STRUCTURE magazine | February 2014

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

February 2014 Steel/Cold-Formed Steel NCSEA Winter Leadership Forum Napa, California March 20 & 21

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FEATURES The San Francisco – Oakland Bay Bridge

26

By Ronald F. Middlebrook, S.E. and Roumen V. Mladjov, S.E.

The San Francisco-Oakland Bay Bridge connects San Francisco and Oakland and is the busiest vehicular link in Northern California. Read about the amazing engineering that went into the design and construction of this iconic crossing in the 1930s. Then get a glimpse of recent improvements and future needs.

The Transformation of the Historic First National State Bank Building – Part 1

30

By D. Matthew Stuart, P.E., S.E., SECB and Ed D. Cahan, P.E., S.E.

The rehabilitation of First National State Bank Building is paramount to the ongoing revitalization of Newark, New Jersey’s historic commercial and business district known as the “Four Corners”. Read about challenges and early options in this two-part article about the restoration of this historic structure.

DEPARTMENTS 36 Great Achievements

39 InSights

By Dmitri Jajich, P.E., S.E. and David Horos, P.E., S.E.

50 Structural Forum

The Progression of High Strength Concrete

San Francisco – Oakland Bay Bridge Second Crossing

By Kevin A. MacDonald

COLUMNS 7 Editorial Important Conference for Principals and Leaders in Structural Engineering Firms

By John A. Malcolm, P.E.

10 Building Blocks Fatigue Evaluation of a GFRP Reinforced Bridge Deck

By Joseph Robert Yost, Ph.D., P.E., David W. Dinehart, Ph.D., Shawn P. Gross, Ph.D. and Philip Reilly

15 Structural Design A Practical Design for Thin Composite Steel-Concrete Floor Systems

By Sompandh Wanant, P.E.

20 Structural Performance

By Jerry Hatch, P.E.

A Building that Teaches

By Glenn R. Bell, P.E., S.E., SECB

February 2014

Buildings Designed to Weather the Storm

43 Spotlight

Frank Heger

CONTENTS

Union Bridge

By Frank Griggs, Jr., P.E.

34 Outside the Box Vertical Turbines in an Urban Environment

By Craig E. Barnes, P.E., SECB

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

By Ronald F. Middlebrook, S.E. and Roumen V. Mladjov, S.E.

22 Historic Structures

February 2014 Steel/Cold-Formed Steel NCSEA Winter Leadership Forum

ON

THE

IN EVERY ISSUE

COVER

Lee Hall III is a 55,000-square-foot addition to Clemson University’s College of Architecture, Arts and Humanities in South Carolina. It was named an Outstanding Project in the NCSEA Annual Awards Program and awarded a LEED Gold certification by the U.S. Green Building Council. See more about this project on page 43.

Napa, California March 20 & 21

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.

STRUCTURE magazine

4

February 2014

8 Advertiser Index 41 Resource Guide (Bridges) 44 NCSEA News 46 SEI Structural Columns 48 CASE in Point

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Editorial

Important Conference for Principals and new trends, new techniques and current industry issues Leaders in Structural Engineering Firms

By John A. Malcolm, P.E.

A

fter experiencing “Gravity” at the theater, I left with a sense of inspiration and awe at witnessing an excellent film, a story about experts, highly trained astronauts, professionals, the best at what they do, able to focus in the most dangerous and stressful circumstances, with a calm reliance on their extensive training to deal with almost any situation. For those who haven’t seen the movie, Sandra Bullock and George Clooney are on a spacewalk when an accident causes everything to go terribly wrong. As depicted in the movie, maintaining focus on their training wasn’t easy, but was faithfully done with amazing results.

Training is similarly important for leaders of structural engineering firms of all sizes. Growth, success, retaining key employees, dealing effectively with conflict and the inevitable lawsuits common to our industry, and successful transition to a new generation of owners do not just happen. Leaders need to be sure they have the tools and information to respond to the expected and unexpected events that occur in a rational, informed manner. We need to prepare in order to make the best possible decisions. Engineers are not trained for this in school. My suspicion is that companies that take these issues seriously are the firms that prosper over the long run and create successful lasting legacies. Mission accomplished The second NCSEA Winter Leadership Forum will be held March 20 and 21, 2014, in the beautiful wine country of Napa, California, at the Meritage Resort and Spa. I encourage principals and leaders in structural engineering firms to attend this conference to learn valuable skills that will enable them to effectively address keeping their firms on the path towards vitality and success. The conference is targeted to address issues – expected and unexpected – of small, medium and large firms.

The Winter Leadership Forum will launch Thursday, March 20th, with Steven J. Isaacs presenting Get the Value You Deserve Without Ruining the Relationship. This is an interactive session, introducing a new approach to negotiations, and will offer a variety of field tested ways to get the value and compensation you deserve from current and future clients. Steven Isaacs is a professional engineer and longtime speaker and educator with FMI Corporation, assisting firms in strategic planning, financial controls, project performance/profitability, negotiation, ownership transition, joint ventures and partnering.

Also on Thursday, owners and principals from small, medium, and large firms will discuss Ownership Transition Case Studies based on their professional experiences. Brian Dekker, President of Sound Structures, Inc., Brian Phair, CEO of PCS Structural Solutions, and Mark Aden, President of DCI Engineers, will present. Each speaker has a unique and interesting way of approaching this key issue. Firms that do not have a transition plan in place will obviously benefit, but so will firms interested in valuation because they are buying or selling, firms interested in ways to keep key employees, and firms wanting to improve their plans. These three presentations will conclude with a roundtable discussion facilitated by Steven Isaacs. This will give all attendees a chance to learn from each other.

STRUCTURE magazine

Steven Isaacs will also be presenting Baby Boomers Delay Retirements: Career Bottleneck at the Top. The trend of older, experienced professionals wanting to work longer and wait for retirement creates challenges. Steven will discuss how to react to this trend and retain talented employees.

On Friday, Jennifer Morrow offers Leadership is a Full-Contact Sport: Dealing with Conflict in the Workplace. This session will focus on effectively managing issues in the office and beyond. Jennifer Morrow is the Executive Director of Commercial Services at ADR (Alternative Dispute Resolution) Systems of America. She consults with law firms and companies on the effective use of mediation, arbitration and all types of dispute resolution processes.

Jennifer Morrow and Kevin Sido share the next topic, Managing the Cost of Conflict: Mediation, Arbitration or Litigation? They will explore the full spectrum of dispute resolution processes and provide tools for evaluating which is best to use. This will guide firms toward making informed decisions and will help minimize the impact on principals’ time, business, and reputations. When the challenge appears suddenly, these tools can be invaluable.

Kevin Sido is an attorney and senior partner in the Chicago office of Hinshaw & Culbertson LLC. He has represented design professionals for 38 years, is an author and speaker on construction law issues, and is the editor of Architect and Engineer Liability, Claims Against Design Professionals. Friday sessions will conclude with his presentation You’ve Been Sued – Now What? What Engineers Need to Know to Structure Their Defense. Realizing that claims will inevitably be filed against structural engineers regardless of merit, this talk will give advice on what to do when the summons is served and in the months that follow.

This should be a great conference to provide leaders with the tools required to address issues important to their companies’ survival and continued vitality. Structural engineers are not astronauts, but without key training our companies are vulnerable to unexpected challenges.

Copy that! Let’s avoid becoming stranded in the void!

After all this learning, there is a reward. No, not a spacewalk, but an opportunity to explore the California countryside. This is a good time to enjoy a long weekend getaway. The resort in Napa is 50 to 60 miles from the airports in San Francisco, Oakland and Sacramento, or just a little over an hour away by car. Shuttles can be arranged. The Meritage features wine tasting and an underground spa, as well as access to Napa and Sonoma Valleys, hiking and biking, golf, a three hour wine train tour, galleries and restaurants. Check the Meritage website for details. Go to http://themeritageresort.com. For further information and to register go to www.ncsea.com under Meetings. Over and out!▪ John A. Malcolm, P.E., is Senior Vice President for Peak Engineering Inc. Lakewood, Colorado. He serves on the NCSEA Continuing Education Committee.

7

February 2014

Advertiser index

PleAse suPPort these Advertisers

Albina Co., Inc...................................... 18 Bentley Systems, Inc. ............................. 51 Cast ConneX......................................... 33 CSC, Inc. .............................................. 31 CTS Cement Manufacturing Corp........ 37 Design Data .......................................... 29 Ecospan Composite Floor System ......... 13 Enercalc, Inc. .......................................... 3

Engineering International, Inc............... 19 ICC....................................................... 38 Integrated Engineering Software, Inc..... 42 Independence Tube Corporation ............. 6 ITW Red Head ..................................... 14 KPFF Consulting Engineers .................... 8 NCSEA ................................................... 9 Powers Fasteners, Inc. .............................. 2

Editorial Board Chair

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

Brian W. Miller

CBI Consulting, Inc., Boston, MA

Mark W. Holmberg, P.E.

Evans Mountzouris, P.E.

The DiSalvo Ericson Group, Ridgefield, CT

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

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

Khatri International Inc., Pasadena, CA

KPFF Consulting Engineers, Seattle, WA

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

Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA

Brian J. Leshko, P.E.

John “Buddy” Showalter, P.E.

John A. Mercer, P.E.

Amy Trygestad, P.E.

HDR Engineering, Inc., Pittsburgh, PA

Mercer Engineering, PC, Minot, ND

Chuck Minor

Dick Railton

Eastern Sales 847-854-1666

Western Sales 951-587-2982

sales@STRUCTUREmag.org

Davis, CA

Heath & Lineback Engineers, Inc., Marietta, GA

CCFSS, Rolla, MO

AdvErtising Account MAnAgEr Interactive Sales Associates

Jon A. Schmidt, P.E., SECB

Craig E. Barnes, P.E., SECB

RISA Technologies ................................ 52 SidePlate Systems, Inc. .......................... 25 Simpson Strong-Tie........................... 5, 17 StructurePoint ....................................... 40 Struware, Inc. ........................................ 24 The Soc. of Naval Arch. & Marine Eng. 12 USP Structural Connectors ................... 11 Western Wood Structures ...................... 28

American Wood Council, Leesburg, VA

Chase Engineering, LLC, New Prague, MN

EditoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE

execdir@ncsea.com

Editor

Christine M. Sloat, P.E.

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STRUCTURE® (Volume 21, Number 2). ISSN 1536-4283.

Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact your member organization(s).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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STRUCTURE magazine

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February 2014

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Building Blocks updates and information on structural materials

C

ast-in-place (CIP) concrete bridge decks are typically reinforced with steel. However, poor durability resulting from steel corrosion has resulted in the use of alternative noncorrosive reinforcement materials. As part of this effort, glass fiber reinforcement polymer (GFRP) reinforcement bars have been used as structural reinforcement for CIP concrete bridge decks. GFRP is a noncorrosive composite material made of glass reinforcing fibers and a vinyl ester resin matrix. In axial tension, GFRP is elastic with brittle rupture at ultimate. Relative to grade 60 steel reinforcement, GFRP tensile strength is about 150%, the elastic modulus is about 20%, and the unit weight is about 25%. Thus, given the material’s high strength and low stiffness, serviceability of GFRP reinforced bridge decks will be an important consideration in design.

Structural design of bridge decks reinforced with steel or GFRP is accomplished using either the traditional method or empirical method.

With the traditional method, the deck is modeled as a continuous beam in flexure, and wheel loads are distributed over an imaginary equivalent strip.

Using this simplified flexural model, design moments are found using established methods of indeterminate analysis. The empirical method recognizes that wheel loads are not resisted by flexure, as is assumed by the traditional method, but rather wheel loads are primarily distributed to supporting girders by compression membrane action in the concrete. Consequently, only minimum reinforcement ratios are specified for the top and bottom mats for the purpose of crack control and to resist a small flexural component resulting from the wheel load.

Fatigue Evaluation of a GFRP Reinforced Bridge Deck

By Joseph Robert Yost, Ph.D., P.E., David W. Dinehart, Ph.D., Shawn P. Gross, Ph.D. and Philip Reilly

Joseph Robert Yost, Ph.D., P.E., is an Associate Professor in the Civil and Environmental Engineering Department at Villanova University. He may be reached at joseph.yost@villanova.edu.

David W. Dinehart, Ph.D., is Professor and Chairman of the Civil and Environmental Engineering Department at Villanova University. He may be reached at david.dinehart@villanova.edu.

South Side - Design by Traditional Method (TR) 39 inches

3 feet

3 feet

3 feet

PennDOT Parapet (typ.)

3 feet

North Side - Design by Empirical Method (EM) 1.5 feet

3 feet

AASHTO Type-II Beam (typ.)

3 feet

8 inch deck

Interior Bay

Exterior Bay

3 spaces at 9 feet = 27 feet

Reinforcement Schedule Trans. Reinforcement

39 inches

Pos. Empirical (MP-EM)

Strong Floor

Note: East-West L = 8 feet

Long. Reinforcement

Top

Bottom

Top

Bottom

total

(# at in.)

(# at in.)

(# at in.)

(# at in.)

(%)

#5 at 4 in.

#5 at 4 in.

#5 at 10 in.

#5 at 5 in.

3.7

Empirical #5 at 12 in.

#5 at 4 in.

#5 at 12 in. #5 at 12 in.

2.3

Traditional

3 feet

3 inch haunch (typ.)

Exterior Bay

Design

3 feet

Neg. Empirical (MN-EM)

Neg.Traditional (MN-TR) Pos. Traditional (MP-TR)

Shawn P. Gross, Ph.D., is an Associate Professor in the Civil and Environmental Engineering Department at Villanova University. He may be reached at shawn.gross@villanova.edu.

Philip Reilly is a graduate student in the Civil and Environmental Engineering Department at Villanova University. He may be reached at preill01@villanova.edu.

For steel reinforced bridge decks in the US, both traditional and empirical design methodologies are specified in AASHTO 2010 (LRDF Bridge Design Specifications). For bridge decks reinforced with GFRP, AASHTO 2009 (LRFD Bridge Design Guide Specification for GFRP-Reinforced Concrete Bridge Decks and Traffic Railings) specifies procedures using the traditional method, and the Canadian Standard Association 2006 (Canadian Bridge Design Code) provides procedures using both traditional and empirical design methodologies. Using the traditional design methodology as specified in AASHTO 2009, GFRP reinforcement is provided to satisfy design requirements at the Strength, Service, and Fatigue and Creep Rupture limit states.

GFRP has been successfully used as reinforcement in many in-service bridge decks in the US and Canada, including the Val Alain Bridge, Miles Road Bridge, Wotton Bridge, Magog Bridge, Morristown Bridge, Route 668 Bridge, and Cookshire-Eaton Bridge, to name a few. In general, design of these GFRP reinforced bridge decks was performed using the traditional method. The corresponding required GFRP reinforcement was controlled by serviceability limits calculated using elastic analysis at the service limit state. However, concrete and GFRP strains measured during controlled load testing of these bridges have been shown to be only a small fraction of the material’s ultimate strength, and well below the predicted magnitudes calculated based on a cracked section elastic analysis. Thus, where serviceability limits control design, the analytical model used for calculation may not accurately represent the actual behavior of the physical system. Consequently, economy may be compromised by unnecessary cost associated with excessive GFRP requirements made necessary by design calculation.

In the current research study, crack width, deflection and material strain measured at the service

Figure 1: Sample details.

10 February 2014

Top clear cover 1.0 inch

top bars

Bottom clear cover 1.0 inch

bottom bars Transverse bars

Longitudinal bars

limit state are investigated after fatigue loading a full scale GFRP reinforced bridge deck.

The bridge deck is reinforced with GFRP as required by design using both the traditional and empirical design methodologies.

Measured data is compared to AASHTO 2009 allowable limits to establish performance compliance.

Experimental Program

MTS Actuator pet

Axle beam

Para

Deck

Load frame

Interior girder Exterior girder

Figure 2: Deck with loading apparatus (MN-TR load case shown).

