STRUCTURE magazine - February 2018

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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February 2018 Steel/Cold-Formed Steel Inside: Hard Rock Stadium, Miami

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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.”

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CONTENTS 33 HARD ROCK STADIUM

By Bruce Burt, P.E., SECB The renovation of the 65,000-seat Hard Rock Stadium included a 14-acre multi-purpose shade canopy weighing more than 17,000 tons. New and adaptive techniques allowed the construction and engineering teams to construct the canopy safely.

Columns and Departments

HISTORIC STRUCTURES

38 Niagara-Clifton Steel Arch Bridge

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

EDITORIAL

7 Making a Difference when Disaster Strikes

By William C. Bracken, P.E.

STRUCTURAL PERFORMANCE

9 An Overview of Fire Protection for Structural Engineers – Part 2

STRUCTURAL SPECIFICATIONS

42 Universal Specifications

By Drew Dudley, P.E.

LEGAL PERSPECTIVES

44 A Contract’s “Miscellaneous” Section – Part 1

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

By Frederick W. Mowrer, Ph.D.

Cover Feature

and Richard L. Emberley, Ph.D.

Features

PRACTICAL SOLUTIONS

25 WAHWEAP MARINA STORE

12 Buried Bridges and Joel Hahm, P.E.

with restaurant, office, and storage spaces. Now, support it on a floating platform. The flotation system was designed to support the weight of the

28 TECHNOLOGY SPEEDS PROJECT CONSTRUCTION

CODES AND STANDARDS

16 Changes to the 2018 National Design Specification (NDS) for Wood Construction

By John “Buddy” Showalter, P.E.,

By Kristofer R. Olson, P.E. Many rural counties struggle with funding for

Bradford K. Douglas, P.E.,

badly needed bridge repairs. Just such a county in Wisconsin teamed

and Philip Line, P.E.

with the State DOT and FHWA to solve the problem with the use of a

30 CHICAGO’S BLOOMINGDALE TRAIL

STRUCTURAL REHABILITATION

20 Timber Truss Bolted Connection Repair and Full-Scale Load Testing

By Zeno Martin, P.E., S.E. and F. Dirk Heidbrink, P.E.

By Scott K. Graham, P.E., S.E. and Jonathan E. Lewis, S.E. The Bloomingdale Trail and Park project turned an elevated portion of an abandoned railway in Chicago into a landscaped park for walkers, runners, and bikers. The bridge over Milwaukee Avenue took a former four-span, simply supported bridge

By Jennifer Anderson

ENGINEER’S NOTEBOOK

48 Evaluation of Cold-Formed Steel Members and Connections

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

SPOTLIGHT

51 Undiluted

By Jonathan Bayreuther, P.E.

STRUCTURAL FORUM

new accelerated construction technique called Geosynthetic Reinforced Soil – Integrated Bridge System.

46 Looking for a Job? – Part 2

By Brian Keierleber, P.E.

By McKay Parrish, S.E. Imagine a two-story Marina convenience store

steel structure and accommodate continually changing lake water levels.

BUSINESS PRACTICES

INSIGHTS

36 Relationships and Results on Design-Assist Projects

and converted it into a single-span, tied arch bridge.

By Scott Van Deren

58 Structural Collapse during Construction

By Jeremy L. Achter, S.E.

IN EVERY ISSUE 8 Advertiser Index 50 Resource Guide – Bridge Resource 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point

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

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February 2018

Editorial

new trends, new techniques and current industry issues

Making a Difference when Disaster Strikes Structural Engineering Emergency Response

By William C. Bracken, P.E.

A

s structural engineers, we make a difference in peoples’ is a fully interactive database that can be updated as needed by the lives every day as we help to ensure society’s health, safety, participant and searched by SEER Committee Members to obtain and welfare. This past year, many structural engineers a listing of participants by certification and location. took this responsibility to another level in the aftermath • Assistance Coordination consists of coordinating and providing of Hurricanes Harvey (in Texas) and Irma (in Florida).

2nd responder assistance to authorities having jurisdiction (AHJs) As reflected in the photos on this page, structural engineers took a or other stakeholders. This assistance ranges from providing lists leadership role as 2nd Responders to these natural disasters through the of properly trained individuals to providing coordination and Structural Engineers Emergency Response (SEER) Program. Structural logistical assistance when needed. engineers performed damage and safety assessments of communities • SEER Committees provide advocacy by educating AHJs, allied devastated by the hurricanes to determine whether structures were suitassociations, the public, and engineers on the benefits of having able for re-habitation. In response structural engineers participate in to Hurricane Harvey, 53 members 2nd response. of the SEER program volunteered In support of these four inito provide responder assistance, tiatives, NCSEA and the ICC with 51 actively deployed to signed an agreement at the end assess more than 13,000 strucof 2017 to join forces on the tures. In response to Hurricane 2nd Responder Roster to create Irma, 84 members of the SEER a single database between the program volunteered to provide two organizations of volunteers responder assistance, with 24 willing and able to serve when actively deployed to assess more disasters strike. than 5,000 structures.

The SEER 2nd Responder The SEER Program is a comDatabase is only as good as the prehensive nationwide initiative structural engineers who are willaimed at locating and deploying ing and able to volunteer and properly trained design profeshave created and updated their sionals into communities after records. If you have post-disasdisasters to assist with Applied ter assessment training, create Technology Council (ATC) style a record today. If you are interdamage/safety assessments. At the ested in bringing post-disaster state level, SEER Committees, assessment training to your local as part of their State Structural area, reach out to your SEA’s Engineers Association (SEA), SEER Committee or reach out work to recruit and educate memto the national NCSEA SEER bers to become 2nd responders. At Committee. the national level, NCSEA and Once a disaster strikes, it may its SEER Committee work to be too late to volunteer. As 2nd establish relationships with allied Responders, structural engineers organizations to support its SEA can continue to make a difference SEER Committees by focusing on and ensure the health, safety, and the following four issues: welfare of society. nd • SEER Committees facilitate and SEER 2 Responders discuss efforts with local officials and property owners.

For more information on deliver requisite training to SEA members so they can be certified as the SEER Program, visit the NCSEA SEER Committee website 2nd responders. This training is offered online through the NCSEA at www.ncsea.com/committees/seercommittee, the SEER 2nd CalOES Structural Assessment Course or FEMA’s National Incident Responder Roster at www.ncsea-seer.com or the NCSEA Emergency Management System and in person through the International Code Response website at www.ncsea.com/resources/emergencyresponse.▪ Council (ICC) Disaster Response Inspector Course.

William C. Bracken is Co-Chair of the NCSEA SEER • Roster Management consists of compiling and maintaining the Committee and CEO of Bracken Engineering. He can nd comprehensive national database of trained 2 responders through be reached at wbracken@brackenengineering.com. the SEER 2nd Responder Roster at www.ncsea-seer.com. This roster

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February 2018

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

American Concrete Institute.................. 24 Anthony Forest Products, Co................. 45 Clark Dietrich Building Systems............ 23 Design Data........................................... 32 Dlubal Software, Inc.............................. 41 Dynamic Isolation Systems..................... 18 ICC........................................................ 35 Integrity Software, Inc.............................. 8 KPFF..................................................... 40 MAPEI Corp. .......................................... 2 MacLean Power Systems......................... 27

NCEES.................................................. 49 New Millenium Building Systems.......... 43 Nordic Structures................................... 37 Nucor Vulcraft Group............................ 59 RISA Technologies................................. 60 Simpson Strong-Tie........................... 4, 19 Structural Engineering Institute of ASCE.... 15 StructurePoint.......................................... 6 Trimble.................................................... 3 Williams Form Engineering................... 21 Wood Products Council......................... 61

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

Errata The following corrections are from STRUCTURE’s January 2018 issue.

Associate Publisher Nikki Alger nalger@STRUCTUREmag.org Creative Director Tara Smith graphics@STRUCTUREmag.org

In the article, Structural Systems (page 26) by Jared S. Hensley, P.E., Figure 1 had a misprint.

B. Force Transfer Around Openings should have read C. Force Transfer Around Openings.

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

In the article Structural Practices (page 20) by Bijan O. Aalami, Ph.D., S.E., Figure 10 was incorrect where part (a) was repeated. Here is the correct figure.

The online versions of both articles have been updated (www.STRUCTUREmag.org).

Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. SidePlate Systems, Phoenix, AZ

Figure 10. Comparison of tendon force at service and ultimate limit (strength) states for bonded and unbonded post-tensioning tendons.

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

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

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

Important news for Bentley Users

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STRUCTURE magazine

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

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

February 2018, Volume 25, Number 2 ISSN 1536-4283. Publications Agreement No. 40675118.

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

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

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

D

escribed in Part 1 of this three-part series overviewing fire protection for structural engineers, fire safety objectives dictate the design of fire protection systems and features in a building.

From life and property protection to the continuity of services and preservation of heritage sites and the environment, an understanding of the objectives of a project is necessary for the correct design of protection features within a building.

Part Two of the series details fire safety systems and features used to fulfill the fire safety objectives chosen for a project.

Building Fire Safety Systems and Features Fire safety objectives are typically addressed through the design and specification of different fire safety systems and features in buildings.

One distinguishing aspect of building fire safety design is the “defense-in-depth” approach that is typically used to contend with the highly transient development of building fires. The “load” imposed by a fire on a building depends on when the fire is detected, when it is suppressed, and how it is confined by fire barriers.

The primary fire safety systems and features installed in buildings include: • Fire prevention features and controls • Flammability of building components and contents • Fire detection, alarm, and communication systems • Fire suppression systems • Structural fire protection • Means of egress • Smoke management The design of these systems and features requires coordination to meet the fire safety objectives.

Fire Prevention Features and Controls Fire prevention features and controls are not always explicitly considered as part of the building fire safety system, but fire prevention is the first line of defense against fire. Standards have been developed for the design and installation of electrical systems, fuel gas systems, heat-producing appliances, and a myriad of other potentially hazardous systems and operations with the implicit purpose of minimizing the potential for these systems and operations to ignite a fire. Fire codes include administrative controls, such as the regulation of smoking and the use of open flames and heat-producing appliances, that are specifically intended to reduce the potential for human activities to cause unwanted fires.

However, despite these fire prevention features and

controls, the potential for fire cannot be eliminated entirely, so most of the focus of building fire safety design is on systems and features that mitigate the consequences of fires that do occur.

Flammability The next line of defense against fire is to control the flammability of building components and contents. This is a commonly overlooked aspect of fire safety design, which should be considered because flammability drives the rate of fire hazard development as well as the peak fire intensity and duration and, consequently, the design of fire mitigation systems. Historically, the flammability of construction elements and interior finishes has been regulated more so than the flammability of furnishings, on the basis that it is easier to regulate elements that are part of the building construction than all the contents introduced into the building following construction.

Structural Performance performance issues relative to extreme events

An Overview of Fire Protection for Structural Engineers From a construction classification standpoint, construction types are distinguished as either combustible or noncombustible. Type I and II buildings require noncombustible materials for all elements of construction. Type III and IV buildings require noncombustible exterior walls, with other elements allowed to be combustible. Type V buildings can have combustible construction for all building elements.

However, there are a few notable exceptions to these requirements.

One of the exceptions has been the introduction of combustible insulation materials into the exterior façades of tall buildings. Motivated by the desire to improve the energy efficiency of these buildings, requirements for noncombustible façades have been relaxed over the past few decades to allow such applications. The recent façade fires at the Grenfell Tower in London and the Torch Tower in Dubai graphically illustrate the need to control the flammability of high-rise façades. In these applications, internal fire safety systems are ineffective and the external reach of the fire department is limited to the lower stories of the building.

The normal load of combustible content in most buildings is sufficient to cause a severe fire if not detected and suppressed relatively early during the growth phase of the fire. For this reason, the design of building fire safety does not typically rely on fuel control as the primary means of achieving fire safety objectives.

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Part 2: Fire Safety Systems and Features

By Frederick W. Mowrer, Ph.D. and Richard L. Emberley, Ph.D.

Frederick W. Mowrer is the Founding Director of Fire Protection Engineering Programs at Cal Poly in San Luis Obispo, CA. Dr. Mowrer is a Fellow of the Society of Fire Protection Engineers and a past-president of the Society.

Richard L. Emberley is an Assistant Professor in the Mechanical Engineering Department and Fire Protection Engineering Program at California Polytechnic State University (Cal Poly).

Fire Detection, Alarm, and Communication Systems Once a fire starts, it must be detected before other mitigation strategies are implemented.

Humans are excellent fire detectors because we can sense low concentrations of smoke and are fairly effective at discriminating between nuisance sources of smoke, such as burnt toast, and hazardous sources of smoke, such as an incipient fire. Unfortunately, humans are not the most reliable type of fire detector because we are not always present, we sleep, and our judgment is sometimes impaired. Furthermore, even when we do detect a fire, we may not always respond consistently or effectively. For these reasons, some form of automatic fire detection is common in many buildings.

The type of fire detection system employed depends on the fire safety objective(s) for the application. At the sensitive end, there are incipient fire detectors and flame detectors that can detect a fire almost immediately after ignition, and in some cases even before ignition occurs. However, these applications are relatively expensive and not suitable for some environments, so their use has been limited. In commercial buildings, smoke detectors provide relatively early detection of fire and are typically required for applications where occupants may be sleeping, such as hotels, apartment buildings, and hospitals. The most common form of fire detector used in commercial buildings in the United States is the automatic sprinkler, which combines automatic heat detection with automatic fire suppression.

Once an automatic fire detector activates, it transmits a signal to a fire alarm control panel.

The control panel may then initiate a number of responses including activation of the fire alarm system in the building, notification of the fire department, elevator capture and recall, reconfiguration of HVAC system operation, closure of fire doors and dampers, as well as other functions. In large buildings, the number of inputs and outputs can become quite complicated, requiring careful specification of the sequence of operations logic during design, comprehensive commissioning, and periodic testing.

One of the problems with traditional tonal fire alarm signals is that they do not communicate clear instructions or information to building occupants. Where phased evacuation is used instead of general evacuation, such as in high-rise buildings, Emergency Voice Communication Systems (EVACS) are typically used to permit selective or general verbal communication from the emergency control center to building occupants during an emergency.

Fire Suppression Systems Once a fire is detected, the next fire safety strategy is to suppress it. The vast majority of fires are not even reported because they are detected quickly by people and manually suppressed before causing any injury or significant damage. However, humans are not always reliable, so automatic sprinkler systems are commonly deployed as the primary engineered fire suppression strategy.

Each sprinkler in an automatic sprinkler system has a heat-sensitive element that activates the sprinkler when it reaches its activation temperature. Once activated, each sprinkler discharges water in a relatively uniform discharge density over the area protected by that sprinkler. The specific water discharge density is designed to reduce the heat release rate from the maximum potential and to control the fire (Figure 1). The design discharge density is based on the hazard classification of the space or commodity being protected.

Sprinkler systems are typically designed for approximately 10 to 20 sprinklers to operate over an area of approximately 1000 to 2500 square feet to control a fire and prevent it from growing larger. Once the fire is controlled, the fire department can complete its suppression when it arrives.

In the absence of an automatic fire suppression system, the fire department must respond and suppress the fire. However, it takes a relatively long time for the fire department to be notified, to respond to the fire scene, and ultimately to discharge water on a fire.

Consequently, it is not unusual for a fire to have “flashed over” and be “fully developed”

by the time the fire department starts to suppress it. A fully developed fire is characterized by ignition of the entire contents of a room resulting in maximum compartment temperatures upwards of 1000°C. Under these conditions, fire represents a serious risk to the building, to any occupants remaining in the building, and to the responding firefighters.

Structural fire protection is the next strategy in the sequence of protection methods to address these risks.

Structural Fire Protection The primary means of controlling the hazard of a “post-flashover” fire is with compartmentation of the building into separate fire areas with fire barriers and fire-resistive structural elements. The traditional approach to structural fire protection has remained virtually unchanged for the past century.

Buildings are classified into one of nine different construction types (IA, IB, IIA, IIB, IIIA, IIIB, IV, VA and VB) based on the combustibility and fire resistance rating of the construction elements. Type I buildings are the most “fire resistive,” while Type V buildings are the least.

The required type of construction is based on several factors, including the height and floor area of the building, the occupancy of the building, the street frontage of the building, and the presence or absence of automatic sprinkler protection. The required type of construction is typically determined by the architect and the fire protection engineer on a project; structural engineers are not typically involved in this determination.

Figure 1. Example of sprinkler activation and control of the HRR of a fire based on water discharge density.

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systems and features installed in the building, as well as on their reliabilities.

Smoke Management

Figure 2. Time-temperature curves for ASTM E119 and an example real fire.

The required fire resistance ratings for different construction elements are based on the type of construction selected for the building.

Fire resistance ratings are determined from the fire testing of relatively large-scale assemblies in a furnace, in accordance with the ASTM E119 fire test specification. The fire test conditions are intended to be representative of exposure to post-flashover fire conditions.

The fire test results are expressed in terms of hourly ratings, e.g., 1-hour, 2-hour, and 3-hour, based on how long a test specimen is subjected to post-flashover conditions while meeting the performance criteria specified in the ASTM E119 test standard. Because results are expressed in hourly ratings, it is a common misconception to expect that the actual period of performance in the field will be the same as the hourly rating achieved in a fire test. This will not be true because the exposure conditions will not be identical in actual fires and because field assemblies will not be identical to the test assemblies (Figure 2).

The term “fire resistance� has two traditional connotations. This term is used to describe the ability of a fire barrier to prevent the spread of fire from one side of the barrier to the other. This term is also used to describe how long a structural element will maintain its load-bearing capacity under fire conditions. The level of fire resistance depends on the fire safety objective. For some situations, the fire safety objective may be to prevent fire spread and to maintain structural integrity for a limited period, e.g., to allow for occupant egress. For other situations, the objective may be to confine a fire and maintain structural integrity until the available fuel load has burned out, e.g., in high-rise buildings.

The traditional approach to structural fire protection requires designers to select fireresistive elements and assemblies that have

been tested and rated in accordance with the ASTM E119 fire test standard. This approach does not consider the connections between elements, the response of an assembly to non-standard fire conditions, or the performance of assemblies with different dimensions than the tested assembly. The emerging practice of structural fire engineering, discussed in Part 3 of this series, allows these interactions to be analyzed in terms of the structural mechanics involved.

Means of Egress The means of egress in a building includes exit access, the exits, and the exit discharge.

The exit is separated from other parts of the building by fire-resistive construction with the intent of providing a safe passageway once occupants reach the exit enclosure. In tall buildings, exit enclosures are also pressurized to prevent smoke infiltration and to maintain a safe environment. Exits must ultimately discharge to a public way to prevent occupants from being trapped in a confined space within or outside a building.

In a prescriptive design environment, the exit capacity must be greater than the occupant load served and the travel distance to exits is limited; the implicit objective of these requirements is to limit the evacuation time. Two or more exits are required, in most buildings, to provide a secondary means of escape in case one of the exits cannot be used during an evacuation.

In a performance-based design environment, the evacuation time is calculated explicitly, with the objective of demonstrating that the required safe egress time (RSET) is less than the available safe egress time (ASET). The ASET is calculated based on the rate of hazard development for the fire scenarios selected for analysis. The ASET depends on the fire safety

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The last building fire safety system addressed here is smoke management. Both passive and active smoke management systems are used to control smoke spread in buildings. Smoke spread is controlled passively through the use of smoke and fire barriers, and by shutting down ventilation systems upon detection of smoke within these systems. Smoke spread is controlled actively by designing ventilation systems either to pressurize adjacent spaces to prevent smoke infiltration or to exhaust smoke directly from the fire zone. The pressurization concept is commonly used in tall buildings, while the exhaust concept is commonly used in atria, sports stadia, and other large open areas.

