STRUCTURE magazine | March 2017

STEEL PRODUCTS

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

SPECIAL SECTION

March 2017 Wind/Seismic – Inside: Provo Tabernacle 2017 Structures Congress

Denver, Colorado April 6 – 8

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CONTENTS Columns/Departments

Features 34 BRB Mast-Frames

EDITORIAL

7 SEI’s New Mentoring Program

By Donna Friis, P.E., et. al

By Leo Panian, S.E.

PRACTICAL SOLUTIONS

38 Historic Renovation of the Provo Tabernacle

9 Damping Wind-Induced Vibrations on Low-Level Lighting Poles

By Shane C. Morrison, Ph.D. and

STRUCTURAL PERFORMANCE

ENGINEER’S NOTEBOOK

12 Building Resiliency

By Brandon Winter, P.E. and Damon Ho, P.E. STRUCTURAL PRACTICES

HISTORIC STRUCTURES

By Paul Noyce and Gina Crevello

60 Golden Gate Bridge

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

TECHNOLOGY

22 Impacts to the Built Environment

INSIGHTS

By Jennifer Strauss, Ph.D. and

64 Architectural Engineering

Richard Allen, Ph.D.

66 The Logic of Ingenuity – Part 4

By Jon A. Schmidt, P.E., SECB

By Gregory K. Michaelson, Ph.D. and

LEGAL PERSPECTIVES

Karl E. Barth, Ph.D. CONSTRUCTION ISSUES

30 Are Your Roof Members Overstressed?

By James M. Fisher, Ph.D., P.E. and

68 Indemnification of the Structural Engineer

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

70 The Art of Hiring an Engineer

PROFESSIONAL ISSUES

52 The Future of Making Structural Things in the Construction Industry

Wade Vorley, AIA

49 Steel Construction

By Larry Kahaner

IN EVERY ISSUE 8 Advertiser Index 72 Resource Guide (Software Updates) 76 NCSEA News 78 SEI Structural Columns 80 CASE in Point

BUSINESS PRACTICES

Thomas Sputo, Ph.D., P.E., S.E.

By Zeno Martin, P.E., S.E. and

By Tony Cameron, P.E.

OUTSIDE THE BOX

26 A New Shape for Short Span Steel Bridges

54 Condensation Related Failure of Wood Roof Sheathing

44 Wood Meets Structural, Aesthetic, and Sustainability Goals at One North

By Stephen P. Schneider, Ph.D., P.E., S.E.

STRUCTURAL DESIGN

LESSONS LEARNED

56 Mechanical Bridging Anchorage of Axially Loaded Cold-Formed Steel Studs

By Nabil A. Rahman, Ph.D., P.E.

16 Metallized Coatings for Corrosion Control

By Michael Gustafson, P.E.

By Jeff Miller, S.E., Jesse Malan, S.E., and Julee Attig

44

Ray C. Minor, P.E.

By Jennifer Anderson SPOTLIGHT

75 Facets to Frames

By Mark Sarkisian, S.E., Neville Mathias, S.E.,

On the cover A significant architectural feature of the original Provo Tabernacle was the woodframed roofs at the four corners of the building.

The tower roofs were rehabilitated in the post-fire reconstruction. See the article on page 38 for more.

Rupa Garai, S.E., and Andrew Krebs, S.E. STRUCTURAL FORUM

82 Risk Aversion

By Stan R. Caldwell, P.E., SECB

STRUCTURE magazine

5

March 2017

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement

by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

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Editorial

SEI’s New Mentoring Program

new trends, new techniques and current industry issues

By Donna Friis, P.E., DBIA, F.SEI, F.ASCE, Caleb Hing, Ph.D., P.E., F.SEI, F.ASCE, Cynthia Smith, P.E., PMP, ALEP, F.SEI, F.ASCE, Christopher Fournier, P.E., SECB, M.SEI, M.ASCE, and Peter Kau, P.E., M.SEI, M.ASCE

T

he newly (2016) established SEI Mentoring Committee aims to develop a formal mentoring program for SEI members and ultimately utilize the lessons learned to formulate a program which can be used to advance the profession.

The genesis of this movement was the result of the recently conducted Firm Leader Survey, and also the desire to achieve the goals indicated within the SEI Vision for the Future.

The survey was developed and deployed to structural engineering firm leaders and senior staff/managers. The online survey was designed to test hypotheses of some of the current practices and assumptions about: internships, mentoring, training, licensing exams, organizational membership, academic curriculum, post-academic training, and hiring trend expectations for change in the next 10-30 years.

The overall survey results were not surprising. Formal mentoring is not common in structural engineering firms. Additionally, about half of the respondents agreed that improvements in mentoring are necessary. For those firms who do implement a mentoring program, the most common training is in-house but lacks a defined budget.

To this end, SEI believes it is essential to establish a readily identifiable professional development mechanism that seamlessly progresses from formal education to professional employment to leadership, and includes authentic mentoring at all levels.

What makes a good mentor? A good mentoring relationship is a two-way street. A mentor is someone who, through knowledge and experience, can offer career and professional guidance to a mentee. The mentor provides guidance, knowledge, expertise, encouragement, and motivation to help the mentee grow. A good mentor should possess the following characteristics: • Willingness to share knowledge, skills, and experience; • Dedicated to the time and commitment required; • Has a positive attitude and acts as a positive role model; • Enthusiastic, encouraging, genuine, and supportive; • Excellent communication skills, including being an active listener; • Values continuous learning and encourages long-term development; • Ability to motivate others by setting a good example; • Achievement of a level of technical competence; and • Ability to act as a resource and provide information about the profession.

What makes a good mentee? The mentee should be willing to receive the guidance, encouragement, knowledge, and expertise from the mentor. The mentee needs to be committed to the relationship for it to be successful. A good mentee should possess the following characteristics: • Willingness to ask questions; • Dedicated to the time and commitment required; • Accepts responsibility for career goals and personal development; • Demonstrates a positive attitude; • Honest, respectful, and flexible; • Accepts constructive criticism graciously and learns from mistakes; • Excellent communication skills, including being an active listener; • Values continuous learning and enthusiastic about long-term development; • Accepting of differing points of view; and • Is open about their needs to the mentor and provides feedback.

Why should you become an active mentor or mentee? The future of engineering will require excellent technical and managerial knowledge and problem-solving skills. Clients are demanding more advanced projects in less time. Mid-level engineers are expected to be at the forefront of building codes and technology.

The hope of SEI is that the Mentoring Program will help the younger generation stand on the shoulders of giants even more effectively than their predecessors. If you are a seasoned engineer, you have an opportunity to impart your wisdom to the younger generation to help pass down your legacy. Moreover, a mentee will have a chance to connect with a senior leader who will help guide you in creating your legacy.▪

Benefits and Goals of Mentoring Programs The goal of mentoring programs is to better prepare the next generation of engineers in their career while providing a platform for seasoned engineers to contribute positively to our profession. This will: • Assist in developing necessary technical and non-technical competencies; • Broaden mentee’s network; • Provide professional guidance; and • Champion the mentee’s professional career.

How do we do it? Our first step is to recruit ten pairs of senior mentors and eager mentees who are willing to commit to a two-year program starting in late 2017. SEI is looking for volunteers to join our mentoring program who meet the minimum requirements below: Mentors: • Technical expert; • Minimum of 15 years of experience; • Active on an SEI technical committee; and • A commitment to 2 hours per month and travel once per year is anticipated.

Mentee: • Interested in becoming a technical expert and advancing their network; • 5-10 years of experience; and • A commitment to 2 hours per month and travel once per year is anticipated.

How to Get Involved The SEI Mentoring Program is for members with all experience levels. Participation in this program can include being a mentor, mentee, program coordinator, contributor to program publications, or just offering your input based on your past successful experience in a mentoring program in which you participated. Your participation is vital to ensure that the launch of this program will be successful. Please contact Donna Friis at friisdl@cdmsmith.com or Suzanne Fisher at sfisher@asce.org to become involved.

STRUCTURE magazine

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March 2017

ADVERTISER INDEX

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EDITORIAL STAFF Executive Editor Alfred Spada aspada@ncsea.com Editor Christine M. Sloat, P.E. publisher@STRUCTUREmag.org Associate Editor Nikki Alger publisher@STRUCTUREmag.org Graphic Designer Rob Fullmer graphics@STRUCTUREmag.org Web Developer William Radig webmaster@STRUCTUREmag.org

EDITORIAL BOARD Chair Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@structuremag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. SidePlate Systems, Phoenix, AZ John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA

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Linda M. Kaplan, P.E. TRC, Pittsburgh, PA Dilip Khatri, Ph.D., S.E. Khatri International Inc., Pasadena, CA

Important news for Bentley Users

Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY Brian W. Miller Davis, CA Mike Mota, Ph.D., P.E. CRSI, Williamstown, NJ

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March 2017

Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT 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 C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org March 2017, Volume 24, Number 3 ISSN 1536-4283. Publications Agreement No. 40675118.

Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student.

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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.

W

ind-induced vibration is an everpresent issue in lighting support design. It can cause seemingly magical movement of lighting poles, even when no storm or extreme wind event is present. Engineers recognize this “pole dance” as resonance. When there is too much of it at high amplitudes of deformation, the structure has a high likelihood of failing.

Typical low-level lighting poles are under 50 feet tall, can range from 4 to 12 inches in diameter, and have wall thicknesses between 1/8 inch to 3/8 inch. These poles are typically manufactured out of aluminum, steel, fiberglass, or concrete, and can come in various shapes – round, round tapered, square, multi-sided, and fluted. The focus of this article is primarily on aluminum and steel poles.

The most common document for lighting pole design is the Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (commonly known as the LTS), published by the American Association of State Highway and Transportation Officials (AASHTO). This specification uses typical structural analysis and design concepts for the design of poles and includes a section on fatigue design. AASHTO LTS utilizes ASCE 7 wind maps and general wind pressure equations and variables for design wind loads. In the AASHTO LTS, the wind pressure variables such as drag coefficients and gust factors are tailor-made for slender, flexible structures such as poles and sign posts, whereas these types of structures are generally outside the scope of ASCE 7. However, there is little guidance in the

Figure 1. Approximate first- and second-mode shapes.

LTS on the use of damping as an effective vibration mitigation device. In general, the fatigue criteria in the LTS are used to examine the fatigue resistance of pole aspects by comparing stresses potentially generated by several types of windinduced vibration (natural wind gusts, vortex shedding, galloping, etc.) with a constant-amplitude fatigue limit (CAFL). The fatigue criteria in LTS are not required to be used for low-level luminaire and sign supports, although there has been some interest in making the fatigue requirements apply for all poles, regardless of size. It is believed that, with proper damping, the majority of motion issues in low-level pole-type structures could be resolved. The typical remedy to a design that does not meet the fatigue requirements is to increase the size and stiffness of the pole to meet the requirements, as needed. This could create significantly over-designed poles for strength just to meet the fatigue requirements. Increasing stiffness may solve a motion issue in a particular mode of vibration. However, by increasing the pole’s natural frequencies, another mode of oscillation may be excited with sufficient wind energy and cause damage; whereas before, the wind energy input in that mode was minimal.

Wind-induced vibration is typically a site-specific phenomenon that is difficult to predict. Both steady, constant winds and periodic wind gusts can set up a resonance in a pole in various modes of vibration. Figure 1 gives the most common modes of vibration seen in service for low-level lighting poles with post-top luminaires, although higher modes of vibration have been known to occur.

First-mode vibration is commonly described by a swaying motion of the pole with the maximum amplitude at the top, while second-mode vibration can usually be described by an “S”-shape, with the maximum amplitude somewhere near two-thirds the height of the structure. Given enough cycles, both modes can be damaging if the amplitudes are high enough, generating sufficient stress that the material or welds begin to fatigue and crack even though the entire pole was designed adequately for strength. Different conditions, however, tend to excite these various modes. First-mode oscillation is excited by gusty winds where the pole’s motion becomes locked-in with the wind gusts. Second-mode oscillation is caused by a steady, constant wind that creates vortices in the along-wind direction of the pole, causing movement perpendicular to the wind direction due to vortex shedding.

First-mode oscillation can also be brought on by vortex shedding, albeit for poles with higher fundamental frequencies. Through experience, it has been found that certain types of poles are

STRUCTURE magazine

Practical SolutionS solutions for the practicing structural engineer

Damping Wind-Induced Vibrations on Low-Level Lighting Poles

9

By Shane C. Morrison, Ph.D. and Ray C. Minor, M.S.Eng., P.E.

Shane C. Morrison is a structural engineer and presently serves on the Engineering Advisory Committee for the Aluminum Design Manual with the Aluminum Association. He can be reached at morrisonforge@gmail.com.

Ray C. Minor is a consulting engineer. He has served on a number of committees in the aluminum pole design and welding community. He can be reached at rayminor@comcast.net.

Figure 2. Vibration tendency, highest to lowest: straight square, straight round, round tapered, round tapered embedded.

more prone to wind-induced vibration than others. They are shown in Figure 2.

Typically, constant diameter poles, such as straight round or square, have the greatest tendency to be affected by wind-induced vibration due to less ability to disrupt the vortices created by a steady-flowing wind.

Tapered poles have a constantly changing diameter that provides less of a chance for vortex shedding lock-in to occur. Resonance set up by periodic wind gusts can occur on the majority of pole types in Figure 2. Most embedded poles are often provided a sufficient amount of damping by the earth they are embedded in, and typically see little issue with vibration. In addition to the pole shape and size, luminaire shape and size also play a major role in determining whether a pole assembly may become resonant or not. Thin, small luminaires (think airplane wings) have a low projected area and are essentially like not having a luminaire at all – this takes away from the vortex-disrupting turbulence that a luminaire can provide. It has been found that if a pole is installed without a luminaire, it has a higher chance of becoming resonant.

In recent years, there have been documented cases of pole-type structures in service that were designed to the fatigue requirements of LTS and experienced harmful resonance, suggesting that simply increasing the stiffness to get out of a range of resonance is not the best answer to solving a potential motion problem. Another course of action, and a tried and true method, is impact damping.

Impact dampers typically consist of some mass that physically contacts a surface in a repeated fashion, as often as needed, to attenuate motion. The quantity of mass can be tuned (most often added) to match the

damping requirements of the structure. Some typical impact dampers and their mode of effective attenuation are presented in Figure 3.

Various forms of the devices in Figure 3 have been around for decades. The first device is essentially a ball in a box and counteracts firstmode vibration, the second device is a rod in a canister and counteracts second-mode vibration, and the third device is a hanging chain and counteracts first-mode vibration. These are placed at the location of expected maximum amplitude of the target mode. As the mass collides with the sides of its “container,” whether that be the pole itself or another device, the impact causes a disruption in the resonance of the structure and helps to absorb some of the resonant energy of motion. With enough collisions, the structure can be effectively dampened to acceptable amplitude levels. For the secondmode damper, the rod is in close proximity to its containment structure – this is necessary because of the low amplitudes and higher frequencies (meaning more rapid stress reversals) associated with this mode of vibration. A larger separation for a second-mode damper, such as for first-mode dampers, would prove ineffective, as the mass would rarely, if ever, contact the sides of the container.

The chain dampers go inside the pole at the top and are attached using a through-bolt with spacers or are hung from a pole cap.

They are encased in a PVC hose and their impacts are not detrimental to the structural integrity of the pole; however, they should not be used where wiring is located near the top of the pole, as the chain could interfere with the wiring. The lead ball damper is attached at the top of the pole using set screws. The lead ball is epoxy-coated, and the lead helps to absorb some of the resonant energy through local deformations. These deformations are small and it is believed do not significantly degrade the performance of the damper over time, although no relatively long-term studies are known to have been conducted. The second-mode damper is placed inside the pole and is typically recognized by 2 bolts protruding on the outside of the pole. Most any of the damping devices presented herein can be retrofitted on existing poles. The cost of a typical damping device such as those presented in this article can range from 1% to 15% of the cost of the pole, depending on pole size. Inspecting the elements of a damping system should be part of a routine pole maintenance schedule to ensure their proper function. A photograph of these devices is presented in Figure 4.

An example of the degree of damping that a small amount of mass can provide is presented in Figure 5. All graphs give the amplitude

STRUCTURE magazine

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March 2017

Figure 3. Damper sketches, left-to-right: first-mode damper, second-mode damper, first-mode damper.

Figure 4. Dampers, left-to-right: hanging chain first-mode damper, lead ball first-mode damper, canister second-mode damper.

versus time from full-scale tests on a lighting pole undergoing free vibration from a pluck test in a motion that is synonymous with first-mode vibration. The subject pole is a 23-foot-long, 6-inch diameter by a 5/32inch wall aluminum pole with a 50-pound mass attached to the top. The graphs were truncated when the amplitude dropped below about ½ inch. In Graph #1, the pole went through approximately 500 oscillations before the amplitude at the end of the pole dropped below a ½ inch. Graphs #2 to #4 are the same pole plucked at the same maximum amplitude, with varying degrees of damping that include multiples of a 2-pound lead ball. For this particular pole, a small amount of mass in an impact damper causes the number of oscillations to drop from around 500 for an

Figure 5. Amplitude vs. time for a first-mode damper system.

undamped system to around 60 for one ball, and down to approximately 20 with 4 balls (the damper boxes can be stacked). In this situation, one can see that there are diminishing returns as the amount of mass in the damper increases. The abrupt change in slope of graphs

#2 thru #4 gives an indication that the pole’s amplitude was low enough that the ball no longer impacted the container. It can be seen that impact damping considerably reduces the number of oscillations that a structure undergoes after the damping is initialized,

and can quickly reduce the amplitude, and thus the stress range, experienced by the pole.

Wind behavior on structures can be difficult to understand – even more so when it becomes apparent that a slight geometry change or change in natural frequencies can be the difference between a lighting pole structure undergoing harmful resonance or not moving at all. Instead of over-designing the structure for increased stiffness, a more cost-effective way to mitigate vibration is to utilize mass/impact dampers – which have been used effectively for decades and can be tuned for sight-specific conditions by adding more mass. Dampers are not a “cure-all,” but they do solve the majority of motion issues due to wind in low-level lighting. Damping can be an often misunderstood, proprietary concoction of fluids, weights, shapes, etc., or it can be as simple in construction as an impact damper. The next time a low-level lighting pole design is in order and resonance is a potential issue, consider damping as a method of vibration mitigation and for providing a longer fatigue life for your structure.▪ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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Structural Performance performance issues relative to extreme events

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ecent natural events have provided material evidence of the social and economic impact to large metropolitan areas when a city is not prepared or lacks a robust recovery plan. More than 230,000 people migrated from New Orleans within the first nine months after Hurricane Katrina. The census data showed only 100,000 returned within the following eight years. The 6.3 magnitude earthquake in Christchurch, New Zealand, in 2011 damaged 70% of the central business district (CBD). Most buildings were deemed too dangerous to occupy. In response, all the buildings in the CBD were closed due to concerns about aftershocks.

Many highly populated cities along the West Coast in the United States are vulnerable to this same fate.

These cities consist predominantly of wood-framed residential and multi-family apartment structures.

Structures of concern are commonly three or more stories in height with ground-floor levels consisting of open storefronts, garages, or tuckunder parking. This type of building is referred to as a soft-story structure.

Thousands of these buildings were constructed to codes which, at that time, did not adequately account for this vertical irregularity. Non-ductile materials and finishes, with low displacement capacities, were often used to provide lateral resistance. Subsequent evidence has revealed that soft-story structures are susceptible to collapse, as observed during the 1989 Loma Prieta and 1994 Northridge earthquakes, and in NEES-Soft Project research and testing conducted at the University of California, San Diego.

Strengthening of buildings with a high potential of risk of significant damage is one way cities are investing in the preservation of their unique character. In the 1980s, the City of Los Angeles implemented an ordinance requiring owners of unreinforced masonry (URM) structures to strengthen their buildings. The realization of that ordinance was evident in the minimal injury from URM building collapses after the 1994 Northridge earthquake. Most recently, cities like San Francisco, Berkeley, and Los Angeles have put in place mandatory retrofit programs for soft-story structures permitted or built before 1978. More cities are currently investing in a plan to adopt similar programs to increase the resiliency of their communities. Typical seismic retrofit methods include using conventionally framed wood shear walls or moment frames to add strength and ductility to the structure.

This article focuses on the use of moment frames.

Building Resiliency Soft-Story Retrofit Solutions

By Brandon Winter, P.E. and Damon Ho, M.S., P.E.

Brandon Winter is a Branch Engineer for Simpson Strong-Tie in Northern California with a primary focus on lateral systems and softstory retrofits. He can be reached at bwinter@strongtie.com.

Damon Ho is a Branch Engineer for Simpson Strong-Tie in Southern California focused on customer and staff technical support for lateral systems, investigation and testing of various field conditions, and development and testing of new products. He can be reached at dho@strongtie.com.

The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

Moment frame assemblies are configurations of beams and columns designed to transfer the bending moment and shear forces through the members and connections to provide resistance to lateral forces. When a moment frame is used to provide the additional strength without obstructing openings, engineers can select one of three types; ordinary moment frames (OMF), intermediate moment frames (IMF), and special moment frames (SMF). The expected performances of the beam to column connection define the classification differences.

AISC 358 Prequalification Seismic Provisions for Structural Steel Buildings (ANSI/AISC 341) provides a guideline for the design of moment frames. Prequalified steel moment connections are published in the Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications (ANSI/AISC 358). Where SMF are used, the design of the moment connection needs to meet the performance criteria in AISC 341, or follow the prequalified connection and detailing requirements in AISC 358. Prequalified moment connections are a specific steel moment connection configuration and details that the AISC Connection Prequalification Review Panel have reviewed to meet the performance criteria for an SMF and incorporated into the AISC 358 standard. AISC 341-10 Seismic Provision provides the cyclic testing program to measure the performance of a moment connection. A connection must achieve a minimum joint rotation of 0.04 radians with at least 0.8 Mp of the measured flexural resistance as one of the criteria for meeting the SMF requirements.

Traditional SMF are designed with the beam yielding under large displacement. The yielding of the beam section provides energy dissipation and is designed to ensure the connection between the beam and the column is not compromised.

The current design philosophy is the product of

Comparison of moment frame connection types.

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Beam deformation of RBS connection at the plastic hinge.

extensive testing of SMF connections after the 1994 Northridge earthquake in California.

SMF are required to have the resilience to withstand large rotation of the connection between the column and beam. The beam must be stabilized using bracing to keep the beam compression flange from buckling when a plastic hinge is formed.

beams to be laterally braced or the member cross section torsionally braced. Bracing needs to satisfy minimum stiffness and strength requirements. Requirements for SMF stability bracing of beams are summarized in AISC 341-10 Section E3.4b.

In structural steel buildings, additional steel beams connected to full-depth shear tabs with slip-critical bolts have little difficulty in satisfying SMF bracing strength and stiffness requirements. Meeting the code-prescribed SMF bracing requirements is far more challenging in wood light-framed structures due to the relatively low strength and stiffness of wood compared to steel. Oversized holes in the wood, vertical deflection of the floor beam, and horizontal deflection of the floor diaphragm are some of the sources of deflection making it challenging to achieve the minimum bracing stiffness AISC mandates for an SMF.

AISC 358-16, Chapter 12

Beam Bracing SMF are expected to withstand significant inelastic deformation during a design earthquake. Typically, bracing at specific locations is required to stabilize the beam from lateral torsional buckling observed under large displacements. Section D1.2b of AISC 341-10 provides beam bracing requirements to prevent undesirable beam buckling failure modes that may occur during the formation of plastic hinges in the beam. In AISC 341-10 Section D1.2b, “Bracing of highly ductile beam members shall have a maximum spacing of Lb = 0.086ryE/Fy.” Special bracing at plastic hinge locations requires both flanges of

To address the design challenges with beam bracing and avoid field welding in wood light-frame structures, Simpson Strong-Tie® developed a field-bolted, partially restrained (Type PR) moment connection. The solution uses a patented Yield-Link™ structural fuse design to provide the moment connection.

The unique capacity-based approach of the Yield-Link design represents a departure from traditional moment frame connections in two notable ways.

1) The energy-dissipating YieldLinks can be replaced similar to a “fuse” in an electrical system after a major event.

Factory installed Strong Frame  Yield-Link™ Structural Fuse Special Moment Frame Joint.

Stiffness model of beam stability bracing in wood construction.

STRUCTURE magazine

2) The beam and column members are designed to remain elastic. This allows the beam to be designed with no SMF requirements for stability bracing of beams.

The soon to be released AISC 358-16 edition of Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications will include Simpson Strong-Tie moment connections in Chapter 12 for special and intermediate steel moment frames.

The traditional beam yielding mechanism for a moment frame is eliminated from the beam and isolated to the replaceable Yield-Link element. The Yield-Link fuses are bolted in the shop using twist-off-type tension-controlled (T/C) bolts. A buckling-restraint plate (BRP) is bolted over the reduced region (stem) of the Yield-Link. The shear tab includes horizontally slotted top and bottom holes to minimize load transfer from the beam to the column.

All shop welds and T/C bolt installations are inspected by a third party. Field installation permits the use of ASTM A325 bolts installed snug-tight at the Yield-Links-to-column and shear plate connection. Cyclic and full-scale shake table testing confirmed the use of snugtight field-installed bolts along with no SMF requirements for beam flange bracing.

The frame reflects a true capacity-based design approach that allows the connection to remain

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March 2017

A bolted frame solution allows the beam and columns to be assembled in parts. This reduces demolition that might otherwise be required for a preassembled frame and allows easy integration into the project’s construction schedule. Architectural impact and labor cost in installation are significantly reduced with the elimination of beam bracing.

