STRUCTURE magazine | June 2014

June 2014 Tall Buildings/High Rise

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE ®

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FEATURES A Monumental Challenge

38

CONTENTS June 2014

By Thomas J. Normile, P.E. and Denise L. Richards, P.E.

Structural improvements to the Statue of Liberty, reopened in 2013 after a 20-month renovation, included installation of new primary and emergency elevators and two codecompliant egress stairs within the pedestal. Read how structural engineers wove these improvements into the fabric of this 126-year old monument.

Tall Building Numbers Again on the Rise

42

DEPARTMENTS 59 Legal Perspectives Couldn’t Care Less: A Malpractice Primer for Structural Engineers – Part 1

By Matthew R. Rechtien, P.E., Esq.

62 CASE Business Practices Not Your Grandfather’s Risks Anymore

By Daniel Safarik and Antony Wood

Examination of tall-building completions in 2012 and 2013 indicate that, although the global financial crisis did result in a brief slowdown, the overall trend for increasing numbers of tall building construction projects continues to rise.

By Brent White, P.E., S.E., SECB

67 Spotlight Green Screen Parking Structure

By Jared Plank, P.E.

74 Structural Forum Communicating Structural Risk

By Dan Eschenasy P.E.

COLUMNS 7 Editorial

29 Just the FAQs

Strategic Planning at the Structural Engineering Institute

By Donald O. Dusenberry, P.E., SECB

10 Structural Practices

Single-wythe Brick Panel Fence Failures

By John Swink, P.E.

32 Historic Structures

Elevators for Tall Buildings

The Colossus of the Schuylkill River

By Jack Tornquist

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

14 Structural Design

36 Engineer’s Notebook

8 Advertiser Index 64 Resource Guide (Tall Buildings) 68 NCSEA News 70 SEI Structural Columns 72 CASE in Point

By Vincent E. Sagan

16 Structural Testing

48 Structural Rehabilitation

Load Testing of Concrete Structures – Part 2

By Gustavo Tumialan, Ph.D., P.E., Nestore Galati, Ph.D., P.E. and Antonio Nanni, Ph.D., P.E.

20 Building Blocks

The Palliation of a Terminally Ill Parking Garage – Part 5

By D. Matthew Stuart, P.E., S.E., SECB and Ross E. Stuart, P.E., S.E.

52 Professional Issues SEI Survey: Current Business Practices and Future Expectations

Innovative Steel Stud Walls for Blast Resistance

By Ady Aviram, Ph.D., P.E., Ronald L. Mayes, Ph.D. and Ronald O. Hamburger, S.E., SECB

24 Structural Performance Performance-Based Seismic Retrofit of Soft-Story Woodframe Buildings

By Stephanie Slocum, P.E. and Steve Wilkerson, Ph.D., P.E.

56 InSights Structural Strengthening using Fiber Reinforced Composite Systems

By Scott F. Arnold, P.E.

By Pouria Bahmani, et al.

STRUCTURE magazine

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June 2014

ON THE COVER

The “world’s tallest twisting tower” with a twist of 90 degrees, the Cayan Tower is a 1,007-foot tall skyscraper located in Dubai, United Arab Emirates. See feature article on page 42.

Photo courtesy of the Cayan Group – Real Estate Investment & Development.

A Joint Publication of NCSEA | CASE | SEI

By James Enright, P.E.

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Cold-Formed Steel Design: Where Do I Find Help?

STRUCTURE

Efficient Design of Steel Plate Shear Walls

IN EVERY ISSUE

June 2014 Tall Buildings/High Rise

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

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Editorial

Strategic Planning at the new trends, new techniques and current industry issues Structural Engineering Institute

By Donald O. Dusenberry, P.E., SECB, F.SEI, F. ASCE

A

mong its many activities, the SEI Board of Governors (the Board) is engaged in long-term strategic planning. Over the past few years, as part of the planning, the Board has met, conducted surveys, and formed task committees to study specific initiatives. In October 2013, one of the task committees issued A Vision for the Future of Structural Engineers and Structural Engineering: A Case for Change, a Vision for the Future Report that focuses on leadership and innovation skills (www.asce/SEI). Based in part on that report, in April 2014 the Board advanced several initiatives.

Develop and advocate a fundamentally new education for structural engineers. The education of structural engineers always will need to teach technical topics, but future engineers will also need a broad base of soft skills with more focus on creativity and risk management.

SEI will lead a blue-ribbon panel to discuss, develop, and potentially promote radically new ways to educate future students. We anticipate that fundamentally different formal education models will position structural engineers to be innovators and leaders even as our role in the construction process changes.

Mentoring and continuing education. As the pace and roles in practitioners’ offices change, focused and effective mentoring and continuing education will become more important.

SEI will study mentoring and continuing education issues that impact structural engineers, and work toward enhancing both. We anticipate that an enhanced focus on mentoring and continuing education will help structural engineers obtain and maintain the skills they need as our profession responds to, and develops in, the changing environment.

Focus on globalization and international opportunities. We need to find ways to help SEI members remain competitive in the global environment, when technology is changing the world marketplace.

We also need to view globalization as a source of opportunities and a new reason to acknowledge global responsibilities.

SEI is planning to form a fifth division – the International Activities Division – that will be the clearinghouse for information and activism for global participation by SEI members. We anticipate that a renewed focus on international and global involvement will position SEI members to lead worldwide structural engineering practice.

Performance-based codes and standards. Few will argue that most of our codes and standards are becoming more complex and more prescriptive. In an age of enhanced realization that our resources are limited, we need freedom to find new ways to solve our constituents’ and society’s problems.

SEI will study how performance-based codes and standards can enhance our solutions. We anticipate that improvements in our codes and standards will liberate structural engineers and encourage innovation, economy, sustainability, and robustness in our solutions to society’s problems.

Summits on matters of common interest. Most science-based professions are dealing with changes in technology and globalization.

So why are we not talking with each other, identifying common issues, collaborating to direct research monies to the most important

STRUCTURE magazine

Based in part on the Vision for the Future Report, in April 2014 the SEI Board of Governors advanced several initiatives. common interests, and leveraging our combined strengths to solve shared problems?

SEI will become a lead facilitator for discussions of issues of broad impact by convening regular summits with other professionals with shared problems. We anticipate that our leadership will enhance the visibility of our profession and help to direct resources to the solution of the most important problems.

Promote the structural engineer as a leader and innovator.

Structural engineers need to emerge as leaders of relevant technologies, of project teams, and as capable innovators. We need to be consulted first in the conceptualization process and be influential members of the core group of every project team.

SEI is studying ways to promote to our own membership, and to others, the notion that structural engineers are leaders and innovators, that our problem-solving skills, knowledge, flexibility, and leadership are essential to the solution of any problem. We anticipate that the SEI membership embracing this concept will find ways to prosper in the ever-changing future.

Promote Structural Engineering Licensure. In addition to the new initiatives mentioned above, the SEI Board of Governors has been working for the promotion of structural engineering licensure in all US jurisdictions. That effort has led to the formation of the Structural Engineering Licensure Coalition, with several organizations working together to advocate for this advanced credential.

We anticipate that consummation of this effort will improve public safety by raising the qualifications for engineers practicing structural engineering in the future.

Stay tuned. These are long-range initiatives that will develop over time, but we hope to give regular updates on progress.

Speak up. SEI is your organization. Please read the “Case for Change” paper and reach out to SEI Director (jgoupil@asce.org) or me (dodusenberry@sgh.com) if you want to contribute to any of these initiatives.

Sponsor. Initiatives authorized by the SEI Board of Governors to advance the profession will incur costs beyond our operating income. You can help by contributing to the SEI Futures Fund at www.asce.org/SEIFuturesFund, which is established to advance the structural engineering profession by investing in its future.▪ Donald O. Dusenberry, P.E., SECB, F.SEI, F. ASCE, is a Senior Principal of Simpson Gumpertz & Heger Inc. Consulting Engineers in Waltham, Massachusetts. He is presently serving as President of the Structural Engineering Institute.

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June 2014

Advertiser index

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Simpson Strong-Tie......................... 13, 23 Soc. of Naval Arch. & Marine Eng. ....... 59 Star Seismic ........................................... 45 Structural Engineers, Inc. ...................... 57 Structural Technologies ......................... 33 StructurePoint ....................................... 63 Struware, Inc. ........................................ 30 USP Structural Connectors ................... 15 Wood Advisory Services, Inc. ................ 60

AdvErtising Account MAnAgEr

Editorial Board

Chuck Minor

Dick Railton

Jon A. Schmidt, P.E., SECB

Eastern Sales 847-854-1666

Western Sales 951-587-2982

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Chair

Burns & McDonnell, Kansas City, MO chair@structuremag.org

Craig E. Barnes, P.E., SECB

Brian W. Miller

CBI Consulting, Inc., Boston, MA

Davis, CA

John A. Dal Pino, S.E.

Degenkolb Engineers, San Francisco, CA

Mark W. Holmberg, P.E.

sales@STRUCTUREmag.org

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Evans Mountzouris, P.E.

Executive Editor Jeanne Vogelzang, JD, CAE

Greg Schindler, P.E., S.E.

Editor

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Christine M. Sloat, P.E.

publisher@STRUCTUREmag.org

Heath & Lineback Engineers, Inc., Marietta, GA

KPFF Consulting Engineers, Seattle, WA

Dilip Khatri, Ph.D., S.E.

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

Associate Editor

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

John “Buddy” Showalter, P.E.

Graphic Designer

Khatri International Inc., Pasadena, CA

CCFSS, Rolla, MO

Brian J. Leshko, P.E.

HDR Engineering, Inc., Pittsburgh, PA

BergerABAM, Vancouver, WA

American Wood Council, Leesburg, VA

Amy Trygestad, P.E.

Chase Engineering, LLC, New Prague, MN

Wanted Structural EnginEEr authorS

The success of STRUCTURE® magazine is attributed to its authors. Our model is to have structural engineers write about structural engineering. That is what makes the magazine’s content so appropriate and useful, issue after issue.

STRUCTURE magazine is always interested in receiving unsolicited content. We encourage you to consider writing an article about a method or process that you have used to solve problems, submit a piece about an exciting project, talk about professional issues impacting your experiences, and share your expertise with an interested audience.

Don’t hesitate. Put pen to paper and write about what you know – structural engineering. Visit the STRUCTURE website (www.STRUCTUREmag.org), click the “For Authors” tab in the navigation bar, and download the Author’s Handbook. Then write a short abstract explaining your article idea and send it to publisher@STRUCTUREmag.org.

We look forWard to hearing from you!

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STRUCTURE ® (Volume 21, Number 6). ISSN 1536-4283.

Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/ yr student; $90/yr Canada; $60/yr Canadian student; $125/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact subscriptions@STRUCTUREmag.org. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board.

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Structural PracticeS practical knowledge beyond the textbook

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levators in high-rise buildings are a necessity. They move people without noticeable waits, transport staff and materials, complement the building design, and enhance the building’s market reputation. Elevators must operate safely and seamlessly.

When buildings are designed, architects enlist the assistance of elevator specialists to determine the proper number, grouping and type of elevators. This approach ensures adequate capacity and provides appropriate waiting times without providing too many elevators. High-rise buildings, those with more than 20 floors above the lobby, can have multiple elevator groups, low-rise, midrise and high-rise for example, and sometimes parking, retail and special use elevators, along with service and material elevators.

In most high-rise structures, elevator cabs are suspended from steel cables which are moved by a hoist machine, which then propels the elevator cab.

This article addresses structural designs to accommodate traction elevators (Figure 1). These elevators can have capacities ranging from 2,500 to 20,000 pounds or more, and travel at speeds ranging from 200 feet per minute (fpm) to more than 2000 fpm.

Key elevator design criteria for the elevator system, and the related building structure are detailed and defined in the Elevator and Escalator Safety Code, ASME A17.1. This code is updated annually and a new version is issued every 3 years by the Code Committee. Local jurisdictions often are tentative in adopting newest codes, wanting to become familiar with the updates and changes before adoption by local law or statute. The national code is a guide, which must be adopted by law in the locale where it will become effective.

The elevator system is made up of multiple components which affect the design of the building structure. Key components include the hoist machine, controls, guide rail system, the elevator car in which passengers ride, and safety systems which stop the elevator under certain conditions. A diagram of the key components is shown in Figure 2.

When traction elevators are included in the building design, the elevator hoist machine is nearly always located above the elevator hoistway.

This standard configuration is most cost effective and it’s design proven to be safe and reliable.

Elevators for Tall Buildings

By Jack Tornquist

Jack Tornquist is Vice President of Technical Support at Lerch Bates Inc. He may be contacted at Jack.Tornquist@LerchBates.com.

Loads Machine support beams or structural concrete slabs on which the hoist machines are mounted are used to provide permanent support for elevator machinery. Static loads, including the machine, the floor supported, and the tension in all loads on cables, can approximate 20-to

10 June 2014

100,000 pounds per hoist machine. Elevator submittal information will include the static loads of all suspended equipment as required by code. Preliminary loads may also be provided by a sales person or consultant and compared to submittal data. The elevator machine beams are provided by the elevator contractor. The rigidity is controlled by the elevator code.

The elevator machine beams and the related structural support deflection cannot exceed L (the length of the beam)/1666. Code historical records cannot be located to verify the intent of the Code committee with respect to this deflection criteria. It apparently was the intent of the Code committee to “have a stiff set of beams.” Designers should be aware that the practical limit for beam length with this deflection criteria is about 20 feet.

Machine beam loads are distributed around the perimeter of the hoistway. Elevator contractors like simple beam connections with beams resting on an angle, or in a recess. However, the structural engineer is responsible for the design of the connection. Beams can be located for efficient connection.

Beams can be below the machine room floor at convenient elevations for support or coped in to structural framing. Elevator contractors can provide blocking to locate the hoist machine at the proper elevation in relationship the machine room floor. Machine beam top flanges must be flush or below the floor. The code prescribes no tripping hazards. The machine room floor load is generally not supported by the machine beams, as the elevator manufacturers do not wish to be responsible for carrying the floor load on their beams.

Dynamic (Impact) loads from elevator emergency stops are also provided on elevator shop drawings. These loads can be distributed on the overhead structure or onto the guide rail system.

Elevators must travel in a nearly absolute vertical path. This ensures the car sill to hoistway sill distance will be maintained at a safe ¾- to 1¼-inch, the maximum allowed by code. A T-section elevator rail provides precise guidance of the car and counterweight in the hoistway.

Guide rails are a rigid column, bottom to top of the elevator travel. Rails are connected to the building structure with steel brackets provided by the elevator installer. Guide rail supports are used to provide lateral support of the elevator manufacturer-provided guide rails. Supports are generally provided at the building floors.

Additional intermediate supports are provided where the guide rail cannot meet code-based deflection and moment of inertia criteria. Spans for standard rails are generally 12-14 feet and much less in areas requiring seismic design criteria. Rails are available in different strengths and sizes which may enable installation without intermediate supports. However, the elevator industry has become less and less willing to engineer

T-Rail Brackets

Rail Clips

Figure 2. Guiderail bracket components.

Figure 1. Gearless.

unique applications and will avoid providing non-standard configurations if possible.

Regardless, designers should be persistent and ask for problem solving assistance.

Building structure, horizontal beams, or vertical tubes provide mounting locations for the elevator rail brackets. Brackets can be installed with steel fasteners, but most often are welded into place. A certified welder must complete this connection as prescribed by the elevator code. Allowable deflections for rail supports as required by the elevator code are ⅛-inch under normal

loading and ¼-inch maximum with seismic activity. Counterweight rails have the same design criteria, but have lower loads; counterweights are not the same mass as the elevator car. Guide rail loads for normal and seismic applications are provided on elevator shop drawings.

Depending on the hoistway construction type, guide rail attachments may be embedded plates in concrete or steel spanning between floors. Additional coordination may be required between architectural and structural disciplines where a fire-rated hoistway

wall is required. There are varying opinions about fire resistance where a tube or column interrupts a rated wall assembly.

Connection of the rails to the brackets is provided by steel clips. The design of these clips allows the rails to act like a rigid column and permits rails to move. Connections also prevent the rails from being displaced as the building moves and flexes over time due to age, settlement, and even temperature changes over the course of a day.

Safety Components All elevators are required by code to have a means to arrest an elevator car moving in the down direction at a certain speed above the design speed. At 10% above contract

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June 2014

(design) speed the hoist motor is shut off. At 15% above contract speed, the car safeties engage, via a clamping action on the guide rails, and the car is stopped. This clamping action transmits a vertical force into the rail columns, which are resting on the pit floor.

Elevator submittals indicate the impact load of safety operation on the pit floor.

Most modern elevators include a device which senses un-intended car movement, in either the up or down direction. This device will stop the moving elevator very quickly via a separate machine mounted brake. Loads from this occurrence are considered in the machine beam reactions.

Should an elevator over-speed in the down direction and the car safeties do not function, at the bottom of the hoistway are buffers mounted on the pit floor. These large “shock absorbers” provide a code dictated slowdown, stopping the car if it proceeds past the bottom landing at speed.

Installation and Access

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To facilitate equipment installation and repair, elevator manufacturers request that hoist beams be provided. Hoist beams provide an attachment point for lifting motors, an elevator car, rails, or other components during initial installation and later if required for equipment repairs. Elevator contractors provide a recommendation for beam capacity with their equipment submittals. Hoist beams do not support moving equipment, so impact loads are not a design consideration. The top surface of the hoist beam should be located at least 2 inches below the roof or surface above to allow placement of a clamp, trolley, or rigging. The bottom of hoist beams and any other mechanical or fire protection equipment must not encroach into the code prescribed minimum machine room height, 7 feet. Hoist beams are typically centered over the hoistway.

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Elevator ride quality is affected by the accuracy and precision of the guide rail installation. Building structures to which the rails are connected also must be installed accurately, with nearly perfect vertical plumbness.

Elevator contractors generally request, via shop drawing details, the hoistway not vary from plumb by more than 1 inch per 100 feet of vertical travel. Elevator ride quality can also be affected by the buffeting of the car when air is “pushed” by the moving cab. At speeds of 700 fpm and higher, hoistways should be larger than standard dimensions to provide space for the air disturbed by the moving car to be cushioned without causing the car to move erratically. Hoistway sizes should be increased by a minimum of 8 inches in overall width and 6 inches front-to-back to allow for air movement. Increasing sizes of hoistways for multiple elevators in a common shaft is generally not required; multiple hoistways mitigate this problem.

In areas where building construction must be designed to consider seismic activity, elevators also must be designed to avoid equipment damage and more importantly to prohibit the car and counterweight from being dislodged from their guide rails and striking adjacent structure , or worst case, the car and counterweight colliding. In seismic areas, hoistways are widened by a minimum of 4 inches and deepened by 2 inches to allow for strengthening of the rail system and its structure.

Industry Advances New technology is changing the elevator industry. All major elevator companies have designed and now aggressively market Machine Room Less (MRL) elevators. In this configuration, the hoist machine which propels the car and counterweights is located in the hoistway rather than above the hoistway in a separate space. Machines are mounted on a structure spanning the top of the hoistway, and in some cases, on the guide rails, which carries the machine loads to the pit floor. This configuration saves some space, though most jurisdictions require a separate secure control space for the elevator controller. Hoistway sizes for the MRL equipment are slightly wider than conventional equipment 4 to 6 inches, and vary significantly by manufacturer.

In heavily populated taller buildings, moving hundreds of persons during a peak period can be challenging. Control algorithms have improved handling capacity and system throughput. However, even the most sophisticated destination based dispatch systems, where users enter destinations via a keypad

STRUCTURE magazine

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June 2014

or screen cannot always handle the highest loads likely. In tall and supertall buildings with Skylobbies, double deck elevators with two connected cabs can improve service. As these cars and the suspended load they represent are substantial, hoistways are at least 12 inches wider and all elevator loads increase.

One company offers two elevators operating independently in the same hoistway to improve service and traffic handling capacity. Hoistways for this equipment are also larger to provide room for duplicate cables, wiring, the cars, and even two hoist machines at the top of the hoistway. This system is the same width as the double deck configuration. None of the systems with two elevators in the same hoistway have currently been installed in North America.

Conclusions As buildings become taller with many groups of elevators, evaluation of the space required for hoistways, machines and controls becomes important. Useable and rentable space available affects the financial viability of the building. Elevator hoistways and related equipment can be stacked, or limited to the footprint of the hoistway, with careful planning. However, this has become more difficult as code revisions now require all equipment to be safely maintainable. Any device requiring maintenance must have a minimum of 18 inches of clear space around it. Also, elevator equipment space must be 7 feet clear height to meet code. Stacking of controllers above machines can be difficult and is dependent on building floor heights and structure. For very high speed, high capacity machines, taller equipment spaces are required. Some of the largest machines may require a 12 foot clear height equipment space.

Additionally, codes periodically change to ensure the safety of first responders and the riding public. Newest codes will require a means to evacuate building occupants using elevators. In some jurisdictions, elevators must be “waterproof ” so they can remain useable in a fire. Equipment for firefighter’s lifts must be separated and preserved to allow fire fighters full use of elevators in an emergency. Also, elevator speed and building height effect emergency use. Model building codes are requiring the maximum time for an elevator to travel to the top floor of 60 seconds.

Elevator car sizes may be larger to accommodate emergency equipment and the first responder team.▪ Much of the information in this article also applies to traction elevators in low and mid-rise buildings.

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Structural DeSign design issues for structural engineers

T

he steel plate shear wall (SPSW) presents a viable structural system to resist lateral forces during earthquakes. A, SPSW is a lateral force resisting system (LFRS) composed of a thin steel web-plate bounded by and attached to a surrounding portal frame. As shown in the Figure, the frame beams are termed Horizontal Boundary Elements (HBEs) and the adjacent columns are the Vertical Boundary Elements (VBEs). The thin unstiffened web-plates are expected to buckle in shear at relatively low lateral load levels and develop tension field action for ductility and energy dissipation. This type of SPSW is referred to as a “Special Steel Plate Shear Wall” LFRS in the AISC Seismic Provisions for Structural Steel Buildings (AISC 341-10).

Current Seismic Provisions do not directly consider the plate frame interaction and assume that the web-plates resist the entire design base shear. The LFRS Seismic Provisions capacity design methodology is then used for design of the HBEs and VBEs bounding the webplate. This combination often leads to uneconomical SPSW design, especially in regards to the HBE and VBE sizing. However, it is possible to design efficient SPSW buildings within the limitations of the governing codes, ASCE 7-10 and AISC 341-10.

This discussion will help navigate ASCE 7-10’s provisions and commentary which are currently lacking in terms of SPSWs. The two seismic forceresisting system types available for selection from Table 12.2-1 of ASCE 7-10, B.26 and D.13, can be broken down further into to a total of three configurations. First, the standard SPSW building frame system (Table 12.2-1, B.26) has a response modification coefficient, R, of 7 and requires the boundary elements to be detailed

Efficient Design of Steel Plate Shear Walls

By James Enright, P.E., LEED AP

James Enright, P.E., LEED AP, is a Project Manager at KPFF Consulting Engineers in San Francisco, CA and an adjunct Lecturer at San Francisco State University. He may be reached at James.Enright@kpff.com.

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

Typical two-story SPSW frame.

similar to intermediate moment frames. The dual SPSW and special moment frame (SMF) system (Table 12.2-1, D.13) has an R of 8 and requires the full detailing requirements of SMFs. ASCE’s lack of commentary regarding how the SPSW dual system may be utilized is likely one of the reasons engineers seldom select SPSWs as their primary LFRS. Structural engineers are accustomed to seeing the SMF and concrete shear wall dual system used in high-rise construction.

Although it is possible to utilize the SPSW in a similar manner, the efficiency of the SPSW does not come into its own unless the SPSW and SMF dual system is also designed within a single frame. It is important to note that all SPSWs, independent of which system is selected, follow a capacity design approach based on the expected web-plate strength and assumed plastic hinge formation at the ends of each HBE. In the single frame dual system case, the SPSW boundary elements are simply detailed as SMF elements. Past research, including that referenced within the commentary of the Seismic Provisions, indicate that the VBEs of code designed SPSW typically contribute to more than 25% of the total frame shear. The Seismic Provisions’ SPSW basis of design commentary states, “the yielding of boundary elements contributed approximately 25% to 30% of the total load strength of the system.” In most cases, selection of the

Nine-story design comparison.

SPSW System B.26

SPSW/SMF Dual System D.13

Story

Web-Plate

HBE

VBE

Web-Plate

HBE

9

th

0.0598 in.

