STRUCTURE magazine January 2019

STRUCTURE JANUARY 2019

NCSEA | CASE | SEI

Concrete INSIDE: SR 99 Tunnel, Seattle

22

Coupling Beam Types Improving School Buildings Northridge: 25 Years Later

8 14 18

The only clip proven to perform in full-scale testing.

The new SCS seismic clip doubles the in-plane capacity of other bypass clips.

The innovative SCS seismic bypass framing connector from Simpson Strong-Tie is engineered for either slide-clip or fixed-clip applications in high-seismic areas. Backed by our real-world, full-scale cyclic testing, the SCS seismic clip delivers the highest seismic loads in the industry.

Trust the value-engineered SCS seismic connector for your next project. Visit go.strongtie.com/scs or call (800) 999-5099.

Š 2019

Simpson Strong-Tie Company Inc. SCS18-E

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

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties, including technicians, fabricators and architects. Its unique functionality enables engineers to integrate the physical design model seamlessly with Tekla Structures or Autodesk Revit, and to round-trip without compromising vital design data.

“We’re able to import geometry from Revit, design in Tekla Structural Designer and export that information for import back into Revit. If an architect makes geometry updates or changes a slab edge, we’ll send those changes back into Tekla Structural Designer, rerun the analysis and design, and push updated design information back into Revit.”

Tekla Structural Design at Work: The Hub on Causeway

For over 55 years, LeMessurier has provided structural engineering services to architects, owners, contractors, developers and artists. Led by the example of legendary structural engineer and founder William LeMessurier, LeMessurier provides the expertise for some of the world’s most elegant and sophisticated designs while remaining true to the enduring laws of science and engineering.

Known for pushing the envelope of the latest technologies and even inventing new ones, LeMessurier engineers solutions responsive to their clients’ visions and reflective of their experience.

An early adopter of technology to improve their designs and workflow, LeMessurier put its own talent to work in the eighties to develop a software solution that did not exist commercially at the time. Their early application adopted the concept of Building Information Modeling (BIM) long before it emerged decades later.

While LeMessurier’s proprietary tool had evolved over three decades into a powerhouse of capability, the decision to evaluate commercial structural design tools was predicated on the looming effort required to modernize its software to leverage emerging platforms, support normalized data structure integration and keep up with code changes.

After a lengthy and thorough comparison of commercial tools that would “fill the shoes” and stack up to the company’s proprietary tool, LeMessurier chose Tekla Structural Designer for its rich capabilities that addressed all of their workflow needs. According to Derek Barnes, Associate at LeMessurier, ” Tekla Structural Designer offered the most features and the best integration of all the products we tested. They also offered us the ability to work closely with their development group to ensure we were getting the most out of the software.”

One Model for Structural Analysis & Design

From Schematic Design through Construction Documents, Tekla Structural Designer allows LeMessurier engineers to work from one single model for structural analysis and design, improving efficiency, workflow, and ultimately saving time. “Our engineers are working more efficiently because they don’t need to switch between multiple software packages for concrete and steel design. Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product,” said Barnes.

LeMessurier engineers use Tekla Structural Designer to create physical, information-rich models that contain the intelligence they need to automate the design of significant portions of their structures and efficiently manage project changes.

TRANSFORMING THE WAY THE WORLD WORKS

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

Efficient, Accurate Loading and Analysis

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

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

Positioning a large scale mixed-use development next to an active arena, a below grade parking garage, and an interstate highway, and bridging it over two active subway tunnels makes planning, phasing and engineering paramount. Currently under construction, The Hub on Causeway Project will be the final piece in the puzzle that is the site of the original Boston Garden.

Despite being new to the software, LeMessurier decided to use Tekla Structural Designer for significant portions of the project. “Relying on a new program for such a big project was obviously a risk for us, but with the potential for time savings and other efficiencies, we jumped right in with Tekla Structural Designer. It forced us to get familiar the software very quickly.”

“Tekla Structural Designer allowed us to design the bulk of Phase 1 in a single model,” said Barnes. The project incorporates both concrete flat slabs and composite concrete and steel floor framing. “Tekla Structural Designer has the ability to calculate effective widths based on the physical model which is a big time saver,” said Barnes. “On this project, the integration with Revit, along with the composite steel design features enabled us to work more efficiently. Adding the ability to do concrete design in the same model was a bonus because we had both construction types in the same building.”

“Tekla Structural Designer helped this project run more efficiently, and in the end it was a positive experience,” said Blanchet.

“Tekla Structural Designer gives us multiple analysis sets to pull from, which gives us lots of control. Most programs don’t have the capability to do FE and grillage chase-down. For the design of beam supported concrete slabs, Tekla Structural Designer allows us to separate the slab stiffness from the beam stiffness, so if we choose to we can design the beams without considering the influence of the slab. In the same model we can use a separate analysis set to review the floor system with the beams and slab engaged,” said Barnes.

Barnes also shared similar benefits with concrete column design. “Tekla Structural Designer does grillage take-downs floor-by-floor, finds the reactions and applies them to the next floor. This allows us to view column results both for the 3-dimensional effects of the structure as a whole and from the more traditional floor-by-floor load take-down point of view.

Doing both has always required significant manual intervention, but Tekla Structural Designer puts it all in one place.” “We reduce the possibility for human error because with Tekla Structural Designer less user input is required,” said Barnes. “Tekla Structural Designer automatically computes many of the design parameters, such as column unbraced lengths. The assumptions made by the software are typically correct, but we can easily review and override them when necessary.”

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

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

ADVERTISER INDEX

Please support these advertisers

American Concrete Institute ........................ 34 Cortec Corporation .................................. 17 GeoDesign, Inc........................................ 29 Geopier Foundation Company.................... 27 Hohmann & Barnard, Inc. ......................30-31 Integrated Engineering Software, Inc. ........... 43 Integrity Software Inc ................................... 4 KPFF ........................................................ 9 Larsen Products Corp................................. 11 NCEES .................................................. 15

New Millennium Building Systems ............... 21 Nucor Vulcraft Group - Redicor ................... 10 Nucor Vulcraft Group - Ecospan .................. 13 RISA ...................................................... 44 Simpson Strong-Tie ............................... 2, 25 Structural Engineering Institute ..................... 33 StructurePoint ............................................. 6 Struware ................................................... 4 Trimble ..................................................... 3

STRUCTURE

®

MARKETING & ADVERTISING SALES

sales@STRUCTUREmag.org

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

EDITORIAL STAFF Executive Editor Alfred Spada aspada@ncsea.com

Publisher Christine M. Sloat, P.E. csloat@STRUCTUREmag.org

Associate Publisher Nikki Alger ADVERTISEMENT - For Advertiser Information, visit STRUCTUREmag.org

nalger@STRUCTUREmag.org

Creative Director Tara Smith

Demos at www.struware.com

Not listed?

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

Visit our website to see what advertising

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

opportunities are right for you!

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

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

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

Quick and easy to use ($45.00).

STRUCTUREmag.org

graphics@STRUCTUREmag.org

EDITORIAL BOARD Chair John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA chair@STRUCTUREmag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. AISC, Littleton, CO Timothy M. Gilbert, P.E., S.E., SECB TimkenSteel, Canton, OH Linda M. Kaplan, P.E. Pennoni, Pittsburgh, PA Charles “Chuck” F. King, P.E. Urban Engineers of New York, New York, NY Emily B. Lorenz, P.E. Precast/Prestressed Concrete Institute, Chicago, IL

Bentley spending out of control?

ADVERTISEMENT - For Advertiser Information, visit STRUCTUREmag.org

®

Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY Jason McCool, P.E. Robbins Engineering Consultants, Little Rock, AR

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

CALL US TODAY: (866) 372 8991 (USA/Canada) (512) 372 8991 (Worldwide) www.softwaremetering.com © 2018 Integrity Software, Inc. Bentley is a registered trademark of Bentley Systems, Incorporated

4 STRUCTURE magazine

Feature Code, and Serial Number!

©

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

Brian W. Miller Davis, CA Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA Eytan Solomon, P.E. Silman, New York, NY STRUCTURE® magazine (ISSN 1536 4283) is published monthly by The National Council of Structural Engineers Associations (a nonprofit Association), 645 N. Michigan Ave, Suite 540, Chicago, IL 60611 312.649.4600. Application to Mail at Periodicals Postage Prices is Pending at Chicago, IL and additional mailing offices. STRUCTURE magazine, Volume 26, Number 1, C 2019 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership. Yearly Subscription in USA $75; $40 For Students; Canada $90; $60 for Canadian Students; Foreign $135, $90 for foreign students. Editorial Office: Send editorial mail to: STRUCTURE magazine, Attn: Editorial, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611. POSTMASTER: Send Address changes to STRUCTURE magazine, 645 N. Michigan Avenue, Suite 540, Chicago, IL 60611.

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

Contents JANUARY 2019

SR 99 TUNNEL IN SEATTLE

By Yang Jiang, Ph.D., P.E., S.E.,

Cover Feature

22

and Andrew Herten, P.E.

The SR 99 Tunnel in Seattle is part of the Alaskan Way Viaduct. The 9,300-foot-long bored tunnel was excavated by a Tunnel Boring Machine, named Bertha, with a 57½-footdiameter cutterhead. The tunnel’s interior structure is comprised of two continuous corbels supporting a series of 650-foot-long moment frame systems of walls and slabs, detailed to expand and contract longitudinally.

Columns and Departments 7

18

Editorial Okage Sama De: I am What I am Because of You

By Corey M. Matsuoka, P.E.

8

Structural Design Coupling Beam Types

By Songtao Liao, Ph.D., P.E., and Benjamin Pimentel, P.E.

14

Structural Failures Improving School Buildings in Indonesia

35

By Lizzie Blaisdell Collins, P.E., S.E., James Mwangi, Ph.D., P.E., S.E., and Mediatrich Triani N.

18

Northridge – 25 Years Later Caltrans Highway Structures

By Mark Yashinsky

26

In the News Changes on STRUCTURE’s Editorial Board

28

Structural Sustainability Thermal Breaks in Building Envelopes

By Scott Hamel, P.E., Ph.D., and Kara Peterman, Ph.D.

35

Spotlight Intuit’s Marine Way Building

By Megan Stringer, S.E.

42

Structural Forum Scope Creep

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

In Every Issue

4 32 36 38 40

Advertiser Index Resource Guide – Anchor Updates NCSEA News SEI Update CASE in Point

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

J A N U A R Y 2 019

5

EDITORIAL Okage Sama De: I am What I am Because of You

By Corey M. Matsuoka, P.E., Chair CASE Executive Committee

I

magine being named the President of the Washington Bullets in 1991, a time when the franchise had fallen on lean times. Everyone is looking at you to turn things around. Then imagine you are a 29-year-old female trying to survive in a business (not unlike our own) that has traditionally been dominated by men. That is Susan O’Malley, the first female president of a professional sports franchise. Not only did she survive, but she also thrived. Susan oversaw the largest ticket revenue increase in the history of NBA franchises, and implemented innovative marketing and customer service initiatives that led to the highest renewal rate of season tickets ever by the franchise.

When she stepped down as president of the Wizards (name changed) in 2007, owner Abe Pollin described her as his “right hand through the past 20 years.”

At this year’s ACEC Fall Conference, Susan was a keynote speaker and she shared her seven seminal ‘rules’ for leadership and life that guided her through her journey. At the end of her speech, she challenged the audience to think about what their ‘rules’ were.

For me, I do not think I have rules, as much as beliefs and values.

As a fourth generation Japanese American growing up in Hawaii, my beliefs and values have been influenced by my Asian heritage and the assimilation of the local Hawaiian culture. From Japan…

1) Okage Sama De. I am what I am because of you. Show respect for those who came before you and helped you to get where you are. On my desk, I have a copy of the handwritten notes containing the basic concepts and organizational bases on which our company was founded. It is dated 1959, the year SSFM was incorporated and written by one of the company’s co-founders. Our company is what it is today because of our founders.

2) Gaman. Enduring the seemingly unbearable with patience and dignity. Initially, I worked as a structural engineer and I wanted to quit after only three months. With a tough boss, long hours, and stress about my design skills (or lack thereof ), I was worried that something I designed could collapse and hurt someone.

I confided in my father (who was also an engineer) that I was thinking of quitting, hoping for an intellectual discussion about my options. He gave me no sympathy and told me to toughen up or “gaman.” Fortunately, I listened to him, and I am still here today.

3) Ganbaru. To do one’s best. This Japanese term is closely related to gaman, relating to persistence and tenacity. Where it differs is that ganbaru also encapsulates the ideals of doggedness and hard work. In practice, it can even mean doing more than one’s best. Early in my career, we would stay at work until the job was complete. Sometimes that meant staying overnight to meet a deadline. The bosses would joke, “Tomorrow morning we

STRUCTURE magazine

better have this submittal complete, or there should be dead bodies on the ground.”

From Hawaii…

1) Aloha. A value of unconditional love. With Hawaii being a mixing pot of races from east and west, I never thought of diversity as being a big challenge. However, I now realize that diversity goes beyond race and includes age, gender, sexual orientation, religion, disabilities, etc. Aloha is the acceptance and inclusion of all of these differences.

2) Ohana. Those who are family, and those you choose to call family. My parent’s friends, whom I have known since childhood, are still Aunty and Uncle. If you are familiar with Disney’s Lilo & Stitch, you know that Ohana means family, and family means no one is left behind. They are still taking care of me today.

3) Kuleana. One’s personal sense of responsibility. As a young principal, I shadowed my boss on a claim negotiation. We had made a few mistakes, and we were going to pay a lot of money.

I remember my boss saying this was one of the hardest things he had to do. I assumed it was because of the money, but that was not it. It was because we made a mistake. The money was the easy part. We were wrong, and we needed to fix it. That was never a question. It was our responsibility, our kuleana.

4) Malama. The value of stewardship, to take care. Living on an island, we take care of our home, as it is the only one we have.

As a family, we are often doing service projects such as cleaning up our parks and beaches, removing invasive species from the land and ocean, and educating the public about sustainability.

5) Pono. The value of integrity, of rightness and balance. At a recent camp, my son’s Scout Master was telling us a story of his son who was a good athlete but had not played baseball since intermediate school. As a senior, the baseball coach was looking for more talent and really wanted his son on the team. The son declined and, when the Scout Master asked him why, he said it would not be fair for him to take the place of a classmate who worked all year to be on that team. It was the pono thing to do.

