importance factor of 1.25 was used, with R equal to 6.0 and a Seismic Design Category D. The calculated base shear was 3,068 kips.

One of the greatest design challenges was solving the soft-weak story discontinuity created by the open 25-foot-tall casino level. The design allowed for limited areas for seismic bracing around the perimeter, as opposed to under the 15-foot-tall office level which could be braced extensively.

The lateral system evolved into a robust and elegant performancebased design utilizing a top-down arrangement of in-line yielding Vierendeel trusses and rotating (as opposed to rocking or racking) buckling restrained braced (BRB) frames, with true pinned bases, in parallel. The Vierendeel trusses pull the overturning moment to the top of the frame which, in turn, enforces a uniform first mode response. Krawinkler fuses at mid-height of the Vierendeel verticals

Figure 5. View of the site with early walls, stilt columns, and tension ties.

STRUCTURE magazine

Structural Analysis and Detailing State-of-the-art pushover analyses were used to assure that the structure can reach 150% of the displacement demand in the maximum considered earthquake without any calculated inelastic demand in the primary structure. The energy demands of the earthquake are absorbed in the designated fuses – the butterfly plates and the BRB columns and braces.

Target displacements in a Maximum Considered Earthquake (MCE) are determined by performing nonlinear analyses on a single-degreeof-freedom system that has the height, frequency, and backbone push-over curve of the subject building through a suite of time histories scaled to the seismicity at the site. Target displacement for

Figure 6. Tension tie connection.

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A Strong Team

Figure 7. Section through HD BIM with key elements.

the Jamul structure was about 3.5 inches. Analysis showed all frames in the Jamul structure can accommodate significantly higher drifts than the target displacement at MCE, without inelastic action in the non-fuse framing.

The special connections associated with this system are the collector connections that jump the columns at the top and bottom of the Vierendeel trusses. These are required to isolate the gravity columns from the inelastic deformations of the butterfly fuses that result in an offset between the top and bottom Vierendeel chords.

Once a structure with an acceptable nonlinear performance was developed, it was analyzed in ETABS using a response spectra approach and checked for code compliance. The structure is designed to conform with all code provisions up to code level forces, after which the designated fuses yield.

The Hollywood Casino Jamul facility celebrated a soft opening on July 30, 2016, and a grand opening in October 2016. That represents a short three years from concept release and RFP for contractors to completion, a feat accomplished by early contractor involvement, an unusual but effective construction sequence, and the use of HD BIM. Collaborative teamwork and problemsolving characterized the project team without which the project could not have succeeded.

• GPLA – SEOR and structural team leader responsible for HD BIM modeling in Tekla, lateral concept development with Exponent, gravity design, design of post-tensioned slabs, temporary garage support system, rebar detailing, and stair detailing.

• Exponent – Responsible for collaboration on concept development, seismic pushover analysis in MASTAN, global lateral analysis in ETABS, and peer review of design execution.

• Detailing Group – Responsible for producing steel shop drawings from cloud-based Tekla model.▪

HD BIM The objective of the structural design process within the High Definition Building Information Modeling process is to deliver a complete design that incorporates all fabrication and erection constructability considerations in a single Tekla model. The HD model is shared in the cloud with all project participants and used to produce shop drawings. This step eliminates the traditional Remodeling/RFI/ Shop Drawing (RRSD) process that is the source of so much paperwork and so many delays in a typical construction project.

The HC Jamul HD BIM includes structural steel, cast-in-place concrete, reinforcing steel, precast concrete, masonry, stairs, and metal deck.

The construction documents, structural steel detailing, rebar detailing, and stair/miscellaneous steel detailing were all completed in the same cloud-based model. Approximately 4,200 tons of structural steel (6700+ drawings), 2,300 tons of rebar (400+ drawings), and 18 stairs (400+ drawings) were detailed in the Tekla model. Tekla technologies enabled the complete and continuous involvement of the SEOR, improving the construction efficiency, economy, and quality of the project. Many International Foundation Class (IFC) reference models were used for project coordination between different design disciplines and subcontractor trades, reducing costly coordination errors.

The model included stairs and all temporary structures and bracing required for the non-standard construction sequence. The complete STRUCTURE magazine

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Gregory P. Luth, Ph.D., S.E., is President and founder of Gregory P. Luth & Associates, Inc. Santa Clara, CA. John D. Osteraas, Ph.D., P.E., is Group Vice President and Principal Engineer, Civil Engineering, Exponent Failure Analysis Associates, Menlo Park, CA.

Project Team Owner: Jamul Indian Tribe Structural Engineer of Record, Steel and Rebar Detailers: Gregory P. Luth & Associates Development and Operations Manager: Penn National Gaming Design Architect and Architect of Record: Marnell Architects Peer Review and Structural Analysis, Casino Structure: Exponent Shop Drawing Production from Cloud-Based Model: Detailing Group SEOR Permanent Soil Nail Retention System and Three Site Bridges: Pirooz Barar & Associates General Contractor: CW Driver Structural Steel Fabricator: Rossin Steel Structural Steel Erector: Asbury Steel Concrete Sub: J T Wimsatt Rebar Fabricator and Placer: CMC Tekla Structures: HD BIM Software

November 2017

POLY INTERNATIONAL PLAZA,BEIJING Evolution of an Icon

By Mark Sarkisian, P.E., S.E., LEED AP BD+C, Neville Mathias, P.E., S.E., LEED AP, and Rupa Garai, P.E., S.E., LEED AP BD+C

Overview A chance to design an “iconic” building is not something one encounters every day. However, that is exactly what the designers at Skidmore, Owings and Merrill LLP (SOM) in their San Francisco office got when they were challenged to come up with a design for the Poly International Plaza project in Beijing, China. It was a project that would further burnish the already stellar image of the client, the China Poly Group, renowned for its superior quality real estate holdings. The project was to consist of three office towers totaling approximately 1.25 million square feet, one 530 feet tall – the “icon” – and two others, more conventional, about half as tall (Figure 1).

The project site, prominently located beside a curved expressway in Dawangjing, a new and fast-growing business district about halfway between the center of Beijing and the international airport, provided the first of many ingredients for a unique design. Shaped by their location, the curved boundaries of the site gave rise to the curved, relatively non-directional forms of the buildings. The structure and façade of the iconic tower, the focus of this article, were further inspired by origami Chinese paper lanterns, symbols of welcome traditionally hung over doorways and believed to attract good luck. The curved, faceted exterior form of the tower, with staggered nodes at every alternate level set on a four-story module and spaced approximately 60 feet apart horizontally, naturally suggested a “diagrid” exoskeleton structure, one capable of resisting lateral as well as gravity loads.

Beijing is located in a region of relatively high seismicity (similar to Oregon and much of Washington), and the diagrid exoskeleton frame was combined with a central reinforced concrete core to yield a dual system that effectively and efficiently resisted gravity and lateral loads. Constructed using concrete filled steel tubes (CFT) for most of its height, the diagrid frame made it possible, by virtue of the continuous helical load paths it afforded (Figure 2), to transmit loads around corners and permit the creation of grand atriums. Unfilled steel tubes were used at the upper levels where concrete fill was not required. The atriums – approximately 410 feet tall and located at the tower ends – let light into the building interior and provided views to the surrounding areas. They also allowed for the introduction of structurally and visually exciting elements within them, like elevators, conference rooms, and spiral stairs (Figure 3).

Figure 1. Poly International Plaza.

STRUCTURE magazine

Structural steel floor framing, spanning approximately 36 feet programs (CSI’s SAP-2000) during the basic design phase. Nonbetween the core and external diagrid frame without interior columns, linear analysis programs (CSI’s PERFORM-3D) were used during and composite metal deck slabs constitute the floor framing system of the performance verification phase, discussed later in this article. A the tower. To avoid imposing significant gravity loads on the diagrid major concern of the project’s structural reviewers in China was the members between nodal levels, and to minimize bending moments in-plane adequacy of the diaphragms bounding the atriums, and the in them, intermediate floor levels were pulled back from the façade impact of cracking of these diaphragm slabs in a major earthquake on and hung from the nodal levels immediately above (Figure 4, page 36). the buckling stability of the diagrid structure. To address this concern, The three buildings on the site share a common three-story reinforced in-plane trusses were created in the diaphragms at these locations, concrete conventionally framed basedesigned to provide equivalence to the ment, and the iconic tower rests on a slab diaphragm strength in case they pile-supported mat foundation. were rendered ineffective.

Designers took advantage of the Diagrid structures tend to bulge in tower’s exterior diagrid system and plan as the diagonal modules comresulting facets, as well as of its press under gravity load, creating pulled-back and hung intermedicircumferential and radial forces in ate floor levels, to develop a double the perimeter and radial floor framing skinned, glazed exterior wall system members, respectively, at nodal levels with automated operable vents at the and corresponding stresses in the diahorizontal creases. This arrangement phragm slabs. This bulging tends to created buffer zones in the spaces reach its maximum value at about between the double exterior walls one-third of the structure’s height and that act to modulate the extremes to decrease at lower levels because of of Beijing’s climate and the buildthe restraint to spread of the strucing’s interior environment, reducing Figure 2. Lateral load paths. a) Diagrid frame (left); ture provided by the ground level the thermal loads on the building’s b) Typical frame (right). and sub-structure slabs. To ensure mechanical systems and saving energy. reliable structural performance, the This expedient served to boost the axial forces in the perimeter and radial tower’s sustainability performance, structural members were determined contributing to its goal of a LEED® neglecting the contribution of the Gold rating. diaphragm slabs, but the diaphragm slabs were nevertheless reinforced to withstand induced stresses and Unique Structural minimize cracking. At levels where the diaphragm stresses were the Challenges highest, delayed concrete-placement The unique form and structural zones were introduced to control slab system of the Poly tower called for cracking. structural design checks and detailing not typically encountered in tall building design. The first challenge Structural was the modularization of the diagrid Verification nodes. The perimeter floor framing connecting the nodes, and the radial The structural verification process in framing connecting the nodes to the China requires buildings with noncore, typically had the same spans over prescriptive structural systems, such as the building height making it possithe Poly tower, to undergo a rigorous ble to standardize the depths of these review by a panel of highly respected members and their intersections with seismic experts selected by the governthe diagrid diagonals. Horizontal and ment from academia and industry. vertical continuity plates, with holes to The experts not only evaluate the facilitate concreting of the CFT mem- Figure 3. Section showing atrium. conformance of such code-exceeding bers, were introduced within the node structures with the basic design and intersections to simplify and standardize their fabrication and erection performance requirements of the codes but also set enhanced per(Figure 5, page 36). Segments of the diagrid, each consisting of a node formance requirements for key components of such structures. The and diagonal arms, were fabricated in the shop, spliced with welds to process considers three levels of seismic hazard: frequent (50-year previously erected segments in the field, and then filled with concrete. return, peak ground acceleration [PGA] 0.07g), moderate (475-year One of the most significant differences between a conventional return, PGA 0.20g) and rare (2500-year return, PGA 0.40g) earthexterior frame and a diagrid frame is that the helical load paths in quake events. Along with various special analysis and design checks, a diagrid structure make it unnecessary for the floor diaphragms to non-linear time history analysis is required to verify conformance with extend all the way to the frame at the ends of the plan (Figure 2). Local the enhanced performance goals set by the seismic expert panel. In and global buckling studies of the diagrid structure, verifying frame the case of the Poly tower, this included no local or global buckling stability in the atrium areas, were performed using elastic analysis of diagrid members in the rare earthquake events, ensuring that nodes STRUCTURE magazine

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November 2017

Figure 5. Typical diagrid node.

with concrete, failure would occur due to buckling of the steel plate walls within the nodes. The wall thicknesses were set to avoid buckling of steel plates within the nodes in the accidental condition where concrete did not completely fill the nodes. This was generally found to not exceed two times the wall thickness of the diagrid members outside the nodes. = Hanger = Hanger = Hanger

Figure 4. Intermediate floor support.