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The experimental program included fatigue loading of a full-scale bridge deck reinforced with GFRP rebar. As shown in Figure 1, the deck is 8 inches thick, supported by four AASHTO Type II girders spaced at 9 feet, has a fascia overhang of 3 feet 3 inches, and is 8 feet in the longitudinal direction. The 8-foot longitudinal width was selected so the deck would be wider than the equivalent strip used in the traditional design method. A 3-inch haunch with GFRP dowel reinforcement between the deck and girder was used as well. The supporting AASHTO girders are non-prestressed, cast-in-place, and in continuous contact with the laboratory strong floor. The experimental parameter is design methodology; with the north half designed by the empirical method (EM), and the south side designed by the traditional method (TR). The reinforcement schedule is provided as a table in Figure 1, where it is noted that the total GFRP reinforcement on the EM side (ρ = 0.023) is 38% less than that on the TR side (ρ = 0.037). The GFRP rebar was provided by Hughes Brothers of Seward, Nebraska. The deck concrete was a PennDOT approved high performance concrete (HPC) mixture used in bridge decks with a target 28 day compressive strength of 4 ksi. Extensive electronic instrumentation was used for deflection, concrete strain, crack width, and force measurement.

A simulated truck axle, consisting of two wheels separated transversely by 6 feet, was used to load the deck. The load portal, hydraulic actuator, and axle beam are shown in Figure 2. The deck was subjected to four load cases, corresponding to the truck axle positioned for critical positive and negative bending moments on both the north (EM) and south (TR) sides (Figure 1). The load case designation is given as MP or MN for critical positive and negative bending, respectively, and -EM or -TR for empirical and traditional design methodology, respectively. Thus, MP-TR represents the load case for positive bending on the traditional

design side. For each load case, the deck was chronologically subjected to 100 cycles at 125% of service load (80 kips), 10 cycles at service load (64 kips), 1,000,000 cycles at the fatigue limit state load (36 kips), and finally 10 cycles again at service load (64 kips). The initial overload cycles at 125% of service were intended to crack the deck to a steady state stiffness condition.

In this way, the effects of fatigue loading are determined by comparing the 10 service load cycles applied before and after the 1 million fatigue load cycles. continued on next page

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Critical Traditional Load Case (MP-TR)

Critical Empirical Load Case (MN-EM)

0 0.00

Crack Width (in)

0 0.000

0.02

(a) Crack width

Critical Empirical Load Case (MP-EM) Deflection (in)

0.108

(b) Deflection

0

100% Allowable

50% Allowable

64

Applied Load (kips)

50% Allowable

Applied Load (kips)

Critical Traditional Load Case (MN-TR)

100% Allowable

64

100% Allowable

Applied Load (kips)

50% Allowable

64

Critical Traditional Load Case (MP-TR) Critical Empirical Load Case (MN-EM) 0

Concrete Comp. Strain (με)

600

(c) Concrete strain

Figure 3: Test results at the end of fatigue loading.

Test Results

RINE ENG MA I

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RCHITECTS LA

&

• THE ERS S NE

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During the overload phase of testing, a crack developed on the top fiber over the interior girder for both negative bending load cases (MN-TR and MN-EM), and for both positive bending load cases (MP-TR and MP-EM) a crack developed on the bottom fiber under the exterior bay wheel load. All four cracks were visible along the entire 8-foot longitudinal width of the deck. No significant additional cracking was visually detected for the remainder of testing.

Recorded behavior for the 10 service load cycles applied after the completion of fatigue loading is presented in Figure 3 in the form of critical crack width, deflection and concrete strain from all sensors and for each design methodology (TR and EM). The residual from all previous load cycles in the load history is included as the offset seen in the figure. In Figure 3 the 100% and 50% allowable limits are shown to provide a reference for degree of compliance. Allowable limits are taken from AASHTO 2009, as 0.02 inches for crack width, L/1000 or 0.108 inches for deflection, and 600 microstrain, corresponding to 0.45f 'c /Ec for concrete strain. Note: in determining the concrete strain limit, the e rat bo nce a l l e co peri p ex velo de end att rn lea are sh eet m n joi

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deck concrete strength of 5,800 psi was used and Ec was empirically determined by the ACI procedure.

The results of Figure 3 are very encouraging as related to compliance with all allowable serviceability limits. For crack width, the maximum value for traditional design occurred for the negative bending load case and was only 24% of allowable (trace MN-TR in Figure 3a). For empirical design, the maximum crack width also occurred for the negative bending load case and was 41% of allowable (trace MN-EM in Figure 3a). Thus, empirical design is critical over traditional design, as would be expected considering the top transverse reinforcement on the empirical side is only 33% of that on the traditional side (reinforcement schedule Figure 1). Regardless, the empirical side crack width was well within the allowable limit.

For deflection, the positive bending load case was critical for both traditional (MPTR) and empirical designs (MP-EM). From Figure 3b, the traditional design deflection is 49% of allowable, and the empirical design deflection is only slightly higher at 53% of allowable. From the reinforcement schedule of Figure 1 it is noted that both sides (TR and EM) have the same bottom transverse reinforcement; therefore, the measured traditional and empirical deflections would be expected to be approximately the same.

Relative to allowable, deflection is slightly more critical than crack width, but still well below the allowable limit.

Concrete strain results in Figure 3c show positive bending is critical for traditional design (MP-TR) and negative bending is critical for empirical design (MN-EM).

Relative to the allowable strain limit of 600 με, MP-TR and MN-EM are only 30% and 44%, respectively. Thus, the performance

STRUCTURE magazine

12

February 2014

of the deck as related to allowable concrete stress of 0.45f 'c is very good, with traditional slightly better than empirical.

Conclusions The results presented evaluate the behavior of a full scale GFRP reinforced bridge deck designed using both empirical methodology and traditional methodology. The deck was initially loaded to 125% of service limit state for 100 cycles, followed by 1,000,000 load cycles at the fatigue limit state, followed by 10 cycles at the service limit state. Critical measurements for crack width, deflection and concrete strain were captured for each of the four different load cases corresponding to critical positive and negative bending for each empirical and traditional design.

Measured responses were compared to allowable limits required by AASHTO 2009.

Test results show that both empirical and traditional designs are compliant with all serviceability limits. Measured crack widths for traditional and empirical designs were 24% and 41% of allowable, respectively.

For concrete stress, these percentages were 30% and 44%, respectively, and for deflection 49% and 53%, respectively. Thus, the critical measured behavior was deflection on the empirical design side, and this was only 53% of allowable.▪

Acknowledgments The authors wish to thank lead sponsor AECOM and co-sponsor McCormick Taylor for providing financial support.

Also, Hughes Brothers is acknowledged for their generous donation of the GFRP rebar.

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Structural DeSign

n recent years, it has become more desirable, and in many cases necessary, for architects and engineers to design buildings and structural frames with beams and girders of limited depth. Shallower structural depth allows building floor-to-floor height to be lowered and the amount of materials used – such as exterior cladding, interior walls, partitions, and stairs – to be reduced. In high-rise building construction, it allows extra floors to be added within the proposed building height.

On expansion projects, a shallower structural depth helps facilitate the need to match the existing floor elevations.

Practical Design This system has been developed for use in building floor construction, specifically for typical rectangular or square column bay areas of around 1,000 square feet. One of the most economical and widely used floor framing systems is the third-point loading of two in-fill beams on girders which span between columns (Figure 1). Conventional composite steel-concrete floor framing consists of rather deep steel beams and girders which provide the most cost-effective design in terms of tonnage of structural steel used. In this article, American Institute of Steel Construction (AISC)-standard structural steel shapes will be used for both composite beams and girders, and will be made as shallow as practically possible. It should be noted that moderate column bay sizes are used in the design examples; however, larger column bays in the range of 30 feet × 45 feet can be designed economically.

Although this system is intended for building floor construction, the concept may be applied to any other composite beams/girders requiring a shallower depth.

The Beam The conventional composite beam, consisting of normal or light weight concrete, composite

design issues for structural engineers

Figure 1: Framing plan.

steel deck and a steel beam, is made shallower by replacing the steel beam section with a shallower (heavier) one. The concrete thickness over the steel deck is between 2½ inches to 4½ inches, and the standard 1½, 2 or 3-inch deep steel deck may be used as required.

Since the total depth of the composite girder is the depth of the system, the total design depth of the composite steel beam should be made as deep as possible but not greater than the total depth of the composite girder (Figure 2). It should be noted that, if desired, square or rectangular steel tubes (HSS sections) may be used in lieu of wide flange shapes and a cover plate at the bottom of the steel section may be added.

A Practical Design for Thin Composite Steel-Concrete Floor Systems

The Girder The composite steel-concrete section consists of an inverted structural tee (WT), a steel plate and a standard steel-concrete composite slab (Figure 3, page 16 ). For the system to be practical, flexible and efficient, the

By Sompandh Wanant, P.E., M. ASCE

Sompandh Wanant, P.E., M. ASCE, is Building/ Structural Section supervisor in the Division of Building Plan Review, Department of Permitting, Inspections and Enforcement, Prince George’s County, Maryland. He may be reached at swanant@co.pg.md.us.

The online version of this article contains additional detailed calculations and references. Visit www.STRUCTUREmag.org.

Figure 2: Typical beam section.

STRUCTURE magazine

15

concrete below the top of the steel deck, the steel deck and the steel plate supporting the deck are neglected from calculations; together they constitute a few percentage points of the total stiffness.

Design Criteria for the Steel-Only Asymmetric Built-Up Section To ensure proper and uniform design of the composite girder section and to set the lower strength limit of the steel-only built-up section, the built-up section must have adequate strength to support the total slab dead load and its supporting steel frames.

Figure 3: Typical girder section.

standard structural tee (WT) and a thick and narrow flange plate are selected. The thick and narrow flange plate provides not only needed strength and minimizes creep and long-term deflection, but also leaves adequate space required for field attachment of the steel deck to the steel girder built-up section. The steel girder built-up section and the steel-concrete composite slab form a very strong T-section flexural member. One major advantage of this composite section is that field welding of the shear connectors to the steel girder top flange is not required since the top flange is embedded in the concrete slab with the top of the flange at or near the top of the concrete slab.

The strength and stiffness of the composite girder can be calculated by transforming the concrete portion into steel using Modular Ratio, n = Es/Ec; Ec = wc3/2(33) (f 'c)1/2. The imaginary homogeneous transformed section is analyzed for its physical properties by the elastic methods of analysis.

As in any T-beam section, substantial flexural horizontal shear exists at the intersection of the web and the flange. This horizontal shear can be determined using the familiar equation, v = VQ/I. For thin concrete slabs above the top of the steel deck, reinforcement is usually required to increase the shear capacity. Shear-friction provisions given in American Concrete Institute (ACI) 318 Section 11.7 and its commentary are referred to for the design of concrete slab shear reinforcement. Figure 4 shows the concrete slab critical shear planes/ surfaces. Slippage at the interface of the concrete and WT web can also occur; steel stud shear connectors are used to prevent slippage at the web. The number of shear studs required can be determined by calculating the difference between the shear

capacity, found using ACI 318 Equation (11-25): Vn = Avf fy µ, and the total design shear at the web. For other critical shear planes ACI 318 (Commentary Section R11.7.3) Equation: Vn = 0.8 Avf fy + Ac K1 is employed to obtain the amount of shear reinforcement. Please refer to ACI 318 for more design information.

With the existence of the steel deck, one may want to consider its strength, along with concrete, to help resist the horizontal shear.

Additional shear resistance of the steel deck (limited to the attachment to the support or the side lap capacity) is beyond the scope of this article. In the design examples, the

Figure 4: Critical shear planes.

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February 2014

Serviceability Requirements AISC Specification for Structural Steel Buildings (ANSI/AISC 360-05) section L5 requires that “The effect of vibration on the comfort of the occupants and the function of the structure shall be considered.” As in any floor system design, the vibration characteristics of the floor system (i.e. the natural frequencies, the amplitude/acceleration due to the certain appropriate dynamic loading) must be evaluated and satisfied.

Refer to AISC Steel Design Guide #11, “Floor Vibrations Due to Human Activity”, for design information and procedure. continued on page 18

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Connections and Choice of Steel Girder Fabrications The system uses standard AISC beam-togirder and girder-to-column connections, so the detailed connections are not shown.

In the examples, the author used the actual girder span in the design calculations, i.e. the column line dimension minus two times the distance between the column center line and the shear plate bolt holes. For a heavy girder-to-column connection where the depth of the girder web is limited, a beam seat may be required at the bottom of the girder; i.e. a standard AISC seated beam connection may be used.

Since it is necessary to provide web openings or drilled holes for the reinforcing bars, and the WT section is cut from a large W section, it may be easier and more cost effective to fabricate the required WT, with the notches for web openings, in a similar manner to fabricating the castellated beam. If this method is chosen, the actual total depth of the WT should be used in the calculations. Alternately, one may prefer to simply make the drilled holes. It should be noted that if asymmetric shape rolled sections are available domestically the fabrication cost will be reduced.

Design Examples Example 1 Design a typical interior composite girder for an office floor space. The depth of the girder shall be as shallow as practically possible; provide shoring as required. W12 columns may be used.

Given: Floor framing as shown in Figure 1 with column line dimensions of 28 ft × 28 ft Beam span = 28 ft, Beam spacing = 28/3 = 9.33 ft Girder span = 28.0 – 2(0.50 + 0.25) = 26.50 ft (Girder frames to W12 column flange) Concrete: 3.25 in, 110 pcf light weight concrete, f 'c = 4,000 psi Composite steel deck: 19 gage, 1.50-inch deep; Structural steel: Fy = 50 ksi Live load = 50 psf; Partition load = 15 psf; Mechanical, electrical and misc. = 5 psf Solution: Dead load: Concrete and steel deck = 40 psf; Total dead load = (40 + 15 + 5) = 60 psf Assumed beam weight = 40 plf Live load: Live load reduction, L = L0 (0.25 + 15 / (KLL AT)1/2 ) (IBC Section 1607.9.1) Live load, L = 50 (0.25 + 15 / (2 × 9.333 × 28)1/2 ) = 50 (0.906) = 45.3 psf Assumed girder weight = 75 plf From the above design parameters, required girder section properties: Sreq’d = 91.8 in3, Ireq’d = 856.4 in4 (Use deflection limits, ∆LL = L / 360 or ∆TL = L / 240).

Design of composite girder: Refer to Figure 4, use 1 inch of concrete cover over the flange plate, try WT 10.5 × 55.5 with 1 in × 4 in flange plate, total girder depth = 12.755 in, effective flange width, beff = 26.50 × 12 / 4 = 79.50 in; using the elastic methods of analysis for transformed section, one can find: Str = 125.2 in3 and Itr = 960.8 in4 (OK). Using Equation v = VQ / I, to find shear stresses at critical locations (Figure 4 ), and ACI 318 Section 11.7 one can find: Slab shear reinforcement: #4 @ 8 inches; and shear studs: ¾ in diameter @ 15 inch.

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Example 2 Design a typical interior composite girder for an office floor with the column bay spacing of 30 ft × 30 ft, and design live load of 80 psf throughout for the flexibility of future corridor arrangements.

Given: Floor framing as shown in Figure 1 with column line dimensions of 30 ft × 30 ft Beam span = 30 ft, Beam spacing = 10 ft Girder span = 30.0 – 2(0.50 + 0.25) = 28.50 ft (Girder frames to W12 column flange) Concrete: 3.50 in, 145 pcf normal weight concrete, f 'c = 4,000 psi Composite steel deck: 20 gage, 2-inch deep; Structural steel: Fy = 50 ksi Live load = 80 psf; Partition load = 15 psf; Mechanical, electrical and misc. = 5 psf Solution: Select 1.50-inch concrete cover over the flange plate (for fire protection), try WT 12 × 73 with 1 in × 4.50 in flange plate, total girder depth = 14.87 in. Following the same design procedure as in Example 1, one can find: Composite Girder, Itr = 1849.6 in4 (Ireq’d = 1555.0 in4), Str = 193.6 in3 (Sreq’d = 151.4 in3). Slab shear reinforcement: (2)#4 @ 12 inch (Spacing ~ 3 times slab thickness, OK). Shear studs: ¾ in diameter @ 14 inches.

