STRUCTURE magazine | October 2013

October 2013 Bridges

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE ®

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FEATURES 26

Historic Arch Bridge Reborn with Progressive Design

By Chad Clancy, P.E. and Mike House, P.E.

The Burnt House Road Bridge, a historic bridge set in the countryside of rural central Pennsylvania, was in need of an update – and it needed it quickly. Closed to traffic in 2009, engineers were faced with the challenge of balancing modern day traffic demands with the community’s preference to preserve the appearance of the original “humped-profile” bridge.

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Bridges for Planes, Trains, but not Automobiles

By David A. Burrows, P.E.

The route for the new PHX Sky Train™ takes the co-mingling of air traffic and ground transportation in some very innovative directions. Not only will the route for the new automated transit system cross over one taxiway and beneath two other taxiways, but construction occurs while the taxiways are active! These crossings presented several design and construction challenges.

CONTENTS October 2013

COLUMNS 7 Editorial A Culture of Risk Management

By Andrew Rauch, CASE Chair

10 Technology The New Technology of Bridge Design

By Scott Lomax and Thomas Duffy, P.E.

14 Engineer’s Notebook Energy Methods

By Jerod G. Johnson, Ph.D., S.E.

16 Historic Structures Engineering History

By Alice Oviatt-Lawrence

21 Structural Forensics Decayed Wood Structures

By Lee Dunham, P.E., S.E.

STRUCTURE

®

32 Structural Testing

ON THE COVER

A Joint Publication of NCSEA | CASE | SEI

The art of bridge design is a timehonored pursuit that, throughout the centuries, has undergone significant advances in engineering and technology as a result of mankind’s passion to conquer the challenges of any given crossing.

Santiago Calatrava’s Jerusalem Chords Bridge is one of several modern bridges that is featured in the article

by Thornton Tomasetti’s Scott Lomax and Tom Duffy on page 10.

October 2013 Bridges

IN EVERY ISSUE 8 Advertiser Index 37 Resource Guide (Seismic/Wind) 44 NCSEA News 46 SEI Structural Columns 48 CASE in Point

Structural Health Monitoring with Interferometric Radar

By Paul J. Bennett, P.E.

DEPARTMENTS 36 Legal Perspectives Consideration

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

39 Great Achievements The Permanent Bridge

By Frank Griggs, Jr., P.E.

42 InSights

Erratum In the Structural Design Column article, Steel Deck Diaphragm Design 101 (August 2013 issue), there is a typo in an equation on page 11. A “2” should have been a superscript, thus squaring the length; instead, the “2” was printed as if multiplying the length by 2. The correct sentence should read: Summing moments about point (a) yields a shear force along the top (building perimeter above opening) of (8.01 k x 6.25 ft. + 0.175 klf x (6.25 ft.)2 / 2) / 30 ft. = 1.78 k (leftward).

The online version of the article has been corrected.

Disproportionate Collapse Design Guidance in the United States

By David Stevens, Ph.D., P.E. and Mark Waggoner, P.E.

43 Spotlight The Harbor Drive Pedestrian Bridge

By Joe Tognoli

50 Structural Forum 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

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October 2013

Building Codes and the Public Domain

By David L. Pierson, S.E., SECB

AL UC TU R

R EE S

ST R

GIN EN

ING IN U NT

N ED UC AT IO

CO

NCSEA

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Editorial

A Culture of Risk Management new trends, new techniques and current industry issues

By Andrew Rauch, CASE Chair

A

few weeks ago, I met with new employees of our firm to introduce our risk management program to them.

It is one of my duties as the risk management director for our office. Because of the economic downturn, I had not had the opportunity to make this presentation for a while, and it felt good to be able to do one again. As I was preparing for this presentation, I had the opportunity to consider risk management and how it really requires that your firm have a culture of risk management. A culture of risk management is the first of CASE’s Ten Foundations of Risk Management. It is not something that can only be touched on occasionally, but must be a constant presence in the design process.

A firm’s culture can be considered to consist of three components: artifacts; shared values, knowledge and learning; and basic unspoken assumptions.

Artifacts are those things that can be seen and heard in your office.

They are some of the first things that employees see when they begin working for you. Maybe it means having a poster showing your commitment to risk management or perhaps the Ten Foundations of Risk Management. Having a person or position responsible for risk management is another visible way to show your commitment.

Putting risk management on the agenda for staff meetings and project management meetings allows risk management issues and lessons learned to be freely discussed.

Shared values, knowledge, and learning create awareness and develop commitment to the risk management process. Share horror stories of real claims that your firm or other firms have endured. Tie risk into a monetary value. Let your employees know how much professional liability insurance costs your firm.

Give them examples of what claims cost and how it can affect firm profitability, their salaries or bonuses, and the firm’s ability to grow. Share the status of ongoing claims with your employees and celebrate when you are claim free. Compare how your firm is doing in relation to industry averages. Take advantage of risk management presentations through CASE, your insurance broker or insurer, or the other sources of risk management information. All of these will provide a constant drumbeat to keep risk management present in their thinking.

Basic assumptions are those aspects of company culture that are not confronted or debated. When these assumptions are challenged, they are usually vigorously defended. By STRUCTURAL their nature, they take longer ENGINEERING to develop than the overt INSTITUTE actions described above. They are also more powerful than

The Ten Foundations of Risk Management

1993-2013

a member benefit

structurE

years

STRUCTURE magazine

6. Scope

2. Prevention & Proactivity

7. Compensation

3. Planning

8. Contracts

4. Communication

9. Contract Documents

5. Education

10. Construction Phase

these actions and can quickly undermine what you are trying to accomplish. For example, suppose your firm has a requirement that all proposals are to be reviewed by a second person. If a principal routinely ignores that requirement and is not confronted, your employees will assume that risk management is really not as important as you claim it is.

For an engineering firm, culture is learned starting with the first day. Employees learn about it based on how things are done around the firm, from marketing to the end of the project. The culture is learned through observation of what really happens each day. It is the unwritten rules which can say that the written rules don’t need to be followed. It reflects the walk, not the talk, and is learned by what gets rewarded, by what the “heroes” do, and by what the leaders tolerate, not by what the leaders say.

In the book of Deuteronomy, the Jewish people were instructed to write the Ten Commandments on their door posts and gates, to teach them to their children, and talk about them when they woke, while they went about their daily business, and in the evening. These commandments were to be an integral part of their daily life, part of their culture. While the Ten Foundations of Risk Management are not as important as the Ten Commandments, they still need to be an integral part of your firm’s culture. So, does your firm have a culture of risk management? If it does, what does it tell your employees? Is risk management important or is it something to which you only pay lip service?

If you would like to learn more about the Ten Foundations of Risk Management, visit the CASE website (www.acec.org/ case/gettinginvolved/toolkit.cfm). CASE has also developed a series of risk management tools to help you institute your risk management program and culture. They are available free to CASE members and for purchase through the ACEC bookstore.▪

®

Celebrating

1. Culture

Andrew Rauch is a principal with BKBM Engineers in Minneapolis, MN and is responsible for overseeing their quality assurance and risk management programs. He is the current chair of the CASE Executive Committee. He can be reached at arauch@bkbm.com.

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October 2013

Advertiser index

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Editorial Board Chair

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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

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AdvErtising Account MAnAgEr Interactive Sales Associates

Jon A. Schmidt, P.E., SECB

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S-Frame Software, Inc. ............................ 4 SidePlate Systems, Inc. .......................... 31 Simpson Strong-Tie............................... 13 Structural Engineering Associates, Inc. .. 24 Structural Engineers Assoc. of Illinois .... 35 Structural Engineers, Inc. ...................... 30 Struware, Inc. ........................................ 33 Taylor Devices, Inc. ............................... 19

American Wood Council, Leesburg, VA

Chase Engineering, LLC, New Prague, MN

EditoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE

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STRUCTURE® (Volume 20, Number 10). ISSN 1536-4283.

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Technology information and updates on the impact of technology on structural engineering Iconic Firth of Forth Bridge, Scotland. Courtesy of Jim Wilson.

T

he art of bridge design is a time-honored pursuit that, throughout the centuries, has undergone significant advances in engineering and technology as a result of mankind’s passion to conquer the challenges of any given crossing. It has evolved through the acceptance of well-established practices, codes and construction techniques. In fact, when new materials or methodologies are brought to the market, it often takes many years for the techniques to gain inclusion in the modern practice of bridge design.

For example, even after the high-strength characteristics of iron were recognized, as compared with timber, iron was still used as a lighter-weight substitute. It was years before it came to be a stand-alone structural material for bridge design.

Steel also went through a similar transformation before it was used as a replacement for iron; welding and bolts replaced rivets; and in today’s modern age, computer analysis and CAD (from matrix methods though FEMs) have replaced hand calculations and hand drafting.

Where are we now in this continuum? Advanced modeling techniques, material choices and analysis methodologies adopted for building practices are not yet fully embraced within the bridge industry.

This paradigm will soon shift, and we anticipate that advanced computational modeling will be one of the next big advances in bridge design.

The need to create crossings has always been one of mankind’s biggest challenges, and often leads to an increase in man’s ambition to have a more enhanced understanding of mechanics and advances in technology and materials. These challenges create opportunities, and some of the greatest leaps in engineering design and construction have occurred from the need to push boundaries. Examples of this are evident from the earliest recordings of Roman cofferdams, to the Great Stone Bridge of the Sui Dynasty (581-618), through to the Industrial Revolution (17601840). The Industrial Revolution in particular

The New Technology of Bridge Design

By Scott Lomax and Thomas Duffy, P.E.

Scott Lomax is a Vice President of Thornton Tomasetti, specializing in engineering for bridges and long-span structures. Scott’s past work includes the World Trade Center Transportation Hub, currently under construction in New York City. Scott may be reached at SLomax@ThorntonTomasetti.com.

Thomas Duffy, P.E., is a Senior Vice President at Thornton Tomasetti and is responsible for project management and business development for Thornton Tomasetti’s Building Performance practice. He has served on the American Road Transportation Builders Association’s planning and design committee.

He sits on the advisory board of the Urban Assembly School of Design and Construction in New York City and has been a mentor and technical advisor for Smith College’s Picker Engineering Program.

Thomas may be reached at TDuffy@ThorntonTomasetti.com.

10 October 2013

was a watershed for advances in materials and design, and coincided with the need to facilitate an ever-expanding infrastructure network.

While Pre-Industrial Revolution bridges were predominantly wood or stone, during the Industrial Revolution, iron became a viable option following the construction of the Iron Bridge that stretched across the River Severn in Coalbrookdale, UK. This can be seen as the beginning of modern bridges produced with a new material palette of industrially produced iron, which gave way to cast iron, wrought iron, steel, and reinforced and prestressed concrete.

This period also saw the development of the Americas, which presented a growing need for extended infrastructure.

In particular, the development of the railway network was instrumental in pioneering works such as the first major crossing across the Mississippi via the Eads Bridge in 1874, directed by Andrew Carnegie through the Keystone Bridge Company; the iconic Firth of Forth Crossing in 1890 near Edinburgh; and the world-famous Brooklyn Bridge in 1883. This era is often heralded as one of great civic works that captured the imagination of the public and expressed the rapidly expanding vision of engineers, architects, entrepreneurs and empire-builders. Engineers played a prominent role during the Industrial Revolution and Victorian era, introducing to society names such as Telford, Brunel, Roebling and Eiffel, and later, Freyssinet & Amman. As architects took a lead role in the design of buildings, the design and construction of bridges remained very much the domain

Gateshead Millennium Bridge. Courtesy of Kay Williams.

Iron Bridge at Coalbrookdale. Couresy of Leon Reed.

of the engineer. Major civil works, including those of Amman, continued to push materials and analysis to new boundaries and spans – notably with the use of cables in suspension and cable-stay bridges. With increased spans came heightened awareness and consideration of wind forces and aerodynamics that led to slender bridges. Following this path, we can see the raw beauty of stressed ribbon bridges, such as ones designed by notable engineer Jiri Strasky, which epitomize both a structural and aesthetic purity that has become the hallmark of signature bridge design. Bridge design continued to be dominated by engineers; however, appreciation of the aesthetic impact was on the rise.

In recent times, we have seen architects play a larger role in bridge design, creating signature bridges that become important objects in the public realm. Many have become landmarks that raise the profile of the bridge design industry, and highlight the importance of an integrated design approach. Bridges by nature are pure, almost raw objects, and as such possess a sculptural quality that is embraced by the public. Through careful design, considering the form, function, detail and potential to create more than just a link, bridges and

bridge designers have become more highprofile than ever. Celebrated engineer and architect Santiago Calatrava is well-known for his esoteric bridge designs, and involvement of well-known designers such as Sir Norman Foster, Zaha Hadid, Wilkinson Eyre and Thomas Heatherwick, amongst others, on some truly innovative bridge projects, has helped raise awareness of the importance of an integrated approach to bridge design.

The domain of architects was more traditionally associated with building design, and in keeping with this trend of architects’ increased involvement in bridge design, it is only natural that some of the recent innovations adopted in building design will be implemented in bridge design. It is clear that there will continue to be advances in material science that push the boundaries of the current palette of materials (steel, cables, wood, glass and concrete) and an expanding role of newer materials such as plastics and composites, like the Sandwich Plate System (SPS). Similarly, continued development of analysis software and understanding of geometric and material nonlinearities will also lend itself to push these materials to new bounds. However, two areas in which we see

Santiago Calatrava’s Jerusalem Chords Bridge.

Couresy of Itay Barlev.

great growth and opportunity for the future of bridge design are the application of advanced geometric modeling and the delivery of the design in a form that can be directly implemented into the fabrication process.

Advanced Computational Modeling (ACM) is a powerful tool for both the conceptual and design development phases. As bridge forms, particularly for footbridges, become more complex, ACM can be used to quickly investigate form-finding and generate various geometrical options. As part of this process, the ACM platform can be used to refine and economize the design and promote early understanding of the structural behavior, visual appearance, fabrication complexities and sustainability issues. ACM can work within many platforms, including Rhino, Grasshopper and Digital Project. These software packages,

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Margaret Hunt Hill Bridge. Courtesy of Amit Rawat.

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233

The Majestic Millau Viaduct by Michel Virlogeux and Sir Norman Foster.

Courtesy of Dave Tappy.

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ubiquitous within the design community, facilitate development of forms that can be quickly exported into a structural analysis package and assessed for preliminary sizing and behavior. The ability to produce early 3D images and renderings is also important, not only for consolidating the design with the team but also for producing visual graphics for clients, competitions and media. By controlling parametric boundaries, it is possible to quickly optimize the design for a number of parameters ranging from weight to solar heat gain, offering early evaluations of issues such as constructability or energy modeling.

An example of this could be a covered pedestrian bridge between two buildings in a hot climate, whereby the project demands a high-profile response. Early ACM work can be used to generate organic structural forms, simulate various coverings from tension fabric to glazing to Ethylene TetraFluoroEthylene, orientate the structure to both an optimized form while providing maximum shading in the areas required, while passing as much natural light as possible. The bridge structure can also quickly be decomposed to show transportable and erectable sections, thereby directing the constructability and early cost evaluation.

Breooklyn Bridge. Courtesy of Bess Adler.

The ability to fluidly converse between software, including analytical packages, is fundamental to the success of this approach. It is important to note that this process continues through design development and is a tool rather than a driver of the design, controlled through a collaborative and integrated process with the entire design team.

The early input of bridge constructability in the design process is also important, as it sometimes dictates the form of a bridge.

Consider the use of stressed-ribbon over a deep ravine where falsework would be cost prohibitive, or a tied arch bridge moved into position in a single operation because of either environmental considerations to avoid temporary works in the crossing or logistical rationale such as a limited closure.

Another link that is critical to the success of a project is the production and delivery of design information in a format that is directly implemented by the contractor/fabricator.

This approach greatly benefits any project and is fundamental for design-build projects with aggressive schedules. While modeling tools, such as Tekla, are the mainstay for this effort, the success ultimately relies upon the knowledge and understanding of the fabrication and construction process. To this end, we have seen enormous benefit to having

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Rolling Bridge. Courtesy of Eric Gjerde.

STRUCTURE magazine

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in-house fabrication expertise embedded within the design team. Qualified staff delivering design materials in the same software platform as the fabricator, and developing the design both in this format and following the methodology in which the bridge is erected, the project can benefit from improved schedule. This minimizes reproduction and RFIs and provides greater quality control due to a common understanding between the design and fabrication team and results ultimately in cost benefits by reducing uncertainty in the design material.