These values and beliefs that I hold dear are because of those that came before me. They showed me what was important and how to be a productive and valued member of society. I hope that I’m doing the same for my children and my staff.

Thank you to my parents, my bosses, and my mentors.

Okage Sama De.■ Corey M. Matsuoka is the Executive Vice-President of SSFM International, Inc. in Honolulu, Hawaii and the chair of the CASE Executive Committee. (cmatsuoka@ssfm.com)

J A N U A R Y 2 019

7

structural DESIGN Coupling Beam Types Practical Reinforced Concrete Building Design

By Songtao Liao, Ph.D., P.E., M.ASCE, and Benjamin Pimentel, P.E.

R

einforced concrete (RC) shear walls are usually the primary lateral force resisting system for reinforced

concrete buildings and adjacent shear wall piers are typically connected with coupling beams above doors or corridors at floor levels. The coupling beams reduce flexural moments in the coupled shear wall piers, provide an energy dissipation mechanism along the entire building height, and improve shear wall system efficiency.

Figure 2. Typical diagonally-reinforced concrete coupling beam with full confinement.

As one of the most critical members in RC buildings, coupling beams should exhibit excellent energy dissipation capacity with only modest stiffness and strength degradation under cyclic loading. Good ductile hysteretic performance is usually achieved by providing sophisticated detailing, which induces construction difficulties. By varying rebar layout schemes and exploring different materials, various types of coupling beams are considered in searching for a balance between ductile hysteretic performance and construction practicality.

Currently there are five commonly-used types of coupling beams which are adopted by building codes and the design industry: • Conventional RC coupling beams • Diagonally-Reinforced concrete coupling beams • Steel coupling beams • Encased steel composite coupling beams • Embedded steel plate composite coupling beams

building design. In low seismic risk areas, conventional RC coupling beam are sometimes sized wider than the connecting shear wall piers in flat-slab buildings.

However, the conventional RC coupling beam does not preserve good energy dissipation capacities under high cyclic shear stresses and significant pinching phenomena present in its hysteresis response.

Diagonal shear failure and sliding shear failure are not avoidable in this type of coupling beam even with closely-spaced transverse reinforcing detailing. Research indicates that conventional RC coupling beams only exhibit satisfactory performance when the nominal gross — section shear stress is below 3√ f´c (psi) and when the beam behavior is flexure-controlled, although the nominal maximum allowable shear — stress limit is 10√ f´c (psi) in ACI 318.

Conventional RC Coupling Beams

In the 1960s, a diagonal rebar layout in concrete coupling beams was proposed to effectively arrest the coupling beam sliding shear failure at the face of the coupled shear wall piers (Figure 2). To date, the diagonally-reinforced concrete coupling beams are recognized as the most effective type of reinforcing details to provide ductile performance with excellent energy dissipation capacity, especially when the span/depth ratio is less than 2. The well-established design provisions and details for diagonally-reinforced coupling beams can be found in the Section 18.10.7 of ACI 318-14, Building Code Requirements for Structural Concrete.

In the design of a diagonally-reinforced concrete coupling beam, the shear forces are resisted by the diagonal rebars only and the moment capacities are automatically provided by the diagonal “truss” members.

— The nominal maximum allowable beam shear stress limit, 10√ f´c (psi), is capped to ensure the coupling beam ductility and deformability.

Although diagonally-reinforced coupling beams exhibit excellent stiffness and highly-ductile energy dissipation capacities, there are some constructionability issues that limit their application: • The practical width of diagonally-reinforced concrete coupling beams is at least 14 inches (16 inches or more is preferable) to accommodate all reinforcement meeting the minimum codeallowed spacing requirements.

Conventional RC coupling beams refer to coupling beams reinforced with horizontal rebars and closely-spaced stirrups. The design and detailing requirements for conventional RC coupling beams are the same as those for RC special moment frame members and are well provisioned in building codes, such as ACI 318 (Figure 1). Due to its relatively simple detailing and ease of construction, the conventional RC coupling beam is the most extensively used coupling beam type in

Figure 1. Typical conventional concrete coupling beam.

8 STRUCTURE magazine

Diagonally-Reinforced Concrete Coupling Beams

Figure 3. Typical encased steel composite coupling beam.

• The on-site placement of diagonal reinforcement is difficult and labor-intensive.

• The effectiveness of diagonal reinforcement decreases significantly when the span-to-depth ratio is larger than 2 and the diagonal rebar inclination angle becomes small, while most architecturally practical coupling beam dimensions in high-rise buildings fall in this range.

Steel and Encased Steel Composite Coupling Beams Steel coupling beams and encased steel composite coupling beams are used as viable alternatives to avoid the construction difficulties inherent in diagonally-reinforced concrete coupling beams. The steel members for the two coupling beam types are implicitly wide-flange steel members, although steel tubes were also used in early research (Figure 3).

Extensive experiments indicate that both steel coupling beams and encased steel composite coupling beams can provide excellent ductility and energy dissipation capacities, which are comparable to those of diagonally-reinforced concrete coupling beams. ANSI/AISC 341-16, Seismic Provisions for Structural Steel Buildings, adopts both types of coupling beams in composite shear wall systems with design and detailing provisions.

Higher Education/Research For these two types of coupling beams, both shear forces and flexural moments are assumed to be entirely resisted by the steel member. The benefits of the concrete encasement are currently ignored Seattle Long Beach due to a lack of data. The concrete Tacoma Irvine encasement provides higher beam stiffLacey San Diego ness and acts as a fire proofing layer for Portland Boise the encased steel beams.

Eugene St. Louis Sacramento Chicago Different from reinforced concrete San Francisco Louisville coupling beams, the code-specified Los Angeles New York maximum allowable shear stress limit — for concrete beams (e.g. 10√ f´c (psi) in KPFF is an ACI 318) can be relieved for the encased Equal Opportunity Employer steel composite coupling beam. Although no research on the interaction between www.kpff.com the steel member and the RC concrete ASU Biodesign Institute C encasement is carried out, a practical size Tempe, AZ range of the steel beam to the coupling

Figure 4. Typical embedded steel plate composite coupling beam.

beam should be maintained to ensure the appropriate composite action of the encased steel composite coupling beam. Similarly, a maximum allowable nominal shear stress limit for the encased steel composite coupling beam is desirable for concrete encasement cracking control, while no value is yet available in the literature.

The most important item in the design of steel coupling beams and encased steel composite coupling beams is the embedment of the steel members. The embedment length design of these two types of coupling beams is usually based on the rigid Mattock-Gaafar embedment model by satisfying the expected coupling beam-shear wall connection shear strength (Eq. H4.1 & H5.1 in AISC 341-16).

Appropriate detailing along the clear span and the embedment regions of the coupling beams are important as well for ductile performance and good energy dissipation capacity. continued on next page

2018

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

ENR SW BEST PROJECT

J A N U A R Y 2 019

9

Redi.

Set. Go.

REDICOR SIMPLIFIES AND ACCELERATES THE CONSTRUCTION OF REINFORCED CONCRETE CORES. Conventional methods of constructing reinforced concrete shear cores can be a challenge. Unpredictable onsite construction timelines frequently delay framing, and unacceptable concrete tolerances or improperly located steel embed plates often bring production schedules to a halt.

Now there’s a better way.

RediCor is a pre-fabricated, ready-to-set modular steel form system that simplifies and accelerates the construction of reinforced concrete stair and elevator cores. Our steel modules are factory builtto-spec with structurally true, load-bearing vertical and horizontal structural connections pre-engineered to ensure that framing fits perfectly – saving time, energy and money.

VISIT US AT REDICOR.COM FOR THE REDICOR STORY. www.redicor.com

TM

Table summary of the five types of coupling beams in RC buildings.

Coupling Beam Type

Code-Specified Maximum Allowable Nominal Shear Stress (Psi)

Applicable SpanTo-Depth Ratio

Practical Maximum Shear Stress (Psi)

Suggested Effective Stiffness in Structural Analysis Model

Construction Feasibility

Energy Dissipation Capacity and Ductility

Shear Force Vertical Distribution

Conventional

10√(f c´)

2.0 ≤ ln /h

4√(f c´)

0.35Ec Ig

Easiest

Poor

No

DiagonallyReinforced

10√(f c´)

ln /h ≤ 1.5~2.0

8.5√(f c´)

0.35Ec Ig

Most Difficult

High

Yes

Steel

N/A

ln /h ≤ 4.0

N/A

0.6Es Isteel

Difficult

High

Yes, max 20%

Encased Steel Composite

N/A

ln /h ≤ 4.0

N/A

0.06 . ln /h . EsItrans (0.35EcIg lower bound)

Difficult

High

Yes, max 20%

Embedded Steel Plate Composite

≈ 18√f c´

1.0 ≤ ln /h ≤ 4.0

≈ 18√f c´

0.35EcIg

Medium

Moderate

Yes

Compared to the diagonally-reinforced concrete coupling beam, the construction of the steel/encased steel composite coupling beam is much more feasible and the disturbance of the construction schedule can be negligible once the contractor becomes familiar with the construction procedure. However, the wide flange steel members tend to interfere with vertical and confinement reinforcement in the coupled shear wall piers, especially those in the boundary element zones of special shear wall systems. To accommodate both the shear wall rebar detailing requirements and steel beam embedment, wider or barbell-shaped wall piers and special detailing must be used. The practice of coping the steel beam flange is not recommended since reducing the flange width will increase the steel beam embedment length and may result

in defects in the protected zone of the encased steel composite coupling beam. Further, embedded steel members complicate any sleeves that may run laterally through the coupling beam, often required for sprinklers.

Embedded Steel Plate Composite Coupling Beam To alleviate the conflict between steel members and shear wall reinforcement, designers can consider the use of embedded steel plate composite coupling beams. As shown in Figure 4 (page 9), headed studs are welded to both vertical faces of the steel plate in a typical embedded steel plate composite coupling beam and pose much less disturbance to shear wall vertical reinforcement,

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

Weld-Crete®—The pale blue bonding agent with over 60 years of superior performance in the field.

Simply brush, roll or spray Weld-Crete® on to concrete or any structurally sound surface. Then come back hours, days or a week later and finish with new concrete, stucco, tile, terrazzo, other cement mixes or portland cement plaster. Plus Weld-Crete’s® low VOC content significantly reduces airborne pollutants that affect health and the environment.

Originators of leading chemical bonding agents… worldwide since 1952

800.633.6668 www.larsenproducts.com

J A N U A R Y 2 019

11

although special detailing is still needed for the horizontal/confinement rebars. The headed studs are necessary to provide appropriate anchorage and transfer forces between the concrete portion and the steel plate. Research indicates that the presence of the steel plates can effectively hinder the development of diagonal cracks and prevent brittle failures of concrete coupling beams, and the embedded steel plate composite coupling beam exhibits much better ductile performance and deformability than comparable conventional RC coupling beams.

Similar to the encased steel composite coupling beam, proper embedment design of the steel plate is critical to ensure good ductile performance of this type of coupling beam. The rigid Mattock-Gaafar embedment model can be used to determine the embedment length of the embedded steel plate by assuming uniform bearing stress from steel plate and headed studs.

In the capacity design of this composite coupling beam, contributions from both the concrete and steel plate need to be considered.

The steel plate is used to supplement the capacities of the reinforced concrete section. Considering the different strain distributions in the RC concrete portion and the steel plate due to their interaction, Su & Lam (2009) proposed a unified design approach for this type of coupling beam. The design rules of thumb are: (a) the ratio of the steel plate depth over the composite coupling beam depth should be limited to be 0.8~0.95; (b) the practical span-to-depth ratio range is 1.0~4.0; (c) minimum shear reinforcement must be provided; (d) minimum embedment length is dependent on coupling beam span/ depth ratio and can vary from 0.35~0.7 times of the beam clear span; (e) The maximum nominal shear stress of the composite coupling — — beam is capped to be 1.5√ f cu Mpa (18 √ f´c psi), and the shear force resisted by the steel plate should be less than 0.45Vu, which limits the use of this coupling beam.

the stiffness difference between the embedded steel plate coupling beam and the associated conventional RC coupling beam is not significant (Su & Lam, 2009), therefore 0.35EcIg is a reasonable reduced stiffness value for the embedded steel plate composite coupling beam ultimate design.

For both steel coupling beams and the encased steel composite coupling beams, the effective bending stiffness needs to be adjusted through iteration since the steel member size is unknown until designed.

Beam Stiffness Reduction

Summary

Under the current strength-based design framework, building analysis and design are predominantly carried out based on linear elastic structural models. Considering the effect of beam cracking, rebar slippage, and steel member fixity point location, reduced coupling beam stiffnesses are suggested in elastic building models depending on the coupling beam types: • Conventional RC coupling beams and diagonally-reinforced concrete coupling beams – ACI 318 specifies 0.35 beam stiffness reduction factor for the ultimate design, which is a well-accepted design industry practice.

• Steel coupling beam – Elastic effective bending stiffness for ultimate design is reduced to be 60% of the original value due to steel beam effective fixity point (AISC 341-16): (EI )eff = 0.6EsIsteel • Encased steel composite coupling beam – Elastic effective bending stiffness for ultimate design was suggested as (Motter et. al, 2017): (EI )eff = 0.06 . l n /h . EsItrans In which l n /h is the beam span-to-depth ratio and Itrans is the transformed moment of inertia of the encased steel composite coupling beam. However, this formula will lead to small stiffness values when the span-to-depth ratio is small. Following industry practice, 0.35EcIg can be used as the lower bound for this kind of coupling beam in building analysis.

• Embedded steel plate coupling beam – To date, no formula has been explicitly proposed for the effective bending stiffness of the embedded steel plate coupling beam. Experiments indicate that

Each of the five types of coupling beams adopted by the industry has its own benefits and limitations, as summarized in the Table.