One of the most effective ways to control smoke spread is to control smoke production and buoyancy forces through automatic fire suppression. By limiting fire size with automatic suppression, both the amount of smoke and the fire-induced forces that drive smoke spread are reduced, in many cases to the point where active smoke management may not be necessary to achieve the fire safety objectives.

Summary Much as it is with the structural performance of buildings, the fire safety of buildings is often taken for granted, until a disaster occurs. Following a disastrous fire such as at the Grenfell Tower, shortcomings become apparent because fire has a way of finding and exploiting the weakest aspects of building fire safety design. In modern buildings, multiple fire safety systems and features are typically part of the design, so multiple failures are generally needed for a catastrophic fire to occur. However, as discussed here, building fire safety does not just happen by chance or good fortune; it requires the careful consideration of fire safety objectives, the coordination of many fire safety systems and features, and effective fire safety management over the lifespan of a building.

Based on the discussion presented in this article, it should be apparent that the traditional role of the structural engineer in building fire safety has been limited. However, this has been changing over the past two decades or so with the emergence of structural fire engineering as a distinct design discipline.

This new role for structural engineers in the design of building fire safety will be discussed in more detail in Part 3 of this series.â–Ş

Practical SolutionS solutions for the practicing structural engineer

Buried Bridges A Nontraditional Approach to Rebuilding the Nation’s Bridge Infrastructure

By Brian Keierleber, P.E. and Joel Hahm, P.E.

I

t is no secret the U.S. infrastructure needs an overhaul. The American Society of Civil Engineers (ASCE) 2017 Infrastructure Report Card gives the nation’s infrastructure an overall grade of D+.

The subcategory of bridge infrastructure fares a bit better, earning a C+ grade, which is unchanged from the previous report card issued four years ago. More than 56,000 of the nation’s bridges were structurally deficient in 2016, and the most recent estimate for the backlog of bridge rehabilitation needs is $123 billion. (Read more at http://bit.ly/2E7GTfM).

Over half of these bridges are owned by cities and counties, and are typically comprised of short-span bridges with spans under 140 feet in length. While the aging bridge inventory and the increased need for repair and replacement are documented and widely acknowledged, the resources for funding continue to lag behind, forcing local, state, and federal Department of Transportation engineers to explore alternatives to traditional bridge replacement options.

One of those alternative designs can be found underground (Figure 1).

An Economical Solution Eighty years ago, structural-plate buried structures – also referred to as steel buried bridges – were used as a more robust alternative to traditional culverts for use in hydraulic and minor crossings. They were primarily used where culverts could not meet flow and size

Brian Keierleber is the Buchanan County (Iowa) Engineer and can be reached at engineer@co.buchanan.ia.us.

Joel Hahm is a Senior Engineer with Big R Bridge and Chair of Transportation Research Board (TRB) Subcommittee AFF70(1) on Buried Bridges. Joel can be reached at jhahm@bigrbridge.com.

Figure 1. A steel buried bridge.

12 February 2018

requirements or where bottomless structures were needed. Structural-plate buried structures have evolved over the years with industry advancements in design and analysis tools, as well as deeper corrugation profiles that allow for longer spans, heavier loads, and higher cover.

They are now a viable design option in almost all cases where a traditional bridge is used and should be considered with other options such as modular, beam, or truss bridges. Almost every small- to medium-span bridge application could likely allow for a buried bridge solution.

They are particularly useful in the 25-foot to 80-foot span range.

A structural-plate buried bridge consists of a series of rings. A ring is one set of plates used to form the shape of the bridge. The standard plate width is 30 inches, and it typically takes three or more plates to form the bridge shape depending on the span and rise of the bridge.

The plate sections can be assembled on site, placed on the footing, and then attached one ring at a time or one plate at a time. The assembly sequence varies based on the structure size, site conditions, and contractor’s equipment and experience (Figure 2).

These types of bridges carry loads through soilstructure interaction, so the bridge structure and the backfill soils surrounding it interact with each other to support the loads. In effect, the backfill material is part of the bridge.

Because of this interaction, the bridge structure is typically lighter than other types of bridge structures and there can be significant savings in structure costs.

Figure 2. Plates being assembled on the Route 2B Bridge replacement project in St. Johnsbury, Vermont.

Structural-plate buried bridges do not require abutments and, unless foundation soil conditions are very poor, do not typically require deep foundations. They can be tailored to site conditions and geometry requirements, and their design includes inputs for site soils and backfill. Locally available materials can often be used in construction.

While they can perform similar functions to a culvert, buried bridge structures usually do not have an invert, have much larger corrugation profiles, and are designed and built for much longer spans. Buried bridges have a longer service life, greater steel thickness, and a 50 percent greater galvanized coating than that of culverts.

The design benefits of a structural-plate buried bridge include: • Accelerated bridge construction (ABC) practices (almost all structural-plate buried bridge projects are ABC projects), • Lower installed costs compared to traditional bridges and rigid structures, • The ability to carry very heavy loads, • Increased resilience through redundant systems and flexibility, • Improved aesthetics through the use of a wide variety of end treatments, • Ease in shipment, as the steel plates stack easily and, in most cases, can be transported to remote sites with limited access one plate at a time on a small truck or other light off-road vehicles if needed, • Easy assembly using local crews, with little to no experience, and light equipment already being used at the site such as skid steer loaders, forklift trucks, and backhoes, and • Lower maintenance and inspection costs than other types of bridge structures.

Figure 3. Steel buried bridges can be designed to support very heavy loads.

One of the most significant benefits of structural-plate buried bridges is their ability to support very heavy loads. Because of soilstructure interaction, they can be designed to carry mining shovels and other equipment weighing over four million pounds, large off-road trucks weighing over one million pounds, and freight train loads (Figure 3).

Another benefit is lead time on design and material acquisition, which is often accelerated because the structure is frequently designed by the time the project is awarded.

Approval drawings can be prepared very quickly and, in many cases, it can take just weeks to go from a signed contract to having a product on site. Many buried bridges can be built in two days or less, excluding foundation work.

A Low-Cost, Easy-to-Build Example The 200th Street Bridge is located about 3.5 miles outside of Jesup, Iowa, in Buchanan County, a rural area that relies heavily on agriculture. Built in 1956, the original timber piling for the 32-foot-long by 20-foot-wide, two-span bridge – a timber stringer/multibeam or girder – was deteriorating and had a weight-limit posted, which limited the types of farm equipment and trucks that could cross over it.

Faced with a backlog of bridges needing repair or replacement and limited funds, the Buchanan County engineer had several challenges to consider when making a decision for this particular project. He needed a structure that could meet the required HL93 design loading for interstate highways

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to accommodate heavy grain and livestock trucks and farm equipment. The design had to consider tight schedule constraints, poor site foundation soil conditions, and less-than ideal-granular backfill. Also, to keep costs down, he wanted to use a local crew.

Taking all factors into consideration, the Buchanan County engineer and project designer/fabricator agreed on a structuralplate buried bridge as the most economical and time-saving solution. A local firm, Zieser Construction, was chosen as the contractor.

The original 200th Street Bridge was demolished in June 2015 and construction on the new bridge began in August. The new bridge was designed, fabricated, and delivered to the site in less than six weeks.

200th Street Bridge Project Details The structure was designed in accordance with Section 12 of the American Association of State Highway and Transportation Officials’ (AASHTO) LRFD Bridge Design Specifications and constructed in accordance with Section 26 of the AASHTO LRFD Bridge Construction Specifications. The designer/fabricator used CANDE®, a finite element analysis program developed for the Federal Highway Administration for analyzing the soil-structure interaction of buried structures, to develop an optimized design.

The structure geometry was customized to meet site constraints and hydraulic requirements, and the design considered properties of site soil conditions and available backfill materials. The bridge was sized to accommodate site hydraulic requirements. The

The 200th Street Bridge replacement was completed in September 2015. It is a 39-foot, 4-inch long single span by 8-foot, 2-inch rise by 45-foot-wide galvanized structural-plate buried bridge, allowing access by all farm equipment and trucks in the area (Figure 5). The installed cost for the bridge was $95,000. In comparison, a let bridge would have cost about $156,000, a significant savings for a limited budget.

Figure 4. The 200 th Street Bridge project during construction.

existing soft, mucky soil required the new buried bridge structure to be supported by H-pile foundations.

The optimized design for this project saved time and costs compared to more traditional “canned” precast structures. Corrugation profile and steel properties provide design flexibility for bridge spans and loadings comparable to or greater than similar-sized precast or cast-in-place concrete structures.

Because a structural-plate buried bridge design was selected, it was possible to increase the effective roadway width with minimal additional cost. This allowed for significant safety improvements, such as two lanes of traffic plus room for oversized vehicles or pedestrians.

The bridge was constructed of deep corrugated galvanized steel plate with a corrugation profile of 15 inches wide (peak-to-peak) and 5.5 inches deep (peakto-valley). The steel thickness was 0.315 inches (0 gauge) with a bolt spacing of 16 inches center-to-center on the neutral axis around the periphery. The completed structure required 18 rings for a final length (bridge width) of 45 feet.

The four-person crew from Zieser Construction had never worked on a structural-plate buried bridge project before but found it an easy process that did not require special skills or equipment. They used a hydraulic excavator for this project. Typically, the equipment needed for a structural-plate buried bridge project of this size in this setting include a backhoe, an air compressor to operate impact wrenches for bolting, and a skid loader or forklift truck to help with staging of the plates at the site (Figure 4).

Long-Term Maintenance Benefits Galvanized structural-plate buried bridges require less maintenance than any other type of bridge system. At the pavement level, there are no bridge deck or joints to clean, maintain, or replace. On the underside, general maintenance consists of removing undesired vegetation and possible cleaning depending on silting or debris, similar to other types of bridges.

Additionally, there is little differential movement or settlement between the buried bridge and adjacent embankments, so the “bump at the end of the bridge” that occurs with traditional bridges and precast structures is effectively eliminated. Due to the soil backfill, differential icing compared to approach embankments is not an issue, improving

Figure 5. The new 200 th Street Bridge.

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safety during winter months and translating to lower inspection and maintenance costs.

For the 200th Street Bridge, the only anticipated maintenance is blading the traveled surface and preventing trees from growing in the channel.

With the success of the 200th Street Bridge project, the Buchanan County engineer is planning to construct additional structuralplate buried bridges. In addition to the many design and construction advantages, the compact structures can be easily stored in the yard or at the site and built when the schedule permits, providing additional time to meet tight schedules.

New Design Tool is Available The Short Span Steel Bridge Alliance has developed a free, web-based design tool – eSPAN140 (accessible at www.espan140.com) – to create customized preliminary designs for rolled beam, plate girder, corrugated structural plate, and corrugated steel pipe short span bridges.

Only three basic inputs are required.

A Smart Choice for Repairing the Nation’s Bridge Infrastructure Bridge design professionals across the country are looking for economical, efficient solutions to meet their growing backlog of projects.

Structural-plate buried bridges provide viable solutions to many of these challenges.

When planning a bridge replacement project, structural-plate buried bridges should be considered as an option.▪

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Codes and standards updates and discussions related to codes and standards

T

he 2018 Edition of the National Design Specification® (NDS®) for Wood Construction was recently published.

The updated standard, designated ANSI/AWC NDS-2018, was approved as an ANSI American National Standard on November 30, 2017 (Figure 1). The 2018 NDS was developed by the American Wood Council’s (AWC) Wood Design Standards Committee and is referenced in the 2018 International Building Code (IBC).

Primary changes to the 2018 NDS and the 2018 NDS Supplement: Design Values for Wood Construction include: • Allowance for incising factors for specific incising patterns and lumber sizes when obtained from the company providing the incising.

• Inclusion of a volume factor for structural composite lumber tension parallel-to-grain values • Inclusion of effective shear stiffness for crosslaminated timber.

• Added equation for withdrawal design values for smooth shank stainless steel nails.

for tension parallel-to-grain design values, Ft. The change occurs in NDS Table 8.3.1, Applicability of Adjustment Factors for Structural Composite Lumber, and Section 8.3.6 Volume Factor. A change was also made to clarify that dry service conditions are associated with conditions in which the moisture content of sawn lumber is less than 16%, as in most covered structures. These changes correlate with ASTM D 5456, Standard Specification for Evaluation of Structural Composite Lumber Products.

Cross-Laminated Timber (CLT) Revisions were made to CLT deflection provisions to include the term GAeff (effective shear stiffness of the CLT section). This is a correlating change with ANSI/APA PRG 320-2017, Standard for Performance-Rated Cross-Laminated Timber, to facilitate the calculation of apparent bending stiffness (EI)app consistent with properties as provided in PRG 320. The revised equation, excerpted from the 2018 NDS, is shown in Figure 2.

Changes to the 2018 National Design Specification (NDS) for Wood Construction

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

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

Changes to Fastener Design

Revision of NDS connection design provisions was primarily in response to significant increases in Components and Cladding (C&C) roof wind pressures in ASCE 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. Wind uplift related changes include new fastener withdrawal and new fastener head pull-through design provisions.

• New withdrawal design provisions for Roof Sheathing Ring Shank nails in accordance with ASTM F 1667, Standard Specification for Driven Fasteners: Nails, Spikes, and Staples.

• New design provisions for fastener head pull-through.

• Revised provisions for calculation of lateral design values for deformed-shank nails such as Post Frame Ring Shank and Roof Sheathing Ring Shank nails.

• Revised timber rivet design-value tables to limit maximum distance perpendicular to grain between outermost rows of fasteners.

• Revised terminology for Fire Design of Wood Members to clarify the difference between “char depth” and “effective char depth” used in structural calculations. Provisions for connections are also revised to more precisely describe the requirements for protection of the connection from fire exposure.

• Changes to the NDS Supplement include removal of Redwood grades requiring “close grain,” addition of Norway Spruce from Norway to foreign species dimension lumber, and addition of shearfree moduli of elasticity for structural glued laminated softwood timber (glulam).

Structural Composite Lumber NDS Chapter 8 on Structural Composite Lumber (SCL) was revised to include a volume factor, CV,

Figure 1. The 2018 NDS is now available and is referenced in the 2018 IBC.

16 February 2018

where smooth shank stainless steel nails are used for roof sheathing attachment, more nails, or nails of greater length or diameter, may be required to provide equivalent withdrawal strength performance for wind uplift.

deformation pattern, were deleted to remove an approximate 10% increase in withdrawal values for such nails relative to smooth shank nails of equivalent diameter. The revised NDS provisions allow these generic deformed shank nails, in accordance with ASTM F 1667, to use withdrawal design value equations for smooth shank nails.

Roof Sheathing Ring Shank Nails

Fastener Head Pull-through Provisions

Roof Sheathing Ring Shank (RSRS) nails were recently added to ASTM F 1667, Standard Specification for Driven Fasteners: Nails, Figure 2. Revised apparent bending stiffness equation for calculating Spikes, and Staples. Design CLT deflection. provisions for RSRS nails have been added to the 2018 NDS. RSRS Added Equation for Stainless Steel nails, which have higher withdrawal design Nail Withdrawal Strength values than smooth shank nails, provide An equation for the withdrawal strength of additional options for efficient attachment of smooth shank stainless steel nails was added. wood structural panel roof sheathing. In many Stainless steel nails have lower withdrawal cases, the specification of RSRS nails produces strength when compared to carbon steel wire a more reduced roof sheathing attachment nails of the same diameter, due to the reduced schedule than permissible by use of smooth surface friction of stainless steel. The differ- shank nails and enables the use of a single ences in withdrawal strength vary with the minimum fastener schedule for roof perimeter specific gravity of wood (Figure 3). When edge zones and interior zones. Recognition stainless steel nails are specified as an alterna- of higher withdrawal strength in the NDS is tive to reference smooth shank carbon steel based on the presence of standardized ring wire (bright or galvanized) nails in wood deformations including minimum 1½-inch construction including shear walls and dia- length of deformations on the nail. In a related phragms, these differences in nail withdrawal change, tabular values for generic threadedstrengths must be considered. For example, hardened nails, which had no standardized

Combined with historical data from tests of lumber and plywood, fastener head pull-through data used to set industry recommendations for wood structural panels was analyzed to develop new fastener head pull-through provisions. Within the range of head diameters, thicknesses, and specific gravities in the NDS, the analysis found that head pull-through is related to the perimeter of the fastener head. New equations based on fastener head diameter, specific gravity, and net side member thickness are as follows: WH = 690 π DH G2 tns for tns ≤ 2.5 DH WH = 1725 π DH2 G2 for tns > 2.5 DH where: π D H = perimeter for fasteners with round heads DH = fastener head diameter (in.)

G = specific gravity of side member tns = net side member thickness An excerpt of tabulated head pull-through values from 2018 NDS Table 12.2F is shown in Figure 4 ( page 18 ).

For design of roof sheathing fastening to resist wind uplift, the addition of head pull-through allows the controlling roof sheathing fastener spacing to be calculated from the lesser of the head pull-through design value or the fastener withdrawal design value from wood in accordance with the NDS. Previously, such design required the use of a combination of design documents including minimum prescribed spacing criteria for wood panels.

Although not specifically addressed by the added head pull-through equations in the NDS, which assume fasteners with round heads, analysis of underlying data is considered to support the use of the fastener head perimeter model for fasteners with other than round heads such as proprietary nails with clipped or oval heads.

Diameter for Threaded Nails

Figure 3. Smooth shank nail withdrawal strength (allowable stress design) from wood in accordance with 2018 NDS.

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February 2018

A change in ASTM F 1575, Standard Test Method for Determining Bending Yield Moment of Nails, clarified that nail bending yield strength, Fyb, is based on the nominal diameter, D, not on the smaller

fire exposure for the required fire resistance time. Protection shall be provided by wood, fire-rated gypsum board, other approved materials, or a combination thereof.

These provisions, while not intended to be technically different from current NDS provisions, clarify that protection of all components of the connection (connectors, fasteners, and wood) must be protected from fire exposure for the required time.

NDS Supplement

Figure 4. Excerpt from 2018 NDS Table 12.2F Head Pull-Through, WH 1.

root diameter, Dr, portion which is stressed in bending in the standard test. This change allowed nail moment capacity from testing to be represented by D and Fyb, and simplification of lateral design value calculation because Dr is not always provided for deformed shank nails. NDS provisions are revised to allow the use of D for deformed shank nails per ASTM F 1667 and applicable bending yield strength for calculating lateral design values.

steel, as opposed to the higher values associated with hardened steel nails per ASTM F 1667, due to greater use of low to medium carbon steel nails in construction. Relative to former tabulated lateral design values for the Post Frame Ring Shank Nail, the combined effect of the use of diameter D in calculation and lower bending yield strength resulted in new design values ranging from 7% lower to 3% higher than previously tabulated.

Lateral Design Values for RSRS and Post Frame Ring Shank Nails

Fire Design of Wood Members

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Lateral design values for RSRS and Post Frame Ring Shank nails are tabulated in accordance with revised provisions based on the use of diameter, D, and applicable bending yield strength. For purposes of lateral design, a deformed shank RSRS or Post Frame Ring Shank nail has the same lateral design values as a smooth shank nail of the same diameter, bending yield strength, and length. For Post Frame Ring Shank nails, revised tabulated lateral design values are based on the bending yield strength of low to medium carbon

NDS Chapter 16 on Fire Design of Wood Members was revised to provide separate calculations of char depth based on nominal char rates for wood, achar, and effective char depth for use in structural calculations, aeff.