= Fail-Safe Stub Column

Conclusion

= Fail-Safe Stub Column = Fail-Safe Stub Column

would not fail before the diagrid members, and ensuring gradual lateral strength loss of the structure progressing to eventual failure.

Progressive collapse studies were required to ensure that, in the event of the catastrophic loss of a critically loaded diagrid member, enough redundancy and alternative load paths could be activated to ensure life safety. As a fail-safe precaution in the event of a hanger failure, stub columns were provided below the hangers with socketed slip connections at their bases. These are intended to engage and to transmit load to the framing of the level below if a hanger fails.

To verify the procedures used for the design of the diagrid nodes, finite element analysis and scaled pseudo-static gravity plus lateral load testing of nodes with and without concrete fill was performed.

Testing showed, as predicted by analysis, if the nodes were not filled

SOM was given a unique opportunity to design an iconic building at a prominent location in the new and fast-growing Dawangjing business district in Beijing. Opportunities presented by the site and cultural inspirations gave rise to a building which evolved to integrate form, function, structure, building systems, and sustainable design synergistically to create what is hoped is a memorable design.▪ Neville Mathias, P.E., S.E., LEED AP, is the Associate Director at Skidmore, Owings & Merrill LLP in San Francisco, CA. Mark Sarkisian, P.E., S.E., LEED AP BC+D, is a Partner at Skidmore, Owings & Merrill LLP in San Francisco, CA. Rupa Garai, P.E. S.E., LEED AP BC+D, is an Associate Director at Skidmore, Owings & Merrill LLP in San Francisco, CA.

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Preserving

Navy History with Design-Build

By Mark Hirschi, S.E. and Frank K. Humay, Ph.D., S.E. Figure 1. Pearl Harbor under attack on December 7, 1941, taken by a Japanese plane.

L

ocated on Ford Island at Joint Base Pearl Harbor-Hickam in Hawaii, Building 26A was constructed in 1935 for an aviation storehouse and an airplane hangar for the Navy’s Fleet Air Base. The facility survived the December 7, 1941, surprise attack on Pearl Harbor (Figures 1 and 2) and in the 75 years since has undergone several changes in use. In 2014, the Navy elected to convert Building 26A into a new training facility for the Center for Security Forces (CENSECFOR). This conversion included repairing exterior deterioration and upgrading the structure to meet current seismic, hurricane, and antiterrorism criteria. A design-build team led

by Hensel Phelps was awarded the $15.1 million contract to update the historic building.

Building 26A consists of 30,000 square feet of open, doubleheight space and 15,000 square feet of adjacent two-story office and support space. The primary structural system in the open bay consists of long-span steel trusses supporting steel purlins and tongue and groove plywood sheathing. The trusses are supported at each end by steel columns encased in concrete. A three-inch-thick ultra-lightweight concrete ceiling with embedded support steel is suspended from the steel purlins, primarily for fire protection. In the office area, the structure consists of concrete-encased steel beams and columns supporting cast-in-place floor and roof slabs. The building is enclosed by ungrouted masonry walls and the foundations consist of shallow spread footings.

The renovation presented several unique structural challenges, including: • Analyzing and strengthening the antiquated unreinforced and ungrouted exterior masonry walls for resistance to current wind, seismic, and blast loads.

• Ensuring structural modifications would preserve the building’s distinctive historical design features.

• Determining existing conditions and documenting modifications made during numerous renovations over the previous 75 years.

• Addressing prevalent structural deterioration, such as corroded steel members, rotted plywood roofing, and cracked masonry and concrete.

These challenges were optimally addressed through the designbuild approach.

Seismic Upgrades The overall design was performed in accordance with the 2012 International Building Code (IBC) as modified by the Navy’s Uniform Facilities Criteria (UFC). Seismic evaluation and subsequent upgrades were designed using ASCE 41-13, Seismic Evaluation and Retrofit of Existing Buildings, for a BSE-1E seismic hazard level with mapped spectral accelerations of SXS = 0.30g and SX1 = 0.13g and a performance level of life safety. Building 26A was assigned to a high level

Figure 2. Building 26A original interior (left) and current interior (right).

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Figure 4. Steel wall bracing.

of stucco to match the remaining historic finish. Preliminary field assessments indicated the existing stucco was in good condition, meaning limited exterior finish work was needed if the stucco was not removed. Tests by the Contractor also found the existing stucco extremely difficult to remove, which increased estimated demolition costs and lengthened the schedule. Furthermore, matching new stucco with the existing historic stucco was a prime concern.

Because of these challenges, the design-build team developed an alternative structural steel bracing system that supports the walls only from the inside of the building (Figure 4). The bracing consists of steel HSS members spanning from floor slab to lightweight concrete ceiling and from ceiling to roof deck. The braces are attached to the masonry walls with steel angles welded to the HSS sections and a combination of tube screen and sleeve anchors connected to the ungrouted masonry walls. Either a wedge of solidified epoxy or an expanded metal sleeve bearing against the interior face shell of the masonry block provide anchor pullout capacity. The design-build team developed a field testing program to confirm the installed anchor’s pullout strength to alleviate any concerns about achieving adequate anchor capacity within the old masonry. This field testing program involved pull-testing anchors to a proof load of approximately twice the maximum capacity needed and holding the proof load for at least two minutes. Seven anchors were tested before construction began, and roughly one out of every 75 anchors were tested during construction.

Figure 3. Bracing and deck connection detail.

of seismicity under ASCE 41-13, akin to a seismic design category of D for new construction.

One significant deficiency uncovered was the lack of a competent structural diaphragm at the roof. Neither existing horizontal rod bracing nor tongue and groove sheathing were found to have adequate strength and detailing for the diaphragm demands. In addition to not having sufficient shear capacity, the existing tongue and groove sheathing was in poor condition. Since the project also required removal and replacement of all roofing materials and insulation, the design-build team decided to replace the wood sheathing with metal roof deck. This substitution not only addressed structural concerns but served as a long-term betterment included within the project budget. Transfer of shear forces to the exterior masonry walls was accomplished using continuous steel angles, which also acted as chord reinforcement (Figure 3). Due to the significant length of the walls, the ungrouted and unreinforced masonry was found to be compliant for in-plane seismic forces.

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Although the exterior masonry walls were found adequate to resist in-plane shear forces, strengthening for resistance to outof-plane forces was required. In addition to seismic forces, wind pressures based on a risk category II with a wind speed of 130 miles per hour were considered.

Previous conceptual planning studies recommended the use of fiber-reinforced polymer (FRP) strips to increase the capacity of all exterior walls. On the surface, this option appeared as the most efficient design solution. However, when considering constructability, existing conditions, and historical preservation, this option presented several major hurdles.

To resist forces in both directions, FRP is required on both the interior and exterior wall faces. Application of FRP on the exterior surface involved several steps, including removal of existing stucco, preparation of the masonry surface, application of FRP, and then reapplication

Figure 5. Extensive repair with FRP strips.

This strengthening option, however, was not without its design challenges. Due to various renovations over the years, as-built drawings did not match actual field conditions. The Contractor performed a 3-D laser scan of the entire building and shared it with the design team to coordinate bracing locations and connections with existing obstructions. Particular attention to the connection detail at the roof was necessary to ensure unintended gravity loads are not imparted to the HSS sections. FRP was still utilized in limited locations not conducive to steel bracing. These locations included roof parapets and walls adjacent to the sliding hangar doors.

Despite the challenges, implementation of this bracing scheme proved a success. With the walls braced from the inside, the originally proposed FRP was largely eliminated and the historic exterior stucco was predominately retained. This reduction in construction effort saved over one million dollars, allowed the contractor to comfortably finish construction a month ahead of schedule, and greatly minimized impacts to the existing historic façade.

Blast Hardening The exterior façade of the building (including masonry walls and hangar doors) was also analyzed for resistance to blast pressures in accordance with UFC 4-010-01, DoD Minimum Antiterrorism Standards for Buildings. As this historic building does not meet the Military’s current conventional construction parameters, dynamic blast analyses were performed on the ungrouted masonry using the United States Army Corps of Engineers’ Single-degree-of-freedom Blast Effects Design Spreadsheet (SBEDS). It was found that no additional strengthening of the masonry walls was required to meet the specified threat scenario.

Project Team Owner: NAVFAC Pacific Structural Engineer of Record: Baldridge & Associates Structural Engineering, Inc. (BASE) Special Inspector of Record: BASE CM/GC: Hensel Phelps Architect of Record: Matsunaga & Associates, Inc. Historical Architect: Mason Architects, Inc. Structural Steel Erector: IG Steel Hangar Door Subcontractor: GPS Specialty Doors STRUCTURE magazine

In addition to the walls, three large, sliding hangar doors were analyzed and subsequently strengthened for blast loading. The doors were retrofitted with heavy steel plates to withstand blast overpressures and a tethering system to keep the doors from falling into the building if they were to shift off their rail supports during a catastrophic event.

During the design of this tethering system, careful attention was paid to avoid adding considerable additional stress to the existing lightweight concrete ceiling. The contractor’s 3-D scanning and site surveys were invaluable tools in coordinating the load path for the tethering system.

Structural Repair Deterioration of the existing structure also posed challenges at Building 26A. For example, several large cracks with significant displacement and slip were identified in the exterior masonry walls adjacent to one of the large hangar doors. To address this condition, the masonry cells adjacent to the crack were filled with expanding foam so that the masonry cells at the crack could be grouted without grout filling the entire wall. This ensured that the building’s seismic mass was not appreciably impacted. Also, FRP strips were added across the large cracks to provide continuity for transfer of forces from one side of the crack to the other (Figure 5).

Significant deterioration in the existing roof and corrosion of several steel members uncovered during demolition also posed considerable challenges. However, since the designers and builders were on the same team, these unforeseen conditions were quickly identified and efficiently addressed with sound, constructible solutions such as incorporating reinforcing plates or providing additional connection hardware that had minimal impact on the project budget and schedule.

The successful upgrade to Building 26A highlights the beneficial aspects of the design-build process, particularly when dealing with historic renovations. This collaborative approach between designers, constructors, and end users fostered creative solutions that resolved many difficult challenges and reduced overall risk in a holistic manner. Even with encountering numerous unforeseen conditions, Building 26A was renovated under budget and ahead of schedule.▪ Mark Hirschi, S.E., is an Associate at BASE and is based in its Chicago office. He can be reached at mhirschi@baseengr.com.

Frank K. Humay, Ph.D., S.E., is Vice President at BASE and is based in its Honolulu office. He can be contacted at fkh@baseengr.com.

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November 2017

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Structural

SuStainability sustainability and preservation as they pertain to structural engineering

A

modern challenge of the engineering profession is to account for the unintended consequences and life cycle costs from impacts of infrastructure on the environment, society, and economy. While this challenge has been realized on a global scale for more than half a century, tools for design professionals in the United States to systematically address this challenge were not developed until the formation of the Leadership in Energy and Environmental Design (LEED) by the United States Green Building Council. LEED, while bringing the building industry forward, did not directly address sustainability of nonbuilding civil infrastructure. However, Envision, developed by the Institute for Sustainable Infrastructure (ISI), did.

Envision acts as an overlay to the planning and design process. Used early in the initial planning phase, it provides insight on stakeholder engagement, optimizing project benefits, and setting up performance goals to maximize the sustainability of the project. In later project phases, it is used as a reminder to follow through on sustainable performance goals within the specifications.

This article discusses Envision’s role in the structural engineering profession and how it is used as a complementary project management tool.

Envision – The Future of Sustainable Infrastructure

By Evan Sheesley, S.E., ENV SP, LEED Green Associate and Amanda Schweickert, P.E., ENV SP, LEED AP BD+C

Envision as an Industry Standard Evan Sheesley is a Project Engineer at BergerABAM focusing on water-front structures and championing sustainable seaport infrastructure in the Pacific Northwest. He can be reached at evan.sheesley@abam.com.