Multi-Story Frames Frame installation where beam is maneuvered into place before bolting together for soft-story retrofit.

elastic under factored load combinations, with inelastic rotation demand confined within the Yield-Link. Under large displacement, the stem of the Yield-Link fuse is expected to yield in both tension and compression. The BRP, along with spacer plates, prevents the stem from buckling under compression cycles. The beam and column member design is based on the maximum rupture strength (Pr_link ) of the stem of the link. Since the rupture strength for a given Yield-Link structural fuse remains constant, the beam and column can be checked to ensure the connection strength does not exceed the elastic limit of the frame members. Full-scale cyclic frame tests consistently demonstrate the high ductility capacity of the system, often reaching and exceeding a story drift angle of 0.06 radians. The Strong Frame SMF connection has successfully demonstrated the ability to meet or exceed the AISC prequalification requirements.

Typical One-Story Moment Frames A wide variety of projects – ranging from single-level frames, under these mandatory retrofit programs, to multi-level and multibay frames in voluntary retrofits and new construction – have benefited from this innovative solution. Single-level frames are common, as many of these ordinances focus the retrofit effort on the first level. In highoccupancy structures with multiple tenants and limited parking space, it is necessary to minimize the time and encroachment during construction. Tenants can continue to occupy the units during construction as the all-bolted Strong Frame SMF requires no onsite welding. Projects are not delayed for welding inspection, installation time and effort is reduced, and risk of fire associated with welding during erection is eliminated.

In many cases of retrofit design, it is necessary to provide access to the frame on the interior of the structure in tight quarters.

A multi-unit wood frame building on a steep hillside in the Potrero Hill neighborhood of San Francisco recently underwent a major remodel and required retrofitting a majority of the structure. A three-story special moment frame was necessary to allow an open façade overlooking San Francisco Bay and the Bay Bridge. Simpson StrongTie worked in conjunction with the EOR, Element Structural Engineers located in the East Bay of Northern California. Several site constraints, such as existing wood framing, a sloping site, offset openings, and minimal space for the beams and columns, made it difficult for a traditional welded SMF design.

The primary challenge for the design team was the inability to accommodate the coderequired lateral beam buckling braces needed for their initial reduced beam section (RBS) frame design (AISC 358-10, Chapter 5).

The EOR approached Simpson Strong-Tie to provide a Strong Frame SMF solution for this unique project. The following are a few of the project details: • The first level consisted of a three-bay frame spanning the overall 50-foot width of the structure, with stepped column heights ranging from 16 feet at one end to 8 feet at the other.

• The upper two levels consisted of a two-story single-bay frame set atop the first-level frame.

• The upper columns were discontinuous from the lower-frame columns. This required the design of a lower-level frame with omega-increased reactions to account for vertical irregularities.

• A field-bolted connection joined upperlevel columns to the beams below.

• The EOR provided the connection of the frame to the existing structure and foundation.

• The frame was completely erected in one day, utilizing all the provided components needed for erection.

• No special tools were required for the simple snug-tight field-bolted connections.

• No onsite welding or special inspection was needed to erect the frame.

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Installed moment frame for retrofit of the lightframe wood building.

Multi-story multi-bay frame on incline site condition.

Conclusion Policy makers are trying to address the social and economic risks of the architectural status quo along the West Coast before the next devastating earthquake. A city can strengthen its community by developing a plan and passing ordinances to minimize the effect of inevitable natural events before they occur. Proactively strengthening vulnerable soft-story buildings enhances the resiliency of a city and its communities, and reduces potential loss and damage.

The Simpson Strong-Tie Strong Frame® special moment frame is a solution for strengthening existing buildings and new construction. Several full-scale soft-story tests from the University of California, San Diego, have demonstrated that the Strong Frame SMF can strengthen existing buildings with design flexibility to fine-tune frame performance to match the demands of the building. The bolt-on/ bolt-off Yield-Link structural fuse allows for rapid replacement and post-earthquake repair. The no-beam-bracing solution provides another tool for Designers when using steel special moment frames in light-frame structures. High performance, design flexibility, and ease of installation combine to make the Strong Frame special moment frame ideal for meeting the needs of cities and their communities.▪

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Pre-assembled: no field welding AISC 358 Pre-qualified No lateral bracing at beam required Code compliant Custom designs available

Hardy Frame from MiTek®, the retrofit experts. Contact us today and learn how easy soft-story retrofit can be at hardyframe.com/softstory or 800.754.3030. ©2017 MiTek, All Rights Reserved

Structural PracticeS practical knowledge beyond the textbook

Galvanic Series

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metallized coating (a metallic alloy applied to a base metal or concrete) is intended, in most applications, to be a form of protection to an underlying metal substrate. The act of applying the coating is referred to as metallizing. Metallizing can be achieved in several ways such as hot-dipped galvanizing or thermal arc spraying, applied in situ or in a shop. Zinc, which was first used in construction in 79 AD, is the most used metal for this process. Half of the zinc produced today is used for corrosion protection of steel.

Zinc is the prominent metal of choice for metallized coatings as it corrodes slower than ferrous metals and is less noble than steel. Noble metals are resistant to chemical actions and oxidation and do not corrode. In the Galvanic Series of Metals, metals are ranked from ‘noble’ to ‘active’ based on the metals’ potential. Zinc is often a good choice as an anode due to its electronegative potential (Figure 1).

In electropotential relationships, when two metals are joined, the more electronegative metal becomes anodic to the more noble metal. At this state, the anodic metal corrodes preferentially to the more noble metal. This is commonly referred to as sacrificial corrosion, where the anodic metal sacrifices itself to the cathodic metal. (The online version of this article includes a Table which demonstrates the corrosion performance of zinc and zinc-based alloys in contact with other metals, as an indicator of bimetallic suitability. In most instances, zinc corrodes preferentially to the metals listed.)

The range of metallized zinc coatings can be seen in Figure 2. This image depicts the types and thickness of the applied metal to the substrate.

These coatings are generally termed as galvanized coatings, though their application methods differ.

The focus of this article is to look at metalized coatings applied to steel and concrete where the coating is used to prevent corrosion and extend the service life of the treated component.

Metallized Coatings for Corrosion Control

By Paul Noyce and Gina Crevello

Paul Noyce is a material science and concrete durability expert for existing and new structures.

He is chairman of the National Association for Corrosion Engineers Standard Technical Group 01 for Reinforced Concrete and serves asChief Technical Officer for Echem Consultants. He can be reached at pnoyce@e2chem.com.

Gina Crevello is a materials conservator and Principal of Echem Consultants. She is a board member of the Association of Preservation Technology. She can be reached at gcrevello@e2chem.com.

Metallized Coatings Metallized coatings are applied to the underlying substrate thermally or by arc-flame spraying. The metal is in the form of a wire which is melted

Figure 2. Various zinc coating thickness comparison.

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Zinc, galvanized steel Aluminum (sheet metal and extrusions) Cadmium Mild steel, cast iron, wrought iron Aluminum bronze Naval brass, yellow brass, red brass Copper Lead-tin solder Admirality brass, aluminum brass Types 410, 416 Stainless steel (passive) Tin Tin bronze, silicon bronze, manganese bronze Nickel silver (copper-zinc-nickel alloys) Lead Nickel Silver Monel, nickel-copper alloys Types 304, 316 Stainless steel (passive)

0.0 -0.2 -0.4 -0.6 -0.8 Electropositive Relative Potential in Volts More Noble

-1.0 Electropositive Less Noble

Figure 1. Basic galvanic series of metals for construction.

and sprayed onto the surface by compressed air.

Once the liquefied metal hits the surface, it cools rapidly and forms a cohesive coating.

Applications directly onto metal surfaces are performed with either zinc or an aluminum alloy.

The metallized coating provides corrosion resistance by acting as a barrier and a sacrificial metal.

Figure 2 illustrates a comparison of the various zinc coatings in cross section.

Applications are carried out in the field or in the shop, dependent on the type of component.

Where components are too large for hot dip galvanizing, metallizing is the first-choice alternative.

Applications in the field are numerous and generally fall under the following categories: 1) Extending the Life of Existing Galvanized Components (Zinc) 2) Alternative to Painted Component, where corrosion resistance is required (Zinc or 85:15 Alloy) 3) Concrete Surfaces for Corrosion Control and Cathodic Protection (Zinc or Al/Zn/ In) and Reinforcing Steel The primary benefit of metallizing is long-term increased durability, particularly in salt-rich environments. Here, metalizing provides a whole life cost advantage over more traditional methods of protection which tend not to perform as well in harsh environments. Entire bridges, which are subjected to salt-rich environments, are prime candidates for metallizing, as are bridge components which are subjected to drainage and runoff.

Galvanized Components The long term corrosion resistance of zinc coatings is mainly dependent on coating thickness and the environment to which the coating is exposed.

When both of these are known, then the time to first maintenance can be determined as seen in Figure 3. This often has a direct correlation on maintenance and life cycle costs. Time to first maintenance is defined as the time it takes for 5% of the steel surface to rust. Coatings are measured in mils, as seen in Figure 3. One (1) mil is equivalent to 25.4 microns (µm) or 0.56 ounces per square foot.

Figure 3. Zinc coating time to first maintenance.

One of the main benefits of galvanizing is the metallurgical bond between the zinc and the underlying steel or iron which creates a barrier that is part of the metal itself. The bond between the zinc and steel is approximately 3,600 pounds per square inch (PSI) which is six (6) times better than bond strengths for

conventional coatings which fall between 300 and 600 PSI. In addition to the bond, galvanizing provides abrasion and impact resistance due to the formation of the zinc-iron layers. Four layers are formed: Gamma, Delta, Zeta and Eta, where each has a different hardness. The Gamma, ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Delta, and Zeta layers have a hardness higher than the underlying metal. This hardness provides abrasion resistance and excellent protection against coating damage. The Eta (top) layer is quite ductile, providing an element of impact resistance as well as an element of self-healing.

Performance data on galvanized coatings dates back to 1926. The American Society of Testing Materials (ASTM) Committee A05 (Metallic-Coated Iron and Steel Products) has been collecting records of performance based on various atmospheric conditions.

Atmospheric conditions are extremely variable, reducing coating life considerably in some instances. Factors affecting coatings can be defined as follows: • Wind Direction • Corrosive Fumes • Pollutants • Amount of Salt Spray • Number of Wetting and Drying Cycles • Duration of Moisture Exposure Applications of galvanizing are extensive.

Structural members of bridges and buildings, electrical utility poles, and artistic structures are commonly treated. Component sizes vary considerably from a small nut or nail to a bridge girder support. continued on next page

In summary, the Bureau determined, by simulating environments, the best use of metallizing would be on radial gates, partially exposed trash racks, and other equipment subjected to a fluctuating immersion environment. The Bureau also determined metallizing to be beneficial in severe atmospheric service environments such as bridges and above-ground piping.

In their test program, the pure aluminum was believed to have offered the best combination of protection in immersion or fluctuating immersion, as long as the water had a pH between 4.0 and 8.5.

Figure 4. In situ galvanizing /metallizing of a steel substrate in service.

In summary, the major benefits of galvanizing are: • Factory Quality Assurance (QA) Controlled • Complete Coverage • Superior Bond to Steel • Hardness of Coating Compared with Steel • Excellent for Indoor or Outdoor Environments When galvanized coatings lose Zn, they can be metallized to extend their service life.

Alternative to Painted Components The most commonly used alternative to painting steel is the application of a metalized coating in the form of zinc/aluminum or 85/15 alloy, 85% zinc, and 15% aluminum by weight. Both options provide a metal coating with superior corrosion resistance over standard paint coatings. Metallizing can be used to cover welds, seams, ends, and rivets to improve corrosion resistance and can be applied up to 10 mils (254µm) thick.

In a testing program supported by the Federal Highway Administration (FHWA), zinc and 85/15 alloy applied at 6 mils outperformed over 40 other coatings. The coatings were exposed for seven (7) years in a harsh marine environment with and without a sealer top coat. These panels showed virtually no corrosion and no deterioration from intentional coating defects at the end of this exposure period.

In 2012, the Bureau of Reclamation carried out a laboratory evaluation of metallized coatings for use on reclamation infrastructure. Five thermal spray alloys and two sealers were investigated using laboratory test methods that included immersion, accelerated weathering, adhesion, and electro-impedance spectroscopy.

Concrete Corrosion Control and Reinforcing Steel Corrosion of reinforcing steel can have detrimental effects on the service life and functionality of a concrete structure. In structures that have high chloride exposure, significant chlorides at the reinforcing steel depth can trigger steel corrosion even in the presence of a highly alkaline concrete. Chloride ion ingress from sea salt, de-icing salt, or contaminated concrete mix constituents breaks down the passive oxide layer without damaging the concrete. Once there is sufficient concentration at the steel surface, along with sufficient oxygen and moisture, corrosion initiates.

In the corrosion reaction, iron dissolution occurs at the anode and two electrons (2e-) are gained elsewhere on the steel to maintain electrical neutrality. The gain of electrons at the cathode reaction results in the formation of alkaline hydroxyl ions at the steel surface.

This reaction is harmless to the steel and the surrounding concrete. Thus, if this reaction is forced to occur by adding current, then the steel is protected. Damage does not occur if the cathodic reactions are controlled; hence, the term cathodic protection.

For this type of corrosion control, an ‘anode’ is installed or applied to a structure and provides current (electrons). In 1992, the Federal Highways Administration was quoted by the Strategic Highway Research Council (SHRP-C/UPW-92-618) stating Author’s note: The high pH of new concrete passivates the steel. The formation of an oxide layer (Fe2O3) or Magnetite protects the steel from corrosion until such time corrosion initiates. As concrete material conditions degrade, by age, through exposure to the elements, construction defects, or other related causes, the steel is no longer protected and is in an environment where it can corrode.

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Figure 5. Metallized coating applied to concrete.

Figure 6. Measurement of coating thickness (Mils).

that “cathodic protection is the only method known to stop corrosion damage regardless of the level of chloride within the structure.”

Two types of cathodic protection are available today: Galvanic and Impressed Current.

Galvanic Cathodic Protection (GCP) is based on the Galvanic Series of Metals where the electronegative metal gives up electrons to the electropositive metal. Impressed current cathodic protection (ICCP) utilizes an external DC power source connected to the anode system to provide current.

Metallized coatings, thermally sprayed (TS) onto concrete, can provide suitable anodes for cathodic protection and corrosion control in concrete. Figures 4 through 9 illustrate application and testing of a TS coating of a bridge pier. TS anodes can be used in either galvanic or impressed current mode, depending upon the circumstances, conditions, and environment near the structure. The types of anodes suitable for a TS application for cathodic protection include: • Zinc (Zn) (GCP/ ICCP) • Aluminum/ Zinc/ Indium (A-Z-I) (GCP/ ICCP) • Titanium (ICCP only)

Figure 7. Coating pull off test.

Figure 8. Completed bridge pier.

Early comparative thermal spray anode performance trials performed by the California Department of Transportation concluded that thermal/flame-sprayed zinc provided the best combination of cost, effectiveness, acceptability, and coating consumption rate for cathodic protection. TS Zn coating types have a long history of reducing life cycle costs of reinforced concrete bridges on a national and international level. Aside from mitigating corrosion through cathodic protection, the zinc retards

migration of the chlorides to the reinforcing bar, and re-alkalization occurs at the steel and concrete interface during the cathodic reaction.

The efficacy and service life of TS alloys on concrete is based on several parameters: • Sufficient Surface Preparation • Adequate & Uniform Coating Thickness • Current Density • Cumulative Charged Passed • Acidification • Pore Solution of Concrete

• Environmental Interactions o Moisture o Precipitation o Wetting and Drying • Bond Strength The electronegative potential of Zn allows for it to function well as an anode in galvanic mode in a moist environment. Al/Zn/In alloys include the use of Indium to activate the Aluminum and have been designed for use where moisture is less abundant. continued on next page

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The Oregon DOT has been successfully employing TS to Oregon’s historic coastal highway system. Their bridge inventory includes over 120 bridges, most of which are reinforced concrete. Over 430,566 square feet of bridge surface area have been treated using thermal-sprayed (TS) zinc anodes in both impressed current and sacrificial cathodic protection (CP) systems.

The Florida DOT’s experiences mirror that of ODOT, whereby studies have shown that anode consumption in a galvanic mode is largely dependent upon moisture and bond.

FDOT also found that if metallized coatings are sprayed directly onto spalls where the reinforcing is exposed, then corrosion activity is slowed, providing a longer duration time between repairs.

For galvanic use, the service life of the alloy is based on coating thickness and current density resulting in anode consumption.

This is largely a function of moisture and chloride exposure. Bridge substructures in marine environments are highly suitable for GCP systems; however, splash zones on bridge piers may require a more robust approach and drier components may be more appropriate for an ICCP system. Both the Oregon DOT and Florida DOT studies identified that if sufficient bond strength is achieved between the concrete substrate and anode, anode service life in ICCP systems may exceed 25 years.

Like traditional cathodic protection systems, TS applied systems have permanently embedded reference electrodes to monitor system performance. This allows for depolarization tests to be performed so that the National Association of Corrosion Engineers (NACE) and British Standards European Norm (BSEN) criteria for cathodic protection can be demonstrated. The successful use of TS systems has also been documented in parking garages, pre-stressed structures, post-tensioned structures, and bridges in non-marine environments exposed to high chlorides.

In 2000, Bennett, et. al, published their work on the use of metallized zinc alloys on a post-tensioned garage in Pennsylvania exposed to deicing salts, a substructure of the M4 Motorway in the United Kingdom exposed to chloride runoff (deicing salts), and a condominium complex facing the Atlantic Ocean situated on Marathon Key, Florida. These studies illustrate the efficacy and success of the TS Zn anodes in a variety of environments, applications, and structure types. All case studies presented achieved the 100mV depolarization criteria required by the NACE Standard SP 208 and BSEN 12696:2012, illustrating the

Figure 9. Application of coating on a concrete wall.

suitability and broad use of TS coatings for corrosion control.

The purpose of the TS applied alloys is to provide a service life extension to both the structure and the concrete repairs, by decreasing the deleterious effects of corrosion to the surrounding concrete and by reducing repair cycles and maintenance costs.

Recently published NACE International Standard SP0216-2016, Sacrificial Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures is now available.

Conclusions Metallized coatings comprise a relatively limited range of alloys applied to a steel or concrete surface to provide greater durability for the service life of the structure or component. These applications can include: 1) batch galvanizing of Zn to steel such as nuts, bolts, and even reinforcing steel, 2) metallizing exposed steel structures, and 3) surface applying alloys to reinforced concrete bridges, garages, and buildings to serve as anodes in cathodic protection systems. Metallized coatings provide a significant service life extension to the treated part or system. Their flexibility in a TS application allows for a variety of uses on complex geometries as well.

The service life of the coating depends on a multitude of factors, all of which are largely environmentally driven. Therefore, consideration for the service environment must be addressed prior to material selection.

Additionally, the success of the metallized

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Definitions Whole Life Costing (WLC) is “an economic assessment considering all agreed projected significant and relevant cost flows over a period of analysis expressed in monetary value. The projected costs are those needed to achieve defined levels of performance, including reliability, safety, and availability”. Source: BS/ ISO 15686-5 Buildings & Constructed Assets.

Life Cycle Costs (LCC) are the cost of an asset, or its part throughout its cycle life while fulfilling the performance requirements. (BS/ ISO 15686-5 Buildings & Constructed Assets: Service Life Planning: Life Cycle Costing.) coating is dependent upon proper surface preparation of the metallic or concrete substrate, and adequate bond strength between the two materials. Whether galvanizing or metallizing, the service life extension of the steel components can be in the range of 25 years before the first maintenance is required.

This makes the use of metallized zinc and associated alloys a cost effective, low maintenance material choice for barrier protection, self-healing, cathodic protection, and managing chloride ingress into a substrate.▪ The online version of this article includes the Table mentioned in this article and detailed references. Please visit www.STRUCTUREmag.org.

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Technology information and updates on the impact of technology on structural engineering

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uildings and residents near the Salton Sea began shimmying and shaking during the swarm of earthquakes that burst from Bombay Beach in late September 2016. Soon, the California Earthquake Prediction Evaluation Council (CEPEC) released a statement. It read: “CEPEC believes that stresses associated with this earthquake swarm may increase the probability of a major earthquake on the San Andreas Fault to values between 0.03 percent and 1.0 percent for an M7.0 or larger earthquake occurring over the next week (to 09:00 hrs PDT, Tuesday, October 4, 2016).” The Twitterverse lit up with nervous Kermits, earthquake maps, and visits to snopes.com to confirm the rumors. That the advisory came just weeks before the annual ShakeOut drill, it served both as a solid reminder that earthquakes can happen at any time and also demonstrated that communicating earthquake hazard is complicated.

The uncertainty that the Southern California public felt during this period of heightened probability for a significant rupture was palpable. The between 33 to 1000-fold increase in the likelihood of an M7.0 or higher event seemed awfully high but, at the same time, a 0.03-1% chance of a rupture seemed quite small. What mitigation actions are appropriate given these numbers? As scientists who do this sort of thing for a living, this was reminiscent of another earthquake advisory that was put out in L’Aquila, Italy.

A seismic swarm began in the region in early 2009 and, after the main shock of April 6, 308 people had died and six scientists were charged with manslaughter. The scientists were ultimately acquitted, but the fact remains that communication of increased earthquake probabilities is a dicey subject. Most earthquake swarms do not culminate in a large main shock, as seen in the Salton Sea area, but they can be a precursor.

The ideal solution, of course, would be the ability to predict earthquakes before they happen and pinpoint precisely the affected populations, the size of the rupture, and the exact time that the shaking would begin. Other natural disasters afford citizens this luxury, where people can be evacuated for a fixed period of time, houses and businesses can be secured, and when it is over, recovery can begin. However, for earthquakes, which do not happen on the same recurrence scales that other disasters do, models rely on current, past, and paleoseismic catalogs to infer recurrence rates and increased stresses on certain faults to define probabilities that an event of a certain size will happen in the future.

California publishes the results of these models in the Uniform California Earthquake Rupture Forecast (UCERF, see Figure 1). The current models indicate that the Northern San Andreas

Impacts to the Built Environment How Earthquake Early Warning Systems Can Aid Recovery Efforts

By Jennifer Strauss, Ph.D. and Richard Allen, Ph.D.

Jennifer Strauss is the scientific liaison for the Berkeley Seismological Laboratory and the head of the Lab’s Earthquake Research Affiliate Program.

She also is the Vice Chair of the ShakeAlert Joint Committee for Communication, Education, and Outreach. She can be reached at jastrauss@berkeley.edu.

Richard Allen is the Director of the Berkeley Seismological Laboratory and Professor and Chair of the Department of Earth and Planetary Science at UC Berkeley. He can be reached at rallen@berkeley.edu.

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Figure 1. Summary of the earthquake rupture probabilities for the major faults in the Bay area.

Courtesy of Jack Boatright, USGS.

fault has a 33% chance of experiencing an M6.7 or greater earthquake during the lifetime of a mortgage loan. That is important for people considering earthquake insurance on their home, cities retrofitting their infrastructure, or for the general knowledge that it is not a matter of if, but when an earthquake will happen. However, unlike earthquake prediction, such forecasts do not provide acute actionable information about imminent threats. The timescales are so large that apathy can set in.

So, the natural next question is: are forecasts the best that modern technology can provide? No. Thankfully there is another tool available. Well, to be fair, it is currently available in Japan and Mexico, and only experimentally on the West Coast of the United States, but it does exist.

ShakeAlert and its partners (Figure 2) are working hard to ensure that tool is widely available as soon as possible. The tool is earthquake early warning.

Figure 2. Shake Alert and Partners.

The 20 seconds of warning the Caltrans workers received was because they were about 90 km from the aftershocks centered in the Santa Cruz Mountains. Had they been closer, the alert time would have been shorter, perhaps even no advanced warning at all.

However, even at that distance, the shaking was strongly felt due both to the soft sediment in the area, which amplified the shaking, and the fact that, for moderate to large earthquakes, the epicenter is not the only point of rupture. continued on next page

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The ShakeAlert Earthquake Early Warning (EEW) system in the United States uses a network of seismic instruments to detect the very first signals that a rupture has begun (Figure 3). The energy emanating from a rupture forms two main wave trains. The P-wave is a compressional wave and is considered ‘nondamaging.’ The second wave train begins with the S-wave and is followed by Love and Raleigh waves. These are associated with much of the damage the built environment experiences during a rupture. The P-waves travel at twice the speed of the S-waves so, as the energy moves away from the epicenter, the P-waves begin to outrun the S- and following waves. ShakeAlert detects the amplitude, frequency, and time for the P-wave. This information is analyzed at a central processing center, which calculates the expected magnitude, location, and origin of the quake, and forwards that information to emergency responders, utilities, transportation centers, and others so that they can take protective action before the heavy shaking reaches their location (Figure 3). ShakeAlert also estimates the local shaking intensity through the use of a UserDisplay, so that users obtain tailored information about shaking thresholds they are likely to experience.

This advanced warning is of critical importance not just for times of calm before a large event, but also during both swarms and aftershock sequences.

Residents of both Bombay Beach and L’Aquila were rattled by the low-intensity shakes that seemed to go on forever. For each shake, citizens were unsure whether the intensity would remain small, or if it would ramp up into a larger damaging event. EEW can bring peace of mind in those situations by providing information for larger events so that people know to drop, cover, and hold on. Swarms can psychologically destabilize an area by their constant shaking, while a large event followed by intense aftershock sequences can physically destabilize a region. First responders sifting through the rubble of the collapsed Cypress Viaduct after the 1989 Loma Prieta, CA quake were aided by a proto-EEW system. USGS and Caltrans installed a combination of sensors, temporary communications systems, and receivers to give about 20 seconds of advanced notice to the workers that an aftershock was about to arrive. Even small to moderate shakes can have a severe impact in areas already compromised by a larger event. In this way, EEW hastens recovery efforts by protecting the workers.

Small to moderate earthquakes behave like a rock thrown into a pond. Concentric circles of disruptive waves emanate from the spot the rock met water. The waves get weaker as they move out, barring local eddy effects.

Moderate to larger earthquakes are more like a tree branch falling into the pond. There is one initial point of contact with the water (the epicenter), but the branch keeps falling and making contact with the water all the way to the ends of the leaves. The once concentric and orderly rings are now a whole series of overlapping rings that can add onto one another and cause larger waves to reach the shore, even far down the pond from where the branch first fell in. Thus, people far away from the epicenter can both have larger warning times and experience high levels of shaking.