W18x65

W14x211

0.0598 in.

W18x65

W14x159

8

th

0.1250 in.

W18x86

W14x211

0.0897 in.

W16x40

W14x159

7

th

0.1250 in.

W16x45

W14x211

0.0897 in.

W16x57

W14x159

6

th

0.1250 in.

W16x45

W14x370

0.1345 in.

W18x65

W14x257

5

th

0.1644 in.

W18x86

W14x370

0.1345 in.

W16x40

W14x257

4th

0.1644 in.

W16x57

W14x370

0.1345 in.

W16x40

W14x257

3rd

0.1875 in.

W18x65

W14x550

0.1644 in.

W16x57

W14x426

2nd

0.1875 in.

W16x57

W14x550

0.1644 in.

W16x40

W14x426

1st

0.1875 in.

W16x57

W14x550

0.1644 in.

W16x45

W14x426

Base

—-

W18x65

—-

—-

W18x65

—-

14 June 2014

VBE

is adequate research on fundamental period approximation of SPSW systems for ASCE and other code councils to update the period approximation equations for SPSW buildings.

Until more provisions are added for SPSW structures, the use of Tmax is good starting point for designers.

In summary listed below are a few key steps for efficient design of SPSW systems for buildings over 2-stories in high seismic regions where equivalent lateral force analysis is used.

• Select the SPSW w/SMF dual system type B.13, R of 8 (single frame w/ both elements) • Calculate seismic response coefficient, Cs using the approximate fundamental period upper limit, Tmax • Size web-plates for 75% of frame shear and complete preliminary SPSW design • Verify SMF design requirements are met for 25% of frame shear • Verify Tmax & Check Drift Requirements▪

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SPSW dual system where the boundary elements are assumed to carry at least 25% of the base shear will result in a significantly more cost effective LFRS. This is due to the compounding effects from the capacity based design procedure for SPSWs. The Seismic Provisions require the web-plate be the only element within this frame designed to resist the code level seismic forces; thus oversizing the web-plate results in excessive boundary elements sizing. Simply selecting the dual system and sizing the web-plate for 75% of the total frame shear will reduce the size of all frame elements. When following the capacity based design procedures for a SPSW, the boundary elements will in most cases already be sized adequately to meet all the SMF requirements to resist 25% of the total frame shear. An SPSW element size comparison for a nine-story prototype building with 6 SPSW frames in each orthogonal direction is shown in the Table. For reference, this prototype building is similar to that of the SACProject Los Angeles structure.

When determining building base shear, ASCE 7-10 does not offer an ideal starting point for initial SPSW element sizing. ASCE 7-10’s approximate fundamental period calculation method is inaccurate and overly conservative.

Updating the approximate fundamental period estimation is probably the simplest code revision recommended to increase SPSW viability as an LFRS for designers to select. Currently SPSWs are lumped into the “All Other Structural Systems” category by ASCE 7-10 (Table 12.8-2) with other systems of far less ductility. The 2012 IBC SEAOC Structural/Seismic Design Manual, published by the Structural Engineers Association of California (SEAOC), suggests that for SPSW structures, engineers should use the upper limit of the approximate fundamental period, Tmax per ASCE 7-05 for initial SPSW design and later validated with the use of computer modeling. Although not written anywhere in the commentary of ASCE 7-10, this assumption does align with both published research and professional design experience.

Simply using Tmax for SPSW period approximation is an acceptable temporary guideline. However, past research aimed specifically at the period approximation of SPSW structures looks further into more substantial changes in the code or creating additional approximation methods for design professionals. There

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Structural teSting issues and advances related to structural testing

Figure 1. Configuration of drums for load test.

A

s discussed in Load Testing of Concrete Structures – Part 1 (STRUCTURE® magazine, April 2014), load testing can be used to determine the ability of a structure to carry additional loads, to establish the safety of structures, to validate strengthening, to gain knowledge on the behavior of a structure, and to supplement, validate or refine analytical work models. Part 1 discussed different aspects of in-situ load testing including the load test program, methods of load application and instrumentation. Part 2 describes the load test protocols and presents case studies to illustrate the use of in-situ load testing in the evaluation of existing concrete structures.

Load Testing of Concrete Structures Part 2: Test Protocols and Case Studies

By Gustavo Tumialan, Ph.D., P.E., Nestore Galati, Ph.D., P.E. and Antonio Nanni, Ph.D., P.E.

Gustavo Tumialan, Ph.D., P.E., is Senior Project Manager at Simpson, Gumpertz & Heger, Inc. Gustavo may be reached at gtumialan@sgh.com.

Nestore Galati, Ph.D., P.E., is Senior Design Engineer at STRUCTURAL TECHNOLOGIES (A Structural Group Inc. Company) Nestore may be reached at ngalati@structuraltec.com.

Antonio Nanni, Ph.D., P.E., is Chair of the Department of Civil, Architectural & Environmental Engineering at the University of Miami. Antonio may be reached at nanni@miami.edu.

Load Test Protocols In the United States, there are two protocols for load testing of concrete structures: Monotonic and Cyclic. These load test protocols are standardized by the American Concrete Institute (ACI) codes in ACI 318, Chapter 20 – “Strength Evaluation of Existing Structures” and ACI 437 – Code Requirements for Load Testing of Existing Concrete Structures and Commentary. The latter is an ACI standard recently developed by ACI Committee 437 which includes a protocol for monotonic load testing with some modifications to the protocol currently specified by ACI 318, and a protocol for cyclic load testing (not included in ACI 318).

The selection of a load test protocol typically depends on different parameters such as the objectives of the load test, site conditions, time constraints, costs, and familiarity with a load test protocol. Thus, ACI 437 permits the use of either the monotonic or cyclic load testing, at the discretion of the engineer.

Monotonic load test protocol has been used for several decades for the structural evaluation of concrete structures. The procedure basically involves loading the structure in a monotonic manner by gradually applying the load until

16 June 2014

reaching the test load magnitude, which is maintained for 24 hours. Measurements are recorded before any load is applied, after each load increment, when the maximum load is achieved, after 24 hours of sustained loading, and 24 hours subsequent to the removal of the test load. The structure is evaluated based on the maximum recorded deflection and the amount of deflection recovery. Monotonic loading can be achieved using dead weights or hydraulic jacks.

Cyclic load test protocol has been used in the last 15 years and provides engineers with an alternate for in-situ load testing. The cyclic load testing protocol involves loading the structure cyclically by applying the load in increments that include multiple cycles of incremental loading and unloading, using hydraulic jacks, until achieving the test load magnitude. The response of the structure is continuously monitored during the load test.

The structure is evaluated using parameters such as linearity of the deflections and permanency of deflections. This load test protocol does not require holding the test load for a 24-hour period.

Because the structure is loaded and unloaded at different load levels, cyclic load testing provides more information about the behavior of the structure, such as boundary conditions and load transfer characteristics, by comparing actual with calculated deflections.

Case Studies Load Testing of Deteriorated Stadium Seating Slabs The condition evaluation of a reinforced concrete football stadium built in the early 1930s revealed extensive internal cracking and delaminated concrete in the seating slabs. Because of the proximity of the football season, load tests were carried out to determine if the internal deterioration had compromised the ability of the seating slabs to safely carry the design live loads. Three representative areas showing severe deterioration were selected for load testing based on the concrete condition of the topside and underside of the seating.

A 24-hour monotonic load test procedure was used to evaluate the seating slabs. Since it was not practical to load all the seating rows, the load had to be applied in a limited area of seating. Thus, prior to performing the load tests, a structural analysis was made to determine the magnitude and extent of the test loads to be applied to the structure. The patch-pattern test loads had to produce internal forces at selected seating rows that would match the forces produced by a uniform load applied to all the rows.

The loads were generated by the weight of water contained in plastic drums. The instrumentation consisted of LVDTs (linear variable differential transformers), connected to a data-acquisition system, for continuously measuring deflections of the structure during loading, at the end of the 24 hour period and after unloading. The load was progressively applied by filling the plastic drums with water. Water meters were used to load the drums to the predetermined volumes of water. The drums were stacked two or three high to achieve the desired test-load magnitude. Figure 1 illustrates the configuration of the drums for the load tests. The load test results showed that the seating risers were able to safely carry the design live loads.

Figure 2. Hydraulic jacks on top of double-tees.

Load Testing of Strengthened Precast Double-Tee Beams The presence of shear cracks near the dapped ends of 1,400 prestressed concrete double-tee beams in a parking garage led to questioning their structural adequacy. The structural analysis showed that the shear capacities of the double-tees were deficient and required strengthening to resist the design loads.

Externally-bonded carbon fiber reinforced polymer (CFRP) laminates were selected for shear strengthening of the double-tees.

Because of the novelty of the use of CFRP as a strengthening material at the time of this project, load tests of the strengthened members were required to demonstrate the CFRP

efficiency. Twenty representative double-tees were selected for load testing.

The double-tees were tested following the cyclic load test protocol. Each load test was performed using the closed-loop method on two isolated, double-tee beams, loaded simultaneously, and using a steel beam to react against the existing inverted tee. Figure 2 shows the view of the top side with the hydraulic jacks used to apply the loads. The load and deflections were monitored using load cells and LVDTs, respectively. The load tests demonstrated the effectiveness of the CFRP strengthening system and the ability of the beams to carry their design loads. continued on the next page

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STRUCTURE - June 2014 HP-H-4C.indd 1

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Figure 3. View of push-down load test setup.

Figure 4. Hydraulic jacks and instrumentation between stadium sections.

Load Testing of Strengthened Two-Way Post-Tensioned Concrete Slabs The condition evaluation and structural analysis of the two-way post-tensioned concrete slabs of a parking garage revealed construction-related deficiencies that affected their structural capacity. These deficiencies were mainly related to incorrect placement of the tendons and mild steel reinforcement at the negative-moment regions, requiring flexural strengthening of negative and positive moment regions, and “punching” shear strengthening of slab/column intersections.

Two strengthening alternatives were considered to address these deficiencies: • Alternative 1: Construction of shear collars to enlarge the slab area to resist two-way shear around the columns.

The shear collars can also reduce the flexural demands by reducing the clear span of the slab.

• Alternative 2: Installation of a CFRP strengthening system externally bonded to the slab topside at areas adjacent to the columns to increase the flexural and “punching” shear capacities of the slabs.

Preliminary cost estimates indicated that the cost of strengthening the decks using Alternative 2 would be about half the cost of Alternative 1.

The time to construct Alternative 2 was also significantly less. In addition, Alternative 2 would result in further cost savings and reduced inconvenience to tenants because renting of offsite parking during construction could be reduced. Before determining the most suitable strengthening alternative, mock-ups of both alternatives were designed, constructed and load tested to confirm their effectiveness.

The load test program consisted of testing these two strengthening alternatives. Due to time constraints it was not possible to cast a concrete collar for the load test. Instead, the concrete collar was simulated by the use of steel shore posts uniformly around the column.

A cyclic-load-test protocol was used to load test a representative bay. A push-down test setup was used to create bending moments and shear

forces along the negative moment region similar to that of a uniformly applied load. The test loads were generated by four hydraulic jacks, two on each side of the column that applied the load to the slab by means of a steel frame. The hydraulic loads reacted against the floors above to effectively push down the test slab. Figure 3 shows an overall view of the load test setup area.

During the load tests, the loads and displacements were continuously monitored by load cells and LVDTs connected to data acquisition equipment, which displayed the load versus deflection curves in real time. For the load test of Alternative 2, five strain gauges were installed on the CFRP laminates. The load tests demonstrated the effectiveness of both strengthening alternatives and the ability of the strengthened slabs to safely support the design loads.

Load Testing of the Lateral Load Resisting System of a Stadium An initial study of a reinforced concrete stadium structure built in the early 1930s raised concerns that modifications to the masonry perimeter infill walls during a major renovation negatively impacted the lateral load-resistance of the stadium structure. The stadium is divided into 36 structurally-independent sections forming an oval shape. Each section consists of a system of reinforced concrete raker beams and deck beams supported by reinforced concrete columns, some of which are laterally braced by tie beams. The raker beams, in turn, support the concrete seating slab of the stadium structure.

The renovation project included removal of some of these infill masonry walls and enlargement of existing openings in a number of the infill walls to improve access to and from the stands. Certainly, these modifications changed the lateral loadresistance parallel to these walls, but their significance was not clear. Therefore, an insitu lateral load-test was planned to evaluate the lateral load-resistance.

A cyclic-load-test protocol was used to load test a representative stadium section. Lateral loads

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were applied to the structure with hydraulic jacks placed along the column lines. The hydraulics were installed at an expansion joint between two adjacent sections of the stadium structure so that the two sections reacted against each other. During the lateral load tests, the applied loads and lateral displacements were monitored using load cells and LVDTs, respectively. Figure 4 shows the line of hydraulic jacks installed between the stadium sections for the load test and the LVDTs attached to fixed points.

The results of the in-situ lateral load testing provided information to create improved “calibrated” analytical models of the structure, including information on the in-plane behavior of the existing perimeter masonry walls. The improved models were used to estimate the lateral load demands on the frame elements (beams and columns) of various other stadium sections, due to load combinations including gravity and crowd-sway loads. The load test results and the structural analysis indicated that all the existing sections are adequate to resist the code-prescribed load and that the lateral load resisting systems did not require to be reinforced.

Final Thoughts In-situ load testing is a valuable tool used in the evaluation and repair of concrete structures. Load testing is typically used to demonstrate that existing or repaired structures can safely resist design loads.

The recently published ACI 562 – Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings and Commentary references ACI 437 for load testing of concrete structures. It is expected that once ACI 562 is adopted by the International Existing Building Code (IEBC) and local building codes, ACI 437 will become standard practice for existing concrete structures, whereas ACI 318 load testing protocol will remain applicable for structures under construction or structures that do not have a certificate of occupancy. It is also expected that after a transition time, the technical committees of ACI will adopt a unified set of loads and acceptance criteria applicable to any type of building.▪

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Building Blocks updates and information on structural materials

O

ver the past 15 years, and particularly following the events of September 11th 2001, there has been increasing demand to incorporate blast resistance in important government and commercial facilities. Exterior walls of such buildings are designed to withstand blast impulse loading without a failure that would endanger building occupants, either through penetration of harmful debris or pressure waves.

Operators of petrochemical facilities are also concerned about similar explosive threats due to large accidental explosions.

To resist these blast threats, designers have typically specified building envelopes comprised of reinforced concrete or masonry walls.

Unfortunately, these walls are costly to build and are not amenable to portable construction, a frequent need for military applications. Recognizing this, the Department of Defense and several other agencies have expended significant funds to develop more economical, light-weight solutions to provide the needed personnel protection against explosive threats. Given their high strength-toweight ratio, and low cost, cold-formed steel stud (CFS) walls would appear to be an outstanding alternative. These researchers have found that steel stud walls constructed using conventional detailing have limited blast resistance, due to premature buckling instabilities that develop in the studs. Attempts to enhance blast resistance of such walls through use of catenary behavior require expensive connections of the stud to the supporting structure, resulting in impractical and costly construction.

Innovative Steel Stud Walls for Blast Resistance From Conceptual Design to Implementation

By Ady Aviram, Ph.D., P.E., Ronald L. Mayes, Ph.D. and Ronald O. Hamburger, S.E., SECB Ady Aviram, Ph.D., P.E. (aaviram@sgh.com), is a senior staff engineer at Simpson Gumpertz & Heger in San Francisco (SGH), specializing in blast- and seismic-resistant design.

Ronald L. Mayes. Ph.D. (rlmayes@sgh.com), is a senior consultant at SGH with significant management and technical experience in earthquake and structural engineering.

Ronald O. Hamburger, S.E. SECB (rohamburger@sgh.com), is a senior principal at SGH and internationally recognized expert in blast and performance-based earthquake engineering.

New Developments A promising option can be found in ground breaking SEB-Wall Systems. SEB-Walls consist of conventional CFS studs sheathed with a composite cement board/steel plate sheathing material such as Sure-Board™ or equivalent, and with enhanced detailing. Simpson Gumpertz & Heger, Inc. (SGH) led an extensive experimental and analytical program to develop the SEB-Wall, and demonstrate its ability to resist high blast threats equivalent to large vehicle bombs or very long duration vapor cloud explosion events. The development program was managed by SCRA Applied R&D under the direction of Mrs. Polly Graham, and was jointly funded by the U.S. Army Research Laboratory (ARL) and the U.S. Air Force Research Laboratory (now Air Force Civil Engineering Center) at Tyndall Air Force Base, Florida. The SEB-Wall development program incorporated lessons learned from past programs on conventional CFS walls conducted by the

20 June 2014

University of California at San Diego (UCSD), University of Missouri-Columbia, Air Force Research Laboratory, Army Research Laboratory, Department of Defense, State Department, and other agencies. The experimental program demonstrated that the SEB-Wall displays significantly enhanced blast resistance, in comparison to conventional stud wall systems.

Initial physical testing for the SEB-Wall development and validation program included numerous blast simulation tests at the UCSD Blast Simulator facilities under the direction of Dr. Gilbert Hegemier and Dr. Lauren Stewart.

This relatively economical and controlled test procedure avoids the use of explosive materials, and allows testing of specimens through multiple increasing impulsive force demands up to failure.

UCSD tested, under multiple actuator impacts, a total of seven full-scale stud wall specimens using high-strength micro-alloy Vanadium steel (HSLA-V) as well as several mild steel stud walls during a previous testing program. The blast simulation tests assessed the response and capacity of two connection types and the effectiveness of different construction details in preventing premature failures and stud instabilities.

The second and third series of tests consisted of live explosive and quasi-static tests at the Air Force Research Laboratory at Tyndall Air Force Base, under the direction of Mr. Casey O’Laughlin. SGH coordinated, designed, and validated these tests under a wide range of blast demands using finite element analysis.

The full-scale field tests confirmed the system’s application for retrofit of unreinforced masonry and as stand-alone construction. The field tests also allowed establishment of sheathing limit states under pressure and identified vulnerabilities in other wall components. SGH developed improved detailing requirements to ensure wall stability under direct pressures. The quasi-static load-tree tests of full-scale wall segments helped determine the static resistance functions of the composite stud-sheathing wall system for use in single-degree-of-freedom simulations. In this test setup, a hydraulic actuator load is distributed to 16 point loads equally-spaced along the length of the specimen, approximating uniformly distributed loading on steel studs. Exterior and interior composite sheathing in all three experimental phases consisted of Sure-Board panels (Figure 1).

Analytical validation by SGH included explicit dynamic finite element analysis using ABAQUS. The analytical results matched the experimentallyobtained force and deformation demands within 10% accuracy. Based on these test results, SGH developed design tools and implementation guidelines for selection and detailing of SEB-Walls to effectively achieve target performance for specified explosive threat levels. Design guidelines, which include single-degree-of-freedom system

approximations and construction specifications, will provide substantial broadening of the applicable range of response limits for stud wall systems previously specified by the U.S. Army Corps of Engineers Protective Design Center.

How does the SEB-Wall Work?

The system primarily comprises a conventional CFS wall with improved detailing to avoid undesirable failure modes, sheathed on both wall sides using composite sheathing.

The sheathing provides important structural benefits to the system including composite action and lateral bracing of the stud, increasing the wall’s flexural capacity under pressure loading, and reducing the deflection demands and resulting wall damage. Critical SEB-Wall design details also include stud lateral bracing, use of strategically-located shear stiffeners, enhanced track or angle connections, and optional granular fill (Figure 2). The design resolves issues of thin steel section susceptibility to local buckling instability, premature shear failure modes, and net section fracture at high deformation demands, while exploiting the high strength-to-weight characteristics of steel. It also enables use of simple, economical, and practical connection details for wall anchorage to either concrete or steel supports.

(b)

(a) Figure 1. Experimental program phases: (a) blast simulation tests at UCSD, CA (b) field tests under live explosives at Tyndall AFB (c) quasi-static loadtree tests at Tyndall AFB.

(c)

Mild or High-Strength Steel The program initially explored the feasibility of using walls fabricated from HSLA-V studs with strengths up to 100 ksi. The research showed that these high-strength walls provide satisfactory resistance to very high blast impulse loads. More common mild (33-50 ksi yield strength) steels in SEB-Walls were also investigated, and it was found that these materials also provide significantly enhanced blast performance relative to conventional walls. On average, the SEB-Wall system can be constructed at approximately 30% less cost than the more traditional concrete or masonry systems. The higher strength steels provide additional cost savings, for a given blast loading, relative to mild steel walls.

Composite Sheathing The sheathing panels consisted of ½-inch thick meshed cement board adhered to 14 gauge mild steel. This sheathing is installed on the wall’s compression side, while a 22 gauge mild sheet steel is installed on the tension side. Together, this sheathing provides enhanced flexural stiffness and strength to the studs through composite action. The sheathing also assists in bracing of the studs

Figure 2. SEB-Wall components and details.

and preventing lateral torsional buckling and other instabilities; and it strengthens the studto-track connection reducing susceptibility to full blow-out failure.

The location of plastic hinges along the length of the stud wall depends on the horizontal panel joint and utility hole layout. Best wall performance is obtained when multiple hinges form along the stud length as this distributes damage and avoids high stress concentrations at a single location, which may result in brittle net section fracture and

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penetration failure. However, due to initial imperfections present in all studs, and the susceptibility of thin gauge steel material to local buckling instabilities, and asymmetrical rotational stiffness, hinge formation along the wall height cannot be fully controlled.

The valuable contribution of the composite sheathing was evidenced throughout the experimental program and finite element simulations. Other sheathing types and layers of sheet steel are also beneficial in increasing stud stability and composite action but were found

to be less effective than composite sheathing.

The amount of composite action contributed by any sheathing depends on the stud material gauge and spacing, and fastener efficacy.

Enhanced Connections Improved stud-track connections allow the SEB-Wall to resist high shear force demands developed under blast loading. Enhanced track connection details include increased track dimensions, multiple screw attachment between studs, track, and composite sheathing, full-depth and thick washer plates, while using post-installed expansion anchor bolts.

Limited tension-membrane stud resistance can be developed using the improved track connection under large stud wall deflections. However, the SEB-Wall does not rely on tension-membrane action for blast resistance. In fact, an alternative bearing connection detail was tested that provides no tensile resistance but is highly effective under extreme impulse demands.

Additional Details To develop the wall’s full flexural capacity, it is necessary to prevent stud instability and premature failure and enhance the interaction of the various components. This requires somewhat different construction detail than typically used in CFS walls. These details include enhanced lateral bracing (i.e., blocking or notched-studs), and shear stiffeners near stud ends. The system allows general contractors and their curtain wall fabricators the flexibility of attaching the wall components by welding or mechanical fasteners such as self-drilling, self-tapping screws. The SEB-wall incorporates construction details developed for practical implementation with the assistance and feedback of cold-formed steel installers and manufacturers.

Why Choose the SEB-Wall over Other Blast Mitigation Systems?

High-Performance The SEB-Wall system provides a four-fold increase in blast resistance relative to conventional CFS walls. The SEB-Wall design successfully resisted blast demands corresponding to a large vehicle bomb (with impulses in excess of 500 psi-msec). This considerably exceeds the capacity of conventional CFS walls with demonstrated explosive threat resistance limited to package bombs (with impulses of less than 100 psi-msec).

The high-performance of the SEB-Wall system is comparable to reinforced concrete and

masonry walls, precast/prestressed concrete panels, and advanced composite systems.

Cost-Effectiveness With a total wall construction cost of $27/ SF (including materials and labor and excluding architectural finishes) corresponding to on-site infill-wall applications, the SEB-wall provides approximately a 30% cost savings in comparison to other high-performance blastmitigating wall systems including reinforced concrete, reinforced masonry, and precast/ prestressed wall panels. Further material savings and reduction in construction costs (or alternatively enhanced blast performance) can be obtained through the use of HSLA-V or other high-strength steels.

Construction of SEB-Walls typically does not involve curing time or complex installation procedures with high indirect costs. The light weight of these systems also makes them more transportable than competing systems.

As a result of these characteristics, the lighter SEB-Wall, designed to be ductile, redundant, and have predictable response, can in many cases provide a more economical solution than concrete or masonry walls.

Construction Benefits The SEB-Wall can be used for retrofit of masonry or other existing wall systems with limited blast resistance, as well as stand-alone applications under direct blast pressures. It can be applied to protect building envelopes from external air-blast explosions using singleor multi- story panels. These systems, which can be installed on site or prefabricated and transported, can be used for expeditionary military applications as well as economically constructed site-built buildings. The practical and easy installation procedure, as well as the potential removal of the blast walls is feasible within this innovative system, allowing modular construction and reuse.

