STRUCTURE magazine | October 2012

October 2012 Bridges

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE ®

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FEATURES 26

Ambassador Bridge Redecking Fosters Growth between Nations

By Michael Borzok, P.E.

As the single busiest land border crossing in North America, owners of the Ambassador Bridge and the Michigan Department of Transportation needed to improve access from I-75 to enable traffic to flow more freely between Detroit and Windsor, Ontario. To do so, they would need to add new ramps to provide direct access from I-75 to the bridge. In order to receive federal funding, a complete structural assessment of the entire structure was required.

29

Collaboration and Innovation Lead to 3 rd Service Life for an Iconic Iron Bridge

By Rich Johnson, P.E. and Steve Olson, Ph.D., P.E.

Constructed in 1877, years before the automobile age and the mass production of steel, this iron bridge enabled horses, wagons, buggies and pedestrians to cross the Sauk River. Read how this iconic iron bridge has been relocated to its third location and has come full circle, once again carrying equestrian and pedestrian traffic.

CONTENTS October 2012

COLUMNS 7 Editorial Be Inspired

By John A. Mercer, P.E., SECB

11 Historic Structures To Engineer is to Sustain

By Alice Oviatt-Lawrence

14 Construction Issues Accelerated Bridge Construction

By FHWA’s Center for Accelerating Innovation and Office of Bridge Technology

18 Structural Practices Strawbale Construction – Part 2

By Kevin Donahue, P.E., S.E., Martin Hammer, Architect and Mark Aschheim P.E.

23 Structural Design Bridge Load Rating Practices for Cranes

By Thomas North, P.E.

IN EVERY ISSUE

Erratum

8 9 9 41

Advertiser Index Noteworthy Bookcase Resource Guide (Seismic) 44 NCSEA News 46 SEI Structural Columns 48 CASE in Point

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

October 2012 Bridges

ON

THE

DEPARTMENTS 33 InSights Apps – Boon or Bane?

By John A. Mercer, P.E., SECB

35 Great Achievements Joseph B. Strauss

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

38 Legal Perspectives Understanding Professional Liability Insurance – Part 1

®

A photo credit was inadvertently missing for the cover photo on the January 2012 issue of STRUCTURE magazine. The photo was taken by David Lamb Photography (www.davidlambphotography.com).

The author of the article apologizes for this omission.

COVER

By Gail Kelley, P.E.

The Ambassador Bridge is critical to trade and tourism between the United States and Canada. It is estimated that 150,000 jobs in the region and $13 billion in annual production are reliant on the crossing. As bridge traffic is expected to increase in the coming years, it is important for the region’s economy that the bridge continue to provide for safe and unobstructed traffic flow between the two countries. The renovation of this bridge is highlighted in this month’s feature on page 26.

43 Spotlight Mike O’Callaghan-Pat Tillman Memorial Bridge

By David Goodyear, P.E., S.E., P.Eng

50 Structural Forum Developing the Next Generation of Structural Engineers – Part 2

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

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 2012

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Editorial

Be new trends, Inspired new techniques and current industry issues

By John A. Mercer, P.E., SECB

T

areas of competence. Like a three-legged stool, each leg needs to be strong. Each organization and its leadership will, hopefully, continue to support their competencies and not venture beyond their area of expertise, attempting to be all things to all structural engineers. Quite an impossibility.

So, what’s in it for you? I am hoping that as you read this editorial and STRUCTURE® magazine, you will begin to formulate an image of where you fit into the bigger picture of the structural engineering community. It doesn’t matter if you are the newest hire at a large structural engineering firm or, perhaps with the downsizing of the recent past, you have decided to venture out on your own and begin your own structural engineering practice, there is a place for you to belong and participate.

As Chair of CASE, I would like to direct a few thoughts to those of you that have decided to venture out on your own, either by yourself or with partners, to create a new firm. The economy has been down considerably but, as I hear from my CASE colleagues, there are signs it is beginning to slowly recover.

If you have had management experience in your prior employment and have all of the contracts and guidelines of practice memorized, you probably have a good start. However, as in all things, the business world rotates and things change. You will need a way to stay up to date with current Best Business Practices, and perhaps add a Risk Management component into your practice.

ACEC, as the mother ship to CASE, has some exciting things presently going on and evolving, to assist firms of all sizes and disciplines. New coalitions have been formulated that will facilitate enrichment of relationships between the engineering disciplines.

Best teaming arrangements will be a result. Participating coalition members will have a better understanding of the scopes of work of their colleagues on projects and how they can synergistically interact to improve the bottom lines of all team members, thereby enhancing Risk Management for all.

I would like to personally invite those of you who are serious about the business of structural engineering to attend the ACEC Fall Conference to be held in Boca Raton, Florida beginning October 14, 2012. CASE and other coalitions will have sessions at the conference and will look forward to your attendance. To check it out, please go to www.acec.org and consider attending.

In today’s world, structural engineers are only good because of “what” and “who” they know. Come join us and participate! See you in Boca.▪

a member benefit

structurE

®

he Council of American Structural Engineers is the premiere organization for principals of structural engineering firms.

Twenty four years of seniority in Best Business Practices and the recently added Risk Management Practices has been a guiding light for structural engineering firms across the nation and across the world.

This editorial is all about your membership and an effort to clarify the “what” each of the three organizations contribute to the structural engineering community. It will paint a picture of WIIFM (what’s in it for me) for practicing structural engineers and firm principals.

The American Society of Civil Engineers (ASCE) is the most senior of organizations. Most structural engineers have been members at one time or another in their career. ASCE supports the Structural Engineering Institute (SEI). SEI has the goal of supporting structural engineers globally with their Codes and Standards committees, clearly a labor of many dedicated professionals from academia to the young structural in their first job out of school. Without the Standards crafted by SEI members, our structural engineering design community would be in turmoil.

The American Council of Engineering Companies (ACEC) is an engineering business organization that supports the Council of American Structural Engineers or CASE. It has been the goal of CASE to positively impact the bottom line of the structural engineering firm from its outset. They accomplish this by developing contracts, practice guidelines and tools for firms to minimize professional liability insurance premiums, and assisting firms to develop a culture of risk management and best business practices. CASE promotes these practices by encouraging firms to become engaged with the Ten Foundations of Risk Management. Structural engineers who are firm principals and who may be on the fast track to exciting management positions will find CASE membership a positive and powerful step in their career paths.

The National Council of Structural Engineering Associations (NCSEA) is the youngest of the organizations and represents a compilation of state Structural Engineering Associations (SEA’s). “Their goal has been to constantly improve the level of standard of technical practice of the structural engineering profession throughout the U.S.” NCSEA has developed a library of training webinars that can enrich the structural engineer’s knowledge of technical issues in the practice of structural engineering.

The stability of the structural engineering profession will STRUCTURAL depend upon the continued ENGINEERING support of these three organiINSTITUTE zations, and their maintaining a focus on the above described

STRUCTURE magazine

John A. Mercer, P.E., SECB (Engineer@minot.com), is the president of Mercer Engineering, PC, in Minot, North Dakota.

He currently serves as Chair of the Council of American Structural Engineers (CASE) and is a CASE representative on STRUCTURE’s Editorial Board.

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October 2012

Advertiser index

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Editorial Board

AdvErtising Account MAnAgEr

Chair

Interactive Sales Associates

Jon A. Schmidt, P.E., SECB

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

Craig E. Barnes, P.E., SECB

Brian W. Miller

Mark W. Holmberg, P.E.

Mike C. Mota, Ph.D., P.E.

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

Evans Mountzouris, P.E.

CBI Consulting, Inc., Boston, MA

CRSI, Williamstown, NJ

Khatri International Inc., Pasadena, CA

The DiSalvo Ericson Group, Ridgefield, CT

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

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

KPFF Consulting Engineers, Seattle, WA

Brian J. Leshko, P.E.

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

John A. Mercer, P.E.

John “Buddy” Showalter, P.E.

HDR Engineering, Inc., Pittsburgh, PA

Mercer Engineering, PC, Minot, ND

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Faculty Position in Structural Engineering

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The Department of Civil and Environmental Engineering and Earth Sciences at the University of Notre Dame (http://ceees.nd.edu/) invites applications for a full-time tenure-track or tenured position in structural engineering to complement the existing faculty. Qualified candidates at all levels (assistant, associate, or full professor) will be considered, with hiring rank and tenure status commensurate with academic accomplishments. The successful candidate must hold a doctoral degree in an appropriate field and must demonstrate potential for high quality research and teaching. The existing faculty has significant strength in natural hazard risk mitigation and sustainable civil infrastructure. In accordance with these strength areas, the department is seeking an outstanding faculty member with a research focus on, but not limited to: infrastructure systems, high-performance and sustainable civil structures, reliability and performance of structures under extreme loading, innovative structural systems, computational mechanics, and foundation-structure interaction. Candidates for the position should be qualified to teach civil engineering courses, with a strong commitment to teaching excellence at both the undergraduate and graduate levels. The successful faculty candidate is expected to develop and sustain an externally funded research program and publish in leading scholarly journals. Applications should be submitted online at http://ceees.nd.edu/position-available as a single PDF with cover letter, detailed CV, statements of research and teaching, and names and contact information for three references. Review of applications will start immediately and continue until the position is filled. The University of Notre Dame is committed to diversity in education and employment, and women and members of underrepresented minority groups are strongly encouraged to apply. The University also supports the needs of dual career couples and has a Dual Career Assistance Program in place to assist relocating spouses and significant others with their job search. Inquiries related to this search can be directed to Dr. Yahya Kurama, Chair of the Structural Engineering Search Committee, at struct@nd.edu.

STRUCTURE magazine

8

October 2012

EditoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE

execdir@ncsea.com

Editor

Christine M. Sloat, P.E.

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

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news and information

NOTEWORTHY

Richard L. Hess Retires from STRUCTURE ® Editorial Board

R

ichard L. Hess, S.E., SECB, F. ASCE is stepping down as a member of the STRUCTURE magazine Editorial Board. Richard joined the Editorial Board in the spring of 2005 as an NCSEA representative. He has been a consulting structural engineer in Southern California for over twenty-five years. He is a Past President of the Structural Engineers Association of Southern California and Chair, Existing Buildings Committee.

Jon Schmidt, Chair of the STRUCTURE magazine Editorial Board, had this to say on Richard’s departure: “Richard Hess has been a wonderful asset to NCSEA and STRUCTURE magazine during his seven years of service on the Editorial Board. I really appreciate his many valuable contributions and wish him all the best.”

Regarding his tenure on the Board, Richard commented: “Having the opportunity to be

on this Board has been a real pleasure and very rewarding, especially because of all the very interesting people from around the country that I have been able to work with. I think that having an Editorial Board consisting of practicing professionals in structural engineering was a brilliant concept that has made STRUCTURE magazine an extremely valuable asset.”

Dilip Khatri, Ph.D., S.E. will replace Mr. Hess as one of three NCSEA representatives to the Editorial Board. Dr. Khatri is a Principal at Khatri International in Pasadena, CA. Dilip provides engineering services related to seismic and structural analysis, project management, structural design and forensic structural engineering. In additional to numerous articles and papers published in STRUCTURE and various ASCE journals, Dr. Khatri has published two books (ICC 2003 and 2004) about masonry design. Dilip also served as

Richard L. Hess, S.E., SECB, F. ASCE

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

a Professor of Civil Engineering at Cal Poly Pomona from 1991 to 1997.

Jon Schmidt said this about Dr. Khatri’s appointment: “It is a pleasure to welcome Dilip Khatri to the Editorial Board. His background and experience as a practitioner, educator, and author will no doubt serve him well in this role, especially given his familiarity with seismic design.”

Please join the STRUCTURE magazine Editorial Board in welcoming Dilip Khatri.▪

book reviews and news

BOOKCASE

How to Read Bridges

A Crash Course in Engineering and Architecture

By Edward Denison and Ian Stewart Reviewed By Brian J. Leshko, P.E.

I

must preface my review of How To Read Bridges by confessing that I am a Bridge Engineer who “reads” bridges every day. I was intrigued when afforded the opportunity to review this book, which summarizes the introductory aspects of bridge engineering… and is written for readers with various types of backgrounds.

Overall, the pocket-sized paperback book is 250+ pages of informative text, full of interesting historic and contemporary photographs, and sketches of representative bridges worldwide. In addition, there is a Glossary of engineering terms, as well as Resources of books and web sites.

The book is divided into two sections – Part I: Understanding Bridges, and Part II: Case Studies. The first part introduces bridge materials (stone, wood, organic, brick, iron, steel, concrete and glass); bridge types (beam, arch, truss, moving, cantilever, suspension,

cable-stayed and hybrid); bridge uses (pedestrian, water, vehicular, rail and military); and illustrious bridge engineers (Isambard Kingdom Brunel, John A. Roebling, Robert Maillart, Santiago Calatrava, Gustave Eiffel, and Benjamin Baker).

The remaining 60% of the book is devoted to representative global case studies of the following bridge types: Beam Bridges (6), Arch Bridges (13), Truss Bridges (8), Opening & Moving Bridges (10), Cantilever Bridges (7), Suspension Bridges (13) and Cable-Stayed Bridges (9). Each case study includes a brief introduction describing the inherent design features of the specific bridge type, followed by several example bridges (numbers in parentheses) that include an historic summary, color photograph(s), and descriptive sketches detailing salient aspects of the bridge.

The book provides a good overview of bridge engineering from an historic perspective,

STRUCTURE magazine

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October 2012

highlighted by iconic structures from around the world. One minor inaccuracy and isolated nomenclature issues were noted by this reviewer; however, neither detracts from the content.

Overall, I enjoyed How To Read Bridges and I am glad to add it to my library of bridge books.▪ Brian J. Leshko, P.E., F. SEI, M. ASCE is a Vice President, Senior Professional Associate, and Bridges & Structures Inspection, Management and Operations Program Leader with HDR Engineering, Inc. in Pittsburgh, Pennsylvania. He is a registered professional engineer in 16 states, a FHWA-Certified Bridge Inspection Team Leader, and a former SPRAT-Certified Level I Rope Access Technician. Brian currently serves on the STRUCTURE magazine Editorial Board.

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Historic structures significant structures of the past

The superb lenticular spans and wide piers, seen from the west. It is the oldest and longest through-truss extant bridge in the U.S. HAER PA-Pitbu,58-9. Jack. E. Boucher, Photographer. 1974.

N

either a fire, a worker falling 80 feet into the river (he was back to work the next morning), nor an ice floe tearing away part of the false work prevented or slowed the construction of one of this country’s most significant bridges.

