STRUCTURE magazine - June 2018 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

Â®

June 2018 Tall Buildings Inside: One Seaport Tower, New York City

A new standard for exposed structure CAST CONNEX Universal Pin Connectors in the Whitney Museum of American Art by Renzo Piano Building Workshop

www.castconnex.com

innovative components for inspired designs

LeMessurier Calls on Tekla Structural Designer for Complex Projects Interoperability and Time Saving Tools

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties, including technicians, fabricators and architects. Its unique functionality enables engineers to integrate the physical design model seamlessly with Tekla Structures or Autodesk Revit, and to round-trip without compromising vital design data. “We’re able to import geometry from Revit, design in Tekla Structural Designer and export that information for import back into Revit. If an architect makes geometry updates or changes a slab edge, we’ll send those changes back into Tekla Structural Designer, rerun the analysis and design, and push updated design information back into Revit.”

Tekla Structural Design at Work: The Hub on Causeway

For over 55 years, LeMessurier has provided structural engineering services to architects, owners, contractors, developers and artists. Led by the example of legendary structural engineer and founder William LeMessurier, LeMessurier provides the expertise for some of the world’s most elegant and sophisticated designs while remaining true to the enduring laws of science and engineering. Known for pushing the envelope of the latest technologies and even inventing new ones, LeMessurier engineers solutions responsive to their clients’ visions and reflective of their experience. An early adopter of technology to improve their designs and workflow, LeMessurier put its own talent to work in the eighties to develop a software solution that did not exist commercially at the time. Their early application adopted the concept of Building Information Modeling (BIM) long before it emerged decades later. While LeMessurier’s proprietary tool had evolved over three decades into a powerhouse of capability, the decision to evaluate commercial structural design tools was predicated on the looming effort required to modernize its software to leverage emerging platforms, support normalized data structure integration and keep up with code changes. After a lengthy and thorough comparison of commercial tools that would “fill the shoes” and stack up to the company’s proprietary tool, LeMessurier chose Tekla Structural Designer for its rich capabilities that addressed all of their workflow needs. According to Derek Barnes, Associate at LeMessurier, ” Tekla Structural Designer offered the most features and the best integration of all the products we tested. They also offered us the ability to work closely with their development group to ensure we were getting the most out of the software.”

One Model for Structural Analysis & Design

From Schematic Design through Construction Documents, Tekla Structural Designer allows LeMessurier engineers to work from one single model for structural analysis and design, improving efficiency, workflow, and ultimately saving time. “Our engineers are working more efficiently because they don’t need to switch between multiple software packages for concrete and steel design. Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product,” said Barnes. LeMessurier engineers use Tekla Structural Designer to create physical, information-rich models that contain the intelligence they need to automate the design of significant portions of their structures and efficiently manage project changes. TRANSFORMING THE WAY THE WORLD WORKS

“Tekla Structural Designer has streamlined our design process,” said Craig Blanchet, P.E., Vice President of LeMessurier. “Because some of our engineers are no longer doubling as software developers, it allows us to focus their talents on leveraging the features of the software to our advantage. Had we not chosen to adopt Tekla Structural Designer, we would have needed to bring on new staff to update and maintain our in-house software. So Tekla Structural Designer is not just saving us time on projects, it is also saving us overhead.

Efficient, Accurate Loading and Analysis

Tekla Structural Designer automatically generates an underlying and highly sophisticated analytical model from the physical model, allowing LeMessurier engineers to focus more on design than on analytical model management. Regardless of a model’s size or complexity, Tekla Structural Designer’s analytical engine accurately computes forces and displacements for use in design and the assessment of building performance.

“Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product.”

Positioning a large scale mixed-use development next to an active arena, a below grade parking garage, and an interstate highway, and bridging it over two active subway tunnels makes planning, phasing and engineering paramount. Currently under construction, The Hub on Causeway Project will be the final piece in the puzzle that is the site of the original Boston Garden. Despite being new to the software, LeMessurier decided to use Tekla Structural Designer for significant portions of the project. “Relying on a new program for such a big project was obviously a risk for us, but with the potential for time savings and other efficiencies, we jumped right in with Tekla Structural Designer. It forced us to get familiar the software very quickly.” “Tekla Structural Designer allowed us to design the bulk of Phase 1 in a single model,” said Barnes. The project incorporates both concrete flat slabs and composite concrete and steel floor framing. “Tekla Structural Designer has the ability to calculate effective widths based on the physical model which is a big time saver,” said Barnes. “On this project, the integration with Revit, along with the composite steel design features enabled us to work more efficiently. Adding the ability to do concrete design in the same model was a bonus because we had both construction types in the same building.” “Tekla Structural Designer helped this project run more efficiently, and in the end it was a positive experience,” said Blanchet.

“Tekla Structural Designer gives us multiple analysis sets to pull from, which gives us lots of control. Most programs don’t have the capability to do FE and grillage chase-down. For the design of beam supported concrete slabs, Tekla Structural Designer allows us to separate the slab stiffness from the beam stiffness, so if we choose to we can design the beams without considering the influence of the slab. In the same model we can use a separate analysis set to review the floor system with the beams and slab engaged,” said Barnes. Barnes also shared similar benefits with concrete column design. “Tekla Structural Designer does grillage take-downs floor-by-floor, finds the reactions and applies them to the next floor. This allows us to view column results both for the 3-dimensional effects of the structure as a whole and from the more traditional floor-by-floor load take-down point of view. Doing both has always required significant manual intervention, but Tekla Structural Designer puts it all in one place.” “We reduce the possibility for human error because with Tekla Structural Designer less user input is required,” said Barnes. “Tekla Structural Designer automatically computes many of the design parameters, such as column unbraced lengths. The assumptions made by the software are typically correct, but we can easily review and override them when necessary.”

“Tekla Structural Designer provided the best fit for our workflow compared to other commercially available software.”

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

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

American Concrete Institute ......................8 Cast Connex ..............................................2 Concrete Reinforcing Steel Institute .........15 Cortec Corporation ..................................40 Decon USA Inc. .......................................21 Fyfe ..........................................................13 Geopier Foundation Company.................33 Hayward Baker Inc. .................................25 Hohmann & Barnard, Inc. .......................35 ICC..........................................................39 Independence Tube Corporation ..............43

Integrity Software, Inc. ...............................8 ITT Enidine Inc. .....................................37 KPFF .......................................................50 NCEES ....................................................36 New Millennium Building Systems ..........23 RISA Technologies ...................................52 StructurePoint ............................................6 Simpson Strong-Tie............................17, 29 Trimble ......................................................3 Weyerhaeuser ...........................................41

STRUCTURE

MARKETING & ADVERTISING SALES sales@STRUCTUREmag.org Joe Murphy jmurphy@STRUCTUREmag.org; Tel: 203-254-9595 Denis O’Malley domalley@STRUCTUREmag.org; Tel: 203-356-9694, ext. 13

EDITORIAL STAFF Executive Editor Alfred Spada aspada@ncsea.com Publisher Christine M. Sloat, P.E. csloat@STRUCTUREmag.org Associate Publisher Nikki Alger nalger@STRUCTUREmag.org

DID YOU KNOW?

Creative Director Tara Smith graphics@STRUCTUREmag.org

As part of the Structural Engineering community, STRUCTURE encourages you to comment on articles!

EDITORIAL BOARD Chair Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@STRUCTUREmag.org

All STRUCTURE articles are posted to

Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT

the website, www.STRUCTUREmag.org.

Erin Conaway, P.E. SidePlate Systems, Phoenix, AZ

Scroll to the end of the article to post a comment. Authors are encouraged to

John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA

reply to your comments when applicable.

Linda M. Kaplan, P.E. TRC, Pittsburgh, PA

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

Timothy M. Gilbert, P.E., S.E., SECB TimkenSteel, Canton, OH

Important news for Bentley Users

Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY Brian W. Miller Davis, CA Emily B. Lorenz, P.E. Precast/Prestressed Concrete Institute, Chicago, IL Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT

• Prevent Quarterly and Monthly Overages • Control all Bentley® usage, even licenses you do not own • Give users visibility of who is using licenses now • Warn and Terminate Idle usage

SofTrack controls Bentley® usage by Product ID code and counts (pipe, inlet, pond, and all others) and can actively block unwanted product usage SofTrack reports and optionally controls usage of all Autodesk® products by Version, Feature Code, and Serial Number!

Additionally, SofTrack provides software license control for all your applications including full workstation auditing of files accessed and websites visited. Many customers also benefit from SofTrack’s workstation specific logon activity reporting. © 2017 Integrity Software, Inc. Bentley is a registered trademark of Bentley Systems, Incorporated

STRUCTURE magazine

SofTrack reports and controls ESRI® ArcMap concurrent and single use license activity

June 2018

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

STRUCTURE® magazine (ISSN 1536 4283) is published monthly by The National Council of Structural Engineers Associations (a nonprofit Association), 645 N. Michigan Ave, Suite 540, Chicago, IL 60611 312.649.4600. Application to Mail at Periodicals Postage Prices is Pending at Chicago, IL and additional mailing offices. STRUCTURE magazine, Volume 25, Number 6, C 2018 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership. Yearly Subscription in USA $75; $40 For Students; Canada $90; $60 for Canadian Students; Foreign $135, $90 for foreign students. Editorial Office: Send editorial mail to: STRUCTURE magazine, Attn: Editorial, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. POSTMASTER: Send Address changes to STRUCTURE magazine, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. STRUCTURE is a registered trademark of the National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

CONTENTS

Cover Feature

Features 18 COLOSSAL INTIMACY By Sarah A. Jorczak, P.E., LEED AP BD+C, and Kevin Borth, P.E., S.E. The structural team for the Church of the Resurrection in Leawood, Kansas, was able to manipulate the building structure and the design software to work within the confines of the complex geometry of a non-orthogonal building shape.

26 STACKED FRUSTUMS CREATE CHICAGO’S NEWEST SUPER-TALL TOWER By David Fields, P.E., S.E., and Ronald Klemencic, P.E., S.E., Hon. AIA The iconic building geometry of Vista Tower with its never-before-seen alternating-stacked frustum geometry posed many challenges for the structural team, challenges well met for this super-tall tower.

22 ONE SEAPORT TOWER

30 BLACK ROCK LIGHTHOUSE SERVICE

By Jeffrey Smilow, P.E., Patrick Chan, P.E., and Ilya Shleykov, Ph.D., P.E. Implementation of an alternative foundation system vetted by

By Erik Kneer, S.E., Erik McGregor, P.E., C.P.Eng., and Mary Kretschmar, P.E.

extensive nonlinear analysis of the combined Superstructure-

The structural engineering for this artwork required a defined “tilt” to the segments of

Foundation-Soil system resulted in a sound structural solution for this

the piece, a need for rapid assembly, and to accommodate a full burn at the end of

high-performance residential tower located in downtown Manhattan.

its display at the Burning Man Festival.

Columns and Departments

CASE BUSINESS PRACTICES

STRUCTURAL TESTING

14 Wind Tunnel Testing for Tall Buildings

42 Does Your Firm Have a Lessons-Learned Process?

By Roy Denoon, Ph.D.

By Bruce Burt, P.E., SECB

STRUCTURAL REHABILITATION

STRUCTURAL FORUM

EDITORIAL

7 Being Civil in an Electrical World By Otto J. Lynch, P.E.

34 Wood Bowstring Trusses By Gloriana Arrieta Martinez, Ph.D.,

CODES AND STANDARDS

Filippo Masetti, P.E., and

9 C hanges to the 2018 Wood Frame Construction Manual

By Edward Major II, E.I.T.

Milan Vatovec, Ph.D., P.E.

By John “Buddy” Showalter, P.E., Bradford K. Douglas, P.E., and Philip Line, P.E.

INSIGHTS

12 Bridges, Fire, and the Structural Engineer Spencer E. Quiel, Ph.D., P.E., and Stephen P. Pessiki, Ph.D.

51 Advantages of Professional Young Member Groups

STRUCTURAL FAILURES

38 The Site Professional’s Value to Legal Defense By John L.A. Lyddane, Esq.

IN EVERY ISSUE 4 Advertiser Index 50 Resource Guide – Tall Buildings 44 NCSEA News 46 SEI Structural Columns 48 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.

STRUCTURE magazine

June 2018

Editorial Being Civil in an Electrical World By Otto J. Lynch, P.E., F.SEI, F.ASCE

y favorite toy as a child was an erector set. Not the fancy new ones that have the precut plastic panels and big rubber tires, but the old ones that were all metal, including the wheels. My favorite structures to build were buildings and bridges. Of course, this led to my desire to be a Civil/Structural Engineer, so I could design and build real buildings and bridges. As a college senior interviewing for what would ultimately be my first job at Black & Veatch, I was asked if I would be interested in designing and building power lines instead of buildings and bridges. “Isn’t that a job for Electrical Engineers?” I asked. It was explained that transmission lines were merely gigantic multiple-span suspension bridges made up of steel, concrete, wood, aluminum, and other materials that required surveying, site work, foundations, and of course project and construction management. Sounds like structural engineering to me!

Every three years, the ETS committee holds a conference specifically for Electrical Transmission and Substation Structures. At the last conference, there were more than 1200 attendees from 20 countries in attendance. Our next conference is November 4 – 8, 2018, in Atlanta. The theme is Dedicated to Strengthening our Critical Infrastructure. 35 papers from nearly 200 abstracts submitted were selected to be presented in a single track at the conference. In addition to the technical sessions, there will be an exhibit hall with over 100 exhibitors and a workshop on the latest developments in ASCE Standards and Manuals of Practices. For program information, see etsconference.org. If you are even remotely interested in learning more about this industry, we invite you to attend. The ASCE Committee on America’s Infrastructure (CAI) issues a Report Card for America’s Infrastructure (infrastructurereportcard.org) every four years; the last one was issued in 2017. I am one of the Energy representatives on CAI. The Energy sector received a grade of D+, which was no change over the 2013 grade. Like most of our infrastructure in America, our electric grids are old and weak. We are also experiencing a change in generation, with renewable energies not being placed where the coal plants are being retired. At the same time, the public is expecting a more consistent and reliable supply of electricity than we have had in the past. Thus, we are experiencing a heightened awareness of outages due to extreme weather events. Our industry is in what I term “The Perfect Storm” and is growing rapidly as we essentially are having to rewire America. It has been thirty years since first realizing that Civil/Structural Engineers play a vital role in our electrical grids, and I have not looked back once on this career choice. I would encourage any younger engineers that might be looking for a fun, challenging, and fastpaced career in a growing business sector to consider looking into becoming a Transmission Line Engineer. If you already are involved in other structural engineering industries but are looking to expand into another market, come to the ETS Conference in Atlanta in November and learn about our industry. Maybe I need to find an old erector set so I can build a transmission tower now.▪

It is surprising to hear people even within our profession that think of transmission and distribution power lines as something that electrical engineers do. While there is obviously a lot of electrical engineering involved in our power grids, once the wires are sized for a transmission line, the rest of it is mostly structural. In fact, ASCE is quite active in the transmission line industry. Under SEI, there are two Standards, ASCE-10 Design of Latticed Steel Transmission Structures and ASCE-48 Design of Steel Transmission Pole Structures. Both standards are used and referenced worldwide. Also, under SEI is the Electrical Transmission Structures (ETS) technical administrative committee. This committee is over many other committees that develop Manuals of Practices for wood pole structures, fiberglass pole structures, concrete pole structures, substation structures, and even loadings which interprets ASCE 7 specifically for overhead power lines and addresses other important loading and design considerations unique to our industry. While I happen to think that all transmission lines are beautiful, there is even a committee on aesthetics that is currently authoring a white paper to assist engineers in making more aesthetically pleasing structures and lines. STRUCTURE magazine

View ASCE’s video, Interchange on Protecting Our Nation’s Power Grid, at https://bit.ly/2r378PT Otto Lynch is President and CEO of Power Line Systems Inc. and has been involved in the design and construction of numerous transmission line projects around the world. He was the pioneer of the then newly emerging LiDAR technology with transmission line design. Otto is an active member on nearly every ASCE, IEEE, and ANSI committee that deals with the physical design and analysis of overhead power lines and is a voting member of both Subcommittee 5 and the Main Committee of the National Electrical Safety Code. He was honored in 2012 with the ASCE Gene Wilhoite Innovations in Transmission Line Engineering Award.