Note on Total Building Cost From Example 2, the steel girder weight is 88.3 plf (15.3 plf for flange plate plus 73 plf for WT). As the estimated beam size is W 8 × 35 (not shown in the example), we calculate the amount of steel to be 6.44 psf of the floor area. By determining the amount of steel required for a conventional composite girder and beam design (W 18 × 60 for girder and W 14 × 26 for beam), we get 4.60 psf. Since the size of the steel columns and lateral bracing members varies greatly, from less than 1 psf to more than 1.5 psf, due to many parameters, let’s assume that the combined weight of columns and bracing members is approximately 1.25 psf. From the above information, we figure the weight increase of the steel frames to be (6.44 + 1.25) / (4.60 + 1.25) = 1.315, or a 31.5 % increase. According to many publications, including AISC’s, the cost of raw material is only about one third of the total cost of the structural steel frames, the rest being the cost of fabrication and erection; and, the cost of the steel frames is about 10 % to 12 % of the total building cost. Therefore, we can conclude that the increase in total building cost is approximately (31.5 / 3) × 0.11 % = 1.16 %. Since the increase in total building cost due to steel weight is very small, it is believed that, in most cases, the saving in cost on the exterior wall (a major cost) and all other interior constructions can adequately offset the additional cost of steel.

Advantages over Other Thin Floor Systems

Use of Computer Programs and Laboratory Testing As shown in the examples, the calculation for strength and stiffness is straightforward, but for everyday design tasks, a computer

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February 2014

Conclusions The above design examples show that a practical thin floor system can be designed and constructed. In both examples, approximately 7 to 9 inches in total girder depth can be saved for most commonly used beam and girder spans. The system utilizes all the elements of conventional composite steel-concrete construction, i.e. normal or light weight concrete, a composite steel deck, welded shear studs, standard structural steel shapes and typical steel-to-steel connections. Though the system generally requires shoring of the beams and girders due to their shallow sections, a significant amount of field welding of shear studs to the girder is not required. Unlike other thin floor systems, this system maintains the use of a thin composite steel-concrete deck and standard structural steel shapes; therefore, the system will be as cost effective and flexible for application as the conventional composite floor construction.▪

Acknowledgments The author would like to thank Eric A. Jackson, an engineer at the Department of Environmental Resources, Prince George’s County, Maryland for the CADD drawing of the figures.

235

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At least a couple of thin/shallow floor systems, such as the Girder-Slab and Slimflor systems, are available for use in North America and Europe. Both systems can be used in several types of buildings, but are best suited for certain applications. The advantages of the proposed thin floor system over these systems are for general applications only: • The proposed thin floor system is much lighter than both the Girder-Slab and the Slimflor systems.

• The composite beam of the proposed thin floor system can span much longer than 30 feet, whereas the Slimflor slab has the span limit of less than 30 feet.

• Due to lighter slab weight, both the beam and the girder can span longer

distances resulting in larger open floor spaces.

• The space between beams and girders may be utilized as rectangular or square recessed ceiling space, or as additional utility space.

• The system is based on the conventional composite floor system, therefore it has all the benefits of composite floor construction, including foundations, seismic load resisting systems; other benefits are floor framing flexibility and lower overall costs.

program will enhance and facilitate the design process. The structural design of the composite girder presented herein should be laboratory tested to confirm the theoretical and design analysis results and to make further design developments should one wish to do so.

Structural Performance performance issues relative to extreme events

I

n the past few years, building for natural disasters – already a consideration for structural engineers – has been thrust into the public eye after recent tornados wiped out entire cities and took many American lives.

Moore, Okla., Joplin, Mo., and Tuscaloosa, Ala. are all recent examples of areas that have experienced the greatest losses, both in infrastructure and human life. Engineers in the construction industry work to stay aware of these challenges when setting out to build safe, strong and durable buildings for tenants and occupants.

This year, the NCI Building Systems annual engineering seminar was focused on building design and the strength needed to withstand natural disasters such as hurricanes, tornados and earthquakes. The training conference, open to engineers throughout the U.S., attracts top researchers in fields relevant to steel construction. Lectures at the seminar were given by William L. Coulbourne, P.E., an expert in building design for tornados, Tom Murray, Ph.D., P.E, professor emeritus in structural steel design, and Chris Moen, Ph.D., P.E., who offered insights into the rapidly developing Direct Strength Method for designing building components.

Buildings Designed to Weather the Storm

By Jerry Hatch, P.E.

Building for Tornados

Jerry Hatch, P.E., is manager of engineering development for NCI Building Systems and chairman of the Metal Building Manufacturers Association Technical Committee.

Previous to his work at NCI, he was active in mid-rise and low-rise conventional building design. Jerry can be reached at Jerry.Hatch@ncigroup.com.

William L. Coulbourne is a national expert in wind and flood mitigation, and has been involved in FEMA Mitigation Assessment Teams and natural hazard damage assessments for close to 20 years. He has become intently focused on building design for tornados after the recent devastating touchdowns in Ala., Mo. and Okla., and he shared new research in his keynote address at the engineering seminar.

Tornados are classified by the National Weather Service in very much the same way as hurricanes: by the most extreme damage they can find anywhere in the storm’s path, even if only a small percentage of the area affected reaches that extreme. In most cases that Coulbourne has studied, the wind speeds in each tornado’s path have been EF-0 (65-85 mph), an EF-1 (86-109 mph), or an EF-2 (110-137 mph), which are comparable to hurricane wind speeds up to a Category 3. As a point of reference, new homes along large portions of the Texas coast are built to withstand hurricane force-winds up to 130 miles per hour.

Coulbourne suggests that the same practices used for hurricane wind resistance could be applied in tornado alley. Translating the same awareness of natural disasters and application of stringent building codes during the

20 February 2014

Comparison – Hurricane to Tornado Wind Speeds Saffir-Simpson Hurricane Wind Speeds

Enhanced Fujita Tornado Wind Speeds

Category

Wind Speed (3-sec peak gust mph)

Category

1

74–95

0

65–85

2

96 –110

1

86 –110

3

111–130

2

111–135

4

131–155

3

136 –165

5

>155

4

165 –200

5

>200

Wind Speed (3-sec peak gust mph)

design process has the potential to significantly improve the safety of homes, businesses and human lives in the event of a tornado. Practices such as creating load path continuity from the roof-to-wall connections through to the floor-to-foundation connections and installing laminated windows to minimize airborne missiles should be used when rebuilding a home damaged by a tornado, and when considering new construction in a high-risk area.

The two most frequent failures during a tornado are roofs lifting off their frames and homes being pushed off their foundations. A significant increase in the preservation of buildings and homes in tornado alley could be possible with a focused approach to the mechanical connections that attach roofs to walls, walls to floors, and floors to the foundation. Current building codes in tornado alley require connections be made with only nails alone, but Coulbourne recommends metal connectors be used for optimal strength and wind resistance, up to 130-135 mph.

“If we could do something for hurricane-like wind speeds in places that get impacted by tornados, while everybody may not have the same level of protection and there could still be fatalities, we could reduce damage and improve the ability for people to survive to a huge extent,” Coulbourne said. “For example, 83 percent of the area affected by the Joplin tornado was an EF-0, 1 or 2. This corresponds to wind speeds represented by Category 1-3 hurricanes. If we look at the wind speeds of the actual tornado events (mostly EF-2s or lower) and compare it to wind speeds we design for along hurricane-prone coastlines, I feel confident we can come up with some solutions that will work.”

A new approach to building for tornados would have its most obvious impact in the safety of building occupants, but it would also make a massive difference in the futures of the towns themselves. Coulbourne notes that when a city has been hit by a tornado, families historically have moved to surrounding towns or wherever family and friends can help them get back on their feet. Families put down roots in these new

towns, and as the population of the original hometown shrinks, the tax base shrinks and it becomes harder for the city to rebuild what is left, making it more unlikely that residents would ever return. A solution that spared more homes and basic infrastructure could preclude such a scenario.

In any discussion related to construction for tornados, Coulbourne stresses that infinitely more important than salvaging a building is the goal of saving lives. Another building option in preparing for extreme weather is to install a reinforced area where people can go to be safe in the event of a tornado.

“If you want to be confident you’ll be protected, put in a shelter,” he said. “Instead of spending the money to make a whole building resistant to tornados, consider putting in a safe room. This is especially important in schools. Most teachers take the children into the hallway, but unless the hallway walls and roof are hardened, there is still a chance the roof may fall on the kids. In a scenario like that, an alternative solution is not to build the whole building better, but instead invest in a safe room, so if the unlikely event of a tornado happens, human lives will still be saved.”

Building for Earthquakes For many years, the basic intent of the building code seismic provisions has been to provide buildings with an ability to withstand intense seismic activity without collapse, even in the event of significant structural damage. The protection of life safety, through the avoidance of earthquake-induced collapse, remains the primary goal of U.S. building codes today.

An understanding of ductility is required to accomplish this goal in building design.

Ductile structures are capable of sustaining large amounts of damage without significant degradation in strength or development of instability and collapse. Steel in particular is a highly ductile building material, as it can allow significant damage to the structure (such as beams bending and buckling) before a full collapse. The damage can help to reduce the earthquake loading on the building by changing its response characteristics. With this understanding, the engineer is tasked to control the locations of damage in a building leading up to collapse, while making sure that collapse does not occur before sustaining prescribed levels of load.

Most of the damage used to control collapse is near the beam-to-column connections.

Several types of connections have been studied and understood in their role to control collapse. The Metal Building Manufacturers

Association (MBMA) has been studying metal building connections, including prequalified connections, for several years in an effort to understand their behavior for seismic applications.

Tom Murray, professor emeritus of structural steel design at Virginia Tech, discussed the testing requirements for prequalifying connections for special and intermediate steelmoment frames for seismic applications. In order to be prequalified, these connections must attach beams to columns while maintaining a flexural resistance at a story drift angle of 0.04 radians, at 80 percent of the nominal strength of the connection. Tests can be conducted specifically for a project or for a representative type of connection.

The connections Murray addressed are the bolted moment connections described in AISC documents as prequalified for certain materials and geometric limitations. He also discussed the permitted test sub assemblages used and the cyclic testing protocols.

Metal buildings are particularly resilient in earthquakes because of their typically low height and light weight. They have a history of good performance in earthquakes and are considered one of the safest materials to build with in earthquake-prone regions.

Demonstrating the positive attributes of metal buildings through calculations has been the task at MBMA for the past several years.

Research on metal building systems has been performed at the University of California at San Diego, and research on related bracing requirements has also been performed at Georgia Tech University.

MBMA has been sponsoring this research in an effort to document metal building behavior for seismic applications. Lightweight, low-rise buildings have performed well with thin elements. As the industry presses into higher and heavier buildings, the thicker elements and prequalified connections Murray described will become more frequent in use. They are an important piece of the puzzle in understanding and extending the use of metal buildings for seismic implications.

Direct Strength Method Cris Moen, associate professor of civil engineering at Virginia Tech, shared his expertise on the American Iron and Steel Institute’s direct strength method (DSM) for coldformed steel design, which provides an easier way to predict the strength of building components (studs, joists) and systems (sheathed walls, roofs). Compared to the Effective Width Method used before it, the DSM does not require iteration or effective

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February 2014

section properties; instead, a cross-section elastic buckling analysis is performed, which can be accomplished with hand calculations or computer-aided numerical analysis, for example the freely available software CUFSM (www.ce.jhu.edu/bschafer/cufsm/). The DSM approach can be found in AISI-S100-12, Appendix 1, North American Specification for the Design of Cold-Formed Steel Members, and is even applicable to members with perforations.

There are three types of buckling limit states evaluated in the DSM: local, global and distortional. Local buckling involves primary plate buckling within a cross-sectional element between fold lines. Global buckling (or Euler buckling) is when a member bends and rotates simultaneously within an unbraced length. Finally, distortional buckling occurs in joists and studs with an open cross-section as restrained flexural-torsional buckling of a compressed lip-stiffened flange.

“The direct strength method is a new and innovative way for cold-formed steel engineers to conceptualize and predict the behavior of cold-formed steel members and systems,” Moen said. “The approach has quite a few advantages, compared to the current method engineers are accustomed to using. As a whole, it is easier to use and a more accurate predictor of capacity because of improved mechanics and the fact that the focus of the calculation is crosssection buckling modes instead of effective width for individual elements. It covers all buckling modes in one method, and complex cross sections are treated consistently throughout the process. Lastly, the DSM brings roof and wall panel, sheathing and insulation to member design.”

The seminar brought up some thoughtprovoking topics in engineering. These new findings can directly impact the thought processes engineers go through during building design. While much has already been tested and proved, continued research in these areas is vital in order for engineers to create the strongest and safest buildings possible.▪

Historic structures significant structures of the past

Cooper plan of Burr arch/truss.

Cooper half truss – note: sidewalk framing not shown.

T

Union Bridge First Bridge across the Hudson River, 1804

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 19th 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.

he Union Bridge, connecting Waterford and Lansingburgh, New York, was the first to cross the Hudson River in its 154 mile course from New York harbor northward.

It was located near a long time ford and ferry crossing. The first act leading to the bridge was passed by the legislature on April 15, 1800 when it authorized building of toll bridges across the Hudson River. Nothing was done until late 1802 or early 1803, when a group of the leading men of Waterford and Lansingburgh proposed the formation of the Union Bridge Company to build a toll bridge at the site. At this time, they probably contacted Theodore Burr, a millwright from Oxford, New York, to advise them on a design.

Burr was born in Torrington, Connecticut. After an apprenticeship to a millwright, he went to Oxford in the 1790s. The only other man who could have been contacted was Timothy Palmer, but he was busy building the Permanent Bridge in Philadelphia. (STRUCTURE® magazine, October 2013) Burr had earlier built a bridge across the Chenango River from his mill to the town of Oxford as well as many mills near his home.

An act dated February 22, 1803 passed the Legislature that stated “John. D. Dickenson, Charles Selden…and their present and future associates, their successors and assigns, be and they are hereby created a body corporate and politic by the name of ‘The president and directors of the Union Bridge Company,’ for the purpose of building a bridge across Hudson’s River, at or near a ferry commonly called Hamilton & Scotts’s ferry leading from Waterford to Lansingburgh…”

It covered the rules by which the corporation should be run and how elections were to be held, etc. It also said “it shall not be lawful for any person or persons to erect any bridge, across the said river within two miles up or down the said river, from the place where the bridge aforesaid

22 February 2014

shall be erected and built by the said company.”

After 75 years, the bridge would become the property of the state. The only clauses dealing with construction of the bridge were in article VIII which stated that “the said bridge shall be built at least twenty-five feet wide, and be well covered with plank not less than three inches thick, the sides of the said bridge to be secured with good substantial railings, and shall be so constructed that at least one opening under the same, of not less than one hundred feet, between the piers, shall be left of the passages of rafts and boats.”

It was on the Waterford Bridge that Burr developed the truss/arch pattern that he later patented in 1806 and again in 1817. His design was adopted for both roadways and railways over the next 50+ years. Unlike Timothy Palmer who built pure truss bridges, he relied greatly on arches to carry a portion of his load and had them built strongly into the stone abutments and piers. His truss was built integrally into his arch with details to ensure the two systems acted together. His bridge consisted of four spans of three trussed arches, yielding twin roadways 11 feet wide. He built a sidewalk along the northerly side of the bridge, outside of the northerly arch, by cantilevering it off the trusses with floor beams that ran continuously across the entire bridge.

The best drawing of the arch/truss pattern was published in Theodore Cooper’s American Railroad Bridges article in the Transactions ASCE in 1889. Cooper won the Norman Medal for the article. He wrote that he had obtained the drawings from associates at RPI, where he graduated in 1857. He illustrated a half span on one of the two river spans. The key feature of the bridge, which originally was not covered, were the arches that started below the deck at the abutments and ran near the top of the top chord at mid span on the shore spans and above the top chord on the river spans. The deck was generally flat, or nearly flat, to accommodate traffic. It rested on cross beams that were set on the bottom chord of the truss.

Cooper’s dimensions of each member of this truss and his splice and connection details are shown in the illustration on page 22.

He had cross bracing between the top chords to stabilize the trusses above the deck level.

Originally the bridge had no roof, so the framing shown is for the 1814 rehabilitation. The height of the truss from bottom of the bottom chord to the top of the top chord was 14 feet 8 inches. His arches were twin 8 x 16-inch members with the verticals, lower chord and upper chord bracketed by the twin arch members. The top chord was a single 12 x 16-inch and his bottom chord was twin 8 x 14-inch. His single verticals were 9 x 12 inches and single compression diagonals were generally 9 x 10 inches, but in the last two panels were 10 x 11 inches. The other diagonals were single 6 x 8-inch. His floor beams were 12 x 14 inches and his top cross bracing consisted of 8 x 10-inch members with knee braces. It is not known if he had diagonals between these cross braces, but it is likely. The span lengths, center to center of piers, were measured from the Waterford side of the bridge: 169 feet, 194.18 feet, 199.44 feet and 164.27 feet.