Still, not one single type of coupling beam is applicable to all cases in building design. The conventional RC coupling beam is often the most feasible and economical coupling beam whenever the beam shear stress is low and the beam is flexure controlled. When coupling beam span-to-depth ratios are small and high shear stresses are expected, the other four types of coupling beams should be explored. The limitations of these types of coupling beams and the associated anchorage requirement should be kept in mind to choose an appropriate coupling beam type for specific projects. As always, the designer should consider the preferences of the construction team whenever possible, as many contractors will have varying opinions related to each methodology.■

12 STRUCTURE magazine

Beam Shear Force Vertical Distribution In high-rise building design, engineers often apply controlling beam design results to multiple floors, avoiding minor changes on a story-tostory basis, i.e. the coupling beam design reinforcements are “grouped” for multiple adjacent floors depending on the variation of beam design shear forces over the building height. Designers may also justify a redistribution of overstressed beams to understressed beams above and below to alleviate rebar congestion. This practice is equivalent to using smaller effective stiffness for coupling beams in analysis and whether it is allowable depends on the ductility and deformability of the coupling beam types.

For conventional RC coupling beams, the deformability and ductility are poor when the beam is under high cyclic shear stress; therefore, shear force vertical redistribution is not recommended. While the other four types of coupling beams exhibit much better ductility and deformability, the lower bound of coupling beam stiffness or shear force vertical distribution can be reasonably applied in building design during the process of designing coupling beams in order to alleviate rebar congestion. For steel coupling beams and encased steel composite coupling beams, AISC 341-16 explicitly permits shear force vertical distribution up to 20%.

The online version of this article contains references.

Please visit www.STRUCTUREmag.org.

Songtao Liao is a Senior Associate at Rosenwasser/Grossman Consulting Engineers, P.C. He is a member of ASCE 7-22 Seismic Sub-committee. (stevenl@rgce.com) Benjamin Pimentel is the President at Rosenwasser/Grossman Consulting Engineers, P.C., He also serves on the Board of Directors of the Concrete Industry Board of New York. (bp@rgce.com)

Pack more into less with Ecospan

®

Get the most out of your space with the Ecospan Composite Floor System.

Thanks to Ecospan’s shallower floor depths, you can have as much usable space in a shorter building as you would typically have in a taller building – giving you more design freedom and saving time, money and manpower in the process. ®

The Ecospan Composite Floor System Vulcraft joist, decking and shearflex fastener ®

Build better ecospan-usa.com 888.375.9787

UL 1, 2, 3 HOURS FIRE RATED STC 57 IAPMO CERTIFIED

Better Partners. Better Products.

Better Outcomes.

structural FAILURES Improving School Buildings in Indonesia An International Collaboration

By Lizzie Blaisdell Collins, P.E., S.E., James Mwangi, Ph.D., P.E., S.E., and Mediatrich Triani N.

P

ost-earthquake observations following recent events in Indonesia point to the significant

vulnerability of school infrastructure in the country. Build Change is a Denver-based international non-profit social enterprise that works with people in emerging nations to design, build, finance, and regulate disaster-resistant houses and schools. Build Change has a program in Padang, Indonesia, and has responded to eight large earthquakes there since the program’s inception after the 2004 Indian Ocean

Typical classroom building – Note the lack of confining elements at door and window jambs, lack of ring beam at the side wall, and very minimal length of wall pier in the longitudinal direction.

earthquake and tsunami. By learning first, through activities like post-earthquake reconnaissance and sub-sector studies, Build Change aims to provide technical assistance to post-earthquake reconstruction – from support in design and building standards through training in construction and material quality. Evidence of damaged and vulnerable school construction was apparent after every visit to the earthquake-affected areas in Indonesia following the Yogyakarta (2006), the Bengkulu (2007), the Padang (2009), the Central Aceh (2013), the Pidie Jaya (2016), the Lombok (2018) and the Palu (2018) earthquakes. More than 1,000 schools were reported to be damaged or destroyed in each of the 2006/2009 and both 2018 events alone.

A Reoccurring Problem Many school buildings in Indonesia are constructed as one-story, partially-confined masonry structures with light-framed roofs. In Padang, the capital city of West Sumatra, this building type makes up approximately 60% of the public school buildings. Confined masonry is a commonly used structural system outside of the U.S. in which unreinforced or lightly reinforced masonry load-bearing walls are constructed and surrounded on the sides, top, and bottom by reinforced concrete elements, or “ties.” These ties help to “confine” the masonry wall. Building codes in seismic regions, such as Chile and Mexico, cover the requirements for this building type to resist earthquakes and, when built properly, low-rise confined masonry structures have resisted earthquakes well. Interestingly, Indonesia’s building code does not cover confined masonry, even though the Ministry of Education’s school construction guidelines promote its use.

Unfortunately, for the observed school buildings of this type in Indonesia, some of the reinforced concrete elements are missing and they are better described as partially confined than fully confined. Confining elements are typically placed at wall intersections but are rarely installed at door and window jambs as would be required for good performance. Wall piers between openings are 14 STRUCTURE magazine

effectively unconfined in these cases and have essentially no more ductility than an unreinforced masonry wall. Often, lintel beams are not installed over window and door openings, leaving the masonry panel above to rest on the wood framing of the opening. In some cases, the required ring beam, or confining beam at the top of the wall, is also missing, leaving the masonry wall panel unbraced at the top and very susceptible to toppling under out-of-plane loading.

In addition to missing key confining elements, problems with configuration and construction quality are frequently observed in these school buildings. The longitudinal walls along the front and back consist mostly Typical inadequate reinforcing in damaged of openings for doors and school buildings.

windows, leaving very few short wall piers to resist earthquake loads. The buildings also typically lack an effective diaphragm, as the light-framed roof is not detailed to act as a diaphragm and not well-connected to the building walls. This is especially problematic in cases where the building has a masonry gable end wall, which remains poorly braced over a much taller height than the rest of the building.

Most of the classroom buildings of this type are built by local builders who may have more experience in construction of smaller non-engineered buildings, like houses, and construction activities are not typically observed by the designer or inspected by local authorities in detail. It is common for smooth Collapse of gable end wall in a classroom building. Courtesy of Educational Department Aceh Tengah. reinforcing bars to be used in the concrete elements, for the brick strength to be low, for the concrete quality to be in the world. Seventy-five percent of Indonesia’s schools are in disaspoor, and for construction details like adequate concrete cover, ter risk areas; the nearly 800,000-square mile country is exposed reinforcing hooks and splices, or mortar quality and placement to large earthquakes, tsunamis, high winds, volcanoes, landslides, to be overlooked. and floods. From these numbers, it is estimated that there could Considering the incomplete confinement and the problems with be between 250,000 to 400,000 buildings of this type within the configuration and construction quality, the performance of these country at risk from earthquakes. buildings has been poor in recent earthquakes, characterized by significant damage, partial collapse, and total collapse in some cases.

Finding a Solution The problem is not localized; many more vulnerable buildings of this type exist in earthquake-prone areas across Indonesia. Indonesia New school buildings are continuously added to the educational is the fourth most populated country in the world, following the infrastructure in Indonesia in an attempt to keep up with demand.

United States, and with over 50 million students attending more However, it is not economically feasible to demolish and replace than 300,000 schools, it also has the fourth largest education system all existing vulnerable buildings as a universal solution. Many of

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

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

Alexander Zuendt, P.E. Zuendt Engineering Record holder since 2011

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

Build your NCEES Record today. ncees.org/records

J A N U A R Y 2 019

15

the existing buildings will remain indefinitely, so cost-effective options for improving them are needed. At the same time, improvements in new building construction methods are urgently needed. This is something the authors are also working with the Ministry of Education to achieve.

To explore solutions for existing classrooms, Build Change worked with the local Education Department in Padang to select a representative school, of the one-story confined masonry type, as an example for developing cost-effective retrofit options using locally-available materials and labor. The authors and their Indonesian colleagues gathered information relevant to the retrofit design to consider various techniques. Information was derived from the Indonesian building code, from existing national and international guidelines, from research performed by others and

by Build Change, and from the authors’ own experiences. Due to the common use of low-strength, single-wythe brick in Indonesia, several researchers in Indonesia and Japan had already developed and tested retrofit techniques to strengthen the slender masonry for in-plane and out-of-plane loading successfully. Solutions included using a cement-plaster overlay or banded steel wire mesh combined with a cement-plaster overlay.

The authors selected a shear wall system for the retrofit, although several other schemes were considered including a moment frame system and a cantilevered column system. The resulting retrofit scheme targeted life-safety performance for the code-prescribed design earthquake and was composed of several key components: • Infilling select wall openings in the longitudinal walls to create sufficient length of the wall and installing confining elements at their boundaries.

• Overlaying walls with steel wire mesh and cement-plaster and, in some cases, rebuilding the wall pier to be thicker masonry to improve in-plane and out-of-plane strength.

• Adding reinforced concrete strongbacks to the transverse walls for out-of-plane bracing.

• Installing a new continuous ring beam at the top of the wall.

• Installing a horizontal bracing system just above ceiling level connected to the ring beam to act as a diaphragm.

• Eliminating any unreinforced masonry above window and door openings by extending the opening upwards to the ring beam and filling the space with light-weight materials instead.

• Eliminating the masonry gables and replacing them with light-weight materials.

In addition to these structural improvements, new braced ceilings were proposed for the classroom interiors, and additional natural light and Installation of the mesh plaster overlay ventilation were proposed for during pilot construction. the transverse end walls.

16 STRUCTURE magazine

Plan view of the retrofit scheme.

Piloting the Retrofit Two single-classroom buildings in the example school were selected for piloting the retrofit construction project. One of these had been lightly damaged by the 2009 earthquake and was no longer in use.

Construction quality supervision was provided throughout the duration of the work to ensure that the contractor followed the construction documents. Additionally, experienced builder trainers frequently visited the site to provide pointers and support to the workers to achieve a good quality construction. Bricks were purchased from suppliers that offered tested and certified-strength bricks.

The construction started in January 2016 on one of the two buildings and the second building was completed in May 2016. Most of the retrofit techniques were familiar to the local builders, except installing the mesh-plaster overlay; however, the required level of construction quality was higher than the builders were accustomed to and this led to some delays. For new techniques, like the wire mesh overlay, extra care was taken in the detailing and on-site supervision of the mesh installation, which the builders were able to master after an initial period of familiarization.

In addition to the construction work, engagement of the school community was a component of the pilot project. Early retrofit planning was accompanied by significant efforts to involve and increase the disaster-risk awareness of the school community. Training materials on the retrofit were developed, and a retrofit awareness workshop was held for representatives of the school council, the Education Department, and the Regional Disaster Management Agency. During construction, Build Change Indonesian staff and members from the school council jointly performed the construction supervision, with discussions on good construction practice and review of construction quality checklist items. The pilot retrofit was also used as an opportunity to raise the topic of disaster-risk and prevention with students and teachers. Presentations on how earthquakes affect buildings were given to the students and the materials were shared with teachers for future use.

The construction of the retrofit improved these two buildings and also permitted the validation of construction cost estimates and constructability of retrofitting details. The total cost of the project, including the construction costs, the design, the construction quality

One of the classroom buildings before and after retrofitting.

supervision and support, and the school community outreach was approximately $32,000 total for both buildings or approximately $27 per square foot.

Lizzie Blaisdell Collins is the Director of Engineering at Build Change, a non-profit social enterprise that works with people in emerging nations to design, build, finance, and regulate disaster-resistant houses and schools. (lizzie@buildchange.org)

Plans for Scale

James Mwangi is the 2017-2018 Simpson Strong-Tie Fellow for Excellence in Engineering with Build Change during his sabbatical year from California Polytechnic University in San Luis Obispo where he is a professor of Architectural Engineering. Through the fellowship, he spent two months in Padang focused on improving school infrastructure in Indonesia. (jmwangi@calpoly.edu) Mediatrich Triani N. is an Architect and the Program Manager for Build Change in Indonesia. (triani@buildchange.org)

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

After the completion of the pilot project, the authors and their Indonesian colleagues have completed the design and construction of a retrofit for the other, larger classroom building at the same school. The larger building has four classrooms and an administrative office. The overall retrofit scheme is the same, with small adaptations. By repeating the retrofit design process and incorporating lessons from the pilot retrofit, the team refined the retrofit design and detailing. The next step is to develop simple guidelines that could be used at a larger scale for the application and adaptation of the retrofit scheme to many more buildings of the same type. This would allow a more prescriptive approach to retrofitting many of the vulnerable classroom buildings in Indonesia, as long as the characteristics of the buildings align with those of the applicable type. In addition to coordinating with the National Ministry of Education and local Education Department in Padang, Build Change is currently seeking partners to support this scale-up of school retrofitting.â–Ş Build Change has 100 technical staff in six programs globally. For more information on Build Change and a downloadable copy of their post-earthquake reconnaissance reports, please visit www.buildchange.org.

The authors would like to thank those that made the work described possible: The Education Department of Padang for their partnership, and Simpson Strong-Tie, the Thornton Tomasetti Foundation, and the New Zealand Embassy in Indonesia for their support.

MCI_5x3.5_02-18.indd 1

2/19/18 8:44 AM

J A N U A R Y 2 019

17

NORTHRIDGE

25 YEARS LATER

Caltrans Highway Structures

By Mark Yashinsky

E

very damaging California earthquake has resulted in changes to the California Department of Transportation’s (Caltrans’)

seismic practice. The most significant changes occurred after the 1971 San Fernando Earthquake. Bridges at that time were designed for a small seismic force, which resulted in extensive damage to bridges and interchanges during the earthquake.

Figure 1. Gavin Canyon Bridges.

Immediately afterward, Caltrans wrote construction change orders requiring more transverse reinforcement and continuous main reinforcement in bridge columns and eliminating a vulnerable lap splice connecting the footing to the column. Also, the minimum seat length at expansion joints, abutment seats, and hinges went from 12 inches to 18 inches (and later to 24 inches). Other changes included the development of a site-specific ground shaking hazard for designing bridges and a capacity-based design method that relied on structural column fuses to limit seismic forces. Caltrans also started a seismic retrofit program to address the many existing bridges that had been under-designed for earthquakes. The San Fernando Earthquake was also the start of the practice of Caltrans sending out a reconnaissance team of licensed engineers to study the damage and write a report with lessons learned, a practice that has continued for every subsequent large earthquake.

The 1987 Whittier Narrows Earthquake was another turning point in Caltrans seismic design of bridges. The previous retrofit program relied on cable restrainers to limit displacement and prevent column damage, but shear damage to the short columns on the Route 605/5 Separation (53 1660) generated enough concern to begin a new retrofit program to wrap bridge columns in steel (or fiber-reinforced polymer) casings on older bridges.