Typically, when speaking of EEW, the first use case that comes to mind is “drop, cover, and hold on.” EEW alerts can trigger trains to slow and stop, reducing derailments. Firehouse bay doors can open automatically to ensure the trucks can exit promptly. Gas shutoff valves activated, lithography tables put into safe modes, school children taking shelter under desks, halting cars at bridge plazas, securing radioactive sources in hospitals – there are many use cases being explored today. EEW in the built environment augments these sorts of automated controls with pre-hazard planning to streamline the recovery effort.

Like the workers on the Cypress Viaduct, building inspectors assessing red and yellow tagged buildings after an event are vulnerable to aftershocks. As the sequence progresses, and hopefully dies down over time, the areas most impacted by each subsequent shaking event would be identified through early warning, even if the epicentral locations migrate over time. Estimated shaking intensity profiles would allow for prioritization of areas to inspect. This, combined with pre-hazard planning and use of scenarios and drills, could provide a set of protocols, vetted well beforehand, that could be selected based on the early warning information.

ShakeAlert is facilitating this pre-hazard planning through partnerships with pilot groups. In February of this year, the ShakeAlert group invited selected beta testers to begin establishing protocols and actions in response to EEW alerts. This allows utilities, schools, and large infrastructure groups to start developing their responses for various scenarios, at the same time as the system build out is underway, to test and validate these actions before the public system goes live. As part of the pilot launch, ShakeAlert transitioned to a production prototype system. This robust and redundant system removes single points of failure such that if

Figure 4. The current and proposed future stations for the ShakeAlert earthquake early warning system are plotted here for the entire West Coast. The blue disks denote current active stations, while the green triangles are proposed locations for new and upgraded installations.

one data center goes offline, another steps in to take its place, providing smooth and continuous information to the users.

ShakeAlert currently relies on approximately 760 seismic stations throughout the West Coast to provide real-time information to the system. New station installations combined with upgrading older stations to real-time capabilities will ultimately get the system to the target of 1,675 stations. The locations of the current seismic stations used for early warning are shown as blue disks, while the proposed future station locations are depicted as green triangles in Figure 4. This configuration will provide dense network coverage around known active faults and population centers, while still providing moderate coverage in other areas (to catch unknown faults, like the one that generated the 1994 Northridge earthquake).

ShakeAlert is halfway there, both in terms of funding and installation of the station buildout. However, ShakeAlert will not become a fully public system unless it can complete the station build-out, secure long-term sustained operational funding, and meet certain reliability standards for the warnings. The build out is proceeding, with more stations added every year. The operational funding, both from state, private, and federal sources, has

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increased over the years and hopefully will continue on a path towards a sustained public safety initiative. Since large to moderate earthquakes do not happen every day on the West Coast, ShakeAlert must use a combination of real-time, archived, and synthetic data to stress-test the system reliability. The U.S. is in a unique position – most of its earthquake hazard lies beneath most of its large population centers. The ShakeAlert algorithms must therefore delicately balance the need to have accurate information, with very few false alerts, while at the same time using the smallest amount of data possible to make the determination and provide the most warning.

Metrics are currently being established, and the system will be tested against those metrics before any public alerts go out.

Currently, the system uses seismic algorithms to characterize the earthquake. These P-wave based approaches have limitations.

They tend to saturate above M8, and they require the rupture to initiate before alerts are generated. Thus, there is always a limit to the amount of early warning provided.

ShakeAlert is working to addresses these issues by combining the operational aspects with academic research. Testing of Global Navigation Satellite System techniques, such as Berkeley’s GlarmS algorithm, will allow the system to punch past the M8 limit by modeling the movement of the fault plane in real time. Berkeley also works on fundamental research into earthquake initiation processes which, while not part of EEW at this time, could increase understanding and provide new techniques for the future.

Earthquake prediction is not possible with the data and understanding currently available, but it is a young science. The future may herald new insights and discoveries that make techniques beyond P-wave detection faster and more reliable.

EEW is an important tool in the preparedness toolkit. Both the Japanese and Mexican early warning systems provide an apparent benefit to those populations. However, it is important to remember that early warning works best when combined with other tools, such as retrofits, automated controls, and pre-hazard planning. People and physical assets are better protected in secure buildings that remain standing after the rupture.

Automated controls can spin up with an early warning alert, moving people and things into safe modes to prevent cascading failures that hamper post-event recovery.

Moreover, of course, pre-hazard planning allows for training on what to do when an earthquake strikes. Early warning just gets you there faster.▪

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he future of short span steel bridge design began in 2009 with a challenge from the Federal Highway Administration (FHWA). FHWA challenged the North American steel industry to develop a cost-effective short span steel bridge with modular components which could be placed into the mainstream and meet the needs of today’s bridge owners, including Accelerated Bridge Construction (ABC). The challenge was issued to help address the U.S. infrastructure crisis of structurally deficient and functionally obsolete bridges, nearly half of which fall in the short span category (defined as bridges under 140 feet).

To develop ideas to meet this challenge, the Short Span Steel Bridge Alliance (SSSBA) organized the Modular Steel Bridge Task Group – consisting of 30 organizations representing the SSSBA, Steel Market Development Institute, National Steel Bridge Alliance, National Association of County Engineers, steel bridge fabricators, University faculty members, steel manufacturers, government organizations, and bridge owners. The group considered many options and decided in October of 2011 that a shallow steel press-brake-formed tub girder technology – also known as folded plate girders – provided the best opportunity for meeting the FHWA goals for economics, innovation, and ABC practices.

A New Shape for Short Span Steel Bridges

By Gregory K. Michaelson, Ph.D. and Karl E. Barth, Ph.D.

About the Technology Gregory K. Michaelson is an Assistant Professor in the Weisberg Division of Engineering at Marshall University and a member of the Short Span Steel Bridge Alliance’s Bridge Technology Center. He can be contacted at michaelson@marshall.edu.

Karl E. Barth is the Jack H. Samples Distinguished Professor of Civil and Environmental Engineering at West Virginia University and a member of the Short Span Steel Bridge Alliance’s Bridge Technology Center. He is the former chairman of the SSSBA Modular Steel Bridge Task Group.

He can be contacted at karl.barth@mail.wvu.edu.

The press-brake-formed tub girder system consists of modular shallow trapezoidal boxes fabricated from cold-bent structural steel plate (Figure 1).

Steel shapes are available in either hot-dipped galvanized or weathering steel options. Once the plate has been formed, shear studs are then welded to the top flanges. A reinforced concrete deck is then cast on the girder in the fabrication shop and allowed to cure, becoming a composite modular unit. Modules are then longitudinally joined using Ultra-High Performance Concrete (UHPC), a relatively new class of advanced cementitious composite materials.

The system offers several advantages over traditional short span steel bridge solutions. The girder itself is incredibly simple to fabricate, requiring minimal welding. Because of the system’s modular composite design, there is a reduced need for additional details such as stiffeners or crossframes. Also, due to the system’s modular nature, the composite unit can be easily shipped to the bridge site, allowing for accelerated construction and reduced traffic interruptions. And, while modular precast concrete decks are recommended, multiple deck options are available. Examples include the use of full-depth/partial-depth precast

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Figure 1. Conceptual view of modular press-brakeformed tub girder system.

concrete deck panels, cast-in-place concrete decks, or more advanced composite decks such as the Sandwich Plate System (a structural composite material comprising two metal plates bonded with a polyurethane elastomer core).

Research and Development As opposed to the cutting and welding required for typical tub girders, the system utilizes cold bending of standard mill plate widths and thicknesses for the tub girder, decreasing fabrication costs and increasing the efficiency and economic performance of steel used in the system. For each standard mill plate, a design study was performed by iterating the proportions of the girder to achieve the maximum possible flexural capacity (initially estimated to be the composite yield moment). For this study, the slope of the webs was kept at a constant 1:4 slope, the inside bend radii of the girders was maintained at a constant value of five times the plate thickness, and the top flange width was kept at a constant value of 6 inches. The concrete deck of the composite unit was at 7.5 feet wide by 8 inches thick. Normal-weight concrete was assumed, with a modular ratio of 8 and a compressive strength of 4 ksi. All plates were assumed for design purposes to have a yield stress of 50 ksi.

Figure 2 shows the results of these assessments for a sample of standard mill plates chosen for the design. From these plots, it is clear that, for each plate width and thickness, an optimum depth is seen at the point of maximum yield moment;

Figure 2. Design comparisons for 96-inch-wide standard mill plates.

Figure 3. Experimental test setup (composite specimen).

increasing or decreasing the depth from this point results in a reduced section modulus and, therefore, a reduced yield moment.

Instead of selecting an optimum depth for each plate, plates with common standard mill widths were grouped together, and an optimum depth was chosen for each group. Wider standard mill plates can be used to generate deeper girders for increased moment capacity and longer spans.

Physical flexural testing of representative specimens to verify the performance and capacity of the proposed system was conducted at West Virginia University. Testing was performed on press-brake tub girder specimens in both composite and non-composite states, beginning in the summer of 2013.

The steel employed for the specimens were 84- × 7/16- × 480-inch standard mill plates of ASTM A709 Gr. 50 steel, donated by

Nucor Corporation, SSAB Americas, United States Steel Corporation, and EVRAZ North America. The composite deck was cast with normal-weight concrete; results from six cylinder tests yielded an average compressive strength of 4.1 ksi.

In addition to physical testing of the press-brake-formed tub girders, assessments were conducted with three-dimensional finite element modeling using Abaqus/ CAE. Element selection for these models included general purpose shells that use a reduced number of Gauss integration points (increasing the computational efficiency of the analysis) and hourglass control, which prevents zero-energy deformation modes and spurious results associated with reduced integration. The steel girders in this study were modeled using a tri-linear elastic-plastic constitutive law including strain-hardening effects. Stress-strain data for the girders was obtained from coupon testing performed at FHWA TurnerFairbank’s Highway Research Center.

Concrete was modeled utilizing a concrete damaged plasticity model available in Abaqus/CAE. Figure 4 (page 28) illustrates a comparison of the data obtained from flexural testing of

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two composite specimens and the results of finite element analysis. As shown, the modeling accurately captures the behavior of the proposed system. Also, the magnitude of force shown is quite noteworthy; a single modular girder is shown to be capable of resisting loads of over four times the standard AASHTO HL-93 design truck (weighing 72 kips).

Design evaluations were performed in accordance with AASHTO LRFD Specifications to assess the feasibility of Figure 4. Comparison of experimental and analytical the proposed system. For each girder, (FEA) results. dead and live load force effects (i.e. moments, shears, and deflections) were computed and compared against prescribed From the Laboratory to the AASHTO limits. In addition, the goal of the Construction Site proposed system dictates the use of standard mill plate to fabricate the steel girder Brian Keierleber, P.E., Chief Engineer of the component of the modular unit. Therefore, Secondary Roads Department of Buchanan when recommending solutions to engineers County, Iowa, was awarded a grant from and owner agencies, preference was given to FHWA Innovative Bridge Research and plates that are produced on a regular basis. Development Program (IBRD) to replace Results of these feasibility studies yielded the Amish Sawmill Bridge at 1358 Dillon the following design options. It should be Avenue in Fairbank, Iowa. The $350,000 noted that while the system is recommended IBRD grant was awarded on the basis of for single spans up to 60 feet in length (due using a “bent steel plate girder section supto plate availability and typical press brake ported on Geosynthetic Reinforced Soil lengths), girders can easily be spliced for (GRS),” laying the groundwork to comspans up to 80 feet: plete the first installation of the proposed • Girders utilizing 72- × ½-inch standard modular press-brake-formed steel tub girder mill plates (applicable for spans up to system in the United States.

40 feet).

Construction on the Amish Sawmill • Girders utilizing 96- × ½-inch standard Bridge began in the late summer of 2015 mill plates (applicable for spans up to and was finished in December 2015 (Figure 60 feet).

5), completing the journey from concept • Girders utilizing 120- × 5/8-inch to implementation in under three years, a standard mill plates (applicable for remarkable feat in the field of bridge engispans up to 80 feet). neering. Local contractors were presented Also, in cases where hydraulic opening or with different composite deck options for clearance requirements dictate the use of the bridge; the winning bid elected to utia shallow section, the selection of a 60- × lize a cast-in-place option. This bridge was ½-inch standard mill plate may be advantageous as the resulting optimum girder design is only 12 inches deep. Also, the optimum design of a 60- × ½-inch standard mill plate girder results in an out-to-out width less than half of the 7.5 feet wide concrete deck (a common upper limit for shipping considerations), meaning two steel girders can be placed along a single composite concrete deck. The resulting “twin girder” composite girder is applicable for spans up to 65 feet.

The initial testing was completed in 2014.

Additional testing is being conducted this year to further evaluate the performance of the longitudinal UHPC closure pour and to provide fatigue testing of galvanized and non-galvanized girders.

not constructed by a local crew since it was federally funded, but it could have been since it was standard bridge construction and no special expertise was required. The bridge was dedicated on January 8, 2016, with a ribbon-cutting ceremony featuring several government and transportation officials. Researchers from West Virginia University, Marshall University, and the University of Wyoming are continuing field performance monitoring on the bridge.

Transforming Short Span Steel Bridge Design Several state Departments of Transportation have expressed interest in building pressbrake-formed steel tub girder bridges in their jurisdictions. Currently, two additional press-brake-formed tub girder bridges are scheduled for construction in West Virginia within the next year. Also, the Ohio Department of Transportation and Muskingum County, Ohio, were awarded an FHWA Accelerated Innovation Deployment (AID) grant to replace a bridge on County Road 7 – Cannelville Road. The $557,600 AID grant will be used to install a pressbrake-formed steel tub girder system with a Sandwich Plate System deck.

The technology is appealing because it offers significant cost savings, ease of shipment and fabrication, accelerated construction, design versatility, and sustainability. Steel is the world’s most recycled material and, at the end of the bridge’s life, it may be transformed into another steel product. With so many benefits, press-brake-formed steel tub girders provide the potential for widespread use in helping to solve America’s critical infrastructure challenges.▪

Figure 5. Completed Amish Sawmill Bridge (Buchanan County, Iowa).

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CONSTRUCTION ISSUES discussion of construction issues and techniques

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Thomas Sputo is President of Sputo and Lammert Engineering, LLC, Gainesville, FL, and Technical Director of the Steel Deck Institute. He may be reached at tsputo50@gmail.com.

Figure 1. Typical membrane layout by roofers.

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James M. Fisher is Vice President Emeritus, Computerized Structural Design, Milwaukee, WI, and Consulting Engineer to the Steel Joist Institute. He may be reached at jfisher.florida@gmail.com.

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By James M. Fisher, Ph.D., P.E., Dist. M.ASCE and Thomas Sputo, Ph.D., P.E., S.E., F.ASCE

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Are Your Roof Members Overstressed?

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embrane roof systems installed on steel roof decks traditionally result in a uniform transfer of wind (uplift) loads from the roof membrane to the steel roof deck and underlying supporting structure (e.g., steel joists). For example, in a built-up membrane roof system – which has been used commonly in the U.S. roofing industry for more than 125 years – the built-up membrane is continuously adhered to rigid board insulation. The rigid board insulation, which is used to span the steel deck’s flutes, is mechanically attached to the steel roof deck in a closely-spaced pattern (e.g., 1 fastener per every 3 square feet), resulting in a near uniform uplift load path. Polymer-modified bitumen roof systems and adhered single-ply membrane roof systems are installed in similar configurations and result in a similar uniform uplift load path.

In the 1960s, single-ply membrane roof systems were first introduced into the U.S. roofing market. By the late 1970s, the seam-fastened, mechanically attached method of installation was first introduced. With this installation method, the single-ply membrane sheet is mechanically attached along its outer edges into the roof deck, which results in a larger tributary uplift load per fastener and placement of fasteners in linear, non-uniform loading configurations of the roof deck and underlying supporting structure.

When first introduced, membrane sheet widths in seam-fastened single-ply membrane roof systems typically were five feet wide, resulting in rows of mechanical fasteners spaced at five feet on-center.

Since the early 2000s, single-ply membrane sheet widths have become wider, with 10-foot-wide sheets now commonplace – resulting in rows of mechanical fasteners spaced at 10 feet on-center.

Currently, single-ply membrane roof systems have clearly overtaken conventional built-up and polymer-modified bitumen membrane systems in market share. The seam-fastened, mechanicallyattached method of installation also has overtaken traditionally adhered methods of application. The National Roofing Contractors Association (NRCA) annual market survey shows seam-fastened, mechanically attached single-ply membrane roof systems make up the majority of all membrane roof systems currently installed.

With the present emphasis on wind resistance in design, a closer look at how seam-fastened mechanically attached single-ply membrane roof systems interact with steel roof deck and joist construction is in order.

A common method of single-ply membrane sheet layout is shown in Figure 1. A common placement of mechanical fasteners is shown in Figure 2. These concentrated line loads can

Figure 2. Typical fastener layout at corner zones.

Figure 3. Line attached membrane under uplift.

Courtesy of the Steel Deck Institute.

severely overstress the steel deck and may also cause the steel joist below the deck to be overstressed under uplift loading. The behavior of such fastening systems, when the roof system is subjected to uplift loadings, is shown in Figure 3. The current trend in securement is for the membrane installer to mechanically fasten the membrane to the deck only along the edge of the sheet rolls to speed up the roof installation, thereby lowering installation costs. Unfortunately, the Structural Engineer of Record, and the steel deck and joist suppliers, are usually unaware of the concentrated load pattern of the roof membrane attachment.

In fact, the architect of record may not be aware of the ramifications of such attachments. The Architectural roofing specifications may simply state that the roof membrane shall be installed per manufacturers recommendations. The roofing installers foreman is the one who generally decides on the exact layout of the membrane sheets on the roof. That decision is made based on what layout can be installed in the fastest and least expensive

manner. Roofing suppliers and FM Global recommend the fastener line loads not be installed parallel to the deck ribs, but rather perpendicular to the deck flutes. Placing the lines of attachment parallel to the deck ribs will only load a one-foot width of the steel deck. This recommendation helps but may not eliminate potential severe overstress of the deck.

Currently, the Steel Deck Institute’s (SDI) position paper, Attachment of Roofing Membranes to Steel Deck (sdi.org), states: “SDI does not recommend the use of roofing membranes attached to the steel deck using line patterns with large spacing unless a structural engineer has reviewed the adequacy of the steel deck and the structural supports to resist the wind uplift loads transmitted along the lines of attachment. Those lines of attachment shall only be perpendicular to the flutes of the deck.”

Deck Strength Example

East-West Perimeters (Attachments Perpendicular to Deck Span) The first line load is 5 feet from the building edge and the second is 10 feet from the edge.

The third is 20 feet from the edge.

First Line Load: The membrane area for the first line load = (5 foot) = 5.0 square feet.

Second Line Load: The membrane area for the second line load = (2.5 feet + 5 feet)(1.0 feet) = 7.5 square feet.

Third Line Load: The membrane area for the third line load = (5 feet + 5 feet)(1.0 feet) = 10.0 square feet. The uplift pressure is 55.8 psf for the first 10 feet from the building edge and 33.3 psf for the remainder of the three span deck.

The maximum moment is 4.32 kip-in and occurs in the second span as a positive moment. For a uniformly loaded deck, the maximum moment is 2.31 kip-inches (negative) and is located over the first support from the building edge.

Note: Fasteners running parallel to the deck flutes is a severe condition and not recommended. If used, the following loading conditions occur.

Line Load: Parallel to Deck Flutes The uplift pressure is 55.8 psf.

The membrane area for the line load = (5 feet) = 5 square foot.

Line Load on 1.0 foot of deck width = (5.0 feet)(55.8 psf )- 4.5 plf = 275 pounds per foot Positive moment = Mw = (0.08)wL2 = (0.08) (0.275 kips per foot)(6.0 foot)2 = 0.79 kip-feet = 9.50 kip-inches.

Negative moment: Mw = (0.10)wL2 = (0.10) (.275 kips per foot)(6.0 foot)2 = 0.99 kip-feet = 11.9 kip-inches.

For a uniformly loaded deck, the maximum negative moment is 2.22 kip-inches.

Corner Condition Zone The uplift pressure is 84.0 psf for the first 10 feet from the building edge, and 55.8 for the remainder of the three span deck.

Line load on 1.0 foot of deck width = [(5 feet)(84 psf )]/2-4.5 plf = 206 pounds per foot for first 10 feet. The division by 2 is to account for load distribution between fastener

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Interior Zone (Field of Roof) Uplift line loads are determined using Component and Cladding ASCE Requirements (ASCE Chapter 30).

The fasteners are placed perpendicular to the deck span and are spaced 1-foot on-center. Therefore, the membrane area is 10 square feet (1-foot x 10-foot-wide sheet). The uplift pressure is 33.3 psf.

North-South Perimeters (Attachments Parallel to Deck Span)

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To illustrate the potential effect of the attachment pattern, determine the deck strength for the following conditions illustrated by Figures 1 and 2. Use Load and Resistance Factor Design (LRFD) Load Combinations and American Society of Civil Engineers’ ASCE 7-1. Thus, the controlling ASCE Load Combination is 0.9D + 1.0W. (Wind calculations are not shown for brevity.)

Given: A roof system located in Kansas City, MO. Category II Building. Exposure C per ASCE 26.7.3. The building is an Enclosed Building with a flat roof (¼-inch per foot). The building is 100 feet by 100 feet in plan and has an eave height equal to 30 feet.

The metal deck is 1.5-inch 22-gage, wide rib (WR) deck on joists 6 feet on-center.

Fy = 33 ksi. The roof dead load on the metal deck = 5 psf. The membrane is 10 feet wide in the interior zones and 5 feet wide in the perimeter zones.

From the SDI Roof Deck Design Manual (RDDM), φMn (negative moment capacity) = 5.358 kip-inches, and φMp (positive moment capacity) = 5.088 kip-inches.

Assume that, at some location in the field of the roof, the fastener line will be located at the center of a deck end span. From a structural analysis of a three span deck, the maximum moment occurs in the end span (positive moment); Mr = 4.85 kip-inches. For a uniformly loaded deck, the maximum moment occurs over the two supports (negative moment); Mr = 1.24 kip-inches.

KPFF is an Equal Opportunity Employer. www.kpff.com The Ardea Portland, OR

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March 2017

lines. Then (5 feet)(55.8 psf )-4.5 plf = 275 pounds per foot beyond.

Based on a continuous beam analysis, the maximum negative moment equals 11.55 kip-inches and occurs over the second interior support from the corner. The maximum positive moment occurs within the third span and equals 9.64 kip-inches. For a uniform load, the maximum negative moment equals 3.48 kipinches and occurs over the first interior support.

The maximum positive moment occurs in the first span and equals 2.73 kip-inches. See Table for a summary of the conditions.

Conclusions North-South Perimeters and Corner Zone failures occurred. It is interesting to note that, with the amounts of overload shown in these calculations, there are not more reported deck and joist failures. There may be a number of reasons for fewer reported failures. For example: 1) The design uplift anchorage of the deck to the joists, while increased for mechanical attachment as compared to adhered membranes, does not exceed the factors of safety in the design of the deck attachment fasteners.

2) The majority of roofs have not seen roof uplift loads of those predicted

by ASCE 7 because the U.S. has not been impacted by a major hurricane in over 10 years.

3) The decks may have higher yield strengths than those used in the design example. The SDI RDDM tabulates roof deck capacity based on a lower bound yield stress of 33 ksi.

Many manufacturers provide decks with yield stresses of 40, 50, or 80 ksi (limited to a 60 ksi design stress by the AISI S100 Standard). A design stress of 60 ksi versus 33 ksi will increase the deck flexural strength by about 70%.

Application When Re-Roofing An important point to note is that, per NRCA, approximately two-thirds of the roofing installed every year is re-roofing of existing buildings. Buildings that are 20 to 30 years old are unlikely to have higher yield strength steel deck. Therefore, caution is required when evaluating roof deck when re-roofing.

Higher Wind Regions The analysis described above was performed on a building located within the basic wind velocity zone of 115 mph per ASCE 7-10.

Particular attention must be paid to the design of the deck for regions where the

Summary table of required deck strength to actual deck strength.

Zone

Moment Mr /φMp Line Load, Mr or (kip-inches) Mr /φMn

Moment Uniform Load, Mr (kip-inches)

Mr /φMp or Mr /φMn

Interior

4.851

0.95

1.242

0.23

East-West Perimeter

4.32

0.85

2.31

2

0.43

North-South Perimeter

2

11.9

2.22

2.22

2

0.41

Corner

11.55

2.16

3.48

2

0.65

1

2

Positive moment, 2Negative moment. φMp = 5.088 kip-inches, φMn = 5.358 kip-inches 1

wind velocity is higher. At higher design wind speeds, a deck which is adequate to support an adhered membrane roof with uniform uplift deck loading may not be structurally adequate to support widely spaced line loads from a mechanically attached membrane roof.

FM Global Requirements Often times, FM Approval Standard 4470, Single-Ply, Polymer-Modified Bitumen Sheet, Built-Up Roof (BUR) and Liquid Applied Roof Assemblies for use in Class 1 and Noncombustible Roof Deck Construction, is required for roof systems. These requirements are more stringent with respect to deck spans and thicknesses because the FM Standard uses a Factor of Safety of 2, whereas the AISI S100 Standard mandates an ASD Factor of Safety of 1.67 for flexure. These requirements can be found on their RoofNav website. Go to www.roofnav.com and select Reference Materials followed by Approval Standards.

The FM Standard provides wind ratings based on fastener row spacing, deck spans, deck thicknesses, and deck yield strengths.

For the above example, for a 33 ksi, 1.5-inch.

WR deck spanning 6 feet, a 20-gage deck is required to obtain a 60 rating (30 psf ASD).