Gustav Lindenthal had enormous energy and drive. He received education to about age 14.

Born in Brün, Austria in 1850, he worked in carpentry, railroad engineering, masonry, and other construction, rising quickly and eventually immigrating to America. A self-actualized learner, he absorbed every bit of knowledge in his midst. Nineteenth century Europeans had an inherent, sustainable approach to construction, emphasizing the use and reuse of durable materials (acquired locally if possible), efficiency, adaptability and elegant aesthetics.

Lindenthal worked as a stonemason for the 1876 Philadelphia World’s Fair Centennial International Exhibition Memorial building’s granite foundation, and then rose quickly to a three-year stint as assistant engineer of construction for Philadelphia’s permanent centennial buildings. He then worked on bridge and rail projects, and by 1879 he called himself a bridge engineer.

The iron and steel Smithfield Street Bridge replaced a weak suspension bridge – Roebling’s first highway bridge of 1845 – over the Monongahela River. Remarkably, Gustav Lindenthal constructed his new bridge with the old twenty-foot lower-clearance bridge remaining in service. False work was erected under the northern section of the bridge that both enabled one lane of the old bridge to stay in service during construction, and assisted in the erection of the six wrought iron plate girders for the new bridge.

Some iron and machinery were retrieved from a proposed, but withdrawn, bridge at the same

site, and efficiently reused here. Thus, source materials were conserved.

The striking lenticular (meaning a “lens” form of the truss-frames) throughtruss bridge constructed from 1881-1883 contains 1070 tons of iron in the superstructure and 322 tons in the foundation. The original one-bay-wide carriageway is two 360-foot spans with trusses comprised of 13 panels, each 27 feet, 71/2 inches.

Wind and sun exposures are the same on all parts of the superstructure: Lindenthal thus equalized the thermal expansion and contraction.

The original bridge spans were 48 feet wide in 1883, leaving an eight-foot overage on the upstream side of the channel piers. Lindenthal designed the original bridge to accommodate future expansion up to 65 feet. He designed and installed reusable, detachable sidewalks to flank the carriageways, another example of sustainability evident in the project. continued on next page

To Engineer is to Sustain

Interior through-truss with the third set of lenticular trusses of 1891 (left) first for horse-drawn trolleys, later for the 1898 electric trolley track. Lindenthal extended the bridge’s service life via planned, sustainable design.

HAER, PA-2 Pitbu, 58-18. Jack E. Boucher, 1974.

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Gustav Lindenthal’s Smithfield St. Bridge Pittsburgh, PA, 1883

By Alice Oviatt-Lawrence

Alice Oviatt-Lawrence is principal of Preservation Enterprises – an international architectural-engineering research and historic-building analysis organization. Alice may be reached at strucBridge@aol.co.uk.

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

The Masonry To raise the old bridge the required twenty feet for river traffic, Lindenthal integrated and added onto the substantial existing sandstone-faced piers partially constructed for the previously proposed but abandoned bridge. The pier centers are filled with concrete, followed by alternate header and stretcher stone-courses, of which each is iron clamped. Lindenthal adapted the 56 foot wide piers not only to elevate the grade of the original 1883 bridge, but also to prepare them for future superstructure expansion with associated loading, which he foresaw.

The existing south abutment of concrete with sandstone facing was reused, but Lindenthal built a new north abutment. The north abutment has a stone backing sized about two or three feet wide by two feet thick by four-toseven foot-long stones, also laid in a header and stretcher pattern. All voids were filled and compacted with concrete, with the finishedface sealed with Portland cement.

The Steel Just before this era, a new, locally manufactured “open hearth” carbon steel emerged, of a smoother and stronger quality than the equally available, but less-uniform, Bessemer steel or wrought iron. Metals were not standardized chemically or for mechanical properties until nearer 1900. Lindenthal tested all the materials going into his bridge, including the cements, the concretes and new steel. When most of the Bessemer steel failed in compression testing, the new steel was integrated into the bridge for the top and bottom chords, pier-posts, diagonal ties and pins. Of the total 1810 tons weight of the original superstructure, 740 tons are steel.

In addition to the increased strength of the new steel, its price dropped from $166 per ton in 1867 to about $30 per ton in the early 1880s. Suddenly, steel-use meant economy both in terms of expenditure and for efficient selection of materials. Lindenthal saved $21,600 in construction costs by specifying the thinner, lighter, and stronger steel.

The specified steel tested for compression at 50,000 to 55,000 pounds per square inch elastic limit, with ultimate strength of 80,000 to 90,000 pounds per square inch. Tests for members in tension proved to be 45,000 to 50,000 pounds per square inch elastic limit, with 70,000 to 80,000 pounds per square inch ultimate strength. Elongation, reduction of area at fracture and cold bending were analyzed via early U. S. testing methods and machines. The sounds generated by punching holes in steel plates and angles were scrutinized; an experienced ear could determine the

firing temperatures, hardness and smoothness of finish. However, there was not yet an absolute scientific method to determine if there were flaws in metals.

The Structure The structure can be visualized via two design concepts (parti): as an arch and cable structure, and/or as a schematic of the distributed loads.

In the first, the upward thrusts on the upper chord ends (arch) are resisted by the pull of lower chord (cable). Lindenthal referred to the lower chord as a cable in 1883. In the second parti, the maximum strength is directly expressed at the truss mid-span, reflecting the greatest bending moment: The truss tapered-end form displays a diminishment of bending moment to near self-equilibrium at the end posts.

The wrought iron vertical web-members transfer loading from the deck to the upper and lower chords, acting in tension vis-à-vis the dead load and the evenly distributed live loads. The verticals act in compression only when the load is unevenly distributed. Lindenthal selected iron here, as the weight was no different than that of the steel web members of the same dimensions.

The adjustable steel eyebar and turnbuckle diagonal web members stabilize the arch and cable system under a variety of distributed loadings, and contribute to the forming of the shape. Each diagonal increases in cross sectional area from the panels nearest the end supports to the mid-span panels.

While Lindenthal and others describe the bridge as a triangulated Pauli-truss, Thomas Boothby and others mathematically prove that it is a “parabolic lenticular truss bridge”.

Lindenthal himself compares a “sine-curve” arc to a circle arc and, after studying circle arcs and parabolic arcs, he states that the difference between the two is a negligible 21/2 inches.

The two truss-ends of the 13 irregularly shaped panels of the lenticular span trusses, where they converge, are supported by a middle pedestal on the pier. The entire assembly is rigid and is fixed cable-to-floor via non-adjustable, stiffened, iron suspenders

Close up of steel plate top and bottom chords, acting as arch and cable. The wrought iron vertical members are seen, with the horizontal intermediate bracing at midpoint running the length of the bridge. HAER, PA-2 Pitbu, 58-18. Jack E. Boucher, 1974.

to prevent vibration and to create an 18-inch camber to the floor assembly of each 360-foot span. Each steel end-post rests on a six-inch pin, bearing on a cast iron pedestal. This allows some friction-restricted rocking. No roller bearings were used at the pier posts.

The bottom chords, consisting of eight to ten eyebars of varying thicknesses, were placed and the iron vertical web members connected in sequence from the ends. Then the steel plate top chords, weighing seven to nine tons each, were placed on the verticals working similarly in from each truss end. A block and tackle pulled the top and bottom chord-ends together into the lenticular form. The top chord is comprised of a box section made up of ten and twelve inch steel-riveted plates and angles, and increases in cross sectional area toward the end posts.

Post Construction The iron rusted immediately. Even after scraping the rusty areas with lime pastes, subsequent ample applications of iron oxide primer and lead paint mixed with raw linseed oil did little to protect the bridge from Pittsburgh’s harsh environment.

A portion of Lindenthal office ‘stress sheet’ or technical drawing: “ Elevation and Plan of the Channel Spans”. In Transactions of the ASCE, Vol. XII, Plate XXIV. Sept. 1883.

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Lindenthal 1881 office illustration: “View of the Two Channel Spans”, showing the massive one-bay-wide, original steel-supported and embellished with iron portals, under a three-bay-wide arcade supporting a mansard roof. Transactions of the ASCE, Vol. XII, Plate XXII. Sept.1883.

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In 1889-1891, with traffic growing apace, Lindenthal was commissioned to add another set of trusses on the upstream side to double the carriageway: one for a publictransit horse-drawn trolley track, and the second for private horse-drawn carriages.

Later, in 1898, one truss set was moved to accommodate a new, wider electric trolley.

Simplified portals framing the two bays were added in 1915. This was all easily accomplished due to Lindenthal’s original master planning and foresight.

Lindenthal’s intentional design for conservation of resources, adaptability of construction, expansion potential, and repair of the structural elements has extended the bridge’s service-life. The floor system was replaced in 1933 with structural aluminum-alloy. Lindenthal (d. 1935) likely approved of the material change, as it embodied his goals of integrating emergent materials of equal or better strength, and of the lightest possible weights, into the bridge.

The Smithfield was rehabilitated in the mid 1990s, at which time the deck was replaced and the bridge painted. The iron structural members require inspection for potential widespread microscopic-cracking and capillary action of water leading to corrosion. Inspection data submitted to the Federal Highway Administration by the State DOT in 2010 indicate that the bridge is holding up well even under a daily traffic load of 6400 vehicles, including continued public transit, and with countermeasures in place to control a scour issue.

With continued inspection and maintenance, the 129 years old Smithfield Street Bridge will continue to exemplify significant, sustainable construction.▪ For more on Gustav Lindenthal, see the Great Achievements article in the August 2010 issue of STRUCTURE magazine (www.STRUCTUREmag.org).

STRUCTURE magazine

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October 2012

ConstruCtion issues discussion of construction issues and techniques

A

ccelerated bridge construction (ABC) technologies are changing the way transportation agencies do business, enabling them to replace bridges in hours instead of months, and significantly reducing overall delivery time. This timely innovation comes when many of the nation’s bridges need repair or replacement, and highways are already congested without the added strain of road closures, which can reduce infrastructure capacity.

The Federal Highway Administration (FHWA) is working with states and industry to promote the increased use of ABC as part of its Every Day Counts initiative to accelerate project delivery, improve work zone safety, and minimize the impacts of transportation networks on the environment. ABC uses innovative planning, design, materials and construction methods in a safe, cost-effective way to improve on-site efficiencies when building new bridges, or replacing and rehabilitating existing bridges.

The use of prefabricated bridge elements and systems (PBES) is one strategy that can meet the objectives of ABC. PBES are structural components of bridges that are built off-site or near the existing structure, and include features that seek ways to reduce mobility impacts and on-site construction times. A prefabricated element is a single structural component of a bridge, such as a full-depth prefabricated deck, a modular deck beam, or a substructure unit. A prefabricated system is an entire superstructure, a superstructure and substructure, or a total bridge built in a modular manner. Prefabricated systems are rolled, launched, slid, lifted, or otherwise moved into place in a short time so that the bridge can be opened to traffic quickly.

Accelerated Bridge Construction Changing How America Builds Infrastructure

By The Federal Highway Administration’s Center for Accelerating Innovation and Office of Bridge Technology

For more information on FHWA’s Every Day Counts initiative, visit www.fhwa.dot.gov/everydaycounts.

To learn more about Highways for LIFE, see www.fhwa.dot.gov/hfl.

PBES Construction Benefits With aging urban infrastructure and growing mobility needs, rapid renewal of transportation facilities is today’s mantra to minimize traffic congestion. Bridge replacement is often on the critical path of construction projects. Building in a more prefabricated manner using PBES can offer advantages over conventional bridge construction, including road user cost avoidance; reduction in work zone crashes; and, cost savings for traffic control, construction engineering and inspection, right-of-way acquisition and weatherrelated time delays.

PBES can eliminate the need for temporary bridges and bypass approaches, often required to free up space at the construction site and accommodate through traffic. Temporary bridges are preferred over long detour routes, but construction costs, acquisition of right-of-way and additional environmental permitting can make that approach expensive. ABC also minimizes the need for staged construction, which may be necessary to accommodate through traffic and the contractor’s storage and staging area, and may incur additional costs for extra capacity, right-of-way acquisition and environmental permitting. Furthermore, staged construction often hampers productivity due to limited work areas and restricted work hours, and it frequently reduces traffic capacity during the construction phase.

Implementing ABC technologies such as PBES may involve additional costs for items such as preliminary engineering, design and mobilization. But ABC’s shorter construction time produces savings through the reduction in traffic control, including items such as signage, barriers, pavement markings, traffic control devices, law enforcement and flaggers. Additionally, agencies may realize cost savings that result from the ability to move a project out of the planning phase

For more information on ABC activities at FHWA, please contact Tim Cupples at timothy.cupples@dot.gov.

Use of accelerated construction techniques on a Utah bridge project attracted local spectators and highway professionals from across the country.

14 October 2012

more quickly; ABC is better suited when it is necessary to address site constraints, and the public and private sectors’ need to maintain mobility. Data collected on FHWA Highways for LIFE demonstration projects showed that using ABC techniques cut on-site construction time an average of 67 percent compared to conventional methods.

Road user costs on these projects dropped an average of 50 percent.

History of ABC and PBES

Workers used ABC techniques to replace 14 Massachusetts bridges in one summer while minimizing impact on drivers.

PBES/ABC implementation. FHWA and AASHTO also cosponsored an international scan on PBES (Prefabricated Bridge Elements and Systems in Japan and Europe, FHWA-PL-05-003, international.fhwa. dot.gov/prefab_bridges/pl05003.pdf). The scan team of bridge experts recommended implementation in the United States of several technologies, including full-depth prefabricated decks and movement systems using self-propelled modular transporters and lateral slides. In the years since the scan, team members have worked to implement these PBES technologies.

PBES in Practice FHWA spearheaded an effort to address the national need for rapid innovation deployment through Highways for LIFE, a pilot program established by the United States Congress in 2005. It focuses on using sophisticated marketing approaches and dedicated teams to deploy innovations faster and more effectively. It also gives highway agencies incentives to use innovations and customer-focused performance goals to build highways and bridges better. PBES is one of the technologies Highways for LIFE chose for its Vanguard Technologies effort, which uses a model deployment process to mainstream innovations at highway agencies nationwide. Use of ABC and PBES resulted in reduced construction durations on several Highways for LIFE demonstration projects.

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October 2012

An example is a 2007 project in which the Utah Department of Transportation (DOT) removed and replaced a bridge over Interstate 215 in Salt Lake City in one weekend. With the help of a Highways for LIFE grant, the agency tried – for the first time – self-propelled modular transporters (SPMT), computer-controlled vehicles that move heavy loads with precision.