June 2018

New Member Benefits Including Unprecedented Digital Access to the Institute’s 200+ Guides and Reports

Other new benefits for individual members include:

• Free media mail shipping • Discounted access to ACI codes and specifications • Discounted access to ACI University’s monthly webinars and on-demand course subscription

Plus ACI’s existing membership benefits.

www.concrete.org/membership

he 2018 Edition of the Wood Frame Construction Manual (WFCM) for Oneand Two-Family Dwellings, designated ANSI/ AWC WFCM-2018, is approved as an ANSI American National Standard (Figure 1). The 2018 WFCM was developed by the American Wood Council’s (AWC) Wood Design Standards Committee (WDSC) and is referenced in the 2018 International Residential Code (IRC) and 2018 International Building Code (IBC). Tabulated engineered and prescriptive design provisions in WFCM Chapters 2 and 3, respectively, are based on the following loads from ASCE/SEI 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures (Figure 2): • 0-70 psf ground snow loads • 90-195 mph 3-second gust basic wind speeds for risk category II buildings • Seismic Design Categories A-D The WFCM includes design and construction provisions for connections, wall systems, floor systems, and roof systems. A range of structural elements is covered, including sawn lumber, structural glued laminated timber, wood structural panel sheathing, I-joists, and trusses. Primary changes to the 2018 WFCM are listed here, and major topics are subsequently covered in more detail: • Updated wind loads from ASCE/SEI 7-10 to ASCE/SEI 7-16 • The inclusion of lower wind speed categories (e.g., 90, 95, 100, and 105 mph) to coordinate with ASCE/SEI 7-16 • Updated fastener criteria to coordinate with 2018 National Design Specification® (NDS®) for Wood Construction including provisions for roof sheathing ring shank (RSRS) nails and fastener head pull-through design values • Revised provisions for roof rake overhangs at gable ends • Revised shear wall assembly allowable unit shear capacities, maximum shear wall segment aspect ratios, and sheathing type adjustments incorporate updated aspect ratio adjustments to be consistent with the 2015 Special Design Provisions for Wind and Seismic (SDPWS)

ASCE/SEI 7-16 Revised Wind Loads The majority of changes to the 2018 WFCM were developed to address increased component and cladding (C&C) wind pressures in ASCE/SEI 7-16. Lower wind speed categories (e.g., 90, 95, 100, and 105 mph) were also added consistent with ASCE/SEI 7-16. For a summary of ASCE 7-16 wind provisions, see the 2017 NCSEA Webinar titled “ASCE 7-16 Wind Provisions – How they affect the Practicing Engineer” by Don Scott, Chair of

both the ASCE 7-16 Wind Load Subcommittee and NCSEA Wind Engineering Committee. Wind pressure changes for roof design can be summarized as follows: • New C&C roof pressure coefficients increase localized pressures on roofs • New C&C roof pressure zones have been added • Interior C&C roof pressures have the most substantial increase on a percentage basis Table 1a (page 10) provides a comparison of ASCE/SEI 7-16 to ASCE/SEI 7-10 C&C roof coefficients, and Table 1b (page 10) provides the same comparison for the larger roof overhang coefficients. Figure 3 (page 10) provides an overview of the various roof zones as defined in ASCE/SEI 7-16 for a gable roof with roof slopes between 7 and 45 degrees. Tables 1a and 1b also show the roof coefficients as implemented for 2018 WFCM chapters 2 and 3. WFCM Chapter 2 uses the maximum magnitude suction loads for roof slopes between 7 and 45 degrees in Roof Zones 1, 2, and 3. WFCM Chapter 3 further simplifies the roof loading requirements by combining Roof Zones 2 and 3 into an end zone and reducing the magnitude of Zone 3 loads by limiting rake overhangs. As a result of these simplifications, the effective uplift pressures on critical roof edge and overhang zones is limited to an 11% increase in WFCM Chapter 3 requirements as shown in Tables 1a and 1b (e.g., -4.1 coefficient under ASCE 7-16 versus -3.7 coefficient under ASCE 7-10). This results in a smaller increase in uplift load requirements between editions of the WFCM than the actual percent increase in design pressures between ASCE/SEI 7-10 and ASCE/SEI 7-16.

CODES AND

standards

Changes to the 2018 Wood Frame Construction Manual By John “Buddy” Showalter, P.E., Bradford K. Douglas, P.E., and Philip Line, P.E. John “Buddy” Showalter is Vice President of Technology Transfer, Bradford K. Douglas is Vice President of Engineering, and Philip Line is Senior Director of Structural Engineering with the American Wood Council. Contact Mr. Showalter (bshowalter@awc.org) with questions.

Roof Rake Overhangs Rake overhang provisions were revised to clarify terminology and limit rake overhang lookout blocks to 9 inches (previously limited to 12 inches) based on increased wind pressures (Figure 4a, page 11). Rake overhang outlooker provisions were expanded to tabulate requirements for overhang spans of 12, 16 and 19.2 inches in addition to 24 inches previously tabulated (Figure 4b, page 11). The smaller span cases were added to address increased wind pressures and remove Figure 1. The 2018 WFCM is conservatism associ- referenced in the 2018 IRC and ated with tabulated 2018 IBC.

STRUCTURE magazine

June 2018

Figure 2. The majority of changes to the 2018 WFCM reflect increased C&C wind pressures in ASCE/SEI 7-16.

Table 1a. Comparison of C&C roof coefficients a (suction).

requirements based only on assumed 24-inch overhang span.

Changes to Fastener Design Wind uplift related changes include new fastener withdrawal and new fastener head pull-through design provisions. Roof Sheathing Ring Shank Nails

ASCE 7-16

ASCE 7-10

Roof GCp - GCpi

-3.8 -3.2 -3.2 -3.2 -2.2 -2.2 -2.8 -2.8 -1.9 -1.9 -1.9 -1.1

20 < Θ ≤ 27

-3.8 -2.7 -2.7 -2.7 -1.7 -1.7 -2.8 -2.8 -1.9 -1.9 -1.9 -1.1

27 < Θ ≤ 45

-2.2 -3.4 -2.2 -2.0 -2.0 -2.0 -1.4 -1.4 -1.4 -1.4 -1.4 -1.2

Maximum (suction) -3.8 -3.4 -3.2 -3.2 -2.2 -2.2 -2.8 -2.8 -1.9 -1.9 -1.9 -1.2

Roof Sheathing Ring Shank (RSRS) nails were recently added to ASTM F 1667 Standard Specification for Driven Fasteners: Nails, Spikes, and Staples. Design provisions for RSRS nails have been added to the 2018 NDS and 2018 WFCM. RSRS nails, which have larger withdrawal design values than smooth shank nails of equal length and diameter, provide additional options for efficient attachment of wood structural panel roof sheathing. In many cases, specification of RSRS nails will produce a reduced roof sheathing attachment schedule than permissible by use of smooth shank nails and enable the use of a single minimum fastener schedule for roof perimeter edge zones and interior zones. Recognition of higher withdrawal strength is based on the presence of 1½-inch length of standardized ring deformations on the nail. Fastener Head Pull-through Provisions Fastener head pull-through design in accordance with NDS 2018 is incorporated into sheathing attachment requirements for resistance to wind uplift/suction forces. For the design of roof sheathing fastening to resist wind uplift, the lesser of the head pull-through design value or the fastener withdrawal design value from wood is used to establish the “fastener uplift capacity,” as shown in Figure 5. Example Compare fastener uplift capacity of 8d Common and RSRS-03 nails as shown in

WFCM Ch. 2 Simplified

-3.8

-2.2

-3.2

WFCM Ch. 3 Simplified

-2.8

-1.9

-2.2

-4.1b

-1.2

-3.7

-1.2

Table 1b. Comparison of C&C roof overhang coefficients (suction). ASCE 7-16

ASCE 7-10 Roof Overhang GCp

Roof Overhang GCp 3r 7 < Θ ≤ 20

-4.7 -4.1 -3.5 -3.5 -2.5 -2.5 -3.7 -3.7 -2.2 -2.2 -2.2

1 -

20 < Θ ≤ 27

-4.7 -3.6 -3.0 -3.0 -2.0 -2.0 -3.7 -3.7 -2.2 -2.2 -2.2

27 < Θ ≤ 45

-2.8 -4.0 -2.8 -2.6 -2.6 -2.6 -2.0 -2.0 -2.0 -2.0 -2.0

Maximum (suction)

-4.7 -4.1 -3.5 -3.5 -2.6 -2.6 -3.7 -3.7 -2.2 -2.2 -2.2

WFCM Ch. 2 Simplified

-4.7

WFCM Ch. 3 Simplified

-3.5 -4.1b

-c -c

-3.7

-2.2 -3.7

a. C&C roof coefficients include external and internal pressures assuming an enclosed structure. b. In 2018 WFCM Chapter 3, the maximum length of rake overhangs (without outlookers) has been limited to 9 inches, so the effective GCp value in overhang zone 3r is less than non-overhang zone 3r or overhang zone 3e. c. In 2018 WFCM Chapter 3, the maximum length of eave and rake overhangs has been limited to 2 feet, so a Zone 1 Overhang would never exist since the edge dimension “a” is always greater than 2 feet.

Figure 5. Fastener uplift capacity is the lesser of withdrawal and head pull through. Assume 180 mph Exposure B wind loads, 19 ⁄32-inch WSP sheathing, framing specific gravity (G) = 0.49 or higher, and rafter spacing = 24 inches. Using 2018 WFCM Table 3.10, the required nailing pattern (i.e., panel edge/panel field) at roof perimeter zones and interior zones is shown in Table 2. In this case, the RSRS nail provides nailing pattern options that reduce required nailing when compared to 8d common smooth shank nails.

Shear Wall Assemblies

Figure 3. Overview of various gable roof zones as defined in ASCE/SEI 7-16.

7 < Θ ≤ 20

Shear wall aspect ratio adjustments were revised to be consistent with the 2015 SDPWS. Shear walls using gypsum wallboard are subject to the following limits (underlines show clarifying text added to 2018 WFCM): Gypsum wallboard walls having aspect ratios exceeding 1.5:1 shall be blocked. Where shear walls are gypsum wallboard only, the maximum aspect ratio shall not exceed 2:1 in accordance with AWC/ANSI Special Design STRUCTURE magazine

June 2018

Provisions for Wind and Seismic (SDPWS) Table 4.3.4. Requirements for shear walls with blocked wood structural panel sheathing are now tabulated assuming a maximum shear wall segment aspect ratio for wind of 2:1 (previously 3.5:1). However, the 2018 WFCM still allows aspect ratio increases up to 3.5:1 for walls with blocked WSP sheathing or structural fiberboard sheathing, provided the unit shear capacity and sheathing type adjustment factor are adjusted in accordance with 2015 SDPWS Section 4.3.3.4.1 Exception 1 for wood structural panel shear walls or Exception 2 for structural fiberboard shear walls.

Applicability to Non-Residential Structures IBC 2309 allows for use of the WFCM for non-residential structures within its scoping limitations: (IBC) 2309.1 Wood Frame Construction Manual. Structural design in accordance with the AWC WFCM shall be permitted

for buildings assigned to Risk Category I or II subject to the limitations of Section 1.1.3 of the AWC WFCM and the load assumptions contained therein. Structural elements beyond these limitations shall be designed in accordance with accepted engineering practice. While WFCM provisions are intended primarily for detached one- and two-family dwellings due to the floor live load assumption associated with those occupancies, many of the WFCM provisions for specific geographic wind, seismic, and snow loads may be applicable for other buildings. For example, wind provisions for sizing of roof sheathing, wall sheathing, fastening schedules, uplift straps, shear anchorage, shear wall lengths, and wall studs for out of plane wind loads are included in the WFCM and are applicable for other use groups within the load limitations of the WFCM tables. Similarly, roof rafter size and spacing for heavy snow and shear wall lengths and anchorage for seismic are applicable within the load limitations of the WFCM tables. Examples of non-residential applications include single-story wood structures or top stories in mixed-use structures in Risk Categories I or II. Applications outside the scope of the WFCM tabulated requirements, such as the design of floor joists and supporting gravity elements for floor live loads greater than 40 psf are beyond the applicability of the WFCM

a) Lookout block detail.

b) Outlooker detail.

Figure 4. Rake overhang outlooker and lookout block details (excerpted from 2018 WFCM).

and must be designed in accordance with accepted engineering practice. This parallels the approach taken in IRC Section R301.1.3, which permits unconventional elements of one- and two-family dwellings to be designed per the IBC.

Table 2. Comparison of RSRS-03 to 8d common nailing patterns for high wind.a Nail Type

Roof Perimeter Zone Nail Spacing (o.c. WSP edge/interior, inches)

Roof Interior Zone Nail Spacing (o.c. WSP edge/interior, inches)

RSRS-03 (L=2.5”, TL=1.5”, D=0.131”, H=0.281”)

6/6

6/12

8d Common (L=2.5”, D=0.131”, H=0.281”)

4/4

6/6

a. Assume 180 mph Exposure B wind loads, 19⁄32-inch WSP sheathing, framing specific gravity (G) = 0.49 or higher, and rafter spacing = 24 inches. b. TL = thread length, D = diameter, H = head diameter, L = length.

Figure 5. Excerpt from 2018 WFCM Table 3.10 showing fastener uplift capacity controlled either by nail withdrawal capacity or head pull-through.

STRUCTURE magazine

June 2018

More Details A section by section list of changes to the WFCM is available in the Appendix included in the online version of this article. Visit www.STRUCTUREmag.org.

Availability The 2018 WFCM is currently available in electronic format (PDF) only. Once the WFCM Commentary is updated, printed copies will be available for purchase. Check the AWC website (www.awc.org) for status updates on the 2018 WFCM.

Conclusion The 2018 WFCM represents the state-ofthe-art for the design of wood members and connections. The 2018 WFCM updates pre-engineered design provisions based on loads from ASCE 7-16 and design requirements from the 2018 NDS and 2015 SDPWS. Both the 2018 IRC and 2018 IBC reference the 2018 WFCM for the design of wood structures.▪ Watch for an upcoming article on navigating the new ASCE 7-16 and 2018 IRC requirements for determining components and cladding roof pressures.

R INSIGHTS

ecent events have repeatedly reminded the engineering community that our transportation infrastructure is susceptible to fire from crashed or overturned vehicles, especially from trucks carrying flammable cargo. Despite these hazards, most bridges in the U.S. are designed and maintained with little, if any, consideration for fire resistance. With approximately 600,000 bridges currently in use in the U.S., fire has caused bridge failures at a rate consistent with other hazards to which engineers dedicate significant amounts of time and money to mitigate. A recent study from the State University of New York at Buffalo surveyed 1,062 bridge failures across the U.S. between 1980 and 2012 (Lee et al., 2013). As shown in Figure 1, common hazards such as flooding, collision, and overload constitute the majority of bridge failures; however, fire causes failure at a rate at least com-

Bridges, Fire, and the Structural Engineer Spencer E. Quiel, Ph.D., P.E., and Stephen P. Pessiki, Ph.D. Spencer E. Quiel is the P.C. Rossin Assistant Professor of Structural Engineering at Lehigh University. Professor Quiel is a past member of the ASCE Fire Protection Committee (2008-17) and is the current vice chair of the PCI Blast Resistance and Structural Integrity Committee. He can be reached at squiel@lehigh.edu. Stephen P. Pessiki is a Professor of Structural Engineering at Lehigh University. Professor Pessiki is a current member of the ACI Committee 216, Fire Resistance and Fire Protection of Structures. He can be reached at pessiki@lehigh.edu.

Fire is not explicitly addressed in the current AASHTO bridge design criteria (AASHTO, 2017), nor is it in most state DOT bridge design manuals. At best, wildfire exposure is briefly mentioned as a consideration in some state DOT documents such as those from Caltrans (2017), but the tanker and cargo truck design scenarios are not directly addressed. The most significant guidance is provided by NFPA 502, which addresses the design of both bridges and tunnels for fire exposure (NFPA 2017). According to Chapter 6 of that standard, the primary structural elements of bridges or elevated highways shall be protected to achieve the following functional requirements: 1) support firefighter accessibility; 2) mitigate structural damage and prevent progressive collapse; and 3) minimize economic impact. The document also states that an “engineering analysis” is needed to determine whether the collapse of the bridge due to fire would have adverse impacts to life safety or other unacceptable implications. The analyst should determine a design fire size and heat release produced by vehicles near or under the bridge. For truss or cable supported bridges, engineering analysis is explicitly required. While the type of “engineering analysis” is not defined, its results would presumably determine the acceptable risk due to fire, including possible collapse scenarios. However, little guidance is provided regarding the available approaches and performance objectives for such an analysis. The document also states that its design provisions only apply for bridges more than 1000 feet (300 m) in length, although most of the overpasses that have collapsed in the last 15 years have lengths under this cutoff. The standard is also unclear as to whether the 1000 feet corresponds to the total length of elevated highway or just the length of each span.

parable to or exceeding those due to earthquake or construction defects, both of which are extensively addressed via design and inspection. Tanker trucks carrying gasoline and diesel have contributed to most of the recent severe bridge fire events, including the total collapse of two spans in the MacArthur Maze I-80//I-580/I-880 interchange overpass in Oakland, CA, in 2007 (Figure 2). Also of concern are flammable materials that are stored underneath bridges, as was the case for the very recent total collapse of an I-85 overpass in Atlanta, GA in March 2017, when a large quantity of HDPE pipe caught fire under the bridge. Fire incidents for long-span bridges include a 2014 fire of a cargo truck on the deck of the Zakim Bridge in Boston, as well as several incidents of single car fires on major bridges in New York City. Fortunately, these fires have generally resulted in minor to moderate structural damage with no collapse, since the fires were relatively small compared to those from tanker trucks. Since most long-span bridges do not restrict the transport of fuel and other hazardous cargo on their roadways, recent infrastructure projects have increasingly specified design scenarios that include tanker truck fires as part of a Threat, Vulnerability, and Risk Figure 1. Cause of failure as a percentage of total surveyed bridge failures (Lee et al., 2013) Assessment (TVRA). STRUCTURE magazine

12 June 2018

The results of this methodology can be used to develop fire mitigation strategies for bridge structures. The further development of tools to fulfill the “engineering analysis” of NFPA 502 and the performance objectives of bridge owners remains an ongoing need for the structural design community.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

STRUCTURE magazine

Figure 2. 2007 tanker truck fire at the MacArthur Maze freeway interchange near Oakland, CA. Courtesy of Philip Liborio Gangi, (https://bit.ly/2HxzI2w).