Recommendations Design recommendations for single-ply roofing when concentrated line securements are used to connect the membrane to steel roof deck instead of uniformly distributed securements include: 1) When FM Global requirements are to be followed, maximum deck spans, deck thicknesses, and deck yield strengths as required by FM Global must be used. a) Based on the maximum concentrated line loads determined from FM Global, specify the required joist net uplift. b) Coordinate your design requirements with the general contractor and the architect.

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March 2017

2) When FM Global requirements are not required: a) Determine the uniform net uplift forces based on the building code in force. b) Using the spacing between the lines of fasteners for the membrane, perform a structural analysis of the deck as a 3-span beam, placing the first concentrated load at the mid-span of the first deck span.

The subsequent loads are placed according to their spacing. This analysis will produce a moment diagram that is close to the maximum that would be achieved from an influence line analysis. c) From this analysis, specify a deck that has a flexural capacity that exceeds the maximum positive and negative design moments. d) If no deck is found that will work, change the spacing of the supports (joists) or alter the spacing of membrane fastening.

Changing the spacing of the membrane fastening is something that requires coordination with the entire roofing team (specifier, manufacturer, and installer). e) Determine the net uplift requirement for all joists based on the final selected line securement spacing and forces. f ) Specify these requirements to the joist manufacturer. g) Coordinate your design requirements with the general contractor and the architect.

Economics Based on experience, using the wide attachment spacing may not be economical when one considers the increase in deck costs and joist costs as compared to the labor savings using the wide securement spacing. For any given project, these cost comparisons should be made.▪

BRB MAST-FRAMES

An Improved Approach for Seismic Bracing

By Leo Panian, S.E.

740 Heinz completed, as viewed from the southwest.

I

n recent years, engineers have been seeking to capture the benefits provided by buckling restrained braces (BRBs) through the exploration of new braced-frame configurations to improve the seismic performance of building structures. One such alternative is the BRB mast-frame system, which enhances seismic performance and offers better architectural compatibility at a lower cost than conventional systems. The case study of 740 Heinz demonstrates the efficacy and cost efficiency of BRB mast-frames.

Tipping Structural Engineers designed the BRB mast-frame system as a response to the disadvantages posed by conventional steel and BRBonly systems. This innovative approach consists of yielding BRBs in series, with a stiff, elastic vertical frame (the “mast”) designed to pivot about its base. The mast redistributes loads between stories, producing a more uniform distribution of inter-story drift and eliminating the possibility of inelastic weak-story mechanisms.

The Design Challenge

The first major application of the BRB mast-frame system was for the 740 Heinz building in Berkeley, CA. This state-of-the-art life sciences building is clad in precast concrete panels with brick veneer and has a footprint of approximately 136 feet by 192 feet, for a total of 110,000 square feet of gross area. The floor framing system consists of steel beams and girders supporting concrete-filled metal deck. Framing is supported by steel columns spaced at approximately 32 feet on-center in both directions.

The seismic lateral-force-resisting system consists of two BRB mastframes in each direction. In the transverse, the frames are located next to the building’s stair cores; in the longitudinal, they are installed at the perimeter façade line. Each BRB mast-frame comprises yielding BRBs connected to a vertically oriented trusslike mast; a true pinned-base connection joins the frame and base. The structure was designed according to the provisions of the 2010 California Building Code; the frames were designed using an R of 7. The seismic analysis relied on a conventional code model response-spectrum method.

The BRB mast-frame’s vertical-truss configuration is a key aspect of the design, as

While there are economies in designing for lower seismic forces, the redundancy provisions of the building code can still require numerous bays of bracing, resulting in a significant number of BRBs. This, in turn, adversely affects architectural programming and cost. Furthermore, BRBs’ reduced stiffness leads to larger building deformations, rendering a structure more susceptible to weak-story mechanisms. Ironically, these disadvantages come with a cost premium.

Tipping’s BRB mast-frame system (left) vs. a conventional BRB scheme.

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740 Heinz Avenue

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March 2017

it can redistribute lateral loads between levels, eliminating soft-story mechanisms. The BRB mast-frame system relies on capacity-design principles to ensure that inelastic mechanisms will form predictably and reliably. To ensure controlled post-yielding response, the mastframe, including the base connections, anchor bolts, pile caps, and piles, was designed to resist amplified omega-level forces.

The frame also allows for equal-capacity BRBs to be used at all levels, owing to the action of the mast, which simplifies construction. In contrast, a conventional code-designed braced frame, in responding to the lateral-force distribution, typically has the strongest BRBs at the base and the weakest at the top.

The Code Conundrum The redundancy factor, ρ, was originally incorporated in the building code to prescriptively compel engineers to consider the number of the lateral bracing elements and their locations. ASCE 7 dictates that a braced-frame system is properly redundant if the number and arrangement of frames are such that the removal of any one brace in the system results in neither more than a 33 percent reduction in story strength nor an extreme torsional irregularity. Otherwise, the non-redundant structure must be designed with a 30 percent increase in the structure’s design base shear.

While adding more frames in the building can eliminate the ρ penalty, this adds significant cost and does nothing to address the potential weak-story failure of the frames. To address this conundrum, Tipping developed the inherently redundant mast-frame configuration to meet prescriptive requirements and improve seismic performance, without the addition of lateral bracing elements.

740 Heinz under construction.

Code Redundancy Analysis and Verification To demonstrate that the BRB mast-frame system met ASCE 7’s redundancy prescription, Tipping created a three-dimensional analysis model to directly assess the performance of the frames with brace elements removed. Using this model, BRBs were systematically removed from each frame at each story to evaluate the redistribution of forces and calculate resulting deformations. The results revealed that the remaining BRBs and diagonal mast members in the modified structure were indeed able to resist redistributed forces. In the controlling case, story strength was reduced by 21 percent, 12 percent less than the codeallowed 33 percent reduction. Furthermore, the maximum story drift ratios did not exceed the limit of 1.4 times as required by ASCE 7.

The Promise of BRB Mast-Frames The inherent redundancy of the system allows for fewer braced frames, improved seismic performance, and more economical construction.

Employing BRB mast-frames at 740 Heinz allowed the number of required frames to be cut from seven conventional BRB frames down to 4 BRB mast-frames; the total number of BRB elements was reduced from 56 to 16. Moreover, because the BRB mast-frames were easily located next to the building’s two stair cores and at the perimeter façade, they did not impinge on the architectural space plan. Lastly, this lateral system saved the project $360,000 in construction costs when compared to a conventional BRB-frame system.

In short, this system holds lots of promise for the future. It is a costefficient, nonproprietary, and simple high-performance system that can be designed in any number of possible configurations, making it an ideal lateral system for any steel braced-frame building.▪ STRUCTURE magazine

Close up of steel frame with BRB mast installed.

35

Leo Panian is a Principal at Tipping Structural Engineers in Berkeley, CA. He can be reached at l.panian@tippingstructural.com.

Tipping Structural Engineers was an Outstanding Award Winner for its 740 Heinz Avenue project in the 2016 NCSEA Annual Excellence in Structural Engineering Awards Program in the Category – New Building $10M to $30M. March 2017

STRUCTURAL ENGINEERING INSTITUTE OF ASCE

2017

STRUCTURES CONGRESS

Denver, Colorado, April 6-8, 2017

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Kick off Structures Congress 2017 by attending the opening plenary program. Hear from the conference co-chairs, SEI leaders and a special keynote speaker.

Dream Big: Sharing the Wonder of Engineering to Inspire the Next Generation Presenter: Greg MacGillivray, Director, Dream Big Chairman, MacGillivray Freeman Films

FRIDAY, APRIL 7 • 11:30 a.m. – 1:45 p.m.

Plenary Luncheon and Awards Program Celebrate the achievements of this year’s award winners, dine with colleagues and hear an outstanding keynote speaker.

Leadership Is a Personal Journey Presenter: Guillermo “Bill” Vidal, P.E. , 44th Mayor of Denver, engineer, author, consultant, Past President and CEO of the Hispanic Chamber of Commerce of Metro Denver

SATURDAY, APRIL 8 • 11:30 a.m. – 1:45 p.m.

Closing Plenary Luncheon and SEI Annual Business Meeting

Enjoy lunch with your colleagues and end this conference with world-renowned keynote speaker Charlie Thornton. Also, hear SEI President Andrew Herrmann, P.E., SECB, F.SEI, Pres.12.ASCE, on our progress to realize the Vision for the Future of Structural Engineering and congratulate the 2017 SEI Fellows.

A Career of Disruptive Innovation Presenter: Charlie Thornton, founding principal of Thornton Tomasetti and founder of the ACE Mentor Program

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Historic Renovation of

the

PROVO TABERNACLE

Courtesy of Dustin Smith

By Jeff Miller, S.E., Jesse Malan, S.E., and Julee Attig, CPSM

C

onstructed from 1883 to 1898, the Provo Tabernacle was a historical treasure of The Church of Jesus Christ of Latterday Saints (LDS) and the local community. It seated 1,500 and featured octagonal stair towers, a high-pitched gabled roof, art glass windows, exquisite woodwork, and a central tower topping out at 167 feet above the ground. The building hosted U.S. presidents, musical performances, school commencements, interfaith gatherings, and community events.

A four-alarm fire destroyed the building (Figure 1) in December 2010.

The exterior was almost all that remained of the Tabernacle. Rather than demolish the structure, the owner enlisted a team of architects, engineers, builders, and historians to assist with an unprecedented reconstruction and restoration project. Reaveley Engineers + Associates (RE+A) was the structural engineering consultant.

LDS Church leadership announced the Tabernacle would be rebuilt as a temple. Architecturally prominent, a temple is considered by members of the LDS Church as the most sacred place of worship. The structure serves a much different purpose than a chapel where regular worship services are conducted. This change in use would require the interior spaces be completely reconfigured within the original building envelope to accommodate new building functions.

Challenges & Objectives A significant challenge faced by the design team was converting a 35,000 square foot historic structure into a modern 85,000 square foot temple without losing historic details. A major excavation would be required to accommodate a basement and sub-basement below the original building, as well as adjacent sub-grade parking, doubling STRUCTURE magazine

Figure 1. Crews respond to Tabernacle fire.

the size of the building. In total, the contractor excavated to 25 feet below grade for approximately 170,000 square feet and 40 feet below grade for approximately 15,000 square feet.

The team had one primary objective: limit settlement or another movement that could cause damage to the existing brick walls. Since the original building had only a crawlspace below the main floor, a system had to be engineered to support and reinforce the existing masonry walls for excavation to take place. The design and construction team explored several excavation and shoring methods that would support the original five-wythe brick masonry walls while excavating two new sub-grade floor levels. A new internal bracing system would also have to be engineered to stabilize the remaining brick walls while the temporary external bracing system that was installed soon after the fire was removed.

38

March 2017

Figure 2. Shotcrete placed on interior face of the brick.

Figure 3. Care was taken with shotcrete placement around reinforcing steel.

The design of the interior bracing system needed to be compact and maximize working space for the contractor. It also had to allow placement of new reinforced shotcrete walls against the interior face of the brick. This bracing system would remain in place until a new structural steel frame was constructed inside the building, and new floor and roof diaphragms were in place to brace the exterior walls.

Selection of the shoring system was influenced by the presence of high groundwater at the site. The sub-basement level and lower part of the basement level would be located below the groundwater elevation. The proposed shoring system would need to ensure placement of the waterproofing membrane below the sub-basement floor and at the exterior face of the foundation walls without compromising the performance of the membrane under significant hydrostatic pressure.

Approach to the Work

Bracing/Reinforcing the Existing Masonry Masonry Testing After the fire, tests were performed on the mortar in the brick walls and revealed minimal damage to the brick and mortar at the interior face of the walls. Most of the damage to the walls was caused by the collapse of the wood roof structure during the fire.

Based on initial observations, it was evident that the mortar consisted of fine aggregate and lime, and was quite weak. Shear strength, compressive strength, and deformation property tests were conducted to assess the mortar’s physical properties. Results indicated the strength of the mortar fell below minimum thresholds. The brick walls did not have sufficient strength to function as shear walls or effectively resist out-of-plane earthquake forces. In short, the brick walls would need to be reinforced and strengthened.

The Solution The original brick walls are anchored to new reinforced concrete shear walls by placing shotcrete against the interior surface of the brick (Figure 2). Two of the five interior wythes of brick (approximately 8 inches) were removed, and that space was replaced with shotcrete.

Essentially, no floor space was lost. The remaining three wythes of brick were permanently anchored to the new shotcrete walls by installing 14-inch to 16-inch-long steel helical anchors into the brick.

In the completed building, the shotcrete walls function as shear walls to resist lateral earthquake and wind loads imposed on the building. The walls also stabilize the existing brick walls against lateral out-of-plane forces.

STRUCTURE magazine

In many areas, the need for thin concrete walls resulted in shear walls and boundary elements that did not comply with prescriptive code requirements. To help the owner gain confidence in the thinner walls performing as desired during an earthquake, the structural engineers completed a performance-based design using non-linear analysis techniques. The results indicated that the thinner shear walls would perform as prescribed to meet code requirements and the owner’s enhanced performance goal of life safety in the Maximum Considered Earthquake.

Because of the reduced thickness, the quantity of reinforcing steel within the walls was greater than normal. Extra care was taken by the contractor to place the shotcrete in the walls while preventing voids behind and between the reinforcing steel. Enhanced inspections were conducted to maintain quality control of the shotcrete placement (Figure 3).

Mechanical rebar couplers were placed at the bottom of vertical reinforcing bars within the shotcrete shear walls so that the bars could be extended into the top of the reinforced concrete foundation walls that were placed during a later phase of the project.

After the brick walls had been reinforced and supported by the new concrete walls, steel beams were attached to the concrete walls creating a reinforcing horizontal “ring” near the elevations where new suspended concrete floors would be placed.

Excavation With the masonry reinforced and strengthened, the next phase was to support the stabilized building shell so excavation could begin. The new composite walls would be supported by cased micro-piles while 30,000 cubic yards of earth were removed.

A series of eight-inch diameter micro-piles were drilled into the ground, on each side of the walls, to a depth of about 90 feet. Some of the piles were battered to resist the temporary lateral loads on the shored walls during construction. Openings were then excavated through the rubble-stone foundation walls just below the brick and shotcrete walls. These openings were aligned between pairs of micropiles. Steel needle beams were placed through the foundation wall openings and connected to the micro-piles (Figure 4, page 40).

Hydraulic jacks were placed between the needle beams and concrete bearing lugs formed into the bottom of the shotcrete walls. The jacks

39

March 2017

Figure 5. Block-outs in foundation walls.

Figure 4. Steel needle beams connected to micro-piles.

were then loaded to transfer the weight of the walls above onto the needle beams and shoring system. The contractor closely monitored the elevation of the walls during this load transfer to ensure only very slight changes in the elevation.

Once the weight of the walls was transferred into the shoring system, adjustable bearing seats were installed on each side of the jacks and the jacks were removed. Excavation of the surrounding soils then commenced with continued monitoring of the elevation of the structure.

As excavation progressed, steel diagonal braces were added between the micro-piles to provide lateral stability and maintain the allowable unbraced length of the micro-piles.

Footings & Foundations

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When the bottom of excavation was reached, a waterproofing membrane was installed and a new 18- to 24-inch thick reinforced concrete mat footing was placed. The new sub-basement level is

approximately 14 feet below the design groundwater elevation.

The mat footing and foundation walls were designed to resist the upward hydrostatic pressures.

The micro-piles served several purposes. First, they temporarily supported the exterior brick walls. Second, they served to support the mat footings for the heavy loads of the new structure. The micro-piles also helped mitigate the potentially liquefiable soils that exist on the site. Lastly, they acted as hold down anchors to resist buoyancy forces created by the water table.

After the new mat footing had been completed, new reinforced concrete foundation walls were constructed between the mat footing and the bottom of the brick walls. Block-outs were formed in the foundation walls around each of the shoring needle beams (Figure 5).

New Superstructure With the foundation system complete, the focus shifted to a new structural steel superstructure inside the shell of the existing building.

The three new floor structures consist of composite steel beams supported by the new shotcrete exterior walls and interior steel columns.

The reinforcing in the floor slabs was connected to dowels previously set in the shotcrete walls. The dowel system was designed to transfer forces between the walls and the floors, which serve as horizontal diaphragms while providing ductile behavior during an earthquake.

The new sloped roof structure consists of a metal roof deck supported by steel beams.

The structure was designed to support the weight and overturning forces imposed by a new center tower matching the pre-1917 original.

The restoration of this key architectural feature was of particular import to the owner (Figure 6).

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To the west and south of the Temple is a new single-level, sub-grade parking garage that connects to an adjacent parking garage. The lid structure over the parking area was designed as a post-tensioned concrete beam and one-way slab system. The typical span of the post-tensioned beams is 60 to 64 feet. Beam spacing varies but is typically about 27 feet-on-center.

This structure supports a beautifully landscaped plaza. The weight of the landscaping overburden (18 to 35 inches of soil), pavements, snow, and plaza live loads combined to create significant loads on the lid structure.

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STRUCTURE magazine

40

March 2017

Figure 7. Wood-framed roofs at the four building corners.

Conclusion

Figure 6. Restoration of center tower.

The concrete beams were designed with higher than normal posttensioning stresses to reduce beam depth as much as practical, while still controlling flexural cracking in the beam section. Careful detailing of the tendon anchorage plates was required to verify that they could fit within the profile of each of the beams. Grade 75 rebar was specified to reduce congestion of the steel reinforcing bars within the beams

Architectural Considerations Restoring the building to its original state and preserving its historic fabric was a primary architectural objective for principal architect Roger Jackson of FFKR Architects.

Preserving and stabilizing the original brick walls was an initial focus. Also of intense interest was restoring the original central tower. In 1917, the tower was removed because its weight caused excessive deflections in the roof members. The new tower is laterally supported by steel braced frames which transfer forces to the shotcrete shear walls through the roof diaphragm and supplemental bracing. Natural light streaming through windows around the tower illuminate an art glass ceiling in the main upper lobby located directly below the tower.

Another significant architectural feature of the original Tabernacle was the wood-framed roofs of the octagonal stair towers at the four building corners (Figure 7). One stair was partially burned and damaged by the fire while the other three only suffered minor smoke damage. The tower roofs were each removed as a single piece, and the one damaged tower was rehabilitated and rebuilt to its original configuration. The original straight wood sheathing on the tower roofs was overlaid with new wood structural panel sheathing to stiffen and strengthen the roof structures. Connections between the base of the tower roofs and the walls below were improved to resist the required wind and earthquake loads.

STRUCTURE magazine

The complex nature of this project demanded unique engineering and construction solutions.

Dynamic, collaborative interactions between owner, architect, structural and geotechnical engineers, contractor and subcontractors generated economic and innovative solutions.

“The contractors and architects have worked in similar situations where they have done underpinning but not at this scale and this height,” said LDS Church project manager Andy Kirby. “The design of this was a process between the architect, our design team, the structural engineers, and the contractors. We came up with multiple options, vetted those out, and then improved it to what you see now.”

Many have called this historic renovation a “once-in-alifetime” project. The team understood what this project meant to the owner and community, and championed this vision from beginning to end.▪

41

Reaveley Engineers + Associates was an Outstanding Award Winner for its Provo City Center Utah LDS Temple project in the 2016 NCSEA Annual Excellence in Structural Engineering Awards Program in the Category – Renovation/Rehabilitation.

Jeff Miller, S.E., is a Senior Principal at Reaveley Engineers in Salt Lake City. He was the Principal in Charge and Project Manager on the project. In 2016, Jeff was recognized as the Utah Engineers Council’s Engineer of the Year.

Jesse Malan, S.E., is an Associate at Reaveley Engineers. An active SEAU member, he has managed the structural design of the 220,000 square-foot research center expansion at Huntsman Cancer Institute.

Julee Attig, CPSM, serves as Reaveley’s director of marketing. She serves on the board of directors for SMPS Utah. She can be reached at jattig@reaveley.com.

March 2017

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Wood Meets Structural, Aesthetic, and Sustainability Goals at One North

By Tony Cameron, P.E.

M

Viewed from the interior courtyard, One North’s intriguing façade incorporates exterior shading, an airtight insulated building envelope, and sustainably harvested, locally sourced cedar siding. Courtesy of Andrew Pogue.

uch has been written about the One North development in Portland, Oregon. The two buildings, known as East and West, feature unique architecture, beyond-code energy efficiency, and a shared community courtyard.

The project has received numerous awards for innovation and sustainability. However, behind the unique exterior lies a story. The team used glulam construction to meet a number of structural and aesthetic goals.

“The most significant structural design challenge we faced with the project was due to the geometric demands of the buildings,” said Tim Terich, partner and principal in charge at Froelich Engineers, the structural engineers for One North. “The irregular shapes of the two buildings and the lateral systems that were spread throughout both required real collaboration between us, Holst Architecture, and R&H Construction. However, because wood is such a flexible and versatile material, we were able to make it work structurally and were also able to meet the owner’s aesthetic and sustainability goals.”

The East Building stands four floors tall with 43,418 square feet. The structure features three floors of Type V-B wood-frame construction over a Type I concrete podium. The West Building has five floors and 35,671 square feet of space. This building has four stories of Type III-B wood construction over a Type I concrete podium. Both feature retail space on the first floor, with offices and creative space above.

Terich explained that the interior of the East building has a large open area with stadium seating, which triggered the need to go to Type V construction. “The interior of the smaller West building did not have that, which meant it was more efficient for us to use Type III-B construction,” he said.

Wood’s Versatility Gave It the Edge Both buildings have unique geometry, and Terich stated that they initially considered using concrete. “But, as we got into it, we knew we could not meet the architectural goals, which were sustainability and a desire to create a warm aesthetic. Concrete has a colder feel and it costs more, and wood is a better choice environmentally.”

STRUCTURE magazine

Glulam beams and columns and tongue-and-groove cedar decking were left exposed throughout the interior. Courtesy of Andrew Pogue.

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They also looked at using steel framing. However, with all the unique angles, steel would have required thousands of shop drawings, all of them unique. “Wood can be modified on site and is so much more affordable,” added Terich. “So, we chose wood for multiple reasons.

Number one was cost. Number two was the fact that wood is a renewable, sustainable material, which was a goal for the owner. And finally, the warmth and feel of the timber were a big driver for the architect.

So we embraced the wood, and gave it a bit of a modern slant.”

of 2-by-6-inch wood studs and wood structural panel shear walls for lateral loads. Stairs and elevators were also wrapped in wood structural panel shear walls. They used continuous threaded rod hold-down systems. “We had to work around some staggered windows, but were able to fish them through in a few areas,” he added.

Because the East building had a very complex geometry with some big openings in the diaphragm, Froelich engineers used rigid and semi-rigid diaphragm analysis. They used the envelope technique to analyze the West building.

Timber Frame Functionality A concrete podium provided fire separation, and allowed them to support the discontinuous loads that “didn’t want to stack and come down all the way through the building,” said Terich. Above the podium, they left the glulam timber frame exposed.

Architectural grade glulam beams in 6¾and 5⅛-inch widths are supported by exposed glulam columns.

A number of glulam beams were manufactured with one or two extra tension laminations for fire resistance. “This was a compromise made with the city code officials,” Terich explained. “We wanted to avoid using automatic smoke curtains as much as possible and, by doing something as simple as adding one or two laminations to the beams, the code officials felt more confident about glulam performance in the event of a fire. It was part of the compromise and solution to achieve that open area.”

He added that the architect was also very interested in the aesthetic of the beam and column connections. “They did not want to use off-the-shelf connectors, even though they would have met code requirements. So, we spent a lot of time strategizing about connections.

Most are concealed knife plate connectors, and some of them became quite complicated in places where we wanted to avoid showing exposed bolt heads or steel plates wrapping around the members. So, we tried to keep all the bearing elements hidden. The result was the clean but warm aesthetic that the architect wanted.”

Innovative Window Frames One of the most unique features of the project was provided by the window frames, referred to as “apertures.” Both East and West

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Structural Considerations One North was designed to the 2010 Oregon Structural Specialty Code, and Seismic Design Category D; seismic controlled the lateral in all cases. A mix of lateral systems was used. Above the podium, however, most were wood structural panel shear walls with a few custom moment frames. “We had to go with the moment frames because we did not have enough shear walls in some places, and we did not want to use any diagonal brace frames,” said Terich.

Both buildings used conventional wood construction for the walls, which consisted

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The sprinkler system in the radiator places an individual sprinkler head near every exposed interior column. Courtesy of Josh Partee 2015.

buildings were modeled in 3D, and then the engineered prefabricated curved frames were attached. Some of the deep set windows were cantilevered, and others were not. The light gauge metal used in the prefabricated frames reduced weight by 60 percent over a steel solution and helped speed installation.

“The actual primary wood structure of the building is more rectangular than it appears,” Terich said. “We used the apertures to make things easier and to add dimension. In some areas, we cantilevered the glulam to provide actual floor area; those are structural. However, in other areas, the metal aperture assemblies were simply bolted to the frame. I would say it is a 50/50 mix. Knife plates and tube steel spans between the floors allow the whole assembly to be attached.

These apertures were then sheathed in wood structural panels. So, there is really a flat plane of structure and then the apertures, which change on every floor, cantilever off the grid.”

Every material had its place. “We used the concrete where needed for the podium, and it worked well there,” said Terich. “We could have built the apertures with wood, but the pre-engineered systems were so easy. We just covered them with wood structural panels to achieve that exterior geometry. Then we exposed the glulams to provide interior warmth.”

He said they were able to achieve their goals both outside and in.

“We got that warm wood look with some modern connections and were able to maintain the integrity of the architectural and sustainability goals while getting the structure to work. It required close collaboration between us, the architect and the builder, but we were all committed to the details. In the end, we were able to meet an extensive variety of goals, in large part because wood is so adaptable.”▪

Project Teams

Constructability of Wood Terich said his biggest surprise came in how easy the two structures were to build. “It is a beautiful but relatively challenging design, so I thought the contractor would have their hands full,” he said. “There were so many elements – the concrete podium, the wood frame, and the metal stud aperture assemblies. I thought it would take longer to build, but R&H Construction brought some real craftsmanship to the table and got it all to fit smoothly.”