Unfortunately, the 1989 Loma Prieta Earthquake occurred before many bridges were retrofitted. The earthquake damaged the double-deck Cypress Viaduct (33 0178), built in the 1950s, that had been designed with vulnerable pinned connections to make it structurally determinant and easier to analyze. The main reinforcement in these connections was not sufficiently developed, and the shear reinforcement was inadequate. This resulted in the collapse of a mile-long segment of the viaduct during the earthquake.

Several other double-deck viaducts around San Francisco sustained severe damage to the superstructure-to-column connections that resulted in their closure and removal after the earthquake. Also, a 50-foot span over Pier 9 on the East Crossing of the San Francisco Oakland Bay Bridge (33 0025), built in the 1930s, collapsed due to inadequate 4-inch-wide seats, reiterating the lesson that seats have to be long enough to support the resulting displaced bridge members during earthquakes. The Struve Slough Bridges (36 0088L/R) in Watsonville were T-girder bridges on piles founded on very soft soil. During the earthquake, the soil shook violently, dragging the piles from their connection with the superstructure which resulted in the pile extensions punching through the bridge deck.

Concerns about the bridge damage prompted the California governor to create a Board of Inquiry that found that Caltrans was doing a good job addressing seismic issues but needed to accelerate the seismic retrofit program. The Board of Inquiry recommended that a standing board of experts should be created to advise Caltrans on its earthquake engineering practices. Thus, the Caltrans Seismic Advisory Board was formed and continues to advise Caltrans on seismic issues.

The need to quickly complete the retrofit program was demonstrated again when the 1994 Northridge Earthquake occurred before the program was completed. Seven bridges, five of which were designed before 1971, were severely damaged during the earthquake but all 60 bridges in the Los Angeles area that had been retrofitted after the Loma Prieta Earthquake performed very well.

18 STRUCTURE magazine

I-5: Gavin Canyon Bridge These two parallel 741-foot-long bridges (53 1797L/R) built in 1955, were designed with table-like center frames that supported the cantilevered spans of the four end frames on highly skewed, 8-inch-long hinge seats. A retrofit in 1974 added restrainers at the hinges. During the earthquake, the outer frames rotated, failing the restrainers, followed by unseating and collapse of the cantilevered spans. In Figure 1, the demolition crew has already started removing the bridge before the reconnaissance team could inspect the damage (the team started in Sacramento and were escorted by the California Highway Patrol down I-5 through various detours to a hotel in Pasadena). Among the lessons learned was that the fundamental mode during an earthquake for a bridge may be rotational, not translational; that long seats, not restrainers were needed to prevent unseating; that high skews make it easier for bridges to become unseated by moving normal to the skew; and, that the anchorage for restrainers is often the location of failure.

However, most of these lessons had been learned during previous earthquakes. After this earthquake, these bridges were replaced with single frame structures.

Route 14/5 Separation and Overhead This 1582-foot-long bridge (53 1960F) on single column piers was under construction (and was still on falsework) during the 1971 San Fernando Earthquake, but it collapsed during the Northridge

Earthquake (Figure 2). There was considerable speculation as to the cause of the failure, but it was eventually decided (and corroborated by analysis) that it was due to the shear damage to short, stiff Pier 2.

Most long bridges have short bents near the ends and tall bents in the middle. As this bridge moved back and forth during the earthquake, the stiffer elements could not displace as much as their taller neighbors and broke. After Pier 2 broke, the superstructure sagged, broke around Pier 3, and slid off Abutment 1 (Figure 2) and Pier 4.

After the earthquake, Caltrans instituted standards to ensure that the columns within a bent, bents within a frame, and frames in a bridge have similar stiffness or period.

Route 118: Mission Gothic Undercrossing These parallel structures (53 2205L/R) included a 506-foot-long 3-span left bridge and a 566-foot-long 4-span right bridge on twocolumn bents and abutments with 4-foot-long seats. The bridges were 98 feet wide with prestressed bent caps (except for Bent 4 on the right bridge). The bridges were designed in 1973 and built in 1976.

They crossed over an intersection and consequently had opposing skews at the two ends. The columns were fixed at the top and pinned at the base. A common detail used on these bridges was architectural flares on the columns, which were assumed to spall off during earthquakes. However, during the Northridge earthquake, the flares did not spall off and reduced the effective column height, resulting in a combination of shear and flexural damage. As can be seen in Figure 3, the bridges displaced transversely during the earthquake. The right bridge (the left side of Figure 3) collapsed while the left bridge settled approximately two feet. Typically, a bridge is locked in by the abutments, which act to limit the movement during earthquakes. It was concluded that having abutments at opposite skews allowed the bridges to move away from the abutments, which contributed to the collapse. After the earthquake, Caltrans funded research at the University of California San Diego, which confirmed the vulnerability of flared columns and a new detail was developed to isolate the flare from the superstructure on new bridges (existing bridges were retrofit with casings around the column and the flare).

Figure 2. Route 14/5 separation and overhead.

and a 12-inch pitch elsewhere. The bridges crossed over a channel, and the concrete for the channel walls was placed against the columns at Bent 3. The structure appeared to have rotated clockwise during the earthquake. Similar to Mission Gothic, the channel wall had the effect of shortening the columns and consequently attracted more seismic force. Also, the top of the channel wall was where the transverse column reinforcement was at a 12-inch pitch. All the columns at Bent 3 failed in shear (Figure 4). The top of some of the columns in Bent 2 formed plastic hinges, probably after the columns in Bent 3 were damaged.

I10: La Cienega-Venice Undercrossing

These parallel 3-span structures (53 2206L/R) were 256 feet long with a variable width (minimum of 200 feet) and a variable skew. Like their neighbor (Mission Gothic Undercrossing), they were designed in 1973 and built in 1976. The bridges were supported on 9 and 10 column bents and tall, end-diaphragm abutments. The columns had a modern design with spirals at a 3-inch pitch at the top and bottom

These parallel, three-frame (7-span) 871-foot-long bridges (53 1609L/R) on 2 and 3 column bents and bin-type abutments were designed in 1962 and built in 1964. The frames were connected with 6-inch-long hinge seats. There was also a connector and an on-ramp on the right bridge. Columns had lapped hoop reinforcement at a 12-inch spacing and were pinned or fixed to pile caps without a top mat or any shear reinforcement. Most of the columns on the right bridge formed plastic hinges at the bottom, although a few columns had plastic hinges at the top (Figure 5, page 20). The column damage was thought to have caused Span 6 of the right bridge to become unseated. However, the superstructures were caught by a storage facility that had been built under the bridges. The foundations were excavated after the earthquake, but no damage was found. It was thought that the thick layer of asphalt and concrete pushed the column damage up to where the columns were more vulnerable (although there was a lap splice between the column reinforcement and the footing).

An observation after the earthquake was that the columns with

Figure 3. Route 118 Mission Gothic Undercrossing.

Figure 4. Route 118 Bull Creek Canyon Channel Bridge.

Route 118: Bull Creek Canyon Channel Bridge

J A N U A R Y 2 019

19

Table 1. Incentive/Disincentive Contracts used after the Northridge Earthquake.

Project

Incentive/Disincentive

Santa Monica Freeway (I-10)

$200,000/day

Gavin Canyon (I-5)

$150,000/day

5/14 Interchange

$100,000/day

State Route 118

$50,000/day

42- #11 bar main reinforcing experienced more damage than the columns with less main reinforcement. This bridge was far to the south of the epicenter (which ruptured to the north), but it was felt that long period shaking was amplified by the soft soil (La Cienega is Spanish for “The Swamp”).

Lessons Learned Collectively, the bridge damage described in this article was just a small part of all the damage that occurred during the Northridge Earthquake. A lot of this damage was due to geometric and structural system issues (high bridge skews, unbalanced structures, and non-prismatic members) that resulted in unexpectedly large demands during the earthquake. This gave rise to the development of rules and procedures to ensure that bridge members are well-balanced and that shear-critical members are not used.

Large skews are still used on bridges but are mitigated either by eliminating in-span hinges or by very large seats at hinges, abutments, and expansion joints. However, abutments with opposing skews should no longer be used since there is nothing to prevent the bridge from moving away from the abutments, as was seen at Mission Gothic UC. Procedures, initiated after the Loma Prieta Earthquake, were improved after the Northridge Earthquake. For instance, after Loma Prieta, Caltrans initiated a practice of accelerating earthquake repairs with A+B construction contracts. Caltrans determined the societal cost per day that the bridge/highway segment was not available and contractors bid on the cost + the number of days required to rebuild the bridge. The first A+B contract was to rebuild the Struve Slough Bridges after the Loma Prieta Earthquake. The contractor who was awarded the project had aggressively bid to complete the two parallel 830-foot long slab bridges supported on 200 driven piles in just 90 days. He managed to complete the project in 55 days (by working around the clock) and made a million dollars in incentives.

Figure 5. 1-10 La Cienega-Venice Undercrossing.

20 STRUCTURE magazine

Due to the success of A+B contracting after the Loma Prieta Earthquake, this type of procurement was used to rebuild all the bridges that collapsed during the Northridge Earthquake. Caltrans economists determined the incentive/disincentive rates based on the projected daily cost for each closed highway (Table 1). The Santa Monica Freeway (I-10) was reopened in 3 months. All of the collapsed bridges were reopened to traffic by November 4, 1994 (10 months after the earthquake). While the highways were being repaired, many frontage roads were cleared and converted to High Occupancy Vehicle lanes to alleviate traffic congestion.

The most significant change to seismic design practice after Loma Prieta was that the ‘R’ factor that had been used to estimate the reduced seismic force in ductile columns was abandoned and a moment-curvature analysis began to be used to determine the displacement capacity of substructure members. The columns’ effective stiffness was calculated to obtain the period, and the appropriate design spectrum was used to get the displacement demand. Caltrans was able to update its seismic design procedure after writing XSECTION to obtain the displacement capacity of columns, PSSECTION to obtain the displacement capacity of prestressed piles, and WFRAME to obtain the displacement capacity of bridge frames. Caltrans is continuing to develop the next generation of earthquake engineering tools that will utilize Nonlinear Time History Analysis (NLTHA) procedures for the seismic design of ordinary bridges.

The methods for generating design spectra have also undergone several changes since the Loma Prieta and Northridge earthquakes.

Before Loma Prieta, the design spectrum was obtained based on the deterministically-derived Maximum Credible Earthquake of the controlling fault and the depth of alluvium at the bridge site.

After the Loma Prieta Earthquake, the shear wave velocity of the soil began to be used for obtaining the design spectrum. After the Northridge Earthquake, it was recognized that near-fault directivity effects increased the demands on long period structures. Response spectra were increased 20% in the long period range for bridges within 10 miles (15 km) from the fault. Also, the envelope of deterministic and probabilistic spectra began to be used to obtain the design spectra for bridges (Figure 6).

The most significant change to seismic design practice after the Northridge Earthquake was new rules requiring adjacent columns in a bent and adjacent bents in a frame to have similar stiffness (ki/kj > 0.75). Moreover, any two bents in a frame and any two columns in a bent were required to have comparable stiffness (ki/kj > 0.50). The periods of adjacent frames were also required to be similar (Ti/Tj > 0.7)

Figure 6. Probabilistic and deterministic spectra with near fault effects and envelope used for design.

Figure 7. Bridge with isolation casings to achieve a balanced design.

to prevent large out-of-phase movement between frames. All of these rules were to prevent the severe damage that was observed after the Northridge Earthquake. A popular technique that began to be used over uneven terrain was isolation casings to give all the bents about the same stiffness (Figure 7 ).

Other changes after the Northridge Earthquake included: • Establishment of Caltrans Seismic Design Criteria (SDC) Version 1.0 in 1999 (now completing Version 2.0).

• Ground shaking hazards were amplified due to near-fault effects, basin effects, etc.

• Besides the ground shaking hazard, liquefaction hazards, lateral spreading hazards, fault offset hazards, tsunami hazards, and more began to be considered in the seismic design of bridges • Memo to Designers (MTD) 20-9 provided rules for reinforcement splices in ductile and capacity-protected members.

• New criteria allowed rocking as an earthquake resisting system for existing bridges.

• New criteria were developed for the retrofit of arch, truss, and other non-standard bridges.

• Caltrans began a robust seismic research program and has invested over $100 million since 1989 to better understand

earthquake hazards and to develop resilient earthquake resistant bridge systems and details.

• Research showed a smaller role played by vertical acceleration in bridge damage.

• Caltrans required k-rail at the ends of damaged bridges after police drove off several bridges.

Caltrans has not experienced a large, damaging earthquake since Northridge. However, Caltrans engineers and managers are confident that all of the efforts spent developing new seismic design criteria and retrofitting existing bridges will yield less bridge damage during the next design-level earthquake.■ A critical element was missing before Caltrans could move from a force-based system to a displacement-based approach for the seismic analysis of new and existing bridges. Three structural analysis programs (XSEC, PSS and WFR) were written by Caltrans’ bridge engineers to determine the displacement capacity of columns, piles and shafts, and bridge frames. For more information, visit https://goo.gl/YLjuBh. Mark Yashinsky has spent the last 34 years as a bridge engineer at Caltrans and has worked in the Caltrans Office of Earthquake Engineering since the Loma Prieta Earthquake. Among his many duties is leading the postearthquake inspection team, developing new seismic criteria, and managing the seismic retrofit program. He has written a number of books, papers, and articles on bridges and earthquakes. (mark.yashinsky@dot.ca.gov)

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

OPTIMIZE YOUR MULTI-STORY DESIGN AND CONSTRUCTION

Advanced long-span composite floor systems Create open spans up to 36 feet with solutions that can be 40% lighter than cast in place. Reduce installation costs and improve field safety. Achieve your vision with architecturally exposed deck-ceiling and acoustical options. Fire, sound and vibration code compliant.

• Efficient Construction • Aesthetics and Performance • Two Distinct Profiles

YOUR N AT IO N WIDE RES O U RC E F O R C U STO M - E N GI N E E R E D ST RUC T UR AL ST E E L B UI L D I N G SYST E M S

www.newmill.com

18-NMBS-2_structure-MSR.indd 1

12/7/18 4:56 PM

J A N U A R Y 2 019

21

SR 99 Tunnel in Seattle

By Yang Jiang, Ph.D., P.E., S.E., and Andrew Herten, P.E.