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

Going forward, there have been several recent studies which have proposed new methods to evaluate the risk, vulnerability, and consequence of a bridge failure based on bridge characteristics, location, and traffic load (Naser and Kodur, 2015). Approaches such as these can help owners and consultants determine where mitigation may be warranted beyond the simplistic 1000-foot length cutoff in NFPA 502. The “engineering analysis” of a bridge’s response to a vehiclebased fire hazard would then consist of four steps (Quiel et al., 2015): 1) Determine the fire’s characteristics: The analyst should determine the fuel source as well as the fire’s potential footprint, flame height, and intensity. This step will produce a heat release rate, duration, and fire geometry. 2) Calculate the heat transfer from the fire to the structural elements: The analyst should carefully consider how the fire is oriented toward the structural elements. If directly underneath, the flames and smoke plume may engulf the elements and provide both radiative and convective heat transfer. If the fire is adjacent to the elements but not underneath or engulfing them, radiation from the flame and smoke will be the primary mode of heat transfer. 3) Calculate the temperature increase of the structural elements: The analyst should determine how much of the element’s surface area is exposed to fire. Convective and radiative heat transfer modes can be considered separately depending on how that element can “view” the fire. Heat balance equations, some of them straightforward and relying on lumped mass assumptions, can be used to calculate the time history of temperature increase for each element. 4) Calculate the material and mechanical response of the bridge structure: The material properties of the fireexposed elements will diminish as their temperature increases – these relationships can be obtained from multiple references. These material performance time histories can then be coupled with a structural analysis which considers in-situ loading, thermal expansion, and potential load redistribution.

June 2018

structural

TESTING

ind tunnel testing is a ‘black box’ to many practicing structural engineers. This article strives to shine a small beacon inside the box and provide the reader with a foundation for asking sensible questions of wind tunnel laboratories. It is written from the author’s experience as a practicing wind engineer, an advocate for wind tunnel testing on major projects, and a client in receipt of wind tunnel test reports. A common puzzle for design teams is knowing when a wind tunnel test will be of value. As a wind engineer, the obvious answer would be “always,” but the more honest response is “it depends.” The typical issues for which a wind tunnel test might be commissioned for a tall building (Figure 1) include life safety issues of accurate determination of local pressures and wind-induced structural loads and responses. Also, typical serviceability issues of pedestrian wind conditions and building exhaust dispersion that contribute to the public and occupant perception of the quality of the built environment are of concern.

Wind Tunnel Testing for Tall Buildings A Bluffer’s Guide By Roy Denoon, Ph.D. Dr. Roy Denoon is Vice President and Principal of CPP Wind Engineering. He has published numerous articles in the field, as well as co-authorinag the CTBUH Guide to Wind Tunnel Testing of High-Rise Buildings and editing the Australasian Wind Engineering Society Quality Assurance Manual for Wind Tunnel Testing of Buildings and Structures.

Codes and Standards

with the seismic lateral loads. This, however, does not take into account the savings that can be achieved in the façade design or ensuring that occupants will not be disturbed by overly frequent perceptible building motion. With particularly slender buildings or those affected by local topography or excessive aerodynamic interference from neighboring buildings, the use of codes may not achieve adequate structural reliability. In these cases, the use of wind tunnel testing ensures that the desired levels of design reliability and robustness are met, consistent with the structural engineer’s professional responsibility. As performance-based design (PBD) gains more traction, wind tunnel testing will become an increasingly important part of achieving design objectives, something that is anticipated to be covered in an upcoming monograph from an ASCE Task Committee and an SEI Wind PBD Pre-Standard.

Test Types There are three commonly used wind tunnel test types for the determination of wind-induced structural loads and responses for tall buildings. These are the high-frequency balance (HFB), high-frequency pressure integration (HFPI), and aeroelastic techniques. The HFB and HFPI are the most common approaches and use rigid aerodynamic models. Both measure the wind forces exerted on the building model and, for high-rise buildings, the dynamic properties of the building are introduced mathematically into the analysis to determine the total response to the wind loading. The HFPI approach (Figure 2) is now applied to the majority of projects, as it uses the same model as the cladding pressure testing. Pressures measured simultaneously over the building surface are integrated to determine the overall wind loads applied to the building.

Wind-induced structural loads and cladding pressures can normally be estimated by building codes or standards. One regularly asked question is, “Why would a wind tunnel test be more accurate than the code?” The simple answer is that all the values in the code were developed from wind tunnel tests and intended to envelop the majority of cases. However, almost all codes include numerous caveats to their applicability for unusual buildings or circumstances, where wind tunnel testing is mandated as an alternative route to compliance. As such, the codes should provide conservative values for the majority of ‘typical’ tall buildings in urban environments while a properly conducted wind tunnel test will give more accurate project-specific design values. These updated values will either result in lower-than-code values with consequent savings in construction cost, or capture unusual effects not covered by the code to ensure adequate design reliability. In the design process, it is very often the structural engineer who takes responsibility for recommending whether wind tunnel testing is conducted. For many, this decision is predicated on the expectation of the significance of wind-induced strengthdesign lateral loads to the design, often based on how these might compare Figure 1. Wind tunnel pressure model. STRUCTURE magazine

June 2018

Figure 3. High-frequency balance model . Courtesy of b&w structural designs, llc.

Figure 2. Close-up of a wind tunnel pressure model.

For most buildings, the aerodynamic damping is positive. This is beneficial in reducing the resonant dynamic response of the building. However, the degree of positive aerodynamic damping is invariably much smaller than the inherent structural damping and within the degree of uncertainty associated with the estimate of structural damping. The aeroelastic test is more important when initial aerodynamic test results show that there is the potential for strong cross-wind (or vortex shedding) response. As the wind speed approaches the

peak for vortex-shedding, negative aerodynamic damping is generated, thus reducing the effective total damping of the building and increasing the building responses.

Wind Engineering Consultant The first thing a trusted wind engineering consultant should be able to provide to designers is advice on what wind effects should be of interest to the design team. This

Time-saving design guides and webinars. Useful design aids in book and on-demand video formats.

STRUCTURE magazine

ADVERTISEMENTâ&#x20AC;&#x201C;For Advertiser Information, visit www.STRUCTUREmag.org

However, for particularly architecturally complex buildings, it may not be possible to have a large enough number of pressure taps to map the pressure fields over the building with sufficient resolution. For very tall slender towers, the limited cross-section of the tower often provides a physical limitation to the number of pressure tubes that can be extracted from the model at once. In this case, HFB testing is the logical alternative. HFB testing (Figure 3) uses a lightweight model mounted on a very stiff balance to measure the applied forces at the base of the model. In this way, the HFB model is working as a mechanical integrator compared with the numerical integration of the HFPI approach. As the construction of an HFB model is less involved and more economical than a pressure model, this is also the technique that is used most commonly early in the design process where the final architecture may not yet be complete. This model is also easier to modify if a range of building shapes are being investigated. Shaping studies are sometimes used during concept design of particularly slender and wind sensitive towers to optimize building shape and minimize building responses. An appropriately designed HFB model can incorporate a number of adjustable features to investigate various architectural changes. The aeroelastic approach differs from the aerodynamic model approaches in that the model incorporates the appropriately scaled dynamic properties of the prototype structure: natural frequencies of vibration, mass characteristics, and damping ratios. The aeroelastic approach is generally more expensive than the aerodynamic techniques. The parameter which the aeroelastic modeling captures, which is not measured in either the HFB or HFPI approaches, is the aerodynamic damping.

Many design guides have CE/PDH companion webinars! See them all by shopping CRSI at www.crsi.org!

June 2018

Figure 4. Graph showing strong cross-wind response.

includes advice about what testing and consultancy would be of value to a project, and identification of any design features that may be particularly wind sensitive or, conversely, beneficial in the performance of the development. Early consultation can help projects develop in a much smoother manner rather than waiting for unexpected results when the form and structure of a building are close to being fixed. Once a wind engineering consultant is on board and a project has reached the stage of preparing for wind tunnel testing, then there should be regular interaction between the wind engineering, structural engineering, and architectural teams. The architectural team is responsible for the supply of the building geometry from which the wind tunnel test model(s) will be built. Generally, the wind engineering consultant will take responsibility for gathering information about the surroundings to build the proximity model. When the test models have been designed, drawings and/or 3D models should be provided to the design team for their checking and approval. This helps to ensure that the model reflects the current design and includes any critical changes that may have occurred since the original issue of architectural information. This will typically happen before the physical test model is constructed to allow for the incorporation of any modifications. The wind engineering consultant should at all times be able to describe, and justify, the approach to testing being used. For the design team, key issues to check are that an adequate radius of surroundings buildings has been modeled. This is a balance of model-scale (for tall buildings this is typically between 1:200 and 1:500 depending on the building height) and the cross-section of the wind tunnel being used. For tall buildings, it would be normal to

include a radius of at least 1200 feet around the building, although 1600 feet is more common, and any other significant buildings outside of this radius that would be expected to impact the flow onto the test building.

Reviewing Test Results Most engineers do not have much exposure to wind tunnel testing and how to interpret and check results, but there are a few resources to aid in this. The first is to make sure that the testing has been conducted to a reasonable standard. This can be done with reference to a number of guides ranging from the descriptive ASCE Manual of Practice No. 67 on Wind Tunnel Studies of Buildings and Structures to the more prescriptive ASCE/SEI Standard 49-12, Wind Tunnel Testing for Buildings and Other Structures. A more concise document, created for design professionals working with tall buildings, is the Council on Tall Buildings and Urban Habitat (CTBUH) publication, Wind Tunnel Testing of High-Rise Buildings, which summarizes what should be expected from wind tunnel tests conducted for tall buildings. The most obvious first check is to compare the loads and local pressures with code values. This is something that should also have been conducted by the wind tunnel laboratory and, if there are significant differences, this should have been highlighted and explained to the design team. Local negative (or suction) pressures, socalled “hot spots,” that are larger than code values are not unusual in limited areas of the building. These are typically a result of very localized flow features, such as conical vortices that result most commonly from architectural discontinuities. However, peak positive pressures that are significantly larger than code values are a flag to raise questions, unless they

STRUCTURE magazine

June 2018

can be shown to be a result of approach wind speed increases, as from channeling between upwind buildings. The same type of channeling can lead to increased structural loads in the along-wind direction. However, the most common reason for high wind loads and responses of tall, slender buildings is cross-wind response, which will often govern for buildings with a height to width ratio of greater than 5 or 6. This is not something that is covered in U.S. loading codes, but simplified estimates can be obtained from online estimators and overseas design standards. An example of base moment response dominated by cross-wind response is shown in Figure 4, identified by a rapid increase in the dynamic response at a wind direction orthogonal to the load while the mean load is close to zero. A more common query is when loads are significantly lower than code values. This can occur when the building is very sheltered by its neighbors. ASCE-7 has a lower limit on loads from wind tunnel tests to account for the removal of such adjacent buildings unless it can be shown that removing such significant sheltering buildings still results in low loads, in which case lower limits can be applied. If, however, a wind tunnel reports loads significantly lower than the 80% cut-off used by ASCE-7, this is a good cue for the design team to start asking questions. Occasionally, a structural engineer will get the opportunity to compare wind tunnel results from two different laboratories for the same building. These almost never agree exactly but should be within 10 to 15% of each other. Where differences are larger, the discrepancies are predominantly due to the interpretation of the site wind climate. While pressures vary with the wind speed squared, dynamic responses can vary with the wind speed cubed or greater. If there is one thing for a structural engineer to check and understand, it is the wind engineering consultant’s interpretation of design wind speeds to ensure that they are both scaled appropriately to any local statutory requirements and that directionality can be rationally explained with respect to the wind climate and surrounding terrain.

Conclusion Wind engineering is a combination of art and science, and it is important for structural engineers to understand just enough to check that the right studies are being conducted and, if not the reasons for unusual results, the appropriate questions to ask to elicit explanations.▪

The best adhesive performs in the worst conditions.

The next generation of Simpson Strong-Tie ® epoxy adhesive is more reliable and versatile. The high-strength SET-3G™ anchoring adhesive performs in extreme in-service temperatures (from –40°F to 176°F) as well as in dry or water-saturated concrete environments to provide the high bond strength values and performance needed for adhesive anchoring applications on your projects. Specify the code-listed SET-3G adhesive for your next project. Visit strongtie.com/set3g or call us at (800) 999-5099.

Code Listed: ICC-ES ESR-4057

Simpson Strong-Tie Company Inc. SET3G17-S

By Sarah A. Jorczak, P.E., LEED AP BD+C, and Kevin Borth, P.E., S.E.

ounded in 1990, Church of the Resurrection is the largest United Methodist Church in the U.S. In 2012, HGA Architects and Engineers (HGA) joined Church of the Resurrection’s mission to create a permanent sanctuary at their 76 acre Leawood, Kansas, campus. Design for the new 140,000 square foot main sanctuary and support space began in November 2012 and spanned a two-year period until construction documents were issued in November of 2014. McCown Gordon Construction broke ground in March of 2015 and completed the construction over a period of two years, ending March of 2017. Projects with demanding design challenges often provide new opportunities for innovation and result in very rewarding engineering solutions. The Church’s desire for an intimate 3,500-seat, lofty, naturally lit sanctuary provided many such challenges. HGA’s architectural vision resulted in canted exterior and interior walls hiding columns and lateral cross-bracing, non-orthogonal beam framing with several convergent connections, and a column-free sanctuary volume with balcony seating.

Ellipse The shape of the sanctuary was inspired by the Church’s request for a distance no farther than 100 feet from pastor to individual parishioner, resulting in an ellipse that cradles the chancel area. This shape set the stage for the building’s complex geometric layout. It became apparent early on that existing software platforms would struggle with the demands of a non-rectilinear and non-circular STRUCTURE magazine

curved grid system. HGA’s design team decided to implement the use of four curves to approximate each ellipse. In addition to the main sanctuary base being an ellipse, the architectural vision for the sanctuary shaped the sloping exterior wall and structural system, creating multiple shrinking ellipses as the building rises. Topping the building off are seven stainless-steel sails inspired by the seven days of the Holy Week. The desire to achieve a canted exterior wall, high ceilings, and long-span open sanctuary volume lent itself to the economy of steel construction. Steel braced frames along the elliptical grids were offset at the collar level, creating a horizontal out-of-plane offset discontinuity to accommodate the sloped sail cladding structure and transfer the lateral wind load (Figure 1). The structural team used linear segmented beam runs between columns in lieu of radiused beams along slab edges to keep steel fabrication costs down. The framing layout of segments built within a curved form created a condition where orthogonal connections were essentially non-existent and generated several complicated connection points with multiple beams converging on a single point. Without the orthogonal relationship between purlins and girders, nor between girders and columns, the use of standard 90-degree single angle and double angle connections became impossible. Consequently, new project typical connections were generated in partnership with the steel fabricator, KC Structural Steel, while remaining mindful of time, money, and erection costs. When the angle was tighter than 45 degrees, single angle bolted connections with the toe of the outstanding angle welded to the girder web were used (Figure 2a).

June 2018

Balcony Trusses

Figure 1. Horizontal offset plan.

When girders framing into column webs were required to have extensive and varying top and bottom flange cuts on both sides of the beam web, a column flange cover plate with skewed single plate bolted connection was created (Figure 2b). A colonnade wraps the sanctuary and opens into a 15,000-square-foot gathering space with 20-foot high ceilings and a continuous skylight dividing the adjacent ancillary structure from the main building structure. Wide flange beams punch through at discrete points from canted column connections at the perimeter of the sanctuary, splaying out in rays. The lateral analysis for the lower ancillary space was performed separately from the main sanctuary form by effectively unfolding the diaphragm and transferring the lateral load back to the building’s lateral force resisting system in the sanctuary via canted column bending (Figure 3, page 20). A combination of hand calculations, modeling in RISA 3D, and modeling in SCIA Engineer was used to accomplish the combined lateral analysis for the sanctuary space and gathering space.

Long Span Roof Trusses

The project required a thin, front profile balcony with a shallow depth truss to accommodate high ceilings and unobstructed sightlines from the back row of the tiered parterre seating. This ensured an open yet intimate and reverent experience. The 1,300-seat balcony is supported by cantilever trusses, with chords as heavy as W14x193 which extend out from pairs of columns spaced on radial grids around most of the elliptical base. The columns, up to W14x211, make up the backspan to the cantilevered balcony and resist the moment via a couple into the foundation system. Vibration serviceability demands controlled the truss design over the required strength. The structural team developed analytical modeling techniques and created project-specific vibration performance criteria using several documents pertaining to vibrations, including: AISC Design Guide 11: Floor Vibrations Due to Human Activity, A Design Guide for Footfall Induced Vibration of Structures (United Kingdom publication, The Concrete Centre), and International Standard ISO 10137 Basis for design of structures – Serviceability of buildings and walkways against vibrations. A separate analysis model was built, including all of the members contributing to the mass and stiffness of the system down to the foundation, to determine the structure’s behavior subject to excitation. Based on the anticipated use of the space, the structural team set a minimum fundamental frequency to meet a peak acceleration limit equal to five percent of gravity with a dynamic loading function criterion for a “lively concert” as defined in AISC Design Guide 11.