Amanda Schweickert is a Project Engineer at BergerABAM specializing in transit structures, bridges, and sustainability.

She can be reached at amanda. schweickert@abam.com.

Envision is an internationally recognized sustainability rating tool developed by the ISI and the Zofnass Program for Sustainable Infrastructure at the Harvard University Graduate School of Design. ISI was founded by three professional organizations, the American Council of Engineering Companies, American Public Works Association, and American Society of Civil Engineers.

After collaborating with agencies, municipalities, universities, consultants, and other existing rating systems, like the United States Green Building Council, the first version of Envision was introduced in July 2011. Later that year, ISI and the Zofnass Program combined their systems to introduce the second version of Envision in February 2012. Envision was originally developed for use in the United States and Canada but has been applied worldwide. In 2012, the Envision Sustainability Professionals (ENV SPs) credential was developed to show proficiency in using the system. Also in 2012, project teams could register for third-party verification to receive Envision certification. Currently, over 4,500 professionals in Africa, Asia, Australia, Europe, North America, and South America have attained their ENV SPs. Although the Envision guidance manual and online rating tools are available at no cost, project teams are taking the next step to verify that their sustainable project performance goals are meeting the sustainability criteria of Envision.

Having projects vetted through a third-party verification process helps demonstrate the sustainability commitments made by the project team while addressing the concerns of their communities. Using this transparent sustainability rating tool has been a great way to communicate and highlight the sustainable infrastructure being implemented.

The majority of projects that have been verified under Envision have been transportation or water focused. As of October, 40 projects have been verified which has contributed to 9.9 billion dollars of sustainable infrastructure.

Envision’s Purpose As suggested by the ISI, the purpose of Envision is to “to foster a dramatic and necessary improvement in the performance and resiliency of our physical infrastructure across the full spectrum of sustainability.” Specifically, it is a guidance tool

Evan and Amanda have been involved with the Institute for Sustainable Infrastructure as third party verifiers, ISI trainers, and members of the Accreditation and Technical committees.

Companies, agencies, and individuals are showing their commitment to sustainable infrastructure by applying Envision in their communities and becoming members of ISI.

42 November 2017

to maximize sustainable performance (i.e., a triple-bottom-line approach).

Using Envision

Envision can be used for all types of infrastructure, but has been implemented the most in water or transportation related projects.

for our industry to make informed decisions and provides sustainability metrics that can be applied to all types of infrastructure. The tools and guidelines are available through the ISI’s website, www.sustainableinfrastructure.org.

The Envision guidance manual has 60 sustainability criteria that are used to evaluate project development. The criteria are organized into five categories: • Quality of Life (QL) – Addresses the quality of life of the surrounding communities, looking at the individual and community as a whole.

• Leadership (LD) – Ensures that leadership and people are in place to plan, develop, and monitor the project.

• Resource Allocation (RA) – Reduces the amount of materials, energy, and water needed for a project, while also looking at the quality and source of these resources.

• Natural World (NW) – Looks at how the project integrates and affects the surrounding natural environment’s land, water, and biodiversity.

• Climate and Risk (CR) – Plans and prepares for climate change resilience and emissions reduction.

An important aspect of Envision is that their credits are interdependent. This allows the project team to maximize project benefits and evaluate competing ideas on how to achieve those goals. It also forces the issues of a holistic approach to maximize sustainability. For example, a project team may want a high level of achievement on credit RA1.3 – Use Recycled Materials and choose a building material with a high-recycled content. However, that same material may not be very durable and may require frequent maintenance or replacement. This would impact the level of achievement from RA1.1 – Reduce Net Embodied Energy and LD3.3 – Extend Useful Life. The performance of a project evaluated using Envision does not hinge on one action or criteria; rather its goal is to consider the balance of all criteria

Envision is meant to be used early in the planning and scoping phases of a project and helps identify goals. While it covers the entire design phase, the biggest impact on a project is solidified at the beginning. For example, it is useful in making the decision on whether a bridge, a tunnel, or a ferry system is the best project for a particular water crossing. Several Envision credits will be impacted depending on the project selected; however, a credit that would achieve the same score is LD1.4 – Provide for Stakeholder Involvement. The best water crossing will require stakeholder engagement. Early in the project is the most appropriate time to identify key stakeholders and implement an engagement plan. Also, it is the most opportune time to determine how the project’s impact on the climate will be accounted for and mitigated.

Envision helps identify and communicate these issues to all project team members. Engineers need to be involved in these early project phases to help evaluate alternatives and potential risks.

Envision provides project managers with tools, like the online checklist and the guidance manual, that can be used to help scope projects, provide items for discussion, and highlight areas of improvement and success in each project. Using the online checklist, project managers will go through 55 questions in the five categories, asking whether the project is meeting specific sustainability metrics.

The Envision checklist is used at the beginning of a project to help identify project goals and scope. The series of questions in the checklist are tied to the Envision criteria to be used as references in later project phases.

The questions are “yes or no” and relatively easy to understand. The checklist does not provide a rating.

The next step in the process is to turn the goals and scope identified by the checklist into criteria and actions. At this stage, the

Envision guidance manual can be used to identify the degree to which each project goal is achieved. Various project alternatives can also be evaluated.

It is never too late to use Envision during the design of a project. Although goals have been set and many decisions have been made – such as the type of project, location, and an environmental impact study (EIS) has been conducted – there are still opportunities to improve sustainability. When a structural design team is working on the final design, they can still review the project for items that were missed in the EIS and suggest alternatives to the client that improve sustainability without impacting the project’s budget or schedule. This is highlighted through the development of specifications.

The Unified Facilities Guide Specifications (UFGS), used on military construction projects, have incorporated sustainability provisions that are customized by the engineer. Specification 03 30 00 for Castin-Place concrete, for instance, includes many conditions that can have an impact on the material’s embodied energy. To maximize the level of achievement in credit RA1.1 – Reduce Embodied Energy and RA 1.3 – Use Recycled Materials, replace energy intensive cement with high fly ash or blast furnace slag content. However, to utilize a high fly ash or slag content, the engineer should specify a 56- or 90-day concrete strength, due to the slower strength gain of those materials. Additionally, the recycled content of the formwork and other construction materials could be specified to reduce the energy intensity.

A simple but effective action is including Envision in the basis of design (BOD) along with specific credits and measures taken by the project team. Including Envision with sustainability goals in the BOD opens communication between team members which increases opportunities to increase sustainable performance. By being proactive, Envision criteria can be used to communicate benefits

Envision’s guidance manual and online tools are free to use. However, 93 projects have decided to verify.

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and discuss changes to the project. While the impact may be small on the current project, the client and other project team members have been introduced to Envision and may then implement it earlier on future infrastructure projects.

Envision is useful as a tool to remind the engineer of sustainable actions that are not currently part of their normal routine, such as the items described in credit CR 2.1 – Assess Climate Threat for instance. Many structural engineers working on coastal projects are familiar with the concept of rising sea-levels; what is not well understood, though, is how to quantify the amount of sea-level rise. The United States Army Corp of Engineers has developed sea-level rise predictions based a climate models and various climate forcing events (www.corpsclimate.us). A good exercise for all coastal projects is to use the models to perform a boundary analysis for impacts to the project from a low to high probability of sea-level rise over the life of the project.

While designing the project to accommodate the maximum level of predicted sea-level rise may be impractical, it gives the client an idea of the potential impacts and an opportunity to build-in a level of adaptability.

As structural engineers, we are familiar with factors of safety as a part of our design calculations because of the uncertainty in operational and nonstationary environmental loading over time. Sensitivity analyses are often conducted to determine a structure’s response to varying soil conditions, boundary conditions, load configurations, and the like. The ability to sustain loading that develops over an extended period of time, such as from sea-level rise, storm surge, and storm intensity, as well as durability from short term loadings, such as earthquakes and tsunamis, are all considered in Envision. Both could have significant impacts to the project and the system of which it is a part.

The Bottom Line Structural engineers play a vital role in delivering safe, reliable, durable, and adaptable infrastructure for society. While doing so, we need to take a holistic approach that looks at more than just our role, but rather how our decisions affect other project elements, affect the existing infrastructure system, and how the project, within in the infrastructure system, will affect the community when it is complete. Sustainability is not easy to quantify but, with tools like Envision, we can better identify, communicate, and implement sustainable project goals.

Ohio River Bridges – East End Crossing (ORB EEC): The tall, elegant, diamond-shaped towers were limited to 300 feet in height to reduce visual impact on the historical setting. The design also evokes the region’s historic lime kilns. Both of these aspects of the design contributed to achieving Envision QL Credit: Preserve Views and Local Character. Photo courtesy of Parsons.

Use of Envision for the Ohio River Bridges – East End Crossing (ORB EEC) During project planning of a major P3 transportation project, the ORB EEC Technical Manager, Parsons’ Steven Nicaise, P.E., Louisville, KY, led the team that developed the sustainability goals, objectives, and performance measures with client stakeholders such as Indiana DOT (INDOT) and the owner, the Indiana Finance Authority (IFA). This led to the requirement for a Sustainability Management Plan in the Technical Provisions.

Resilience and durability were included in the contractual requirements through the Accident and Terrorist Vulnerability Assessment and multiple Corrosion Protection Plans and Durability Plans.

Therefore, the project’s overall technical and sustainability requirements were well-aligned with Envision credit guidelines.

The following credits were influenced by structural engineering, with the most significant impacts in the Quality of Life (QL), Leadership (LD), and Climate and Risk (CR) categories: QL 2.1 Enhance Public Health and Safety QL 2.2 Minimize Noise and Vibration QL 3.2 Preserve Views and Local Character QL 3.3 Enhance Public Space LD 1.3 Foster Collaboration and Teamwork LD 2.1 Pursue By-Product Synergy Opportunities LD 3.1 Plan Long-Term Monitoring and Maintenance LD 3.3 Extend Useful Life RA 1.4 Use Regional Materials CR 2.2 Avoid Traps and Vulnerabilities

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CR 2.3 Prepare for Long Term Adaptability CR 2.4 Prepare for Short-Term Hazards CR 2.5 Manage Heat Island Effects Corrosion Protection Plans (LD 3.1, LD 3.3, CR 2.2, CR 2.3): This plan addressed detailed material selection – such as the use of weathering steel for the superstructure, performance-based concrete mix designs based on exposures, and maintenance needs for components to extend useful service life.

Structural Health Monitoring System (LD 3.1, LD 3.3, and CR 2.3): A risk assessment was performed and a corresponding system selected to evaluate weather conditions and structural forces and movements along the structure.

Accident and Terrorist Vulnerability Assessment (CR 2.4): A risk assessment was performed to determine the magnitude of risk and the protective measures available to mitigate risks.

Through these and other measures, a Platinum award was achieved for the ORB EEC project.