Courtesy of Pete Saloutos

T

he recently completed SR 99 Tunnel was constructed as part of the Washington State Department of Transportation’s (WSDOT) Alaskan Way Viaduct Replacement Program.

The existing Alaskan Way Viaduct (AWV) is an aging double-deck highway structure in Seattle, Washington, that was built in the 1950s.

The Viaduct has been deteriorating due to age as well as damage resulting from the 2001 Nisqually earthquake. The SR 99 Tunnel consists of three segments: the South Approach, the Bored Tunnel, and the North Approach. The South and North Approaches include cut-and-cover tunnels and U-sections.

The bored tunnel begins south of downtown Seattle in close proximity to the seawall of Elliott Bay, tends north along the existing Alaskan Way Viaduct, then crosses under the Viaduct, traverses under downtown Seattle, and emerges north of downtown Seattle just east of the Space Needle (Figure 1). The bored tunnel is 9,300 feet long with an outer diameter of 56 feet and was excavated by an Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM), named Bertha, with a 57½-foot-diameter cutterhead. The bored tunnel was the largest in diameter in the world at the time of design (Figure 2).

At its lowest point, the tunnel crown is at elevation -95 feet, and it is 215 feet deep at its greatest depth below grade. Development along the alignment consists of on-grade and elevated roadways, buildings ranging from single-story to high-rise structures, railroad and sewer tunnels, and public and private utilities.

In December 2010, WSDOT awarded the SR 99 Bored Tunnel Design-Build Project to Seattle Tunnel Partners (STP) based on best technical solution and cost. STP is a joint venture between Dragados USA and Tutor Perini Corp. The design team includes HNTB Corporation, Intecsa of Spain, Hart Crowser, Inc., and EMI Inc. HNTB was responsible for the design of the lining and approach structures. After close to two years of design and preparations, TBM Bertha was launched and began drilling in July 2013. Only five months later, Bertha halted drilling due to overheating of some of her components.

After two years of repair and preparation, Bertha resumed mining in February 2016 and finally broke through into the receiving pit in April 2017. Although the TBM work was put on hold Figure 1. SR 99 Bored Tunnel and Approaches.

22 STRUCTURE magazine

during Bertha’s repair, construction of the approaches and some interior structures continued during that time.

Geology Seattle is located adjacent to Puget Sound in the Puget Lowland between the Olympic Mountains to the west and the Cascade Range to the east. The Puget Lowland has been subject to several glacial advances, resulting in a complex stratigraphy of glacial and non-glacial soil deposits. Along its alignment, the tunnel traverses through variable glacially over-consolidated soil deposits with high groundwater pressures of up to 5.2 bars (Figure 3). These deposits are often highly variable within relatively short distances due to the inconsistency in erosion and deposition during the multiple glacial events and interglacial periods.

Design Design geologic sections were selected to assess the geologic variability along the tunnel alignment, as well as topographic/geometric variability and building structure locations. As shown in Figure 3, 15 geologic sections (shown in blue) were selected for static design and 8 sections (shown in red) for seismic design. For consideration of potential future development, the contract required an evaluation of a 7,000 psf building surcharge applied at the height and width limits of WSDOT’s right of way above the tunnel, which are 54 feet above the crown and 84 feet wide. Existing building and structure foundations vary from spread footings and mat foundations to deep shafts and piles, ranging from 8 to 63 feet long and as close as 16 feet above the tunnel crown. Buildings along the tunnel alignment range from 13 to 546 feet tall with basement excavations ranging from approximately 0 to 87 feet deep.

Dual levels of design earthquakes were considered for the design of the tunnel liner. The Expected Earthquake has a 108-year return period and is associated with Operational Performance Objectives, while the Rare Earthquake has a 2,500-year return

Figure 2. SR 99 Bored Tunnel configuration.

Figure 3. Geotechnical profile and design section locations.

period and is associated with Life Safety Performance Objectives.

Construction Under the Expected Earthquake, minimal damage to the liner segments, joints, and water tightness is anticipated because the lining is There were significant challenges during the construction of the designed to respond in an elastic manner. Concrete compression strain south and north settlement mitigation measures as well as with the is limited to 0.003, and tensile strain in reinforcing steel is limited interior structures.

At the tunnel’s south end, the beginning of the tunnel drive, the to 0.002. Under the Rare Earthquake, the objective is to prevent the collapse of the tunnel liner. Inelastic deformations are allowed under tunnel has very shallow ground cover above and is in close proximity the Rare Earthquake but are limited to the acceptable levels; concrete to the Alaskan Way Viaduct’s pile foundations. The shallow depth strain is allowed to exceed 0.003 but limited to 0.005 provided that of tunnel overburden, combined with a water table near the ground the strain is predominantly due to flexure. The tensile strains in a surface, required jet grouting the soil and utilizing an encapsulating mild reinforcing steel are limited to 0.06 for reinforcing bars up to box structure of a 5-foot-thick buoyancy slab with vertical tension piles (5 feet in diameter). This held down the structure’s buoyancy US #10 size and 0.045 for US #11 size and larger.

The tunnel liner was analyzed and designed for two conditions. uplift and mitigated the risk of surface settlement during the tunnel The first condition included only the tunnel ring, representing the boring machine’s mining. The tunnel profile is at 4% initially and, scenario at the end of the tunneling operations. The second condition once the tunnel descends beneath an overburden depth able to resist included the completed tunnel during in-service condition, includ- the tunnel’s uplift force, there is no need for a buoyancy slab. The ing the tunnel lining, the interior structures, the systems, and any so-called box structure stops, however, and a wall of isolated concrete associated loads. The strength design of the liner is in accordance piles, or drilled shafts, extend between the tunnel and the adjacent with AASHTO Load and Resistance Factor Design (LRFD) method, Alaskan Way Viaduct footings. which takes the statistical variability of member strength and the Initially, the tunnel’s alignment and the AWV are parallel, but where magnitude of the applied loads into account. The load factors in the AWV veers west, the tunnel crosses beneath. At this intersection, AASHTO have been modified according to the Federal Highway the wall of concrete piles stops and adjacent footings are mitigated Administration Manual. from potential settlement instead with rows of vertical and battered Analysis of the bored tunnel included loading from seismic defor- micro-piles (Figure 4).

At the tunnel’s north end, the completion of the tunnel drive, mations and ground accelerations considering three primary modes of deformation during seismic ground movement: (1) ovaling, the tunnel has sufficient overburden and a deeper water table so (2) axial, and (3) curvature deformations. Deformations of the as not to require being held down by a box structure. The primary concern is mitigating against surface soil surrounding the liner due to the seismic wave propagating from bedrock through soil settlement. Settlement risk to existing buildmedia, without the liner, were computed with ings was mitigated with rows of protective micro-piles. a continuum model, and the ground deformations were imposed on the liner through The tunnel’s interior structure is comprised supporting elements (non-linear springs) of two continuous corbels supporting a series using beam-on-spring models by performof 650-foot-long moment frame systems of walls and slabs, detailed to expand and coning non-linear dynamic time history analysis on both transverse and longitudinal models. tract longitudinally. The lower roadway walls The results from the time history analysis are primarily pin connected to the corbels show that the maximum ovaling is about below and fixed to the upper roadway slab 1.5 inches or 0.2% of the ring diameter for and traffic barriers above. The upper walls the Rare Earthquakes. It is observed that are pin connected on each end, detailed to maximum ovaling is generally in a diagonal accommodate transverse seismic deformation direction, which is consistent with the open of the frame or tunnel ring. The electrical round cavity deformation caused by a free-field room and egress corridor slabs are cantileground shear distortion. The liner segment vered from the interior walls; the cantilevered gaskets were also evaluated for water tightness slabs and upper roadway walls are clear of under this maximum ovaling, as well as the the tunnel ring sufficient to accommodate maximum longitudinal curvature through the the anticipated ring ovaling due to seismic Figure 4. AWV settlement mitigation. ground movement (Figure 5, page 24 ). use of a 3-D finite element model. continued on next page J A N U A R Y 2 019

23

Figure 5. Section – Tunnel Interior Structure (TIS).

The tunnel ring and its interior structure were constructed in a factory-line style system. The TBM erected the ten precast ring segments as part of its excavation/advancement. Segment arrangement was dictated by the highway’s design alignment, as the ring’s profile was designed so the rotation of it would incrementally change the TBM’s heading. Workers on the tail of the TBM drilled corbel dowels into the ring segments at locators blocked out prior to casting. Behind the tail, workers installed a rail just inside each corbel face to support the traveling form system gantry. Carpenters built end-forms for each corbel in 50-foot intervals, the ring surface was prepped, corbel reinforcement cages were trucked in and placed, embedded conduits installed, and traveling forms were lowered into place and concrete pumped in by ready-mix trucks. All the while, the invert of the tunnel was kept free of obstructions for passage of the ring segment hauler and shift changes of workers (Figure 6).

Construction of the walls was similar, with skip forming, preassembled reinforcing cages, and cast-in-place with a rail supported traveling formwork (Figure 7).

Project success would not have been possible without an ability to design a permanent structure that could be built while not obstructing temporary work activity such as the TBM excavation removal, the ventilation duct below the crown, or material delivery along the invert (Figure 8).

Figure 7. Skip forming for upper slab of interior structure.

24 STRUCTURE magazine

Figure 6. Tunnel interior structure corbel construction.

Conclusion The SR 99 Bored Tunnel will open to traffic in February 2019, signifying the official completion of the project that began in 2011.

The STP team had encountered and overcome enormous challenges in managing, designing, and constructing the project that included one of the largest and recording-setting bored tunnels in the world, and resulted in a significant and long-lasting infrastructure in Seattle that will be enjoyed by generations to come. The SR 99 Tunnel also opens areas that were occupied by AWV for improvement and affords Seattle the opportunity to make it a world-class waterfront city. Demolition and decommissioning of the Alaska Way Viaduct and construction of the new Alaskan Way street along the waterfront are scheduled to begin in early 2019.■ Yang Jiang is a Principal Engineer with HNTB Corporation in Bellevue, WA. Yang is the Engineer of Record and lead engineer for the SR 99 Bored Tunnel. (yjiang@hntb.com) Andrew Herten is a Senior Project Engineer with HNTB Corporation in Bellevue, WA. Andrew managed the cut-and-cover tunnel structural design as well as project-wide post-design services for the SR 99 Tunnel Project. (aherten@hntb.com)

Figure 8. TBM delivery during TIS construction.

One frame.

Countless possibilities.

Structural Steel Connections.

Streamlined.

AISC 358-16

Introducing our Strong Frame special moment frame Yield-Link connection — a time-saving and cost-effective solution for structural steel construction. Our patented and code-listed Yield-Link is a bolted steel moment connection, eliminating costly field welding and inspection, and expediting fabrication and assembly. Because the connection is easily replaceable after a seismic event, it can reduce the time and expense in getting a building back in use. ®

Patented Yield-Link Structural Fuse ®

®

Visit go.strongtie.com/yieldlink to learn more about our innovative Yield-Link solution. © 2019 Simpson

Strong-Tie Company Inc. SMFYLC18

in the NEWS Changes on STRUCTURE’s Editorial Board

A

s is typical in many a new year, 2019 brings several changes to the STRUCTURE Editorial Board. Barry Arnold, P.E., S.E., SECB, is stepping down as Chair of the Editorial Board. Barry has served as Chair since 2016 and, unsurprisingly, has discovered that his duties as Vice President of ARW Engineers (Ogden, UT) increasingly require his attention. He is an untiring advocate of the structural engineering profession, having served as President of the National Council of Structural Engineers Associations (NCSEA), the Structural Engineers Association of Utah, and continues to serve on NCSEA’s Structural Licensure Committee.

Barry said of his departure, “Serving as the Editorial Chair of STRUCTURE magazine has been an experience without equal. Beyond the daily barrage of emails, the numerous calls to the publisher, and what seemed like an endless queue of small and large issues, I had the privilege of working closely with some of the structural engineering profession’s most exceptional, committed, and unique individuals. The editorial board is not for the Barry Arnold, P.E., S.E., SECB faint of heart – it requires devotion to the magazine’s mission, strict adherence to deadlines, and a deep passion and love for the structural engineering profession. It has been my privilege to serve with board members who possessed these qualities, and I thank them for their tireless commitment and role in making STRUCTURE magazine a success each month.

I have sincere gratitude for NCSEA’s past and current Executive Directors, Jeanne Vogelzang and Al Spada, respectively, who trusted me to Chair the editorial board. STRUCTURE magazine is an excellent publication because of the efforts of the Management, Board, Publisher, and volunteer authors; it is their efforts that make the magazine admired and respected by the readers.

I am sure that the New Chair, John Dal Pino, will continue in the long tradition of offering the magazine’s readers interesting and useful topics to strengthen and educate the engineering profession. I wish John and the entire Editorial Board success in this endeavor.”

As Barry mentioned, John Dal Pino, S.E., assumed the duties of Chair as of January 1st and has been working closely with Barry throughout the latter half of John Dal Pino, S.E. 2018 to prepare for his role. John is a Principal with FTF Engineering located in San Francisco, California, and served as a CASE representative on the STRUCTURE Editorial Board since May 2014. Currently, John is on the Professional Practices Committee of SEAONC, past chair of the National Guidelines Committee at CASE, and served as President of the Structural Engineers Risk Management Council (SERMC).

Also retiring from the STRUCTURE Editorial Board is Greg Schindler, S.E. Greg has been a member of the Editorial Board since 2004. He is a Life Member of the Structural Engineers Association of Washington (SEAW), serving as Seattle Chapter President in 26 STRUCTURE magazine

1992. Greg has also been involved with NCSEA since its inception, serving as the SEAW delegate for many years, as chair of the NCSEA awards program, and a member of the CAC subcommittee on Special Inspections and Testing.

He represented NCSEA on the board of directors of the Building Seismic Safety Council and served as NCSEA president in 2000-2001. Greg recently retired after 38 years at the Seattle office Greg Schindler, S.E. of KPFF Consulting Engineers.

Barry Arnold had this to say about Greg’s departure: “Greg has served loyally and diligently on the Editorial Board for 14 years. During his time on the Board, Greg has taken on the role of Board Secretary and Review Committee Chair. Greg worked with hundreds of authors to develop article content that fit STRUCTURE magazine’s mission statement and addressed the needs of a very diverse readership. The profession has benefited greatly from Greg’s dedication and commitment to the magazine and the structural engineering profession. His efforts are praiseworthy, and he will be missed on the Editorial Board.”