Wind in the Sails The stainless steel “sails” soaring above the stone clad base of the church and the non-rectilinear shape of the church are not described in building code provisions for the application of lateral loads to a building structure. The structural team had to develop a rational approach to apply prescriptive code lateral loads to the sail structure. After several discussions among members of the structural team, and a few brainstorming sessions with structural department members from HGA’s other offices, the team decided to apply wind loading perpendicular to a plane that represents the curving sail cladding

Meeting the client’s desire for a lofty, open sanctuary space meant incorporating long-span roof trusses. Sloped wide-flange beams at the roof deliver loads to the trusses. Due to the sanctuary’s elliptical geometry, all six roof trusses differ, resulting in six distinct truss designs ranging from 110 feet long and 8 feet deep to 181 feet long and 13 feet deep, with truss chords ranging from W14x61 to W14x109. The panel points over most of the truss length are spaced at 10 feet to align with the wide flange beams, while the outermost panels made up the difference between the standard 10-foot module and the spacing between the support columns. The truss-bottom chords bear on the support columns, and the outermost “vertical” truss web members are sloped to facilitate the cladding structure for the “sails” that reach skyward on the building’s exterior. The structural engineers worked closely with the architects early in the design to identify truss geometry constraints such as panel width (to facilitate catwalks and mechanical systems) and truss depth based on proposed ceiling structures. The structural team parameterized the truss depth in SCIA Engineer to quickly run through design iterations, searching for the most efficient design while meeting the constraints. Figure 2. Typical connections. STRUCTURE magazine

June 2018

Art Glass

Figure 3. Sanctuary space.

marching around the building at 30-degree sectors to cover wind loading from any direction. Portions of the building were identified as windward, leeward, or sidewall, depending on which sector the wind was assumed to be blowing (Figures 4 and 5). The structural team used the architect’s Rhino sail geometry model to define planes representing main portions of the sails. Design wind pressures per ASCE 7-10, peaking at 46 psf, were assumed to act perpendicular to these planes. The design wind pressures were broken down into X, Y, and Z components, using vectors normal to the assumed plane and imported as applied loading in the analysis model.

Figure 4. Sail wind loading.

One component of the sanctuary project gave structural engineers an opportunity to provide expertise for an extraordinary element. Church of the Resurrection is home to the largest stained-glass window installation in the world. The 93-foot by 37-foot stainedglass window provides the reverent backdrop during services and acts as a beacon to the community. Each of the 161 individual stained-glass panels is supported by vertical and horizontal aluminum mullions. The aluminum mullions tie back to architecturally exposed structural steel HSS 8x2 tubes. The HSS members provide the lateral support for the 5 psf internal wind pressure and delicately control the serviceability limitations of the art glass installation. The structural engineers, glass artisans, and the construction team carefully coordinated design requirements to develop appropriate deflection limits, installation details, and erection tolerances. Each HSS member spans 46 feet from collar level to the underside of the roof deck above. The allowable maximum wind load differential deflection experienced across the 5-foot 2-inch height of one individual glass panel was L/175.

Conclusion The structural team was able to manipulate the building structure and design software to work within the confines of the complex building geometry. The desire for an open and lofty sanctuary warranted an economizing design of long-span roof trusses and occupant comfort-driven design for shallow depth cantilever balcony trusses. The nonorthogonal building shape necessitated a practical lateral load application and analysis process for design wind loads. The team’s mindful placement of braced frames within the architectural form created a discontinuous lateral load path to reconcile. HGA structural engineers elevated their thinking and developed innovative solutions to meet the challenge of making the sacred vision for this building a reality. This was accomplished by creatively analyzing irregular diaphragms, accommodating slanted columns, and developing appropriate structural steel backup design criteria for the world’s largest stained glass window installation. The Church of the Resurrection is a recent recipient of the ACEC 2018 Engineering Excellence Minnesota Grand Award and National Recognition Award.▪ Sarah A. Jorczak, P.E., LEED AP BD+C, is an Associate Vice President in the Structural Engineering department and liaison to the Arts, Cultural, and Education (ACE) market sector at HGA Architects and Engineers. Sarah can be reached at sjorczak@hga.com. Kevin Borth, P.E., S.E., is a Senior Associate in the Structural Engineering department at HGA Architects and Engineers. Kevin can be reached at kborth@hga.com.

Figure 5. Wind load sectors.

STRUCTURE magazine

June 2018

CONNECTION SYSTEMS

SHEAR REINFORCEMENT SYSTEMS

SHEAR CONNECTOR SYSTEMS

FAÇADE CONNECTION SYSTEMS

MOUNTING TECHNOLOGY

Anchor Channels

“JORDAHL® anchor channels now have an ICC Evaluation Report for seismic zones A to F.“ Elisabeth Smith, Development Engineer at JORDAHL

NEW ICC-ES Evaluation Re po ESR-2854

JORDAHL® anchor channels for structural connections For more than 100 years JORDAHL® anchor channels and T-bolts have guaranteed the reliable anchoring of loads to concrete. Providing simple and fast installation, the JORDAHL system provides easy location adjustment for structural concrete connections without the time consuming hassle of welding or drilling. The JORDAHL range of JTA and JXA hot rolled channel proﬁles provide high capacity and reduce in-built stresses allowing high dynamic load capability. This enables their ability to accommodate both high and rapidly ﬂuctuating loads over millions of cycles without metal fatigue. Just the sort of anchoring reliability needed for

DECON USA INC. 103 East Napa Street, Suite B Sonoma, CA 95476 Tel (866) 332-6687 www.deconusa.com

your project. The JXA range of JORDAHL® toothed anchor channels also enables secure mechanical resistance to longitudianl gravity loads or seismic loads with reliable performance verified by ICC-ES Evaluation Report ESR-2854. Design to applicable codes is easily achieved using our innovative JORDAHL® EXPERT software. The software can be downloaded for free from our website. Our team offers unequalled costomer service and engineering assistance. We would be pleased to offer support on a project basis, and look forward to working with you.

urrently under construction, Fortis Property Group’s One Seaport residential tower will become one of downtown Manhattan’s first residential skyscrapers directly fronting the East River. The slender tower, designed by Hill West Architects, will stand 57 stories high to a height of 662 feet above grade. The structural system of the building consists of concrete flat plate construction and a reinforced concrete shear wall. Concrete strengths of up to 12 ksi were used to enhance strength and provide adequate stiffness. Additional lateral stiffness is provided by an outrigger and belt wall system that engages perimeter columns. This system provides flexibility in the architectural layout and increases structural efficiency.

Structural Challenges Main challenges in the structural design include controlling lateral deflections, accelerations, and overturning of the structure due to wind forces and the building’s high aspect ratio (15+:1). In addition, foundation design considerations related to the depth of suitable substrate to support the high-rise tower were a concern. Pairing the high slenderness ratio together with deep foundation elements resulted in a structure which is much more flexible compared to the same building supported directly on typical Manhattan bedrock. A total of 4 tuned liquid dampers are incorporated to ensure occupancy comfort from dynamic motion and limit building accelerations. Courtesy of Fortis Properties

ONE SEAPORT TOWER 161 Maiden Lane, New York, NY By Jeffrey Smilow, P.E., F.ASCE, Patrick Chan, P.E., and Ilya Shleykov, Ph.D., P.E.

Foundation Consideration One Seaport’s site sits upon East River landfill that dates to the turn of the eighteenth century. With rock situated at 132 to 166 feet below grade, initial evaluations of deep foundation systems such as drilled piles and caissons, common to high-rise structures, were performed. The difficulties associated with drilling elements to such depths resulted in extremely high foundation bids from a limited number of contractors. An alternate system, not commonly utilized to support high-rise structures, was proposed. The solution used a jet-grout soil improvement system, to depths of 55 feet below grade, into the sand layer. WSP, geotechnical consultant RA Consultants, and specialty contractor Hayward Baker collaborated on the design and analysis of a soil improvement system that provided the strength and stiffness capable of supporting a reinforced concrete mat as the building’s foundation system.

Detailed Analysis and Challenges Although the soil improvement system and foundation mat proved to be a cost-efficient system, there were design challenges due to the inherent stiffness of the system. Careful consideration and mitigation of the adverse effects were required throughout the design Figure 1. Global finite element model of and construction phases for the superstructure-foundation-soil.

June 2018

Figure 2. Layout of mat foundation.

Figure 3. Rock anchor details; a) Not accessible for re-tensioning; b) Accessible for re-tensioning.

tower to achieve the acceptable level of building performance under wind events. Variation of dynamic properties due to the effect of the foundation system were also included in the assessment of loads and induced vibrations during wind tunnel studies. Due to the high winds along the eastern shoreline of lower Manhattan and the tower’s high slenderness ratio, the effect of overturning forces was a central focus in the analysis and design of the proposed tower. Nonlinear finite element analysis of the combined Superstructure-Foundation-Soil system for lateral and gravity loads indicated that lateral stiffness of the tower, and consequently its deformations and second-order effects, are highly dependent on the foundation system performance (Figure 1). Uplift forces under the mat resulted in the use of +150-footlong rock anchors with capacities of 580 kips (Figure 2). Detailed non-linear analyses were carried out to understand how the loss in pre-stress forces in the anchors, as a result of the settlement of the building, would affect the overall behavior of the tower under wind events. The four conditions studied, taking into consideration the phase of construction at which rock anchors are pre-tensioned, are: • Condition 1 – foundation mat + rock anchors (100% loss of pre-tension). Under this condition, the axial deformation of the rock anchors would result in the largest building movement. • Condition 2 – foundation mat + rock anchors (pre-tensioned, no losses considered). In this ideal condition, no axial deformation of the rock anchors would occur due to pre-stress forces in the anchors. continued on next page

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

INNOVATION

ENABLED BY STEEL Structural steel shouldn’t demand rigid thinking. Create open spans with optimized space. Achieve stunning architectural visions while answering complex engineering challenges. Improve the cost and performance of your next project.

Get inspired Elevate your design solutions. Download this free guide.

newmill.com/elevate

YOUR NATIONWIDE RESOURCE FOR CUSTOM-ENGINEERED STRUCTURAL STEEL BUILDING SYSTEMS

18-NMBS-2_structure-INNOV.indd 1

STRUCTURE magazine

June 2018

4/27/18 9:24 AM

• Condition 3 – foundation mat + rock anchors (pre-tensioned, losses considered due to expected settlement). This condition represents a case where rock anchors are pre-stressed prior to construction of the superstructure. • Condition 4 – foundation mat + rock anchors (pre-tensioned, losses considered due to expected settlement, with accessible anchors re-tensioned ). This condition represents when rock anchors which are accessible are re-stressed post construction of the superstructure (Figure 3, page 23).

Analysis Results The rotation of the mat and uplift were analyzed to understand the overall lateral Figure 4. Distribution of soil pressure and location of uplift areas under mat foundation for movement of the tower. Figure 4 captures the gravity load and 700-year return-period wind load (Conditions 1 through 4). portions of the mat which have uplift due to an ultimate level (700-year) design wind load for each of the four conditions studied. From the diagrams, it can be seen that the level of pre-tension forces in the anchors will play a significant role in the extent of the mat exposed to uplift, as a result of the rotation of the foundation mat and, hence, lateral movements and stiffness of the tower. Concomitant adverse effects of the mat rotations include a noticeable increase of tower deformations, as well as increased secondary effects, and are indicated in Figures 5 and 6. In comparison with an ideal fixed base condition, lateral deflections increase by 73% and secondary moments caused by P-Delta effects increase from 3% to 16% when all pre-tensioned forces are lost due to building settlement. Based on study results, final foundation system design was tuned to mitigate adverse effects of foundation flexibility on the tower’s global performance. The uplift area at the interface between foundation mat and underlying soil was sufficiently minimized, as shown in Figure Figure 5. Top lateral displacement for 50-year return-period wind load normalized with 4 (Condition 4). The contribution of global P-Delta respect to Condition 0 (fixed base). effects resulting in secondary moments was reduced to 5%. These factors, along with utilization of tuned sloshing dampers at the top of the tower, provided an efficient structural system within elegant and slender architectural form. Implementation of an alternative foundation system vetted by extensive nonlinear analysis of the combined Superstructure-Foundation-Soil system resulted in a sound structural solution for this high-performance residential tower located in downtown Manhattan. Moreover, the solution provided savings of approximately $6 million to the owner, Fortis Properties Group.▪ Jeffrey Smilow, P.E., F.ASCE, is USA Director of Building Structures at WSP|PB, Principal-in-Charge of the project. Patrick Chan, P.E., is Senior Vice President of Building Structures at WSP|PB, Project Director. Ilya Shleykov, Ph.D., P.E., is Associate of Building Structures at WSP|PB, Analysis Project Manager.

Figure 6. Ratio of base moment due to 700-year return-period wind load, considering P-Delta effects and foundation stiffness, to base moment without second-order effects.

STRUCTURE magazine

June 2018

ising along the Chicago River, Vista Tower poses a neverbefore-seen structural challenge: how to design a 1,200-foot-tall building constrained by a plan width of 80 feet and vertical support elements that offset at every level. After years of planning and design, construction is underway on Chicago’s third tallest tower, using an aggressively unique building geometry and lateral bracing system arrangement. The iconic architectural vision of Studio Gang’s Jeanne Gang, in conjunction with Magnusson Klemencic Associates’ (MKA) innovative structural solutions, has been realized and is scheduled to be completed in 2020.

Centerpiece of an Urban Renewal The Lakeshore East neighborhood on the Chicago waterfront has redesigned itself during 200 years of re-envisioning lakefront priorities. Residing just south of the Chicago River, the shoreline was originally used for wharves and docks as the city built itself at the mouth of the river in the early 1800s. When the city became a pivotal inland shipping and transportation hub, the area was transformed into the rail yard for the Illinois Central Railroad in the 1850s. Later, the rail yard was transferred off the waterfront, and this 28-acre property was reformed into a municipal golf course, hidden between 40-foot-tall viaducts. During the urban renewal of the late 1900s, this land was master-planned for residential, hotel, and park use, reconnecting the dynamic commercial core of Chicago’s Loop to its vibrant waterfront and extending the walkable, publicly-activated Millennium Park north to the Chicago River. Vista Tower is one of the final parcels of the Lakeshore East development to be built and is situated and sized to be the centerpiece of this urban residential village.

Stacked-Alternating Frustums In its essence, Vista Tower is a combination of many parts. The building will include three uses; hotel, apartments,

Building rendering across Chicago River. Courtesy of Magellan Development Group.

Stacked Frustums Create

Chicago’s Newest Super-Tall Tower By David Fields, P.E., S.E., LEEP AP, and Ronald Klemencic, P.E., S.E., Hon. AIA

STRUCTURE magazine

June 2018

and condominiums, vertically stacked. The primary form of the building is three connected towers of 100, 75, and 50 stories, offset in plan to create distinct and unique site-lines for the buildings’ occupants. Composing these towers are unique, geometric elements: 13-story frustum blocks stacked and alternated in both plan and elevation. A frustum is defined as a truncated cone or pyramid. The form selected for Vista Tower’s building blocks is cut from a pyramidal shape, resulting in a square-sided volume tapering from 90 feet at its widest to 80 feet at its narrowest. The 100-story section of the building uses seven frustums flipped end-for-end with each instance so that the end form is a very narrow, vertically undulating exterior. The lowest frustum tapers for more than 13 stories and lands on a 5-story vertical base, bringing the total story count to 100. The 75-story section of the building includes five frustums, again alternated end-for-end as they stack, but with the inverse orientation from the frustums in the adjacent 100-story mass. This has the effect that any given floor is smaller than the floor below it in some areas and larger than the floor below it in other areas. To complete the pattern, the 50-story section of the building follows suit, again stacking a smaller number of frustums also with inverse orientation from the adjacent mass. The resulting façade has eight corners at shifting locations on every level, allowing for no consistent vertical or horizontal lines. Supporting 100 unique floor plans with a rational column arrangement proved to be fundamental in shaping the buildings’ structural DNA. Locating straight columns justified with the exterior of the narrowest frustum levels would place them five feet inside the glazed corners on the widest floors of the frustum. This would have created an untenable condition in which the most desirable part of the units, the corners, were compromised in both floor plan use and view of the surrounding city. An alternate solution was explored where column locations follow the tapering building exterior, shifting at every floor and remaining tight to the façade. With column axial loads as

Shear wall layout shown in plan.

great as 15,000 kips at the base, the implication of shifting columns presented real challenges to global stability and building balance. This geometry ultimately proved viable, incorporating column horizontal offsets of approximately 5 inches at every level. Since the stepping of columns is consistent around each frustum, the effect to the overall system is negligible. The exception is, at the top and bottom of each frustum, where the direction of column stepping reverses. This required a significant lateral restoring force at that elevation, supplied by the floor slab. At frustum wide points, the induced force is an outward pull on the slab, felt in two directions at corner columns. This tension is handled with mild reinforcement, located mid-height in the slab and carried entirely across the floor plan to an “equal and opposite” column. At frustum narrow points, the equilibrating force compresses the slab. This results in a P-delta condition for the slab, causing the slab’s initial gravity moments and deflections to be amplified by the induced axial forces. The developer’s goal of maximizing clear height and having clean slab soffits meant this P-delta problem needed to be solved without adding beams or other thickened elements that would conventionally carry compression. Analyzing these slabs as compression elements, while considering the gravity deflections and slab post-tensioning as initial conditions, revealed an arrangement of supplemental reinforcement necessary to keep these elements stable. Another critical design decision, stemming from having 100 unique floor plans, was determining how much granularity to apply to the detailing of the slab reinforcement (rebar, post-tensioning tendons, and studrails). The most optimized design suggested every level entailed a unique design, perfectly matched to the spans. However, the resulting volume of details would create a massive burden on the contractor to manage shop drawings, fabrication, storage, placement, and special inspection unique to each level. The other extreme would be to apply the design for the worst-case slab, the widest level and longest spans, to all levels in that frustum. This solution would be both overly wasteful of material and would create an overload of load-balancing from the post-tensioning tendons when applied to the short-span levels. The chosen design approach hit the mid-point between these competing interests of optimization and constructability. Each 13-story block of slabs is broken into three designs, considering small, medium, and large span levels separately. Other than the 20 levels of hotel, STRUCTURE magazine

parking, and mechanical use, the remaining 80 levels are covered by just 18 unique slab designs.