It used SPMTs to remove the old structure and move the new prebuilt one into place, cutting the mobility impacts from months to days. As a result of this experience and other projects that used ABC techniques, the Utah DOT made use of ABC technologies part of their standard practice in 2010. The trend grew to other state DOTs sent representatives to watch Utah’s bridge move.

Highways for LIFE helped lay the groundwork for Every Day Counts (EDC), the initiative FHWA launched in 2009 to

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In the past, states that tried ABC technologies frequently did so on an as-needed basis, rather than in a more programmatic manner. Efforts to change the paradigm began in 1996 with a national initiative to encourage widespread use of innovations to accelerate construction of highway projects with longer service lives and lessen user delay and community disruption. A catalyst was publication of Transportation Research Board (TRB) Special Report 249, Building Momentum for Change, which called for creation of a strategic forum to promote accelerated construction of highway infrastructure.

In 1999, TRB formed the Task Force on Accelerating Innovation in the Highway Industry (A5T60). Its objectives were to identify the barriers to innovation, advocate continuous quality improvement, encourage development of strategies that generate beneficial change, and create a framework for informed consideration of innovation. In 2000, the TRB task force hosted a Washington, DC workshop and shared its findings with FHWA and the newly formed American Association of State Highway and Transportation Officials (AASHTO) Technology Implementation Group (TIG).

AASHTO created TIG to champion widespread implementation of ready-to-use technologies likely to yield significant benefits. In 2000, TIG chose PBES for nationwide implementation. In partnership with FHWA, a select number of Lead States championed PBES to other bridge owners and stakeholders across the country through tactics such as presentations, workshops, videos, and a website with PBES projects, publications and research information. Among many deployment activities, TRB A5T60, FHWA and AASHTO TIG began a series of Accelerated Construction Technology Transfer workshops in 2002 that included ABC techniques.

When the PBES Lead States Team disbanded in 2004, AASHTO’s Subcommittee on Bridges and Structures Technical Committee for Construction took on the responsibilities of working with FHWA to continue

GRS-IBS technology, which uses layers of compacted granular fill and fabric sheets of geotextile reinforcement to provide bridge support, is part of FHWA’s Every Day Counts initiative to accelerate project delivery.

identify and deploy market-ready innovations aimed at speeding up project delivery, making roads safer and protecting the environment. EDC uses a state-based model in which FHWA Divisions, its frontline agents, work with state DOTs and other highway community stakeholders to make innovations standard practice. It focuses on high-priority initiatives to accelerate technology and innovation deployment, and get highway projects open to the public faster.

From that menu of technologies, tactics, and techniques, each state chooses the options that work best for its highway program.

FHWA teams work with the states to mainstream their selected initiatives and develop performance measures to gauge success.

PBES earned a spot on the roster of the first round of EDC initiatives, introduced in 2010, and 46 state DOTs and Federal Lands Highway Divisions are now using PBES. Since October 2010, 887 bridges have been designed or constructed in an accelerated manner using PBES. In one example, the Massachusetts DOT used prefabricated bridge elements to replace 14 superstructures on I-93 in Medford, shrinking a four-year project to just one summer.

The agency constructed the superstructures using modular decked beam elements that were built off-site, and installed them on weekends during 55-hour windows to minimize impact on travelers.

Expanding on Success Building on the success of PBES in the first round of EDC, FHWA made ABC part of the second round of initiatives it announced in August 2012. This time, EDC is promoting two other ABC technologies in addition to PBES: slide-in bridge construction and the geosynthetic reinforced soil integrated bridge system (GRS–IBS). Over the next two years, FHWA’s EDC teams will work closely with transportation agencies and industry to deploy these solutions.

Slide-in bridge construction is a costeffective technique for quickly replacing an existing bridge. A new bridge is built on temporary supports parallel to the old one. Once construction is complete, the road is closed and the existing bridge structure is demolished or slid out of the way. The new bridge is slid into place, tied in to the approaches and open to traffic within 48 to 72 hours. A number of states have constructed bridges using slide-in construction.

GRS-IBS is a construction method that combines closely spaced geosynthetic reinforcement and granular soils in a new composite material. It is used to construct abutments and approach embankments that are less likely to settle and create a bump at the end of the bridge. The GRSIBS is easy to build and maintain, and 25 to 60 percent more cost-effective than conventional construction methods. So

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October 2012

far, 74 GRS-IBS bridges have been built in 26 states, seven of which are part of the National Highway System.

FHWA has developed various technical resources to help states use ABC, available at www.fhwa.dot.gov/bridge/abc. Among them is Accelerated Bridge Construction (FHWAHIF-12-013), which documents some of the current states of practice in using PBES for ABC. As a result of the increased awareness that EDC has created for PBES/ABC, state highway agencies are developing their own ABC websites, including the Massachusetts DOT (www.eot.state.ma.us/acceleratedbridges) and the Utah DOT (www.udot.utah.gov/ main/f?p=100:pg:0::::T,V:1991).

The success of prefabrication is directly linked to the ability of industry to fabricate high-quality elements. The bridge industry has responded by investigating numerous materials and systems that can give design engineers the tools to design prefabricated bridges. Trade organizations such as the National Concrete Bridge Council, the National Steel Bridge Alliance, the Expanded Shale, Clay and Slate Institute, and the American Composites Manufacturers Association have provided the bridge community with technical assistance to ensure that prefabricated elements can meet accelerated construction needs and provide durable, long-lasting bridges.

The Future of ABC The need to rebuild significant parts of the nation’s infrastructure has been well documented. Thousands of bridges need to be replaced, but the public prefers that those jobs be done with a minimum of traffic disruption – a feat that has been likened to changing the oil in a car with the motor running. Highway agencies and industry are looking to ABC as a viable way to respond to the challenge.

ABC is a proven approach to reduce the mobility impacts arising from construction-related congestion on a typical bridge project, from years to weeks or even days. This greatly reduces the impact on the public and the economy.

Surveys of highway users have documented an overwhelmingly positive response to ABC projects. These are the customers of the transportation industry, and their tax dollars pay for the system. More and more, highway agencies and industry are taking a businesslike approach to infrastructure reconstruction in which the customer is the focus of the project. ABC has given the highway community the ability to change fundamentally the way it builds – and rebuilds – the nation’s infrastructure.▪ All photos courtesy of FHWA.

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Structural PracticeS practical knowledge beyond the textbook

This is the second of a two-part series examining the engineering and design of strawbale buildings.

The first part, September 2012 issue of STRUCTURE, provided an overview of the structural system and best practices for the design and detailing of strawbale walls to resist in-plane lateral loads. Part 2 addresses out-of-plane response, resistance to uplift, and support of gravity loads.

In-plane and Out-of-plane Behavior Part 1 of this article showed that, for in-plane loading, plaster skins on strawbale walls act as cantilevered vertical rectangular sections braced by the straw bales. This differs from light-framed wood shear panels, which can be idealized as cantilevered elongated I-sections with posts and hold-downs where the shear panels act as webs and the hold-down posts act as vertical flanges.

For straw bale walls spanning vertically subjected to out-of-plane loading, the straw bales act as webs between the plaster flanges to form composite I-sections, unlike the case of wood-framed walls where the rectangular section wood studs span vertically to supports. Under uniform out-of-plane loading, a constant bending stress is maintained for strawbale walls if the ratio H/T0.5 is held constant, instead of the more common H/T for rectangular studs or solid walls, where H is the strawbale wall height, and T is the wall thickness T. This is because bending moment is a function of H2 for all uniformly loaded walls, but section modulus is a function of T for strawbale walls with their I-sections instead of T2 for rectangular studs or solid walls. So increasing the out-of-plane aspect ratio by reducing T has a smaller effect on out-of-plane bending stress as compared with a typical rectangular or solid wall.

This is reflected in the H/T 0.5 slenderness factors in the current IBC strawbale code proposal. In contrast, increasing the strawbale in-plane aspect ratio by reducing wall length L has a greater effect on strawbale in-plane bending stress than for a typical cantilever I-section type shear wall, such as a wood panel wall with hold-downs. This is reflected in the penalty for in-plane aspect ratios greater than 1:1 in the current IBC strawbale code proposal.

Although the behavior models of strawbale walls and light wood-framed walls are quite different, the stiffnesses of strawbale walls and wood-framed walls are well matched. The in-plane stiffness of a typical hard-skin strawbale wall is about onethird greater than a typical wood shear panel wall, and the in-plane stiffness of a typical soft-skin wall is about one-third less than a wood shear panel wall. For out-of-plane loads, the stiffness of either a hard-skin or soft-skin wall is generally in between that of a 2x4 stud wall and a 2x6 stud wall. Because of this, strawbale walls are very well suited for use in flexible diaphragm

Strawbale Construction Part 2: Out-of-plane, Uplift and Gravity Behavior and Design

By Kevin Donahue, P.E., S.E., Martin Hammer, Architect and Mark Aschheim P.E. Kevin Donahue, Structural Engineer, and Martin Hammer, Architect, have practices in Berkeley, California. Mark Aschheim is Professor and Chair of the Department of Civil Engineering at Santa Clara University.

An expanded version of this article, including references, is available online at www.STRUCTUREmag.org.

The proposed code provisions along with an archive of important tests, research results and analyses of system behavior are available at www.ecobuildnetwork.org.

18 October 2012

and wood shear wall buildings, and none of the special detailing of concrete or masonry walls in wood construction is required.

Behavior of Walls Subjected to Out-Of-Plane Loading While resistance to superimposed vertical and in-plane lateral loads is provided by designated structural components, every wall must be able to resist out-of-plane forces. As presented above, strawbale walls achieve this through composite action between the plaster and mesh “flanges” and the strawbale “web.” Because the plaster flanges are much stiffer than the strawbale core, if a composite section is modeled as an I-section, the transformed web is very thin. Therefore, shear deformation of the straw bale core has a much larger contribution to out-of-plane strawbale wall deflection than in other typical wall systems for which flexural deformation is dominant. Under a uniform out-of-plane load w, the mid-height deflection due to shear deformation of the straw web (wH2/8G(straw)A(straw)) of a soft-plaster wall is somewhat larger than the mid-height deflection due to flexure (5wH4/384E(plaster) I(overall-section)). For a hard plaster wall, the stiffness of the skin relative to the extreme flexibility of the straw web causes the shear deflection term to dominate and flexural deflection term to become negligible.

The dominance of shear deformation in the out-of-plane behavior of hard plaster walls results in virtually all deformation taking place in the straw webs, which deform as nearly perfect shear parallelograms, and almost no deformation taking place in the plaster flanges, which tend to remain rectangular. However, the hard skins themselves initially form a secondary system to resist out-ofplane load by bending as tall thin panels, until they crack in bending near mid-height. The midheight crack causes a loss in stiffness, at which point the skins form rectangular sections between the cracks and supports (Figure 1). This secondary system generally takes about twenty percent of the load, but in an extreme case (for example, if the hard skins are two-inches thick and the straw bales are fifteen-inches thick), the secondary system can take eighty percent of the load before cracking. Such a wall was tested in Mill Valley, CA in 2001, with the measured results matching the model (Figure 2). The tested wall showed the high initial stiffness associated with the intact secondary system, followed by a loss of stiffness upon mid-height cracking, confirming the secondary bending of the skins. The flexural

polypropylene mesh, the weakest combination of plaster and mesh included in the IBC strawbale code proposal, carries a tensile force of 400 pounds per foot at out-of-plane yielding. Component testing shows the mesh itself has an ultimate tensile strength of 450 pounds per foot. Therefore, an allowable tensile load of 200 pounds per lineal foot for any recognized reinforced skin is reasonable, and easily supported by the minimum proposed spacing of staples at top and bottom boundaries of 2 inches on center (since a 16-gauge staple has an allowable shear value of 55 pounds).

Considering both skins together, the allowable tensile load would be 400 pounds per lineal foot, which would be an unusual loading, likely occurring only in a high-wind region and requiring special design and detailing to ensure proper anchorage.

Figure 1: Model for post-cracking wall behavior.

crack in the tension face plaster of the Mill Valley wall clearly shows bending in the skin (Figure 3).

Subsequent test results consistently correspond to these models, and have demonstrated that properly detailed soft or hard skin walls are able to resist outof-plane loads well over 100 psf. For high load conditions, given the composite section model, the engineer can easily isolate and check individual components of the out-of-plane system for strength. Typical load conditions are addressed in the design parameters section below.

Behavior of Walls Subjected to Uplift Loading The capacity of plastered strawbale walls to carry uplift and gravity loads depends on the capacity of the plaster skins to carry axial force. As discussed, both the in-plane and out-of-plane models rely on the skins taking axial force, so an understanding of tensile and compressive capacity of the skins in uplift and gravity loading is also applicable to the in-plane and out-of-plane models. For uplift, testing shows that a soft plaster reinforced with 2 inch by 2 inch high-density

Figure 2: Two-phase wall behavior under out-of-plane loading. Courtesy of Bruce King, Ecological Building Network.

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Figure 3: Flexural crack in plaster tension face of test wall laid flat with applied load above.

Behavior of Walls Subjected to Gravity Loading Load-bearing strawbale walls support superimposed gravity loads by engaging the plaster skins in compression using properly detailed load paths. Nonload-bearing walls support their self-weight and may be used as infill in post-and-beam frames, either within the strawbale core or bordering the wall. The frames are designed to carry gravity loads and possibly uplift loads.

Uplift loads are typically carried by the plaster reinforcement acting in tension, while gravity loads are carried by the plaster acting in compression. Buckling of the plaster skins must be considered where compression is carried: local buckling of an unbraced portion of skin or, where the skin is adequately braced by the straw, global buckling of the entire wall. In the case of global buckling, the critical Euler buckling load depends on the balanced relationship between the flexure and curvature produced by axial force acting through a small lateral displacement (“P-delta”), and the moment of inertia “I”, which is the global flexural stiffness of the wall

Table showing development of allowable gravity loads.

Baseline Plaster Material Strength (psi)

1.5

100

3600

9

400

Soil-cement

1

1000

24,000

30

800

Lime

7/8

600

12,600

25

500

Cement-lime

7/8

1000

21,000

26

800

Cement

7/8

1400

29,400

37

800

Plaster Type Clay

section in the out-of-plane direction. There is no such feedback interaction between the vertical P-delta and shear deformation in the out-of-plane direction. Since strawbale walls tend to be quite flexible in out-of-plane shear but quite stiff in out-of-plane flexure, the critical buckling load π 2EI/H2 is very high, over 10,000 pounds for a typical eight foot tall soft-skin wall and over 1,000,000 pounds for a typical eight foot tall hard-skin wall.

