STRUCTURE magazine - November 2018

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

November 2018 Steel/Cold-Formed Steel Inside: Binghamton University, NY

Learn more: www.castconnex.com/products/high-strength-connectors Industrial Facility, Livingston, California Eichleay Engineers Project photograph: Summit Engineering, Santa Rosa

High Strength Connectors for SCBF. Eliminate Field Welding and Reduce Cost. www.castconnex.com

ŝŶŶŽǀĂƟ ǀĞ ĐŽŵ ƉŽŶĞŶƚ Ɛ ĨŽƌ ŝŶƐ ƉŝƌĞ Ě Ě Ğ Ɛ ŝ Ő Ŷ Ɛ

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

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

American Concrete Institute ....................25 Adhesive Technology Corp .........................8 Canadian Wood Council ..........................51 Cast Connex ..............................................2 Clark Dietrich Building Systems ..............37 Decon USA Inc ........................................33 Design Data .............................................40 Dlubal Software .......................................22 GeoDesign, Inc. .......................................17 Integrated Engineering Software, Inc........30 Independence Tube Corporation ..............42

Integrity Software, Inc. ...............................4 KPFF .......................................................36 New Millennium Building Systems ..........39 Post-Tensioning Institute..........................38 RISA ........................................................52 Simpson Strong-Tie............................15, 29 StructurePoint ............................................6 Struware .....................................................4 Trimble ......................................................3 USG Corp................................................34

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

Demos at www.struware.com

Not listed?

Wind, Seismic, Snow, etc. Struware’s Code Search program calculates these and other loadings for all codes based on the IBC or ASCE7 in just minutes (see online video). Also calculates wind loads on rooftop equipment, signs, walls, chimneys, trussed towers, tanks and more. ($250.00).

Visit our website to see what advertising

CMU or Tilt-up Concrete Walls Analyze solid walls for out of plane loading and panel legs next to or between openings by automatically calculating loads to the wall leg from vertical and horizontal loads at the opening. ($75.00 ea)

opportunities are right for you!

Floor Vibration Program to analyze floors with steel beams and/or steel joist.

Compare up to 4 systems side by side ($75.00).

STRUCTUREmag.org

Concrete beam/slab Program to provide bending, shear and/or torsional reinforcing.

Quick and easy to use ($45.00).

Creative Director Tara Smith graphics@STRUCTUREmag.org

EDITORIAL BOARD Chair Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@STRUCTUREmag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. AISC, Littleton, CO John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA Linda M. Kaplan, P.E. Pennoni, Pittsburgh, PA Timothy M. Gilbert, P.E., S.E., SECB TimkenSteel, Canton, OH

Bentley spending out of control?

Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY

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

®

Brian W. Miller Davis, CA Emily B. Lorenz, P.E. Precast/Prestressed Concrete Institute, Chicago, IL

• Prevent Quarterly and Monthly Overages • Whitelist allowed applications, block all others SofTrack controls Bentley® usage by • Control all Bentley® usage, prevent overages Product ID code and counts (pipe, inlet, • Block use of all un-owned Bentley® applications pond, and all others) • Automatically queue users when access is and can actively blocked, notify when license ready block unwanted • Give users visibility of who is using licenses now product usage • Warn and optionally terminate idle usage SofTrack reports and • Historical Usage Reporting of all applications optionally controls ® • Introducing: Bentley CONNECTIONS Visa usage of all Autodesk® (desktop) per-user control products by Version,

CALL US TODAY: (866) 372 8991 (USA/Canada) (512) 372 8991 (Worldwide) www.softwaremetering.com

Feature Code, and Serial Number!

©

© 2018 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

4

November 2018

Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT Greg Schindler, P.E., S.E. Sammamish, 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 11, 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 Columns and Departments

HISTORIC STRUCTURES

31 Halsted Street Vertical Lift Bridge

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

EDITORIAL

7 Elephants and Inspiration

By Ed Quesenberry, S.E., P.E.

CODE UPDATES

LEGAL PERSPECTIVES

35 On the Subject of Indemnification – Part 1

By Gail S. Kelley, P.E., Esq.

9 Updated AISI S100-16

By Helen Chen, Ph.D., P.E., Roger Brockenbrough, P.E., and Richard Haws, P.E.

INSIGHTS

38 Regulating Urban Rooftop Wind Turbines

By Dan Eschenasy, P.E., SECB

STRUCTURAL FAILURES

12 Unrecognized Knowledge

By Julie Mark Cohen, Ph.D., P.E., SECB

26 BINGHAMTON UNIVERSITY ENERGY R & D BUILDING

STRUCTURAL ANALYSIS

16 When Humans Make Structures Shake

By Julia Graham, Shayne Love,

By Chris Latreille, P.E.

and Sonia Beaulieu

The Binghamton University Energy R & D Building extensively uses curved, round Hollow Structural Sections (HSS) members as a structural framing system and the primary visual components of the architecture. This article focuses on the exposed structure in which each component utilizes a round HSS shape with a profile that

STRUCTURAL DESIGN

20 Variable Modulus of Subgrade Reaction – Part 1

By Apurba Tribedi

has double curvature.

STRUCTURAL PERFORMANCE

23 Functional Recovery and Seismic Vulnerability

By Taryn Williams, S.E.

ENGINEER’S NOTEBOOK

41 Surface Preparation of Concrete Joints

By Gregory McCombs, S.E., and Steven Petroff, P.E.

SPOTLIGHT

43 Two Towers, One Structure

By Patrick Ragan, S.E.

IN EVERY ISSUE 4 Advertiser Index 44 NCSEA News 46 SEI Update 48 CASE in Point 50 Resource Guide – Software Updates

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

5

November 2018

Editorial Elephants and Inspiration

By Ed Quesenberry, S.E., P.E.

O

ne day, I learned that our firm had been awarded the Oregon Zoo Elephant Lands project, a new 6-acre development to replace the existing, old exhibit that housed a herd of seven Asian elephants. Suddenly, the reality of having to design structures to withstand abuse from elephants standing 14 feet tall and weighing 14,000 pounds settled in. Not finding “Elephants” listed in Table 4-1 of ASCE 7-10, it became quickly apparent that this was not going to be like any other project I had designed. As it turned out, the elephants repeatedly reminded me of many great things about our profession, lessons that serve to inspire me at work to this day.

by the behavioral characteristics of the elephants. Zookeepers provided anecdotal information on what worked and did not work in the old habitat, and we spent hours observing the elephants, making refinements to our design as we learned more about them. The result speaks for itself, as the zookeepers and elephants are happier and safer than ever before. We need to push past resistance and insert ourselves early in the process to ensure that our designs are effective at meeting the users’ needs.

Elephant Lesson No.3: Projects are Teaching Opportunities How often do you receive a call like this: “I have this project, and I was told I need an engineer to stamp it. Do you do that?” There are signs that our profession is trending toward commoditization, and one contributing factor is a lack of knowledge of what structural engineers do. Much of the spotlight on the Elephant Lands project was focused on the integrity of the structural design. Consequently, there were many opportunities for us to explain to non-engineers how and why we arrived at our engineering solutions. The display of genuine interest in what we do made me realize that, as practicing engineers, we must be willing to take the time to explain how great and essential our profession is, and to capitalize on opportunities to do so. When the head elephant keeper introduces me as “Packy’s structural engineer,” another of these opportunities presents itself. Then it’s show time!

Elephant Lesson No.1: Structural Engineering is a CREATIVE Profession It is sometimes easier and more profitable for us to design in cruise control but, for the future of our profession, we must continually strive to build creativity and innovation into our designs. Overly prescriptive building codes and limited construction budgets can lull us into allowing our designs to draw from a very small box of conventional solutions and standard details. Creativity is often limited to the selection of the optimal lateral force resisting system, offering input on the building grid or, at its most mundane, selection of the perfect post-installed anchor. For me, it took one look at Packy, one of the largest Asian elephants in captivity at the time, to realize that I was going to have to put on my creative hat. Armed with my knowledge and experience, I was able to design barrier fencing, shade shelters, interactive elements, and buildings that could survive any loading scenario Packy could create, while protecting animal welfare, meeting the architect’s aesthetic requirements, and allowing for an enhanced visitor experience. Packy precluded me from hiding behind the code and inspired me to think outside the box.

Demonstrating creativity is the key to elevating the status of the Structural Engineer in the design process.

Elephant Lesson No.4: We Make the World a Safer Place It is relatively easy to get lost in our analysis and problem solving and forget about the impact our work has on the world around us. It took witnessing the elephants being introduced to their new facility for me to remember this. In their old facility, the elephants were confined to a relatively small space; I was accustomed to seeing them looking bored and lazy. When the massive door to the new outdoor habitat opened, the herd bounded out and began exploring with vigor. According to the keepers, the elephants have never been healthier and they attribute that to the design of the new facility. Being in a safe place designed just for them, they are flourishing. As structural engineers, we make this happen every day. Whether we are establishing, restoring, or enhancing the safety of structures, we make the world a safer place every day we show up to work. We must not lose sight of this; it is our primary directive as structural engineers.

Parting Elephant Epiphany

Elephant Lesson No.2: Get to Know End Users

Innovative structural designs and creative problem solving require some level of inspiration. In today’s workplace, it is difficult to find this inspiration amidst the noise of endless emails, compressed schedules, and everchanging code requirements. It may not be there on every project but, when you find it, capitalize on it and show everyone what you can do. I continue to draw inspiration from the elephants that I met a few years ago. Here’s to you finding your own Packy soon!■

As structural engineers, we can add more value to the design process by involving ourselves in early discussions with end users of the buildings we design. On building projects, the Architect is typically responsible for determining the needs and desires of the end users or owners and crafting their design to meet those needs and desires. Packy and his herd taught me that the structural engineer could and should have more relevance in this discussion. People are inside buildings for most of their lives; they would benefit from understanding what those buildings are made of and how they are expected to perform.

In the case of Elephant Lands, the entire structural design was driven STRUCTURE magazine

Ed Quesenberry is the founding Principal of Equilibrium Engineers LLC and serves on the NCSEA Board of Directors. (edq@equilibriumllc.com)

7

November 2018

HIGHEST PERFORMING ANCHORING EPOXY − PERIOD − ER-591 ACI 355.4 / AC308

MH61032 ANSI / NSF 61

DOT Approved

The first and only Code Compliant anchoring adhesive approved for bulk dispensing systems!

Visit www.atcepoxy.com for the full line of IBC/IRC Code Compliant anchoring systems for every jobsite and weather condition.

Download the new PRO ANCHOR DESIGN Software.

FAST CURE. COLD TEMPERATURE.

www.atcepoxy.com

1.800.892.1880

atcinfo@atcepoxy.com

I

n 2016, AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members (or Specification), was updated with an entirely new layout which is parallel in format with ANSI/AISC 360, Specification for Structural Steel Buildings. Also, the Direct Strength Method has been integrated into the body of AISI S100, which enables engineers to design cold-formed steel members with unconventional cross-sections.

This reorganized Specification emphasizes design in the main body with the more involved calculations moved into the appendices, such as determination of effective widths and buckling equations for complex sections. A more detailed section-by-section cross-reference between the 2012 edition and the new edition is provided at the beginning of the Standard. An outline of the general steps to determine member strengths is also provided. This article introduces the reorganized Specification, chapter-by-chapter, to familiarize engineers with the new layout and point out the significant changes in the new edition.

Chapter A, Scope, Applicability, and Definitions.

This chapter outlines the scope and applicability of the Specification: cold-formed steel structural members can be designed using AISI S100-16 through the design provisions provided in the Specification (excluding those in Chapter K).

However, if the composition or configuration is beyond those design provisions, the member strength can be determined by tests, by rational engineering analysis with confirmatory tests, or by rational engineering analysis with the following safety and resistance factors: For members, Ω=2.00 (ASD); φ=0.80 (LRFD) or 0.75 (LSD) For connections, Ω=3.00 (ASD); φ=0.55 (LRFD) or 0.50 (LSD).

In this new edition, the above safety and resistance factors have been revised to provide better alignment between the testing provisions and the provisions for rational engineering analysis.

Chapter B, Design Requirements. This chapter lists the essential design requirements: design for strength, structural members, connections, stability, structural assemblies and systems, serviceability, ponding, fatigue, and corrosion effects.

The Specification also points to the appropriate chapters or sections for the design provisions.

In addition, the application limitations for the Effective Width Method (EWM) and the Direct Strength Method (DSM) are provided, and these limitations are consolidated and greatly simplified.

Chapter C, Design for Stability. This chapter includes design provisions for considering structural system stability and member stability. It is required that the structural system stability be considered in accordance with Section C1. The provisions provided in Section C1 are developed based on the AISC Direct Analysis Method, which requires that the whole structure be analyzed, and

members and connections designed, with the following effects considered: 1) Flexural, shear, and axial member deformations, and all other component and connection deformations that contribute to displacements of the structure; 2) Second-order effects (including P-Δ and P-δ effects); 3) Geometric imperfections; 4) Stiffness reductions due to inelasticity, including the effect of residual stress and partial yielding of the cross-section; 5) Stiffness reduction due to cross-section deformation, or local and distortional buckling; 6) Uncertainty in the system, member, and connection stiffness and strength.

Three approaches are permitted: a) Direct Analysis Method Using Rigorous Second-Order Elastic Analysis: Determines the required strengths which include the both P-Δ and P-δ effects, initial imperfections and adjustment of stiffness. The available strengths are then determined using the Specification provisions with the effective length factors, Ky and Kx, equal to one. b) Direct Analysis Method Using First-Order Analysis: Determines the required strength by considering initial imperfections and adjustment of stiffness in the structural analysis. Both P-Δ and P-δ effects are considered using multipliers B1 and B2 (as provided in Specification Equations C1.2.1.1-3 and C1.2.1.1-6). The available strengths are determined as described in (a) above. This method is limited to structures that support gravity loads primarily through nominally vertical columns, walls or frames. c) Effective Length Method: Determines the required strength through linear elastic analysis. The P-Δ and P-δ effects are considered by applying the effective length factors to members when the available strengths are calculated. This method is limited to structures that (i) support gravity loads primarily through nominally vertical columns, walls or frames; and (ii) the maximum second-order drift does not exceed 1.5 times the maximum first order drift.

Chapter D, Members in Tension. This chapter includes tension member design provisions similar to those in the previous Specification edition.

Chapter E, Members in Compression. The column member design provisions consider the following possible failure modes: yielding and global buckling, local buckling interacting with yielding and global buckling, and distortional buckling. Both the EWM and the DSM can be used for the design. For members with holes, comprehensive design provisions are provided with the DSM approach.

STRUCTURE magazine

CODE

updates

Updated AISI S100-16

continued on next page

9

November 2018

By Helen Chen, Ph.D., P.E., Roger Brockenbrough, P.E., F.ASCE, and Richard Haws, P.E. Helen Chen is Manager of the Construction Standards Development of the American Iron and Steel Institute. She is directly involved in the development and update of AISI construction standards. (hchen@steel.org) Roger Brockenbrough is an Engineering Consultant involved in the development of technical information to facilitate improved designs in steel. He is a Member of the AISI Committee on Specifications and an Emeritus Member of the AISC Committee on Specifications. (rogerlbrock@msn.com) Rick Haws is a past chair of the AISI Committee on Framing Standards and is the current chair of the AISI Committee on Specifications. (rick.haws@nucor.com)

Figure 1. Example of a profiled deck.

Figure 2. Cold-Formed steel framing with structural wood sheathing.

Chapter F, Members in Flexure. Similar to column member design, flexural member design also considers yielding and global buckling, local buckling interacting with yielding and global buckling, and distortional buckling. For flexural members, provisions are provided to determine the inelastic reserve capacities when members are not subject to local or distortional buckling. The provisions for flexural members with holes are also provided with the DSM approach.

Chapter G, Members in Shear and Web Crippling. This chapter determines the shear strengths of members with or without holes, with or without web stiffeners, and web crippling strengths.

Chapter H, Members Under Combined Forces. This chapter includes the following interaction checks for members subjected to combined forces: 1) Combined tensile axial load and bending; and combined compressive axial load and bending 2) Combined bending and shear 3) Combined bending and web crippling 4) Combined bending and torsional loading In this edition, the interaction equations for ASD, LRFD, and LSD are unified wherever possible.

Chapter I, Assemblies and Systems. This chapter contains the design provisions included in Chapter D of the previous Specification

editions. The following changes and additions were made: 1) For floor, roof, or wall steel diaphragm construction, three AISI standards are referenced for different applications: a) AISI S310, North American Standard for the Design of Profiled Steel Diaphragm Panels, should be applied for diaphragms and wall diaphragms constructed with profiled steel panels and decks (Figure 1). The safety and resistance factors for this type of diaphragm systems have been moved from the Specification to AISI S310. b) AISI S240, North American Standard for Cold-Formed Steel Structural Framing, should be used for diaphragms constructed with wood structural panels, shear walls covered with flat steel sheets, wood structural panels, gypsum boards or fiberboard panels, or strap braced cold-formed steel stud walls (Figure 2 ). c) AISI S400, North American Standard for Seismic Design of Cold-Formed Steel Structural Systems, should be followed for additional seismic design requirements.

2) For cold-formed steel light frame construction (Figure 2): a) AISI S240 should be followed for framings subjected to gravity and wind loads; and

Figure 3. Special bolted moment frame.

b) AISI S400 should be considered in high seismic load design (Seismic Design Category greater than A) and the seismic modification factor, R, not equal 3.

3) For special bolted moment frames (Figure 3) under seismic loads, AISI S400 should be followed.

4) For metal roof and wall systems (Figure 4), the compressive and flexural strengths of members covered with metal roof and wall panels can now be determined analytically through the DSM approach where the buckling forces or moments should be determined including lateral, rotational, and composite stiffness provided by the metal deck or sheathing; bridging and bracing; and span continuity. These added provisions would enable engineers to design systems that may be outside the limitations of the empirical equations.