Increased use of wood as a fire protective covering has made it important to provide provisions for calculation of the expected achar separate from aeff. Previous versions of the NDS have only provided aeff, which is increased 20% over achar to account for loss of strength and stiffness due to elevated temperatures in uncharred wood near the char front.

Design of connections for fi re was also clarified as follows: Wood connections, including connectors, fasteners, and portions of wood members included in the connection design, shall be protected from

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February 2018

NDS Supplement design values are unchanged from prior NDS Supplements with only a few exceptions. New and revised grades of machine stress-rated lumber and machine evaluated lumber are added.

Redwood grades requiring “close grain” were removed due to general lack of availability for commercial use. Other revisions include the addition of Norway Spruce from Norway to foreign species dimension lumber and the addition of shear-free moduli of elasticity for structural glued laminated softwood timber (glulam). As a compendium of product types, species, grades, and sizes, a note has been added to the NDS Supplement to alert designers and product specifiers to check for availability of sizes and grades of products before specifying.

Conclusion A section by section list of changes to the NDS is available in an appendix to this article, free to download from the AWC website.

The 2018 NDS with 2018 NDS Supplement is currently available in electronic format (PDF) only. Once the NDS Commentary and other support documents to be included in the 2018 Wood Design Package (WDP) are updated, printed copies will be available for purchase. Check the AWC website (www.awc.org) for status updates on the 2018 WDP. The 2018 NDS represents the state-ofthe-art for the design of wood members and connections. Added head pull-through design values and withdrawal provisions for RSRS nails provide design options to address increased design wind uplift pressures resulting from ASCE 7-16 and an added withdrawal equation for stainless steel smooth shank nails are among the significant changes in this edition. The 2018 NDS is referenced in the 2018 IBC.▪

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Structural rehabilitation renovation and restoration of existing structures

H

eavy snow accumulations on the roof of an elementary school in central Oregon in January 2017 caused structural damage to six wood roof trusses that span approximately 75 feet. The trusses were found to have some bolted connection failures at heel plates, as well as three split and fractured web elements also associated with their bolted connections. Snow load on the roof was reportedly around 40 pounds per square foot (psf ), while the trusses were initially designed for 30 psf. Despite the significant snow load imposed on trusses with compromised heel connections and fractured web elements, they did not collapse or exhibit excessive deflection. After an initial assessment in January 2017, other engineers designed and directed temporary repair and stabilization for the trusses to allow for continued occupancy until a permanent repair could be determined and implemented.

Timber Truss Bolted Connection Repair and Full-Scale Load Testing

By Zeno Martin, P.E., S.E. and F. Dirk Heidbrink, P.E.

The original design of the trusses used glued laminated (glulam) timber elements for top and bottom chords and web members, with steel gusset plates and large (1¼-inch diameter) bolts to connect the wood elements. The trusses were designed initially per the 1970 Uniform Building Code (UBC) and constructed and placed into service around 1973.

Each of the six trusses had limited prior repairs, designed and implemented in 1981, to address splitting of the wood elements near the large bolts.

From the 1970 UBC through the 1986 National Design Specification® for Wood Construction (NDS®), provisions existed to design 1¼-inch diameter bolted wood connections. Starting with the 1991 NDS and still today, provisions are only provided for maximum bolt diameters of 1 inch. This code change was made following reported field problems with larger diameter bolts, and the results of research conducted in the 1980s that showed large diameter fasteners could induce perpendicular-tograin stresses in the wood that can lead to the wood splitting before the expected bolted connection load carrying capacity can be reached.

Other engineers and the school district expressed concerns that the large diameter bolted connections were inadequate, as demonstrated by their performance that led to repair in 1981 as well as the performance problems found in January 2017. Other engineers had advocated for complete removal and replacement of the trusses, whereas the authors opined that the trusses were repairable. Due to the skepticism expressed by others that the trusses were indeed repairable, the authors suggested that, in addition to the customary structural engineering calculations demonstrating adequacy, full-scale load testing could also be performed to prove that the repaired trusses were capable of sustaining required design loads. Wiss, Janney, Elstner Associates, Inc. (WJE) was hired by the school district to design repairs to the trusses, conduct full-scale load testing, and perform structural observations during construction. Repairs were designed to address physical damage due to the load imposed on the roof as well as to provide upgrades to mitigate the potential splitting problems known to occur from the large diameter bolts.

Zeno Martin is an Associate Principal with Wiss, Janney, Elstner Associates, Inc. He can be reached at zmartin@wje.com.

F. Dirk Heidbrink is an Associate Principal with Wiss, Janney, Elstner Associates, Inc. He can be reached at fheidbrink@wje.com.

Excerpt from design drawings for added HeadLOK screws placed around existing bolts to clamp wood and resist splitting.

20 February 2018

Analysis and Repair Design Structural analysis of the trusses was made to determine load effects in truss elements, including bolted connections, when subject to design loads. Allowable stresses for the 1973era glulam elements were taken from the 1970 UBC, the code in effect when this material was installed. Also, and for reference purposes, allowable stresses were “converted” to a contemporary equivalent and also checked against design load demands.

The following approach was used to determine an allowable design capacity for the bolted connections: 1) Calculate the capacity per the 1986 NDS. This represents the most relevant NDS with provisions for bolts larger than 1-inch in diameter.

2) Calculate bolt row tear-out following the 2015 NDS Non-Mandatory Appendix E for determining Local Stresses in Fastener Groups.

This applies to tension connections only.

3) Upon review of AITC Technical Note 8, Bolts in Structural Glued Laminated Timber, and detailed review of its three references, assign an empirical adjustment factor based on the referenced testing to reduce the 1986 NDS calculated capacity.

4) Select an allowable bolted connection design value based on the lower of item 2 or item 3.

The glulam elements themselves were found to be within allowable limits when subjected to the design loads. A number of bolted connections were found to have demands that exceeded the capacity. Where demands exceeded allowable capacity, an improvement was designed to resolve the overstress condition. The locations with the largest overstress corresponded to locations with observed physical damage, confirming the model results.

Based on the analysis, there New heel plate connection at the bottom chord and supplemental were two general groupings of HeadLOKs installed on the diagonal bottom surface. outcome and repair approaches: 1) Where design demands exceeded large diameter bolts. The HeadLOK was allowable bolted connection capacities chosen for its small diameter shaft (0.19from 1% to 30%, then supplemental inch), large diameter head (0.625-inch), HeadLOK timber screws by FastenMaster and short thread length (2-inch). The were added around the bolted connection small diameter shaft does not promote to resist potential tension perpendicularsplitting and the large head separated to-wood-grain splitting induced by the from its threads by several inches serves ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Repaired truss.

Pools filled with water on the roof during load test of the repaired truss.

to clamp the glued wood laminations together. The capacity of wood to resist tension perpendicular to grain is so low that there are no allowable design values.

Assuming allowable tension perpendicular grain stress is equal to allowable radial tension stress to represent capacity, the analysis shows the supplemental HeadLOK more than doubled or tripled, depending on location, the ability to resist tension perpendicular-to-grain splitting in the plane of the bolts.

2) Where design demands exceeded allowable bolted connection capacities by more than 50% (there were no results between 30% and 50%), steel plates were added to bypass the original bolted connection.

This occurred at all truss heel connections and all first truss verticals inward of the heel. This new steel plate was bolted to the existing steel gusset plate using AISC 360-10 Specification for Structural Steel Buildings design provisions and screwed to the existing wood using Simpson Strong-Tie SDS screws.

In addition to the analysis and calculations that demonstrate the adequacy of the repair, load testing was also performed.

the truss. The truss was then monitored for any signs of distress and was instrumented to measure deflections due to imposed loads. The evaluation criteria included a limitation on the maximum truss deflection. A second criterion was a limitation on the maximum residual deflection after unloading the structure, i.e., rebound. Finally, the portion of the structure tested was to show no evidence of failure.

The maximum superimposed test load was the 30 psf roof snow design load which, when applied over the tributary area of the truss, equates to 30,453 pounds. The total weight of water needed for the test was then determined to be equal to the snow load (30,453 pounds) plus removed ceiling tiles and their metal support grid (1,493 pounds) minus the pool self-weight (215 pounds). The total weight of the created load was 31,731 pounds, which equates to 3,805 gallons of water.

The loading method used five premanufactured 870-gallon capacity wading pools with approximate dimensions of 118 inches by 79 inches by 26 inches deep. Since the five pools were to place the load in discreet “patch� locations over the span of the truss rather than the idealized uniform snow load, an analysis was made of pool placement to most closely match load effects from uniform loading. The total weight was divided equally into the five pools.

The contractor fabricated a five-part manifold using PVC pipe, fittings, and valves to control the amount of water added to each pool. The pools were filled using a hose from a water truck to the manifold. Amounts of water in the pools were distributed by monitoring the gallon flow meter and measuring water depths in the pools.

As a precaution, post shores were installed below the tested truss, which extended to the concrete slab-on-grade floor. The post shores immediately below the truss were installed

Load Testing Upon completion of repair of the first truss, load testing was performed to verify the efficacy of the repair before advancing the same repair on the remaining five trusses. The load test protocol was developed based on ASTM E196-06, Standard Practice for Gravity Load Testing of Floors and Low Slope Roofs, and ANSI/ TPI 1-2014 Appendix B, Proof Load Tests For Site-Selected Trusses. The load test consisted of applying specified test loads via water filled pools placed on the roof to impose a load on

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February 2018

such that there was a gap to allow for truss deflection during the load test. The load was applied in four stages representing 25, 50, 75 and 100% of the test load. The final test load was kept in place for six hours. Deflection measurements were made using cable-extension transducers (string pots) anchored to the floor and extended to the bottom of the truss. Maximum deflection at the center of the truss from testing was 0.825 inches, which equates to about L/1090 and was significantly less than building code-allowable deflections.

The repaired truss passed the load test by meeting both the maximum deflection criteria and the residual deflection criteria and had no distress or failure during the test.

Summary and Conclusion Repairs were designed to address wood splitting failures and deficiencies associated with large diameter bolts in a truss. New steel plates were added in strategic locations, as were self-drilling small diameter screws around the bolted connections, to clamp the wood around the bolts and reduce the potential for the wood to split due to stress imposed by the bolt. As part of the repair process, the repair was implemented on one truss and proof load testing was conducted to demonstrate the repair could resist the full design load. Approximately 32,000 pounds was placed on the roof via water filled pools over the truss and held for six hours.

Truss deflections were monitored during testing and after to record the recovery. The truss passed the proof load test and similar repair was then implemented to the other five trusses.

The repair approach used a novel method to reinforce around larger diameter bolts to substantially improve their capacity. The repair saved significant time and money over the full replacement option that was also considered.â–Ş

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Wahweap Marina Store T

By McKay Parrish, S.E.

he Wahweap Marina Store is located in the Wahweap Marina on the south end of Lake Powell, just south of the ArizonaUtah border near the beginning of the Grand Canyon. Situated between the docks and houseboats, the Wahweap Marina Store is a 10,144-square-foot floating platform that supports a 6,655-squarefoot convenience store, restaurant, and office space. The second floor of the structure consists of a 1,425-square-foot covered deck that allows visitors to relax and enjoy their surroundings.

This floating facility has been designed to meet the long-term needs of the owner in their specific areas of operation and service, as it accommodates the constantly changing water levels of the lake.

The Challenges The owner needed a space that could handle the various services offered. There were several challenges that the design team faced: 1) The structure was required to house office space for boat rentals, restaurant space, and a convenience store for groceries and other retail goods. All of this needed to fit within the existing docks where houseboats are moored year around.

2) A storage space within the facility was essential. The owner needed to have the ability to store additional merchandise on site and limit the number of trips transporting goods along the docks.

3) The final freeboard elevation of the structure needed to align with the adjacent docks, and at an elevation where small watercraft could dock with bumpers and occupants could easily enter and exit their boats.

4) Determining construction sequencing of the float system, with ballasting and launching restrictions, was crucial to the design. The structure needed to be constructed during the tourism off-season so that it did not interfere with boat launch ramps and visitor parking.

Deciding how to launch the structure, and when and where to build each section of the structure, was discussed at length.

Designing the Flotation System The facility has been designed to accommodate the constantly changing water level of the lake. Previous projects with this client have incorporated the use of long cylindrical tanks that can be filled with water (as STRUCTURE magazine

needed) to buoy up and ballast the floatation system. For this project, the owner requested that a mechanical room and storage room be placed beneath the structure and that all of the ducts, piping, and sump pumps be placed within this space. The owner needed a maximum of 28 inches of freeboard (distance between the top surface of the walking deck and the top surface of the water) to allow for neighboring docks to be attached at similar levels and to allow boats to pull up to the walkway. Creating a storage area that was too deep would produce too much buoyancy, making it difficult to tie the platform to surrounding structures. Steel truss systems were used in the design of the deeper storage section of the hull to transfer forces throughout the structure, increasing global stiffness and meeting the required buoyancy objectives.

The “T” shaped hull section was designed to mitigate any warping or twisting of the platform with the changing loads.

To verify the hull was watertight, the exterior shell plates were continuously welded together. The construction documents indicated that the contractor was to test the welds for leaks using soapy water and compressed air and to repair any locations where bubbles formed. As a back-up, a system of sump pumps was installed throughout the hull.

The design of the floatation portion of the structure is based on Archimedes’ principle that any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. More simply put, the buoyancy of the hull supporting the structure is equal to the weight of the displaced fluid. Therefore, it was imperative that all dead and live loads on the structure were accounted for and that the water displaced by the hull was accurately calculated. Designing the supporting structure to meet a minimum dead and live load criteria prescribed in the code works great for typical buildings with foundations. Using these same design loads also works well for designing the components of the structure. However, to accurately determine the buoyancy of the hull and the amount of freeboard during operation is a different matter. To understand the different freeboard levels in the water, a spreadsheet was created to consider 4 different load combinations to maintain the 28 inches (maximum) of freeboard that the owner was requesting. Utilizing simple graphics showing the changes in freeboard assisted the team in determining realistic freeboard elevations for planning and installing the floating docks around the new facility (Figure 2, page 26).

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February 2018

Figure 1. Structural steel framing for the Wahweap Marina Store.

Figure 3. The platform being launched from the boat ramps into Lake Powell.

Launching a Building There were many discussions regarding the means and methods of launching a building of this size and complexity in such a remote location. Historically, there have been years where the water levels of the lake have risen 12 inches per day during springtime runoff. One option for construction was to build the hull of the structure on or near the ramps at a water level elevation the lake would likely reach in the spring based on historical data. In retrospect, the designers were thankful that option was dismissed. The winter when construction occurred was a drought, and the water levels never approached the proposed historical water elevation at which the hull would have been built.

It was decided that the hull would be constructed at the top of the boat ramp in the parking lot and launched before the concrete deck was poured and the steel structure above was erected. The hull portion of the structure was constructed using wide-flange beams and HSS beams that were designed as a truss system to distribute loads throughout the platform evenly. This “T” shaped floatation system is approximately 8 feet deep in the middle section and 5 feet deep in the side sections.

The sides and bottom of the floatation’s structural hull are covered with ¼-inch and 5⁄16-inch steel plates and angles, and the top of the flotation structure consists of a sloping 7½-inch suspended concrete slab on metal deck. The lower section of the hull houses all of the mechanical equipment and also doubles as a storage room. The upper structure consists of exposed HSS beams and battered columns that project away from the building and provide the lower deck with

shade. The point loads from these columns are transferred to the truss system and distributed across the hull. The upper patio area is constructed with a 4½-inch suspended concrete slab on metal deck with a covered steel roof system above. Wood-sheathed steel stud shear walls provide lateral resistance. In the freshwater-marine environment, the owner found that painting exposed steel and maintaining the building envelope was adequate to mitigate the corrosion of the structural hot rolled and cold-formed steel.

Shortly after the hull was launched, the contractor called to explain that the deeper 8-foot “T” portion of the structure was so buoyant that the two 5-foot-deep sides of the hull were not touching the water (Figure 5 ). This construction issue was quickly remedied by temporarily filling the lower 8-foot-deep portion of the hull with water so as to not cause reverse loading of truss members within the hull.

This allowed the suspended W-2 deck and concrete topping slab, that covers the hull and acts as the floor for the store, to be poured without causing damage to the truss members. Careful consideration was taken in pouring the 10,144-square-foot suspended concrete floor. It was poured systematically to mitigate torsion in the structural members and to keep the platform level.

Initially, the owner wanted to build steel ballast tanks in strategic locations throughout the hull structure to counterbalance any heavier sections of the building and help keep the overall structure level on the water. Once the building was constructed, a concrete topping slab was placed within the 8-foot-deep section of the hull. At this point, the building sat level on the water and the owner decided that the

Figure 2. Example of the buoyancy calculation.

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February 2018

Figure 4. A section through the hull as it was being fabricated on the launch ramp.

Figure 5. The deeper section of the hull was so buoyant that the shallower sides are suspended above water shortly after being launched.

expensive ballast tanks and drainage systems were no longer needed and could be omitted.

The new facility is now located on the same site as the original facility that was constructed in the early 1960s and had experienced several additions and renovations over its 50-year life. The original facility had little or no storage space, had deficient mechanical systems, and only had a small convenience store; hence the replacement. The construction process undertaken with the new convenience store allowed the majority of the new facility to be constructed away from the site and moved into place after the existing building was disconnected from the docks and removed. This construction sequencing allowed for the continual operation of the existing facility while construction of the new facility was occurring nearby. As a result, marina patrons enjoyed minimal disruption in services.

Being involved from the early programming stages of the project allowed the design to evolve, with all consultants contributing to

arrive at the best solutions. Pooling together all resources necessary to meet deadlines, along with continual construction administration throughout the building process, helped ensure a successful outcome.â–Ş

Project Team Owner: Aramark, Wahweap Marina Structural Engineer: ARW Engineers, Ogden, UT General Contractor: Lake Powell Construction, Page, AZ Architect: VCBO Architecture, Salt Lake City, UT McKay Parrish, S.E., is a Senior Project Structural Engineer at ARW Engineers in Ogden, Utah. He can be reached at mckayp@arwengineers.com.

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February 2018

Technology Speeds Project Construction

Award-Winning Design Showcases Accelerated Construction Technique

By Kristofer R. Olson, P.E.

The completed CTH KW Bridge over Pratt Creek.

W

hen Dodge County was faced with two deteriorat- simplified construction method uses basic earthwork techniques, ing bridges requiring replacement, coupled with allowing local governments the opportunity to use their own staff cutbacks in infrastructure funding and a decreas- in the construction of the bridge. These advantages save both time ing budget, they looked at implementing a new and money. accelerated construction technique called Geosynthetic Reinforced OMNNI Associates, Inc., was tasked by the county to design the Soil – Integrated Bridge System (GRS-IBS). What they learned is two bridge replacement projects using this new construction method. that, for qualified structures, implementing GRS-IBS can save time, Only one other bridge in Wisconsin utilizes GRS-IBS, so unique money, and resources. challenges were encountered during the design process.

Dodge County, like many rural counties in Wisconsin, was struggling with how to fund their badly needed bridge repairs and replacements.

Unique Design Challenges Working closely with the Wisconsin Department of Transportation (WisDOT), the two agencies determined that, if they paired two of Constructability the county’s bridge replacement projects together, they had a unique opportunity to participate in the Federal Highway Association’s The abutments are constructed like a landscaping block wall, with Every Day Counts (EDC) Accelerated Bridge Construction (ABC) alternating layers of geotextile and crushed aggregate while using program. The EDC program was developed to identify innovations modular blocks as a facing to protect the supporting layers. Site that can speed up the delivery of highway projects, as well as address shrinking budgets.