With a design in hand, the Directors started advertising for masons to build the abutments and piers in early April 1804 and started asking the stockholders to make payments on their subscription in mid May, with the first installment of $5.00 due May 24, 1804. Local newspapers carried many articles on the construction of the bridge, with the Lansingburg Gazette advertising on March 6, 1804 for “40 stone masons to build abutments and piers of a bridge across the Hudson River, the work to commence the 5th day of May, next.” On June 19 it wrote, “the erection is proceeding rapidly, the abutments, (on shore sides) and one of three piers are already near finished, and the frames of the arches are in a state of equal preparedness. Concerning the abutments and piers, there is not the least doubt that they will render the bridge secure from ice in spring seasons.” When they state the frames of the arches are progressing, they mean that the timber was cut to size and

assembled into the truss and arch forms on a field near the bridge with all holes for iron bolts and trunnels (tree nails or oak pins) needed for erection drilled. The parts would then be disassembled and, when the piers were completed, re-erected on wooden false work in the river.

The bridge opened with a major celebration on December 3, 1804. The opening was attended by the Governor of New York and many dignitaries who marched from Lansingburg to the VanSchoonhoven Hotel on Second Street in Waterford where the Bridge Company had prepared a meal. The procession consisted of a band, Artillery Company (in full uniform), citizens, Masonic Brethren, Members of the Assembly and Senate, Clergy, the Governor and the President of the Bridge Company, with the builders of the bridge last in line. When they reached the center of the bridge, a 17-gun salute was fired representing the 17 states of the Union at that time. At the dinner following the parade, it was common that the people in attendance make a series of toasts. A Director toasted Burr – “Theodore Burr – May the display of wisdom, strength and beauty in Union Bridge, be a lasting monument of his skill in architecture, and secure him patronage, so long as he shall be able to lay down designs on trussle [trestle]-board.” Burr made the following toast, “May the Union Bridge prove a lasting benefit to those who have borne the expence of building it.”

The Lansingburgh Gazette wrote: It unites a degree of strength and elegance which reflects the highest credit on those gentlemen...The arches are supported by three pillars and two abutments; these are built of wrought stone thro’out, laid in tarris and lime mortar, and strongly bound by bars of iron, placed transversely through them at intervals of about three feet from each other…The floor of the Bridge rests upon the chord of the arches, which is on a level with the banks of the river on each side. This gives to it an air of convenience very inviting to travelers. On the whole, we deem it one of the

Interior showing framing with arches reinforced for trolley tracks – note: iron rods from arch to added floor/deck beams placed in 1901.

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February 2014

Union Bridge – under repair from Erie Canal boat looking towards Lansingburgh.

finest specimens of art which this country has produced; and in point of usefulness, we believe it is not exceeded by any; and it forms not only cheap but safe passage across the Hudson, and will, at no very distant period, undoubtedly become the grand thoroughfare from the eastern to the western country.

The Troy Gazette, in its December 11 issue, was even more complimentary and almost poetic, writing: It is with much pleasure (says the Waterford Gazette) we announce the completion of the bridge at this place, which for architecture, strength and beauty, exceed, perhaps, any thing of the kind in the United States. On examination it will be found that its symmetry is just in all its parts, which reflected the highest honor on its engineer, Mr. Theodore Burr and when one beholds with what regularity and dispatch the plans of the architect have been executed by Mr. Samuel Shelly, under whose immediate superintendence the work has progressed we conceive no less praise to him is due. While we are also contemplating this noble structure let us descend beneath the waters and there fixing our minds on its rocky base gradually emerge from the stream, behold,

Portal at Tollhouse.

with wonder and admiration, three stately columns, whose strength appear to battle the destruction of time and whose magnitude cause the winds to murmur as they pass, and the waves to return in perpetual eddies upon themselves. Here we behold the skill of masonry exemplified in Mr. James McElroy, under whose direction the pillars arose, and on whom much econium has justly been bestowed.

The tolls included $0.30 for every four wheel pleasure carriage, drawn by four horses, $0.125 for every wagon and two horses, and $0.02 for every foot passenger. Its cost to build was only $50,000.

In a period of seven months, Burr, McElroy and Shelly had built a 726-foot long bridge of arch supported trusses that far exceeded in length any truss or arched bridge in the United States at that time. Palmer was just finishing his Permanent Bridge in Philadelphia in late 1804, with its opening in early January 1805, but his bridge was in three spans with the longest being 195 feet.

Later, after Palmer’s Permanent Bridge was covered, the Board of Directors in 1814 (after reconstruction) ordered that it too be covered. The covering and repair, possibly rebuilding, to the bridge between 1812 and 1814 cost $20,000.

Horse drawn trolley cars used the bridge for many years, paying a yearly fee of $750 in the 1860s and later increased to $2,000 per year. Electric trolley cars started using the bridge in 1889 and heavier Hudson Valley interurban trolley cars weighing over 25 tons started to use the bridge around the turn of the century. A local newspaper reported, “1901, partly on account of the deterioration in the structure but largely to provide for the increased load of large interurban trolley cars. Extensive repairs, costing $28,000, were made to the bridge.

Additional 4 x 7-inch strips were bolted to

Union Bridge, Engineering News 1889.

Union Bridge, 1804-1909.

the tops of the stiffener arches and intermediate rod hangers were put in to support additional floor beams.” Apparently 7 tiers of 4 x 8-inch strips were added to the two center spans and four tiers of the same size added to the shorter shore arches. The top chord bracing and roof structure was modified greatly to provide the necessary height for the trolley cars. The rebuilding was by Palmer C. Ricketts and Joseph Lawson of Rensselaer Polytechnic Institute.

Engineering News wrote in 1889, “At the time the Waterford Bridge was built, therefore, it was the greatest existing wooden span in the world, and the first glance at the design shows that it was not only of a strictly original type but was a much more scientifically designed structure than any which had preceded it. For aught we know, it may be the greatest wood span which is standing today, so many of the short list of greater wooden spans having been burned or replaced by iron.” The magazine carried a full article on the bridge and its construction, thus bringing it to the attention of the engineering profession.

The bridge lasted until 1909 when it StruWare, Inc was destroyed by fire. The Troy Budget Structural Engineering Software reported the “blazing bridge was a spectacle worth going miles to see.” Motorman The easiest to use software for calculating Walter Wright of the United Traction wind, seismic, snow and other loadings for Company was crossing the bridge when IBC, ASCE7, and all state codes based on he “looked downward and saw a spitethese codes ($195.00). ful flame leaping from possible faulty CMU or Tilt-up Concrete Walls with & insulation in the flooring. Soon the longwithout openings ($75.00). covered bridge, acting as an horizontal chimney, was blazing furiously.” This Floor Vibration for Steel Bms & Joists ($75.00). was followed by the separation of a gas Concrete beams with torsion ($45.00). main mounted to the bridge and, within a period of only 35 minutes, three of the Demos at: www.struware.com four spans had collapsed into the river.

STRUCTURE magazine

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February 2014

Engineering News published two articles on the bridge after the fire. The first on July 14, 1909 by H. N. Peck of Boller and Hodge gave a brief history of the bridge and the plans for the new steel bridge. The second was a description of the fire by Oscar Hasbrouch, a Cohoes Civil Engineer, on July 22, 1909.

A new steel bridge, designed by Boller and Hodge and fabricated and erected by the Phoenix Bridge Company, was erected on the same piers and stands today over 105 years after its construction. The two bridges, having a combined service life of 210 years on the same masonry piers, were designated as National Historic Civil Engineering Landmarks in 2013.▪

Bridge burning, July 1909 and aftermath.

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THE SAN FRANCISCO – OAKLAND

BAY BRIDGE

By Ronald F. Middlebrook, S.E. and Roumen V. Mladjov, S.E.

T

Figure 1: Bay Bridge with new east crossing.

he San Francisco-Oakland Bay Bridge is one of the greatest American bridges. Built during the Great Depression, the bridge soon became known as the “working horse of Northern California,” carrying the heaviest traffic in the region.

“This marks the physical beginning of the greatest bridge yet erected by the human race.”

General Information

President Herbert Hoover at the groundbreaking ceremony, 1933

The San Francisco – Oakland Bay Bridge opened to traffic in 1936.

It connects San Francisco and Oakland and is the busiest vehicular link in Northern California (Figure 1).

The bridge is actually several structures with distinctly different systems, strung together to form about a 8.5-mile (13.7-km) cross-bay roadway, nearly 4.4-miles over water (7.1km). The main portions of the original were: • West crossing: Nearly 2 miles (3,140 m) from San Francisco to Yerba Buena Island (YBI), including a twin suspension bridge with central spans of over 2310 feet (704 m) (Figure 2).

• YBI segment: 1800 feet (549 m) featuring a tunnel and short concrete viaduct.

Figure 2: West crossing.

• East crossing: A more than 2-mile (3,417 m) crossing from YBI to Oakland, consisting of several different steel truss systems: four short (approximately 288-foot; 88 m) spans on YBI, followed by the 2420-foot-long (738 m) cantilever structure (Figure 3), then five deep through-truss spans at 509 feet (155 m), fourteen deck-truss spans at 288 feet (88 m), and the remainder on simple land-based steel structures.

The original bridge was designed by Ralph Modjeski, Charles Purcell et al. and built by American Bridge Company using steel from United States Steel. At the time of completion, it was the longest bridge in the world and featured the second longest suspension span (2310 feet; 704 m), the third longest cantilever truss span (1400 feet; 427 m), the deepest pier foundation (243 feet; 74 m) below water surface at low tide), and the largest bored tunnel. The west crossing was the only major bridge with two consecutive suspension spans.

The bridge, with its three major segments, is listed on the National Register of Historic Places (NRHP). The Register’s comment is: “One of the largest and most important historic bridges in the country.”

Figure 3: East crossing (to be demolished).

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February 2014

BRIDGE ELEMENT

ORIGINAL EAST BRIDGE

NEW EAST BRIDGE

Total Length miles (meters)

2.1 (3,377)

2.2 (3,513)

Main Span feet (meters)

1400 (427)

1266 (386)

Secondary Spans feet (meters)

509 (155)

525 (160)

10

10

280,000

324,000

3.5

11.75

1936

2013

85 (416)

347 (1,694)

78 (not comparable)

6,450

Traffic Lanes Vehicles per Day Construction Time (years) Completed Steel psf (kg/m ) 2

Cost in US $ Millions President Herbert Hoover, who was originally a mining engineer, had followed the development of the design of the bridge during his presidency. He was particularly interested in its effect on employment in trying times. Calling this project, “The greatest bridge yet erected,” shows its importance to Hoover.

The entire bridge deserves its exalted historic credentials, from the graceful sweep of the west crossing suspension structure, through the YBI tunnel and viaduct, to the steel cantilever truss section, to the through-truss and deck-truss spans. It was built in just 3½ years, at a cost then estimated at $78 million. It was, and still is, one of the greatest engineering achievements of the 20th century.

Design and Construction

(Caltrans) reported for building just the superstructure of the new east crossing replacement – 266,750 tons (242,000 metric tons), or 347 psf (1,694 kg/m2). A testament to the wisdom of the design for the Bay Bridge’s west crossing is that, 62 years later, Japanese engineers chose a very similar design for the towers of the longest bridge span in the world: the Akashi-Kaikyo (or Pearl) Bridge, with a central span of over 6530 feet (1,991m).

Earthquake Damage The bridge’s east crossing was locally damaged during the Loma Prieta earthquake of 1989. A 50-foot (15-m) section of the top deck slipped off its support at an expansion joint; that end of the section then collapsed onto the lower deck (Figure 4). One motorist was killed.

Caltrans subsequently decided to replace the entire east crossing, calling it an Earthquake Safety project; an important decision because it meant that only the pre-existing traffic capacity would be restored.

After several years of discussion, planning and design, construction on the new east crossing finally began in January 2002, and it was completed in September 2013.

The Bay Bridge is a double-decker. The original design featured six automobile lanes on the top deck (three in each direction). The bottom deck provided three truck lanes and two lanes (one in each direction) for an interurban commuter train. Around 1960, the arrangement was converted to five eastbound lanes of traffic on the lower deck and five westbound lanes on the upper deck.

The bridge was designed and built using state-of-the-art techniques available in the 1930s. For example, the engineers specified the higheststrength steel available for critical elements. Nickel (55 ksi; Grade 380 West Crossing Improvements MPa) and silicon steel (45 ksi; Grade 311 MPa) for the east crossing and East Crossing Replacement make up 62% of the total steel used there, and 72% of the cantilever section. Even the carbon steel used in this bridge was higher-strength The west crossing (and its approach) underwent seismic improve(37 ksi; Grade 255 MPa) than is normally used today. High-strength ments in a five-year project beginning in 1999, at a reported cost of cable steel (120 ksi; Grade 828 MPa) was specified for the west crossing approximately $759 million. The improvements included massive suspension cables. The entire bridge required 167,100 tons (151,593 rollers installed between the roadway and bridge supports and 96 metric tons) of structural steel, or 115 psf (561 kg/m2). new viscous dampers inserted at critical points to allow movement.

The Bay Bridge and its neighbor, the Golden Gate Bridge (completed The bridge’s twin suspension spans were strengthened by adding new in 1937), represent the culmination of more than 100 years of devel- steel plates and replacing half a million original rivets with almost opment of bridge engineering and construction in the United States. twice that many high-strength bolts. New bracing was added under To fully appreciate the achievement of completing both decks, and all of the “laced” truss diagonals the construction so quickly, consider the technical connecting the upper and lower road decks were level of the industry at the time. In addition to replaced. In total, the project added about 8500 the lack of modern devices – heavy equipment, tons (7,710 metric tons) of structural steel. vehicles, cranes, etc. – all steel connections were The east crossing replacement was designed made using rivets, requiring much more time and

by T.Y. Lin International, Moffat & Nichol labor than modern high-strength bolting and weldEngineers, Weidlinger Associates and Donald ing. Compare this achievement with the 12 years MacDonald Architects. It is comprised of a singleit took to build the new replacement bridge just tower, self-anchored suspension steel span of 1266 for the east crossing! feet (386 m) and a 14-span (525 feet; 160 m each) Amazingly, the 167,100 tons (151,593 metric concrete skyway. The new crossing has added tons) of steel used for the entire Bay Bridge in shoulders and a bicycle lane. (Since there is no 1936 is considerably less than the tonnage that bicycle lane on the west crossing, it will not be the California Department of Transportation Figure 4: Local damage to the east crossing. possible to bike the entire length of the bridge.)

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February 2014

The cost is about $6.5 billion for a length of nearly 2.2 miles (3,513 m). Current plans are to demolish all of the original east crossing structures from YBI to Oakland, and presumably recycle as much material as possible. Demolition is currently estimated to cost at least $250 million.

Comparing the two east span bridges – the original (1936) and the replacement (2013) – gives an idea of the efficiency of the old bridge (see Table, page 27 ).

Traffic Capacity and Population Demographics With only five traffic lanes in each direction, traffic movement is greatly compromised, especially during commute hours. Traffic capacity has remained the same from 1960 to 2012 and is no different with the east crossing replacement.

In 1936, the Bay Area population was about 1,650,000. By 1990, it was about 6,024,000, and by 2010, it was 7,150,000. The projected population in 2025 is 8,880,000, rising to 9,031,500 in 2035 (50% greater than in 1990).

Traffic growth has been even more rapid. When the bridge originally opened in 1936, the traffic equivalent was 50,000 vehicles.

As early as 1947, Frank Lloyd Wright called the traffic congestion on the Bay Bridge intolerable. By the late 1990s, this critical highway link carried about 280,000 vehicles on an average day.

In 2000, it was evaluated as 324,000 vehicles on average. In other words, the growth in demand has increased nearly six-fold over the past 75 years.

Currently, during commute hours it can take up to 30 minutes to drive the 4.4 miles (7.1 km) from water’s edge to water’s edge across the bridge. That translates to only 9 miles per hour (14 km/h), and sometimes it is even worse, especially if there is an accident on the bridge.