5) For steel rack system design, ANSI MH16.1 is referenced.

Chapter J, Connections and Joints. This chapter contains all the design provisions included in Chapter E of the previous Specification editions. The tension rupture provisions for a single bolt, or a single row having multiple bolts perpendicular to the force, are revised. As shown in AISI S100 Table J6.2-1, the revised provisions contain a single shear lag reduction factor for all flat sheet bolted connections

Figure 4. Metal building system.

STRUCTURE magazine

10

November 2018

AISI S100-16 Table J6.2-1 not having staggered hole patterns. The reduction factors Shear Lag Factors for Connections to Tension Members for bolted connections of angle or channel members are Description of Element Shear Lag Factor, Usl specified as well in Specification Eqs. J6.2-6 and J6.2-8.

Also, design references for cold-formed steel connecting (1) For flat sheet connections Usl = 0.9 + 0.1 d/s (Eq. J6.2-4) to hot-rolled steel, aluminum, concrete, masonry, wood, not having staggered hole patterns and plywood are added to Commentary Section J7. These (2) For flat sheet connections Usl = 1.0 design provisions and references are deemed proper for having staggered hole determining connection strengths when other materials patterns control the strength.

(3) For other than flat sheet Chapter K, Strength for Special Cases. This chapter connections includes the complete list of AISI test standards, and (a) When load is Usl = 1.0 and the provisions to determine the structural performance transmitted only by Ant = Area of the directly connected elements (strengths) via tests or via rational engineering analysis transverse welds with confirmatory tests. In this edition, the Statistical Data (b) When load is Usl= 1.0 for the Determination of Resistance Factor (as shown in transmitted directly to AISI S100 Table K2.1.1-1) have been consolidated and all the cross-sectional greatly simplified. For diaphragm formed by profiled steel elements (c) For connections of For a welded angle: panels, the tests should be in accordance with AISI S310. angle members not Usl = 1.0 – 1.20 x L  0.9 (Eq. J6.2-5) Chapter L, Design for Serviceability. This chapter includes meeting (a) or (b) the provisions for determining the moment of inertias but Usl shall not be less than 0.4. above used in serviceability calculations. The flange curling For a bolted angle: 1 checks are included in this chapter. A rational approach (Eq. J6.2-6) U sl = 0 .5 b 1 2x is introduced in the Commentary when DSM is used.

1 .1 + + Chapter M, Design for Fatigue. This chapter contains the b2 + b1 L fatigue design provisions similar to those in the previous (d) For connections of For a welded channel: Specification edition. channel members not Usl = 1.0 – 0.36 x L  0.9 (Eq. J6.2-7) Appendix 1, Effective Width of Elements. This appendix meeting (a) or (b) but Usl shall not be less than 0.5. above contains all the provisions for determining the effective For a bolted channel: widths under different edge conditions and stress distribu1 (Eq. J6.2-8) U sl = tions, which were included in Chapter B of the previous bf x + + 1 .

1 Specification edition. bw + 2bf L Appendix 2, Elastic Buckling Analysis of Members. This appendix provides information and references needed to AISI S100-16 Table K2.1.1-1 determine the member buckling stresses or stress resultants Statistical Data for the Determination of Resistance Factor with either numerical or analytical approach. These buckling Type of Component Mm VM Fm VF stresses or resultants are used throughout Chapters C to H. Appendix A, Provisions Applicable to the United States and Mexico. This appendix includes the provisions that are Members applicable to the United States and Mexico only. In this Tension 1.10 0.10 1.00 0.05 edition, the country-specific provisions are consolidated 1.10 0.10 1.00 0.05 Compression or eliminated wherever possible.

1.10 0.10 1.00 0.05 Flexure Appendix B, Provisions Applicable to Canada. This appendix includes the provisions that apply to Canada only.

1.10 0.10 1.00 0.05 Shear and Web Crippling S:\_Working Issues\2018_Issues\251811-Nov 18\Ready For Layout\C-Codeupdates-Chen-1811-F.Do In addition to updating AISI S100-16, AISI cold-formed 1.05 0.10 1.00 0.05 Under Combined Forces steel framing standards were updated in 2015. Users can 1.00 0.10 1.00 0.05 Other Member Limit States1 download all AISI newly published standards from the website www.aisistandards.org. To help design engineers Connections and Joints better understand AISI S100-16, the companion document, AISI Cold-Formed Steel Design Manual, has been Welded Connections 1.10 0.10 1.00 0.10 updated and published in 2018. This new edition of the 1.10 0.08 1.00 0.05 Bolted Connections Design Manual provides design examples that illustrate 1.10 0.10 1.00 0.10 Screw Connections the newly added design provisions.■

Power-Actuated Fasteners

A similar article was published in Proceeding of Twenty-Third International Specialty Conference on Cold-Formed Steel Structure. Content is reprinted with permission.

The online version of this article contains a Sidebar (Outline for Determining Member Strengths) and references. Please visit www.STRUCTUREmag.org.

1.10

0.10

1.00

0.10

1.10

0.10

1.00

0.15

Connections to Structural Concrete

1.10

0.10

0.90

0.10

Connections to Wood

1.10

0.15

1.00

0.15

Other Connectors or

Fasteners2

Notes:

1 For member limit states captured in testing but not covered in AISI S100.

2 For steel-to-steel connectors and fasteners not already listed in the table.

Sidebar STRUCTURE magazine November 2018 11 Member Outline for Determining Strengths:

structural

An investment in knowledge pays the best interest.

– Benjamin Franklin

FAILURES

F

orensic practice in structural engineering typically entails seeking technical causes of failures. Occasionally, discussions of technical causes are disseminated through publications or conference presentations. However, the underlying or root causes of failures are seldom disseminated, because they are rarely sought.

Seeking root causes are frequently not the objective in litigation. Root causes are found in the “discipline of design” (Roe et al., 1967), specifically in design decisionmaking, which relies on technical knowledge and judgment between value and utility. Structural engineering design decisions follow from civil (structural) engineering university education, tradition and culture in practice, licensure, peer review, and continuing education.

One example of unrecognized knowledge and a subsequent failure occurred in the early 2000s with high-strength, hard steel threaded rods of ASTM A722 Gr 150 material that were galvanized for use as waler bolts in a marine environment. The rods fractured soon after installation. The author presented highlights from a sealed legal matter (with fictionalized participants and location) in STRUCTURE, February 2015. The technical cause for the failure was hydrogen embrittlement and stress corrosion caused by the galvanizing. The root cause was the lack of recognition of available, pertinent knowledge. In 1974, ASTM A143, the Standard Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement, was revised to include: “In practice hydrogen embrittlement of galvanized steel is usually of concern only if the steel exceeds approximately 150 ksi (1100 MPa) in ultimate tensile strength, or if it has been severely cold worked prior to pickling.” In 1975, ASTM A722, the Standard Specification for High-Strength Steel Bars for Prestressed Concrete, was adopted. This is an example of available and pertinent knowledge unrecognized by structural engineers making design decisions.

A second example pertains to the minimization of locations of seismic-resistant steel framing.

This can result in disproportionately large framing members that possess “size effects” within

Unrecognized Knowledge Recurring Structural Failures

By Julie Mark Cohen, Ph.D., P.E., SECB Julie Mark Cohen is a Consulting Structural and Forensic Engineer and Independent Science and Technology Studies Scholar. Part of her research is sponsored (4/1/2017 to 3/31/2019) by a grant entitled “A Study of Knowledge Flow and Recurring, Costly Infrastructure Failures”

by NSF’s Science, Technology, and Society program. Using her research results, she will be writing a book entitled Unintentional Structural Failures

by Design. (jmcohen@jmcohenpe.com)

STRUCTURE magazine

12 November 2018

welded beam-column connections, thus leading to a technical cause of fracture. The root cause is that “lumping” of resistance does not follow systems theory regarding an optimal distribution of resistance which should be uniform throughout the system. The majority of fractured welds that occurred before and during the 1994 Northridge earthquake, and were discovered after the earthquake (FEMA, 2000), possessed size effects. These connections resulted from a judgment that value (most probably labor cost savings) took precedence over utility. Structural steel “design” textbooks, from the 1970s and later, supported this judgment because they showed structural plans with minimal locations of lateral load-resistance. However, they failed to inform readers that connections with larger shapes had not been fabricated and tested in laboratories.

From over thirty years of research, the author has identified and substantiated eight categories in which relevant, pertinent knowledge from related engineering fields has not been used and failures have ensued, either shortly after structures were placed in service or after several years in service. These areas include: 1) Striving through design decisions for structural performance objectives by minimizing, not optimizing; 2) Not using systems design characteristics, such as stability, symmetry, redundancy, load path, continuity, coupling (soil-foundation-structure interaction); 3) Not heeding warnings and recommendations in ASTM standards and steel industry documents against galvanizing high-strength, hard steel with Fu ≥ 150 ksi.

4) Not accommodating deformation incompatibilities resulting from thermal and non-thermal effects; 5) Assuming that concrete is impermeable; 6) Not acknowledging behaviors (stress risers) that follow from size effects, boundary conditions, etc.; 7) Not designing structures in moist environments to adequately shed water; and, 8) Not designing structures to be inspected, maintained, repaired, and replaced.

This article introduces the first two of the eight areas, design and systems thinking.

Structural Forensic Investigations

which is the activity pursued through technological thought, utilizes lateral (associative) thinking, which is almost exclusively synthetical to purpose rather than analytical. It synthesizes or creates as a primary activity rather than dissects,” stated Peters.

Regarding engineering practice and education, Holgate (1983) stated, “...engineering is nothing more than the achievement of clearly specified technological objectives for the lowest possible cost in cash. This view has been reinforced for engineering students by the fact that, with a few notable exceptions, textbooks entitled ‘Design of Structures’ are predominantly concerned with the techniques of conceptual analysis. This contrasts strongly

documents about materials and systems would have been readily available and disseminated to structural engineers. Several documents In their investigations, forensic structural useful to structural engineering practice were engineers often perform independent caldeveloped by federal agencies, such as early culations for which they rely on the same 1960s research by the U.S. Army on the galconsensus documents (i.e., codes, standards, vanizing of maraging steels. Most of these and specifications) that were used to design documents were marked “unclassified,” but the failed structures. These documents conjust sat on bookshelves. Regarding the lack of tribute to the knowledge bases for technical dissemination of federally-sponsored research, opinions presented to attorneys and help Alic (2008) stated, “The post-[WWII] shift an expert working for an attorney to assess in U.S. technology and science policies has an engineer’s performance relative to the been somewhat misunderstood. It was not “standard of care.” That is, the knowledge only a shift toward support for research but with which the forensic engineers are famila shift away from support for [knowledge] iar forms the knowledge basis for a trier of diffusion.” He presented an agriculture- and fact (i.e., judge or jury) to military-focused discussion, determine whether a pracbut his points apply equally Structural engineering is too important to society titioner met the standard of to subject matter of relevance for the profession not to strive to eliminate recurring, to structural engineers. care. Is this good enough for the future of the structural Systems design can be costly structural failures whose root causes are in engineering profession and understood by considering unrecognized, pertinent knowledge. society?

Systems Thinking (undated), Unintentionally overlookwhich includes this definition: ing available and pertinent knowledge may with the attention to mechanical engineering, “a holistic approach to analysis that focuses be intellectual blindness, but it is not neces- where much thought has been given to the on the way that a system’s constituent parts sarily negligence. However, negligence may mental processes involved in design and to interrelate and how systems work over time be found in the lack of recognition of one’s the development of the activity.” and within the context of larger systems. The ignorance and not seeking advice on how to On design philosophy, Holgate stated, systems thinking approach contrasts with ameliorate the situation. What do structural in the architectural field, “many books are traditional analysis, which studies systems engineers not know, why do they not know available, written by architects for architects, by breaking them down into their separate it, and how can they learn it? on the selection of structural form and the elements...” understanding of structural behavior, two Smith (1969), a professor of electrical fields which have traditionally received little engineering, defined a 1960s system as “a comUnderstanding of Design attention in engineering texts.” He continued, bination of diverse but interacting elements Design, 3-D design, and design decision-making “Discussion of the merits and demerits of integrated to achieve an overall objective. are terms that mean different things to archi- particular designs, which is quite common The elements may be human beings, devices, tects and structural engineers. Also, systems in the architectural world, is definitely plants, organizations, or means for processing design and systems design thinking are another discouraged...” information, energy, and objects.” He continset of terms that mean different things to Reinforcement of Holgate’s comments is ued, “The increasing complexity of man-made electric power systems engineers, nuclear seen in the 1951 New York State Construction systems and the increasing availability of prinpower engineers, and mechanical engineers Code in the enabling act (Szendy, 1951). Two ciples and technique for predicting system as compared to structural engineers. These of the five “objectives of and specific stan- behavior have resulted in a new activity called differences would not necessarily be a prob- dards” are relevant: (1) “To formulate such ‘systems engineering.’ Systems engineering is lem, except that the author has found a direct standards and requirements, so far as may be not a branch of engineering; systems problems correlation between structural failures and practicable, in terms of performance objec- occur in every branch of engineering, and a relevant wisdom of those outside structural tives, so as to make adequate performance for given system may involve elements from many engineering that has repeatedly gone unrec- the use intended the test of acceptability,” and different branches. It is not a principal function ognized by structural engineers.

(2) “To permit to the fullest extent feasible, of engineering; some engineers develop sysIn the mid-1800s, as buildings increased use of modern technical methods, devices and tems, others design or operate them. However, in complexity, architects relinquished their improvements which tend to reduce the cost the systems engineer performs a unique funcresponsibilities for structural framing, pass- of construction without substantially affect- tion in a complex engineering project and ing them to civil engineers who specialized ing reasonable requirements for the health, success in performing this function requires in structural engineering. Peters (1991) safety and security of the occupants or users a special type of training and a special set of noted both architects and structural engi- of buildings.” characteristics.” [Smith seemed to have been neers engage in what he called “technological unaware of the Systems Design Engineering thought, which incorporates two diametriprogram at the University of Waterloo that Understanding of Systems cally opposed views of the world.” Architects was started in 1964.] primarily use associative thinking in contrast Looking back to the Cold War after WWII, In the late 1960s, several catastrophic structo structural engineers who use hierarchically it might be thought that, given the increase tural failures occurred, including the May ordered, vertically logical thinking. “Design, in funded engineering research, research 16, 1968, disproportionate partial building STRUCTURE magazine

13

November 2018

collapse of a 22-story precast concrete residential building in East London, England. This failure was caused by a natural gas explosion in a corner apartment on the 18th floor. In 1970, the Building Regulations in the United Kingdom were amended so that this type of accident would not trigger a disproportionate collapse. Specifically, provisions were included for short-duration, extreme pressure loads applied to a small portion of buildings.

In 1970, similar requirements were adopted

by New York City (NYC, 1970). Structural “members shall provide adequate protection against progressive collapse under abnormal load, where progressive collapse is interpreted as structural failure” over given vertical and horizontal extents of buildings. Both codes repeatedly used “wall panels” and “walls” in their requirements. It is thought that these were references to precast concrete construction.

Although both codes were concerned about continuity and load path, they did not explicitly mention 3-D design or systems thinking.

Lessons to Learn Since the late 1960s, each failure has been treated as an independent event with its own technical explanation, some resulting in code changes (i.e., Pearson and Delatte, 2005), none altering the manner in which structural design textbooks were being written. Forensic investigators have primarily sought out quantifiable errors and omissions.

Some investigators have attempted to identify patterns of failures by categorizing them according to structural member type, type of structure, year of design, volume, and dimensions, along with material type, geographic location, and more. These efforts have been carried out by insurers for their proprietary purposes of risk management and underwriting. As a result of focusing on technical causes of failures, root causes have generally gone unnoticed, thus not offering information to develop “feedback loops” to correct deficiencies and inadequacies in structural engineering education and practice.

Structural engineers use or go beyond the minimum requirements published in jurisdiction-adopted codes with their referenced standards, which is necessary, but not necessarily sufficient. The use of these consensus documents implies an expectation of reliable, predictable structural performance intended by the governing codes. These codes include an expectation of structural degradation but not structural collapse, such as for an earthquake that exceeds the design parameters based on a stated probability of exceedance in a specified number of years. However, these documents

have not included much, if any, wisdom and experience of engineers in related fields.

Recent Structural Engineering Practice After the Northridge earthquake, the author (1994) pointed out, “Many structures damaged in the earthquake pulled apart in the same manner in which they were designed – that is, as a collection of two-dimensional vertical and horizontal planes of framing. This lack of breadth and depth leads to structural framing schemes – not 3-D systems – with inadequate reliability for safety, both globally and locally.

Therefore, it is not possible to fully consider the soil-foundation-structure interaction in order to develop adequate building-specific performance criteria for anticipated levels of ground shaking.” A number of photographs are in the reconnaissance literature, including the structural collapse of the California State University’s Northridge precast concrete parking structure.

For many decades, building codes have misused the word system, thus misleading its users. For example, in the Uniform Building Code (UBC, 1967), the “type of arrangement of resisting elements” was described in terms of system, with terms such as building framing systems, box system, dual bracing system, and so on. In contrast, “a ductile moment resisting space frame” is not referred to as a system. The present author (Cohen) noted that an “arrangement” is not a 3-D system.

In another example, the latest International Building Code (IBC, 2015), the referenced standard for seismic-resistant framing types is ASCE/SEI 7-10. In the more recent ASCE/ SEI 7-16 (2016), structural system, the basic lateral and vertical seismic-force-resisting system, and a combination of systems are not defined.

The Commentary included the phrase, “...a geometrically complex arrangement of seismicforce-resisting systems...” Cohen also noted that each building has one 3-D structural framing system which includes seismic-resisting subassemblages, which, according to Smith (1969) and others, should be an integration of “diverse but interacting elements.”