Envision adds benefit to the infrastructure we build for society, and a knowledgeable, multidisciplinary team is essential to optimize a project’s sustainability performance. Structural engineers contribute by considering procurement distances, material embodied energy, recycled content, protection strategies, improved durability, adaptability and resilience, end-of-life disassembly and disposal, and other factors that influence the life cycle environmental performance of the structure. Familiarity with Envision credits can inform early design configuration, material choice, and structural detailing decisions. In this way, structural engineers can contribute to the ability of our infrastructure to withstand potential future risks and vulnerabilities associated with climate change.▪

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Historic structures significant structures of the past

M

asonry arch bridges date from 1,300 BC, but it was the Romans who developed the form for bridges, aqueducts, and buildings. Many of them, like the Pont du Gard Aqueduct, circa 50 AD, still stand after almost two millennia. Cast iron arch bridges were built in England starting in 1779 with the Coalbrookdale Bridge across the Severn River, which still stands. Later, Thomas Telford built many cast iron arch bridges. His first was the Buildwas Bridge just upstream from the Coalbrookdale Bridge. Many of his bridges are still in service. The French built several Old view of the bridge, with Brownsville on the right from Sherman Day’s Historical Collections of the State of Pennsylvania. iron bridges across the Seine, most notably a pedestrian bridge, the Pont des Arts, in 1804. The Delafield first argued that a bridge at the Dunlap’s French engineer A. R. Polonceau built the Pont Creek site preceded the National Road and du Carrousel over the Seine in 1834 with cast iron that it was not the responsibility of the Federal tubular arches and a span of 150 feet. In the United Government to upgrade it. He was told to proStates, James Finley used wrought iron links for ceed but then suggested a different location that his chains and suspenders in his early suspension would make a better connection with the existing bridges. Theodore Burr used wrought iron chains covered bridge across the Monongahela. On May in some of his early wooden arch/truss bridges.

13, 1833, he was overruled and ordered to rebuild the bridge at its current location. For the wooden bridges in his section, he adopted “the plan of superstructure patented by Col. Long, of the corps of United States Engineers, denominated Jackson Bridges. Several of that denomination have been raised, and will soon be completed. All experiCaptain Richard Delafield was assigned the task enced workmen, who have had an opportunity of upgrading the National or Cumberland Road of seeing them, express their entire satisfaction east of the Ohio River in the early 1830s and given of the principle, and view it as a valuable system a budget of $300,000 to do so. The road was built of bridge architecture.” At Will’s Creek, he urged between 1811 and 1833, generally with masonry a wooden bridge but was forced, by terms of a arch or wooden bridges. The states through which legislative act by Maryland, to take over the mainit passed (Maryland, Virginia, Pennsylvania) tenance of the road and build a major masonry agreed to take over maintenance of the road once bridge. At Dunlap’s Creek, he could have built the Federal Government repaired it to their satis- another wooden bridge but chose to build a firstfaction and built the required toll booths. There of-its-kind, in the United States, cast iron arch were two major bridges in Delafield’s section, bridge with a span of 80 feet and a rise of 8 feet. one at Cumberland, Maryland, over Will’s Creek No record of conversations between the Chief of and the Dunlap’s Creek Bridge. A bridge on the Engineers and Delafield exists, but it is hard to road existed across Dunlap’s Creek in Brownsville, believe that Delafield did not have a hard sell on Pennsylvania, before 1794 and before the con- his proposal, especially since the bridge would struction of the National Road. The bridge crossed take up almost 15% of his total budget.

Dunlap’s Creek separating Brownsville from On September 30, 1833, he wrote, “In the estiBridgeport, Pennsylvania, a short distance above mates of services of the year I have asked for an where it merged with the Monongahela River. A appropriation for a cast-iron bridge for Dunlap’s wooden bridge at the site collapsed in 1808 and Creek, induced so to do from the circumstances of James Finley (STRUCTURE, November 2008), finding no durable stone that will resist the thrust a resident of Brownsville, built one of his chain of the arch required to span the creek…preferring bridges at the site in 1809. It collapsed in 1820 it to a wooden structure perishable from the decay under a load of snow and a six-horse team. A of timber, and exposed to fire…” new wooden bridge was built by Isaac Core in Even with a much higher first cost, he convinced August 1821. When Delafield arrived in 1832, the the Chief of Engineer, Gen. Charles Gratiot, that Core bridge needed replacement. Lt. Mansfield it was a good investment. Brownsville was home to indicated it would not last another year. A four several iron works and was not far from deposits span covered bridge built in 1833 crossed the of iron ore. He purchased pig iron from a mill Monongahela River just upstream from the junc- in Portsmouth, Ohio, and had the iron cast in tion of Dunlap’s Creek and the river.

Brownsville at the Herbertson Foundry. Delafield,

Dunlap’s Creek Arch Bridge (1839) The First Cast Iron Bridge in the United States

By Frank Griggs, Jr., Dist.

M.ASCE, D.Eng., P.E., P.L.S. Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an Independent Consulting Engineer.

Dr. Griggs can be reached at fgriggsjr@twc.com.

46 November 2017

although a graduate of West Point, had little prior experience in iron bridge building and was even feeling his way in the design and construction of wood and masonry bridges.

He wrote on March 31, 1836, of his design, “In some one of my communications of last fall, I intimated that I had matured in my mind the plan of the Cast Iron Bridge to be constructed over Dunlap’s Creek – differing in its principles of construction from any of which I could find a notice by either English or French Engineers…

Presuming you would be pleased to see the plans before I can have them in my power to file copies of them in your Department, and that the Secretary of War might wish to see the plans of the first iron bridge to be constructed in the country, I have directed Lt. McKee to pass through Washington, on his way to Brownsville.”

The wrought iron was forged in John Snowdon’s Vulcan Iron and Machine Works, also in Brownsville. Attached to his 1837 Annual Report was a memoir on the bridge entitled, Memoir on the Dunlap’s Creek Bridge on the Cumberland Road East of the Ohio, and two drawings of the bridge. It was signed on September 27, 1837, by both Delafield and Lt. George W. Cass.

View showing tubular sections and cast iron latticing. Steel work in the right, foreground supports sidewalks added in 1920.

His design consisted of five rows of elliptical tubular castings, spaced 5.77 feet on center, bearing on spring plates embedded in the masonry. Each tube consisted of 9 castings (called voussoirs after masonry practice) cast with flanges with holes to bolt the sections together. They were built on wooden falsework set in the creek bottom. Why Delafield

adopted an elliptical shape rather than a more common circular shape is not clear. His outer ellipse had a major (vertical) axis 2 feet 6 inches in length and a minor (horizontal) axis 10¾ inches in length. All 45 tube sections were identical and had a wall thickness of 1.37 inches. A total of 250 castings were required for the entire bridge. He wrote, “the voussoirs

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HAER drawing of arches, spandrel, bracing, and decking.

composing the same rib are not in immediate contact; …to prevent lateral motion, cross plates traverse at right angles all the ribs, and are as many in number as there are joints between the voussoirs of each rib. The cross plates are 24 feet 7 inches from out to out, 2 feet 6 inches wide and 2½ inches thick.” They were not solid, as a rectangular cutout 4 feet 10 inches wide and about 12 inches high was placed between each voussoir to cut down on the weight. Even with the cutouts, the cross pieces weighed almost 2½ tons.

Between the voussoirs and the deck, he noted, “...supporters are composed of open ribs resting vertically on the hollow elliptical ribs and present the figures of triangles (two rows above the other).” On these supports, he had curved cast iron floor plates one inch thick, bolted together to support the 1-foot 6-inch thick McAdam metal paving that was kept in place laterally by 1-foot 6-inch “road covering plates” along the edges of the bridge.

X braces (St. Andrew’s crosses) were placed between each row of tubes for lateral bracing, supplementing the large cross plates.

The abutments were huge, being 25 feet across the front, 42 feet high, and 14 feet thick in addition to long wingwalls on the Brownsville side of the bridge. The masonry alone amounted to one-half the cost of the entire bridge.

Since this was to be a first of its kind, Delafield knew that no contractor would submit a fixed price for the iron superstructure fabrication and construction, and chose to build it on a kind of “Cost Plus” basis, writing, “I propose having the castings made by a foundry at Brownsville, purchasing all of the material myself, paying the mechanics and

laborers for the time actually employed, and as a rent for the foundry, use of the lathes, engines, workshops, tools, and skill and service of the Proprietor and foreman, give a percentage upon the wages of the people employed by this course. I secure a choice of metal and can control the mode of casting in any way it may be found desirable.”

Delafield and his colleagues had many difficulties in building the bridge and keeping the cost within budget. One of Delafield’s assistants, Lt. Cass, stated, “Everything seems to have gone wrong since commencement of this work and I do hope that I may never have such another job in my life. It has from the beginning to this time given me more trouble and uneasiness than a work of 10 times the magnitude ought to have done…”

Delafield’s 1835 – 1837 annual reports note several difficulties: • September 1835 – Difficulties obtaining rights-of-way delayed the start of the project.

• September 1836 – Unprecedented wet weather, high water in the river, and great scarcity of mechanics prevented completion by this date. However, the southwestern abutment was completed and the northwestern abutment had been built three feet high.

• Half of the 140 tons of pig iron had been delivered to the foundry by the fall of 1836. Patterns for the casting of the bridge were complete and castings were proceeding rapidly.

• Increased prices for pig iron over original estimates ($35 versus $55 per ton) increased costs. “A long and protracted correspondence grew out of the location

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of this bridge, by the refusal of the authorities of the town of Bridgeport to permit it being located on the site selected by the engineer as best suited for the public interest.”

• November 1837 – The masonry of the Dunlap’s creek bridge was finished in September 1837. The cast-iron for the arch of the bridge was not finished. The five center sections of the elliptical cylinders (voussoirs) and two flooring plates remained to be cast. A few pieces of castings (St. Andrew’s crosses, and road-sustaining plates) remained to be fitted together. The wrought-iron railing remained to be made.

• By late 1837, it was necessary for Delafield to request an increase in appropriations again. He noted all of the issues outlined in the report and expounded on the “novelty of the undertaking.”

Some traffic started to cross the bridge in 1838, but it was not completed with railings until 1839. Its grand opening was on July 4.

The railings and finish work had to be scaled back due to funding problems.

The bridge came in well above Delafield’s original estimate, eventually costing just under $40,000. A masonry bridge would have cost, if the stone was locally available, about $24,000 and a wooden bridge only about $7,000. The high cost of cast iron and the problem of fitting the faces of the cast iron for the bridge resulted in very few bridges of this type being built. This was especially true since the cast and wrought iron trusses, starting with Squire Whipple’s bridges, became very cheap to build. The bridge, however, has served travelers for over 178 years and recent inspections have shown the iron is still in excellent condition.

Similar bridges were General Montgomery Meigs’ Pipe Aqueduct Bridge in Washington, D.C., built in 1860, and Wendel Bollman’s Pipe Bridge in Baltimore in 1877. Both of these bridges used circular pipes which are the most efficient shapes to carry compressive loads, l/r, equal in all directions, and to conduct water at the lowest wetted perimeter per unit of cross sectional area.

The Dunlap’s Creek Bridge is on the National Register of Historic Places (1978) and is also a National Historic Civil Engineering Landmark (1978). Sherman Day wrote in his 1842 book, Historical Collections of the State of Pennsylvania, “It is the only one of its kind and probably the most splendid piece of bridge architecture in the United States.”

Delafield went on to a noteworthy career, becoming Superintendent of West Point and Chief of Engineers for the United States Army.▪

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issues affecting the structural engineering profession

Professional issues

Work-Life Balance, Flexibility Benefits, and Caregiving Structural Engineering Engagement and Equity (SE3) Committee Survey Results

By Angie Sommer, S.E. and Natalie Tse, S.E., LEED AP BD+C

R

esults of the 2016 SE3 Study discussed in Part 1 (STRUCTURE, April 2017) focused on overall career satisfaction, development, and advancement. Part 2 of this series (STRUCTURE, August 2017) focused on compensation, overtime, and the gender pay gap. This article highlights the survey findings regarding work-life balance, flexibility benefits, and caregiving. A full report that includes all the findings discussed in this series can be found at SE3project.org/full-report.

Work-Life Balance “Work-life balance” is a popular phrase in modern discussions of employment and engagement. Research, articles, and ongoing studies attempt to address common concerns arising from an imbalance between the time spent at work and the time spent outside of work attending to other “life” interests or tasks, such as exercise, hobbies, errands, and care of children or dependents. Twenty-two percent of the respondents to the 2016 SE3 survey reported being either dissatisfied or very dissatisfied with their work-life balance (Figure 1 shows this breakdown by position). Poor work-life balance was also one of the top reasons that respondents considered leaving the profession and one of the leading reasons that respondents reported leaving the profession.