From an engineering perspective, Terich said it was a satisfying challenge working with the variety of materials to achieve the goals of the building. “I was not sure we would be able to pull off the geometry of these buildings until we really got into it,” he said. “But wood is so adaptable, which is exactly what we needed when we had to tie into some of the less adaptable elements, such as the moment frames and the tube steel columns which support various areas.”

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Radiator Team Developer: Kaiser Group, Inc. Structural: Munzing Structural Engineering Architect: Path Architecture One North Team Developers: Karuna Properties II, LLC; Nels Gabbert, LLC; Owen Gabbert, LLC Structural: Froelich Engineers Architecture: Holst Architecture Tony R. Cameron, P.E., is a Staff Engineer at APA-The Engineered Wood Association. He can be reached at Tony.Cameron@apawood.org.

March 2017

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STEEL CONSTRUCTION Companies Improve Products to Keep Up with User Demands

By Larry Kahaner

S

teel users are demanding changes and companies are responding with updates, enhancements, and new products.

Amber Freund, Vice President – Operations at RISA Technologies (www.risa.com), says that the company’s software receives new features on a frequent basis. “With regards to recent steel-related improvements, the latest releases added the ability to get both analysis and code checks for cold-formed steel face-to-face and tube members,” she says. “Our staff, composed of structural engineers, researched a number of codes and white papers to provide this ability.

We added this feature after receiving requests from users who wanted to use face-to-face cold formed shapes but couldn’t find examples of how to calculate their capacity.”

Another major new feature is baseplate design within RISAConnection.

Says Freund: “For years we have had users asking for the ability to get baseplate design for their RISA-3D models without needing to enter the forces into another program manually. By providing full integration between RISAConnection and RISA-3D, the forces are automatically transferred, and you can now get baseplate design for your RISA-3D models on a Per-Load-Combination basis. This ability means that your baseplate and anchor bolt forces are much more accurate than using envelope forces, giving you the most realistic and economical baseplate designs.”

As for industry trends, Freund sees an increased reliance on software to do engineering calculations. “This is a trend that has been ongoing for at least 20 years, and we see no end in sight. Project schedules no longer afford engineers the time to do hand calculations, and permitting officials now require rigorous 3D analysis for many structures that hand calculations were previously considered adequate,” says Freund. (See ad on page 84.)

ClarkDietrich Engineering Services (www.clarkdietrich.com) officials would like SEs to know about their TrakLoc Drywall Framing System. The system offers multiple assemblies including the TrackLoc Fixed Length Stud (TLF), the TracLoc Adjustable Stud Assembly (TLA), the TrakLoc Deflection Stud Assembly (TLD), and the TrakLoc Elevator Stud (TLE), according to Chad Casbon, Director of Engineering. “Each system offers the benefit of a snap and lock connection between the top/bottom track and each stud that does STRUCTURE magazine

not require screws. Also, they all allow installation from the floor, eliminating the need for lifts which saves time and money. We see an increasing number of circumstances where long-length studs need to be stocked in high rise buildings without the problems associated with closing streets and using cranes, for which a major component is cost. Traditional cold-formed steel members can be spliced, but that requires engineering, more labor, and unknown performance in terms of stiffness. TrakLoc offers a pre-engineered solution with minimal labor and is backed by testing that ensures an expected performance.

I would suppose that most engineers are not aware of some of these logistical job site problems nor are they likely familiar with potential solutions like TrakLoc.” The company highlights its involvement with the new Sacramento Kings Arena, the Golden 1 Center, which included 65,000 linear feet of metal stud wall framing. “The project included unique challenges that were solved through collaboration with the framing contractor.

One such challenge was the construction of 48-foot tall exterior wall panels that were erected and stacked in a 22-inch wide cavity between the new building and an existing building. All metal stud members were pre-measured and pre-cut to minimize waste and maximize efficiency.” Casbon adds: “Another design challenge was the free-standing, self-supporting concession stands with cantilevered canopies framed completely out of cold-formed steel members. All seismic design requirements that are typical in California were satisfied without the addition of more expensive hot-rolled steel members.”

“Through the use of BIM, creative engineering, and collaboration, ClarkDietrich Engineering and the other design team members were able to maintain the open space nature of the Arena without compromising any of the desired systems. These efforts resulted in the completion of this fast-paced, high-profile project on time,” Casbon says.

Stuart Broome, Business Manager for Engineering at Trimble Solutions (www.tekla.com/us), says that Tekla Structures has been the chosen software solution for steel detailers around the world for many years but more recently has become popular with other disciplines, especially structural engineers. “The fact that it can be used for construction documents as well as shop drawings makes it

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very appealing to structural engineers, and its ability to model in any material, including cold formed, means that it is extremely versatile.”

As for new versions, Broome says: “Tekla Structures 2017 has many enhancements, especially in the areas of rebar modeling and drawing production. I expect that Tekla Structures will continue to gain momentum as the structural engineer’s BIM solution of choice because of the ability to work to a high level of detail and pass valuable information downstream. Structural engineers appear to be getting more interested in producing ‘truly constructible’ models rather than ‘design intent’ models which can often be open to interpretation.

Tekla Structures does this well, without much additional modeling time and without the model size becoming unwieldy.”

Broome also notes that Tekla Structural Designer (TSD – Trimble’s analysis and design solution) has seen many improvements and additions in the last 12 months. “The one that has been most well received is the ability to model and design a wide variety of foundations. Pad footings, strip footings, pile caps, and raft foundations are all now included,” he says. “However, it is the ability of TSD to work so well within the BIM environment that is continuing to drive our business. TSD 2017 continues to deliver in this area whether you are using Revit or Tekla Structures as your BIM platform. The fact that TSD is a physical modeling solution rather than a traditional ‘wire frame’-based analysis tool make this integration very easy for us to provide.”

More enhancements are part of Tedds 2017, including code updates.

“Tekla Tedds has always been a favorite of our clients. However, now that Tedds has been available in the U.S. market for some years, our clients are starting to venture beyond the component calculations included in the structural calculation library and are now using Tedds as it was originally intended–as a total calculation production suite.”

Adds Broome: “Tedds includes code tables, code graphs, section data, section property calculator, 2D frame analysis, and the ability to write electronic calculations in an MS Word environment. Structural engineers appear to be placing value on the capacity to produce, submit, and archive all of their structural calculations electronically.

We expect this trend to continue.”

How’s business? “ I say this every year,” Broome adds, “and I can say it again this year – business has never been better. I have seen a huge shift in attitudes to new technology over the last five or six years. Structural engineers seem to be moving from being afraid of change to now striving for improvement. The race to be the most productive and competitive is on, and we think our clients have the best chance of winning that race. We look forward to sharing in their success.” (See ad on page 3.)

Ben Follett, U.S. Product and Marketing Manager at Nemetschek (www.nemetschek.com/en), is also weighing in with his company’s updates. “Our version 17 release is planned for May. With that release will come updates to all the steel-related codes, updates for

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6/02/2017 16:25:13

the AISI code, as well as updates for the AISC 360 codes. We also have a project for composite improvements that will finalize or solidify our work for composites based primarily on user feedback and user beta testing. The hope is that we are providing users the composite workflow that they have been asking for and we have been trying to achieve,” he says.

He notes that the company has always been customer driven and will remain so. “That is our number one goal. We answer questions within the same day for all of our customers. On the developer side, we truly only develop based on customer feedback,” Follett says. “If there are things that need to be added or need to be changed, or if our priorities are one thing but our customer or group of customers or group of potential clients think that they should be another, then obviously we are going to be very open to making that.”

For the future, Follett sees the continuing interest in interoperability not only between the architect and the engineer but between the engineer and the fabricator. “I think that is going to play a critical role going forward. Trying to determine how to better exchange data or models is important because we often spend much time and money on change orders during the construction phase. A lot of that could be mitigated by having better coordination and cooperation between the engineer and the fabricator, and ultimately the contractor.”

Nick Decker, the Senior Industry Specialist at Bluebeam, Inc. (www.bluebeam.com), says the company takes great pride in partnering with customers to create new features and fine-tune workflows that eliminate the tedium of repetitive, time-consuming tasks. That optimizes collaboration and workflow efficiency. “Every new iteration of Bluebeam Revu grows with and responds to the evolving workflow needs of our customers. Structural engineers use Revu every day to expedite reviews and preserve value,” he says. “Bluebeam Revu delivers enhanced PDF-based takeoff and workflow automation tools that span the entire project lifecycle and maximize workflow efficiency, making for a powerful end-to-end solution.

“The Batch Markup Summary feature in Revu 2016 allows the project team to produce a single comprehensive report detailing the changes made across an entire document set. With expanded data sorting and filtering capabilities, running multiple reports in both PDF and Excel formats is easier than ever.”

Decker adds: “The Legends feature enables engineers to visualize the markup data directly on the PDF, which was a highly requested workflow enhancement. By summarizing the markup data in a customizable table, the legend on the PDF automatically updates in real time, providing the user with data at a glance.”

Decker notes that Bluebeam Revu is used by customers in more than 100 countries. He says: “Bluebeam Revu is used by 94% of top US contractors, 86% of top U.S. design firms, 92% of top designbuild firms, 74% of top international design firms, and 78% of U.S. specialty contractors. Bluebeam was also ranked as one of the nation’s fastest growing technology companies by Deloitte Technology Fast 500 three years in a row.”

As for what trends he is seeing, Decker says that project teams are becoming more dynamic, handling more projects across increasingly larger geographical areas. “Having an open, lightweight platform on which to collaborate with team members across the globe has become a necessity and not a luxury. Beyond that, engineers and designers are STRUCTURE magazine

wearing more hats than ever and utilizing more software solutions to complete their daily tasks. To expedite those workflows across independent systems, engineers are requesting systems talk to each other, and that file types be viewable and editable across multiple software platforms. This explains the rise of APIs for system integrations and open file formats, like IFC.” According to Carlos de Oliveira, P.Eng, co-founder and President of Cast Connex Corporation (www.castconnex.com), headquartered in Toronto, Ontario, architecturally exposed structural steel (AESS) is omnipresent in modern airports. The company is currently supplying components for Austin–Bergstrom International Airport and Charlotte Douglas International Airport, and has in the past supplied castings for airports from coast to coast to coast – from critical structural elements in the seismic-retrofit of Oakland International Airport to its Universal Pin Connectors and Architectural Tapers used at the ends of AESS braces in Bangor International Airport.

In Austin–Bergstrom International Airport designed by Gensler and Architectural Engineers Collaborative, CAST CONNEX® Universal Pin Connectors™ are used at the ends of key AESS elements on the exterior of the new terminal expansion, while custom designed castings support AESS roof trusses spanning 90-feet across the terminal.

For the Charlotte Douglas International Airport Concourse A Expansion project, CAST CONNEX provided pre-tender concept development support to Perkins+Will, C Design, and Stewart Engineering, and is supplying design-built custom cast steel column bases that not only provide fire- and blast-resistant structural supports for the 145-foot long roof trusses, but are also a key part of the new building’s architectural expression.

“While educational, cultural, and commercial projects continue to be our company’s ‘bread and butter,’ airports and transit terminals are sectors where steel castings can flex their structural and architectural muscle,” says Carlos. “It is in those large scale projects where we get to push the boundaries in terms of providing highly integrated elements that are critical to both the structural performance of the buildings as well as to their overall architectural quality.” (See ad on page 2.)▪

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March 2017

Professional issues issues affecting the structural engineering profession

T

here is a disturbance in the Force. Can you feel it?” This quote can be applied to many different subjects in the universe, including what is going on in the construction industry here on earth. We do not have floating cars and diplomatic robots fluent in six million languages yet, but the construction industry is being transformed like never before.

While there are sure to be growing pains along the way, it is also an exciting time to be in the industry.

There are so many changes happening in the construction industry, as a whole, that it would be remiss not to stop and consider what the impact is to structural engineering, fabrication, and construction. Three key factors are shaping the future of designing and making structural systems in the global construction industry. These include: • Global adoption of Building Information Modeling (BIM) • Changing project delivery methods • Dawn of the “Era of Connection”

The Future of Making Structural Things in the Construction Industry

By Michael Gustafson, P.E.

Michael Gustafson is currently Business Strategy Manager for Structural Engineering, responsible for establishing long-term Business Strategy for structural analysis, design, detailing, and fabrication with Autodesk. He can be reached at michael.gustafson@autodesk.com.

BIM

The most significant trend to impact the discipline of structural engineering since the advent of personal computing is the adoption of BIM. Beginning in the early 2000s, it established a way for project teams to improve collaboration by working within a common, multi-discipline, three-dimensional environment. Structural engineering firms initially adopted BIM to meet client contract provisions, but now see the return-on-investment as a result of better-coordinated designs that are easier to communicate to their clients. Additionally, the benefits of BIM have also been recognized by owners who – along with government agencies across the world – are now driving BIM mandates for their projects.

The benefits of BIM are real, and engineering and fabrication firms are seeing them every day.

However, BIM is not the only trend impacting the industry. There are other challenges beyond new technology that are driving change and disrupting the structural industry we know.

Changing Project Delivery Methods Despite the proven benefits of BIM in engineering and the use of model-driven processes in fabrication, structural engineers still feel the competitive pressures from increasing project complexity, globally dispersed teams and accelerated project schedules – compounded by a lack of skilled labor entering the workforce. To overcome these challenges, project teams are reshaping how they design and collaborate so

52 March 2017

New technology and processes are rapidly changing the way that structural engineers, detailers, and fabricators deliver projects.

they can generate new value streams for their firms and remain competitive.

For example, if engineers, fabricators, and builders can contractually work together with shared risk and reward, the benefits are significantly greater. Because of this, we see firms change how they deliver projects in a number of ways: – Engineering firms and construction firms are merging to provide combined, integrated designthrough-construction services.

– Engineering firms are forming business partnerships (like informal partnering and joint ventures) with detailing or fabrication companies to offer integrated services that allow them to extend their design-assist offerings further upstream.

– Firms are delivering projects with more innovative contractual models like Design-Assist, Design-Build, or Integrated Project Delivery.

Have these delivery models already been used in the past? Yes, they have. What is different now, and likely to continue into the future, is that technology is transforming the actual process of designing, building, and connecting teams in a way that is magnifying the benefits of using these more collaborative delivery models.

Dawn of the Era of Connection We are now on the cusp of a new era of connected design, manufacturing, construction, and building operation that is driven by the digitization of information and connectivity between people, places, and things, also referred to as the Internet of Things. Here are a few of the trends that we see growing from this era of connectivity that will surely impact how structures are designed and built over the next decade: – New structural materials and systems will emerge that are smart, connected, adaptive, and sustainable. Examples of this are selfhealing concrete, 3D printed nanostructures, and structural systems that dynamically adapt to changes in their environment.

– Computational methods using machinelearning will automate simple engineering tasks while assisting engineers to perform

more complex engineering tasks. This will empower engineers to offer more high-value services.

– Global work sharing will become commonplace as the world scales its cloud infrastructure and services, making engineering and detailing services more accessible and competitive.

– An engineering education will focus on high-value, problem-solving skill sets.

Craft and labor training will require new technology skill sets that are more manufacturing-centric.

– Manufacturing processes will be hyperconnected with the buildings that enclose them to optimize and minimize energy consumption and minimize their carbon footprint.

– Manufacturing-driven innovations like machine learning, lean manufacturing, and modular construction will transform the construction site in response to a growing shortage of skilled domestic labor.

– The sharing economy will disrupt how construction projects are funded, designed, built, and operated. This will be enabled through the connectivity of teams, manufacturing and job site processes, and building operations.

The common theme that will emerge is a hyper-connectedness between people and things that will allow the production of ideas and building products in a much more effective and sustainable way. So how seriously should you consider these trends? Are others in the industry already preparing for these changes?

An excellent view of the road ahead can be had by looking at the British Government.

Beginning in 2016, they require all government projects to use BIM. This mandate is a part of Britain’s ‘Construction 2025’ joint strategy which sets out how industry and government will work together to put Britain at the forefront of global construction over the coming years. Britain believes that using digital design with smart construction methods will give them a competitive advantage over other world economies. In other words, if they can reduce the costs to build and operate their infrastructure, they will be more competitive than other economies that do not. Their success will put pressure on other economies to follow suit with digitally connected infrastructure to compete in a global economy.

New materials, better-connected project teams, the sharing economy – it is a lot to digest. One thing is certain – the future of making structural things promises to be an exciting ride.▪

BIM was used by Odeh Engineers to successfully deliver the complicated MassArt Residential Hall, Boston, MA. Courtesy of Odeh Engineers.

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Lessons Learned problems and solutions encountered by practicing structural engineers

C

ondensation on interior surfaces can cause corrosion and wood decay if not addressed promptly. Repair and restoration of decayed structural elements are important. Equally important is determining the source of the problem, so it does not reoccur.

Condensation is moisture vapor collecting on a cold surface – in this case, wood roof sheathing at the interior of the building. This article presents a case study of an investigation on a tilt-up concrete warehouse with a low slope wood framed roof system, with insulation and vapor barrier located below the wood structural roof deck. The authors have found this construction type to be prone to condensation problems that can be related to small changes in interior temperature or humidity.

Case Study

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

Wade Vorley is a Senior Associate at Wiss, Janney, Elstner Associates, Inc., Seattle, WA. He can be reached at wvorley@wje.com.

The online version of this article includes references. Please visit www.STRUCTUREmag.org.

their more temperate climates. Reno, however, can become frigid in the winter and more heating is required for interior comfort. This building is heated with eight direct-fired natural gas heating units. All of the combustion byproducts from the heaters, which includes water vapor, are blown into the interior warehouse space when the heaters are in use.

In 2012, during a tenant improvement, wet and decayed OSB roof sheathing was discovered. A subsequent investigation by others found that vast areas of the OSB had high moisture content and specific locations had advanced wood decay, causing localized loss of structural capacity (Figure 3).

Near Reno, Nevada, a 500,000 square foot single story warehouse was constructed in 2007. By 2012, large portions of the wood structural panel oriented strand board (OSB) roof sheathing was found severely decayed from moisture collecting on its underside. In 2013, Wiss, Janney, Elstner Associates, Inc. (WJE) was retained by an attorney representing the owner to Moisture Monitoring evaluate and monitor moisture conditions at the at Roof Deck underside of the OSB roof sheathing, as well as to design structural repairs.

To evaluate interior moisture, WJE obtained The subject building has 8-inch thick tilt up monitoring devices from OmniSense, LLC, which concrete walls, with the roof deck about 32 to included two G3 Wireless Gateways and eleven 38 feet above the concrete slab-on-ground. The S900 wireless temperature, relative humidity, and roof structure is wood panelized construction moisture content sensors (T+RH sensors). Ten with steel trusses and steel columns. From the T+RH sensors were installed inside the building, top down, the general roof assembly includes distributed throughout. At two locations, T+RH the following: sensors were placed at 10 feet above the slab, just • Single ply thermoplastic roofing below the vapor retarder and at the bottom surmembrane attached via screws to the face of the OSB. At the other locations, sensors wood sheathing were placed only on the bottom surface of the • Separation sheet OSB. One sensor was placed outside to collect • 15/32-inch thick OSB exterior temperature and humidity readings. The • 2×6 lumber purlins at 2 feet on-center, gateways collected data from the sensors wirelessly spanning 8 feet • Steel trusses at 8 feet on-center, spanning 50 feet The roof is insulated with R19 fiberglass batt insulation placed below the OSB and between the 2×6 purlins, with a white vinyl vapor retarder stapled to the purlins below the insulation (Figures 1 and 2). The vapor retarder was not continuous and was not sealed around penetrations. The authors have studied similar warehouse buildings in Washington, Oregon, and California where the buildings are only provided Figure 2. Typical vapor barrier discontinuity at the plane of steel with minimal heating systems due to truss web members.

Condensation Related Failure of Wood Roof Sheathing

By Zeno Martin, P.E., S.E. and Wade Vorley, AIA, RRC

Figure 1. Typical wood roof assembly.

54 March 2017

Condensation Problems in Low Slope Roofs

Moisture Content and Dew Point Differential Moisture Content (%) At Underside Of OSB

Dew Point Differential (Temperature minus Dew Point)

30

40 35

25

20

25

15

20 15

10

10 5

5

7/18/16

6/18/16

5/18/16

4/18/16

3/18/16

2/18/16

1/18/16

12/18/15

11/18/15

9/18/15

10/18/15

8/18/15

7/18/15

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Figure 4. Approximate 3-year summary of moisture content and dew point differential conditions at the underside of the OSB roof deck.

conditions, made condensation worse. Once the OSB is wet, the fiberglass batts adjacent to the OSB, as well as the vapor barrier, serve to trap the moisture and inhibit drying.

This problem is not unique to this particular building. The authors have seen similar problems in other wood panelized roofs with fiberglass batt insulation under the roof deck.

Both APA and AITC have publications discussing the problem and ways to minimize moisture entrapment in panelized wood roof systems.

A repair was implemented to restore the vertical and lateral load carrying capacity lost due to the decay of the wood roof sheathing.

New plywood was placed over the existing OSB. The existing OSB was retained in place and allowed to dry. A new roofing membrane was then placed over the plywood. This was the preferred construction approach by the owner to minimize disruption to the tenant spaces below. An evaluation of the existing structural elements found that they had reserve capacity to accommodate the weight of the added 15/32-inch thick plywood roof sheathing and its fasteners. Screws, No. 8 x 2½-inch long (WSNTL from Simpson Strong-Tie), attached the new plywood to the existing framing and were designed to maintain diaphragm capacity. In this repair method, the plywood overlay only treated the symptom, so changes were also made to address the cause of the condensation.

Solutions Figure 3. TPO roofing cut open. Decayed OSB roof sheathing cannot resist penetration. Courtesy of Ray Wetherholt.

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In this particular building, the discontinuous vapor barrier allowed the relatively warm, moist air to contact the cold OSB surface, leading to condensation. In theory, a vapor barrier with low permeability that is sealed at all penetrations can act as an air barrier, preventing air movement to the underside of the wood deck.

However, in practice, with the vapor barrier intersected by thousands of steel angle truss web members, there are too many discontinuities and penetrations to create an effective seal.

The moisture added to the air by the directfired heating units, which increased the dew point temperature of the air and increased the severity and duration of condensation

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which was uploaded to the cloud via a built-in cellular modem. Real-time or archived data can be accessed from any internet connection. Data was collected for this project over a three-year period.

The graph in Figure 4 shows a summary of overall trends over the three years. Data in Figure 4 shows an average value from the six sensors located on the underside of the OSB. The moisture content of sheathing in specific locations reached over 35 percent and lasted for a longer duration than indicated by the average. Figure 4 also shows a line defined as the “dew point differential,” which is the air temperature at the underside of the OSB roof deck minus the dew point temperature of the air at the same location.

The dew point is the theoretical temperature at which moisture in the air condenses into liquid water. Condensation occurs when dew point differentials approach zero. The graphs illustrate that the incidence of higher moisture content in the OSB correlated with low dew point differentials. The growth of decay fungi in wood products can be prevented by maintaining a moisture content of 20 percent or less. Monitoring data shows periods of time in the winter months where moisture contents of the OSB exceed 20 percent.

The methods of reducing condensation considered were: 1) reducing the amount of moisture in the interior air that is directly adjacent to the wood deck and 2) increasing the temperature of the wood deck. Reducing moisture in

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the air at the deck can be achieved by sealing or reinstalling the vapor retarder (which was impractical) or by making changes to the heating and ventilation system. Increasing the temperature of the OSB sheathing requires the installation of rigid insulation above it.

Installation of rigid foam insulation on top of the wood roof sheathing was recommended by the authors but was ruled out due to cost.

The authors brought in Mechanical Engineer, Mark Scott, P.E. of MEP Engineering to evaluate and propose changes to the heating and ventilation systems at the buildings. In the summer of 2015, the direct-fired heating units were removed and replaced with indirect-fired heating units. The new heating units use a heat exchanger and exhaust the natural gas combustion byproducts, including water vapor, to the exterior of the building to maintain a dryer interior environment. As shown in Figure 4, this change significantly reduced the condensation and moisture build up in the wood roof deck during the winter months.

Conclusions Condensation problems in a low slope warehouse roof can be severe and potentially cause significant problems for the structure. Severe decay in large areas of the wood roof sheathing was found in this case study building before the building was even five years old. Structural damage was repaired with a plywood overlay, and, through a thorough study of interior moisture issues, recommendations were offered to reduce the potential for future condensation. In the end, the condensation problem was solved by implementing changes to the heating system in the building by removing the direct-fired heaters and installing new indirect fired heaters that use a heat exchanger. This change was found to lower moisture content in the wood roof deck dramatically.▪

EnginEEr’s notEbook aids for the structural engineer’s toolbox

S

TRUCTURE’s February 2017 Engineer’s Notebook discussed the design requirements and methods to laterally brace (bridge) axially loaded cold-formed steel stud walls. This article provides the design requirements and methods to anchor, or complete the load path, for the lateral bracing (bridging) of axially loaded cold-formed steel stud walls.

Design Requirements The design requirements for the bridging components of axially loaded cold-formed steel studs are described in AISI S100-12 North American Specification for the Design of Cold-Formed Steel Structural Members, Section D3.3, and Section B3.1 of AISI S211-12 North American Standard for Cold-Formed Steel Framing – Wall Stud Design.

The bridging forces are assumed to accumulate linearly with respect to the number of studs, and the load path must be completed for the bridging forces. The forces accumulate and must be removed periodically as the force in the bridging row reaches the design capacity of the bridging member.

The mechanism for resisting the cumulative bridging force is known as the “anchorage” of the bridging. Figure 1 illustrates the accumulation of

Mechanical Bridging Anchorage of Axially Loaded Cold-Formed Steel Studs

By Nabil A. Rahman, Ph.D., P.E.

Figure 2. Anchorage of bridging using flat-strap cross bracing.

the bridging force according to the design requirements of AISI S100 and AISI S211. When using the AISI S211 approach, there is no explicit brace stiffness requirement compared to the approach in AISI S100. As a result, AISI S211 uses a more conservative strength requirement, 2% compared to 1% used in AISI S100.