An explanation may be found in a statement

by ISE (2018): “Since WW2 the focus of engineering education has been around analytical technique. Over the last 20 years more thinking about conceptual design has been included in engineering teaching, but in civil and structural engineering it is still mainly taught as just another module, alongside soil mechanics and steel design. Design should be half the equation, analysis the other half. Creativity tells you what to analyse [sic], then analysis follows.

STRUCTURE magazine

14

November 2018

Without teaching conceptual design from the outset, students can’t have a full understanding of why they’re learning analysis.”

This “half the equation” focus can be seen in today’s hierarchy of engineering involvement in a typical building project. That is, it would seem that structural engineers have drifted away from participating in conceptual design and even schematic design. By the time they are invited to enter the project during design development, they have already lost opportunities to design 3-D framing using systems thinking. There is no proof that this approach to structural design offers predictable, reliable performance and reduces the risk of structural failure.

Conclusions Structural engineering is too important to society for the profession not to strive to eliminate recurring, costly structural failures whose root causes are in unrecognized, pertinent knowledge.

The author’s research has resulted in several recommendations for structural engineers “to increase the competence... of the engineering profession” (ASCE 1976 and NCSEA 2011), including but not limited to the following: 1) Participate in discussions with education policymakers at ASCE (the “lead society” for CE at ABET) and NCSEA to increase the number and improve the content of required undergraduate engineering courses for those interested in structural engineering.

2) Improve practice policy by participating in conceptual and schematic design, and conducting project-specific research to procure available, pertinent knowledge for design.

3) Educate owners, lenders, and government agencies on the importance of peer review by structural engineers and those in project-specific related engineering fields.

4) Request continuing education courses that contribute to structural engineers’ knowledge base at the graduate level in structural engineering, structural design, structural analysis, materials science, systems thinking/design, etc.

5) Prepare articles on structural failures that have resulted from substantiated underlying lack of knowledge from related engineering fields; disseminate to the structural engineering community, preferably in professional magazines.■ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

Proven strength equals proven moment capacity.

Introducing our new, improved RCKW rigid kneewall connectors.

Our redesigned RCKW clips provide optimal moment resistance and added load versatility.

Tested as an entire assembly to save you design time, RCKW connectors anchor to the base of exterior kneewalls, overheads, roof parapets or interior partial-height walls, and feature unique anchor-hole options to meet your building’s load capacity needs.

Couple RCKW connectors with RCKWS stiffeners when you need to maximize strength and stiffness values. To learn more, visit strongtie.com/rckw or call (800) 999-5099. Š 2018 Simpson

Strong-Tie Company Inc. RCKW18-E

ANALYSIS

H

When Humans Make Structures Shake Understanding and Minimizing Footfall Vibrations

By Julia Graham, Shayne Love, and Sonia Beaulieu Julia Graham is a structural dynamics specialist with RWDI who has delivered vibration control solutions for more than 70 building projects, including 20 hospitals and research centers. (julia.graham@rwdi.com) Shayne Love applies his expertise in nonlinear dynamic systems to a range of projects at RWDI, requiring structural mitigation of motion. (shayne.love@rwdi.com) Sonia Beaulieu oversaw the Boston College work described herein in her role as a senior project manager; she is also the project delivery leader for RWDI’s infrastructure division. (sonia.beaulieu@rwdi.com)

100

Peak Acceleration (% Gravity)

structural

umans are restless creatures, always moving. They also tend to congregate and enjoy being restless together. Locate all this restlessness in just the wrong spot in a susceptible structure, and the structure is likely to join in – by vibrating in resonance. Structural amplification of human footfalls – walking, jogging, running, jumping, dancing – can be annoying at best and dangerous at worst.

Indoor Footbridges, Shopping Malls, Dining and Dancing

1

Forces from human footfalls can produce unacceptable vibration for a variety of reasons. For example: • The activity has a high fundamental frequency (relative to the range of human activity), like running • The activity is rhythmic and synchronized, for example: aerobics • The structure is particularly susceptible, as for a flexible, long span • Spaces with different expectations are adjacent, as in offices next to a gymnasium A large Boston College recreation center introduced challenges in all these areas. It also reflects two architectural trends that necessitate close consideration of vibration issues.

First, the design uses long, unsupported spans for gymnasium areas. In general, interior long spans are attractive because they permit more flexibility in space planning, better use of daylight, and better adaptability to future uses. In the Boston College structure, they provide an exceptionally large column-free space for sports.

Such long-span, flexible structures are more likely to vibrate even under low-frequency forces such as those generated by footfalls.

Second, the center is a mixed-use facility with multipurpose workout spaces located near offices. The co-location of disparate activities in the same structure is central to trends

ISO Baseline Curve for RMS Acceleration

1

10 Frequency (Hz)

Figure 1. Criteria for peak acceleration in floor vibration. The acceleration depends on the fundamental frequency of response of the floor. (Adapted from American Institute of Steel Construction [AISC])

in “live-work-play-eat-shop” development.

The issue is that human tolerance of vibration depends strongly on context. In mixed-use structures, the tolerable level changes from one space to the next, but the vibration does not.

Key Concepts Design for vibration must consider three things: the source, the transmission path, and the receptor – that is, the person, machine, instrument, or structural element affected by the vibration. Although that sequence reflects how vibration occurs, here it is useful to change the order and start with the receptor. After all, the receptor’s experience determines whether a design is successful.

Receptor: Perception Usually, the goal of vibration control is human comfort but, in some cases, design centers on the performance of sensitive equipment. The focus here will be on humans, but many of the same concepts apply to other receptors.

Human perception of vibration depends on three factors. The first two are frequency and

Rendering of the New Boston College recreation center. Courtesy of CannonDesign, Inc.

STRUCTURE magazine

Offices, Residences

0.1

0.01

Red Flags

Rhythmic Activities, Outdoor Footbridges

10

16 November 2018

(a)

1000

500

0

0

0.5

1

1.5 2 Time (seconds)

(b)

103 Spectral Amplitude (N)

Footfall Force (N)

1500

2.5

3

the activity, the size of any groups, and the locations of the individuals or groups.

10

2

Transmission Path

101 100 10-1

10-2

0

1

2

3

4 5 6 7 Frequency (Hz)

8

9

10

Figure 2. a) Typical footfall force; b) harmonics for someone walking at about 2 steps per second.

– perhaps equivalent to someone running on the footbridge – a person could tolerate a vibration of only 5% g.

The bottom curve needs further clarification: It is the threshold of perceptibility. Below this level, vibration is not perceived. (Note that it uses a slightly different measure: the root mean square [RMS] acceleration.)

Source The critical feature to know about the source is its frequency content. Various types of frequency analysis can be used. Footfall forces are usually low frequency: • Walking: 1.5 – 2.2 Hz • Running: 2 – 4 Hz • Descending stairs: 1 – 4.5 Hz • Synchronized crowd bobbing: 1 – 3 Hz Both the fundamental walking frequency (Figure 2a) and higher harmonics (Figure 2b) should be considered, but harmonics are usually of less concern, as discussed in the next section.

Models of the cumulative force of footfalls include assumptions about the frequency of

STRUCTURE magazine

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

amplitude, which are perceived physiologically. The third is usage or context, which crucially determines how vibration is perceived psychologically. The degree to which people will tolerate vibration varies significantly depending on circumstance: location (on the street, in the gym, in the office, in the home), time of day (morning, evening), duration (seconds or hours), and so on.

Figure 1 shows acceptable levels for floor vibration in spaces occupied by humans; values below the curves are tolerated. This graph relates all three features: frequency, amplitude, and context. However, these curves are frequently misunderstood, with the result that buildings have mitigation issues that could have been avoided. Thus, it is worth going back to basics to unpack what the graph conveys.

First, the y-axis: how much the structure moves. Here is the first source of confusion: The y-axis quantifies amplitude not as displacement but as peak acceleration. To see why acceleration works as a stand-in for amplitude, consider two structures moving at the same frequency or, equivalently, taking the same time for one cycle but at different amplitudes. The structure that travels through a greater amplitude must move faster to cover more distance in the same time. It thus experiences greater acceleration when the structure’s motion changes direction.

Second, the x-axis: frequency. Here the axis measure is not complicated, but the human response is. Usually, extreme stimuli evoke extreme responses. For vibration, counterintuitively, the upturn at both ends of the curve shows that we are less sensitive at the extremes of frequency. For example, consider the left endpoint of the top curve. It means that someone in an outdoor context could tolerate vibration at 10% g (where g is gravitational acceleration) and 1 Hz – equivalent to someone walking slowly (or jumping) on a lively outdoor footbridge.

However, if the motion were at 4 Hz

How a dynamic system responds to the forces of vibration will depend on the characteristics of the system’s transmission path: its mass, stiffness (restoring force), and damping (energy dissipation).

Every oscillator has a frequency at which it responds more strongly: its natural frequency.

When the forcing frequency is near the natural frequency, the effect is resonance: the oscillation is amplified. When the system has no way to dissipate the incoming vibrational energy – that is, it has low damping – the result will be a large resonant response.

The primary issue for occupant comfort occurs when the fundamental frequency of the activity (Figure 2a) aligns with the natural frequency of the floor. The higher harmonics can also excite the structure, but they are a lesser concern because they have lower amplitude and thus carry less energy; floors also tend to be less responsive at these higher frequencies.

RWDI models flooring systems using methods based on those recommended by the Steel Construction Institute (P354) and Concrete Center (CCIP-106). Because the models are based on finite element methods, loading and response can be determined for any point on the floor; in addition, multiple vibration modes can be investigated.

An essential aspect of evaluating the results is the frame of reference. The response of a structure can be modeled and quantified in several ways: for example, peak-to-peak response,

17

November 2018

100

isolate low frequencies. However, courts, and multipurpose rooms for yoga, floating floors can be custom spin, and other fitness classes. Construction 10 designed to the appropriate frequen- began in spring 2017 and is expected to be cies, e.g., for fitness centers. complete by summer 2019.

1 Another very common proposal CannonDesign requested a review of vibraStructural is resilient flooring. It is entirely tion issues because of a combination of two Frequency ineffective. Such flooring is usually features: 0.1 designed to minimize impact force 1) Two unusually long unsupported spans: Attenuation on joints, so people are not injured a) A tennis court gym at 115 feet by 0.01 0 2 4 6 8 10 while exercising. Resilient flooring 137 feet (35 meters by 42 meters) Walking Frequency (Steps/second) does not filter at the right frequencies b) A four-court basketball gym with Figure 3. Relation of floor response and forcing frequency. to prevent floor vibration. suspended track at 107 feet by 161 This floor would amplify footfall vibration from running When significant additional feet (33 meters x 49 meters) (2 – 4 Hz). A transmissibility of 1 means the floor transmits damping is needed and cannot be 2) A concrete-on-concrete floor system the vibration force perfectly, without amplification or achieved by other structural means, for these spans, using precast double attenuation. Vibration can be mitigated by tuning a floor’s one solution is to add a mechanical tees placed on a precast bent natural frequency away from the forcing frequency. damping system. An advantage of These spans are much larger than the typione-third octave frequency response (which such systems is that they can be precisely cal concrete span of 30 feet by 30 feet (9 uses “bins” to group higher frequencies), tuned to the needed frequency. meters by 9 meters). The concrete floor narrow-band frequency response, and root system is not unusual but, for transmission mean square (RMS) acceleration. Because the of vibration, concrete-on-concrete joints Case Study data are being processed differently in each of behave differently than more conventional these frames of reference, the magnitude of The purpose of vibration analysis is to deter- concrete-on-steel structures. response will be different. Thus, when evaluat- mine whether the frequency of the source will These structural choices were made because a ing whether the structure’s response exceeds provoke a resonant response in the structure. multistory design was necessary to accommocriteria, the criteria and the response data The steps in a vibration analysis are: date the desired program within a constrained must be from the same frame of reference.

• Identify the frequency characteristics site. The designers explored structural systems Response data in the time domain can be and forces of the source to minimize structural depths and maximize converted to any frame of reference.

• Model the vibration modes of usable volumes of space for activities. Postthe structure tension precast concrete bents provided both • Evaluate the structure’s response at the shallowest depth and the structural capaMitigation the source frequencies, including bilities necessary for the stacked program, as Strategies for mitigating vibration issues can source harmonics well as an aesthetic complementary to the be architectural or structural. Architectural • Compare the response to the tolerance Collegiate Gothic style. mitigations might involve moving the recepcriteria, using criteria matching the RWDI was asked to evaluate three scenarios: tors (e.g., offices) or moving walking paths or frame of reference used for response 1) Use of tennis court gymnasium activity locations. Structural changes might • Model response with mitigation (unsupported span) involve using heavier floors, stiffer beams, solutions in place 2) Use of four-court basketball/running interstitial posts, or supplementary damping.

RWDI undertook this type of analysis for a gymnasium (unsupported span) Human tolerance of vibration depends on fre- recreation center designed by CannonDesign 3) Use of a multipurpose exercise space quency, with higher tolerance at the extremes of for Boston College, Newton, Massachusetts. adjacent to offices, located in the frequency. Thus, a key to structural mitigation The four-story, 244,000-square-foot structure tennis court gymnasium is to use the floor to filter vibration at the right will provide four basketball courts, three tennis Figure 4 shows the concrete system under frequency. That is, the floor can be “tuned” courts, swimming pools, two multiactivity construction, and Figure 5 shows the finite to be less responsive at the forcing frequency. The effectiveness of this strategy depends on where the forcing frequency falls on the floor’s response curve, as shown in Figure 3.

One such solution is a floating floor – with a caveat. This type of floor is given a fundamental frequency much lower than the source so that it acts as an isolator at higher frequencies. Floating floors are used very successfully for machinery, but typical floors intended for that application do not work well for human activities Figure 4. Long-span concrete flooring system under construction, showing precast double tees placed on a precast bent. because they are not designed to Courtesy CannonDesign, Inc.

Transmissibility

Amplification

STRUCTURE magazine

18

November 2018

Figure 5. A finite-element model of four-court basketball gymnasium showing concrete-on-concrete unsupported span.

element model of the four-court basketball gymnasium.

Concrete does not introduce any issues as a transmission medium. However, the presence of concrete-on-concrete interfaces does require adjustments to the calculations. Such interfaces will deteriorate differently than typical concrete-and-steel interfaces. Cracked concrete usually acts as a solid member because the friction between the elements holds it together. Here, the beams are expected to deteriorate by crumbling at the edges, leaving a gap between a tee and the beam on which it rests. The model was adjusted by treating the beams as pin-connected instead of continuous.

Another adjustment was in the selection of loading scenarios. Standard occupancy loading was not appropriate; instead, the model had to account for concurrent uses by distinct groups engaged in different activities (running vs. basketball). Experience with smaller scale fitness centers helped in selecting scenarios to consider. Several typical scenarios were identified – for example, unsynchronized runners on the track. The model was used to calculate two figures: 1) the floor stiffness required to meet criteria under these typical scenarios, and 2) at

that stiffness, the number of people who could participate without exceeding the criteria.

Figure 6 shows an example of the response mapping. The results were unexpected. The designers were concerned about potential issues in the gymnasium areas, but the only location to exceed criteria was somewhere else entirely: a multipurpose space adjacent to offices, in an area with conventional construction. If 50 people were to perform synchronized aerobics in the multipurpose space, the vibration in the office space could exceed the criterion for offices.

The reason for this result is relative mass. In the gym, runners are a very small mass exciting a much more massive structure; even a very flexible structure will not respond much.

In the multiuse room, even though the space is much stiffer, more mass (50 people) is exciting a smaller area.

Because of the unconventional flooring strategy, the project structural engineer was required to include performance specifications in the design document. A similar vibration analysis was performed for the general contractor to demonstrate that subsequent modifications meet the performance specifications.

Keeping Restless People Happy Generally, a building that has vibration problems is likely always to have vibration problems. Once built into a structure, such issues are among the most difficult to address through retrofits. Thus, extra advanced scrutiny in the following cases will be well rewarded by a higher performance structure.

• Long, flexible structures are most likely to show an undesirable response to human movement.

• Mitigation efforts are best focused on removing vibration response in the 4 to 8 Hz range, where human tolerance is lowest.

• Special consideration must be given when people in adjacent spaces will have different expectations. Vibration does not respect the boundaries of building programs.

By being alert to these critical scenarios, designers and engineers can help ensure that people can enjoy their ceaseless activity without having it bounced back at them – or at their neighbors.■ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

Project Team

<0.05%g

<0.10%g

<0.25%g

<0.5%g

<1.0%g

<1.5%g

<2.5%g

Office Criteria

<5.0%g Multipurpose Criteria

Figure 6. Modeled vibration levels for evaluating the effect of aerobics activity adjacent to office areas.

The turquoise areas within the fuchsia outline at center indicate that the maximum predicted vibration would exceed the office criterion of 0.5% g.

STRUCTURE magazine

19

November 2018

Owner: Trustees of Boston College, Chestnut Hill, MA Structural Engineer of Record: CannonDesign, Inc., Boston, MA Specialty Structural Engineer (precast concrete bents) and Design Manager: Blue Ridge Design Inc., Winchester, VA Architect of Record: Cannon Design, Inc., Boston, MA Construction Manager: Skanska USA, Boston, MA

structural

S

oil-Structure-Interaction (SSI) is a broad and interesting topic. Because of its complexity and unpredictability, engineers often require the use of sophisticated analysis techniques, including specialized software.

Modulus of subgrade reaction (Ks) is one of the key parameters used in mat (or Figure 2. Subgrade modulus of a uniformly loaded flexible foundation. raft) foundation design. It approximately represents soil response at any given point under2) The ratio between base pressure, q, on the neath a mat foundation. This key parameter is very foundation and the corresponding soil useful for FEM-based mat foundation design. settlement, s, will remain constant. q Spring constants can be calculated from Ks values, Ks = s and corresponding spring supports can be applied underneath a foundation. A detailed discussion where, q = contact pressure or on this topic can be found on a related article subgrade reaction titled, Correlation between Soil Bearing Capacity s = soil settlement and Modulus of Subgrade Reaction (STRUCTURE, Ks is known as the coefficient of subgrade December 2013). reaction or modulus of subgrade reaction.