As the world population continues its migration to cities, and mega-cities emerge in Asia and Latin America, we will see continued challenges to cross new spans. The importance of aesthetics and the contribution of bridges to the urban fabric means that an integrated design team – combining architectural form with engineering elegance – is fundamental to the success of landmark bridge projects.

This process demands highly skilled and collaborative engineers, architects and designers working seamlessly together in design, fabrication and construction. The future of bridge design requires reinventing this collaboration through the use of new platforms for developing and delivering the design materials.▪

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EnginEEr’s notEbook

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F Energy Methods What Does the Future Hold?

By Jerod G. Johnson, Ph.D., S.E.

Jerod G. Johnson, Ph.D., S.E. (jjohnson@reaveley.com), is a principal with Reaveley Engineers + Associates in Salt Lake City, Utah.

A similar article was published in the Structural Engineers Associations-Utah (SEAU) Monthly Newsletter (September, 2012). It is reprinted with permission.

Figure 1: LA 38 Record from SAC Database.

or most of us, our training as structural engineers has included significant attention toward transient seismic events.

They can have such destructive potential as to occupy a major role in the geometry, design and detailing of our projects.

For decades, prescriptive methods in codes have predicated design around a peak transient condition that presumably produces a peak base shear reaction and a peak rooftop displacement. These phenomena then become the basis of criteria for the seismic design.

These methods have arguably served us well, and ample evidence gathered in post-earthquake reconnaissance efforts suggests that structures designed and detailed in accordance with contemporary codes have a far greater potential for satisfactory performance than other structures. Even so, we are far from being able to state definitively that we can precisely characterize the nature of expected ground motions. As evidence of this concept, we need only consider changes in prescriptive earthquake design provisions that seem to follow in the wake of every major seismic event.

When considering the diversity that can occur among earthquake ground motions, we need not look any further than databases and ground motion suites commonly used for research and hypothetical studies. Consider two seismic acceleration records from the SAC Database derived for soft sites (Soil Type E), one delivering a peak ground acceleration (PGA) of 0.78g and the second a PGA of 0.80g. Based on these parameters alone and without actually looking at the accelerograms, we might conclude that these events should produce structural motions with comparable peak transient characteristics (drift and base shear).

As we examine such behaviors, this indeed seems to be the case, with these ground motions producing peak transient base shear reactions of 1,416 kips and 1,618 kips, respectively, on a prototypical shear

14 October 2013

wall structure. So if we subscribe to methods driven by current codes, we might conclude that these two events result in similar seismic demands on the structure. However, a closer look at the records as shown in Figures 1 and 2 might lead us to draw a different conclusion. While there are similarities in peak acceleration and frequency content, there are two major differences that are apparent.

• The first record has a slightly higher peak acceleration, but only has one pulse reaching a magnitude of nearly 0.8g. The second record has no fewer than six major pulses, all of which reach nearly 0.8g.

• The first record produces roughly 12 seconds of significant accelerations, while the corresponding duration for the second record is approximately twice as long.

The second record actually imposes a much higher overall demand on the structure than the first, primarily as an increase in element hysteretic cycles driven toward peak element displacements (or rotations). How can this demand be quantified in a practical sense? Ordinates from response spectra for these events produce similar accelerations, and response history analyses produce a similar result as we look at peak transient response.

Clearly, conventional methods fall short.

Alternative analysis methods gaining favor in the research community include energy approaches.

While many of these methods have been around for years, they have garnered greater attention recently in light of the Sendai Earthquake on March 11, 2011. Why is this so? The duration of this event was far longer than most others on record. Whereas earthquakes typically produce major shaking for 20, 30 or perhaps 40 seconds, Sendai continued shaking for minutes, leading many initially to doubt the validity of the recordings. It is clear that such events hold the potential for sustained lateral motion, and therefore an increased structural demand.

Researchers Park and Ang developed energy methods to address this issue. Their coupled approach accounts for peak transient response along with total energy demand, with energy capacity derived

1

from hysteretic relationships not unlike nonlinear pushover curves.

The Park/Ang approach is embodied in the equation:

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

where the first portion of the equation (M/u) represents peak transient displacement over maximum capable nonlinear displacement. The balance of the equation reflects the ratio of accumulated energy over maximum capable energy at maximum capable nonlinear displacement. This equation produces a scalar value not unlike a unity check. Results greater than 1.0 reflect structural failure, and results less than 0.4 reflect a structure that can likely be re-occupied immediately. Intermediate values reflect a structure that may be reasonably recovered.

Using this approach, it may not be surprising that results of the analysis for the previously mentioned test structure subjected to the two ground motions are significantly different.

The first produces a damage index calculation (D) of 1.02, and the second a value of 16.2. This demonstrates that the structure would not survive the latter event, whereas the former is just over the failure threshold.

In other words, the energy method shown here predicts that one earthquake creates a demand almost 16 times greater than the other … and this from two records of nearly equal peak ground accelerations.

Only time will tell what future codes may prescribe, and energy methods may eventually become mainstream. In the meantime, since current code methods do not address earthquake duration, what is the most prudent course of action? Do we now ask our geotechnical counterparts to address not only spectral accelerations and soil type, but also earthquake duration? Their fees (and likely their background) are probably not sufficient for that level of sophistication.

Under current codes, it is not practical or economical to address earthquake duration (among other ground motion characteristics) in our designs. Duration, like so many other aspects of future ground motions, is a great unknown. Trying to characterize it accurately is like trying to understand a city by taking pictures of the back yards of a few residents.

Rather, the more prudent approach is to pay careful attention to seismic detailing. Thoughtful detailing in accordance with current code prescriptions (which we should be doing anyway) can make a major difference with respect to the energy portion of the equation listed previously.

Ductile detailing will increase the maximum capable nonlinear displacement, thereby raising the denominator in the latter half of the equation and lowering the calculated damage index. This translates to greater nonlinear displacement capability and a more resilient structure.▪

0.6

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Historic structures significant structures of the past

C

aptains steering nineteenth century heavy shipping-traffic remained vigilant when navigating the waterway of the 850-foot wide Hell Gate Sector of New York City’s East River, which is flanked by two Manhattan islands and land eastward in Queens, New York. Notoriously ferocious waters, unexpected currents, and huge rocks lurked below the turbulent surface. Yet this economically essential waterway provided major regional freight operations.

Prior to the Hell Gate Bridge project, freight trains and trucks, for example from New England, stopped at rail termini, such as at Morris Point in the Bronx, and transferred their shipments onto floating barges bound for a destination terminal, such as in New Jersey, thereby facilitating distribution of goods westward. But the shipping back and forth in the waterways became so congested with ferried traffic that those involved called for modernization.

To expedite a solution to such overcrowding and for safety reasons, citizens pressured Congress to finance a deeper channelway. Congress, by 1885, allocated approximately $600,000 for the U. S. Army Corps of Engineers to blast 9554 cubic yards of rock out of the Hell Gate channel using 11,808 pounds of nitroglycerine, along with 1218 pounds of “giant powder” (TNT) and 8445 pounds of “black powder” (exploding TNT).

Blasting one cubic yard of rock required about nine-tenths of a pound of nitroglycerine – the largest single blast removed 300,000 cubic yards of rock. The Burleigh Drill, diamond drills, and handwork removed more rock. Later, the East River at Hell Gate was dredged from 26 feet of original depth to 40 feet.

As marine traffic flourished, so too did the aggressive pursuit of railroad expansion. Engineers after 1890 knew that the Pennsylvania Railroad was

Engineering History Gustav Lindenthal’s New York City Hell Gate Bridge ~1917

By Alice Oviatt-Lawrence

Alice Oviatt-Lawrence is principal of Preservation Enterprises, an architecturalengineering research and historic-building analysis organization. She serves on the SEAoNY Publications Committee, and may be reached at StrucBridge@aol.co.uk.

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

Recent overview of the project looking south, showing the flagship Hell Gate Bridge and the 4-span Little Hell Gate inverted bowstring arches in the foreground.

Towers probably by Henry Hornbostel, Architect.

Courtesy of www.loc.gov. HAER. NY-121-16. G. Weinstein, Photographer. 1996.

16 October 2013

The New York connecting railroad route. Half of the project is viaducts and bridges. Courtesy of Popular Mechanics Magazine, v. XX: 621. 1913.

evaluating opportunities for expansion, including construction of a monumental railroad bridge to span the Hell Gate waterway, to connect New England with Long Island through, and into, New York City and westward.

Therefore, the New York Connecting Railroad Company incorporated in 1892, by Oliver Barnes and Alfred Boller, among others. By 1900, a double-track, light Cooper E-40 cantilever bridge design by Boller emerged for the site, but was not accepted.

The existing bridge over the Hell Gate waterway became a reality soon after the turn of the 20th century. In 1900, the Pennsylvania Railroad, together with the New York, New Haven & Hartford Railroad, acquired the 1892 New York Connecting Railroad Charter, with rights to traverse the Hell Gate waterway. To facilitate access to New York Pennsylvania Station, tunnels were in the works as well. After the definite electrification of trains, the Pennsylvania Railroad from 1904-1910 constructed two single-track tunnels under the Hudson River and four tunnels beneath the East River, all traveling through Manhattan’s newly constructed, classical-style 1911 Pennsylvania Station (McKim, Mead and White; demol. 1965.)

The President of the Pennsylvania Railroad selected Lindenthal as “Consulting Engineer and Bridge Architect” of the “East River Bridge Division” of the Hell Gate Bridge project in 1904, at the end of Lindenthal’s term as New York City Bridge Commissioner (1902-4).

In 1905, Lindenthal, after first considering a three-span continuous truss and a three-span cantilever design, presented two steel-arch designs: One a crescent arch, with the top and bottom chord termini converging, and the other

The Masonry Footings, Tower Foundations and Towers

Completing Hell Gate arch top chord over rough waters. structural members manufactured for the floor first act as backstays and counterweights. (Left & Right). The tremendous weights of the towers at the abutments resist the thrust of the bottom chord of the arch where almost all of the forces are transmitted. www.loc.gov HAER 3616-11 Taken 9/30/1915.Accessed Nov. 2012.

a spandrel arch design, with the termini of the top and bottom chords splaying apart.

While the Pennsylvania Railroad aspired to a world-class railroad, Lindenthal worked to create an historically noteworthy, substantial and visually unforgettable railroad entrance to New York City. Lindenthal’s natural European attention to quality, long service-life, and aesthetics coincided with contemporary urban movements working to improve the aesthetics of the built environment.

Lindenthal and his 95 assistants, including Othmar Ammann and David Steinman, prepared the designs and specifications for several miles of viaducts running from the Bronx, into Queens, and three bridges; a fixed metal truss bridge over Bronx Kill, the noteworthy Little Hell Gate skew-deck four-span reverse bowstring, and the flagship four-track spandrel-arch bridge over Hell Gate. Construction began with the July, 1912 ground breaking.

The Pennsylvania Railroad’s Joseph N. Crawford, Consulting Engineer, made the initial surveys and wash-borings. Later, coreborings ordered by Lindenthal established the depth to bedrock, confirming on the Wards Island side depths of 55 feet to 140 feet below the mean high water line.

Geological problems on the Wards Island side necessitated difficult, dangerous and complex caisson construction, which was handled by the New York Connecting Railroad’s Chief Engineer, P. G. Brown, Civil Engineer.

Here, the tower base and foundation rest on 21 caissons sunk to great depths. Of interest are two rows of deep interlocking reinforced caissons of 30 feet by 125 feet, which act solely to resist the arch thrust and place 20 tons per square foot pressure on the bedrock.

On the Long Island (Queens) side, the excavated tower base, with its foundation weight of eight and one half tons per square foot, is 49 feet thick. It rests on Gneiss bedrock encountered at 15 to 38 feet below the ground surface, and is 104 feet by 140 feet at the base.

Architect Henry Hornbostel designed the 225-foot high portal towers in the project. continued on next page

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BEFORE

AFTER

The Romanesque-Revival towers have groundlevel footprints of 103 feet by 139 feet, with the towers then tapering slightly inward up to an entablature, above which an array of simple, well crafted, stepped cornice-moldings support a parapet of repeated small Roman arches. A large Roman arch perforates each of the four tower wall elevations, flanked by two loopholes (medieval vertical slits).

The design concept of the portal towers is a synthesis of historic meaning with new materials and technologies. The towers, appearing to be solid, protective, load-bearing stone castlekeeps, become instead grand-arched open City Gates, built of concrete with vertical and horizontal steel reinforcing rods and granite facings.

The concrete is waterproofed via its careful mix, by smooth-finish toweling before setting, by proper sloping of the concrete for quick water run off, and by the provision of good drain holes. The mortar mix is one part Portland cement, two parts sand, and four parts gravel. There are steel girders in the track floor and roof where the trains pass through the portals.

The Steel The bridge is constructed of 18,900 tons of extra-heavy hard steel. All the rolled steel – and the forged and cast steel pieces after annealing – was tested for bending and tension, multiple times and under various loads. Carbon content in the hard steel measured 0.27 to 0.34 percent.

Chemical content was controlled, resulting in maximum sulphur of 0.05 percent, and phosphorus ranging from 0.04 to 0.06 percent. Tests of the hard steel yield point calculated as +/- 38,000 pounds per square inch, and the ultimate tensile strength +/71,000 pounds per square inch.

While Lindenthal with certainty used nickel steel alloy for the eye bars and pins in his 1909 cantilevered Queensborough bridge, and considered its use for parts of Hell Gate, he based his decision to not use it on price ($40 more than carbon steel per ton) and on what was thought at the time to be a comparatively insignificant structural advantage. Lindenthal originally specified some structural steel for some parts (floor system and suspenders only) of Hell Gate Bridge but the American Bridge Company provided 100% hard steel for the same price.

In 1910, Lindenthal upgraded the original specifications of the 1904 Pennsylvania Railroad standard live loading of Cooper E-50 to the New York, New Haven and Hartford’s Cooper E-60 loading.

Inside Hell Gate Truss arch, looking down onto the tracks. The truss is 53 feet wide over 4 tracks.

Note the lateral bracing and the heaviness of the structural materials. The sidewalks flanking the tracks are capable of supporting an overhead trolley.

Courtesy of DaveFrieder.com. All Rights Reserved.

The Hell Gate Arch Superstructure The two-hinged spandrel arch Hell Gate Bridge, including the towers, is 1017 feet, six inches long (977 feet between towers), 93 feet wide at the floor trusses (60 feet between truss centers), and is comprised of 100% hard steel. The ratio of rise to span is 1: 4.5, with the height of the arch from mean high water at 305 feet. No piers in the water or false work were permitted, so as to not block the river traffic under the bridge’s required 134-foot vertical clearance. It was the most heavily loaded bridge of its day.

The rectangular box-sections are by-andlarge of two-inch thick single plates. There are 23 equal sized truss panels, each 42½ feet long. The parabolic bottom chord is a stiffened, double rectangular closedbox, hinged at the abutments where the force equals 28,652 kips or 94.4% of the total force.

Four static conditions for the Hell Gate Bridge’s interesting erection sequence, perhaps best summarized in Ammann’s Transactions of the ASCE paper of 1918 (Parenthetical comment is added): 1) Cantilever condition. During erection of first six panels, the truss held at end of top chord by lower backstay.

2) Cantilever condition. During erection of remaining panels, truss held at top chord Point 11 by upper backstay.

3) Three-hinged arch condition. Backstays released and trusses connected at bottom chord Point 22 Wards Island side, which acted as hinge, top chord

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23-23 (center), and diagonal 23 Wards Island side – 22 Long Island side not connected at 23 Wards Island side.

Arch left in this condition until all steelwork had been erected.

4) Final or two-hinged condition. All steelwork erected and all members of the center panel fully connected.

The bottom chord arch members were the heaviest to be lifted. The superstructure resists wind pressures of 3100 pounds per linear foot, and lateral forces of 1500 pounds per linear foot, creating 4600 pounds per linear foot of total lateral resistance. The American Railway Engineering Association in 1914 specified total combined lateral and wind force resistances of only 800 pounds per linear foot.

The two ends of the steel arch met in the middle over Hell Gate waterway, aligning exactly, in 1915. During the next year, the viaducts and track floor were under construction.

The Viaduct Spans & Approach Piers Most of the project rests on elevated viaducts spaced at 90 feet and averaging 100 feet high.