If AISI S100 is used, brace stiffness must be evaluated for each stud in accordance with Section D3.3, and the accumulation must also be considered. Although AISI S100 does not provide a method to accumulate the stiffness requirements for multiple studs, the Architectural Engineering Journal research paper Bracing Demand in Axially Loaded Cold-Formed Steel Stud Walls (Sputo and Beery, 2008) suggests the following equation for this stiffness accumulation: βrb,n = βrb [0.4n2 + 0.5n] where, βrb,n = Required brace stiffness for multiple studs with (n) number of equally spaced intermediate brace locations βrb = Minimum required brace stiffness to brace a single compression member n = Number of equally spaced intermediate brace locations

Nabil A. Rahman is the Director of Engineering and R&D for The Steel Network, Inc. and a Principal at FDR Engineers in Durham, NC. He is the current chairman of ASCE-SEI Committee on Cold-Formed Steel Members. He serves as a member of the Committee on Specification and Committee on Framing of the American Iron and Steel Institute (AISI), and a member of ASCE Committee on Disproportionate Collapse. He can be reached at nabil@steelnetwork.com.

Anchorage Methods

Figure 1. Accumulation of bridging force based on AISI S100 and S211.

56 March 2017

The method of bridging anchorage may vary depending upon the magnitude of bridging force accumulated in the bridging row, as well as the preference of the design engineer.

One of the common methods of bridging anchorage consists of flat-strap cross bracing attached from the bridging line to the bottom of the wall on each side of the stud (Figure 2).

The system functions in tension only to transfer cumulative bridging forces to the bottom track and the floor slab; thus a cross bracing pattern is required to anchor stud bridging for buckling

in either direction of the wall. For this type of system, the designer should specify the strap size; thickness and width, as well as the connection requirements at both the bridging line and the bottom track of the wall. Stiffness resistance is obtained through a combination of the stiffness of the flatstraps, the stiffness of the bottom track, and the connections between them.

When the bridging member is a cold-rolled channel inserted through the punch-outs of the studs, the concept of anchoring the bridging to the bottom of the wall can also be achieved with a diagonal piece of a stud or track welded to the bridging line and the bottom track, as shown in Figure 3. Welding is typically preferred when wall panels are assembled in a panel shop versus being assembled on site.

An alternative bridging anchorage method consists of a “strong-back” stud oriented so that the strong axis is perpendicular to the bridging row, and attached to both the bridging line and the top and bottom of the wall. The stud acts in bending about its strong axis and transfers the bridging force into the floor slab through a series of clips, as shown in Figure 4. The designer must specify the stud type and connections

Figure 3. Anchorage of bridging using welded diagonal brace.

Figure 4. Anchorage of bridging using a strong-back stud.

to be used based on the cumulative force in the bridging line. Stiffness resistance is obtained by a combination of the stiffness of the bridging member, the stiffness of the strong-back stud, and the stiffness of the connection between them. This type of anchorage system may also be used with a flat-strap bridging method by using two

strong-back studs attaching the web of the strong-back to the flat-strap on each side of the wall, as well as to the top and bottom track. The two strong-back studs do not need to be at the same location but may be alternated for ease of installation.

Another method of bridging anchorage is using a built-up stud column placed at

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specific intervals along the wall length, such as wall openings, as shown in Figure 5. The built-up stud section should be capable of resisting the applied axial load as an unbraced section, as well as resist the cumulative bridging forces within the plane of the wall. Thus, a combined loading condition exists, the applied axial load and the bending loads induced from the bridging row as well as any out-of-plane pressure acting on the built-up column. The use of a weldment or HSS member is an option for the built-up member if larger capacity and stiffness are desired.

Bridging anchorage is critical to completing the load path, and ensuring that the tendency of the studs to buckle in flexural and torsional buckling modes is restrained by the bridging. Th e type of bridging method used will determine the anchorage spacing and the possible anchorage methods. It should be pointed out that the bridging methods that are capable of resisting load in both tension and compression may require a single anchorage point along the wall length. However, tension-only bridging systems always require a minimum of two anchorage locations along the wall

Figure 5. Anchorage of bridging using a built-up section.

length to resist the buckling of the wall in either direction.

For a numerical design example illustrating the design of a bridging member and its anchorage, refer to Cold-Formed Steel Engineers Institute TN W400-16, www.cfsei.org. The design example provides

the detailed calculations for lateral bracing (bridging) and bridging anchorage of axially loaded studs, and compares the AISI S100 and AISI S211 bracing design alternatives available to design engineers. It is shown that in most cases, despite the need to design for larger force when using AISI S211, the more conservative strength requirement in AISI S211 proves advantageous over using AISI S100 for the following reasons: • Strength calculations for both methods are similar and fairly straight forward, while stiffness calculations can be quite lengthy.

• Stiffness calculations require estimation of the stiffness of the connection between the stud and the bridging, and the connection between the bridging and the anchorage member. Estimation of these values requires advanced analysis and testing, and the data may not be readily available for designers.

• The accumulation of stiffness for more than a few studs is difficult to achieve with available standard bridging details.▪

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Historic structures significant structures of the past

T

he Golden Gate Bridge, designed by Joseph B. Strauss and Charles A. Ellis, is one of the best-known engineering structures. It was the longest suspension bridge in the world for many years, with a span of 4,200 feet. Proposals for a bridge across the Golden Gate started in 1869 and were reinvigorated almost 50 years later. In 1916, James Wilkins, a newspaperman but formerly a civil engineer, began his campaign to bridge the Gate.

His proposal was for a suspension bridge with a 3,000-foot central span and clearance over the bay of 150 feet. World War I kept any progress from being made but, in 1918, Richard Welch, a member of the Board of Supervisors, requested Congress to authorize a Federal survey of the channel between the Presidio and the Marin Peninsula, reviving interest in the project. The survey was done and its results were given to Michael O’Shaughnessy, the City Engineer.

O’Shaughnessy believed a bridge was possible but had little idea as to how much it would cost to build.

Joseph B. Strauss became involved in the project when he met the City Engineer and the two of them started talking about a bridge across the Gate. Strauss, with little experience in suspension bridges, thought it was possible to build a bridge but told O’Shaughnessy that he did not have enough information to make an estimate of its costs.

In late August 1919, the Board of Supervisors told O’Shaughnessy to proceed with a study of the bridge. He then requested the United States Coast and Geodetic Survey to make soundings of the channel bottom at the probable bridge site. The survey was completed in May 1920.

O’Shaughnessy, with the results of the two federal surveys in hand, wrote a letter to three prominent engineers, Strauss, Francis McMath, and Gustav Lindenthal, in which he stated, “Everybody says it cannot be done and that it would cost over $100,000,000 if it could be done.” McMath did not respond, and Gustav Lindenthal wrote that the bridge could not be built for less than $60,000,000 and probably would cost upwards to $77,000,000. Strauss asked how much O’Shaughnessy thought the Board would be willing to pay for the bridge, to which Michael responded $25,000,000.

Strauss set to work preparing a preliminary design for a bridge he could build for less than the amount considered reasonable. He had never designed a bridge of this magnitude, or a suspension bridge of any span, and enlisted Charles Ellis

Golden Gate 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@verizon.net.

Read more about Joseph Strauss and Charles Ellis in the Great Achievements article in the STRUCTURE magazine archives, October 2012 issue at www.STRUCTUREmag.org.

60 March 2017

to start work on the design. They first designed a hybrid structure consisting of cantilever spans with a cable suspension bridge spanning between the ends of the two cantilevers.

Strauss reasoned that, at Charles A. Ellis. approximately 4,000 feet, a cantilever of the required span would be too heavy and that a suspension bridge would be too flexible. He, therefore, designed his bridge as a combination of Joseph B. Straus. both: an anchor span of 1,320 feet, a cantilever arm of 730 feet, a 2,640-foot wire cable suspension span, and then another 730-foot cantilever arm and 1,320-foot anchor span. The total length of the bridge was 6,700 feet and was designed to carry four lanes of traffic and two lanes of trolley tracks. Also, there would be long approach viaducts on both ends of the bridge. He estimated he could build the bridge for $17,250,000.

At an organizational meeting on January 13, 1923, a Bridging the Golden Gate Association was formed to promote the bridge and give backing to Strauss’ and O’Shaughnessy’s plans. The Association appointed Strauss as the engineer.

On December 20, 1924, the War Department gave conditional approval of the plans along with several conditions, including the need to submit final plans to the War Department for approval.

In 1925, to gain support for his proposal, Strauss had Ellis send the plans to two prominent engineers, George Swain of Harvard and Leon Moisseiff of New York City. Swain noted the plan was “perfectly practicable.” Moisseiff was less impressed but responded that the estimate “is about correct and may be exceeded by not more than $2,000,000.” Later that year, Strauss asked Moisseiff to prepare a plan for a conventional suspension bridge. Moisseiff made the report and forwarded it to Strauss on November 15 with a cover letter stating, “In accordance with your letter of acceptance of June 8, 1925, I present herewith to you a report on a comparative design for a suspension bridge with a single span stiffening truss based on identical specifications and prices as the cantilever-suspension type proposed by you for the Golden

Strauss Hybrid Design 1921 (San Francisco Chronicle May 18, 1934).

Gate Bridge at San Francisco, and on which I made a report to you on July 27, 1925.”

His seven-page report was for a bridge with a main span of 4,000 feet with two 35½-inch diameter cables and 735-foot-high towers.

He estimated the bridge could be built for $19,400,000. Strauss now had two designs in hand but decided for the time being to stick with his hybrid structure.

In 1927, The Engineering News Record came out in opposition to the bridge, stating in an editorial, “No competent engineer has said that the Golden Gate cannot be bridged, however, it is a far cry from that which is possible, regardless of cost, to that which is feasible from the financial viewpoint…It is natural therefore that such a bridge scheme, unsupported by data about the various problems involved should be opposed by the engineers of San Francisco…it was…a mortification to the proud Golden State and a misfortune to the engineering profession… No scheme for the bridge at the Golden Gate that meets all or any of these requirements has yet been proposed.”

The first step taken by a new Board of the Golden Gate Bridge and Highway District, formed in spring of 1929, was to name Alan MacDonald, a local contractor, as

Manager to coordinate the surveys, borings, and preparation of the plans for the District. The Board, however, was not willing to name Strauss as Chief Engineer without going through the process of interviewing other engineers. They interviewed Ralph Modjeski, Gustav Lindenthal, O. H. Ammann, Charles Evan Fowler, Charles Derleth, Waddell & Hardesty, Jacobs & Davies, Leon Moisseiff, George Swain, and Strauss. The Board named Strauss Chief Engineer in August 1929. After some reluctance, Ammann, Derleth, and Moisseiff agreed to serve as consultants. Their first meeting was held on August 27, 1929, with Strauss, Ellis, the three consultants, the President of the Board, two other members of Board, and Major F. A. Savage in attendance. The first meeting was to determine the kind of bridge, where it should be built based upon previous boring data, and to set up an organizational structure to utilize the skills of each consultant. They decided it should be a suspension bridge with the main span 4,200 feet long by placing the Marin (North) pier 200 feet closer to the shore.

This would result in a considerable saving in foundation cost. It was evident from the beginning that Ellis and Moisseiff would handle structural design, with Derleth and ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Tower Plans 1931 (Engineering News Record May 28, 1931).

Ammann advising on other matters, and Strauss interfacing with MacDonald and the District Board.

Shortly after, Strauss, Ammann, and Moisseiff left for the East, with Strauss naming Ellis as his personal representative to set up specifications for the borings and oversee them. Little work could be done until these results were completed. In early March 1930, the borings were completed, and Ellis returned to Chicago to begin designing the bridge. Strauss told the District Board that the preliminary designs would be completed in September, but Ellis indicated

it would normally take a year to finalize the design of a structure of this magnitude. This was one of the first and many disagreements between Strauss and Ellis over the next year and a half. By June 12, 1930, Ellis was ready to show his preliminary work to Strauss and the Consultants.

The preliminary plans showed a significant amount of work done in a very short time, and they were well received by the District Board.

Ellis began working on finalizing the plans as it was made clear to the Directors that the plans presented were preliminary and conceptual in nature, and were only prepared to make an estimate of costs. He worked on finalizing the design of stiffening trusses and the design of the arch span, which would cross the Fort at the Presidio. His main effort, however, was in finalizing the design of the towers. In the preliminary design, he had made many simplifying structural assumptions, which he wanted to review and minimize.

On February 6, 1931, Strauss The Golden Gate Bridge. Courtesy of HAER. wrote to Ellis, “the information regarding the solution of the towers is very attention he was getting from the Board. gratifying, and indeed I am very glad that He wired Ellis insisting he take his vacayou have been able to work it out this way. tion starting December 5, 1931. Ellis wrote, The change will apparently not only better “Three days before the end of the two weeks the design but also will enable us to reduce period he (Strauss) wrote a letter criticizthe cost of the towers to some extent.” On ing my conduct of the work, and stating March 18, the Consultants met in Chicago very clearly that the structure was nothing to discuss the Specifications. Strauss wanted unusual, and did not require all the time, to use the specifications for Ammann’s study and expense which I thought necesGeorge Washington Bridge as the basis of sary for it, and closed by instructing me to his specifications, which he wanted to “be turn over all papers to Charles Clarahan, the best specifications yet written and to his assistant and former student, and take serve as a sort of model for future engineers an indefinite vacation without pay.” With to follow.” Opened in 1931, the George that, Ellis’ official connection with the bridge Washington Bridge over the Hudson River ceased, and he was never given any credit for had a main span of 3,500 feet. his work by Strauss.

Strauss wrote a set of specifications for Ellis to Not much work was completed in 1932 review, but Ellis found “nothing could be done due to funding problems and lawsuits. with them.” He then wrote his own specifica- Construction began on January 5, 1933, tions, which, “with only slight revisions by with the McClintic-Marshal Construction the consultants,” were adopted. The plans and Company as the General Contractor and specifications were sent out to contractors in the steel supplied by the Bethlehem Steel April 1931, with bids due June 17.

Company of Pennsylvania.

The towers had, with the inputs of Irving They had trouble placing the southern Morrow, the consulting architect, taken tower caisson that was 1,000 feet out into on their general form even though Ellis the ocean, but the rest of the construccontinued to improve on his analysis and tion continued without incident. The steel design. Strauss was becoming more and more towers were painted the distinctive internaupset with Ellis and his asking for more time tional orange (orange vermillion). John A. to make his revised calculations, and the Roebling’s Sons spun the 36-inch diameter STRUCTURE magazine

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cables that were 7,659 feet long and contained 27,572 wires, making them the largest cables ever spun at that time. Using new techniques, they completed their work on May 20, 1936, two months ahead of schedule. The suspenders were placed, and the longitudinal stiffening trusses hung from them. The decking was then placed, providing for the six lanes of traffic.

The bridge was completed and opened May 27, 1937, for pedestrians and May 28 for motor vehicles.

A grand celebration was held, and the center of attention was Joseph B. Strauss, who composed a poem for the occasion. On September 30, 1937, Strauss presented his Report of the Chief Engineer to the Board of Directors of the Golden Gate Bridge and Highway District describing the design and construction of the bridge.

ASCE named the bridge as a National Historic Civil Engineering Landmark in 1984. It was also designated one of the Seven Wonders of the Modern World in 1994.

In 2001, it was named a Civil Engineering Monument of the Millennium. The Golden Gate Bridge was the longest suspension bridge in the world until the Verrazano-Narrows Bridge opened in 1964 with a span of 4,259 feet. The bridge is currently the 14th longest span in the world. In 2012, the Board of Directors of Golden Gate Highway and Transportation District and the American Society of Civil Engineers finally recognized Ellis for his work on the bridge.

This series of articles on suspension bridges started with James Finley’s chain bridge built in 1809 over the Schuylkill Falls, with spans of 153 feet carrying wagons and carriages. It is completed with the Golden Gate Bridge, with its 4,200 feet carrying automobiles, trucks, etc. The longest span suspension bridge is now the Akashi Kaikyō Bridge in Japan, with a main span of 6,532 feet that opened in 1998.

Other suspension bridges have been proposed with spans projected upwards of 10,000 feet. John A. Roebling and Charles Ellet, Jr., the founders of the wire cable bridge in the United States, both had written that bridges with spans of up to 5,000 feet using wrought iron wires were possible. Those two engineers would, without a doubt, be impressed with how far their vision was carried out, not only in the United States but lately in Japan, China, and Denmark.▪

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InSIghtS new trends, new techniques and current industry issues

I

was part of a conversation recently among a group of practitioners where someone wondered about what was studied in an Architectural Engineering (ArchE) program.

Earning a Bachelor’s Degree in Architectural Engineering myself, this curiosity surprised me.

After all, I had presumed, in the several decades since graduating, Architectural Engineering had surely become ubiquitous in the profession in which most of us practice. But it prompted me to realize it had been some time since I thought about the attitude that persisted at the time of my graduation: Engineers hear the word Architect, and Architects hear the word Engineer – therefore, someone with such a degree did not belong to either group.

In a quick internet search, I found that only 37 universities in the U.S. offer a Bachelor’s of Science Degree in Architectural Engineering, 9 offer Master’s Degrees and, surprisingly, only one offers a Doctoral degree. In comparison, 265 universities offer a B.S. degree in Civil Engineering, and nearly 190 with M.S. and 120 with Ph.D. programs.

With this significant disparity in Colleges and Universities offering the B.S. ArchE degree or higher, I had to admit that maybe the Architectural Engineering degree was not as commonplace as I had come to believe.

In general, only an academic department can confer a degree; thus, an Architectural Engineering Department is recognized by the College of Engineering as an independent academic unit. Among the many criteria required to be an academic department are an authorized faculty and a designated course of study leading to an undergraduate or graduate degree. While the curriculum can often overlap with the CE program, it is neither a discipline within CE or a discipline within Architecture – Architectural Engineering is a recognized field of study on its own.

The courses of study within ArchE can be grouped into 3 general categories: • Structural, • Environmental & Building Energy, and • Infrastructure & Construction Management.

It is perhaps Environment & Building Energy courses and approved electives that distinguish the B.S. ArchE degree over one in Civil Engineering. Environment & Building Energy courses focus on the building environment, having coursework that might include: lighting & electrical systems, HVAC systems, plumbing & fire safety, acoustics, solar energy, renewable energy, and sustainability. ArchE graduates with this emphasis have gone on to successful careers in architectural lighting for building interiors

Architectural Engineering What, exactly, is it?

By Stephen P. Schneider, Ph.D., P.E., S.E.

Steve Schneider is a Senior Project Manager for BergerABAM, Inc. He holds a B.S.ArchE degree from the University of Colorado, Boulder, an M.S and a Ph.D. in Civil Engineering from the University of Washington, Seattle, and practices structural engineering in the Portland, OR area. Steve is also a member of the STRUCTURE magazine Editorial Board. He can be reached at steve.schneider@abam.com.

64 March 2017

and exteriors, energy design of the building envelope, and renewable energy resources, to name a few.

Electives in the ArchE curriculum focus on architectural considerations and are the primary link to a course of study in Architecture. These classes are often taught in conjunction with, and by the faculty in, the Architecture program.

Coursework can include: architectural history, architectural appreciation, and introductory architectural design courses where the student might go through the full development and design of a building from an architect’s perspective. Each topic likely needs a two-course sequence to complete. Architectural history, for instance, is the study of architectural styles throughout the ages and requires a full academic year to cover the topic well.

As for the coursework that emphasizes Structures or Construction Management, many of the classes needed to fulfill these requirements are the same classes taken by CE students with a similar emphasis. In essence, for certain classes there is no difference between the ArchE and CE programs.

As for my ArchE experience, my emphasis was structural engineering. The curriculum was an exceptional way to study the design and construction of the built environment. Because of my interest in architecture, this was better for me than what was offered through a CE program which requires classes in transportation, environmental sciences, and the like. And the program afforded me the flexibility to focus on structural engineering. As an undergraduate, I took graduate-level classes in structural dynamics, framed structural analysis and an introductory course in finite elements. I was taking these classes with a few of my ArchE classmates and CE students studying for their M.S. degree.

So… Architect or Engineer? Undoubtedly, ArchE is an engineering program. Architects focus on building layout and aesthetics while the Architectural Engineer will impact its design, function, and construction. If your work is primarily structural engineering and you are looking for a new hire, you should not discount someone with an ArchE degree because of a lack of understanding about their educational background. If your client base is predominantly architects, someone with an ArchE degree can be an excellent fit.▪

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Outside the BOx

the out-of-the-ordinary within the realm of structural engineering

The Logic of Ingenuity Part 4: Beyond Engineering

By Jon A. Schmidt, P.E., SECB

T

his series began with the premise that the “logic of inquiry” in science, as expounded by Charles Sanders Peirce, also serves as a “logic of ingenuity” in engineering. I would like to revisit this notion by examining the aim of inquiry as asserted by Peirce in the title of one of his most famous essays, “The Fixation of Belief” (www.peirce.org/writings/p107.html). It appeared originally in the November 1877 issue of Popular Science Monthly as the first of six articles under the heading, “Illustrations of the Logic of Science,” and subsequently as CP 5.358-387 and EP 1.109-123. According to the text: Doubt is an uneasy and dissatisfied state from which we struggle to free ourselves and pass into the state of belief; while the latter is a calm and satisfactory state which we do not wish to avoid … The irritation of doubt causes a struggle to attain a state of belief (CP 5.372-374, EP 1.114).

The first part of this quote indicates how the second part can be generalized: The irritation of dissatisfaction causes a struggle to attain a state of satisfaction. This happens to be exactly what Henry Petroski described as the governing principle of all invention and innovation in his 1992 book, The Evolution of Useful Things: “… the form of made things is always subject to change in response to their real or perceived shortcomings, their failures to function properly” (p. 22).

He clearly had physical artifacts in mind, but the basic idea pertains to anything produced by humans – including scientific theories.

In other words, contrary to the common (but misleading) definition of engineering as “applied science,” science is – at least in some ways – analogous to a discipline of engineering. Some might dispute this by claiming that science, unlike engineering, is primarily in the business of finding truth. Peirce agreed when discussing “science” as a collaborative endeavor by a large community of investigators working together over an extended period of time. However, for a single individual under ordinary conditions: … the sole object of inquiry is the settlement of opinion. We may fancy that this is not enough for us, and that we seek, not merely an opinion, but a true opinion. But put this fancy to the test, and it proves groundless;

The Logic of Ingenuity The process of (abductively) creating a diagrammatic representation of a problem and its proposed solution, and then (deductively) working out the necessary consequences, such that this serves as an adequate substitute for (inductively) evaluating the actual situation. for as soon as a firm belief is reached we are entirely satisfied, whether the belief be true or false (CP 5.375, EP 1.114-115).

Therefore, truth is the goal of inquiry only in the long run, and only in the sense that our ongoing interaction with nature – what Peirce called the “Outward Clash” (CP 8.41-43, EP 1.233-234) – prevents us from ever being permanently satisfied with our beliefs by periodically confronting us with evidence that some of them are false. By contrast, the goal of ingenuity is something that we hope to achieve in the short term: solving a problem, typically despite incomplete knowledge and limited resources.

Adapting Peirce’s phrasing once again: The irritation of uncertainty causes a struggle to attain a state of decision; or as he wrote in the subsequent article, “How to Make Our Ideas Clear” (www.peirce.org/writings/p119.html), “The final upshot of thinking is the exercise of volition” (CP 5.397, EP 1.129; 1878).

This implies that the logic of ingenuity may be applicable to the contemplation of any potential activity that could be undertaken voluntarily.

It thus extends beyond engineering, into the much broader domain of ethics. And yet, by his own admission, Peirce did not have much to say about that subject until relatively late in his career. In a 1903 lecture, he classified it with esthetics and logic as “The Three Normative Sciences” (CP 5.120-150, EP 2.196-207): For normative science in general being the science of the laws of conformity of things to ends, esthetics considers those things whose ends are to embody qualities of feeling, ethics those things whose ends lie in action, and logic those things whose end is to represent something … That is right action which is in conformity to ends which we are prepared deliberately to adopt (CP 5.129-130, EP 2.200).

Peirce came to see that logic is a form of ethics because thought is a form of conduct; and that self-control is essential to both thinking well and acting well because we cannot influence the past or the present – only the future. In

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another lecture later the same year, he posed the question, “What Makes a Reasoning Sound?”

(EP 2.242-257) and answered it by explicitly drawing a parallel with what makes an action morally right. Daniel G. Campos, a philosophy professor at Brooklyn College of the City University of New York, summarized six stages identified by Peirce in a 2015 paper, “The Role of Diagrammatic Reasoning in Ethical Deliberation” (Transactions of the Charles S. Peirce Society, Vol. 51, No. 3, pp. 338-357): 1) Affirming ideals that together constitute a worldview and shape one’s character.

2) Establishing an intention to behave in accordance with those ideals.

3) Formulating rules of conduct, “practical maxims for what ought to be done in circumstances that fall under a more or less vague description.”

4) Making a resolution for how to act if and when a specific occasion arises that is foreseen through the use of “semiotic imagination – the ability to create and transform signs – guided by practical knowledge of what paths events may follow.”

5) Converting this resolution into a determination, an abiding disposition that is “capable of effectively guiding conduct.”

6) Engaging in a critical review of one’s actions in relation to all of the above, which produces approval or disapproval of the former – and sometimes revision of the latter.

Peirce wrote of the fourth step, “This resolution is of the nature of a plan, or, as one might almost say, a diagram” (EP 2.246). Prompted by this hint, Campos suggested that each of the others is likewise analogous to an aspect of diagrammatic reasoning – although, in both cases, “we must keep in mind that this is a continuous process and that its various stages may be more or less emphatically experienced in different contexts.” In the same order as above:

Jon A. Schmidt (jschmid@burnsmcd.com) is a Senior Associate Structural Engineer in the Aviation & Federal Group at Burns & McDonnell in Kansas City, Missouri.