Ongoing and Future Efforts The development program described in this article qualified the use of SEB-Walls as blastresistant non-load-bearing elements. The US Army Corps of Engineers Protective Design Center still imposes strict limits on the use of CFS walls in load-bearing applications.

These restrictive requirements (imposing elastic response limits on CFS walls and minimal rotational demands on their connections) were established due to a lack of experimental or analytical data supporting more liberal criteria. The Air Force Civil Engineering Center at Tyndall Air Force Base and SGH

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are developing a comprehensive experimental program supported by high-fidelity analytical simulations to enable resistance characterization of conventional and enhanced steel stud wall construction and validation of a new set of response limits for load-bearing applications.

Summary The SEB-wall is an innovative and cost effective system proven to resist large vehicle bomb threats and long-duration vapor cloud explosion events resulting from distant accidental explosions. The SEB-wall system relies on the flexural capacity of either mild or highstrength steel studs, composite sheathing, strategically-located lateral bracing, and enhanced connections for wall anchorage, resulting in a practical and economical solution for blast protection. Special yet simple construction and installation details are crucial to ensure adequate performance of these non-conventional curtain wall systems.

The implications of the SEB-wall research and development program extend well beyond the Department of Defense and multi-national petrochemical industries.

Many other governmental, commercial and residential applications can directly benefit from the use of this light-weight, high-performance and cost-effective wall system for building protection. In addition to cost savings of approximately 30% compared to other blast mitigation wall systems, additional benefits resulting from the use of the SEB-wall can include reduction in material quantities (reduced foundation size resulting from the use of lighter wall systems), simplified installation procedures, and expedited construction duration.▪

Acknowledgements The SEB-wall research and development program was initially sponsored by the U.S. Army Research Laboratory under Cooperative Agreement DAAD19-03-2-0036 and managed by the Advanced Technology Institute dba SCRA Applied R&D. Additional funding and technical support was provided by the U.S. Air Force Research Laboratory (now Air Force Civil Engineering Center) at Tyndall Air Force Base, Florida for execution of field and quasi-static tests. Construction materials and labor for select tests were also donated

by Intermat Inc. Any opinions, findings, and conclusions expressed in this material are those of the authors and do not necessarily reflect those of the funding agencies.

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Code Listed: ICC-ES ESR-2802

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Strong-Tie Company Inc. SMF13

Total

Structural Performance

∆N

∆Tns N

WN

∆Tor N ∆Total Eff

∆Total j Wj

∆Tns j

∆Tor j

∆ F

Total

Tns Eff

=Vb

∆Tor Eff

hN

WEff = M Eff g

hj W1

performance issues relative to extreme events

h Eff

h1 Vb = Sa WEff

(a) (a)

(b) (b)

Figure 1. Translational and torsional displacements in a torsionally unbalanced building: (a) multi-story building (b) equivalent SDOF model of multi-story building.

A

s early as 1970, the structural engineering and building safety community recognized that a large number of two-, three- and four-story woodframe buildings, designed with the first floor used either for parking or commercial space, were built with readily identifiable structural deficiencies, referred to as a “soft story”. Often these buildings also have a strength deficiency when compared to the stories above, in which case they are also classified as “weak”. The majority of these multi-story woodframe buildings have large openings and few partition walls at the ground level. This open space condition results in the earthquake resistance of the first story being significantly lower than the upper stories. Thus, many of these multi-story woodframe buildings are susceptible to collapse at the first story during earthquakes. Furthermore, in-plane torsional moments and consequently rotational displacements, can be induced when the center of rigidity (i.e. the point where seismic force is resisted) of a story does not coincide with the center of mass (i.e. the point where seismic force is applied). In this case, the building experiences additional displacement due to torsional moment, which causes more damage and increases the chances of collapse.

This article presents the first generation of Performance-based seismic retrofit (PBSR) and resulting retrofit design using a combination of wood structural panel sheathing and Simpson Strong-Tie® Strong Frame® steel special moment frames. PBSR is essentially the same as performance-based seismic design (PBSD) with the exception of additional constraints on the design due to existing structural and nonstructural assemblies. The PBSD method is a design methodology that seeks to ensure that structures meet prescribed performance criteria

Performance-Based Seismic Retrofit of Soft-Story Woodframe Buildings

By Pouria Bahmani, A. ASCE, John W. van de Lindt, Ph. D., F. ASCE, Steven E. Pryor, P.E., S.E.., Gary L. Mochizuki, Mikhail Gershfeld, S.E., Douglas Rammer, P.E., Jingjing Tian and Michael D. Symans, Ph.D.

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

24 June 2014

under seismic loads. In the PBSR, retrofits were installed such that the building meets the performance criteria at the DBE and MCE level and its torsional response reduces to an acceptable range. In this retrofit design methodology, retrofits are not limited to the bottom story (like those of the FEMA P-807 retrofit methodology).

They can also be applied to the upper stories to increase the strength of the building, leading to better overall performance of the structure.

The seismic performance of the retrofitted building with PBSR procedure was evaluated numerically and validated by a full-scale fourstory wood-frame building that was tested in the summer of 2013 at the NEES (Network for Earthquake Engineering Simulation) at UC San Diego large high performance outdoor shake table facility. The test was part of the NEES-Soft project, which consists of a number of tasks including extensive numerical analysis, development of a performance-based seismic retrofit methodology, and a major testing program with testing at five university-based laboratories to better understand the behavior of these at-risk structures and the retrofit techniques.

Performance-Based Seismic Retrofit (PBSR) In performance-based seismic retrofit (PBSR), which is a subset of performance-based seismic design (PBSD), the stiffness of the structure is distributed along its height and in the plane of each story such that a target displacement can be achieved under a specific seismic intensity, taking into account nonlinear behavior of the structure.

The PBSR method presented herein can be used to retrofit existing buildings such that all stories meet the performance criteria; and it can be used to retrofit buildings that are weak under both translational forces and torsional moments.

Displacement-based design was originally proposed by Priestley (1998) and later modified by Filiatrault and Folz (2002) to be applied to wood

Parking

3048 mm (10')

2743 mm (9')

2743 mm (9')

3048 mm (10')

Kitchen

Light Well

Bedroom 1

Stairs

Bedroom 1

Kitchen

2743 mm (9') 1829 mm (6') 2743 mm (9')

Entrance

7417 mm (24'-4")

Storage Stairs

2438 mm (8')

Laundry Room

Bath

Bath

Bedroom 2

3048 mm (10')

Dining Room

Dining Room

Living Room

Living Room

2743 mm (9')

2743 mm (9')

(a)

7417 mm (24'-4")

11684 mm (38'-4")

11684 mm (38'-4")

4877 mm (16')

structures. Pang and Rosowsky (2009) proposed the direct displacement design (DDD) method using modal analysis and, later, Pang et al (2009) proposed a simplified procedure for applying the DDD method which was eventually applied to a six-story light-frame wood building and tested in Miki, Japan (van de Lindt et al., 2010) validating the simplified procedure. Finally Wang et al (2010) extended the work of Pang et al.

(2009) to allow correction as a function of building height. This design methodology determines the required lateral stiffnesses over the height of the building such that the building meets the target displacement defined by the building code. This method serves as the basis for a PBSR procedure by distributing the required in-plane stiffness of each story to eliminate the torsional response of the structure (i.e., reducing the in-plane eccentricity) (Bahmani and van de Lindt, 2012). However, for cases in which eliminating torsion cannot be achieved, PBSD that allows some level of torsional response can be used as the basis for design of retrofits for such buildings (Bahmani et al., 2013).

In torsionally unbalanced buildings, inplane torsional moments, and consequently rotational displacements, can be induced when the center of rigidity of a story does not coincide with the center of mass. In this case, additional rotational displacements due to torsional imbalance should be taken into account whenever they occur. Figure 1a presents an N-story building with lumped masses of Mj for the j th story. The total displacement of the center of mass of the j th story is a summation of displacement due to lateral force (∆Tns. j ) and displacement due to torsional moment (∆Tor. j ). Elimination of the torsional response of the structure can be achieved by distributing the retrofit in the plane of each story such that the retrofitted building becomes a structurally symmetric building (i.e., ∆Tor. ≈ 0). However, if the torj sion cannot be feasibly eliminated, the PBSR approach can be applied by assuming a ratio between the displacement caused by lateral force and torsional moments, and then satisfying the assumption while applying the retrofit. A three-story torsionally unbalanced woodframe building was retrofitted using PBSR methodology without eliminating torsion by van de Lindt et al. (2013).

In order to simplify the PBSR procedure, the structure can be modeled by an equivalent single degree of freedom system (Figure 1b).

The effective weight (WEff) and lateral force distribution factors (Cv) can be calculated based on the approach outlined in NEES Wood Report-05 (2009). The fundamental

Bedroom 2

3048 mm (10')

(b)

Figure 2. Floor plans for the four-story building: (a) ground story (b) upper stories.

(a)

(b)

Figure 3. (a) Completed 4-story 4000 square-foot building. (b) Isometric view of the building.

translational period of the building can be obtained from the displacement response spectrum, which is developed based on the design spectral acceleration maps of ASCE710 (2010) and should be modified to take into account the effect of equivalent damping.

The next step is to obtain the effective lateral stiffness, and consequently the distribution of the stiffness for lateral load resisting elements at each story. The last step is locating the lateral load resisting systems (i.e., shearwalls or other retrofit assemblies) such that the design satisfies the initial assumption that is made regarding the contribution of torsional response to the total displacement. If the contribution of torsional response is assumed to be close to zero (i.e., eliminating the torsion), then the lateral force resisting elements should be placed such that the CR and CM at each story become very close to each other at the target displacement. The required lateral stiffness can be provided by using the secant stiffness (at the target displacement) of the lateral force resisting elements (i.e., standard wood shearwall, steel moment frame, etc.).

The PBSR procedure described in this article was applied to a four-story multifamily soft-story wood frame building with a soft-story at the ground level and was tested at the outdoor shake table at NEES at UC-San Diego. The building was designed to have less than 2% inter-story drift with 50% probability of non-exceedance (PNE)

STRUCTURE magazine

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June 2014

at all stories using PBSR methodology subjected to MCE level by eliminating torsional response of the building.

Shake Table Testing A full scale four-story building was constructed at the outdoor shake table facility at NEES at UC San Diego. On the ground floor, there was a large laundry room, a storage room, and a light well. The light well was included since many of these buildings are surrounded by other buildings on two sides and therefore have two essentially solid sides and two open sides. The test building was designed to replicate these conditions, thus making it, in many ways, a worst case scenario. The interior wall density in the upper stories was high, but this is in line with many soft-story woodframe buildings of that era. The outside was covered with horizontal wood siding (1x8 in. Douglas-Fir grade No 2 or BTR) with two 8d common nails connected to each vertical wall stud. The inside walls were covered with gypsum wall board instead of plaster. Figure 2a shows the ground story and upper story floor plans for the building (plan dimensions are 24 feet x 38 feet). Each of the upper three stories had two two-bedroom apartment units as can be seen in Figure 2b. Figure 3 shows the finished building ready for shake table testing at the UCSD NEES laboratory. continued on next page

Steel Special Moment Frame and Wood Structural Panel Retrofits

WSW - 1

WSW - 3R

WSW - A

WSW - A

WSW - 3

WSW - D

(a)

(b)

Figure 4. Location of the PBSR retrofits: (a) at the ground story (b) at the upper stories.

(b)

(a)

(c)

Figure 5. (a) East span of Strong Frame installed parallel to the motion of shake table. (b) ATS rods and stud pack inside wood shearwall. (c) Plywood panels at upper stories.

In the PBSR procedure, the objective was to design the building such that all the stories experience the same level of peak inter-story drift. This utilized the capacity of the upper stories to resist seismic loads and increased the probability of survival of the building under higher earthquake intensities. To achieve this goal, the four-story test building was retrofitted with a Simpson Strong-Tie Strong Frame steel special moment frame (SSMF) at the ground level and 15�32-inch thick sheathingrated plywood shear wall panels with different nail schedules and tie downs on the selected walls of the upper stories. The steel frames were designed and located such that they did not interfere with the intended use of the space (i.e. vehicle parking), or conflicted with any other architectural aspect of the building. Figure 4 presents the location of Strong Frames and wood shearwalls (WSW) that were installed to retrofit the building.

Simpson-Strong-Tie Anchor Tie-Down System (ATS) rods were used to transfer uplift forces, induced in the wood shear walls during the earthquake, to the foundation or in case of

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The Hollo-Bolt® Fasteners may be used to resist wind loads, and seismic loads in Seismic Design Categories A, B and C. 3.0 DESCRIPTION

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Nominal Hollo-Bolt® sizes include 5/16 inch (M8), 3/8 inch (M10), 1/2 inch (M12), 5/8 inch (M16), and 3/4 inch (M20), with each size of bolt available in three lengths.

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3.2.2 Body (sleeve) with Integral Collar, Body (sleeve without collar), Collar and Cone: The parts are manufactured from free cutting carbon steel Grade 11SMn30 or 11SMnPb30, conforming to BS EN 10087, having a minimum tensile strength of 62,400 psi 2 (430N/mm ) (sizes up to LHB16) or 56,500 psi (390N/mm2) (size LHB20); or cold drawn steel AISI C10B21, having a minimum tensile strength of 2 68,000 psi (470N/mm ).

3.2.3 Rubber Washer: The measured on the A scale 80-90.

shore

hardness

is

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STRUCTURE magazine

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June 2014

Conclusion Overall the PBSR method was validated with the level of accuracy that would be expected for this type of testing. The peak inter-story drift response was approximately 2.5% at story 3 with the average of all stories being well under 2%. Full results will be presented in a forthcoming project report which will be available at www.nees.org in 2014.▪

Acknowledgments This material is based upon work supported by the National Science Foundation under Grant No. CMMI-1041631 and CMMI1314957 (NEES Research) and NEES Operations. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the investigators and do not necessarily reflect the views of the National Science Foundation. A sincere thank you to Simpson Strong-Tie for their financial, personnel, and product support throughout the project, including the engineering support for the SMF in San Diego. Thank you to the USDA Forest Products Laboratory for their continued

250

1

2

SSMF X-Dir. SSMF Y-Dir.

3

4

5 60 50

200

40

150

30

100

20

Y

50

X

X-Dir.

0 0

(a)

25

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75

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10 0 150

125

Lateral Displacement, (mm)

Lateral Force, (Kip)

3000

Y-Dir.

W16x57 Column

W14x38 Column

W12x50 Beam

W14x38 Column

W12x50 Beam

Lateral Force, (kN)

Lateral Displacement, (inch)

(b)

Drift (in) Drift (in)

Max. translation in X-Dir, (mm)

2 0 -2 0 2 0 -2 0

Drift (in)

Max. translation in X-Dir, (in)

2 0 -2 0

Drift (in)

Figure 6. (a) Strong Frame SMF installed parallel to the motion of shake table. (b) Backbone curves of the Strong Frame SMF’s installed parallel and perpendicular to the motion of shake table.

Story Number

shear walls above the SSMF to the frame, (i.e. to provide overturning restraint). It should be noted that both the Strong Frame and wood shearwalls were placed such that the center of rigidity moved toward the center of mass at each story, which effectively eliminated the concerns associated with torsional response of the structure. Figures 5 and 6 shows the Strong Frame, plywood panels, and ATS rods used to retrofit the building.

In order to test the retrofitted building, the building was subjected to the similar ground motions that were recorded during the 1989 Loma Prieta and 1992 Cape Mendocino earthquakes. The earthquakes were scaled to DBE and MCE levels with maximum spectral accelerations of 1.2g and 1.8g, respectively. Before and after each seismic test, a white noise test with a root mean square (RMS) amplitude of 0.05g was conducted to determine the fundamental period of the building and its modes shapes, and to obtain a qualitative feel for damage based on changes in building period. Figure 7 presents the building profile at its maximum deformations for five seismic tests along with a time-history response for the test with the highest response. It can be seen that all the stories experience approximately 2% inter-story drift which meets the performance criteria (i.e., under 2% drift with only non-structural damages).

2 0 -2 0

(a)

0.69 -0.82

Story 1

0.69

-0.82

5

5

5

5

10 1.63 1.63 -1.96 -1.96

15

20

25

30

35

40 Story 2

10

1.94 1.94 -2.68 -2.68

15

20

25

30

35

40 Story 3

10 0.31 0.31 -0.25 -0.25

10

15

20

25

30

35

40 Story 4

15

20

Time (sec)

25

30

35

40

(b)

Figure 7. PBSR – Strong Frame SMF Retrofit: (a) building maximum deformation profile (b) Time-history response to Cape Mendocino Earthquake record with PGA of 0.89g.

funding through a cooperative agreement with Colorado State University. Thank you to Co-PI’s Weichiang Pang and Xiaoyun Shao for their contributions to the overall project. The authors kindly acknowledge the other senior personnel of the NEES-Soft project:, David V. Rosowsky at University of Vermont, Andre Filiatrault at University at Buffalo, Shiling Pei at South Dakota State University, David Mar at Tipping Mar, and Charles Chadwell at Cal-Poly; the other graduate students participating on the project: Chelsea Griffith (WMU), Jason Au and Robert McDougal (CPP); and the practitioner advisory committee: Laurence Kornfield, Steve Pryor, Tom Van Dorpe, Doug Thompson, Kelly Cobeen, Janiele Maffei, Douglas Taylor, and Rose Grant. A special thank you to all of the REU students Sandra Gutierrez, Faith Silva, Gabriel Banuelos, Rocky Chen, Connie Tsui, Philip Thompson, and Karly Rager.

Others that have helped include Asif Iqbal, Vaishak Gopi, Ed Santos, Tim Ellis, and Russell Ek. Finally, our sincere thank you to the NEES and all site staff and site PI’s at NEES@UCSD for their help in preparing for the tests.

A similar article was published in the Wood Design Focus (Winter 2013). Content is reprinted with permission.

STRUCTURE magazine

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June 2014

Pouria Bahmani, A. ASCE, is a Ph.D. Candidate, Civil and Environmental Engineering at Colorado State University, Fort Collins, CO. Pouria can be reached at pbahmani@engr.colostate.edu.

John W. van de Lindt, Ph.D., F. ASCE, is the George T. Abell Distinguished Professor in Infrastructure, Civil and Environmental Engineering at Colorado State University, Fort Collins, CO. John can be reached at jwv@engr.colostate.edu.

Steven E. Pryor, P.E., S.E., in the International Director of Building Systems with Simpson Strong-Tie, Pleasanton, CA. Gary L. Mochizuki, is a Senior Research and Development Engineer at Simpson Strong-Tie, Pleasanton, CA. Mikhail Gershfeld, S.E., is a Professional Practice Professor, Civil Engineering at Cal Poly, Pomona, CA. Douglas Rammer, P.E., is a Research Engineer with Forest Products Laboratory, Madison, WI. Jingjing Tian is a Ph.D. Candidate, Civil and Environmental Engineering at Rensselaer Polytechnic Institute, Troy, NY. Michael D. Symans, Ph.D., is an Associate Professor, Civil and Environmental Engineering at Rensselaer Polytechnic Institute, Troy, NY.

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Question: I have observed many brick fences throughout the west and southwest. Most are in excellent condition, but some require repair or reconstruction. Can you explain the variation in performance and how best to design them?

Answer In the 1970s, Acme Brick Company developed a design for building thin brick fences with a single layer of clay brick in panels suspended between reinforced brick posts on drilled piers. Panels are reinforced with joint reinforcing, which is designed to carry wind loads and the much lower stresses from gravity loads on the brick. Typical panels span between posts that are 10 to 12 feet on center.

Hundreds of miles of these fences have been built in Texas, as well as in other parts of the country. Many of those fences show no signs of distress after 20 or more years of wind and weather exposure. Properly designed, we expect them to last fifty years or more. But there are also a number of fences that have deteriorated in ten years or less, and must be replaced. That deterioration has occurred because those who built the fences either did not understand the design or did not use the right materials and workmanship.

The Panel and Post System Figure 1 shows a perspective view of the major components of the fence system.

Posts are built with two faces of clay brick tied together with wire reinforcing (Figure 2, page 30).

The design calls for 3/16-inch diameter wire that is either hooked on the ends or welded as ladder

wire to engage the brick faces. A core of grout is formed and poured between the brick faces to create a composite post that carries wind loads in bending to a drilled concrete pier. Pockets are formed approximately three inches deep on each side of the posts to receive the reinforced brick panels.

Panels are isolated from the posts with compressible foam to prevent hard contact between them that could cause crushing or spalling with differential movement. Panels are typically laid in place on temporary forms and remain three inches clear of the ground or mud slabs below. Wire reinforcing in the bed joints is designed to resist out-of-plane bending from wind loads. Vertical bending stresses from the weight of the brick are typically about one percent of the wind load stresses, so they are not significant to the design.

Just the FAQs questions we made up about ... Masonry

Requirements for Strength and Durability Strength requirements are straightforward: • Piers must be drilled deep enough to resist overturning loads from wind on the panels and posts in the soils encountered at the site. NCMA TEK 14-15A provides some guidance for pier design to resist wind loads, but soil types vary widely and may require deeper piers.

• Posts must be sufficiently reinforced and grouted to carry overturning wind loads to the drilled concrete piers below. continued on next page

Single-wythe Brick Panel Fence Failures

By John Swink, P.E., LEED AP

John Swink, P.E., LEED AP, is the Director of Technical Services for Acme Brick Co., Fort Worth, Texas and a member of the Masonry Standards Joint Committee of The Masonry Society. He can be reached at jswink@brick.com.

Figure 1. Perspective view of post and panel fence system.

STRUCTURE magazine

29

Figure 3. Fence breaking apart from corrosion of joint reinforcing. Fence was less than 2 years old at time of photograph in 2005, Austin, TX.

Figure 2. Detail sections of typical posts showing reinforcing.

• Pier reinforcing need not be more than a single bar in the center, since shear loads are low and shear reinforcing is not necessary.

• Panels can be either prefabricated or laid up onsite, but must have reinforcing designed for the wind loads.

• Panel reinforcing must have sufficient cover to prevent corrosion. The masonry code and specification (TMS402/602) requires 5/8-inch cover.

This may be difficult or impossible to achieve with 25/8-inch brick and ladder wire. Consider a single wire at the centerline for these bricks.

• Reinforcing wire must be hot-dip galvanized or stainless steel to prevent corrosion.

• Steps must be taken to assure adequate bond between brick and mortar and between mortar and reinforcing. Oil must be removed from stainless steel wire.

When Things Go Wrong

There have been a number of failures of fence panels (Figure 3). These are seen as cracks developing between mortar and brick. As cracks progress, mortar spalls off and rusted reinforcing appears near the surface. This can result from one or more of the following causes: • Poor bond between brick and mortar.

• Insufficient cover on wire reinforcing.

• Wire reinforcing may not be hot-dip galvanized after fabrication.

Poor mortar bond can result from using mortar with too high an air content. For that reason, portland-lime Type S mortar is recommended, but good results can be achieved with high quality masonry cements as well. Workmanship plays the most critical role in achieving mortar bond, including timely placement of brick after stringing mortar, proper moisture content and workability of mortar, and pre-wetting of certain brick that have high initial rates of absorption. There is also a StruWare, Inc potential for failure if mortar is overStructural Engineering Software sanded. When bond is poor, a crack can develop between brick and mortar The easiest to use software for calculating that allows a path for water to reach the wind, seismic, snow and other loadings for wire reinforcing and cause corrosion.

IBC, ASCE7, and all state codes based on One way to assure that the bricklayer these codes ($195.00). will achieve good mortar bond is to CMU or Tilt-up Concrete Walls with & design the panels without shelf angles without openings ($75.00). supporting the bottom course. If the panels are built on temporary forms, Floor Vibration for Steel Bms & Joists ($75.00). which are removed after 1 to 3 days, any Concrete beams with/without torsion ($45.00). brick that are not properly bonded will fall off the bottom of the panel when Demos at: www.struware.com the forms are removed. This is an early STRUCTURE magazine

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June 2014

quality test for the bricklayer’s workmanship.

But many fence builders insist on laying the brick on steel angle lintels at the bottom of the panels. Those lintels keep any poorly bonded brick from falling off, and it may take several years before general deterioration of the mortar and corrosion of the joint reinforcing become evident.