Wind Resistance and Optimization Buildings of 500 feet and shorter are often braced with windload resisting framing that neatly disappears into the floor plan. Typically, a concrete wall assembly, arranged to surround the central core of elevators, stairs, and shafts, braces the tower leaving the remainder of the floor plan open and free for efficient room layouts with unobstructed views at the perimeter. For taller towers, the concrete core alone is too narrow to provide the requisite strength and stiffness. A ratio of building height to lateral system stance of 12:1 is aggressive. For Vista Tower, the ratio of building height to core width is approximately 40:1, which required widening the stance of the lateral system beyond just the core. In the east-west direction of the tower, a convenient geometry was provided by the presence of two primary circulation cores, one in the 100-story portion and one in the 50-story portion. By slightly adjusting the offset of tower masses, the cores were aligned in plan and connected with a concrete wall running along the length of the corridor between them, creating a spine for the building plan. The

Base overturning moment from variable wind direction.

June 2018

Tuned liquid sloshing damper tank layout.

result is a coupled dual-core shear wall assembly resisting wind forces from the predominant direction, the West. Through detailed wind tunnel studies, it was determined that the prevailing winds caused a strong cross-wind response. This is a condition when the wind blowing on a building in one direction causes forces and sway in the perpendicular direction. Cross-wind response is generally prevalent at higher wind speeds when vortices forming on the backside of building discontinuities release and reform with cyclic timing. When the frequency of release starts to match the buildings’ natural frequency of sway, resonance begins, and cross-directional forces amplify. These effects were revealed and quantified by wind tunnel testing in Guelph, Canada, by Rowan, Williams, Davies and Irwin (RWDI). RWDI’s testing revealed that cross-directional loads in the north-south direction were 16 percent greater from westerly winds than from winds actually blowing in the north-south direction! Resisting these north-south wind loads proved to be the most significant structural challenge of the project and the most impactful to the hotel and residential unit layouts. Creating a north-south lateral system with a stance close to 12:1 required activating the entire building width. One common solution to this problem is to use a series of outriggers extending from the core to exterior columns at discreet elevations, engaging them in the global system. These outriggers are often multi-story concrete walls or steel trusses and can be very disruptive to unit planning and construction sequencing and regularity. In addition, to achieve the stiffness that is sought by this widened footprint, the exterior columns typically need to be much larger than other tower columns. A study of this core and outrigger solution revealed a requirement for 10-foot square columns in order to reach the target building stiffness. An alternate approach was taken to activate the full width of the tower in bracing the building, which was less disruptive to unit planning than the 10-foot-square column option. From the foundation to Level 71, buttress walls extend from the Western core to encapsulate units on the building exterior. This geometry creates a multi-cell STRUCTURE magazine

core reaching across the full building width. Since the buttress walls extend over many successive levels rather than at discreet outrigger elevations, they can be perforated in many locations, allowing for corridor circulation through the walls at every level and large window openings through the exterior walls. Super-tall towers face the additional challenge of providing for occupant comfort during wind events. The frequencies at which these towers sway can resonate with occupants’ senses and can lead to discomfort and nausea. This effect is measured in very small levels of acceleration, with an industry-accepted limit for residential occupancy at 18 milli-g during a 10-year storm. Although the buttressed core provides ample strength, additional measures were needed to dampen peak lateral accelerations during the predicted sway of the tower. MKA employed six tuned liquid sloshing damper tanks (TLSD’s) strategically located in the upper stories. Four north-south oriented TLSD’s reside in the top two stories, flanking the elevator overrun and machine rooms. Two east-west oriented tanks are located at the 87th story, stacked and held tight to the core. Taken together, these dampers will contain more than 400,000 gallons (about 1,500 tons) of water. In a further attempt to optimize the lateral bracing system, a final round of wind tunnel testing was conducted to evaluate multiple concepts representing minor but impactful geometric changes. One concept stood out as a clear winner: an upper-story blow-through level. The 87th story is 28 feet tall and clad with a grill that will appear solid from the ground while allowing wind to pass through the tower at this elevation. The blow-through effect directly relieves a portion of the wind force but also disrupts the flow and amplitude of wind forces for several stories above and below. Along with the switch to porous roof screens, the net effect of the blow-through level is a 24 percent reduction of the cross-wind lateral response.

A Vision Realized An iconic building geometry enhances a city’s skyline, inspires all who see it, and increases a developer’s end value. However, a great design is only great if it is built. This poses the challenge to a structural team to deliver a building that meets the developer’s pro forma requirements and utilizes an arrangement of elements that can be practically constructed, all without compromising the original architectural vision. MKA’s design of Vista Tower has realized these goals, integrating the need for open floor plans and a diverse building program with the robust structural frame necessary to support and keep stable this super-tall tower. The never-before-seen alternating-stacked frustum geometry of Vista Tower is now rising quickly on the Chicago River.▪

David Fields, P.E., S.E., LEED AP, is a Senior Principal at MKA, leader of the firm’s Residential Specialist Group and a key member of MKA’s Performance-Based Design and Earthquake Technical Specialist Teams. David is also active on several national committees developing related codes. He can be reached at dfields@mka.com. Ron Klemencic, P.E., S.E., Hon. AIA, is the Chairman and C.E.O. of MKA. A past 5-year Chairman of the Council on Tall Buildings and Urban Habitat, Ron’s focus is complex high-rise and mixed-use designs. He can be reached at rklemencic@mka.com.

June 2018

One frame. Countless possibilities.

Up to six stories tall and unlimited bays, Strong Frame ® special moment frames provide countless design possibilities. Our 100% field-bolted Strong Frame multi-story, multi-bay solutions meet all code requirements, resist the most demanding lateral loads and let you create spacious, beautiful buildings.

Patented Yield-Link™ Structural Fuse Technology

Let Simpson Strong-Tie Strong Frames be the building blocks of your custom solution. Watch our Strong Frame case study video at go.strongtie.com/strongframe or contact us about our design services at (800) 999-5099. © 2018 Simpson Strong-Tie Company Inc. SFMB18

A Shining Beacon in the Desert

By Erik Kneer, S.E., LEED AP BD+C, Erik McGregor, P.E., C.P.Eng., and Mary Kretschmar, P.E.

he Black Rock Lighthouse Service (BRLS) was the tallest independent art installation at Burning Man in 2016. The installation consisted of an array of four main, occupiable lighthouses. Three leaning lighthouses (ranging in height from 15 to 40 feet tall) surround a central, 60-foot tall lighthouse, all interconnected by three 20-foot long cable and rope suspension bridges (Figure 1). Holmes Structures was engaged to assist the artists with the structural design of the project.

Prelude For the uninitiated, Burning Man’s website describes the festival as “an annual experiment in temporary community dedicated to radical self-expression and radical self-reliance.” It began in 1986 on Baker Beach in San Francisco as a celebration of the summer solstice. After four years, it outgrew its original location and moved to the Black Rock Desert Playa in Nevada, approximately 120 miles north of Reno. Every year, nearly 70,000 people make the pilgrimage and brave the harsh desert conditions to take part in the creation of the temporary artist community named Black Rock City. As the festival grew over the years, so did the scale and complexity of the festival’s ambitious artworks. Artists are now creating interactive pieces that are dozens of feet tall, weighing thousands of pounds or covering thousands of square feet. Creative structural engineering is essential to protecting the life-safety of festival goers (commonly known as “Burners”) as they experience this massive art while maintaining the aesthetic integrity of the installations. The Black Rock Lighthouse was conceptualized years ago by the father and son artist team of Max and Jonny Poynton. They envisioned the installation to be, “A crystal-like cluster of Lighthouses inspired by the juxtaposition of creating a destination for fun and shelter by something that is meant to warn you of danger. This adult jungle gym aims to become a destination where participants come to seek shelter, play, meet up with friends, and navigate the inland sea that is the Playa.” STRUCTURE magazine

They began assembling a team of artists, carpenters, community organizers, fundraisers, architects, and engineers in late 2015 to start the planning and design of the ambitious project. For four months, the core design team iterated on architectural and structural concepts to help realize the artists’ dream of Lighthouses in the desert. The project build began in March 2016 and was based at American Steel Studios in Oakland, California. For six months, a crew of up to thirty carpenters, artists, and volunteers labored to prefabricate the majority of the installation into panels that could be easily loaded onto a flatbed truck, shipped to the Black Rock Desert, and assembled on-site. Though there is no formal building permit review process, the Burning Man Organization has recently started requiring that larger installations such as the Black Rock Lighthouses undergo a third-party peer review. This project used the 2015 International Building Code (IBC) as the reference standard.

Illusion of Danger One of the artists’ main design objectives was to imbue the installation with a sense of danger. The designers’ challenge was to evoke notions of instability while providing discrete measures to ensure life-safety. The towers had to lean 10 to 25 degrees out-of-plumb without visible wires or braces, so each wall was designed to share load and function together as a single octagonal column unit. A base “wedge” element was designed to create the tilt in each tower but allowed for an open interior without truly vertical supports. Built-up corner posts with holdown anchors developed the overturning tension into the ground soil anchors and served as panel connection points. The P-Delta effects from the leaning towers were also resisted by suspension bridges aligned with the direction of lean. Conservatism was built into the design by ensuring that the leaning towers could stand up without the need for the suspension bridges. Vice versa, in the case where the soil anchors could fail, the bridges would be sufficient to prevent collapse.

June 2018

The wedge element that enabled the Lighthouses to lean also allowed the panels for each structure to be fabricated as if the Lighthouses were vertical and assembled upright. The Lighthouses were eventually craned into place and secured to the wedges at appropriate angles (Figure 2), a process prototyped and tested at full-scale, prior to erection, at American Steel using overhead bridge cranes. The bridge system consisted of two ⅝-inch diameter cables at Figure 1. The Black Rock Lighthouses. Courtesy of Jesse Rather. Figure 2. Installation of towers onto wedges. the top and bottom with salvaged wooden planking between the two bottom cables. Vertical ties were and floors, the Lighthouses were able to be completed very rapidly placed along the length of the bridge allowing for the four cables with a relatively small crew. to act together. Each cable was then secured to the towers with an The floors of the Lighthouses were constructed with laminated anchor rod and blocking to resolve the horizontal force of the cables veneer lumber (LVL) floor joists in a unique “Star of David” patback into the tower floor diaphragms (Figure 3). tern. This layout allowed spans for the floor beams to be reduced They were designed to sway and rock as people crossed between and keep to the octagonal footprint of the structure. The center observation decks and the open rope-mesh side rails gave clear views of the star allowed for staircase openings and complete vertical of the 30-foot drop below. The narrowness of the bridges (only 18 circulation for views up into the Lighthouse (Figure 4, page 32). inches wide) added to the sense of danger and limited the traffic Floor sections were fabricated to fit on a flatbed truck instead to one-way flow, thereby reducing the design loading. A delicate of transporting an entire diaphragm. balance was crafted between the bridges and lighthouses with seemThe walls were constructed as traditional shear walls for the lateral ingly opposing structural and aesthetic goals of safety and “death force resisting system. Aware that many art installations on the Playa defying” danger. are interactive, and sometimes not interacted with as intended, the Lighthouses were designed with the extra loading of festival-goers potentially climbing up the side. The walls were considered as floors Prefabrication and Rapid Assembly for the leaning towers, and the “Star of David” design offered a direct There is only a fourteen-day window before the opening of the festival in strut load path to brace the walls out of plane. which structures can be built on site, so completion of a project of this Conventional light-framed construction was used, with Simpson scale is impossible without significant prefabrication for rapid assembly. Strong-Tie hardware, to maintain simple and uniform construction Platform framing was chosen for the construction of the Lighthouses for the volunteer labor force, some of whom were not carpenters. for ease of construction and to increase the safety of the building. Prefabrication simplified the geometrically complex construction. Wall panels were prefabricated floor to floor, with floor panels Important details in construction could be verified by the engineers sandwiched between wall panels (Figure 3). With the on-site con- and a team of experienced carpenters in the shop. While the goal was struction reduced to just the connection of joints at the wall panel the speed of construction on the Playa, it took six months to construct

Figure 3. Connection details. Bridge anchorage (left); floor to wall connection (right).

STRUCTURE magazine

June 2018

the standardized panels before the installation. “Evidence-based design” (a.k.a. testing) is a very useful tool for out of the box projects of this nature. Pushing the limits of “artistic license” and mocking up full-scale tests before final implementation provides an added sense of security and confidence in the solutions. In addition to testing the wedge assembly process mentioned previously, the suspension bridges also underwent a similar process prior to installation. With a geoFigure 4. Central core. metric, nonlinear analysis done as the primary design for the cable suspension bridges, the results were taken to the shop to validate. There it was constructed between temporary support points for full-scale dynamic testing, e.g., jumping up and down by build-crew volunteers. This design process allowed for the quick verification of the safety of the bridges without needing to apply overly conservative loading. Conservative loadings would make it difficult to maintain the slim “rickety rope bridge” aesthetic.

Playa Build Burning Man has a strict “leave-no-trace” policy for protecting the ground surface at the Playa. In fact, build crews are required to clean up every nail, clip, or noncombustible product remaining after a structure is burned, a tradition at the festival. Therefore, the design could not include excavation or placement of any pre-cast concrete or steel foundations to anchor the structure to the ground. Additionally, the surface of the Playa has very low bearing strength, so spreading the load on the compression side of the Lighthouses was essential. Foundation tension was addressed with four-foot-long, lightweight, aluminum ground screws made by American Earth Anchor. Justification for their capacity was determined by performing in-situ testing in the first days allowed on site. The base needed to accommodate a flexible anchorage design that could use multiple screws if necessary, depending on the test results. The Penetrator PE-46 Guy headed anchor allowed the pairing of multiple anchors to an eyelet on the bottom of the holdown’s threaded rod. The foundation compression loads were evaluated using a global analysis that treated the fully sheathed wall panels as an equivalent composite octagonal section and distributed the compression forces around the side walls with double base plates across the Playa’s surface. Flexibility and adjustment in the field proved to be a critical part of the construction process, with Special Inspections provided by the Structural Engineer of Record. The engineering team was on the Playa during the build and able to give instant recommendations for fixes as they occurred. This construction process was a unique experience for the design engineer who rarely has an opportunity to assist directly in construction, thereby providing an extra layer of Quality Assurance. Even though all details were designed as typical, it became apparent when installing the bridges that the connection points were STRUCTURE magazine

not truly uniform. An engineer needed to be with the crew installing the bridges to ensure design intent was followed. Mock ups, generous factors of safety, and applying a belt-andsuspenders methodology allowed the project to proceed smoothly through construction, even when changes in the field exceeded specified tolerances. The mix of volunteer labor and a design that was heavily iterative at the early stages led to one of the base wedges constructed with an additional 10 degrees of tilt! Coincidentally, an early iteration of the design happened to assume an extra 10 degrees, and the calculations were not revised when the amount of lean was reduced. This additional factor of safety was a saving grace in the field, allowing the accommodation of the surprise tilt without any changes required.

End of Life As is customary for many of the large installations at the festival, the Lighthouses were indeed burned. The Burners gathered at a mandated 400-foot radius burn perimeter immediately following the namesake Burning of the Man in a celebratory burn ceremony at 12:30 am on the second to last night of the festival. The structure was purposely built without any heavy timber to help facilitate a full burn to ashes. The Lighthouses still burned for approximately 12 minutes before collapsing onto the Playa. For the curious, the burn video link can be found in the Figure 5 caption. During the installation, the Lighthouses experienced 60+ mph wind and dust storms, sustained no damage, and served as a place of refuge for festival goers. It was enjoyed by over 70,000 people and served as a true monument on the Playa. With its operable rotating spotlight in the center tower and total of 12 flamethrowers fixed to the tops of the Lighthouses, it was truly a beacon for everyone there. The artwork now only exists in photos and the collective memory of those who experienced it, including the engineers that worked on this once-in-a-lifetime project.▪ Erik Kneer, S.E., LEED AP BD+C, is an Associate Principal, Erik McGregor, P.E., C.P.Eng., is a Project Engineer, and Mary Kretschmar, P.E., is a Structural Designer for Holmes Structures based out of San Francisco, CA. The authors comprised the design team.

Figure 5. Black Rock Lighthouse burn. Courtesy of Jesse Rather. To view a video, visit https://bit.ly/2JLNaRr.

June 2018

Geotechnical Engineer: Chung & Vander Doelen Engineering Ltd Structural Engineer: Stephenson Engineering Ltd General Contractor: Reid & DeLeye Contractors Ltd Geopier Installer: GeoSolv Design/Build Inc.