He serves as Secretary on the NCSEA Board of Directors, chairs the SEI Engineering Philosophy Committee, and shares occasional thoughts at twitter.com/JonAlanSchmidt.

The online version of this article contains detailed references. Part 3 of this series appeared in the November 2016 issue.

Visit www.STRUCTUREmag.org.

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1) Ideals correspond to a set of “framing hypotheses” that comprise a representational system.

2) An intention corresponds to the purpose of the exercise.

3) Rules of conduct correspond to “heuristic[s] … that direct an inquirer to employ a certain method of solution depending on the general type of problem under investigation.”

4) A resolution corresponds to “a mathematical model that may be formulated and investigated abstractly but is intended to apply to a concrete state of things.”

5) A determination corresponds to the intellectual virtue of judgment that eventually emerges from “mathematical experience.”

6) Review corresponds to the observation of the results of diagram manipulation.

This analysis aligns with my persistent claim that engineering is an especially systematic way of willing – if I am right, then the former’s distinctive reasoning process should be paradigmatic for the latter. However, contrary to the profession’s traditional reputation, this does not entail the use of a quantitative model in every instance. For example, rather than an abstract formalization, it might be – and in ethical scenarios, often is – constructed as a narrative instead. After all, engineering mostly deals with material phenomena, which Peirce conceptualized as “inveterate habits becoming physical laws” (CP 6.25, EP 1.293; 1891). The behavior of people, on the other hand, is always subject to change – our habits are far more malleable, which makes us far less predictable.

Regardless, the key to success is having the ability to discern the significant aspects of reality and consistently capture them, before definitively selecting a way forward from among multiple viable options. The logic of ingenuity is thus itself a carefully cultivated habit that facilitates imagining possibilities, assessing alternatives, and choosing one of them to actualize – in engineering, in science, or in any other endeavor.▪

LegaL PersPectives

discussion of legal issues of interest to structural engineers

Indemnification of the Structural Engineer

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

T

he article Understanding Indemnification Clauses published in the January 2017 issue of STRUCTURE provided an overview of indemnification clauses. A second article, Understanding the Difference Between Indemnification and Insurance, published in the February 2017 issue of STRUCTURE took a closer look at indemnification clauses and compared indemnification with insurance. In both of those articles, the focus was on the indemnification obligations of the structural engineer. In this article, we will look at indemnification of the structural engineer.

In a typical commercial contract, one party is providing goods or services, and the other party is purchasing the goods or services. The indemnification clause will typically require that the party providing the goods or services indemnify the purchaser against third-party claims arising from the provider’s negligent acts, errors, or omissions. Thus, the indemnification clause might read: Consultant shall indemnify and hold harmless the Client, and the Client’s employees, directors, officers, and lenders from and against liabilities and expenses arising from third-party claims, including attorney’s fees where recoverable under applicable law on account of negligence, to the extent caused by the Consultant’s negligent acts, errors, or omissions.

Some contracts contain a mutual indemnification clause; the clause may be worded such that each party assumes the same obligation to the other party, or the party paying for the goods or services can take on a more limited indemnification obligation. As an example, ConsensusDOCS 240, Standard Form of Agreement Between Owner and Architect/Engineer, contains mutual indemnification obligations in Articles 7.1.1 and 7.1.2. Mutual indemnification clauses tend to be rare, however, particularly in contracts that have been drafted by the client; structural engineers usually need to negotiate for indemnification. While a general indemnification against claims arising from the client’s negligence may not be necessary, a structural engineer should require indemnification against certain risks.

Drawings Contracts vary with respect to ownership of the engineer’s work product (referred to in the AIA documents as the “Instruments of Service”). Some contracts are written such that the engineer grants the Owner a nonexclusive license to use the work product.

Other contracts are written such that the Owner obtains the copyright to the work product upon payment for the engineer’s services. In either case, the Owner will typically want to be able to use the plans and specifications for maintaining, altering, or adding on to the project. Some Owners want to be able to use the documents on other projects.

Regardless of what the engineer negotiates with respect to ownership of the drawings, it is a good idea to require the Owner to indemnify and defend the engineer against claims arising from the use of the drawings on other projects or changes made to the drawings by others.

The wording of such clauses depends on the scope of work, but two commonly used provisions are: The Owner agrees to indemnify, defend, and hold Engineer harmless from any claims arising from changes made to the documents by others or from Owner’s use of the Documents on any other project without engagement of the Engineer.

The Owner agrees to indemnify, defend, and hold Engineer harmless from any claims arising from Owner’s use of the Documents for any purpose other than the purpose they were prepared for under this agreement.

Hazardous Materials / Existing Site Conditions Many contracts make the engineer liable for claims arising from hazardous materials brought onto the site by the engineer unless the engineer was acting under the specific direction of the Owner. However, the engineer should not be liable for claims arising from hazardous materials already existing on the site or brought onto the site by others, unless the engineer has exacerbated the situation through its negligence. When hazardous materials are a concern, the engineer may

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want to require that the contract includes a clause similar to the following: The Owner agrees to indemnify, defend, and hold Engineer harmless from any claims arising from hazardous materials existing on the site or brought onto the site by others, except to the extent the Engineer has exacerbated the situation by its negligent acts, errors, or omissions.

Likewise, if the project involves renovation of an existing structure or the subsurface conditions are unknown, it may be advisable to require the Owner to provide a general indemnification against claims arising from existing site conditions, except to the extent the engineer has exacerbated the situation through its negligence. The engineer’s liability should be limited to its negligence; the Owner should bear the risk of existing site conditions.

Access Agreements Engineers who do site investigations will sometimes need to enter onto a third party’s property; this applies especially to engineers who do geotechnical investigations. Often, the property owner will want the engineer to sign an Access Agreement that requires the engineer to indemnify the property owner from any claims arising from the investigation and any damage to the property, regardless of whether the engineer is negligent. This is not unreasonable, as the property owner should not be expected to bear these costs. However, the engineer’s liability for this work should not be greater than its liability under its contract with its client.

To be covered by professional liability insurance, the engineer’s indemnification obligations should be limited to the extent caused by the engineer’s negligence. When an engineer anticipates having to enter onto another party’s property to perform the work required by its contract, it should consider including a clause such as the following in the contract: If Consultant is required to sign an Access Agreement to enter onto the property of a third party, Client shall indemnify, defend, and hold Consultant harmless from any claims arising from its work on the third party’s property, except to the extent caused by the Consultant’s negligent acts, errors or omissions.

Subconsultants

Disclaimer: The information in this article is for educational purposes only and is not legal advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances.

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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Conclusion To indemnify another party means to agree to financially protect them against specified claims, either by directly paying costs they are liable for or by reimbursing them for the costs they have incurred.

While negotiation of the indemnification in a design agreement typically focuses on the engineer’s obligations, the engineer should also make sure that it is appropriately indemnified both by its client and by its subconsultants. The actual indemnification requirements will vary, depending on the project, but typical issues that are addressed in the design contract are indemnification for the Client’s use of the drawings on other projects and indemnification for STRUCTURE magazine

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Depending on the scope of work, an engineer may need to hire subconsultants to perform certain aspects of the work. Often, the prime contract will explicitly require the engineer to pass all indemnification obligations down to its subconsultants. In such cases, the engineer should make sure it negotiates terms that its subconsultants will agree to. As an example, professional liability insurance does not cover defense of indemnified parties. If the engineer agrees to defend the Owner against any allegations of negligence arising from its services, it may have trouble getting its subconsultants to agree to the flow-down requirement.

Even if the prime contract does not require that the indemnification obligations flow down to subconsultants, the subcontract should include an appropriate indemnification clause. Typical wording might be: Subconsultant shall indemnify and hold harmless the Engineer, and the Engineer’s employees, directors, officers, and lenders from and against liabilities and expenses arising from third-party claims, including attorney’s fees where recoverable under applicable law on account of negligence, to the extent caused by the Subconsultant’s negligent acts, errors or omissions.

It is also important that the subconsultant be required to carry sufficient insurance to cover its indemnification obligation.

Ultimately, the engineer will be required to provide indemnification in accordance with the prime agreement. If the subconsultant does not have insurance to cover claims due to its negligence, the engineer will be likely be held liable.

claims arising from existing site conditions.

When negotiating subcontracts, the engineer should ensure that its subconsultant’s indemnification obligations are appropriate for its contract and that the subconsultant has insurance to cover these obligations.▪

Business Practices

business issues

The Art of Hiring an Engineer 5 Ways to Secure Your Next Best Hire

By Jennifer Anderson

B

ased on over 18 years of experience, it has become evident that hiring an engineer takes finesse, patience, commitment, and creativity – it is more of an art than a science.

For all of the left-brained engineers reading this right now, do not panic when hiring is referred to as an “art.” You do not need to get in touch with your inner poet, but you do need to evaluate how you are engaging candidates. It is the connection of one human being to another that makes or breaks the hiring process.

For all of the potential job-seekers out there, read on. This information will help you to understand the perspective of your next hiring manager!

As an engineer, you may be thinking that you do not want to mess around with all the “people stuff” of hiring. You want it to be easy, mathematical, like an equation – plug in accurate variables to get the right answer – every time. However, my friends, it is not that way. “People stuff” is real. Moreover, do not forget, you are a person too. So, you do have very real experience in how to engage with another human being.

Presumably, your hiring process includes important steps like: • Asking rigorous engineering questions • Checking references • Evaluating past work samples • Ensuring that your hiring process is organized and efficient In addition to those key steps, here are five important ways to add finesse to the art of hiring an engineer: Seek to Understand Dr. Covey, of 7 Habits of Highly Effective People fame, was a champion of a habit that he coined as first seek to understand, then be understood. (If you have not read that book yet, do it. It will change your world – for the better. Promise.) When you are looking to understand a job candidate, it is important that you get to know that person. You do not need to invite them to your house for a dinner party, although that is an excellent way to get to know people. Seek to understand what is important about that person’s life. Questions to ask might include:

a) Tell me your “I became an engineer because…” story. b) While in college, what was the focus of your project’s team? How did you fit into the group dynamic? c) How do you spend your extra time? d) To what programs or organizations do you volunteer your time? Why are you involved?

After asking those types of questions, share your own “I became an engineer because…” story. Help that candidate to connect with you as an individual. Remember, your goal is to get to know them on a personal level.

Helping them understand your background will allow both of you to relax and enjoy the conversation more.

Eat Together

somewhere you have already been. However, the point is to think outside the box with this “normal” activity of eating.

The importance of this alternate eating experience is that it will help you connect over something unique and interesting for both of you. Plus, you will get an idea how the candidate handles new and different experiences. Those natural (and often visceral) reactions will give you much insight into that candidate’s thinking, behavior, motivations, and more. The other benefit is that you will both be outside of your comfort zone, so no one has the upper hand. In the end, we all eat, but the experience of eating can help you to uncover characteristics about a job candidate that an interview would not have allowed you to discover.

There is something sacred about eating together that goes back to the beginning of time. We all eat, although we do not necessarily like the same food. Connecting with a job candidate over a meal can be a fun and interesting way to get to know each other better.

Invite the job candidate to a lunch interview, but only after the first in-office interview when you are pretty sure that you want to invest the time to get to know them better.

Ask the job candidate to pick an interesting and different restaurant. You may be a steak-and-potatoes type of person, but now is the time to try something new and different. Ideally, have them pick a restaurant they have never been to either. Now, I understand that in some small markets, there are fewer restaurant options, so you may have to eat

Invite the candidate to spend a day in the office with you. If they are too busy with their other full-time job, you may have to do a half day or an afternoon. An entire day is beneficial because people can be on their best behavior for a couple of hours. It is a lot harder to play nice in the sandbox when you have that afternoon sugar slump.

The technique of inviting someone into the office all day is not something required for every applicant, rather when you are working to impress and win over a particular candidate. “Show me,” do not just “tell me.”

Having a candidate in the office all day helps you to engage with them differently than the normal 1- to 2-hour interview. It is helpful for them and your firm.

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Spend the Day in the Office

Obviously, play it safe. Have the candidate sign a non-disclosure agreement so that they can interact openly and respectfully. Include opportunities for private conversations with key team members. As a manager, you may opt not to go to lunch with the job candidate, but rather send him/her to lunch with another engineer. Let them talk without the boss listening in – but, choose which engineer you send wisely.

Network, Network, Network The best way to find people to join your firm is through networking in-person. Find events that align with your sector of the industry and attend regularly. It is important to make this a priority so that you have the consistency of meeting and re-engaging with people associated with the events.

One thing you need to remember about networking is that you are not likely to walk into a room, meet the perfect candidate, interview and hire them right there at the networking event. Rather, it is going to take time to connect with people. If you are going to get involved with networking, plan for a marathon, not a sprint. If you, or someone from your team, is attending regular networking events, be prepared for being out of the office for a few hours. Do not think

of networking as contrary to “getting work throw out. The reason you want all of your done.” Rather, embrace networking as one of employees to have business cards is that you your job responsibilities. It is very important! never know when they are going to cross paths with someone that could be a great hire. The Little Things Matter simple, small token of handing off a business Remember when your mom told you to write card shows that the company and the person thank-you notes because a hand-written note care, and take their business seriously. Arm means much more than a verbal thank you? your people with the right tools as it will Well, the same admonishment applies in busi- make a difference. ness. Sending a meaningful, hand-written In the end, you need an engineering canthank-you note to candidates who interview didate to have the technical skills necessary with your company will help you to stand out. to get the job done. Vet those skills, put Sure, emails are also great, not to mention easy the applicants to the test, and uncover to finish and send off quickly. However, if you what they know. Beyond math and sciwant to make a strong human connection, ence, skills required to succeed in today’s send a hand-written note. business world also include communicating, Another example of the little things is listening, reading body language, courtesy, business cards. It is always an amazing cir- respect, and more. Give yourself, and the cumstance when someone does not have a candidates, the opportunity to get to know business card for the company for which they one another by allowing the art of connectwork. Why would you not arm your employ- ing on a personal level. Remember, you are ees with business cards? They are inexpensive both humans.▪ and may seem insignificant, but business cards Born into a family of engineers, rarely get thrown away. Think outside of the but focusing on the people side of box when it comes to creating business cards engineering, Jennifer Anderson too. An unusual and memorable card that (www.CareerCoachJen.com) has nearly the author was given was thin metal etched 20 years of experience helping companies with a company logo, employee name, email, hire and retain the right talent. She may be and cell number of the employee. That is one reached at jen@careercoachjen.com. card that most people probably would never ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Dlubal Software, Inc. Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: SHAPE-THIN / SHAPE-MASSIVE Description: Calculates the section properties of custom open, closed, built-up, and non-connected thin-walled cross-sections consisting of one or more materials. Perform an elastic or plastic stress analysis including torsion effects. Determines section properties of thick-walled cross-sections and performs a full stress analysis. Optimal integration with RFEM for further structural analysis.

Product: RFEM Description: Structural analysis program which includes USA/International design codes for steel, concrete, timber, CLT, aluminum, glass, and fabric/ membranes. Capable of non-linear analysis of member, plate, and solid elements complete with code references and detailed design results. Direct interfaces with BIM and CAD software to incorporate seamless and bi-directional data exchange.

IES, Inc. Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis 17.0 Description: IES introduces the new version 17.0! It is far easier. It is much faster. It is crazyaccurate. It is widely versatile. And, as it has for over 23-years, it will improve your bottom-line and your smile.

Integrity Software, Inc. Phone: 866-372-8991 Email: sales@softwaremetering.com Web: www.softwaremetering.com Product: SofTrack Description: Save money on monthly, quarterly and annual Bentley® license fees! SofTrack provides automatic control to prevent over-usage of Bentley licenses. Ensure licensed applications are used within your license limits. SofTrack includes support for all Bentley licensing policiesand can automatically block usage of products you do not own.

news and information from software vendors

Software UpdateS

Losch Software Ltd.

RISA Technologies

SCIA, Inc., a Nemetschek Company

Phone: 323-592-3299 Email: LoschInfo@gmail.com Web: www.LoschSoft.com Product: LECWall Description: The industry standard for precast concrete sandwich wall design also handles multi-story columns. LECWall can analyze prestressed and/or mild reinforced wall panels with zero to 100 percent composite action. Flat, hollow-core, or double tee configurations are supported. Complete handling analysis is also included.

Phone: 949-951-5815 Email: info@risa.com Web: www.risa.com Product: RISAFloor ES Description: RISA offers everything you need for concrete design. For concrete floors, including beams and two way slabs, nothing beats RISAFloor ES for ease of use and versatility. The design of columns and shear walls with RISA-3D offers total flexibility.

Integration between RISA-3D and RISAFloor ES provides a complete building design.

Phone: 410-207-5501 Email: info@scia.net Web: www.scia.net Product: SCIA Engineer Description: Looking to migrate to or improve your 3D design workflows? SCIA Engineer offers an easy way to plug structural analysis and design into today’s BIM workflows. Tackle larger projects with advanced non-linear and dynamic analysis. Plug into BIM with IFC, and bi-directional links to Revit, Tekla, and others. Free demo!

Opti-Mate, Inc.

S-FRAME Software

Phone: 610-530-9031 Email: optimate@enter.net Web: www.opti-mate.com Product: Bridge Engineering Software Description: Merlin Dash software for analysis, design or rating of bridges with steel and prestressed concrete girders. Descus software for grid analysis and rating of bridges with horizontally curved plate or box girders. TRAP software for truss bridges and SABRE for sign structures. AASHTO specifications are included.

Phone: 604-273-7737 Email: info@s-frame.com Web: s-frame.com Product: S-FOUNDATION Professional 2017 Description: S-FOUNDATION Pro 2017 released!

New pile features include soil definitions to calculate deflections, axial forces, compression, and tension along each pile length. Quickly and easily model, auto-detail, and optimize pile supported foundations.

Seamlessly transfer model data Analysis or easily import support data from 3rd party analysis software.

Product: SCIA Design Forms Description: Integrate custom checks into your FEA workflow. Script custom calculations that can run as standalone checks or link to SCIA Engineer’s FEA workflow. Having the ability to write your own checks inside your FEA software is a real game changer. Try it for free!

All Resource Guide forms for 2017 are now available on the website, www.STRUCTUREmag.org.

Simpson Strong-Tie® Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Strong-Wall® Shearwall Selector Description: Helps Designers select the appropriate shearwall solution for a given application in accordance with the latest code requirements. continued on next page

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March 22-24, 2017 NASCC San Antonio, TX

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April 6-7, 2017 Structures Congress Denver, CO

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Industrial Engineering Ingenieurbüro Mauss © www.ibmauss.de/en

Software UpdateS

news and information from software vendors

Simpson Strong-Tie®

StruMIS LLC

Product: CFS Designer™ Software Description: Design cold-formed steel beam-column members according to AISI specifications. Analyze and design complex span and loading configurations, including system design for framed openings, shearwalls, x-braces, floor joists, and roof rafters.

Phone: 610-280-9840 Email: j.hardy@strumis.com Web: www.strumis.com Product: STRUMIS Description: Steel estimating and fabrication management information software which provides unrivalled features and benefits globally. Our software is driven by our continuous collaboration and communication with our customers. Our customers speak; we listen, ensuring the best material and time savings, in turn reducing overheads and increasing efficiency and productivity.

Standards Design Group, Inc. Phone: 806-792-5086 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Wind Loads on Structures Description: WLS4 software allows wind load computations for the ASCE 7-98, 02 or 05, Section 6 and ASCE 7-10, Chapters 26-31. WGD5 performs calculation to design window glass according to ASTM E 1300-09. BRDG 2007 finds its basis in the ASTM F 2248.

Strand7 Pty Ltd Phone: 252-504-2282 Email: info@strand7.com Web: www.strand7.com Product: Strand7 Description: An advanced, general purpose, FEA system used for a wide range of structural analysis applications. Strand7 can be used as a standalone system, or with Windows applications such as CAD software. It comprises preprocessing, solvers (linear and nonlinear static and dynamic), and post-processing.

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

Product: Tekla Structural Designer Description: Fully automated and packed with many unique features for optimized concrete and steel design. Helps engineering businesses win more work and maximize profits. From the quick comparison of alternative design schemes through to cost-effective change management and seamless BIM collaboration, Tekla Structural Designer can transform your business.

SECB ConCEptS

Product: Tekla Structures Description: Create and transfer constructible models throughout the design life. From concept to completion. Allows you to create accurate and information-rich models that reduce RFIs and enable structural engineers proven additional services. Models are used for drawing production, material take offs, and collaboration with disciplines like architects, consultants, fabricators, and contractors.

Veit Christoph GmbH Phone: +49 711 518573-30 Email: info@vcmaster.com Web: www.vcmaster.com/en Product: VCmaster Description: The most comprehensive software application for digital technical documentation in the field of structural engineering. The dynamically calculated and reusable documents offer an excellent opportunity to increase efficiency for structural analysis.

All Resource Guide forms for the 2017 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

An Upcoming Opportunity to Promote Your Credentials

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Visit our Booth!

AIA Conference April 27 – 29 Orlando, Florida

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takeholders is not a term frequently used by or familiar to the Structural Engineer. From the engineer’s perspective, a stakeholder is any individual, industry, business, or municipal entity that has an interest in what the engineer does. As SECB is a voice/representative for structural engineering practitioners, it can be thought of as having the same extended list of stakeholders that the practitioner has. Often, architects don’t acknowledge or appreciate the benefits they receive from the professionalism of their structural engineer consultants. SECB will be supporting a booth at the 2017 AIA Conference in Orlando, April 27th – 29th. This will be our [your] opportunity to present to architects and remind them of the importance of the SECB credentials – projects engineered by an SECB certified engineer are designed by a professional who is in compliance with the education, training, and L EN G A experience required of SECB certificate holders. Perhaps you could use this opportunity as a marketing platform with your architectural clients. Ask them to visit the SECB booth to CERTIFICATION BOARD learn more about the certification process.

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award winners and outstanding projects

Spotlight

Facets to Frames Form Inspires Structure in Beijing

By Mark Sarkisian, S.E., Neville Mathias, S.E., Rupa Garai, S.E., and Andrew Krebs, S.E. Skidmore, Owings & Merrill LLP was an Award Winner for its Poly International Plaza project in the 2016 NCSEA Annual Excellence in Structural Engineering Awards Program in the Category – New Buildings over $100M.

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he elliptically shaped faceted exterior of the 530-foot (161.2-meters) tall Poly International Plaza iconic tower in Beijing was inspired

by Chinese paper lanterns to shimmer as it reflects the sky. It is the first structure of its kind, incorporating a four-story super diagrid frame module without perimeter columns and designed to remain essentially elastic in a region of high seismicity. As a non-prescriptive structural system, careful attention was paid to the behavior of the structure, and enhanced analysis and design objectives were set and met.

major seismic event, in-plane steel floor bracing was introduced to act as a substitute for the diaphragm slabs and stabilize the diagrid.

Structural Efficiency The diagrid module, four stories tall and 60 feet (18 meters) across between nodes, was fabricated using concrete filled steel tubes that work with a central reinforced concrete core to resist gravity and lateral loads. With nodes occurring every two floors, intermediate levels were suspended from nodal levels above to avoid loading diagrid members in bending between nodes, thus increasing the efficiency of the structure. This integrated system architecturally allows for a natural double exterior curtain wall system to accommodate the extreme climate of Beijing.

Non-linear Analysis Extensive non-linear pushover and response history analyses were undertaken, using Perform-3D, in the two principal directions which included material and geometric non-linearity (P-Delta effects) and strength degradation effects. The analyses indicated that shear wall link beams yield first, followed by yielding of some diagrid members at the base. Shear walls take relatively low shears, with no yielding in the rebar at the boundary zones of the walls. The non-linear analyses confirmed that the global structure is life-safe in a rare earthquake event.

Helical Load Paths By virtue of the diagrid system, lateral loads are transmitted to the base along helical load paths, not relying on a continuous diaphragm slab at the building ends. The exoskeletal diagrid system on the perimeter acts in tandem with the concrete walls at the building core to provide a dual gravity and lateral load resisting system with multiple continuous and redundant load paths. Also, global buckling stability afforded by the three-dimensional form of the diagrid makes it possible to introduce large, architecturally exciting atria into the ends of the plan.

Redundancy and Progressive Collapse The hangers supporting the intermediate floors were extended down to the nodal floors below without contact and with vertical slip joints at the bases, ensuring that they do not load on the floors below. In the event of a localized hanger failure, the hanger extension member would drop and come into contact with the floor structure below, transferring the loads. Selected diagrid members with high axial forces under gravity load were removed and progressive collapse analysis performed to ensure that a global progressive failure of the perimeter diagrid frame would not occur.

Buckling Analysis Extensive buckling analyses were performed to confirm that the diagrid members would yield before local or global buckling occurs.

To ensure the stability of the diagrid at the atria, even if the surrounding slabs crack in a

Hoop Stresses Significant tensile hoop and radial forces in the diaphragms and floor framing were noted at mid- level floors, resulting from the tendency for the diagrid frame to bulge under gravity loads. These forces are resisted by the perimeter steel framing members at nodal levels and radial steel floor framing members that connect the diagrid nodes to the inner concrete core, as well as by additional diaphragm slab reinforcement.

Diagrid Node The integrity of the diagrid structural system relies on the performance of the welded nodes.

The diagrid nodes were modularized and consist of two horizontal steel plates in line with

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the perimeter beam flanges, one vertical steel plate centered on the node work-point, and vertical curved plates between the horizontal flange plates aligned with the diagrid sections above and below. Finite element analyses were performed for representative diagrid nodes.

Reduced scale tests (cyclic and monotonic tests) were conducted at the China Academy of Building Research (CABR) in Beijing. The tests confirmed the importance of providing concrete within the nodes to ensure that eventual failure occurs beyond the nodes, and to reaffirm the adequacy of the node design.