The idea of supplementing traffic capacity across the bay is not new.

Numerous studies over the past 60 years have been conducted for new crossings (both bridges and tunnels). None of these studies were pursued, for environmental, political, economic and other reasons.

However, these efforts show a great deal of continuing interest in reducing the pressure on cross-bay traffic.

T I M B E R

Figure 5: New east crossing: Skyway and self-anchored suspension bridge (SAS).

Courtesy of MTC and Caltrans.

Seeking a rational solution for this “problem,” some of the possibilities include: • Expanding Bay Area Rapid Transit’s (BART) underwater, cross-bay tunnel. BART has already reached its maximum capacity during peak commute times. Enlarging the system would be fraught with technical difficulties, high cost and environmental problems.

• Adding more ferries. The Bay Bridge ended the ferry system era long ago. Ferries imply more automobiles to get to and from the water’s edge. This would be a giant step backward.

• Adding a second bridge parallel to the existing Bay Bridge.

This idea has already proven more practical in other cities around the world.

Considering these limited options, a second bridge seems to be the most logical approach to solve the restricted capacity of the existing bridge.

Considering the fact that the replacement of the old East crossing structure took more than 17 years, now is the time to begin planning and designing a completely new second SFO Bay Bridge alongside the present one using the retrofitted, old east crossing structures.

The Structural Forum column in this issue (page 50) summarizes the argument for this course of action.▪

B R I D G E S

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Ronald F. Middlebrook, S.E. (ronfranco@gmail.com), is retired from Middlebrook + Louie in San Francisco, California, and is a Past President of the Structural Engineers Association of Northern California (SEAONC).

Roumen V. Mladjov, S.E. (rmladjov@louieintl.com), is a Senior Associate with Louie International in San Francisco, California, and was a member of the Engineering and Design Advisory Panel for the Bay Bridge.

A similar article appeared in the IABSE Conference Rotterdam Report, May 2013.

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STRUCTURE magazine

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February 2014

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

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the TRanSFoRm aTion

HiSToRiC FiRST naTional STaTE Bank BUilding of the

Newark New Jersey – Part 1

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

M

ore than 100 years after its original construction in 1912, the First National State Bank Building in Newark, New Jersey (Figure 1) is ready to return to prominence. Located near the intersection of Broad and Market Streets, one of America’s busiest intersections just after the turn of this century, the rehabilitation of this structure is paramount to the ongoing revitalization of Newark’s historic commercial and business district known as the “Four Corners”. The structure consists of a 12-story mid-rise building with concrete slabs, steel I-beams and built-up steel columns; an adjacent three-story addition with concrete slabs and steel W-shape beams and columns constructed at an unknown date; and a more recent four-story structural steel, masonry block and brick stair and elevator tower at the very rear of the property.

Figure 1: Existing façade prior to renovations.

Figure 2: Exposed existing spandrels after east masonry wall demo.

STRUCTURE magazine

The facility was originally designed as a bank and office building; however, in recent years most of the upper floors remained vacant while the ground floor was used occasionally by retail and office tenants. The developer engaged Pennoni Associates Inc (Pennoni) to perform the structural engineering services required to transform the building into a mixed-use facility consisting of a hotel with restaurant, dining, and retail spaces. These services included designing a two-story overbuild above the existing three-story addition, designing a nine-story stair and elevator addition at the rear or east side of the footprint of the existing 12-story structure, strengthening the existing roof structure above the 12th story to support an occupied terrace, and several other structural modifications required to complete the overall adaptive reuse.

Designed by prominent American architect Cass Gilbert, whose other works include the Woolworth Building in New York City and the United States Supreme Court Building in Washington, D.C., the First National State Bank Building is a classic example of “skeleton” construction, for which Gilbert was one of the earliest pioneers.

Skeleton construction consists of a primary steel frame directly supporting exterior brick walls as a non-load-bearing cladding system.

This method of construction formed the basis for modern high-rise construction methods still employed by engineers and architects today, and served as an advancement of the “cage” method of construction.

Cage construction involved steel frames supported by steel columns with thickened exterior brick walls that supported their own selfweight, similar to the previous method of using exterior brick walls to support the adjacent floor framing.

In order to support the exterior brick cladding on the steel frame, the structure of the First National State Bank Building utilized a double spandrel beam in which the interior member supported the

30

February 2014

Figure 3: Cass Gilbert drawing titleblock.

Figure 4: Cass Gilbert drawing 1st floor framing.

adjacent floor framing and a small portion of the exterior brick cladding, while the exterior member supported only the exterior brick cladding (Figure 2 ). Both spandrel beams framed to, and were supported by, the same steel column, but the exterior member required an extended single plate shear connection because it did not align with the column centerline.

Due to the historical significance of many of the structures designed

by Cass Gilbert, structural drawings of many of his buildings, including the First National State Bank Building, have been preserved by the New York Historical Society as well as the Library of Congress.

In addition, the original mid-rise structure and the adjacent low-rise

addition were added to the National Register of Historic Places in 1977. The structural drawings were prepared on linen sheets, and due to their age and fragility, the New York Historical Society would not allow the drawings to be removed from their office for reproduction purposes. Therefore, each drawing sheet was laid out on a table at the Historical Society’s office and photographed for future use in analyzing Te the existing structure No dd for the required modifications. The first step was pac w ava s201 taking a photograph ked ilabof an 3 overall drawing, followed by taking closenew with e le and up photographs of of the same drawing that could be laced xcit fea portions ing tu together in sequentialresorder so that the entire drawing could be viewed in greater detail at Pennoni’s Philadelphia office (Figures 3 and 4 ). This

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Structure - Half page.indd 1

STRUCTURE magazine

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February 2014

1/3/2014 11:40:49 AM

Figure 5: Existing encased bent prior to renovations.

Figure 6: 4 th & 5 th floor addition north elevation cantilevers.

process was repeated until the entire set of original drawings, including all notes, schedules, and details, were photographed.

A review of the drawings revealed that the second floor of the mid-rise building was originally constructed as a mezzanine area overlooking the first floor lobby below. However, at some time during the life of the building the remaining portion of the second floor was infilled with steel and concrete framing similar to the original structure. Existing drawings for the infill framing were not available.

Extensive field investigations were still necessary in order to supplement missing information on the structural drawings, and to confirm that the members shown on the drawings were actually in place.

Structural drawings were not available for the low-rise addition, so more extensive field investigations were required in order to determine the structural members for this portion of the building. In both portions, steel beams were encased in concrete and steel columns were encased in hollow clay tile blocks, a common method of providing fire protection during the early 20th century (Figure 5 ). The concrete and clay tile encasements were removed from a portion of the beams and columns in order to perform the field investigations.

Physical properties of selected steel beams and columns were measured, then compared to the physical properties of steel beams and columns in two AISC published databases for historic shapes and specifications in order to verify that the members shown on the existing structural drawings were in fact used in the actual construction. AISC databases were also used in order to establish the yield strength of the steel at the time of fabrication; however, steel coupons were also taken from beams at various locations in both the mid-rise and the low-rise buildings in order to determine the chemical and material properties of the steel, including weldability and actual yield strength. Finally, concrete cores were taken in several locations in order to verify the thickness, unit weight, and compressive strength of the slabs. Locations chosen for the concrete cores included the roof of the mid-rise and low-rise buildings in order to determine if topping slabs were present to provide drainage, and at the typical floor in both the mid-rise and low-rise buildings to determine the slab construction.

The results of the field investigations, in conjunction with available structural drawings, were used to determine the structural capacity of the existing building.

The renovation of the low-rise building called for a two-story addition consisting of hotel rooms and a rooftop terrace. The first challenge encountered was the need to recess the north face of the vertical

extension from the existing north elevation of the original facility because of a National Register of Historic Places and State Historic Preservation Office (SHPO) requirement not to alter the sightlines of the building as viewed from Broad Street. As a result, the north exterior wall of the new addition was set back from the north exterior wall of the existing low-rise below. The existing interior and exterior columns along the south exterior wall were used to support the new addition, but a large cantilever at the new fourth and fifth floors was required to support the portion of the addition on the north side of the interior column line (Figure 6 ). Excessive deflections at the cantilever were mitigated by using an upward camber equal to the total dead load deflection, and by providing slightly deeper members than those required for strength design only.

A second challenge encountered with the design of the 2-story addition was determining the capacity of the existing columns and foundations that would be required to support two new floors.

Using the physical column properties measured during the field investigations and the mechanical properties established via the steel coupon testing, the columns were determined to have significant reserve capacity based on their unbraced lengths and the loads applied by the three existing framed floors. In fact, it was determined that the low-rise building had been designed for a full 12 stories to match the high-rise tower, but the construction had stopped at the third floor, which then served as a roof over the second floor. This conclusion was confirmed during demolition of the clay tile providing fire protection around the low-rise columns and further investigation of the existing topping slab on the low-rise roof. At these locations, the existing columns were found to have bolt holes in their webs and flanges to accept splice plates for future columns above.

Part 2 of this article will appear in a future issue and will discuss renovations associated with life safety improvements and enhancements to the space utilization of the 12th floor and roof.▪

STRUCTURE magazine

32

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.

Ed D. Cahan, P.E., S.E. (ECahan@Pennoni.com), is a project engineer with Pennoni Associates Inc in Philadelphia, Pennsylvania.

February 2014

Outside the BOx highlighting the out-of-theordinary within the realm of structural engineering

I

Rotation/wind speed test results from various turbine blade configurations.

n 2010, promoters and marketers agreed to construct a very visible power-generating project utilizing solar and wind in one of the busiest urban locations in the world – Times Square, New York. The power generated from this installation would provide lighting for the Ricoh billboard in the center of Times Square, with excess power stored in large batteries for periods of no sunlight and calm winds. At the inception of the project, photovoltaic panels had become fairly commonplace, but large vertical turbines utilizing wind resources to generate power had not been undertaken to this magnitude. From an environmental standpoint, the reduction of 52 short tons of carbon dioxide per year was very attractive. When CBI Consulting became involved, the scope of work was simply to confirm compliance of the 40-foot-long structure with the New York State Building Code.

The turbines had been manufactured in California and trucked across the country. From the manufacturer’s standpoint, the turbines were a product, not a structure requiring the services of a licensed engineer. The engineer for Ricoh, who had designed the supports for the turbine which projected from the Ricoh Building, sought assurance that the loads provided by the manufacturer were realistic and that the turbines, measuring 6 feet 7 inches in diameter by over 40 feet long, were of sufficient size to be classified as a structure according to the City of New York. What appeared on the surface to be a relatively simple task quickly turned into a complicated analysis, and involved the services of an erector and a mechanical engineer with knowledge about bearing function. Putting trailer truck-sized objects on the face of a building in Times Square was not going to be an easy task.

The calculations provided by the manufacturer were very basic, consisting of the weights of the turbines at the building connection points. When

Vertical Turbines in an Urban Environment

By Craig E. Barnes, P.E., SECB

Craig E. Barnes, P.E., SECB, is the Founding Principal of CBI Consulting Inc. Craig is also a member of the STRUCTURE Editorial Board. Mr. Barnes can be reached via email at cbarnes@cbiconsultinginc.com.

34 February 2014

CBI began working on the project, one of the turbines was already in place on the side of the building and the manufacturer, having delivered the product, felt that its job was done. The engineering issues that had to be addressed in order to satisfy the local requirements included the following: • Were the loads provided by the manufacturer accurate and sufficiently encompassing so that the brackets provided by the building engineer’s design were adequate?

• As a two-component manufactured product, but a one-component installation, were the loads appropriately distributed to the support points?

• Were the bearings that would allow the unit to spin adequate for the job?

• Would the turbine freewheel during high winds, or would it lockdown or modulate so as not to self-destruct?

• What was the appropriate load combination for design?

• How would the aerodynamic characteristics of the turbine change if ice were to form on the vanes?

• How did the effective wind surface change with ice build-up?

• How could the units be rigged for installation and removal so as to maintain appropriate alignment?

• Would it be possible to service/replace the generator and more wear-sensitive elements, such as the bearings, without having to remove the turbines from the building?

It became apparent that the engineering for manufacturing the product and the engineering for transporting and erecting the product were entirely different things. The realistic environmental loads (wind, ice, seismic) magnified the challenges even more. The manufacturer had success with a single 20-foot turbine, but needed two 20-foot turbines stacked in order to meet the allowable space on the building while generating the appropriate amount of power. Stacking the units made sense from a product standpoint, but

View from turbines from grade.

Mid-point collar connection between two 20-foot turbine sections.

created unknowns with respect to how the loads would be distributed to the building and within the combined product.

With regard to wind issues, test reports for other models of the manufacturer’s product were not considered acceptable by the approving authorities (see chart on page 34). In order to verify the product design assumption that the turbine would stall and not self-destruct when the wind speed reached 80 miles an hour, the manufacturer performed a full-scale wind test of a 20-foot turbine at its site in California.

Hess Engineering Inc. of Los Alamitos, CA observed and reported on this test. Having verified the manufacturer’s design assumptions with regard to high wind performance, it was still unknown how much load would need to be resisted by the connections to the building.

Furthermore, what would be the wind effect on the components of a product consisting primarily of individual vertical panes and a central steel core? Product engineering calculations were absent in this regard.

Clearly, wind passes over the open turbine in a manner similar to the behavior of an airplane wing, but the percentage of wind that passes through was unknown. Treating the turbine as a two-dimensional solid sign placed a large penalty on both the product and the building supports. Through a process of rationalization, CBI determined that assuming a 76% solid sign would be an appropriate basis for generating the design loads that would be resisted by the connections to the building. The parties agreed that it was not necessary to combine a full code-level wind with the increased crosssection that might result from ice build-up.

In fact, review of historical wind patterns in Times Square suggested that it would be almost impossible for this location to receive the code-prescribed, design-level wind load. In addition, the installation was planned for no more than a 10-year life.

Proceeding forward, calculations revealed that reinforcement of supports for the turbine would be necessary. The product manufacturer disagreed with the approach, and did not agree to participate in the re-engineering of the product support components.

Calculations confirmed the structural sufficiency of the vanes and the pipe core.

With loading issues resolved, the 5,300pound turbines were removed by North Shore Sign from the Ricoh building and brought to North Shore’s shop on Long Island. The Ricoh project sponsors initially engaged North Shore solely to undertake the erection, but it turned out that their well-equipped metal fabrication shop would be needed for the structural retrofit. Once the turbines were at the shop and while they were being observed on the flatbed, it became apparent that even for the short period of time that they had been in place, components of the central bearing between the two 20-foot lengths had been sufficiently misaligned to cause scarring of certain components.

That revelation highlighted the need to investigate the flexing movements of the turbines while being loaded for shipment at the manufacturer’s plant, flexing during cross-country transport, and erection from the horizontal to the vertical position in Times Square. The erector had received no guidance from the manufacturer as to the erection process, and simply used steps to which they were accustomed for normal billboard erection. In order to assess the movement that the units experienced, the team engaged the survey component of Nitsch Engineering of Boston to record flexing of the turbines during the erection process. That data would be used

by CBI Consulting for a micro-evaluation of joinery elements.

Engineering analysis revealed that using the current erection process would require the turbine unit to be disassembled and retrofitted with a more robust central connection.

Alternatively, an external structural steel strongback frame consisting of hollow structural sections (HSS) and extending the length of the two units – connected to the turbine at the top, bottom, and midpoint – would restrict the flexing so that the existing components would not be overstressed. The team chose the latter course of action as the best option. To provide further assurance, North Shore fabricated a structural metal containment collar to ensure that damage to the central connector, unseen

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February 2014

40-foot turbine arriving at Times Square.

40-foot turbine suspended from the crane during installation process.

Solar panel installation with turbines in place.

during the erection process, would not progress to a point of instability.

During the process of sorting out structural issues, the manufacturer of the turbine developed a more efficient generator component. Furthermore, the new generator was also reported to be more robust and more easily swapped out for repairs should they become necessary. This would allow the turbine to remain in place for periodic servicing.

Although the component itself was more costly, using it would eliminate the estimated cost to remove and erect the turbines (approximately $250,000 to cover working off-hours), Time Square traffic disruption, and the commitment of labor, materials, and equipment.