The Structural Engineer’s Role Single-wythe panel fences are engineered structures. But because they are typically 6 feet high or less, they may not be regulated by local building codes. We recommend that every municipality require a qualified structural engineer to design and supervise construction of brick panel fences. Design is relatively simple and repetitive, so design time for each project is very low. There is a design and construction guide on the Acme Brick website at http://brick.com/pdf/tsd/TSD210.pdf.

The author has also prepared a spreadsheet that can be used to design joint reinforcing in the panels for different brick thicknesses and wind loads.

Field supervision need not be continuous, provided the engineer develops confidence that the masonry contractor understands the construction methods and is willing to follow them explicitly. It is also recommended that quality masonry fence contractors be selected and thoroughly trained in this very specialized form of structural brick masonry. That training and skill can be a very profitable opportunity for quality masonry contractors, and the quality brick fences they build should last for 50 years or more.▪

Historic structures significant structures of the past

I

n 1811, the only bridge crossing the Schuylkill River near Philadelphia was Timothy Palmer’s Permanent Bridge that opened in 1805 (STRUCTURE®, October 2013). Ferries continued to serve the community at the Upper Ferry (Sheridan’s) and the Lower Ferry (Gray’s). Both of these ferries at times also had floating bridges adjacent to them. As early as January 30, 1811, an Act was submitted to the legislature authorizing “A company for erecting a permanent bridge over the River Schuylkill at or near where the floating bridge of Abraham Sheridan is at present situate, known by the name of the upper ferry in the County of Philadelphia.” The legislature approved it and the governor signed it on March 28, 1811. Section 9 of the act stated, “And be it further enacted by the authority aforesaid…a good and complete bridge shall be erected at the place aforesaid by said company, at least thirty feet wide with a good and sufficient railing on each side…” The Act included a statement that nothing would authorize the company “to erect the same in such a manner as to injure, stop or intercept the navigation of the said river by boats, rafts or other vessels without masts.”

Abraham Sheridan’s floating bridge and ferry was featured in an article in the Massachusetts Magazine (September 1792) entitled “Description of the UPPER FERRY, on the River Schuylkill, near the city of Philadelphia.”

An announcement by the Bridge Company in the fall of 1811 stated that the company would accept proposals for “a permanent bridge over the River Schuylkill at or within two hundred feet north of Sheridan’s floating bridge. The bridge is to be as high as the Permanent Bridge at Market Street and not have more than one pier (a single arch would be preferred) and to be thirty six feet wide…”

On the date specified, Thomas Pope submitted the only proposal for his Flying Pendant cantilever bridge. He wrote, “The said estimate of $50,000 is to be considered the separate expense of the structure alone, after the foundations of the two abutments are prepared for its reception.” Two days later Robert Mills, a local architect, submitted two additional proposals. One was for an uncovered bridge that would cost $36,674, or $35,074 without a toll house. Mills noted, however, that “the timbers above the floor of this

The Colossus of the Schuylkill River

By Frank Griggs, Jr., Dist.

M. ASCE, D. Eng., P.E., P.L.S.

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

Dr. Griggs can be reached at fgriggs@nycap.rr.com.

Wernwag’s Colossus 1812 structure from broadside.

32 June 2014

Sheridan’s Upper Ferry Floating Bridge – ferry rope in foreground.

bridge are proposed to be lined or cased within as well as without, and secured from injury of rains.” The other proposal “has the passage ways covered in every particular relative to traveling conveniences…” The cost of this covered bridge would be $44,174, but if the tollhouse and other parts “not absolutely requisite to the convenience and strength” were deleted, the cost could be as low as $38,564. The proposal contained much less detail than Pope’s. Apparently the managers did not like any of these initial proposals, as they took no action.

At the time, Lewis Wernwag was well-known in Philadelphia for work on the construction of his Economy bridges at Bridesburg over Frankford Creek and near Bristol over Neshimany Creek.

Both were early examples of a cantilever bridge.

He submitted his proposal on November 14 writing, “Mr. Wernwag proposes to contract to build a bridge with the necessary abutments and piers according to his plan and to give security for the performance in a penal sum equal to the amount of the cost of the said Bridge on the following terms and conditions. Supposing the cost of the Bridge to be forty thousand dollars and he thinks it will not exceed thirty six thousand dollars, he expects to have five thousand dollars, for his superintendence.” He signed a contract with the company on December 5, 1811 that placed much of the responsibility on him, with the exception that the company would buy the materials based upon Wernwag’s recommendations and pay the workmen. The contract stated in part, “Whereas the said Lewis Wernwag hath furnished… a Plan of a Permanent Bridge to be erected over the river Schuylkill at the Upper Ferry… and hath proposed to superintend the building of said bridge, to collect all the materials necessary for the making and erecting the same and to find fit and suitable Workmen to do all the work…that he will forthwith proceed to collect all the materials necessary for erecting the said bridge and at all times to keep employed a full complement of capable and

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suitable workmen…And he will from the date hereof until the end of one year from and next after the first cornerstone of the abutments of the said Bridge is laid…devote his whole time and attention to the best interests of the said party of the second part…In consideration of all which services to be rendered and performed by the said Lewis Wernwag and in full compensation thereof and for the Plan of the said Bridge and the use of Tools and Apparatus…the sum of three thousand dollars…and they further agree to make him a complement of five hundred dollars.”

Wernwag originally recommended a 400foot span with five arches but on January 6, 1812, the managers approved “of the plan of one arch in the construction of the Bridge about to be built with our funds, and that the chord thereof be from 300 to 350 feet as may be judged by the managers to suit best with the foundations of the two abutments.”

A corner stone laying, Masonic ceremonies, on the easterly abutment took place on April 28, 1812. The cornerstone included a copper plate indicating Louis Wernwag as the bridge’s architect.

The easterly abutment rested on rock that was close to the surface and went in without difficulty, but the westerly abutment was a major problem. Niles Weekly Register wrote an article on January 23, 1813, entitled “American Ingenuity” and stated, “The western abutment, with its wings, is built on 599 piles, driven through a frame containing two hundred and seventy-five thousand feet (board feet) of timber, well connected, as well by the combination of the parts by iron bolts, weighing on the whole three tons. This abutment is sixtytwo feet front on the river, and forty feet thick.” Wernwag started work on this foundation in the summer of 1812, placing his timber grid and driving wooden piles ranging in length from 15 feet to 30 feet, and finished in early September.

On July 2, he made a major change in the original design of the bridge, which was to have five arches spanning the river.

He determined that three arches would do the job instead. The Board wrote that they, “do agree that a superstructure formed of three ribs be erected, upon condition that Lewis Wernwag shall superintend the sawing, construction & framing of the two outside ribs now conditionally omitted, and every part thereof with whatever else belongs thereto as well as the complete erection of the same…without the said Lewis

William Strickland, official drawing of the Board of Managers.

Wernwag claiming any further compensation therefore than the managers are now under contract to pay.”

The final 340-foot 3-inch span far exceeded any bridge of its time. The deck width was variable with two carriageways and two sidewalks.

At the top of the curve, the ribs were 13 feet 1 inch apart and 21 feet apart at the abutment.

The overall width was 33 feet at the peak and 50 feet at the abutment. The rise of the lower chord/arch was 19 feet 11 inches. Wernwag summed up his report with, “The ribs, the cart-way, and the string-pieces, form so many arches, which are all connected and secured by ties, braces and bars of iron, in such a manner as to form one connected and combined whole, equal in strength, perhaps, to any thing that human ingenuity could devise. “ The Niles Weekly Register of January 23, 1813 wrote of the arches, “Each of these ribs is composed of six small ones, in thickness six inches, and of the average depth fourteen inches – the small ribs are placed on their edges, two in breadth and three in depth, and so formed as to be at the abutment equal to a solid mass of timber, four feet deep and one foot thick gradually diminishing in size, so as to be at the apex but three feet deep and one foot thick. They are prevented from coming into contact by one inch iron bars placed between them, six feet asunder, but are connected together by large iron bands also six feet apart, well secured, and susceptible of being drawn together as the timber dries, by strong screws.”

On January 7, 1813, the bridge opened and Poulson’s Advertiser carried a brief notice when it stated, “On Thursday last the centres were removed from this beautiful edifice in the presence of a large concourse of people – when was exhibited an arc of three hundred and forty feet three inches straight cord; being ninety six feet longer than any single arc in Europe or America. This truly elegant structure was completed thus far in eight months, and rests

Colossus by Thomas Birch.

upon stone abutments of vast solidity, containing together 7000 perches of stone.”

The bridge to this date cost a total of $64,500 including the cost of property and monies given to the ferry companies. It was estimated that the rest of the construction including covering would cost $20,550.

Shortly after removal of the scaffolding, the northerly wingwall of the westerly abutment cracked. It was clear that the wall was being pushed northerly by the backfill material. In spite of this problem, on March 13, 1813, the Board determined that “it is expedient to roof and finish the bridge” and selected Robert Mills as their designer and builder. He proposed a very decorative siding and roofing and was given the contract to enclose the bridge and build the tollhouses for the sum of $4,520, not including the cost of materials. His proposal and contract were very detailed, with a circular toll house to be built with a colonnade surrounding the walls. The work was to be completed within six months.

Apparently something was still going wrong on the northerly wingwall on the westerly abutment, and Wernwag was called in to remove “the defect in the bridge” which he did with great effort. By early May, however, another problem developed that caused Wernwag and the managers a great deal of alarm. The westerly abutment face, which up to this time was stable, started to shift. The northerly end rotated about the southerly end, causing the two northerly ribs to rise up in the middle. The Board wrote, “Mr. Wernwag, is, at his own proper cost removing the earth from behind the abutment, with an expectation that the weight of the Bridge upon the wall will bring the piles to their original bearing: In this experiment, the managers have no very great confidence. It was due however to Mr. Wernwag to suffer him to make the trial.” He was successful in this effort and

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the managers wrote, “It was reserved for the genius of America to throw a single arch over a river, three hundred and forty feet wide, without any other support than its abutments, for in no part of the old world can such an instance be shown. ” The Board commissioned a drawing of the bridge by William Strickland to be part of the final Report.

One of the most copied images of the bridge was Birch’s. It was reproduced on Staffordshire China and many versions of it reproduced in European books.

Its title as the longest span lasted until 1815, when Theodore Burr built his McCall’s Ferry Bridge, was reclaimed when Burr’s bridge was taken out by ice in 1818. The bridge lasted until September 1, 1838 when it was consumed by fire after a life of only 26 years. The directors were anxious to rebuild the bridge but lacked the finances to do so for several years. In 1842, Charles Ellet, Jr., on the same site, built the Fairmount Suspension Bridge. Its central span was 358 feet and it was the first major wire cable suspension bridge in the United States, lasting until 1870. It was replaced with an iron bridge by Jacob Hays Linville.

The span, along with its beautiful covering, resulted in the bridge being called the Colossus after the famous Colossus of Rhodes Statue, one of the Seven Wonders of the Ancient World. It is likely that Wernwag himself named it the Colossus, as on his 1813 Broadside he calls it his Patent Bridge Colossus. Wernwag’s accomplishment was to build the longest single span bridge in the world in just over eight months, with the woodwork taking only three months.

Fletcher and Snow wrote in their 1934 Transactions ASCE article on “A History of the Development of the Wooden Bridges” that “this bold design, scientific and architecturally beautiful, probably was never surpassed in America.”▪

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

W

hen the author first started his structural engineering career in the 1980s, common coldformed steel applications in buildings were primarily limited to steel roof and floor deck, interior non-load bearing partition walls, and curtain wall framing; in other words, secondary members. As a structural engineer designing buildings, one could rely on manufacturers’ literature, such as steel deck catalogs, or delegate the design of these cold-formed steel applications to contractors or specialty structural engineers through performance specifications.

Significant experience in cold-formed steel framing design was not required.

With the increasing use of cold-formed steel framing as the primary structure for roof, floor, and load-bearing walls in buildings with multiple stories (mid-rise construction), experience in cold-formed steel framing is now required.

Unfortunately, it is often the case that very little exposure to cold-formed steel design occurs in undergraduate education. The fundamentals of structural steel behavior and design often focuses on hot-rolled steel. The reference document of choice is the American Institute of Steel Construction (AISC) Steel Construction Manual, which includes the AISC Specification for Structural Steel Buildings, which does not address cold-formed steel. It was not until graduate school, and later while working for an engineering firm, when the author learned about cold-formed steel behavior and design.

For many, cold-formed steel design information that is practical, clear, and easy to use can be difficult to find. Thankfully this void in information has been recognized by the cold-formed steel framing industry and is being addressed through the efforts of the Cold-Formed Steel Engineers Institute (CFSEI) and the American Iron and Steel Institute (AISI). The mission of CFSEI, an organization composed of primarily structural engineers, is “to enable and encourage the efficient design of safe and cost effective cold-formed steel (CFS) framed structures.”

This mission is being partially accomplished through the development of Technical Notes on Cold-Formed Steel Construction, more commonly known as Tech Notes (Figure 1).

Tech Notes address fundamental design issues as well as frequently asked questions pertaining to the design and construction of cold-formed steel structural members and connections. In addition to providing discussion of the design concepts and methods, Tech Notes typically illustrate the design with numerical example problems, and some include design aids. Tech

Cold-Formed Steel Design: Where Do I Find Help?

By Vincent E. Sagan, P.E.

Vincent E. Sagan, P.E., is an Associate Principal with Wiss, Janney, Elstner Associates, Inc. (WJE). He serves on the AISI Committee on Specifications for the Design of Cold-Formed Steel Structural Members and is Chair of the CFSEI Executive Committee. He can be reached at vsagan@wje.com.

36 June 2014

Figure 1. Typical CFSEI Tech Note.

Notes are written by structural engineers experienced in cold-formed steel design, and thoroughly reviewed by members of the CFSEI Technical Review Committee. The authors and reviewers volunteer their time to fulfill the mission of CFSEI. For the experienced hot-rolled structural steel design engineer, cold-formed steel member design does not differ dramatically from hot-rolled steel design, other than the consideration for local buckling, which can be easily avoided in hotrolled steel design, and distortional buckling, especially with the availability of computer software programs and design catalogs. However, connection design is often the major stumbling block for an engineer transitioning to cold-formed steel design. Different fasteners, including screws (Figure 2) and power-actuated fasteners (PAFs), are more commonly used in cold-formed steel framing. Eccentricities resulting from the singlysymmetric and point-symmetric member sections and single angle connections are normal design considerations. To assist the engineer, the following CFSEI Tech Notes have been developed: • Screws for Cold-Formed Steel-To-Wood and Wood-To-Cold-Formed Steel Attachments (F101-12) reviews the design provisions of the AISI North American Specification for the Design of Cold-Formed Steel Structural Members, the National Design Specification® for Wood Construction (NDS®), and the APA-The Engineered Wood Association (APA). It also discusses design and detailing of the connection of cold-formed steel members to wood structural supports, and the attachment of wood structural panels and sheathing to cold-formed steel members.

Figure 2. Typical cold-formed steel screw connection for a diagonal brace connection.

Triple Protection Against Corrosion

Figure 3. Cold-Formed Steel Design Manual.

Increase Corrosion Resistance Figure 4. Cold-Formed Steel Framing Design Guide.

• Welding Cold-Formed Steel (F14010a) provides information on the applicable codes, processes, procedures, design considerations, fabrication, and inspection.

AISI efforts to provide information to the structural engineer include publishing the Cold-Formed Steel Design Manual, AISI D100 (Figure 3), and multiple design guides. The Cold-Formed Steel Framing Design Guide, D110 (Figure 4 ), has been prepared to assist the structural engineer to design cold-formed steel framing systems. A key element of this guide is the “real world” numerical design examples. The design examples address the following framing systems: • Wind bearing infill wall with screw connection using a sheathed design approach • Wind bearing infill wall with welded or screw connections using an unsheathed design approach • Wind bearing wall with strip windows utilizing welded connections • Floor and axial load bearing wall stud systems utilizing screw connections The connection design Tech Notes described above, as well as other Tech Notes on other subjects, including durability, curtain walls, trusses, shear walls, and inspection guidelines, a summarization of AISI D110, and construction details are available from www.cfsei.org. Questions may be addressed to: info@cfsei.org, 800-79-STEEL (1-800797-8335), or the “Ask An Expert” form (www.cfsei.org/contact_us_1.htm).▪

STRUCTURE magazine

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June 2014

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• Evaluation of Screw Strength (F70112) provides design guidance for the evaluation of the screw itself when subjected to pure shear, pure tension, and combined shear and tension.

Also included are nominal strength values for screws in pure shear and pure tension.

• Cold-Formed Steel Truss to Bearing Connections (F501-11) provides general educational information regarding the cold-formed steel truss to bearing connection, including loading to consider, the responsible design professional for this connection, and general design methodology.

• Screw Fastener Selection for Cold-Formed Steel Frame Construction (F102-11) provides basic information for selecting the appropriate screw type based on the end-use application.

• Pneumatically Driven Pins for Wood Based Panel Attachment (F300-09) discusses the specification, selection, and field inspection of pneumatic driven pins.

• Powder-Actuated Fasteners in ColdFormed Steel Construction (562) explains their installation, behavior, and good design detailing.

• Corrosion Protection of Fasteners (D10013) examines the corrosion process, available fastener finishes, methods of measuring corrosion, and the relative durability of fastener finishes.

Designing Life Safety Renovations for the

Statue Liberty of

By Thomas J. Normile, P.E. and Denise L. Richards, P.E.

Statue of Liberty National Monument. Courtesy of National Park Service.

T

he Statue of Liberty National Monument reopened to visitors July 4, 2013 after a 20-month renovation to upgrade visitor access, egress, safety, and comfort.

Structural improvements included installation of new primary and emergency elevators and two independent, fire-rated, and code-compliant stairs within the pedestal. The improvements include new egress routes that extend through the War of 1812-era Fort Wood surrounding the monument.

Working under the auspices of the National Park Service, as part of a multi-disciplinary design team led by Mills + Schnoering Architects, Keast & Hood Co. provided comprehensive structural engineering design and construction administration services. The team used Building Information Modeling (BIM) software, regular in-person and online meetings, and a commitment to creative problem-solving to ensure the renovation went smoothly.

Weaving new structural elements through a 10-story, 27-squarefoot shaft punctuated by obstructions presented unique structural engineering challenges. The 126-year-old monument’s location on an island accessible only by barge intensified the task.

Statue Structure A gift from the people of France, the Statue of Liberty National Monument was constructed in 1886 and consists of a 151-foot tall STRUCTURE magazine

statue atop a 127-foot tall pedestal. French sculptor Frederic Auguste Bartholi designed the statue; Gustave Eiffel, designer of the Eiffel Tower, designed its supporting structure. American architect Richard Morris Hunt designed the granite-clad, cast-in-place concrete pedestal.

The monument sits in the center of the former Fort Wood on Liberty Island in New York Harbor. The infilled plaza, known as the terreplein, lies between the perimeter fort walls and the monument pedestal.

The Statue of Liberty must withstand both gravity and lateral loads.

The Eiffel structure within the statue contains four primary vertical pylons, the centroid of which is eccentric to the pedestal below.

At the top of the pedestal, two pairs of girders cross in the shaft.

These girders transfer gravity loads to the pedestal concrete and transfer uplift loads to a series of large tension straps that extend down to a second set of Eiffel girders located near pedestal mid-height. The lower girders are embedded into the walls of the pedestal at a point where there is enough concrete dead load above to resist the large overturning forces that result from wind acting on the statue. Each Eiffel girder is a series of four built-up I-sections laced together with plates riveted to the top and bottom flanges.

Pedestal levels are named 1P (ground level) through 7P (top level).

Level 3P falls slightly above the terreplein. Above 3P, the interior shaft measures 27 feet square, and the wall thickness varies from six to 18 feet to support the granite cladding. Below 3P, the pedestal steps outward. Earlier renovations widened the center shaft below 3P from

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floor levels and the existing pedestal walls support the new stairs. The floor structure consists of concrete slabs on steel deck supported by structural steel framing. The stair stringers employ rectangular hollow structural sections. New beams connect to the existing pedestal walls with post-installed anchors. One stair exits the pedestal at 3P while the other extends down through the pinch point to 1P. Between 3P and 4P, both stairs pass through the center of the Eiffel girders. To maintain fire separation, a fire-rated glass enclosure supported on the stringers envelopes one stair. There were extremely tight tolerances between the new stairs and the Eiffel girders, which the new structures were not permitted to touch.

Determining the elevator support structure presented another significant design challenge. Several options were considered, including shaft wall on structural steel framing, concrete unit masonry, precast, and cast-in-place concrete. Ultimately, cast-in-place concrete was chosen because it could be sculpted to suit the tight clearances and existing spatial irregularities, and because it was aesthetically consistent with the historic fabric surrounding it. A self-consolidating, 4000 psi concrete was used to cast 7.5-inch thick architectural concrete walls. Concrete arrived on site in ready-mix trucks that traveled by barge to the island

Structural revit model and monument terminology.

Courtesy of Keast & Hood Co.

Collaboration with BIM

Enclosed stair structure passing through Eiffel girders between levels 3P and 4P. Courtesy of Brian Rose.

10-feet square to 27-feet square on 1P and approximately 15-feet square between 2P and 3P. This narrow location is known as the “pinch point.”

The statue contains a double-helix stair that extends from the top of the pedestal to the crown. Prior to this project, access to and egress from the base of the statue was via two open stairways that hugged the outside walls of the pedestal’s central vertical shaft.

Design success hinged on effective systems integration. The collaborative design process and use of BIM software proved essential. In 2009 when design commenced, most firms involved in the project were fairly early in the BIM adoption period but chose to use BIM because of the project’s geometric complexity.

Led by Mills + Schnoering Architects, each design consultant produced a BIM model. Teammates participated in regular meetings and web conferences, shared their models, and resolved conflicts to coordinate all designs. Although the contract documents consisted of traditional drawings and specifications, BIM easily enabled the presentation of both two-dimensional and three-dimensional views on the drawings to aid visualization by the contractors. The construction phase proceeded with very few requests for information (RFIs) related to design intent or inter-disciplinary coordination issues, proving the benefit of the BIM approach.

Surprises in the Field Discovery of unexpected field conditions drove a high level of structural involvement during construction. The most significant of these

Design Challenge The fundamental design challenge was determining how to fit an elevator and two, code-compliant egress stairs within the narrow shaft of the pedestal.

Following removal of the old stairs and two elevators, two primary physical constraints influenced the new layout: the pinch point of pedestal concrete between levels 2P and 3P, and the Eiffel girders at pedestal mid-height. When these two constraints were overlaid in plan, only two locations could accommodate the main elevator through the full height of the pedestal: at the center or along the west wall.

The west elevator location was chosen because it enables both new stairs to rise through the center opening of the Eiffel girders, creating a more interesting interpretive experience for visitors.

For most of the pedestal height, one stair is located on the shaft’s north side and the other is located on the south side. Intermediate STRUCTURE magazine

New elevator shaft and stair framing above level 3P. Courtesy of Keast & Hood Co.

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The pedestal under construction. Courtesy of Harper’s Weekly, Volume XXIX, No. 1485, June 6, 1885.

discoveries arose quite early. After removal of the old stairs and elevator, the contractor demolished some of the mass concrete foundation at 1P to create the new elevator pit.

Logistical and operational considerations precluded pre-construction materials testing within the pedestal. However, participants in the 1984-85 renovation recalled the pedestal concrete as extremely hard and difficult to penetrate. Given the expectation of relatively high-strength existing concrete, the new elevator shaft walls were designed to bear directly on the base slab at 1P. The elevator pit was expected to require laborious demolition of the mass concrete foundation. Unfortunately, after breaking through a thin concrete wearing slab, workers could easily remove the remaining concrete with hand tools. This unexpected finding triggered a detailed investigation and testing; the result was that, although quite deep and uniform, the concrete at 1P was also quite lean with an average strength of 1,200 psi. Consequently, the elevator shaft base was redesigned as a mat foundation to gently distribute the load of the new shaft walls over the existing lean concrete.

The unexpectedly low concrete strength raised questions about existing material strength and suitability of the new connections to the historic concrete throughout the monument. Tests expanded to all pedestal levels in two phases: core sampling and compression testing to determine the approximate compressive strength of the existing material, and pull testing of anchors proposed for new steel connections.