GEOPIER IS GROUND ® IMPROVEMENT Geopier rigid inclusions were installed in soft, compressible soils to support a 12-story condo with 2-levels of below grade parking. Geopier rigid inclusion systems enable you to: • • • •

Improve variable fill soils in place Replace deep foundations Control settlement Increase soil bearing capacities

REQUEST FEASIBILITY ASSESSMENT 800-371-7470 • info@geopier.com www.geopier.com/feasibilityrequest

structural

REHABILITATION

Wood Bowstring Trusses Part 1: Investigation, Repair, and Rehabilitation By Gloriana Arrieta Martinez, Ph.D., Filippo Masetti, P.E., and Milan Vatovec, Ph.D., P.E. Gloriana Arrieta Martinez is a Junior Structural Engineer at Simpson Gumpertz & Heger, Inc. She can be reached at gamartinez@sgh.com. Filippo Masetti is a Senior Project Manager at Simpson Gumpertz & Heger, Inc. He can be reached at fmasetti@sgh.com. Milan Vatovec is Consulting Principal at Simpson, Gumpertz & Heger, Inc. He can be reached at mvatovec@sgh.com.

art 1 of this 2-part article addresses structural behavior and assessment methods. Part 2 will focus on analysis and repair options. Due to increasing costs and restrictions associated with redevelopment (replacement) of existing buildings, as well as municipal initiatives geared to promote the preservation of the existing building stock, repair and rehabilitation of existing buildings have become economically and politically attractive options for property owners. Adaptive and direct reuse of old, historical, and sometimes archaic structures requires careful engineering assessment of their ability to continue to safely perform under current building code requirements. This is no easy endeavor and requires a thorough investigation of existing conditions, analysis to determine in place structural capacity, and creativity to conceive effective, yet practical and economically feasible solutions. Buildings featuring timber bowstring trusses are no exception. Bowstring trusses were a popular solution for structurally supporting roofs from the 1900s through the 1950s, especially in buildings where large, open spans were desired (manufacturing facilities, garages, warehouses, among others). Many buildings with this type of roof support are still in service today; given their age and inherent vulnerability (e.g., to environmental, load, and other factors), their adequacy and reliability have become a common reason for concern.

Behavior and Original Designs Bowstring trusses typically feature a parabolically shaped top chord constructed of several wood elements (laminations) mechanically connected through the depth of the member. The bottom chord is often constructed of straight timber members with bolted splices. Both the top and bottom chords consist of two parallel members separated by a gap. The gap accommodates connections to vertical and diagonal web members which frame in between the chord members. The web elements are either discrete members or are a lattice system (continuous arrangement of web members) (Figure 1). The top and bottom chords are typically connected by a U-shaped

steel strap that wraps around the end of the truss and is bolted to the chord members. The ends of the truss bear on columns or are situated inside pockets within masonry walls. The typical span for these trusses is between 50 to 100 feet and the typical height is between 10 to12 feet. Bowstring trusses structurally behave as a tied arch. The shape of the top chord (parabolic) results in generally uniform compressive stresses in top chord elements under uniform loads. The thrust forces at the ends of the top chord are resisted by the bottom chord, which acts as a tie; these forces are transferred to the bottom chord through the U shaped steel straps at the ends of the truss. Due to this arch like behavior, stresses in web members are relatively small under uniform load. These structures were developed (and designed) to withstand dead, live, snow, and wind loads, which general practice and most building codes in effect at the time of construction considered as uniformly distributed loads. Generally, snow drift loads, non-uniform wind loads, point loads (e.g., due to mechanical units on the roof ), and seismic loads were not considered at the time of original construction.

Field Investigation Two of the most significant challenges when investigating bowstring trusses are lack of documentation and restricted access. Drawings of existing bowstring trusses are rarely available. When this is the case, evaluation of the truss structural capacity must rely solely on field documented information; therefore, performing a thorough visual inspection is paramount. However, up close access to all truss members and their connections, while necessary, is often very challenging due to existing obstructions and concealed conditions. A combination of small aerial lifts and ladders usually allow navigation through existing equipment and hung features to achieve sufficient access. Even though each structure presents unique features, once access is achieved, most field investigations follow the same methods. A discussion on conventional investigation methods, along with typical and recurring distress/deterioration mechanisms found by the authors in recent investigations, is presented below.

Typical Investigative Methods General Visual Inspection

Figure 1. Bowstring trusses in which web elements are discrete (left) and are a lattice system (right).

STRUCTURE magazine

June 2018

This includes careful documentation of the general truss configuration, member sizes, top and bottom chords construction, connection details, and boundary and support conditions. General roof characteristics (e.g., location and height of parapets, truss spacing, roofing construction)

should also be documented during this phase. Finally, observation of readily visible distress (e.g., full member splits, shakes, rot, etc.) is critical. General observations of the overall condition of the structure should be accompanied by more specific observations in focus areas. Non-Destructive Testing Often, decay in wood elements is hidden (material properties can be significantly affected without a change in appearance). Therefore, non-destructive techniques can and should be employed to supplement and confirm visual observations. Hammer sounding, surface pick tests, moisture-meter readings, and resistance to drilling with a resistograph are all methods both effective and relatively simple to implement. Resistograph tests are especially useful to determine the extent of deterioration (in many cases concealed) through the width and depth of large-sized members (Figure 2). These tests add time to the investigation; as such, their frequency (i.e., the number of tests) and location should be carefully considered to allow for a sufficiently representative sample. Core Sampling Core samples are typically extracted for microscopic examination and species identification.

Wood species, member composition (e.g., the presence of laminations), and damage at a cellular level can be assessed by a qualified professional based on the microscopic evaluation of core samples. Because there might be more than one species of wood in a single truss, extracting at least one core sample from each type of member (i.e., top chord, bottom chord, and web members) is a good practice to follow. Visual Stress Grading This technique includes close-up inspection of wood members to identify and locate grade-affecting natural characteristics (defects) in wood, such as knots, the slope of grain, checks, and splits. Size, type, and location of knots, as well as the slope of grain, are typically the two characteristics that have the most significant effect on the strength of a wood member. Presence and distribution of natural defects, wood species, and moisture content can be used to calculate allowable design values for each visually graded member. This is done in accordance with methodology outlined in ASTM D245, Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber. Applying this method in the field

Figure 2. Resistograph test to determine the extent of deterioration at the bearing end of a bowstring truss embedded in masonry.

is time-consuming; therefore, it is typically performed on a limited, appropriatelysized, and representative sample of truss members. The sample should include several members of each type and size throughout multiple trusses. Probing Some truss features may be concealed at the time of the investigation. For example, the

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

H O H M A N N & B A R N A R D, I N C.

JUST THE FACTS. ore

bef

AFT

PASS

Independent testing clearly shows the 2-SEAL™ THERMAL WING NUT ANCHOR’s steel core intact and engaged on the left, and on the right ... POSITIVELY NOTHING.

ore

bef

AFT

www.h-b.com/justthefacts

FAIL

Images from test #F4749.01-121-24, taken at 3rd party testing facility, INTERTEK-ATI.

STRUCTURE magazine

June 2018

Deterioration Mechanisms Drying Shrinkage

Figure 3. Exploratory probe opening at the bearing end of a bowstring truss embedded in masonry.

bearing ends may be embedded in masonry, connection details may be concealed by hung components, and existing paint (or other finishes) may impede identification of characteristics that affect stress grading (such as knots). Exposing these conditions may require making exploratory probes (Figure 3) and removing paint or finishes. The probing campaign should be carefully planned to minimize disruption to the existing operations.

Timber members are typically green at the time of installation (moisture content greater than 19%). As the members dry in service, they shrink. Restrained shrinkage may result in checks and splits or other compatibility-driven distress. For example, shrinkage related issues can significantly compromise the dowel bearing strength of bolts, possibly leading to connection failure. Engineers performing the field inspection should pay close attention to connections that include multiple rows of bolts (especially if they include steel plates that can constrain and distress wood members), splices, and connections in tension-loaded members. Exposure to Moisture Wood is susceptible to fungal deterioration (decay or rot) when consistently or repeatedly exposed to moisture; decay will likely occur when the wood reaches a moisture content of 20% or higher. This moisture content can be easily achieved near roof leaks (near gutters or around the perimeter of skylights), or at the ends of trusses embedded in pockets within masonry walls. Ends of trusses embedded in masonry are especially susceptible to this

type of deterioration, given their inability to dry once they have been exposed to moisture. Additionally, the presence of water at truss ends can also lead to corrosion of the U shaped steel straps. Embedded bearing ends should be investigated through a combination of probing, visual observations, surface pick tests, and resistograph tests.

Conclusions The assessment of bowstring trusses should identify all features that would affect the ability of the structure to function as intended and designed. These include loads that differ from the original design loads (due to change in use, added mechanical equipment, the evolution of building codes, etc.) and deterioration of specific members of the truss. An experienced investigator should select the appropriate investigation techniques to identify the deterioration mechanisms affecting the structure. Then, rather than just addressing the symptoms (e.g., rot, fracture, etc.), the repair strategy for bowstring trusses, just like for any other structure, must focus on, consider, and eliminate the underlying sources of identified issues or problems.▪

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

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

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

STRUCTURE magazine

June 2018

Build your NCEES Record today. ncees.org/records

Structural FailureS The Site Professional’s Value to Legal Defense By John L.A. Lyddane, Esq.

hen litigation follows structural failure, the value of experienced on-site observers should not be understated. Those on-site professionals who prefer to leave such matters to insurance investigators and hired expert witnesses need to reconsider. Without a solid basis in fact, the legal process has a decreased probability of achieving the justice which is expected.

The Legal Process Stripped to its basic components, the legal process involves three stages leading to the allocation of responsibility and assessment of damages based upon underlying facts. The parties begin by exchanging pleadings which, in theory, contain the basis of the contractual and legal claims among the parties. This stage is followed by discovery in which documentary, testimonial, and other evidence are developed and exchanged. The third stage involves the process of mediating or adjudicating the various claims. The quality of justice rendered during this process is dependent upon professionals from diverse callings contributing their best efforts to a process which many of them do not fully understand. Without high-quality factual input on the underlying event, the ability of those professionals to reach a valid resolution of the claims is severely impaired. The better understood the on-site professional’s role is, the more likely it is that the process will achieve an evidence-based resolution.

Immediate Concerns at the Time of the Event The primary advantage that the on-site engineer or other professional brings to the process is the factual understanding of the circumstances before, during, and after the structural failure. The investigators who will respond will not have the same technical ability to make valid observations even if they have arguably equivalent expertise. After the safety of personnel, equipment, and structures is secured, the on-site professional is presented with an accident scene where information may already have begun the process of deterioration. Those in control of the site may have an obligation to mitigate the further effects

of the failure by protecting the remaining structure, which may effect changes to the site almost immediately. It is the background and experience of the onsite professional which makes him/her critical to the process of documenting the event for future proceedings. The most professional law enforcement responders will not photograph the scene of structural failure with the same attention to important details which can define the failure. The on-site engineer is also in a better position to assess which subcontractors were involved in the aspects of the work leading to the event, and who among the workers on-site has the requisite understanding and vantage point to assist in the process of determining cause and effect. Although there are formal processes on the construction site for reporting incidents, there is a valid reason to commence the information gathering process even before the dust has cleared. A recent case involving extensive flooding of a New York City apartment complex was determined without a jury trial based largely on a seconds-long video clip taken by an astute building employee during the process of the water entry. Because the metadata from the employee’s mobile phone allowed the court to determine exactly when the flooding occurred, the claims of the plaintiffs could be conclusively disproven without a lengthy trial. The employee who made the video was only trying to show his supervisor what he was dealing with in real time but, in doing so, he created a valuable piece of evidence. The on-site professionals secured the video clip, recognizing that it was an important piece of evidence. It would have been unlikely that their incident reporting process would have identified this defining piece of evidence.

STRUCTURE magazine

June 2018

The on-site professional hopefully has the depth of understanding to appreciate who among the witnesses to the event are the persons with the expertise to understand what they have witnessed and can explain it in proper and understandable terms. A first responder may be able to take down names and contact information of the bystanders but, without an appreciation of the work and the skills applied to complete it, the resultant list may not include the witnesses which a court and jury will need to hear from to do justice. How far the on-site professional should proceed in securing the recollection and observations of witnesses is debatable, but establishing and recording their identity is always useful. It is not always the closest observer to the structural failure who has the valuable evidence, and the on-site professional has the best opportunity to better identify witnesses in that category. Frequently there are critical pieces of evidence which may be secured and labeled at the scene of the failure for subsequent analysis and use. Where the stone facing on a building under construction failed, it was possible to test samples of the fractured facing to demonstrate that the stone supplied to the job site did not satisfy the architect’s criteria for strength. The supplier of the stone had produced samples for testing prior to cutting the stone facing, but the samples had come from a separate area of the quarry, and the tested stone met the established criteria. In a case where the failure of the tubular steel leg of a hospital gurney caused severe injury to a patient who was being transported, the risk manager of the hospital secured the wheel assembly which had broken off the gurney, labeled it, and placed it in the closet in his office. Months later, when the lawsuit had been initiated and reached the point where the attorneys became interested in testing the gurney, that gurney was no longer available. However, the risk manager was able to produce the wheel assembly from his closet and establish a sound chain of custody documentation. The tubular steel portion of the gurney leg was sent to a metallurgist who was able to establish that the failure of the gurney leg was the consequence of a manufacturing defect of which the hospital and its orderly could not have been aware. Without that critical piece of evidence, the hospital would likely have been

People Helping People Build a Safer World

premiumACCESS ™ makes your codes mobile and saves you time Reduce your research time, access the code anywhere with an Internet connection. premiumACCESS online subscriptions offer convenience, choice and comprehensive digital options. Enhanced features make it easier than ever to: • Save time with advanced search and internal linking. • Collaborate with colleagues and share annotations. • Increase productivity.

FREE

Demo available!

premiumACCESS provides access to the complete code text in an easy-to-navigate format and offers a variety of helpful functions to streamline everyday code research.

1-year and 3-year subscriptions now available for: International Codes® | State Codes | Standards | Commentaries

2018 I-Codes ® just added! Try the FREE demo today at codes.iccsafe.org

Long-Term Preservation of Evidence Once physical evidence is secured, records are made, or images are captured, the body of evidence must be appropriately preserved

STRUCTURE magazine 39 June 2018 18-15103_premACC_Structure_Mag_Ad_2thirds_Update_FINAL.indd

18-15103

2/27/2018 12:12:54 PM

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

held responsible for a serious accident which it had no opportunity to prevent. Making an accurate judgment as to what is important to preserve immediately after a structural failure is not a simple task. There may be a confusing set of circumstances to begin with, compounded by the relationships among parties that create indemnification and other responsibility which is not apparent to the observer. Years later, when the insurance coverage and the relationship among the parties are clarified, the issues in litigation may be entirely different from what was expected at the time of the event. However, even so, careful attention to the evidence of the cause of structural failure in the period immediately following the event has a value which is impossible to duplicate as days pass following the event. The on-site professional should also recognize that he could be found to have a legal responsibility to preserve evidence following a structural failure under the legal doctrine known as spoliation. (Spoliation of evidence is the intentional, reckless, or negligent withholding, hiding, or destroying of evidence relevant to a legal proceeding.) Where a party has control of the location of an accident, and the ability to safeguard and preserve important evidence, there can be a legal responsibility to prevent evidence from being lost, or even an obligation to take affirmative steps to preserve evidence. If this obligation is not met, another party to the ensuing litigation may be able to show that it is legally disadvantaged by the loss of that evidence and request that the Court cure that disadvantage. Courts have precluded opposing evidence, determined issues as a matter of law, and given limiting instructions to jurors to deal with spoliation claims. Clearly, the prevention of a spoliation issue is preferable to having to devise a cure. In an era where high-quality photographs and video are routinely produced from handheld devices possessed by virtually everyone, it may be difficult to explain the absence of good evidence from those who were in a position to obtain it at the time of structural failure. There is a natural reluctance of non-attorneys to become involved in situations which might lead to litigation but, weighed against the possible loss of evidence which may be important to disproving legal claims, the potential inconvenience and discomfort must be seen in context.

of custody issues or other questions regarding the identity of physical evidence after removal from the site in question. Without labeling and careful records of the chain of custody, one piece of masonry, wire, or metal may be indistinguishable from another. If the evidence cannot be reliably tracked from the failure to the courtroom, it will probably not be admissible evidence at trial. With regard to photographs, the evidentiary rules are generally less stringent. Once the photographs are dated (and timed if possible), the collection itself is usually adequate to show where the photographs were taken. The field of vision overlaps from one photograph to another, allowing them to be identified as a collection from the same site. If the witnesses at deposition or trial can identify the photographs as “fair and accurate depictions” of the objects portrayed, the photographs will usually be qualified as evidence. The dating of each photograph is critical, however, because it is likely that photographs will be taken by others and some will be taken after the fact. The subsequently-taken photographs may not reflect the conditions at the time of the structural failure and may not be able to pass the “fair and accurate” threshold to become evidence at trial. Dated photographs avoid many of those issues.