A mat foundation is often analyzed using a It is important to note that the assumptions menconstant value of Ks. Many argue this approach tioned above are considered erroneous as the real is over-simplified and may yield erroneous contact pressure significantly differs from these output for the sake of convenience. simplified assumptions.

This article addresses this complex issue by first briefly discussing the theory and then Contact Pressure providing a solution for FEM based mat founand Settlement dation analysis. A new method (Settlement Profile Part 1: Fundamentals Convergence Method) has been developed by the A uniformly loaded flexible foundation on a perand Current Practices author to calculate and distribute Ks, and apply fectly elastic material of clay will have uniform spring supports at all supporting points. base pressure and will take the shape of a bowl or

By Apurba Tribedi trough. A foundation will suffer the maximum deflection at the center and will gradually reduce Subgrade Reaction towards the edge (Figure 1).

Apurba Tribedi is a Senior Director at As the term suggests, contact pressure is the base As discussed above, modulus of subgrade reacBentley Systems Inc., Anaheim, CA. pressure between the bottom of the foundation tion is the ratio between the contact pressure (apurba.tribedi@bentley.com) slab and the supporting subgrade medium. In (q) and its corresponding settlement (s). For a other words, contact pressure is the subgrade reac- uniformly loaded flexible foundation, contact tion on the footing base due to the application of pressure remains uniform throughout the founThe online version of this article load on top of the foundation. dation, but settlement decreases from the center contains references. Please visit From observations, one can easily conclude that a towards the edge, so q/s or modulus of subgrade www.STRUCTUREmag.org. loaded foundation will deflect and, as a result, the reaction increases from the center towards the supporting subgrade medium will settle. The mag- edge (Figure 2). nitude and the profile of the settlement will depend It is reasonable to predict that the modulus of on soil characteristics, foundation properties, and subgrade reaction will not be uniform, and it will loading. Determination of the contact pressure is increase from the foundationâ&#x20AC;&#x2122;s center towards the crucial for foundation design, yet calculations can be edge. It is known as variable modulus of subgrade very complicated. For larger foundations, like mats or reaction, which is part of the broader topic of rafts, determination of contact pressure can be even Soil-Structure interaction (SSI). more complex. However, because of its importance, a simplified theory has been developed to estimate The Winkler Spring subgrade reaction; the theory is known as the theory of subgrade reaction.

The current practice is to use a commercially availThe theory of subgrade reaction is primarily able FEM program to analyze mat foundations. based on the following two The foundation is typically modeled as bending assumptions: plates, and the supporting soil is modeled as 1) The soil medium is a discrete compression-only springs connected to perfectly elastic mateplate nodes. Those springs are known as Winkler rial. So, it obeys Hookeâ&#x20AC;&#x2122;s springs. It is a popular modeling paradigm because law and stress is linearly of its simplicity. proportional to strain Winkler idealized a soil model consisting of (or settlement). closely spaced identical but mutually independent Figure 1. Contact pressure and settlement on flexible foundation.

DESIGN

Variable Modulus of Subgrade Reaction

STRUCTURE magazine

20 November 2018

a flexible foundation will not settle uniformly under a uniformly distributed load and will maintain continuity with the supporting soil medium.

Effect on Design

K s (psi/in)

40

80

Difference (%)

σmin kip/ft

1.078

0.761

41.66 %

σmax kip/ft

2.741

3.156

13.15 %

Moment (kip-ft/ft)

5.312

3.927

35.27 %

2 2

As we look at the theory of subgrade reaction, it is essential to study the effects of three parameters on mat foundation design. Those parameters are: 1) Uniform Ks and the numerical value of Ks 2) Distribution of Ks 3) Structural rigidity

Uniform Ks

As discussed earlier, current practice is to use FEM-based software packages to do mat foundation analysis. Also, most software packages accept input of a uniform Ks and automatically generate compression-only Winkler springs to model the supporting soil medium underneath the mat slab.

Table 1. Key value comparisons for two uniform Ks values.

linear springs. For such an idealized model, when the foundation is subjected to partial loading, foundation deformation is confined to the loaded region only. In other words, springs directly below the loaded area will be subjected to deflection, and any other springs beyond the loaded area will remain unaffected. For an arbitrary loaded area, spring deformation is directly proportional to the load applied on the top of the spring.

Terzaghi introduced modulus of subgrade reaction using the following mathematical expression. q Ks = s where, q = contact pressure intensity and s = soil settlement The above equation can be rewritten as Ks = P⁄A s Ks = P A×s where, P = force on foundation, A = contact area, and s = soil settlement It is similar to force-per-unit-volume or force-per-unit-area for unit deflection, or pressure for unit deflection.

Soil Continuity The behavior of an idealized model is far from reality. The Winkler model lacks continuity within the supporting soil medium. Soil beyond the loaded area must be affected to maintain continuity. A very stiff foundation with stamp loading will settle uniformly just beneath the footing, but the continuity must remain with the supporting soil medium. Similarly,

Case Study Take the example of an elementary, square mat foundation supporting four columns and analyze the foundation with two different values of Ks; first with Ks = 40 pounds/in²/in and then Ks = 80 pounds/in²/in.

Modeling Mat geometry: Square Mat 12 x 12 x 0.5 feet Soil Modulus of Subgrade Reaction: 40 pounds/in²/in, 80 pounds/in²/in Column Loading: 40 kips each (compressive) Solution

concluded that engineers should select the value of Ks very carefully and should always seek help from qualified geotechnical engineers to provide the best-estimated value.

It should be noted that the model mentioned above is a straightforward mat foundation scenario with arbitrarily assumed mat dimensions and loading. In the next section, we will look at more realistic examples by referring to two published case studies.

Parametric Study Mr. Horvilleur and Mr. Patel (SP-152: Design and Performance of Mat Foundations) studied the effects of different soil and structural parameters on mat foundation design, including dishing effect. The study was accompanied by parametric studies on two actual mat foundations, one of which is described below. The most critical parameters studied were: 1) Mat Flexural Properties EI 2) Effect of Mat Shear Deformations 3) Modulus of Subgrade Reaction, Ks The discussion herein is limited to Ks. NCNB Corporate Center The NCNB Corporate Center is a 60-story concrete building in which two different foundation systems were used. The perimeter columns were supported by deep concrete caissons bearing on 150 ksf rock. The core columns were supported on a core mat having dimensions 84 x 93 x 8 feet. The mat was founded on partially weathered rock with an average modulus of subgrade reaction of 290 pci (290 psi/in).

Two analyses were conducted. First using Ks = 290 psi/in and then Ks = 580 psi/in.

Figure 3 shows variations for pressures and moments for two K values. The maximum change in pressures was 7%. However, there was a 30% change in positive moment and a 43% change in negative moment. It is interesting to note that the variations of the results are in line with the earlier simple case study.■

A commercially available software, STAAD Foundation, has been chosen for the analysis.

It automatically generates compression-only springs to model the supporting soil medium.

Study two types of output as followings: 1) Effect on base pressure distribution 2) Effect on bending moment A summary of results is tabulated in Table 1, which shows considerable differences in results for different uniFigure 3. NCNB Corporate Center – difference in pressure distribution for different Ks. form Ks values. It can be

STRUCTURE magazine

21

November 2018

RFEM 5 FEA Structural Analysis Software

Powerful, Easy, and Intuitive © www.taros-nova.cz © www.wtm-engineers.de

© www.mgm-ki.pl

© www.taros-nova.cz

© www.psp-ingenieure.de

© www.novumstructures.com

© www.enartec.it

Nonlinear Analysis

CLT

Steel

Glass

Concrete

Form-Finding

Timber

Dynamic Analysis

Aluminum

BIM Integration

DOWNLOAD FREE 90-DAY TRIAL

© www.enartec.it

Structural Analysis & Design Software Dlubal Software, Inc.

www.dlubal.com

30 South 15th Street, 15th Floor, Philadelphia, PA 19102

Tel.: (267) 702-2815

info-us@dlubal.com

R

esilience has become a common term among engineers, policymakers, and the national community of construction industry professionals. NCSEA recently formed a Resilience subcommittee to develop positions and recommendations on issues concerning resilience-based planning and design. For engineers engaged in seismic design, the lessons of the 2011 Christchurch earthquake, in which the central business district comprised largely of code-designed buildings was rendered unusable, have impacted the way many engineers think about seismic risk and building performance in earthquakes. This change in thinking has also influenced the way engineers frame conversations with their clients, building owners, and building occupants about post-earthquake expectations of buildings. The seismic life-safety standard has been the design basis for most buildings explicit (or implicit) in building codes for decades. However, this standard has no defined requirements for buildings after earthquakes, such as when they can be reoccupied or how much they will cost to repair. These questions are at the heart of the current resilience conversation.

To address these issues, two pieces of legislation were introduced in the California Assembly in 2018, one for new buildings, and one for existing buildings. Both have the potential for significant long-term impact on how new buildings are designed and whether existing buildings are seismically retrofitted. The Structural Engineers Association of California (SEAOC) has participated in the legislative process for both of these bills, through its Legislative Committee, state-wide technical committees, and regional member organizations, and by working directly with the bills’ author and other industry stakeholders.

This article provides a summary of the issues for those interested in potential national trends and for those who work in California.

California Assembly Bill 1857 AB 1857 was introduced in the California Legislature by Assembly Member Adrin Nazarian on January 10, 2018. The proposed legislation addressed performance standards for earthquake safety in new buildings.

The current text of the bill requires the California Building Standards Commission (CBSC) to assemble a working group comprised of certain state entities and members of the construction and insurance industries (including SEAOC). The bill requires the group to consider, by July 1, 2022, whether a “functional recovery” standard is warranted for all or some building occupancy classifications and whether the standard should be mandatory or voluntary. The bill defines “functional recovery

standard” as a set of enforceable building code provisions that provide specific design and construction requirements intended to maintain or restore a building’s post-earthquake structural and nonstructural capacity to support the basic intended functions of its pre-earthquake use within a maximum acceptable time.

If the working group determines that a functional recovery standard is warranted, the group must estimate the cost of compliance and advise the CBSC on whether the standard should apply only to specific seismic design categories, or to the entire State. If the group determines that a functional recovery standard is not warranted, the group must assist with producing a guidance document for building owners, architects, engineers, insurance agencies, and local jurisdictions regarding functional recovery after a

structural

PERFORMANCE

Functional Recovery and Seismic Vulnerability seismic event. The bill authorizes the CBSC to issue regulations based upon the recommendations from the working group for nonresidential occupancies only.

SEAOC took a position of Support for AB 1857 after some critical revisions were made to the original text. The bill passed the Assembly on May 29, 2018, and is now being considered by the Senate. The full text of the current bill is available at https://bit.ly/2xZbjjW. For an opportunity to see SEAOC’s work in the legislative arena, a video of the April 11, 2018 hearing on AB 1857 is available at https://bit.ly/2zRATsv. Starting at the 37-minute mark until the 53-minute mark, Assembly Member (and AB 1857 author) Adrin Nazarian, SEAOC Legislative Committee Chair Ryan Kersting, seismologist Dr. Lucy Jones, and EERI Executive Director Heidi Tremayne testify in support of this bill.

Since the bill’s introduction, SEAOC participated in several rounds of amendments. The current text of the bill represents a significant departure from where it started. As introduced in January 2018, the bill initially required: …engineered buildings to be built to an immediate occupancy standard regarding seismic safety. Until an immediate occupancy standard is adopted, the [California Building Standards] commission shall adopt … a strength and stiffness standard for engineered buildings that is one and one-half times the level of the current standard.

The language of this bill, which essentially imposed the same requirements currently in place for California hospitals on all newly-designed buildings, was a concern for many structural engineers. The goals of the bill were not clear;

STRUCTURE magazine

23

November 2018

California Legislation Moves to Improve Seismic Resilience

By Taryn Williams, S.E. Taryn Williams is a Senior Project Manager at Simpson Gumpertz & Heger in San Francisco, CA. Taryn is the Past President (2017-2018) of the Structural Engineers Association of Northern California (SEAONC), a Board member for SEAONC and the Structural Engineers Association of California (SEAOC), and a Board member of the Association for Preservation Technology International (APTI). (tnwilliams@sgh.com)

it did not define “immediate occupancy” and did not explain the intent behind an enhanced design requirement. Further, imposing a higher design standard on all buildings has cost implications – not only for the design and construction of the structural system, but for nonstructural systems (such as partitions, mechanical/electrical/plumbing systems, and contents), the functionality of which significantly impacts the post-earthquake recovery of a building. Additionally, it was unclear whether such a standard should apply to all newly-designed buildings, or whether some would be exempt.

California Assembly Bill 2681 AB 2681 was introduced in the California Legislature on February 15, 2018, also by Assembly Member Adrin Nazarian. This bill mandates inventories of “earthquake-vulnerable buildings” or “potentially vulnerable buildings” (as defined and used throughout the bill’s text), with consideration of their recovery functions in providing essential services after an earthquake.

The current text of the bill begins with context about the large expected economic losses after major seismic events, the existence of vulnerable building types, and the need to quantify the vulnerability of California’s building stock as a first step to reduce these losses.

The bill defines “potentially vulnerable buildings” as those within a specific seismic hazard zone (generally where peak ground acceleration is greater than 0.3g in a code-level earthquake, which generally has a 475-year return period), and of certain construction types (such as unreinforced masonry, non-ductile concrete, pre-Northridge steel moment frames, soft/weak/open front lightframed buildings, and designed prior to certain editions of the building code).

Excluded from this legislation are residential properties with one to four dwelling units, mobile homes, hospitals, and schools. (In California, hospitals and schools are regulated by separate state agencies with more stringent design requirements.)

The bill defines “recovery function” as a building occupancy involving one or more of the following: multi-family housing, skilled nursing or residential care, designated emergency shelters, grocery and packaged food stores, pharmacies and medical supply stores, medical provider offices, K-12 schools, essential services provided by a city or county identified in their local hazard mitigation plan, essential services buildings (defined in the California Health and Safety Code), and communications centers or broadcast stations.

New Zealand’s Christchurch aftermath.

The bill requires cities and counties to inventory their building stock before January 1, 2021, to identify potentially vulnerable buildings using publicly available information (such as tax assessor’s record surveys, census data, housing data, building permit records, past or ongoing earthquake mitigation program records, and online searches), and to identify what recovery functions a potentially vulnerable building contains. By June 1, 2021, building departments must notify building owners if their buildings are on the list. Owners notified that their building is potentially vulnerable must obtain a letter from a licensed engineer by June 1, 2022, confirming whether the building is one of the “potentially vulnerable” types as defined in the bill. If the letter states that the building is not one of the potentially vulnerable types, the building department must remove it from the inventory. If an owner does not respond, the building remains on the inventory. By January 1, 2023, building departments must submit their inventories to the State of California. If a building department notifies the state that the building is retrofitted or replaced, the state will remove the building from the inventory.

Before the legislation can take effect, the state is required to identify, by January 1, 2020, funding mechanisms to offset the costs to building departments.

SEAOC has taken a position of Support for this bill after a significantly revised version passed the Assembly. The Senate is now considering the bill. The full text of the bill is available at https://bit.ly/2OAnKMy. The original bill mandated not only inventories, but seismic performance evaluations of “potentially vulnerable” existing buildings performed by structural engineers (with consideration of safety, repair costs, and recovery time). This created a largely unfunded mandate

STRUCTURE magazine

24

November 2018

and was politically controversial, even among engineers. The term “potentially vulnerable” was not as well-defined as in the current bill.

Following the bill’s introduction, the SEAOC Board engaged the SEAOC Existing Buildings Committee to develop a list of what SEAOC considered “potentially vulnerable” existing buildings, which was provided to the bill’s authors during the amendment process.

SEAOC also worked with the bill’s author to modify the language of the bill to limit it to an inventory-only process.

SEAOC and its Legislative Committee continue to participate in conversations with Assembly Member Nazarian, his staff, and other interested parties as the language of both bills evolve.

These two recent bills in California may impact future legislation across the United States. Concepts such as resilience and functional recovery may become more prevalent across the country as states begin to react to the consequences of the new ASCE 7 seismic and wind requirements, and the national resilience conversation broadens. Engineers, owners, insurers, and other stakeholders are beginning to think about what happens to buildings after natural disasters, and how designing them for performance beyond life safety may cost less over the life of the building (in terms of repairs and downtime) and ultimately help communities recover.■ UPDATE – Since the original writing of this article, both bills passed the California assembly and senate, but were unexpectedly vetoed by the governor in late September 2018. The bills are expected to be reintroduced, and possibly modified, in the next legislative session.

SEAOC will continue to work with the bills’ author and conduct outreach to educate the new governor on the relevant issues following the November 2018 election.

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

Binghamton University Energy R & D Building

By Chris Latreille, P.E.

This is the second and final article in a two-part series highlighting the fabrication and erection of the building with a specific focus on the exposed structural steel. For general information about the project, please refer to the Part 1 article, which can be found in the August 2015 issue of STRUCTURE.

Figure 1. Revit and SDS\2 renderings.

T

he new 105,000-square-foot Energy R & D building is complete. A grand opening ceremony was held in August 2017. This $45 million research facility houses physics and chemistry programs focused on energy technologies of the future. The building is a critical component in the development of Binghamton Universityâ&#x20AC;&#x2122;s science programs.

The extensive use of curved, round HSS members as a structural framing system and the primary visual components of the architecture is what makes this project unique. Building Information Modelling (BIM) was implemented extensively throughout the phases of design, detailing, and fabrication.

Autodesk Revit was used to produce the Construction Documents, and SDS\2 software was used to model and detail the exposed HSS framing.

As noted in the first article, there are four structural systems in the building that utilize curved, round hollow structural steel (HSS): the Atrium Roof, the Link Rotunda, the Tree Stair, and the Canopies. These members served individually as the primary load-carrying components of their respective portions of the structure and are also combined into assemblies for trusses and frames.