Tests of plastered walls with superimposed gravity loading confirm that both local skin buckling and global buckling of the wall are not observed modes of failure. These tests, along with out-of-plane tests, show that the bond between plaster skins and the strawbale core is adequate to allow the bale core to brace the plaster skins and act as a web in the plaster-bale assembly. Observed failure modes in gravity tests of plastered walls are crushing of the plaster skin or failure at the top or bottom plaster boundaries. For this reason, best practices described in subsequent sections for load-bearing and shear walls call for continuous support along the bottom edge of the plaster skins. For loadbearing walls, direct bearing at the top edge is preferred. However, load transfer through properly designed mechanical fasteners is acceptable for gravity load and necessary in the case of uplift.

Design Parameters To limit stresses in reinforced hard-skin plasters under out-of-plane loading, the unsupported height of walls with hardskin plasters is limited to 9T0.5 feet for a 40 psf out-of-plane service load, where T is the strawbale core thickness in feet. This limit corresponds to service tensile and compressive forces in hard-skin chords of 400 pounds per foot. Tests demonstrate that a hard plaster reinforced with steel mesh carries a tensile force of 600 pounds per foot at out-of-plane yielding, and

Vertical Wall Strength Factor (plf ) of Safety

Proposed Allowable Gravity Load (plf )

Plaster Thickness (inches)

develops an ultimate tensile strength of at least 960 pounds per foot. Component testing shows the mesh itself has an ultimate tensile strength of 1960 pounds per foot, indicating that the failure mode of the reinforced plaster is something other than failure of the mesh in tension. Unsupported height of walls with soft-skin plasters is limited to 8T0.5 feet for a 30 psf out-ofplane service load. This corresponds to a service tensile and compressive force in the soft-skin chords of 244 pounds per foot.

Tests demonstrate that a reinforced softskin carries a tensile force of 400 pounds per foot at out-of-plane yielding, and develops an ultimate tensile strength of at least 640 pounds per foot. Component testing shows the plastic mesh alone has an ultimate tensile strength of 450 pounds per foot, indicating that the failure mode in the soft-skin case is a combination of the mesh and plaster acting together to supply the required tension. Compressive skin stresses in all cases are well under tested capacities, and both tested and calculated service load deflections are less than allowable limits of H/180 for hard-skin walls and H/120 for soft-skin walls.

Out-of-plane testing consistently shows failure occurring in the body of the strawbale assembly near mid-height, and not at the top and bottom supports, but design parameters establish a minimum stapling of the plaster mesh at top and bottom boundaries to ensure adequate out-of-plane support of all walls. For walls up to 10 feet in height, staple spacing of 6 inches, top and bottom, provides adequate resistance for out-of-plane loading of 30 psf based on the allowable withdrawal values in the 2012 IBC for the staples specified in the IBC strawbale code proposal. For walls taller than ten feet or with out-of-plane loading greater than 30 psf, the maximum staple spacing is reduced to 4 inches. Hard-skin walls with service loads greater than 40 psf, soft-skin walls

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with service loads greater than 30 psf, or walls exceeding the height limits stated in the IBC proposal require a design addressing critical sections. A seven-step methodology for checking such highly loaded walls is presented on pages 96-101 of Design of Straw Bale Buildings by Bruce King, et al (2006).

For uplift loading, each skin with a recognized stapled mesh is given an allowable tensile value of 200 pounds per foot. For uplift loads exceeding this value, a detailed design is required similar to that required of walls with high out-of-plane loading. In all cases, uplift forces above the top stapled skin boundary must be designed with a conventional code-compliant load path to the skin boundary.

Proposed allowable gravity loads for plastered strawbale walls are provided in the Table. Height limits ensure that crushing of the plaster governs over buckling. Allowable gravity loads are then established from the baseline strengths of the recognized plasters. The results of testing coupled with conservative factors-of-safety (particularly for hard-skin walls) provide confidence that local buckling of the skins will not occur.

The Table values are also conservative and consistent with results from gravity tests of full-scale walls. Bottom edges of all plaster skins are continuously supported, and applied loads are transferred to the top edges of plaster skins by continuous direct bearing or through mechanical fasteners.

Concluding Remarks Collective understanding of the structural behavior of strawbale wall systems has increased enormously since the days when pioneers built the first load-bearing strawbale houses in the Sand Hills of Nebraska over 130 years ago.

The essence of those first walls – bales stacked on a foundation, covered with plaster, with openings for doors and windows – remains in the many variations of straw bale wall systems now employed throughout the world.

Significant differences exist as well. While the original buildings were load-bearing, most strawbale buildings today are post and beam with strawbale infill. Today’s buildings are often significantly larger than the early buildings and sometimes are two stories.

Substantial advances in the understanding of strawbale wall behavior have occurred through the testing, research and practice of architects, engineers, and researchers, who have focused on this inherently green material of construction. A sufficient basis now exists for the design of strawbale walls to meet modern performance expectations.▪

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versized and overweight Rough Terrain (RT) and All Terrain (AT) commercial cranes are used extensively at dam projects, and continuously cross bridges that serve the requirements of the public agencies or private utilities that own them. Depending on the state jurisdiction, these cranes will be trailored or driven under a variety of local and multistate permit programs. The effects of crane loads on bridges are a frequent concern due to the variability in age, design, construction, and condition of the bridges. Currently, the only guidance available for analysis is criteria outlined in AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications and AASHTO Guide Manual for the Condition Evaluation and Load and Resistance Factor Rating of Highway Bridges (LRFR).

The information presented in this article will help determine safe loading capacity and placement of several types of classifications of oversized cranes on a bridge. It is based on vehicular loading and requires an analysis methodology that extrapolates an allowable crane permit loading from the bridge design or legal loading. The differences between vehicular & crane live and static loads, axle configurations and load placements are discussed. There are recommendations for making

informed decisions on adjustments in impact loads, live load distributions and lane loading based on the strength and service requirements outlined in the evaluation and rating procedures in the AASHTO LRFR and LRFD specifications.

This article will also present an outline for planning a crane operation on a bridge that includes consideration of working loads, placement and minimizing risks.

design issues for structural engineers

Current Design Philosophy The current bridge design criteria adopts a conservative reliability index that imposes checks to ensure serviceability and durability without incurring a major cost impact. Bridges are initially screened for strength and serviceability limit states based on LRFD design level of reliability. If a bridge does not meet these requirements, the current LRFR rating procedures are used and intended to balance safety and economics. In most cases, a lower target reliability is chosen for load rating at the strength limit state.

Basic Rules & Assumptions

Bridge Load Rating Practices for Cranes

Bridge load ratings have some basic rules and assumptions. All load ratings are based on existing structural conditions, material properties, loads, and traffic conditions. The bridge is assumed to be subject to inspections at regular intervals.

The past performance of an existing bridge is also considered a good indicator that it has adequate capacity. Most bridges are likely to have experienced a more extreme load than what is considered during evaluation. And finally, any changes in existing structural conditions, material properties, loads, or site traffic conditions may require a re-evaluation of capacity.

Design Loads-Trucks vs Cranes

Figure 1: AASHTO design and legal loads.

Structural DeSign

There are several major and minor differences between crane and truck loading on a bridge.

For a standard truck load rating, three different types of loads are considered (Figure 1).

The first is a design loading and is considered a first-level assessment. This is an HL-93 load per AASHTO LRFD requirements and is outlined in LRFR 6.1.7.1.

The second is AASHTO legal loads described in LRFR 6.1.7.2. These include Type 3, Type 3S2 and Type 3-3 vehicular loading and are intended as a second level rating that provides a single safe load capacity for a given truck configuration applicable to AASHTO and State legal loads. The live load factors are based on the truck traffic STRUCTURE magazine

23

By Thomas North, P.E.

Thomas North, P.E. is a structural engineer in the Engineering and Construction Division for the Portland District, U.S. Army Corps of Engineers.

Thomas can be reached at thomas.north@usace.army.mil.

conditions at the site. Strength is the primary limit state for load rating, with service limit states being selectively applied.

The third type is a permit loading and is outlined in LRFR 6.1.7.3. Permit loading is primarily a check for safety and serviceability for passage of vehicles over a bridge that are above legally established weight limitations. The permit rating should only be applied to bridges having sufficient capacity for AASHTO legal loads.

The types of cranes that may see service on a bridge are classified as All Terrain (AT), Rough Terrain (RT), and Crawler (track) cranes. AT or RT cranes will have outriggers for increased capacity that extend between 20-24 feet and may be spaced 20-25 feet apart. Most of these cranes require the addition of counterweights to develop full capacity. The gross vehicle weight (GVW) for a standard design truck is 72,000 lbs.

For comparison, an AT crane with a routine or annual permit or an RT crane will have a GVW that varies from 50,000 to 160,000 lbs. The GVW of a crawler crane can vary from 50,000 to 230,000 lbs.

AT cranes have a multi axle configuration, a telescoping cantilevered boom and can have a rated capacity of up to 300 tons (Figure 2). The center-to-center wheel spacing can be about 8 feet, with axles typically spaced 5-6 feet apart. These types of cranes combine the road speeds of truck carriers with off road capabilities. They can have features that may include large pick and carry ratings, all axle drive and steering, and can have suspension systems that equalize axle loading on uneven surfaces while the crane is moving or static. Because of their multiple axle configurations, most AT cranes are road legal or may require permits with a specialized boom trailer.

RT cranes are two axle carriers with a telescoping cantilevered boom and can have a rated capacity of up to 100 tons (Figure 3).

These types of cranes have oversized tires that make travel easier on unimproved construction site roads. The center-to-center wheel spacing can be about 8-9 feet, with axles typically spaced 15 feet apart. Cranes of this type can travel an operating speed of about 30 mph. RT cranes typically have a high center of gravity and are not considered road legal due to higher axle weights.

Crawler cranes are propelled by two treads mounted on an extremely stiff base. The tread configurations may be about 17 feet long by 3 feet wide (Figure 4). Each has a separate clutch, brake and lock for independent control of travel and turning. Crawler cranes are not road legal and

Figure 2: All Terrain (AT) crane.

Figure 3: Rough Terrain (RT) crane.

must be transported with a crawler carrier.

Crawler cranes have a lower cost and rental rate than other types of cranes, but their transit costs are higher.

Dynamic Loads For vehicles, the dynamic load allowance is primarily a function of pavement surface conditions. It is defined in LRFR 6A.4.4.3 and outlines the required impact factor as 33% of the live load. For an approach with minor surface deviations and depressions, it can be adjusted to 20%. For smooth riding surfaces at approaches, deck and expansion joints, the impact factor can be adjusted to 10%. For legal loads, the dynamic load allowance per LRFR 6A.4.5.5 can be applied for permit load rating. This means that for slow moving permit vehicles (10 mph or less), the dynamic load allowance may be eliminated.

The live-load factors for permit loads were derived for the possibility of simultaneous presence of non-permit trucks on the bridge when the permit vehicle crosses the span.

An adjustment can be made on the live load factor depending on vehicle type and traffic conditions. For permit loads, Table 6A.4.4.2.3a-1 allows an adjustment of live load factors from 1.8 to 1.4 for routine commercial traffic.

If traffic can be closed in the opposite lane, Table 4.6.2.2.2b-1 in the LRFD specifications provide specific reductions in live load distribution for single lane loadings of interior beams.

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October 2012

Figure 4: Crawler crane.

Cribbing and Shoring For most instances, cribbing is required to distribute the outrigger loads on the bridge deck (Figure 5). Overloading from improperly placed outriggers can initiate cracking due to general or punching shear failure. Cribbing and shoring can be made from timber, steel or a combination of both with an effective

width “b” and length “c”. Maximum design efficiency can be obtained when b = c; however, the existing bridge geometry, width, girder spacing and type of loading will control the shape of the cribbing. For timber, a check for horizontal shear stress needs to be made.

Although the typical practice is to allow some increase in allowable stress for short duration loads, a more rational approach is to forgo these increases because the outrigger loads are calculated without consideration for wind and other dynamic effects. For steel, shear is not as critical condition to check. Cribbing members that are oversized and stiffer will deflect less and provide a more even load distribution; however, the cribbing needs to be checked to verify that members bear uniformly on the base. Filling, leveling or blocking may need to be added.

Loading Near Slopes and Abutments The effects of surcharge loading need to be taken into account when operating heavy cranes near slopes and abutments. Surcharge loading decreases with added distance; therefore, to determine a safe position for crane set up, a check for stability may be required.

If stability is an issue, surcharge loading may be eliminated or resisted with the placement of pontoon shoring on top of the abutment and placement of diagonal shoring along the abutment wall.

The Planning Process A crane loading plan is needed to assess the loads, establish how the crane will be positioned in place, determine the crane motions and what special equipment will be required. The load information needs to include the combined gross vehicle weight, counterweights, blocks, slings, lifting beams and other lifting accessories. The movement and positioning of a crane on a bridge deck has to be a controlled operation where travel paths have to be predetermined and adhered to. Operating positions and crane motions must be controlled, and all loads, operating radii and horizontal boom angles must be known in advance. The crane motions to be considered are hoisting, swinging, booming (in or out), traveling (if allowed) and sufficient allowance for some deviation in position and maneuvering. A lower risk crane operation employs a minimum of control and control engagements, low motion speeds and durations, as well as shorter boom lengths and picking radii.

The crane loading plan should be reviewed and approved by a licensed professional Engineer who is charged with the overall responsibility for bridge-capacity evaluation and has a minimum of five years of bridge design and inspection experience. The following is a sample specification requirement for a crane loading plan on a bridge: 1) Crane Loading Requirements • A loading diagram shall be submitted and approved prior to operating any Figure 5: Typical outrigger & shoring placement. equipment or vehicles in excess of 72,000 lbs GVW • No vehicular traffic will be allowed in and axle loads of 32,000 lbs. the opposite lane or in the same span • The loading diagram will include, that the crane is positioned on. but not be limited to, providing • Crane speeds will be limited to 5 mph information on the following: or slower. There will be no sudden 1) A typical section and plan view stops or starts. of the bridge, the position of the 2) Shoring Requirements wheel loads and wheel spacing of If using timber, call out the required the crane.

2) Crane gross vehicle weight (GVW), grade, Fc, Fb and Fv values.

• If using steel, call out the required required counter weights and center grade and any weldments. of gravity from the axis of rotation.

• Shoring and blocking must be 3) Location and weight of axles before accurately aligned as shown on the and after counter weights are plan. installed.

• Crane operations may cause the 4) All outrigger loads. shoring to work loose. All wedges, 5) Required crane boom length, weight shims and position of the shoring shall and location of center of gravity. This be checked daily. should also include the effects of guy • All wedges, shims or fillers must be lines, upper spreader and jib mast. made of hard wood or steel. No soft 6) If using a jib, the length, weight and wood materials will be allowed. location of the center of gravity.