The Dodge County bridges met the requirements for using an accelerated construction method, GRS-IBS, developed by the Federal Highway Administration (FHWA). They were both small, single-span bridges over low flow waterways. Constructed in 1947 and 1950, the bridges were at the end of their useful life and were structurally deficient due to the poor condition of the steel girders and timber abutments. GRS involves building a reinforced soil foundation for the abutments, which eliminates the need for traditional concrete abutments and piling. IBS is a method of bridge construction that blends the roadway into the superstructure support. The geotextile reinforcement is gradually lengthened from the lower layers to the top layers to provide a smooth transition from roadway to bridge.

Projects can be completed in as little as several weeks versus several months using this technology. The Typical GRS-IBS cross-section.

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February 2018

conditions, such as span length, road alignment, and geotechnical issues, dictate the layout of the GRS-IBS abutment. The bottom GRS layers are sized considering loads and ratio to wall height, and each subsequent layer is longer to integrate the roadway approach.

When Dodge County began investigating construction options, they intended to construct the bridges with their own maintenance staff and equipment. GRS abutments are well-suited for construction by municipal crews because they do not require specialized equipment or experience in bridge building. However, Dodge County has a limit on the depth of the abutment excavation by county staff, as they do not own large equipment for deep excavations or a pile driver for installing a cofferdam.

Controlling Stream Flow The two bridges were located on small streams with similar hydraulic characteristics. Although GRS-IBS abutment under construction. the streams are low flow, their drainage basins are flat and rarely run dry. WisDOT requires that designers consider The grant requirement for the project to be bid eliminated the a two-year rain event could occur during construction. In the case possibility of county crews building the bridges. of the project bridges, the two-year flow volume was about half of Construction Method the 100-year event and required cofferdams to isolate the abutments from the streams.

Construction began on July 5, 2016, and both roadways were open to traffic on September 17, 2016. A compressed schedule of 35 working Scour Determination days for the construction of both bridges was identified in the contract.

A critical consideration during the design phase is scour. Scour is the As in any new process, there is a learning curve. This innovative construcloss of streambed material caused by the flow of water. The Reinforced tion method was new to the state, county, engineers, and contractors.

Soil Foundation (RSF) is a level layer of structural fill wrapped with Also, almost every material used for the construction of the bridges a geotextile that supports the GRS abutments. The RSF must be was an alternative to the normal method of structure construction. The lower than the expected scour depth to prevent global failure of the learning curve and two high water events resulted in the contract taking abutment system. It is necessary to calculate scour for a 200-year rain a few days longer than anticipated. However, as the project progressed, event. Scour countermeasures can be designed to protect against the the contractor became more efficient in their operations. calculated scour and reduce the depth of the RSF layer.

Award-Winning Design and Construction

Soil Conditions A subsurface soils investigation must be performed to determine if the soils at the project site can support the loads of the GRS abutments.

The soils must provide acceptable bearing capacity while also resisting short- and long-term settlement. It is important that competent soils are found at relatively shallow depths to minimize the height of the wall and reduce the excavation required and corresponding cost. FHWA says the wall height should not exceed 30 feet, while WisDOT caps the height at 22 feet. For the project bridges, the depth to competent soils was 16 feet and 18 feet from the road surface.

Compressed Design Schedule As Dodge County evaluated their options, WisDOT suggested pursuing a grant to fund the project. A typical bridge replacement project in Wisconsin has a 15- to 18-month schedule to complete various stages of design and reviews, as well as environmental documentation, utility coordination, and right-of-way acquisition. For the Dodge County projects, the grant funding required that the project be bid by construction contractors within six months after the grant was awarded. Significant coordination and cooperation between the designers, reviewers, environmental agencies, and utilities were required to meet the compressed design schedule.

STRUCTURE magazine

During construction of the GRS abutments, Dodge County hosted a Project Demonstration Day in coordination with WisDOT’s Bureau of Structures to showcase the GRS-IBS technology. This learning event provided an opportunity for county highway departments, municipalities, design consultants, WisDOT staff, and construction contractors to learn about the innovative technology, its benefits, and the applications for future projects.

The project (CTH KW Bridge over Pratt Creek and CTH S Bridge over Shaw Brook) won both the state and national Project of the Year award from the American Public Works Association.

In addition, the CTH KW Bridge won an Excellence in Highway Design (SW Region) from the Wisconsin Department of Transportation.â–Ş

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Kristofer R. Olson is a Structural Engineer in the Transportation Group at OMNNI Associates, Inc., an engineering consulting firm based in Appleton, Wisconsin. He can be reached at kris.olson@omnni.com.

Link to WisDOT video and time-lapse building of the bridge: www.youtube.com/watch?v=oqSrYzrNkh8 or www.omnni.com.

February 2018

Chicago’s Bloomingdale Trail

Innovative Erection Procedures for the Milwaukee Avenue Bridge

By Scott K. Graham, P.E., S.E. and Jonathan E. Lewis, S.E.

O

riginally a railway line developed in 1873, the Bloomingdale Line carried passenger and freight trains from the near north side of Chicago 35 miles out to the western suburbs. In 1910, a portion of the line in Chicago was elevated to help reduce pedestrian accidents at street crossings. By the late 1990s, rail traffic on the line had declined substantially, eventually halting in the early 2000s. The railway line sat largely abandoned until 2013 when the City of Chicago purchased a 2.7-mile segment of the railroad right-of-way and engaged Walsh Construction (Walsh) to develop this segment into The Bloomingdale Trail and Park, also known as “The 606.” This adaptive reuse project turned the railway into a landscaped elevated park for walkers, runners, and bikers, connecting multiple city neighborhoods and spurring economic development.

The 606 repurposed more than 30 of the original steel bridges or concrete viaducts, including perhaps the most iconic component of The 606. The bridge over Milwaukee Avenue took a former four-span, simply-supported bridge and converted it into a single-span, tied-arch bridge. The Engineer of Record for the project was Collins Engineers Inc.; Wiss, Janney, Elstner Associates Inc. (WJE) served as the construction and erection engineer, assisting Walsh with an innovative erection plan for the bridge.

Existing Four-Span Bridge The original four-span bridge over Milwaukee Avenue was 26 feet wide by 98 feet long and had a skew of approximately 45 degrees (Figure 1).

The structural framing consisted of a reinforced concrete deck on top of transverse steel floor beams that spanned between three main longitudinal built-up, riveted steel plate girders. The girders were simply-supported by three interior steel piers and two reinforced concrete abutments.

The existing reinforced concrete deck was removed and, since the anticipated loads for the new trail were significantly less than train loads, approximately two-thirds of the existing steel floor beams were also removed. Next, localized structural repairs were made to the main longitudinal steel girders, primarily to address areas of corrosion-related deterioration that had occurred over the 100+ year life of the structure. Once repairs were installed, the entire structure was sandblasted and primed. Final painting occurred after the new bridge was fully erected.

STRUCTURE magazine

Jacking Procedure for the Existing Bridge To improve vertical clearance on Milwaukee Avenue, the final elevation of the new bridge needed to be approximately 3 feet 6 inches higher than the original elevation of 13 feet 6 inches. A jacking procedure was developed to lift the bridge off of its existing bearings up to its design elevation. The procedure began with the installation of new web splice plates and new top and bottom flange splice plates to make the simplysupported longitudinal girders continuous from abutment to abutment.

The newly established continuity reduced the number of required jacking points from 24 (one at both ends of each simply-supported girder) to 12. The end spans of the girders cantilevered out past the interior jacking points, allowing unencumbered access to the existing reinforced concrete abutments and helping to facilitate the concrete repairs and new bearing installation. In general, the jacking procedure involved installing jacking towers and hydraulic rams underneath the longitudinal girders adjacent to the interior pier supports. The hydraulic rams – linked by a manifold – lifted the bridge from the piers and abutments in ¼-inch increments, while ¼-inch shims were placed on the piers. This limited the amount of displacement that would occur if hydraulic pressure was lost. As the hydraulic rams approached their full stroke (approximately 18 inches), they were locked into position; the shims were removed and new temporary steel shoring stools were installed on top of the piers.

The girders were then lowered and secured to the new stools. Next, the hydraulic rams were relieved and a new custom jacking stool was placed underneath each ram. This lifting process continued until the bridge was raised to a height slightly above the final design elevation.

New shoring stools, dimensioned such that they would support the girders at the final design elevation, were installed on top of the piers.

The bridge was lowered and secured onto the new custom shoring stools, and then temporary diagonal bracing was installed to maintain a laterally braced structure during for remainder of construction. The elevated structure is shown in Figure 2.

Erection Procedure for Arch Assembly Costs and logistical considerations for installing shoring and falsework over the busy Milwaukee Avenue corridor led the construction team to

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February 2018

Figure 1. Existing bridge structure.

Figure 2. The elevated bridge structure.

explore other innovative alternatives for erecting the three steel arches atop the in-place bridge. Ultimately, the team obtained permission to erect the arches in an adjacent grocery store parking lot and then lift the entire arch assembly from the parking lot to the existing elevated bridge structure. Each arch consisted of three separate HSS steel tube pieces that were laid horizontally and field-welded together. After all three arches were fully assembled, the first arch was tilted vertically using a crane and placed on top of horizontal steel HP sections – laid out to match the intended configuration of the bearing assemblies on the final bridge.

A second crane tilted the second arch vertically and placed it on top of the steel HP sections. New steel cross framing was installed between the first and second arches. The third arch was installed similarly (Figure 3).

Lifting the Arch Assembly Interferences and crane limitations prohibited the assembly to be moved directly from the parking lot to the bridge, so it was done in two stages. First, the crane was placed in the parking lot and attached to the three-arch assembly at four points – two near the peak of each exterior arch (Figure 4). The three-arch assembly was lifted onto temporary timber bearing pads located adjacent to the existing bridge structure. Second, the crane moved to Milwaukee Avenue and the three-arch assembly was lifted off the timber mats, placed onto the elevated bridge structure, and bolted to the top flanges of the existing longitudinal girders. The flexibility of the arch assembly allowed the erection team to move the base plate connections into alignment with relative ease.

Tensioning Procedure for Arch Assembly Installing and tightening steel cables to suspend the continuous longitudinal girders of the bridge, enabling the removal of all three intermediate pier supports beneath the bridge, was the final step.

Clevises secured cables to the arches and a custom socket secured them to the longitudinal girders. The girders were disconnected from the shoring stools on the piers and tensioning occurred in each cable over

Figure 4. Lifting the arch assembly.

the course of three iterations, each iteration adding approximately one-third of the full target load. “Full” load was intended to include all dead load plus some additional pretension as specified in the bridge design documents. Each socket was tensioned using a custom steel fixture and two calibrated load cells. The custom steel fixture and load cell assembly was designed to bypass the socket nuts (Figure 5).

Separate loading nuts on top of the steel fixture and load cell assembly were turned, approximately in unison, to add tension to the cable until the target load was reached. Socket nuts below the custom fixture were tightened against the socket, again approximately in unison, until the readouts from the load cells were reduced to zero, thereby transferring the load to the socket nuts (Figure 6 ).

After two iterations of tensioning, the bridge lifted off of the temporary shoring stools. A third iteration added pretension to the cables. A final pass recorded the actual load in the cable by installing the custom steel fixture and load cell assembly and tightening the loading nuts until the washers beneath the socket nuts became loose. The load in each load cell was recorded, and the socket nuts were tightened until the load in each load cell returned to zero to transfer load back. With the bridge spanning between the abutments, the existing steel piers were removed and the final coat of paint was installed.

Summary Enjoyed by hundreds of thousands of recreational users since its opening in June 2015, the new “606” path is a creative repurposing of an existing, abandoned railway line. The newly adapted Milwaukee Avenue Bridge is a signature element of the trail. In recognition of the innovative design and construction techniques, the bridge won the 2016 National Steel Bridge Alliance award for Special Purpose structures.▪ Scott K. Graham currently works out of the WJE office in downtown Chicago and can be reached at sgraham@wje.com.

Jonathan E. Lewis currently works out of the WJE office in downtown Chicago and can be reached at jlewis@wje.com.

Figure 5. Custom steel fixture and load cell assembly.

STRUCTURE magazine

Figure 3. Erecting the three-arch assembly.

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February 2018

Figure 6. Tightening a cable and reading the load.

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Hard Rock Stadium

E

recting a 14-acre shade canopy, weighing more than 17,000 tons, over an existing NFL stadium in one offseason presented exceptional challenges to the Hard Rock Stadium project team. Hillsdale Fabricators of St. Louis, Missouri, assisted by erection engineers Ruby+Associates of Bingham Farms, Michigan, were up to the task. A complete transformation of the 30-year old stadium is highlighted by the beautiful new canopy, and the engineering behind its erection tells a unique story.

Designed by architect HOK and structural engineer Thornton Tomasetti, the structural steel canopy is part of a $500 million renovation of the 65,000-seat stadium. Upgrades include four massive, canopy-supported video boards, additional suites, and improved seating intended to appeal not only to Dolphins fans but also to the Super Bowl selection committee. The canopy provides shade over the stadium seating while leaving the area above the playing field open. Support is provided by a total of eight reinforced concrete super columns. At each corner, transfer trusses spanning between pairs of super columns support a 350-foot tall mast. Sixty-four locked coil steel cables, up to 300 feet in length, contribute to support of the canopy. This arrangement of structural elements provides redundancy in hurricane-prone Miami but also makes the canopy structure highly indeterminate, a feature that proved quite challenging when attempting to control the distribution of dead loads into the various structural members.

The Team Ruby+Associates, Structural Engineers, provided full erection engineering services to fabricator/erector Hillsdale Fabricators. Redaelli Tecna S.P.A. of Milan, Italy, furnished the structural cable and fittings and assisted in their installation. Redaelli also provided significant cable expertise and important feedback on the design of the cable tensioning system. Terracon of Winter Park, Florida, performed geotechnical studies of the soil bearing capacity beneath the mobile STRUCTURE magazine

SHADE CANOPY

By Bruce Burt, P.E., SECB

Courtesy of Miami Dolphins

cranes and temporary shoring. Esskay Structures of Tamilnadu, India, was retained by Hillsdale Fabricators to provide the fabrication details for the canopy and developed a 3D Tekla model that was used extensively in erection planning. Hillsdale Fabricators’ construction and engineering staff also provided vital input and coordination.

The “No Shoring” Alternate One of the primary objectives in developing the erection plan was minimizing the impact of the canopy installation on the existing stadium below. Typically, a structure of this magnitude requires extensive shoring to provide temporary support during construction. The bid documents contained a suggested erection procedure that utilized 24 shoring towers. Not only would this shoring have been expensive and time-intensive to install, but it would also have required considerable repair to the finished stadium spaces after removal. An innovative steel erection plan was devised requiring minimal shoring and no alterations to the existing stadium to overcome these constraints.

One element of the erection scheme, borrowed from bridge construction techniques, was the use of balanced cantilevers. By sequencing construction such that loads imposed on the supporting structure stayed in balance, each corner of the structure could be erected in its entirety. To support this portion of the canopy until the permanent cables could be installed, temporary tendons consisting of W12x96 sections were positioned along the masts. The tendons permitted each of the corner areas of the canopy to be completed independently, allowing Hillsdale flexibility in erection sequencing as fabricated steel was delivered to the site.

Another method used to limit shoring, commonly employed in the power industry, is the subassembly of components into large, selfsupporting sections. Hillsdale was very familiar with this method, having employed it successfully on numerous complex power plant projects. This concept was taken one step further for the stadium project by incorporating the two 450-foot outer sideline trusses and

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February 2018

Temporary tendons support balanced cantilevers.

Four-crane lift using custom-designed lift frames.

two 350-foot outer end zone box trusses into four enormous lifts. Two custom-designed lifting frames, each weighing only 35,000 pounds but capable of safely lifting 350 tons, ensured loads were equally shared by the four massive cranes used to perform each lift. The erection scheme also utilized the locked coil steel cables, ranging in size from 3½ to 5 inches in diameter, for support of portions of the canopy structure during construction. Careful analysis was necessary to determine the erected geometry and to control construction loads in the structural members. During erection, portions of the structure were temporarily suspended in place by mobile cranes while the cables were attached in midair. The canopy assemblies were installed in a super-elevated position, allowing the canopy weight to tension the cables and deflect the canopy into its final location. The cable tensioning system was designed to provide up to 1,200,000 pounds of pretension in case the cables required re-tensioning after most of the canopy load was in place.

The erection sequence was specifically designed to limit most cables to a single tensioning action; however, for some cables, a two-stage tensioning process was required to maintain geometric alignment and prevent undesired dead loads in certain members. During the second tensioning, the sideline cables were loaded to 924,000 pounds tension.

The cable tensions and structural deformations predicted in modeling were sufficiently accurate that no cables required further tensioning to meet project loading and alignment parameters.

Software Proves Critical 3D modeling was used in nearly every facet of erection planning, including structural analysis, modeling the behavior of the structural cables, performing clearance studies, developing rigging and erection plans, and determining crane placements.

The distribution of loads and the overall deformation of a highly indeterminate structure like the Hard Rock Stadium Shade Canopy was dependent on the varying stiffness of the many structural components during the erection process. Although it expedited steel erection, the elimination of shoring increased the complexity of the analysis significantly. The erection procedure had to take into account the deformation of the structural members and support cables at each stage of erection to ensure that the prefabricated and sub assembled components would fit together and that the geometry of the completed structure was within acceptable tolerances. Cable lengths and pre-tensioning requirements,

Seven cranes were used to erect the canopy.

Completed canopy.

Partial Tekla model.

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Complex & Challenging It took the combined skills of the construction and engineering team, borrowing diverse techniques from both bridge building and heavy industrial construction, to safely and successfully complete the Hard Rock Stadium canopy in time for the first 2016 NFL preseason game. In mid-2016, with canopy construction well underway, Hard Rock Stadium was selected to host Super Bowl LIV, to be played in 2020.

As structures increase in complexity, new and adapted techniques will be required to facilitate their construction. This project is an excellent example of the need for innovation and advanced analytical procedures in meeting the demands of current and future building design.▪

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erected geometry, as well as member construction loads and deformations, were determined using SAP2000 modeling software. The SAP model contained 52 separate construction stages, with the deformation and member forces of each sequence influencing the deformation and member forces of the subsequent sequence.

A detailed 3D model of the shade canopy was developed during fabrication detailing using Tekla Structures. Portions of the overall model were extracted to capture the erection subassemblies. From these extracted subassemblies, the exact weight and center of gravity of lifted components were determined and rigging locations identified. The extracted Tekla models were then imported to RISA 3D to determine rigging loads and to confirm that construction loads did not exceed member capacities. The Tekla model was also used to check installation clearances and to determine which splice plates to attach on the ground and which to install in the air. Also, Tekla was used to produce the rigging lift arrangement drawings.

The Tekla model was also employed to perform crane clearance studies and to determine the placement of the construction cranes.

To-scale 3D models of the cranes were imported into the Tekla model, and crane positions were adjusted when a clearance study determined they were too close to the existing structure.

InSIghtS new trends, new techniques and current industry issues

T

he concept of “design-assist,” and what makes it a success, is often a mystery in the construction industry. Some already have a strong opinion about this project delivery system based on prior experience; others may have no experience at all. With that understanding, this article offers insight into the characteristics and keys to a successful design-assist project from the singular perspective of a steel fabricator with designassist experience.

To begin, do not get hung up on the formal “contractual method” being utilized.