Detailing Detailers at Schenectady Steel, the steel fabricator, built an SDS\2 model using the two-dimensional (2D) Construction Documents. Building the SDS\2 model from scratch allowed the detailers to get familiar with the complex geometry of the exposed structural systems and their components, and allowed the model to serve as a check on the accuracy and completeness of the Contract Documents.

During design, the Revit model allowed for modeling of the structural shapes and geometry but did not accurately capture connection information or details at joints.

This level of modeling represents a Level of Development (LOD) of 300. For LOD 300, each structural element is represented graphically in terms of quantity, size, shape, location, and orientation, and this information is sufficient in terms of producing 2D construction

Figure 2. HSS prior to final cutting (left) and birds-mouth cuts (right).

documents. The SDS\2 model developed by the fabricator captured all components needed for fabrication of the steel providing a higher LOD (400+). This more-detailed model included all of the individual parts and pieces that make up an assembly and showed how they fit together. Structural steel shop drawings showing final cut geometry were produced from this higher-LOD model. Information on LOD for BIM can be found in the BIM Forumâ&#x20AC;&#x2122;s specification. Figure 1 shows images from Revit and SDS\2 that illustrate the LOD difference.

Fabrication

shop drawings. Parameters such as length, radius, and locations of inflection points of curves were measured for each member.

There was minimal repetition in the truss size and geometry, which added to the required level of checking and double checking.

Once checked, the next step was fitting them all together.

Fabrication of the round, curved steel required a lot of welding and grinding to make joints appear continuous, thereby concealing the actual weld. Some of the assembled shapes were unwieldy and required custom jigs to connect all of the components (Figure 3).

Fillet welding was used as much as possible, particularly at the truss web connections. The web geometry was laid out so that fillet welding could be used around the entire circumference of the webs in most locations. However, for members connecting at shallower angles, portions of the profile of the birds-mouths had to be prepared with a beveled edge; partial-penetration groove welding was used for those portions. Fillet welding was supplemented, where geometry allowed, to complete the all-around welds for each component.

Even with the printable templates, there was still plenty of fitting and touch-up work required for each assembly. The fabricator compared it to an elaborate and heavy pipe railing system due to the amount of grinding and birds-mouthing needed to assemble the individual components. Once the fabrication of each truss was complete, another round of finishing was conducted. This entailed further grinding and polishing of exposed welds to provide a genuinely uniform appearance.

The Rotunda, Tree Stair, and Canopies were mostly assembled in the shop and shipped to the site. Tops of branch members were welded in the field. The Atrium truss structure is more elaborate and required careful coordination to make sure each piece would fit in the field. An aggressive schedule added to the coordination effort since Schenectady Steel fabricated all of the trusses and JPW Structural Contracting, another steel fabricator based in Syracuse, New York, fabricated the tree columns that support the trusses. The girder trusses could not be test-fitted to the tree columns before erection at the site. However, Schenectady Steel did test-fit several purlin trusses to the girder trusses in the shop. The close coordination and rigorous quality control measures proved effective and made the erection process go smoothly.

Each component of the exposed structure utilizes a round HSS shape with a profile that has double curvature. A majority of the members consist of smaller sizes of round HSS for the truss webs, tree stair supports, and canopies. These could be cold bent in double curvature with a small and unnoticeable straight section at the inflection point.

The larger, round HSS sections had to be bent in single curvature and then cut, rotated, and welded back together. These include the branch supports for the Rotunda and tree columns in the Atrium.

The round HSS members were cold-bent by Oakley Steel Products in Bellwood, Illinois. Each piece was shipped to Schenectady Steel longer than required. The extra length was needed for overrun in order to fit the pieces into the machine that bends the steel and allows for final cutting and fitting during fabrication. Schenectady Steel then measured the steel and cut it to length with the appropriate birdsmouth profile (Figure 2). A majority of these profiles are unique since there are over 20 different truss arrangements and the curved web members have varying geometry with respect to the curved and sloped bottom chords. The actual cut geometry is fairly complex since most connection interfaces consist of a round shape coming into another round shape at an angle. The fabricator utilized templates that could be cut out and adhered to the steel so that the ironworkers could cut the birds-mouth shapes exactly. All of these templates were produced Erection using the SDS\2 software.

The detailer developed a quality control program specific to the The Contract Documents specified suggested locations of field splices project for assembly of the trusses. This involved checking the physical for the Atrium, and the fabricator and erector generally followed material and laying out each component of the assembly to ensure it met the dimensional requirements of each truss. The shop drawings provided all of the work points and correct dimensions, but the actual pieces had to be assessed multiple times at numerous locations to ensure they met the geometry noted in the Figure 3. Ground welds (left) and jig for tree columns (right).

STRUCTURE magazine

27

November 2018

Figure 4. Thermally broken connections at rotunda and atrium.

those suggestions. The steel was erected with minimal shoring and temporary supports. Temporary seated connections were developed for the purlin trusses to allow for more rapid and safe erection and verification of acceptable field fit-up. The seats were made from steel pipe, one size larger than the truss chord, that was cut in half. Holes were then drilled to accommodate erection pins.

As discussed in the first article, six of the ten Atrium tree columns are outside of the building envelope. Thermally broken connections, utilizing thermal isolation material (TIM), were used at the curtain walls to reduce thermal bridging. This technology was also used at the Rotunda structure since the lower branch members and concrete column are outside of the building (Figure 4 ).

Field connections for truss chord and branch members were made using complete penetration groove welds with backing. These welds are generally located where the members come together at an inflection point (straight portion of the member). The exposed sides of these welds were ground smooth to provide the appearance of a continuous structure. The fabricator and erector agreed on temporarily bolted tabs at these locations, which were later removed.

The Architect selected a dark green color for the exposed roof deck and conventional wide-flange roof framing and white for the curved HSS. This contrast, along with up-lighting on the columns, enhances the appearance of each space and each point of view of the structures.

Figure 5 shows the final Link Rotunda structure as viewed from the first floor looking east. Figure 6 shows the final Tree Stair structure as viewed from the first floor looking west.

The Energy R&D building is one of a kind. The exposed structure is the product of close collaboration between design professionals and contractors and is unique from both a visual and structural standpoint. Blending form and function was a key objective and was achieved in each component. The structure itself is more expensive than other systems but, as the primary architectural feature, it allowed for the elimination of a number of finishes that normally concealed a more functionally-driven system, thereby balancing the cost.

Each member of the team brought skill and ingenuity to the project, getting behind the concept from the very beginning. Overall, the Energy R&D building is one that invokes pride for those involved in its creation, and will serve as an important facility for Binghamton University now and in the future.

Special thanks to Robert Gennett of Schenectady Steel for contributing to this article.â&#x2013; Chris Latreille, P.E., is a Principal with Ryan Biggs | Clark Davis Engineering and Surveying, D.P.C., and works in the firmâ&#x20AC;&#x2122;s Finger Lakes office in Skaneateles Falls, NY. (clatreille@ryanbiggs.com)

Project Team Owner: Binghamton University, Binghamton, NY Structural Engineers: Ryan Biggs | Clark Davis, Engineering and Surveying D.P.C., Skaneateles Falls, NY Architect: William Hall, Binghamton University, Binghamton, NY General Contractors: Fahs Construction Group, Binghamton, NY, and Andrew R. Mancini Associates, Inc., Endicott, NY Structural Steel Fabricators: Schenectady Steel, Schenectady, NY, and JPW Structural, East Syracuse, NY Photography: Architectural Photography & Design, Inc., Greene, NY

Figure 6. Tree stair.

Figure 5. Rotunda first floor.

STRUCTURE magazine

28

November 2018

Repair and strengthen all in one shot.

Repair, protect and strengthen concrete and masonry structures in one application and significantly reduce your clientsâ&#x20AC;&#x2122; installed cost. The new FRCM Externally Bonded Composite Strengthening System combines high-performance sprayable mortar with carbon fiber mesh to create thin-walled, reinforced concrete shells without adding significant weight or mass to the structure.

To learn more visit go.strongtie.com/frcm or call (800) 999-5099.

Š 2018 Simpson

Strong-Tie Company Inc. FRCM17E

“

VisualAnalysis offers excellent value

”

Structural Software Easy. Versatile. Productive.

When you need answers today: VisualAnalysis delivers!

Download your free trial today:

iesweb.com

800.707.0816

Historic structures Halsted Street Vertical Lift Bridge

By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S.

I

n 1893, John A. L. Waddell (see bio in STRUCTURE, February 2007) designed, based on the designs of Squire Whipple, a lift bridge over the south branch of the Chicago River at South Halsted Street. Plans were made to replace a damaged swing bridge at the site with another swing bridge but the “lake navigation interests” objected, arguing that the old bridge was “always a serious obstruction to navigation.” Their argument was heard by the Corps of Engineers who ruled that they “would not permit him [the Commissioner of Public Works Aldrich] to build any structure which would narrow the water-way to such an extent as would a rotating draw span.” A vertical lift bridge was then considered, along with bascule spans. Waddell wrote a paper on the design of his bridge on November 16, 1894, and it was published in the 1895 Transactions ASCE. He introduced the paper by describing the problems he had in getting his design accepted. He wrote, “After making a thorough study of the problem, Mr. Aldrich decided upon building a lift-bridge similar to the one designed previously by the writer for the proposed crossing of the ship canal at Duluth; and after considerable delay permission was obtained from the War Department to build the structure, with the proviso, however, that the clear headway be increased from 140 to 155 feet above mean low water…

But it was not until the beginning of 1893 that the contract for building the bridge was finally signed, sealed, and delivered. Even then the tribulations of those interested in the enterprise were not at an end, for the letting of the contract was irregular, in that there was no money in the City Treasury to pay for the bridge; therefore, according to the usual custom under such conditions, reliance was placed on the Finance Committee and Board of Aldermen voting, later on, the necessary funds. Under ordinary circumstances this irregularity would have done no harm; but in this case it was otherwise, because it gave each Alderman and each city official an opportunity to tie up the work, if he so desired, by alleging that the scheme was impracticable and that the bridge could not possibly work successfully...

Another main cause of difficulty and delay was the continual changing of city

officials, for in the two years during which this bridge subject was on the tapis there were three changes of administration, involving the election or appointment of three Mayors, three Commissioners of Public Works, and three City Engineers, to say nothing of minor officials.”

He then described the bridge utilizing many illustrations.

He wrote, “The bridge consists of a Portion of plate showing lift span in a closed position and an open single Pratt truss through- position – dotted lines. span of 130 feet, in seven equal panels, and having a truss depth of 23 wrought-iron rods that are attached to the feet between centers of chord pins, so supends of rockers, at the middle of each of ported and constructed that it may be lifted which is inserted the 15-inch equalizing vertically to a height of 155 feet clear above wheel or pulley previously mentioned… mean low water. At its lowest position, the The bridge is designed to carry a douclearance is about 15 feet, which is sufficient ble-track street railway, vehicles, and foot for the passage of tugs when their smokestacks passengers... It has a clear roadway of 34 are lowered. The span differs from ordinary feet between the counterweight guides in bridges only in having provisions for attachthe towers, the narrowest part of the strucing the sustaining and hoisting cables, guide ture, and two cantilevered sidewalks, each rollers, etc., and in the inclination of the end 7 feet in the clear, the distance between posts, which are battered slightly, so as to central planes of trusses being 40 feet, and bring their upper ends to the proper distance the extreme width of suspended span 57 from the tower columns and their lower ends feet, except at the end panels, where it is to the required positions on the piers. increased gradually to 63 feet.”

At each side of the river is a strong, thorWaddell wrote, “Chicago engineers as a body oughly braced, steel tower, about 217 feet were opposed to this type of bridge; and the high from the water to the top of the hous- then highest authority on bridges in America, ing, exclusive of the flagpoles, carrying at the late George S. Morison, stated flatly that its top four built-up steel and cast-iron it could not possibly operate and that it sheaves, 12 feet in diameter, which turn would be impracticable to raise the span off on 12-inch axles. Over these sheaves pass the piers. On the strength of this statement, the 4-inch steel wire ropes (32 inches all) the city Engineer made all the arrangements which sustain the span. These ropes are for canceling the contract for the construcdouble; i. e., two of them are brought tion although some of the substructure had together where the span is suspended, and been completed and a large proportion of the the ends are fastened by clamps, as shown metalwork had been manufactured. It took in Fig. 1; while, where they attach to the some very earnest pleading by the writer to counterweights, they form a loop, which persuade him to permit the work to proceed, passes around a 15-inch wheel or pulley and the said pleading would have been unsucthat acts as an equalizer in case the two cessful had it not been for an important fact adjacent ropes tend to stretch unequally. pointed out. Viz., that the city of Chicago The counterweights, which are intended would have had to pay the full contract price just to balance the weight of the span, con- for the structure whether it were built or not.” sist of a number of horizontal cast-iron The contract called for the bridge to be lifted blocks about 10 x 12 inches, in section, and in less than one minute while adjacent swing 8 feet 7 inches long, strung on adjustable spans were taking over 2 minutes to open

STRUCTURE magazine

31

November 2018

completely. Waddell also had to guarantee the proper functioning of the bridge.

The company building the lifting mechanism, with city backing, would not guarantee the operation using electric motors. Waddell designed the bridge with two 65 HP motors, mounted on the lift span, to provide the supplemental lifting power. Instead, he had to use two 78 HP steam engines located in a room below the approach roadway. Waddell had to consent to these changes to demonstrate the reliability and suitability of lift bridges in situations with large volumes of river traffic. He was promoting the fact that his bridges could be raised in under one minute only as necessary to provide safe passage by various height ships, while a swing bridge had to be fully opened for all shipping. He wrote, “On this score, though, he desired to make no complaint, for he was well content in having had an opportunity to prove the practicability of his lift-bridge designs, even with the accompanying irksome restrictions.” The contract to build the bridge was not signed until early 1893. After many financial problems and changes in city administration, the bridge was opened in late 1893. He wrote, “This was certainly a great triumph for a comparatively young engineer in a struggle with the local technical body, including the highest bridge authority in America.”

Waddell’s article also included portions of his specifications and additions by T.W. Heerman’s on the operating machinery, Samuel Rowe on miscellaneous matters associated with the bridge, and W. W. Curtis on the erection of the bridge. It also was discussed by several engineers at the meeting at which it was presented, and later by several other written discussions. They were generally positive, but many thought the bridge was costly to build and operate and would not be competitive with swing or bascule spans.

Waddell listed the advantages of a lift span over a swing span as follows: “1st. A lift-bridge gives one wide channel for vessels instead of the two narrow ones afforded by a center-pivoted swing-bridge.

2d. There are no land damages in the case of a lift-bridge, as the whole structure is confined to the width of the street. These land damages in the case of some swingbridges amount to a large percentage of the total cost of structure.

3d. Vessels can lie at the docks close to a lift-bridge, which they cannot do in the case of a swing-bridge; consequently, with the former, the dock front can be made available for a much greater length between streets than it can with the latter.

4th. The time of operation for a lift-bridge is about 30% less than that for a corresponding swing-bridge.”

These were the same arguments Whipple made in support of his Hotel Street Bridge in Utica, New York. Waddell concluded his paper writing, “If the contract for building a duplicate of the Halsted Street lift-bridge were to be let today, at present prices, with close competition, and if the engineer were allowed full sway in making plans and specifications for substructure, superstructure, approaches, and machinery, based upon correct data, it is not too much to say that the entire cost would be reduced Halstead Bridge. Courtesy of Haer. to, at most, $150,000, instead of $200,000, which is about what the structure itself would cost, exclusive of outside extras.”

After the bridge opened and had been operating for a while, Waddell indicated that in the future, if he had “carte blanche in the designing, he would, based upon his experience on this initial lift span, make the following improvements,” 1) Curve the rear column and arch the overhead girders at the tops of towers so as to improve the general appearance.

2) Operate by electricity instead Halsted Street, view of lifting span with a control tower of by steam. on top of the span.

3) Place the machinery house in one of the towers and wrote, “The principal details of the structure dispense with the operating are not unusual. It is the idea, the design house on the span… as a whole that is novel. The great height 4) Omit the water tanks as an unnecessary of the structure and the great weight to be precaution and rely on the great capaclifted were adversely criticized by engineers ity of the electric motors to overcome and laymen alike; but, while a better type of any temporary unbalanced load. movable bridge suitable for the conditions 5) A simpler and less expensive adjustwhich governed the design of the Halsted ment at feet of rear columns.

Street Lift-Bridge has since been developed, 6) Cast steel instead of cast iron for all there was nothing better in that day. All things machinery. considered, it is a substantial and creditable 7) Catch the balancing chains in buckets piece of work which will serve its purpose placed on top of the span instead of admirably for many years to come.” hanging them to the counterweights.

Waddell went on to design and build many With the bridge opening and successful vertical lift bridges around the United States. operation, even though expensive due to He and Harrington received several patents the use of steam engines to supply power, that gave the firm of Waddell & Harrington a the era of the long span, high lift, vertical near monopoly on this style of bridge for years.■ lift bridge slowly began. It was impressive, Dr. Frank Griggs, Jr. specializes in the restoration as a first attempt, that the bridge was so successful and had considered so many of of historic bridges, having restored many 19 th the features that were to become a part of Century cast and wrought iron bridges. He was most future lift spans. Waddell would not, formerly Director of Historic Bridge Programs for however, build another lift span for many Clough, Harbour & Associates LLP in Albany, years, as many of his colleagues viewed it as NY, and is now an Independent Consulting an expensive solution. John L. Harrington, Engineer. (fgriggsjr@twc.com) who became Waddell’s partner in the future,

STRUCTURE magazine

32

November 2018

We set standards!

There is nothing ʻjust likeʼ or ʻas good asʼ genuine DECON® Studrails.