• Prior coordination and approval for such loads shall be obtained before Conclusion proceeding. No exclusion trucks, multi-axle specialized hauling vehicles The response of crane loads on bridges is a (SHV) or mobile cranes will be allowed function of the variability in the age, design, on the bridge deck without prior construction, and condition of the bridge. By review and approval. knowing the differences between vehicular • Any SHVs authorized to drive on the and crane live loads, what the axle configurabridge deck will at all times be required tions are and where the loads are being placed, to have all lift axles lowered and fully the effects of crane loads can be quantified engaged while the vehicle has any load. using a combination of adjustment of live load For cranes, all specialized boom trailers impact, load factors, load distribution and will be required to be engaged until removal of lane load requirements based on a final set up with the outriggers are Strength II design permit load criteria in the made and approved.

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STRUCTURE magazine

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October 2012

Ambassador Bridge Redecking Fosters Growth between Nations

By Michael Borzok, P.E.

A

s the single busiest land border crossing in North America, the Ambassador Bridge is critical to trade and tourism between the United States and Canada. It is estimated that 150,000 jobs in the region and $13 billion in annual production are reliant on the crossing. As bridge traffic is expected to increase in the coming years, it is important for the region’s economy that the bridge continue to provide for safe and unobstructed traffic flow between the two countries.

Motorists traveling on I-75, a major highway that carries traffic through Detroit, could not easily access the bridge from the interstate.

The Detroit International Bridge Company (DIBC), the owner of the Ambassador Bridge, and the Michigan Department of Transportation (MDOT) wanted to improve access from I-75 to enable traffic to flow more freely between Detroit and Windsor, Ontario. To do so, they would need to add new ramps to provide direct access from I-75 to the bridge.

In order to receive federal funding for the new ramps project and to ensure the safety of motorists crossing the bridge, the MDOT required a complete structural assessment of the existing structure.

The effects of decades of heavy use, complicated by the fact that a comprehensive load rating had not been done in a number of years, would need to be assessed. Thus, the Ambassador Bridge Gateway Project was created. The $230 million project is the largest single construction project ever undertaken by MDOT and was created to ensure that the iconic structure will be able to bear the load of

Deck replacement of the suspended spans included installation of new steel stringers.

STRUCTURE magazine

future bridge traffic, and serve both the United States and Canada for years to come.

The DIBC turned to bridge engineering firm Modjeski and Masters, which had served as design consultant when the Ambassador Bridge was originally constructed in 1929, to lead both the assessment and design phases. Modjeski and Masters began by developing a detailed asset management plan that provided a well-defined strategy for addressing critical needs first and prioritizing others. The plan would ultimately involve an in-depth inspection, and the assessment and instrumentation of numerous members on the bridge. Next, they completed a comprehensive load rating, which identified the need for structural repairs to ensure the safety of the traveling public.

Along with the repairs, an internal inspection of the main cables was performed, which included a determination of their strength.

Major repairs, as outlined in the comprehensive assessment, were underway in 2007 and included the replacement of 30% of the suspender ropes, the rehabilitation of various structural members and, ultimately, a redecking of the main span. Bridge lanes on the main span also needed to be widened to accommodate 12-foot lanes – today’s industry standard.

During the redecking design phase, the engineering team faced a series of challenges that had to be addressed early in the process.

Featuring a main span of 1,850 feet, the Ambassador Bridge was once the longest suspension bridge in the world. A suspension bridge of this magnitude, located 150 feet above water level, is a dynamic structure that requires specialized structural expertise during the design phase.

Maintaining weight distribution and preventing instability during and after construction were critical to preserving structural integrity and, in turn, motorist safety.

A solid Jersey-type barrier presented the first major challenge for the design team. Another consultant, engaged before Modjeski and Masters, had already created deck replacement plans that were ultimately put on hold. As part of their work, however, a solid concrete barrier was specified from end to end. The design team knew a solid barrier could potentially cause a suspension bridge to become unstable during certain wind events. The team engaged an aerodynamic consultant who created a scale model of the bridge that was tested in a wind tunnel, and confirmed that the solid concrete barrier was creating instabilities during strong winds. Working together with the DIBC, it was determined that the concrete barrier would need to be substituted with an open barrier in order to improve aerodynamics.

Further complicating bridge behavior was the widening of travel lanes, and the removal of a sidewalk located on only the western side of the bridge. The original bridge had four 11-foot travel lanes – one foot per lane too narrow for today’s safety criteria. Pedestrian and bicycle traffic

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were previously allowed to cross between the United States and Canada, but following the September 11, 2001 terrorist attacks, the U.S. Department of Homeland Security prohibited all pedestrian traffic at international crossings. To accommodate today’s 12-foot lane standard, the design included removing the sidewalk to create more space.

However, removing the sidewalk, and replacing it with heavier roadway, presented a new challenge in maintaining bridge balance. To account for the weight imbalance, the design called for the replaced deck to be made up of a combination of lightweight and normal weight concrete. In addition, concrete ballast was added to the westernmost side of the bridge, along with a curb consisting of heavyweight concrete.

Another challenge involved traffic flow during the construction stages. Since so much commerce relies on this crossing, it was essential that traffic continue moving throughout the entirety of the redecking contact. The project was broken into four stages, which would allow for three of the four traffic lanes to remain open The rehabilitation of the suspended spans was performed in stages. at all times, as required by the DIBC. Final contract plans were completed in early 2010, and the construcThe deck was removed in 145-foot sections using a gantry crane to tion phase began in June 2010. The construction phase commenced lift and remove each piece. Once the deck was lifted away, construction with the installation of Safespan® decking underneath the bridge. Once teams could remove old stringers and perform repairs to floorbeams, the Safespan® was installed, construction teams began the redecking a majority of which could not be accessed with stringers still in place. process. Active work zones required a temporary concrete safety barrier New stringers were then installed, followed by the placement of new to protect construction teams from bridge traffic. However, at 1,850 steel grid panels, which were then filled with concrete. As noted previfeet in length, a temporary concrete barrier spanning the entire bridge ously, a combination of lightweight, normal weight and heavyweight would once again impact bridge behavior. Redecking would need concrete was used across the four phases to maintain balance and to take place incrementally; to determine the appropriate segment prevent any alterations to the bridge’s geometry. This process was length, a 3D finite element analysis model was created to assist with repeated for each phase of the construction process, with stages one construction staging analysis. Results of the evaluation determined and four requiring the additional step of installing open railings on that 145 feet was a safe maximum length for each section without either side of the bridge. The fourth phase of redecking was finalized impacting the weight distribution of the bridge. Additional weight in May 2012, and construction teams are expected to remain on site corrections were needed as segments of decking and stringers were until the end of the summer to perform clean-up work. removed – steel ballast was used on top of the temporary concrete Not only is the structural health of the Ambassador Bridge critical barrier and was repositioned as new roadway was constructed. to shared commerce between the United State and Canada, but so is using North American products and labor to complete the redecking. The Ambassador Bridge Gateway Project and the redecking of the main span of the Ambassador Bridge are important to growth and rebuilding for the Detroit-Windsor region. With more than 4.6 million passenger cars and 2.6 million truck crossings every year, the rehabilitated 83 year old main span of the Ambassador Bridge can now safely accommodate current traffic and forecasted traffic increases in coming years.▪ Michael Borzok, P.E. is a Senior Project Manager at Modjeski and Masters, Inc., headquartered in Mechanicsburg, PA. Michael can be reached at mjborzok@modjeski.com.

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

Staged construction was used to help maintain traffic.

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October 2012

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Collaboration and Innovation Lead to 3 rd Service Life for an Iconic Iron Bridge

By Rich Johnson, P.E. and Steve Olson, Ph.D., P.E. Oblique view.

M

innesota was sprouting like a wheat field in 1877, but the growth could not continue unless improvements were made to the state’s fledgling transportation system.

One such improvement built that year was a 162-foot Parker truss span in Sauk Centre, MN, located in the central part of the state. Years before the automobile age and the mass production of steel, the bridge enabled horses, wagons, buggies and pedestrians to cross the Sauk River.

The bridge was well constructed, with several primary members composed of wrought iron. The inclusion of wrought iron, which stands up to corrosion better than steel, likely played a significant role in the long lifespan of the bridge at multiple locations.

By the 1930s, the bridge no longer met the needs of the Sauk Centre community, but enterprising Minnesotans found a new use for the span. It was disassembled and in 1937 was re-erected in a wilderness area in northern Minnesota, where it carried State Highway 65 over the Little Fork River in Koochiching County, near the small town of Silverdale. For 70 years, Minnesota Bridge #5721 carried logging trucks and other vehicles at this scenic northern Minnesota location.

But as the 21st century dawned, the Silverdale Bridge again faced obsolescence. Besides the fact that the bridge was too narrow for modern highway traffic needs, its badly deteriorated floor system made its load capacity marginal at best. It was time for #5721 to “hit the road” again.

In 2009, the bridge was disassembled and stored in a Minnesota Department of Transportation (MnDOT) facility. During the

following two years, a collaborative effort between engineers and historians led to the bridge’s evaluation, rehabilitation and re-erection at a Minnesota Department of Natural Resources (MnDNR) trail near Stillwater, MN, just northeast of the Twin Cities. The bridge not only has been preserved but it has come full circle, once again carrying equestrian and pedestrian traffic.

The disassembly, relocation and re-erection project was confronted by significant technical hurdles, but those hurdles were overcome through the collaboration of engineers and historians who devised innovative solutions.

A Bridge to Minnesota History Years before it was dismantled, the Silverdale Bridge was recognized as worthy of historic preservation. In the 1980s and 90s MnDOT, the Minnesota State Historic Preservation Office (SHPO) and their consultants inventoried the state’s bridges and identified those with historic significance. Roughly 200 bridges built prior to 1956 were identified as either on or eligible for inclusion on the National Register of Historic Places. Among them was the Silverdale Bridge, which was added to the National Register in 1998.

In 2006, HNTB Corporation and Mead & Hunt prepared a Management Plan for Historic Bridges in Minnesota under the auspices of MnDOT, SHPO and the Federal Highway Administration.

The Silverdale Bridge was one of twenty-four bridges identified for preservation by MnDOT. “Maintaining historic properties, including bridges, helps people to understand where they came from – what previous engineers and communities hoped for and what they were able to achieve,” the historic bridge management plan stated. “By protecting these reminders of the state’s engineering and transportation legacy, the present and the future can be built, since their preservation can save valuable tax-payer dollars and recall a community’s hopes and dreams.”

Formulating a Strategy Cross bracing, verticals, diagonals and counters.

STRUCTURE magazine

Based on the goals of the historic bridge management plan, engineers and historians worked together to develop a preservation strategy for the bridge. Team members determined that widening

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October 2012

and strengthening the bridge for continued use at the Silverdale site would require dramatic changes to the bridge, including a substantial loss of historic material and alteration of character-defining features.

The team ultimately decided the course of action would be to move the bridge to a new site with less demanding expectations on the venerable structure. MnDOT worked with MnDNR to identify the most appropriate site. The stakeholders zeroed in on the Gateway Trail, the most heavily used DNR trail in Minnesota. As part of an abandoned railroad corridor that has been converted to trail use, the Gateway Trail traverses several at-grade crossings with heavily traveled roadways. The team identified an at-grade crossing with sight distance challenges near Stillwater that made it a good candidate for a grade separation bridge.

Laser Scanning Gathers Crucial Data

Below deck, stringers, sway bracing at abutment.

While the premise of the bridge relocation project was sound, its execution was no easy task. For example, plans related to the 1870s bridge construction had vanished into history, and only a handful of sheets were available from the 1930s disassembly and re-erection.

To overcome the lack of crucial information, the consultant team decided to use laser scanning of the bridge to collect geometric data prior to disassembly and as major components were removed.

This technique, which employs a terrestrial laser-imaging system that creates highly accurate three-dimensional images, proved to be extremely useful. Fastener patterns taken from the scans of original portal members and end floor beams were used to detail replacement members. In addition, the scan data facilitated the capacity evaluation of the eyebars that had suffered defects during removal operations.

The information gleaned from this geometric evaluation enabled 88 of the 96 original wrought iron eyebars to be incorporated into the bridge at its third location.

A Bigger Job Than Anticipated Extensive rehabilitation was required before Bridge #5721 could be moved to its new home. The re-assembly contractor carefully removed the iron truss components and transported them to White Oak Metals Inc., a steel fabricator in west central Minnesota. There the components were blast cleaned and revived.

After blast cleaning, it was apparent that many of the primary truss eyebars had been damaged during disassembly, despite the great care taken by the construction contractor. The disassembly contractor’s hardened tools produced nicks and gouges in the heads of the eyebars as the pinned connections were taken apart. Damage to a floor beam and to several upper chord members also was noted once the members were blast cleaned.

The need for replacement end floor beams, replacement portal members and replacement stringers was expected from the start. But the need to replace 8 of the 96 primary eyebars, as well as the need to fix an interior floor beam and several top chord members, had not been anticipated when the re-assembly contract was let.

New Technologies Boost Old Components As design work progressed, it became clear that the truss span would lack the capacity to carry full pedestrian loads and a normal weight concrete deck once the bridge was relocated to the Gateway Trail site. To minimize the need to strengthen the primary truss members of the historic structure, the designers decided to use an innovative lightweight concrete deck (110 pcf ). This innovation constituted one of the most significant aspects of the new design.

This approach was not a typical MnDOT practice, and it is believed that only one other bridge deck of this type has been constructed in Minnesota. The contractor’s initial lightweight mix design did not meet freeze-thaw durability testing requirements, but a revised mix design passed the tests.

Collaboration Produced Another Innovative Solution Designing the bridge railing for the new site posed yet another significant challenge for the design team: meeting safety concerns while minimizing visual changes to the historic structure.

To meet the challenge, engineers and historians collaborated to devise this solution: Three horizontal rails from the second bridge site were re-used at the third site. The top re-used rail was set at 54 inches, which is the typical

Railing details.

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Project Participants Owner: MnDOT (legacy), MnDNR (present) Designer: HNTB/Olson Nesvold Engineers Cultural Resource: Mead & Hunt Contractor: Minnowa Construction Software: STAAD III and Lusas (analysis) Cloudworx by Leica (laserscanning data) TAY24253 BraceYrslfStrctrMag.qxd

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Page 1

Portal frame.