While there is a wide range of contractual options, the following information is directed toward the process and spirit of the design-assist concept. In the scenario visualized below, the steel fabricator has been on-board at the Schematic Design (SD) or Design Development (DD) levels with the general contractor requesting participation in design completion and trade coordination.

The ultimate goal of a design-assist approach is to encourage collaboration between the design team, multiple trade partners, and the general contractor to achieve benefits not available in a traditional design-bidbuild process. The benefits of the design-assist process include improved constructability at the job site, faster construction schedules, and budget savings for the client.

Relationships and Results on Design-Assist Projects

By Scott Van Deren

Shared Mutual Interests Scott Van Deren is active in business development at Drake Williams Steel, an AISC certified fabricator, in Denver, CO, and was previously President & CEO at Mountain Steel & Supply Co in Denver. Scott currently serves as Chairman of Associated General Contractors of Colorado and sits on the market development committee for the American Institute of Steel Construction in Chicago, IL. He can be reached at svanderen@dwsteel.com.

We often live and work in isolated silos. While the Structural Engineer of Record (EOR) may be contracted with the architect, the steel fabricator is usually contracted with the general contractor. The architect and general contractor typically establish the communication channels. However, despite the imposed distance and indirect communications, the EOR and fabricator share mutual interests based on common priorities for the project.

The structural design is the critical path as the EOR is making the architects vision into a reality.

Once at the job-site, erection of the fabricated steel frame is the critical path and the key to the overall schedule, allowing other trades to begin their work.

With limited time for the initial design and accommodating owner changes, the engineer is continually chasing deadlines and coordinating with the architect to issue a complete structural package. Likewise, during the completion of design, the fabricator is chasing structural design changes and unexpected additions to scope from the owner.

Driven by deadlines and often working with incomplete information, the EOR and fabricator

share a sense of urgency to deliver the structural backbone for the project. This mutual interest presents an opportunity to exit isolated silos and work as a collaborative team. A successful approach to design-assist entails scheduling joint meetings between the steel fabricator and the EOR early in the process. The technical expertise of the EOR and the practical experience of the fabricator can be best utilized when communicating directly.

Better Understanding On each project, it seems that communication increases, the email traffic is intense, addendums are being issued, and Request for Informations (RFIs) are flying. The sheer volume of communication, however, is not always effective. While three dimensional modeling software and electronic communication provide tremendous capability, they do not always lead to a concise understanding between construction team members.

An example is the steel tonnage on a project being miscommunicated by different parties. The total tons is often calculated by the EOR from the Revit design model and used as a benchmark by the contractor’s preconstruction team. With insufficient time to complete a comprehensive preliminary design, the EOR may utilize the model to determine initial shaft sizes and may be unaware that the contractor will distribute the package for pricing to subcontractors. Simultaneously, the steel fabricator may be preparing updated budget pricing based on this Revit model and other “fill in the gaps” assumptions. For example, an astute fabricator will include base plates, connection material, stiffeners, kickers, and other miscellaneous structural material in the preliminary pricing proposal.

While both parties are calculating accurate “total” tons, they are considering different factors and will reach a different conclusion.

A contractor may report this difference to an owner or conclude during a design meeting that the fabricator’s tons are heavy. In a recent in-person design-assist work session based on schematic design drawings, this “miscommunication” was quickly discovered and resolved.

With a new understanding and mutual respect in place, additional discussions of material

36 February 2018

availability, preferred connection designs, and cost-effective edge condition details ensued. The EOR, steel fabricator, and ultimately the contractor reached a better understanding of the tonnage required for a complete steel scope. This meeting eliminated confusion and provided a streamlined communication process.

An effective meeting for a complicated project that includes the architect, engineer, contractor, fabricator, erector, and possibly other major trades may not be possible. Regardless of the communication method, how can there be more direct communication and better understanding between engineer and fabricator? In-person meetings, sharing the design model, Skype meetings, and conference calls offer the opportunity to collaborate early to avoid bottlenecks and misunderstanding. Not more communication, but meaningful communication is the key.

Pro-Active Leadership To some extent, construction team members are reliant upon the general contractor to establish a communication structure.

Leadership is not a title, however, and any pro-active member of the project team can

assert influence on collaborative processes and direct communication.

A recent progress meeting for an office building produced a surprising result. Cost of the roof structure increased despite the engineer’s effort to reduce member sizes. In this case, the fabricator created a summary to clearly show the decrease in overall weight and the increased number of beams, which drove the cost higher.

The summary was pro-active, as there had been no request for an analysis of weight or number of fabricated beams. This helped shape the direction of the design early in the process, eliminating expensive re-design later.

Seeking similar ways to provide leadership at different points in the process can have a positive impact on project outcomes. An engineer may alert the fabricator of potential changes, perhaps a complex roof structure that has not been fully developed or a floor that has not yet considered loads from mechanical systems. Similarly, an engineer could reach out with questions for a fabricator related to material availability or details regarding bolted or welded field connections. This pro-active approach may result in the EOR and fabricator forming a relationship, creating a trusted ally to address project issues.

Conclusion The design-assist process is not a panacea for all industry challenges. Genuine collaboration means working through difficult issues and potential disagreement about solutions.

The impact and payoff of a design-assist approach, however, can be significant for the project team as well as the project. For example, efficient connection details developed with consideration for labor savings, at the job-site or fabrication shop, reduces project costs. Likewise, developing these details early in the process allows greater profitability for the EOR by eliminating costly re-design. Improved constructability and shortened construction schedule benefit the owner and contractor alike.

An integrated design-assist team can create tangible results by recognizing shared mutual interests. Willingness to initiate direct and effective communication builds trust among team members. Pro-active leadership may be provided by the EOR or any team member willing to share a unique solution or lead by example.

The challenge is to create better understanding through relationships and define the results that are possible for the next designassist project opportunity.â–Ş

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Historic structures significant structures of the past

S

amuel Keefer’s suspension bridge that opened in 1868 just below the Falls of Niagara was replaced by the NiagaraClifton Steel Arch Bridge. Leffert L. Buck (STRUCTURE, December 2010) replaced Keefer’s wooden towers with iron and later replaced and widened the wooden suspended structure with iron in 1888. When the suspended deck structure of his replacement bridge blew down in a wind storm on January 9, 1889, Buck was retained to design and build the replacement structure, which opened on May 7, 1889. Again in 1895, he was called in to design a new bridge at the site because the bridge company wanted to run electric trolleys over it.

In selecting an open-spandrel arch form, Buck decided “to brace the ribs instead of the spandrels of the arch.” He doubted “whether a braced-rib arch is as economical as a braced-spandrel arch where the latter form can be adopted,” and [he believed] “that the latter form can be made much more graceful than the former, though opinions

Niagara-Clifton Steel Arch Bridge

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

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

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

differ as to their comparative beauty.” It would be the longest arch bridge in the world at the time, exceeding Gustave Eiffel’s Duoro Bridge in Portugal by almost 50%. Buck chose the bracedrib arch for the following reasons: • The long span of the arch resulted in the braced-rib arch being less expensive.

• The deck floor could not be level because of the difference of elevation of the ground on the opposite sides of the gorge, so the arch could not be symmetric.

• This form of an arch would not intercept the view of the falls from points below. In other words, the vertical and horizontal web pattern for the braced-rib arch would not be as solid looking as that of a spandrel arch.

• It would reduce the load that the anchorages would have to resist due to the dead load of the arch prior to when “the parts met and became self-sustaining.”

Having chosen the braced-rib design, Buck then worked out a plan that would maintain (as close as possible) the existing alignment of the suspension bridge and its connecting roadways and future trolley lines. On the Canadian side of the bridge, he could maintain the centerline precisely.

However, on the American side, he had to deviate from the ideal line due to “the tail-race of the Niagara Company’s tunnel,” which was directly under the suspension bridge. This was not a problem for a suspension bridge with no supporting structures in the gorge, but would not permit the construction of the skewback foundations at the desired elevation (40 feet above mean high water) and position required for an arch bridge.

The bridge’s foundations for the skewbacks were founded on “boulders, ranging between pebbles and blocks of several cubic yards in size, closely and firmly bedded in a matrix of gravel.” Buck then, just as C. C. Schneider had done 12 years earlier at his cantilever bridge (STRUCTURE, September 2015) just downstream, built his “foundations of concrete, with flaring sides to give ample base, extending back to the vertical face of the solid rock.” It was necessary to go to solid rock to support the lateral thrust of the arches. He believed that “next to solid rock such a foundation of boulders and gravel is, perhaps, as secure as need be desired, fortified as it is by a backing of solid rock.” He extended his foundations with limestone from Chaumont, Canada, placed on the concrete until it reached the steel skewbacks. He began work on the foundations in September 1895 and completed them in June of the following year.

The superstructure, of braced-rib arches, was described by Buck as follows: The span of the arch is 840 feet from centre to centre of the end pins. Its rise is 150 feet from the level

Completed Niagara-Clifton Steel Arch Bridge. Courtesy of HAER.

38 February 2018

Erection plan.

of the end pins to the centre of the rib-trusses at the crown of the arch, measured vertically.

The span is divided into twenty main panels of 42 feet each. The rib-trusses are battered at an angle with the vertical of 6°47’. The transverse distance from centre to centre of the end pins is 69.047 feet, and from centre to centre of the top chords at the middle of the span 30.25 [feet].

The top and bottom chords at the arch-ribs are united in solid web sections at 10 feet 6 inches from the centres of the end pins. The web-sections and the end posts bear on steel castings, which in turn bear on pins 12 inches in diameter and 5 feet 10 inches long. The pins are supported by cast-steel shoes, which rest on seats in built steel shoes arranged to distribute the pressure uniformly over the faces of the masonry abutments...

There are double systems of stiff laterals in the planes of both the top and bottom chords of the arch-ribs; these are reinforced by auxiliary braces, to reduce laterally their unsupported lengths. The main laterals are further supported at their intersections by vertical struts and diagonal rods, which come opposite the secondary panel-points. There are also heavier rods at the main panel points.

Finally, Buck built an inverted bow-string truss at each end of the arch to complete the bridge. He wrote that these “bow-string spans are not beautiful” but were the best solution as the rock under the shore end of the trusses was solid only near the surface. If he used a conventional parallel chord truss supported on its lower end panel points, he would have to cut through this rock and into underlying rock, which would “soon crumble and disintegrate.”

The top chord of the bowstring served as part of the tie-back system adopted to erect the bridge.

While the design of the bridge was exceptional, the erection techniques adopted were perhaps more exceptional. Traffic across the suspension bridge could not be interrupted to any significant degree while the new bridge was built under it. The erection, Buck wrote, “involved two main problems: first, to support the halves of the ribs without falsework until they met

at the middle and, second, to overcome the interference between the old bridge and the new structure during erection...The arch was so high that its north rib interfered with both the stiffening-truss and the floor of the suspension bridge. It was desired to keep the old bridge intact as long as possible, for purposes of erection as well as for the maintenance of traffic.”

His solution was to build falsework from the bank out to a position just short of the skewbacks and build a tie back system from which ties could run down and support the arch as it cantilevered out over the river.

He designed a toggle mechanism, along with its foundation, to apply tension to the main tie link which ran from the toggle to the top of the end vertical of the bridge. With this toggle, the entire arch could be lowered by simply letting-off on the toggle and if necessary, with more difficulty, lift the ends of the arch as required. The end vertical portion of the arch was also stiffened by building temporary cross bracing with the vertical placed over the second panel point. These diagonals would be removed after the arch closed.

The erection sequence was as follows: When the anchorages and their connections were in position, the end bents of the mainspan were raised and were connected with the anchorages. The first panels of the arch-span, 42-foot long, were then built out on each side of the river, resting on short bents of falsework in front of the abutments. When these panels were completed the first fore-anchorages A were connected, and by means of the adjusting links at a the weight of the panels were lifted clear of the falsework. Then the second panels, each 42 feet long, were built out and the second set of fore-anchorages were connected and adjusted.

Thus the work was continued from both sides of the river to the middle.

Because the ends of the arch approached each other over the river with the center diagonals and lower chord in place, the toggles were loosened, and the ends of the arch came together at a pin. At this stage, the arch was a

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true three-hinged arch. The center top chords and the vertical member at the center of the arch were then riveted into place, leaving a gap for a jacking mechanism that Buck designed.

In Buck’s words, the arch was “converted into a two-hinged arch by means of hydraulic jacks, with the top chords apart at the centre until the requisite stress for the amount of dead load then carried was imparted to them.”

The gap between the ends of the top chord was three inches, which was “exactly as calculated.” He calculated that the top chord should have a load in it of 375,000 pounds and that the ends would have to be separated by 9 inches. After jacking the ends apart 6 inches, temporary shims were inserted to hold the ends apart “while permanent cast-steel blocks were planed to the correct thickness.”

After the blocks were ready, the jacks placed the specified load into the top chords. Once the jacks indicated the specified load, the temporary shims became loose and the permanent members were inserted, indicating to Buck “the accuracy of the calculations and of the shop work and the field measurements.” Buck wrote that he was “not aware of any other case in which the stress in a main member has been directly measured otherwise than by means of the strain.” After the top connection was made, the pin in the bottom chord was covered with a plate that was riveted into place thus making the structure a true two-hinged arch.

The replacement of the existing floor structure, supported by the suspension cables to the arch structure, was difficult due to the interference of the bottom chord of the suspension bridge and the top chord of the arch for a significant portion of the length of the structure. After considering several plans, Buck decided to remove “the entire stiffening-truss, except its top chords, and also the floor system of the old bridge together with auxiliary chords from these points (panel #14) to the centre, and to carry the travelers and a temporary floor directly on the cables.

The top chords of the old stiffening-truss were

Toggle drawing.

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kept intact to serve as a track for the traveler.

Notwithstanding the removal of the stiffening-truss, the old bridge remained remarkably steady under the influence of wind and the concentrated loads imposed by the travelers, which weighed about 25,000 pounds each.”

The new floor system was put in, working from the middle of the river towards the shores. The travelers continued to be carried on the top chords of the old stiffening-truss. At the middle, the cables of the suspension bridge came below the top chords of the arch and there was serious interference between the south cables and the floor-framing and rib-laterals for the new work.

Of course, the cables could not be removed until the entire stiffening-truss had been removed, and the latter was needed both for traffic and for transportation of materials. Therefore some of the top laterals of the rib at the middle were omitted, and a temporary floor-framing was arranged by building around the cables. When the permanent floor was completed on one side of the bridge, the cables were cut at the middle and removed... After the removal of the cables, the permanent floor system and omitted riblaterals were finally placed in position. The floor beams and stringers were laid one panel at a time, 42 feet of the old stiffening truss

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being removed each time to make room for the new work. A small movable bridge was used to span the gap between the old work and the new while each panel length was being removed or constructed.

Work on the erection of the superstructure of the bridge began on March 1, 1898, and was completed by June 30 of the same year. The total project was completed on August 10, 1898. “The longest continuous period during which the traffic was stopped was about 3 days; the aggregate time during which it was interrupted was about 7 days.

The celerity and precision with which the bridge was erected were largely due to the engineering staff and manufacturing department of the Pencoyd Ironworks, the contractors for the superstructure.”

The first electric streetcar crossed the bridge filled with dignitaries on June 30, 1898. The Niagara Gazette, in a first-page account, ran the headline “First Car across the Gorge.” It continued “the first electric car to cross the gorge and inaugurating international trolley traffic was car No.19 of the Niagara Falls Park & River Railroad which made the trip at 7:15 o’clock last night over the upper steel arch bridge. Only a few people, including the members of the press, were notified that the trip would be made and consequently the crowd to witness the first trip was not very great.” Richard S. Buck was on the first trip across the bridge along with the leaders of the railroad company.

The formal opening of the bridge to pedestrians and vehicles came on September 27, 1898. Between June 30 and September 27, trolley cars ran back and forth across the bridge on a regular schedule. With the completion of this bridge, Buck now could claim three of the sixteen longest arch bridges in the world, as well as three of the six longest arch bridges in the United States.

In 1900, Buck submitted a paper on this bridge to the Proceedings of the Institution of Civil Engineers, a British publication, entitled “The Niagara Falls and Clifton Steel Arch Bridge.”

It is not clear why he chose to present the paper in a foreign journal rather than an American journal. Possibly it is because he had recently (December 1898) been granted membership in the Institution, still not a common thing for American civil engineers, and wanted to become better known to his British colleagues.

The bridge was taken out in an ice jam in 1939 and replaced by an arch bridge downstream by Waddell & Hardesty.▪

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Structural SpecificationS

updates and discussions on structural specifications

Universal Specifications A Step in the Right Direction

By Drew Dudley, P.E.

I

nefficiencies exist in the design-bid-build delivery of typical commercial construction projects. There is a solution that requires little additional effort by the design team. The object is to provide bids that are more accurate, create less haggling over change orders, generate a better relationship between the contractor and the design team, and ultimately lead to a less costly project. For brevity, this article focuses on an example project and follows the path of a contractor with respect to reinforced concrete scope. Before diving into the example project, an overview of the typical design and construction process for a design-bidbuild commercial project is presented.

An Overview An owner typically engages an architect in developing the schematic design for the building. Once the program and general massing of the building are agreed upon, the architect or owner engages a structural, MEP, and civil engineer, and begins progressing towards the construction documents. The design team prepares drawings and specifications, or specs, which collectively constitute the construction documents, to communicate their design with the potential contractor. The drawings typically include general notes, floor plans, sections, and details. Specs typically include administrative, product, quality assurance, submittal, and execution requirements. Before submission of the construction documents, the architect collects the relevant specs from each sub-consultant and compiles them into a project specification, which even on relatively small projects can easily reach thousands of pages.

The creation of a spec for a project typically begins with a master spec that is created and maintained either by the design firm or by a national source such as MasterSpec, CSI Manu-Spec, or SpecText. These specs generally follow the Construction Specifications Institute’s (CSI) MasterFormat standard which is an indexing system for organizing construction data, particularly specifications. The master spec will generally contain every material, product, and scenario that could pertain to the subject of the spec. On a typical project, as much as 50% of the master spec could be irrelevant to the project at hand. The national sources typically include features that assist in refining the spec for the project. However,

some manual editing is typically required. For example, the structural reinforced concrete spec (03 30 00 CSI MasterFormat) includes everything from standards for cementitious materials, reinforcement, hot and cold weather concrete, and welding of reinforcement. Items such as the cementitious and reinforcement standards usually apply to any project; however, items such as welding of reinforcement only apply to a small number of projects. Prudent designers edit the master spec until it is tailormade for the project; this includes adding any special requirements as well as removing any portion that does not apply to the project.

Unfortunately, standard practice in the industry is for the spec book to be bloated with numerous items that do not pertain to the project since it is less effort for the designer to leave superfluous items in the spec.

Once the construction documents are substantially complete, they are typically issued as a “Bid Set” when the project is to be delivered via the conventional design-bid-build arrangement. At this point, the general contractors who wish to bid on the project have a few weeks to compile bids from their sub-contractors. Due to the short bid period, the general and sub-contractors rely heavily on the drawings and largely ignore the spec book.

After the contract has been awarded and construction begins, the general contractor issues submittals, as required by the specifications, such as shop drawings, product data, and calculation packages with the intent to show the design team how they plan to construct the building and that this plan adheres to the construction documents.

The design team reviews the submittals to assess whether they are in general conformance with the construction documents. If items are found to be non-compliant, the design team indicates the non-compliant items to be corrected in the subsequent “For Construction” submittals.

Alternatively, if the items are more severe, the design team requires the contractor to correct the non-compliant items and resubmit their plan for an additional review.