Since 1988 DECON® Studrails have provided a superior engineered and economical solution to enhance punching shear capacity in elevated flat plate slabs, post-tensioned slabs, foundations, and hold-down applications. Always at the cutting edge of technology, it was punching shear research performed by DECON® and its consultants that formed the foundation of report ACI 421.1R by ACI Committee 421. This report has provided the basis for the design procedures contained in the current ACI 318, IBC and CSA A23.3 design codes.

■ ■ ■ ■

Replace stirrups, hairpins and column capitals Significantly reduce reinforcement congestion Faster and easier to install No anchor slip

■ Superior seismic performance ■ ICC ES Evaluation report ESR-2494 ■ Our state of the art software and engineering staff are always available to assist you in your Studrail design!

JORDAHL USA Inc.

JORDAHL USA Inc. 103 East Napa St., Suite B 103 East Napa St., Suite B Box 1486 POPO Box 1486 Sonoma, 95476 Sonoma, CA CA 95476 Tel (866) 332-6687 Tel (866) 332-6687 www.jordahlusa.com www.jordahlusa.com

anchored in quality

USG Structural Solutions

WHAT DANGERS ARE HIDING IN YOUR POURED CONCRETE ROOF DECK? USG Structural Panel Concrete Roof Deck Choose a dry construction method that’s a safer alternative to poured concrete.

Learn more at usg.com/structuralroofdeck

© 2018 USG Corporation and/or its affiliates. All rights reserved.

The trademarks USG, IT’S YOUR WORLD. BUILD IT., the USG logo, the design elements and colors, and related marks are trademarks of USG Corporation or its affiliates.

LegaL PersPectives On the Subject of Indemnification

Part 1: An Overview of the Indemnification Obligation

By Gail S. Kelley, P.E., Esq., LEED AP

I

ndemnification obligations are an important part of almost every design agreement.

Stated simply, to indemnify someone means to financially protect them against specified claims. The party providing the financial protection (the “Indemnitor”) can be required to pay the amount of a judgment or settlement that is owed by the other party (the “Indemnitee”), or more commonly, can be required to reimburse the Indemnitee for costs the Indemnitee has incurred because of the specified claims.

As noted in previous articles in the January, February, and March 2017 editions of STRUCTURE, indemnification provisions in design agreements that have been drafted by owners are often worded in such a way that the indemnification obligations are not covered by professional liability insurance. These three articles suggested changes to the wording of commonly encountered indemnification provisions; this article will take a step back and look at the concept of indemnification in general.

but generally because there is no contract between the parties. For example, in the case Diplomat Resorts Limited Partnership v. Tecnoglass, LLC, (Fla. 4th DCA 2013), a hotel owner hired a contractor to furnish and install glass shower doors. Due to an apparent defect in the manufacturing process, many of the shower doors spontaneously fractured. The hotel owner sued the contractor and obtained a judgment for the costs it incurred in replacing the doors. However, because it was unlikely that the contractor would be able to satisfy the judgment, the hotel owner took an assignment of the contractor’s claims against the company that manufactured the shower doors. The hotel owner, standing in the shoes of its contractor through the assignment, then asserted a common law indemnification claim against the manufacturer.

Common Law Indemnification

Contractual Indemnification

Under the common law – the law that courts apply when there is no contract between the parties or there is no contract provision that is relevant to the dispute – there is an implied right of indemnification. Common law indemnification is sometimes referred to as equitable indemnification, meaning that it is required by the courts under basic concepts of fairness. Under the common law right to indemnification, someone who has been held vicariously liable (responsible) for damages caused by someone else can seek indemnification from the party who actually caused the damages. Typical situations where vicarious liability arises are when an employer is held vicariously liable for damages caused by an employee or a principal is held responsible for the actions of its agent (someone acting on its behalf ). Judges who allow equitable indemnification will often justify it with wording such as: Where one who has committed no actual wrong is held vicariously liable for the wrongdoing of another, he has a right to indemnification from the actual wrongdoer.

Common law indemnification claims do arise in the design and construction context,

The owner of a building will almost always be sued when there is an injury or property damage even tangentially related to the building. Realistically, the injured party usually has no way to determine who (or what) caused the injury; they may only be able to establish that the injury was caused by the Owner’s property. Even though most design agreements say that the Engineer is an independent contractor and not acting as the Owner’s agent, the Owner will likely be held vicariously liable for any claims arising from the Engineer’s services.

While the Owner could file a claim against the Engineer for common law indemnification, very few owners are willing to take their chances with common law indemnification, particularly on large projects. A party seeking common law indemnification must prove they are entitled to indemnification; many states require the party seeking indemnification to be completely blameless or at the most “passively” negligent. Thus, most design agreements explicitly require the Engineer to indemnify the Owner for claims arising from the Engineer’s negligence.

STRUCTURE magazine

35

November 2018

Who Should Be Indemnified While it is not unreasonable for Owners to require indemnification from the Engineer if the Engineer is negligent, Owners sometimes use language that is completely inappropriate, both with respect to what claims must be indemnified against and who must be indemnified.

It should be noted that, in terms of an indemnification obligation, the word “Owner” needs to be interpreted rather expansively to include anyone who holds “an insurable interest” in the project. This generally means the Lender and any investors as well as the Owner in the usual sense of the word. One of the main reasons that the claim is brought against the Owner (in addition to the fact that the injured party may not know who actually caused the injury) is that the building represents an asset that can be attached to satisfy a judgment in the injured party’s favor.

The injured party’s chances of being able to collect on the judgment are much less certain if it brings the claim against a subcontractor whose insurance has already been exhausted from paying other claims.

It is reasonable that anyone with an ownership stake in the building will want to be financially protected against claims due to the Engineer’s negligence. Thus the indemnification clause will often include the Owner’s assigns, successors, affiliates, parent companies, and subsidiaries as indemnified parties, along with their respective employees, officers, directors, members, and managers.

Although it is unlikely that an individual employee or officer would be held liable for the Engineer’s negligence, this indemnification request is not unreasonable; likewise, it is not unreasonable for the Owner to require

indemnification of its other (current and future) business entities.

When the Engineer is a subconsultant to another design professional, the Engineer will typically be required to indemnify the Prime Consultant as well as the Owner. This is reasonable since under most design agreements, the Prime Consultant is responsible for the work of its subconsultants and thus can be held liable for the Engineer’s negligence.

What is not reasonable, however, is for the Engineer to be required to indemnify the other consultants, contractors, insurance carriers, sureties, and attorneys for the Owner and the Prime Consultant. It is possible that the Engineer could be partly responsible for a claim, along with another consultant.

However, if it is alleged that the Engineer is partly responsible, the Engineer needs to be named in the claim, along with the other consultant. While claims involving multiple parties can, and usually do, get complicated, if the Engineer is involved in the defense of the claim, it has an opportunity to ensure that it is only held liable to the extent of its own negligence.

If the other consultant is the only party named in the claim, and the Engineer has agreed to indemnify the consultant, the consultant could settle the original claim and then bring a claim for indemnification against the Engineer

alleging that the damage was partly (or entirely) due to the Engineer’s negligence. The consultant may also try to recover its legal fees for the original claim from the Engineer. While the Engineer can defend against the claim on the grounds that it had no liability for the injured party’s damages, judges and juries tend to find that all parties involved bear some liability unless the allegations against a particular party are completely ludicrous. Assuming that the court finds that the Engineer’s negligence partially caused the damages, the Engineer will be held liable for part of the settlement or judgment without having been able to participate in the original lawsuit.

Indemnification of the consultant will likely not be covered by professional liability insurance – professional liability insurance is designed to cover the Engineer’s common law indemnification obligations for its negligence.

Under the common law, the Engineer’s indemnification obligation is limited to those that could be held vicariously liable for its negligence, which is essentially the entities that hold an insurable interest in the Project. In addition, few (if any) professional liability policies cover defense of an indemnified party, so the attorneys’ fees that the consultant incurred in defending against the original lawsuit will almost certainly not be covered. In contrast,

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

2018 LOS ANGELES ARCHITECTURAL AWARDS 2017 AIA MERIT AWARD

if the Engineer is named in the original claim, both its defense and indemnification of the claim will be covered, provided the policy limits have not been exhausted by other claims.

This same reasoning applies if it alleged that the Engineer and the Contractor are jointly responsible for a claim. The Engineer should be named in the claim; it should not agree to indemnify the Contractor. The Engineer should also not agree to indemnify the Owner’s (or the Prime Contractor’s) insurance carriers, sureties, or attorneys. None of these entities can be held vicariously liable for the Engineer’s negligence, so there is no reason the Engineer should be required to financially protect them.

Including these entities as Indemnitees does nothing other than complicate the handling of any claim (and increase the costs).

Conclusion This article has discussed the concept of indemnification, particularly with respect to who should be indemnified and what is covered under professional liability insurance. It is not unusual for design agreements to have a separate exhibit with a list of entities that must be indemnified; sometimes the indemnification clause itself may include a long list of required Indemnitees. Often, it can be difficult to determine the relationship between the entities and the Owner or the property; in such cases, it is prudent to add the clause “provided any such entity holds an insurable interest in the property” to the end of the list. This will limit the Indemnitees to those who could actually be held liable for the Engineer’s negligence. The second article in this series will look at the defense obligation that is often found in the indemnification clause.■ Disclaimer: The information in this article is for educational purposes only and is not legal advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances.

Shriners Hospital, Los Angeles, CA Photo by Tom Bonner

SUPPORTING

INNOVATION IN ARCHITECTURE

KPFF is an Equal Opportunity Employer www.kpff.com

Seattle Tacoma Lacey

San Francisco Los Angeles Long Beach

St. Louis Chicago Louisville

Portland Eugene Sacramento

Irvine San Diego Boise

New York

STRUCTURE magazine

36

November 2018

Gail S. Kelley is an LEED AP as well as a professional engineer and licensed attorney in Maryland and the District of Columbia. Her practice focuses on reviewing and negotiating design agreements for architects and engineers.

She is the author of Construction Law: An Introduction for Engineers, Architects, and Contractors, published by Wiley & Sons. (gail.kelley.esq@gmail.com)

Š 2018 ClarkDietrich Building Systems

InSIghtS Regulating Urban Rooftop Wind Turbines

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

T

owards the end of 2008, the New York City (NYC) Buildings Department (DOB) became aware that wind turbines had been installed on a couple of rooftops. The department is and has been firmly in favor of sustainable initiatives, but there were concerns these installations had insufficient engineering control. New York City’s high density of buildings and pedestrian traffic create a condition where any loose and free-falling piece of equipment may result in a severe accident. The DOB considered regulations appropriate to the situation. In fact, several other sustainable initiatives, such as rooftop solar panels and green roofs, also led to changes in code or legislation.

Wind turbine’s specific regulations should be of interest to structural engineers as they may be commissioned to participate in the selection of the type of turbine and to design the supporting installations (e.g. independent foundations, roof supporting structures, guys or even masts).

Since, in 2008, there were no existing regulations for the installation of wind turbines in large United States cities, the NYC regulation had to be developed from scratch. The research found general news articles about public concern with the safety of rooftop wind turbines and reports of accidents in engineering publications attributed to lack of long-term reliability of the turbine’s blades and support structure. The department’s primary mission,

public safety, required a method to certify the reliability of the turbine equipment, the safety of the installation, and the suitability of the supporting structure. In 2009, the DOB issued Bulletin 2009-015 describing a protocol for testing and approval acceptance criteria of wind turbines. Under certain limitations, it allowed for the approval of pilot projects.

The bulletin was the result of the collaboration of professionals from several DOB units (Sustainability, Technical Certification and Research, Structural, Zoning). The DOB continued work towards a simplified approval process. Familiarization with the issues was achieved by talking to manufacturers and utilities, and by studying any existing standards. A Commissioner’s Forum on Urban Wind Turbines in 2010 was attended by specialized engineers, manufacturers, and several international guests. Pertinent to DOB’s research was the presentation by Dutch planning officials who described their experience with bottlenecks (public acceptance, long approval process) and their proposals to improve the process (agreements between neighbors, a method of location selection for adequate wind) or participate in design peer reviews.

Superseding the previous Bulletin, Technical Buildings Bulletin 2011-004 allowed a simplified protocol for the approval of wind turbine installations. The bulletin relies heavily on the

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

Does your post-tensioned concrete project

HAVE WHAT IT TAKES?

2019 PTI Project Awards

2017 PTI Project of the Year

Recognizing Excellence in Post-Tensioning Applications

Ritz-Carlton Residences, Waikiki Beach, HI

FOR ALL ENTRY INFORMATION, VISIT POST-TENSIONING.ORG/PROJECTAWARDS STRUCTURE magazine

38

November 2018

International Electrotechnical Commission’s (IEC) extensive set of standards. The 201104 Bulletin protocol is relatively simple for turbines whose sweep area is less than 7 meters2 (labeled as 3 meters diameter in the bulletin text) as long as “Testing certification and listing or labeling shall be by a thirdparty testing laboratory accredited under International Organization of Standardization/ Electrotechnical Commission’s (ISO/IEC) Standard 17025-2005.” The certification ensures the reliability of the proposed turbine as it covers safety and function tests, power performance measurements, duration test, and environmental tests. In such cases, the application needs to undergo only a limited review by the third-party testing laboratory and the installation can be signed off by a New York State Licensed Professional (Engineer or Architect applicant) in lieu of a DOB inspector.

Any turbine exceeding a 7 meter2 sweep-area requires a peer review that would cover structural, electrical, mechanical, noise design, and installation. In all cases, the turbine’s owner needs to submit, for approval, a monitoring plan for the installation. The DOB bulletin requires monthly monitoring in the first year after installation and biannual after that. This monitoring is to focus on conditions that may lead to public safety hazards (integrity of the turbine and support system, blades condition, shutdown system, etc.).

Wind turbines used for electrical microgeneration are referred to as small wind turbines (SWT) and are defined by IEC and by the American Wind Energy Association (AWEA) as “a system of 200 meter2 (2153 feet2) rotor swept area or less that converts kinetic energy in the wind into electrical energy.” Note that the term “small” is for comparison with other types of turbines and does not refer to the size of blades. In fact, according to Underwriter’s Laboratories, SWTs are intended to be stand-alone (not grid connected) and are “wind turbines where a user or service person cannot or is not intended to enter the turbine to operate it or perform maintenance.” The DOB’s choice to restrict the use of the simplified procedure to turbines with sweep area less than 7 meters2 was mostly derived from the results of previous pilot installations as well as from the IEC International Standard 61400-2, Design Requirements for Small Wind Turbines.

To allow product standardization to cover most applications, the IEC 61400-2 created four SWT classes that are defined in terms of wind speed and turbulence parameters.

In practical terms, a manufacturer will perform the structural design of a type of wind turbine to meet one of the four SWT classes as listed and prescribed in Tables 1 and 2 of IEC 61400-2. The turbine type will include this class in its label. Specific values bound each class for Vave, annual average wind speed at hub height and Vref, reference wind speed averaged over 10 minutes. Note that, with the exception of turbines with sweep area less than 2 meters2, the manufacturer’s structural design needs to include the mast. “The values of wind speed and turbulence parameters are intended to represent the characteristic values of many different sites and do not give a precise representation of any specific site.” To guide the prospective owner in the selection of the turbine type adequate to the local project site, the structural engineer needs to understand the standard’s treatment of extreme wind conditions and relate it to the specifications of the NYC Building Code. The standard lists the required wind load cases to be used in the design for operating and extreme wind conditions. IEC indicates that during extreme winds, the turbine is expected to be parked (stand still or idling) and the design shall use the Ve50, which is the extreme expected 50-year 3-second wind speed (IEC provides a formula that relates Ve50 to Vref). In addition, IEC 61400-2 places

serious emphasis on the design for fatigue. It also enumerates the type of tests and verification required. Rooftop turbines are usually SWTs with rotor sweep areas smaller than 2 meters2. For this subset of SWTs (less than 2 meters2), the manufacturer is not required by IEC standards to include the support structure as part of the delivered system. The manufacturer needs to provide installation instructions and to specify various clearances, maximum allowable tower top deflections, and loads. The support structure, including all elements in the load path, remains to be designed by the local structural engineer using manufacturer’s data, instructions, and specifications.

The DOB Bulletin is not specific to rooftop installations but, clearly, this is the most common application given the size of the turbine and NYC conditions. Up to this date, no accident has been recorded, but there were several complaints about wind turbine noise.

A City Council (NYC) local law that is about to take effect allows the noise level to reach a maximum of 5 decibels above the ambient sound level at the property line.

In recent years, a limited number of wind turbines were installed. There is no information on their power efficiency. It is expected that those installed on high rooftops will be more productive. There are significant

opportunities in NYC where there are about 500 buildings taller than 500 feet. To encourage the development of clean energy production, a newly enacted local law requires a “wind resource assessment” that will map areas where winds have an average speed of at least 11 miles per hour for at least three months a year.

Some definitions from IEC: Swept area – projected area perpendicular to the wind direction that a rotor will describe during one complete rotation.

Support structure (for wind turbines) – part of the wind turbine comprising the tower and the foundation Reference wind speed (Vref) – basic parameter for wind speed used for defining SWT classes. Other design-related climatic parameters are derived from the reference wind speed and other basic SWT class parameters Small wind turbine (SWT) – a system of 200 meter2 rotor swept area or less that converts kinetic energy in the wind into electrical energy Parking – situation to which a wind turbine returns after a normal shutdown■ Dan Eschenasy is the New York City Buildings Department Chief Structural Engineer. He is an Honorary Member of SEAoNY and a member of the SEI Structural Design for Fire Conditions Standard Committee.

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

39

November 2018

4/27/18 9:24 AM

How SDS/2 Helps You

“We made the decision back when we started the company to go with SDS/2 for a lot of reasons. One, a great reputation. I had experience with them in the past, and I knew that they were the kind of people to stand behind their software. They work hard to make the best detailing software in the world. And it continually gets better and better. There’s nothing SDS/2 can’t do with steel. And we’ve proven that.