Conclusion This landmark tower leverages a pure diagrid structural system to introduce full height atria and other shared interior spaces, and create unique, light-filled areas. The project, now complete, stands as a visible icon in the new district’s skyline.▪ Mark Sarkisian, S.E., Partner; Neville Mathias, S.E., Associate Director; Rupa Garai, S.E., Associate Director; Andrew Krebs, S.E., Associate, Skidmore, Owings & Merrill LLP in San Francisco, CA.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

Licensure

SE Progress? The License-sure Is! NCSEA Structural Licensure Committee Chairs: Kristin Killgore, ZFI Engineering and Alan Kirkpatrick, Kirkpatrick Forest Curtis PC A strong undercurrent of activity kept the Structural Licensure Committee busy during the past year. The committee remains committed to tracking the latest licensure activities, setting meaningful goals, and empowering states to adopt consistent licensure laws. Right now, there are currently 23 states with some form of structural licensure distinction and 13 that have an active SE licensure effort. The committee has set forth goals to understand the unique set of conditions and stakeholders in each state, and to help others recognize the collective importance of holding structural engineers to a higher standard of practice.

During the past year, the committee made plenty of changes, only some of which are mentioned here, but all of which kept our attention focused on advancing structural licensure. Many changes came after long-standing committee member and chair, Joseph Luke, stepped down to devote more time to the Structural Engineering Certification Board (SECB) and Kristin Killgore and Alan Kirkpatrick agreed to co-chair the committee.

The transition of chairs has been smooth thanks to Joe and his predecessor, Susie Jorgensen. Joe provided tremendous leadership and invaluable insight to the committee during his tenure as chair, and we are grateful for his contributions. He remains active with the committee as his home state of Texas continues along the path to meaningful structural licensure.

In September of 2016, the committee met during the NCSEA Summit at Walt Disney World where each represented state gave a comprehensive report on their progress. The annual meeting provided an excellent forum for the exchange of ideas which fostered many meaningful discussions about current licensure activities. Among the issues discussed was NCEES Motion 12, which was defeated in August of 2016. Approval of the measure would have amended the Model Law and Model Rules by adding language for structural engineers that parallels language for professional engineers and professional surveyors. Reasons behind the motion’s defeat have served to make us more effective and wiser in our support of SE licensure.

The forum at the Summit also brought to the committee’s attention multiple issues that relate to basic licensure concepts: • Who are the primary stakeholder organizations interested in SE licensure?

• Why are they interested?

• What common language can be used to cultivate consistent messaging?

• What does it mean exactly to be a “Roster State”?

• What are the most commonly asked questions about licensure?

• How can we simply describe legislative acts that promote licensure?

These are issues the committee continues to discuss with consideration from all sides.

Momentum from the Summit helped shape our priorities for 2017. Our first goal for the year is to clearly define licensure issues to Member Organizations by identifying frequently used terms in the licensure lexicon. This will serve to create a consistent message and an understanding of objectives with all players, including outside organizations. Next, we are developing an easily accessible document of facts, questions, and answers. Finally, we are improving our part of the NCSEA website so that it can effectively communicate essential information to anyone seeking it, but more specifically to Member Organizations who want to begin pursuing structural licensure.

The NCSEA Summit was a great success and very insightful for everyone who attended. The next may seem far away, but we know that deadlines creep deceptively quickly. The committee continues to work on articles that provide insightful points for anyone who wants to become a persuasive voice in their community. We are looking to visit Member Organizations that are not pursuing SE Licensure to discuss efforts moving forward and we hope to pick up some new members along the way. Our goal is to draw feedback from these visits so that we can better address our goals for 2017 and, after October’s Summit, refine our goals for 2018.

When we meet in Washington this fall, our committee will be prepared to inspire all those ready to take on structural licensure.

SE Review & Refresher Course Next Live Course: Lateral—March 18-19, 2017 Registration includes: • Recordings available 24/7 after the course • Seminars led by notable experts • Updates to important codes and references • Recommended publication guide STRUCTURE magazine

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Did you miss the Vertical SE Refresher course? The recordings are now available for purchase from NCSEA. 24/7 access to the seminars provides you with all the study time you need!

visit www.ncsea.com for more information March 2017

Last Notice for Presentations

CalOES SAP

The California Office of Emergency Services (CalOES) Safety Assessment Program (SAP), hosted by NCSEA, is one of only two post-disaster assessment programs that will be compliant with the requirements of the forthcoming Federal Resource Typing Standards for engineer emergency responders.

Based on ATC-20/45 methodologies and forms, the SAP training course provides engineers, architects, and code-enforcement professionals with the basic skills required to perform safety assessments of structures following disasters. Licensed design professionals and certified building officials will be eligible for SAP Evaluator certification and credentials following completion of this program and submission of required documentation.

Register for the March 24th course at www.ncsea.com.

Call for Abstracts

Submissions due March 10, 2017 The 2017 NCSEA Structural Engineering Summit Committee is seeking presentations of up to 75 minutes that deliver pertinent and useful information that Summit attendees can apply in their structural engineering practices.

Submissions on best-design practices, new codes and standards, recent projects, advanced analysis techniques, management, business practices, and other topics that would be of interest to practicing structural engineers, are desired.

More information on www.ncsea.com.

NCSEA Awards

NCSEA Excellence in Structural Engineering Awards

NCSEA News

Professional Training

National Council of Structural Engineers Associations

News from the National Council of Structural Engineers Associations

Each year, NCSEA awards the Excellence in Structural Engineering Awards.

This program annually highlights some of the best examples of structural engineering ingenuity throughout the world. Structural engineers and structural engineering firms are encouraged to enter the awards program. Projects are judged on innovative design, engineering achievement, and creativity. The awards are presented in seven categories: • New Buildings Under $20Million • New Buildings $20Million to $100Million • New Buildings over $100Million • New Bridges/Transportation Structures • Forensic/Renovation/Retrofit/Rehabilitation Structures up to $20 Million • Forensic/Renovation/Retrofit/Rehabilitation Structures over $20 Million • Other Structures

webinar subscriptionS As low as $750 wherever you go whenever you need them

Entries are due July 18, 2017. Visit www.ncsea.com for more information.

NCSEA Special Awards

The Special Awards are presented each year at the Summit to NCSEA members who have provided outstanding service and commitment to the association as well as the structural engineering field. Nominations for this year’s awards will be accepted until July 18, 2017. However, some awards may not be awarded each year. The awards can be presented in four categories: • James Delahay Award • NCSEA Service Award • Robert Cornforth Award • Susan M. Frey Educator Award Find out more on www.ncsea.com.

NCSEA Webinars

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More detailed information on the webinars and a registration link can be found at www.ncsea.com.

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May 2, 2017 Structural Steel & Bolting: Special Inspections with the IBC & AISC Robert E. Shaw, Jr., P.E.

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April 4, 2017 Special Inspections for Masonry John Chrysler, P.E.

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April 18, 2017 Upcoming Changes to AISC 341 - Seismic Provisions for Structural Steel Buildings James O. Malley, S.E.

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March 16, 2017 Draining Low-Sloped Roof Structures - Rain Issues for the Structural Engineer John Lawson, S.E.

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Structures Congress 2017 Technical Sessions

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Thursday, April 6, 2017 TRACK

BLAST AND DISPROPORTIONATE COLLAPSE

WOOD AND TIMBER/ BUILDING CASE STUDIES

SEISMIC/TALL BUILDINGS

REINFORCED CONCRETE/ASCE CODES

BRIDGE PRACTICE

BRIDGE RESEARCH

9:30 AM – 10:30 AM

Recent Developments in Blast Design and Analysis

Case-Studies: Recent Mass Timber Building Projects in North American

Seismic Analysis

Repair and Rehabilitation

Pedestrian Bridges and Tunnels

Innovative Materials for Concrete Bridges

11:00 AM – 12:30 PM

Analysis and Testing for Blast Loading

Fire Performance of Wood Structural Systems

Behavior of Full-Scale RC Special Moment Frame Components Subjected to Collapse-Level Earthquake Loadings

ACI 562-16: A Code for Repair of Existing Concrete Structures

Erection and Construction of Steel Bridges

Retrofit and Rehabilitation of Bridges for Multiple Hazards

1:30 PM – 3:00 PM

Multi-Hazard Response of Structures Subjected to Extreme Loads

Case Studies 1 – Building Retrofit Challenges

Tall Buildings

Meet the New ASCE 37-14: Design Loads on Structures During Construction Standard

Rehabilitation and Replacement

Connection Challenges Including Seismic Loading in Accelerated Bridge Construction

3:30 PM – 5:00 PM

Structures Subjected to Impact Loads

Building Case Studies 2 – Structural Design Challenges

Performance-Based Design of Tall Buildings: From Research to Applications

ASCE 41-17: A First Look

Monitoring, Serviceability and Smart Bridges

Seismic – Bridge Analysis

BRIDGE PRACTICE

BRIDGE RESEARCH

Friday, April 7, 2017

TRACK

BLAST AND DISPROPORTIONATE COLLAPSE

MASONRY/ PERFORMANCEBASED DESIGN

ASCE 7-16

OPTIMIZATION AND INNOVATION/ COLORADO STRUCTURES

8:00 AM – 9:30 AM

Challenges in Modeling Collapse of Reinforced Concrete Structures

ASCE 7-16 Overview What’s New in the 2016 Edition

Masonry Design and Detailing

Modern Developments in Structural Optimization

Rail Bridges

Seismic – Concrete Bridges

10:00 AM – 11:30 AM

Use of Numerical Techniques in the New Alternative Load Path Analysis Guidelines

ASCE 7-16 Seismic: Learn from the Experts

Masonry Inspection, Evaluation and Research

Innovative Systems and Components

Long Span Bridges

Resilience and Sustainability

2:00 PM – 3:30 PM

Blast and Disproportionate Collapse Resistance of Pre-Cast/Pre-Stressed Concrete Construction

ASCE 7-16 Wind: Learn from the Experts

Performance-Based Design

Iconic Colorado Structures

The Federal Highway Administration (FHWA) Long-Term Bridge Performance (LTBP) Program

Analysis and Fatigue in Steel Bridges

4:00 PM – 5:30 PM

Recent Applications of Disproportionate Collapse Analysis to New and Existing Building Design

ASCE 7-16 Tsunami: The New Resiliency Approach and Design Provisions

Seismic Behavior of Steel Columns – Experimental Findings, Nonlinear Modeling & Evaluation Criteria for PerformanceBased Earthquake Engineering

Selected Colorado Contributors to Engineered Concrete Structures

Innovative Solutions using Ultra-High Performance Concrete (UHPC)

Bridge Analysis and Modeling

Saturday, April 8, 2017 TRACK

BLAST AND DISPROPORTIONATE COLLAPSE

EXPANSIVE SOIL/ COLD FORMED STEEL

DISPROPORTIONATE COLLAPSE/WIND

STEEL

BRIDGE PRACTICE

BRIDGE RESEARCH

8:00 AM – 9:30 AM

Updates to the ASCE Manual of Practice, Structural Design for Physical Security

Expansive Soils: A Force To Be Reckoned With

Guidelines for Alternative Load Path Analysis

The AISC 15 Ed. Steel Construction Manual

Reuse of Bridge Foundation: Technical Challenges and Developments

Autonomous Condition Assessment of Transportation Infrastructure

10:00 AM – 11:30 AM

Novel Techniques for Progressive Collapse Analysis

Cold-Formed Steel Topics

Wind Engineering

Steel

Fatigue and Fracture Assessment of Bridge Resilience and Development of Retrofit Methods

Structural Health and Performance Monitoring of Railroad Infrastructure

th

Register early and save. For more information including registration and housing, visit our website at www.structurescongress.org.

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EDUCATION/ SUSTAINABILITY

RESEARCH

PROFESSIONAL PRACTICE 1

BUSINESS PRACTICE

NATURAL DISASTER

NONBUILDING STRUCTURES

Enhancing Recruitment of Graduate Students Through Active Organizational Participation

Condition Assessment of Structural Systems under Service Loads

Successful Successions: Planning for Leadership Transitions in a Structural Engineering Firm

Ethics for the Practicing Engineer

An Overview of the M7.8 April 16, 2016 Ecuador Earthquake

Extreme Loads on Offshore Structures 1

Designing Beyond Strength – Mentoring and Teaching the Importance of Aesthetics and Performance

Health Monitoring

Lateral Analysis: Right Way/ Wrong Way with Software

For the Entrepreneurs – The Business of Consulting Structural Engineers

ASCE/SEI Assessment of the Chile Earthquake of 2010

Extreme Loads on Offshore Structures 2

Still in Use: Structural Engineering History and Contemporary Design Practice

Innovations in Sustainable and Resilient Structural Materials

Changing Structural Engineering Workforce and Work Places: Challenges and Opportunities

Politics and Public Policy for Civil Engineers

Advances in Determination of Snow and Wind Loads

Foundations for Nonbuilding Structures

Sustainability

Progress in Innovative Mass Timber and Timber Hybrid Structural Systems

Technology and Our Profession- How Do We Keep Our Sanity?

BIM: Management, Marketing, and Merit

Topics in Pre-Disaster Planning Scenarios, Post-Disaster Response, and Utilizing Drones for Structural Condition Assessments

Constructability Issues for Nonbuilding Structures

STRUCTURES UNDER EXTREME LOADS

CASE

CLAIMS

NATURAL DISASTER

Natural Disasters-Wind, Waves, and Shaking

New Research Frontiers in Structural Resistance to Fire

Contractual Risk Transfers for Professionals: Mastering Indemnity, Insurance and the Standard of Care

Resolving an Engineering/ Construction Dispute using Litigation and Mediation

Tornado Characterization, Modeling and Simulation

Seismic Effects on Water Facilities

Bridge Practices

Structural Fire Engineering Design Practice

Construction Administration as a Risk Management Tool

Sharing the Story of a Real Claim Defamation, Libel and Slander

Tornado Loading and Building Response

Storage Racks

Seismic Assessment

Seismic Performance of Structures

Projects with the Largest Losses and Claim Frequency

The Story of a Claim Resolved by Mediation

Induced Seismicity Issues for Structural Engineers

Topics in Performance of Nonstructural Components

Materials, Testing and Computational Modeling

Challenges in Modeling Collapse of Reinforced Concrete Structures

Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable

Sharing the Story of a Real Claim The Condo

Panel Discussion: New ASCE/SEI Standard for Estimation of Tornado Wind Speeds

Seismic Response of Nonstructural Components

EDUCATION

FORENSICS

INTERNATIONAL PROFESSIONAL PRACTICE

PROFESSIONAL PRACTICE – STORIES

RESILIENT AND SUSTAINABLE COMMUNITIES

STRUCTURAL ENGINEERING TODAY

New Trends in Structural Engineering Education and Mentoring

Forensic Investigations of Structural Damages and Failures – Part 1

Structural Engineering Business Innovations

Gaining a Foothold in International Engineering Work

Building Resilient and Sustainable Communities: Engineering Advances

Calculating Your Professional Risk(s): The Fewer Moving Parts, the Better

Industry/Academic Capstone Model Program

Forensic Investigations of Structural Damages and Failures – Part 2

A Few Stories to Ease the Everyday Tensions

Working Internationally – Codes, Ethics, and Work Life Balance: A Young Professionals Perspective

Building Resilient and Sustainable Communities: Including Sociological Impacts in Engineering Practice

Complex Structures

View the interactive Technical Program, including all presenters and abstracts at www.structurescongress.org.

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The Newsletter of the Structural Engineering Institute of ASCE

IES

NONBUILDING STRUCTURES & NONSTRUCTURAL COMPONENTS

Structural Columns

April 6 – 8, 2017 – Denver, Colorado

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Risk Management Tools Available Foundation 3: Planning – Plan to be Claims Free • Must have a plan for the firm to be claims free.

• Train staff to plan, then implement the plan.

• The plan needs to be simple, understandable, and inclusive to be effective.

• Have Policies and Procedures that are workable and followed.

• Communicate and repetitively reinforce the plan.

• The plan may need to adjust as conditions change.

Tool 3-2 Staffing and Revenue Projection Firms are provided a simple to use and easy to manipulate spreadsheet-based tool for predicting the staff that will be necessary to complete both “booked” and “potential” projects. The spreadsheet can be further utilized to track historical staffing demand to assist with future staffing and revenue projections.

Tool 3-1 A Risk Management Program Planning Structure This tool is designed to help a Firm Principal design a Risk Management Program for his or her firm. The tool consists of a grid template that will help focus thoughts on where risk may arise in various aspects of their engineering practice and how to mitigate those risks. Once the risk factor is identified, a policy and procedure for how to respond to that risk is developed.

This tool contains 10 sample risk factors with accompanying policies and procedures to illustrate how one might get started.

The tool is designed to insert custom risks and policies to tailor it to individual firms.

Tool 3-3 Website Resource Tool This tool lists website links that contain information that could be useful for a Structural Engineer. A brief description of the website is also included. For example, there is information about doing business across state lines, information regarding the responsibility of the Engineer of Record for each state, links to each State’s Licensing Board, and more.

Tool 3-4 Project Work Plan Templates Preparing and maintaining a proper Project Work Plan is a fundamental responsibility of a project manager. Work Plans document project delivery strategies and communicate them to the team members. Project Managers will use this template to create a project Work Plan that will be stored with the project documents.

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

CASE Risk Management Convocation in Denver, CO April 7, 2017 The CASE Risk Management Convocation will be held in conjunction with the Structures Congress at the Hyatt Regency Denver and Colorado Convention Center in Denver, CO, April 6 – 8, 2017. For more information and updates go to www.structurescongress.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 7: 8:00 am – 9:30 am Contractual Risk Transfers for Professionals: Mastering Indemnity, Insurance and the Standard of Care Moderator/Speaker: Ryan J. Kohler, Collins, Collins, Muir + Stewart, LLP 10:00 am – 11:30 am Construction Administration as a Risk Management Tool Moderator/Speaker: Daniel T. Buelow, Willis Towers Watson 2:00 pm – 3:30 pm Projects with the Largest Losses and Claim Frequency Moderator: Mr. Timothy J. Corbett, SmartRisk Speaker: Brian Stewart, Esq., Collins, Collins, Muir + Stewart, LLP 4:00 pm – 5:30 pm Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable Moderator: David W. Mykins, P.E., Stroud Pence & Associates STRUCTURE magazine

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Top executives and distinguished public figures will highlight the 2017 ACEC Convention in Washington, D.C., April 23 – 26. 1,500 participants are expected.

Jacque Hinman, CH2M chair/CEO; Fred Werner, AECOM president, design and consulting services; and Greg Kelly, WSP | Parsons Brinckerhoff president/CEO, U.S. and South America, will discuss industry prospects with Fortune magazine Senior Editor Geoff Colvin.

Former White House Director of Communications Nicolle Wallace will kick off the Convention, which will also include Members of Congress, Cook Political Report Editor Amy Walter, Pennsylvania Secretary of Transportation Leslie Richards, and many other notable speakers.

TV star Kevin Nealon will host the 50th Anniversary Gala of the Engineering Excellence Awards. For more information and to register, www.acec.org/conferences/annual-convention-2017.

SAVE the DATE! Applying Expertise as an Engineering Expert Witness June 15 –16, 2017; Boston, MA Engineers are often asked to serve as expert witnesses in legal proceedings – but only the prepared and prudent engineer should take on these potentially lucrative assignments. If asked, would you be ready to say yes? This unique course developed exclusively for engineers, architects, and surveyors, will show you how to prepare for and successfully provide expert testimony for discovery, depositions, the witness stand, and related legal proceedings.

Applying Expertise as an Engineering Expert Witness is a focused and engaging 1½ day course that will run you through each step of the qualifications, ramifications, and expectations of serving as an expert witness.

For more information about the course, please contact Katie Goodman 202-682-4377 or kgoodman@acec.org.

Opportunities and Risks for Consulting Engineers P3 and DB approaches on public infrastructure projects continue to increase, leaving consulting engineers with more questions than ever. That is why, to make conscientious, prudent decisions about P3 and DB project opportunities and risks, you need access to reliable expertise and the latest knowledge.

The second edition of Public-Private Partnerships and DesignBuild: Opportunities and Risks for Consulting Engineers presents new industry information and experience on P3 and DB approaches and offers timely recommendations about the rewards, challenges, and risk exposures for engineering firms looking to succeed in today’s still-evolving P3 and DB project work environment.

New to the Second Edition: • DB opportunities, roles, risks, and contracting practices • Dispute resolution processes in P3s and DB

• Contractual availability and sound implementation of fair and appropriate dispute resolution processes in the assessment and management of P3 and DB projects Readers will also find updated information on risk allocation and professional liability issues specific to P3 and DB projects.

Edited by David Hatem and Patricia Gary of Donovan Hatem LLP, along with the contributions of 14 subject matter experts, Public-Private Partnerships and Design-Build: Opportunities and Risks for Consulting Engineers, Second Edition provides an objective, realistic, and practical resource for you to make informed and balanced judgments about pursuing P3 and DB projects.NCSEA members can contact Heather Talbert (htalbert@acec.org) about obtaining this book at the ACEC Member Price of $99.

Donate to the CASE Scholarship Fund!

Share Innovative Ideas!

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 $20,000 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 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 in educational support.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. Contact Heather Talbert at htalbert@acec.org to donate.

STRUCTURE magazine

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!

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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CASE is a part of the American Council of Engineering Companies

Public-Private Partnerships and Design-Build

CASE in Point

Market Leaders, Celebrities to Star at ACEC Convention

Structural Forum

opinions on topics of current importance to structural engineers

Risk Aversion

By Stan R. Caldwell, P.E., SECB

T

he public generally takes the safety of the structures around them for granted, and for good reason.

A landmark study by Robert E. Melchers in 1987 compared the annual risk of death due to a variety of activities. He found that smoking is a high-risk activity, with about 1,000 deaths/million smokers/year.

Automobile travel is a moderate-risk activity, with about 210 deaths/million motorists/ year. Swimming is similar, with about 175 deaths/million swimmers/year. Air travel is a surprisingly low-risk activity, with about 24 deaths/million flyers/year. Structural failures, however, cause only about 0.12 deaths/million users/year. The public freely accepts the risks inherent in automobile and air travel, and most accept the risks inherent in swimming.

Those risks are 200 to 1,750 times greater than the risks associated with structural failures. That begs the question: Are structures too safe?

Structural engineers can claim most of the credit for safe structures. During their years in college, students are taught that a structural failure is never an acceptable outcome. They learn that the consequences of structural engineering mistakes can be severe. For example, when a medical doctor makes a mistake, a single patient might be injured or killed. In contrast, when a structural engineer makes a mistake, hundreds of people might be injured or killed. Also, a structural engineering mistake might cause enormous economic loss and environmental damage.

As structural engineers enter the profession, the importance of avoiding mistakes is repeatedly stressed by their employers and professional liability insurers. They learn the dangers that lurk in their contracts, their construction documents, their field work, and their emails and other project records.

At some point, they learn the financial realities of their profession. Based on revenues, structural engineers have the highest claims of all engineering disciplines. The average individual claims against structural engineers are about three times greater than those of any other engineering discipline.

With these concerns firmly established in the minds of all practitioners, the structural engineering profession has become very averse to risk. This approach has certainly served the public very well, as evidenced by the statistics noted above. However, risk aversion is now threatening the prosperity, and perhaps even the future, of the profession.

A century ago, many structural engineers worked as master builders. You probably know some of their names: Gustave Eiffel, John Roebling, Othmar Ammann, James Eads, Eugene Freyssinet. It is a long list. They took responsibility for most aspects of their projects, including planning, design, financing, construction, and maintenance. Eventually, due in part to liability concerns, structural engineers began to limit their responsibilities.

Today, many limit their services to investigation, design, and construction observation.

Some also decline certain types of projects that are perceived to be a high liability, such as condominiums.

For decades, structural engineers have accepted (or created) an environment that is driven by increasingly prescriptive codes and standards. To avoid risk, few engineers intentionally venture beyond the many requirements stated in these documents.

Consequently, they now are sometimes viewed by the public as mathematical technicians who meticulously follow detailed “recipes” to produce adequate designs. They are no longer seen as valued professionals.

In this environment, structural engineers have mostly forfeited their ability to exercise professional engineering judgment, which is the very essence of their professional engineering licensure.

Continuing on the current path will lock most structural engineers into a supporting role in a shrinking profession bound by prescriptive design requirements. This will be a profession with diminished stature, one that will be less rewarding to practitioners, and one that will be less appealing to the bright students of the future. As the pressures of automation and globalization are added to this environment, the profession will

certainly face marginalization and might eventually face obsolescence.

To ensure their future, structural engineers must find new paths outside their current comfort zones. They must learn to actively manage the technical and business risks on all of their projects. This will require mastering new tools and, importantly, having the discipline to use them daily. If fully understood and actively managed, risk can be a powerful asset. To become more creative and innovative, and thereby to be able to offer more value to their clients, structural engineers must be willing to accept reasonable risk.

Also, structural engineers must once again make professional engineering judgment the primary reason why structural engineers are valuable and why creative people aspire to be structural engineers. This means cautiously going beyond the prescriptive requirements of current codes and standards, and making design decisions based on knowledge and experience. One path is to develop special expertise in a niche area, such as the rehabilitation of old structures, where codes and standards might not readily apply. Another path and a broader one is to embrace performance-based design.

While not for the faint of heart, and while not appropriate for every project, this is rapidly becoming a popular method of venturing beyond the requirements of current codes and standards.

In summary, the profession of structural engineering has evolved into one that is overly risk averse and overly prescriptive.

Change is required if the profession is to thrive in the future. Two paths forward are niche specialization and performance-based design. These are likely not the only paths.

It is evident, however, that the status quo does not lead anywhere that most structural engineers want to go.▪ Stan R. Caldwell (StanCaldwellPE.com) is a consulting structural engineer in Plano, Texas. He can be reached at stancaldwellpe@gmail.com.

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

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Live Instructional Webinars Scheduled Every Wednesday DeWALT HangerWorks plug-in for Autodesk Revit is a tool that automates the placement and engineering design of hangers and seismic bracing for MEP systems such as duct, pipe, conduit and cable tray. Prefabrication sheets, bill of materials, total station layout points and engineering reports such as point load calculations are included.

For additional information or to get started using HangerWorks contact: DWGTP@gogtp.com