Compression test results showed a puzzling variety of strength results ranging from 700-9,500 psi, and noticeable differences in material strengths above and below 3P. The answer to this mystery lay in the history of construction and subsequent alterations of the monument. At 3P – the pedestal’s original entry point – the interior of the pedestal starts to open up and become wider and the exterior walls become thinner. Historic photos show visitors ascending an exterior staircase from the terreplein to 3P. On the interior, the narrow pinch point presents at 3P. Records showed the original shaft as a constant ten feet square from 3P down to the base at 1P. The original concrete above 3P was, as rumored, quite hard with an average strength of 4,500 psi, whereas below 3P, the average strength of the original concrete was a mere 1,500.

It became clear that the original designers saw the construction below 3P as a mass concrete foundation wherein a much lower strength could be justified. Above 3P, the walls of the pedestal thin considerably but employ a higher-strength material. Understanding this original STRUCTURE magazine

New handrail in the crown at the top of the spiral stairs.

Courtesy of National Park Service.

Tight clearances for new steel at the existing Eiffel girders.

Courtesy of Keast & Hood Co.

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June 2014

Statue of Liberty National Monument. Courtesy of Brian Rose.

design approach proved the range of concrete strengths made perfect sense. Once confident in where and why material strength differed, the structural team adjusted post-installed connection details to suit varying concrete strengths at different locations within the monument.

Another discovery revealed undocumented vertical chases that once hid electrical raceways. Thin concrete covered the raceways to match surrounding solid concrete, making them impossible to discern visually. Ground penetrating radar helped identify locations.

After documenting the chases, engineers redesigned affected steel connections to avoid connecting a new floor beam or stringer to a concealed chase.

National Pride Given the geometric and logistical complexity of the project, success could easily have been elusive. However, a committed team of designers and contractors used the coordination efficiencies of BIM and a shared sense of purpose and national pride to effect a successful outcome. Every team member involved in the Statue of Liberty renovation considered it an honor to preserve and improve the landmark, and ensure its continued safety and accessibility for generations of visitors.▪

View of pedestal interior above level 3P after demolition.

Courtesy of Keast & Hood Co.

Thomas J. Normile, P.E., is a structural engineer and principal of Keast & Hood Co. He served as principal in charge and played an active role in the collaborative design process of the Statue of Liberty renovation. He can be reached at tnormile@keasthood.com.

Denise L. Richards, P.E., is a structural engineer and associate of Keast & Hood Co. She served as project manager for the Statue of Liberty renovation. She can be reached at drichards@keasthood.com.

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Project Team Owner: National Park Service Structural Engineer: Keast & Hood Co., Philadelphia, PA Architect: Mills + Schnoering Architects, LLC, Princeton, NJ Mechanical Engineer: Joseph R. Loring & Associates, Princeton, NJ Construction Manager: Atkins Global Consulting Engineering, New York, NY General Contractor: Joseph A. Natoli Construction Company, Pine Brook, NJ Steel Subcontractor: Weir Welding, Carlstadt, NJ Concrete Subcontractor: Macedos Construction, Flemington, NJ

June 2014

Tall Building Numbers Again on the Rise

By Daniel Safarik and Antony Wood

B

y all appearances, the small increase in the total number of tall-building completions from 2012 into 2013 is indicative of a return to the prevalent trend of increasing completions each year over the past decade. Perhaps 2012, with its small year-on-year drop in completions, was the last year to register the full effect of the 2008/2009 global financial crisis, and a small sigh of relief can be let out in the tall-building industry as we begin 2014.

At the same time, it is important to note that 2013 was the secondmost successful year ever, in terms of 200-meter-plus (656 feet) building completion, with 73 buildings of 200 meters or greater height completed. When examined in the broad course of skyscraper completions since 2000, the rate is still increasing. From 2000 to 2013, the total number of 200-meter-plus buildings in existence increased from 261 to 830 – an astounding 318 percent. From this point of view, we can more confidently estimate that the slowdown of 2012, which recorded 69 completions after 2011’s record low of 81, was a “blip” and that 2013 was more representative of the general upward trend.

Of course, each year is extraordinary. Here are some of 2013’s key milestones: • 2013 was the second-most successful year on record for completion of buildings 200 meters or greater in height. In 2013, 73 such buildings were completed, second only to the 81 completions of 2011.

• For the fourth year running, nine supertalls were again completed in 2013. These 36 supertalls total nearly half the total number of supertalls that now exist (77).

• Across the globe, the sum of heights of all 200-meter-plus buildings completed globally in 2013 was 57,946 feet (17,662 meters) – also the second-ranked in history, behind the 2011 record of 71,004 feet (21, 642 meters).

• Of the 73 buildings completed in 2013, twelve – or 16 percent – entered the list of 100 Tallest Buildings in the World.

• For the sixth year running, China had the most 200-meterplus completions of any nation, at 37 – located across 22 cities.

• The tallest building to complete in 2013 was the 1,165 feet (355-meter) JW Marriott Marquis Hotel Dubai Tower 2 in Dubai, UAE. • Three of the five tallest buildings completed are in the United Arab Emirates, for the second year in a row.

• The city of Goyang, Korea, has debuted on the world skyscraper stage with eight 200-meter-plus buildings completing in 2013.

STRUCTURE magazine

• Panama added two buildings over 200 meters, bringing the small Central American nation’s count up to 19. It had none as recently as 2008. Of the 73 buildings over 200 meters completed in 2013, only one, 1717 Broadway in New York, was in the United States.

Key Worldwide Market Snapshots of 2013 Asia Asia completely dominated the world tall-building industry, at 74 percent of worldwide completions with 53 buildings in 2013, against 53 percent with 35 buildings in 2012. Asia now contains 45 percent of the 100 Tallest Buildings in the World.

The Shard, London, 1,004 feet, completed 2013. Courtesy of Renzo Piano Building Workshop, William Matthews Photographer.

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June 2014

Tallest buildings by year. Courtesy of CTBUH.

STRUCTURE magazine

the same way that so many Chinese cities have entered the world’s consciousness over the past dozen years. continued on next page

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China remained the heavyweight and overall undisputed champion of tall-building construction in 2013. A total of 37 two-hundredmeter-plus buildings were completed – 50 percent of the global total – up from 24 in 2012. The sum of heights of all 200-meter-plus buildings in China in 2013 was 29,121 feet (8,876 meters), compared to 19,104 feet (5,823 meters) in 2012, an increase of 52.4 percent.

These buildings were spread across 22 cities. Shenzhen proved to be the most active skyscraper city, doubling its number of completions from the previous year, from two to four. It was closely tailed by Chongqing and Shanghai, which tied at three. Nanjing, Shenyang, Suzhou, Hefei, Tianjin, Nanning, Xiamen and Guangzhou each claimed two completions. Of these, Hefei and Xiamen are first-timers; these cities have never completed buildings of 200 meters or more until 2013.

The tallest building completed in China in 2013 was the 1,089-foot (332-meter) Modern Media Center in Changzhou.

Korea had the next-largest number of tall completions in the Asian region, though its figure of nine buildings was almost entirely due to the opening of an eight-building complex, the Tanhyun Doosan project, whose subtitle, appropriately enough, is “We’ve the Zenith.”

Goyang, a city of 1.5 million near Seoul, is now on the world skyscraper map in

June 2014

Middle East As a region, the Middle East recorded completion of 12 buildings of 200plus meters in height, forming 16 percent of the world total in 2013.

This is a decrease from 16 buildings for 24 percent of last year’s total.

While last year’s score was boosted by the completion of the Abrajal-Bait Endowment, a single seven-building complex in Saudi Arabia, the United Arab Emirates (UAE) remained a dominant player in 2013, increasing from five to 10 completions, a national total second only to China’s. The UAE has been in the top four nations since 2008 and the top three since 2010. For the second year in a row, three of the five tallest buildings completed globally this year are in the UAE. Dubai laid claim to the title of both the world’s tallest building completion of 2013 , the JW Marriott Marquis Hotel Dubai Tower 2 (1,165 feet, 355 meters), as well as the “world’s tallest twisting tower” – not a category maintained by CTBUH, but impressive nonetheless – with the 1,007-foot (307-meter) Cayan Tower.

Abu Dhabi completed The Gate, whose captivating sky bridge connecting its four towers caught the eye of the 2013 CTBUH Awards Jury which selected it as a Finalist in the Best Tall Buildings Middle East category.

Europe Europe completed four tall buildings in excess of 200 meters in 2013, and increased its total number of supertalls (greater than 984 feet or 300 meters) in existence from one to three (the first was Capital City STRUCTURE magazine

Tower in Moscow in 2010). In 2013, Europe also had two buildings (The Shard, London and Mercury City, Moscow) in the world’s 10 tallest completions for the first time since 1953, when two of the seven Moscow “sisters” (MV Lomonosov State University and The Ministry of Foreign Affairs) were completed.

Among the two supertalls to complete in Europe last year was The Shard, which is not only the United Kingdom’s tallest at 1,004 feet (306 meters), but one of the more hard-won victories (anywhere, let alone in the UK) of developer persistence amidst financial crisis, regulatory scrutiny, historic-preservation and traffic-flow constraints.

The 339-meter Mercury City tower put Russia on top of the continent, while the 722-foot (220-meter) DC Tower I brought Austria – which broke the 200-meter threshold only once before with 1999’s Millennium Tower – further into the fold of “European Tall.”

The Americas North America’s share of total 200-meter-plus completions during 2013 dropped from 6 to 1 percent of worldwide figures. Panama comprised the totality of tall buildings completed in Central America in 2013. There were no completions of tall buildings over 200 meters in South America.

Panama continued to punch above its size, completing two 200-meter-plus buildings, the 876-foot (267-meter) Bicsa Financial Tower and the 807-foot (246-meter) Yoo and Arts Tower, both in Panama City. The expansion of the Panama Canal and the appeal

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June 2014

of buying real estate on an urban, tropical seashore continued to attract commercial and residential interest to a country that now has 19 tall buildings over 200 meters, but had none as recently as 2008.

In the United States, heavy construction and a slew of new proposals made 2013 an exciting year in New York City, though only one 200-meter-plus building, the 755-foot (230meter) Marriott Courtyard and Residence Inn Central Park Hotel at 1717 Broadway, was actually completed.

The balance of US interest is in the series of super-slim luxury residential towers now cropping up along 57th Street and in Lower Manhattan; here, slenderness ratios, not pure height, are the object of much discussion. Still, it will be several years before many of these “billionaire needles” are completed.

Of the 73 two-hundred-meter-plus buildings completed in 2013, the share of pure office buildings continued to decline, from 39 to 34 percent. Pure-residential functions comprised 30 percent of 2013 completions.

Mixed-use buildings ticked up slightly, to 30 percent, up from 29 percent in 2012. Four of the completions were hotels, comprising five percent of the total (against one percent in 2012).

Tall Buildings in 2013 –

by Structural Material

Concrete remains the building material of choice for tall buildings globally, holding steady at 63 percent of completions.

Composite construction increased from 26 to 32 percent in 2013, while all-steel construcCayan Tower, Dubai, 1,007 feet, completed 2013. tion remained a distant third at three percent, Tall Buildings in 2013 – Courtesy of Cayan Group – Real Estate Investment a far shot from 1970, when 90 percent of the 100 Tallest Buildings in the World were & Development.

by Function constructed of steel.

This past year saw the continuation of several trends in building funcWhat can we draw from this? It has a lot to do with where construction, which the CTBUH has been tracking over the past decade. These tion is occurring and the differing floorplates dictated by multiple trends are more consistent than the number of completions, which uses. Concrete is the leading material in China, for instance, where it suggests that the story of tall building composition and purpose is at is easy to come by, and the lion’s share of activity this past year was in least as interesting, and possibly much more nuanced, than that of China. A residential or hotel section with compartmentalized apartpure height and number. ments might best make use of concrete, with its thick cores, smaller ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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spans and sturdy rigidity. An office section may call for large unobstructed floorplates, which is more easily accomplished in steel. As more mixed-use buildings enter the market, it follows that there is an increasing requirement for mixed construction types within a single building.

year. This building was the subject of piracy rumors early last year when a highly similar tower group, the Meiquan 22nd Century in Chongqing, was revealed. The race is on in earnest to see if the original finishes before the “copy.”

• The China Broad Group’s Sky City J220, an (828-meter), 220-story building to Impact of 2013 on the 100 be constructed entirely of prefabricated modules, may or may not have gotten Tallest Buildings in the World underway, according to conflicting reports, Although this was a very successful year in and may or may not complete in 2014. terms of tall-building completions, it has held Either way, the world will be watching. close to the average set for the last few years Unshaken by skeptical peers, the media when it comes to the number of skyscrapers and bureaucratic hurdles, Broad Group of 200 meters or greater to enter the list of Chairman Zhang Yue has vowed the the 100 Tallest in the World. In 2013, 12 project – aiming to become the world’s new buildings entered the 100 Tallest in the tallest before Kingdom Tower takes the World List. In 2012, that number was 13. The title – will continue. all time record since accurate recordkeeping • One World Trade Center, New York, when it completes in 2014 at its began in 1970 was in 2011, when 18 buildintended symbolic 1,776 feet (541 ings finished that year entered the 100 Tallest meters), the building will gain status as in the World list.

Mercury City Tower, Moscow, 1112 feet, completed the United States’ and North America’s An interesting phenomenon also occurred at 2013. Courtesy of Igor Butyrskii. tallest building. the bottom of the 100 Tallest in the World list, • The first of the crop of “superslim” towers in Midtown indicating just how fleeting the status of tall buildings can be today.

Manhattan, New York City, the 1,004-foot (306-meter) Panama’s 932-foot (284-meter) Trump Ocean Club International One57, will complete, upping the ante for its even-slimmer Hotel & Tower, finished in 2011, entered the 100 Tallest in the World rivals along 57th Street. list that year, and was removed in 2013. The Central American nation’s 922-feet (281-meter) Torre Vitri joined Korea’s 932-foot (284-meter) Three International Finance Center in Seoul on the 100 Tallest in the About CTBUH World in 2012; both were out just a year later in 2013.

On the other hand, it took 83 years for the 972.2 foot (282.6-meter) The Council on Tall Buildings and Urban Habitat is the world’s Trump Building at 40 Wall Street (originally the Bank of Manhattan leading resource for professionals focused on the design, conBuilding) in New York, finished in 1930, to be shown the 100 Tallest struction, and operation of tall buildings and future cities. A in the World exit door in 2013. Its place was well-earned – the last not-for-profit organization, founded in 1969 and based at the time this building was “trumped” was in 1930, when the “secret Illinois Institute of Technology Chicago, the group facilitates spire” of the Chrysler Building pushed 40 Wall Street to the status the exchange of the latest knowledge available on tall buildings of “world’s second-tallest” at the very last moment. around the world. The Council also maintains the world’s largest free database on tall buildings, The Skyscraper Center. The CTBUH also developed the international standards Conclusion – And a Look Ahead in 2014 for measuring tall building height and is recognized It’s fair to say that 2013 was a year of recovery and a return to the still as the arbiter for bestowing such designations as “The relatively “new normal” of year-on-year growth in skyscraper comple- World’s Tallest Building.”▪ tions. While zero megatall (1,969-plus feet; 600+ meters) and nine supertall (300-plus-meters) buildings were completed in 2013 (against Daniel Safarik is editor of publications at CTBUH. He was one megatall and nine supertalls in 2012), there was no shortage of formerly director of marketing for Brooks + Scarpa Architects, and activity in planning phases, suggesting that the malaise of the global has written about technology for business publications for 15 years. recession may finally have been shaken off in many regions.

Daniel can be reached at dsafarik@ctbuh.org.

In 2014, we predict between 65 and 90 buildings of 200 meters or more will be completed. This year will no doubt be an exciting Antony Wood is executive director of CTBUH. He is responsible for one, and a year of continued growth. Here is some of what’s in store: the day-to-day running of the Council and steering in conjunction • Up to 13 of the scheduled completions in 2014 will be with the Board of Trustees, of which he is an ex-officio member. supertalls (300 meters or higher).

Based at the Illinois Institute of Technology, Antony is also a Studio • The Torre Costanera, at 984 feet (300 meters), will be South Associate Professor in the College of Architecture at the Illinois America’s tallest building and its first supertall.

Institute of Technology, where he convenes various tall building • Twisting towers will continue to enter the vanguard of tall in design studios. Anthony can be reached at awood@ctbuh.org.

2014 – the KKR2 Tower of Kuala Lumpur, Malaysia, and the Spine Tower of Istanbul, Turkey, lead the list.

The authors gratefully acknowledge research assistance by • A typically curvaceous Zaha Hadid-designed tower, the Marty Carver and Marshall Gerometta of CTBUH. Wangjing SOHO T1, will complete in Beijing, China this STRUCTURE magazine

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June 2014

Structural rehabilitation renovation and restoration of existing structures

T

his article is a continuation of a previous four-part series entitled The Triage, Life Support and Subsequent Euthanasia of an Existing Precast Parking Garage.

Part 4 appeared in the April 2014 issue of STRUCTURE magazine. Pennoni conducted a follow-up structural condition assessment a little more than one year after the original investigation, which was completed in December 2012. The Owner requested the additional evaluation due to a delay in the implementation of the previously recommended temporary repairs and concern about the ongoing deterioration of the garage.

Observations Pennoni observed a few minor additional conditions that related primarily to damage inflicted by snow removal equipment, and also noted an increase in previously observed deterioration, including: 1) The deterioration of the precast, prestressed inverted “T” girders had increased approximately 68% for cracks and approximately 34% at spalls.

Cracks and spalls (including subsurface delaminations) were quantified by measured length and area, respectively, during both the original and follow-up assessments.

2) The deterioration of the doubletee channel slabs had increased approximately 5% for cracks and approximately 9% at spalls.

3) Several parking spaces on the second level had been closed off since the original investigation, typically below existing third-level girders or double tees that were exhibiting increased deterioration.

More significant and severe accelerated deterioration was observed at two specific areas of the garage, including: Level 3 Existing Barricaded Area – At a portion of the third or top level, which had been previously closed off, additional deterioration was evident at the girders located at the perimeter of the barricaded area. At one of the perimeter girders, the exposed prestressing strands had additional section loss, with six strands exhibiting a total or nearly complete loss of cross-sectional area.

Level 3 Precast Double Tees – The 24-inch-deep precast double tees experienced an increase in deterioration of approximately 2% for cracks and 11% at spalls. During the original investigation, cracking and efflorescence was concentrated in the double-tee flanges in the area of the garage closest to the southern or outer arc of the

The Palliation of a Terminally Ill Parking Garage Part 5: The Follow -up

By D. Matthew Stuart, P.E., S.E., F. ASCE, F.SEI, SECB, MgtEng and Ross E. Stuart, P.E., S.E.

D. Matthew Stuart, P.E., S.E., F. ASCE, F.SEI, SECB, MgtEng (MStuart@Pennoni.com), is the Structural Division Manager at Pennoni Associates Inc. in Philadelphia, Pennsylvania.

Ross E. Stuart, P.E., S.E. (RStuart@Pennoni.com), is a project engineer at Pennoni Associates in Philadelphia, Pennsylvania.

48 June 2014

Figure 1.

facility. During the follow-up investigation, it was observed that the cracks in the flanges had migrated down into the stems of the double tees, almost exclusively at the end bearings. The new cracking was severe enough to create large spalls, exposing the embedded reinforcing of the double-tee stem (Figure 1). The exposed reinforcing, which appeared to be associated with the embedded bearing plate assembly, exhibited significant corrosion. Where the cracking was not severe enough to result in spalling of the concrete, the cracks exhibited corrosion by-product (rust) stains, which indicated subsurface deterioration of the internal reinforcing.

Analysis of Accelerated Deterioration Barricaded Area The percentage increase in cracks and spalls observed at the precast double-tee channel slabs and girders was consistent with the 2- to 3-year remaining service life, in the absence of any repairs that the original 2012 Pennoni report predicted. However, the increased deterioration of the girders on the third level at the area closed to parking was a concern. The two perimeter girders were positioned directly below the bollard barricades. Therefore, live loads could still be imposed on these structural members, because parking was allowed in the adjacent tributary areas supported by the same girders. A review of the existing shop drawings for the girders indicated that the member that exhibited the worst reinforcing corrosion was constructed with seventeen ½-inch-diameter prestressing strands. Therefore,

Figure 2.

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based on the observed loss of six strands, the reduction in the capacity of the girder would be approximately 35%.

The imposed loads on the third-level girders are 100 pounds per square foot (psf) of dead load and 40 psf of live load. A 35% reduction of the total load on the girder was required to offset the observed loss of prestressed reinforcement due to corrosion. Therefore, all of the 40-psf live load – which corresponds to 29% of the total service load and 35% of the total factored load – needed to be removed from the girder. As a result of this critical situation, Pennoni notified the Owner of the condition immediately after the condition assessment and recommended that the areas closed to parking on the third level be increased so that no live loads could be imposed on the referenced perimeter girders at the original barricaded area (see Figure 2, page 49).

Precast Double Tees The rapid deterioration of the precast double tees observed at the third level on the outside arc of the garage occurred as a result of three primary factors. First, as indicated in the 2012 Report, the water-soluble chloride content by weight of cement in the double-tee flanges exceeded the ACI recommended limit for precast concrete. Therefore, any internal embedded reinforcement in the double tees would be more susceptible to corrosion.

Second, the affected double tees were located at the outside arc of the garage at the low point of the sloped third level, such that precipitation – including road salts brought in by vehicles – collected in this area. Even though no deicing salts were directly applied to the upper level of the garage, this resulted in a concentration of the contaminated drainage runoff on the surface of deck above the deteriorated double-tee stems. At these same locations, failures and gaps in the sealant used at the joint between the ends of the double tees and support girders, as documented in the 2012 Report, allowed the collected moisture and road salts to penetrate down into the same area of the double-tee stem ends that were exhibiting the worst deterioration.

Third, the 2013-2014 winter weather, which included record-breaking snowfall and an increased frequency and magnitude of freeze-thaw cycles, had also contributed to the accelerated deterioration of the double-tee stem ends. This is because the cracks there were susceptible to damage from freeze-thaw cycles.

The damaged cracks allowed for the infiltration of the contaminated moisture into the embedded stem-end bearing assembly reinforcement, which then resulted in corrosion of the steel.

Figure 3.

The level and severity of the corrosion, spalls and damaged concrete at the stem ends of the double tees indicated that the structural integrity of the bearing conditions had more than likely been compromised at a number of locations. This was of particular concern because there was very little (if any) redundancy available in the existing bearing assembly; therefore, the failure of this portion of the member would be non-ductile (i.e., without warning), which would result in a third-level double tee suddenly and catastrophically collapsing onto the next lower level. This dynamic impact would more than likely also cause, in turn, the collapse of the second-level double tee immediately below.

Pennoni notified the Owner of this unsafe condition immediately after the condition assessment and recommended that several of the double tees be shored. Subsequent conversations with the Owner determined that the recommended shoring could not be installed immediately due to extended lead times involved with retaining a shoring contractor, leading to the decision that the affected areas should be immediately closed from use (Figure 3).

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June 2014

Conclusions The original 2012 Pennoni report concluded that the repair of the garage was neither practical nor technically feasible because of the lack of available long-term methods of repair for the prestressed girder reinforcing in the presence of high chloride content, and that the garage should therefore be demolished and replaced. However, to extend the life of the garage to provide adequate time to design and construct a replacement garage, the report recommended that the girders be temporarily repaired with a passive galvanic system and permanently shored, and that yearly inspections of the garage be conducted.

As a result of the accelerated deterioration that occurred between the end of 2012 and the start of 2014, Pennoni recommended instead that regularly scheduled monthly condition assessments be conducted at the garage, and that the repair work associated with the previous report be initiated within the next year. This approach, in conjunction with the 2014 emergency remediation measures, will ensure that the facility remains partially usable and safe until the new garage can be constructed.▪

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Professional issues issues affecting the structural engineering profession

H

ow will the practice of structural engineering and the industry as a whole evolve from its current state?

What are the opportunities and challenges in our continually changing industry? To answer these questions and more, the ASCE Structural Engineering Institute (SEI) surveyed structural engineering leaders nationwide in January 2013. Questions ranged from basic demographics to operational issues, licensure, and the ranked importance of external influences on the professional in the coming decade. The Business Practices Committee developed many of the questions with the intent of taking the engineering community’s pulse about its concerns and interests; feedback from the survey will have an impact on the committee’s future work.

This article looks at survey responses, indicative of what senior structural engineers anticipate may change in our industry. Based on responses from senior leaders, there is a lot of uncertainty about globalization and the resulting commoditization of the profession.