Flexibility Benefits In the past several decades, more women have been entering the workforce globally. In 1950, women comprised approximately 30% of the U.S. workforce; today they comprise nearly half (The Council of Economic Advisers, 2014). As women used to commonly be primary caregivers to children, this change in the number of women in the workforce makes raising children more difficult for parents who are often now both employed outside the home. (Eldercare is similarly difficult; nearly two-thirds of people providing unpaid elder care have jobs, and about half of caregivers work full-time.) This evolution of family life requires a new corporate culture that accommodates the needs of working parents.

Although having children or dependents is common (51% of respondents have children or dependents), survey findings indicate a stigma

Figure 2. Flexibility benefits offered by employers vs. used.

STRUCTURE magazine

Figure 1. Satisfaction with work-life balance.

associated with employees who care for children. Even though many firms now offer “flexibility benefits,” such as flexible work schedules, maternity/paternity leave, reduced hours, and the ability to work from home, many individuals are hesitant to take advantage of these benefits. Additionally, only 19% of respondents had taken time off from their structural engineering careers, with maternity/paternity/ parental leave identified as the primary reason.

Some respondents are indifferent to coworkers using flexibility benefits, but others expressed criticism of their peers who choose to use them. Reasons indicated included a perceived reduction of productivity, decreased motivation, decreased accountability to clients, and significant inconvenience to other staff, the last of which is the most commonly cited complaint regarding those who either work remotely or have reduced schedules. Twenty-two percent of the respondents who do not have children or dependents indicated that they were sometimes left to “pick up the slack” for their coworkers with children or dependents. Thirty percent of the respondents reported that they feel they work harder than their peers with children, and 30% of the respondents also reported that their managers expect them to work more hours because they do not have children.

Of the benefit options surveyed, respondents indicated that a flexible daily work schedule is the benefit most commonly offered by employers and the most widely used. Over 70% of the respondents stated that their company offers flexible daily work schedules, and nearly the same number reported that they use or would use this benefit if it were offered, as shown in Figure 2.

The biggest discrepancies in benefits that were offered versus those that were used or desired were weekly schedule flexibility and parental leave with full benefits. Only about one-third of the respondents’ employers offer weekly schedule flexibility (e.g., working four tenhour days instead of five eight-hour days). In comparison, more than half of the respondents said they have used or would use this benefit if it were offered. Nineteen percent of the respondents reported that their companies offer parental leave with full benefits (paid maternity or paternity leave after having a child), while 41% of the respondents indicated that they have used or would use this benefit if it were offered.

Findings from this survey align with other recent discourse that suggests that modern corporate culture in the United States generally does not embrace the needs of caregivers by allowing them to tend to both family and work obligations (Slaughter, 2015). While many companies

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offer flexibility benefits, they are often negotiated on a person-by-person basis and not well supported by management or other staff. Studies show, however, that increased flexibility benefits can help alleviate employee stress about balancing family with work and can result in improved employee happiness, health, loyalty, and productivity (The Council of Economic Advisers, 2014). Another recent study reports on a systematic management approach that can be used to more effectively manage flexibility needs without burdening non-caregivers with additional workload (Fondas, 2014).

Advancement of Respondents with Children Respondents with children reported advancing at a slower rate than those Figure 3. Career advancement. without children, regardless of gender.

On average, it took respondents without children 8.5 years to reach the senior engineer/project manager level, 11.6 years to reach the associate/shareholder level, and 14.7 years to reach principal/owner.

It took respondents with children 11.5 years, 13.7 years, and 14.9 years, respectively, to reach those positions, as shown in Figure 3.

At every position level, female respondents were less likely than male respondents to have child dependents, which may contribute to the finding that female respondents reach each level of employment except principal/owner more quickly than male respondents (as discussed in the Career Development section of the 2016 SE3 Survey Report). At the principal/owner level, 85% of male respondents reported having children, compared to only 61% of females, as shown in Figure 4.

Despite the difficulties reported, the respondents with children reported higher overall satisfaction with their career than those without children.

Caregiving Responsibilities When asked to estimate the percent that they contribute to caregiving responsibilities, on average women responded that they contribute 65%, while men reported that they contribute 35%. Women were also significantly more likely to feel that having children has affected their career. In fact, for both genders, as an employee’s percent of caregiving responsibilities increased, so did his or her feeling that children had

Figure 5. Effect of children on a career.

affected his or her career, as shown in Figure 5. Because more men are taking on a larger percentage of caregiving responsibilities compared to previous generations, this issue no longer applies only to women.

As the percentage of caregiving increased, respondents were more likely to report a decrease in motivation and productivity. For the 192 respondents who reported having more than 50% of the caregiving responsibilities in their family, 22% reported a decrease in motivation at work after having children, and 21% reported a reduction in productivity. In comparison, of the 563 respondents who reported having less than 50% of the caregiving responsibilities, only 6% reported a decrease in motivation at work after having children, and 12% reported a decrease in productivity.

Loss of motivation and productivity was more concentrated in women, which correlates directly to the higher rate of caregiving responsibilities that women reported. When asked about work motivation after having children, 41% of men reported an increase in motivation, compared to only 21% of women, and only 7% of men reported decreased motivation, compared to 21% of women. When asked about work productivity as a working parent, 19% of women reported a decrease in work productivity relative to life without children or dependents, compared to 13% of men.

Looking at these factors together for women with children – a higher percentage of caregiving responsibilities, stigmas in the workplace against those who use flexibility benefits, and correspondingly less productivity and motivation after children – it is not surprising that women are less satisfied with work-life balance, which was reported as their top reason for considering leaving the structural engineering profession. It is also clear that better engagement of female engineers – or even engineers of all genders – depends heavily on changing the perception of the value of parenting. If employees feel supported in their work and life outside work and are allowed flexible schedules as needed to care for children and dependents, then perhaps they would engage better within the profession after transitioning into a working parent role and, in some cases, stay in the profession when they may have otherwise left.▪ The online version of this article contains references.

Please visit www.STRUCTUREmag.org.

Angie Sommer is an Associate at ZFA Structural Engineers in San Francisco, California. She is the primary author of the 2016 SEAONC SE3 Survey Report and is the 2016-17 co-chair of the SEAONC SE3 Committee. She can be contacted at angies@zfa.com.

Natalie Tse is a Senior Engineer at KPW Structural Engineers in Oakland. She was the 2015-16 co-chair and co-founder of the SEAONC SE3 Committee and can be reached at n.tse@tippingstructural.com.

Figure 4. Respondents with children.

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Professional liability

issues affecting the structural engineering profession

Digital Stamping A Strategic Plan for Design Professionals

By David A. Ericksen, Esq.

A

mong all the professions, design professionals are unique in that only they hold professional stamps to seal their work product. That seal carries genuine significance. As the Ontario Board of Engineers has stated, [The engineer’s stamp] assures the document’s recipient that the work meets the standards of professionalism expected of competent, experienced individuals who take personal responsibility for their judgments and decisions.

Accordingly, application of the design professional’s stamp should be treated with respect and restraint. However, as electronic design, demands, and opportunities expand, traditional respect and restraint for the design professional stamp can be tested.

While there can be, and are, many variations as to the interplay of design professional stamps and the corresponding signature, the three principal categories at this time are: 1) traditional use of the “wet” stamp with a “wet” signature over it; 2) an electronic seal with a wet signature; and 3) an electronic seal with a digital signature.

In the progressive variations above, each step creates greater potential for the unauthorized use or replication of the design documents with the corresponding seal and signature. Even though it would be “unauthorized,” such use can and does implicate losses of intellectual capital from wrongly converted work product and risks liability from those unintended uses. To counter this, design professionals may consider the five-step plan below.

Internal Written Policy of Intent and Practice Every component of the design should be intentional. That is particularly true with respect to the application of a professional seal and signature. In firms with multiple architects or engineers, that practice should be consistent across the company. When there is a question as to the validity (or misuse) of a professional seal or signature, reference to an internal policy may often be the key to the response and defense, if necessary. Such a policy need not be long or cumbersome, but it should be written, shared internally, and

reinforced. Such a policy may be built from the following four elements.

Limited Application Not every sketch, report, or letter by a professional architect or engineer should be stamped. In fact, it should be just the opposite. Ideally, the professional stamp and signature should only be applied to a final work product (plans and specifications mostly, but also reports and certifications as necessary or required). Iterative drafts and correspondence should never be “stamped” unless extraordinary circumstances and demands exist with corresponding justification and limitations. The significance of the professional stamp and the potential messaging to those who receive, review, and rely on professionally sealed documents demands such restraint and intentional application.

Limited to Wet Stamp Whenever Possible The simple reality is that original wet stamping and original wet signatures cannot be replicated or misused nearly as easily as electronic or digital seals or signatures. Accordingly, the stated policy preference should always be to use the original or wet stamp and signature.

Log of Electronic/Digital Applications Where project demands or modern practices warrant or justify the use of electronic or digital seals and signatures, the publication of such documents should be tracked in a formal log. The log identifies the subject documents and associated information such as date, version number, number of pages, the applicable project or site, the intended recipients or users, and the transmittal date. When consistently followed, such a log provides at least two key benefits. First, it reaffirms the intentional and limited use of the professional stamp. Second, where there is a question as to subsequent modifications, corruption, or misuse of documents bearing the stamp or signature, it provides a reference point to disprove and defend against claims that the use was properly permitted.

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Statement of Limitation Finally, any design professional seal or signature should apply only to those documents actually published by the design professional.

Where the seal or signature is digital, it risks both that the underlying documents may become corrupted or manipulated, or that it could be replicated for unauthorized use.

Accordingly, design professionals should make clear that their seal and signature validly applies only to the documents as they published them at the time the seal or signature was applied, and not to anything thereafter. A directive or disclaimer on the documents themselves, and in close proximity to the seal or signature, could provide: Design Professional’s electronic or digital seal or signature is effective only as to that version of this document as originally published by Design Professional. Design Professional is not responsible for any subsequent modification, corruption, or unauthorized use of such document. To verify the validity or applicability of the seal or signature, contact Design Professional.

Such a directive or disclaimer, with the corresponding invitation for follow-up contact, has the tandem benefits of controlling and securing the value and integrity of the design professional’s work product, as well as potentially opening the door to further or new engagements for professional services on that or other projects.▪ David A. Ericksen is a principal shareholder in and immediate past President of the law firm of Severson & Werson in San Francisco, California, and leads the firm’s Construction and Environmental Practices. David can be reached at dae@severson.com.

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softWare UPDates

news and information from software vendors

ADAPT Corporation

CADRE Analytic

Hexagon PPM

Phone: 650-218-0008 Email: florian@adaptsoft.com Web: www.adaptsoft.com Product: ADAPT-PTRC 2017 Description: Easy-to-use, reliable, and indispensable production software for rapid design of RC and PT concrete slabs and beams. Utilizing an intuitive 2D modeling interface and the Equivalent Frame Method, take advantage of the latest features including design code updates, reinforcement curtailment, hybrid design, and investigation of existing structures.

Phone: 425-392-4309 Email: cadresales@cadreanalytic.com Web: www.cadreanalytic.com Product: CADRE Pro 6.8 Description: Finite element structural analysis.

Loading conditions include discrete, pressure, hydrostatic, seismic, and dynamic response. Features for presenting, displaying, plotting, and tabulating extreme loads and stresses across the structure and across multiple load cases simultaneously. Basic code checking for steel, wood, and aluminum.

Product: ADAPT-Builder Shear Wall Design Description: Offers the only fully integrated solution for the design of complete concrete buildings using one model: gravity design of reinforced concrete or post-tensioned floor systems, lateral analysis, column design, shear wall design, shallow foundation design, and automated inclusion of lateral frame actions in slab and foundation design.