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

to ensure its value to the disposition of subsequent claims. Procedures on site will vary widely, but the central concern is that the evidence is kept in a format which assures that it will continue to be available and identifiable when needed months or years later. Labeling the evidence with the name of the individual who collected it and the date and location where it was collected is a necessity. Further explanatory information may also be useful. If physical evidence is removed from the site of failure, it is useful to have photographs of that evidence as it existed before it was removed. Preserving the collected evidence is of critical importance, again because of potential spoliation issues. If the evidence were removed from the site and subsequently lost, its import would certainly be magnified by parties who may not have had access to it or responsibility for its preservation. Those who do bear responsibility for the evidence will not only have difficulty explaining how at first it was worthwhile to secure and preserve it as evidence, but also will have difficulty explaining its lost importance when they became unable to produce it for analysis by the other parties to the dispute. Photographing the collected and labeled evidence is helpful, especially if there are chain

Cooperation with Defense Efforts Virtually all insurance policies written to cover property damage and personal injury liability contain a “cooperation clause” of some variety. The insurer will pay the damages for covered events, but the insured parties have the obligation to assist the insurance company and the defense attorneys in gathering, protecting, and understanding the evidence which relates to the claims. Because of the inherent problems in determining the cause of structural failure in a complex environment, insurers require, by contract, that they are given prompt notice of the event of structural failure even before a claim is advanced. The on-site professional needs to develop a sense for which events are likely to result in future claims and work up the chain of command to assure that proper notice is given. This will involve both internal risk management personnel as well as any insurers whose coverage may become involved in compensating for property damage or personal injury. There may be more than one set of insurance interests involved, but that determination will not be made by the site professional. Once the appropriate notifications are made, investigators, attorneys, and consultants will be retained. Contact should be established with a clearly-defined liaison relationship among the insured, the insurer, and defense counsel. The preserved evidence and identity of witnesses will be an early subject of discussion. The defense of any subsequently presented claims will be greatly facilitated by the prior efforts of the on-site professionals to understand and preserve the evidence, which will hopefully establish the causes of the structural failure.

Conclusion Most sites of structural failure are complex in that a number of trades and subcontractors are present and the potential contributors and witnesses may be numerous. The knowledgeable personnel on the site at the time of the event are a valuable resource which needs to be tapped to assure the correct outcome of the resulting claims.▪ John L. A. Lyddane is a Partner at Dorf & Nelson, LLP who has extensive experience in jury trials of technically complicated liability matters, including professional liability cases and construction-related lawsuits. He may be contacted at jlyddane@dorflaw.com. MCI_5x3.5_02-18.indd 1

STRUCTURE magazine

2/19/18 8:44 AM

June 2018

REFRAMING THE FRAMING CONVERSATION. ALWAYS BUILDING. TIMBERSTRAND® LSL TimberStrand® LSL is your does-it-all building solution. From tall walls, to columns, to rim board, it provides the strength to build upward without going over budget. Engineered to accommodate large holes and longer spans, TimberStrand® LSL delivers the strength and versatility you need. Call 888.453.8358 or go to Weyerhaeuser.com/woodproducts to find your Territory Manager and closest Trus Joist® dealer.

CASE BuSinESS PrACtiCES Does Your Firm Have a Lessons Learned Process?

How Your Firm Can Learn from Its Mistakes as Well as Its Successes By Bruce Burt, P.E., SECB

espite advances in artificial intelligence and the increased sophistication of modeling software, at least for the time being, the decision-making process at engineering firms remains the domain of people. To err is human, as they say, and the consequences of a mistake can be painful to an engineering firm. How should a firm deal with this inevitability? The first line of defense is effective quality control that involves a robust checking and review process. Avoiding the costly, reputation-damaging, and perhaps even deadly consequences of an error should be the top priority of every engineering firm. Most firms have a quality control system in place to identify and correct major errors. Still, mistakes of a lesser magnitude happen frequently. Give a recent engineering graduate even a little responsibility and “teachable moments” will result. If your firm is small, it is easy enough to ensure the right folks learn from these teachable moments. However, what if your firm is not small? Even a firm of twenty-five engineers has several projects, and the staff probably are not in tune with the day-to-day activities of their colleagues. Moreover, as firm size increases, institutional knowledge becomes more and more difficult to transmit throughout an organization. One method for sharing firm knowledge is the adoption of a “lessons-learned” process. The process need not, and should not, be restricted to identifying and limiting mistakes. It can be adapted to identifying best practices, sharing “tips and tricks,” capturing new processes or propagating other learning opportunities. There are several keys to an effective lessonslearned process. • A firm’s culture must allow for admissions of error in a non-judgmental way. Mistakes happen, and it is in a firm’s best interest to learn from them. Mistakeprone employees will be identified, regardless of a lessons-learned process. However, good employees make mistakes too, and the very best employees will have the self-confidence to promote a culture that allows for self-admission and permits their firm to learn and grow. Some firms might consider an anonymous submission process, but in small and medium-sized firms that may prove

difficult. A firm can present lessons learned sensitively and responsibly, maximizing the benefit of the knowledge gained while minimizing its costs, both monetarily and in employee self-esteem. • The process must be well known and understood throughout the organization. Firm leaders must strongly advocate its use. • It must be simple to initiate. Many lessons learned are lost because there is not a good way to capture them in the moment, with deadlines and other project demands constantly looming. Ideally, initiation of the process should be sticky-note simple. Encapsulating the lessons learned may be involved but creating the “sticky note” in the moment is important for ensuring follow through. • It must have lasting benefit. NASA implemented its acclaimed Lessons Learned Information System in 1994. However, in a review performed in 2012, the Office of Inspector General found that over the prior several years very little data was being inputted to the system and virtually no one was still using the database (Office of Inspector General Report No. IG-12-012, March 6, 2012). • The lessons-learned process should be used for more than just error mitigation. A lessons-learned program can be a vital data entry point into a firm’s knowledge base. What comprises an effective lessons-learned process? Here are four essential components: 1) Identify. The learning opportunity should be recorded on a lessons-learned worksheet (the sticky-note was just an analogy!) as soon as possible after its identification. 2) Resolve. Resolution of the issue should be documented. If an error, how was the error resolved, including time and cost involved and any repercussions? If the issue was another form of learning opportunity, perhaps the methodology along

STRUCTURE magazine

June 2018

with the time and cost of its development could be outlined. 3) Learn. The issue should be analyzed to extract the learning opportunity. Learning opportunities can take many forms: a process change, the adoption of a Best Practice, or a firm-wide teachable moment are examples. 4) Disseminate. Probably the least effective means of dissemination is email, given the massive volume of messages that flash onto our computer screens every day. Taking some time at the beginning of a company meeting might be a good way of introducing the teachable moment and any new resources associated with it. Finally, the data must be retrievable. The most significant risk in expending the time and energy to develop a lessons-learned process is that the lesson is lost with the passage of time. This is a dilemma all technical firms face regarding knowledge management. Experienced workers move on or retire, new analytical methods emerge within a small subset of a firm, sophisticated software is used in new and creative ways, and new time-saving procedures are tried out on a project to great success or perhaps failure. For the firm to maximize its learning opportunities, it must not only have an effective lessons-learned process but an effective means of dispersing that information throughout the organization. A lessons-learned process can be a critical piece of a firm’s knowledge management strategy. Executed effectively, it can capture and accelerate knowledge transfer within an organization, a vital capability in today’s rapidly evolving technical environment.▪ Bruce Burt is Vice President of Engineering with Ruby+Associates, Inc., a constructability-focused structural engineering firm located in Bingham Farms, Michigan. He is a member of the CASE Contracts Committee. Bruce can be reached at bburt@rubyandassociates.com.

WHAT’S BETTER THAN ONE GREAT TUBE COMPANY?

TWO GREAT COMPANIES In November 2016 Independence Tube became a Nucor company, in January 2017 Southland Tube also merged under the Nucor banner, bringing two great tube producers together. Nucor Tubular Products is positioned to bring you all of the latest updates and innovations in pipe and tube manufacturing. Independence Tube and Southland Tube offer the same great products, same great quality, same great 24/7 customer secure portal, same great rolling schedule and on time delivery. But now more of it. We have 5 locations with over 2,000,000 square feet of manufacturing space under roof.

Grades include: • ASTM A500 • ASTM A513 • ASTM A252 • A53 grade B Type E ERW • ASTM A1085 • ASTM A135 and ASTM A795 Sprinkler Pipe

Sizes include: Squares: ½" x 16" gauge through 12" x .625" wall Rectangles: 1 ½" x 1" x 16 gauge through 16" x .625" wall Rounds: .840" OD x .109" wall through 16" OD x .688" wall

This is one time that more of the same is better. Nucor Tubular products—your one source for quality tube products.

NCSEA Publishes Structural Glass Guide

NCSEA News

of glass as a structural element in buildings only has been embraced by the building industry the last 40 to 50 years.

This is most apparent in the fabrication sector, which has

seen the size limits of glass panels grow in response to demands from Designers.

While the use of glass in buildings has existed for hundreds of years, and the use of load-bearing and load-transferring structural glass has become more

commonplace in recent years, it remains an unfamiliar

material to many engineers. This is due in part to the focus on the traditional four materials – steel, concrete,

timber, and masonry – both in Engineering Education and Professional Certification. This lack of industry-

wide experience and knowledge is a reflection of the

lack of documentation of glass in prevalent codes. Additionally, the brittle nature of glass does not make it a

common construction material in this risk-averse sector. Momentum is picking up, however, as the modern pursuit

of “transparency” has come to a point where what was once exotic is now becoming commonplace.

Marcin March, P.E., CEng, MIStructE Franklin Lancaster, P.E. Edited by: Phil Khalil, P.E.

Design Guide

News form the National Council of Structural Engineers Associations

Glass is a material over 12,000 years old. Though the use

Engineering Structural Glass

Recently published with the assistance of the NCSEA Publications Committee, NCSEA’s Engineering Structural Glass newest publication is now available for purchase as a paperback or digital copy! The Engineering Design Guide Structural Glass Design Guide is aimed at structural engineers who are experienced in designing building structures and elements using traditional materials but with little to no experience in using glass to transfer forces. While the use of glass in buildings has existed for hundreds of years, and the use of load-bearing and load-transferring structural glass has become more commonplace in recent years, it remains an unfamiliar material to many engineers. This is due in part to the focus on the traditional four materials – steel, concrete, timber, and masonry – both in Engineering Education and Professional Certification. An incrementally growing body of ambitious and complex all-glass structures is helping to popularize a once esoteric material. This guide is intended to assist Engineers in understanding the basic theory and criteria for designing with this new construction material. The purpose of this Design Guide is to provide the Engineering Professional with sufficient background knowledge and current methods to determine the specification of glass elements in buildings. Engineering Structural Glass Design Guide was authored by Marcin March, P.E., C.Eng, MIStruct, a Structural and Facade Engineer based in San Francisco, CA, and Franklin Lancaster, P.E., a Professional Engineer in New York, and edited by Phil Khalil, P.E., a Structural Engineer in New York. To purchase, visit www.ncsea.com/publications. An incrementally growing body of ambitious and

complex all-glass structures is helping to popularize a once esoteric material. This guide is intended to assist Engineers in understanding the basic theory and criteria for designing with this new construction material.

645 N. Michigan Avenue Suite 540 Chicago, IL 60611 www.ncsea.com

ISBN: 978-0-9998913-0-8

Call for Entries: NCSEA Excellence in Structural Engineering Awards NCSEA’s Excellence Awards annually highlight some of the best examples of structural engineering ingenuity throughout the world. Visit www.ncsea.com to enter your project now! Entries are due July 17, 2018.

Why Attend the Structural Engineering Summit this October? This year’s Structural Engineering Summit in Chicago, IL, is set to be the best and the biggest event in NCSEA history. There are more sessions, more opportunities to network, and more exhibitors than ever! The 2018 Summit is packed with educational opportunities. With over 25 presentations led by structural engineering and business experts, the education at this year’s event will span many topics over five tracks and three general sessions, including Ron Klemencic, P.E., S.E., Thursday Morning’s Keynote; Stacey Hanke, Thursday’s Leadership Plenary; and Ashraf Habibullah, Friday’s Luncheon Keynote. The Summit also features many networking opportunities and activities. On Wednesday morning, Atlas Tube will host a tour of its manufacturing mill; this free tour is optional, but will offer one CEU. Later that evening, the Trade Show will open to host the Welcome Reception. Open to all attendees, this event is a great opportunity to visit with your peers as well as with the exhibitors. Those events are followed by the (optional) Structural Engineering River Cruise on the Chicago River. This one-of-a-kind event, hosted by SEAOI & NCSEA and sponsored by Atlas Tube, will feature special presentations about the architecture surrounding the river delivered by Chicago Engineers & SEAOI Members, our personal docents of the evening. Thursday will host A Celebration of Structural Engineering, an evening event hosted by Computers & Structures, Inc., that celebrates the immeasurable contributions of the structural engineering profession and the ways in which structural engineers are essential to the progress of humanity! The Summit then closes with the NCSEA Awards Banquet & Reception which honors engineering projects and leaders in the field. This banquet features the presentation of the Excellence in Structural Engineering Awards, honoring the best examples of structural engineering ingenuity throughout the world, as well as the NCSEA Special Awards, given to NCSEA members who have provided outstanding service and commitment to the association and the field. The 2018 Structural Engineering Summit is a can’t miss event! Registration is open now. This year’s registration fees are split into two main categories: Full Conference Plus and Basic Conference Registration. Both categories offer full conference options for First Time Attendees, Young Engineers, and Spouse/Guests. Full Conference Plus includes ALL activities, including the SE River Cruise. Visit www.ncsea.com for more information about this year’s Summit, including registration information, this year’s host hotel, Exhibitors, and the current schedule. STRUCTURE magazine

June 2018

Nominations are being accepted for the 2018 NCSEA Special Awards. The Special Awards are presented at the NCSEA Structural Engineering Summit to NCSEA members who have provided outstanding service and commitment to the association and to the structural engineering field. NCSEA Service Award This award is presented to an individual who has worked for the betterment of NCSEA to a degree that is beyond the norm of volunteerism. It is given to someone who has made an indisputable contribution to the organization and the profession. Congratulations to 2017 Recipient: James O. Malley, P.E., S.E.

Robert Cornforth Award This award is presented for their exceptional exemplary service to an Organization and to

to an individual dedication and NCSEA Member the profession.

Congratulations to 2017 Recipient: Theodore Smith, P.E., S.E. Susan M. Frey NCSEA Educator Award This Award is presented to an individual who has an interest in, and extraordinary talent for, effective instruction for structural engineers. The award was established to honor the memory of Sue Frey, one of NCSEA’s finest educators. Congratulations to the 2017 Recipient: Edwin T. Huston, P.E., S.E.

NCSEA News

NCSEA Special Awards

Submissions are due by July 17, 2018. To learn more about the NCSEA Special Awards, and about last year’s recipients, visit the Awards section of www.ncsea.com.

The International Code Council (ICC) and the National Council of Structural Engineers Associations have a long history of supporting building safety and design professionals with joint publications, design and building safety conferences, disaster response, and ICC-ES product evaluations, which has benefited manufacturers, code officials and the design community. An agreement between NCSEA and ICC-ES includes procedures for review, by structural engineers, of selected proposed acceptance criteria involving complex structural products and systems, ensuring feedback from the structural engineering community when ICC-ES is considering new and innovative products or systems. This partnership has long been known to include a discount for ICC Publications for NCSEA Members. The discounts cover many titles in various topics, such as 2018 International Building Code, Seismic Design Using Structural Dynamics Based on 2015 IBC/ASCE 7-10/ACI 318-14, Steel Construction Manual, 15th Edition, and Guide to the Design of Building Systems for Serviceability. These publications, and many more, are discounted up to 25% for NCSEA Members. This benefit can be easily accessed by logging into the NCSEA Member Portal and clicking on the “ICC Publications” link. More recently, both associations announced plans to form an Oversight Committee to work together to form a joint Disaster Response Network. NCSEA and the ICC signed an agreement to join forces on NCSEA’s Structural Engineering Emergency Response (SEER) 2nd Responder Roster to create a single database between the two organizations of volunteers willing and able to quickly and effectively serve when disasters strike. In the aftermaths of Hurricanes Harvey and Irma in 2017, 75 2nd Responders were deployed from the database to assist in damage and safety assessments. However, the SEER 2nd Responder Database is only as good as the structural engineers who are willing and able to volunteer and have created and updated their records. If you have post-disaster assessment training, create a record today. If you are interested in bringing post-disaster assessment training to your local area, reach out to your SEA’s SEER Committee or reach out to the national NCSEA SEER Committee. In another move to strengthen this partnership, NCSEA has joined the ICC Preferred Education Provider Network. The ICC Preferred Education Provider Program recognizes and promotes ICCapproved educational courses offered by over 430 education providers, focusing on the areas of construction codes, standards and guidelines, as well as building construction materials, products, and methods. Plan check engineers, building/special inspectors, building officials, designers, architects, and civil/structural engineers can now enjoy NCSEA webinars while earning continuing education units that meet the renewal requirements of their ICC certifications.

NCSEA Webinars June 21, 2018 How to Verify SE Software Sam Rubenzer, P.E., S.E. July 10, 2018 The Disruption of Structural Fire Protection Practice in the U.S. Kevin J. LaMalva, P.E. July 19, 2018 Introduction to Seismic Design – Low Seismic Thomas F. Heausler, 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. STRUCTURE magazine

June 2018

News from the National Council of Structural Engineers Associations

ICC and NCSEA Strengthen Partnership to Reinforce Building Safety

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Learning / Networking

SEI/ASCE Live Webinars

ASCE Free E-learning Webinars

Learn from the Experts

Career Booster Series sponsored by the ASCE Committee on Younger Members: June 12 – Negotiating Skills July 10 – Managing Challenging Projects www.asce.org/continuing-education/elearning-webinars

June 8 – ASCE/SEI 41-17: Analysis Procedure Changes A New ASCE Live Webinar Individual Certificate Fee Discontinued. Register at Mylearning.asce.org for these and much more.

NEW Book: Concrete Foundations for Turbine Generators

State-of-the-art practice guide MOP 136 provides practical guidance for the analysis, design, and construction of concrete foundation turbine generators.