HENRY E. “HAL” CARTEE, JR., P.E., CO-OWNER CARTEE-BERRY & ASSOCIATES

See how SDS/2 can increase your bottom line at sds2.com/profitability 1501 Old Cheney Rd., Lincoln, NE 68512 // 800-443-0782 // www.sds2.com

EnginEEr’s notEbook Surface Preparation of Concrete Joints

By Gregory McCombs, S.E., and Steven Petroff, P.E.

T

he Building Code Requirements for Structural Concrete are specified in the American Concrete Institute’s ACI 318-14. As stated in Section 1.2.5, “This code covers the materials, design, construction and strength evaluation of structural concrete members and systems in any structure designed and constructed under the requirements of the general building code.”

The code defines a Joint as the portion of a structure common to intersecting members.

Joints in concrete may be either or both construction joints or shear-friction joints such as new concrete placed against hardened concrete. In principle, the two joints are the same. An example of a joint being a construction joint and a shear-friction joint is a concrete wall placed on a hardened concrete footing. This wall may be a concrete shear wall or a concrete foundation wall used to transfer the shear forces from a light-framed wall or masonry shear wall to the footing.

Are there special preparations for a concrete joint? For example, can a concrete shear wall or foundation wall transferring shear forces into a footing simply be cast on the hardened concrete footing without any surface preparation? ACI 318 Section 26.5.6.2(d) states that “Construction joints shall be cleaned and laitance removed before new concrete is placed.” Note that the commentary to section 26.5.6.1(b) and 26.5.6.1(c) refers to section 22.9 for the necessary surface preparation if shear-friction is invoked in the design. Additionally, in Table 22.9.4.2, friction coefficients for shear friction calculations are provided. When concrete is placed against hardened concrete, the contact surface condition is required to be “free of laitance.” Removal of laitance is not limited to concrete-to-concrete joints only. Per ACI 530.1-13/ASCE6-13 Section 3.2B, “Prior to placing masonry, remove laitance, loose aggregate, and anything else that would prevent mortar from bonding to the foundation.” Essentially, these code sections require preparation prior to placing concrete or masonry against previously hardened material. It is recommended that the engineer review Section 26.5, “Concrete production and construction,” as there are multiple requirements that may not be obvious, such as Section 26.5.6.2(f ) requiring

that the new concrete is prewetted prior to concrete placement.

So, what is laitance? ACI Concrete Terminology, ACI CT-16, defines laitance as: “a layer of weak material derived from cementitious material and aggregate fines either: 1) carried by bleeding to the surface or internal cavities of freshly placed mixture; 2) separated from the mixture and deposited on the surface or inter-

‘‘

Are there special preparations for a concrete joint? For example, can a concrete shear wall or foundation wall transferring shear forces into a footing simply be cast on the hardened concrete footing without any surface preparation?

‘‘

nal cavities during placement of the mixture.”

Relating to the example described above, when the concrete footing is cast, the top surface is screeded, floated, and finished. This process brings up the fines and covers the aggregate with concrete fines technically referred to as laitance. Laitance can cause a plane of weakness and reduce the bond between the concrete surfaces, creating a slip plane.

There are several methods used to clean the concrete surface and remove laitance.

Many procedures are identified in the National Research Council-Conseil National de Recherche Canada (NRC-CNRC) Construction Technology Update No. 24.

Below is a brief list with a basic description of the methods itemized in the document.

• Chemical Cleaning: Concrete contaminated with oil or grease can be cleaned and scrubbed with detergents or other chemicals.

• Mechanical Cleaning: Mechanically clean the concrete surface by using rotary or impact devices.

• Impact Tools and Scabblers: Brush hammers, scabblers, and needle guns can be used to remove several millimeters of concrete surface.

• Scarifiers: Scarifying devices use a rotating disc cutting wheel. They can be used for cleaning, grinding, or milling.

• Blast Cleaning: This includes wet or dry sandblasting, shotblasting, and water jet cleaning.

STRUCTURE magazine

o Sandblasting: Sandblasting machines are generally used to remove laitance, dirt, oil, and other contaminants. o Shotblasting: Shotblasting machines use steel shot to clean and scarify concrete surfaces. Excellent for removing large depths of concrete surface. o WaterBlasting: This method uses a high-pressure water jet to prepare the concrete surface.

• Acid Etching: Acid etching removes enough concrete paste to provide a rough concrete surface. This method has limitations per ACI Committee 515.

• Flame Cleaning: This method is used to prepare concrete surfaces to receive special coatings such as on slabs.

• Washing and Brushing: After the concrete has stiffened and the water has evaporated from the concrete surface, usually a couple of hours after the concrete is placed based on climatic conditions, brush and water are used to remove the laitance and clean the concrete surface. Care must be taken not to dislodge the aggregate.

• Wire Brush and Washing: The laitance can also be removed while the concrete is still green using a wire brush and water to clean the concrete surface.

ACI 318 and ACI 530.1 are clear that, for all construction joints consisting of fresh concrete or masonry placed against the hardened material, the laitance is required to be removed and the surface must be clean. While the means and methods of surface preparation, including laitance removal, is the responsibility of the contractor, the engineer may consider adding laitance removal to the specifications as well as the general structural notes on the construction drawings. In accordance with ACI 318 Section 22.9.1.4 and Section 22.5.6.2(e), surface preparation requirements of the shear plane assumed for design shall be specified in the construction documents.■

41

November 2018

Greg McCombs is currently retired, having worked as an engineer in California for 18 years and another 5 years in Utah. He currently volunteers his time as a member of the Seismic Committee of SEAU. (spideygsm24@icloud.com) Steven Petroff is a Project Engineer at ARW Engineers in Ogden, Utah, and serves on the Seismic Committee and Resilience Committee of SEAU. (stevenp@arwengineers.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.

Spotlight Two Towers, One Structure

By Patrick Ragan, S.E. WSP was an Award winner for its Hanking Center project in the 2017 Annual Excellence in Structural Engineering Awards Program in the Category – New Buildings over $100M.

T

he Hanking Center in Shenzhen is China’s tallest steel-framed structure, rising 70 stories and 1,140 feet, with over 1,000,000 square feet of office space above six levels of retail. Tour an office floor and you will find a wide-open space with views in all four directions, but you will not find a restroom or an elevator lobby. That is unless you cross a narrow bridge spanning the 35 feet back to the service core, which is a separate 68-story, 1,110-foot tower.

By separating the building services from the office space, architects at Morphosis created a more open office layout while maximizing daylight and views from office and circulation areas alike. But acting separately, the two towers would have been far too slender to resist wind and seismic overturning forces effectively. The resulting challenge was to structurally link the two towers, taking advantage of their larger, combined footprint without compromising the visual separation that is so critical to the architectural form.

Complicating matters further, the design wind loads in Shenzhen are more than twice as large as in typical inland areas of China. Located along China’s southern coast, Shenzhen has a warm, tropical climate similar to that of Miami. And like Miami, Shenzhen’s wind loads are controlled by hurricanes – or typhoons as they are called in Asia. For the Hanking Center, 100-year wind pressures exceed 100 psf at the top of the building, and the resulting factored wind overturning forces were comparable to the overturning forces from a 2,500-year seismic event.

The unique architecture and high wind loads invited a creative structural solution. Designers at WSP in Chicago – formerly Halvorson and Partners – devised a mega-braced tube structural system in which rectangular concrete filled tube (RCFT) steel columns along the combined building perimeter are linked with built-up steel boxshaped diagonal braces, maximizing overturning resistance against broad-face wind loads. The mega-bracing, arranged on a four-story module, is complemented by secondary bracing around stair and elevator cores which is arranged on a one-story module. Further linkage was achieved by providing outrigger and belt trusses at three of the five mechanical levels.

Although several initial structural concepts were developed with reinforced concrete shear walls instead of steel bracing, it was soon determined that the primarily steel mega-braced scheme would be the optimal choice for the Hanking Center. In addition to allowing for more transparency and a clearer visual separation between the two towers, the applicable Chinese codes allowed the steel scheme a more favorable interstory drift limit (H/250) than would be allowed for a concrete (H/500) or composite structure (H/400).

With the larger interstory drift limit, enough material reductions were possible that the primarily steel scheme was estimated to be roughly equal cost or even slightly cheaper than the competing concrete wall schemes. However, the applicability of the H/250 drift limit for a scheme with RCFT columns had to be agreed upon by the Expert Panel Review Board, which is composed of leading professionals and academics in China and has the authority to approve the design or block the project from moving forward. WSP demonstrated that even STRUCTURE magazine

under relatively large wind displacements, the mega-braced tube system effectively minimizes shear distortion, which is the type of deformation associated with damage to cladding, partitions, or other non-structural elements. This is because the bracing arrangement links all the columns together such that the entire tower deforms primarily in bending rather than shear, so plane sections remain essentially planar. Ultimately, the expert panel agreed to allow the H/250 drift limit, confirming one of the main advantages of the steel structural system.

To ensure that the two towers behave dynamically as a single structure, two sets of W14x159 diaphragm x-braces are placed at every fourth floor, matching the module of the mega-bracing. These diaphragm braces were designed to resist a variety of special load conditions, including unequal wind pressures on each side of the tower, and to remain elastic even under a 2,500-year earthquake.

Also, a comparison of modal analysis results demonstrated that the diaphragm braces are sufficiently stiff so that lateral and torsional mode shapes are essentially the same as they would be if fully rigid diaphragms were assumed to exist on each floor.

Less than eight months after beginning work on the schematic design, WSP presented structural drawings, along with a comprehensive analysis and design report, to the Expert Panel in Shenzhen.

The report included a review of system irregularities, special requirements for “critical” elements (including the braces holding the two towers together), nonlinear time history analysis under 2,500-year earthquake loads, construction sequence analysis, progressive collapse resistance, and finite element analysis of the mega-brace connection nodes. Following the presentation, the Hanking Center was approved by the Expert Panel. Steel erection topped out in early 2017, and the building will open in 2018.▪

43

Patrick Ragan is an Associate with WSP in Chicago. He is a member of the ASCE Tall Buildings Committee and the Task Committee on the Design and Performance of Tall Buildings under Wind Loads. He may be reached at patrick.ragan@wsp.com.

November 2018

NCSEA News

News form the National Council of Structural Engineers Associations

Existing Buildings Subcommittee Looking for Feedback

This past September, the NCSEA Code Advisory Committee’s Existing Buildings Subcommittee met at the office of Simpson Gumpertz & Heger (SGH) in Chicago to discuss code change proposals to the 2021 International Existing Building Code (IEBC).

The committee is working on submitting close to 20 code change proposals for the 2021 IEBC due in early January 2019. The committee is focused on securing feedback from each NCSEA Member Organization.

How does the IEBC work for your state and do you have specific Pictured at the September meeting, from left to right: Jerry Maly, amendments to it?

Bill Bracken, Marko Schtanus, Anthony Piderit, Elizabeth Jones, Is some code language confusing?

Mike Sheridan, James Hauck, Dave Odeh, Mike Fillion (Chair), Your feedback is important to the committee as it develops clear Ben Harris & NCSEA Executive Director, Al Spada. SGH has been code language and works to ensure that issues particular to your a gracious host for meetings in Chicago, Boston & San Francisco. region are addressed. Send comments and questions to your SEA’s NCSEA delegates to start the conversation in your state, or directly to the Chair of the Existing Buildings Subcommittee, Michael Fillion, at mrf.structure@verizon.net.

WE’RE GOING TO DISNEYLAND November 12–15, 2019 | Save The Date

Join us next November in Anaheim, California, for the 2019 Structural Engineering Summit! The Structural Engineering Summit draws the best of the structural engineering field together for the best practical education, a dynamic trade show, and compelling peer-to-peer networking at a growing event designed to advance the industry.

NCSEA’s Summit Committee is seeking presentations that deliver pertinent and useful information that is specific to the practicing structural engineer.

Visit www.ncsea.com to submit an abstract.

Subscribe to Knowledge with NCSEA’s Webinar Subscription Enhanced Benefits. Expert Speakers. Unlimited Attendees.

NCSEA’s newly enhanced Yearly Webinar Subscription is the most user- and wallet-friendly plan to date! This Live and Recorded Webinar Subscription offers all the same benefits as before, but now includes even more. With this annual plan, you get: • 20+ live webinars a year, featuring the highest-quality speakers available.

View the upcoming schedule at www.ncsea.com.

• New! Receive an unlimited number of free CE certificates for each webinar – no more $30 fee – so multiple viewers at the same location can receive credit for every live webinar with no additional costs.

• Unlimited 24/7/365 access to NCSEA’s Recorded Webinar Library – more than 100 relevant and high-quality webinars.

• New! A brand new and enhanced education website. NCSEA’s Education Portal provides easy access to all of your education content, including: • Purchase history • Earned Certificates to track your PDHs with ease Sign up for your Yearly Live and Recorded Webinar Subscription now! www.ncsea.com

STRUCTURE magazine

44

November 2018

New York City will host the 2019 International Association for Bridge and Structural Engineering (IABSE) Congress with the main theme of The Evolving Metropolis. According to Wikipedia, a Metropolis is “a large city which is a significant economic, political, and cultural center for a country or region and an important hub for regional or international connections, commerce, and communications.” What better place than the financial hub and (possibly) architectural center of the U.S., and perhaps the world, than Manhattan in New York City.

The 2019 Congress will take place September 4–6, 2019 at the Javits Center in New York, NY. The Evolving Metropolis will address the social and economic needs of

the world with sessions on Durable Bridges and Affordable Housing, as well as numerous other important and current issues present in our world.

The scientific program will include Plenary and Concurrent Sessions over three days. Panel discussions and Poster Sessions will also be incorporated.

The Organizers invite the world’s structural engineering community to share their experiences with colleagues and friends, and have unique open discussions and forums on what the future holds for engineering tomorrow’s structures. Learn more by visiting www.iabse.org/newyork2019.

Webinar: Introduction to Engineering Structural Glass Design

NCSEA Webinars

Register by visiting www.ncsea.com.

November 13, 2018 Engineering Structural Glass, an Introduction to the Engineering Structural Glass Design Guide Marcin March, P.E., C.Eng, MIStructE This webinar is an introduction to the new NCSEA Engineering Structural Glass Design Guide.

November 29, 2018 Changes to the 2016 TMS 402/602 Building Code for Masonry Structures Richard Bennett, Ph.D., P.E. The 2016 TMS 402 Building Code Requirements for Masonry Structures contains two major technical changes. These changes will be covered along with examples illustrating the application of the provisions.

December 6, 2018 New Solutions in the New Design Guide 21 on Welding Duane K. Miller, Sc.D., P.E. This webinar will cover changes in the recently published AISC Design Guide on Welding. It will be of value to engineers who are often challenged by codes to make welding-related decisions but often lack the background to make informed decisions.

December 11, 2018 Understanding the AISC Direct Analysis Method of Design Donald White, Ph.D. This webinar lays out the key fundamental concepts associated with the Direct Analysis Method; various aspects of the method’s practical application are discussed.

Courses award 1.5 hours of continuing education after the completion of a quiz. Diamond Review approved in all 50 States.

STRUCTURE magazine

45

November 2018

News from the National Council of Structural Engineers Associations

November 13, 2018 – This webinar is an introduction to the new NCSEA Engineering Structural Glass Design Guide which provides the Engineering Professional with sufficient background knowledge and current methods to determine the specification of glass elements in buildings.

It 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. The intent of this Guide is to collate relevant design references, requirements, and analysis methods into a single source for easy reference, and to assist in determining the capacity of glass elements, augmented or reduced by the various relevant factors, so that glass elements can be designed successfully and safely.

Each attendee will receive a downloadable version of the guide as part of their registration. Visit www.ncsea.com to register for the November 13th webinar.

NCSEA News

2019 IABSE Congress: The Evolving Metropolis

Advancing the Profession

The News of the Structural Engineering Institute of ASCE

Welcome to the SEI Futures Fund Board SEI welcomes Jon D. Magnusson, P.E., S.E., NAE, F.SEI, Dist.M.ASCE, Senior Principal at Magnusson Klemencic Associates, as the newest member of the SEI Futures Fund Board. He was recently nominated by the SEI Futures Fund Board and appointed by the SEI Board of Governors for a five-year term.

Jon comments: “Structural engineering is an incredibly creative profession. There is nothing quite as satisfying as starting with a blank sheet of paper and filling it with the products of ingenuity, science, and practical knowledge to create a design that will guide a team of builders. Every aspect of civilized society depends on the work of structural engineers.

SEI is the preeminent structural engineering organization, powered by volunteers, and financial resources are needed

to leverage efforts to realize our Vision for the Future of Structural Engineering.

In four years as President of the ASCE Foundation, I’ve seen firsthand what the philanthropy of ASCE members does for civil engineering. The SEI Futures Fund serves a vital role in moving the structural engineering profession forward as we prepare for new challenges ahead. Transferring generational knowledge and leadership, adopting new technologies and methods, and navigating the business and legal environment are all critical issues that we face. It is our profession, and if we don’t work to make it better and position future generations for success, who will?

It is exciting to help build on what the SEI Futures Fund has already done and to dream about what can be done for the profession beyond what is possible with dues alone. It is vital for us all to support SEI initiatives with our time and financial resources.”

SEI Futures Fund in collaboration with the ASCE Foundation Your partner to:

• Invest in the future of structural engineering • Support student and young professional involvement in SEI • Provide opportunities for professional development Learn more and give at www.asce.org/SEIFuturesFund.

Check out full news items and calls for SEI committee participation at www.asce.org/SEI.

Learning / Networking

NEW Whole Building Life Cycle Assessment Reference Building Structure and Strategies A guide for the project team to define and model the structural system within the reference building design as required by green building standards and rating systems, by the SEI Sustainability Committee Special Project Working Group. Available in print and e-book at ascelibrary.org.

Learn more and register at

www.etsconference.org.

SEI Update

#ETSC18 View program, scholarship opportunities for students and young professionals, and register at www.structurescongress.org. #Structures19

Membership

Join or Renew SEI/ASCE For innovative solutions and learning, to connect with leaders and colleagues, and to 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 800-548-ASCE (2723).