Phone: 281-477-8148 Email: geoffrey.blumber@hexagon.com Web: www.coade.com/products/gtstrudl Product: GT STRUDL Description: For over 40 years, GT STRUDL has offered structural engineers a complete design solution, now including 3D CAD modeling and 64-bit high-performance computation solvers into all versions. Our structural analysis software is a highquality database-driven system for comprehensive frame and finite element analysis, and steel and reinforced concrete design.

Concrete Masonry Association of CA & NV

IES, Inc.

Applied Science International, LLC Phone: 919-645-4090 Email: support@appliedsciencent.com Web: www.extremeloading.com Product: Extreme Loading for Structures 5.0 Description: Efficiently study structural failure from any number of actual or possible extreme events such as blast, seismic, and progressive collapse. Easily model structures composed of reinforced concrete, steel composite and other structures with all as-built and as-damaged details.

Product: SteelSmart System 8.1 Description: Provides construction professionals with an essential tool engineered for both fast and accurate design. Available design modules include: Curtain Wall, Load Bearing Wall, X-Brace Shear Wall, Floor Framing, Roof Framing, Roof Truss, and MomentResisting Short Wall.

Bentley Systems Phone: 800-BENTLEY Email: samantha.langdeau@bentley.com Web: www.bentley.com Product: STAAD, RAM, RM Bridge Description: Efficiently model, analyze, and design any structure, from a single foundation to an entire stadium, and even a complex bridge. Consider multiple design alternatives quickly and early in your design process and perform even the most advanced analysis.

2017ANNUAL TRADE SHOW IN PRINT is online now at

www.STRUCTUREmag.org .

Phone: 916-722-1700 Email: info@cmacn.org Web: CMACN.org Product: CMD15 Design Tool Description: Structural design of reinforced concrete and clay hollow unit masonry elements for design of masonry elements in accordance with provisions of Ch. 21 2010 through 2016 CBC or 2009 through 2015 IBC and 2008 through 2013 Building Code Requirements for Masonry Structures (TMS 402/ACI 530/ASCE 5).

DEWALT Phone: 800-524-3244 Email: anchors@dewalt.com Web: http://anchors.dewalt.com/anchors/ Product: DEWALT Design Assist (DDA) Description: A world-class connection design software for concrete anchoring. It offers new innovative features, applications, and products.

DDA has a streamlined, interactive and flexible user-interface. Users can quickly model, optimize, and compare multiple solutions and then design, document, and specify in just minutes.

Dlubal Software, Inc. Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: SHAPE-THIN Description: Calculate section properties of custom open, closed, built-up, and non-connected thinwalled cross-sections consisting of one or more materials. Optimal integration with RFEM for a full structural analysis. 3D realistic rendering. Complete code checks in design modules such as RF-STEEL AISC and RF-ALUMINUM ADM, including local buckling checks of slender elements.

Product: RFEM Description: Intuitive and user-friendly FEA software complete with USA/International design codes for steel, concrete, wood, CLT, aluminum, glass, and fabric/membranes. Capable of non-linear analysis of member, plate, and solid elements including code references and detailed design results. Direct interfaces with BIM and CAD software incorporate seamless and bi-directional data exchange.

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Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis Description: When you need answers, get them from models that are easy to create in IES structural software.

VisualAnalysis is an excellent value for engineers who solve frames, trusses, or just about any kind of civil/ structural problems. IES offers free video-based training and email technical support.

INTEGRITY SOFTWARE, INC. Phone: 512-372 8991 Email: sales@softwaremetering.com Web: www.softwaremetering.com Product: SofTrack Description: Save money on monthly, quarterly and annual Bentley® license fees! SofTrack provides automatic control to prevent over-usage of Bentley licenses. Ensure licensed applications are used within your license limits. Includes support for all Bentley licensing policies. Automatically block usage of products you do not own. Ask about Autodesk control.

MDX Software Phone: 573-446-3221 Email: sales@mdxsoftware.com Web: www.mdxsoftware.com Product: MDX Software Curved & Straight Steel Bridge Design & Rating Description: Used by many top design firms and DOTs to design and rate steel girder bridges for compliance with LRFD, LRFR, LFD, and ASD AASHTO Specifications.

Opti-Mate, Inc. Phone: 610-530-9031 Email: optimate@enter.net Web: www.opti-mate.com Product: Bridge Engineering Software Description: Includes analysis, rating, and AASHTO code check using the WSD, LFD, and LRFD specifications. User defined live loads can also be analyzed. MERLIN DASH steel I-girders, reinforced or prestressed concrete girders; DESCUS I curved I-girders; DESCUS II curved box girders; SABRE sign and luminaire structures, and TRAP truss bridges.

softWare UPDates

news and information from software vendors RISA Technologies

Trimble

Veit Christoph GmbH

Phone: 949-951-5815 Email: info@risa.com Web: risa.com Product: RISAConnection Description: RISAConnection is at the cutting edge of next-generation connection design software.

Featuring full 3D visualization, Shop-drawing style views, and expandable engineering calculations for all limit states, RISAConnection is an essential tool for engineers who use steel. Its complete integration with RISA-3D and RISAFloor allow one-click connection design for entire structures.

Phone: 770-426-5105 Email: kristine.plemmons@trimble.com Web: www.tekla.com Product: Tedds Description: Perform 2D frame analysis, access a large range of automated structural and civil calculations to U.S. codes, and speed up your daily structural calculations.

Phone: 711-518573-30 Email: info@vcmaster.com Web: www.vcmaster.com/en Product: VCmaster - Intelligent Engineering Software Description: Comprehensive, affordable and userfriendly software solution for compiling professional structural design calculations. A unique combination of reliable calculation capacity and extensive text processing features. Includes more than 60 interactive design aids to AISC 14th edition and ACI-318.

Empowers engineers to automate design calculations.

Free 60-day trial version available.

SCIA Inc. Phone: 443-393-3616 Email: b.follett@scia.net Web: www.scia.net Product: SCIA Engineer Description: Structural modeling, analysis, design, reporting, and interoperability in ONE program.

Design and optimize to the most recent codes. Tackle large projects with advanced non-linear and dynamic analysis. Plug into BIM with IFC support and bidirectional links to Revit, Tekla and others. Learn how you can start boosting your productivity.

Simpson Strong-Tie Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: CFS Designer™ Software Description: Design CFS beam-column members according to AISI specifications and analyze complex beam loading and span conditions.

Intuitive design tools automate common CFS systems such as wall openings, shearwalls, floor joists, and up to eight stories of load-bearing studs.

Product: Tekla Structural Designer Description: Revolutionary software that gives engineers the power to analyze and design buildings efficiently and profitably. From the quick comparison of alternative design schemes through to cost-effective change management and seamless BIM collaboration, Tekla Structural Designer can transform your business.

Product: Tekla Structures Description: Create and transfer constructible models throughout the design lifecycle. From concept to completion. Allows you to create accurate and information-rich models that reduce RFIs and enable structural engineers proven additional services.

Models are used for drawing production, material take offs and collaboration with disciplines like architects, consultants, fabricators and contractors.

Not listed?

All 2017/2018 Resource Guide forms, including the 2018 TRADE SHOW IN PRINT, are now available on our website: www.STRUCTUREmag.org.

Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

StructurePoint Phone: 847-966-4357 Email: info@structurepoint.org Web: www.structurepoint.org Product: Concrete Design Software Suite Description: Concrete design software programs updated to ACI 318-14 for concrete buildings, concrete structures, and concrete tanks. Reinforced concrete structural software includes programs for design of columns, bridge piers, beams, girders, one and two-way slabs, shearwalls, tilt-up walls, mats, foundations, tanks, and slabs-on-grade.

StrucSoft Solutions Ltd. Phone: 514-538-6862 Email: a.gordon-stewart@strucsoftsolutions.com Web: http://strucsoftsolutions.com Product: MWF

Description: The full cold-formed steel framing package for Revit, building on MWF Pro Metal’s capabilities by allowing engineers and estimators to engineer and determine optimal elements for your project. Take advantage of a finite element analysis engine and the almost limitless amount of configurations you expect from MWF.

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Tacoma Lacey Portland Eugene Sacramento

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offers “ VisualAnalysis excellent value. ”

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ShapeBuilder Custom Member Shapes

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IES Building Suite $4460 VAConnect Base Plate, Connection Design

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award winners and outstanding projects

Spotlight

The Petersen Automotive Museum Façade

By Jeff Denton, P.E., S.E.

Wallace Engineering Structural Consultants, Inc. was an Outstanding Award Winner for its Façade System for the Petersen Automotive Museum Renovation project in the 2016 NCSEA Annual Excellence in Structural Engineering Awards Program in the Category – Special Use Structures.

C

onstruction began in 2014 on a major renovation of the Petersen Automotive Museum in Los Angeles, California. The museum’s interior and exterior were fully remodeled at a total cost of $125 million. The centerpiece of the renovation is an entirely new and very dramatic façade.

Located at 6060 Wilshire Boulevard, in the Museum Row section of the Miracle Mile, the Petersen faces stiff competition from nearby museums, including the LA County Museum of Art, the La Brea Tar Pits, and the underconstruction Academy Museum.

The museum’s Board of Directors sought to update, expand, and raise the profile of the museum from a niche automotive collection to a widely recognized landmark. To accomplish this goal, they called on architecture firm Kohn Pedersen Fox’s New York office, who envisioned the bold new façade.

The Petersen Automotive Museum opened in 1994. It was founded by publisher Robert E. Petersen, who made his fortune producing magazines Hot Rod, Car Craft, and Motor Trend, among others.

The three-story reinforced concrete structure that would become the museum first opened in 1962 as a U.S. branch of the Japanese department store Seibu. It was designed by Los Angeles modernist architect Welton Becket. The original building featured a precast concrete façade, removed as part of the renovation over a minor protest by local architecture enthusiasts.

Design Team The design architect for the project was Kohn Pedersen Fox (KPF). Façade design assist, fabrication, and installation was performed

by A. Zahner Company. Wallace Engineering provided structural engineering and design services for the façade. Saiful Bouquet was the structural engineer for the building structures.

Ribbons The signature element of the new façade is an array of curved stainless steel ribbons flowing over the walls and roof of the museum. They are designed to convey a feeling of automotive speed and strength and echo the aerodynamic curves of smoke trails seen in a wind tunnel test. KPF

likened the ribbons to a new body wrapping the existing chassis of the museum.

The ribbons are clad with brushed stainless steel on the front and dimpled red aluminum on the building side. The ribbons average 30 feet long, but in some areas span up to 46 feet.

Due to the ribbons’ undulating shape, a straight internal member would not suffice. Wallace investigated several options for the ribbon structure. Welded segments of steel HSS or pipe were considered first but deemed too heavy and difficult to fit within the 12-inch-thick volume. Space frame trusses would be much lighter but would require too many parts and connections. The lightest option was a stressed-skin approach, where the visible surfaces become the structural element. This was eliminated due to the difficulty of concealing connections and because it would require excessive per-panel analysis and detailing. Ultimately, a central 6.5-inch diameter CNC-rolled aluminum pipe was chosen. The smaller diameter allowed movement within the ribbon volume and simplification of most of the pipe paths from dual to single curvature, further reducing cost.

The end connections are designed as fixed to minimize deflections of the relatively flexible aluminum pipes and prevent visible angular discontinuities at the support points. Since the connection must permit axial movement caused by thermal expansion while resisting moment in three directions, a steel collar was used to capture the aluminum pipe, with stainless steel shims to prevent corrosion between dissimilar metals.