Lindenthal originally designed the viaduct piers as steel trestle, so that as the marshy ground below shifted, settled, or was drained for future underground infrastructure, the metal piers and girders assembly could then be adjusted. Authorities noted that since nearby mental and prison inmates housed on the islands could climb metal trestles to escape, Lindenthal in 1914 redesigned the piers as horizontally and vertically reinforced arched concrete supports for the approach viaduct deck plate girder spans. Masonry ordinarily would have been less economical than metal trestle; however, due to high steel prices at the time, concrete became economical.

The American Bridge Company controlled the Wards and Queens plate girder erection.

After the arch closed, the Company distributed, on the ground by the viaduct piers, the dismantled backstay structural members and the plate girders which had been used as counterweights during the arch assembly. A locomotive crane on temporary track lifted the members sequentially into place to construct the track floor.

McClintic-Marshall Construction Company handled the Randalls Island and Bronx viaduct sections. Here, girders were riveted and paired up at the shop, and delivered right to the track. A 50-ton steel derrick car or locomotive crane operating on temporary track positioned the girders.

Materials Testing & Construction Observations

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Lindenthal was credited by his peers for being the first to use all phases of a bridge under construction for experimental testing.

At the time, engineers still worked under theoretical assumptions and individual experience; all advocated acquiring greater scientific knowledge.

To that end, Bauschinger, in Germany, developed a sensitive extensometer (accurate to 1 x 10-6 ) with which he tested deformation and elongations of mild steel, and investigated metal fatigue. Lindenthal may have read publications of tests on riveted trusses (Mesnager, 1899) using Rabut’s extensometer, as Lindenthal employed them on parts of New York’s Queensborough Bridge (1909).

Lindenthal resolved to use Hell Gate to share with the profession the findings from this new scientific experimentation.

He acquired Howard extensometers and attached them before, during and after construction to all parts of the bridge and equipment.

The extensometers were then monitored. The extensometers attached to the Hell Gate eye bars, for example, revealed uneven stresses during erection. After controlled adjustments, the extensometers reflected a gradual leveling-out of the eye bar stresses to a final, uniform 20,000 pounds per square inch. While measuring the forces on both stays as seven truss panels were placed, the hydraulic jacks put the forward stay in tension and released the lower stay. When too much compression occurred, both stays could be immediately adjusted.

Steinman, in 1918, remarked that the Hell Gate was probably the only bridgeto-date to be scientifically analyzed for bridge stresses. Published studies continued for years after completion, conveying important technical information to other engineers. The superb bridge remains in active service with no major repairs necessary, having outlasted many other railroad bridges. Hell Gate Bridge opened to traffic The Hell Gate Bridge today: The truss arch in March 1917, for a project cost of about members structure highlighted under sunlight.

TAY24253 BraceYrslfStrctrMag.qxd 9/3/09 10:09 AM J. Page Courtesy of Adam Kirk 12011. $20 million.▪

Post Construction The detailed project records of all forces and tests related in various papers at the time facilitated thorough, subsequent inspections. The original lead paint held up for sixty years. After repainting in 1991, and again in 1996 after Congress allocated $8 million for non-lead paint jobs, Amtrak specified two coats of epoxy primer, a red urethane coat in “Hell Gate Red”, followed by a clear finish coat.

The paint faded immediately after both applications. Lawsuits ensued, after which findings were that the paint manufacturer had changed pigment suppliers without ensuring chemical content.

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any existing structures in North America experience ongoing moisture intrusion and resulting decay that significantly compromises the integrity of wood members.

If left unmitigated, advanced decay in wood members supporting roofs, exterior walls, deck assemblies and floor systems can and does impair the capacity of these elements to support code-prescribed loads. The result is that portions of existing structures can become unfit for occupancy. The economic and environmental impacts are considerable as well; these include demolition and disposal of building materials before the end of their expected service life, expenditure of remediation labor and materials (every year, a significant percentage of new framing lumber goes toward fixing decayed portions of existing buildings) and loss of use costs. Substantial re-roofing and re-cladding projects can expose a veritable hidden jungle of decay.

Detailed collection of field data on resulting section loss can provide valuable information as to the extent of structural damage and allow the engineer to re-construct a history of impairment for the structure. This article presents a method developed by the author for engineers to reasonably determine the occurrence of structural impairment of a decayed wood structure over its service life, and discusses its practical application in assisting with property insurance claims.

Residual Capacity in Wood Structures The majority of wood framed buildings consist of thousands of elements connected together in such a way so as to create a superstructure.

When engineers design wood structures with repetitive members (such as studs, joists and rafters), or members with slight variation in geometry and loading (such as beams and posts), these members are typically grouped according to function and load demand, and required member sizes are matched with available standard sawn or manufactured lumber dimensions. In some cases, member sizes are controlled by the attributes of interconnection; in other cases they may be oversized for architectural reasons; however, they should always be scheduled on drawings to ensure economy in construction. In this way, the elements that comprise existing wood structures have a range of residual capacity. If designed properly, members should have some level of “oversizing” – some have a little, some have a lot, but the majority fall somewhere in between.

Decay in the Built Environment What is Decay Fungi?

Decay fungi are primitive plants that feed on the sugars (cellulose) in wood. Fungi grow by lengthening and branching of tubular cells called hyphae, in a manner similar to the roots of plants (Highley).

In nature wood decay fungi live on dead wood and in living trees, however, a small percentage are particularly well adapted for consuming wood that has been cut and worked into products used to build structures (Edmonds). The most destructive of these is brown-rot decay fungi, which preferentially attack softwoods. Since softwood species have predominantly been used in building construction, brown-rot decay fungi are the most common agents of decay in wood buildings (Carll and Highley).

Structural ForenSicS investigating structures and their components

Just Add Water In order to grow, fungi require favorable temperatures, a supply of oxygen, adequate moisture and a suitable food supply (Carll and Highley). Constructed buildings offer a ubiquitous oxygen supply and temperatures that are comfortable to humans, which are also ideal for the growth of decay fungi (Morris). Wood moisture content is therefore the most important factor in determining decay. Decay fungi require free water, so wood must be above the fiber saturation point (about 28% MC on a dry weight basis) but below the waterlogged condition to decay (Edmonds). Even though modern building enclosure design and construction have come a long way in the last 20 years, many existing buildings lack the proper means of protection against water intrusion. When breaches in waterproofing systems result in water intrusion, moisture contents in framing elements can elevate from those at equilibrium moisture content (equivalent to 8-10% in most parts of the country) to those conducive to growth of decay fungi in a relatively short amount of time.

Some components of exterior wall assemblies, such as batt insulation, can trap and hold water against framing members.

Decayed Wood Structures

High-Early Strength Loss Engineers that design with concrete are familiar with the concept of “high-early strength gain”.

With decay, engineers need to be familiar with the concept of “high-early strength loss”. Decay initially affects toughness, or the ability of the wood to withstand impacts. This is generally followed by reductions in strength values related to static bending (Wilcox). Eventually, all strength properties are seriously reduced. Strength losses during the early stages of decay can be considerable. continued on next page

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21

Reconstructing a History of Impairment

By Lee Dunham, P.E., S.E.

Lee Dunham, P.E., S.E., is a structural engineer specializing in the investigation and repair of existing structures. Originally hailing from Fredericton New Brunswick, Canada, Lee is a Senior Associate with OAC Services, Inc., an architectural, engineering and construction management firm in Seattle, WA. He may be reached at ldunham@oacsvcs.com.

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

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Just Point, Shoot and Measure!

1.

2.

3.

4.

“The Hidden Menace”. Advanced brown rot decay in wood framing members in Pacific Northwest buildings; 1 – despite their appearance as rim joists, these are actually double 2x12 beams bearing at a corner post in a multi-family residential building; 2 – impaired elevated walkway beam, rim and studs; 3 – glulam header with advanced decay and structural impairment at right side bearing; 4 – double 2x10 rim with full section loss below a low-slope roof in a single family residence.

By the time weight losses in wood members resulting from decay have reached 10%, loss of most mechanical properties may be expected to exceed 50% (Highley). When wood is in the advanced stages of decay, it essentially has lost all strength.

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Decay Progression Although the precise growth rate of brown-rot decay in wood framed buildings is generally not determinable to a high degree of scientific certainty, research in the field of wood science has provided sufficient knowledge to allow the shape of the decay ‘curve’ to be bracketed with an upper bound and a lower bound. In this way, decomposition envelopes can be reliably determined for wood structures, as the data available from laboratory and field studies are based on the same wood used in buildings, the same decay fungi (brown-rot) and similar moisture and temperature environments.

Structural Impairment The Usual Suspects Polytec GmbH 76337 Waldbronn · Germany www.polytec.com

Advancing Measurements by Light

The most common locations for water intrusion at the exterior walls of buildings are at windows, doors, corners and other transitions in the building enclosure system.

Certain types of cladding systems have a poor track record of managing water. Water

STRUCTURE magazine pol_130783_rsv61_e_60x254.indd 1

15.08.13 11:10

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that has leaked into a building can wet vertical and horizontal wood framing elements.

Where water collects at and saturates horizontal wood surfaces, the saturation spreads horizontally. As goes the water, so goes the decay. A typical location of advanced decay in framed walls is at the base of studs, plates and rim joists. The list of “usual suspects” at post and beam structures such as decks includes beam ends and the tops and bottoms of posts. Deterioration can occur at locations where bending stresses are the highest, such as cantilever points for beams at balconies. However, practically speaking, the most common mechanical properties affected are compression perpendicular and parallel to the grain, as water gets funneled to and accumulates at bearing points which often coincide with architectural corners or transitions. Dowel-type connections between wood elements such as nails, screws and bolts are also commonly affected. Low-slope roofing systems, if not constructed properly, can also be ripe for decay resulting from water intrusion and/ or condensation of internal vapor caused by the lack of proper ventilation.

Diminished Load Carrying Capacity When a structural member is damaged or weakened through diminishment of some

Time Distribution of Impairment Time distribution of the occurrence of impairment to wood framing elements in a building over its service life can be reliably modeled using a combination of applied structural engineering, wood science, and basic statistics.

Step 1 – Investigation and Research Typically, wood goes into a building sound, and (hopefully) dry. When deterioration of existing wood framing elements is observed some time after construction, the question is – how did it get from point A (dry, sound) to point B (decayed, impaired)? Typically, for buildings constructed in the last 30 years, construction dates can be gleaned from building department records. Sometimes, maintenance records kept by building owners can provide an understanding of water intrusion history and timing of any past repairs. Engineering investigations can include studying the arrangement and condition of the building enclosure components that permitted long term water entry. In some cases, service life of failed waterproofing can be estimated based on experience and industry knowledge. In terms of rate of decomposition of wood in buildings due to decay, an engineer can provide reliable extrapolations of the most aggressive rate of decay and the least aggressive rate of decay, and use these in combination with estimated earliest and latest decay start times (based on water intrusion history and/ or specific envelope failures) to reasonably estimate a decomposition envelope applicable to the building in question.

Step 2 – Estimating Time Ranges for Impairment For each member affected by decay, measure the section loss at the time of observation.

As described in Figure 1, next calculate the section loss that corresponds to the point at which the member’s load carrying capacity becomes impaired. Then plot the impaired section loss relative to the observed loss on a graph. Superimposing this on the estimated decay envelope, determine the points in time when the impairment threshold intersects the upper and lower bounds of the decomposition envelope. This gives a range of years – the impairment range – for each member.

Repeating this exercise for other affected members in the structure provides a group of impairment ranges. If the sample is representative of the different types of structural damage documented at the building, so too is the set of impairment ranges.

Step 3 – Empirical Probability Distribution Step 2 results in a set of ranges that represent likely time frames for various members to have entered a state of impairment. Plotting all the impairment ranges on a graph provides a relative frequency distribution of impairment over the service life of the building. With a straightforward mathematical calculation, this frequency distribution can be converted to an empirical probability distribution. These plots can then be used to estimate the percentage of structural impairment in any period of interest throughout the service life of the building. continued on next page

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material aspect, it is called impairment.

When load carrying capacity is diminished by decay to the point that the member can no longer support the associated code load demand, the member is impaired in its capacity. In order to determine if the member is impaired, the engineer is required to calculate the capacity of the remaining “good wood” and compare this to the calculated load demand on a case by case basis. Impairment thresholds are defined by the engineer based on his or her engineering judgment, and in a manner that is consistent with provisions set forth in governing building codes.

Cross hole sonic logging of drilled shafts per ASTM D6760.

Figure 2 is the result of analyses performed on a series of wood framed buildings in Seattle, based on the methodology summarized in this article. The author collaborated with Professor Robert Edmonds, Emeritus Professor and wood decay expert at the University of Washington, to model the decay envelope applicable to these buildings. The buildings were constructed in the mid-1980s; observation of decay damage was documented during a 2008 reclad. Building enclosure conditions permitting long-term water intrusion (such as failed sealant joints) were documented. Known areas of past framing repairs were used as a check on the decomposition envelope. The total area under the curve represents 100% of the impaired framing members. When long term decay meets a range of residual capacity, there is a smaller percentage of members entering a state of impairment in the early and later years, and a larger percentage in the middle years.

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Property Insurance Disputes Some property insurance policies include an additional coverage that has been interpreted by courts to cover certain types of structural damage. In some cases, this includes structural Figure 2: Empirical probability distribution of impairment over service life. impairment caused by decay. Substantial structural impairment caused by decay can result in considerable financial losses that create a dispute between the insured building owner and/or two are not required to be based on perfect scientific certainly, but or more insurance companies that insured the building during rather, on the “more probable than not” civil case law standard. The different periods of the building’s service life. role of the forensic structural engineer in such cases begins with In these cases, structural engineers are often retained to assess the a reasonable investigation of the damaged building. This involves deterioration of wood framed structures caused by decay, and pres- either representative sampling by means of destructive testing, or ent opinions on the extent and timing of impairment. Opinions in some cases, a census of damage taken when cladding assemblies are removed in whole or in part. The engineer then carries out an analysis using the data obtained to form his or her opinions.

There are two “gate-keeping” standards used by courts to decide whether or not scientific evidence is admissible. Both are aimed at identifying scientific evidence that is reliable. One is the “Daubert” standard used by Federal Court, and the other is the older “Frye” standard employed by some state courts. Both are similar in that they aim to weed out “junk science”. The methodology presented in this article has passed both the Daubert and Frye standards in recent insurance disputes involving buildings in the Seattle area.

Even though the methodology summarized here pertains to wood structures, the Author suggests that a similar approach may be applied to steel and reinforced concrete structures.

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STRUCTURE magazine

Conclusions Long term water intrusion can wreak havoc on structures. Structural engineers that consult on existing buildings and other structures should familiarize themselves with the types of conditions that can result in water intrusion, and elements of the superstructure most prone to damage, such that owners receive diligent advice. In working with contractors and architects, structural engineers should take a proactive interest in waterproofing.

Analyses that allow damaged buildings to tell their own story can be powerful tools when applied in a reasonable and reliable way. When the standard of proof is “more probable than not”, and unbiased engineering methodologies are applied to representative data consistently, reasonable and reliable impairment ranges can be estimated. When required to resolve disputes involving decayed wood structures, engineers should consider using the applied science approach set forth in this article to determine the occurrence of structural impairment of a building or other structure over its service life.▪

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October 2013

Historic Arch Bridge Reborn with Progressive Design

By Chad Clancy, P.E. and Mike House, P.E.

T

he Burnt House Road Bridge, a historic bridge set in the countryside of rural central Pennsylvania, was in need of an update – and it needed it quickly. After being closed to traffic in 2009 following an underwater inspection that revealed undermining of the foundations, the Pennsylvania Department of Transportation (PennDOT) needed a solution that would quickly bring the bridge back into operation for the nearly 2,100 cars that cross the bridge on a daily basis.

Constructed in 1912, the bridge carries Burnt House Road over the Yellow Breeches Creek in Dickinson Township – about 30 miles outside of Harrisburg, PA. At nearly 100 years old, the single-lane bridge already had a posted load limit of only three tons, which was not conducive for normal traffic – let alone nearby quarry traffic.

After the 2009 closure, Dickinson Township, which owns Burnt House Road, and PennDOT, the bridge’s owner, embarked on an evaluation process to determine if the original bridge could be rehabilitated or if it would need to be replaced altogether. Bridge engineering firm Modjeski and Masters was engaged for preliminary and final design, and faced the challenge of balancing the community’s preference to preserve the appearance of the original “humpback” bridge with modern day traffic demands.

