STRUCTURE magazine - September 2018

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

September 2018 Concrete

Inside: Boston Public Library

CONNECTION SYSTEMS

SHEAR REINFORCEMENT SYSTEMS

SHEAR CONNECTOR SYSTEMS

FAÇADE CONNECTION SYSTEMS

MOUNTING TECHNOLOGY

Anchor Channels

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

Inc.!

Decon USA is now Jordahl USA USA Inc., on Dec t tha We are pleased to announce Inc. USA ahl Jord will be changing names to ct. with immediate effe

JORDAHL® anchor channels for structural connections For more than 100 years JORDAHL® anchor channels and T-bolts have guaranteed the reliable anchoring of loads to concrete. Providing simple and fast installation, the JORDAHL® system ensures easy location adjustment for structural concrete connections without the time consuming hassle of welding or drilling.

The JORDAHL® range of JTA and JXA hot rolled channel profiles provide high capacity and reduce in-built stresses allowing high dynamic load capability. Therefore they have the ability to accommodate both high and rapidly fluctuating loads over millions of cycles without any signs of metal fatigue. Just the sort of anchoring reliability which is needed for your next project.

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

The JORDAHL® range of JXA toothed anchor channels enables secure mechanical resistance to longitudinal gravity loads or seismic loads with reliable performance verified by ICC-ES Evaluation Report ESR-2854. Design to applicable codes is easily achieved using our innovative JORDAHL® Expert software. The software can be downloaded for free from our website. Our Team offers unequalled customer service and engineering assistance.

We are pleased to support you in your next project and looking forward to working with you.

anchored in quality

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

Adhesive Technology Corp. ......................18 American Concrete Institute ....................39 Concrete Reinforcing Steel Institute .........24 Cortec Corporation ..................................15 CTP Inc. ..................................................29 Dayton Superior Corporation ..................21 Decon USA Inc. .........................................2 Fyfe ..........................................................37 Integrated Engineering Software, Inc........51 Integrity Software, Inc. ...............................4 Khatri International Inc. ..........................31

KPFF .......................................................16 MacLean Power Systems...........................35 MAPEI Corp............................................41 Nucor Vulcraft Group ..............................17 RISA Technologies ...................................52 Simpson Strong-Tie............................11, 25 Structural Engineers, Inc. .........................36 StructurePoint ............................................6 Struware, Inc. ...........................................50 Trimble ......................................................3 USG Corporation ....................................33

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STRUCTURE

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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 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

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John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA Linda M. Kaplan, P.E. TRC, Pittsburgh, PA

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

Important news for Bentley Users

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

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September 2018

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 9, C 2018 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership. Yearly Subscription in USA $75; $40 For Students; Canada $90; $60 for Canadian Students; Foreign $135, $90 for foreign students. Editorial Office: Send editorial mail to: STRUCTURE magazine, Attn: Editorial, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. POSTMASTER: Send Address changes to STRUCTURE magazine, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611.

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

CONTENTS Cover Feature

26 HANDLE WITH CARE

By Peter J. Cheever P.E., and Nathan C. Roy, P.E. To update Boston's Central Library and provide continuity between the landmarked McKim and Johnson Buildings, renovation required major structural challenges including a new 36-foot opening through a load bearing masonry wall. Cover graphic courtesy of Robert Benson.

Columns and Departments

STRUCTURAL PERFORMANCE

34 Restrained vs. Unrestrained

By Kevin J. LaMalva, P.E.,

22 SIMPLICITY RULES ON THE PALOUSE

Therese McAllister, Ph.D., P.E., EDITORIAL

7 Updating the Vision for the Future of Structural Engineering

By David Cocke, S.E.

STRUCTURAL DESIGN

8 Base Plate Design for Post-Installed Anchors

By Richard T. Morgan, P.E.

BUILDING BLOCKS

12 So Many Admixtures

and Luke Bisby, Ph.D.

By Luke Heath S.E., and Thomas Skaggs, Ph.D., P.E. RISK MANAGEMENT

The new Elson S. Floyd Cultural Center, on the Pullman

36 Who Protects the Good Samaritans?

campus of Washington State University, is distinguished by an undulating wood roof structure. There are just a handful

By Randy Lewis

of right angles to be found in this unique building, and not a single connection in the roof is repeated.

CASE BUSINESS PRACTICES

38 Geotechnical Reports as Contract Documents?

By Bart Miller, P.E.

to allow the conversion of an unoccupied roof to

40 Using BIM for Wood Framed Construction Projects

By Joe Penepent, P.E., Anthony Reid,

By Jim Westover, Phoebe Lam,

Kurt Voigt, P.E., and Chris Rodes

and Jon Houck

STRUCTURAL COMPONENTS

HISTORIC STRUCTURES

19 Shaft Wall Solutions for Wood-Frame Buildings – Part 1

By Richard McLain, P.E., S.E.

By Emily P. Appelbaum, P.E., and R. Scott Silvester, P.E. National Hospital required structural strengthening

INSIGHTS

14 Joist Projects

30 A HOSPITAL’S OASIS A long-held desire for a Healing Garden at Children's

By William S. Phelan

CONSTRUCTION ISSUES

Features

42 Whipple Hotel Street Lift Bridge

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

an outdoor respite for young patients. New loads necessitated numerous structural modifications.

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

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

September 2018

Editorial Updating the Vision for the Future of Structural Engineering A Challenge for Younger Professionals

By David Cocke, S.E., F.SEI, F.ASCE, SEI President-Elect

W

e are facing critical challenges that will affect the future • Promote performance-based codes and standards. of our profession. For our younger professionals – what • Lead multi-disciplinary summits on technical matters of broad interest. should we be doing to make the Structural Engineering Profession • Promote structural engineers as leaders and innovators. not only survive these changes, but thrive for the duration of your • Advocate for structural engineering licensure. career and for those that follow?

Ten years have now passed since SEI adopted the Vision Statement, The challenge is to respond to changes that will impact our profes- and five years since the Board accepted the Case for Change report. sion and ensure that our profession stays robust and relevant. Many How much progress has been made? Are we on the right track? Does of these changes are already affecting the vision need to be modified? how we do business. It is imporWhat needs to be done to make tant to note that we do not control it happen? Those are among the these changes, but we do have to questions that we must continue respond to them. It would be easy to ask as we march forward from to continue with the daily routine where we started in 2008. of practicing structural engineering In the fall of 2017, another Board and not notice these changes, except of Governors’ Task Force was when forced to react. However, formed to review, check progress, being reactive does not help us and update the Case for Change to control our future. Engineers document, and I am honored are excellent planners – let’s be to be chairing that group. Our proactive, and plan and engage approach has been to first review to positively impact the future of the activities to-date associated Check out A Vision for the Future of Structural Engineers: our profession. with each of the initiatives identia Case for Change at https://bit.ly/2M1QVXq Some of the changes that will fied in the document. Also, we have and SEI Futures Fund efforts to support the impact us include rapid advances collected data from the previous in technology that could end up efforts, led a panel discussion at Vision at www.asce.org/SEIFuturesFund replacing some of our workplace the 2018 Structures Congress, and skills; increasing complexity in the building codes and standards; the conducted a survey of the conference attendees. We have completed increasing need and demand for continuing education; the changes in personal interviews of the original Case for Change task force members global access to structural engineering technology and skills; increas- and have engaged with the specific groups that are responsible for ingly interdependent global economies; the increasing demand for each of the initiatives listed above. more courses in our structural engineering education programs; and The initiatives included in the Case for Change document are farour increasing responsibilities in the design and construction industry. reaching. It has also become apparent that some additional initiatives Ten years ago, the SEI Board of Governors recognized these coming may need adoption, including support of diversity and more emphasis changes and took steps toward addressing them. The first step was to on technology changes. conceptualize the vision of the profession in the future. They created It is extremely important to continue to monitor our vision and adjust this Vision Statement. It, in part, states: as necessary. The world is changing, especially with the ever-accelerIn 2033, The Structural Engineering Profession will be: ating advances in technology and our “shrinking” global industries.

• A unique, fully engaged profession with a strong identity, SEI especially needs help with the initiatives involving mentorship, • Recognized for the contributions of the profession, technology, promotion of SEs as leaders and innovators, and diversity.

• Stewards of the built environment, and This is where YOU come in. We need your help, your energy, and • Attractive to the best and brightest. your perspective. Some of us “seasoned” professionals will undoubtThe second step was to identify potential changes and develop edly be retired by 2033, so it is even more critical for those that will initiatives to help us achieve our vision. In 2011, the Board formed still be practicing – and leading our profession. We not only a follow-up Task Force to specifically identify topics and strategic need our young professionals’ input but, even more, your issues to consider for action. The document, A Vision for the Future leadership. Will you accept the challenge?▪ of Structural Engineers: A Case for Change, was the result. That group identified several initiatives: Would you like to get involved, or do you have some comments? Contact • Reform structural engineering education.

SEI Director Laura Champion at lchampion@asce.org or SEI President-Elect • Improve mentoring and continuing education.

David Cocke at dcocke@structuralfocus.com.

• Strengthen our role as global leaders in the structural engineering profession.

STRUCTURE magazine

7

September 2018

“B

structural

ase plate design” is a frequently misunderstood term, particularly when discussing attachments for post-installed anchoring applications. This article explains how the concept of base plate design, which is typically understood in the context of “column base plate design,” is not necessarily relevant to fixture attachment for post-installed anchoring applications.

DESIGN

Typical Base Plate Design

Base Plate Design for Post-Installed Anchors

By Richard T. Morgan, P.E. Richard T. Morgan is the Manager for Software and Literature in the Technical Marketing Department of Hilti North America. He is responsible for PROFIS Anchor and PROFIS Rebar software. (richard.morgan@hilti.com)

The term base plate is commonly understood as referencing a steel plate placed beneath a column to distribute applied loads to a concrete member.

The plate is assumed to act as a cantilever beam fixed at the edges of the column, defined by the geometry of a structural profile (Figure 1). If a wide-flange section is used as a column, the base plate design can be summarized as follows: • Select a plate length (N) and width (B).

• Check the concrete bearing capacity using these plate dimensions.

• Plate bending can be assumed to occur at the cantilevered plate sections defined by the parameters (m) and (n).

• Calculate the plate thickness (tp) via the internal bending moments assumed to occur at each cantilevered section of the plate Column base plate design assumes the plate is rigid. In other words, the plate cross-section remains plane under loading, and the plate does not undergo any significant deformation from bending. Although no plate is ever truly rigid, it is reasonable to assume a column base plate is rigid. This is because typical column base plate geometry precludes any significant plate deformation or bending under loading.

The rigid plate assumption permits the stress/ strain behavior of the anchor bolts and the concrete to be modeled as elastic. An elastic stress/ strain model permits a linear analysis to be used

n

Pu

0.95d

0.95d m N

B

0.8f

n

bending line

m

B n

bending line

bending line

bending line

bending line

bending line

0.8f

bending line

n

bending line

m

MPuu

m

Figure 1.NColumn base plate design parameters.

Mplate Mplate

m

m bending line

bending line

in determining the compression stress in the concrete under the plate (σconcrete), the tension loads acting on the anchor bolts (Tanchor), and the internal bending moments used to calculate the plate thickness (Figure 2 ).

Typical column base plate design involves large axial compression loads, possibly acting in conjunction with an externally applied moment.

Column anchor bolts are subjected to tension if the applied loads/moments create uplift on the column. It is possible for no tension loads to act on the anchor bolts if the column is subjected to pure axial compression or axial compression with a small external moment.

Sometimes, column anchor bolts may only be used for erection to comply with Occupational Safety and Health Administration (OSHA) requirements. Column anchor bolt design can be predicated on the steel strength of a ductile anchor element, or on brittle failure modes such as concrete breakout. Column base plate design for shear loads can include shear load acting directly on anchor bolts, but it can also preclude shear load acting on the anchors through the use of shear lugs or embedding the column base into concrete. It is also possible that gravity load acting on the column creates enough frictional resistance between the base plate and concrete surface to preclude any direct shear load acting on the anchors.

Fixture Attachment Column base plate attachment is not a typical post-installed anchoring application. Typically, post-installed anchors are used to attach a “fixture” such as a ledger angle, equipment support, handrail support, or plate. The loads acting on these fixtures are much smaller compared to typical column loads, and the anchors used to attach these fixtures are more likely to be subjected to direct tension and shear loads rather than Mu compression loads. Furthermore, postinstalled anchorage designs controlled by the steel strength of the anchors are typically not achievable.

Generally speaking, the fixture stiffness is assumed to be greater than the post-installed anchor stiffness, thereby permitting a rigid fixture design assumption that uses a linear analysis to calculate the tension loads acting on the anchors. These loads can then be checked against calculated anchor tension design strengths. The American Concrete Institute (ACI) standard ACI 318, Building Code Requirements for Structural Concrete, includes provisions for calculating post-installed and cast-in-place anchor design strengths.

The parameters given in ACI 318 for

Figure 1. Column base plate design parameters.

STRUCTURE magazine 2018 8 September Figure 1. Column base plate design parameters.

Mu gravity for the anchors that are Pu in tension based on the rigid assumption.

It is important to realize what typical anchor design software calculations do not consider. linear-elastic • No check is performed to distribution determine if the rigid fixture assumption is valid. If the fixture is rigid, a linear elastic stress/strain distribution can σconcrete be used to calculate tension loads on the anchors. The fixture thickness is important in ascertaining if a rigid Tanchor assumption is valid. Software that permits users to input any fixture thickness, or utilizes a Figure 2. Rigid assumption uses a linear-elastic strain/strain model. “minimum required” thickca1 s1 1.5hef ness to perform a linear-elastic analysis, is not validating if the Nua fixture is rigid. The minimum required fixture thickness in anchor design software is used to dimension the nodes for a finite element rigid analysis. Most software packages permit this minimum thickness to be waived, and any thickness to be input.

• Stiffness parameters relative to a profile shape attached to the fixture are not considered.

Software users can typically input any profile shape, or no profile shape, and the calculated tension loads on the anchors are independent of Figure Figure Anchoring-to-concrete provisions assume fixture fixture is rigid. is rigid.

3.3.

Anchoring-to-concrete provisions assume any stiffness parameters relative to the profile.

A non-rigid fixture experiences non-linear • The bearing strength of the concrete is not tensile stress/strain behavior. Anchor tension checked. Column base plates are sized to loads calculated using a linear-elastic model minimize the bearing stress on the con- may be significantly less than loads calculated crete. Only the compression stress in the using a non-linear model. A non-rigid fixture concrete beneath the fixture relative to the tends to re-distribute loads among anchors. location of the neutral axis is considered. Anchor design for a non-rigid fixture should What parameters, with respect to a rigid ideally be controlled by ductile steel failure of versus non-rigid fixture, should be considered the anchors to account for re-distribution of for typical post-installed anchoring attach- anchor loads. Anchor design, using ACI 318 ments involving a ledger angle, equipment anchoring-to-concrete provisions, does not support, handrail support, plate, etc.? If a rigid consider parameters relevant to a non-rigid fixture assumption is valid, then the tension fixture. In particular, calculations that include loads acting on the anchors can be calculated a tension eccentricity modification factor could using a linear-elastic model, and anchor tension be unconservative if the fixture is not rigid design strengths can be calculated using ACI because load re-distribution is not considered.

318 anchoring-to-concrete provisions. If the Therefore, unless specific considerations are analysis indicates that a rigid fixture assump- taken, anchor design using a non-rigid fixture tion is not valid, the fixture must be modified can be unconservative in terms of the loads or re-designed to be rigid or alternative anchor- assumed to act on the anchors and the calcuing solutions must be considered. lated anchor design strengths.

hef

calculating these anchor design strengths are derived from testing with a fixture that has a greater stiffness than the stiffness of the anchors; in other words, the fixture can be considered “rigid.” Therefore, a fundamental assumption when designing any anchorage using ACI 318 anchoring-to-concrete provisions is that the fixture being attached is rigid (Figure 3).

Software that performs ACI 318 anchoringto-concrete calculations is readily available.

Many software packages perform what they term “base plate calculations,” but clarification is necessary as to the type of calculations actually being performed. Anchor design software typically performs calculations to determine the magnitude of the tension load acting on each anchor determined to be in tension, and the magnitude of the shear load acting on each anchor determined to be in shear. These loads are then checked against anchor design strengths calculated using ACI 318 anchoring-to-concrete provisions.

Anchor design software does not perform base plate design in the context of column base plate design. Instead, fixture dimensions are utilized in conjunction with loads and moments acting on the fixture to calculate resultant loads acting on the anchors. The fixture is assumed to be rigid, permitting a linear elastic stress/strain distribution to be utilized in conjunction with compatibility equations and statics to calculate the resultant loads. Individual anchor tension loads can be calculated once the resultant tension load is known. Tension eccentricity parameters are calculated if the resultant tension load is eccentric with respect to the anchors in tension. Concrete compression stress beneath the fixture is calculated, but no analysis of concrete bearing strength with respect to axial compression load is performed. Shear calculations do not check if the fixture thickness is sufficient to transfer shear loads into the anchors.

Typical anchor design software functionality can be summarized as follows: • Locate the neutral axis of the fixture using a rigid assumption.