Ribbon Support Structure The ribbons at ground and roof levels are supported by large steel structures cantilevering upward. Despite the organic nicknames – trees and shrubs – given during the design process, the design inspiration of these elements sprung from a more appropriate source. They are intended to mimic the branching exhaust pipes of an automobile’s engine manifold. Each support consists of three or four bundled 10-inch steel pipes that run vertically near the base, then splay apart to support the ribbons. They stand

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up to 35 feet tall with a 40-foot horizontal reach and are anchored directly into the top of the building’s existing concrete columns. Though the pipes appear to be bent from single pieces of straight steel, the tight bend radius required the use of structural steel castings.

To limit the additional forces placed on the existing museum structure, a series of HSS columns and girts, dubbed the “exoskeleton,” were hidden inside the new rainscreen to carry vertical forces to the foundation and carry lateral loads to the floor diaphragms. This also served to reduce the number of penetrations through the building envelope. Horizontal outriggers attached to these exoskeleton columns reach through the rainscreen to support ribbons running near the walls.

Design Process To properly determine seismic forces and movements of the complicated structure, Wallace Engineering and Saiful Bouquet shared analysis models, creating a combined model to properly study the interaction between the two systems. This allowed for dynamic analysis and a more accurate understanding of the effect of the new architectural components on the original structure.

Conclusion An in-depth and iterative collaboration between members of the design team led to a successful project and an unforgettable structure. Critical reviews of the new façade’s design have been mixed, but few would dispute that the museum’s goals were met.

Pedestrians and drivers alike stop to stare at the distinctive structure, attendance is up since the museum’s reopening, and the project was recently awarded a 2017 American Architecture Award.▪ Jeff Denton is a Structural Engineer specializing in façades and architectural metalwork in the Kansas City, Missouri office of Wallace Engineering. He can be reached at jdenton@wallacesc.com.

News form the National Council of Structural Engineers Associations

2017 Excellence in Structural Engineering Awards The National Council of Structural Engineers Associations is pleased to announce the finalists and outstanding project recipients of the 2017 Excellence in Structural Engineering Awards. This year’s awards program saw over 100 entries in seven different categories. A total of 24 projects were chosen as finalists and one outstanding project was chosen as an overall winner from each category. The awards were presented at the 2017 NCSEA Structural Engineering Summit in Washington, D.C. on Friday, October 13th during the annual NCSEA Awards Banquet. Learn more about the projects by visiting the awards tab on www.ncsea.com.

Congratulations to the outstanding project winners of the 2017 Excellence in Structural Engineering Awards!

New Bridges or Transportation Structures

Forensic / Renovation / Retrofit / Rehabilitation Structures over $20 Million

Sellwood Bridge Replacement – Portland, OR T.Y. Lin International

The Sellwood Bridge in Portland, Oregon, replaces a 1925-era structure in a geologically unstable area. The 1,976.5-footlong bridge, 1,275 feet of which is steel deck arch, carries two 12-foot-wide vehicular lanes, two 6.5-foot-wide bike lanes, and two 12-foot-wide sidewalks, and will accommodate future streetcar service. To reduce project impacts, the existing bridge was slid over to a detour alignment until the replacement span was completed, minimizing traffic disruption and reducing construction time and costs. The new bridge has an advanced ductility-based seismic design for both operating and strength level earthquakes. Construction of the Sellwood Bridge was completed in February 2017.

The Bay Area Metro Center serves as the regional headquarters for various government transportation entities. The client had a limited budget to convert this heavy, former World War II assembly plant (a 500,000 SF, reinforced concrete structure) into commercial offices.

Holmes Structures provided a cost-effective retrofit that reduced building mass and added selective perimeter strengthening without altering the foundation. Performancebased engineering was used to design a retrofit that leveraged the capacity of the existing structure. The economical solution resulted in a light-filled and engaging workplace as well as an overall aesthetic transformation of the existing building.

Other Structures

Broad Museum Veil – Los Angeles, CA John A Martin & Associates, Inc.

Forensic/Renovation/Retrofit/Rehabilitation Structures under $20 Million The Desmond Building – Los Angeles, CA Skidmore, Owings & Merrill LLP

NCSEA News

Bay Area Metro Center – San Francisco, CA Holmes Structures

The Desmond Building in Los Angeles has recently been infused with new life through a full renovation and seismic retrofit.

Designed in 1916, the building stood empty for many years.

Now converted to high-end creative offices that maintain the original industrial aesthetic, successful implementation of a rigorous, code prescriptive retrofit solution enabled the addition of a lightweight, income-generating sixth story, while preserving the historic character of the century-old building.

Given the City’s current focus on seismic safety of such buildings, The Desmond exemplifies how many other historic properties in Los Angeles can be safely renovated while including new additions.

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The veil at the Los Angeles Broad Museum is a structural exoskeleton that drapes over the building’s interior vault. As the defining feature of this world-class institution, this porous yet absorptive screen, made of 2,500 fiberglass reinforced concrete (FRC) panels and 650 tons of steel, forms a 3-D series of open cellular components that channels light into public spaces and galleries and activates connections between the museum and the surrounding Downtown streetscape. An elegant steel frame realized through use of rigorous analysis, testing, and creative support strategies allows this stand-alone piece useful for functional as well as aesthetic functions.

November 2017

The Exchange at 100 Federal Street – Boston, MA McNamara · Salvia Structural Engineers Designed as the shining new heart of Boston’s Financial District, The Exchange at 100 Federal Street is a structural steel and glass pavilion that will function as a public gathering and event space, delivering a contemporary addition responding to the form of the existing 37-story, 1971 office building. The angular volume is a solid steel space frame with exposed bolted connections, where honest structure is celebrated, and shape and detailing were carefully considered for efficiency. This project highlights the benefits of collaborative design loops, integrating owner, design, and construction teams to activate a pedestrian commuter thoroughfare with a landmark structure.

National Council of Structural Engineers Associations

2018

Structural Engineering Summit

SAVE THE DATE OCTOBER 23-26, 2018 SHERATON GRAND

New Buildings $20 Million to $100 Million

CHICAGO, IL

The Center for Character & Leadership Development (CCLD) is an education and research center, supporting the Air Force Academy’s mission to integrate character and leadership development into all aspects of the Cadet experience. The CCLD represents an important and symbolic addition to the U.S. Air Force Academy’s campus, which SOM designed in 1954. With a focus on constructability and maximizing material efficiency, the CCLD’s cantilevering, 105-foot Skylight structure, consisting of a triangulated system of Architecturally Exposed Structural Steel plates of varying depth, interpret the disciplined campus geometry through a unique structural approach.

New Buildings More Than $100 Million Mercedes-Benz Stadium – Atlanta, GA BuroHappold Engineering

As the new home for the National Football League’s Atlanta Falcons and the new Atlanta United, a Major League Soccer team, the multi-purpose Mercedes-Benz Stadium will cover almost 2 million SF and accommodate seating for approximately 80,000 fans, providing a premier venue that will establish a new precedent in the structure of long span roofs.

NCSEA Webinars November 14, 2017 Mass Timber Design: Engineering the Next Generation of Wood Construction Ricky McLain, P.E., S.E. December 7, 2017 Special Inspection for Wood Construction – An overview for Engineers & Inspectors Tim Hart, S.E., LEED AP December 14, 2017 ASCE 7-16 Seismic Provisions Overview John Hooper, P.E., S.E. Register at www.ncsea.com. Courses award 1.5 hours of continuing education after the completion of a quiz. Diamond Review approved in all 50 States.

Webinars run at 10:00 am Pacific, 11:00 am Mountain, 12:00 pm Central, and 1:00 pm Eastern.

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News from the National Council of Structural Engineers Associations

U.S. Air Force Academy Center for Character and Leadership Development – Colorado Springs, CO Skidmore, Owings & Merrill, LLP

STRUCTURE magazine

NCSEA News

New Buildings Less Than $20 Million

Learning / Networking

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

NEW ASCE/SEI Live Webinars – Learn from the Experts November 2: ASCE/SEI 41-17 Seismic Evaluation and Retrofit of Existing Buildings – A Summary of Major Changes November 9: Wind Design for Industrial Facilities Individual Certificate Fee Discontinued. Register at Mylearning.asce.org for these and much more.

Check out the full program of technical sessions and events at www.structurescongress.org. Registration opens early November.

SEI Young Professional Scholarship (35 and younger) to participate at Structures Congress.

Apply by December 1 at www.asce.org/SEI. NEW Scholarship for Students to participate and get involved at Structures Congress.

Apply by January 5 at www.asce.org/SEI-Students.

Membership

Join SEI/ASCE

Join for innovative solutions and learning, to connect with leaders and colleagues, and enjoy member benefits.

Make the most of your membership – get involved in an SEI Committee effort (technical, standards, business/professional) or local Chapter www.asce.org/SEILocal.

Join/Renew at www.asce.org/SEI. Recruit new members and earn rewards at message.asce.org/mgam.

SEI Online

Discover New ASCE 7 Online

ASCE 7 Online is a new interactive platform that offers a user-friendly experience. ASCE 7 Online incorporates interactive tools and features rich functionality such as redlining, toggling between SI and Customary unit measurements, plus the ability for engineers within a firm to share notes and highlights. Individual and Corporate subscriptions available at http://asce7.online.

Students and Young Professionals

Bridging the Gap between College and Professional

Like many students, I joined ASCE in college to participate in the Steel Bridge Competition and to meet fellow students with whom I could study and use as a resource to get through the tough classes.

I enjoyed being able to be a leader of the group and the recognition I received from it. When I finished college and moved on to my professional career, I left ASCE at college. There was no need for Steel Bridge or study buddies anymore. I felt it had served its purpose and was grateful but ready for the next step. Little did I realize how important ASCE is in the next steps... Read more at www.asce.org/SEINews

By Jennifer Zabik, P.E., F.SEI, M.ASCE , ZT Engineering, Winter Garden, FL Recipient of a SEI Young Professional Scholarship to participate at Structures Congress 2014 SEI Local Activities Executive Committee STRUCTURE magazine

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Your Blueprint for the Future

Begin Your Career Search with Career Connections.

• Job listing database w/600+ jobs • Searchable by title, geography, salary and more • Interviewing & resume tips

Careers.asce.org @ASCEJobs

Thank you to 2017 SEI Sustaining Organization Members: Alfred Benesch & Company Boswell Engineering Geopier Foundations

Hardesty & Hanover International Code Council Schnabel Foundation Company

Simpson Gumpertz & Heger Inc. Simpson Strong-Tie Walter P. Moore

SEI Elite Sustaining Organization Members

“As a longtime partner and advocate of SEI and ASCE, Michael Baker shares SEI’s commitment to advance and serve the structural engineering profession.” Kurt Bergman, CEO of Michael Baker International

Learn more and join today at www.asce.org/SEI-Sustaining-Org-Membership.

SEI Futures Fund – Investing in the Future of Structural Engineering As communities at home and abroad continue to recover from this season’s hurricanes, earthquakes, and other natural disasters, structural engineers are hard at work – assessing and rebuilding damaged bridges, buildings, and other structures, and developing better ways to plan and design for greater resilience.

More than ever, structural engineers have a critical role as leaders and innovators to improve the safety and well-being of our communities.

The SEI Vision for the Future is our plan to ensure a bright and dynamic future for structural engineering – to prepare the next generation of structural engineers to be leaders and innovators. The SEI Futures Fund, in partnership with the ASCE Foundation, leverages contributions to fund SEI Vision initiatives such as student and young professional scholarships, global initiatives, and professional development.

Your gift to the SEI Futures Fund will strengthen SEI efforts to build a vibrant community of structural engineers to lead into the future!

Learn more and give at www.asce.org/SEIFuturesFund.

Errata SEI Standards Supplements and Errata including ASCE 7 See www.asce.org/SEI-Errata. If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org.

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The Newsletter of the Structural Engineering Institute of ASCE

As an SEI Elite Sustaining Organization Member, Michael Baker also enjoys complimentary participation in the SEI Student Career Networking Event April 20 at Structures Congress 2018 in Ft. Worth.