Context Sensitive Design Calms Community Concerns Because of the community’s attachment to the visual aesthetic of the original bridge, context sensitive solutions were an important design consideration. These solutions needed to not only preserve the look of the original bridge, but also to improve bridge functionality and safety for pedestrian and vehicular traffic.

The replacement bridge design is composed of a wider bridge that now accommodates two lanes of vehicle traffic with a sidewalk that facilitates safer pedestrian traffic. A new sidewalk was incorporated STRUCTURE magazine

on the same side of the road as nearby Stuart Park – an added safety feature for park visitors and Yellow Breeches Creek fishermen alike.

The new, three-barrel arch structure chosen for the replacement bridge serves a dual purpose. First, the center barrel is raised relative to the outer barrels, which maintains the humped profile that was important to the community. Second, the large opening of the center barrel improves hydraulic functionality by better accommodating stream flow and preventing an increase in backwater, which in turn reduces the risks of flooding nearby properties.

Finally, the new bridge’s stone facade was created to replicate the look of regional limestone used in the construction of nearby historic structures. Arch headwalls were fabricated using stacked stone pattern formliners to give the appearance of stone. The concrete was then stained to mimic the regional grey limestone.

Accelerated Construction Reduces Environmental Impact Other improvements were incorporated into the designs to streamline construction, improve traffic flow and decrease future maintenance.

Because Burnt House Road is a primary travel route through Cumberland County, and the bridge was already closed to traffic, getting a new bridge back into operation as quickly as possible was important to PennDOT and Dickinson Township officials.

Accelerated construction alternatives were evaluated, and the final designs incorporated 30-ft. pre-cast CON/SPAN arch units to streamline construction time.

The Yellow Breeches Creek is deemed a high-quality, stocked and naturally producing trout stream. The Pennsylvania Fish and Boat Commission regulates in-stream construction to prevent disruptions to trout reproduction. As such, in-stream construction activities between March 1 – June 15, and October 1 – December 31 are prohibited.

Because the available window for construction time is limited by these

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October 2013

regulations, the use of prefabricated arch units drastically reduced the amount of time construction teams needed in-stream access.

Asphalt Deck Streamlines Future Maintenance Another benefit to the use of CON/SPAN units was the ability to incorporate an asphalt deck versus a reinforced concrete deck. Bridge redecking typically occurs every twenty to thirty years, and can be a lengthy process with a substantial price tag and can often require substantial bridge closures. Repaving saves future costs associated with ongoing bridge maintenance, reduces traveler headaches and improves bridge longevity. Further, PennDOT’s ultimate goal is to transfer ownership of the new bridge to Dickinson Township, so future maintenance and its impact on the local taxpayer was an important consideration.

Improved Alignment and Traffic Flow To facilitate better traffic flow across the bridge, the project also involved modifications to the horizontal alignment of Burnt House Road. Prior to the bridge replacement project, the road had a distinct “kink” immediately prior to the bridge on the south side. The design team incorporated a new alignment that eliminated the kink, enabling traffic to flow more freely across the bridge.

One of the major challenges the design team faced when creating a new alignment was working within the given right of way. Because of historic structures nearby, including a stone farmhouse, ruins from a stone barn and nearby wetlands – all of which were important historic and aesthetic components of the bridge setting – the new alignment would need to be created in a way that avoided any impacts on these elements.

Gilbert Cornwell, former Dickinson Township resident of more than fourteen years, believes he speaks for local residents when he says he is “very pleased” with the new bridge. “I have heard people talking who wanted the bridge to be shut down completely, and now they say it’s a very nice bridge. We are very pleased with the new bridge.”

Township manager, Laura Portillo commented that “the beauty of the bridge speaks volumes” and added that many residents comment on how great it looks; that it kept the feel of the old bridge.

The Burnt House Road Bridge replacement project served a critical need in Dickinson Township, PA. Closed to traffic because of its current condition, the township needed a new bridge that maintained the same aesthetic qualities – quickly. Modjeski and Masters incorporated design features such as prefabricated CON/SPAN arches to streamline construction, while at the same time focusing on context sensitive design solutions to maintain a similar bridge profile and appearance STRUCTURE magazine

Courtesy of Cumberlink.com.

to best compliment its natural setting. The new Burnt House Road Bridge will ultimately save taxpayer dollars by reducing the amount of future maintenance, while helping to prevent future lengthy bridge closures due to redecking.▪

27

Chad Clancy, P.E., is a Structural Project Manager at Modjeski and Masters with 20 years of experience as a bridge designer. He can be reached at CMClancy@modjeski.com.

Mike House, P.E., is a Lead Highway Engineer at Modjeski and Masters with 15 years experience in transportation design and construction and can be reached at MDHouse@modjeski.com.

October 2013

for Planes, bridges

Trains, buT noT auTomobiles

By David A. Burrows, P.E., LEED AP BD+C

British Airways 747 crossing beneath the Taxiway “R” bridge, June, 2012. Courtesy of City of Phoenix Aviation Department.

A

s described in the August edition of STRUCTURE® magazine, Phoenix Sky Harbor International Airport opened the first stage of their automated transit system, PHX Sky Train™, on April 8, 2013. Thousands of passengers have already boarded the Sky Train and experienced the comfortable five minute ride from the 44th Street Station through the East Economy Lot Station, over Taxiway “R” (more than 100 feet above Sky Harbor Blvd.), ending at Terminal 4.

The next phase, known as Stage 1A, is currently under construction and continues Sky Train’s route from Terminal 4 to Terminal 3. Scheduled to be open in early 2015, Stage 1A, similar to the Stage 1 construction, faces the task of crossing an active taxiway. Unlike the first Stage’s crossing above Taxiway “R”, the current phase of construction crosses beneath Taxiways “S” and “T”. Both Stages’ taxiway crossings presented several design and construction challenges.

The World’s First On Oct. 10, 2010, a celebration to mark the re-opening of Taxiway “R” was held by the City of Phoenix with members of the City’s Aviation Department, designers, contractors and media watching as the first two planes taxied under the new bridge. Nowhere in the world had this been done before, a bridge carrying trains over an active taxiway; even more remarkable, a taxiway that handles planes as large as Boeing 747’s. Delivered a week ahead of schedule and approximately 35 percent below the initial budget, there was reason to celebrate. To make this crossing a reality, creative problem solving by both design and construction teams was necessary.

Design Constraints An area 340 feet in length and 75 feet in height above Taxiway R was needed to provide the clearance required for Group V Aircraft (Boeing 747’s). Additionally, to stay below the Part 77 surface established by the Federal Aviation Administration for safe aircraft operations, the height of the bridge was limited. Thus, a narrow vertical band of approximately 40 feet remained within which the bridge could be built. Taking into account the vertical curve and bridge barrier, the vertical band reduced further to just over 30 feet.

STRUCTURE magazine

A US Airways jet passes beneath the Taxiway R crossing with the PHX Sky Train overhead. Courtesy of City of Phoenix Aviation Department.

In addition to the challenging geometry was the schedule constraint for constructing the bridge. Because the construction required the taxiway to be closed, a limited shutdown period of six months was possible due to airport operations. The timing of the shutdown was an additional factor to be managed. Due to seasonal traffic volumes, the closure had to occur between Spring Break and Thanksgiving. If this window was missed, it would delay construction of the bridge, which would delay the entire project. Obviously, it was critical to choose the correct structure and get the design and construction right the first time.

Eight alternatives were evaluated and ranked based on impacts to the taxiway, long-term maintenance, cost, aesthetics and special considerations specific to each structure type. Evident from a drive on metro-Phoenix’s freeway system, concrete box girders are a popular choice, which require little maintenance, only routine inspection and, in many cases, a lower life-cycle cost. Aesthetically, the box girder was the most streamlined and least obtrusive choice, fitting nicely with surrounding concrete structures and adjacent guideway. Thus, a cast-in-place box girder bridge was chosen.

Concern arose regarding the cost of falsework supporting a superstructure 90 feet above grade during construction. In order to minimize disruption to the taxiway, end spans (which did not require a taxiway

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October 2013

A Southwest Airlines 737 crosses over the newly completed Taxiway “S” bridge.

Courtesy of Visions in Photography.

shutdown) would be constructed first. To reduce falsework cost, the CM-at-risk contractor recommended that the designers determine a way to re-use the end spans’ falsework for main span construction.

Design based on this concept was completed in July, 2009.

The contract to build the bridge was awarded in September, 2009.

With the demand for construction impacted by the recession, the bridge contractor found an abundant supply of falsework material, and proposed supporting all three spans simultaneously until post-tensioning was complete. Therefore, the elements added to accommodate the reuse of falsework were no longer necessary. A redesign of the bridge, which eliminated supplemental post-tensioning and closure pours, was completed in three weeks; a quick turnaround to keep construction on schedule.

Construction Phase Challenges A construction worker within the tight clearances of Taxiway “R”. Courtesy of

800-562-8460

STRUCTURE magazine

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October 2013

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Tight construction clearances were common and unavoidable during Hensel Phelps Construction Co. construction. While the taxiway remained open, construction began with pier foundations. Due to the close proximity of traffic on Sky Harbor Blvd and a bridge over a nearby local street, the foundation for the eastern main pier proved particularly difficult to construct. This was overcome by installing the drilled shafts from existing grade, rather than excavating first and drilling from the bottom of footing grade as conventionally done. A trench filled with slurry was placed to form the perimeter of the pile cap to allow for the 10-foot deep cap excavation without impacting the adjacent area.

Another challenge encountered while building the superstructure was in forming the deepest sections of the webs near Design/Build the main piers. Because the webs tapered in thickness, working space for forming Earth Retention and stripping became extremely limited Foundation Support (as shown in upper right graphic). Once the floor and webs of the girders for the Slope Stabilization end spans were constructed, the taxiway was shut down in April 2010 to begin the Ground Improvement construction of the main span. The deck Dewatering was poured continuously over all three spans, and post-tensioning of the bridge occurred in early September 2010.

Donald B. Murphy Contractors, Inc. Arguably the biggest challenge to conWWW.DBMCONTRACTORS.COM struction was the tight and unmovable

schedule. It required tremendous planning efforts that included several hour-by-hour internal schedules for weekend and critical activities, such as falsework lowering.

Executing necessary restrictions on Sky Harbor Blvd. and surrounding roadways, required countless emails and hours of phone calls to communicate between contractors, airport operations, airlines, vendors, and the travelling public. Crews worked through most holidays and weekends, and out of 307 available shifts, the contractor worked 272 shifts or nearly 90 percent of the total time available.

Taxiways “S” & “T” Going Below the Surface

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In contrast to the highly visible crossing above Taxiway “R”, the crossings below Taxiways “S” and “T” will be invisible to all but the passengers on the Sky Train. Why cross above one taxiway only to then cross beneath another two? Extensive coordination and planning determined that an elevated Taxiway “R” crossing provided the optimal alignment into the Terminal 4 Station. Additionally, the amount of utility relocation required by constructing beneath the taxiway made that option infeasible. Utility relocations, while a concern, weren’t as problematic at Taxiways “S” and “T”. However, because the two taxiways, at 210 feet wide, are only separated by 50 feet; placing a pier between them would violate clear zone requirements. The resulting span length would be 600 feet, a superstructure capable of that span, apart from being uneconomical would have been impossible to fit in the narrow vertical band described for the Taxiway “R” crossing.

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Work on the Taxiway “S” anchor slab. Courtesy of Visions in Photography.

surprising. While understandable, the potential consequences of unknown utility lines directly conflicting with new construction can be disastrous. Instances of unforeseeable conflicts arose in Stage 1 construction, which cost several weeks of construction time to resolve. With only a six month construction duration for each undercrossing, a delay due to a hidden conflict could disrupt the schedule for the entire project and, more importantly, the operations of the airport which requires that all taxiways be open from Thanksgiving to New Year’s day.

Design Innovation To mitigate the risk of utility conflicts, the designers took an innovative approach to the undercrossing design. The design contemplated adding a new span on the south end of each taxiway. Typically, construction for a new bridge abutment would require a large amount of excavation and thus greatly increase the chance of uncovering unknown utilities.

Therefore, the designers developed an abutment wall consisting of 54-inch diameter drilled shafts approximately 50 feet long at 10-foot spacing, restrained at the top by an anchor slab and with the gap between each shaft filled with a reinforced shotcrete wall. This allowed the new abutment to be built with no excavation behind the drilled shafts, except for the shallow depth required for the anchor slab shear keys.

Another innovative idea that mitigated schedule risk was to use the existing taxiway bridge abutment as a support for

STRUCTURE magazine

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October 2013

the new span. The initial design proposed building a new pier adjacent to, but outside the footprint of the existing abutment, with a reinforced concrete slab to span the short gap between the two supports. During final design, this concept was eliminated after determining that loading from the new span would cause less stress than the fill behind the existing abutment. With a relatively small amount of concrete added to the existing abutment to accommodate the new span, the duration of construction was shortened.

As required by Airport Operations, only one taxiway could be shutdown at a time.

Construction began with Taxiway “S” on May 22, 2012 and was completed five days ahead of schedule on November 14, 2012. The new superstructures were built using the “soffit fill” technique, where the superstructure was built directly on compacted fill and, after post-tensioning, the fill is excavated to reveal the soffit of the bridge. This technique also contributed to shorter construction durations. Taxiway “T” was shut down on January 7, 2013 and was re-opened with its new span on June 11, 2013, three weeks ahead of schedule.

The cost for both undercrossings came in approximately ten percent below the initial budget.▪ David A. Burrows, P.E., LEED AP BD+C, is a senior structural engineer at Gannett Fleming, Phoenix, Arizona. He was the lead engineer for the design of the Taxiway R crossing. David can be reached at dburrows@gfnet.com.

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Structural teSting issues and advances related to structural testing

B

ridge deflection and vibration data are often useful for structural health monitoring (SHM), load rating determination, change in use, or retrofitting.

Deflection and vibration data are typically gathered through nondestructive testing (NDT) or nondestructive evaluation (NDE) methods. For most bridges, this means installing accelerometers, strain-gauges, linear variable differential transformer (LVDT), or string pot type instrumentation, which sometimes requires a temporary restriction of bridge use, and technicians must gain access to the bridge’s structural members which can involve fairly hazardous work, both to install the instruments and to remove them when the study is complete. Once the bridge is instrumented, the data is traditionally transmitted via cell-phone signal and then processed. While these traditional methods do generally produce reliable data, they can be time consuming and costly.

In the past few years, a new NDE instrument has arrived in North America that presents structural engineers with an attractive option for acquiring bridge deflection and vibration data. The instrument is known as IBIS, which is an acronym for Image By Interferometric Survey. And while this instrument may look like a whimsical character in a Pixar film (Figure 1), rest assured that it’s all business!

IBIS relies on advances in radar technology – interferometric radar, to be specific – to measure deflection of structural members as a function of time. When a strong radar reflection is obtained, the instrument can measure deflection to an accuracy of 1/250th of an inch for all structural elements in the line of sight. Data can be acquired at a rate of 200 Hertz, which allows the user to measure structural vibrations up to 100 Hertz.

This provides plenty of range for most structural engineering purposes, because the most meaningful vibration data from civil infrastructure is typically below 100 Hertz. The instrument can be used at distances as much as 3,200 feet away from the structure, although closer ranges are typically used for bridges. The non-contact nature

Structural Health Monitoring with Interferometric Radar

By Paul J. Bennett, P.E., CBIE

Paul J. Bennett, P.E., CBIE, is a Managing Engineer with Exponent Failure Analysis Associates, and is based in their Boulder, Colorado, office.

Paul may be reached at pbennett@exponent.com.

Figure 2: Ideal radar reflector.

32 October 2013

Figure 1: IBIS Instrument.

of IBIS, along with its quick set-up, is one of the main differentiating features when compared to typical current instrumentation.

How it Works Radar relies on the Doppler Effect, wherein the reflected radar waveform reveals the location of an object. Radar has long been used to track the movement of objects, but the range of discernible movement typically was measured in feet. In the case of bridges and other structures, however, we are interested in measuring much smaller amounts of deflection. By noting the phase change in the reflected wave form (as is the case with interferometric radar), IBIS achieves a high degree of accuracy when measuring deflection and vibration.

As one might suspect, the instrument works well only when the object to be measured is a good radar reflector. Thus, bridges shaped like the stealth bomber are a bad match for IBIS. For the remaining bridges out there, steel proves to be a good reflector, whereas concrete and timber do not reflect radar well. For concrete or timber bridges, an ideal radar reflector can be installed (Figure 2) on the structural member in question.