• Determine the compression stress in the concrete beneath the fixture based on the rigid assumption.

• Determine the resultant tension and resultant compression loads acting on the anchors based on the rigid assumption.

• Determine the load distribution on the anchors in tension based on the rigid assumption.

• Determine the eccentricity of the resultant tension load with respect to the center of

continued on next page

STRUCTURE magazine

9

September 2018

Figure 4. Finite element analysis for plate rigidity.

Courtesy of IDEA StatiCa.

Design Approaches When designing post-installed anchors, analysis to ascertain whether the fixture being attached should be considered rigid or nonrigid is relevant, but not always necessary. For example, it is reasonable to assume the fixture is rigid, without additional analysis, if the fixture can be considered unlikely to undergo significant deformation or bending for a given anchor configuration and embedment depth.

For many post-installed anchoring applications, the relatively close anchor spacing and relatively shallow embedment depths at which the anchors are installed preclude significant fixture deformation or bending. However, assessing whether a rigid fixture assumption is valid becomes particularly relevant for applications that involve attachment of a thin fixture because parameters such as anchor geometry and installation, profile eccentricity, and fixture geometry could result in significant fixture deformation or bending taking place (Figure 4).

Verifying that the stress in a fixture resulting from loading is less than the yield stress of the fixture is one parameter for determining if a rigid fixture assumption is valid. This parameter by itself, however, is not necessarily sufficient to determine if the rigid assumption is valid. Parameters relative to displacement must also be taken into consideration in order to validate a rigid fixture assumption. Post-installed anchor stiffness is defined by the parameter load/displacement and can be established via product testing.

If the tension load acting on an anchor is

known, and the anchor stiffness is known, the amount of displacement the anchor is anticipated to undergo can be calculated for a fastening application. Fixture displacement can be defined by the deflection that results from tension loads acting on the fixture, and from compression stress that develops between the fixture and concrete under loading.

Its thickness influences fixture deflection. Increasing the fixture thickness can decrease the amount of deflection the fixture experiences. Therefore, determining the amount of stress in a fixture, the deflection it undergoes, and the amount of anchor displacement that results from a given loading condition provides a more indepth assessment as to whether a rigid fixture assumption is valid.

Following are suggestions for ascertaining whether a rigid fixture assumption is valid.

Given: • Fixture geometry, thickness, yield stress, modulus of elasticity (e.g., for a ledger angle or a plate) • Structural profile geometry (if any) (e.g., structural tubing or equipment post) • Anchor geometry, embedment depth, stiffness, and modulus of elasticity (e.g., for post-installed anchors) • Concrete compressive strength and modulus of elasticity • Tension load and/or moment acting on the fixture that results in tension loads on the anchors 1) Check the maximum stress developed in the fixture ( f fixture,max) versus the fixture yield stress ( f fixture,yield). a. If f fixture,max < f fixture,yield OK. b. If f fixture,max > f fixture,yield Rigid assumption not valid.

2) Check fixture deflection caused by the tensile load (δfixture,tension) and fixture deflection caused by compressive load between the fixture and concrete surface (δfixture,compression). Set parameters for a limiting fixture deflection (δfixture,max) with respect to a rigid assumption. a. If δfixture,tension and δfixture,compression are < δfixture,max OK. b. If δfixture,tension or δfixture,compression are > δfixture,max Rigid assumption not valid.

3) Check anchor displacement (δanchor) for the highest loaded anchor in tension.

STRUCTURE magazine

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September 2018

Set parameters for a limiting minimum displacement (δanchor,min) with respect to a rigid assumption based on anchor stiffness data. Maximum displacement is limited by anchor qualification test criteria. a. If δanchor > δanchor,min OK. b. If δanchor < δanchor,min Rigid assumption not valid.

If the analysis indicates that a rigid fixture assumption is not valid, an easy solution is to increase the fixture thickness. An alternative solution is to add stiffeners to make the fixture rigid. Typically, increasing the fixture thickness is more cost-effective than designing and fabricating stiffeners.

Whatever fixture thickness is used should also be checked to verify that it is adequate to transfer shear load into the anchors. This is a good design check because a thin fixture could tear. Minimum fixture thickness parameters for anchors subjected to shear loads should be established.

If designing a column base plate, verify that the concrete bearing strength is adequate for the fixture geometry and applied loads.

Once analysis indicates that a rigid fixture assumption is valid, anchor design for both tension and shear load conditions can proceed using ACI 318 anchoring-to-concrete provisions. The anchor capacities calculated with these provisions can be checked against the anchor loads calculated using the rigid analysis. As previously noted, tension design of anchors using ACI 318 anchoring-toconcrete provisions is predicated on the fixture being rigid. The fixture thickness established through a rigid analysis is also relevant to anchor calculations for shear load conditions. ACI 318 anchoring-toconcrete provisions for shear are predicated on the fixture having sufficient thickness to transfer applied shear loads into the anchors without tearing.

Summary This article explained the differences between what can be termed “base plate design” and “fixture design,” primarily in the context of post-installed anchoring applications. Unlike most column base plates, fixtures attached with post-installed anchors may not be rigid and may, therefore, be subject to deformation and bending. A good design practice, particularly when considering attachment of a thin fixture, is to check whether a rigid fixture assumption is valid for that fixture.

Assuming a fixture is rigid, when analysis might indicate otherwise, could lead to an unconservative anchorage design.▪

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building

BLOCKS

So Many Admixtures How Do They Impact Structural and Other Key Properties?

By William S. Phelan William S. Phelan is Senior Vice President of Marketing and Technical Services for the Euclid Chemical Company. He is an Honorary Member and Fellow of ACI. ACI 212.3R-10, Report on Chemical Admixtures for Concrete, was chaired by Mr. Phelan. (euclidchem@att.net)

A

dmixtures are used to modify and improve the properties of fresh and hardened concrete. The use of the proper admixtures can result in increased workability, cementitious efficiency (psi per pound of cement), and optimum setting time with mixes, even those with low water/ cementitious ratios. The setting time of concrete can be modified or extended for long distance transportation of concrete by using retarding admixtures or can be modified or accelerated to provide rapid set and/or high early strength concrete by using accelerating admixtures. Today, concrete mixes contain water reducing and/ or high-range water reducing admixtures. The concrete mix designs for slump or slump flow (spread) and self-consolidating concrete (SCC) can be proportioned with the setting time for the agreed upon placement program and modified as the season changes. The goal in all cases is to minimize water of convenience.

Selection of Concrete Admixtures Concrete admixtures should be selected per the specifications and should be used as recommended by the manufacturer or the project testing laboratory.

• Air-entraining admixtures are used to create stable uniform air bubbles properly spaced to provide long-term freeze/thaw resistant concrete. Proper air content, 6% +/- 1½% and low water/cement ratios (< 0.50), are essential for long-term durable concrete. Conversely, trowel finished slabs require air content < 3%.

Concrete with high air content creates a sticky surface and is therefore very difficult to properly trowel. Air meters or unit weight measurements must regularly be made to ensure proper air content. Unit weights are always the best choice since air meters can give false readings.

• Water reducing and high-range water reducing admixtures are used in all concrete today to minimize water of convenience, which was often added in the past to allow concrete to be easily placed or pumped. Typically, they can increase a 2-inch to 3-inch slump to 5½-inch to 7-inch slump. That is the target slump envelope for laser screed strike offs for industrial slabs-ongrade. Trowel finished floors require consistent slumps and setting times. The finishing process of strike off, floating, and troweling must follow the placing process. In other words, if the slump or slump flow varies significantly, the finishing process does not flow smoothly. The concrete does not stiffen and set in order of placement.

This is a significant problem for concrete crews.

• The owner of the project and his design team must clearly specify the concrete requirements.

The specification and drawings must be clear and identical. In many cases, the specification updates are not transferred to the drawings.

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• Exposed industrial floors are designed to achieve the 3 Ms, “Minimal Joints, Minimal Cracks, and Minimal Curling.” (Concrete Construction, April 2015 Issue). The industry today wants joints only at the column lines (60 feet +/-).

• High-range water reducing admixtures are used at low dosages in slabs and toppings. Higher dosages are used to achieve flowing concrete (9 inches +/- 1 inch of slump) or are used to achieve self-consolidating concrete with spreads of 20 to 30 inches. The target spread is typically +/- 2 inches. In heavily reinforced members, the mixes require a 28-inch or higher spread.

• High-range water reducing or high-range water reducing retarding admixtures are required in high-performance concrete. High-performance concrete mixes are used for a wide range of concrete mixes from towers to slabs-on-grade.

Today, the range of strengths is 4,000 psi to 16,000 psi at 28 or 56 days.

• The concrete producer must provide a re-dosage chart for high-range water reducing admixture usage on site. The chart provides guidance for high-range water reducing admixture additions required to ensure that concrete is in the agreedupon slump or spread range (self-consolidating concrete (SSC)). It is imperative in reinforced, formed concrete members that the target spread is achieved for each placement. Lower spreads may result in blockages.

• Today, SCC should be used for reinforced formed members. Vertical members are as thin as possible and heavily reinforced since maximum rental space is required for all floors. It is imperative in reinforced members to have a consistent spread for self-consolidating concrete mixes. Lower spread mixes could hang up concrete in congested areas.

• Shrinkage reducing admixtures are increasingly being used. Clients are not happy with cracks in their high-performance concrete. Highperformance concrete specifications should have a maximum shrinkage requirement of 0.04% at 28 days. Owners of high-performance concrete industrial slabs want joints only at column lines (60 feet +/-). Their shrinkage requirements should be < 0.02% at 28 days.

Shrinkage tests are to be in accordance with ASTM C157 Modified, 7-day moist cure.

Bridge decks and parking decks should also require low shrinkage mix designs.

• Macro-synthetic fibers today are specified and used in many non-reinforced slabs-on-grade, slabs-on-metal deck, and toppings in lieu of welded wire mesh. (The Steel Deck Institute requires 4 pounds/cubic yard for shrinkage and crack control).

• Proposed mix designs should be submitted to the design team for review. If they conform to the specification, a test placement is recommended to be scheduled.

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• Test placement of trowel finished floors must be large enough to allow a riding trowel machine. The test placement must confirm that the concrete placing procedures and finishing process are satisfactory.

• Non-chloride, non-corrosive accelerating admixtures are used in many concretes.

They are required to “normalize” set and achieve early strength gain in concrete placed at temperatures below 40°F. They are also used at high dosages (onsite) to achieve rapid set and/or high early strength for high-performance concrete for bridge decks and other locations where out of service time must be minimized. Freeze-resistant concrete is often selected in areas where cold weather concrete procedures are difficult to achieve.

This concrete is not required to conform to the requirements of ACI 306, Cold Weather Concreting.

• A specially formulated accelerator is used in freeze-resistant concrete. This concrete is chosen for many cold weather concrete applications. The contractor should prepare a plan for placing, finishing, and curing to assure that the specified hardened properties are achieved.

• High-performance concrete generally requires multiple admixtures to ensure proper workability, slump or slump flow, optimum setting time, and early final strengths.

• Very high early strength concrete (4,000 psi in 12 hours) requires an onsite dosage of a specially formulated accelerating admixture.

• Hydration control admixtures are increasingly used in major cities and other locations where the time frame from batching to discharge onsite can be lengthy.

They are used to extend the time for proper workability and/or spread by several hours.

Set Retarding Admixtures Set retarding admixtures help extend the working time of concrete by slowing down the hydration process of cement. Set retarding admixtures prolong the dormant period, allowing increased workability and slump life.

Silica Fume The use of silica fume in concrete has increased significantly in recent years. The benefits are: • High compressive and flexural strength for structural capacity • Low permeability for greater resistance to water

• High early strength gain for faster turnaround time • Improved freeze/thaw and scaling resistance • Increased abrasion and chemical resistance

Admixture Benefits The use of the cited admixtures results in maximum mix enhancements in both the plastic and hardened concrete. Plastic concrete benefits are: 1) Slump or slump flow SCC of choice 2) Rapid or extended set times and increased workability.

Hardened concrete benefits are: 1) Increased compressive and flexural strengths 2) Lower shrinkage

Successful Sequencing Key sequencing activities include: • The key elements of the project are agreed upon by the owner, the design team, and the construction team.

• Proper plans and specifications are prepared, reviewed, and accepted by the construction manager and the concrete team.

• The construction manager assembles the concrete team.

• The construction schedule is discussed and agreed upon.

• The concrete contractor outlines his detailed concrete construction schedule. The required mix designs are submitted for review. They should be agreed upon, and any changes should be discussed. High-performance concrete mixes often end up being resubmitted since one or more types of information are usually missing or unclear.

• Successful test placements onsite are mandatory for high-performance concrete. The floor placements must be large enough to confirm that the required floor finishing process is satisfactory. Formed member placements should be one story high and as wide as the construction team requires.

Floor finishes vary to some degree. A large test placement requires the actual placing, finishing, and curing methods and procedures to be in accordance with the specification.

• The contractor should prepare minutes of the pre-concrete meeting and distribute within 5 days to all parties, including the owner/owner’s representative, architect, and engineer.

• The concrete contractor should state that his proposed mix designs will enable

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him to properly place, pump, finish, and achieve the concrete quality required by the specifications.

• The concrete producer should provide a high-range water reducing re-dosing chart onsite to ensure that every mix is within the approval slump or spread envelope.

• Heavily reinforced formed members require self-consolidating concrete with a spread of 28 inches +/- 1 inch.

The majority of concrete mixes have a water content higher then what is needed to hydrate the cement properly. Proper mix designs minimize this water of convenience and optimize the slump or slump flow with approved water reducing and/or high-range water reducing admixtures.

In general, high strength concrete for reinforced formed members has a negative water slump. The required slump or slump flow is entirely achieved with higher than normal high-range water reducing admixture dosages.

This is undoubtedly true of high strength concrete, i.e., 8,000 psi to 16,000 psi.

Example: 10,000 psi at 28 or 56 days is required The w/cm is 0.30 The water content is 250 lbs/cy (0 or negative slump) The cementitious content is 833 lbs/cy The mix is designed to be flowing (9 inches +/- 1 inch slump) or SCC The high-range water reducing admixture provides the slump or spread.

Trowel finished floors and slabs are often placed with slumps of 5½ inches to 7 inches at the point of deposit. These mixes must have a water slump of 2 inches to 3 inches. Lower water slumps present finishing problems.

A negative water slump means that the water content alone would not allow the concrete to be properly mixed. All of the slump or spread is achieved by the use of the high-range water reducing admixture.

Summary All concrete today contains admixtures to enhance the concrete performance in the plastic and hardened state. Proper air-entrained concrete is necessary to provide resistance to freeze-thaw cycles. Water reducing and high-range water reducing admixtures are used to enable the user to select the optimum slump or slump flow for their project. While maintaining a low water content, shrinkage is related directly to water content, paste content, and water/cement ratio.▪

construction C ISSUES

onstruction projects, big and small, have phases. What happens during the early phases can dictate how smoothly the project will go and how much it will cost in the end.

Consulting early with the steel joist supplier can help prevent delays and cost overruns by avoiding commonly made early-phase mistakes.

Specifying Uplift

Joist Projects Top 10 Design and Specification Mistakes to Avoid

By Joe Penepent, P.E., Anthony Reid, Kurt Voigt, P.E., and Chris Rodes

Sometimes, contract drawings will not adequately specify net uplift wind loadings on a roof. For example, the contract drawings may only indicate the components and cladding for a 10-squarefoot area chart. This information is inadequate to calculate the component and cladding net uplift value for the joists, which are typically based on a 100-square-foot tributary area or more. Other times, a designer may only include a chart such as seen in Figure 1. Pressure tables such as this do not provide sufficient load information to the joist manufacturer. It is better to provide the joist loads intended by the structural engineer. An owner could be surprised by unexpected costs associated with the need for additional rows of bridging to brace the bottom chords sufficiently, or by increasing bottom chord sizes to provide sufficient uplift resistance.

only one supplier has the potential of increasing cost because the customer is not going to get a competitive bid.

A different supplier may be able to recommend a product that better addresses the design and engineering challenge, and be less expensive. There may also be regional requirements that the specifier is not aware of. For example, an EOR may specify a product they are familiar and comfortable with that is not available in their region. The engineer may not realize it is going to cost more to bring it into the area. It might also be the case that a particular product is patented in such a way that it requires special components and procedures that can add to material and erection costs.

Cold-Formed Components Much like the mistake of specifying specific manufacturers, not allowing cold-formed angles or members is a matter of comfort and preference.

Snow Drifts The authors of this article are all with New Millennium Building Systems. Joe Penepent is a Sales Engineer; Anthony Reid is a Joist Detailer; Kurt Voigt is an Engineering Manager; and Chris Rodes is a Design Supervisor. For questions or comments regarding this article, contact info@newmill.com.

Even when they are not required, snow drifts are often specified around rooftop units (RTUs). For a square mechanical air conditioning unit on a roof, the Engineer of Record (EOR) needs to look carefully at the specifications for snow drift requirements in accordance with ASCE 7-10, Minimum Design Loads for Buildings and Other Structures.

Section 7.8 indicates, â&#x20AC;&#x153;If the side of a roof projection is less than 15 feet long, a drift load is not required to be applied to that side.â&#x20AC;?