Correction of non-compliant items is rarely a no-cost affair. If the non-compliant issue is derived from the specifications and is outside normal practice, then it is likely a cost that the contractor is not willing to absorb. Especially if the issue results from a conflict between the drawings and specifications, wherein the design team defaulted to the standard note: “If

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conflicting requirements exist in the construction documents then the most stringent application shall apply.” Regardless of whether the contractor absorbs this cost or issues a change order, the relationship between the design and construction teams will likely be strained moving forward.

An Example Scenario Instead of looking only at this process in the abstract, it is beneficial to consider a specific scenario. A $5M commercial project has just been issued for bid. The construction documents consist of 100 drawing sheets and a 2,000-page (plus) specification (spec) book between the architect, structural, MEP, and civil engineers. The prospective contractors have twoweeks to submit qualifications and bids to the owner before a general contractor is selected.

The general contractor sends out the construction documents to a list of sub-contractors for the items he/she will not self-perform. For the reinforced concrete, the estimating department dives into the drawings, assessing quantities, materials, degree of difficulty, and time required, to determine the cost and schedule associated with that scope. They also scan through the spec book to identify items such as the required type of vapor retarder, submittal requirements, and materials testing required. After they compile all their numbers, the contractor submits a bid and, if the bid is low, he/she is awarded the project.

As the project kicks off, the contractor receives his concrete mix design submittal from the local ready-mix plant, which he ultimately submits to the design team. After a week or two, the submittal is returned “Revise and Resubmit” with a comment from the structural engineer that expansive hydraulic cement is required for the structural slab in lieu of traditional Portland cement, as indicated in section 2.1 of specification 03 30 00, to control and reduce drying-shrinkage cracks for the architecturally exposed concrete floor. The contractor notifies the ready-mix plant of the requirement, and the plant responds with a $50,000 change order. In reality, the contractor may have already been aware of this requirement but decided to ignore it with the thought that other contractors may miss it and thus come in with a lower bid, or that there would be a chance to request a substitution once construction kicked off. Regardless, at this point, the contractor has to decide whether to

absorb this cost or issue a change order. The chances of getting a change order approved are slim since the requirement was clearly listed in the specifications; however, the contractor could argue that items of such significant cost implication should have been explicitly noted in the drawings. Regardless of the path taken, the relationship between the contractor and design team is now soured and may have detrimental consequences to the remainder of the project.

A Reasonable Solution The exact scenario described above is not common on the majority of projects; however, it is not uncommon for cost or schedule sensitive items to be brought to the attention of the contractor after the project has been awarded. Moreover, they usually come from requirements buried somewhere in the spec. A plausible solution to this issue is for owners or authorities having jurisdiction (AHJ) to adopt a universal set of specifications that are to be used on every project within their domain. The design team would still be allowed to modify, add, or delete items from the universal specifications as long as these items are highlighted in some fashion. Once they become familiar with the universal specs, this process would allow contractors to quickly scan through the spec book to identify items that are out of the

ordinary. The additional effort required by the design team to highlight these items would be minimal. Potential benefits include less overhead for the contractor since estimating is now a quicker and more certain process resulting in more accurate bids, less costly surprises during construction, and a better relationship between the construction and design team. Owners in other markets such as universities, K-12 school districts, and State Departments of Transportation (DOT’s) have already recognized the benefit that universal specifications provide and require a process similar to the one proposed above. It is understandable that large owners who oversee numerous projects every year are in a better position to create and maintain universal specifications than a small business owner or a real estate developer who may oversee one or two projects every year.

Nonetheless, small-scale owners could benefit from their AHJ adopting universal specifications that are tailored for their jurisdiction.

The process of creating and maintaining a set of universal specifications would not be foreign to AHJ’s which already undertake a similar process when they adopt a version of the International Building Code with jurisdictionspecific amendments. Ideally, the AHJ’s would engage local developers, contractors, architects, and engineers in the creation and maintenance process so the specs would reflect best practices

in the region. This approach would provide a quasi-construction management at-risk (CMAR) environment in which all parties that have a stake in the project are engaged to balance design, cost, and constructability to find the optimum solution.

Ultimately, the adoption of universal specifications is by no means an all-encompassing remedy for the myriad of difficulties inherent in the commercial building process; however, it is a step in the right direction. There will still be contractors who selectively ignore requirements within the specifications to gain a pricing advantage and subcontractors who provide their bids minutes before the deadline with qualifications and exclusions instead of quoting the project as specified in the construction documents. However, universal specifications with added, deleted, or modified sections that are highlighted will make these types of actions harder to defend and with time become less frequent.▪ Drew Dudley is the owner and manager of Dudley Engineering, LLC, College Station, TX. He is a structural specialist for Texas Task Force 1, an urban search and rescue team affiliated with both the FEMA and Texas Division of Emergency Management systems.

Drew is an adjunct professor at the University of Houston College of Architecture.

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LegaL PersPectives

discussion of legal issues of interest to structural engineers

A Contract’s “Miscellaneous” Section Part 1: Governing Law and Forum Selection Provisions

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

I

n the best of all possible worlds, engineers and their clients will negotiate their contract, the engineer will provide the agreed-upon services, and the client will pay the agreed-upon amount. In the real world, there is always the chance that something will go wrong, there will be a dispute, and the dispute will result in arbitration or litigation. In such cases, some of the seemly innocuous provisions in the “Miscellaneous” section of the design agreement can take on alarming significance. Two such provisions are the Governing Law and Forum Selection provisions.

A governing law provision, also referred to as a choice of law provision, specifies that the law of a designated jurisdiction will govern disputes arising out of the agreement, regardless of where the dispute is adjudicated. A forum selection provision specifies the location of the adjudication. Since these concepts are often contained in the same section of the agreement, they are sometimes blurred together.

However, it is important to understand the difference between the two. This article looks at governing law provisions; a second article will look at forum selection provisions and the closely related venue selection provisions.

Governing Law The law of contracts (the law that courts use to interpret contracts) is primarily state, as opposed to federal, law. In the U.S., all states except Louisiana are common law states, which means that when there is no statute addressing an issue, the issue will be decided under the law that has developed through previous case decisions. This is referred to as a common law system and was inherited from the English court system. (Louisiana inherited its legal system from France and thus has a civil law system. Under a civil law system, there is less emphasis on previous case decisions and more emphasis on the laws passed by the legislature, as codified into the governing code.)

Common law legal systems follow the principle of stare decisis, which holds that a dispute involving the same issues as a previously decided case must be decided in the same way. However, when the court in a particular state decides a dispute, only the cases

from that state are binding on the court. The are presumptively enforceable as long as there court might look to cases in other states for is some relationship between the transaction guidance, particularly if it is a “matter of first and the jurisdiction whose law would govern. impression” (there is no relevant case law in that state), but the cases of other states do Conflicts of Law Principles and not create binding precedent. The courts of Governing Law Statutes one state can interpret the wording of a contract completely differently from the courts In addition to its substantive laws (also of another state. referred to as its internal laws), each state Also, there are a number of statutes (laws will have procedural choice of law prinpassed by the state legislature, like mechanic’s ciples that govern when its laws will apply. lien laws and anti-indemnity statutes) that It is common in choice of law provisions apply to design agreements, and the laws of to say that the laws of a particular jurisdifferent states can be very different. As a diction apply “without giving effect to its result, which state’s law governs a dispute conflict of law principles.” This carve-out can have a significant effect on the outcome. is used to make sure that the conflicts of A governing law provision attempts to ensure law principles of the chosen state’s laws that the law of a designated jurisdiction will do not result in the application of another govern the dispute. For a project in the U.S., state’s law, thereby circumventing the intenthe specified jurisdiction would be a state. For tion of the parties. Sometimes the choice an international project, the Table of statutory governing law provisions. specified jurisdiction could be a country, if the country State Statute only had one legal system, Ariz. Rev. Stat. § 32-1129.05 i.e. “the laws of Sweden.” Arizona In countries such as the Colorado Colo. Rev. Stat. § 13-21-111.5(6)(g) U.S., Canada, and Mexico, Connecticut Conn. Gen. Stat. Ann. § 42-158m which have a federal system 815 ILCS 665/10 of government with both Illinois federal and state or provin- Indiana Ind. Code § 32-28-3-17 cial courts, the appropriate Kansas Kan. Stat. Ann. § 16-121(e) state or province must be Louisiana La. Rev. Stat. § 9:2779 specified.

Minnesota Minn. Stat. § 337.10

Choice of Law – Enforceability

Historically, courts would not enforce governing law provisions, as they were viewed as an attempt by private parties to usurp the legislative function by selecting which law would apply to their transaction.

However, courts now give greater emphasis to the parties’ right to contract on whatever terms they choose unless there is an overriding public policy concern.

Courts generally hold that governing law provisions

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Montana

Mont. Code § 28-2-2116 (1)

Nebraska

Neb. Rev. Stat. § 45-1209

Nevada

Nev. Rev. Stat. Ann. 108.2453(2)

New Mexico

N. M. Stat. Ann. § 57-28A-1

New York

N.Y. Gen. Bus. Law, Chapter 35-E, § 757

North Carolina N.C. Gen. Stat. § 22B-2 Ohio

Ohio Rev. Code § 4113.62 (D)

Oklahoma

Ok. Stat. Ann. tit. 15, § 15-821

Oregon

Or. Rev. Stat. § 701.640

Pennsylvania

73 Pa. Stat Ann. §514

Rhode Island

R.I. Gen. Laws § 6-34.1-1(a)

Tennessee

Tenn. Code § 66-11-208(a)

Texas

Tex. Bus. & Com. Code Ann. § 272.001

Wisconsin

Wis. Stat. § 779.135 (2)

February 2018

of law provision will specify that only the “substantive laws” or “internal laws” of a particular state apply so that the conflict of laws principles do not come into play.

While the “without giving effect to its conflicts of law principles” language is often included as a matter of course in governing law provisions, it is not really necessary.

Conflicts of law principles are only relevant to contracts that do not contain a valid governing law provision. If the contract unambiguously states that the laws of a particular jurisdiction apply, a court is unlikely to invalidate the parties’ agreement based on conflicts of law principles, as long as there is a reasonable basis for choosing the law of that jurisdiction. However, there are specific statutory governing law rules that cannot be modified by contract. In particular, 22 states have passed laws that require the state’s laws to govern contracts for design and construction projects in the state, regardless of the parties’ wishes. The Table provides a listing of these states and a citation to the relevant section of the code.

In general, the language of these laws is similar to that of the Ohio code:

Ohio Rev. Code § 4113.62 (D)(1) Any provision of a construction contract, agreement, understanding, or specification or other document or documentation that is made a part of a construction contract, subcontract, agreement, or understanding for an improvement, or portion thereof, to real estate in this state that makes the construction contract or subcontract, agreement, or other understanding subject to the laws of another state is void and unenforceable as against public policy.

The only one that is significantly different is the Pennsylvania law, which only applies to claims for payment. (The governing law statute is a provision of the Pennsylvania Contractor and Subcontractor Payment Act.)

Conclusion A client that has properties or projects in several states will typically want all of its design agreements to be governed by the law of the state in which it has its headquarters.

This simplifies matters for its legal team, as the lawyers do not have to research the case law and statutes of different states. For the same reason, a design professional will

likely want all of its design agreements to be governed by the law of the state in which it has its principal office. If the project is in a state such as Massachusetts, which does not have a governing law provision, the parties are free to negotiate which state’s law will be used to settle disputes. Part 2 of this series will look at forum and venue selection provisions; Part 3 will look more closely at some of the state laws applicable to design agreements as well as some of the factors to consider when negotiating which state law will govern an agreement.▪ Gail S. Kelley is a LEED AP as well as a professional engineer and licensed attorney in Maryland and the District of Columbia. Her practice focuses on reviewing and negotiating design agreements for architects and engineers.

She is the author of Construction Law: An Introduction for Engineers, Architects, and Contractors, published by Wiley & Sons.

Ms. Kelley can be reached at Gail. Kelley.Esq@gmail.com.

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Business Practices

business issues

Looking for a Job? Part 2: Research and Interview Techniques to Land Your Next Job

By Jennifer Anderson

W

hen embarking on a successful job search, it is paramount to effectively research companies and interview with them.

The information gathered allows you to make a better decision on a company when changing jobs. You want to make a good move… moreover, companies want you to make a good decision too. They are putting a lot on the line when adding a new person to the team.

In Part 1 of this series (STRUCTURE, January 2017), the article provided insight into how to approach the job search differently. This article focuses on research preparation and interview techniques that make a difference in how well you perform in an interview.

Effective Research Thorough research is essential to determine if a company is a right fit before applying for a position. Today, companies are more transparent; they share updated information on websites, company blogs, LinkedIn, Facebook, and other social media sites.

(NOTE to hiring managers: Make sure you are leveraging the internet to tell the story of your company so that you will attract the right candidates.)

Leverage that public information as much as possible. Four key areas of research include Social media, SEA websites, company websites, and GlassDoor.com.

Many social media sites host company profiles: LinkedIn® – Review the LinkedIn profiles of the company’s team. Browsing a wide variety of people in the firm, not just the President and Principals, provides an idea of the collective talent including individual educational backgrounds, previous employment, groups, and associations. Individual recommendations can be very insightful as well.

Twitter – Follow the company and the employees who have Twitter accounts. The posts give you timely and relevant information about the company. If they do not have a Twitter account, it is not a bad thing; it is just not a priority for the company.

Facebook – Follow their company page to learn more about the company culture. Do

NOT friend anyone at the company, unless you actually know them. Facebook has the potential to be a good source of information about what it is like to work at the company and the culture of the firm.

NCSEA, local state SEAs, SEI, and CASE firm websites are sources of information regarding structural firms. You will find information about award programs that showcase areas where the firm is recognized. You can also find out more about how they interact in the structural engineering community.

Good firms make it a priority to participate by encouraging team members to be involved in growing the industry.

Keep in mind that companies typically do not post any bad press on their website.

However, it is still important to learn about the leadership team, projects the firm specializes in, job descriptions, and more. Take the time to read company blog posts – hopefully not all marketing hype – to understand more about the culture of the firm.

Smart companies recognize that transparency about their firm is an ideal way to attract the right team members. GlassDoor.com encourages current and past employees to rate companies for a multi-dimensional look at the firm. If the company does not have a GlassDoor account, don’t think that they are hiding information; they may not have realized the power of the tool yet.

All-in-all, plan to invest about 40 hours of research per company with which you

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interview. While that may seem like a lot, the time spent educating yourself about the company helps you to make a more strategic decision about your next job.

Effective Interviewing After spending hours networking and researching, all that hard work has paid off – it is time for the interview! Although an interview can be nerve-wracking, it is better to view the process as an excellent opportunity to connect with people. Getting to know people at the company is important; you will be spending a big chunk of your day with them, every day.

There are two main things to consider when preparing for an interview; first what you want to know about them and second what you want them to know about you. Each party is evaluating the other for a good fit.

It is critical that you prepare these two items ahead of the interview.

Ask Solid Questions Write down your questions before going to an interview. I cannot tell you how many times a manager has been upset that a candidate did not have any questions. Preparing thoughtful and conversational questions helps you to uncover if you want to work for the company and shows that you prepared. Do not just ask about the pay and benefits package. Instead, prepare 4 or 5 questions for each of the following categories: about the company, the

leadership team, the position, and the team you will be joining.

Bring Professional Materials Prepare information about your experience to bring to the interview. Help them to understand your experience by providing a professional portfolio and professional recommendations.

Your professional portfolio can easily be shared using a personal website, a PowerPoint, or printed materials to showcase what you have accomplished professionally. While some projects are private, most are quite public; you should be okay to share information about what you have worked on in previous roles.

However, be careful to respect NDA and privacy laws. Update your portfolio regularly, so it is ready when needed.

Professional recommendations are a fantastic way to leverage what other people have to say about you. Gather recommendations from past bosses, peers, vendors, educators, and customers. In fact, your marketing team may have asked you to get recommendations from customers on projects on which you have worked. Keep copies of recommendation letters for your records. An easy way to keep track of your recommendations is on LinkedIn – where recommendations stay with your profile no matter where you work.

Prepare Mentally and Physically Take these steps to relax and enjoy the interview time with the prospective new employer: 1) Take the day off from work. You have no idea how long the actual interview will last, and you want the flexibility to spend as much time with the company as possible. Recruiters try to give you an idea of how much time to plan to be at the company, but you can relax and be more confident if you are not trying to squeeze in an interview during a long lunch break.

2) Wear clothes that are comfortable and colors that look good on you. Be professional in a way that reflects your personality. Check your clothes a week before the interview.

3) Gather all your documents for the interview the night before or earlier. Print out your questions and use a padfolio to take with you. Include a nice pen, business cards, your portfolio, two copies of your resume, and copies of your recommendations.

4) Get a good night’s rest and eat healthy food. If you do not get enough sleep or are too wired from caffeine, you could

find yourself jittery and anxious in an interview. If you have the time before the interview, get some exercise. Even a 30-minute quick walk will energize you more than an energy drink.

The Interview During the interview, keep the following situational tips in mind to help you maximize this valuable time with a prospective company: 1) Arrive 10-minutes early. Unless instructed otherwise, arriving too early causes stress on the manager interviewing you, but 10-minutes early shows that you care to arrive on time and that you are respectful of the interview process.

2) Do not chew gum, but maybe a mint to freshen your breath. I once witnessed an applicant walk up to the entrance of a building and then suddenly stop, look around, and spit out his gum into a bush just outside the front door. The manager was there waiting for the applicant and saw this happen. Do you think he got the job?

3) If there is more than one person meeting with you at the same time, like a panel interview, write down all their names across the top of your notepad in the order that they are sitting. It is okay to tell them that you are writing down their names to remember them, if they ask. It reduces interview stress if you can readily recall their names.

4) Some companies like to have candidates do a series of back-to-back interviews, which can be exhausting. If you need a break, for bathroom or water, let them know. You are human, and it is ok to have a short 5-minute break.

5) If they invite you to lunch, you should go. If you have specific dietary concerns, suggest a couple of restaurants that work for your needs. However, be flexible about eating out and just find something on the menu that aligns with your dietary needs.

Never pass up the opportunity to eat with a prospective employer.

6) Do not be afraid to tell them that you prepared some questions – remember that managers get upset if you do not ask questions. Use your question sheets to write down short notes during the interview.

7) After the interview, you should send handwritten thank you notes, so make sure to get business cards from the interviewer and anyone else involved in talking to you. Send a thank you note within two days of the interview. You may be tempted only to send a thank you email but if you

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want to stand out, send a written thank you note as well.

8) One of the most significant stressors of an interview comes after the interview when you have not heard from the company for a week… or three weeks. Before you leave the interview, find out what the next steps are in the interview process. The managers and HR team are busy with more than considering you as a new team member, so be reasonable with how much time they need to follow-up with you after the interview.

After the Interview Set aside time after the interview to think about what you have learned about the company. You can take that information and do some additional research.

With answers to your well thought out questions, you hopefully have a better understanding of the firm, their projects, the team, leadership, and overall company culture. Take some time to reflect on what you learned and think about if the company is aligned with what you want to be known for in your career (a.k.a. your personal brand).

If you have concerns, questions, or misgivings, honor that your gut is telling you to do more research. Hopefully, during the interview, the door was left open for you to follow-up and ask more questions if needed.

You may need to talk to people who used to work at the firm as well – again, LinkedIn is a source to connect with individuals who used to work there. Please do not take a job knowing there are red flags; it has the potential to be a disaster later. You owe it to your career to get answers up front before accepting a job offer.