These reflectors work well, but the process of installing them presents some of the same hazards associated with the aforementioned traditional instrumentation, although the process is simpler than installing instruments because the reflectors do not require hard wiring.

Because IBIS relies on radar, data can be obtained from a remote point, as long as a clear line of sight is available. For most highway overpasses, establishing a clear line of sight is not a problem. For bridges over waterways, however, finding a clear line of sight may be a challenge if substantial vegetation is present, although this difficulty can usually be overcome.

Once a location with a clear line of sight is found, the IBIS instrument can be set up in about 15 minutes, and data collection can begin immediately. The instrument is connected to a conventional laptop and operated with Matlabbased software provided by the manufacturer.

The user views an X-Y radar plot that shows radar

Profile

100 90 80

SNR [dB]

70 60 50 40 30 20

20

40

60 80 Rangebin index

100

120

Figure 3: Radar reflection plot. Peaks correspond to members that are reflecting radar well. On the X‑axis, each rangebin equates to 2.46 feet distance from the instrument.

reflection on the Y-axis and distance from the instrument on the X-axis. The peaks correspond to objects that are reflecting radar well, shown as a high signal-to-noise ratio (SNR) (Figure 3). Using a laser distometer, the user can determine which structural members correspond to which peaks on the radar plot. At this point, data are being collected under live loads from a remote point, for all objects that are reflecting radar well. For a bridge with steel cross frames connected to girders, the user can typically gather data on all the cross frames at one time, provided they are all visible. The instrument accounts for the unique angle to each object it is measuring.

Because IBIS is radar based, the movement in structural members is along the line of sight of the radar. At first thought this might seem like unusable data, but because such a small amount of movement can be measured,

Figure 4: By measuring the original distance to the structural member (X1) and the distance to the member after a load is applied (X2) and knowing the angles, IBIS calculates actual vertical displacement (Y).

the minor amount of movement along the line of sight can be used (via trigonometry) to calculate vertical displacement. Once the user inputs the angle of the radar head, IBIS then automatically does the math to export vertical displacement data. Figure 4 shows an exaggerated view of this concept.

When data collection is complete, the data can be viewed immediately in a Matlab-based post-processing software package, which allows the engineer to validate the data set and view deflection data in both the time and frequency domains. Because data are often obtained for several cross sections along the length of the bridge, one-dimensional vibration (vertical direction) data can be viewed quickly – the data can be plotted as a line plot along the length of the bridge and that data can be animated as a function of time, with a click of a button.

Experiment Most engineers will recognize the value of an instrument that can be set up in minutes and will collect deflection/vibration data on all structural elements in the line of sight without requiring direct access to the bridge.

However, when it comes to IBIS’s claims of accuracy and ease of use, this engineer was as skeptical as any who might think it sounds too good to be true. Therefore, a field experiment was undertaken to measure vibrations on a cable-stayed pedestrian bridge (Figure 5) and verify the data collected using traditional accelerometer methods.

The subject bridge is a 243-foot long pedestrian bridge owned by the City and County of Denver. The bridge provides pedestrian access over the Platte River, from Sixteenth Street in downtown Denver to a nearby area known as the Highlands. The bridge was built in 2003 and features two steel masts, nine structural steel strands, 16-inch diameter steel tubes as

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Figure 5: Cable‑stayed bridge.

STRUCTURE magazine

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October 2013

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StruWare, Inc

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x 10

2011.07.30-11.33.01-global1

5

Rbin Rbin Rbin Rbin Rbin Rbin Rbin Rbin Rbin

Line of Sight Acceleration [mm/s 2/Hz]

2.5

2

1.5

1

0.5

0

Figure 6: IBIS set‑up beneath cable‑stayed bridge.

the main girders, steel floor beams, and timber stringers and deck.

Global vibration data were desired for the bridge as a whole, along with local vibration data on the steel strands and towers. These data were obtained by setting up the IBIS instrument adjacent to one abutment and viewing the length of the bridge (Figure 6).

Due to a cross member (shown by the arrow in Figure 6), not all floor beams were in the line of sight. However, data on nine floor beams were obtained simultaneously from one set-up. Data were acquired on multiple occasions during different seasons, and the data consistently indicated that the global natural frequency of the bridge, in the vertical direction, was 1.98 Hertz.

Figure 7 is an IBIS-generated plot that shows vibration data for nine floor beams.

Global natural frequencies at 1.98 Hertz, and local natural frequencies at 2.66 Hertz on the floor beams, are noted in Figure 7.

The data shown in Figure 7 were obtained in less than two hours, including set-up time and multiple iterations.

Next, vibration data were obtained by setting up IBIS at nearly the same elevation as the bridge deck while collecting data on the structural steel strands, steel masts, and steel guard rails. Data for the structural steel strands were acquired through four different set-ups. Vibration and deflection data were obtained on all of the subject elements, and the data consistently showed a global natural frequency of 1.98 Hertz and local vibration modes of interest. Independent data

4 8 13 19 24 29 55 66 71

1

1.5

2

2.5 frequency [Hz]

3

3.5

4

Figure 7: Vibration data from nine floor beams on cable‑stayed bridge.

collection with an accelerometer verified the IBIS data. Additional laboratory work with accelerometer data consistently verified the IBIS data. We are also aware of similar work by other researchers that has validated IBIS data using other methods.

Limitations The most obvious limitation to the IBIS system is that it requires a clear line of sight to the structure; therefore, vegetation and other obstructions can make it difficult to use. Also, IBIS can’t distinguish between different structural elements that are closer than 2.46 feet apart from each other, and this is not adjustable. While this typically doesn’t translate to a real-world problem in bridge structures, it is worth noting.

IBIS also has a limitation in that the object you are viewing must be larger than 0.70 inches. Again, this is rarely a limitation, but in the case of small diameter steel rods or cables, it could be a factor to consider. A work-around would involve installing an ideal radar reflector on the object, as described above.

Finally, the typical IBIS set-up measures displacement in only one dimension (one degree of freedom). In many applications, mode shapes of two (or more) degrees of freedom are of interest. This is especially true for suspension bridges and other structures with dominating torsional mode shapes.

While two-dimensional mode shapes are not quickly accomplished with IBIS, other researchers have used alternative IBIS set-up

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configurations to obtain two-dimensional mode shapes, proving it is possible.

Conclusions Due to advances in technology, radar is now a useful NDT/NDE tool for evaluating bridges and other structures. The IBIS radar technology has limitations, such as the need for a clear line of sight and restrictions on size and composition of members that can be measured, but in situations that aren’t subject to those limitations, the instrument has proven to be an accurate and efficient method for measuring deflection and vibration in bridges. Data are obtained in a non-contact manner, without interrupting the use of the structure, and data acquisition and compilation are completed much more rapidly than is possible using traditional strain-gauge and accelerometer methods.▪

Acknowledgements The author thanks Larry Olson and Olson Instruments, Inc., of Wheat Ridge, Colorado, for providing the IBIS instrument for use in this research. Olson Instruments is a vendor for the IBIS instrument in North America, providing instruments and operators, as well as user training. This work was completed as part of a master’s thesis at the University of Colorado at Denver and, as such, the author is grateful to the following for their guidance and assistance: Dr. Fredrick Rutz, Dr. Rui Lui, and Dr. Kevin Rens, all of the University of Colorado at Denver.

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LegaL PersPectives

discussion of legal issues of interest to structural engineers

Consideration

View of the Court

What makes it Good and Valuable?

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

F

rom time to time, an A/E may be presented with a contract that starts off with the phrase “For good and valuable consideration, the parties do hereby covenant...” Alternatively, the consideration may be described as “mutually-agreed upon.” This begs the question – what is consideration? And what makes it good and valuable?

Legal Meaning The confusion is partly due to the fact that the legal meaning of the word consideration (its meaning when used in legal documents such as contracts) has nothing to do with its ordinary meaning. When used in a legal document, “consideration” means something of legal value. Consideration can be money or goods (either tangible or intangible), but it can also be a promise to do something or refrain from doing something.

Required for Both Parties A contract is not enforceable in court unless both parties provide consideration. In a typical business contract, both parties provide consideration in the form of a promise. One party promises to either supply goods or perform a service; the other party promises to pay for the goods or service.

The requirement for consideration is an attempt to ensure that the contract is a legitimate bargained-for agreement. Often a promise will indicate what someone will try to do, or would like to do, but there is no guarantee they will be able to carry out their promise. A court will not penalize someone for failing to keep a promise if the other party did not provide anything of value in exchange.

This means courts will not enforce a promise of a gift or a promise to provide a free service.

Even if the other party does not receive the gift or service, its position is no worse than it was before the promise was made.

A Promise not to Do Something Although consideration is typically a promise to do something, it can also be a promise not to do something. This is referred to as forbearance and is the basis for settlement of a claim.

If a party believes, in good faith, that it has a claim against another party, whether for breach of contract or some type of injury, their promise NOT to sue is their consideration for the settlement. The other party’s consideration is the amount it pays for the settlement.

It is not valid consideration unless the party is giving up something it is legally entitled to do, however. As an example, a neighboring business might be parking its trucks in such a way that it is difficult to access a project site. The project owner could promise to pay the drivers a certain sum when the project is complete if they promise to park their trucks somewhere else. If it turns out that it is not legal to park in front of the job site anyway, the contract is not enforceable. Nevertheless, the owner might want to ensure access to the site. The parties could make the agreement, and if both sides carried out their side of the bargain as agreed, there would be no problem. However, if the owner subsequently refused to pay, the drivers could not get a court to enforce the contract.

Action versus Promise As noted above, the typical business contract consists of reciprocal promises; this is referred to as a bilateral contract. It is also possible to have a unilateral contract, where one party’s consideration is a promise and the other party’s consideration is an action. In unilateral contracts or agreements, the promise will typically be conditional. For example, the client may agree to pay the A/E an additional fee if the drawings are finished by a certain date. The A/E might not think this can be done, so is not willing to agree to the specified date, but decides to try and ultimately succeeds. The client’s consideration is the (conditional) promise to pay an additional fee. The A/E’s consideration is the action of getting the drawings done by the specified date.

The party must not be under a pre-existing duty to perform the requested action. If the A/E’s contract required the drawings to be done by the specified date, it would not be supplying any consideration. If the owner refused to pay the additional fee, the A/E would have no basis for a claim. There is nothing to prevent the owner from paying the agreed upon fee, but the payment would be a gift, rather than fulfillment of the agreement.

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Although a contract is not enforceable unless both parties provide valid consideration, the parties’ right to contract under their own terms is a cornerstone of contract law in this country.

Thus, courts will not examine whether the consideration provided by each side is equivalent, or even appropriate. The only exception is if there are allegations of fraud or duress, i.e. if one of the parties misrepresented the value of the goods or services it provided, or one of the parties was forced to sign the contract by threats of physical violence.

Sometimes contracts, particularly contracts for real estate, use the phrase “For good and valuable consideration and ten (10) dollars.”

It does not matter whether the money referred to is ever exchanged. When both parties have signed a contract agreeing that the money was exchanged, neither party can subsequently claim that the exchange never took place.

Good and Valuable Consideration Finally, to answer the original question, good consideration is defined as consideration founded on natural affection, generosity, love or moral duty. By itself, good consideration is not enough to make a contract enforceable; the consideration must also have legal value.

Valuable consideration must involve doing something one does not already have a legal obligation to do, or refraining from doing something one has the legal right to do.

The phrase “good and valuable consideration” was once common in contracts; the intent was to emphasize that the parties were exchanging valid consideration and thus the contract was enforceable. Although the phrase is not used in any of the current industry standard form contracts (AIA, EJCDC, ConsensusDOCS), it is sometimes used in custom contracts. There is no harm in including the phrase in a contract, but it really has no meaning; it is generally clear enough from the contract language whether the consideration is valid. And if the consideration is not valid, describing it as good and valuable will not make the contract enforceable.▪ Gail S. Kelley, P.E., Esq., is a LEED Accredited Professional as well as a licensed attorney in Maryland and the District of Columbia. Ms. Kelley can be reached at Gail.Kelley.Esq@gmail.com.

a listing of seismic/wind firms, suppliers and software companies

SeiSmic/wind Guide

Hayward Baker Inc.

Materials American Wood Council Phone: 202-463-2766 Email: lmerriman@awc.org Web: www.awc.org Product: (SDPWS) Standard with Commentary Description: The AWC Special Design Provisions for Wind and Seismic (SDPWS-08) covers materials, design and construction of wood members, fasteners, and assemblies to resist wind and seismic forces.

Software

Phone: 800-456-6548 Email: info@HaywardBaker.com Web: www.HaywardBaker.com Product: Ground Improvement Description: Hayward Baker Inc., annually ranked #1 Excavation/Foundation Contractor by Engineering News-Record, provides Design-Build ground improvement solutions for support existing or planned structures that require support for wind or seismic loads.

Premier SIPS

Engineered Products Cast Connex Corporation Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Cast ConneX Scorpion Yielding Connectors Description: Provides a symmetric hysteretic response in high-performance braced frames through the use of off-the-shelf, highly ductile, collapse-resistant, and inherently redundant Scorpion Yielding Connectors.

Product: Cast ConneX High-Strength Connectors Description: Simplify and improve connections to round HSS brace members in seismic-resistant braced frames (SCBF and OCBF) by eliminating field welding and providing highly compact connections.

Gripple Inc. Phone: 630-406-0600 Email: grippleinc@gripple.com Web: www.grippleseismic.com Product: Gripple Seismic for Nonstructural Components Description: Provides solutions for projects requiring seismic design or Anti-Terrorism/Force Protection (AT/ FP) for Nonstructural Components. Gripple provides evaluations and calculations in order to determine the solutions needed for your project, and then gives you the seismic cable bracing and/or vibration isolation products and engineering services to fulfill those solutions.

Hardy Frames Phone: 800-754-3030 Email: dlopp@mii.com Web: www.hardyframe.com Product: Hardy Frame Panels, Brace Frames and Special Moment Frames Description: HFX-Series Panels and Brace Frames are fabricated with galvanized Cold Formed Steel to standard wood stud heights and the HFX/S-Series are fabricated to standard steel stud heights; custom heights are also available. Our Special Moment Frame is a structural steel product that uses SidePlate® moment connections.

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. See more companies in the 2013 Annual Trade Show issue!

Phone: 800-275-7086 Email: info@pbssips.com Web: www.premiersips.com/bc Product: Premier SIPs Description: Used for many years in all types of shear wall applications, including in high wind and seismic locations. The panels are exceptionally strong in racking diaphragm shear capacities. Premier SIPs are suited for use in single- and multi-family residential and commercial/institutional structures.

Simpson Strong-Tie Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Connector and Lateral Systems for Seismic and High-Wind Resistance Description: Simpson Strong-Tie offers a wide variety of code-listed, field-tested connector and lateral systems products for seismic and high-wind resistance.

The new Strong Frame® special moment frame with the patented Yield-Link(TM) structural fuse represents the latest innovative lateral system solution from Simpson Strong-Tie.

The Steel Network, Inc. Phone: 919-845-1025 Email: tdigirolamo@steelnetwork.com Web: www.steelnetwork.com Product: VertiClip SLB-HD and StiffClip LB-HD Description: New enhanced seismic curtain wall connections for seismic design categories D, E & F. The new connectors allow installers to connect curtain wall studs to the structure without welding time/cost, while addressing seismic requirements in ASCE 7-10 and California Building Code. Both restrict use of PAF’s to attach curtain wall.

Williams Form Engineering Corp.

Phone: 616-866-0815 Email: williams@williamsform.com Web: www.williamsform.com Product: Anchor Systems Description: Williams Form Engineering Corporation has been providing threaded steel bars and accessories for rock anchors, soil anchors, high capacity concrete anchors, micro piles, tie rods, tie backs, strand anchors, hollow bar anchors, post tensioning systems, and concrete forming hardware systems in the construction industry for over 90 years.

Applied Science International, LLC Phone: 919-645-4090 Email: sscoba@appliedscienceint.com Web: www.appliedscienceint.com Product: Extreme Loading® for Structures – Seismic Analysis Description: Used to design new or analyze existing structures against the effects of seismic events. ELS provides engineers with quick and efficient method of evaluating an entire structures as-built conditions against seismic events.

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

Digital Canal Corporation Phone: 800-449-5033 Email: glageju@digitalcanal.com Web: www.digitalcanalstructural.com Product: Wind Analysis Description: Wind Analysis is structural engineering software that completely automates ASCE’s “Minimum Design Loads for Buildings and Other Structures” (7-10 in version 9 and 7-05 in version 8). It calculates and analyzes wind forces on ASCE determined structures and provides detail report.