On one project, the authors looked at the actual RTUs and were able to save the customer approximately $70,000 while remaining within the code. Some specifying engineers may be relying on design software that does not account for the exceptions, such as automatically applying a drift load around an RTU even if it is unnecessary.

Figure 1. Pressure tables such as this do not provide sufficient load information to the joist manufacturer. It is better to provide the joist loads intended by the structural engineer.

Steel Manufacturers Often, drawings will list manufacturers that are no longer in business. Even if the supplier is still operating, specifying STRUCTURE magazine

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Figure 2. Indicating revisions with clouding can save project time by making it easier to locate the change.

September 2018

However, doing so may limit the number of manufacturers available, hinder the ability to receive multiple bids, and drive up the cost.

Some specifiers do not like cold-formed members because, when they have an issue or need to make a modification, they do not know what to do with the cold-formed in terms of properties because they cannot look it up. Consulting with a joist engineer can help clarify options.

Cranes When crane loading on the joists is specified, suppliers have to account for the cyclic loading in the joist design, otherwise known as fatigue. The joist supplier needs to know the craneâ&#x20AC;&#x2122;s classification, the type of crane, and how it is being controlled; that determines the impact and fatigue factors that are used in the joist design.

If the crane classification is not available in the structure design phase, it is essential to provide it as soon as it is available. The fatigue these joists would be subjected to is similar to bending and straightening a paper clip repeatedly. Eventually, the paper clip will snap. When the joist supplier has this specific information, they can design the joists to handle the repeated loading of the cranes over the lifespan of the building.

Figure 3. Joist camber can be integrated into a building design to offset deflection and save project cost.

quality and project length. When revision marks on drawings are not called out with clouding, locating revisions becomes a tedious process. Most importantly, there is greater potential for suppliers or contractors to miss something. Hunting through 100 pages of detailed drawings to find one changed area requires a lot of unnecessary time and effort. It sounds like a simple thing, but it can increase the time of a project and potentially cause a problem if a revision is missed.

Moments of Inertia Engineers of Record will sometimes specify unnecessary moments of inertia. Moments of

inertia can increase member weight considerably because they drive chord sizes for the joists or girders. The authors have found, on many occasions, the moments of inertia that were specified really were not required or were over-specified. They could have been reduced considerably, which saves money.

Moments of inertia are most often specified related to the stiffness of a roof relative to deflection and ponding. For example, with respect to water on the roof, the EOR needs to make sure the roof is not going to develop too much of a bowl effect that would cause water to pond, progressively increasing the weight supported by the roof and eventually causing a collapse. continued on next page

Chord Splices

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Occasionally, the architect will forbid chord splices. Perhaps they have experienced a supplier that has used a leftover piece of steel to splice, which may not look aesthetically pleasing. The fact is, the Steel Joist Institute allows for chord splices and sometimes they are unavoidable. Standard raw material lengths and even the length of delivery trucks put a limit on joist length.

Moreover, if the design calls for a 65-foot joist, a chord splice will be required.

The cost for weld splices in the factory is nominal, and they can be completed in an aesthetically pleasing manner. If the concern is about the reliable performance of a chord splice, the joist supplier engineers and manufactures the splice to address this. A shop chord splice weld by itself is typically more than sufficient to handle the load. Good suppliers typically shop weld additional material such as a rod or bar to supplement the strength of a welded butt splice.

Revisions on Drawings The quality of drawings goes a long way in determining the overall outcome of a construction project, both in terms of MCI_5x3.5_02-18.indd 1

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2/19/18 8:44 AM

Ponding is a legitimate reason to specify a moment of inertia. However, sometimes EORs use assumed or estimated moments of inertia in their structural models to analyze the behavior of the overall structure. Those moments of inertia are sometimes then specified in the bid and design documents, and many times are not accompanied by a note that lesser values may be permissible. In such cases, the joist manufacturer would provide a joist or girder that meets the specified moment of inertia but may be considerably heavier than required to resist the design loading. EORs should be risk averse but, if they talk to suppliers during the design phase, they will be provided information to make better assumptions or estimates early in the design, which allows them to have a handle on relative cost impacts.

Deflection Limits vs. Camber

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Similarly, the imprecise specification of deflection and camber can potentially lead to added project costs. When EORs are designing for a line or point load, such as a curtain wall or something heavy hanging off the joist, they often will specify a deflection limit for the joist carrying those elements. The deflection limit is generally pretty stringent, and it is

usually not clear to suppliers under what load combinations or load categories they need to be looking at the deflection.

In the absence of specific direction, the project may end up with a much heavier joist than necessary. Camber in the joist essentially arches the joist upward and may help offset some of the deflection. If deflection limits of 1 inch are specified, with just a little clarification – such as, if it is 1inch below a horizontal line, 1 inch below where the joist starts cambered with no applied load, or if it is 1 inch below top of joist after all dead loads are applied – the joist supplier can discuss the use of camber with the EOR, saving the owner money.

Longer Welds Another early-phase mistake that often leads to unnecessary costs is large weld sizes specified on chord toes or on chords attaching to columns or tie plates. Weld size can drive material thickness. For example, if a 3⁄8-inch fillet weld at 4 inches long is specified on the bottom chord of a joist with 5⁄16-inch thick chords, it would need to be bumped up to be 7⁄16-inch thick just to receive that weld. To save money, an EOR could specify a smaller weld that is longer. Instead of a 3⁄8-inch weld,

Figure 4. A change in weld size on this drawing saved the project money by reducing the amount of steel required on the chord receiving the weld.

they could specify a ¼-inch weld. That ¼-inch weld only has to be 50% longer to be the same strength and would use 33% less welding material.

Having a conversation with the joist manufacturer about chord thickness and weld size early in the project can save time and money. No one wants to be surprised when chord thickness has to be increased because of weld size that may increase the structure weight and require changes.

Conclusion 2014 AwArd of ExcEllEncE, AssociAtEd BuildErs And contrActors ExcEllEncE in construction AwArds

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Owners are pushing to save cost by compressing project timelines, telling the architect to push critical details further down stream to the structural engineer, who pushes them to the fabricator, who pushes them to the joist manufacturer.

Making these avoidable mistakes and trying to save time upfront by leaving out information in the drawings just transfers that work to a different stage of the project and can lead to mistakes, RFIs, and cost overruns. Convenience, comfort, and inertia should not outweigh construction best practices. Taking extra time at the early stages of a project, and consulting with steel suppliers as early as possible, can save time and money and increase safety and quality.▪

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I

t is relatively common for light wood-frame commercial and multi-family buildings to include shaft walls made from other materials.

However, with an increase in wood construction nationwide, many designers and contractors have come to realize that wood-frame shaft walls are a code-compliant means of reducing costs and shortening construction schedules.

Part 1 of a two-part series, this article provides an overview of building code considerations and detailing. Part 2 will examine fire design requirements, construction constraints, and other potential differences associated with specific applications such as stairs, elevators, and MEP shafts.

Fire Barrier Construction Shaft enclosures are specifically addressed in Section 713 of the 2015 International Building Code (IBC). However, because shaft enclosure walls are to be constructed as fire barriers per Section 713.2, many shaft wall requirements directly reference provisions on fire barriers found in Section 707.

Provisions addressing materials permitted in shaft wall construction are given in both the shaft enclosures section (713.3) and fire barriers section (707.2). These sections state that fire barriers can be constructed of any material permitted by the building’s type of construction.

This means that light-frame wood construction or mass timber may be used for shaft wall construction in Construction Types III, IV, and V per the construction type definitions in IBC Section 602. The one exception is when shaft walls in Type III or IV Construction are also exterior walls. This requires that the exterior/ shaft walls be fire-retardant-treated wood framing or non-combustible framing.

Per IBC Section 713.4, shaft enclosures are required to have a fire-resistance rating of not less than 2 hours when connecting four or more stories. A fire-resistance rating of not less than 1 hour is required for shaft enclosures connecting less than four stories.

Continuity IBC Section 707.5 states the requirements for fire protection continuity of fire barriers. It requires that fire barriers “extend from the top of the foundation or floor/ceiling assembly below to the underside of the floor or roof sheathing, slab or deck above and shall be securely attached thereto. Such fire barriers shall be continuous through concealed space, such as the space above a suspended ceiling.”

This is one of the main distinctions between a fire barrier and fire partition. A fire partition (for example, a corridor wall) is permitted to terminate at the underside of a fire-resistance-rated

floor/ceiling or roof/ceiling assembly while a fire barrier is required to extend up to the underside of the floor/roof sheathing.

This continuity condition is depicted in the code commentary in a simplistic form where the shaft wall runs parallel to the floor framing (Figure 1). However, in platform-frame buildings, there are usually shaft walls that directly support perpendicular framing elements. It is essential to understand that continuity of the assembly can be maintained even in these scenarios.

Having a single fire-resistance-rated assembly running from the bottom to the top of a shaft enclosure with no interruptions, such as a masonry wall, is considered by some to be the clearest path to meeting this requirement. However, given the potential costs and structural challenges associated with integrating masonry shaft walls in wood-frame buildings, wood-frame shaft walls are becoming increasingly popular.

The requirement is for continuity, but this does not dictate the use of only one assembly. Since fire protection continuity does not equate to wall framing continuity, using means of fire protection other than the tested wall assembly in the depth of the framed floor can be an effective way of providing the required continuity.

Ultimately, the detail used will reflect what the building official accepts in terms of fire protection continuity of the shaft wall’s required fire-resistance rating. In varying degrees (depending on the detail), the shaft wall will need to be interrupted to attach the adjacent floor framing and floor sheathing. The methods used at this floor-to-wall intersection will also depend somewhat on the floor framing configuration. See “Detailing Floor-to-Wall Intersections” below for examples of ways designers have detailed this condition.

structural

COMPONENTS

Shaft Wall Solutions for Wood-Frame Buildings Part 1: Codes and Detailing

By Richard McLain, P.E., S.E. Richard McLain is a Senior Technical Director in the Project Resources and Solutions Division of WoodWorks. He is Executive Director of the Structural Engineers Association of Vermont and a member of the ASCE Structural Wind Engineering Committee, SEI Blast Protection of Buildings Standards Committee, and NIBS Offsite Construction Council Board. (ricky.mclain@woodworks.org)

Supporting Construction IBC Section 707.5.1 requires that “The supporting construction for a fire barrier shall be protected to afford the required fire-resistance rating of the fire barrier supported.” In the scenario where a fire barrier wall line is vertically discontinuous (e.g., fully stopped at a floor and does not continue below that floor), it is clear that the floor is indeed a direct support. For example, if the floor were to fail after 1 hour of fire exposure, the wall above could not continue to contain the fire for 2 hours. However, in the condition where a fire barrier wall is supported directly Figure 1. IBC Commentary Figure 707.5 – continuity of fire barriers. below a floor by

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accordance with ASTM E 814 or UL 1479, with an F (flame) rating of not less than the required fire-resistance rating of the wall penetrated (per Section 714.3.1.2).

As noted, the option given in IBC Section 714.3.1.2 is the most common approach and typically involves the use of a tested, approved firestop system to seal around structural penetrations in shaft walls.

Figure 2. Stair landing beam shaft wall structural penetration prior to fire caulk installation.

Assemblies & Intersections

another fire barrier, the fire endurance of the floor assembly that lies between the two fire barrier assemblies would not affect the ability of the fire barrier above and below to perform for the full duration of their intended fire resistance. In this scenario, maintaining the code’s continuity requirements for the wall through the floor depth should also satisfy the supporting construction requirements.

Structural Shaft Wall Penetrations It is often necessary to penetrate a shaft wall with a structural member such as floor sheathing, a landing beam, or floor joists (Figure 2 ).

The allowance for these penetrations comes from IBC Section 713.8, which states that “Penetrations in a shaft enclosure shall be protected in accordance with Section 714 as required for fire barriers. Structural elements, such as beams or joists, where protected in accordance with Section 714 shall be permitted to penetrate a shaft enclosure.”

IBC Section 714.3 requires that penetrations into or through shaft walls comply with Sections 714.3.1 through 714.3.3. Section 714.3.2 requires that either: 1) Penetrations shall be installed as tested in an approved fire-resistance-rated assembly (i.e., incorporated during the conduct of an ASTM E119 test of the wall or floor assembly, per Section 714.3.1.1) or, more commonly, 2) Protected by an approved penetration firestop system installed as tested in

The first step in detailing shaft wall construction is to select the rated wall assembly that is appropriate for the application. The assembly type chosen will depend on several application-specific constraints, including space available for the wall assembly, accessibility to finish gypsum wallboard, the height of the shaft, acoustic needs, and construction efficiency. In some cases, the floor-to-wall intersection detailing necessary for plan approval may affect the type of wall assembly chosen.

As noted, per IBC Section 713.4, shaft enclosures are required to have a fire-resistance rating of not less than 2 hours when connecting four or more stories. A fire-resistance rating of not less than 1 hour is required for shaft enclosures connecting less than four stories. See Figure 3 for various options.

Double wall options provide opportunities for higher acoustically-rated assemblies and/or a way to decouple membrane continuity and structural support. In particular, better acoustical performance may be desired when shaft walls separate the shaft from a residential unit or other occupied space. For more information on acoustical performance of light-frame wood walls, see the WoodWorks publication, Acoustical Considerations for Mixed-Use WoodFrame Buildings.

Some designers also utilize shaftliner panels.

Shaftliner panels are typically thicker than a normal gypsum panel (1-inch-thick is common) and come in sizes that can be installed easily between CH-, CT-, or H-studs. These studs are cold-formed steel sections that hold the

Figure 3. Options for fire resistance rated, wood frame wall assemblies that could be useful for shafts.

shaftliner panels together and eliminate the need for gypsum panel joint finishing. Some assemblies are tested with a supporting wood structure (UL U375), and others are not (GA ASW 1000). This is an important distinction to make when discussing continuity and structural support. Even if included in the tested wall assembly, the wood walls are usually assumed not to be providing part of the wall’s fire-resistance rating. The 1-hour or 2-hour rating can typically be accomplished solely with the shaftliner panels. If tested with a supporting wood structure, only lateral bracing of the shaftliner panels is assumed. The weight of the panels is carried through the panels to the foundation unless specifically detailed otherwise.

Assemblies such as UL U336 have an option for a single wood-frame wall supporting a double shaftliner gypsum membrane. A second wood wall could be used on the other side of the double gypsum membrane to support floor framing (i.e., stair and landing framing).

Alternatively, only one wood wall could be used (on the non-shaft side), and the gypsum membrane could face the inside of the shaft.

This allows structural support of the main floor and roof framing to occur without penetrating the membrane. See Figure 4 for options.

Height Limitations A common question that arises when utilizing shaftliner panels is that of limiting heights, both floor-to-floor and overall. Many shaftliner manufacturers publish maximum floor-to-floor heights and/or maximum system height limitations. An example is assembly UL U375 which allows a total system height up to 66 feet but requires different H-stud clip angle spacing depending on total system height.

The limiting height of these systems is due to the fact that they are designed to be nonload bearing walls. As the self-weight of the wall assembly accumulates throughout the height of the wall, axial stresses on the nonload bearing steel studs could increase to the point where they become inadequate, creating a need for a limiting height. Also, these walls are generally designed for a minimal internal horizontal pressure, typically about 5 pounds Figure 4. Shaftliner panels, 1- and 2- hour ratings.

1-Hour Single Wall

1-Hour Double Wall

2-Hour Single Wall

2-Hour Double Wall

1-Hour Wall with Shaftliner

2-Hour Wall with Shaftliner

• UL U305 • GA WP 3510 • UL U311 • IBC 2012 Table 721.1(2), Item 14-1.3 • UL U332

• UL U341

• UL U301 • UL U334 • IBC 2012 Table 721.1(2) Item Number 14-1.5 • IBC 2012 Table 721.1(2) Item Number 15-1.16

• UL U342 • UL U370 • GA WP 3820

• UL V455 • UL V433

• UL U336 • UL U373 • UL U375 • UL V455 • UL V433 • GA ASW 1000

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Detailing Floor-to-Wall Intersections

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Once the typical wall assembly for the shaft has been selected, the detail at the fl oor-to-shaft intersection should be addressed. The look of this detail will depend on the floor framing type and bearing condition.

One method used by designers to demonstrate continuity of the shaft wall through the floor cavity is having the wall gypsum stop at the underside of the floor framing Figure 5: Floor-to-shaft wall intersection detail with and installing wood blocking in the floor blocking between floor joists. cavity. The concept is that approximately every 1.5 inches of wood blocking thickness provides 1 hour of fire protection. This rationale is codified through IBC Section 722.1, which references Chapter 16 of the American Wood Council’s National Design Specification® (NDS®) for Wood Construction for calculated fire resistance of exposed wood members. NDS Chapter 16 indicates that the nominal char rate of a number of wood products, including solid sawn lumber and structural composite lumber, is 1.5 inches per hour. See Figure 5 for an example of this detail.