Of his tenure, Greg noted: “I would like to thank the board of directors of NCSEA for allowing me the opportunity to serve as one of the editors of this renowned magazine. After fourteen years on the editorial board, I believed it was time to step aside and allow for new ideas and new energy on the board. Over the years, I have watched this publication grow from a small quarterly newsletter to the highly respected and well-read magazine that it is today. I have every issue, except for a couple, including the very first volume printed in the winter of 1994.

This magazine has become the premier publication for the structural engineering profession in large part due to the dedicated efforts of the totally volunteer Editorial Board comprised of practicing engineers from throughout the industry. I want to thank the leaders of the Editorial Board for their guidance in establishing the consistent editorial quality of the magazine. There have been very few editorial chairs in the 25-year history of the magazine, which speaks to their dedication and commitment to our profession. They are: Rawn Nelson, Craig Cartwright, Jim DeStefano, Jon Schmidt, Barry Arnold, and the incoming chair John Dal Pino. I know that John will continue that legacy.

Thanks also to the other editors and the many authors that I have worked with over the years. Serving on the editorial board has been my pleasure, and a very interesting and rewarding experience.”

Also stepping down from the Editorial Board is Stephen P. Schneider, Ph.D., P.E., S.E., after 13 years on the Board.

Steve received his Ph.D. at the University of Washington in Seattle, became a fully tenured faculty member at the University of Illinois at Urbana-Champaign, and has been a structural engineering consulStephen P. Schneider, Ph.D., P.E., S.E. tant in the Portland, OR area since the

early 2000’s. He is currently a Senior Project Manager at BergerABAM. Barry Arnold had this to say about Steve’s departure: “Since 2005, Steve has served faithfully on the Editorial Board. For thirteen years, the readers of STRUCTURE have benefited from his dedication and commitment to the magazine and the profession. Steve’s service is commendable and greatly appreciated, and he will be missed.” Of his tenure, Steve noted: “I am grateful to have had the opportunity to work on the Editorial Board since 2005, helping make STRUCTURE magazine the premier source of information relevant to the Eytan Solomon, P.E. Charles “Chuck” F. King, P.E. Jason McCool, P.E. structural engineering community today. It has been highly rewarding to work with authors to publish timely We are also pleased to announce Charles King of Urban Engineers and technical and project articles, and to shepherd articles that help Eytan Solomon from Robert Silman Associates as new members nomithe business operation of an engineering consulting office. After nated by CASE. Charles is responsible for operation and management 13 years, it is time to allow a different perspective on the Editorial of their New York City office and has more than 30 years of experience Board, but I hope to stay active with the magazine by submitting on complex transportation projects. His organizational skills will be quite worthwhile articles for future issues.” valuable in his new role. Eytan is an Associate in their New York City office STRUCTURE magazine welcomes three new Board members in and brings well-rounded experience in new construction, adaptive re-use, 2019. The Board is pleased to announce that Jason McCool of Robbins historic preservation, and the use of unconventional building materials.

Engineering, Little Rock, AR, will join the Editorial Board as a Please join STRUCTURE magazine in sending Barry, Greg, nominee by NCSEA. We know that he will contribute much to the and Steve best wishes in their future endeavors. And welcome to content and quality of the magazine with special expertise in welding Jason, Charles, and Eytan; their experience, expertise, and engineering. Jason brings with him experience in writing and editing, input will be wonderful additions to the STRUCTURE magazine team.■ and comes highly recommended by his peers.

Please watch for a message from John Dal Pino about his vision for STRUCTURE magazine during his tenure. It is anticipated that this will run in the February 2019 issue.

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

GEOPIER GROUND IMPROVEMENT CONTROLS STRUCTURE SETTLEMENT GIVE YOUR STRUCTURE STABILITY Work with Geopier’s geotechnical engineers to solve your ground improvement challenges. Submit your project specifications to receive a customized feasibility assessment and preliminary cost estimate at geopier.com/feasibilityrequest.

GEOPIER IS GROUND IMPROVEMENT®

800-371-7470 • geopier.com info@geopier.com

J A N U A R Y 2 019

27

structural SUSTAINABILITY Thermal Breaks in Building Envelopes Recent Research Findings

By Scott Hamel, P.E., Ph.D., and Kara Peterman, Ph.D.

T

hermal bridges occur when a component of high thermal conductivity causes excessive heat flow through the building insulation envelope. A large variety of conditions can cause thermal bridging, including cladding (shelf angles, grillage posts, canopy beams), metal wall studs, window mullions, and poor corner detailing. Thermal bridges through the envelope by structural steel frames are either linear penetrations, such as shelf angles, or point penetrations, such as cantilever beams or rooftop columns.

Bridging of structural steel penetrations can be particularly significant due to the high thermal conductivity of steel, which is roughly 1,500 times that of typical insulations, and the relatively large cross-sections passing through the envelope. Furthermore, many structural steel details which form thermal bridges are continuous around the building perimeter. The physical phenomenon is exacerbated by the building design process itself which involves a number of professionals with differing roles and responsibilities. Engineers, often mechanical engineers, responsible for envelope design and the elimination of heat loss and thermal bridging are not permitted to touch the structural framing, while structural engineers are not generally educated or consulted about thermal issues.

Thermal Breaks One solution to bridging is to create a thermal break, whereby the structural member is “broken” by inserting a section of material with low thermal conductivity that is aligned with the insulation envelope. This solution is complicated by the strength of the thermal break materials which are generally inversely proportional to thermal conductivity. Finding the right balance between strength, stiffness, thermal conductivity, constructability, and economy is a challenge. In addition, the “broken” steel must be integrally connected to the building structural system, often requiring additional steel fasteners which act as thermal bridges themselves.

Design and installation of structural thermal breaks are not currently addressed by code provisions in the United States; structural engineers have nonetheless begun applying 28 STRUCTURE magazine

Example of a structural steel; a) thermal bridge and b) thermal break.

thermal-break strategies. Despite prohibition by the Research Council on Structural Connection (RCSC), custom designed endplate moment connections have been used that incorporate a low-conductivity pad/ shim material such as wood, fiberglass, or fiber reinforced polymers (FRP) sandwiched between steel plates connected with bolts penetrating the assembly. Trends toward green construction and LEED certification have also prompted development and marketing of proprietary materials and products called Manufactured Structural Thermal Break Assemblies (MSTBA). MSTBA manufacturers generally also offer engineering services that provide capacities of the connections.

Covering Insulation and Condensation

the difference between the coldest inside surface temperature (obtained from simulation) and the outside air temperature with the temperature differential across the envelope.

The temperature index is a dimensionless ratio that is independent of the temperature difference between the outside and inside air.

ASHRAE has not yet codified a TI limit, but it has been suggested that 0.7 is an appropriate lower limit based on typical interior temperature and humidity.

Depending on climate, the price of heating fuel, the size and number of thermal-bridges, and the cost of creating thermal breaks, heat loss due to bridging may be an acceptable outcome. However, the damaging effects of condensation may not be. One method of mitigating condensation is “covering insulation,” insulation wrapped around the steel member surface on one or both sides of the bridge. While having only a minor effect on heat flow, covering insulation can drastically affect the condensation potential. The addition of covering insulation caused the TI of a continuous beam to increase from 0.57 to 0.85, while the addition of a thermal bridge only increased it to 0.70. However, little

Excessive heat flow and energy loss are not the only issues with thermal bridges. Localized regions of low temperature on interior steel surfaces can result in condensation from interior atmospheric humidity, leading to mold growth, staining, and ice or water damage.

Meanwhile, the exterior surfaces may be hot enough to cause melting, resulting in ice damming, pooling water, and corrosion.

One method of evaluating the potential for condensation for a particular detail is by calculating its Temperature Index (TI). The Temperature Index is a European Effect of covering insulation and thermal break on the Temperature standard that compares Index (TI) of a W-shape penetration.

Comparison of heat flow rate and thermal-break pad thickness.

research has been conducted on covering insulation and more studies are necessary to determine its required length, thickness, and appropriate application situations.

Structural and Thermal Testing and Modelling

Structural testing at UAA indicated that neoprene pads, despite their prevalence in some regions, are inappropriate for use in structural connections. FRP pads, however, central to the NEU work, demonstrated very high strengths and stiffnesses as shims in snugtight bolted connections. This research led to design recommendations for incorporating a range of shims in structural cladding details. These may be accessed via a report published by the Charles Pankow Foundation (www.pankowfoundation.org).

When to Use a Thermal Break Designers must carefully consider the thermal conductivity and mechanical properties of the break, the structural application, and installation approach to adequately mitigate energy loss at the building envelope while maintaining the structural integrity of the connection. Test results show only a minor

improvement for most common solutions.

Test results also demonstrate that some details, while decreasing the potential for condensation, actually increases the overall heat flow through the detail when compared to the control condition with no thermal break.▪ Scott Hamel is an Associate Professor of Civil Engineering and the Director of the Trueblood Cold Regions Engineering Laboratory at the University of Alaska Anchorage. Scott is a member of the SEI Thermal Bridging Task Force and is actively involved in the Structural Engineers Association of Alaska (SEAAK). (sehamel@alaska.edu) Kara Peterman is an Assistant Professor in the Department of Civil and Environmental Engineering at the University of Massachusetts Amherst. Kara is a member of the Committee of Framing Standards for the American Iron and Steel Institute, the SEI Thermal Bridging Task Group, and the Structural Stability Research Council. (kdpeterman@umass.edu).

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

Two recent studies at the University of Alaska Anchorage (UAA) and Northeastern University (NEU) in Boston, MA, highlight the thermal and structural behavior of some common thermal-break strategies. Various thermal-break details were experimentally tested in a “Calibrated Hot-Box” to determine heat-flow and surface temperature characteristics, which were used to validate an extensive series of 3-D Finite-element thermal models. The models tested included various configurations of pad materials, thicknesses, and bolt materials.

Representative results for thermal breaks with varying materials and thicknesses indicate that, despite the low thermal conductivity of the pads, the increased cross-sectional area of the connection and the penetrating bolts cause minor reductions in heat flow. For neoprene pad thicknesses of less than 25mm (1 inch), heat flow increases compared to a continuous penetrating member.

Reasonable reduction in the heat flow does occur with relatively thick pads, greater than 76mm (3 inches). FRP shim pads reduce heat transfer through the building envelope across the range of pad materials considered, though the magnitude of improvement can vary significantly by type of thermal bridge and their connections to the structural system (continuous or discrete).

Converting the bolts to stainless steel further reduces heat flow by 5% to 20%, with the bolt’s effectiveness increasing with pad thickness.

Results of heat flow tests in the calibrated hot box with various pad materials and thicknesses.

J A N U A R Y 2 019

29

We A nc h REDUCE THERMAL TRANSFER With the

TBS

Thermal Brick Support System »

A groundbreaking brick veneer support system that reduces thermal bridging in relief angles, to improve the energy efficiency of your building!

»

Saves man-hours and provides additional energy savings by allowing for the installation of continuous insulation behind the support angle.

»

The system can be designed for use with standard concrete inserts, or our serrated SHARKTOOTH INSERT for maximum adjustments in multiple directions to accommodate construction tolerances.

»

Each job is designed and engineered in house to meet your specific project needs!

»

Available in Hot-Dip Galvanized or Stainless Steel (Type 304 & 316) finishes

»

MANUFACTURED IN THE USA!

CREATING A

HIGHER STANDARD FOR THE MASONRY INDUSTRY

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

hor Th e

WORLD

STEEL REINFORCED WING MAINTAINS INTEGRITY DURING NFPA 285 TESTING.

THERMAL 2-SEAL TM ANCHORS

CONCRETE THERMAL 2-SEAL™ WING NUT

Hohmann & Barnard’s line of Thermal 2-SEAL anchors use a proprietary UL-94 coating to create a thermal break at the insulation, and a stainless steel barrel that transfers one-seventh the thermal energy of a standard zinc barrel.

In addition, the use of a dual-diameter barrel with EPDM washers make our 2-Seal line the only anchors on the market to seal both the insulation AND THE AIR BARRIER.*

THE BEST

THERMAL ANCHORS

ON THE MARKET

THERMAL 2-SEAL™ with 2-Seal BynaTie

*Competitors’ single-barrel anchors only seal at insulation leaving the air & vapor barrier vulnerable if not installed perfectly perpendicular to the wall.

v i sit www. h -b . c om or ca ll 1-8 0 0 -6 4 5 -0 6 1 6 T O D AY!

ANCHOR updates Adhesives Technology Corporation Phone: 800-892-1880 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: ULTRABOND® Anchoring and Doweling Products Description: A leading manufacturer of construction and industry related adhesives in epoxies, urethanes, acrylics, ester blends and polyureas. ULTRABOND®, CRACKBOND®, and MIRACLE BOND® are some of the most recognized products in North America.

ULTRABOND HS-1CC is currently the industry’s highest performing anchoring epoxy.

Bluebeam, Inc. Phone: 866-496-2140 Email: mwilliams@bluebeam.com Web: www.bluebeam.com Product: Bluebeam Revu Description: Innovative, cloud-based PDF editing, markup and collaboration solutions that set the standard for workflow efficiency for +1 million design and construction professionals worldwide. Revu delivers enhanced PDF-based takeoff and workflow automation tools that span the entire project life cycle and give your organization the competitive edge.

Chicago Clamp Company Phone: 708-343-8311 Email: info@chicagoclampcompany.com Web: https://chicagoclampcompany.com Product: Upper Deck Fall Protection Anchorage Description: Using the corrugations in the standard roof deck, these headers slide into place and clamp to the top chord of the bar joist or wide flange supports.

Together, the headers and clamps easily form an anchor point for fall protection systems.

Dlubal Software, Inc. Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: Effectively analyze complex connection layouts utilizing surface and solid elements, automatic finite-element meshing, mesh refinements, and surface intersection capabilities. Perform required ultimate and serviceability limit state designs of reinforced concrete according to ACI and other international standards. Accurately represent soilstructure interaction with multiple soil layers.