The main lesson learned from this experience is that product design, manufacturing, and engineering for a product of this complexity requires careful and thoughtful planning and coordination by all parties, well in advance of budgeting and manufacturing. The product engineer may be working with a completely different perspective than the structural engineer in the vertical construction industry.▪

Great achievements

notable structural engineers

Frank Heger

By Glenn R. Bell, P.E., S.E., SECB

F

rank Heger was a vanguard of the engineering industry, a visionary with his work, and a champion for public safety. From the late 1970s to 1982, the author witnessed the evolution of Frank’s most well-known work in geodesic spheres, “Spaceship Earth” at Disney’s Epcot Center. In 1980, he developed the revolutionary Soil-Pipe Interaction Design Analysis (SPIDA) software – the first-ever computer program combining heavy mathematical and theoretical computations for the design of buried pipe systems. In addition, Heger performed outstanding investigative work for the L’Ambience Plaza Collapse in 1987, which led to receiving the 1992 Construction Index Excellence Award for his personal research into the matter.

From 1955 to 1963, Heger served as an associate professor at Massachusetts Institute of Technology (MIT). In 1956, he joined two of his MIT colleagues, Werner Gumpertz and Howard Simpson, to found Simpson Gumpertz & Heger Inc. (SGH). The author personally was fortunate enough to spend over two decades under Frank’s tutelage, working on projects which were challenging, iconic, and innovative. The following highlights just a few of his many tremendous achievements.

House of the Future After World War II, the United States had grown weary of years of turmoil, and the Walt Disney Company sought to provide some relief. Disney enlisted the Monsanto Chemical Company to construct a solarheated house made entirely out of plastic, a

rarely used, ultramodern material for the time.

In turn, Monsanto asked Marvin Goody at MIT’s Plastics Research Laboratory to help design the house. Part of the expectation was to change the perception of plastics from a cheap substitute material to a high-quality engineered material that would keep construction costs down and achieve modern results.

Thus, the year 1954 proved to be a turning point in the use of structural plastics.

Heger was an assistant professor at the time and was put in charge of structural engineering on the project. He partnered with fellow MIT professor, and frequent collaborator, Albert Dietz. Despite modest knowledge of plastics, the two engineers determined that the structure had to be especially stiff, and that creep and deformation due to long-term loads had to be carefully predicted. They paid close attention to dead weight, live loads, wind loads, snow loads, earthquake loads, and thermal stresses due to a possible 100º F difference in temperature between the exterior and interior. The uneven nature of solar heating and the inability of fiberglass-reinforced plastics (FRP) to yield before failure added significantly to the project’s complexity.

Heger and Dietz designed the house to have a central core with four symmetrical cantilevered wings. The wings, floor, ceiling, and roof of the house were constructed as a continuous piece to provide the greatest stiffness and strength using the least amount of plastic. The designs of the walls and cross-sections were based on a careful analysis of forces within the structure.

The lead-up to construction included a host of tests. A six-week strain and deflection test

Monsanto house of the future.

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Frank Heger at his desk.

under the full design load of 50 psf showed no appreciable creep. Other laboratory tests demonstrated that materials could bear a 75º F heat differential, nearly double the planned loads for a forty-eight hour cycle, with no tendency to creep or otherwise malfunction. The demonstration house at Disneyland would be the real test. Millions visited the house during its decade-long life as an attraction. When set for demolition, it was said that a wrecking ball bounced off the house. It was eventually cut apart by hand. The project’s success heightened Heger’s burgeoning reputation as an authority on structural plastics, leading to decades of work on future projects.

Expo ‘67 World Expositions (Expos) offered a chance for the international community to showcase cultural and societal pride. In the 1960s, amid great international tension due to the Space Race and other issues, the U.S. pavilion planners for the Montreal Expo ’67 sought to create a technically complex and memorable structure. They asked visionary architect Buckminster Fuller to design the pavilion.

Fuller first proposed a dome-shaped pavilion making use of tensegrity, an experimental design geometry he had developed involving a series of rods and cables assembled so that tension and compression members alternated in a series. The concept’s unique nature meant that no one instinctively knew if the design would work. Fuller and the planners needed someone with structural engineering expertise to make the necessary design computations, and their search led them to Heger.

Triple Protection Against Corrosion Frank Heger at Expo ‘67.

three-point tests, full-scale tests on both embankment and trench-laid pipe, and his broad knowledge of constitutive soil properties, he created a computer program called Soil-Pipe Interaction Design and Analysis (SPIDA). Designers could use it to analyze pipes and soil as separate but interconnected systems, and to evaluate the necessary reinforcement for a pipe based on these analyses.

Frank’s revolutionary software was the first that could execute complicated mathematical and theoretical computations in the design of buried pipe systems. Engineers no longer had to calculate the forces on each section of pipe by hand, as SPIDA could solve these equations at an unprecedented speed, allowing engineers to design pipe networks quickly and confidently. The development of SPIDA also led to the discovery that pipes buried using the sloped-wall trench method needed nearly twice the reinforcing steel as similarly situated pipes buried using the vertical trench method. Before the creation of SPIDA, it was believed that these methods required the same amount of steel.

SPIDA

Simpson Gumpertz & Heger

Heger recognized that buried infrastructure is the life-line of our society, and ensuring the long-term performance of buried infrastructure components and systems requires a thorough understanding of structural behavior, material response, and the effects of the environment. He capitalized on his experience with materials and structural behavior to advance the industry in the design and investigation of buried pipes. In the late 1980s, the American Concrete Pipe Association (ACPA) approached Heger and SGH to design a computer program that would analyze soil characteristics and design pipes.

Heger’s understanding of pipe technology and design showed in the innovative solution that he developed for the ACPA. Using

Heger enjoyed more than four decades working in the field that he loved with his closest colleagues. He often said that SGH’s success was because he hired people who were smarter than he was. The author always found this curious coming from a true genius. It is doubtful that he ever succeeded in hiring anyone who surpassed his intelligence and vision, but it reflected Frank’s attitude toward working with people.▪ Glenn R. Bell, P.E., S.E., SECB (info@sgh.com), is the Chief Executive Officer at Simpson Gumpertz & Heger Inc. in Waltham, Massachusetts.

STRUCTURE magazine

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February 2014

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The team ultimately decided to pursue a geodesic geometry and designed a 250-footdiameter, three-quarter geodesic sphere. Until this point, mapping geodesic geometry onto a sphere had never been attempted for anything so large in scale. Heger’s design and calculations served as invaluable contributions.

The construction of the dome posed many challenges. The drawings called for the entire structural skeleton to be exposed, evoking latticework, so all of the members from top to bottom needed to be uniform in appearance.

However, because the highest members did not require much strength in comparison to lower components, using uniform members throughout the dome would have been inefficient. Heger innovatively chose to design the dome using hollow cylindrical tubes to keep a uniform appearance while minimizing material. Moving down the sphere, he designed cylinders with increasingly thicker walls, until the members at the bottom of the dome were solid.

In response to the architects’ desire for a lacy aesthetic, Heger and his team conceived, designed, and tested a novel system of welded cast steel hubs for the individual joints. Like the dome’s members, the hubs had to support the dome, as well as contribute to its appearance. To be sure of the hubs’ strength, Heger designed and built a testing machine that would apply the peak values of compression and tension forces expected within the dome.

Heger envisioned a structure that was inherently stable during construction, and he spent a good deal of time convincing the construction crews that, because geodesic domes are self-supporting, external scaffolding was unnecessary. The contractor reluctantly agreed and proved him correct when construction was completed without issue.

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new trends, new techniques and current industry issues

InSIghtS

The Progression of High Strength Concrete

By Kevin A. MacDonald, FACI

T

he definition of high strength concrete continues to change. This change occurs as the art of achieving a particular strength is reduced to practice, and the structural requirements push at the edge with needs for higher strength. One such example is the CN Tower in Toronto, with its required strength in 1976 of 5000 psi. At that time, this was difficult to achieve.

Today 5000 psi concrete is routinely used and produced without special precautions.

In the manufacturing of high strength concrete, there are significant differences from those seen in practice just a few years ago.

Cementitious components and content, admixtures aggregates and curing have changed.

Once the province of high cement contents and silica fume, much of the developments over the last decade have revolved around a better understanding of, and attention paid to, the microstructure of the concrete. High strength concrete can be modeled as a three phase system – the paste, the aggregate and the interface between them (Figures 1 and 2). By taking this approach, an engineered composite material can be designed.

Actions taken to modify the interfacial transition zone between the aggregate and paste have increased the load transfer between the paste and aggregate; thereby increasing the strength of the concrete. It is the action of meta-kaolin, silica fume and other finely divided materials in modifying this interfacial transition zone that originally led to significant increases in strength. These materials were once used at high replacement levels, frequently greater than 10%. While high strength was often achieved, the workability and susceptibility to fracture of the concrete were problems that ultimately limited the strength.

In modern high strength concrete, blends of smaller quantities and fractions of silica fume result in large increases in strength without compromising the ability of the mixtures to be placed. In many cases, ternary or even quaternary blends of pozzolanic material with Portland cement are seen in practice.

One of the reasons for these blends is that the heat generated during the hydration process can cause residual stress within the paste, and reduce the strength of the concrete. While these types of effects can readily be removed in metals by annealing, no such process is

Figure 1: Thin section of concrete showing microstructure of paste. Red arrows are typical flyash particles.

Figure 2: Thin section of concrete showing microstructure of paste. Note the relatively low degree of hydration of the slag particles (red arrows).

available for concrete. The curing process must be engineered to control the hydration reaction so residual stresses are minimized.

Temperature monitoring or other devices are used to track the progress and monitor the reaction that produces the binder.

The literature at the turn of the 20th century often referred to the curing process as annealing. While having very little to do with the concept of heat treating of metals, this curing, when performed properly, is a critical factor in the performance of higher strength concrete.

Strengths up to 20,000 psi have been realized using pozzolanic materials, dispersants, limestone modified cements and careful attention to aggregate materials selection. The limestone acts to nucleate the reaction and reduces the quantity of unhydrated-cement.

Admixture technology has progressed.

Stabilizing admixtures and dispersants with a low affinity for the solid surface, where a large fraction of dispersant remains in solution, has allowed mixtures to be held in a state of “suspended animation” while the concrete is placed. They can perform predictably, allowing scheduling of the construction process.

Retarders, dispersants and stabilizers will increase the strength.

One of the difficulties that the designer of high strength concrete mixtures encounters is the ability to have workable concrete with very low water/cement ratios. Use of modern high-efficiency dispersants (super plasticizers) has led to observed autogeneous drying of materials due to hydration or vaporation due to high temperature. As a consequence, some very low water/cement ratio concrete have shown good performance in the laboratory but poor performance in the larger structural

members, where the heat of hydration is not as readily dissipated and where the sample is not immersed in water for 28 or even 56 days.

These limits are advancing by innovations such as the use of lightweight aggregate for internal curing and steel whiskers to distribute stresses.

Aggregate materials are no different. As the paste strength increases, and the interfacial transition zone densifies, the strength of the aggregate or the presence of fractures therein become a limiting factor. Reducing the maximum particle size and carefully selecting the geological origin of the materials can lead to significant improvements in strength.

Recognition by the design and construction team that the concrete strength does not need to be achieved at seven or 28 or even 56 days, but only as the structure is loaded, allows mixtures that have relatively low cement contents and very high pozzolanic replacement to achieve compressive strengths in excess of 15,000 psi.

Care must be taken in the production of high strength concrete in order to ensure that the performance of the concrete in situ is what was intended in the design. Raw materials, batching and handling at the plant and at the installation site must be controlled. Without an understanding of the importance of high strength concrete at the production plant and by the individual vehicle drivers, it will be more difficult to achieve performance of the structure.▪

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February 2014

Kevin A. MacDonald, FACI, is President and Principal Engineer for Beton Consulting Engineers LLC, Mendota Heights, MN. He was named a Fellow of ACI in 2004. Kevin can be reached at kmacdonald@betonconsulting.com.

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STR_7-13

Bridge resource guide

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

ADAPT Corporation

LARSA, Inc.

Description: Easy-to-use and practical software for 4D construction phase analysis of any segmentally constructed bridge. ABI calculates time-dependent behavior of concrete, tendons, and stays. Particularly well suited for balanced cantilever and spliced girder bridges. Handles geometry, camber, and stress control during construction and reports service load design values.

Description: Advanced software for the design and analysis of bridges and structures, LARSA 4D addresses the specialized needs for a variety of bridge types including cable-stayed, suspension, and curved. Standard in leading U.S. firms for bridge design and construction analysis, and continues to lead innovation in analysis and support.

Web: www.adaptsoft.com Product: ADAPT-ABI

Bentley Systems

Simpson Strong-Tie

Web: www.Larsa4D.com Product: LARSA 4D

MDX Software

Description: A powerful modeling and analysis solution for small to medium-sized concrete bridges of all types: precast, cast-in-place, reinforced, and post-tensioned. This comprehensive bridge information modeling (BrIM) system offers a synthesis of geometric modeling, substructure, superstructure analysis and design, and load rating in a single, information-rich environment.

Description: Steel bridge design and rating software according to AASHTO, ASD, LFD, LRFD, LRFR specs.

Pile Dynamics, Inc.

Web: www.pile.com/pdi Product: Systems for QA-QC of Bridge Foundations

Description: A comprehensive software for structural design and analysis. Used worldwide by engineering firms, government organizations, contractors, and project consortia, RM Bridge sets the standard for both routine and signature bridge design and delivery.

Description: Pile Driving Analyzer® (Dynamic Load Testing, Pile Driving Monitoring) Pile Integrity Tester Thermal Integrity Profiler (for cast-in-place foundations) GRLWEAP (Pile Driving Simulation/Wave Equation Analysis) PIR (ACIP/CFA Automated Monitoring Equipment); Cross-Hole Analyzer (Single/Crosshole Sonic Logging); SPT Analyzer (SPT hammers Calibration); E-Saximeter (Blow Count, Driving Logs, Energy Measurements) LITE (Steel Pile Depth).

Cintec Reinforcement Systems

POSTEN Engineering Systems

Product: RM Bridge

Web: www.postensoft.com Product: POSTEN Multistory

Web: www.cintec.com Product: Archtec

Description: Reinforcement of masonry arch bridges to bring them up to code.

CTS Cement Manufacturing Corporation Web: www.ctscement.com Product: Rapid Set® Low-P™ Cement and Type-K Cement Shrinkage Compensating Concrete

Description: Complete bridge deck overlays faster with Rapid Set Low-P cement. Get better quality, lasting performance and an in-place cost less than Portland cement concrete. Type-K Cement Shrinkage-Compensating Concrete has been used in over 800 bridge decks with reduced permeability, excellent durability, virtually no cracks and increased concrete life cycle.

Devco Software, Inc.

Web: www.devcosoftware.com Product: LGBEAMER v8

Fabreeka International, Inc. Web: www.fabreeka.com Product: Expansion Bearing

RISA Technologies

Hayward Baker Inc.

Description: A complete range of geotechnical construction techniques for build or design-build solutions for new bridge construction and remediation of existing bridges, specializing in deep foundations, foundation rehabilitation, and ground improvement. Old and new bridges benefit from decades of advancement of geotechnical construction techniques.

Description: Simpson Strong-Tie offers anchoring and fastening products for concrete and masonry, including: codelisted solutions; cold-formed steel connectors; direct fastening systems; general purpose anchors and fasteners; restoration products; carbide drill bits, and accessories. For the new Product Guide visit the website.

Strand7 Pty Ltd

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. Preprocessing, solvers (linear and nonlinear static and dynamic capabilities) and post-processing. Features include staged construction, quasistatic solver for shrinkage and creep/relaxation problems.

StructurePoint

Web: www.StructurePoint.org Product: Concrete Design Software

Description: spColumn is widely used for design and investigation of bridge piers, shear walls as well as typical framing elements in structures including slenderness effects and biaxial loading. Can also investigate irregular sections with any reinforcement layout that are impossible to find on design charts or to do by hand.

Western Wood Structures

Web: www.risa.com Product: RISA-3D

Description: With RISA-3D’s versatile modeling environment and intuitive graphic interface, you can model any structure from bridges to buildings in minutes. Get the most out of your model with advanced features such as moving loads, dynamic analysis, and over 40 design codes.

Structural design has never been so thorough or easy!