Another option would be to extend the wall gypsum on the floor side of the shaft Figure 6: Floor to shaft wall intersection detail with wall up to the underside of the floor/roof gypsum extending to the underside of sheathing sheathing between the floor/roof joists. This between trusses. would require interruptions of the gypsum per square foot (psf). The prescriptive allowable at the joists. See Figure 6 for an example of height tables published by the manufacturer this detail. The joist is merely a structural can potentially be increased when the project’s penetration, which is allowed in shaft wall structural engineer analyzes the cold-formed construction as noted above when protected steel stud sections to determine their capacity according to Section 714. against the project’s actual loading conditions.

A third option would be to install a floor Most CH-stud manufacturers provide struc- beam parallel to and just inboard of the shaft. tural section properties for their products that This beam would be used to support all of the can be used for this purpose. Most of these framing perpendicular to the shaft wall such sections are available in 25-gauge and 20-gauge that the only element penetrating the shaft options, so using the slightly thicker 20-gauge wall is the floor sheathing. This option is only option might help in making a wall height feasible if the length of the shaft wall is such work. Additionally, 4-inch-deep and 6-inch- that a reasonable beam size can still be used. deep CH-stud sections are typically available Walls or beams parallel to and just beyond and would have higher load capacities than the ends of the shaft are used to support the the standard 2½-inch-deep option. The wall ends of the beam mentioned above. stud and system manufacturer should be conA final option would be to run the gypsum sulted for input on options that exceed their continuously behind the floor joists up to published allowable height tables. the underside of the floor/roof sheathing.

If a proposed shaft wall using shaftliner The joists would be hung from the wall with panels does not meet the total system height a top flange hanger capable of spanning over limitations, supporting the mass of the wall one or two layers of gypsum.▪ at intermittent heights off the adjacent floor This article is excerpted from the structure is an option. Maintaining the wall’s WoodWorks paper, Shaft Wall Solutions fire-resistance rating at the support attachfor Wood-Frame Buildings, available at ment locations is a primary design objective if choosing this option. www.woodworks.org.

Simplicity Rules on the Palouse Elson S. Floyd Cultural Center at Washington State University

By Luke Heath S.E., and Thomas Skaggs, Ph.D., P.E.

W

hen Washington State University (WSU) set out to build the new Elson S. Floyd Cultural Center on their campus in Pullman, they had a number of goals: bring the Universityâ&#x20AC;&#x2122;s diverse cultural organizations together under one roof, incorporate natural building materials native to the area into the structure, and build something unique yet iconic that would serve as a marquee building. The resulting 16,000-square-foot structure, created through a design-build collaboration with PCS Structural Solutions, GGLO Design, and Absher Construction, is distinguished by an undulating wood roof structure intended to emulate the rolling prairies of the Palouse, native to the local Nez Perce Tribe.

There are just a handful of right angles to be found in this unique building, and not a single connection in the roof structure is repeated.

In other words, it was a structural engineerâ&#x20AC;&#x2122;s dream.

Engineers understand the challenge of creating simplicity out of complexity when everything is unique. With this project, a design/ build approach and a wood structure held the keys to success. In fact, the team determined that the design/build budget could not have been met if this particular roof structure had been built using a material other than wood.

Making a Statement Most engineers agree that the best part of a design/build project is the initial stage, when ideas are big and concepts are still being developed. This project was no exception. Five teams submitted STRUCTURE magazine

designs; each had three opportunities to present their concepts to WSU and the bridging team.

Initially, architects at GGLO conducted pedestrian footpath studies to determine access and building alignment; they also did daylight studies since the structure needed to protect artwork inside. However, the team was in last place after the first meeting; their second design also did not meet client goals. So, with the clock ticking, the architects started over and developed the final design on the proverbial napkin, leaving engineers at PCS Structural Solutions just a week to figure out how to make it all work. They did, WSU administrators were sold, and the design/build team of PCS/GGLO/Absher was hired.

The resulting design went from a building that would make a statement architecturally to a building that makes a statement both architecturally and structurally.

Design/Build There are many challenges when taking a design/build approach but, sometimes, design/build is the only way to approach a complex project like this. Although a design/build format is common for larger contracts, this was just a $16 million project, so stakes were high.

WSU wanted to use native materials and the University has a deep appreciation for wood products and technologies. They also liked the curved roof concept, so the resulting structure controlled much of the design. However, the team needed to balance the projectâ&#x20AC;&#x2122;s complexity against the financial constraints of their design/build requirements, so

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8¾- x 36-inch glulam roof beams were erected onto a steel infrastructure; steel columns were tilted toward the center of the building at the large spans to accommodate lateral spreading.

Double curvature glulam beams were seated onto the steel column pedestals using round capital plates to showcase the structural steel column-to-glulam beam connections.

it was critically important to work together. Architects at GGLO were looking for a statement, the engineers were looking for structure, and the contractor was looking for speed and ease of construction. Lead time was also critical; there was an early bid package for foundations and structure, which put additional pressure on the consultants to provide product in a timely manner. All challenges led the team to design a wood roof structure constructed with glulam beams.

Wood provided both form and function. Glulam beams met complicated loading requirements and the sinuous structure, constructed with glulam girder beams left exposed to the interior, reflected elements of Nez Perce basket weaving traditions.

to divorce everything they knew about typical building construction and entirely rethink the construction process.

Eastern Washington has a ground snow load of 30 psf so, depending on the spans and cantilevers, adjacent beams had drastically different deflections due to the irregular shape of the floor plan. Typically, arched beams are restrained by buttress action or through the use of steel tie rods. However, adding these elements to resist the 30,000 pounds of thrust at each beamline would have compromised the building’s aesthetics. With no physical buttress, the building would behave like a breathing mechanism as live loads were applied and removed. Wall finishes and ceilings were designed with appropriate gaps that would allow the building to expand and contract as the beams deflect and force the walls to move out of plane.

PCS determined that the only way to control lateral deflection and accommodate the differential deflections between adjacent members was to engineer the glulam beams based on stiffness rather than strength alone. They used STAAD, the 3D structural analysis and design software, to help determine the interaction of beam deflection with adjacent beams and to calculate the various load cases of wind and snow drift. To minimize lateral spreading and differential deflections, they specified 8¾- x 36-inch glulam beams. They intentionally tilted the steel columns 1 inch toward the center of the building at the large spans to accommodate for the lateral spreading, so that the columns would be plumb when the building’s dead load was applied.

The contractor monitored column displacements during construction, and particularly during snow events, to ensure modeling accuracies.

The Elson S. Floyd Cultural Center has a total of 62 curved girder glulam beams which were constructed with Port Orford cedar, a naturally decay-resistant species. Except at the steeper roof sections (which required tighter spacing), the beams were spaced at 8-foot centers. Glulam fascia beams, 31⁄8 x 18 inches, were curved out of plane to define building shape and act as the diaphragm chord. The remainder of the roof was constructed with canted and sloped 4x8 beams spaced 48 inches on-center, covered by two layers of plywood sheathing laid at 45-degree angles to each other.

Altogether, the project contains 125,000 board feet of glulam, which was treated with a UV coating to protect the wood from Eastern Washington’s harsh, arid sun. Staff at APA – The Engineered Wood

Creating Simplicity from Complexity Building complexity required close collaboration and accurate 3D drawings, so everyone on the team used Revit. The contractor also used a total station to increase the accuracy of the site measurements; the design was so fluid that there was no common roof elevation.

The undulating roof design required a wide variety of glulam types – single curvature beams, reverse double curvature beams, out-of-plane curvature beams, as well as turned and tapered glulam columns. The team knew they needed a roof structure that could replicate itself; too much deviation would lose on both cost and constructability. Because spans and cantilevers varied for each beam, it was difficult to provide a common beam size that would work for all conditions and meet budget.

Shipping was also a consideration; the beams were manufactured 600 miles away and trucked from Vancouver, Washington, so maximum beam length was 65 feet.

The team decided to make all the beams consistent with the same radius, 86 feet 3 inches. What changed, though, was the top condition of the beams. Beveled plates added to the top of each glulam beam adapt to the ever-changing roof slope.

Allow the Building to Breathe Structural engineers at PCS were challenged to account for the flexible building design. To fully understand how the building would deflect and how the beams would behave against adjacent members, they had STRUCTURE magazine

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Association (APA) provided PCS engineers with recommendations regarding flashing details to protect the glulam beam tails, which were left exposed to the exterior.

Request for Information (RFI) related to a misaligned glulam beam connection.

Details for the steel connecting the 4x8 purlins to the glulam beams were equally complex. Due to the biaxial bending on the beams, there were no off-the-shelf products available to suit the canted, sloped, and skewed conditions that were required at each unique connection. To speed erection, fabricated 16 gauge bent U-shaped plates with pre-drilled holes were preinstalled on the ground before the glulam beams were lifted into place.

Connection Complexity

Every angle and connection was unique, requiring the use of simple and repeatable connectors to meet the design/build budget. Since the roof structure and many connections were left exposed, the solutions needed to be efficient yet elegant to complement the architecture. Many of the beam-to-column connections are kerfed to Design Goals, hide the connectors’ side plates from view.

Structural Solutions Custom tapered WTs and round capital This single curvature beam was connected to a turned double-tapered glulam column using a kerfed plates are used on top of the columns to connection to hide the connector’s side plates from view. With a design/build project, money and showcase the structural steel column-tobudget are essential; the cheapest solution glulam beam connections. does not always originate from lower material costs. In this situaConnections between the concrete shear wall and the glulam bear- tion, the use of custom glulam beams were slightly more expensive. ing were complicated, due to the varying geometries. Steel plates However, repeatable yet adjustable connections sped construction embedded into the walls made it easier for the contractor to set beam and reduced complexity, saving headaches and money. seats at the correct elevation, skew, and slope. To speed erection At the same time, the unique wood roof structure allowed the time, engineers designed steel brackets with bent side angle plates. design/build team to meet WSU’s aesthetic and cultural goals while The connection had an adjustable swivel bearing seat that readily accommodating the complex structural challenges of the loading accepted the various beam bearing slopes. Once the beam was set at on this undulating roof structure. Even though every angle the correct elevation, the bracket was welded to the embedded steel. and every connection was unique, the team was able to This detail was so successful that the contractor did not have a single create simplicity from complexity.▪

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STRUCTURE magazine

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Luke Heath, S.E., is the Managing Principal of PCS Structural Solutions Portland Office. Actively mentoring the next generation of engineers, the following is a link to an awardwinning video he created for increased awareness of structural engineering. https://vimeo.com/216094160 Thomas Skaggs, Ph.D., P.E., is the Manager of product evaluation in APA – The Engineered Wood Association’s technical services division. Before joining APA, Skaggs’ research at Virginia Tech was in the area of metal-plate-connected wood trusses. He can be reached at tom.skaggs@apawood.org.

Project Team Owner: Washington State University, Pullman, WA Structural Engineer: PCS Structural Solutions, Tacoma, WA Architect: GGLO Design, Seattle, WA Contractor: Absher Construction, Seattle, WA Glulam Fabricator: Calvert Company, Vancouver, WA

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T

he Boston Public Library’s Central Library is located on the historic Copley Square of Boston, Massachusetts, which also includes other historic structures such as Trinity Church by H.H. Richardson, the Fairmont Hotel by Henry Janeway Hardenbergh, and the John Hancock Tower by Henry Cobb. The BPL Central Library is comprised of the original McKim Building ca. 1895 and the Johnson Building ca. 1972. Designed by the architectural firm William Rawn Associates of Boston, Massachusetts, the renovation to the Boston Public Library (BPL) Johnson Building seeks to welcome the public, engage young patrons, and update the Library to continue as a place for life-long learning and exploration.

Significant structural alterations of the project included creating a double height volume along Boylston Street and provided a longmissing link connecting the Johnson Building with its entrance along Boylston Street and the adjacent McKim Building with its entrance at Copley Square. LeMessurier and William Rawn Associates focused on these goals through early coordination, careful attention to the detail, and consideration of the construction process. Well thought out structural details with regard to the construction sequencing were key in keeping the library open during construction while accomplishing the Architect’s vision. LeMessurier, as structural engineer for the transformation and original Johnson Building, had the history, performed precise analysis, and scrutinized the data to provide early insight on structural possibilities to complete the transformation.

Handle with Care

Renovation of the Boston Public Library Johnson Building

McKim Building The Boston Public Library was established in 1848 as the first large, free, municipal library in the United States. BPL was the first public library to lend books, the first to open a branch library, and the first to house a children’s room. The library was initially located in two rooms in a former Boston schoolhouse. Soon after, the Library realized the need for a larger facility and commissioned the first new building in 1858 on Boylston Street.

By 1885, BPL again needed a larger facility to accommodate its growing collection. The Library turned to the well-known architect Charles Follen McKim of the New York firm McKim, Mead and White to design a new central location. Construction started in 1888 on a site in the newly created Back Bay. The McKim Building was located on the prominent corner of Boylston and Dartmouth Streets with its main entrance facing Copley Square, across from the recently completed Trinity Church by H.H. Richardson. The monumental civic building was created in the Renaissance Revival Beaux Arts style. The building, square in plan with a center courtyard, features Milford pink granite for the exterior façade as well as murals, paintings, and sculptures throughout the interior creating a grand public monument for the people of Boston. Rafael Guastavino Sr designed tile vaults for the floors and vaulted spaces of the McKim Building. Over seven types of tile vaulting were used throughout the McKim Building. The project was the first major building in the United States where tile vaulting was used for structural support while being exposed from below as an architectural finished ceiling.

By Peter J. Cheever P.E., and Nathan C. Roy, P.E.

Johnson Building By the late 1960s, BPL needed to supplement the McKim Building to accommodate the library’s ever-growing collection. BPL turned to noted architect Philip Johnson to design an addition to the McKim Building. Johnson was the first recipient of the Pritzker Architecture Prize in 1979 and defined several architectural movements over the course of his career, from his early modern structures to his later postmodern buildings. The late modernist Johnson Building was a contrast

Boston Public Library McKim Building.

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to the McKim Building, with ornamentation kept to a minimum. The Johnson Building is located to the west of the McKim Building, with its main entrance on Boylston Street, a main east-west thoroughfare through Boston and location of the Boston Marathon finish line.

Johnson’s vision was to harmonize with the exterior of the McKim Building by using the same Milford pink granite and observing the existing cornice and roof lines of the McKim Building. Johnson created an inward facing fortress that separated the inside and outside spaces.

Construction of the Johnson Building started in 1968. Similar to the McKim Building, the Johnson addition is square in plan on a three by three module with the center interior atrium, Deferrari Hall, paralleling the center exterior courtyard of the McKim Building.

The project presented design challenges that required innovative structural solutions. The building was built directly adjacent to the original McKim Building which is supported on wood piles. In addition, the Johnson Building basement extends an additional 18 feet below the existing library structure. The entire east side of the Johnson Building adjacent to the McKim building cantilevers 10 feet 6 inches from the foundations which allowed for excavation and construction while not disturbing the McKim Building. The building is supported by a 3- to 7-foot-thick reinforced concrete mat slab bearing on Boston Blue Clay, the first mat slab foundation in Boston. The mat slab not only supports the weight of the building but also resists over 1,000 psf of hydrostatic pressure.

Typical floor construction consists of two-way, reinforced concrete flat slabs with columns spaced at 19 feet 4 inches on-center each way.

A unique approach using 20-inch-thick two-way post-tensioned waffle slabs spanning 58 feet, and supported by 32-inch composite steel plate girders spanning 58 feet, allow for large column-free spaces at the mezzanine and second floor. To contain the back-of-house book stacks for the research collection, while meeting the floor to floor constraints and overall building height of the existing McKim Building, the upper five levels are suspended from steel hangers. The hangers extend to a system of 16-foot deep interconnecting steel trusses and plate girders at the roof level. Sixteen 13-foot by 13-foot reinforced concrete cores located at each corner of the 3 by 3 plan module extends the full height of the building to support the steel roof framing and act as the lateral system.

The entire east side of the addition, adjacent to the McKim Building, consisted of two-way reinforced concrete slabs supported by reinforced concrete columns and walls extending the full height of the building.

The east side cantilevers 10 feet 6 inches from the foundations.

Johnson created a wall of granite plinths in front of the ground floor black tinted windows to create a separation between the library and the outside world. Johnson “didn’t see any sense reading a book looking at automobiles” and wanted the building to define an “in and out

Section through Johnson Building.

STRUCTURE magazine

Johnson addition. McKim Building left.

feeling” for library patrons. Public criticism of the Johnson Addition was that it was cold and uninviting with no connection between the interior and exterior. The only ground floor access between the Johnson Building, with its main entrance on Boylston Street, and the McKim Building, with its main entrance on Copley Square, was through an inaccessible, narrow corridor, up a set of stairs and through a set of double doors.

William Rawn Renovation To update the Library and provide continuity between the landmarked McKim and Johnson Buildings, BPL turned to the Boston architectural firm William Rawn Associates. Over 150,000 square feet of public space of the Johnson Building was updated and transformed in the $78 Million renovation. The renovation reimagines programming of spaces for young patrons including a new children’s and teen’s room, enhances experiences for adults with new books collection, tech central, as well as movie and music spaces, and enriches the connection to the community with updates to the Rabb Hall, Kirstein Business Library, retail café, and WGBH studio.