At this point in the job search, you know what you want your personal brand to be, you have networked, done your research, and prepared for and participated in an effective interview. You mailed thank you notes to everyone with whom you met. You know approximately when to expect to hear back from them. Well done! Hopefully, you will get an offer. When you do receive any job offer, you are poised to make a thoughtful and educated decision as to whether you want to join a new company.▪ Born into a family of engineers but focusing on the people side of engineering, Jennifer Anderson (www.CareerCoachJen.com) has nearly 20 years helping companies hire and retain the right talent. She may be reached at jen@careercoachjen.com.

EnginEEr’s notEbook

aids for the structural engineer’s toolbox

Evaluation of Cold-Formed Steel Members and Connections

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

W

hen damaged cold-formed steel members or connections are identified, it is imperative they are assessed to determine the extent of the compromise to the structural integrity and the load carrying ability. Often, such assessment has to be made quickly to contain the propagation of damage to adjacent members and to protect the public welfare. Replacement of material is always an option. However, it may not be the most economical or expeditious solution.

For guidance on proper inspection considerations, the reader is encouraged to review the Cold-Formed Steel Engineers Institute’s (CFSEI) TN G500 Guidelines for Inspecting Cold-Formed Steel Structural Framing in Low-Rise Buildings. A summary of that document follows.

Use Uncoated Base Steel Thickness The available strength of a member or connection is evaluated using the uncoated base steel thickness. The amount of coating is determined by coating weight, measured in ounces per square foot (oz/ft2). For example, a G60 coating indicates 0.60 oz/ft2. For the determination of base thickness for cold-formed steel coated material, 1 oz/ft2 = 0.00168 inches per the American Society of Testing and Materials’ ASTM A653. For this example, G60 coated sheet contributes 0.001 inches (0.60 x 0.00168) to the measured thickness.

Consider Using the Actual Yield Strength of the Member When evaluating a member’s strength, it would be prudent to estimate, or determine by testing, the actual yield strength of the member. The American Iron and Steel Institute’s AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members, Chapter F, indicates that the mean value of the material factor, Mm, which is the ratio of the minimum specified yield stress to the as-delivered yield stress, may be taken as Mm = 1.10. Thus, for remediation computations, it may be permissible to use 1.10Fy. In fact, testing has shown that Grade 33 material is typically 40 to 45 ksi.

Damage to cold-formed members and connections can vary significantly in type and degree. CFSEI TN G500 provides guidance on evaluating the capacity of the member and connection. Common damage includes: Large Web Holes AISI S100 enables the strength evaluation of cold-formed steel members with web holes. For hole patterns that are not repetitive, as defined by the provisions of S100, the AISI S100 Commentary provides guidance regarding the use of a “virtual hole method” for assessing the available strength. CFSEI TN G900, Design Methodology for Hole Reinforcement of Cold-Formed Steel Bending Members, provides guidance for reinforcing.

Large Flange Holes

Use Realistic Loads Do not use conservative loads. For example, do not use a design load of 50 psf when 40 psf may be satisfactory per the American Society of Civil Engineers’ ASCE 7.

Based on a study of actual floor loads, the American Institute of Steel Construction’s AISC Design Guide 11 recommends using a live load of 11 psf for office floors and 6 psf for residential floors when performing a floor vibration analysis.

AISI S100 has specific design provisions in Section B2.2 for the evaluation of uniformly stiffened compression elements with holes. The specification is silent regarding holes in partially stiffened and unstiffened compression elements. In the absence of such provisions, one may consider applying the Section B2.2 provisions to partially stiffened and unstiffened compression elements.

In such cases, the safety factor should be

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taken as 2.0 in accordance with AISI S100 Section A1.2.

For large holes in the tension flange, the nominal moment capacity may be evaluated using the following provisions of AISC 360-10, Specification for Structural Steel Buildings, Section F 13, Proportions of Beams and Girders: If FuAfn ≥ YtFyAfg, no modification is required.

Where Afn = net tension flange area, Afg = gross tension flange area, Yt = 1.0 for Fy/Fu ≤ 0.8, otherwise 1.1 If FuAfn < YtFyAfg, Nominal Flexural Strength = Mn = (FuAfn/Afg)Sxt Coped Web A profile having one or more flanges removed results in a web element with a free edge. The available shear buckling strength for a web element may be determined by the provisions of AISI S214, North American Standard for Cold-Formed Steel Framing – Truss Design: Coping is permitted in accordance with the following, as applicable: a) At a coped support location with a coped flange and a bearing stiffener having a moment of inertia (Imin) greater than or equal to of 0.161 in.4 (67,000 mm4), the available shear strength [factored resistance] shall be calculated in accordance with Section C3.2 of AISI S100 and reduced by the following factor, R: R = 0.976 - 0.556c - 0.532dc < 1.0 h h where c = Length of cope dc = Depth of cope h = Flat width of web of section being coped Imin = Moment of inertia determined with respect to an axis parallel to the web of the member t = Design thickness of section being coped b) At a coped support location with a coped flange where a bearing stiffener having a moment of inertia (Imin) less than 0.161 in.4 (67,000 mm4), the strength at the heel is governed by web crippling determined in accordance with Section C3.4 of AISI S100 and reduced by the following factor, R:

R = 1.036  0.668c  0.050dc < 1.0 h h The above equations shall be applicable within the following limitations: h/t ≤ 200, 0.10 < c/h <1.0, and 0.10 < dc/h < 0.4 Notched or Coped Flanges A notched or coped flange may result in a free edge or an unstiffened compression flange element. The available member flexural strength may be computed by treating the flange as an unstiffened compression element in accordance with AISI S100 Section B3.1.

Member Splice If it becomes necessary to splice two coldformed steel members to achieve a desired member length, CFSEI TN W106, Design for Splicing of Cold-Formed Steel Wall Studs, offers design guidance. The two most common types of splices used in cold-formed steel construction are the “back-to-back splice” and the “track capped splice.” The design methodology presented in TN W106 is based upon the eccentrically loaded connection elastic

method as presented in Part 7 of the AISC Manual as well as in Chapter 8 of Steel Design

by William Segui.

Member Not Meeting Manufacturing Tolerances If the cross-section profile does not comply with the AISI S200, North American Standard for Cold-Formed Steel Framing – General Provisions, manufacturing tolerances, careful measurement of the cross-section, and the application of AISI S100 provisions may be employed to determine the available strength.

Dings and Dents Generally, small dings and dents have no impact on the structural integrity of a member; however, engineering evaluation is required when determining the impact of a ding or dent in a compression element of the cross-section. For example, if the flange or flange lip has been bent inward or outward, the member may be analyzed using the provisions of AISI S100 by utilizing the in-situ dimensions of the cross-section. Dings or dents in tension members are likely of little consequence on the available strength and can usually be discounted. During placement

of a C-section, it may be possible to rotate the member and locate the ding or dent on the tension side of a flexural member or at a location of lesser applied moment.

In addition to evaluating a damaged member or connection and developing a remediation plan, responsibility for remediation should also be addressed and understood. AISI S202, the Code of Standard Practice for ColdFormed Steel Structural Framing provides guidance pertaining to the responsibilities of the various individuals involved in the remediation work.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

Roger LaBoube is Curator’s Distinguished Teaching Professor Emeritus of Civil Engineering and Director of the WeiWen Yu Center for Cold-Formed Steel Structures at the Missouri University of Technology. Roger is the current chairman of the American Iron and Steel Institute’s Committee on Framing Standards. Roger can be reached at laboube@mst.edu.

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February 2018

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Phone: 770-514-2268 Email: langston.bates@bekaert.com Web: www.bekaert.com Product: Steel Wire Strand, Stay Cables, PC Strand, PT Tendon Strand Description: Bekaert is a market leader in steel wire transformation and coating technologies. We produce steel reinforcement solutions for bridges that are Made and Melt in America. Our product portfolio includes Galvanized or Black Cable Stays, PC Strand for Prestressed Concrete, and Galvanized or Black Strand for Post-Tension applications.

Cast Connex Corporation

Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Cast Steel Nodes and Connectors Description: The use of cast steel nodes and connectors in steel bridge structures can provide improved fatigue performance, enhanced structural resilience, and can reduce the total life-cycle cost of pedestrian, road, and rail bridges.

Dynamic Isolation Systems

Phone: 775-359-3333 Email: sales@dis-inc.com Web: www.dis-inc.com Product: Lead Rubber Bearing (LRB) for Base Isolation of Bridges Description: Allows bridges to survive earthquakes with no damage while providing cost savings on substructures due to reduced forces. LRBs require no maintenance and are extremely durable.

Fibercon International Inc.

Phone: 724-538-5006 Email: info@FiberconFiber.com Web: www.fiberconfiber.com Product: Steel Reinforcing Fibers Description: FIBERCON steel fiber reinforcement, when distributed in the concrete paste, becomes an integral part of the matrix providing a crack interceptor at each randomly placed fiber. High fiber count allows FIBERCON fibers to provide reinforcement against micro-crack growth in all directions and keeps microcracks from becoming macro-cracks.

LUSAS

Con-Struct Bridges

Phone: 616-261-8630 Email: gnelson@tegcivil.com Web: www.constructbridge.com Product: Con-Struct Prefabricated Bridge System Description: Offers many benefits and has provided a cost effective and extremely durable answer for prefabricated bridges throughout the United States.

With options that can meet all of your bridge building needs, Con-Struct is the preferred prefabricated bridge choice when building new or replacing existing bridges.

DEWALT

Phone: 845-230-7533 Email: mark.ziegler@sbdinc.com Web: www.DEWALT.com Product: Power-Stud HD5 Expansion Anchors Description: A fully threaded, torque-controlled, wedge expansion anchor. The anchor is manufactured with a hot-dip galvanized carbon steel body and stainless steel expansion clip. Nut and washer are included. Suitable base materials include normal-weight concrete, sandlightweight concrete and grouted concrete masonry.

Tested in accordance with ASTM E488.

Dlubal Software

Top Firms (Engineering & Construction), Suppliers, Coatings, Software Developers/Vendors

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: Capable of linear, non-linear, static and dynamic analysis, RFEM is complete with moving load generation, influence lines, cable form-finding, parametric modeling, and multi-material design considerations. The powerful yet user friendly FEA software is seamless in the design and analysis of pedestrian and highway cable-stayed, suspension, arch, and beam bridge structures.

Phone: 646-732-7774 Email: terry.cakebread@lusas.com Web: www.lusas.com Product: LUSAS Bridge / LUSAS Civil & Structural Description: Finite element analysis software for accurate and cost-effective design of steel and concrete bridges and other structures. Use for fundamental frequency, seismic, dynamic, nonlinear, buckling, fatigue, staged construction, soil-structure and rail track-structure interaction. Vehicle-load optimization facilities provide worst-case loading patterns.

AASHTO and other design codes are supported.

New Millennium Building Systems

Phone: 260-969-3582 Email: rich.madden@newmill.com Web: www.newmill.com Product: Stay-in-place Steel Bridge Deck Description: New Millennium is a nationwide provider of custom-engineered and manufactured steel building systems, including stay-in-place steel and concrete form systems for bridges. Our RhinoDek® solution is galvanized and polymer laminated for spanning over brackish and salt water, for new construction and bridge rehabilitation.

Nordic Structures

Phone: 514-871-8526 Email: arenaud@nordicewp.com Web: www.nordic.ca Product: Nordic Lam Description: Nordic Structures offers a range of turnkey services covering all the steps of wood bridge design and construction. The culture, experience, and expertise of our team set Nordic Structures apart as a company able to meet the highest standards of quality and performance.

For more information, visit the website.

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S-FRAME Software

Phone: 203-421-4800 Email: info@s-frame.com Web: s-frame.com Product: S-CONCRETE Description: Efficient concrete design and detailing solution available for column, beam, and wall sections.

Easily modify design parameters to generate the optimum design. Optimize a single section or evaluate thousands of concrete sections at once. S-CONCRETE generates comprehensive reports with clause references, equations employed, intermediate results, and diagrams.

Simpson Strong-Tie

Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: SET-3G™ High-Strength Anchoring Adhesive Description: The latest innovation in epoxy adhesives.

The high-strength anchoring adhesive can be installed in extreme concrete temperatures from 40°F to 100°F, as well as in dry or water-filled holes in concrete. SET3G provides the high bond strength values needed for a variety of adhesive anchoring applications.

Product: FX-70® Structural Piling Repair and Protection System Description: Repair damaged concrete, steel, or wood piles in place with the FX-70 system that utilizes custom fiberglass jackets and high-strength grouting materials. The FX-70 system eliminates the need to dewater the repair site or take the structure out of service, dramatically reducing the overall cost of restoring damaged structures.

Strongwell

Phone: 276-645-8000 Email: bmyers@strongwell.com Web: www.strongwell.com Product: GRIDFORM™ Description: A prefabricated fiber reinforced polymer (FRP) double-layer grating, concrete-reinforcing system with integral stay-in-place (SIP) form for vehicular bridge decks. Eliminates expensive and labor-intensive rebar and reduces overall project time, while providing a superior end product.

Trimble

Phone: 770-426-5105 Email: kristine.plemmons@trimble.com Web: www.tekla.com Product: Tekla Structures Description: Higher automation of fabrication and 4D project management. Extensive range of steel profiles including elliptical and tubular, and individual connection details with welds and bolts save time.

Drawings and reports can be automatically generated from the constructible 3D model. Detailed model also brings efficiency to bridge maintenance and repairs.

Listings are provided as a courtesy.

STRUCTURE® magazine is not responsible for errors.

award winners and outstanding projects

Spotlight

Undiluted

By Jonathan Bayreuther, P.E. McNamara·Salvia Structural Engineers was an Outstanding Award Winner for its Exchange at 100 Federal Street project in the 2017 Annual Excellence in Structural Engineering Awards Program in the Category – New Buildings under $20M.

I

n the beginning, there was a folded sheet of graph paper, all sharp angles and crisp lines. It was a simple concept for a bold new entry pavilion, dining, and dynamic event space for the 41-story, 1971 office building at 100 Federal Street.

Situated on a busy thoroughfare in the heart of Boston, MA, the purpose of the soaring 50 foot-tall, glass-covered angular addition would be to create an inviting, year-round draw for patrons and pedestrians alike. Lofty goals to be sure, but inevitably strong design concepts need to be diluted to something less striking, or cheaper, or easier. Don’t they?

Embracing this challenge and determined to disprove the norm, the Architect (Perkins+Will) and Structural Engineer (McNamara·Salvia), set out on an intensely collaborative design journey, determined to deliver a space to match the concept’s design intent and exceed the Owner’s (Boston Properties) expectations.

With these imperatives in mind, McNamara·Salvia and Perkins+Will began a series of conceptual working sessions to decide on design priorities. Given the sharp faceted exterior, and the intent for the entire façade and roof to read as a single folded sheet of glass, the desire was to keep all elements on the interior as sharp and narrow as possible. Initial structural concepts included multiple standard steel shapes such as wideflanges, tubes, or fabricated trusses, some of which would need to be enclosed in a metal panel or gypsum wrap to achieve the sharpedged goal. None of these could achieve a narrow enough profile (less than six inches wide including finishes) and still span the required seventy-five feet.

Built-up box sections might have met the desired aesthetic, but fabrication costs would have been prohibitively high, as would the corresponding field-welded connections.

In the interest of cost and ease of erection, field-bolted connections were taken as a requirement. From there, McNamara·Salvia, building on an ongoing collaborative relationship with Cives Steel in Augusta, Maine,

Courtesy of Perkins+Will

presented a simple, yet ironically innovative idea: solid plate steel with exposed bolted connections. The shapes could be cut from standard 50 ksi plate stock, entirely shopwelded and field-bolted, and would require no architectural finishing wrap. Where rolled shapes might be more efficient for weight, finishes would have more than negated any savings, and the solid plate shapes enhance the angular feel of the interior space.

Cognizant that meeting budget expectations were a priority, a pricing exercise, again building on collaborative relationships with Cives Steel and including Turner Construction, was performed comparing conventional rolled shapes to the solid plate concept. Solid plate steel was found to be more cost-effective than all other options for the depths and widths required by the design, even factoring in allowances for carefully specified limited Architecturally Exposed Structural Steel (AESS).

With the Owner’s blessing on solid plate with exposed connections, a new series of working sessions began. Tracing paper and pencil gave way to Rhinoceros and Revit models on the Architectural side, and RAM Elements and Revit on the Structural side, and concepts for simple double-shear plated slipcritical connections were tested. Before final documentation, a scale 3-D printed mockup of one of the connections was built for owner and design team review.

Like many buildings, the partnership of Architect and Engineer is tested in the details.

The structure needed to be optimized for weight and connection geometry to control cost and increase efficiency, which can often conflict with aesthetic intent. The main structural system is a series of solid steel plate portal frames at fifteen feet on-center that start at street level, and twist and bend up and over the roof of the pavilion. The frame members

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range from four inches thick by twenty-eight inches deep to two inches thick by eighteen inches deep. These frames are laterally braced at five feet on-center by smaller plates that also serve as curtainwall mullions. Initial modeling resulted in framing and connections optimized for weight and bolt count.

From there, the most minor adjustments were made in member or connection geometry to smooth jumps in size between members or bolt counts between connections. Thickening of the main members was avoided as much as possible since ¼ inch of additional thickness on the deepest member would add one ton of steel. Member depths were also selectively increased to result in a smooth gradient from deep to shallow along the plane of the roof.

In the end, the increase in steel tonnage was limited to less than 10% over baseline, and piece sizes and connections were repeated as often as possible.

With little else in the way to distract the eye, steel in its simplest rolled form is celebrated throughout the structure. Exposed, bolted connections are rhythmic down the length of the space and smoothly blend into the uniformity of the design while clearly showing their purpose. Even the lighting scheme is tuned to play on the dynamic shapes formed by the white-painted steel members to let the angles shine through the glass. The successful realization of the aesthetic experience is the result of intentional design and construction team collaboration. From folded paper to a striking steel space frame, the concept remains true and undiluted.▪ Jonathan Bayreuther is a Senior Project Manager with McNamara·Salvia Structural Engineers, Boston, MA. He may be reached at JBayreuther@mcsal.com.

Are You Taking Advantage of Every Member Benefit?

NCSEA News

News form the National Council of Structural Engineers Associations

NCSEA Member Portal Provides More Benefits for SEA Members

The NCSEA Member Portal contains member benefits that you must log in to access. Established in 2015, the Member Portal was created to host member-only documents, contact information, and member perks. As a member of your state’s SEA or member organization (SEAOC, SEAoO, FSEA, etc.) you are also a member of NCSEA and receive additional benefits through us! These benefits are now easier to find and access. After compiling the feedback we received, we combed through the Member Portal as well as www.ncsea.com to streamline the process of accessing content, creating a better user experience.

Recently, emails have been sent to SEA members containing login information, but our information is only as good as the information you use to renew your membership with your state organization.

Meaning, if you haven’t updated your information with them in a while you might be logging in with an old email; that’s ok, you can update it as soon as you login. If you haven’t received this email or need additional help logging in, please contact the NCSEA office at ncsea@ncsea.com.

Fast forward a bit; you’ve logged in, now what? What do you have access to? Once you’ve logged in, you will see a new tab on top titled “Member-Only Resources.” This drop down gives you access to four, easy to follow categories: SEA Resources, NCSEA Committees, Young Member Groups, and ICC Publications. So what is included?

• Tools for Your SEA • A list of Recommended Speakers to use for your webinars or in-person meetings • Benchmarking Data - Compare your actions with other SEAs. • Outreach Resources - Tools to better connect with the media and general public.