Web: www.s-frame.com Product: S-STEEL Design

Web: www.westernwoodstructures.com Product: Timber Bridges

Description: Timber bridges are naturally beautiful, durable and cost-effective. Western Wood Structures designs and supplies vehicular, pedestrian, golf course, park and residential bridges, using the highest quality, pressure-treated, glulam timber. Experience our enduring commitment to quality, achieved through our performance as an on-time designer, supplier and erector of timber bridges.

Wheeler

Description: Use S-STEEL to design your steel structures – all or partial. Code check and auto design for both strength and serviceability. S-STEEL supports composite beam design, staged construction, numerous steel design codes and a large choice of optimization criteria and constraints.

Comprehensive design reports include equations, clause references and interactive graphics.

Product: S-FRAME Analysis

Description: Slide and expansion bearings for bridge deck.

Web: www.HaywardBaker.com Product: Geotechnical Construction

Description: With sophisticated post-tensioning algorithms, only POSTEN automatically & efficiently designs the tendons and rebar (no hours of fiddling with drapes). The only Post-tensioned concrete software that includes design of moment frames, seismic & wind, columns, torsion, and truly sustainable design (with LEED documentation).

S-FRAME Software Inc.

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, including the 2010 Supplement (2013 IBC) compliant. ProTools include shearwalls, framed openings, X-braces, joists and rafters.

Description: Simpson Strong-Tie offers repair, protection and strengthening systems for concrete and masonry, which complements its anchor systems offering. The line includes products for: general concrete repair; crack repair; nonstructural injection; joint sealing; performance coating, and specialty products. The product guide is available at website.

Product: Anchoring and Fastening Products

Web: www.mdxsoftware.com Product: MDX Software

Web: www.bentley.com Product: LEAP Bridge

Web: www.strongtie.com Product: Repair, Protection and Strengthening Systems for Concrete and Masonry

Description: A powerful yet easy-to-use 4D structural analysis and design environment. Featuring linear and advanced nonlinear analysis capabilities, multiple design code support, a variety of material models, flexible load combination methods and fully integrated steel design, reinforced concrete section design and foundation design tools.

Web: www.wheeler-con.com Product: Panel-Lam

Description: Shop manufactured Timber Bridge Kits suitable for vehicular and recreation applications.

Williams Form Engineering Corp.

Web: www.williamsform.com Product: All-Thread-Bars

Description: Williams Form Engineering Corporation has been providing threaded steel bars and accessories to the bridge construction industry for over 90 years. Williams’ pre-stressing/post tensioning 150 KSI All-Thread-Bars are high tensile steel bars available in seven diameters from 1 to 3 inches with guaranteed tensile strengths to 969 kips.

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.

STRUCTURE magazine

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February 2014

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Spotlight

A Building that Teaches

By Dmitri Jajich, P.E., S.E. and David Horos, P.E., S.E., LEED® AP Skidmore, Owings & Merrill LLP was an Outstanding Award Winner for the Lee Hall III project in the 2013 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings $10M to $30M).

T

he integration of form and structure is implicit in the earliest known definition of architecture – Vitruvius’ ideal of “firmness, commodity, and delight.” The design of Clemson University’s newest addition to their School of Architecture, Lee Hall III, is a case study in the contemporary application of this ageless idea in a space that aspires to instruct its design-oriented occupants every day.

The 55,000-square-foot glass and masonryclad structure encourages informal learning through observation of its energy efficient design and exposed functional and structural systems. It houses academic programs in architecture, art and planning, faculty offices and student work-space. The building was designed by Thomas Phifer and Partners with locally based McMillan Pazdan Smith Architecture. Transolar was the climate engineers, and Skidmore Owings & Merrill LLP (SOM) provided the structural engineering.

Lee Hall III comprises an open 35-feet-tall double-height space that houses a secondary internal structure of mezzanines and bridges.

Nearly all of the building’s superstructure components are steel and provide a direct manifestation of the architectural expression.

The structure’s roof is a lightweight composite concrete deck structure supported by exposed W14 steel beams. The roof rises four feet in a gentle arc to help drain a planted green roof, which is punctuated by 25 seven-foot diameter skylights located directly above steel “column trees”. The “column trees” are the most prominent feature of the building and consciously draw attention to the structural steel system.

They are comprised of 10.75-inch diameter seamless steel pipes with 1-inch thick walls and four curving “arms” built-up out of flat 1.25- and 1-inch thick steel plate. The unusually thick-walled pipe columns (ASTM A106 pipe typically used in high-pressure oil and gas-line construction) allowed for their remarkable slenderness and enhance their dramatic elegance.

The four curving “arms” that top each column reach out and support two parallel rows of continuous W14 steel beams while opening the roof directly above each column to a skylight.

Each of the twenty-five column trees has its own unique geometry due to the changing curvature of the roof, but all column tree arms were fabricated entirely from flat plate, the geometry of which was determined from simple geometric rules. The realization of complex, organically inspired free-form architectural shapes from the careful assemblage of flat plate and straight pipe was a key to the project’s success.

The subtly curving roof extends beyond the glazed curtain walls at the north and south faces of the building, where the edge of the structure is supported by a row of super-slender “Y” columns. The outdoor roof is rendered as a trellis made of perforated metal panels supported by exposed W6 steel beams. The exterior “Y” columns are reminiscent of the interior “column trees”, but flattened into a two-dimensional plane. Although the geometry of each “Y” column is different, the castings connecting the vertical base of the “Y” to the branching arms are identical. Repetition of the same casting geometry made the connections feasible from a cost standpoint.

At each end of the masonry-clad east and west walls, brick hovers beyond the building enclosure in an 18-foot double cantilever with no lateral support bracing. These cantilevered brick “wing walls” shade the ends of the north and south window wall in a subtle but dramatic extension of the brick surface.

The cantilevering steel structure resists vertical brick loads, and lateral wind and seismic loads, in a manner similar to an airplane wing.

The pedagogical value of Lee Hall III’s structural steel derives from its elegant dual functions – as both a load-carrying system and a sculpturally expressive medium. It is equally instructive that this successful marriage of function and form was achieved without expensive or unconventional fabrication techniques, special finishes, exotic connections, nor the higher tolerance “AESS” designation typical of this type of design and construction.

Rather than simply applying AESS requirements to all the exposed steel, the architects and the structural engineer identified only those aspects of AESS that were critical to the project’s success (e.g., tighter tolerances

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were not required, but removal of mill marks from the window wall’s steel was) and specifically defined exposed painted structural steel requirements specific to the job. Remarkably, all the architectural steel in Lee Hall III was fabricated and detailed no differently than conventional structural steel. The entire team worked closely to refine conventional simple connections and fabrication techniques that could be built without undo expense. All connections were fully detailed in the structural drawings so the alignment, appearance and architectural character could be evaluated prior to the shop-drawing phase, thereby eliminating the fabricator’s connection engineering time and costs. Although one of the structure’s signature features is a curving, warped roof, no curved steel was used in the building’s frame – the geometry is a series of simple faceted arcs which nearly matches a true curve. The structural drawings clearly and simply conveyed the geometry – and alleviated the need for three-dimensional modeling or digital files.

The result of this innovative structural design approach and intensive coordination is a conventionally constructed building that showcases the expressive use of structural steel, while keeping costs in check. Lee Hall III’s structure is minimal, but clearly expressed as a rational system whose logic is inextricably linked with the building’s architecture. It stands as a model for its varied design-savvy users.▪ Dmitri Jajich, P.E., S.E., currently works from SOM’s London office.

David Horos, P.E., S.E., LEED® AP, is Director of the Structural Engineering Studio at SOM.

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Focus on Education

New Subscription Plan offers Unlimited Live NCSEA Webinars Plan your 2014 continuing education hours with NCSEA’s new Webinar Subscription Plan. For just $750, you can receive unlimited live NCSEA webinars for one year.

The subscription plan is open only to NCSEA members – members of NCSEA Member Organizations and NCSEA Sustaining, Associate and Affiliate members, and membership status will be verified. It includes live NCSEA webinars only and has a guarantee that a minimum of ten webinars, and up to 24, will be offered. A subscription plan can be started at any time. The one-year plan begins on the first day of the month in which the subscription application is received.

Each webinar includes speaker slides, notes, and one free PDH certificate. If others watch the webinar with the subscriber and wish to obtain a certificate, they may purchase a certificate for $30 within two weeks of completing the webinar. After two weeks, additional certificates will not be available.

The individual subscription plan was developed in response to numerous requests from small structural engineering firms and sole proprietorships, for webinars they could afford, states NCSEA Executive Director Jeanne Vogelzang. “Offering a plan like this, to NCSEA members only, is also expected to benefit our Member Organizations (MO’s), who can offer the plan as an incentive for new members to join, as well as a reason for

3 Reasons to Sign Up for the NCSEA Webinar Subscription Plan 1. A flat rate of $750 gives you access to all live NCSEA webinars over the course of one year. If you attend just 10, your cost is $75 per webinar, a savings of over 70%!

2. NCSEA online webinars are targeted, quality programs, led by experts and leaders in structural engineering, all from the comfort of your own computer. All webinars are NCSEA Diamond approved for 1.5 PDH hours.

3. It’s one more benefit of NCSEA membership – only our members can take advantage of this terrific plan!

Sign up today at www.ncsea.com! current members to renew. NCSEA has a proven track record, having offered webinars since 2006, and structural engineers who sign up for this plan know they will get their money’s worth in excellent, and abundant, continuing education.”

Lateral Review Course for SE Exam Set for March The NCSEA SE Review Course, offered by NCSEA in conjunction with Kaplan Engineering, will hold its Lateral Course March 8-9. The Vertical Course, held January 18-19, 2014, was recorded and can be played back anytime. This targeted review assists engineers in preparing for the SE Exam, and includes: Over 28 hours of instruction with an emphasis on building design: • Including sessions on exam strategy and bridge design • Key topics of structural code

• Efficient analytical methods • New material in the 16-hour Structural exam • Typical exam questions • Problem solving techniques • Exam day skills • 24/7 playback – study anytime There are significant discounts available for groups taking the course. Log on to www.ncsea.com under Education, for more information and to register for the course.

NCSEA News

NCSEA Webinars March 13, 2014 Floor Vibrations: Technical Background and AISC Design Guide 11, Part 1 Brad Davis, Ph.D., S.E., Department of Civil Engineering, University of Kentucky March 27, 2014 Floor Vibrations: Technical Background and AISC Design Guide 11, Part 2 Brad Davis, Ph.D., S.E., Department of Civil Engineering, University of Kentucky April 10, 2014 Load Generators – What Exactly is My Software Doing?

Sam Rubenzer, P.E., S.E., FORSE Consulting 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. Register at www.ncsea.com.

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March 20 – 21, 2014 • The Meritage Resort & Spa, Napa, California

This interactive session includes a new approach to negotiations, and will offer a variety of field-tested ways to get the value and compensation you deserve, from current and future clients.

Steven Isaacs, P.E., Division Manager, FMI Corporation, assists firms in strategic planning, financial controls, project performance/ profitability, negotiation, ownership transition, joint ventures and partnering.

Brian Dekker

– Steven Isaacs Professionals enjoy and count on on their work, salaries, and benefits, and, especially today, are less willing or able to retire. Determine how your firm should react to retain talented employees.

Ownership Transition Case Studies

– Jennifer Morrow This session will focus on effectively dealing with conflict in the workplace and beyond.

Discuss and develop new strategies and best practices, and learn what other principals are doing and thinking.

Brian Phair

Baby Boomers Delay Retirements: Career Bottleneck at the Top

How does a firm transition ownership?

Leaders of three engineering firms that have confronted these issues will tell how they did it.

Mark Aden

The Winter Leadership Forum will take place at the beautiful Meritage Resort & Spa in Napa, California.

The Resort is centrally located in idyllic Wine Country at the southern tip of Napa Valley and has an evening shuttle for guest transportation to Downtown Napa’s restaurants and tasting rooms.

Register at www.ncsea.com

Jennifer Morrow, MDR, Executive Director of Commercial Services at ADR (Alternative Dispute Resolution) Systems of America, LLC, consults with law firms and companies on the effective use of mediation, arbitration and all types of dispute resolution processes.

Jennifer Morrow

Kevin Sido

Managing the Cost of Conflict: Mediation, Arbitration or Litigation?

– Jennifer Morrow and Kevin Sido This session will explore all dispute resolution processes available and provide tools for evaluating when to use which process. Learn the nomenclature, know your options and make more informed decisions to minimize the impact on your time, your business and your reputation.

You’ve Been Sued – Now What?

What Engineers Need to Know to Structure Their Defense – Kevin Sido What should the Structural Engineer do when the summons is served and in the months that follow?

Robert L. Miller Associates & Sound Structures, Inc. (7 staff) Brian Dekker, President

PCS Structural Solutions (40 staff) Brian Phair, CEO

Leadership is a Full-Contact Sport: Dealing with Conflict in the Workplace

News from the National Council of Structural Engineers Associations

Steven Isaacs

Friday

Major Corporate Platinum Sponsor:

DCI Engineers (185 staff) Mark Aden, President

Last year I gained some valuable insights into how to differentiate our firm from our competitors in a challenging economy. The speakers provided fresh and practical lessons that I have applied throughout this year in real project pursuits. I found the Winter Leadership Forum very relevant and I look forward to attending again in the future.

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Michael Cochran S.E., SECB Associate Principal, Weidlinger Associates Inc. 2013-2014 SEAOC President

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The 2013 Winter Leadership Forum was a great experience providing useful fundamental management insights for individuals running an engineering office or thinking of starting their own firms. I highly recommend the Winter Leadership Forum to anyone to help keep them abreast of currently developing management practices.

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Bart Miller, P.E. Principal, Walter P Moore

Kevin Sido, attorney, is a senior partner in the Chicago office of Hinshaw & Culbertson. He is an author and speaker on construction law issues, and the editor of Architects & Engineers Liability, Claims Against Design Professionals.

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Get the Value You Deserve Without Ruining the Relationship – Steven Isaacs

Take Your Seat at the Table

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Winter Leadership Forum

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Attend the Structures Congress 2014 A premier event for structural engineers.

New ideas. New science. New resources. New colleagues. New business practices.

Boston, Massachusetts, April 3-5, 2014 Reasons to Attend • Learn from dynamic technical sessions – choose from more than 120 sessions • Take part in the Council of American Structural Engineers (CASE) Spring Risk Management Convocation • Network with colleagues – more than 1,200 attendees expected • Be inspired by two (2) renowned keynote speakers in Opening & Closing Plenary Sessions: Ioanni (Yannis) Miaoulis, Ph.D., President & Director of the Boston Museum of Science, and Tim Love, AIA, Utile Architecture & Planning • Attend a Pre-Conference Seminar & earn additional PDHs: Post-disaster Safety Evaluations, in cooperation with California Office of Emergency Services (CalOES) & Applied Technology Council (ATC) – 6.0 PDHs, or Design of Sustainable Thermal Breaks – 3.5 PDHs

“I’ve attended a great many Structures Congresses since my first one in Houston, back in 1983. I learn something new and important every time. I urge my colleagues, both those just getting started and those who are masters in their profession, to attend.”

William F. Baker, Jr., P.E., S.E., F.ASCE Partner, Skidmore Owings and Merrill LLP

Earn up to 18.5 professional development hours (PDHs).

Register now for the best rates, Early bird registration available until February 12, 2014. Visit the Structures Congress website at www.structurescongress.org.

2014 Fazlur Khan Distinguished Lecture Series The dates and speakers have now been set for the 2014 Fazlur R. Khan Distinguished Lecture Series to be held at Lehigh University, Bethlehem, PA. 1st Lecture: James R. Harris, Principal, J. R. Harris & Company, Denver, CO The Evolution of Building Design to Resist Earthquakes Friday, February 21, 2014 – 4:30 pm 2nd Lecture: Jon D. Magnusson, Senior Principal, Magnusson Klemencic Associates, Seattle, WA Structure Becoming Architecture: Case Studies of Aesthetics, Form, and Efficiency Friday, March 21, 2014 – 4:30 pm

New Features in Third Printing of ASCE 7-10

Visit the Lehigh University website at www.lehigh.edu/~infrk/ for additional information.