The renovation transforms the experience of the public both inside and by removing the exterior granite pillar walls, bringing light into the building. Removing the mezzanine at the Boylston Street entrance creates a welcoming two-story Boylston Hall. A key feature to the renovation is creating a “link” connecting the Johnson Building and McKim Building.

Structural Renovation The renovation required four significant structural challenges to realize the architect’s vision: 1) removal of the mezzanine slab along Boylston Street; 2) replacement of a concrete column at the new glass elevator shaft; 3) removal of load-bearing concrete walls at the McKim link; and, 4) creating a new 36-foot opening through the McKim load-bearing masonry wall.

A two-story high Boylston Hall at the main entrance of the Johnson Building along Boylston Street was created by removing over ten thousand square feet of two-way reinforced concrete slabs. The majority of columns in the area could be easily removed as they supported only the mezzanine; recall that the existing upper concrete floors were suspended from hangers supported from the steel roof trusses. Five columns in the central

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William Rawn Transformation of Johnson Building. Courtesy of Bruce T. Martin.

Left: 1972 construction. Center: steel framing installed. Removed structure highlighted in red. Right: Final condition.

portion extended to the second floor while an additional five at the east side, adjacent to the McKim Building, extended all the way to the roof. LeMessurierâ&#x20AC;&#x2122;s structural drawings provided recommended construction sequencing as well as schematic shoring and bracing concepts to be used by the contractor in bidding and coordination with their specialty construction engineer. Columns extending above the mezzanine were temporarily braced during demolition. The mezzanine slab was shored along column strips and saw-cut around columns to allow for demolition while preventing damage to the existing building. New reinforced concrete encasements were provided to address the increased unbraced-length in the final condition. The reinforced concrete mat slab was analyzed to confirm that it was sufficient to resist the hydrostatic water pressure considering the reduced self-weight resulting from the removal of the mezzanine slab.

One column at the east side could not be encased in concrete, as it was to be adjacent to a new glass-enclosed elevator. William Rawn Associates desired transparency at the glass elevator, and a concrete encased column concept conflicted with this idea. The structural solution was to shore the existing building and replace the 16-inch x 16-inch reinforced concrete column with a new 10-inch x 10-inch steel column between the first and second floors. The contractor and their shoring engineer designed a temporary shoring system to encase and grab the existing reinforced concrete column above the second floor through a system of channels, plates, and through bolts to transfer the load to four temporary columns extending from the second floor to the mat slab. The shoring system allowed for the removal and replacement of the column without influencing the occupied spaces above the third floor.

Two 10-inch-thick by 8-foot-long reinforced concrete walls of the Johnson Building, each supporting over 450 kips of load, were removed below the second floor to create the connection between the Johnson and the McKim buildings. In addition, a 4-foot 2-inch opening was made in each of the walls above the second floor. The walls not only supported vertical load but also acted as cantilevers extending from the mat slab foundation. The wall sections to remain on either side of the new opening above the second floor were reinforced with concrete sections on either side of the wall, creating two reinforced concrete columns per wall. Cantilever steel framing was provided to support the wall above the second floor. Two W24 beams, one on either side of each wall, cantilever 10 feet with a 10-foot backspan and are supported by a system of girders and columns. Locating beams on either side of the walls, and utilizing W12 needle beams centered below the newly created columns (i.e., two W12 per wall), allowed for the demolition of the walls without the need for temporary shoring of the existing structure. The original reinforced concrete mat slab provided flexibility in locating new columns as required to meet the architectural layout without the need for new foundations. The steel framing was preloaded with jacks for the estimated wall load to limit deflection, reduce the required steel tonnage, and protect the existing Johnson Building. Deflections were monitored during preloading to ensure that calculated wall loads used for preloading were accurate and the building was not raised.

One of the most important project milestones, the opening of the McKim connection, required a 36-foot opening in the McKim Buildingâ&#x20AC;&#x2122;s century-old load-bearing brick masonry wall. Structural steel framing was provided to support the existing 30-inch-thick

Temporary shoring with McKim wall removed. Johnson concrete walls left.

Final structural framing for McKim wall. Johnson concrete walls removed.

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unreinforced masonry brick wall which supported a load of over one million pounds. Rigid steel framing was provided above and below the opening to not compromise the masonry wall and terracotta masonry floor arches, as well as to adequately distribute the load to the original granite foundation wall and timber piles below.

Recommended sequencing along with concept shoring schemes were shown on the structural drawings. Both the final structural steel framing and temporary shoring were preloaded with jacks to limit deflections and protect the existing McKim Building, including the unreinforced masonry walls and terracotta masonry floor arches. Fourteen independently controlled hydraulic jacks were used during preloading of the shoring while nine inflatable air jacks were used to preload the final framing. Deflections were monitored during preloading of both the shoring and final framing with no measurable deflection after jack removal.

Final Inscriptions on both the McKim and Johnson Buildings read, “The Public Library of the City of Boston – Built by the People and Dedicated to the Advancement of Learning.” One key to the success of the ambitious transformation of the BPL Johnson Building was the early and continued coordination between William Rawn Associates and LeMessurier with consideration of the existing structural systems, as well as the opportunities and design constraints that those systems presented. The renovation provides a long-missing link connecting the Johnson Building with its entrance along Boylston Street and McKim Building with its entrance at Copley Square.▪

Boylston Hall with McKim link far right. Courtesy of Robert Benson.

The online version of this article contains references.

Please visit www.STRUCTUREmag.org.

Peter J. Cheever, P.E., is President of LeMessurier and is on the ASCE Committee on Design of Steel Buildings. (pcheever@lemessurier.com) Nathan C. Roy, P.E., is an Associate at LeMessurier and teaches at the Boston Architectural College. (nroy@lemessurier.com)

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A Hospital’s Oasis

By Emily P. Appelbaum, P.E., and R. Scott Silvester, P.E.

Roof after renovation. Courtesy of Sam Kittner.

T

he patients at Children’s National Health System’s main campus in Washington, D.C., needed fresh air. Going outside, however, is not always simple for hospitalized children, many of whom are not fully mobile or are connected to medical equipment. In addition, the hospital fronts a major urban avenue with little in the way of green space. In 2013, hearing of the significant logistical obstacles that hospital staff overcame to grant one terminally ill patient’s request to go outside, a donor stepped forward to turn the hospital’s long-held desire for a Healing Garden into reality. Additional donors joined in, including the foundation of the late philanthropist, horticulturist, and gardener Rachel “Bunny” Lambert Mellon. (Mellon oversaw the redesign of the Rose Garden and Jacqueline Kennedy Garden at the White House, elements of which are incorporated into the Healing Garden.) The result is now known as the Bunny Mellon Healing Garden dedicated to the First Ladies of the United States, in recognition of that venerable group’s longstand- Roof before renovation. ing commitment to Children’s National. However, before the garden could become a reality, the project’s structural engineer had to design structural strengthening to allow the conversion of the unoccupied roof to an outdoor respite for young patients and their families.

Design Approach

Existing Building The building, originally constructed in the 1970s and expanded in subsequent decades, sits on a tight site. No suitable space for a garden exists at ground level, so the hospital proposed creating the garden on an existing 7,200 square-foot, unoccupied gravel ballasted roof located halfway up the six-story building. Surrounded on three sides by the building’s iconic sloped and mirrored walls, the garden opens on its fourth side to views of the U.S. Capitol and the National Mall.

STRUCTURE magazine

The building portion located beneath the garden consists of full-story medical “use levels” alternating with half-story “interstitial levels,” each of which serves the use level below. Three pairs of 60-foot-long steel truss girders spaced at 30 feet on-center (o.c.) occupy the full 8-foot height of the interstitial level below the garden roof. Each truss consists of five 12-foot-wide sections, or panels, separated by web panel points. The trusses support roof framing on their top chords and interstitial-level framing on their bottom chords. At the roof level, steel beams support a concrete slab on composite metal deck and frame into the truss top chords at panel points. Half a story below at the interstitial level, steel beams spaced at 30 feet o.c. span to the building columns and the midpoints of the truss bottom chords and support a 7½-inchdeep cellular metal deck floor.

The original structural drawings indicate that the roof structure was designed for a uniform live load of 100 psf to enable a future vertical building expansion. The interstitial levels were designed for a light live load for maintenance access plus a superimposed dead load to support hung ceilings and MEP components.

To support new roof garden dead loads in addition to a 100 psf live load, the roof structure would need to be strengthened. Internal scheduling constraints for the Healing Garden project meant that the hospital needed to secure a permit and begin construction of structural work before the final rooftop landscape design – including elements such as trees, planters, mounded soil, pavers, and concrete sitting walls – could be completed and approved. To allow the structural design to progress ahead of the landscape design, the design team and owner

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overburden loading; and listed maximum allowable superimposed dead loads for each region, ranging from 40 psf at the walking surfaces to more than 400 psf at the deepest planter boxes. The diagram also designated roof areas as either non-occupiable (e.g., at planter boxes) with an un-reducible design live load of 30 psf or occupiable (e.g., at walking surfaces and grass mounds) with a reducible design live load of 100 psf. This approach allowed construction of structural strengthening to begin before the architect finalized the rooftop design.

Structural Challenges Overburden loading diagram.

worked to establish roof loading parameters, evaluating a number of possible load layouts based on the weights of potential overburden materials and profiles. The studies culminated in the selection of a layout that balanced the vision for the garden with the need for an efficient and cost-effective structural strengthening scheme. The team agreed to locate the heaviest elements, including trees and a granite fountain, above existing columns and truss girders to limit the amount of strengthening. The structural engineer created a roof loading diagram for the permit drawings. The diagram specified locations of discrete elements such as trees and a tall cantilevered glass wall at the free edge of the roof; defined regions of heavy, medium, and light

The new overburden loads necessitated reinforcement of the existing roof slab, beams, and truss girders for strength and serviceability. Where needed, supplemental beams shortened the existing slab span, and new bottom flange plates stiffened existing beams. The truss girder strengthening was more complicated. The original building drawings included truss elevations with member sizes and design forces but did not provide detailed connection information for the truss joints.

Original shop drawings were not available. Early in the design phase, the structural engineer entered the congested interstitial space with the contractor, who made localized probes in finishes for observation and documentation of existing truss framing members and connections.

That upfront effort helped to reduce strengthening scope and cost since the engineer was able to calculate a higher capacity for the observed truss connections than the design forces published on the drawings. continued on next page

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demanded unusual finesse and skill from the ironworkers and other subcontractors. Because the work area was located above a functioning laboratory and within a running hospital, the general contractor labored under strict noise, dust, and smoke control limits, installing temporary exhaust fans and a welding smoke evacuation system and covering existing air-handler intakes with carbon filters. Early exploratory work in the design phase minimized conflicts between existing and new ducts, pipes, and conduits and the new structural steel. Where unforeseen conditions did arise, the structural engineer and contractor collaborated to devise rapid solutions.

An Accessible Oasis

New truss V-Web with temporary hanger rod in the foreground.

Even so, the most highly loaded trusses required extensive modifications to the existing joints, including enlarging the connections by welding new gusset plates to the existing truss chords and webs.

The overall truss geometry also required modification to support the new loads. At a typical original truss, configured as a hybrid Pratt/ Vierendeel system, each of the four outer panels contains a single diagonal web member while the fifth, central panel remains open. The interstitial-level beams that frame into the midpoint of the truss bottom chord from each side support 900 square feet of deck in total and bear on the chord in the open central panel, delivering a concentrated load to the bottom chord halfway between panel points. Under the design interstitial floor and roof garden loads, the flexure induced in the truss bottom chord due to this configuration, combined with the chord forces due to overall truss behavior, would overstress the bottom chord. The truss strengthening scheme addressed this by adding new diagonal web members in a “V” shape within each center panel to create new panel points where the interstitial-level beams connect to the bottom chords.

To relieve the bottom chords of flexure while the new “V” webs were being constructed in the open truss panels, the structural engineer specified staged installation of temporary support framing. The steel erector installed hanger-rod-and-beam assemblies between the ends of the interstitial-level beams and the existing roof beams, then disconnected the ends of the interstitial-level beams from the bottom truss chords, temporarily rerouting the interstitial-level load from the truss chords to the roof beams at panel points. Following construction of the new panel points and installation of other truss strengthening elements, the erector reconnected the interstitial-level beams to the truss chords at the new panel points and removed the hanger rods.

The structural engineer worked closely with the general contractor to ensure that the staged load transfer met the design intent.

Major renovation projects, especially those that change the use of an existing space, can be primed for success when the owner, architect, and contractor recognize the value of involving the structural engineer early in the project and maintaining that engagement through assessment, design, and construction phases. Potential benefits of this approach include the following: • The structural engineer can provide valuable information about the relative structural impact of the design concepts under consideration. In a green roof conversion project, that can help guide the landscape design of overburden materials and arrangements while controlling the amount of costly strengthening needed.

• By accessing and observing the configuration and condition of existing structural framing prior to designing modifications, the structural engineer can produce a more efficient design and minimize the likelihood of encountering unexpected conditions and conflicts during construction.

• In a project with complex site and programmatic constraints, collaboration between the structural engineer and contractor during the design and construction phases can establish an atmosphere of cooperation and facilitate constructible and creative design solutions.

In April 2017, the Bunny Mellon Healing Garden dedicated to the First Ladies of the United States opened in a special ceremony featuring First Lady Melania Trump, family members of the late Bunny Mellon, and key supporters of the project. The garden, which is open yearround, is now a popular space for children and families at the hospital to play, relax, and reconnect with nature. In the end, the project’s architect, consultants, and general contractor all donated a portion of their services to the creation of the garden, and all are proud of the collaboration that helped to create an outdoor oasis for young patients in our nation’s capital.▪

Construction Unique site constraints heightened the complexity of the contractor’s job. Working in a space with low clearance and many obstacles

Emily P. Appelbaum, P.E., is a Senior Staff II in the Structures group at Simpson Gumpertz & Heger (SGH). (epappelbaum@sgh.com) R. Scott Silvester, P.E., is a Principal in the Structures group at Simpson Gumpertz & Heger (SGH). (rssilvester@sgh.com)

Truss elevation with added V-Web.

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structural

PERFORMANCE

M

ost structural fire protection designs in the U.S. are conducted using prescriptive code requirements. This approach allows designers to select fire resistant assemblies from available listings that are qualified through standard furnace testing. Standard furnace testing exposes structural elements to a standard fire to determine a fire-resistance rating, typically expressed in hours. For certain listings, the designer must decide if the assembly is “restrained” or “unrestrained.”

Indeed, architects routinely ask structural engineers to provide guidance on what classification should be assigned.

This article reviews the history of this paradigm and provides considerations for designers tasked to classify restraint.

ASTM introduced “restrained” and “unrestrained” classifications into the ASTM E 119, Fire Test Standard, in the 1970s.

This binary classification is primarily based on a series of furnace tests in which restrained steel beam and slab assemblies were able to sustain the applied loading longer (i.e., the assemblies do not experience runaway deflection) under heating, as compared to the corresponding unrestrained condition.

In a standard furnace test, a composite floor beam and concrete slab assembly is considered “restrained” if both components horizontally bear directly against the edges of the furnace at the outset of the test; the assembly is considered “unrestrained” if the ends of the beam and slab can thermally expand without contacting the furnace edge. Many listings in the UL Fire Resistance Directory permit reduced fire protection thicknesses to achieve fire resistance ratings if the designer can demonstrate that the assembly will be “restrained” when it is constructed as part of an actual structural system.

Figure 1a. Structural floor assembly for ASTM E119 test.

Restrained vs. Unrestrained Within the Context of New Industry Guidance

By Kevin J. LaMalva, P.E., Therese McAllister, Ph.D., P.E., F.SEI, and Luke Bisby, Ph.D., P.Eng., FIFireE

Kevin J. LaMalva is a Senior Staff II/ Fire Safety at Simpson Gumpertz & Heger Inc. and Chair of the ASCE/ SEI Fire Protection Committee. (kjlamalva@sgh.com) Therese McAllister is the Community Resilience Group Leader & Program Manager at the National Institute of Standards and Technology and a Member of the ASCE/SEI Fire Protection Committee. (therese.mcallister@nist.gov) Luke Bisby is Professor of Fire and Structures at the University of Edinburgh. He is also a Member of the ASCE/SEI Fire Protection Committee. (luke.bisby@ed.ac.uk)

Figure 1b. Floor end restrained by welds to support for restrained test.

Figure 1c. Floor end unrestrained (resting) on support for unrestrained test.

Restraint Conditions Many factors may affect the resulting restraint conditions of specific structural components during a fire, and these factors may actually enhance or decrease the resulting structural performance. For instance, a floor beam within a structural system may undergo thermal expansion under heating, which may impose lateral loads on the girder and column support points.

Depending on the characteristics of the support points, the thermal expansion may be resisted or the thermally-induced lateral loads may exceed either the beam or support capacity. Unlike furnace testing, the support points may also STRUCTURE magazine

need to resist subsequent thermal contraction during cooling.

The UL Directory, the American Institute of Steel Construction’s (AISC) ANSI/AISC 360-16 Appendix 4, and other publications provide guidance on determining thermal restraint conditions. However, it is the authors’ opinion that the current paradigm requires judgment from the designer. Since standard furnace testing for fire resistance does not consider structural system response, this judgment may be inconsistent among designers. In a composite floor beam and concrete slab assembly, both components would be restrained equally by the furnace framing during a “restrained” furnace test. In actual building construction,

34 September 2018

however, the beam and slab may experience varying degrees of restraint. This can result in differential longitudinal movement under fire exposure, particularly if the structural components are not acting compositely.