ENERCALC, Inc. Phone: 800-424-2252 Email: info@enercalc.com Web: www.enercalc.com Product: Structural Engineering Library Description: Design of anchors and anchor bolts typically requires a thorough development of applied loads, and may require analysis of full structures or connected components. The Structural Engineering Library can assist in determining those loads and performing those analyses.

32 STRUCTURE magazine

Gripple Inc. Phone: 630-406-0600 Email: grippleinc@gripple.com Web: www.gripple.com Product: New Spider Concrete Insert Description: The next-generation Spider Concrete Insert is available for wood or metal deck, and has a versatile design that allows it to be used with either Gripple Cable Hangers or various sizes of threaded rod to suspend services. This allows one concrete insert for all requirements.

Heckmann Building Products Phone: 708-865-2403 Email: paul@heckmannanchors.com Web: www.heckmannanchors.com Product: Masonry Anchors and Ties Description: Heckmann's has been manufacturing masonry anchors for 96 years, since 1923.The Pos-ITie® Brick Veneer Anchoring system was introduced in the mid 1980s and was the first barrel screw veneer anchor in the industry. Check out our website for a full line of anchoring systems and stone anchors.

IES, Inc. Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VAConnect Description: Design steel base plates and get full anchorage calculations per ACI. With our Transparent ReportingTM feature, see handcalculation reports that clearly document your design. Free-trial is available in 2 minutes, with no obligation.

The Masonry Society Phone: 303-939-9700 Email: tmsmeetings@masonrysociety.org Web: www.masonrysociety.org Product: Masonry Publications Description: A non-profit, professional organization of volunteer Members, dedicated to the advancement of masonry knowledge. Through our Members, all aspects of masonry are discussed. The results are disseminated to provide guidance to the masonry and technical community on various aspects of masonry design, construction, evaluation, and repair.

MKT Fastening, LLC Phone: 800-336-1640 Email: charley@mktfastening.com Web: mktfastening.com Product: Sup-R-Stud V-TZ Description: A wedge anchor designed for use in cracked or uncracked concrete. Each wedge anchor is marked with lines to denote minimum and maximum embedment of the fasteners. The Sup-R-Stud V-TZ holds ICC-ES report #ESR 4278.

Product: Sup-R-Bolt Description: A large diameter concrete screw rated for cracked or uncracked concrete. Its one piece finished hex head design is stamped with identifying marks for diameter and length of the bolt. The required hole diameter equals the anchor diameter for ease of use.

No special drill bits are required.

Simpson Strong-Tie® Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: SET-3G™ High-Strength Anchoring Adhesive Description: SET 3G is the latest innovation in epoxy adhesives. The high-strength anchoring adhesive can be installed in extreme concrete temperatures from 40°F to 100°F, as well as in dry or water-filled holes in concrete. Provides the high bond strength values needed for a variety of adhesive anchoring applications.

Product: Titen HD® Heavy-Duty Screw Anchor Description: The Titen HD screw anchor is now available in Type 304 and 316 stainless steel.

Type 316 is the optimal choice for applications in corrosive environments such as near chemicals or salt water. A cost-effective solution for less extreme applications, including in wet, moist or damp environments.

Trimble Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com Product: Tekla Tedds Description: Automating everyday structural designs, the Tekla Tedds’ library includes anchor bolt design per ACI 318 Appendix D. The calculation includes comprehensive checks for tensile and shear failure of anchors, and is available as part of a free trial.

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

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

Wej-It Fastening Systems

Phone: 203-857-2200 Email: info@wejit.com Web: www.wejit.com Product: Wej-It® High Performance Anchors Description: Founded in 1952, Wej-it invented the Original Wej-It Wedge and has continually expanded product offerings to include a complete range of highquality and innovative light to heavy-duty mechanical and adhesive anchoring products.

J A N U A R Y 2 019

FESSIONA RO

E

O

STRUCTURES CONGRESS 2019

LO

UR

DEV

S

EARN UP TO

L

P

REGISTER TODAY!

PMENT H

Orlando, Florida April 24–27

The Premier Event in Structural Engineering JOIN US TO LEAD AND INNOVATE: • Unique blend of academic and practice content to build your career • Learn from the experts, including those that develop ASCE/SEI Standards • Special Sessions: Grenfell Tower | Workshop,on Conceptual Design | Improve Your Communication/ Presentation Skills • More Innovative Executive Sessions – short presentations, dynamic learning and interaction • Keynotes: SE in Regenerative Medicine | Indispensable Structural Engineering | Reimagining FantasyLand at Magic Kingdom • A fantastic evening Celebrating the Future of SE hosted

by CSI • Meet the Leaders for Students and Young Professionals • Women in Structural Engineering (WiSE) Reception • Exhibit Hall and Vendor Sessions – engage with industry • Flex Registration for your company • Sign up to take the M.IStructE Exam • Fun in Orlando – Disney, golf, and more

HYATT REGENCY ORLANDO

www.structurescongress.org | #Structures19 To exhibit/sponsor, contact Sean Scully sscully@asce.org

ACI University All-Access Digital Subscription

ACI 212.3R-10

Report on Chemical Admixtures for Concrete

Reported by ACI Committee 212

The American Concrete Institute announces a new all-access subscription to ACI University webinars and on-demand courses. This 12-month subscription includes all ACI monthly webinars and ACI’s 200+ on-demand courses. Multi-user options are also available. Visit www.aciuniversity.com to subscribe

Prices as low as $99.00

200+ On Demand Courses | Live Webinars | Multi-User Options | 55+ Different Topics

www.ACIUniversity.com

SPOTLIGHT Intuit’s Marine Way Building A New Kind of Workplace

By Megan Stringer, S.E., LEED AP BD+C

I

n the heart of Silicon Valley, Intuit’s Marine Way Building (MWB) is a new kind of workplace. Intuit has vitally influenced and facilitated people’s financial lives for over three decades with a mission to “power prosperity around the world.” As part of the company’s headquarters, the MWB provides a sustainable, healthy, and interconnected work environment. The four-story, LEED Platinum commercial office building has an array of amenities over its 185,400 square-feet, including one story of below-grade parking, a vast all-hands meeting space, conference rooms, lounges, a café, bike facilities, numerous terraces, and a green roof. Holmes Structures served as the Structural Engineer of Record for this project and worked closely with the design team to bring the owner’s vision to fruition.

After reviewing numerous structural design options for materiality, a concrete post-tensioned flat slab system was selected for its spanning capabilities, ease and speed of construction, high floor-to-ceiling heights, and future floorplan flexibility. The gravity support of the concrete slabs consists of concrete columns on a mat foundation while the lateral system, designed to a Risk Category of III, is comprised of concrete shear walls and a concrete diaphragm.

Key design challenges were met and solved along the way. One obstacle was realizing the architect’s desire for a flat soffit with large cantilevers on all sides of the building.

The perimeter columns were set-back from the edge of the building, creating 12-foot typical cantilevers and providing a main

STRUCTURE magazine

circulation path around the building’s perimeter.

At the roof level, slab cantilevers range from 12 to 27 feet and were achieved through post-tensioning and long-term deflection analyses that considered cracked section properties. The flat soffit meant Holmes Structures was an Award Winner for its Intuit project in the 2018 that only upturned beams Annual Excellence in Structural Engineering Awards Program in the Category (where required) were – New Buildings $20M to $100M. Photos courtesy of Jeremy Bittermann. allowed in the building and had to fit within the raised floor depth. concrete’s embodied carbon by 32% (from the Another structural challenge was engineering NRMCA industry average) through concrete an open and interconnected four-story-tall specifications and close collaboration with the atrium and all-hands meeting space. This space contractor and concrete supplier. Maximum provides a community hub for both the MWB savings were achieved in the mat foundaand the Intuit campus at-large, accommodating tion with 50% cement replacement, while 500 people. Structurally, it required a 60-foot the walls and columns yielded 15% cement by 90-foot column-free zone at the first level replacement. Conversations with local concrete of the building. As the floor plate steps in at suppliers and contractors were paramount to the higher levels, a 90-foot spanning truss sup- achieving a low embodied carbon concrete mix. ports the upper floors and transfers the loads These discussions about concrete specifications to the atrium’s perimeter columns. The truss are worth having as owners, architects, and was designed with steel wide flanges encased rating systems increasingly ask for mixes with in concrete. Holmes Structures had to consider reduced cement.

The LEED Platinum MWB building is just the constructability of the truss details as well as construction sequencing to ensure its successful one part of Intuit’s master plan to update its installation. Holmes Structures also engineered Mountain View headquarters. The MWB a distinct blue feature stair that climbs across opened in 2016, and Intuit and its employees the atrium to connect three levels, improving are ecstatic with their new space. Having met the building’s circulation. Additionally, the the client’s objectives on the MWB, Holmes firm accommodated discontinuous columns Structures and the rest of the design team at the first floor with large (four-foot wide, are engaged for the next phase of campus three-foot-deep) transfer beams; these allowed updates with increased sustainability goals. space for the necessary drive The team is applying both positive feedback aisles below at the basement and lessons learned from the MWB, parking level. driving momentum forward for Beyond general struc- Intuit’s next chapter.■ tural engineering, Holmes Project Team Structures also took an active role in enhancing Structural Engineer: Holmes Structures the project’s sustainability.

Architects: WRNS Studio and Since the client had high Clive Wilkinson Architects sustainability goals, the Contractor: Hathaway Dinwiddie firm used embodied carbon Construction Company as a metric for design decisions. Once the design team Megan Stringer is a Senior Engineer with Holmes selected a concrete strucStructures and leads the firm’s sustainability ture, Holmes Structures efforts. (megan.stringer@holmesstructures.com) successfully reduced the J A N U A R Y 2 019

35

NCSEA News NCSEA Awards Firms for Structural Engineering Excellence NCSEA is pleased to announce the winners of the 2018 Excellence in Structural Engineering Awards, which annually highlights some of the best examples of structural engineering ingenuity throughout the world. These awards are presented in seven categories, three to four project winners are chosen per category, and one project from each category is honored as an Outstanding Project Winner.

The 2018 Outstanding Project Winners are: New Buildings under $20 Million Project: Ocosta Elementary School and Tsunami Evacuation Tower – Westport, WA Engineering Firm: Degenkolb Engineers – San Francisco, CA New Buildings $20 Million to $100 Million Project: Bahá’í Temple of South America – Santiago, Chile Engineering Firm: Simpson Gumpertz & Heger – Waltham, MA New Buildings over $100 Million Project: University of Texas Engineering Education and Research Center – Austin, TX Engineering Firm: Datum Engineers/Datum Gojer Engineers – Austin, TX New Bridge and Transportation Structures Project: Nigliq Bridge – Colville River, AK Engineering Firm: PND Engineers Inc. – Anchorage, AK Forensic/Renovation/Retrofit/Rehabilitation Structures up to $20 Million Project: Preservation and Seismic Strengthening of Congregation Sherith Israel – San Francisco, CA Engineering Firm: Wiss, Janney, Elstner Associates, Inc. – Emeryville, CA Forensic/Renovation/Retrofit/Rehabilitation Structures over $20 Million Project: University of Connecticut Downtown Hartford Campus – Hartford, CT Engineering Firm: Silman – New York, NY Other Structures Project: Halo Board at Mercedes-Benz Stadium – Atlanta, GA Engineering Firm: HOK – Atlanta, GA The Outstanding Projects were announced at the Awards Banquet on October 26 at the 2018 NCSEA Structural Engineering Summit in Chicago, IL. All 2018 Excellence in Structural Engineering Award winners were published in detail in the December 2018 issue of STRUCTURE magazine (pages 22–27).

Call for 2019 Excellence Awards Entries To be eligible for the 2019 Excellence in Structural Engineering Awards, projects must be substantially complete between January 1, 2016 and June 30, 2019. Projects will be judged on innovative design, engineering achievement and creativity. Structural engineers and structural engineering firms are encouraged to enter this year’s program. Entries are due Tuesday, July 16, 2019. To learn more about the projects and the entry process, visit www.ncsea.com.

36 STRUCTURE magazine

News from the National Council of Structural Engineers Associations

Young Engineers Gather at NCSEA Summit Structural engineers and NCSEA members from across the country joined at the Sheraton Grand in Chicago, Illinois for the 2018 Structural Engineering Summit. This year’s conference had a record number – 600 attendees; more than 130 were young engineers, the highest young engineer attendance in the history of the Summit. For the second year, the Summit's Young Engineer Track held seminars designed specifically for professionals early in their careers, focusing on topics they may not learn in school as well as soft skills to help them ease into the professional world.

The Summit also hosted the Young Member Reception event on Wednesday which not only provided a time for young engineers to network, but also celebrated NCSEA’s young members. The 2018 Summit Scholarship winners were honored at the reception along with the Young Member Group of the Year Finalists and the official Young Member Group of the Year, the YMG of the Structural Engineers Association of Massachusetts. NCSEA thanks Computers & Structures, Inc. for their sponsorship of this year’s Young Member Award recipients.

Thank you to all the young engineers that participated this year and thank you to the Young Member Group Support Committee who continues to develop and support events for young engineers.

Subscribe Now and Don’t Miss a Webinar in 2019

NCSEA’s enhanced Yearly Webinar Subscription is the most user- and wallet-friendly plan to date! At $995 per year, each live webinar is less than $40! This Live and Recorded Webinar Subscription offers all the same benefits as before, but now includes even more.

What do you receive as a Subscriber?

• 25+ live webinars a year featuring the highest-quality speakers available.

• All the webinars listed below + even more on www.ncsea.com.

• Unlimited 24/7/365 access to NCSEA’s Recorded Webinar Library – more than 120 relevant and high-quality webinars.

• Unlimited CE certificates for each webinar. For no additional cost, host multiple viewers at the same location and everyone can receive credit for each live webinar.

• NCSEA’s Education Portal provides easy access to all of your education content, including purchase history and PDH tracking.

Set your education up for the year and sign up for your Yearly Live and Recorded Webinar Subscription now!

Visit www.ncsea.com to subscribe for instant access.

NCSEA Webinars

Register by visiting www.ncsea.com.

January 22, 2019

Resilient Design & Risk Assessment Using the Quantitative & Building-Specific FEMA P-58 Analysis Method Curt B. Haselton, Ph.D., P.E. This course will cover how the FEMA P-58 analysis method is now being used in practice for both resilient design of new buildings and risk assessment of existing buildings for earthquake hazards.