Despite concern about the future, many respondents recognize the opportunity to improve the relevance and respect of the profession by harnessing evolving technology and improving education and licensure. In the era of BIM and with code updates on a 3-5 year cycle, there is a need to have personnel on staff who are technologically capable. But, the more important need is for management to be able to synthesize new ideas, integrate them into the business quickly and effectively, maintain consistency with the engineer’s standard of care, and ultimately, be profitable.

SEI Survey: Current Business Practices and Future Expectations

By Stephanie Slocum, P.E. and Steve Wilkerson, Ph.D., P.E.

Stephanie Slocum, P.E., is an Associate with Hope Furrer Associates, Inc. She may be reached at sslocum@hfurrer.com.

Steve Wilkerson, Ph.D., P.E., is Vice-President at Cardno Haynes Whaley. He may be reached at stevew@ziasoftware.com.

Survey Demographics Invitations for the online survey were emailed to 10,065 members of SEI and NCSEA and 352 completed responses were received, resulting in a 3.5% response rate. 72% of respondents represent senior leadership positions such as owners, presidents, and lead engineers of their respective firms. The remaining respondents include project managers and senior/project engineers.

78% of respondents have more than 5 years tenure at their current employer, and 25% have more than 25 years tenure. Approximately half identify “structural engineering consulting firm” as the primary practice type. The remaining respondents include those within academia, large A/E or E/A firms, government, and specialty areas such as forensic engineering. Most respondents (86%) work in the private sector. 50% of respondents work at firms with 25 or fewer total staff, and 17% are employed at firms with

52 June 2014

more than 500. Most respondents serve one or more market sectors, with commercial the predominant sector (84%.) The other most heavily represented sectors include K-12/higher education (65%), industrial/energy/defense buildings (62%), healthcare (58%), and multifamily residential (58%). The top three client bases are building owners, contractors, and architects at 71%, 67%, and 62%, respectively.

Survey Results Results indicate four primary areas of potential changes and opportunities: globalization, education requirements (both academic and continuing education), licensure, and technology.

Engineering as a Commodity How do survey respondents expect the engineering profession to change in the next 10-30 years? Figure 1a illustrates that more than 50% are concerned that structural engineering services will become a commodity. Many see a direct correlation between globalization and commoditization of the industry due to both increased global competition and the automation of analysis and drafting. One responder noted, “Globalization is increasing the availability of engineers for working on projects, putting a lot of downward pressure on U.S. (engineer) labor rates. Conversely, inconsistent registration and continuing education requirements are making it very expensive for the individual to maintain licenses.

Thus the individual engineer sees salaries declining, but the cost to be an engineer increasing.”

Further exploring this question, how do senior leaders anticipate their individual firms will adapt in response to the larger anticipated industry changes? The question posed in Figure 1b dealt with training and licensure issues. More than half of respondents acknowledge licensure needs to evolve; however, a larger percentage indicated an emphasis on training, academic, and continuing education. Nearly three out of four (72%) thought the way we train engineers in the workplace would have to change.

Educating the Engineer To attract and retain future structural engineers, respondents expect to see significant future changes to education. Most agree we will see changes in the following areas: • on-the- job training (72%), • academic education (68%), • continuing education (64%), and • licensure requirements (54%).

Respondents that typically hire engineers with a Masters degree are 27%, while the remainder hire candidates with either a Bachelors or a Masters degree. At the same time, only 23% of responders

Rate your agreement with the following statements on how you expect to see change in the next 10-­‐30 years: Contractor-­‐led procurement threatens the independent professional stature of future structural engineers

46%

Contractor-­‐led procurement will provide new opportuniAes for future structural engineers

45%

Increasing globalizaAon threatens to commodiAze the future of structural engineering

53%

Increasing globalizaAon will posiAvely affect future structural engineers

27%

Evolving automaAon threatens to commodiAze the future of structural engineering

59%

Evolving automaAon will posiAvely affect future structural engineers

42%

Structural engineers will have wider responsibiliAes on future projects

54%

Structural engineers will have a expanded roles in future projects

48%

Figure 1a. Respondents’ expectations of future industry change.

Figure 1b. Respondents’ anticipated adaptations to future change.

Does your firm offer and fund any of the following types of training?

Offer "other" training type not listed

5.6%

Offer user groups or roundtable discussions

19.5%

Offer a corporate university program

9.9%

Offer execu>ve coaching

12.7%

Offer outside training seminars, conferences, or classes

69.5%

Offer reference books or materials for self-­‐study

52.0%

Offer online training system

40.1%

Offer in-­‐house training by an outside consultant

35.0%

Offer in-­‐house training by firm employees No funded training at this >me, we hope to soon Do not offer any training

indicate “students are generally well prepared when they start their careers at your firm.”

45% indicate “there is considerable variation from one school to the next, so we are careful from which school we select engineers.”

Notable disagreement occurs among responder comments regarding academic education. Some comment that engineering education is too broad and students do not graduate with sufficient technical skills. Others note graduates have insufficient written and communication skills. Comments staunchly in favor of graduate education requirements contrast with those who believe additional education requirements will cause “unnecessary burdens.”

Gaps between theory knowledge and practical knowledge in some college programs are also noted. Interestingly, 92% of respondents indicate they only have specific knowledge of the academic program and university from which they graduated. This suggests that varied opinions on education may be based more upon specific personal experiences, versus a broad knowledge of recent graduates or the education curriculum in general.

Continuing education and training opportunities after graduation also vary widely. Figure 2 illustrates that 69.5% of firms offer out-of-firm funded training such as seminars, conferences, or classes. 20% offer no funded training opportunities. Interestingly, several responders in leadership positions comment that they will need to provide better training and continuing education opportunities in the future to retain employees. “As new generations of professionals come into the organization, they will want formal programs that will move the companies in that direction in order to attract and retain talent,” according to one respondent.

The quality and relevancy of continuing education requirements is also of general concern.

One responder notes, “The continuing education requirements have created an industry unto itself, which charges confiscatory rates for classes that have little to do with what most of us…use day-to-day.” Multiple responders indicate the frequency of code revisions causes a challenge with regard to continuing education: “The codes are continually changing... for the better, I’m not sure, to be exhaustively confusing...that’s a definite yes.”

55.1% 4.3% 15.0%

Figure 2. Methods of providing continuing education and training.

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Stamp of Approval Many of those surveyed saw licensure concerns, continuing education, and code revisions to be linked. “Frequent code changes make keeping up with the definition of the ‘standard of care’ more challenging,” states one responder. “Creating a national license will help reduce the efforts to get renewals

Rate the influence of each of the following on the poten2al to drive change in your profession in the next 10-­‐30 years: Other influences

10% 53%

Environmental influences 35%

Social influences

45%

Poli0cal influences

73%

Delivery methods 63%

Globaliza0on

93%

Technology

Respondents recognize both significant opportunities and challenges in the area of technology. One respondent notes “Structural engineers will need to find new ways to develop their skills and roles in projects. Automation of analysis and design will replace the work of the early years of SEs’ training. This will eliminate some of the important present training activities, and require engineers to enter the work force at a higher level…Our role could evolve into a higher level of contribution to project conceptualization and success.”

Interpretation of Survey Findings

71%

Educa0on

Figure 3. Moderate or strong influences with the potential to drive industry change.

completed so more time is (available) for other things like education.”

Who pays for licensure? 62% of respondents’ firms pay for licensure exam fees.

37% also provide paid leave for exams, and 28% provide paid exam prep classes.

86% of respondents indicate their employer pays for professional registration fees in at least one state. Responders across the board have concerns about inconsistencies between states regarding licensure. As one respondent succinctly notes, “Structural engineers need to do a better job of selfregulating licensure.”

The Human Side of Technology Technology is clearly rated by respondents to be the strongest potential influence and driver of change as shown in Figure 3.

New technologies create both challenges and opportunities. Several responders note concerns related to the automation of analysis resulting in “designs without a full understanding of overall (structural) performance.” Not surprisingly, there were also many comments regarding BIM, both positive and negative.

What do these findings tell us? Our interpretation is focused on how the structural engineer is positioned for business.

The following two key questions emerge from the results above that affect how we run our businesses: 1) Does globalization of the engineering profession mean commoditization of structural engineering services?

2) How do external pressures and constantly changing factors affect our ability to provide a high quality product that will ensure the success of our individual firms?

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Guarding the Industry Question 1 clearly raises concerns. Fear of commoditization would devalue the profession as engineering services become cheaper to obtain in a global market. However, the potential problem is more or less self-correcting; firms charging low fees in order to compete may find their work quality suffers.

Commoditization suggests the overall quality of the product would be less in the long term.

If a firm continually rises to the challenges of a changing environment by attracting top talent and performing high quality work, it will be recognized as a resilient and reliable business partner that contributes value to projects commensurate with their fee structure. These firms will continue to be successful.

Turning Change into Opportunity There is clearly a positive side to change and this is reinforced by the significant optimism in how structural engineers see the future (Figure 1a). However, there is no question that the majority of engineers think that changes such as globalization, automation, and new procurement methods are more likely to negatively impact the profession. Engineers are largely analytical and driven by facts, so it is not surprising they are willing to accept negative outcomes from forces beyond their control. However, with the exception of the response to changes due to globalization, the number of respondents with a positive outlook was 40% or more of the total.

One response from the survey question “What opportunities are created or challenges are caused by changes in your profession?” speaks to this point while clearly demonstrating the tendency of structural engineers to remain grounded in reality, as follows: “Inherently, Structural Engineers are excellent problem solvers. We are capable of processing large amounts of data from multiple sources, and developing safe and economical solutions to very complex problems. This makes us capable of becoming leaders in the business of providing extremely valuable services to the societies in which we

live. Unfortunately, we have allowed lawyers, insurance companies, politicians, global corporations, banks, and investment firms to devalue our professional worth. Hence, I strongly believe that structural engineers have a duty to band together as a collective entity, use our superior problem-solving abilities, and wisely use the influence we have left to improve the societies we serve...”

Balancing Technology and Experience From Question 2, we can draw some conclusions about what structural engineers identify as the most important ways to influence the quality of their work. Figure 3 shows that among senior leaders, the three strongest factors driving change are delivery methods, technology, and education. Of these, technology seems to be a universally accepted factor, as 93% of respondents acknowledge that it has an impact.

Presuming that technological improvements continue to make analysis and design a more automated task, respondents recognize the need to manage the integration of technology into the design process. One comment succinctly states, “the industry’s dependence on technology is increasing so fast that graduates do not have a good grasp on the basics of design.”

The increasing adoption of technology has direct implication on training; as junior engineers rely more on technology, it will require the engineer of record to be more involved in the training process. Junior engineers likely know the software well, but lack the experience to be able to recognize questionable outcomes. The engineer of record fulfills the role of a “detached overseer” who is relying on his experience to anticipate expected outcomes.

The Ongoing Education Process Figure 1b indicates that senior leaders see a need to change the way junior engineers are trained to do their jobs. This, combined with over half of respondents expecting changes in licensure, indicates that the way we practice

The SEI Business Practices Committee: Chair, Joseph Di Pompeo, P.E., SECB, M. ASCE – President, Structural Workshop, LLC Amol (Andy) Fulambarkar, P.E., M. ASCE – Principal, Soil & Structure Consulting, Inc. Paul Hause, P.E., M. ASCE – President, Structural Consultants, Inc. Patrick McCormick, P.E., M. ASCE, F.SEI – President, Brander Construction Technology Scott Rosemann, P.E., M. ASCE, LEED AP – C.O.O., Rosemann & Associates, P.C. STRUCTURE magazine

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Sidebar In 2011, the SEI Board of Governors (BOG) met and identified four strategic initiatives for the board as they move forward. They are: 1) Expectations and Role of the Future Structural Engineer 2) Structural Engineering Licensing 3) Continuing Education 4) International Links and Globalization As shown in the survey data for the type of changes expected in the next 10-30 years and the drivers and influences in the SE industry that were collected for this report, the respondents’ views are closely aligned with those of the BOG’s. It is apparent by the BOG’s actions and the survey results that we, as structural engineers, will need to address these issues. project oversight may need to adapt. With concerns about the fast-paced code cycle, experienced engineers are also under the gun to keep their knowledge up-to-date while managing production staff.

Engineers don’t believe in a quick fix either.

The discussion about the continuing education process and the effectiveness of classes provided by CEU consulting firms indicates that engineers would rather be responsible for training their own people. The training process is an ongoing one for EITs who develop the proficiency needed to pass licensure exams. If engineers are only trained to “pass the test”, they will fail to develop the engineering judgment needed for the unique requirements of each project. This fact connects the concerns seen in survey responses about the need for changes in licensure and training/education, and the threat of commoditization of the profession.

SEI Visioning and Strategic Initiatives The survey results and interpretations present interesting insight into current and anticipated concerns for practicing engineers. From a larger perspective, the results also validate the SEI Strategic initiatives (see sidebar). As practicing engineers, we continually see change, but in the short term can fail to acknowledge the need to adapt. To find out more about the Vision for the Future of Structural Engineering: A Case for Change, you can read the 2013 report from the SEI Board of Governors (available at www.asce.org/sei/about-sei/ under Strategic Visioning), which contains additional information about the survey and recommendations for further action.▪

InSIghtS new trends, new techniques and current industry issues

T

ypically, the term fiber reinforced polymer (FRP) composite is used to describe product applications in the aerospace, military or recreational industries, (e.g. skis, boats, race cars, or golf clubs). However, over the last twenty-five years, the civil infrastructure industry has been conducting continual testing and multi-million dollar project applications of FRP composite materials.

Even though the other abovementioned industries have remained the primary consumers, the use of FRP composites in civil infrastructure is fast becoming a major contender.

History of FRP The 1980s brought the first applications in the FRP industry, where research and testing was successfully completed to structurally strengthen and rehabilitate concrete columns as an acceptable alternative to steel jacketing. Its first major breakthrough occurred when seismic retrofits successfully increased the ductility of full-scale reinforced concrete bridge columns (Figure 1). Later testing expanded to include full-scale tests of wall specimens, a five-story masonry research building, a six-foot diameter column and column-arch rib joints. These remarkable tests provided the necessary avenue to develop the industry. To date, the number of applications have grown in leaps and bounds.

Thirty years of testing, designing, and installing FRP systems has proven to be an effective retrofit solution when properly implemented.

This implies that structural testing and research are no longer limited to just retrofitting bridge columns, but have now been broadened to

Structural Strengthening using Fiber Reinforced Composite Systems The State of the Industry

By Scott F. Arnold, P.E.

Scott Arnold, P.E., is the Director of Engineering and Research & Development at Fyfe Company. He has been working with the Fyfe Company on the design and development of FRP strengthening systems for the last twenty years. Scott can be reached at scott@fyfeco.com.

Figure 2. Various applications of FRP systems.

56 June 2014

Figure 1. Testing and repair of a full-scale bridge column.

investigate other structural elements, such as beams, slabs, walls, and pipes in order to provide shear strengthening, flexural strengthening, axial load strengthening, lap splice enhancements, corrosion repair & protection, and blast mitigation (Figure 2). Recent tests have focused on developing various ways of anchoring and detailing FRP systems in order to improve efficiency and deal with complex geometries. Although there has been a vast amount of research completed, there are still budding areas which have not been fully explored, including using FRP to strengthen steel structures and to provide additional shear resistance to plywood and gypsum wall buildings. As this industry continues to grow, there will always be a corresponding increase in the advances and uses of the FRP composite materials.

Evolution of FRP With each passing year, the number of projects designed and installed can range in price from thousands to multi-million dollars. As engineers become more comfortable and confident with the abilities of FRP, there has also been a

Summary of required testing per ICC AC 125.

Large-Scale Structural Testing

Composite Testing

Environmental/Durability Testing

• Columns • Beam-column joints • Beams • Walls • Wall to floor joints • Slabs

• Young’s Modulus • Poisson’s Ratio • In-Plane Shear Modulus • Coefficient of Thermal Expansion • Glass Transition Temperature

• Exterior Exposure • Freezing and Thawing • Aging • Alkali Soil Resistance • Fire-Resistant Construction • Interior Finish • Fuel Resistance • Adhesive Lap Strength • Bond Strength • Drinking Water Exposure

past applications. This means each project will have its own clearly-defined performance criteria, which will be met using the approved design guideline, in order to satisfy the desired design goal. That being said, the contractor also plays an important role in the installation of the FRP composite. If they are not properly trained or certified, this could potentially be a weak link in the success of the FRP system. It is always noteworthy to compare each project with conventional repair methods. Even though FRP is a high cost composite, high strength properties, the ease of installation and the lightweight/low-profile nature have turned it into an excellent tool for strengthening and rehabilitating a variety of structures.

Conclusion The FRP industry first began with seismic retrofits of bridge columns, but has since gained momentum in its variety of applications. Even with the vast amount of research completed, there are still areas where the capabilities of this powerful strengthening tool have yet to be discovered. As research progresses and continues to prove the effectiveness for numerous applications, it will always be necessary to concurrently investigate cost compared to conventional retrofit solutions. This will afford a true understanding of how these relatively expensive materials provide a cost benefit when all aspects of the installation process are considered. At the end of the day, as technology advances and the FRP industry continues to grow, we expect to see the true potential of this industry begin to flourish in the years to come.▪

Figure 3. World map – countries with FRP design guidelines/code requirements.

the main objective of AC 125 is to provide confidence to the engineering community in regards to the design and installation of the FRP materials when directly compared to conventional repair methods.

Since this time, the American Concrete Institute has developed, concurrently with the ICC, a design guideline of Software and ConSulting FRP composites for both concrete (ACI 440.2R-08) and masonry structures (ACI 440.7R-10). This eventually sparked a global chain reaction with FLOORVIBE v2.10 • Software to Analyze Floors for Annoying Vibrations over 30 countries around the world now • New release using an approved FRP design code or • Demo version at www.FloorVibe.com • Calculations follow AISC Design Guide 11 Procedures guideline (Figure 3), including Canada • Analyze for Walking and Rhythmic Activities (CSA S806-12), United Kingdom (TR • Check floors supporting sensitive equipment • Graphic displays of output 55/TR 57), Germany (Allgemeine • Data bases included Bauaufsichtliche Zulassung), and New CONSULTING SERVICES Zealand (CodeMark).

• Expert consulting available for new construction In the end, no matter the size or locaand problem floors. tion of the project, each design and Structural Engineers, Inc. installation is unique and no assumpRadford, VA 540-731-3330 tmmurray@floorvibe.com tions can be made purely on the basis of

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growing need to create a design guideline and code for these materials, due to the differences between the different types of systems (e.g. glass fiber systems, carbon fiber systems or aramid fiber systems).

After the 1994 Northridge Earthquake in Southern California, the International Code Council (ICC) Evaluation Service developed the first acceptance criterion for the use of FRP systems as an approved building material, per current building codes, to strengthen both concrete and masonry structures. This acceptance criterion (AC 125) not only states the design requirements for the FRP systems, but also describes the required large-scale structural testing, physical and mechanical properties testing, environmental and durability testing, and quality control measures necessary during installation to obtain approval. The Table gives a brief list of all the required testing to meet the abovementioned requirements. Ultimately,

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discussion of legal issues of interest to structural engineers

LegaL PersPectives

Couldn’t Care Less: A Malpractice Primer for Structural Engineers Part 1

By Matthew R. Rechtien, P.E., Esq.

To entitle a plaintiff to maintain an action, it is necessary to show a breach of some legal duty due from the defendant to the plaintiff.

Cox v. Burbidge (1863).

That great principle of the common law… declares that it is your duty so to use and exercise your own rights as not to cause injury to other people. Gray v North-Eastern Rail Co (1883).

The business of the law of torts is to fix the dividing lines between those cases in which a man is liable for harm which he has done, and those in which he is not…. The law of torts abounds in moral phraseology (The Common Law, Oliver Wendell Holmes, Jr).

With an understanding of claims and liability, we turn to torts, the very name of which originates from the French word for “wrong.” Simply put, torts are a species of claim, or cause of action, and therefore a species of liability.

What kind of claim are they? According to the Georgia Supreme Court (in Union Tel Co v Taylor), torts are claims founded on breaches of non-contractual duties that the law imposes on one party with respect to another. “Non-contractual” is a critical qualifier, for the touchstone of contractual is consent. Thus, tort duties are those that the law imposes, in certain circumstances, regardless of consent.

The estimable jurist, Oliver Wendell Holmes, Jr., ably drew the distinction in his magnum opus The Common Law:

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Justice Holmes’ quote reflects another truth: torts are a broad topic within the law. There is a great variety of them. Indeed, not all torts are “sins” of commission. Torts arise from not only malfeasance, but nonfeasance and misfeasance, too. The law, to illustrate by a simple example, imposes a duty to drive with reasonable care, regardless of consent. A driver may breach that duty by nonfeasance (e.g., neglecting to brake), misfeasance (e.g., making too wide a turn), and malfeasance (e.g., speeding). This example illustrates another important concept in tort law.

Although tort law tells us how we should drive, it does not require us – as a general matter – to drive. In other words, tort law, with few exceptions, does not require action, but, if we do act, it governs our actions.

In terms of substance, there are as many specific torts as kinds of conduct that society eschews. There are intentional torts, like battery and libel. There are property torts, like trespass and conversion; strict torts, where liability attaches regardless of care or intent.

Then there is negligence, a tort that arises from one’s failure to act with proper care. continued on next page

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STRUCTURE magazine

Kinds of Torts, and Negligence Generally

RINE ENG MA I

The liabilities incurred by way of contract are more or less expressly fixed by the agreement of the parties concerned, but those arising from a tort are independent of any previous consent of the wrong-doer to bear the loss occasioned by his act. If A fails to pay a certain sum on a certain day, or to deliver a lecture on a certain night, after having made a binding promise [i.e., a contract] to do so, the damages which he has to pay are recovered in accordance with his consent that some or all of the harms which may be caused by his failure shall fall upon him. But when A assaults or slanders his neighbor, or converts his neighbor’s property, he does a harm which he has never consented to bear, and if the law makes him pay for it, the reason for doing so must be found in some general

Justice Holmes’ final line is the nub of the duties tort law imposes on us all; they arise from society’s (typically through the judicial branch) view as to the norms of acceptable conduct.

&

Understanding the basics of tort law presumes an understanding of liability. Liability is legal responsibility. As the Idaho Supreme Court put it in Feil v. Coeur, liability is the condition of (in certain circumstances) being bound by law and justice to pay an indebtedness or discharge an obligation. Or, put differently by the California Supreme Court in Lattin v.

Gillette, liability is the state or condition of a person after he has breached a legal obligation. Although there are all sorts of liability (contractual, equitable, criminal, etc.), at the end of it all, liability, its imposition and avoidance, is what tort law is all about. That

Torts, Generally

view of the conduct which every one may fairly expect and demand from every other, whether that other has agreed to it or not.

ETY OF NAV A CI O

Liability and Claims, Background

is because the liability of one arises from the claim of another. A claim, also called a “cause of action,” is a set of facts that, if established, invest a person with a right to relief, enforceable in court. In a word, then, a claim is what creates liability.

• THE ERS S NE

Tort – the word is familiar (even in a nonpastry context), as are its menacing children: malpractice and negligence. They trigger visceral reactions in many a structural engineer (and lawyer). The word “tort” creeps in and out of the public consciousness, perhaps most often with its partner du jour: “reform.”

We hope to avoid torts. As structural engineers, however, we cannot ignore them, for tort law sets the standard that our professional engineering services are expected to meet or exceed.

The purpose of this article, the first in a two-part series, is to provide the reader with a basic understanding of the building blocks of tort law generally, before graduating on to explore the fundamentals of malpractice law, for, as the proverb says, “better the devil you know than the devil you don’t know.”

In this last category lies this article’s subject. Even negligence, however, subdivides into a number of categories: ordinary negligence, gross negligence, and negligence per se, to name a few. Gross negligence is a conscious act or omission in reckless disregard of a legal duty and of the consequences to another. Negligence per se is typically negligence that arises from violation of a statute. Finally, ordinary negligence arises from the lack of using “ordinary care.”

This article and the second installment to follow, concerns professional negligence, commonly known as malpractice.

Malpractice What is malpractice then? Black’s Law Dictionary defines malpractice as “[a]n instance of negligence or incompetence on the part of a professional.” In short, malpractice is professional negligence. It is a kind of tort, a kind of claim. It gives rise to certain liability.

As a kind of claim, malpractice consists of a set of facts to be established, elements, if you will. The elements of malpractice are a duty, its breach, resulting damages, and a causal link between the two. We close this article by examining that first element – duty – before turning to the others in Part 2.