Enercalc, Inc.

ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: www.enercalc.com Product: Structural Engineering Library 6 Description: The nations most used software system for structural design of building components. The SEL has powerful modules for wind & seismic loadings on structures following major code requirements. All of the component design modules also allow wind & seismic loadings and extensive load combinations.

Georgia Tech – CASE Center Phone: 404-894-2260 Email: joan.incrocci@ce.gatech.edu Web: www.gtstrudl.gatech.edu Product: GT STRUDL Description: Includes seismic design and analysis capabilities, with comprehensive Linear/Nonlinear, Static/ Dynamic analysis features for Frame and Finite element structures. Includes moving load generation, response spectrum, transient, and pushover analyses. Models plastic hinges, discrete dampers, tension/compression only members and nonlinear connections. Optional modules for Base Plate Analysis and Multi-Processor Solvers.

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Software (continued)

Triple Protection Against Corrosion

LARSA, Inc.

S-FRAME Software

Phone: 800-LARSA-01 Email: info@larsa4d.com Web: www.Larsa4D.com Product: LARSA 4D Description: Analysis and design software addresses the needs for bridges and structures including “4D” time effects. With features such as pushover, progressive collapse, nonlinear time history within stage analysis, and a full inelastic element library, LARSA 4D is the standard at leading firms for design, construction, and seismic analysis.

Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: Structural Office R11 Description: A complete structural analysis, design and detailing management system, featuring powerful FEM and FEA solutions, steel and concrete design tools, powerful BIM and Cad links, and the ability to support any material type, S-FRAME is widely adopted in a variety of industries, both commercial and industrial.

POSTEN Engineering Systems Phone: 510-275-4750 Email: sales@postensoft.com Web: www.postensoft.com Product: POSTEN Multistory Description: The most efficient & comprehensive post-tensioned concrete software in the world that not only automatically designs the Tendons, Drapes, as well as Columns for you, but also is the only software built to design multistory post-tensioned structures for wind and seismic forces.

Increase Corrosion Resistance

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Powers Fasteners

Repel Water

Phone: 985-807-6666 Email: jack.zenor@sbdinc.com Web: www.powers.com Product: PDA Anchor Design Software Description: A real-time anchor design software program which includes options for seismic analysis.

By utilizing this free software package, engineers can design using any Powers Fasteners mechanical and adhesive anchors qualified for use with ACI318 Appendix D. Includes normal weight, lightweight concrete, and concrete-filled metal deck.

Prevent unsightly appearance to concrete

Reduce Chloride Permeability

RetainPro Software Phone: 949-721-4098 Email: info@retainpro.com Web: www.retainpro.com Product: RetainPro 10 Description: The latest release of this long standing excellent earth retention structure design software.

RetainPro 10 fully supports Seismic loading on retaining walls using either user entered values or internally calculated Mononobe-Okabe equations.

Wind loads on projecting stems are also allowed.

Increase the life expectancy of metals, steel and rebar

RISA Technologies

Add Corrosion Inhibitor to Cement All®, Mortar Mix, Concrete Mix and DOT Repair Mix for triple protection against corrosion

800-929-3030 ctscement.com

Phone: 949-951-5815 Email: info@risatech.com Web: www.risa.com Product: RISA-3D Description: Feeling overwhelmed with the latest seismic design procedures? RISA-3D has you covered with seismic detailing features including full AISC 341/358 code checks. Whether you’re using RISA3D’s automated seismic load generator, or using the built-in dynamic response spectra analysis/design capabilities, you’ll get designs and reports that will meet all your needs.

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Product: S-FRAME Analysis Description: A structural modeling and analysis program, features advanced methods for seismic and wind load analysis including pushover, nonlinear quasistatic, base motion time history analysis and hysteresis material models. S-FRAME includes powerful BIM and CAD links and a model validation tool for viewing or animating analysis results including time-history.

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

StructurePoint Phone: 847-966-4357 Email: info@structurepoint.org Web: www.StructurePoint.org Product: PCA-StructurePoint Engineering Software Description: Analysis and design software programs for the reinforced concrete buildings, bridges, tanks, and special structures including tilt-up and retail buildings. Work quickly, simply, and accurately using over 100 years of experience of concrete design and technology built into a suite of software programs and extensive support and consulting services.

Struware, LLC Phone: 904-302-6724 Email: email@struware.com Web: www.struware.com Product: Struware Code Search Description: Calculates wind, snow and seismic loadings in accordance with the International Building Code, ASCE 7, and state building codes based on these codes.

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. See more companies in the 2013 Annual Trade Show issue!

notable structural engineers

Great achievements

The Permanent Bridge America’s First Covered Bridge

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

A

crossing of the Schuylkill River on the extension of Market (Formerly High) Street in Philadelphia had been a pressing need for many years when, in 1723, an act was passed entitled “An Act for establishing a ferry over the river Schuylkill, at the end of the High Street of Philadelphia.” In 1767, a bridge over the river at the Middle Ferry was first proposed.

On January 31, 1769, a model and plan for a multiple span wooden bridge from Robert Smith, a well-known Philadelphia architect, was submitted to the Assembly for its review.

He wrote that due to the “difficulty of bridging the River Schuylkill near this City,” he has been induced to attempt an “Improvement on the Designs of Wooden Bridges raised on stone Piers, with Hopes that one might be constructed with equal Security, and much less Expence than any heretofore published.”

He reported that his design was supported by many with a knowledge and judgment in the field, and described his bridge as follows: “by a simple method, of suspending the platform below the Arch that sustains it, by which Means the Piers are better secured than by any other method, and applying the Arch in the Side to strengthen it, and the Whole well covered to secure it from the Weather. Thereby saving a great deal in the Frame, and lessening the height; that he has drawn a Plan and Elevation for such a Bridge, made a Model of one Arch and two piers, and with great Respect to the Honourable House begs Leave to present the same to them, in Hopes that the Ingenious may turn their thought to the Subject, and make such

Gilpin’s Chain Bridge 1774.

Smith’s proposed covered bridge 1787.

further improvements thereon, as may render it of some Service to the Public, Whenever the Legislature shall find the Province in a Capacity to execute a Design of such Utility and Importance to the whole community.” In 1774, Thomas Gilpin, a well known citizen of Philadelphia, “brought forward a plan of a permanent bridge over the river Schuylkill at Philadelphia the passage of which had always been conducted at the three ferries opposite to the city; for this purpose he obtained soundings of the river at the centre ferry at Market Street – the distance here across the river was found to be 546 feet 6 in(ches) with a channel of 250 feet from 17 to 26 feet deep at low water gradually shallowing to the shore on each side but nearest to the east shore. Mr. Gilpin’s idea was to reduce the width by (using) abutments on each side to 300 feet waterway and across that, to form a chain bridge upon a very simple plan; the whole expence was estimated at less than $30,000.”

Peale’s Bridge.

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In 1787, a plan was published in the Columbian Magazine for a four span covered bridge that was likely a rework of the earlier Robert Smith design, who died in 1777. He was the only person in America that had proposed covering an arch supported wooden truss bridge to protect it from the weather.

He seems to have a double arch in each span with diagonals in compression, and notes in the lower left hand corner that the sketch is for a “plan of a bridge to be built across the Schuylkill.” He suggested four (4) one hundred foot spans with two approaches each 140 feet long. In his description of the arches Smith simply says, “E, shews the manner of framing before the weather boards are put on.”

The next round of proposals came in the late 1790s. Charles Willson Peale, the noted painter, started publishing articles in the local newspapers in 1796 about a 390-foot single span bridge he designed and asked the Select Council to view his model. He was issued a patent on January 21, 1797, for a bridge he indicated would fit the Market Street site and followed it up with a pamphlet of 16 pages entitled An Essay on Building Wooden Bridges describing his patent for a laminated wood arch. His arch was built up of 1-inch thick plank laid on the flat with overlapping sides, and the planks butted to one another with the entire wooden deck pegged with hemlock trunnels.

On January 25, 1797, a memorial was submitted to the Legislature stating in part “To the Honourable Senate and House of Representatives of the Commonwealth of Pennsylvania in General Assembly met. The memorial of the subscribers respectfully

sheweth, that they are desirous, from motives both of public and private interest, to promote the establishment of a company for erecting a permanent bridge over the River Schuylkill, at or near the city of Philadelphia.” Judge Richard Peters was successful in having an act passed entitled “An Act to authorize the Governor of this Commonwealth to incorporate a Company, for erecting a Permanent Bridge over the Schuylkill River, at or near the City of Philadelphia” on March 16, 1798.

The company was formally incorporated and patent letters issued on April 27, 1798 when Peters and others reported to the Governor that the necessary number of shares had been subscribed. The act did not specify what kind of a bridge would be built. It was over two and a half years before work began on the bridge, as the directors were determining what kind of a bridge they could afford to build and who would design and build it for them. The story of the origins, trials, tribulations and ultimate success of the bridge is told in A Statistical Account of the Schuylkill Permanent Bridge, prepared for the bridge directors in 1806.

William Weston, an English engineer/ builder, was then in the country working on several canals. The directors of the bridge asked him, based upon his experience in England, to design a stone bridge, probably

Strickland painting of the permanent bridge. Note Wernwag’s 1812 Colossus Bridge in right background.

three spans, for the site. He designed one that was “elegant, plain, practicable and adapted to the site with very minute and important instructions for its execution.”

It was said he submitted the plan gratuitously “and from friendly and disinterested motives.” The directors later “discovered that the expense of erecting a stone bridge, would far exceed any sum, the revenue likely to be produced would justify.”

On October 18, 1800, the directors began work on the easterly abutment. This was followed by the easterly pier using Weston’s plan and it was generally followed “tho’ the circumstances compelled a considerable departure

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Based upon their experience with the easterly pier, Weston developed a plan for the deeper westerly pier before he left for England. It was “original and calculated for the Spot on which it was to be placed. It was faithfully and exactly executed under the care of Mr. Samuel Robinson, who was then Superintendent of the Company’s Work.” It was completed, after much difficulty, in the spring of 1803. With the foundations in place, Palmer began his work as the designer/ builder for the superstructure in 1804.

The directors spent so much money on the foundations that they needed a superstructure that would be cheap and fast to build.

Construction of the superstructure on falsework went well, and the Directors planned on opening the bridge January 1, 1805. The Poulson American Democrat and Advertiser wrote “We are informed

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STRUCTURE magazine

from it, as the Work advanced.” This pier rested on firm granular material outside the main river channel and was completed in the fall of 1801. At this time, Peters, in his Statistical Account… wrote: “We knew that no iron superstructure of such a span had been erected.

We sent for Mr. Timothy Palmer, of Newburyport, a celebrated practical wooden bridge architect. He viewed our site, and gave us an excellent plan of a wooden superstructure. But he pointedly reprobated the idea of even a wooden arch extending farther than between the position of our intended piers, to wit, 187 feet. He had at the Picataway Bridge, erected an arch of 244 feet; but he repeatedly declared, that whatever might be suggested by theorists, he would not advise, nor would he ever again attempt, extending an arch, even to our distance, where such a heavy transportation was consistently proceeding.”

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that upon the completion abovementioned, the directors with a few of those who were sensible of the importance and who aided in its promotion, were to dine together on the day of its opening – deference, however, to the recommendation of the clergy of different denominations for setting apart the first day of January, as a day of public thanksgiving has induced them to meet at the Bridge for that purpose on this day, (December 31) during which it will be free of toll for foot passengers, and a collation will be extended to all workmen employed.”

The builders were still working on the bridge over the next six months before any serious discussion took place by the Building Committee and Directors on covering it. It appears, however, that Peters had frequently suggested covering the bridge, possibly based upon the earlier recommendation of Robert Smith. Apparently, the other directors of the bridge did not share Peters’ desire to cover the bridge. The United States Gazette printed a communication from Peters to the Board on June 11, 1805 in which he made his case for covering the bridge. After briefly describing the early problems of building, the foundation and superstructure, he wrote: “I hold it therefore a duty peculiarly incumbent on me, who originated, and have faithfully laboured in the execution of an enterpize, in which so many have embarked their property, to make an effort for the completion and safety of a work on which the value of their advances so materially depends. Under this impression, I bring before you the subject of covering the bridge and herewith present several drafts of covers, adapted to the frame.

From the time of the first idea of a wooden superstructure, I have never wavered in my opinion of the indispensable necessity of the cover. I was surprised (a long time after I had conceived it to have been a general sentiment) to find myself in minority on this subject though I was not entirely alone. I have reason now to hope that the sentiments of the stockholders have materially changed…”

Peters published a letter from Palmer, dated December 10, 1804, who was writing in response to a request from Peters to discuss the advisability of covering the bridge. Palmer wrote: “To some questions you put to me some time since, relative to the durability of timber bridges without being covered, sides and top, I answer from experiences I have had in New England and Maryland – that they will not last more than 10 to 12 years; to be safe for heavy carriages to pass over…And it is sincerely my opinion,

Official plan of bridge with ornate siding and roof on half truss (east), Philadelphia on the right.

Note deep westerly pier.

that the Schuylkill bridge will last 30 and perhaps 40 years, if well covered – You will excuse me in saying that I think it would be sporting with property; to suffer that beautiful piece of architecture (as you are pleased sometimes to call it) which has been built at so great expense and danger, to fall into ruins in 10 or 12 years.”

Peters, in his Statistical Account article, claimed the idea of covering the bridge, stating: “The President’s proposition and general design of the cover, were approved, and reported by the committee.” The article also stated that Palmer “(who is believed to be the original inventor of this kind of wooden bridge) permitted with much candor, considerable alteration in the plan, accommodatory to the intended cover, the design whereof is original. These were so much approved by him, that he considers the Schuylkill Bridge superstructure the most perfect of any he has built.”

Located in the largest city in the United States at the time, the bridge attracted the attention of many architects and builders who placed their impressions in books and articles that were distributed around the world. The first account of the bridge in print was Owen Biddle’s The Young Carpenters Assistant; or, A system of architecture, adapted to the style of building in the United States, first published in 1805. Biddle compares the bridge with the Limnat Bridge of Grubenmann’s and concludes, “the design is more simple, its strength greater, its parts better combined, and more assistant of each other, and there is no useless timber, or unnecessary complexity in any of its parts.” He credits William Weston, Thomas Vickers and Timothy Palmer for their work on the bridge while describing his work on the covering of the bridge. For Palmer, he notes

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that it was “a masterly piece of workmanship…the Bridge Company had succeeded in (a) great undertaking. Neither the Board, or their committee who have been constantly and actively engaged in all stages of the work, possessed a scientific knowledge of Hydraulic Architecture, even T. Palmer is self taught in the art of wooden-bridge building; tho’ he has carried it to such high perfection.”

The bridge, with its spans of 150, 195 and 150 feet, wasn’t as permanent (it was called the permanent bridge to distinguish it from the floating bridge that had earlier crossed the river at the Middle Ferry) as they thought, but it did last well beyond Palmer’s 40-year estimate. Samuel Kneass rebuilt a new wooden bridge on the same foundations in 1850 to carry the tracks of Philadelphia-Columbia Railroad in addition to carriages and pedestrians. The railroad required a level deck, so there was no way the Palmer Bridge with its 8-foot camber could be adapted to that purpose. Kneass’ bridge remained in use until November 20, 1875, when it was destroyed by fire. It was rebuilt in less than 30 days for a sum of $75,000 and opened in December 1875. This bridge was later replaced by a steel cantilever bridge in 1887.▪ Dr. Griggs specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an independent Consulting Engineer. Dr. Griggs can be reached at fgriggs@nycap.rr.com.

InSIghtS

new trends, new techniques and current industry issues

Disproportionate Collapse Design Guidance in the United States

By David Stevens, Ph.D., P.E., M. ASCE and Mark Waggoner, P.E., M. ASCE

D

isproportionate collapse of structures continues to be an exciting topic in structural engineering, given its public safety implications, philosophical aspects, technical challenges, and opportunities for designers to expand their technical skills while proposing unique solutions. Research is actively underway in the US and many other countries, in both university and government laboratories, and technical sessions on disproportionate collapse at recent Structures Congresses have been lively and well-attended.