January 29, 2019

Ethics in the Practice of Engineering Robert Kirkman, Ph.D. This webinar will consider the function of engineers in their societal role as professionals, and the habits or dispositions of character appropriate to that role.

February 12, 2019 Insurance and Indemnification: What You Don’t Know Can Cost You

Gail Kelley, P.E., Esq. This webinar attempts to reduce the confusion that can arise when trying to decipher the sometimes very-creative wording of an indemnification clause by taking a step back and looking at what it actually means to indemnify another party.

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

J A N U A R Y 2 019

37

SEI Update Best Wishes from SEI/ASCE for a Happy, Healthy, and Prosperous New Year!

What’s on your to-do list for 2019?

We invite you to get involved to advance structural engineering and your career: Join an SEI Committee effort (technical, standard development, business/professional and more), or an SEI Chapter or Grad Student Chapter to connect and learn in your local area. www.asce.org/SEI

Advancing the Profession

Call for participation – New Foundation Standard Seeking volunteer committee members to work on developing new standard ASCE/SEI XX – Criteria for the Design and Construction of Foundations. Scott DiFiore, Principal, Simpson Gumpertz & Heger Inc. will chair the cycle. Practicing engineers, researchers, building officials, contractors, and construction product representatives are all needed and welcome. Apply to join the committee by March 31, 2019, via

https://goo.gl/pMXLrK Select “SEI” from the Institute drop down and then “Design and Construction of Foundations.” Carefully indicate the Membership Category for which you are applying. Associate members can be accepted until balloting begins. Eligible regulatory members can qualify for travel reimbursement per ASCE Travel Policy. Questions?

Contact Jennifer Goupil at jgoupil@asce.org.

Membership

Join or Renew SEI/ASCE

For innovative solutions and learning, to connect with leaders and colleagues, and to enjoy member benefits such as SEI Member Update monthly e-news opportunities and resources – visit www.asce.org/myprofile or call ASCE Customer Service at 800-548-ASCE (2723).

SEI Online

Structural Engineers – Saving Lives Throughout my life, I have seen and been directly impacted by various natural disasters where the designs of structural engineers have saved the lives of thousands of people. I have grown up and continue to live in a hurricane-prone area, and have stayed through direct hits from Category 4 hurricanes which have washed away entire neighborhoods. I remember, during one of these events, an interstate bridge was washed out due to the

Follow SEI on Twitter @ASCE_SEI

Errata 38 STRUCTURE magazine

hurricane storm surge and intensity, traveling further inland than ever expected. That event was survived without any casualties due to structural failures, which is amazing after seeing the walls of water that moved through the cities. Then, in the following days, as people got back to their normal lives, there was a major impact caused by the loss of the interstate bridge.

Read the full article and the latest news items including SEI Colorado Chapter Survey, Goal-setting, and Long-term Planning at www.asce.org/SEI.

SEI Standards

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

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

News of the Structural Engineering Institute of ASCE Learning / Networking View full program and register at www.structurescongress.org.

Take the IStructE Exam to Practice Globally

IStructE will offer its Supplementary Examination for MIStructE (effectively Chartered Engineer status in the UK) again at Structures Congress 2019. Registered Structural Engineers (U.S.) can apply for Chartered Membership of IStructE via a streamlined exam/interview route. At the first exam at Structures Congress 2018, the quality of candidates was very high; 70% passed and were elected to membership.

To learn more, contact membership@istructe.org.

NEW SEI/ASCE Live Webinars – Learn from the Experts January 11 Seismic Design of Steel Horizontal, Saddle-Supported Tanks January 18 Seismic Assessment and Strengthening of Buildings and Structures in Areas of Low to Moderate Seismicity February 11 Frost-Protected Shallow Foundations: Design and Construction Register at Mylearning.asce.org for these and much more.

ASCE Week Panama February 2019

New and popular seminars, and a technical tour of the Panama Canal www.asceweekinternational.org.

Joint International Conference:

Collaboration Efficiency Safety •

•

Dubai, UAE | 29-30 September 2019

Iconic Global Structures:

what can we learn?

Join structural engineers and project stakeholders to explore the successes and challenges of constructing nine complex structures across the world. Participate in panel discussions with industry experts to share best practice and promote the highest standard of engineering globally.

Learn more at — https://structuresdubai2019.cvent.com

J A N U A R Y 2 019

39

CASE in Point Did you know?

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

962 962-B Tool 2-2 Tool 2-3

National Practice Guidelines for the Structural Engineer of Record National Practice Guidelines for Specialty Structural Engineers Interview Guide and Template Employee Evaluation Templates

Tool 3-2 Tool 3-5 Tool 4-3 Tool 5-1 Tool 5-2

Staffing and Revenue Projection Staffing Schedule Suite Sample Correspondence Guidelines A Guide to the Practice of Structural Engineering Milestone Checklist for Young Engineers

NEW!! CASE Tool 3-5: Staffing Schedule Suite By effectively projecting and balancing workloads, firms can maximize employee productivity and profit by reducing employee burnout and turnover.

This tool helps firms answer the following questions: • What are our employees working on day-to-day and week-to-week?

• Do we have enough work to keep our people busy, productive, and profitable?

• Do we have enough staff members to complete current assignments on-time?

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

CASE Practice Guidelines Currently Available CASE 962-F: This document, A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer, was developed to assist all parties associated with the bidding and construction administration phases of a project, with the primary emphasis on those issues associated with the structural engineer (SER). It is important that the design team remains proactive in communicating with the contractor and the owner after the construction documents have been issued. This communication during the construction phase, as well as during the pricing and bidding process, should have as its primary goal the assistance, interpretation, and documentation for the improvement of the constructed project. This is an outline of the SER’s roles after the construction documents have been issued for construction. It provides guidance on pre-bid and preconstruction activities through the completion of the project. The appendices contain tools and forms to assist the SER in applying this guide to their practice.

CASE 962-G: Increasing complexity of structural design and code requirements, compressed schedules, and financial pressures are among many factors that have prompted the greater frequency of peer review of structural engineering projects. The peer review of a project by a qualified third party is intended to result in an improved project with less risk to all parties involved, including

the engineer, owner, and contractor. Many aspects of the peer review process are important to establish before the start of the review, to ensure that the desired outcome is achieved. These items include the specific goals, scope and effort, the required documentation, the qualifications and independence of the peer reviewer, the process for the resolution of differences, the schedule, and the fee. The intention of CASE 962-G, Guidelines for Performing Project Specific Peer Reviews on Structural Projects, is to increase awareness of such issues, assist in establishing a framework for the review and improve the process for all interested parties

CASE 962-H: This document, National Practice Guideline on Project and Business Risk Management, is intended to assist structural engineering companies in the management of risk associated with projects and to provide commentary regarding the management of risk associated with business practices. The guideline is organized in two sections that correspond with these two areas of risk, namely Project Risk Management and Business Practices Risk Management. The goal of the guideline is to educate and inform structural engineers about risk issues so that the risks they face in their practices can be effectively mitigated, making structural engineering firms more successful.

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

40 STRUCTURE magazine

News of the Council of American Structural Engineers CASE Winter Planning Meeting February 7-8, 2019

Friday – February 8

The 2019 CASE Winter Planning Meeting is scheduled for February 7-8, 2019, in Tampa, FL. The agenda includes:

Thursday – February 7

1:00 pm – 5:30 pm CASE Executive Committee Meeting 6:00 pm – 8:00 pm CASE Roundtable Speakers: NCSEA SE3 Committee Members

7:30 am – 8:30 am Shared Breakfast 8:00 am – 12:00 pm CASE General / Toolkit Committee Meeting CASE Contracts Committee Meeting CASE Guidelines Committee Meeting CASE Programs & Communications Committee Meeting 12:00 pm – 1:00 pm Lunch 1:00 pm – 4:30 pm CASE General / Toolkit Committee Meeting CASE Contracts Committee Meeting CASE Guidelines Committee Meeting CASE Programs & Communications Committee Meeting 4:30 pm – 5:00 pm Committee Wrap-up Session

If you are interested in attending the meeting or have any suggested topics/ideas from a firm perspective for the committees to pursue, please contact Heather Talbert at htalbert@acec.org.

2019 Small Firm Council Winter Seminar What You Need to Know When You Grow February 7-9, 2019; Tampa, FL

The Small Firm Council’s 2019 Winter Seminar will teach the ins and outs of how the structure, culture, and business of your firm will change as you increase in size and project load. Mark Goodale, of Morrisey Goodale, returns with a follow-up seminar, What You Need to Know When You Grow, that will address the day-to-day changes you make as you grow your firm, and answer the following: • When is it time to hire administrative staff and human resources?

• How can I maintain my company’s culture as I grow?

• How do I retain employees if I want to stay the same?

This seminar will also feature an open roundtable discussion and a special session on how to adequately protect your small firm against new threats and liabilities.

About the Speaker: Mark Goodale is a co-founder of Morrissey Goodale. His breadth of experience includes organizational development, strategic planning, mergers & acquisitions, marketing, and executive search. He is a trusted advisor and coach to dozens of industry executives.

Before helping to establish Morrissey Goodale, Mark was the Corporate Strategic Marketing Manager at PBS&J (now a part of Atkins) where he was charged with improving and implementing progressive corporate initiatives geared to position the firm for successful, large-scale client pursuits. Before that, he worked at ZweigWhite

for over a decade and headed the firm’s strategic business planning and marketing business units.

Mark has authored numerous articles for industry magazines such as Civil Engineering Magazine, CE News, and Consulting Specifying Engineer. He has been quoted many times in various industry publications and newspapers, and is featured in the Morrissey Goodale/ Axium video series, “Building High-Performance Organizations.”

Mark was also a frequent contributor to ZweigWhite’s publications and events, and authored The Healthcare Market for AEP and Environmental Consulting Firms, the first of ZweigWhite’s market intelligence reports.

Always a top-rated speaker, Mark delivers presentations around the country on a wide variety of management topics at AIA, ACEC, NSPE, CSE, and ZweigWhite events.

Mark received his MBA from the Sawyer School of Business at Suffolk University where he now teaches Business.

Registration: ACEC Coalition Members - $399 ACEC Members - $499 Non-members - $599 To register for the seminar: https://goo.gl/9ua2qs Questions? Call 202-682-4377 or email at htalbert@acec.org.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

J A N U A R Y 2 019

41

structural FORUM Scope Creep

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

S

tructural engineers frequently provide special or extra services without receiving appropriate additional compensation. Does this phenomenon seem familiar? It can be due to scope creep, which is a malady that afflicts nearly all practitioners. If profits do not meet expectations, scope creep is usually part of the problem.

The project team may foresee special services at the beginning of a project, but because they are not related to the primary structural system, they are not included in a structural engineer’s basic scope of work. Special services often include the review, analysis, or design of nonstructural elements and their attachment. For example, on building projects: • Skylight framing, window and curtain walls, cladding, and doors • Window washing systems • Non-load-bearing interior partitions and ceilings • Anchorages, pads, brackets, and platforms for MEP equipment • Guide systems for elevators, escalators, and conveyors • Handrails and guardrails • Stage equipment, catwalks, and acoustical fixtures • Sculptures, screens, and decorative work • Retaining walls not attached to buildings • Fountains, culverts, tunnels, and other site work • Antennas, flagpoles, lighting, and signage Special services also include certain tasks that are traditionally excluded from a structural engineer’s basic scope of work. For example, special services may comprise the following on building projects: • Investigation or field verification of existing conditions • Coordination of special wind studies and wind tunnel tests • Coordination of special seismic studies and shake table tests • Preparation of additional documents for phased construction • Preparation of additional documents for fast-track construction • Preparation of estimated material quantities

• Preparation of estimated construction costs • Preparation of shop drawings and erection drawings • Design for special energy and sustainability requirements • Design for special fire resistance requirements • Design or review of excavation retention or trench bracing • Design or review of construction shoring • Design of future expansion and tenant improvements • Preparation of certifications and permit applications

“

These examples of special and extra services are narrowly focused on building projects, but similar lists could be developed for other types of projects such as bridges, other civil structures, and industrial facilities. On many projects, scope creep erodes the profits that structural engineers were planning to achieve.

On some projects, scope creep leads to serious financial losses. Why does scope creep occur?

There are two primary reasons.

First, structural engineers’ scopes of work are not always clearly defined in written professional services agreements for all projects. Many engineers continue to accept assignments based on verbal agreements, or they work under the terms of their proposals that were never formally accepted in writing. Other engineers routinely accept agreements that were drafted entirely by their clients, often without their review or input. When the scope of work is not clearly defined before work commences, an engineer is in a poor position to request additional compensation later.

Second, many structural engineers are reluctant to request additional compensation when they are asked to provide special or extra services. They fear that such requests might adversely affect their relationships with their clients and impair their opportunities for future projects. Sadly, these fears are not entirely unfounded. However, additional compensation is almost never offered except in direct response to a clearly stated request from an engineer.

The key to controlling scope creep is discipline.

Structural engineers must have the discipline to secure a signed professional services agreement that clearly defines their scope of work and compensation before starting every new project. Then, they must have the discipline to secure an agreement for appropriate additional compensation before providing any special or extra services. Discipline can be difficult to maintain on every project, but it is essential to profitability.▪

”

The key to controlling scope creep is discipline.

Extra services are services that arise due to unforeseen circumstances during the design or construction of a project. For example, extra services on building projects may include: • Evolving revisions to the size or scope of a project • Changes proposed by the owner, architect, or consultants • Changes or substitutions proposed by the contractor • Changes due to undiscovered or unanticipated conditions • Changes due to newly adopted codes or other regulations • Changes due to a value engineering exercise • Changes due to a construction cost overrun • Revisions that are inconsistent with prior instructions • Services necessitated by deficiencies in the contractor’s work • Services necessitated by delays in the contractor’s work • Additional representation required at the construction site • Services as an expert witness in a project-related dispute

Stan R. Caldwell (StanCaldwellPE.com) is a consulting structural engineer in Plano, Texas.

(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, the Publisher, or the STRUCTURE® magazine Editorial Board.

42 STRUCTURE magazine

J A N U A R Y 2 019

“ Confidently Meet Your Deadlines ” Structural Software Easy. Versatile. Productive.

Get the tools that will help you succeed:

Download your free trial today:

iesweb.com

800.707.0816