Great Team Produced Great Results This project enabled Minnesota to sustainably re-use a state asset and preserve a historical segment of the state’s infrastructure, for the benefit of residents and visitors. The project faced significant challenges, and it could not have attained success without the hard work, creativity and collaborative spirit of the project engineers and historians. The positive results of their efforts demonstrate the high level of innovation that can be achieved through the collaboration of dedicated experts from different fields.▪ Rich Johnson, P.E. is Group Director of Seattle Office Bridges and Tunnels at HNTB Corporation. He can be reached at rjohnson@hntb.com.

Steven A. Olson, Ph.D., P.E. is president of Olson & Nesvold Engineers, P.S.C. He can be reached at steve.olson@one-mn.com.

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height of bicycle railings in Minnesota. The other two rails were evenly spaced below the top rail and the curb, much as they were at the second site.

A stainless steel mesh was placed behind the rails to limit the potential for debris to reach the roadway below the bridge.

Above the top rail, stainless steel marine cables were installed on a 6-inch spacing to provide an 84-inch tall railing for equestrian trail users.

The marine cables and stainless steel mesh greatly enhanced the safety of the bridge and, since they imposed very little visual impact on the railing, it retains much the same look that greeted users of the bridge at its second location.

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Apps – Boon or Bane?

By John A. Mercer, P.E., SECB

V

olumes of new apps are exploding on iTunes for the iOS iPhone, iPod or iPad, and in the Android Market for the Android OS. Currently restricted to my smartphone for Android apps, the iPhone, iPod, and iPad seem to have a more extensive selection.

This discussion on apps will focus on their usefulness in the structural engineering community. Each engineer will have to make his or her own decision on the user friendliness or appropriateness of an app. The article is not intended to recommend or endorse one app over another.

The Boon One of the benefits of apps for your smart phone or tablet is the convenience of having a tool at your fingertips that doesn’t require you to be at a desktop computer in your office.

Some apps have a WOW factor that the structural engineer can use to woo their clients and help them understand the relationships of structural elements that have been designed by more sophisticated software programs. These apps can be categorized as interpretive utilities that allow the structural engineer to do a fly through of a structure, illustrating a three dimensional image of a building model and all of its structural components.

Fortunately, we have some of the materials associations, structural steel, wood, reinforced concrete and their derivatives, producing their own utility apps that provide quick checks of material codes for beams and columns. They have developed, tested and endorsed simple beam and column apps that allow the structural engineer to carry a design calculator in his or her pocket with their smart phone or tablet.

To find some of these, simply Google search the key phrase “structural engineering apps” and you will get a list of links to some of the apps that are currently available. Also, go to the appropriate material association web sites to download their latest app creation.

All apps I’ve reviewed indicate updates and new versions related to improvements and bug fixes. Most have a “star rating”. You may wish to be especially careful of those without ratings, unless you intend to spend the time to do your own testing and confirmation of the apps providing correct results. Verifying accuracy should actually be done even if it has been rated. In my experience, I seem to find the bugs in programs as I use them. Keeping a jaundiced eye on the horizon to make sure your solution makes sense is still a good idea.

• How is this documented?

• Is the simple design code check sufficient?

• Is there an approved change order?

• How does this impact the contract amount?

• How about the construction or delivery schedule?

• How is YOUR liability impacted?

Some apps allow printing to a printer or a PDF file, or emailing your results to yourself. Keeping track of things will require more sophisticated apps. Perhaps a smart app programmer will come up with a universal solution or may already have. We will have to keep an eye peeled for that.

It may be appropriate for STRUCTURE® magazine to print an App Survey similar to the Software Guide they have once a year. There may also be the need for one of our three engineering associations to host a Blog to discuss the merits of certain apps, as well as keep a rating and comment system independent from the iTunes and Market.

It’s your world. How would you use an app in your engineering practice? If you find a good one, let us know.▪

The Bane Lest we forget the Hyatt Regency structural failure in the early 1980s…

A hypothetical situation: You are on a project site, and a contractor makes a request for a modification to, or a substitution of, a structural member. You have an app on your smart phone that will allow you to make a quick design code check. What do you do?

• Have you received a written RFI? • How do you communicate to the remainder of the Build team that there is a possible change in the structure?

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John A. Mercer, P.E., SECB (Engineer@minot.com), is the president of Mercer Engineering, PC, in Minot, North Dakota.

He currently serves as Chair of the Council of American Structural Engineers (CASE) and is a CASE representative on STRUCTURE’s Editorial Board.

What apps do Structural Engineers use?

Let us know what apps you are using. Fill out our survey at www.STRUCTUREmag.org. There’s a button on the homepage that will take you to the mini-survey; or use your QR-Code app and scan this code – it will take you right to the homepage!

October 2012

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notable structural engineers

Great achievements

Joseph B. Strauss

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

S

trauss is best known for the Golden Gate Bridge which opened May 27, 1937 with a span of 4,200 feet, making it then the longest span suspension bridge in the world. Joseph’s engineering career spanned from 1892 to 1937, over which one observer called him, a “human dynamo.” He was born in Cincinnati on January 7, 1870, the youngest of four children. His mother was a well-known musician and his father an artist. He lived not far from Roebling’s Cincinnati Bridge, and it is thought that this bridge sparked his interest in bridge design. He attended Hughes High School and was elected class president.

Upon graduating, Strauss was asked what he intended to do with his life.

He responded that he would accomplish something that “had never been done before.”

The first step in that quest was to enroll at the University of Cincinnati in 1888. At the time, a formal Civil Engineering Department did not exist. Civil Engineering was a part of the Mathematics and Civil Engineering department. The Civil Engineering Professors were Henry Eddy and Edward Hyde, who both offered a program that included a series of courses with a required thesis, which was “a discussion of some practical problem in engineering or the investigation of some theoretical question of importance” with associated drawings. His senior class consisted of 15 students, with only two majoring in Civil Engineering.

He became the class president and also the class poet. His thesis was the design of a bridge to cross the Bering Strait, connecting N. America with Asia. He graduated in 1892 and traveled east to Trenton, New Jersey where he became a draftsman for the New Jersey Steel and Iron Company. It was a very large company in the 1880s, and the Delaware Bridge Company was the bridge design arm of the firm. This team built many major bridges until in 1884, when Charles Macdonald left the company to form the Union Bridge Company. Strauss remained with Union Bridge until 1894, when he returned to the University of Cincinnati to serve for part of one year as an Instructor of Civil Engineering replacing a professor who died in December 1894. At the end of the year, Joseph went to the Lassig Bridge and Iron Company of Chicago for two years working as a detailer, inspector, estimator and designer.

He then spent two years as a designer for the

Sanitary District of Chicago, which was in the process of building a drainage channel Joseph B. from Chicago to Lockport using Strauss water from Lake Michigan.

The project was finished in 1899 and Strauss became a Principal Assistant Engineer in charge of the Chicago office of Modjeski and Angier.

The firm was one of the leading designers of bridges in the country and designed some of the early movable, generally swing, bridges across the Chicago River. Strauss was charged with studying the use of bascule bridges across the river that would not need a mid-river swing pier. The earliest bridges used cast iron ingots to serve as counter-weights to lift the span about a horizontal axis located on the bank of the river. Legend has it that Strauss presented a new design that would use concrete counterweights, with his own system of links to lift the bridge. Modjeski did not like the plan, so Strauss resigned and appears to have become associated with the Rall Bascule Bridge Company, serving as Chief Engineer for a year.

Theodore Rall was granted a patent for a bascule bridge in 1901, and built his first bridge with a span of 26½ feet over the Miami and Erie Canal for the Pittsburg, Fort Wayne and Chicago Railroad. Apparently Strauss believed he could do better than Rall and opened up an office in Chicago under the name the Strauss Bascule (Concrete) Bridge Company.

The first bascule span Straus built on his own was for the Wheeling and Lake Erie Railroad in Cleveland, Ohio over the Cuyahoga River.

He had to build it with his own finances to

Sault St. Marie Bascule Bridge 1913.

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Wheeling and Lake Erie Bascule span, Strauss’ first design.

prove his concept. Opening in 1905, its span was 150 feet and used concrete as its counter weight. Since concrete was not as dense as cast iron, Strauss had “to so arrange the construction as to obtain either a longer leverage or the counter weight for to so dispose the counter weight as to obtain room for the greatly increased volume required by the concrete.” This was the basis of his first patent issued in September 1903. He had a full page advertisement of this bridge and his patented ribbed concrete bridge in the March 1906 issue, page 448, of Engineering World.

The Chief Engineer for the Wabash Railroad Company wrote, ““I consider the bridge lately put up for the Wabash Railroad Company at Cleveland the cheapest and best lift bridge on the market today. It is so well balanced that it can be stopped in any position and will remain there after the brakes have been released… I understand that the bridge has been looked at by many Engineers, and all those who are unbiased have declared it to be the best structure of its kind they have seen.” continued on next page

Louisville and Portland Canal vertical lift bridge 1915.

had a monopoly on their construction in the United States and elsewhere. One of his longest and most innovative spans was across Sault Ste. Marie for the Canadian Pacific Railroad crossing of the United States Canal.

The span center to center of piers was 336 feet, and the top chords when closed were linked to support compression. The bottom chords were linked to support tension, thus making a complete truss under live loads. It was the first of its kind and was the longest span double leaf bascule bridge, longer in span than any vertical lift bridge at the time.

Another unique design was Strauss’ vertical lift bridge, like the one he built across the

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The ribbed concrete bridge, patent number 811257, was for a concrete, or concrete and steel, bridge having hollow concrete forms for beam girders and hollow concrete forms for transverse joists. These were then connected by steel bars and loops, the hollow forms being erected to form a frame and filled with concrete to form a concrete bridge using prefabricated forms.

Strauss’ second was the Kinzie Street Bridge for the Chicago and Northwest Railroad, completed in 1908 with a span of 170 feet.

The design worked as he had anticipated, and it was the first in hundreds of bridges of this type he built around the United States. Over several years he developed four variations on his design that are called the heel trunnion, the vertical overhead counter weight, the underneath counter weight and the simple span type. In addition, he made a plan for an improved vertical lift bridge. He was selected to build his longest single leaf bascule, the St. Charles Air Line Railroad Bridge, over the Chicago River on 16th Street.

The full story of the history of development of the Bascule Bridge and Strauss’ role in it can be found on line at www.historicbridges.org/ illinois/chicagobridges/pdf/strauss.pdf.

Strauss continued to patent various aspects of bascule design, and with them practically

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Louisville and Portland Canal in Kentucky in 1915. The span length was 210 feet and Strauss called this his direct-lift bridge.

Strauss obtained patents on these two bridges. A full list of his patents can be found at www.engrlib.uc.edu/strauss/patents/ patentslist.html. His first bascule and Patent #1,453,084 issued on April 24, 1923 was for a hybrid suspension-cantilever for the Golden Gate Bridge (not shown on list). His last bridge patent, #2,054,995 also not shown on list, was granted in 1936 for connecting suspension tower legs with cross bracing as in the Golden Gate Bridge.

In 1922, Joseph branched out from specializing in movable bridges to designing all bridge types when he hired Charles A. Ellis. Ellis resigned as a Professor of Civil Engineering at the University of Illinois in 1921 to work with Strauss. To broaden his list of potential clients, Strauss changed the name of the company to Strauss Engineering Corporation, Consulting Bridge Engineers. The letterhead advertised bascule, lift, swing and long span bridge designs, and Ellis was the prime designer of the long span bridges.

One long span bridge was the Longview, Washington Cantilever (now the Lewis and Clark Bridge) across the Columbia River. The bridge opened in 1930 with a cantilever span of 1,200 feet and a total length of 2,722 feet. It was the longest span cantilever bridge in the United States at the time. Another was Montreal Cantilever over the St. Lawrence River with Monsarrat & Pratley of Montreal.

This bridge opened in 1930 and had a main cantilever span of 1,097 feet. He also designed major bridges at Peoria, Illinois over the Illinois River, at Quincy over the Mississippi River and at Independence over the Missouri River. He entered and won national and international bridge competitions between 1911 and 1926.

A Catalogue Strauss published can be

For more on the engineers of the Golden Gate Bridge, and the interactions between Joseph Strauss and Charles Ellis, see the articles by Reinhardt Ludke, The Real Story of the Golden Gate Bridge, in the July and August 2012 issues of STRUCTURE® magazine.

Golden Gate Bridge 1937 to present.

At last the mighty task is done; Resplendent in the western sun The bridge looms mountain high; Its Titan piers grip ocean floor, Its great steel arms link shore with shore, Its towers pierce the sky.

Strauss submitted his final report in 1937 and died May 16, 1938 at the age of 68.

He was buried in Glendale, California. His tomb in the mausoleum has a bronze plaque on it with his name, life span and a basrelief image of the Golden Gate Bridge, his proudest creation. Engineering News Record in reporting his death gave a brief summary of his career, but wrote, “although credit for the design and building of the bridge belongs to members of his firm, to Prof. C. A. Ellis, then of his firm, and to members of the consulting Board, the Golden Gate Bridge nevertheless is Strauss’ achievement.”

Throughout his career Strauss, was indeed a human dynamo designing and building some of the major bridges of the period. His inventions in other areas were equally outstanding. For all his genius and innovation, he is mainly known as the designer of the Golden Gate Bridge. Even that accolade has been tarnished by his treatment of Charles Ellis and the contentious, patent related, relationships he had with other engineers at that time.▪ Dr. Griggs specializes in the restoration of historic bridges, having restored many 19th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an independent Consulting Engineer. Dr. Griggs can be reached at fgriggs@nycap.rr.com.

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found at www.engrlib.uc.edu/strauss/ articles/brochure/brochure.pdf. He published his first catalogue in 1907.

His major bridge, however, was the Golden Gate Bridge in San Francisco, California.

His first work in San Francisco was when he designed and built a variation of his bascule bridge as an amusement ride, named the Aeroscope, at the 1915 Panama-Pacific International Exposition. A bascule bridge followed over Islais Creek, and it was at this time he met Michael O’Shaughnessy, the City Engineer who was interested in building a bridge across the Golden Gate. Starting in 1919, Strauss worked with O’Shaughnessey on plans for a bridge. His first design was for a hybrid Cantilever-Suspension Bridge in 1921. He estimated he could build the bridge for just over $17,000,000. Other engineers thought the bridge would cost well above that.