Duty “[O]bjective standards [for the level of care owed by professionals] avoid the evil of imposing a different standard of care upon each individual.”

Heath v Swift Wings, Inc (1979).

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The practice of structural engineering imposes on its practitioners the duty to exercise the ordinary (customary) skill of the profession. Although each jurisdiction’s

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Having defined the duty of structural engineers, the question arises: to whom is this duty owed. formulation varies somewhat, the Minnesota Supreme Court, in Richard Dempsey Contracting Co, Inc v Atlas Pile Driving Co, ably put it: “[o]ne who … render[s] professional services is under a duty … to exercise such care, skill, and diligence as men in that profession ordinarily exercise under like circumstances.” If he or she does not, he or she has committed malpractice.

This deceptively simple formulation packs several concepts that are central to malpractice law. First, as the Wisconsin Supreme Court held in Nowatske v Osterloh, the care required is not the care an “average” member of the profession would exercise; that would suggest that half of the members of the profession could not meet the standard. Instead, the required care is that which members of the profession would ordinarily exercise under like circumstances.

Second, courts measure the required care objectively. They compare the care that structural engineers use against that benchmark, rather than their own personal abilities or habits. And although this objective standard may be hard to measure (more on that below), the care that structural engineers “ordinarily exercise under like circumstances” simply does not vary engineer to engineer.

Third, in describing the care a structural engineer must take, the above-formulation also clarifies the limitations of a structural engineer’s obligations. For example, because an engineer need only exercise ordinary care, it is not a warrantor of his or her plans. In other words, an engineer is not liable (at least not in malpractice) for every aspect of his or her design that causes injury – only for those where the engineer failed to exercise proper care. As another, an engineer has no legal obligation to “be the best.” He or she need only be ordinary.

Fourth, as a malpractice claim inevitably presents the question of what care is ordinary in the profession, it usually invites the admission of expert testimony. In Aetna Ins Co v Hellmuth, Obata & Kassabaum, Inc, for example, a federal appeals court confirmed that where a design professional is engaged in work that is technical in nature, and not a matter of common knowledge, a plaintiff must offer expert evidence on the standard of care to give the jury sufficient evidence on which to make a determination. The exception, of course, is the rare

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case where that degree of care is obvious to the layperson. In MJ Womack, Inc v State House of Representatives, for example, a Louisiana case, a court held that expert testimony was unnecessary to prove that an engineer’s failure to discover and design around non-removable x-bracing in a renovated structure breached the standard of care.

One final observation: the standard of care varies with the specialization of the profession.

Multiple courts have held that specialists who hold themselves out as having higher skills are held to a higher standard of care.

Having defined the duty of structural engineers, the question arises: to whom is this duty owed. Put differently: who are the potential plaintiffs? In days gone by, that class was often limited to those who hired the professional. Thus, the 1926 case of Geare v Sturgis dismissed a claim against a design professional for injuries suffered from a roof collapse, holding that the design was not liable to third parties, after the owner accepted the project. That restriction has eroded steadily (if not uniformly) over the years. In a 1959 case (Pastorelli v Associated Engineers, Inc), the Rhode Island Supreme Court held that a design professional owed his duties not just to his employer, but also to future patrons of the building.

In the second article in this series, we will continue by examining the other elements of, and common defenses to, malpractice claims.▪ Matthew R. Rechtien P.E., Esq., (MRechtien@BodmanLaw.com), is an attorney with Bodman PLC in Ann Arbor, Michigan, where he specializes in construction law, commercial litigation, and insurance law. Prior to becoming a lawyer, he practiced structural engineering in Texas for five years.

Disclaimer: The information and statements contained in this article are for information purposes only and are not legal or other professional advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances. This article contains general information and may not reflect current legal developments, verdicts or settlements; it does not create an attorneyclient relationship.

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CASE BuSinESS PrACtiCES

business issues

Not Your Grandfather’s Risks Anymore

By Brent White, P.E., S.E., SECB

T

he Author recently had a conversation with a structural engineer who has been retired for over fifteen years. During his career, he observed many changes in the practice of structural engineering and the tools available to assist in his practice. The conversation turned to the current state of structural engineering and the many challenges today’s practicing structural engineer faces. He was amazed at the various “balls that need to be kept in the air” to successfully practice engineering and compete in today’s marketplace.

These differing challenges are really an identification of risks we face as we practice structural engineering today. The list of risks is lengthy. In reality, the practice of engineering is a practice of managing risks. The very act of analyzing and designing a structural system of any type is recognition of risk and the ability to apply physics, mechanics, skill and some artistic license to manage understood risk.

Beyond the science of engineering, our practices face risks that must be properly managed if we are to remain competitive in the marketplace. This engineering market we are all part of places risk on us and our firms. Project delivery methods, projects schedules, fee pressures, scope creep, the level of expectation from client and owner, the use of building information modeling (BIM), expanding codes and design guidelines are all examples of increased challenges and risks that the retired engineer, mentioned above, may not have been forced to deal with.

From the author’s personal experience, the only reasonable way to recognize, understand, and manage risk is to have risk management be an integral part of firm culture. Risk management is everyone’s business. Maybe a better way to say it is that it is an obligation of every member of the firm. With varying degrees of experience and understanding, it can be a daunting task to keep everyone on the same page relative to risk management and risk avoidance. Active participation in professional associations is an essential element in developing a firm culture of excellent technical skills and successful business practice. Technical training and knowledge gained through professional associations is vital. Just as vital is the knowledge and understanding available though professional associations such

He was amazed at the various “balls that need to be kept in the air” to successfully practice engineering and compete in today’s marketplace. as CASE (Coalition of American Structural Engineers) relative to crucial business practice and risk management.

CASE has outlined 10 foundations of risk management and business practice activities providing value to members. The foundations are: Culture, Prevention & Proactively, Planning, Communication, Education, Scope, Compensation, Contracts, Contract Documents, Construction Phase. CASE has developed numerous products around these foundations that assist firms in addressing business practice issues and developing risk management skills. There are over 60 guidelines, contracts, and other tools that directly address many of the challenges mentioned in this article. These tools can help practicing structural engineers and firms enhance risk management development and business practices knowledge.

One example of an excellent publication that most firms can benefit from is A Guide to the Practice of Structural Engineering. This document is a concise training tool for younger or inexperienced engineers that teaches the business of consulting structural engineering.

Most engineers complete academic studies feeling much more confident in technical skills with little understanding of how the business of engineering works.

A Guide to the Practice of Structural Engineering is an updated and revised tool that can assist in the acclimation of less experienced structural engineers to the business and operation of a successful consulting engineering business. This concise and invaluable document was developed by a group of structural engineers who, through their collective experience, recognized the need to speed up the development of young engineers.

The PDF format allows the user to learn the various aspects of the consulting engineering business by topics. The user can learn and understand in a self-paced atmosphere,

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and can verify his/her understanding by completing the interactive quiz at the end of each section. This tool is also a great refresher for more experienced engineers that are beginning to face the demands of project and business management.

A second example is a tool entitled Create a Culture for Managing Risks and Preventing Claims. Centered around the foundation of Culture, this tool outlines methods and activities that are intended to help a firm in developing a culture of risk management and claims prevention. Changing the culture of an organization that has been deeply embedded can be challenging, however this tool was developed to assist firms in meeting this challenge. The recommendations and methods are adaptable to any firm size, and are structured to assist in developing and understanding that risk management begins at the cultural level of the firm.

Today’s challenges can be met. It requires a different set of tools and knowledge than the aforementioned retired engineer may have needed, but those tools are available, and the author finds them invaluable.▪ Brent White, P.E., S.E., SECB (brentw@arwengineers.com), is president of ARW Engineers in Ogden, Utah. He serves as the chair of the CASE Toolkit Committee and is a past-president of the Structural Engineers Association of Utah.

A listing and description of all CASE publications can be found on the CASE website, www.acec.org/case. All tools are free of charge for CASE member firms. Tools are available to non-member firms for nominal fees. If you are interested in joining CASE, refer to the website or contact Heather Talbert, htalbert@acec.org.

Work quickly.

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Analysis, design & investigation of reinforced concrete beams & one-way slab systems

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Finite element analysis & design of reinforced concrete foundations, combined footings or slabs on grade

StructurePoint’s suite of productivity tools are so easy to learn and simple to use that you’ll be able to start saving time and money almost immediately. And when you use StructurePoint software, you’re also taking advantage of the Portland Cement Association’s more than 90 years of experience, expertise, and technical support in concrete design and construction.

Visit StructurePoint.org to download your trial copy of our software products.

For more information on licensing and pricing options please call 847.966.4357 or e-mail info@StructurePoint.org.

STR_7-13

TALL BUILDINGS GUIDE Software ADAPT Corporation Phone: 650-306-2400 Email: info@adaptsoft.com Web: www.adaptsoft.com Product: ADAPT-Edge for Load Takedown and Column Design Description: The ideal tool for rapid load takedown and column design of concrete buildings. Offers both a tributary-based and 3D FEM analysis loading of columns. Use Edge’s integrated column design module or export all tributary and load values into a flexible XLS format. Seamlessly imports building models from Revit Structure.

Product: ADAPT-ABI for 4D Geometry Control for Buildings Description: Model building frames and calculate critical geometry control factors, including differential shortening of supports, required superelevation of levels, and long-term deformation of critical structural elements. Using an intuitive 4D construction phase planner, time-dependent effects of phasing, creep, shrinkage and relaxation of steel are explicitly considered.

Bentley Systems Phone: 610-458-5000 Email: katherine.flesh@bentley.com Web: www.bentley.com Product: RAM Structural System Description: A specialized engineering software tool for the complete analysis, design, and drafting of both steel and concrete buildings. It optimizes workflows through the creation of a single model by providing specialized design functions for buildings and by providing thorough documentation.

Product: AECOsim Building Designer Description: A single building information modeling (BIM) software application for multidiscipline teams. Enables architects, structural, mechanical, and electrical engineers to design, analyze, construct, document, and visualize buildings of any size, form, and complexity. It includes capabilities of former products: Bentley Architecture, Bentley Mechanical, Bentley Electrical, Structural Modeler.

Concrete Masonry Association of California and Nevada (CMACN) Phone: 916-722-1700 Email: info@cmacn.org Web: www.cmacn.org Product: CMD12 Description: Structural design of reinforced concrete and clay hollow unit masonry elements.

Design of masonry elements in accordance with provisions of Ch. 21 – 1997 UBC, 2001 – 2013 CBC or 2003 – 2012 IBC and 1999 – 2011 Bldg.

Code Requirements for Masonry Structures (TMS 402/ACI 530/ASCE 5).

expertise in tall building design and construction

CSC

New Millennium Building Systems

Phone: 877-710-2053 Email: sales@cscworld.com Web: www.cscworld.com Product: Fastrak Description: An essential design and drafting software for steel buildings. Structural engineers use Fastrak to design simple or complex steel buildings.

Produce clear and concise documentation including drawings and calculations, all to US codes.

Phone: 260-868-6000 Email: kevin.disinger@newmill.com Web: www.newmill.com Product: Steel Joists, Decking and Castellated Beams Description: New Millennium engineers and manufactures steel joists, metal decking, FreeSpan castellated and cellular beams. Our free BIM steel joist design component is available for download at the website.

Product: Tedds Description: A powerful software that will speed up your daily structural and civil calculations. Using Tedds you can access a large library of automated calculations or write your own, while creating high quality and transparent documentation.

Devco Software, Inc. Phone: 541-426-5713 Email: rob@devcosoftware.com Web: www.devcosoftware.com Product: LGBEAMER v8 Description: Analyze and design cold-formed cee, channel and zee sections. Uniform, concentrated, partial span and axial loads. Single and multi-member designs. 2007 NASPEC (2009 IBC) compliant. ProTools include shearwalls, framed openings, X-braces, joists and rafters.

Integrated Engineering Software Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis Description: A great tool for tall building design including area loads, streamlined design features, and a “stay out of your way” attitude. Tall buildings are more than just a “total model” and VisualAnalysis is excellent for all kinds of investigations and analysis.

ITW Red Head Phone: 630-338-6491 Email: marketing@itwccna.com Web: www.itwredhead.com Product: Truspec Design Software Description: Using Truspec anchor calculation software, architects and engineers can now design concrete anchoring connections in minutes in accordance with ACI 318 Appendix D.

Nemetschek Scia Phone: 877-808-7242 Email: info@scia-online.com Web: www.nemetschek-scia.com Product: Scia Engineer – New Version Description: Easily plug structural design into your Tall Building workflow. Leverage complex architectural models into analysis and pass back optimized models for coordination. Link your custom calculations and checks to Scia Engineer’s advanced FEA engine. Create professional engineering reports that are simple to update as designs change. Try for FREE!

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Powers Fasteners Phone: 985-807-6666 Email: jack.zenor@sbdinc.com Web: www.powers.com Product: Powers Design Assist Description: Software to design to ACI 318 Appendix D.

RISA Technologies Phone: 949-951-5815 Email: info@risatech.com Web: www.risa.com Product: RISAFloor Description: RISAFloor and RISA-3D form an unrivaled building analysis and design package.

Modeling has never been easier whether you’re doing a graphical layout, importing a BIM model (from Autodesk Revit Structure), or prefer spreadsheets.

Full code checks and optimization for six different material types.

S-FRAME Software Inc. Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: S-FRAME Analysis Description: A powerful, efficient 4D structural analysis and design environment with fully integrated steel, concrete and foundation design and optimization tools. Use S-FRAME to perform linear or advanced non-linear analysis on buildings and industrial structures. Includes advanced BIM and CAD links.

Product: S-STEEL Design Description: Design and optimize steel buildings with S-STEEL, an S-FRAME integrated steel design solution. Code-check and auto design for both strength and serviceability to multiple design codes.

S-STEEL supports composite beam design, staged construction, and numerous optimization criteria and constraints. Comprehensive design reports include equations, clause references and interactive graphics.

All Resource Guides and Updates for the 2014 Editorial Calendar are now available on the website, www.STRUCTUREmag.org.

Listings are provided as a courtesy.

STRUCTURE® magazine is not responsible for errors.

Strand7 Pty Ltd

Decon® USA Inc.

Simpson Strong-Tie®

Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: An advanced, general purpose, FEA system used worldwide by engineers, designers, and analysts for a wide range of structural analysis applications. It comprises preprocessing, solvers (linear and nonlinear static and dynamic capabilities) and postprocessing. Features include staged construction, quasi-static solver for shrinkage and creep/relaxation problems.

Phone: 866-332-6687 Email: sales@deconusa.com Web: www.deconusa.com Product: Anchor Channels Description: Decon USA is the exclusive representative of Jordahl in North America. Hot rolled Anchor Channels are embedded in concrete and used to securely transfer high loads. Their main application is for flexible connections of glazing panels to high-rise buildings. Anchor Channels with welded-on rebar or corner pieces are available.

Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Simpson Strong-Tie CFS Designer Software Description: Design CFS beam-column members according to AISI specifications and analyze complex beam loading and span conditions. Intuitive tools automate common systems such as wall openings and compression posts for shearwalls. CFS Designer supports design with Simpson Strong-Tie® curtain wall and bridging connectors.

Product: Studrails® Description: The North American standard for punching shear enhancement at slab-column connections. Produced to the specifications of ASTM A1044, ACI 318-08, AND ICC ES 2494. Studrails are also increasingly being used to reinforce against bursting stresses in banded post-tension anchor zones.

Product: Simpson Strong-Tie Utility Clips Description: The new SSC steel-stud utility clip and the low-cost, multi-use SFC steel framing connector are ideal for a variety of stud-to-stud and stud-to-structure applications. The SJC steel joist connector is designed for various CFS joist, rafter and underside of steel-deck applications. Visit the website for more information.

StructurePoint Phone: 847-966-4357 Email: info@structurepoint.org Web: www.StructurePoint.org Product: Concrete Software Description: spMats – Analysis & design of reinforced concrete foundations, combined footings or slabs on grade. spSlab – Analysis, design & investigation of reinforced concrete beams & one-way and two-way slab systems. spWall – Finite element analysis & design of reinforced, precast ICF & tilt-up concrete walls. spColumn – Design & investigation of rectangular, round & irregularly shaped concrete column sections.

Suppliers

Halfen USA Phone: 800-423-9140 Email: pschmidt@halfenusa.com Web: www.halfenusa.com Product: Anchor Channels Description: Halfen is a global manufacturer of adjustable anchoring systems for curtain walls and glazing applications. Designed to accommodate construction tolerances, eliminate the need for drilling and reduce hazards from welding or projecting bolts.

ITW Buildex

Cortec Corporation Phone: 651-429-1100 Email: jmeyer@cortecvci.com Web: www.cortecvci.com Product: MCI 2005 Description: Migrating Corrosion Inhibiting admixture for protection of embedded steel reinforcing. Works independently of chloride exposure and does not adversely affect concrete mix properties (ASTM C1582). Documented performance worldwide, and used in substructures of many tall buildings, including the tallest building in the world, Burj Khalifa.

CTS Cement Manufacturing Corporation Phone: 800-929-3030 Email: jong@ctscement.com Web: www.ctscement.com Product: Type-K Shrinkage-Compensating Cement Products Description: Install concrete structures and industrial-size floors using Type-K shrinkagecompensating cement products with no curling, no drying shrinkage cracking and no intermediate saw cut joints. Keep your concrete in compression through the life of the concrete.

Product: Rapid Set® Cement Products Description: Cement products for concrete repairs, restoration and new construction. Achieve high durability, fast strength gain and structural strength in one hour.

Phone: 800-848-5611 Email: marketing@itwccna.com Web: www.itwbuildex.com Product: Teks Select Description: Selectively hardened self-drilling and tapping fasteners that attach similar or dissimilar metals and have a Grade 5 performance. Teks Select fasteners replaces the timely process of using nuts and bolts by cutting the installation time in half.

Vulcraft/Verco Group Phone: 402-844-2570 Email: mike.klug@nucor.com Web: www.vulcraft.com Product: Steel Decking Description: Used in many applications, but is particularly well suited to roofing and flooring.

Vulcraft/Verco group manufactures many different types of deck, including roof deck, floor deck, composite floor deck and cellular deck. A full line of deck accessories, such as end closure and pour stop, is also available.

Product: Steel Joist and Joist Girders Description: Open web-steel joists and joist girders are an engineered, truss-like construction component used to support loads over short and long spans.

Steel joists and joist girders provide an economical system for supporting floors and roofs. Vulcraft joists and joist girders are designed/manufactured in accordance with the Steel Joist Institute.

Malcolm Drilling Co., Inc. Phone: 253-395-3300 Email: jstarcevich@malcolmdrilling.com Web: www.malcolmdrilling.com Product: Geotechnical Construction Description: The premier geotechnical specialty contractor in the United States, providing drilled shafts and deep foundation systems, Design/Build earth retention systems, underpinning, Ground Improvement and construction dewatering for more than 50 years.

Schöck USA Inc. Phone: 855-572-4625 Email: info@schock-us.com Web: www.schock-us.com Product: Schöck Isokorb® type CM Description: A load bearing thermal insulation element for cantilever concrete slabs such as balconies. The element transfers bending moment stress and shear forces. The integrated hanging and perimeter tensile reinforcement, fitted as standard, saves the unnecessary and costly use of extra stirrups or hooped mat.

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All past issues

News, Events, Book Reviews, Letters to the Editor and more!

www.STRUCTUREmag.org

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Spotlight

Green Screen Parking Structure

By Jared Plank, P.E. American Structurepoint, Inc. was an Award Winner for the Cummins Parking Structure project in the 2013 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings $10M to $30M).

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parking structure that is aesthetically pleasing, built in a historic architecturally iconic downtown, and constructed at 63 percent of the national average cost is hard to achieve, but this is exactly what was accomplished in Columbus, Indiana.

Cummins, Inc. knew it would be expanding the offices of its global corporate headquarters and adding a new parking structure in downtown Columbus. Since the city of Columbus is rated in the top ten of the most architecturally significant cities in the country, this announcement drew some concerns from local officials that a large structure may not mesh well with the existing adjacent buildings.

With the help from architects and engineers of Indianapolis-based consulting firm American Structurepoint (in association with KRJDA), Cummins was able to present a plan to city officials that attracted positive attention. Their parking structure would feature a “living” exterior that promised to blend the new project into the downtown architecture. Cummins received city approval to construct their 954space, 291,300-square-foot parking structure.

The parking structure was designed by American Structurepoint and built by F.A. Wilhelm Construction Co., Inc., of Indianapolis.

A “green screen” on two sides of the fivestory structure is perhaps the most unique feature of this parking structure. The modular green wall system adds 7,000-square-feet of living, growing vines that take cues from the original concepts utilized in the landscape and architecture of Cummins’ nearby award-winning headquarters building. The green screen system softens the two facades and adds beauty and visual interest. It also addresses the city’s requirements that vehicles parked within not be visible from the street.

The system’s galvanized steel frames create a wonderful composition and rhythm, which reflect the staccato effect of window and door openings found in many of the adjacent urban

buildings. They also help filter direct sunlight and shield views of the cars from the street and adjacent buildings.

Self-contained planters support long-term mass vine growth. The insulated containers feature a heat trace wire system designed to prevent root damage during cold temperatures, as well as an automatic irrigation system that detects when the growing medium is dry and provides water as needed. The community will watch the structure literally grow through the years, as its vines fill in and expand. Its appearance will constantly be changing, adding to its visual interest to those who see it develop.

Cummins also desired an open, secure, and cost-effective parking structure. Openness was achieved by utilizing a moment frame lateral load resisting system in lieu of shear walls.

Security was aided by providing full glass facades at each stair tower. The overall parking structure expressed its aesthetics principally through exposing structural elements and enhancing them. This approach allowed for a cost-effective and visually pleasing parking structure.

Two-way, cast-in-place, post-tensioned concrete slabs form the two stair tower roofs, with the roof of the southwest stair tower cantilevering more than seven feet in all directions from a central concrete core wall. Precast concrete stairs were used in a unique manner by cantilevering from a central concrete core wall. This created a lighter, open feel to the stair tower element by reducing the size of the external structure. The effect is a gentle stepped slope wrapping around the core and a secure feeling with unobstructed penetrating exterior light. A 20-foot-tall white precast concrete trellis ties into the west elevation, matching the adjacent iconic headquarters building concrete trellis and creating an

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approachable, pedestrian-friendly walkway and a framework for vegetation.

Adhering to sustainable design principles for the project, a post-tensioned one-way slab and beam system was chosen for its excellent performance in this aggressive environment.

One of the governing design parameters was durability over time, specifically in regards to corrosion. To address this issue, American Structurepoint implemented a multi-pronged approach to maximize building life, including utilizing high-strength concrete with low water/cement ratio; epoxy coated reinforcing, additional concrete cover, post-tensioned tendon and anchorage protection, higher prestress levels to reduce cracking, smaller drainage areas and selective admixtures and sealers to inhibit corrosion. With all of these pieces considered together, the design life of the structure is significantly greater than a typical precast or mild reinforced parking structure.

The overall cost of the structure came in at about $10,600 per parking space. The national average at the time of construction was around $16,700 per parking space. The design provides superior quality and durability for an exceptional price. The parking structure opened in September 2012, after only nine months of construction. It’s now literally a living part of the architectural fabric of downtown Columbus.▪ Jared Plank, P.E., is a project manager in the Structural Group at American Structurepoint, a multi-discipline engineering firm in Indianapolis, Indiana. He is also the current President of the Indiana Structural Engineers Association. Jared can be reached at JPlank@structurepoint.com.

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Emile Troup Ben Baer Marc S. Barter Michael Tylk Craig Barnes David Bonneville William Holmes Robert Johnson Edwin T. Huston William L. Lavicka Ronald Milmed

The nomination form is available at www.ncsea.com.

The deadline is July 11.

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Gene Corley Rawn Nelson Tim Slider Norm Scheel Fred Cowen Craig Cartwright Stephanie Young Ronald Hamburger Jon Schmidt Timothy Mays Edwin T. Huston Marc S. Barter Emile Troup Michael Tylk Greg Schindler

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July 22, 2014 DoD Minimum Antiterrorism Standards for Buildings Jon A. Schmidt, P.E., SECB, BSCP, Director of Antiterrorism Services, Burns & McDonnell

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NCSEA Cornforth Award honorees

July 15, 2014 Parking Garage Repairs: Identification, Evaluation, the Process and the Repair David Flax, Euclid Chemical Company

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NCSEA Service Award honorees

June 17, 2014 Practical Design of Complex Stability Bracing Configuration Donald White, Ph.D., Professor, Georgia Institute of Technology School of Civil and Environmental Engineering

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At the NCSEA Annual Conference each year, special awards are given to NCSEA members who have provided outstanding service and commitment to the association and to the structural engineering field.