In addition to research developments, the state of disproportionate collapse design guidance continues to advance in the United States, with three recent and significant events: (1) initiation of a performance-based design standard for disproportionate collapse by SEI; (2) development of new General Services Administration (GSA) design guidelines, soon to be released; and (3) the recent release of Change 2 to the Department of Defense (DoD) design guidelines.

SEI recently formed the Disproportionate Collapse Standards Committee (DCSC), whose goal is to develop a consensus-based approach for designing structures to resist disproportionate collapse. The first full committee meeting was held at the Pittsburgh Structures Congress in May 2013, with many of the 50 or so members in attendance. Subcommittees for each of the nine planned chapters have been formed, and corresponding white papers have been developed. The DCSC hopes to finish the standard within five years.

The development of this SEI standard is noteworthy for a number of reasons. This will be the first consensus-based standard developed in the United States for disproportionate collapse; many other countries already have such design guidance. Perhaps more significantly, this standard will be performance-based; a lively discussion of the merits of prescriptive- and performance-based design occurred at the Pittsburgh meeting, and the committee decided to pursue a performance-based approach, in line with developments in design procedures for other extreme events (e.g., seismic).

The development of the standard will be challenging, given that this will be the first performance-based disproportionate collapse

…significant advances have been made and are underway in the design of structures to resist disproportionate collapse. design approach anywhere in the world, and thus will require careful deliberation. The proposed performance-based design method intends to incorporate proportionality through the use of a suite of hazards of varying size and corresponding categories of performance.

Research is currently underway on the appropriate levels of performance that can be readily supported by available methods of design.

GSA has recently undertaken the development of a new set of guidelines for progressive collapse design, tentatively titled Alternate Path Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects. When issued, this document will replace the 2003 GSA guidelines. The goals are to bring alignment with the security standards issued by the ISC and GSA, and to reduce inconsistencies between GSA and DoD design approaches. The focus of the guidelines is mitigating progressive collapse due to man-made explosive threats at the ground level and in high-risk public areas.

These guidelines are threat-dependent and incorporate a risk-based approach, such that application is dependent on the required level of protection as determined by the Facility Security Level (FSL) or facility-specific risk assessment. Reduction of progressive collapse potential can be achieved either by precluding failure of load-carrying elements for a defined threat or by bridging over their loss.

The Alternate Path (AP) method, in conjunction with new redundancy requirements, is used exclusively for verifying that the structure can bridge over a lost load-carrying element; tie forces and specific local resistance are not employed. In the new GSA guidelines, the AP method is based on the methodology and performance requirements presented in the DoD Unified Facilities Criteria (UFC) 4-02303, Design of Buildings to Resist Progressive Collapse, and ASCE 41, Seismic Rehabilitation of Existing Buildings, with some modifications and additions. The intent of the redundancy requirements is to distribute progressive collapse resistance up the height of the building without explicitly requiring column/wall

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removal scenarios at each level. One significant difference from UFC 4-023-03 is that the acceptance criteria for existing buildings will allow a specified amount of local damage in the vicinity of the column or wall removal location, providing that the designer can show that the damaged or failed portion does not create deleterious loading on the floors below.

After four years of application of the 2009 version of UFC 4-023-03, DoD released Change 2 in June 2013. There are a number of significant modifications and improvements, including revised peripheral tie force equations that now directly include façade loads, resulting in smaller peripheral tie forces for framed structures. For one-way load-bearing walls, both the wall loading and façade loading are included in the peripheral tie force requirements. The applied load combinations were revised to remove the 0.9 factor on the dead load, as well as the lateral load requirement. The example problems in the appendices now include a cold-formed steel project. The enhanced local resistance approach was recast in an LRFD format.

Finally, the cost of implementing progressive collapse design requirements was investigated as part of the effort to revise the 2009 UFC 4-023-03, using cost estimates for the four example problems.

In summary, significant advances have been made and are underway in the design of structures to resist disproportionate collapse. The next major development will be the release of the GSA design guidelines in 2013, followed by the release of the ASCE SEI disproportionate collapse design guidelines, hopefully within the next five years.▪ David Stevens, Ph.D., P.E., M. ASCE (dstevens@protection-consultants.com), is a Senior Principal at Protection Engineering Consultants in San Antonio, Texas.

Mark Waggoner, P.E., M. ASCE (mwaggoner@walterpmoore.com), is a Principal at Walter P Moore in Austin, Texas.

award winners and outstanding projects

Spotlight

The Harbor Drive Pedestrian Bridge

By Joe Tognoli T.Y. Lin International was an Outstanding Award Winner for the Harbor Drive Pedestrian Bridge project in the 2012 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Bridge & Transportation Structures).

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Courtesy of Brooke Duthie.

he Harbor Drive Pedestrian Bridge in San Diego, California, is located in the downtown area of the city near San Diego Bay. For many years it has been the goal of the City to complete a pedestrian and bicycle link between the historic Balboa Park area of the city, through downtown, all the way to the Bay and Harbor area. The last step in the link from the Park to the Bay is blocked by the local trolley tracks, several sets of freight train tracks, and a busy downtown thoroughfare. In 2004, the City commissioned the Centre City Development Corporation (CCDC) to design and build a bridge to complete the approximately 1.9 miles (3 km) route linking the Park to the Bay. CCDC recognized that the high profile project location needed a landmark structure to act as the gateway to the city and as an icon of the revitalized downtown area of San Diego.

Through a series of community outreach meetings, a self-anchored suspension bridge with a single inclined pylon was selected.

The main span of the bridge is 354 feet (108 m) and the pylon is 131 feet (40 m) tall. The pylon is inclined at a 60 degree angle from the horizontal and leans over the deck to support the single pair of suspension cables. Thirty-four individual suspenders attached to the main cable support the wide

Figure 1: Typical section (Fukuhara, 2005).

Figure 2: Radial load and arch effect provide equilibrium (Fukuhara, 2005).

deck from the top of the railing at one edge of the deck only, as shown in Figure 1. This is a bridge where architecture and engineering are integral. For instance, the inclination of the pylon and the horizontal curve in the bridge deck allow the suspenders to be anchored to only one side of the bridge deck.

From the typical section of the bridge shown in Figure 1, the unbalanced nature of the deck becomes very apparent. It seems as if the deck wants to rotate clockwise around the suspender support point at the left edge of the section. The torsion generated by the unbalanced support location must be compensated in some way. The best solution would be to get the line of action of the supporting force to pass through the center of gravity of the bridge section. An unsymmetrical cross-section was developed to try to move the center of gravity of the section as far to the left as possible. Unfortunately, the center of gravity could not be shifted far enough to achieve a balanced design. The support point was then moved to the top of the railing in an effort to move the line of action farther to the right in the section.

Figure 2 shows that in order to achieve equilibrium, an additional horizontal force is needed to balance the horizontal component of the suspender force. To provide this necessary horizontal balancing force, the deck of the bridge was designed with a horizontal

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curvature. In this way, the axial compression in the deck generates a radial force directed outwards that can be made to balance the horizontal reaction from the suspenders. Due to the over 19.7-foot (6m) wide deck, the final geometry of the structure fell short of the balanced condition. Still more balancing torsion was needed to reach equilibrium in the section. Since the deck had already been constructed on a horizontal curve, an additional radial inward force could be added to the equation at a distance above the center of gravity to provide the balancing torsion needed. The additional radial force was provided in this case by the addition of a longitudinal post-tensioned cable at the location of the top of the railing post.

Conclusion The high profile location of the final link in the pedestrian route from the historic Balboa Park, to the downtown and San Diego Bay areas, led to the selection of a truly unique and exciting bridge. The design and detailing of this project required some innovative solutions that both challenged conventional bridge methods and provided new architectural models for future bridge designers.

Innovation is demonstrated in the project from the basic selection of the bridge type to the smallest details of the design. Construction of the bridge was completed in the spring of 2011. The bridge now stands as an icon for the City of San Diego.▪ Joe Tognoli currently serves as a Vice President and Principal Bridge Engineer at T.Y. Lini International . Over his 22 year career, Mr. Tognoli has led the design of many award-winning bridge projects including non-conventional structures and dramatic aesthetic designs.

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

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News form the National Council of Structural Engineers Associations

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President’s Report C. Ben Nelson, P.E., SECB It is hard to believe that nearly one year has passed since I was honored to become NCSEA’s president for 2013, representing our 43 (recently 44!) Member Organizations (MO’s) and their 10,000 individual members. I set six goals for my year as President, which I shared with you at our Annual Conference in St. Louis. I am now pleased to be able to deliver a favorable report on progress made toward these goals, accomplished with the help and selfless contributions of our committees that form the backbone of NCSEA. 1. Much of my Presidency focused on our Young Member Group initiative. As part of the Membership Committee, the Young Member Group (YMG) Support Committee was formed shortly after the 2012 Annual Conference in St. Louis. It is populated with several of our recent Young Member Scholarship winners and others that volunteered. The committee is charged with providing support to our MO’s who seek to establish Young Member groups within their organizations. Committee members Heather Anesta, Emily Guglielmo and Jason Partain, having already created the NCSEA YMG Support Guide that was introduced at the 2013 Annual Conference, are currently working with, or assisting in the formation of, YMG’s in 24 chapters and MO’s of NCSEA. In 2013, five structural engineering firms sponsored new Young Member scholarship winners at the Atlanta conference. The momentum that is building with YMG’s is truly inspiring.

2. We created an ad-hoc Website Redesign Committee to redesign our website from the ground up. Thanks to a great reference from the Structural Engineers Association of Oregon, we commissioned the same website designer and launched the new NCSEA website in September just before the Annual Conference. The ad-hoc committee hosted several conference calls to solicit feedback which was incorporated into the new platform. Carrie Johnson, Brian Dekker and all of our NCSEA staff, particularly Susan Cross, converted the ideas into reality in just ten months. A follow-up component of the new website will occur in late 2013/early 2014 to include on-line webinar registration, conference registration, and roster-updating capabilities.

3. The Continuing Education Committee, under the leadership of Carrie Johnson and Mike Tylk, continues to be one of our most active committees, and, as a result, NCSEA is the leader in providing valuable and practical continuing education for practicing structural engineers throughout the country. The committee introduced a successful new format for NCSEA’s winter meeting now titled the Winter Leadership Forum, organized over 20 webinars taught by industry leading experts, and made ongoing refinements to the SE Exam Review Course, developed in partnership with Kaplan Education Services.

4. Our Structural Licensure Committee, under the leadership of Susan Jorgensen, continues to work with our MO’s toward the adoption of structural engineering licensure in every state.

Working with state legislators is neither easy nor expeditious, but together with the newly formed Structural Engineers Licensure Coalition (SELC) with SEI, SECB, and CASE, we remain committed to promoting licensure for Structural Engineers.

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It is a battle worth fighting and our Structural Licensure Committee’s efforts are making a difference.

5. The Membership Committee is pleased to welcome the Structural Engineers Association of Wyoming, joining NCSEA as our 44th Member Organization! Delegate John Shaffer and Young Member Jera Schlotthauer joined us at the Atlanta Annual Conference and represented one-half of their inaugural membership roster. Combining outreach with the University of Wyoming and other young members is a formational guideline of their MO. 6. Our Advocacy Committee, under the co-leadership of Brian Dekker and Rick Boggs, has made strong and steady progress with its many subcommittees. One of the best ways to see how the Advocacy Committee represents our NCSEA members is to view their page on the new NCSEA website. There, you will find videos of some of their projects, including several that debuted at the Atlanta Annual Conference; and you might just see some glimpses of yourself from Atlanta in the near future!

Finally, I want to recognize the longstanding and tremendous contributions of two icons in NCSEA who are stepping down from their committee chair positions. Ron Hamburger chaired our important Code Advisory Committee (CAC) for eight years. As chair, he oversaw the six separate subcommittees of the CAC, all of which are structured to work with Model Code and Standards issues and activities and the ever-important charge of generating and responding to code changes over many code cycles. His stalwart leadership will be missed. At Ron’s recommendation, Tom DiBlasi has agreed to take over leadership of the CAC. Craig Barnes has chaired the Basic Education Committee since its inception in 1999. The committee surveys Universities and colleges and promotes a recommended core curriculum for structural engineering students working to obtain recognition as structural engineers in the workplace. At Craig’s endorsement, Brent Perkins has agreed to assume leadership of the Basic Education Committee. NCSEA thanks and congratulates Ron and Craig for their devotion to the work of NCSEA and for their proven invaluable leadership capabilities.

All of NCSEA’s committees are composed of, and led by, dedicated volunteers. These volunteers are the heart and soul of NCSEA, and their commitment to service cannot be overstated.

For those who volunteer on one or more of our committees, please know that our national membership thanks you for your time and devotion. For those interested in serving, please complete the volunteer form available on the homepage of our new website. For those who are thinking about getting around to it someday, I encourage you to volunteer at your local state level and perhaps at the national level someday. When you give back to our profession, you WILL make a difference in more ways than you might realize.

It has been my great privilege, honor and pleasure to serve NCSEA as its President this past year. Since first being named delegate for Colorado in 2000, and continuing on in various roles with SEAC and the NCSEA Board of Directors, this has proven the most humbling volunteer action I’ve undertaken in my 29 year career. Most importantly, I would do it all again, without hesitation!

October 2013

Three Levels of Ownership Transition: Yesterday, Today, and Tomorrow Small Firm – Brian Dekker, Sound Structures, Inc. Medium-Size Firm – Brian Phair, PCS Structural Solutions Large Firm – Mark Aden, DCI Engineers

NCSEA Webinars October 15, 2013 Formwork: As-Cast Surface Finishes Kim Basham October 25, 2013 California Emergency Management Agency: Safety Assessment Program (full-day program) Jim Barnes October 29, 2013 2012 I-Codes Structural Provisions for Existing Buildings: IBC Chapter 34 and IEBC David Bonowitz November 5, 2013 Changing the Paradigm for Engineering Ethics Jon Schmidt

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Diamond Reviewed

Registration information will be available soon at www.ncsea.com.

Wyoming becomes the 44th NCSEA Member Organization Structural engineers in the state of Wyoming recently formed the 44th official NCSEA Member Organization, the Structural Engineers Association of Wyoming (SEAWY).

The group’s NCSEA Delegate is John Shaffer, and the Alternate Delegate is Jera Schlotthauer. SEAWY’s Board of Directors is comprised of Shaffer, Schlotthauer, Joe Hall, and Greg Shavlik.

They plan to meet on a quarterly basis. Schlotthauer is also developing a Young Members Group as part of the new MO. “It is particularly inspiring to see our newest MO establish their organization with Young Members in mind as a formational objective,” stated NCSEA President Ben Nelson. “Delegate John Shaffer and Young Member Jera Schlotthauer joined us at the Atlanta Annual Conference and represented one-half of their inaugural membership roster. Welcome SEAWY!”

Check out the NEW www.ncsea.com!

The newly redesigned website of NCSEA features easier navigation, structured to help you find what you are looking for in three clicks or less.

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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.

You’ve Been Sued – Now What? What Engineers Need to Know to Structure Their Defense–Kevin Sido Realizing that claims will inevitably be filed against Structural Engineers regardless of merit, what should the Structural Engineer do when the summons is served and in the months that follow? Learn from this experienced attorney how to structure a solid defense.

News from the National Council of Structural Engineers Associations

Baby Boomers Delay Retirements – Career Bottleneck at the Top – Steven Isaacs Attend this session to learn about a variety of processes intended to break the Baby Boomer logjam at the top and create new pathways to leadership, that are both visible and attainable, for high-potential candidates deserving consideration.

Managing the Cost of Conflict: Mediation, Arbitration or Litigation? – Jennifer Morrow and Kevin Sido This session will explore the full spectrum of 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.

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Thursday, March 20 Get the Value You Deserve Without Ruining the Relationship – Steven Isaacs This interactive session, beginning with a new approach to negotiations, will offer a variety of field-tested ways to get the value you deserve, both financially and beyond.

Friday, March 21 Leadership is a Full-Contact Sport: Dealing with Conflict in the Workplace–Jennifer Morrow This session will focus on critical skills for effectively dealing with conflict in the workplace and beyond.

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The second NCSEA Winter Leadership Forum will gather leading structural engineers at the Meritage Resort & Spa in Napa, California, to interact in an engaging environment focused on leadership, networking and game-changing strategies:

NCSEA News

Winter Leadership Forum to feature conflict resolution, transition issues, and wine-tasting

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The Newsletter of the Structural Engineering Institute of ASCE

Structural Columns

2014 Ammann Fellowship Online Application Now Available The O.H. Ammann Research Fellowship in Structural Engineering is awarded annually to a member or members of ASCE or SEI for the purpose of encouraging the creation of new knowledge in the field of structural design and construction. All members or applicants for membership are eligible. Applicants will submit a description of their research, an essay about why they chose to become a structural engineer, letters of recommendation, and their academic transcripts. In 2013, four SEI members were awarded Ammann Fellowships. This year SEI has developed an online application to make submitting easier.