• Free Recordings from NCSEA Communication Webinars.

• NCSEA Committee Minutes - An inside look at what NCSEA Committees are doing.

• Young Member Group Resources • How do you start a new YMG? What tools will help you succeed?

• ICC Publication Discounts - visit this page to save on the materials you need!

• Your NCSEA Record - Keep your contact information and preferences up-to-date to ensure delivery of NCSEA and other membership-related materials.

• And more!

The best way to utilize these additional benefits is to get started now. Login, take a look around, and make sure you are getting the most of your membership by using all the assets it offers!

Call for NCSEA Resilience Committee Corresponding Members NCSEA’s Code Advisory Resilience Subcommittee has solidified eight Voting Members and now requests each member organization to name a Corresponding Member. SEA Boards are asked to send contact information for selected members, or any questions, to David Bonowitz, at dbonowitz@att.net.

If your SEA has an active Resilience program or committee, the chair or vice chair (or their designee) would be a good choice as your Corresponding Member. If not, an active member of your Code or other technical committee would be a strong choice.

The ideal Corresponding Member will be an active SEA member with committee experience and a demonstrated interest in design, planning, or policy for natural hazards risk reduction. The role of each Corresponding Member is to represent your SEA, to be a liaison between your local efforts and the national committee, and to organize interested members within your own SEA. NCSEA members interested in serving as Corresponding Members are encouraged to contact their SEA Boards for endorsement. For more about the Resilience Subcommittee, please visit their webpage: www.ncsea.com/committees/resilience.

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Visit the Careers page under Resources on www.ncsea.com to sign up!

NCSEA’s Enhanced Webinar Subscription gives members access to: • 20+ live webinars annually, featuring experts in the field.

• NEW! An unlimited number of free Continuing Education certificates • Unlimited access to NCSEA’s Recorded Webinar Library 24/7/365 • NEW! The newly enhanced, user-friendly Education Portal to provide you easy access to your education history.

Subscribe now on www.ncsea.com!

Young Member Group Spotlight NCSEA encourages SEA Young Member Groups to submit their activities and events to be highlighted on the Young Member Group Spotlight page on www.ncsea.com. Events can be emailed to Young Member Group Support Committee New Media Coordinator, Maher Eltarhoni at meltarhoni@360enggroup.com.

The most recent YMG Spotlight comes from the Structural Engineers Association of Colorado. On September 27th, the SEAC YMG held an AASHTO (American Association of State Highway and Transportation Officials) Bridge Review Session for young engineers who were preparing to take the P.E. or S.E. exam in fall. Speaker Jon Emenheiser, who practices bridge engineering locally, has taken the 8 hr. P.E. exam, the 16 hr. S.E. exam, and the California S.E., led the study session for the young engineers.

His presentation included AASHTO P.E. and S.E. exam overview, bridge design overview, code references, and design examples.

The format was not just a presentation; it also served as a study session, allowing attendees access to someone with a wealth of knowledge in an area of practice that most engineers designing buildings do not typically have access to. This event not only included valuable information, but allowed time for discussion, specific questions, and example problems.

NCSEA Webinars February 27, 2018 Designing for Resilience: The Role of the Structural Engineer But what is “resilience” and how will it affect structural engineering? In brief, resilience-based design shifts the emphasis from the safety of buildings to the recovery of communities from natural hazard events.

Speaker: David Bonowitz, S.E. March 6, 2018 Welding Problems and Practical Solutions This webinar will describe welding-related problems that may be encountered and offer practical solutions that will resolve the problem in a dependable and economical manner.

Speaker: Duane K. Miller, Sc.D., P.E. March 29, 2018 Snow Drift Loading – Current Procedures and Future Directions The webinar will provide a detailed review the current ASCE 7 provisions for snow drift loading as well as expected future improvements.

Speaker: Michael O’Rourke, P.E., Ph.D. Register at www.ncsea.com.

Webinar time: 10:00 am Pacific, 11:00 am Mountain, 12:00 pm Central, 1:00 pm Eastern.

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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February 2018

News from the National Council of Structural Engineers Associations

NCSEA and the ICC signed an agreement at the end of 2017 to join forces on NCSEA’s Structural Engineering Emergency Response (SEER) 2nd Responder Roster to create a single database between the two organizations of volunteers willing and able to serve when disasters strike.

One of main issues at the focus of NCSEA’s SEER Committee is management of this national database of trained 2nd Responders (www.ncsea-seer.com). This is a fully interactive database that can be updated as needed by the participant and searched to obtain a list of participants by certification and location. In the aftermaths of Hurricanes Harvey and Irma in 2017, seventy-five 2nd Responders were deployed from the database to assist in damage and safety assessments.

The SEER 2nd Responder Database is only as good as the structural engineers who are willing and able to volunteer and have created and updated their records. If you have post-disaster assessment training, create a record today. If you are interested in bringing post-disaster assessment training to your local area, reach out to your SEA’s SEER Committee or contact the national NCSEA SEER Committee.

Secure Access to the Highest-Quality Webinars at an Incredible Value

NCSEA News

NCSEA, ICC Join to Expand 2nd Responder Roster Database

Learning / Networking

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

SEI/ASCE Live Webinars Learn from the Experts

February 7 – 21st Century Bridge Evaluation: New Technologies and Solutions February 9 – Advanced Topics in Seismic Design of Nonbuilding Structures and Nonstructural Components to ASCE 7-16 Individual Certificate Fee Discontinued. Register at Mylearning.asce.org for these and much more.

Taking the S.E./P.E. Exam this Spring?

ASCE Exam Review Courses take the guesswork out of your study plan and prepare you for exam day. Qualified experts deliver interactive courses that will build your confidence. You will receive access to recorded webinars and reference material. Group rates are available for 2 or more engineers preparing in the same location. Register today! www.asce.org/live_exam_reviews

New Books from ASCE Press - www.asce.org Engineering Ethics: Real World Case Studies

Entrusted by the public to provide professional solutions to complex situations, engineers can face ethical dilemmas in all forms. In Engineering Ethics: Real World Case Studies, Starrett, Lara, and Bertha provide in-depth analysis with extended discussions and study questions of case studies that are based on real work situations.

Public Speaking for Engineers

Veis takes readers step-by-step through the process of preparing for a presentation including speech planning, design, and delivery, emphasizing the importance of understanding your audience.

Join Us at Three NEW Special Large-Group Sessions April 19 at Structures Congress in Ft. Worth Dialog with the experts on:

What is the Appropriate Process for the Design of Steel Connections: Contractor Design VS Engineer of Record Design?

How to be a Powerful Leader Tools and techniques to enable leaders to set strategic direction, align resources, inspire action, and be accountable for results, for you and your firm to: • Improve employee engagement • Motivate a changing workforce • Balance competing priorities • Simplify complexity Addressing Challenges in Structural Engineering Education and Practice Discuss strategies with NAE members and practicing structural engineers.

Learn more and, for the best rate, register by February 14 at www.structurescongress.org.

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February 2018

SEI Student Career Networking Event April 20 at Structures Congress in Ft. Worth

Employers: Sign up now to participate, be included in event promotions, and receive student profiles in advance of the event. www.asce.org/SEI-Sustaining-Org-Membership.

Students: Plan now to connect one-on-one with employers for SE positions and internships. Learn more at www.asce.org/SEI-Students.

SEI Online

Check out SEI News at www.asce.org/SEI including: SEI/ASCE Post-Disaster Assessment in St. Thomas

SEI Graduate Student Chapters and Growing

Membership

SEI Elite Sustaining Organization Members SEI Elite Sustaining Organization Members enjoy complimentary participation in the SEI Student Career Networking Event, April 20 at Structures Congress 2018 in Ft. Worth.

Reach more than 30,000 SEI members year-round with SEI Sustaining Organization Membership. Show your support for SEI to advance and serve the structural engineering profession. Learn more and join today at www.asce.org/SEI-Sustaining-Org-Membership.

Join or Renew SEI/ASCE Membership

For innovative solutions and learning, to connect with leaders and colleagues, and enjoy member benefits. Make sure to select SEI with ASCE membership to receive benefits such as SEI Member Update monthly e-news opportunities and resources â&#x20AC;&#x201C; visit www.asce.org/myprofile or call ASCE Customer Service at 800-548-ASCE (ext. 2723).

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

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The Newsletter of the Structural Engineering Institute of ASCE

SEI Graduate Student Chapters (GSCs) enhance the education of students preparing to become structural engineers and engage student members in SEI for a successful transition from college to career. GSCs organize and manage visiting speakers, prospective student events, field trips, participate in SEI, perform outreach activities, and more. Participating in a GSC can help members broaden their view of what it means to be a structural engineer.

Undergraduate students are also invited to connect and participate.

Georgia Tech University of Central Florida Lehigh University University of Illinois, Urbana Northeastern University University of Texas, Arlington Notre Dame University University of Wyoming Oregon State University Virginia Tech Penn State University West Virginia University Learn more at www.asce.org/SEILocal.

Structural Columns

Students and Young Professionals

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Practice Guidelines Currently Available CASE 962 – National Practice Guidelines for the Structural Engineer of Record The purpose of this document is to give firms and their employees a guide for establishing Consulting Structural Engineering Services and to provide a basis for dealing with Clients generally and negotiating Contracts in particular. Since the Structural Engineer of Record (SER) is usually a member of a multi-discipline design team, this document describes the relationships that customarily exist between the SER and the other team members, especially the team leader. Further, this Guideline promotes an enhanced Quality of Professional Consulting Structural Engineering Services while also providing a basis for negotiating a fair and reasonable compensation. Additionally, it provides a basis for Clients to better understand and determine the Scope of Services that the Structural Engineer of Record should be retained to provide.

CASE 962-A – National Practice Guidelines for the Preparation of Structural Engineering Reports for Buildings The purpose of this document is to provide the structural engineer a guide for not only conducting conditional surveys, code reviews, special purpose investigations, and related reports for buildings but includes descriptions of the services to aid with the client risk management communication issues. This Guideline is intended to promote and enhance the quality of engineering reports. A section of this Guideline deals specifically with outlines for various reports.

While it is not intended to establish a specific format for reports, it is believed there may be certain minimal information that might be contained in a report. The Appendix includes disclaimer language which identifies statements one might consider to clarify the depth of responsibility accepted by the report writer.

Currently, the coordination and completeness of Documents vary substantially within the structural engineering profession and among the various professional disciplines comprising the design team. The SER’s goal should be meeting both the owner’s and the contractor’s needs by producing a complete and coordinated set of Documents. Owners and contractors generally understand that some changes to the Documents will occur, because they realize that no set of Documents is perfect. The SER must focus on completeness, coordination, constructability, and the reduction of errors in order to minimize potential changes.

CASE 962-B – National Practice Guidelines for Specialty Structural Engineers (Updated in 2017) This document has been prepared to supplement CASE’s National Practice Guidelines for the Structural Engineer of Record by defining the concept of a specialty structural engineer and the interrelation between the specialty structural engineer and the Structural Engineer of Record. CASE encourages the concept of one Structural Engineer of Record for an entire project. However, for many, if not most projects, there may be portions of the project that are designed by different specialty structural engineers. The primary purpose of this document is to better define the relationships between the SER and the SSE and to outline the usual duties and responsibilities related to specific trades. This is done for the benefit of the owners, the PDP, the SER, the SSE, and the other members of the construction team. The goal is to help create positive coordination and cooperation among the various parties.

You can purchase these and the other CASE Risk Management Tools at www.acec.org/case/news/publications.

Share Innovative Ideas!

Does your firm have an innovative idea or method of practice?

Looking to get more involved in short duration projects?

We are inviting you to “share the wealth” and submit a proposal for a web seminar topic, publication, or education session you would like to see CASE present at an upcoming conference.

Our forms are easy to use, and you may submit your information

via email. Go to www.acec.org/coalitions and click on the icon for Idea Sharing to get started.

Questions? Contact us at 202-682-4332 or email Katie Goodman at kgoodman@acec.org. We look forward to helping you put your best ideas in front of eager new faces!

Donate to the CASE Scholarship Fund!

The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at a minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given $25,000 to help engineering students pave their way to a bright future in structural engineering.

We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest

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young talent from a dwindling pool of engineering graduates.

One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives for educational support.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction, and you do not have to be an ACEC member to donate! For more information contact Heather Talbert at htalbert@acec.org to donate.

February 2018

11:00 am – 12:30 pm The Good and the Bad of Delegated Design: How to Work With/As a Specialty Structural Engineer Moderator/Speaker: Kevin Chamberlain, DeStefano & Chamberlain Inc. 1:30 pm – 3:30 pm Construction Dispute Resolution through Forensic Engineering Moderator/Speaker: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. 3:30 pm – 5:00 pm Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable Moderator: Corey Matsuoka P.E., SSFM International, Inc.

Save The Date!

CASE’s Business of Structural Engineering Seminar

June 6 – 8, 2018; Anaheim, CA

Once again CASE will put on the industry’s only seminar dedicated solely to improving your firm’s business practices and risk management strategies. Join us and learn about The Business of Structural Engineering for training and collaboration with industry leaders and project managers from firms of all sizes, intended to improve your structural engineering practice.

Immerse yourself in topics designed to help engineers learn better ways of reducing areas of risk and liability on projects

while learning of tools to implement better business practices within your firm.

The Seminar is geared towards Owners, Principals, Project Managers, and Risk Managers – If you are concerned with risk management, new trends, and profitability, you cannot afford to miss this event!

Registration for the event will open Mid-March, seats will be limited.

For more information about this seminar, contact Heather Talbert, htalbert@acec.org or 202-682-4377.

Business of Design Consulting March 14 – 17, 2018

Managing your A/E business for success requires technical knowhow and a broad awareness of today’s best multi-disciplinary business practices. Firm managers must understand the rules of management/finance and how they work in the real world.

To meet the business challenges in the current economy, managers need to: • Understand the intricacies of human relations and related legal elements; • Create and manage client relationships and client expectations; • Manage risk and draft/adapt contracts; • Know the fundamentals of business development; and • Understand ownership transition and employee satisfaction factors.

ACEC’s highly regarded Business of Design Consulting course is a unique playbook for building leadership and managing your firm at the most effective levels. Join us in Phoenix, AZ, March 14 – 17, where ACEC’s expert faculty of industry practitioners will cover contemporary best practices and critical operational management methods. The program agenda highlights current strategies for critical, need-to-know business topics that will keep your business thriving despite a churning business environment.

Attendees will learn specific skills and techniques to help them manage change and build success in performance management, strategic planning and growth, finance, leadership, ownership transition, contracts and risk management, marketing, and more!

For more information and to register, visit http://bit.ly/2qKFIkC.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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February 2018

CASE is a part of the American Council of Engineering Companies

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

The following CASE Convocation sessions are scheduled to take place on Friday, April 20: 9:30 am – 10:30 am Managing Design Professionals’ Risk in the Design and Construction of Property Line Building Structures Moderator: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. Speaker: Kriton A. Pantelidis, Esq., Welby, Brady & Greenblatt, LLP

CASE in Point

CASE Risk Management Convocation in Fort Worth, TX

Structural Forum

opinions on topics of current importance to structural engineers

Structural Collapse during Construction How Should the SER Respond?

By Jeremy L. Achter, S.E., LEED AP

S

tructural Engineers of Record (SER) should all be well trained by insurance providers and legal professionals to avoid the realm of means and methods of construction – that sometimes grey area where the contractor is responsible for temporarily supporting partially erected structural elements even though they may not fully understand the statics of force transfer, temporary construction loads, and effects of environmental loads that may occur. To further clarify responsibility, the construction documents usually include verbiage to indicate that the contractor shall be responsible for providing adequate temporary shoring and bracing until the entire structural system is complete.

However, there may come a time when you are called to a project site to assess the damage caused by a partial or full structural collapse that occurred during construction. The collapse could be attributed to one of many factors.

Defining the Scope and Doing the Assessment Before visiting the site, it is important to protect yourself and your firm. Depending on the specific situation, you are probably not completing this assessment pro bono or as part of your original scope of services. If this is the case, you should negotiate a change in scope for the additional work and track all time and expenses separately. Your insurance carrier likely has an example contract to use in this situation.

Time is of the essence. Every day the site is down, the overall project schedule is threatened. The contractor may shut down the site, or a portion of it, until a report is completed that assesses the situation. The report may be completed by the SER or the builder’s insurance carrier, or both. You should only go to the site after your client, the contractor, and the owner agree on your purpose and role at the site. Once this groundwork is complete, get to the site as soon as possible and complete the assessment expeditiously before any contamination of the evidence occurs.

To exercise your due diligence, walk the site with a set of plans while accompanied by the job site superintendent or their designated representative. Make your intentions and

scope limitations clear and do not deviate from them. Depending on the agreement with your client, your only responsibility may be to help the contractor determine what elements are salvageable, repairable, or need to be replaced. Assessing remaining shoring or temporary shoring of the collapse may be outside your scope of work and may open the door to increased liability. If the contractor is making an insurance claim, their insurance carrier will likely have a representative come to the site to complete an assessment similar to yours. This should not affect what you are doing; it is just something to be aware of.

While on site, clearly indicate which elements appear to be damaged by highlighting beams, columns, or any other damaged element on a set of plans. Make notes and take pictures of the damage. In a multi-story structure, upper-level framing may be damaged beyond repair but framing below that level might be okay to remain in place. For example, if an upper-story column has buckled, try to determine if the damage extends to the framing or connections below. If no damage is visible in the framing or connections below, a new column may be able to be spliced just above the floor line. If testing is required to assess a weld that you suspect may be compromised, indicate this in your report so a testing agency can be hired as soon as possible.

When assessing a failure, it is essential to follow the load path through the members and connections. When a connection has failed, a closer observation may reveal that failure transferred unexpected moments into the column. In these cases, check the plumbness and straightness of the column. Also, consider what damage might have occurred to unseen structural like elements like base plates and footings. Finally, consider what type of repairs might be needed. Is a repair feasible or more economical than full replacement?

Dealing with the Media Dealing with the media is another aspect that may need to be considered. While the following is not legal advice or a legal opinion, and

every situation is different, it is suggested that the engineer not talk to the media, especially if an investigation will be on-going. While it may seem harmless, your comments may incriminate you or jeopardize your firm’s access to insurance coverage. You should also be careful not to incriminate others, as that might be seen as slander.

If the building official contacts you, you should cooperate with their investigation and answer their questions. However, it is best to verify the identity of the person who is contacting you. There have been cases where a builder contacted the design professional acting as a building official and obtained information that eventually led to the engineer being sued. Also, if you suspect that the collapse was a result of a design flaw, refrain from commenting and discussing the situation with anyone other than your insurer and lawyer.

Learn Something A partial or complete collapse during construction can be devastating, but don’t forget that it can also be a learning opportunity. In the middle of this unfortunate circumstance, look for opportunities to learn and improve.

Prepare Preparing in advance for the possibility of a collapse on your project may be a wise consideration for every SER and every consulting office. Considering that potential liability issues are involved, it may be well to receive recommendations and training from your firm’s insurer. They may have training materials and a list of specific do’s and don’ts related to these situations that the SER should be aware of. Any efforts of any type related to dealing with a collapse should be coordinated through a designated individual/official in the firm to maintain consistency and protect the firm’s interests.▪ Jeremy L. Achter is an Associate Principal with ARW Engineers, in Ogden, Utah.

Jeremy is a member of STURUCTURE’s Editorial Board and can be reached at jeremya@arwengineers.com.

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

STRUCTURE magazine

58

February 2018

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