The NCSEA Service Award is presented to an individual who has worked for the betterment of NCSEA to a degree that is beyond the norm for volunteerism. The award is given to someone who has made a clear and indisputable contribution to the organization and to the profession.

The Robert Cornforth Award is presented to an individual for exceptional dedication and exemplary service to the organization and to the profession. The award is named for Robert Cornforth, a founding member of NCSEA and treasurer on its first Board of Directors, a member of OSEA, and secretary of the Oklahoma State Board of Registration for Professional Engineers and Land Surveyors.

Nominations for the Robert Cornforth Award must be submitted by NCSEA Member Organizations.

Last year NCSEA instituted the Sue Frey Award, established to honor the memory of one of NCSEA’s finest 2013 NCSEA Service Award instructors, who passed away honoree Greg Schindler with 2013 in May, 2013. NCSEA post- NCSEA president Ben Nelson humously recognized Sue Frey as the inaugural winner, in recognition of her genuine interest in, and extraordinary talent for, effective instruction for practicing structural engineers. Subsequent winners of this award will be asked to present a special webinar to NCSEA members at a deeply discounted cost, as a continuing legacy to Sue Frey.

The nomination form for these awards is available at www.ncsea.com, and the deadline date for nominations is July 11. Nominations are requested for all awards; however, awards are based on worthy recipients and may not be awarded each year.

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Diamond Reviewed

These courses will award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program. Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern. NCSEA offers three options for registrations to NCSEA webinars: Ala Carte, Flex-Plan, and Yearly Subscription. Visit www.ncsea.com for more information or call 312-649-4600.

New Subscriber Bonus For a limited time, new subscribers to the NCSEA individual webinar subscription plan ($750/year for unlimited NCSEA 1.5 hour live webinars) will receive one week of access to a 2014 past webinar of their choice. New subscribers may choose from the following webinars: • Kim Basham: Troubleshooting Low-Strength Concrete • Ron Hamburger: The Performance Basis of ASCE 7-10 • Bill Thornton: Prying Action in the AISC Manual of Steel Construction – Historical Development and Current Usage • Maryann Phipps: Understanding ASCE 7-10 Requirements for Seismic Design of Nonstructural Components • Brad Davis: Floor Vibrations: Technical Background and AISC Design Guide 11, Part 1 • Brad Davis: Floor Vibrations: Technical Background and AISC Design Guide 11, Part 2 • Sam Rubenzer: Load Generators – What Exactly is My Software Doing?

• Nestor Iwankiew: Structural Fire Resistance – Overview, Codes & Standards, Background • Bill Coulbourne: Designing Buildings for Tornadoes Don’t miss the opportunity to view a year’s worth of webinars for only $750 and see that webinar you missed earlier this year!

June 2014

September 17-20

New Orleans, LA

Astor Crowne Plaza Hotel

The NCSEA Annual Conference will feature: • Structural Engineering Education Designing Buildings for Tornadoes • Trade Show Bill Coulborne, P.E., Director of Wind & Flood Hazard Mitigation, • Awards Banquet, including the NCSEA Applied Technology Council The presentation will use information recently developed from Excellence in Structural Engineering research and disaster assessments to illustrate how to perform Awards and the NCSEA Special Awards

Educational Sessions will include:

wind pressure calculations for buildings that are expected to survive a tornado event. It will include the most recent thinking on how to develop wind pressures for these events and how to apply those pressures in building design, with examples to illustrate the concepts.

Conference Keynote: Prepare Your Practice: Why Your Strategic Plan is Doomed to Fail Kelly Riggs, founder and president of Vmax Performance Group, a business performance improvement company, is a powerful speaker and dynamic trainer in the fields of leadership, sales development and strategic planning. Kelly returns to NCSEA after his highly-rated presentation at the 2013 NCSEA Winter Leadership Forum.

News from the National Council of Structural Engineers Associations

ACI 562 Building Code for Repair of Existing Concrete Structures Keith Kesner, Senior Associate, WDP & Associates, Chair of ACI 562, and Kevin Conroy, Senior Engineer, Raths, Raths & Johnson, Secretary, ACI 562 The presentation will describe the development of ACI 562-13, “Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings” and its relationship with current building codes. Special attention will be given to the evaluation of existing concrete structures and the design of the repairs.

NCSEA News

2014 ANNUAL CONFERENCE

Wind Loads for the Practicing Structural Engineer: Code Simplifications and Common Mistakes Emily Guglielmo, S.E., Associate, Martin/Martin; member of ASCE 7 Committee This session focuses on generating wind loads for building structures with the practicing structural engineer in mind. It includes example problems, new code provisions, simplified methods, and common mistakes relating to wind loads on buildings.

The Most Common Errors in Seismic Design and How to Avoid Them Tom Heausler, P.E., S.E., Heausler Structural Engineers; member of ASCE 7 Seismic Provisions Committee The presentation will identify the most common errors that structural engineers make when doing seismic design and performing calculations. The presentation will then demonstrate the proper application of Codes and Standards so as to avoid errors and misapplications when designing in both low and high risk design categories.

2014 NCSEA Excellence in Structural Engineering Awards Highlighting the best examples of structural engineering ingenuity throughout the world

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There are eight categories, and eligible projects must be substantially complete between January 1, 2011 and December 31, 2013.

Entries are due Friday, July 11, 2014, and awards will be presented at the NCSEA Annual Conference September 19th in New Orleans. More information and entry form available at www.ncsea.com.

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Student to Practicing Engineer – Gaining Competency After the University This is a panel discussion on technical topics and practical applications not covered in college, as well as resources to increase competency. The goal is to assist and encourage the audience to create technical training programs which address the transition of a young engineer from a student to valuable team member.

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

In Memory of W. Gene Corley Structures Congress 2015 Portland, Oregon, April 23-25, 2015

Call for Proposals Submit your abstract and/or full session proposal today for Structures Congress 2015. SEI is currently accepting proposals for complete sessions and abstracts for individual papers to be presented at Structures Congress 2015. The Structures Congress provides a forum to advance the art, science, and practice of structural engineering.

All proposals are due June 11, 2014.

Visit the Structures Congress website for details about abstract and session proposals www.structurescongress.org.

Save the Date

W. Gene Corley, Ph.D., P.E., NAE, F.SEI, Dist.M.ASCE, was Senior Vice President of CTL Group, in Skokie, Ill., and he served on the SEI Board of Governors from 2003-2006. Dr. Corley is most recognized in the engineering community for his work on the advancement of structural engineering design criteria, the advancement of structural engineering as a profession, and his efforts related to forensic engineering. In addition, he was vocal on separate but uniform licensure for structural engineers in an effort to distinguish, elevate the perception of, and otherwise advance the profession. A selection of Dr. Corley’s journal articles and proceedings papers is free to registered users (registration is free) and subscribers. Free access to the papers is available at http://ascelibrary.org/page/inmemorygenecorley until June 30, 2014.

Global Engineering Conference 2014

December 10–12, 2015 Hyatt Regency, San Francisco Second ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures. Look for the Call for Proposals in Fall 2014.

Local Chapter News SEI Maryland Chapter

October 7–11, 2014, Panama City, Panama ASCE and EWB-USA are marking the 100th anniversary of the opening of the Panama Canal, a remarkable engineering achievement that led ASCE to name the canal one of the Seven Wonders of the Modern World in 1994. Conference highlights include program topics focusing on construction, financial, political, and engineering aspects of Giga projects. In addition, there will be tours of the Panama Canal and historical ruins of Panama City. Registration now open, for more information see the ASCE website: http://content.asce.org/conferences/annual2014/.

ASCE-171 ETS2015 CONFERENCE WEB/EMAIL BANNERS

The SEI Maryland Chapter has continued to undertake a full program of activities. At their April meeting they hosted a presentation on Engineering Ethics and Growing Complexities.

The chapter’s May meeting will be on the topic of historic structures and the group is planning a tour of Baltimore’s Washington Monument. Recent chapter tours have included the Pennsylvania State Capitol building in Harrisburg to learn more about their remediation, the Powers Fasteners in Towson, Maryland, and a construction tour of the Horseshoe Casino in Baltimore. Visit the Maryland Chapter website at: http://ascemd.org/sei/ for more details.

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Call ELECTRICAL for Abstracts Now Open TRANSMISSION

The Virginia Tech Graduate Student Chapter has been busy scheduling multiple events for the Spring 2014 semester. The chapter has several speakers and webinars scheduled for the coming months. They are working in collaboration with other graduate and undergraduate chapters on campus. These include the Earthquake Engineering Research Institute (EERI) Virginia Chapter, the Virginia Tech Geotechnical Student Organization (GSO), and the undergraduate ASCE chapter. In addition, they sent eight students to the Structures Congress, had a group attend the NASCC Steel Conference in Toronto, and are planning future conference trips.

Visit the SEI website at www.asce.org/SEI to learn more.

CONFERENCE 2015 The conference will provide a forum for transmission and substa| tion engineers to exchange ideas, concepts, and philosophies, Grid Modernization – Technical Challenges & Innovative Solutions while providing new engineers with the opportunity to learn more about the art and science specific to transmission lines and ELECTRICAL TRANSMISSION structures, substation structures, and foundation engineering. & SUBSTATION STRUCTURES CONFERENCE 2015 The Conference Steering Committee is currently accepting | Grid Modernization – Technical Challenges &in Innovative Solutions sessions, with abstracts of papers to be presented technical case studies strongly encouraged. A poster session format may also be provided. Visit the SEI website at www.asce.org/SEI for more information and to submit your proposal. All proposals are due September 10, 2014.

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June 2014

September 27- October 1

Structures Congress 2014 in Boston April 3–5, 2014, was a great success with more than 1,300 attendees. Participants enjoyed 12 tracks of technical sessions, two engaging plenary sessions, exhibit hall, and multiple networking opportunities. Read the summary on the SEI website at: www.asce.org/SEI.

Congratulations to the 2014 SEI Student Structural Design Competition winning teams:

2014 Best of the Best at Structures Congress

1st Place: California State University Fullerton Independence Tower Project

New Class of SEI Fellows SEI welcomed 29 new fellows during the Closing Plenary session of the Structures Congress in Boston. The Structural Engineering Institute of ASCE established the SEI Fellow (F.SEI) grade of membership to recognize a select group of distinguished SEI members as leaders and mentors in the structural engineering profession. Visit the SEI website at www.asce/SEI to learn more about becoming a SEI fellow. The benefits of becoming an SEI Fellow include recognition via SEI communications and at the annual Structures Congress, along with a distinctive SEI Fellow wall plaque and pin, and use of the F.SEI designation.

There is no increase in dues for the SEI Fellow member grade.

SEI Fellows are invited to serve on the selection committee for future SEI Fellows. See the list of new fellows on the SEI website at www.asce\SEI. STRUCTURE magazine

2nd Place: Villanova University Cambodia Pre-School Project

3rd Place: University of Texas – Pan American Ingenium Institute Project Each year the Student Structural Design Competition showcases excellence in undergraduate structural engineering. Student teams present their projects at the Structures Congress. The competition is generously supported by the SEI Futures Fund, which provides Structures Congress registration to the finalist teams.

View the winning projects and learn more about participating in the 2015 Competition at: www.asce.org/SEI.

Five Free PDHs for ASCE and SEI Members ASCE and SEI members are invited to select and participate in up to five ASCE On-Demand Webinars yearly and earn PDHs for each one you complete and pass – at no additional cost.

Choose from a list of archived webinars for a customized education program. Receive state-of-the-practice education from your home or office. Start earning your free PDHs today at: https://secure.asce.org/ASCEWebsite/Benefits/Membership/ FreeOnDemandWebinars.aspx.

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The Newsletter of the Structural Engineering Institute of ASCE

Congratulations to the following winners: • Craig Barnes, P.E., F.SEI, M. ASCE, for the Best Presentation on The Case of You Bought the Barn: What Engineers Should Know • Wisam Kaskas, EIT, for the Best Poster on The Allowable Stress, Load Factor, and Load and Resistance Factor Evaluation of the Historical Swing Steel Truss RiversideDelanco Bridge • Peter Babaian, P.E., S.E, M. ASCE, who won the iPad Mini prize drawing Craig’s and Wisam’s presentations were selected as most informative and well-prepared by conference attendees; they will each receive a complimentary full registration to attend Structures Congress April 23–25, 2015 in Portland, Oregon. Thanks to Walter P Moore for sponsoring the 2014 Best of the Best.

Structural Columns

Summary of Structures Congress

Books for Engineers

CASE in Point

The Newsletter of the Council of American Structural Engineers

National Practice Guidelines for Specialty Structural Engineers CASE 962B

This document has been prepared to supplement CASE’s National Practice Guidelines for the Structural Engineer of Record by defining the concept of a specialty structural engineer and the interrelation between the specialty structural engineer and the Structural Engineer of Record. CASE encourages the concept of one Structural Engineer of Record for an entire project.

However, for many, if not most projects, there may be portions of the project that will be designed by different specialty structural engineers.

The primary purpose of this document is to better define the relationships between the SER and the SSE, and to outline the usual duties and responsibilities related to specific trades. This is done for the benefit of the owners, the PDP, the SER, the SSE and the other members of the construction team. The goal is to help create positive coordination and cooperation among the various parties.

You can purchase all CASE products at www.booksforengineers.com

Upcoming ACEC Online Seminars – July If You Haven’t Planned It, You Can’t Control It – 2014

Thursday, July 10, 2014; 1:30pm to 3:00pm Eastern Project budgets, schedules, scopes of work, quality, overhead costs, resource utilization...there are literally dozens of “things” that go into running a successful practice. Too often, engineers and engineering managers take a crisis management approach to controlling those “things.” The result?

Blow ups by management when expectations fall short and frustrated, confused employees who “thought” they were doing a good job. Taking the time to plan properly is an investment that cannot be overlooked, and one you’ll want to make to meet your goals and support your employees. www.acec.org/education/eventDetails.cfm?eventID=1558

Defining a Winning Social Medial Channel Strategy

Tuesday, July 15, 2014; 1:30pm to 3:00pm Eastern This webinar covers the tools and techniques to help you identify and leverage the social media channels needed to achieve your strategic goals. From editorial planning to content distribution, this webinar will review the top social media channels and how each can be used to improve viral reach and grow sales.

Who Should Attend Attendees should include business owners, executives, sales professionals, and individuals interested in establishing themselves as the Trusted Advisor. This core topic applies to all size businesses. www.acec.org/education/eventDetails.cfm?eventID=1607

So What if You Stamp or Sign it? The Meaning of Using Your Professional Seal

Wednesday, July 16, 2014; 1:30pm to 3:00pm Eastern We’ve heard that, in some engineering and architecture firms, the rush to get a project done and move on to the next task has occasionally resulted in some design professionals perhaps STRUCTURE magazine

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not always understanding or appreciating (or remembering) all of their obligations as a licensed design professional. Affixing your seal and signature to any document, coupled with using an acronym such as “PE” in your correspondence signature lines and on business cards, really means something. Furthermore, the Owner and the public have a right to rely on your professional expertise and ethics in the exercise of your professional obligations. What should a PE do to avoid these minefields? www.acec.org/education/eventDetails.cfm?eventID=1608

Creating a Social Media Policy

Wednesday, July 23, 2014; 1:30pm to 3:00pm Eastern When it comes to social media for professional service firms, there seems to be two camps – those who fully embrace it and those that avoid it at all costs. The firms that avoid it often do so because they are afraid of the consequences.

No matter what camp you fall in to, social media can’t be ignored. Your employees are using it in some way even if it isn’t a company standard. Creating a Social Media Policy focuses on the essential workflow that every firm needs to be successful when using these online tools. Having a policy in place empowers your staff to be the firm’s most publicly vocal cheerleaders while protecting the firm overall from detractors that could have an overall negative impact on the firm’s bottom line. www.acec.org/education/eventDetails.cfm?eventID=1596

Getting Out? Know Your Options

Thursday, July 24, 2014; 1:30pm to 3:00pm Eastern If you are mulling over leadership and ownership transition, your timing couldn’t better. Join Morrissey Goodale’s Nick Belitz for an exploration of exit strategies available to consulting engineering firms, including employee ownership, ESOPs, private equity, merger of equals, and firm sales.

The webinar will also include a case study of an engineering firm leader weighing his options and the expected financial return the firm’s owners may expect in each given scenario. www.acec.org/education/eventDetails.cfm?eventID=1577 June 2014

April 27-30, a record 1,400 ACEC members attended the ACEC Annual Convention in Washington, D.C., meeting with 300 Senators, Congressmen, and Capitol Hill staffers to urge passage of long-term transportation, water/wastewater infrastructure, and energy legislation.

600-plus attended the black-tie Engineering Excellence Awards Gala, which recognized 147 preeminent engineering achievements from throughout the world. The Wacker Drive and Congress Parkway Reconstruction in Chicago, IL were honored with the 2014 Grand Conceptor Award on April 29th. The engineering work for the reconstruction project was done by TranSystems/Alfred Benesch/T.Y. Lin/Burns & McDonell/ Infrastructure Engineering/Parsons Brinckerhoff/Lochner.

The award citation referred to the project as “one of the most complicated ever completed by the City of Chicago since it involves complex staging to keep 60,000 vehicles (ADT Wacker Drive), 75,700 vehicles (ADT Congress Parkway) and a staggering 150,000 pedestrians moving through the construction zone.”

ACEC’s Annual Convention also marks the induction of a new ACEC Executive Committee. Richard Wells, VicePresident of Kleinfelder, succeeded Gregs Thomopulos as ACEC Chairman for 2014-2015 at the spring meeting of the ACEC Board of Directors.

CASE Summer Planning Meeting – SAVE THE DATE The CASE Summer Planning Meeting is scheduled for August 5-6th in Chicago, IL. The night of August 5th will feature a discussion with a representative from Willis A/E practice on risk management and contracts. If you are interested in attending the roundtable/meeting, please contact CASE Executive Director Heather Talbert at htalbert@acec.org.

20 th Senior Executives Institute Become a Confident Engineering Class Now Open for Registration Expert Witness – June 5-6, 2014 For 20 years, ACEC has offered the premier executive leadership course designed specifically for the A/E/C community – the ACEC Senior Executives Institute (SEI). SEI is an intensive 18-month program taught by recognized experts and instructors from The Brookings Institution, national universities and business consulting organizations. The classes meet for five separate four or five-day sessions.

The next class, SEI Class 20, is now open for registration and will begin in September, 2014.

For more information, contact Dee McKenna, Deputy Director, ACEC Business Resources & Education Department, at dmckenna@acec.org or 202-347-7474.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

STRUCTURE magazine

Become A Confident Engineering Expert Witness • Earn new firm services revenue • Enhance your professional credentials • Expand personal opportunities • Qualify for recognition as an Engineering Expert Witness Gain the knowledge you need to become an effective and sought-after engineering expert witness! Engineers are often asked to serve as expert witnesses in legal proceedings – but only the prepared and prudent engineer should take on these potentially lucrative assignments.

If asked, would you be ready to say yes? You will after attending Become a Confident Engineering Expert Witness!

Developed exclusively for engineers, architects, and surveyors, this unique course will show you how to prepare for and successfully provide expert testimony for discovery, depositions, the witness stand, and related legal proceedings.

For more information, contact Ed Bajer, ebajer@acec.org or visit www.contractscentral.org/expertwitness/index.cfm.

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CASE is a part of the American Council of Engineering Companies

ACEC BUSINESS INSIGHTS

CASE in Point

ACEC’s 2014 Annual Convention and Legislative Summit

Structural Forum

opinions on topics of current importance to structural engineers

Communicating Structural Risk

By Dan Eschenasy P.E., F.SEI

T

he British have tasked two organizations – CROSS (Confidential Reporting on Structural Safety) and SCOSS (The Standing Committee on Structural Safety) – to work jointly to collect information on structural failures, to maintain a database and to provide reports interpreting the data. When reading CROSS’ alerts and reports in its newsletters, I cannot help but reflect on the way we communicate risk within the United States, and question if our current practice is capable of providing adequate warnings about some potential structural risks.

The lessons learned from extraordinary environmental events are well disseminated. A hurricane or earthquake happens in a short period of time and in a defined geographical area. This relative unity of time and place facilitates observations of common modes of structural failure. These failures take place as buildings are subjected to combinations of loads close to or exceeding code design values. However, what about structural collapses that occur under service loads? How many incidents happen in the absence of rare environmental events? What are the causes?

Because these failures occur isolated in time and geography, we look at them as separate cases. Despite being very rare, are they unique?

Is it possible to document trends using the present outlets for sharing information? In my view, identification of risk requires the determination of both failure cause and the probability of its occurrence.

Generally, forensic engineering analyses are commissioned for the cases that are likely to involve litigation or substantial insurance payments. Some of the flashier or more notorious cases, and their related lessons learned, become the object of presentations at congresses or articles published in technical journals. But, the more benign cases might remain completely off the radar and some others are not shared, due to legal concerns. Because they record only cases that were published, even the larger compilations fail to include benign cases.

Forensic engineers that specialize in particular technical domains may have the opportunity to observe some failures of

similar modes. Derived from multiple cases, their lessons learned are more relevant to the engineering practice, but still do not carry the weight conferred by statistical analyses.

In my opinion, case studies cover only the descriptive aspect of risk communication.

Case analysis alone is not capable of providing a sense of trends or probability of occurrence associated with the identified cause.

K. Wardahana and F. Hadripriono’s Study of Recent Building Failures in the United States covers a building stock with large variation in age, structural type, height, function, code regulation, etc. The authors searched reports in technical magazines and mainstream press to examine building failures between 1989 and 2000, but were only able to identify 225 incidents. The information thus collected could not be characterized as a random sample or as a comprehensive population.

Consequently, the reach of the findings was limited and the authors could only present distributions of different categories (type of errors, types of occupancy, building height, etc.) within the population of failures they had assembled from mainstream media.

The media can be useful for communicating some structural problems to a larger, but local public. Many of the examples listed by R.Ratay in Changes in Codes, Standards and Practices Following Structural Failures are in debt to the local press coverage that made the public sensitive to building or construction failures.

The mainstream media report building failures, but this is not their main mission. The information is of unequal reliability, as it is provided by reporters typically having little technical knowledge on the reported subject.

Searching these reports will not produce even a reliable number of failures as data is skewed towards geographic areas with larger press presence and days when other more sensational news are missing. Most reporting is done only immediately after the accidents and follow-up reporting is rare, although essential information might be uncovered later.

Clearly more relevant technical findings can result from the polling of engineering firms.

M. O’Rourke and J. Wikoff in Snow Related Roof Collapses and Implications for Building

Codes were able to closely identify some of the main causes of roof collapses during the winter of 2010-11 using practicing engineers’ responses to questionnaires.

It is my view that we need a system where the entire engineering profession is engaged in reporting in-service building failures. Each report should be a communication of facts and, where possible, a description of potential risk. The systematic collection of such reports will lead to the formation of a database that in turn will allow use of statistical tools to determine correlations and probability of occurrence. Some examples of areas of potential findings are: evaluation of the adequacy of some provisions of past or present building codes, information on the in-situ aging of materials or of specific details, identification of common type of human or design errors, and identification of types of structures at a higher risk of aging or of less reliable building solutions. When working on a particular project, practitioners would be able to search for information on the potential weaknesses of that type of building or detail.

Comprehensive data collection is possible. Some federal and local governmental entities manage to keep track of some specific accidents or failures of structures. For example, both the Occupational Safety and Health Administration and the New York City Department of Buildings record construction accidents and make public a short description of each. Fire statistics are also collected nationwide.

The design of the reporting system should be simple, yet sufficient for effective use of the information. One would have to clarify the definition and level of failure to be reported, to decide if one needs to count failures during the construction process, and to establish categories of failures (e.g. envelope vs structural frame, architectural vs engineered systems, etc.) in a standardized format.

When managed and maintained by engineers, a standardized system of communicating risk will provide benefits that far exceed the effort required by its development.▪ Dan Eschenasy, P.E., F.SEI, is the New York City Buildings Department Chief Structural Engineer. He is an Honorary Member of SEAoNY.

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C 3 Ink, or the STRUCTURE® magazine Editorial Board.

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