Reach more than 30,000 SEI members year-round with SEI Sustaining Organization Membership.

Show your support for SEI to advance and serve the structural engineering profession.

Structural Columns

Advancing the Profession

CASE Practice Guidelines Currently Available

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE 976-A – Commentary on Value-Based Compensation for Structural Engineers The importance of receiving adequate fees for structural services is vital for an engineering practice to thrive. If fees are not adequate, the structural engineering professional becomes a commodity; libraries are not maintained, computer software and equipment becomes out-dated, and the quality of our product declines significantly.

Value-Based Compensation is a product of the concept that there are specific services, which may vary from project to project, that provide valuable information to the client and whose impact on the success of the project is far in excess of prevailing hourly rates. Value-Based Compensation is based on the increased value or savings these innovative structural services will contribute to the project. As a result, the primary beneficiary of an innovative design or a concept is the owner, but the innovative engineer is adequately compensated for his knowledge and expertise in lieu of his time CASE 976-C – Commentary on Code of Standard Practice for Steel Buildings and Bridges The 2010 COSP addresses many recent changes in the practice of designing, purchasing, fabricating, and erecting structural steel and is, therefore, a continuation of the trend of past improvements and developments of this standard. It is important to note the Structural Engineer can change any of the requirements of the Code of Standard Practice by specifying an alternative in the Contract Documents.

This document discusses the list of changes published in the preface to the 2010 Edition and provides some commentary on these changes. This document also addresses areas of the COSP that may not be well understood by some SERs but will likely have an impact on the structural engineer’s practice of designing and specifying structural steel.

CASE 976-D – Commentary on 2010 & 2015 Code of Standard Practice for Steel Joists and Joist Girders The specification for joists and Joist Girders can provide an economic structural solution, but there are very specific requirements that must be understood by all parties. The updated 2010 SJI COSP provides a more practical approach to specifying joists, to introduce new design terms for use by the structural engineer, and to identify and clarify topics that may have been subject to varying interpretation in the past. The more recently released 2015 SJI COSP provides additional clarifications and minor revisions.

This commentary provides observations and analysis of the revisions and additions in both documents and discusses specific aspects of the COSP that have a direct impact on the structural engineer’s practice of specifying steel joists. A familiarity and understanding of the entire SJI COSP is necessary to ensure the proper design and documentation of steel joists and Joist Girders. However, the commentary’s discussion highlights sections of particular interest to the specifying structural engineer.

You can purchase these and other Risk Management Tools at www.acec.org/coalitions/coalition-publications.

CASE’s Business of Structural Engineering Seminar June 6 – 8, 2018; Anaheim, CA Once again, CASE will put on the industry’s only seminar dedicated solely to improving your firm’s business practices and risk management strategies. Come and join us and learn about The Business of Structural Engineering for training and collaboration with industry leaders and project managers from firms of all sizes, intended to improve your structural engineering practice. Immerse yourself in topics designed to help engineers learn better ways of reducing areas of risk and liability on projects while learning about tools to implement better business practices within your firm.

The Seminar is geared towards Owners, Principals, Project Managers, and Risk Managers. If you are concerned with risk management, new trends, and profitability, you cannot afford to miss this event! Registration for the event will open Mid-March, seats will be limited. For more information about this seminar, contact Heather Talbert, htalbert@acec.org or 202-682-4377.

New EJCDC Commentary Now Available!

The EJCDC D-001: Commentary on the 2016 EJCDC Design-Build Documents provides guidelines for use in establishing and administering a contract between a project owner and a design-builder, and for related subcontracts with design professionals, constructors, and advisors.

As a supporting document that is key to the most effective use of the Design-Build Family of Documents, EJCDC D-001 contains: • A summary of the content and use of each of the D-Series documents • Discussion of key preliminary steps on a design-build project • An introduction to D-512, EJCDC’s new Agreement between Owner and Design-Builder for Progressive Design-Build • Commentary regarding noteworthy provisions of the 2016 Standard General Conditions and Supplementary Conditions of the Owner To order your complimentary copy, go to www.acec.org/bookstore.

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The CASE Risk Management Convocation will be held in conjunction with the Structures Congress in Fort Worth, TX, April 19 – 21, 2018. For more information and updates go to www.structurescongress.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 20: 9:30 am – 10:30 am Managing Design Professionals’ Risk in the Design and Construction of Property Line Building Structures Moderator: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. Speaker: Kriton A. Pantelidis, Esq., Welby, Brady & Greenblatt, LLP 11:00 am – 12:30 pm The Good and the Bad of Delegated Design: How to Work With/As a Specialty Structural Engineer Moderator/Speaker: Kevin Chamberlain, DeStefano & Chamberlain Inc. 1:30 pm – 3:30 pm Construction Dispute Resolution through Forensic Engineering Moderator/Speaker: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. 3:30 pm – 5:00 pm Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable Moderator: Corey Matsuoka P.E., SSFM International, Inc.

Leading Innovation, Fostering Growth: Essentials to Achieving a Sustainable, Profitable Business February 1 – 3, 2018; Austin, TX Looking to grow your business? Who isn’t!

Whether it’s how to market, what key firm positions to fill, how to organize the firm into teams, or when it is time to delegate more, it is your leadership that ultimately grows your business. That is why you will want to join other small firm leaders from around the country for an in-depth examination of three strategic agendas your firm will need to become more successful and profitable.

Seminar topics will focus on: • Sustainability – Promoting on-the-job learning and growth, and seeking new ways to improve your management process and protocols • Serviceability – Creating client value and a superior client experience through firm innovation and thought leadership • Survivability – Focusing on consistently generating and investing profits to expand your firm’s influence into current and prospective target markets This seminar is for firm leadership tasked with making decisions, such as owners, principals, HR professionals, CEOs, and CFOs.

Mark has authored numerous articles for industry magazines such as Civil Engineering Magazine, CE News, and ConsultingSpecifying Engineer. He has been quoted many times in various industry publications and newspapers and is featured in the Morrissey Goodale/Axium video series, Building HighPerformance Organizations. Mark was also a frequent contributor to ZweigWhite’s publications and events and authored The Healthcare Market for AEP and Environmental Consulting Firms, the first of ZweigWhite’s market intelligence reports.

Always a top-rated speaker, Mark delivers presentations around the country on a wide variety of management topics at AIA, ACEC, NSPE, CSE, and ZweigWhite events.

Mark received his MBA from the Sawyer School of Business at Suffolk University where he now teaches Business.

Registration ACEC Coalition Members – $399 ACEC Members – $499 Non-members – $599

About the Speaker

Location

Mark Goodale is a co-founder of Morrissey Goodale. His breadth of experience includes organizational development, strategic planning, mergers and acquisitions, marketing, and executive search. He is a trusted advisor and coach to dozens of industry executives.

Before helping to establish Morrissey Goodale, Mark was the Corporate Strategic Marketing Manager at PBS&J (now a part of Atkins) where he was charged with improving and implementing progressive corporate initiatives geared to position the firm for successful, large-scale client pursuits. Before that, he worked at ZweigWhite for over a decade and headed the firm’s strategic business planning and marketing business units.

Hilton Garden Inn Austin Downtown & Convention Center 500 North IH 35 Austin, Texas 78701 Phone: 877-782-9444 use group code: ACEC Special Rate – $189/night until January 4, 2018, or until block sells out To register for the seminar: http://bit.ly/2z2Mbrn Questions? Call 202-682-4377 or email at htalbert@acec.org

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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November 2017

CASE is a part of the American Council of Engineering Companies

2018 Small Firm Council Winter Seminar

CASE in Point

CASE Risk Management Convocation in Fort Worth, TX

Structural Forum

opinions on topics of current importance to structural engineers

Who Hijacked My Plan Review?

By David Pierson, S.E.

H

istorically, societies have placed Many would say that the public at-large has And, often, due to the effort required to probe a high value on professionals, some responsibility to pay for such a review. In so deeply into the design, they are outsourctrusting that those who possess this paradigm, since the structures we design ing this work. Since the cost to taxpayers the higher knowledge associated are integral to society and their proper per- is now excessive, they generally require the therewith will serve the interests of society formance will affect many people, taxpayers applicant to pay for the “review” (more accuwith that knowledge. But now, perhaps due to should pay for some level of review of the rately described as a critique) through assessed political or economic pressures, we find soci- documents. Since they pay the salaries of the fees. This seems wrong. Essentially, they are ety struggling to determine the value of having building department employees, perhaps part mandating a peer review without giving the licensed, regulated professional engineers. of that can justifiably be allocated to plan applicant the right to choose if it is done, Traditionally, the status of being a profes- reviews. In this case, the review should be who will do it, or how much it will cost. If sional comes with an associated increase in a cursory, high-level review. The effort and the jurisdiction wants to have this level of responsibility. As professional structural engi- associated costs should not be more than a control over our work product, then they neers, ours is the responsibility to provide small percentage of the effort put forth by the should stamp the documents and assume the structural designs that protect the health and engineer of record in the course of preparing associated responsibilities and liabilities. safety of those who use them. The significant the documents.

We need to get involved (and it may require risk associated with providing these us to get a bit political) in finding designs is an ever-present reality. As a way to reign in this plan review The trend, however, seems to be toward long as society is willing to recognize process that is morphing into someincreasing government oversight. More and this responsibility by granting us the thing it ought not to be. We should status of a professional license, we make it clear that we deserve to be more, we find the authority having jurisdiction need to remain vigilant in abiding recognized as professionals and, by the high standards of professional delving deeper into the design process, seeking when we stamp construction docupractice associated with structural ments, our clients and the public to find the smallest of errors in our drawings engineering. at large can know that the work and calculations.

So, what does it mean when we complies with the high standards stamp and sign construction docurequired of us. It is not perfect – we ments with a professional engineer’s stamp?

I occasionally submit stamped construction are not perfect – nor do our clients or society I hope it means that we are certifying that, documents and receive the following com- expect us to be perfect. However, we adhere to the best of our knowledge, those docu- ment: “Are you a licensed engineer authorized to our code of ethics, and we only prepare ments comply with the building code and, to perform work in this state?” Having ascer- documents that we are qualified to produce if properly constructed, will result in a safe tained this, the jurisdiction then approves and we stand behind them. Perhaps a limited structural system. We abide by a code of ethics the plans, relying on the state’s professional review is helpful – just to see that we comthat requires it to be so. In accomplishing this licensing board as their means of acting plied with the appropriate code and that our work, it is our responsibility to have proper in good faith to protect the citizens under load path appears to be complete. However, QA/QC procedures in place, which may their jurisdiction. This approach seems to be enough of the endless critiques. Stop letting include an independent peer review. more common in states where the prevailing jurisdictions force owners (or the public) to Generally, the documents we prepare are political attitude leans toward smaller, limited pay to have our work evaluated, line by line, submitted to a jurisdiction. What, then, government. This certainly shows significant by a person (often not even licensed as a prois the purpose of a plan review conducted respect for the status of a licensed professional fessional engineer) who is being paid hourly, by this jurisdiction? This is a complicated engineer. has no incentive to stop critiquing, and has issue and crosses over into a political realm.

The trend, however, seems to be toward no skin in the game.▪ However, it seems to boil down to a simple increasing government oversight. More and matter – how much does the jurisdiction more, we find the authority having jurisdicDavid Pierson (davep@arwengineers. trust us? Perhaps they believe that there tion delving deeper into the design process, com) is a Vice President at ARW Engineers should be a “belt and suspenders” approach seeking to find the smallest of errors in our in Ogden, Utah. He currently serves as – that an independent review may find drawings and calculations. They are acting vice-chairman of TMS 402/602 and is past something inadvertently overlooked by the more like a professor grading an exam. They chairman of the Utah Uniform Building engineer. This may be justified, but who look for opportunities to reject decisions we Codes Commission. should pay for that? make utilizing our professional judgment.

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

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