Several organizations have conducted furnace tests to address the ASTM E 119 restraint conditions. AISC and AISI funded furnace testing of steel floor assemblies, which demonstrated that restraint from the furnace frame provided no fire resistance benefit in the specific cases tested. This testing resulted in modifications to a specific UL listing (D982). NIST performed furnace testing of steel trusses (Figures 1a, b, and c) and found that an unrestrained assembly achieved a higher fire resistance rating when compared to an equivalent restrained assembly. These test results demonstrate that the effect of restraint varies among different structural systems and restraint conditions, and cannot be easily simplified in practice, especially in a binary fashion.

New Industry Guidance The 2016 edition of ASCE/SEI 7 has a new Chapter 1 section on Fire Resistance. This section addresses structural fire protection by

specifying the prescriptive approach as the default option for structural fire protection design. As an alternative, Chapter 1 permits use of structural fire engineering in accordance with the standard’s newly added Appendix E (Performance-based Design Procedures for Fire Effects on Structures). To compliment Appendix E, the ASCE/SEI Fire Protection Committee has also developed a new manual of practice on structural fire engineering, which is approved and scheduled for release this October.

When structural fire engineering is employed, analysis of structural system response inherently considers the amount of structural restraint that is actually present within a particular building design.

However, when the prescriptive approach is used, the degree of restraint may be difficult for a designer to judge with a high level of confidence. In light of this, designers may choose to take a conservative approach when classifying restraint conditions per ASTM E 119. Notably, the International Building Code (IBC), Section C703.2.3, states that in-place conditions should be considered unrestrained unless structural documentation is provided that demonstrates a restrained condition in actual construction.

In all cases, the authority having jurisdiction

may be consulted as to the proper interpretation for a given project.

Summary Clearly, there is a conflict between the boundary conditions and general limitations of standard furnace testing to represent realistic mechanical behavior, and the understanding of how structural systems actually perform under fire exposure. ASCE/SEI 7-16 and the upcoming manual of practice highlight this conflict, for they both prohibit designers from intermingling aspects of the prescriptive method with structural fire engineering.

Accordingly, the current paradigm’s reliance on a designer’s judgment is highly problematic. Similar to most other aspects of the prescriptive approach, an industry-consensus prescription on the matter within the IBC and/or the ASTM E119 standard would relieve designers of an unrealistic obligation.

Acknowledgment: The authors would like to thank Dr. Jose Torero (University of Maryland) for his added insight/support.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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September 2018

Risk ManageMent Who Protects the Good Samaritans?

Resources

By Randy Lewis, CPCU

AIA Disaster Assistance Handbook/ 

I

n many jurisdictions, design professionals who volunteer their services following disasters should be concerned about liability. Having effective Good Samaritan laws can help.

It was quite a year. With hurricanes, floods, wildfires, tornadoes, and more, 2017 set records for natural disasters in the U.S., costing lives and over $300 billion in damages.

We also saw many good people, architects and engineers included, step forward to protect their fellow citizens and speed recovery efforts.

Their expertise in assessing structures and infrastructure was crucial to local, state, provincial, and federal governments overwhelmed by the need to perform numerous inspections in a short period of time. They performed these tasks under difficult or dangerous conditions and, in many cases, for no fee.

If you were among these volunteer A/Es, you might have unwittingly incurred liability for your good deeds. It depends on the laws where you live or work.

Good Samaritan Laws

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In many U.S. jurisdictions, the law does not provide much protection from liability for negligent acts, no matter how good your intentions.

While most states have enacted some form of Good Samaritan legislation to protect individuals from liability for negligent acts committed while voluntarily providing emergency care, some of these laws do not explicitly extend protection to architects and engineers. The laws in Canada do not provide legal protection or immunity to an architect or engineer providing professional services on a voluntary basis, but according to the claim staff of XL Catlin in Canada (the author’s company), this does not

appear to be a major driver of claims and there has been no vocal push for federal legislation.

What this means is that, in those states with no – or weak – Good Samaritan A/E laws, architects and engineers could be sued for merely trying to do the right thing in the midst of, or immediately after, a crisis. The threat of being sued can be enough to drive A/Es away from trying to help.

For example, following the September 11, 2001, terrorist attacks, many New York architectural and engineering firms that volunteered to help their fellow citizens later found themselves entangled in massive lawsuits that had little or nothing to do with their services. Consequently, in the wake of 2012’s Superstorm Sandy, New York and New Jersey A/Es, eager to help assess damaged properties, feared they could be sued if a property owner disagreed with their assessment. At the time, neither state had Good Samaritan laws that extended to design professionals.

On the other hand, after devastating tornadoes hit Alabama in 2011, which had passed its Good Samaritan law in 2005, many design professionals felt it was safe to step forward to provide crucial assistance, inspecting thousands of buildings for safety.

State Laws Vary

In 36 U.S. states, Good Samaritan laws specifically protect architects and engineers.

However, these statutes vary widely as to the kind of immunity they grant and to whom.

For example, Massachusetts has a broad law that grants immunity to licensed professional engineers, architects, environmental professionals, landscape architects, planners, New Release land surveyors, contractors, subnd Software based on the AISC Design Guide 11 2 Ed. contractors, and Vibrations of Steel-Framed Structural Systems Due to Human Activity suppliers who volIt’s like having an in-house floor vibration expert! FloorVibe v3.0 helps solve problems unteer in a natural with structure vibration due to human activity in offices, residencies, health clubs, convention centers, and buildings housing sensitive equipment and occupancies. Plus, linear disaster or catastrostairs and footbridges. phe within 90 days • Expert Advice such as what live loads to use, how to estimate damping, recommended acceleration or velocity limits, and more. of the end of the • Makes use of the new complex analysis procedures for sensitive equipment emergency. and occupancies in DG11 2nd Ed. easy.

Elsewhere, Good • Has Databases for hot-rolled sections and castellated beams.

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Samaritan laws are • Automatically generates Notes and Warnings. USC and SI units. less comprehenOrder or upgrade at FloorVibe.com. E-mail FloorVibe@gmail.com sive. For example,

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September 2018

AIA Safety Assessment Program https://bit.ly/2vx0kvV The “Emergency Services” and  “Pro Bono Services” chapters in XL Catlin’s Contract eGuide for Design Professionals, as well as a sample Emergency Services Agreement, are available on the Learning Management System (LMS). https://bit.ly/2n724by Good Samaritan State  Statute Compendium https://bit.ly/2ODKgBo National Incident Management  System online training https://training.fema.gov/nims some states’ laws apply only to architects and engineers, while others may include land surveyors, contractors, and equipment operators.

Some states limit the period for immunity to 30 or 60 days following a disaster. A few states extend protection to structural inspections only, while others include architectural, damage assessment, engineering, or surveying services. One state, South Carolina, only gives immunity to licensed architects and engineers who provide emergency services at the request of the governor. Most states’ laws exclude protection for acts of gross negligence or willful misconduct by the A/E. To learn more about the laws in your state, the American Institute of Architects has an excellent resource, the Good Samaritan State Statute Compendium. The document discusses the advantages of Good Samaritan laws, details each state’s protections for architects, and includes model legislation for those interested in understanding and advocating for the adoption of such legislation by states. (See sidebar)

Federal Protection At the federal level, there is not much help for A/E Good Samaritans. The 1997 Volunteer Protection Act (VPA) offers immunity for volunteers serving nonprofit organizations or government entities. Currently, the VPA only limits third-party suits but allows lawsuits by the government and non-profit sponsors.

States can also opt out of the VPA or place additional constraints on eligibility.

There have been several unsuccessful efforts to pass a federal law that would protect

architects, engineers, and construction volunteers following an emergency. A federal law would provide coverage nationwide, which would negate the differences between state statutes. Ideally, it would also mean that design professionals could help across state lines without worrying about licensing issues.

Recent Legislative Activity Good Samaritan bills have been introduced in a few states in recent years – with mixed results. In 2016, New Hampshire enacted a law to give design professionals immunity when they volunteer during a natural or human-made disaster. In 2015, Ohio passed a bill that provides immunity to architects, engineers, and surveyors, as well as contractors and tradespersons, who volunteer their services during a declared emergency. New Jersey passed Good Samaritan legislation for A/Es in 2014.

However, a 2016 bill failed in Mississippi and, despite several attempts, New York still has no law on the books.

training is available from the National Incident Management System’s online courses.

Sign up for a volunteer network. Many state and local agencies have programs in place to use volunteers with appropriate disaster assistance training. In some states, volunteers who are registered with disaster response programs are entitled to workers compensation and liability protection.

Get an agreement, if possible and practical. In the aftermath of a disaster, try to get a written agreement for your services, even if you’re not accepting a fee. A simple agreement will suffice; the AIA and EJCDC both

publish short-form agreements, and the XL Catlin Design Professional team has a sample Emergency Services Agreement available in their Learning Management System.▪ The online version of this article includes a detailed reference. Please visit www.STRUCTUREmag.org.

Randy Lewis brings over 20 years working in the insurance industry. Currently Randy manages the risk management and client education programs of XL Catlin, a recognized leader in the AEC community. (randy.lewis@xlcatlin.com)

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The American Institute of Architects (AIA), American Council of Engineering Companies (ACEC), National Society of Professional Engineers (NSPE), and other organizations have long advocated for state laws that provide immunity from liability that arises from voluntary architectural or engineering services.

Many offer model Good Samaritan laws that states may adopt.

Most of these organizations also advocate a uniform federal statute that would provide civil immunity for design professionals providing volunteer services. (See sidebar)

What Can You Do? Find out if your state/province has a Good Samaritan law. If it does and falls short, work with your professional society and licensing boards to broaden the legislation to provide better protection. If your state/province does not have such a law on the books, you and your colleagues should urge your legislators to enact one.

Get disaster assistance training. The AIA’s Safety Assessment Program trains engineers, architects, and other certified professionals as building evaluators. These individuals help local governments evaluate the post-disaster safety and habitability of homes, buildings, and infrastructure. Additional disaster response STRUCTURE magazine

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September 2018

CASE BuSinESS PrACtiCES Geotechnical Reports as Contract Documents?

By Bart Miller, P.E.

T

here are various methods for incorporating the recommendations of Geotechnical Reports into structural drawings and specifications, and for engaging the Geotechnical Engineer in the design process. Invariably, Structural Engineers extract pertinent design and construction information from Geotechnical Reports to use as the basis for foundation-related design and detailing directives included in contract documents. Often, Geotechnical Reports are provided to the contractor as a reference document. Structural Engineers may also request or require the Geotechnical Engineer to review structural drawings and specifications to confirm the correct interpretation of geotechnical recommendations. In some areas, Geotechnical Engineers even provide signed and sealed specifications, usually for earthwork, piers, piles, etc., to be included with the contract documents.

However, under no circumstances should Structural Engineers specify the Geotechnical Report itself to be a contract document.

Common Misconceptions Some argue that specifying Geotechnical Reports as contract documents creates the following perceived benefits: • Ensures that the Geotechnical Engineer will be held responsible for the accuracy of the geotechnical recommendations; • Absolves the Structural Engineer of responsibility for any inaccurate soil-related provision that comes directly from the geotechnical report; • Eliminates the possibility of transferring information incorrectly or incompletely, and reduces the likelihood of misinterpretation by the Structural Engineer; • Saves the Structural Engineer time in copying information from the Geotechnical Report into his drawings and specifications.

The first two “benefits” wrongly assume that the Geotechnical Engineer is not responsible for his/her work if the report is not a contract document, or that the Structural Engineer will be held directly responsible for precisely following recommendations from a Geotechnical Report. Neither is correct under normal circumstances. The Structural Engineer does not assume responsibility for the soil-related aspects of the foundation design by merely transferring Geotechnical Report recommendations into the contract documents. Similarly, specifying the Geotechnical Report as a contract document does not assign

additional responsibility to the Geotechnical Engineer for their own engineering work.

The Geotechnical Engineer is responsible for the soil-related recommendations used in the design of the building foundation. If those recommendations are later deemed not to meet the Standard of Care, as defined by what other Geotechnical Engineers would recommend in the same situation with the same data, then the Geotechnical Engineer is held to the same standard for the soil-related design recommendations as Structural Engineers are for the structural design of the foundations.

The second two “benefits,” while true to a degree, are insignificant compared to the very substantial risks the Structural Engineer may assume as a result. Saving a small amount of time during the design phase, or circumventing the responsibility for careful interpretation, does not offset the potential consequences.

Risks Geotechnical Reports, along with other consultant reports such as wind tunnel reports, snow and ice studies, etc., should never be specified as contract documents. Consider the following: • Geotechnical Reports contain opinions and alternative recommendations (multiple foundation system options, slab on grade construction methods, etc.) from which a Structural Engineer may choose as the basis of the design depicted in the structural drawings and specifications. This nonspecific information creates confusion for the contractor, who expects and requires specific directives.

• Geotechnical Reports are not written with the purpose of being included as a contract document and therefore are not written in mandatory language. Non-mandatory language creates ambiguity for the contractor in design and construction requirements.

• Because structural drawings are obliged to provide specific requirements in mandatory language, Geotechnical Reports, and structural drawings will never completely agree, which invites a claim by contractors citing contradictory information in the contract documents.

• If the Structural Engineer specifies the Geotechnical Report as a contract document, without the clear intent and written approval of the Geotechnical Engineer, then the Structural Engineer may assume liability for its accuracy.

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Structural Engineers should reference Geotechnical Reports in structural drawings, commonly in the general notes or design criteria documents, to identify the source of information included in the contract documents pertinent to the foundation design. These reports should be made available to the construction teams as reference documents, but not contract documents.

Structural Engineers should clearly indicate on the contract documents that the design team is not responsible or liable for the accuracy of the information presented in the Geotechnical Report, as is consistent with established legal precedent and the Standard of Care.

Interpretation Structural Engineers are responsible for interpreting various consultant reports and then specifying precise design and construction requirements. Perhaps no consultant report is more prone to misinterpretation leading to construction claims than the Geotechnical Report.

Because the contractor is only bound to information included in the contract documents, Structural Engineers must recognize the importance of reading Geotechnical Reports completely and carefully, and editing structural drawings and specifications to match. Many Structural Engineers start with “typical” details and boiler-plate specifications encompassing information for a variety of soil types and ground conditions that require vigilant editing to be consistent with soil conditions defined in the Geotechnical Report. Without proper editing, not only will the contract documents not reflect the appropriate soil conditions and requirements for the project, but the Structural Engineer may become liable for the content in the structural drawings and specifications that does not meet Geotechnical recommendations.

Structural Engineers should consider requesting or even requiring the Geotechnical Engineer to review and comment on the structural drawings and specifications as they pertain to site preparation, foundation systems, and slabs on grade. In general, early and consistent communication with the Geotechnical Engineer will ensure the proper interpretation of the Geotechnical Report and improve the overall documentation of the foundation design.▪ Bart Miller is a Principal and Senior Project Manager for Walter P Moore. (bmiller@walterpmoore.com)

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InSIghtS Using BIM for Wood Framed Construction Projects A Residential Architect’s Perspective

By Jim Westover, Phoebe Lam, and Jon Houck

A

s more architects make the switch beams and, in some cases, shear walls.

Architects also need to clearly communicate from two-dimensional CAD to BIM, However, it is not necessary to have every to the engineer, at the beginning of a projstructural engineers are faced with a similar stud or rough opening modeled. In short, ect, which elements need to be modeled and decision as to whether or not it makes sense architects would like the engineer’s model which elements can merely be “drafted” in the to adopt BIM. Some structural engineers who to include the major structural elements plans. These requirements may vary dependdesign primarily in wood have taken longer to that need to be coordinated with the archi- ing on the complexity of the project. For make the switch than those designing larger tecture. However, when engineers model example, typical door and window headers Type I, II or III projects where clients or these elements, it is critical that they are usually do not need to be modeled. However, architects require the work be done in BIM. located accurately in plan and elevation. if the doors or windows terminate at the Architects who made the early switch to BIM Otherwise, architects will need to spend underside of the exposed structure, then the were drawn to it because of the enhanced time adjusting or re-modeling these items, size and placement of those elements become 3-D visualization, more effective client critical and it may be necessary for them presentations, and better design and to be accurately modeled. If the architect Architects need to up their game clearly communicates these requirements drawing coordination. However, there is a significant learning curve and front, the engineer can craft their fee by producing BIM base models up time investment when adopting BIM, proposal to include the appropriate level which explains why many architects that are more accurate without of modeling, with more detail provided and engineers may be hesitant to make as an additional service if required. excessive or unnecessary detail. Engineers who make the switch to BIM the switch.

So, how important is it for structural will also need to take full advantage of engineers to adopt BIM? For larger steel and in which case, the engineers may as well the program by producing dimensionally concrete buildings, BIM has become essential. be working in two-dimensional CAD and accurate and appropriately detailed models.