Vision for the Future Report

Several important updates to ASCE 7-10 are included in the 3rd printing; these changes are also available as Supplement 1, which can be downloaded free on the ASCE website. The new content includes an expanded seismic commentary that replaces the commentary for Chapters 11-22. This new commentary features more background on design criteria and requirements for building (and non-building) structures and nonstructural components, and material-specific detailing requirements. In addition to Supplement 1 and this new commentary, an updated Errata 2 is also available for download from the ASCE website.

Visit the SEI website at www.asce.org/SEI and click on the ASCE 7-10 cover photo to see a list of supplements.

STRUCTURE magazine

3rd Lecture: Charles H. Thornton, Chairman, Charles H. Thornton & Company, LLC, New York, NY Renaissance, Rebirth and Disruptive Innovation Friday, April 11, 2014 – 4:30 pm

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What will the structural engineering profession be like in the future? What will the qualifications of structural engineers include? These questions, along with an introspective look at how the profession arrived in its current form and mechanisms for change, are explored in A Vision for the Future of Structural Engineering and Structural Engineers: A case for change. Produced by a Task Committee, appointed by the SEI Board of Governors, the report pictures the qualifications structural engineers of the future will need in order to respond to changes that are happening now and will continue in the future. Visit the SEI website at www.asce.org/SEI to learn more about the SEI Board of Governors’ current efforts and priorities, the 2011 Strategic Initiatives, and the 2008 Strategic Visioning.

February 2014

Quad Cities Chapter The Quad Cities Chapter took a tour of the Gerdau Ameristeel steel rolling plant in Wilton, Iowa on October 29, 2013. The facility is composed of a shredder, melt shop including an 80-ton capacity furnace, rolling mill and finishing/packaging end.

They produce merchant flats, angles and Special Bar Quality (SBQ) steel car leaf springs, round corner squares and cold draw flats. The tour was lead and hosted by Gerdau’s Regional Engineering Manager, Robert Howard, P.E. Mr. Howard did an excellent job preparing and giving a top-notch tour – everyone was impressed by the magnitude, efficiency and quality of the process. At the time of the tour, attendees were able to see A36 structural angles being rolled. There were 16 structural engineer attendees, including 3 students from Western Illinois University.

University of Texas at Arlington Chapter

Pittsburgh Chapter National Steel Day: Tour of the Former J&L Steel Mill On October 4, 2013, Chuck Betters of CJ Betters Enterprises welcomed ASCE SEI and affiliates for a tour of the former J&L Steel Mill and his company’s recycling operation on the site.

Members of the engineering community, including SEI, local student chapters, and retired professionals were afforded the opportunity to tour the site. The tour began with an extensive history of the facility, which included before and after aerial photos of the site. Samples of recovered materials were passed around, and an explanation of the latest technology in slag recovery was provided, along with how the company handles the variety of materials found during the recovery process. The group then visited the site, stopping frequently to view machinery, unprocessed materials versus finished products, excavation techniques, and the latest piece of equipment currently under construction. For more information about SEI Pittsburgh activities, please contact Linda Kaplan at lkaplan@gfnet.com.

St. Louis Chapter On October 18, 2013, St. Louis SEI Chapter completed another successful full day seminar event. The event awarding 6 PDHs to attendees, included 10 speakers on a variety of topics including buildings, bridges, investigative case studies, and BIM, as well as an exhibit hall. Key note speaker for the event was SEI president Donald Dusenberry discussing the roles of future structural engineers. The event was held at the Masonry Institute of St. Louis. Visit the SEI website at www.asce.org/SEI to learn more.

STRUCTURE magazine

Errata SEI posts up-to-date errata information for our publications at www.asce.org/SEI. Click on “Publications” on our menu, and select “Errata.” If you have any errata that you would like to submit, please email it to Paul Sgambati at psgambati@asce.org.

New Committee on Seismic Evaluation of Structures at Water and Wastewater Facilities SEI’s Technical Activities Division recently established the Seismic Evaluation of Structures at Water and Wastewater Facilities Committee. The purpose of the committee is to develop a guidance document to provide a consistent methodology for seismic evaluation of existing Water and Waste Water treatment (W & WW) facilities in any level of seismicity.

Structures associated with W & WW facilities often include special use buildings, rectangular and circular water holding basins, and large diameter pipelines which are not specifically addressed in existing guidance documents and standards for seismic evaluation of structures. The document is intended to be used by design professionals, utility districts, and municipalities looking to seismically evaluate existing W & WW facilities.

Committee members should be actively engaged in design and evaluation of water and wastewater facilities. To apply, fill out the online SEI Technical Activities Division application at www.asce.org/SEI.

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The Newsletter of the Structural Engineering Institute of ASCE

The University of Texas at Arlington SEI Graduate Student Chapter held their first two engineering seminars in October. On October 11 Alena Mikhaylova, Ph.D. Candidate, presented her research experience of spending her summer in East Asia under an NSF scholarship. Her research was on performance of steel fiber in precast concrete pipe construction. A good number of students and faculty attended and the presentation was very well received.

Later in the month Hugh Martin of Hanson Pipes & Precast presented on the design of a precast concrete inlet structure.

Join your local SEI Chapter or Structural Technical Groups (STG) to connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area.

If there is not an SEI Chapter or STG in your area, talk with your ASCE Section/Branch leaders about the simple steps to form an SEI Chapter.

Some of the benefits of forming an SEI Chapter include: • Connect with other SEI local groups through quarterly conference calls and annual conference • Use of SEI Chapter logo branding • SEI Chapter announcements published at www.asce.org/SEI and in SEI Update • One free ASCE webinar (to $299 value) sponsored by the SEI Endowment Fund • Funding for one representative to attend the Annual SEI Local Leadership Conference to learn about new SEI initiatives, share best practices, participate in leadership training, and earn PDHs. • SEI outreach supplies available upon request Visit the SEI website at www.asce.org/SEI for more information on how to connect with your local group or to form a new SEI Chapter.

Structural Columns

Get Involved in Your Local SEI Chapter

The Newsletter of the Council of American Structural Engineers

Updated for 2013 Tool 7-1: Client Evaluation Have you ever wanted to fire a client but didn’t know how? At what point in the relationship, should you fire a client?

CASE Tool No. 7-1, Client Evaluation, is a tool intended to help firms track who the better clients are and which clients are less favorable.

The CASE Toolkit Committee has revised this tool for 2013 to include: • A spreadsheet allowing flexibility to input data on clients over a 5 year period and compare clients based on revenue and expenses.

• The ability to adapt the spreadsheet to track projects instead of clients.

Foundation 1: Culture – Create a Culture of Managing Risks & Preventing Claims Tool 1-1: Create a Culture for Managing Risks and Reducing Claims (Updated in 2013) The most comprehensive CASE tool that provides sample templates and presentations that aid in creating a culture of risk management throughout the firm.

This tool has been updated in 2013 to include: • Updated PowerPoint presentations, scripts, and sample statements that allow users to modify for their own use.

• Case studies that highlight best practices and procedures to manage liability and limit risk.

Tool 1-2: Developing a Culture of Quality This tool was developed to identify some ways to drive quality into a firm’s culture. It is recognized that every firm will develop its own approach to developing a culture of quality but following these 10 key areas offer a substantial starting point.

The tool includes a white paper and customizable PowerPoint presentation to facilitate overall discussion.

Foundation 2: Prevention & Proactivity – Act with Preventative Techniques, Don’t Just React Tool 2-1: A Risk Evaluation Checklist Don’t overlook anything! A sample itemized list of things you should look for when evaluating a prospective project.

Tool 2-2: Interview Guide Getting “the right people on the bus” is one of the most important things we can do to mitigate risk management and yet we never learn about interviewing skills in school. It is the second tool related to the Second Foundation of Risk Management, Prevention and Proactivity. The tool will help your firm conduct higher quality interviews and standardize the process among all your staff.

Tool 2-3: Employee Evaluation Templates This tool is intended to assist the structural engineering office in the task of evaluating employee performance. The evaluations provide a method to assess employee performance and serve as an integral part of the company’s risk management program.

Tool 2-4: Project Risk Management Plan This plan will walk you through the methodology for managing your project risks, along with a few common project risks and templates on how to record and track them.

Tool 2-5: Insurance Management: Minimize Your Professional Liability Premium This tool is designed as a guide to help you provide critical additional information to the underwriter to differentiate your firm from the pack.

All of these tools and more are available at www.booksforengineers.com.

CASE in Point

CASE Risk Management Convocation in Boston The CASE Risk Management Convocation will be held in conjunction with the Structures Congress at the Sheraton Boston Hotel and Hynes Convention Center in Boston, MA, April 3-5, 2014. For more information and updates go to www.seinstitute.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 4:

7:00 AM – 8:15 AM

CASE Breakfast: The Storms are Coming, the Storms are Coming: The Need for a Revolution in Engineering Approaches to Climate and Disaster Risk Stephen Long, The Nature Conservancy

Developing an Internal Culture to Managing a Firm’s Risks Speaker – Michael Strogoff, Strogoff Consulting

1:30 PM – 3:00 PM

SE Agreements and Lessons Learned Speaker – Steven Schaefer, Schaefer Associates

3:30 PM – 5:00 PM

8:30 AM – 10:00 AM

Key Components to Starting Your Own Successful Engineering Practice – Panel Discussion Moderator – Chris Poland, Degenkolb Engineers

Mobile Technology for the Field Speaker – Theron Peacock, Woods Peacock STRUCTURE magazine

10:30 AM – 12 Noon

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Best Management Strategies in Business of Design Consulting Course March 19 -23, 2014; Chicago, IL This comprehensive 2014 update on the primary underpinnings of the successful A/E business, ACECs highly regarded Business of Design Consulting course is a unique playbook for building leadership and managing your firm at the most effective levels.

The 3½-day agenda is taught by an experienced faculty of industry practitioners and highlights current strategies for a wide array of critical, need-to-know business topics that will keep your business thriving despite a churning business environment, including how to manage change and build success in performance management, strategic planning and growth, finance, leadership, ownership transition, contracts and risk management, marketing, and more!

For more information and to register for the course, visit our website at www.acec.org/education/eventDetails.cfm? eventID=1473.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Upcoming ACEC Online Seminars – March Why Clients REALLY Select Your Firm March 4, 2014; 1:30 pm to 3:00pm Eastern Learn the best practices for building client relationships that last. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1508.

Design and Construction Cases in the Courts March 6, 2014; 1:30 pm to 3:00 pm Eastern Looking at notable 2013 appellate decisions concerning professional services agreements, construction contracts, and related rights and liabilities. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1538.

PR Tips, Tactics and Insights to Build Your Brand March 12, 2014; 1:30 pm to 3:00 pm Eastern Enhance your public image, gain greater visibility, and influence the opinions of target audiences, decision-makers, media and the public-at-large through effective PR strategies and positioning. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1519.

STRUCTURE magazine

Ensuring Profitable Growth, Developing Winning Strategies for Solid Measurable Results March 18, 2014; 1:30 pm to 3:00 pm Eastern To change your results and succeed in today’s competitive marketplace, you must adapt and change what you are doing. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1509.

Ethical Decision Making for PEs: Today’s Standards and Benefits March 20, 2014; 1:30 pm to 3:00 pm Eastern An in-depth look into the ACEC Professional and Ethical Conduct Guidelines, applicable standards of practice, and ethical For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1528.

Rebranding your Firm – Why? What? And How? March 25, 2014; 1:30 pm to 3:00 pm Eastern Navigate the process of why (or why not), what, and how to complete a successful engineering firm rebranding project. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1518.

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CASE is a part of the American Council of Engineering Companies

The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABETaccredited engineering program.

We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates.

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

In addition, the CASE scholarship offers an excellent opportunity for your firm to recommend eligible candidates for our scholarship. If your firm already has a scholarship program, remember that potential candidates can also apply for the CASE Scholarship or any other ACEC scholarship currently available.

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

ACEC Business Insights

CASE in Point

Donate to the CASE Scholarship Fund!

Structural Forum

opinions on topics of current importance to structural engineers

San Francisco – Oakland Bay Bridge Second Crossing

By Ronald F. Middlebrook, S.E. and Roumen V. Mladjov, S.E.

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he Bay Bridge is one of the grandest engineering achievements in American history, as described in the article on page 26. However, the recent renovation has not added a single lane to relieve traffic congestion, which has a negative impact on the Bay Area and California economies. There is one obvious solution for the problem – to build a second crossing between San Francisco and Oakland on an alignment approximately parallel to the original bridge.

After initially proposing this idea, the authors completed a feasibility study. We believe that the new bridge should be a double-decker, saving 15% of the cost versus two side-by-side decks and saving 50% of the shade cast on the Bay. The west span should be a new suspension bridge in harmony with the existing, with complementary spans up to 2500 feet (760 m); the east span can be a new bridge with spans similar to the existing east portion, but it would be more efficient to retrofit and relocate the existing structures onto new foundations on piles near the current alignment (see Figure).

The old existing structure is currently planned for demolition. Saving and reusing it is only one option for building this portion of the second crossing, but it seems to be the best. The existing east span foundations are the most deficient part of the old bridge, while its superstructure has performed well during the past 80 years of service. Our study makes use of effective methods of strengthening the existing trusses, such as transforming the system to several continuous structures, reinforcing or replacing some elements found deficient, replacing the existing concrete deck with orthotropic or other lightweight steel decks, etc. Such reuse is a rare opportunity to create the much-needed second trans-bay crossing faster and for less cost.

The feasibility study proves that a new Second SFO Bay Bridge Crossing is perfectly achievable.

The new west span – as a suspension or cablestayed bridge of up to 2500 feet (760 m) – is not a problem for today’s construction techniques.

Currently there are more than 40 such bridges with spans longer than 2500 feet. Based on our study, the new east span could be easily built with modern steel trusses and orthotropic or other lightweight decks, or by relocating the

existing structures to new foundations using high-capacity jacks on barges with temporary piers.

Preserving and reusing 60,600 tons (55,000 metric tons) of steel is also a significant economic and environmental saving.

The main achievements of the new crossing would be increasing the trans-bay traffic capacity and providing a bicycle lane between San Francisco and Oakland. It would add four new lanes to the Existing Bay Bridge and proposed second crossing. existing five in each direction, thus increasing the overall capacity by 80%. building simultaneously the Bay Bridge and By 2035, the Bay Area population is esti- the Golden Gate Bridge during the Great mated to increase by 50% from 1990, when Depression. This project is completely within the traffic congestion was already very heavy. the capability of American engineers and The California Department of Transportation builders; the only challenge is to persuade (Caltrans) needed five years of planning and federal and California state transportation design plus nearly 12 years of construction to authorities to begin working immediately build just one half of a full crossing, so it is on planning and designing the new crossing. obvious that we are running out of time to solve The advantages of the second Bay Bridge the problem. crossing are: The estimated steel quantities for the second • Solving the traffic congestion on the crossing are 152,670 tons (138,500 metric current bridge; tons), including over 99,200 tons (90,000 • Using the most innovative techniques metric tons) for new structures and 53,460 tons available to build a new crossing within (48,500 metric tons) for retrofitted members reasonable time and cost; from the old east span; 78,800 tons (71,500 • Providing an additional transportation metric tons) for the new west crossing (includlink at considerable materials and cost ing the San Francisco approach and Yerba savings; Buena Island transition structures), and 73,850 • Completing the pedestrian/bicycle lane tons (67,000 metric tons) for the east crossfor the full length between Oakland ing, only 20,400 tons (18,500 metric tons) of and San Francisco; which would be new steel. This project can • Setting an example for efficient use of be completed in less than five years, including funding for infrastructure renovation; design competitions and construction. Based and, on recent construction of similar bridges, the • A great opportunity for our engineers estimated cost is $2.55B. The efficiency of and builders to revive the art of the second bridge crossing is demonstrated by American bridge engineering.▪ comparing the 152,670 tons for this entirely steel structure with the 266,750 tons (242,000 Ronald F. Middlebrook, S.E., can be metric tons) of steel used for the new east crossreached at ronfranco@gmail.com. ing replacement, which is about half as long as the overall new proposed crossing and mainly Roumen V. Mladjov, S.E., can be reached a concrete bridge. at rmladjov@louieintl.com.

Accomplishing a second Bay Bridge crossing is a challenging task, but not at all comparable to the problems that our predecessors had to A similar article appeared in the IABSE overcome some 80 years ago, designing and Conference Rotterdam Report, May 2013.

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.

STRUCTURE magazine

50

February 2014

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