ASCE WEEK Save the date and join us for a career-invigorating event of inspiring speakers, dynamic learning, networking, collaboration with partners, and fun social events. Session and Abstract proposals due June 5 at www.structurescongress.org #Structures19

JOIN US!

A CONTINUING EDUCATION EVENT

Las Vegas, Nevada September 23–28, 2018

Green Valley Ranch Resort Spa & Casino

www.asceweek.org #ASCElearn

Check out the program and register at www.etsconference.org #ETSC18

Membership

SEI Sustaining Organization Membership

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

THE MISSING PIECE IN COMPLETE BUSINESS PROTECTION PROFESSIONAL LIABILITY PROGRAM

OVER 25 YEARS OF EXPERIENCE IN THE ENGINEERING INDUSTRY

Don’t wait until it’s too late. Protect yourself and your firm against negligent acts, errors, and omissions with competitive, reliable, and secure coverage.

SEI Elite Sustaining Organization Members

Request a quote today!

ASCEinsurance.com/PLdefense2 800.650.ASCE (2723)

182247-B-ASCE-PLE-MAG-PAD

Join or Renew SEI/ASCE For innovative solutions and learning, to connect with leaders and colleagues, and enjoy member benefits such as SEI Member Update monthly e-news opportunities and resources – visit www.asce.org/myprofile or call ASCE Customer Service at 800548-ASCE (2723). Follow @ASCE_SEI

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. STRUCTURE magazine

June 2018

SEI News Check out SEI news at www.asce.org/SEI, including: Structural Stability Research Council (SSRC) 2018 Annual Stability Conference. The Structural Stability Research Council (SSRC) held its 2018 Annual Stability Conference in Baltimore, Maryland, April 10-13. The SSRC disseminates research related to structural stability among the engineering profession. Research topics included experimental tests on steel tub girders and curved twin girders. The SSRC also organized a short course for practicing engineers, Tools for Designing Members with Slender Elements by Kara Peterman and Cristopher Moen.

Call for New Members ASCE 41 Seismic Evaluation and Retrofit of Existing Buildings

Practicing engineers, researchers, building officials, contractors, and construction product representatives are all needed and welcome.

Students and Young Professionals

Young Professionals Represent ASCE at Emerging Leaders Alliance (ELA) Conference, November 4–7, 2018.

Thank you

Thank you to the SEI Futures Fund and Donors www.asce.org/SEIFuturesFund for generous support investing in the Future of Structural Engineering at Structures Congress in Ft. Worth for: • 30 Student and Young Professional Scholarship Recipients • Keynote Speaker • Livestream Pilot From a Student Scholarship Recipient: “Thank you for this excellent opportunity. There is no doubt that this conference was an exceptional experience for everyone in attendance. Personally, this was the best opportunity I have ever had for career networking and interactions with professionals in my desired field. I was exposed to an abundance of knowledge and information about the profession and was able to learn at a constant rate. I took more out of this conference than I have from any career fair or information session that I previously participated in. I will look at this as the first major step in the development of my professional network. The career networking event was very beneficial for me and provided an opportunity for a possible internship. The Congress did a good job of providing abundant learning opportunities while maintaining a very fun atmosphere. I found my passion for Structural Engineering dramatically increased.” Matthew Tyler, S.M.ASCE, Virginia Tech

Advancing the Profession

SEI/ASCE Awards

Congratulations to 2018 SEI Fellows and SEI/ASCE Award Recipients www.asce.org/SEI. STRUCTURE magazine

June 2018

The Newsletter of the Structural Engineering Institute of ASCE

Apply by July 1 at www.asce.org/emerging_leaders_alliance. ELA provides advanced leadership training in topics such as social styles, leading innovation, global and virtual team leadership, and more, with members of leading engineering, research, and scientific organizations. The desired applicant has earned a BS in engineering within the past few years and is an Associate or Member of ASCE. Selected applicants receive complimentary conference registration, and are responsible for travel expenses and lodging.

Structural Columns

SEI Online

The Newsletter of the Council of American Structural Engineers

CASE Risk Management Tools Available Foundation 2: Prevention & Proactivity–Act with Preventative Techniques, Don’t Just React • Anticipate problems and situations that may occur • Identify potential risks and mitigate before they become problematic • Develop processes to prevent errors, duplication, and misunderstanding • Take positive actions at the beginning of projects; do not procrastinate. Many conditions can be altered by positive actions Tool 2-1: A Risk Evaluation Checklist Don’t overlook anything! A sample itemized list of things you should look for when evaluating a prospective project. Tool 2-2: Interview Guide Getting “the right people on the bus” is one of the most important things we can do to mitigate risk management and yet we never learn about interviewing skills in school. This tool will help your firm conduct higher quality interviews and standardize the process among all your staff.

Tool 2-3: Employee Evaluation Templates This tool is intended to assist the structural engineering office in the task of evaluating employee performance. The evaluations provide a method to assess employee performance and serve as an integral part of the company’s risk management program. Tool 2-4: Project Risk Management Plan This plan will walk you through the methodology for managing your project risks, along with a few common project risks and templates on how to record and track them. Tool 2-5: Insurance Management: Minimize Your Professional Liability Premium This tool is designed as a guide to help you provide critical additional information to the underwriter to differentiate your firm from the pack. You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

Share Innovative Ideas! Does your firm have an innovative idea or method of practice? Looking to get more involved in short duration projects? We are inviting you to “share the wealth” and submit a proposal for a web seminar topic, publication, or education session you would like to see CASE present at an upcoming conference. Our forms are easy to

use, and you may submit your information via email. Go to www.acec.org/coalitions and click on the icon for Idea Sharing to get started. Questions? Contact us at 202-682-4332 or email Katie Goodman at kgoodman@acec. org. We look forward to helping you put your best ideas in front of eager new faces!

Pathways to Executive Leadership

CASE in Point

Class Three Registration Open Soon! A practical, focused program for new leaders facing the challenges of a continuously evolving business environment. To be successful at taking on higher levels of leadership responsibility and prepare for the demands of being owners, new practice builders need specific and relevant training in the intricacies of leading an A/E firm in ever-changing, always uncertain economic times. Pathways to Executive Leadership is an intensive leadership program for early-career elites and promising mid-career professionals with 8-12 years of experience who are just beginning to lead and think strategically about their practices and careers. The reality-based curriculum focuses on the core skills necessary to think strategically in their markets, build effective teams, and deliver great service for their most valued clients. Target Audience: Pathways to Executive Leadership fills a vital gap and creates a strong connection between ACEC’s Business of Design Consulting curriculum and the Senior Executive’s Institute STRUCTURE magazine

capstone program. It targets those who are making the transition between managing one team (e.g., project managers) to those managing managers and multiple teams. This program is designed to establish habits for long-term high-performance and to create a trusted, national network of colleagues with which to make the journey. Flow of Learning: Budding practice builders face numerous challenges; new skills are required to manage people and the uncertainty of a continuously evolving business environment. Pathways to Executive Leadership will lead participants through a practical curriculum focused on becoming more balanced in their personal and professional life, more influential in team development, coaching, and client relationships, and more strategic in their business relationships to build a strong client portfolio. For more information, contact Katie Goodman, 202-6824332, or kgoodman@acec.org. June 2018

More than 650 members attended the black-tie EEA Gala in Washington, D.C., which was emceed by actor/comedian Kevin Nealon and honored 146 engineering projects from around the world. The Bayonne Bridge Project won the 2018 Grand Conceptor Award as the year’s best engineering achievement in the ACEC Engineering Excellence Awards. The joint venture of HDR and WSP USA constructed a new bridge platform 64 feet above the existing highway, which was then demolished, in order to provide sufficient navigational clearance for huge “Panamax” cargo ships entering the Port of New York and New Jersey. ACEC’s Annual Convention also marks the induction of a new ACEC Executive Committee. Sheladia Associates President/ CEO Manish Kothari took the gavel as 2018-2019 ACEC Chair, succeeding Sergio Pecori of Hanson Professional Services, Inc. ACEC members paid tribute to ACEC President/CEO Dave Raymond’s nearly 20-year “reign” at the Council at various Convention functions. The ACEC President and CEO will be retiring at the end of the summer.

A Brand New Manual for Writing Your Next Winning Proposal There’s a better way to learn how to write winning proposals, and it is not by “trial and error” or “on the job.” ACEC’s newest publication, 33 Proven Secrets to Writing Successful Client-Centered Proposals, offers quick insight into the techniques needed to craft proposals that stand out in a crowd of qualified competition and position your firm to win. Perfect for new A/E/C seller-doers and business developers who are tired of writing late, last-minute proposals that lose

more often than win, this book represents the accumulation of “lessons learned” experience. 33 Proven Secrets is your guidebook to everything about proposals they did not teach you in school. With 60 pages of proposal writing expertise, this book is the perfect addition to any new staffer’s welcome pack or in-house orientation. It can even be a useful resource for more seasoned engineers looking to refine their writing skills.

Looking for More Professional Development? “Can I Borrow Your Watch?” A Beginner’s Guide to Succeeding in a Professional Consulting Organization offers new engineers a head start in the business of professional consulting. Covering a range of topics including writing reports, project management, client relationships, proposals, and financial management, this essential guide is tailored to the unique needs of engineering firms and

the skills and experiences young consultants need to be successful in a large organization. Both books can be purchased through the ACEC bookstore: www.acec.org/bookstore. For more information, contact Maureen Brown (mbrown@acec.org).

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

STRUCTURE magazine

June 2018

CASE is a part of the American Council of Engineering Companies

On April 15-18, a record 1,500 ACEC members attended the ACEC Annual Convention in Washington, D.C., meeting with Senators, Congressmen, and Capitol Hill staffers to advocate for major infrastructure legislation in 2018. The House of Representatives cleared an aviation infrastructure bill shortly thereafter that expands the use of QualificationsBased Selection (QBS) on federally-funded projects, a key priority for ACEC’s “citizen lobbyists” during the Convention lobbying effort. The FAA reauthorization bill boosts funding for federal airport programs over five years and includes provisions to expand the commercial use of Unmanned Aircraft Systems (UAS). In anticipation of Congress taking up the Water Resources Development Act (WRDA) in the near future, ACEC members also advocated for key water infrastructure priorities, including the State Revolving Fund (SRF) program for drinking water projects and reauthorization and expansion of the Water Infrastructure Finance and Innovation Act (WIFIA).

CASE in Point

ACEC’s 2018 Annual Convention and Legislative Summit

Tall Buildings guide Cast Connex Corporation

Dynamic Isolation Systems

ITT Enidine Inc.

Phone: 416-806-3521 Email: info @castconnex.com Web: www.castconnex.com Product: High Integrity Blocks™ Description: Heavy, weldable, solid steel sections which exhibit up to 65 ksi yield strength in all three directions of loading and through the full cross-section of the section. Ideal for use within the center of multiaxis loaded connections where lamellar tearing of hot rolled plate may compromise quality and strength of the connection.

Phone: 775-359-3333 Email: sales@dis-inc.com Web: www.dis-inc.com Product: Viscous Wall Damper (VWD) Description: VWDs are maintenance free, compact rectangular dampers that are incorporated into typical building openings. They reduce story drifts and forces in the structure to provide superior seismic protection and resiliency. Architectural flexibility and smaller structural sections can be achieved by using VWDs which leads to significant cost savings.

Phone: 716-662-1900 Email: ben.eder@itt.com Web: www.itt-infrastructure.com Product: Seismic and Wind Protection Devices Description: Take your durability and survivability to the next level. Turn to ITT Enidine’s portfolio of infrastructure seismic control solutions and 20-plus years of experience. Our highly engineered structure protection components and custom solutions can solve your most critical application challenges.

Dlubal Software, Inc.

ENERCALC, Inc.

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: Complete with USA/International Standards for steel, concrete, timber, CLT, glass, and aluminum, the user-friendly software allows for efficient modeling, a powerful non-linear analysis, and highly detailed design results for all multi-material tall buildings. In addition, direct interfaces with BIM and CAD software incorporate seamless and bi-directional data exchange.

Phone: 800-424-2252 Email: info@enercalc.com Web: http://enercalc.com Product: Structural Engineering Library (SEL) Description: Steel design is easy/fast with SEL. Beams, columns, 2D frames, force distribution in bolt groups…SEL handles it all. SEL’s new 3D sketches make it fast & easy to setup, confirm and “what-if ” your calculations. Member optimization improves efficiency & saves time! Seismic / Wind modules included.

S-FRAME Software

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

SUPPORTING

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

IN ARCHITECTURE

Phone: 203-421-4800 Email: info@s-frame.com Web: s-frame.com Product: S-STEEL Description: Design and optimize steel buildings with S-STEEL, an S-FRAME integrated steel design solution. Quickly run a performance assessment and auto design for strength and serviceability. Supports composite beam design, staged construction, and numerous optimization criteria and constraints. Comprehensive and transparent engineering reports include equations and clause references.

Simpson Strong-Tie® Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: CFS Designer™ Software Description: With CFS Designer software, you can 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.

StructurePoint Seattle Tacoma Lacey

Long Beach Irvine San Diego

Portland Eugene Sacramento San Francisco

Boise St. Louis Chicago Louisville

Los Angeles

New York

Phone: 847-966-4357 Email: info@structurepoint.org Web: www.structurepoint.org Product: spColumn Description: Featuring a flexible graphical interface in the new spSection module for creating and modifying irregular sections, spColumn is used for design and investigation of columns, shear walls, bridge piers, and typical framing elements in buildings and other structures subject to combined axial and flexural loads.

Trimble Phone: 770-426-5105 Email: kristine.plemmons@trimble.com Web: www.tekla.com Product: Tekla Structures Description: Move from design-oriented to construction-oriented engineering and enable structural engineers improved additional services. With an open and collaborative environment, you can easily work with other disciplines and reduce RFIs for complete control from concept to project completion.

KPFF is an Equal Opportunity Employer. www.kpff.com The Tower at Old Post Office Plaza St. Louis, MO

STRUCTURE magazine

June 2018

Structural Forum Advantages of Professional Young Member Groups By Edward Major II, E.I.T.

eing a young engineer can seem incredibly daunting. You are surrounded by professionals who tell you “that is not how I did it when I was in your position.” While I have several years until I can obtain my P.E. license, many of my coworkers and supervisors have their professional licenses. They recognize that, as a young engineer, I have a lot to learn. They have been exceptional at teaching me through involvement on projects and inclusion in conversations. When not in the office, though, I expand my knowledge base with my involvement in professional societies such as ASCE and NCSEA, and their respective young member groups. These young member groups are subsets of the larger societies and their sections/branches. They allow me to converse and interact with those in a similar career position. Who else knows better what it is like starting off at the bottom of a tall ladder than someone standing next you at the bottom? I would like to take this chance to outline what I believe to be the three most important advantages of professional societies – and more importantly, their young member groups.

Not to state the obvious, but networking is crucial You have heard it time and again through college: Networking is key. Network with your peers. Network with professionals. Did you listen? If so, you are on the right path. As overly used as it is, it is more than worth repeating: networking is crucial. Several years ago, I knew an engineer who was laid off. There was nothing she could have done to prevent it. Within two weeks, she was employed again. She found another job so easily because she kept her network strong. Keep current with your network. Maintain your LinkedIn profile and keep your employment history up to date. By staying involved with a young member group (or simply a professional society in general), you will always have material and updates to post. Share a flier for your group’s next event or meeting. Share some words of wisdom taught to you by an older, more experienced engineer.

In person, be brave and talk to that senior engineer at the evening social your group is hosting. Do you think they are just there to stand around? These experienced engineers come to your events because they want to talk to you. The more you actively connect with your network, the more likely they will be able to help you when you are in a tough spot.

Continuing education…because learning never stops

Middle school STEM outreach by the ASCE Pittsburgh Younger Member Forum.

For professional engineers reading this, you know all too well what this means. Three words: professional development hours. To keep your license current, you need to prove to your state board that you are keeping up with the times. As codes change, designs become more complex, and architects push boundaries, you must adapt. There are many ways you can earn continuing education credits to renew your license, but memberships in professional societies give you access to a multitude of resources and PDH opportunities at a discount. In addition, you will have an easy time meeting new peers. Young member groups want a diverse following of young engineers, young professionals, and seasoned professionals to facilitate interaction among their members. Offering technical events for professional development hours achieves this goal and thus helps you grow your network (see advantage number 1 above).

Improve your management and public speaking skills This is especially important if you are on track for a management position or even if you find yourself conversing with your clients as a project manager. While serving as the technical/employment chair for the Pittsburgh ASCE Younger Member Forum, I was responsible for sharing the committee’s plans for technical events. If I was not

proficient at public speaking when I started in this position, I certainly am now. On the management side, we plan the events. This involves booking a venue, ordering food, registering attendees, and important administrative tasks. If you are on track for a management position in your career, take advantage of being a leader in one of the professional organizations in your area. It is the best training you will find. These are the three benefits that I have found most crucial during my involvement with young member groups. There are countless more. Your personal experiences in these organizations will define what you find most valuable about them. While some may relish the social events and the comradery of being with fellow engineers, others value the technical events and continuing education opportunities. The important part is that you find what you need in one of these groups. Whatever your needs are as a young engineer, you cannot satisfy them alone, but your network can help.▪ Edward Major II is a structural engineer for WBCM in Pittsburgh, PA. He is active with several professional organizations, including Pittsburgh Section ASCE Younger Member Forum and as the inaugural President of the Structural Engineers Association of Western Pennsylvania Young Member Group. He can be reached at ejmajor629@gmail.com.

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

June 2018