For residential wood framed construction, it the architects can model those structural Structural elements that are modeled should has not been as critical but will become more elements themselves. be located accurately in plan and at the correct so as more architects and engineers make the For the architect/engineer team to fully elevation so that they match the structural switch. Engineers who do adopt BIM, and take advantage of BIM, some things need to details and can be coordinated with the architake advantage of its capabilities, may have happen. Architects need to up their game by tectural plans and details. In engineering a distinct advantage over their competitors producing BIM base models that are more firms where non-engineers do the drafting, in getting work with architects who work in accurate without excessive or unnecessary the design engineers will need to clearly comBIM. However, those who do switch to BIM detail. They must use discretion regarding municate the three-dimensional information but do not take advantage of the program what gets modeled and what gets drafted. to the BIM modeler so that the model accuwith accurate modeling may not experience Modeling everything in too much detail is rately reflects the engineer’s intent. much of an advantage. a huge time sink and does not necessarily As powerful as BIM is, it is still just a tool For many residential architects, their early benefit the project. For instance, rather for design and documentation. It is not a models were relatively simple, so it was less than modeling details, it may make more replacement for excellent, creative structural important for their consultants to use BIM. sense to cut sections in the model and then design. Architects will still choose to work However, as architects increase their knowl- draft over them in the BIM program. It with engineers who provide exceptional edge and improve their models, it becomes does not make sense to model each piece service, produce efficient, elegant designs more advantageous for them to work with of flashing, every layer of waterproofing, or (regardless of the software used), and are good consultants using BIM. every nut and bolt. communicators and team players. However, So, the question arises as to whether archiStructural engineers working in BIM may as more residential architects and engineers tects choose engineers who are working in request the architect provide a base model make the move to BIM, those who stick with the same BIM program over those who are of LOD 200 (using the U.S. National BIM two-dimensional CAD may find themselves still working in two-dimensional CAD. Standard for BIM “Level of Development” at a competitive disadvantage.▪ From an architect’s perspective, it depends ranging from LOD 100 to LOD 500). This All authors are employed by William Duff on how well the engineer takes advantage of is still a fairly basic model, but it provides a Architects, Inc., in San Francisco.

BIM and the extent to which the engineer’s reasonable framework for the structural engiJim Westover is a Partner and Principal. use of BIM improves the project process. neer to begin their work while the architect It is certainly advantageous if the engineer adds more detail to the model. For woodPhoebe Lam is an Associate and Project can accurately model the primary structural framed structures, the architect may strive Manager and Director of Operations. elements: wood posts and beams (other to produce a finished model with an LOD Jon Houck is Job Captain. than standard headers), steel posts, steel between 300 and 350.

“

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Historic structures Whipple Hotel Street Lift Bridge Utica, New York 1873

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

T

he Hotel Street Lift Bridge, constructed in Utica, New York, in 1873, was a first of its kind and a gateway to long-span lift bridges in later years. In the 1850s, the Erie Canal Board adopted Whipple bowstring trusses (STRUCTURE, January 2015) to cross the canal in cities requiring a span of 72 feet, as that was the standard span for the Whipple bowstring. The enlarged Erie Canal, in the countryside, was 72 feet wide at the surface with a 10-foot towpath. In cities requiring a lesser span of 60 feet wide, vertical masonry walls were typically used with a 10-foot towpath. In the scenario, the towpath was at the street level of all of the city streets the canal crossed. However, when a Whipple bowstring truss was used to allow for a 72-foot span, the trusses had to be raised accordingly to provide clearance between the bottom of the truss and the mules/horses pulling the canal boats.

Therefore, with a deck level about 11 feet above the towpath, the city street was required to be sloped up to the bridge. Since there is a limit on the grade a team of horses can pull a loaded wagon up, longer slopes were required. The required fill infringed on businesses along the streets. On a few occasions, the Board adopted side mounted swing bridges; however, when in an open position, they took up valuable frontage along the canal. Whipple designed side mounted iron swing bridges across the Erie and the Louisville and Portland Canals, as well as wood and iron swing bridges across the Welland and Dundas Canals in Canada.

Given some unique challenges at the location, Whipple was asked by state officials to determine the feasibility of a lift bridge at Hotel Street in Utica to eliminate the high fills. Whipple described the situation as follows, In 1871 the Legislature of New York passed an act authorizing the construction of a swing-bridge over the Erie Canal on Hotel Street in Utica, for the purpose of enabling heavy loads to cross the canal without encountering the steep grades by which the stationary bridges of the city are necessarily approached. But the canal being only 59 feet wide at that point, a pier in the centre was inadmissible, while a bridge mounted on a pier upon the shore, would be so long, and occupy so much room when open, that it could not be constructed and used without the abatement of one or more valuable business stands. This would have involved an amount of expense, which neither the

state authorities nor the citizens to be benefited by the bridge were willing to incur.

In this condition of the case, the writer was consulted as to the practicability of devising a plan of draw-bridge which could be operated by lifting up instead of swinging horizontally, whereby the anticipated benefits could be enjoyed without incurring so much expense, and occupying so much valuable space. The Hotel street bridge after reconstruction. idea at once struck me as highly feasible, and November 2014) in the orientation they the suggestion was answered accordingly. would have had if the bridge was being used In pursuance therewith, the plan of a “lift as a deck truss and supported them on four draw-bridge” was arranged, for which letters cast-iron columns. In his own words: patent were issued about two years ago. The plan The work consists of a stationary truss bridge being thought favorably of by parties concerned, spanning both the water-way and towing-path an appropriation was made in 1873 for the supported by 4 corner piers and towers, sufconstruction of such a bridge at the locality above ficiently high for the suspension of a movable named, and a contract entered into therefore. floor or platform under the lower truss-chords After some study, Whipple applied for and to permit the passage of canal boats underand obtained a patent and was granted it neath the platform-together with other parts December 24, 1872 (patent #134388). He about to be named and described. began his application with, The movable platform, extending from the This improvement is especially applicable upon berm bank to the inner edge of the towing navigable canals through cities and villages, as path, is suspended by iron suspension rods (one it occupies much less space and requires less time at each end of each transverse floor-beam) passin operating it than is required for the pivot or ing up through the cast iron connecting pins of swing draw-bridge. No claim is here made to the truss chords and inside of the hollow truss posts, original invention of lift draw-bridges in general, being connected at the upper ends with wire or of any particular plan for the stationary trusses, rope passing over large sheaves or pulley-wheels, or of any particular mode or arrangement of or and connecting with counterpoise weights to applying the winding power to the winding drum, balance the weight of the platform… m, in case it be used, or the working power to the He described the lift mechanism as follows: transverse shaft, f, in case of the power weight The platform being thus mounted and counterbeing dispensed with… I do claim as my invenpoised, is lowered to the grade of the street for the tion, and as not before known or used, passage of land vehicles and raised for the pas1) In the construction of lift draw-bridges, the sage of boats underneath, by application to the combination of the counterpoised vertical transverse shaft of power sufficient to overcome movable way or platform, the trusses, the the friction of the working parts, with a greater suspension rods, chains, or ropes, the longior less surplus to act as an acceleration force… tudinal shafts on each side of the bridge, and The counterpoise weights consist of 12 castthe transverse shaft or shafts and gearing, iron boxes (6 upon each side), 9 inches square, substantially as and for the purposes specified. with length corresponding to the length of truss 2) The longitudinal and transverse shafts conpanels, weighing about 800 pounds each, and nected by gearing to effect the simultaneous containing about a like amount of pig-iron… rotation of the shafts and a uniform vertiFor winding up, the plan adopted was a cal movement of all parts of the platform, tread-wheel, 9 feet in diameter upon a vertisubstantially as specified. cal shaft, with a bevel pinion working into gear 3) The combination of the power-weight and segments attached to the winding-drums, which winding-drum, m, upon the transverse shaft run loose upon the transverse shaft in winding, for the purpose of working the draw, suband in running down operate by means of a dog stantially as set forth. or catch and a ratchet wheel made fast to the As can be seen, he had taken his Whipple shaft, essentially in the manner of the working double-intersection trusses (STRUCTURE, of a clock propelled by a weight…

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In conclusion, I will only remark that this plan of draw-bridge (applicable to railroad or common street purpose) is, of course, solely adapted to canal navigation, where boats require a head-room of 12 or 14 feet in height only; and for such use it seems clearly to possess the following advantages over other plans: 1) It does not obstruct the navigable channel like a swing-bridge on a pier in the centre of the canal.

2) It occupies much less space than a swing bridge mounted upon a shore pier and is less seriously affected by the action of wind.

Lift bridge patent drawing.

3) It is considerably less expensive in construction; and The Utica Morning Herald of September 16, 4) It is more easily managed and worked than 1873, reported, “the structure will be new in any other canal draw-bridge, except possi- design, being the first one of its kind ever put bly the swing-bridge, with centre pier and up. The inventor is the well-known bridge narrow boat-channels on either side. builder, Squire Whipple. He has obtained letWith this design, the deck of the bridge ters of patent for the design, and engineers are when in a down position was on the same level awaiting the results of the test here to put up as the towpath and crossing street. When in the same kind of bridge elsewhere should it the up position, it provided 12 feet of clear- prove successful in Utica... The whole mechance for the canal boats and mules. With anism is so simple that any blacksmith can Whipple’s plan and patent in hand, the state repair it when out of order... The cost of the passed Chapter 766 of the Laws of 1873 bridge outside of pier work and incidentals authorizing the construction of a lift bridge will be about $10,000.” He built the bridge at Hotel Street in Utica. On August 20, 1873, in partnership with S. W. Chubbuck, who ran a contract was signed for the construction of a foundry on upper Whitesboro Street. The “A Whipple Patent Draw (or lift) Bridge over bridge opened on time and within budget. the Erie Canal at the City of Utica in accor- On September 14, 1883, just less than 10 years dance with the provisions of Act Chapter 766 after it was opened, the bridge was destroyed Laws of 1873.” The contract price was $100 by a canal boat carrying a large load of lumber. per foot for the bridge superstructure, and The Utica Morning Herald wrote, the work was to be completed on or before The bridge tenders are Alexander C. Jones and January 1, 1874. The hand-written specificaGeorge Butts. They saw a boat approaching tions attached read, in part, as follows, from the west and attempted to lift the bridge The trusses to be of wrought and cast iron, proas usual. The machinery of the bridge would portioned according to the specification adopted not operate, and the roadway did not stir. The by the Canal Department for the Construction captain of the boat saw the dilemma of the men of the Whipple Trapezoidal Truss Bridges; and and attempted to stop his boat which had on connected at both upper and lower chords by a heavy load of lumber…The boat which was seven inch wrought iron I beams weighing 20 moving slowly touched the bridge and in less lbs. to the lineal foot, extending from truss to time than it takes to write it, pushed it from truss, with suitable end connections. its foundation, and it toppled over into the The trusses so formed and connected are to be canal a total wreck. The roadway which is in supported by four hollow iron towers or pillars, the canal is probably uninjured, but the supthirty inches in diameter at the base, ten inches porting cast iron pillars which formed the upper at the top and twelve feet high with suitable part of the bridge, the framework piers which cap pieces to receive and support the ends of support the entire weight, the stair approaches trusses. These towers are to stand upon the stone and iron rail were completely demolished and foundation herein specified... will be of value only as scrap iron. The wire The bridge is to be provided with a suitable cables on which the bridge hung are twisted, and convenient stage or platform to be occupied and the whole is about as bad a wreck as was by the operator while attending and working ever seen anywhere. It lies in the bottom of the bridge with convenient means of access the canal, completely obstructing navigation. thereto; and decking covered with tin to protect The bridge, however, was rebuilt using lathim from storms covering the whole width of ticed wrought iron angles for the four cast iron the bridge and not less than twelve feet of its pillars. Most of the operating mechanism was length in the central portion thereof. salvaged and placed back into the structure.

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Patent drawing showing lift mechanism and treadwheel.

Fixed stairs and a walkway were added to permit pedestrians to cross the canal when the span was in an up position.

Thirty-one years later, the Utica Sunday Tribune of September 20, 1914, printed an article on the front page entitled “An Antiquated Bridge Lifted by Leg Power.” It read in part, One of the queerest and most obsolete bridges along the whole course of the Erie Canal is at Hotel street in the very heart of Utica. The thousands of persons who see it or pass over it every day are so accustomed to this relic that they seldom, if ever, think of the ancient form. A few hundred feet further west, at Seneca Street, is an ultramodern bridge, in which the operator has but to move a lever and electricity raises or lowers the huge platform. But at Hotel street, men still furnish the power to raise and lower the bridge by means of a treadmill on which they walk, like a dog turning an old-fashioned churn.

The bridge served until 1921 when it was taken down as the canal was filled in. The Utica Saturday Globe of March 12, 1921, ran a picture of the bridge and the adjacent John Street lift bridge, along with an article entitled “Those Bridges-Hotel and John Street [also a lift bridge but not a Whipple] Structures Soon to Be a Memory.” The bridges were gone by the end of the month.

With the construction of this bridge, probably the most complex structure he had designed and built since his weigh-lock scales at Utica in 1841, Whipple had, from his semiretirement in Albany, pointed the way to the long-span lift bridges of J. A. L. Waddell that were later built around the country starting in Chicago in 1894.▪ Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an Independent Consulting Engineer. (fgriggsjr@twc.com)

NCSEA News

News form the National Council of Structural Engineers Associations

NCSEA Awards 13 Summit Scholarships to Young Members 2018 celebrates the sixth year of NCSEA’s Young Member Scholarship program. NCSEA is excited to announce that a total of thirteen young engineers are being awarded scholarships to NCSEA’s Structural Engineering Summit this year, making the 2018 Scholarship program the largest since its start in 2013! NCSEA thanks Computers & Structures, Inc. (CSi) for their sponsorship of this year’s scholarship recipients. Visit www.ncsea.com to view each of the recipients’ essay answers.

Congratulations to the 2018 Scholarship Winners!

Jennifer Arrowood is a project engineer with Kirkpatrick Forest Curtis PC and is a member of the Oklahoma Structural Engineers Association.

Christopher Barlow is a structural engineer IA with CannonDesign and is a member of the Structural Engineers Association of Massachusetts.

Maher Eltarhoni is an engineer intern with 360 Engineering Group and is a member of the Oklahoma Structural Engineers Association.

Landon Harmon is a project engineer II with Mackenzie and is a member of the Structural Engineers Association of Oregon.

Swarna Karuppiah is a graduate engineer with Datum Engineers, and is a member of the Structural Engineers Association of Texas.

Scott Kinney is an engineer with Walter P Moore and is a member of the Structural Engineers Association – Metro Washington.

Alicia Klaubert is a structural engineer with BVH Integrated Services and is a member of the Connecticut Structural Engineers Coalition.

Edward Major II is a structural engineer with Whitney Bailey Cox & Magnani, LLC, and is a member of the Structural Engineers Association of Pennsylvania.

Lena Raffin is a structural engineer with HGA and is a member of the Structural Engineers Association of Wisconsin.

Ted Saltz is an engineer with Thornton Tomasetti and is a member of the Structural Engineers Association of Massachusetts.

Did you know?

Christopher Smith is a structural engineer with Allen & Hoshall and is a member of the Tennessee Structural Engineers Association.

Lenard Tran is a structural design engineer at Patterson Engineering, and is a member of the Structural Engineers Association of California.

Hunter Wheeler is a graduate student at Kansas State University and is a member of the Structural Engineer’s Association of Kansas and Missouri.

NCSEA offers discounted registration to the Structural Engineering Summit for young engineers? Not only can you save on registration, but there are special events, resources, and even an entire education track dedicated to young engineers. Visit www.ncsea.com/register to secure your deal now!

Young Member Group of the Year Finalists Announced

Each year, NCSEA awards the Young Member Group of the Year award at the Structural Engineering Summit. This award recognizes Young Member Groups that are providing a benefit to their young members, member organization, and communities. Each finalist group receives a complimentary registration to send a representative to the Summit, and the winning group will receive a cash prize. NCSEA thanks Computers & Structures, Inc. (CSi) for their sponsorship of this year’s Young Member Group of the Year Award.

This year’s Young Member Group finalists are from Structural Engineers Association of Massachusetts, Structural Engineers Association of New York, Structural Engineers Association of Utah, and Structural Engineers Association of Washington. The winning Young Member Group of the Year will be announced at the NCSEA Structural Engineering Summit.

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Have you secured your spot, yet? Register today for the only event designed by structural engineers for practicing structural engineers. The NCSEA 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 an event designed to advance the industry.

Attendance at the Summit has grown more than 100% in the last three years and the Trade Show has increased its exhibitors by more than 30%. This year’s Summit will be the largest in NCSEA history! The Trade Show will host the most exhibitors to date, each day offers more educational tracks than ever before, and there are bigger and better events to look forward to. Visit the NCSEA website to learn more about the extracurricular events offered this year or any of the over 30 educational sessions.

Don’t miss your chance to be a part of this dynamic and growing event, register now at www.ncsea.com/register!

The California Office of Emergency Services (CalOES) Safety Assessment Program (SAP), hosted by NCSEA, is highly regarded as a standard to train emergency second responders. The training has been reviewed and approved by FEMA’s Office of Domestic Preparedness.