STRUCTURE magazine

46

November 2018

Advancing Performance-Based Structural Fire Engineering Design in the U.S. teams have been selected to provide regional representation and will serve as Team Leads: • Najib Abboud, Ph.D., P.E, M.ASCE, Senior Principal, Thornton Tomasetti, with Thomas Gernay, Aff.M.ASCE, Johns Hopkins University • Larry Griffis, P.E., F.SEI, M.ASCE, Senior Principal, Walter P Moore, with Jose Torero, CPEng, CP, M.ASCE, University of Maryland • Ron Klemencic, P.E., S.E., F.SEI, F.ASCE, Chairman and CEO, Magnusson Klemencic Associates, with Erica Fischer, P.E., M.ASCE, Oregon State University • Kevin LaMalva, P.E. M.ASCE, Senior Staff II, Simpson Gumpertz & Heger, with Negar Elhami-Khorasani, Ph.D., A.M.ASCE, University of Buffalo “We are grateful to the Charles Pankow Foundation for their overall vision and funding of this important project to help advance performance-based design,” says LaMalva. “Our team seeks to demonstrate the benefit of structural engineers serving as integral participants in the field of structural fire protection, which has remained relatively unchanged for a century.

Specifically, structural engineers have the ability and tools to deliver more efficient and economical designs while also providing more intrinsically-safe structures to fire. ASCE/SEI’s new Standard Appendix and Manual of Practice are key advancements that will guide this effort.”

Work on the project is to be completed in October 2019.

SEI Global Activities Visit to Colombia On September 10, at the invitation of the ASCE Colombia Section, SEI Board member Satyendra K. Ghosh, Ph.D., F.SEI, F.ASCE, gave a presentation at Universidad de los Andes in Bogota, Colombia, on Code Provisions for Earthquake-Resistant Design for New Construction. Then Dr. Ghosh traveled to Cartagena, presenting on the same topic to members of the Association of Seismic Engineering (AIS) and the Permanent Advisory Commission of the Regime of Earthquake Resistant

Constructions (CAPRCSR). This was the core group involved in the update of the Colombian code NSR-10. On September 12, he gave a keynote address at “Reunión del Concreto 2018” on ASCE 7-16 and the NSR-10 Colombian Regulations for Earthquake Resistant Construction Update, with more than 200 people in attendance. Reunion del Concreto is a major event held every two years by the Asociación Colombiana de Productores de Concreto (ASOCRETO). The event attracts participants from many Latin American and other countries including the United States. Learn more about SEI Global Activities at www.asce.org/SEIGlobal.

SEI Online

Follow SEI on Twitter @ASCE_SEI

Errata

SEI Standards Visit www.asce.org/SEIStandards to: • View ASCE 7-22 Committee Meeting schedule and archive • Submit proposals to revise ASCE 7

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

47

November 2018

The News of the Structural Engineering Institute of ASCE

On September 7, ASCE/SEI and the Charles Pankow Foundation signed an agreement for a $230,000 research grant to develop, write, and publish the stateof-the-art exemplar procedural guidance to properly execute a performance-based structural fire engineering (SFE) design in accordance with the new ASCE/SEI 7-16 Appendix E industry standard. The project will employ a scientific and engineering approach using the procedures outlined in ASCE/SEI Manual of Practice Structural Fire Engineering (MOP 138), to quantify the fire exposure and structural behavior of existing building designs during fire. Recognized experts in performance-based design will peer review the design brief and final report. The final document will be freely available to the public.

The project team is led by Principal Investigator (PI), Kevin LaMalva, P.E., M.ASCE, Senior Staff II/Fire Safety with Simpson Gumpertz & Heger, Inc. He helped lead the effort for the development of Appendix E and is the Editor of MOP 138 and a recognized expert in structural fire protection engineering with a profound understanding of the building code environment for fire safety and the challenges raised by the adoption of SFE in practice. Including the PI, the following collaboration of structural engineering firms and academic advisors create design teams that will be Industry Champions. The design

SEI Update

Advancing the Profession

CASE in Point

The News of the Council of American Structural Engineers

Did you know?

CASE has tools and practice guidelines to help firms deal with a wide variety of business scenarios that structural engineering firms face daily. Whether your firm needs to establish a new Quality Assurance Program, update its risk management program, keep track of the skills your young engineers are learning at each level of experience, or need a sample contract document – CASE has the tools you need!

CASE has a whole sample contract library for firms to use to enhance their internal contract documents. The following documents/templates are recommended to review/use if your firm needs to update its current contract documents, or need to create one.

All CASE Contract Documents are reviewed and updated by outside legal counsel every five years.

CASE #1: An Agreement for the Provision of Limited Professional Services CASE #2: An Agreement Between Client and Structural Engineer of Record for Professional Services CASE #3: An Agreement Between Structural Engineer of Record and Consulting Design Professional for Services CASE #4: An Agreement Between Owner and Structural Engineer for Special Inspection Services CASE #5: An Agreement for Structural Peer Review Services CASE #6: Agreement for Use with and Commentary on AIA Document C141 Standard Form of Agreement Between Architect and Consultant, 1997 Edition and AIA Document C142 Abbreviated Standard Form of Agreement Between Architect and Consultant, 2007 Edition CASE #7: Commentary on AIA Document A295-2008 General Conditions of the Contract for Integrated Project Delivery, 2008 Edition CASE #8: An Agreement Between Client and Specialty Structural Engineer for Professional Services CASE #9: An Agreement Between Structural Engineer of Record and Testing Laboratory

CASE #10: An Agreement Between Structural Engineer of Record and Geotechnical Engineer of Record CASE #11: An Agreement Between Structural Engineer of Record (SER) and Contractor for Transfer of Computer Aided Drafting (CAD) files on Electronic Media CASE #12: An Agreement Between Client and Structural Engineer for Forensic Engineering (Expert) Services CASE #13: Prime Contract, An Agreement Between Owner and Structural Engineer for Professional Services CASE #14: Supplemental Form A, Additional Services Form CASE #15: Commentary on AIA Document A201 General Conditions of the Contract for Construction, 1997 Edition CASE #16: An Agreement Between Client and Structural Engineer for a Structural Condition Assessment Tool 8-1: Contract Review Tool 8-2: Contract Clause and Commentary Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents Tool 9-2: Quality Assurance Plan

Manual for New Consulting Engineers An HR Favorite for New Hires

ACEC’s best-seller, “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.

This essential guide is tailored to the unique needs of engineering firms, and the skills and experiences rookie consultants need to be successful in a large organization, including: • Proposal Preparation • Financial Management

• Client Relationships • Project Management • Staff Management With over 140 pages of consulting expertise, this resource 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 skills.

To order this book, go to www.acec.org/bookstore. Bulk ordering is available; for more information contact Maureen Brown (mbrown@acec.org).

33 Proven Secrets to Writing Successful Client-Centered Proposals 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 didn’t 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.

To order these books, go to www.acec.org/bookstore. Bulk ordering is available; for more information contact Maureen Brown (mbrown@acec.org).

STRUCTURE magazine

48

November 2018

Foundation 9: Contract Documents – Produce Quality Contract Documents • Understand the definition of contract deliverables • Include staff in the work planning effort • Develop written design criteria • Capitalize on similar designs without starting over on each project • Establish reasonable schedule expectations • Share agreement/contract information with staff • Tailor project documents to project delivery method • Integrate the BIM/CAD team

Tool 9-2: Quality Assurance Plan High-quality client service – from project initiation through construction completion – is critical to both project success and

Foundation 10: Construction Phase – Provide Services to Complete the Risk Management Process • Train staff for the CA work • Clarify SE’s role during submittal review and construction site visits • Get to know the Superintendent and other vital players • Document efforts well • Make site visits and reports meaningful • Follow up on changed construction tasks • Strive toward the goal of a successful project Tool 10-1: Site Visit Cards This tool provides sample cards for the people in your firm who make construction site visits. These cards provide a brief list of tasks to perform as a part of making a site visit, such as: What to do before the site visit; What to take to the construction site; What to observe while at the site; and What to do after completing the site visit.

Tool 10-2: Construction Administration Log Construction administration is a time when good recordkeeping and prompt response is essential to the success of the project and to limiting the risk of the structural engineer. For this reason and many others, a well-organized and maintained construction administration log is essential.

You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

Fresh EJCDC Contracts to Meet Modern Market Demands

EJCDC’s newly released 2018 Construction (C-Series) Documents are a significant modernization, revision, and expansion of the 2013 C-series and now the state-of-the-art in construction contract documents.

The updated edition comprises 25 integrated documents, including: • Fundamental contract documents such as the Standard General Conditions, the Small Project Agreement, and Supplementary Conditions • Forms for gathering information needed to draft bidding documents • Instructions for bidders and a standard bid form • Bonds including bid, performance, warranty (new for 2018), and payment bonds • Administrative forms, such as change orders and a certificate of substantial completion EJCDC C-700, Standard General Conditions of the Construction Contract, has been extensively refreshed and updated, too. The new EJCDC 2018 C-Series also includes expanded and updated “Notes to Users” and “Guidelines for Use” to provide more specific instructions, and it eliminates the need for notary and corporate seals.

To purchase these and other EJCDC documents, go to www.acec.org/bookstore.

CASE Winter Planning Meeting SAVE THE DATE!!

The 2019 CASE Winter Planning Meeting is scheduled for February 7-8, 2019, in Tampa, FL. If you are interested in attending the meeting or have any suggested topics/ideas from a firm perspective for the committees to pursue, please contact Heather Talbert at htalbert@acec.org. An agenda will be published in early December!

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

STRUCTURE magazine

49

November 2018

CASE is a part of the American Council of Engineering Companies

Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents This guide discusses the purpose, the background behind the issue, the essential aspects of design relationships, communication, coordination and completeness, guidance for dimensioning of structural drawings, effects of various project delivery systems, document revisions, and closes with recommendations for development and application of quality management procedures. A Drawing Review Checklist is attached.

The key to achieving the desired level of quality throughout the profession is for each structural engineering firm to focus on and develop its own specific quality management plan, and to implement that plan on each project. This guideline will assist the structural engineering profession in achieving that goal.

maintaining key client relationships. This tool provides guidance to the structural engineering professional for developing a comprehensive, detailed Quality Assurance Plan suitable for their firm.

CASE in Point

CASE Risk Management Tools Available

Software UpdateS ADAPT Corporation

MKT Fastening, LLC

Structural Engineers, Inc.

Phone: 650-218-0008 Web: www.adaptsoft.com Product: ADAPT-Builder 2018 Description: Completely redesigned user interface; delivers greater productivity and ease-of-use. A complete analysis and design solution for concrete buildings in low seismic zones. For post-tensioned podium slabs, mid-rise flat slab buildings, or any complex concrete building structure.

Phone: 800-336-1640 Web: www.mktfastening.com Product: MKT Anchor Design Software Description: New Anchor Design software – now available to assist with calculations meeting ACI 318 and IBC design requirements. Runs on Windows operating systems, calculates in metric or imperial units for mechanical or adhesive anchoring systems.

Phone: 540-239-6355 FloorVibe v3.0 Web: FloorVibe.com Product: FloorVibe v3.0 Description: New Release – based on AISC DG 11 2nd Ed. Vibrations of Steel-Framed Structural Systems Due to Human Activity. Solve problems with vibrations due to human activity in offices, health clubs, convention centers, and areas with sensitive equipment and occupancies. Plus, linear stairs and footbridges.

MiTek/Hardy Frame

Aegis Metal Framing, a division of MiTek USA Phone: 314-851-2226 Web: www.aegismetalframing.com Product: Steel Engine Description: AutoCAD based building modeling software. Auto frames CFS walls and MiTek's UltraSpan floor and roof truss systems in a BIM compatible format. Links to the Aegis Truss Design software to design floor and roof trusses. Panel drawings and material lists are easily created.

Bluebeam, Inc. Phone: 866-496-2140 Web: bluebeam.com Product: Bluebeam Revu Description: End-to-end digital workflow and collaboration solution; improve project communication and streamline processes. By utilizing PDF, Revu enables a common data environment for owners, architects, engineers, and contractors, including 3D models and images.

Dlubal Software, Inc. Phone: 267-702-2815 Web: www.dlubal.com Product: RFEM Description: Intuitive and user-friendly nonlinear FEA software complete with USA/International design codes for steel, concrete, wood, CLT, aluminum, glass, and fabric/membranes. Recent code updates include the 2018 NDS for CLT, AISC 360-16 for steel, and the ASCE 7-16 for load combinations, snow, and wind loads. Free 90-day trial version.

ENERCALC, Inc. Phone: 800-424-2252 Web: http://enercalc.com Product: Structural Engineering Library/RetainPro/ ENERCALC SE Cloud – ENERCALC 3D Description: NEW – 3D component sketches in Structural Engineering Library. Numerous functionality & performance improvements to ENERCALC SE subscription-based cloud application platform – now with NO STARTUP FEE; includes Structural Engineering Library, RetainPro (earth retention structure design), and ENERCALC 3D (finite element analysis and design).

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

Phone: 800-754-3030 Web: www.hardyframe.com Product: MiTek/Hardy Frame Special Moment Frame Design Manager Description: Enables you to easily input SMF design parameters then submit directly to our engineering department for the most economical, job specific design that uses SidePlate technology and all of its advantages.

RISA Phone: 949-951-5815 Web: risa.com Product: RISAFloor Description: Designs and optimizes building systems constructed of steel (including composite), concrete, wood, and CFS, as well as combinations. Updates include drawing grid improvements with the addition of construction lines, Floor to Floor copy, updates to AISC steel design and NDS wood design, and more.

Product: RISA-3D Description: Designs and optimizes steel, concrete, masonry, wood, cold-formed steel, and aluminum with a fast, intuitive interface. Latest version includes partial member end releases, strap/hold down design for wood shear walls, updates to AISC steel design and NDS wood design, and more.

S-FRAME Software Phone: 604-273-7737 Web: s-frame.com Product: S-CONCRETE Enterprise Description: New Multi-Story Designer quickly processes results and generates engineering design reports for large structures analyzed with ETABS® using S-CONCRETE Enterprise. Design and detail columns, beams, and walls with ACI 318-14 support. Standalone application or as ICD in S-FRAME which includes continuous beam design.

Simpson Strong-Tie® Phone: 800-925-5099 Web: www.strongtie.com Product: CFS Designer™ Software Description: Design CFS beam-column members according to AISI specifications and analyze complex beam loading and span conditions. Intuitive design tools automate common CFS systems such as wall openings, shearwalls, floor joists, and up to eight stories of load-bearing studs.

Product: AutoCAD® Plugin for AutoCAD 2012-2019 Description: Allows you to insert Simpson Strong-Tie products directly into AutoCAD drawings by pulling the most recent content from our website. Insert orthographic views directly. Also insert perspective drawings for AutoCAD 2012 (and newer) Menu software.

STRUCTURE magazine

50

November 2018

STRUCTUREPOINT Phone: 847-966-4357 Web: www.structurepoint.org Product: spColumn Description: Featuring a flexible graphical interface in the new spSection module for creating and modifying irregular sections; 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: 678-737-7382 Web: www.tekla.com Product: Tekla Structural Designer Description: Fully automated with unique features for optimized concrete and steel design.

Helps engineering businesses win more projects and maximize profits, from quick comparison of alternative design schemes through cost-effective change management and seamless BIM collaboration.

Product: Tekla Tedds Description: Automates repetitive and error prone structural and civil calculations, allowing engineers to perform 2D frame analysis, access a large range of automated structural and civil calculations to U.S. codes, and speed up daily structural calculations.

Visicon Inc. Phone: 650-218-0008 Web: www.visicon.com Product: Visicon BIM Tools Description: Works with Revit, ETABS, ADAPT, or IFC BIM models. Visicon is a BIM model viewer and manager specifically designed for structural engineers that need to quickly and easily extract relevant information from models. Data extraction, quantities, change management, coordination, markups, and more.

WoodWorks® Software Phone: 800-844-1275 Web: www.woodworks-software.com Product: WoodWorks Design Office Suite Description: SHEARWALLS: designs perforated and segmented shearwalls; generates loads; rigid and flexible diaphragm distribution methods. SIZER: designs beams, columns, studs, joists up to 6 stories; automatic load patterning. CONNECTIONS: wood to: wood, steel or concrete. New version coming soon!

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

Design wood structures effectively, economically and with ease!

Design Office

SIZER Gravity Design

2x4

DATABASE EDITOR Customize Materials

SHEARWALLS Lateral Design

PDF

Adobe

WOOD STANDARDS

(US version)

CONNECTIONS Fasteners

PDF

Adobe

WOOD STANDARD (CDN version)

Download a Free Demo at woodworks-software.com

AMERICAN WOOD COUNCIL

US Design Office 11

Canadian Design Office 10

NDS 2015, SDPWS 2015, IBC 2015 and ASCE 07-10 compliant

CSA O86-14 (Update 1 & 2) and NBC 2015 compliant

New version coming this Winter. Will conform to NDS 2018, SPDWS 2015, IBC 2018 and ASCE 07-16

Use Promo Code STRUCMAG and receive a 10% discount towards your purchase!

www.woodworks-software.com

800-844-1275

Project: Center for Naval Aviation Technical Training Complex | Engineer: SMR-ISD Consulting Structural Engineers Photo by Pablo Mason, courtesy of Harper Construction Company

DESIGN OF COMPLEX STRUCTURES MADE EASY RISA offers a comprehensive suite of design software that work together to simplify even the most complex projects.

As a result, engineers can work efficiently on a variety of structures in a mix of materials including steel, concrete, wood, masonry and aluminum. With RISA, designing complex structures has never been easier. risa.com

Copyright © 2018 RISA Tech, Inc. All rights reserved. RISA is part of the Nemetschek Group. RISA and the RISA logo are registered trademarks of RISA Tech, Inc.

WHERE VISION BECOMES STRUCTURE