This fellowship award is at least $5,000 and can be up to $10,000. The deadline for 2014 Ammann applications is November 1, 2013.

For more information and to access the online application visit the SEI website at www.asce.org/sei/ammann-fellowship/.

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.

ASCE Week – A Continuing Education Event November 4-8, 2013 This event brings together our most popular face-to-face seminars in one location and offers two special field trips for you to choose from. Earn up to 36 PDHs. Structural topics include Design for High Wind and Flood, Design of Anchors, Forensic Report Writing, Instrumentation and Monitoring, and more. Register by October 11 and save up to $800. Visit the ASCE Week webpage at www.asce.org/asceweek for more information.

Save the Date

2014 SEI Student Structural Design Competition Attention Undergraduate Student Teams and Faculty Advisors Innovative projects demonstrating excellence in structural engineering are invited for submission. Awards include an opportunity to present finalist designs at Structures Congress 2014 in Boston, MA, April 3-5, 2014, cash prizes, and complimentary registration for Structures Congress (up to three student registrations and one full registration for the faculty advisor). Entries are due January 3, 2014 for design projects completed in 2013.

For more information and to apply, visit the SEI website at www.asce.org/SEI.

Get Involved in Your Local SEI Chapter 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 SEI Local Leadership Conference to learn about new SEI initiatives, share best practices, participate in leadership training, and technical tours.

• 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.

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Nominations are being sought for the 2014 SEI and ASCE Structural Awards. The objective of the Awards program is to advance the engineering profession by emphasizing exceptionally meritorious achievement, so this is an opportunity to recognize colleagues who are worthy of this honor.

Nomination deadlines begin October 1, 2013 with most deadlines falling on November 1, 2013.

Visit the SEI website at www.asce.org/SEI for more information and nomination procedures.

American Society of Civil Engineering Structural Awards Jack E. Cermak Award This award was created by the Engineering Mechanics Division/ Structural Engineering Institute to recognize Dr. Jack E. Cermak’s lifetime achievements in the field of wind engineering and industrial aerodynamics.

Shortridge Hardesty Award This award was instituted in 1987 by the firm Hardesty & Hanover to honor the contributions of Shortridge Hardesty as the first chair of the Column Research Council (Structural Stability Research Council since 1976). The Shortridge Hardesty Award may be given annually to individuals who have contributed substantially in applying fundamental results of research to the solution of practical engineering problems in the field of structural stability.

Ernest E. Howard Award This award may be presented annually to a member of ASCE who has made a definite contribution to the advancement of structural engineering, either in research, planning, design, construction, or methods and materials. This award was instituted and endowed in 1954 by Mrs. Howard in honor of her husband, Ernest E. Howard, Past President of ASCE. Walter L. Huber Civil Engineering Research Prizes In July 1946, the Board of Direction authorized annual awards on the recommendation of the Society’s Committee on Research to stimulate research in civil engineering. In October 1964, Mrs. Alberta Reed Huber endowed these prizes in honor of her husband, Walter L. Huber, Past President of ASCE. Up to five prizes may be awarded for notable achievements in research related to civil engineering and are often seen as helping to establish careers of the top researchers in civil engineering.

Moisseiff Award The Moisseiff Award recognizes a paper contributing to structural design, including applied mechanics, as well as the theoretical analysis or construction improvement of engineering structures, such as bridges and frames, of any structural material. The award STRUCTURE magazine

Raymond C. Reese Research Prize The Raymond C. Reese Research Prize may be awarded to the author(s) of a paper published by ASCE that describes a notable achievement in research related to structural engineering and recommends how the results of that research (experimental and/ or analytical) can be applied to design. The prize was established in 1970 in honor of Raymond C. Reese.

Structural Engineering Institute Awards Contact SEI directly for more information on these awards – visit the SEI website at www.asce.org/SEI. Dennis L. Tewksbury Award The Tewksbury Award recognizes an individual member of the Structural Engineering Institute who has advanced the interests of SEI through innovative or visionary leadership; who has promoted the growth and visibility of SEI; who has established working relationships between SEI and other structural engineering organizations; or who has otherwise rendered valuable service to the structural engineering profession.

Walter P. Moore, Jr. Award This award honors Walter P. Moore, Jr. for his dedication to technical expertise in the development of structural codes and standards. The award is made annually to a structural engineer who has demonstrated technical expertise in and dedication to the development of structural codes and standards. The contribution may have been in the form of papers, presentations, extensive practical experience, research, committee participation, or through other activities.

Gene Wilhoite Award The Wilhoite Award recognizes an individual who has made significant contributions to the advancement of the art and science of transmission line engineering. The SEI Technical Activities Division Awards Committee makes recommendations regarding who should receive the Gene Wilhoite award.

However, they seek the opinions of members as to which papers are meritorious. If a reader encounters a paper that s/he believes is outstanding for any reason, please convey this information along with a statement as to why s/he considers the paper exceptional to Susan Reid at sreid@asce.org.

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The Newsletter of the Structural Engineering Institute of ASCE

Norman Medal and J. James R. Croes Medal The Norman and Croes Medals recognize papers that make a definitive contribution to engineering science. The Norman Medal was instituted and endowed in 1872 by George H. Norman, M.ASCE. The Croes was established by the Society on October 1, 1912, and is named in honor of the first recipient of the Norman Medal, John James Robertson Croes, Past President of ASCE.

was established in 1947 in recognition of the accomplishments of Leon S. Moisseiff, M.ASCE, a notable contributor to the science and art of structural engineering.

Structural Columns

CALL for 2014 SEI/ASCE Award Nominations

New CASE Documents

CASE in Point

The Newsletter of the Council of American Structural Engineers

Foundation 9 – Contract Documents: Produce Quality Contract Documents Foundation 10 – Construction Phase: Provide Services to Complete the Risk Management Process

Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents Welcome to the Tool No. 9-1, CASE RMP Tool Kit Committee’s A Guideline Addressing Coordination and Completeness of Structural Construction Documents. The Tool Kit Committee has repackaged a previously released CASE document with upgrades and additions! A summary test and answer key have been added to the Appendix of the original document. It is recommended that engineers read this Guideline and take the test at the end of the document. More experienced engineers should then sit down with the engineers to go over the various subjects and answer any questions. The CASE Drawing Review Checklist will be a valuable tool to take away from this experience and implement into normal office use.

Tool 10-1: Site Visit Cards This tool provides sample cards for the people in your firm who make construction site visits. These cards provide a brief list of tasks to perform as a part of making a site visit: What to do before the site visit; What to take to the construction site; What to observe while at the site; What to do after completing the site visit. The sample cards include several types of structural construction, plus a general guide for all site visits.

Tool 10-2: Construction Administration Log

Tool 9-2: Quality Assurance Plan

Construction administration is a time when good record keeping and prompt response is essential to the success of the project and to limiting the risk of the structural engineer. For this reason and many others, a well-organized and maintained construction administration log is essential

The plan provides guidance to the structural engineering professional for developing a comprehensive detailed Quality Assurance Plan suitable for their firm. A well developed and implemented Quality Assurance Plan ensures consistent high quality service on all projects, and includes: 1) Quality Control Review; 2) Firm-wide Standards and 3) Construction Quality Assurance.

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

CASE Business Practice Corner If you would like more information on the items below, please contact Ed Bajer, ebajer@acec.org.

Indemnity Is the Most Litigated Contract Clause Indemnification is a duty to make good on any loss, damage or liability incurred by another party, and the right of that party to claim reimbursement for its losses. A bad clause can also include a duty to defend (pay legal expenses) that could go into effect even though you have no liability yourself. It is usually the right of a secondarily liable party to recover from a primarily liable party. Agreeing to an indemnity clause is ultimately a business decision. Try to use your own appropriately-worded indemnity clause. Explain that a duty to defend clause is not covered by your insurance policy. It is better to have no indemnity clause than a bad one.

Telecommuting When considering adopting a telecommuting policy, employers may carefully weigh the potential for equipment and facilities cost savings, the ability to recruit and retain employees outside the local market, and an increase in morale and productivity against the sometimes complex logistics of remote work. Yet there are a few considerations of remote work that sometimes slip through the cracks. Taxes – states that may be hungry for revenue may look to collect if they STRUCTURE magazine

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find you have employees in them even though no office.

Unemployment – if the employee has to be laid off, in which state do they file and where does the employer pay unemployment insurance? Claims are usually filed in the state where the work is performed. The ability to retain valuable employees may outweigh the potential problems. Be sure you know the state from which the employee will be working to fully understand your responsibilities.

A Positive Note These articles have contained warnings and admonitions about the snares and pitfalls of contracts and legal exposure in the engineering and construction industries. What is not emphasized strongly enough is the positive side. It should be noted that when the engineer does what he or she has been trained to do and performs services within the orbit of his or her expertise, the risk of making a mistake or being sued for an error or omission is greatly reduced. The temptation to assume greater responsibility should be tempered with the realistic evaluation of the legal exposure that goes with it.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

October 2013

Strong Lineup of Risk Management Sessions at ACEC Fall Conference The CASE Convocation offers a full day of sessions on Monday, October 28 dedicated to best-practice structural engineering: 10:30 am What’s Next, the Legal Aspects of Building Information Modeling, Sue Yoakum, Donovan Hatem LLP 2:15 pm Practical Insurance Advice, Brian Stewart, Collins, Collins, Muir + Stewart; Tom Bongi, Caitlin; Atha Forsberg, Marsh 4:00 pm Developing an Internal Culture to Manage a Firm’s Risk, Michael Strogoff, Strogoff Consulting 5:30 pm ACEC/Coalition Meet and Greet Register now at www.acec.org/conferences/fall-13/.

Other Fall Conference Highlights include: • Mitch Daniels, Former Indiana Governor and President, Purdue University, on The Private Sector and Public Projects • CEO Panel on Trends in Private Client Methods – Commercial, Industrial, Energy • Victor Mendez , FHWA Administrator on “MAP-21 and the Future of the Federal Highway Program” • Expert Panel Discussion on Transportation Funding Options and Outlook • Fred Studer, Dynamics GM, Microsoft on How Technology Will Transform the Business of Engineering • CEO Roundtables • CIO and CFO Industry Sessions • Emerging Leaders Forum • 30 Industry Education Sessions offering 21.5 PDHs

Beware the Risks Posed by Non-Standard Construction Contract Documents November 6, 1:30-3:00 pm Properly drafted construction contract documents will reduce the contractual risk to consulting engineers and minimize the potential for exposure to costly litigation.

In Beware the Risks Posed by Non-Standard Construction Contract Documents, Gerald Cavaluzzi, vice president and general counsel,

Essentials of A/E Financial Management, Valuation, and Transition Planning Thursday, November 14, 2013 – Friday, November 15, 2013; Chicago, IL Faculty: David Cohen, Principal, Matheson Financial Advisors This course will explore the impact a volatile economy has on financial management above and beyond revenue, profits, backlog, and staff size. Participants will learn to effectively extract and apply key financial measures such as breakeven overhead rate, target billing multiplier and labor utilization percentage.

Attendees will also examine various performance, liquidity and leverage ratios, and how to benchmark these results to make the causal link to shareholder value including the acceptable valuation methodologies for engineering firms and the valuations relationship to internal owner transition planning. For more information and to register, www.acec.org/education/searchDetails.cfm?eventID=1486.

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ARCADIS U.S., and Kevin O’Beirne, principal engineer and manager of standard construction documents, ARCADIS U.S., will demonstrate how to reduce the risk of becoming involved in a dispute or lawsuit arising from the use of non-standard construction contract documents; discuss why you should be concerned about using non-standard documents; identify provisions that commonly pose liability issues; and, outline a program to limit these risks. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1458.

How to Write and Edit Readable Proposals November 12, 1:30-3:00 pm Your primary goal in a proposal is to persuade a client that your firm is perfectly suited to the project. In Writing and Editing Readable Proposals, David Stone of Stone & Company will show you how to make the content of your proposal easily accessible and understood. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1466.

Reducing Project Costs Through Risk Assessment and Management November 19, 1:30-3:00 pm Project risk is becoming more and more of an issue with clients. As a result, firms need to develop and consistently update an effective risk mitigation strategy. In Reducing Overall Construction Costs through Risk Assessments and Management, Renee Hoekstra of Rha will demonstrate how to integrate risk management into your current program/ project management. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1465.

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CASE is a part of the American Council of Engineering Companies

ACEC Business Insights: Upcoming ACEC Online Seminars

CASE in Point

CASE Risk Management Convocation

STRUCTURAL FORUM

opinions on topics of current importance to structural engineers

Building Codes and the Public Domain

By David L. Pierson, S.E., SECB

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short time ago, I started working on a project that will be designed for construction in Europe. As such, I decided that I ought to know European construction law. I quickly found my way to the Eurocode, the governing building code for the European Union.

Thinking that I ought to purchase it, I turned to the Internet. I discovered that it is not available from Amazon, and no online version shows up on any search engine. I need it in English, so there is only one place to go to buy it.

What is the cost? Well, if I want individual volumes – one covers snow loads, another wind loads, etc. – they run between $250 and $350 each. As it turns out, there are a total of 52 volumes. But wait – I get a discounted price of $9,971 if I buy all of them together!

I am still looking for alternatives – otherwise, I could be using 20% of my fee just to purchase the required code. If there is a silver lining here, it is that they do not update the Eurocode every three years.

This was the catalyst for me to start inquiring about things that I should have questioned when I was a younger engineer. I do not mind paying for textbooks, design guides, seminars, etc. To every squirrel his nut, I say. If you create value, then protect it, and make others pay for it. That is free-market activity. However, I have always been somewhat bothered when, in the course of my design work, I find that there is a code with which I need to comply that I do not already have, and it is going to cost me part of my fee to acquire it. Even worse, that code often references other codes or standards that I may not already have.

The key question is this: Is it right, in a country governed as a representative republic, that the government can create a law with which persons must comply (under threat of statesanctioned penalties) and then not make the complete text of that law available for free in the public domain? Is it proper that the government forces a person to purchase the law – from a private organization – in order to find out exactly what the law requires? Is

this not where we find ourselves now with building codes and referenced standards?

I am somewhat astonished that our profession has acquiesced to the situation in which we currently find ourselves. Does every jurisdiction that mandates a building code make it available to design professionals in the public domain? Or are you required to buy it, and then buy it again and again, every three years? I have tried to figure out if there are any similar situations in other professions or occupations, but so far I have been unable to come up with any.

In 2002, there was a legal case (Veeck vs.

Southern Building Code Congress) in which the U.S. Fifth Circuit Court of Appeals held that a building official was not violating copyright law when he put the adopted building code online for free access. This case essentially held that the model codes themselves are protected by copyright, but once they are enacted into law, they become part of the public domain. Because of that case, the organization Public Resource tries to publish the enacted building codes for every state online, making them available as free PDF files. However, in general, they only have the text of the code itself.

My next question is a simple extension: What about the various industry standards that are referenced within that code? Those standards bind me legally as part of the building code. Just because they are published in different books does not diminish the fact that I, as a design professional, am bound to

know what is in them and to comply with them. Yet the total cost to purchase all of the referenced standards could easily exceed the $10,000 that is being asked for the Eurocode.

Under what legal doctrine can I be compelled to engage in commerce with a third party in order to determine what is in the law?

I submit that once a building code is adopted by any authority having jurisdiction, then that jurisdiction should be required to make available in the public domain, free of charge, not only the code, but also all referenced standards within that code that are legally binding, Perhaps this would require changes to how building codes are developed and promulgated. I think it is time that we address this.

And before anyone goes jumping to the conclusion that the solution is elimination of the building codes, I would argue that this is not the correct answer. A staunch political libertarian may claim otherwise, but I maintain that building codes do have a necessary place in our society.

It is completely proper, however, to debate what the scope of the building codes should be, what their objectives ought to be, and how they should be developed. But that sounds like a topic for another time and place. In the meantime, does anyone know someone willing to trade a complete Eurocode for, say, a kidney?▪ David Pierson, S.E., SECB (davep@arwengineers.com), is a Vice President at ARW Engineers in Ogden, Utah.

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

October 2013