This SAP training course provides engineers, architects, and code-enforcement professionals with the basic skills required to perform safety assessments of structures following disasters. Licensed design professionals and certified building officials will be eligible for SAP Evaluator certification and credentials following completion of this program and submission of required documentation.

NEW! The fee for this course has been lowered by more than 40%; making it accessible to more people. Register for the November 9th course by visiting www.ncsea.com.

NCSEA Webinars September 13, 2018 ICC Storm Shelter Design: Code Criteria & Project Challenges John Funk, P.E. The speaker will discuss the current IBC and ICC code provisions, how it can apply to locating the shelter in a project, and material selection to design a storm shelter.

September 20, 2018 Overview of Changes & Additions in ACI 318-14 Royce Floyd, Ph.D., S.E. This webinar will provide a general overview of the reorganization of ACI 318, Building Code Requirements for Structural Concrete and Commentary for the 2014 edition.

September 27, 2018 Designing Wood-Frame Structures for High Winds Ricky McLain, P.E., S.E. This presentation will cover the design of a building’s wind-resisting system, including wind load calculations, diaphragms, shear walls, and collectors. Load path continuity will be discussed, as will unique design considerations for designing wood-frame structures to resist uplift, in-plane, and out-of-plane wind loads.

October 4, 2018 Retrofit of Existing Structures for Protective Applications Aldo McKay, P.E., and Marlon Bazan, Ph.D., P.E., S.E. This webinar will provide architects and engineers with a general overview of key factors to consider when evaluating existing structures, and will discuss the advantages of using advanced nonlinear dynamic analysis methods to maximize the contribution of the existing structural system.

Register at www.ncsea.com. Courses award 1.5 hours of continuing education after the completion of a quiz.

Diamond Review approved in all 50 States.

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September 2018

News from the National Council of Structural Engineers Associations

Secure Training to Become an Emergency Second Responder

NCSEA News

The 2018 Summit is less than two months away!

Learning / Networking

SEI Update

The News of the Structural Engineering Institute of ASCE

SEI/ASCE Live Webinars – Learn from the Experts

September 5 Introduction to the Seismic Design of Nonbuilding Structures to ASCE 7-16 September 7 An Introduction to ASCE 7-16 Wind Loads: A Three-Part Series September 10 Vibration of Concrete Floors: Evaluation, Acceptance, and Control September 12 Engineering Mid-Rise Buildings of Wood Construction September 18 Structural Supports for Rooftop-Mounted Equipment September 21 Risk Management and Rehabilitation of Existing Structural Foundations for New Infrastructure Facilities September 26 Practical Life-Cycle Analysis for Bridges – NEW September 27 Ethics: The Road All Engineers Must Follow September 28 Glued Laminated Timber and Cross Laminated Timber: Mass Timber for a New Generation of Wood Construction Register at Mylearning.asce.org for these and much more.

www.etsconference.org | #ETSC18

Conference Highlights • • • • •

Learn during great technical sessions Earn up to 18 PDHs Attend the Pre-Conference workshop Experience the Thursday Southwire Tours Make connections with over 100 Exhibitors

Save the date for inspiring speakers, dynamic learning, networking, collaboration with partners, and fun social events. www.structurescongress.org #Structures19

ELECTRICAL TRANSMISSION & SUBSTATION STRUCTURES CONFERENCE 2018 Atlanta, Georgia | November 4– 8 Dedicated to Strengthening our Critical Infrastructure

Membership

Recruit New Members and Earn Rewards

For each newly joining professional member that you refer to ASCE (you can refer up to 5 at a time), you will receive a $50 Amazon gift card. And, make sure they add SEI as their Institute! message.asce.org/mgam.

Join or Renew SEI/ASCE

For technical, professional, and leadership experience to advance your career and the profession. www.asce.org/SEI.

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

Follow SEI on Twitter @ASCE_SEI

SEI/ASCE Awards Nominate by November 1 at www.asce.org/structural-engineering/structural-engineering-awards.

Errata

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata.

If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org.

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September 2018

SEI Futures Fund and Donors Support Young Professionals to Develop Standards

ASCE 7-22 Wind Loads Subcommittee Historian

Read more at https://bit.ly/2P4ec9O.

Advancing the Profession

SEI Futures Fund Announces 2019 Funded Initiatives

Thanks to generous donor contributions, the SEI Futures Fund Board has committed more than $100,000 in funding for these strategic SEI programs in 2019: • Increased support to twenty Student Scholarships to Structures Congress • Increased support to twenty-five scholarships for Young Professionals to Structures Congress • Increased support for Young Professional Engagement on SEI Standards Committees • Facilitation training for SEI local leaders • SEI Standards lecture for SEI Chapters • Support for SEI Sustainability workshop • Support for SE Licensure research

Investing in the Future of Our Profession Your partner in: • Investing in the future of structural engineering • Supporting student and young professional involvement in SEI • Providing opportunities for professional development Learn more and give at www.asce.org/SEIFuturesFund.

Advance to SEI Fellow The SEI Fellow (F.SEI) grade distinguishes members as leaders and mentors in the profession.

Review criteria and complete your application package by November 1 to be recognized at Structures Congress in Orlando www.asce.org/SEIFellows.

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September 2018

The News of the Structural Engineering Institute of ASCE

SEI Codes and Standards Activities received a 2018 grant from the SEI Futures Fund to support the SEI Codes and Standards Young Professional (CSAD-YP) Program. The grant directly supports young professionals by providing full travel funding to attend standards meetings for which they have been selected as a Secretary, Balloteer, or Historian. The program is extremely successful in attracting talented, energetic young professionals to apply for, join, and fill vital roles on SEI Standards committees.

The program currently supports 20 young professionals on 9 committees. For the ASCE 7-22 cycle, the program received 47 applicants for 16 positions; many talented, qualified applicants were unable to be accepted.

The young professionals that have committed to the program are very eager, capable, and enthusiastic to participate in the prestigious SEI standards committees. One young professional commented that to be able to be a member of SEI standards committees, sit side-by-side and work with such prominent members of the profession is not only inspiring but also quite beneficial to network building and achieving other professional goals, such as tenure. Program feedback has been extremely positive from all stakeholders; it benefits the individuals selected as the CSAD-YPs, the committee itself, as well as SEI and the profession, to continue to cultivate luminaries in structural engineering.

“Since graduating from college and entering the workforce, I have always been interested in being involved in the ASCE/SEI 7 Wind Load Committee to help learn and enhance the future wind provisions to be as accurate and interpretable as possible. The CSAD YP program has helped immensely to provide support and backing to help me learn the code and standards development process and become involved in the technical discussions and proposals to make changes to wind load chapters of ASCE/SEI 7. Specifically, the Historian position has and will continue to allow me to learn the language of the code, and be involved in all of the changes to the wind load chapters. This helps me gain a better understanding of how the components of the code and the commentary work together to provide as much information as possible to the practicing engineer. I know that without this program it would have been much more challenging to have support from my firm for the time and expenses Greg Holbrook, P.E., required. Additionally, I am grateful that this program will help me to further grow within SEI and become M.ASCE; CDM Smith more involved and knowledgeable in codes and standards moving into future code cycles.”

SEI Update

Students/Young Professionals

CASE in Point

The News of the Council of American Structural Engineers

Did you know…

CASE has tools to help firms deal with a wide variety of business scenarios? Whether your firm needs to establish new procedures or simply update established programs, CASE has the tools you need!

If your firm needs to update its current Risk Management Program or establish a program within your firm, the following documents will guide employees:

962-H: Tool 1-1: Tool 2-1: Tool 2-4: Tool 3-1:

National Practice Guideline on Project and Business Risk Management Create a Culture for Managing Risks and Preventing Claims A Risk Evaluation Checklist Project Risk Management Plan A Risk Management Program Planning Structure

CASE Risk Management Tools Available Foundation 7: Compensation – Prepare and Negotiate Fees that Allow for Quality and Profit Develop fees based on work effort (task hour) and value to be delivered • Make allowances for unknown conditions • Share the back up for your fee with the client when appropriate • Negotiate based on the scope of work • Be willing to walk away • Don’t continue to work for losing clients Tool 7-1: Client Evaluation Do you know who your best clients are? Do you know where you should be focusing your marketing and sales efforts to maximize the financial performance of your firm? You may be surprised.

This tool will help you answer those questions by analyzing the amount of work and profit for each client.

Tool 7-2: Fee Development This tool is intended to be used within a consulting firm to stimulate thought and consideration in the development of fees.

Engineers in firms that may be experiencing new responsibilities as project engineers and project managers often ask the question — “How do we decide on fees?” This tool may be a useful primer for these employees and lead to a further discussion with firm management on the firm’s fee development strategies.

Foundation 8: Contracts – Identify Onerous Contract Language Negotiate Clear and Fair Agreements • Understand ever-changing contract language and demands • Use a CASE, AIA, or another accepted base contract • Modify the contract for each project, as needed • Use a contract that you can understand • Use the contract to reasonably share project risks • Get a signed contract • Utilize legal review when appropriate Tool 8-1: Contract Review Do you (or your legal counsel) review every contract to find onerous clauses? Do you know what they are? Do you always find them? This tool will help you find these clauses or words throughout the document.

Tool 8-2: Contract Clauses and Commentary (New, July 2018) This Contract Clause Review and Commentary tool is intended to assist in your review of contracts and potentially alert you to clauses that may be problematic. Although not fully encompassing for all potentially onerous or problematic clauses, this tool highlights several clause types that occur often and may cause concern.

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

And the Winner is…

The CASE scholarship, administered by the ACEC College of Fellows, is awarded every year to a deserving student seeking a Master’s degree in an ABET-accredited engineering program.

Since 2009, the CASE Scholarship program has given over $20,000 to engineering students to help pave their way to a bright future in structural engineering. CASE strives to attract

the best and brightest to the structural engineering profession, and educational support is the best way we can ensure the future of our profession.

The 2018 winner, Kristine Obenour, will graduate May 2019 with a Master’s Degree in Structural Engineering from Florida State University.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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Additional Risk Management Strategies for Bottom-Line Results at ACEC Fall Conference In addition to the CASE sponsored sessions, the ACEC Fall Conference will feature more than 30 advanced business programs, including the following sessions focused on managing a firm’s liability and risk:

Design-Build and Consulting Engineer Risk: The Better Path Forward David J. Hatem, Donovan Hatem, LLP and a panel of experts Ethics in Engineering – An Overview Randy Lewis, XL Catlin How to Deal with Terms and Conditions from Prime Design Firms Stephanie H. Burton, Gibbes Burton, LLC Extreme Weather Events and Resilient Design: Risk Management Considerations for Engineers Patricia B. Gary, Donovan Hatem, LLP; and a panel of experts The Conference will also feature: • Peter Sheehan will share his expertise on how firms can grow and thrive in today’s challenging market.

• Mick Ebeling will share his inspirational philosophy of creating “Technology for the Sake of Humanity.”

• Jon Meacham, Presidential Historian, will utilize his knowledge and understanding of historical context to comment on current affairs.

For more information and to register, go to www.acec.org/conferences/fall-conference-2018.

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 STRUCTURE magazine

• 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).

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September 2018

CASE is a part of the American Council of Engineering Companies

October 28-31, ACEC is holding its Fall Conference at The Bellagio, Las Vegas, NV. CASE will be holding their convocation on Monday, October 29. Sessions include: 10:45 am Understanding Professional Liability Insurance Speaker: Brandon Perry, Victor O. Schinnerer & Company 2:00 pm Professional Liability Claims – From Inception to Resolution Speaker: Charlie Geer, Greyling 3:45 pm From Scope Creep to Profitability: Managing Change, Risk, and Client Expectations Speaker: Andrew D. Mendelson, Berkley Design Professional The Conference also features: • CEO roundtables; • Exclusive CFO, CIO, Architect tracks; • Numerous ACEC coalition, council, and forum events; and • Earn up to 21.75PDHs

CASE in Point

ACEC Fall Conference Features CASE Risk Management Convocation and More!

ANcHor GuiDe American Wood Council

IES, Inc.

S-FRAME Software

Phone: 202-463-2766 Web: www.awc.org Product: Special Design Provisions for Wind and Seismic Description: Proportion, Design, and Detail engineered wood systems, members and connections in lateral force resisting systems. Design to resist wind/seismic forces by allowable stress design or load and resistance factor design. Nominal shear capacities of diaphragms and shear walls provided. Includes design provisions for connections (for hold-downs and anchor bolts).

Phone: 800-707-0816 Web: www.iesweb.com Product: VAConnect Description: Design base plates by AISC Design Guide #1 and anchorage calculations for ACI 318.

Both of these, independently, are difficult by hand!

With VAConnect you will get your jobs done quickly and accurately. Works alone or with IES VisualAnalysis.

Phone: 604-273-7737 Web: s-frame.com Product: S-FOUNDATION Description: Design, analyze, and detail foundations with S-FOUNDATION 2018, the most customizable and automated foundation management solution available. Seamlessly transfer model data from S-FRAME Analysis or 3rd party analysis software.

Manages your underlying model as you model, analyze, optimize the foundation.

Dlubal Software, Inc.

LNA Solutions, Inc.

Phone: 267-702-2815 Web: www.dlubal.com Product: RFEM Description: Stress analysis of complex connection layouts utilizing surface and solid elements, automatic finite-element meshing, mesh refinements, and surface intersection capabilities. Perform required strength and serviceability limit state designs of reinforced concrete to ACI-318 and other international standards.

Represent soil-structure interaction with multiple soil layers for foundation stresses and settlements.

Phone: 888-724-2323 Web: www.LNAsolutions.com Product: Type C BoxBolt Expansion Anchor Description: Build with Confidence! Type C BoxBolt Expansion Anchor now ICC-ES Approved for Seismic Design Categories A-F! The perfect solution for steel applications where access is limited to one side. Eliminates drilling or welding and installs easily with basic hand tools. Hot-Dip Galvanized for a corrosion-resistant finish.

ENERCALC, Inc.

Meadow Burke

Phone: 800-424-2252 Web: http://enercalc.com Product: Structural Engineering Library/RetainPro/ Enercalc SE Cloud Description: Design of anchors and anchor bolts requires a thorough development of applied loads, involving the analysis of full structures or connected components. Structural Engineering Library (SEL) and ENERCALC SE Cloud can assist in determining loads and analyzing your solution using your chosen codes/standards via its Loads and Forces modules.

Phone: 240-267-0401 Web: www.MeadowBurke.com Product: Super Lynk Description: A fast, strong, and discrete way to permanently connect concrete panels to footings.

Requires only a single bolt to make the connection and can easily be concealed within the normal grout line process. The engineered, patent-pending connection system meets ACI 318-14 16.2.4.3 (b).

Product: 304|316 Stainless-Steel Titen HD® Heavy-Duty Screw Anchor Description: The Titen HD screw anchor is now available in Type 304 and 316 stainless steel. Type 316 is the optimal choice for applications in corrosive environments such as near chemicals or salt water.

Type 304 is a cost-effective solution for less extreme applications, including in wet, moist, or damp environments.

RISA Inc

Uniform Evaluation Services

Phone: 949-951-5815 Web: risa.com Product: RISAConnection Description: For the baseplate and anchor design of your RISA-3D and RISAFloor model. Column reactions, including bi-axial moments, for each load combination are used to achieve a design that is more accurate than enveloped reactions. With RISA-3D and RISAFloor integration, RISAConnection is the new standard for baseplate and anchor design.

Phone: 909-937-9675 Web: www.Uniform-ES.org Product: Evaluation Report Description: Uniform ES is accredited by the American National Standards Institute. A Uniform ES report ensures continuous compliance to documents such as sections 104.11 and 1703 of the International Building Code. Our integrity is built on 80 years of experience with the qualifications and competence of our technical staff.

Gripple Inc.

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

Phone: 630-406-0600 Web: www.gripple.com Product: Spider Cast-in-Place Concrete Insert Description: A cast-in-place concrete insert solution providing a suspension point for mechanical and electrical services. Ready-to-use kit includes Spider insert, cable hanger with swivel toggle end fixing that inserts into the Spider from below, and Gripple fastener for securing the cable hanger to suspend services.

Simpson Strong-Tie Phone: 800-925-5099 Web: www.strongtie.com Product: Anchoring, Fastening, and Restoration Systems for Concrete and Masonry Description: Comprehensive catalog for our line of mechanical anchors, anchoring adhesives, direct fastening solutions for concrete, steel, CMU, and metal decking, and products that repair, protect, and strengthen structures. A quick-reference Product Selection Guide on pages 4-6. Product-specific design tables available at the webesite.

Trimble Phone: 678-737-7382 Web: www.tekla.com Product: Tekla Structural Designer Description: With Tekla Structural Designer, engineers have the power to analyze and design multi-material buildings efficiently and cost effectively. Physical, information-rich models contain all the intelligence needed to fully automate design and document projects, including end force reactions communicated with two-way BIM integration, comprehensive reports and drawings.

Demos at www.struware.com 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).

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)

Product: Tekla Structures Description: An Open BIM modeling software that can model all types of anchors required to create a 100% constructible 3D model. Anchors can be created inside the software or imported directly from vendors that provide 3D CAD files of their products.

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

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

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

Quick and easy to use ($45.00).

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September 2018

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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.