In 1925, Strauss had Leon Moisseff prepare a design for a pure 4,000 foot span suspension bridge, which he estimated would cost $19,400,000. Strauss kept promoting a bridge until 1929 when the legislature approved formation of the Golden Gate Bridge and Highway District opening the way for construction. The Board was not willing to give Strauss the design without considering proposals from other leading bridge engineers of the time. After interviewing many other engineers, the Board named Strauss as Chief Engineer with O. H. Ammann, Leon Moisseff and Charles Derleth as consultants. Charles Ellis prepared the preliminary plans and presented them on June 12, 1930. At the time it seemed to most of the players that Ellis was the brain behind the design, which apparently did not please Strauss. Friction continued between Strauss and Ellis. On November 26, 1931, Strauss told Ellis to take a vacation and turn all his calculations, etc. over to Charles Clarahan. Later Strauss effectively fired Ellis.

From that time on he never gave Ellis any credit for the design.

The bridge was built between 1933 and 1937, and opened May 27, 1937 for pedestrians and May 28 for motor vehicles. With its 4,200 foot main span, it was then the longest suspension bridge in the world and its towers, primarily the work of Ellis, were admired for their beauty. Strauss wrote a poem on its completion that began with:

LegaL PersPectives

discussion of legal issues of interest to structural engineers

Understanding Professional Liability Insurance Part 1

By Gail Kelley, P.E.

L

ike most businesses, architecture and engineering (A/E) firms generally carry commercial general liability (CGL) insurance to cover their liability for injury or damage to others. Because CGL policies are written on a standard form developed by the Insurance Services Office (ISO), an insurance-industry trade association, the coverage provided by different insurers is fairly similar.

While the standard CGL form does not exclude professional liability coverage, most insurers add an endorsement stating that the policy does not apply to injury caused by “the rendering or failure to render any professional service.”

An A/E who wants coverage for professional liability must thus purchase a separate policy.

This is the first of a two-part article that presents a general overview of E&O policies, the professional liability policies that cover claims against A/Es. In contrast to CGL policies, there is no standard E&O insurance form, and the coverage available from different insurers varies considerably. In addition, because insurance is governed by state law, policies issued in certain states may have special exclusions or qualifications.

Professional Liability Coverage Under a professional liability policy, the insurer agrees to pay damages that the insured party is legally obligated to pay as the result of claims that are covered by the policy. The insurer also agrees to pay the expenses associated with defending against the claim. These are, respectively, the insurer’s duty to indemnify and duty to defend.

E&O policies will give the insurer the right to examine the insured’s books and records, as they relate to the professional liability coverage. If the insurer discovers any material risk, hazard, or condition that the insured did not disclose in its policy application, the insurer has the right to modify the policy, charge an additional premium, or void the policy. Similarly, the insurer has the right to void the policy if the insured submits a fraudulent claim.

Definition of a Claim Professional liability policies define a claim as a demand for money or services that alleges a

wrongful act, where a wrongful act is a negligent act or omission by an insured, or a person or entity that the insured is legally liable for.

Although E&O policies invariably state that the wrongful act must occur in the performance of professional services, the term professional services is usually not well defined. For example, the policy may simply say that professional services means those services that the insured is legally qualified to perform for others in the practice of engineering, architecture, landscape architecture, surveying, or construction management.

Most E&O policy applications require the A/E to list and describe the services it provides. To minimize disputes over what is covered, the A/E should provide a detailed description of its practice areas and services.

An A/E who is concerned about coverage of certain services can ask its broker to include an endorsement (amendment) stating the coverage limits for those services.

Claims Made and Reported/Claims Made Under the current ISO form for CGL insurance, policies are written on an “occurrence basis” which means that there is coverage for an injury or property damage that occurs during the policy period, regardless of when the claim is made. In contrast, professional liability policies are typically written as either “claims made and reported” or “claims made.” Under a claims made and reported policy, a claim is only covered if it is first made against the insured during the policy period and is reported to the insurer during the policy period, or any applicable extended reporting period. Under a claims made policy, a claim must be first made against the insured during the policy period.

However, the policy usually only requires that the claim be reported to the insurer “within a reasonable time.”

Because of the additional reporting requirement, claims made and reported insurance is generally less expensive than claims made insurance. However, the reporting requirement means that coverage could be denied for a claim that was made against the insured during one policy period and not reported until the next policy period.

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Retroactive Date One of the key elements of a professional liability policy is its retroactive (prior acts) date. Most professional liability policies are for a period of one year, but if the policy is a renewal, coverage for wrongful acts will typically be retroactive to the inception date of the first policy obtained from the insurer.

Claims arising from wrongful acts committed before the policy’s retroactive date are not covered, even if the claim is made during the policy period. Many policies also specify a “knowledge date” (typically the inception date of the policy). The policy may preclude coverage of any claim that the insured knew about prior to the knowledge date, even if the wrongful act was committed after the retroactive date.

If the insured changes insurers or allows its policy to lapse, the retroactive date of the new policy will normally be its inception date.

However, most insurers allow the insured to purchase coverage for acts committed before the inception date of a new policy, provided the insured had comparable insurance from another carrier. This is often referred to as “nose coverage.” When changing insurers, the insured may want to purchase nose coverage such that the retroactive date of its new policy is the same as the retroactive date of its previous policy. Even with nose coverage, however, the new policy will not cover any claims the insured knew about at the inception of the new policy, as such claims should have been reported to the previous insurer.

Step Rating Each time a claims made or made and reported policy is renewed, the insurance carrier’s exposure increases because the retroactive period is a year longer. The rate tables for most insurance carriers reflect the increased exposure by “step rating” their policies; until a policy is full rated, the premiums increase yearly, even if the insured has not had any claims.

Rate tables vary, but most policies become fully rated within five to ten years of inception. At that point, changes in premium will reflect the claims history of the insured or the insurance carrier, changes in the insured’s practice areas or coverage limits, and changes in the general insurance environment.

Coverage of Damages

Notice

Professional liability policies cover the insured’s liability for awards, settlements, and monetary judgments, including interest. Although criminal fines, penalties, taxes, and matters that are uninsurable under the applicable state law are not covered, if the insured is legally liable for a tax, fine, or penalty assessed against a third party, it will generally be covered.

Some policies cover punitive damages, provided punitive damages are insurable under the applicable state law. (About a third of the states do not allow insurance to cover punitive damages as a matter of public policy.) Policies typically do not cover a reduction of fees because of a design error, unless the reduction is agreed to in advance by the insurer. Likewise, policies typically do not cover charges for services provided by the insured for redesign work.

The insured is typically required to provide the insurer with written notice of a claim, but most policies allow e-mail and fax correspondence as well as regular mail.

Potential Claims Most policies state that if the insured becomes aware of circumstances that might lead to a claim, there will be coverage for a claim made after the end of the policy period, provided the insured gives notice of the potential claim before the end of the policy period. The notice must state the alleged wrongful act and implicated professional services, the specific nature and extent of the alleged injury or damage, and how the insured became aware of the potential claim.

Extended Reporting Period

Limits of Liability The limits of liability of a policy will be stated on the policy’s declarations page. Most policies have a limit for each claim, as well as an aggregate limit for the policy period. The limits of liability are the most the insurer will pay, regardless of the number of insureds, the number of claims, or the number of individuals or entities making claims. When the limits of liability are exhausted, the insurer’s obligation to defend and indemnify against claims made during that policy period is fulfilled.

A claims made and reported policy will typically include an automatic extended reporting period (grace period) of 30 or 60 days for no additional premium. Coverage is provided for a claim reported to the insurer during this grace period, as long as the claim was first made against the insured during the policy period.

If the policy is not renewed, the insured can

purchase an additional extended reporting period. This optional extended reporting period, often referred to as “tail coverage”, is usually purchased in yearly increments, with the premium being a percentage of the policy premium.

The limits of liability applicable to the extended reporting periods will be the limits of liability remaining under the terminated policy. The right to give notice of a potential claim terminates at the end of the policy period, however; there is no right to give notice of a potential claim during an extended reporting period.

Conclusion The first part of this two-part article has discussed general issues related to coverage of claims; the second part looks at the insurer’s duty to defend and its right of subrogation as well as common exclusions to coverage.▪ Gail S. Kelley, P.E. is a LEED Accredited Professional as well as a licensed attorney in Maryland and the District of Columbia.

Ms. Kelley is the author of Construction Law: An Introduction for Engineers, Architect, and Contractors, published in 2012 by John Wiley & Sons.

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Multiple claims arising out of a single act or omission, or a series of acts or omissions, are generally treated as a single claim for the purposes of coverage limits. Coverage applies only if the earliest claim was first made against the insured during the policy period.

Deductibles Most policies have a deductible for each claim; some also have an aggregate deductible. If there is an aggregate deductible, the insured is not liable for any more expense claims during the policy period once the aggregate deductible is reached. If there is no aggregate deductible, the insured is liable for expenses up to the deductible on each claim. Policies generally state that only reasonable and necessary claim expenses qualify in satisfaction of the deductible, and that the insurer will determine whether expenses incurred by the insured qualify.

On most policies, the limits of liability apply as excess over the deductible.

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award winners and outstanding projects

Spotlight

Mike O’Callaghan-Pat Tillman Memorial Bridge Clark County, Nevada, USA and Mohave County, Arizona, USA

By David Goodyear, P.E., S.E., P.Eng T. Y. Lin International was an Outstanding Award winner for the Mike O’Callaghan-Pat Tillman Memorial Bridge project in the 2011 NCSEA Annual Excellence in Structural Engineering Awards Program (Category – New Bridge and Transportation Structures).

S

oaring 900 feet above the Colorado River, the Mike O’Callaghan-Pat Tillman Memorial Bridge frames one of the foremost engineering wonders of the world – the Hoover Dam. The 1,900 foot long Colorado River crossing is the centerpiece of the $240 million, four-lane Hoover Dam Bypass Project. The lead Agency for the project was the Central Federal Lands Division of the US Federal Highway Administration, led

by Dave Zanetell as Program Manager (PM).

The Bypass design team consisted of HDR, Jacobs and TY Lin International (TYLI). HDR managed the consultant team and led design of the Nevada roadway, Jacobs led design of the Arizona roadway, and TYLI led the design of the landmark Colorado River span.

With a main span of 1,060 feet, this bridge is the fourth-longest, single-span concrete arch bridge in the world. In addition to the NCSEA Outstanding Project Award, this project was also awarded the ASCE OPAL and ACEC Grand Conceptor Awards for design.

Like most Agency let projects, the bridge design effort began with a bridge type study.

However, the new crossing had been studied since 1968, and the PM saw an opportunity to use past work to screen bridge type candidates and move directly into final design. Stakeholders all agreed that a deck arch bridge was preferred, and the design team moved forward to assess the options within that bridge type.

The type study focused on concrete and steel arch structures at two different span lengths – one at 1,060 feet and the second at 1,325 feet to span a rock fault zone being studied in parallel with the type study. Once the geologists confirmed that the rock formations would allow the shorter span, the economical choices came down to the concrete arch with composite deck and a Glen Canyon-type trussed steel arch. .

A defining moment for the project came prior to a stakeholder meeting to discuss the draft type study. Dave Zanetell reviewed the draft type study report authored by David Goodyear.

He confided in David his concern that the type selection needed to reflect the special character

Photo courtesy of Jamey Stillings Photography.

of the Hoover site. The cost estimates showed a small preference for the concrete alternative, but Dave’s perspective was clearly broader than first cost. While a repeat of a Glen Canyon-type steel design might be easier to administer, he believed it would not be the right solution for the Hoover site and the generations of visitors to the Dam. This foresight was an example of the talent that would result in a signature project that realized budgetary and contextual design results. As designers we can dream, but without visionary clients, dreams are rarely realized.

The ensuing meeting with the Design Advisory Panel affirmed the type selection recommendation, and the Executive Committee of Agency leads unanimously selected the design you now see framing the view of Hoover Dam. The character and form of the bridge is classical, but the bridge design is unique. Every innovation was vetted by CFL and the Structural Management Group convened to review design, from the choice to use high strength concrete for stiffness of the long span arch to the unique composite connection between the steel tub girders and post-tensioned integral concrete caps. The framing system and sections that were defined at the end of the type study withstood the scrutiny of final design and review, with the only change in structural section being a 6-inch deepening of the integral concrete caps.

Building this form was anything but simple.

Reaching over 1,000 feet across a hard rock canyon in 120-degree heat is a challenge not for the faint of heart.

The construction contract was awarded in September of 2004 to Obayashi-PSM, JV. The Bridge was built using a variety of limited access techniques similar to those assumed for design. The arch ribs were supported with temporary stay cables hanging from temporary

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towers. The towers in turn were supported over the skewback piers, which had been designed for this erection method. The concrete segments for the arch were poured using four headings of self-advancing form travelers. Most of the arch segments were placed at night to avoid the triple-digit desert temperatures.

The construction project was beset with a major accident at the beginning of arch construction.

Winds resulted in the loss of the high-line crane needed to service work over the canyon. Instead of crippling the project, this event produced a more organized and determined construction team that would go on to achieve impressive results in completing the 52 cast-in-place arch sections on an accelerated schedule, closing within ¾-inch over the midpoint of the canyon!

Conclusion The Mike O’Callaghan-Pat Tillman Memorial Bridge now frames the view of the Black Canyon from Hoover Dam for the coming generations of tourists, and is the cornerstone in a new, efficient highway system funnelling commercial traffic between the states of Nevada and Arizona. The project reflects the skill and determination of the people who built it, all of whom take pride in their accomplishment.▪ David Goodyear, P.E., S.E., P.Eng is the Chief Bridge Engineer for T.Y. Lin International, and led the design for the new Colorado River Bridge at Hoover Dam as the Engineer of Record. David has served as Chairman of the PTI Committee on Cable-Stayed Bridges and was a member of the NCHRP team that authored the initial Concrete Segmental Guide Specifications with PTI.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

The 2012 NCSEA

Special Awards Honorees

The following awards were presented at the Awards Banquet on October 5 during the 2012 NCSEA Annual Conference in St. Louis.

The James M. Delahay Award Jim Robinson, P.E., S.E., SECB The James M. Delahay Award is presented at the recommendation of the NCSEA Code Advisory Committee to recognize outstanding individual contributions towards the development of building codes and standards. It is given in the spirit of its namesake, a person who made a long and lasting contribution to the code development process.

Jim Robinson is the president of Robinson Associates Consulting Engineers, Inc., a structural engineering firm in Atlanta. A graduate of Georgia Tech, Jim holds a Bachelor of Civil Engineering and a Master of Science in Civil Engineering, both with a major in Structures. He has served as a board member of the Applied Technology Council, The Structural Engineers Association of Georgia, the American Council of Engineering Companies, the Coalition of American Structural Engineers, and the International Concrete Repair Institute/Georgia. Jim currently serves as a member of the NCEES Structural Exam Committee and as a Diplomat of the Board of Forensic Engineering and Technology of the American College of Forensic Examiners, as a member of the ASTM Forensic Engineering Committee, and as a member of the National Academy of Forensic Engineers, where he has been elected Senior Member. In the area of Code Development, Jim has served on the Standard Building Code’s Wind Load Committee, the International Building Code’s Structural Committee, NCSEA’s General Engineering Code Advisory Committee, and NCSEA’s Special Inspections Code Advisory Committee; and he currently serves on NCSEA’s Wind Engineering Code Advisory Committee. In his spare time, he loves to talk about, play with, and entertain his three grandchildren.

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

Emile Troup, P.E. Emile Troup served as Regional Engineer for AISC and, subsequently, as a consultant on the application and design of steel structures. Now retired, he is a past president of NCSEA and was the first recipient of the association’s Robert C. Cornforth Award in 2001. He received Lifetime Achievement Awards from AISC in 2003 and the Connecticut Structural Engineers Coalition/ACEC in 2006, as well as the award for Outstanding Civil Engineering Alumnus of Northeastern University in 2004. Emile is a life member of ASCE and BSCE, as well as a member of the Fire Protection Committee of the Council of American Structural Engineers, the AISC Specification Task Group on Structural Design for Fire Conditions, and the Task Group on QA/QC. He is a member of SEAMass, a past president of the Boston Society of Civil Engineers, and a past trustee of The Engineering Center Education Trust (Boston). Emile has served as Coordinator of Vendor Relations for NCSEA for over 10 years, managing and coordinating the trade show for NCSEA’s Annual Conference.

He is retiring from this position after the 2012 Annual Conference in St. Louis. NCSEA thanks Emile for his tireless efforts on behalf of the association. We are all going to miss that ten-gallon cowboy hat and dry sense of humor.

Michael Tylk, S.E., SECB Michael Tylk has 40 years of experience and volunteerism in the structural engineering field. Retired from his position as a principal in the firm of Tylk Gustafson Reckers Wilson Andrews LLC (TGRWA, LLC), he received his Master of Science in Architectural Engineering and his Bachelor of Architecture from the University of Illinois, Urbana-Champaign. Mike has served as president, treasurer and director for both NCSEA and SEAOI; and he was the recipient of the NCSEA Robert C. Cornforth Award in 2004. He also served on the SEAOI Structural Engineers Political Action Committee and the Structural Engineers Foundation. Mike has been a member of the Chicago Committee on High Rise Buildings and the AISC Code of Standard Practice Committee, as well as many ad-hoc committees and advisory boards for the City of Chicago. He has been chairing the NCSEA Winter Institute since 2005, covering every aspect of the meeting, from planning and chairing to moving materials cross-country and hosting the social hour.

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Ronald Milmed, P.E., SECB The Robert C. Cornforth Award is presented to an individual in recognition of exceptional dedication and exemplary service to the organization and to the structural engineering profession. Nominees are presented to the NCSEA Board by the Member Organizations.

News from the National Council of Structural Engineers Associations

Ronald Milmed, P.E., SECB, currently enjoying his retirement, was a vice president and principal for Bliss and Nyitray of Miami, Florida, where he worked for over 40 years. A registered professional engineer in Florida, he served as Project Principal and Project Engineer for a large variety of structural design projects.

Milmed is a founding member of FSEA and has served on the Board and two terms as president in 2006 and 2007. He was instrumental in forming local FSEA chapters in Ft. Myers, Jacksonville, Orlando, Tampa, Palm Beach and Tallahassee, and he served as president of the South Florida chapter for 2001 and 2002. He serves on FSEA’s Licensing Committee, chaired the Peer Review Committee and the Bylaw Committee, serves as FSEA’s liaison to the Florida Board of Professional Engineers, and was co-chair of FSEA’s Peer Review Committee to the Broward County Board of Rules and Appeals. He was recently awarded life membership in FSEA in recognition of his contributions. Ron is also a past board member of ACI South Florida and a past Board member of NCSEA, where he continues to serve on the Licensing Committee and as FSEA’s delegate.

NCSEA News

The Robert C. Cornforth Award

NCSEA Webinars October Tools for Structural Assessment

The first in a two-part series, topics for this webinar will include performing good visual surveys, tools for establishing structural geometry, sampling for destructive testing, laboratory testing and analysis of structural materials, and non-destructive testing.

Presenter: Matthew Carlton, P.E., has served as the project manager large-scale projects involving construction and design defects, materials failures, structural deterioration, and collapses, and has evaluated and designed repairs for concrete, steel, masonry, and wood structures and a variety of architectural systems.

This course will award 1.5 hours of continuing education.

The times are 10:00 am Pacific, 11:00 am Mountain, 12:00 pm Central, and 1:00 pm Eastern. Approved in all 50 states. $225 –NCSEA member, $250 – SEI/CASE member, $275 – non-member, FlexPlan option available.

For more information and to register for these webinars, visit www.ncsea.com.

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Training for Post-Disaster Assessment

This California Emergency Management Agency (CalEMA) Safety Assessment Program (SAP), presented by NCSEA, is one of only two post-disaster assessment programs that will be compliant with the requirements of the forthcoming Federal Resource Typing Standards for engineer emergency responders. The program consists of three webinar segments held over one day’s time. Licensed design professionals and certified building officials will be eligible for SAP Evaluator certification and credentials following completion of this program and submission of required documentation.

Presenter: Scott Nacheman, MSc.Eng., AIA is a Vice President in the Chicago office of Thornton Tomasetti and coordinates the firm’s Property Loss Consulting Practice within the Chicago office, with responsibilities for response and condition assessment of damage caused by fires, hurricanes, tornados and structural collapses. He currently chairs NCSEA’s Structural Engineers Emergency Response (SEER) Committee and has served as a firefighter, fire lieutenant and instructor in New York and Illinois, as well as a Structures Specialist with regional, state and Federal Urban Search and Rescue Task Forces.

Only $500/site for the day, with unlimited attendees.

Save the Date!

Winter Leadership Meeting

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Part 1: Visual & Physical Surveys, Destructive and Non-Destructive Testing

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The Newsletter of the Structural Engineering Institute of ASCE

Structural Columns

2012 Electrical Transmission and Substation Structures Conference Columbus, Ohio November 4-8, 2012 A new generation of utility engineers is overcoming unprecedented challenges to find Solutions to Building the Grid of Tomorrow.

The Electrical Transmission and Substation Structures Conference is widely recognized as a one-of-a-kind conference that focuses specifically on transmission and substation structure issues to help utility engineers meet the daily challenges of today’s high-stakes energy environment. This must-attend event offers an ideal setting for learning and networking for utilities and suppliers.

Tours: Participants will have the unique opportunity to witness several transmission construction techniques and supplier demonstrations in a single day. Demonstrations will take place at three (3) American Electric Power (AEP) facilities located within a 30-minute drive from the Hyatt Regency Convention Center.

For more information visit the ETS conference website at http://content.asce.org/conferences/ets2012/index.html.

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.

2013 Ammann Fellowship Call for Nominations The O. H. Ammann Research Fellowship in Structural Engineering is awarded annually to a member 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, and their academic transcripts.

This fellowship award is at least $5,000 and can be up to $10,000.

The deadline for 2013 Ammann applications is November 1, 2012.

For more information and to download an application visit the SEI website at http://content.seinstitute.org/inside/ammann.html.

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New Concrete Transmission Pole Structures Manual Now Available Prestressed Concrete Transmission Pole Structures: Recommended Practice for Design and Installation is a complete engineering reference on staticcast and spun-cast prestressed concrete poles for electric distribution and transmission power lines. This Manual of Practice contains critical information for all aspects of a prestressed concrete pole project, including applications, concepts, materials, connections, foundations, manufacture, installation, and testing. This manual was prepared by SEI’s Task Committee on Concrete Transmission Pole Structures of the Committee of Electrical Transmission Structures.

Topics in this manual include: considerations for the design process; specifications for concrete and steel materials; design choices, criteria, and methodology; quality assurance during manufacture; assembly and erection; and inspection, maintenance, and repair.

Appendixes offer sample documents showing specifications for the purchase of static and spun cast prestressed concrete poles.

Utility engineers responsible for the design of transmission and distribution lines, pole manufacturers, power line constructors, and inspectors will find this manual to be useful for basic training and as an ongoing reference.

To order, visit the ASCE Bookstore website: www.asce.org/bookstore.

Call for 2013 SEI/ASCE Award Nominations Nominations are being sought for the 2013 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, 2012 with most deadlines falling on November 1, 2012.

Visit the SEI Awards and Honors page at http://content.seinstitute.org/inside/honorawards.html for more information and nomination procedures.

October 2012

Northeastern University Raytheon Amphitheater Thursday, October 18, 2012 5:30 – 9:00pm Miami, Florida October 24-26, 2012

SEI/ASCE Student Structural Design Competition Call for Applications SEI sponsors a structural design competition for student teams.

Innovative projects demonstrating excellence in structural engineering are invited for submission. A written submission will be judged, and three finalist teams will be invited to present their designs at the Structures 2013 Congress in Pittsburgh, PA, May 2 – 4, 2013. The finalist teams will be judged on an oral presentation during the conference, and 1st, 2nd, and 3rd place awards will be determined as a combination of the written and oral presentations. Awards include cash prizes and complimentary registration to the conference for the three finalist teams (up to three student registrations and one full registration for the faculty advisor). The three finalist teams will be notified within four weeks of the submission deadline and invited to Structures 2013 Congress to compete for the final awards and cash prizes.

Details regarding the oral presentation will be provided with the invitation to Structures Congress 2013.

Eligibility: Any team of undergraduate civil engineering students is eligible to submit a structural design. Projects from classes and other university assignments may be used (e.g. capstone design classes, senior assignments, class design projects). Projects solely performed as an employee of a design firm for which no university credit was obtained are not eligible. A maximum of one design from each university will be allowed. Any structural engineering design will be accepted, including but not limited to new building and bridge design, and existing building and bridge retrofit.

For more information about the Student Structural Design Competition and how to enter, visit the SEI website: www.asce.org/SEI. STRUCTURE magazine

Become an SEI Fellow SEI established the SEI Fellow (F.SEI) grade of membership to recognize a select group of distinguished SEI members as leaders and mentors in the structural engineering profession. SEI members who meet SEI Fellow criteria are encouraged to apply to advance to the grade of SEI Fellow. The benefits of becoming an SEI Fellow include recognition via SEI communications and at the annual Structures Congress along with a distinctive SEI Fellow wall plaque and pin, and use of the F.SEI designation.

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

Visit www.asce.org/SEI for SEI Fellow benefits, requirements, and instructions to apply online.

Completed application packages are due December 1 for induction at Structures Congress the following year.

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The Newsletter of the Structural Engineering Institute of ASCE

This is the first conference to focus exclusively on wind and flood topics of interest to professionals who design, engineer, regulate and build projects in hurricane affected areas.

Visit the conference website at www.atc-sei.org/ to view the technical program and see why the educational sessions make this an event not to be missed. Industry luminaries such as Larry Griffis, Chris Jones, David Prevatt, Ron Cook, Scott Douglass and Peter Irwin will be there. Topics include wind design using ASCE 7-10, building code changes in Florida and in the 2012 International Building Code, storm surge inundation modeling, and discussion of wind pressure modeling using new wind tunnels.

Join moderator Jerry Hajjar and panelists: Matthys Levy, Mike Davis, Matt Eckleman, and Josiah Stevenson, as they present a panel discussion on the issue of Design in a Time of Change. A thoughtful dialogue amongst all design professionals – students, researchers, and practitioners – is sought to advance the current state of practice to new design paradigms in a time of change.

This event is open to the public and sponsored by the Structural Engineering Institute of ASCE; space is limited and pre-registration is required. More information is available on the SEI website at www.asce.org/SEI. Cooperating organizations include Boston Society of Civil Engineers Section and Northeastern University.

For more information or to register visit the SEI website at www.asce.org/SEI.

Structural Columns

Boston Design Forum

Two New Tools from CASE

CASE in Point

The Newsletter of the Council of American Structural Engineers

Tool 4-5: Project Communication Matrix and Coordination Log Poor communication is frequently cited among the top reasons for deteriorated client relationships and claims. It is the intent of The Project Communication Matrix and Coordination Log tool to make it easier to maintain consistent project communication standards, and to document and communicate project coordination decisions. This Excel-based tool, which is easily adaptable for each individual firm’s needs, provides an easy to use and efficient way to (1) establish and maintain project-specific communication standards, and (2) document key project-specific deadlines and program/coordination decisions that can be communicated to a client or team member for verification.

Tool 5-4: Negotiation Talking Points This tool provides an outline of items to consider during fee negotiations for private sector and for public sector projects.

The tool offers suggestions of what to do and what not to do in different sets of circumstances, and provides reminders of ethical and professional obligations that must be kept in mind during these negotiations.

CASE Tool 4-5 and 5-4 are available at www.booksforengineers.com.

Glenn Bishop Awarded CASE Past Chairman’s Award Glenn Bishop, the founding member of LBYD, Inc. was awarded the CASE Past Chairman’s Award for over 20 years of service to CASE. Glenn received his Bachelor and Master of Science degrees in Civil Engineering from The University of Alabama. He serves on the University of Alabama Leadership Board for The School of Engineering, The University of Alabama Civil Engineering Department Board of Advisors and The University of Alabama at Birmingham School of Engineering Board of Advisors. As an active member of the American Council of Engineering Companies (ACEC), Glenn served as President of the Alabama Chapter of ACEC.

LBYD, Inc. was one of the founding members of CASE, with Glenn as their lead representative. He has been an active contributor to the CASE National Guidelines Committee, serving as the chair from 2004-2008, and was an integral participant in the preparation of documents, such as the commentary on AISC Code of Standard Practice for Steel Buildings and Bridges and Guideline Addressing Coordination and Completeness of Structural Construction Documents. His name is on every current CASE national practice guideline. Glenn continues to serve CASE and the National Guidelines Committee through his ongoing participation.

Get an ACEC Designation Set the Standard for Management and Leadership Excellence Executives at engineering firms develop a unique skill set that transcends the technical practice of engineering – the skill and adroitness of running an engineering business. Experience managing programs, projects, personnel and budgets will drive a firm’s profitability. These vital skills are not learned in technical programs, but are acquired through company programs, from industry groups, such as ACEC, and via direct business practice experience.

ACEC, as the industry leader in best business practices, recognizes that business acumen is critical to success, but difficult to quantify for a client. ACEC is proud to offer its designation program – a way for our members to codify their experience and use it to market their services.

ACEC’s Professional Designation programs are designed to recognize a singular attainment of relevant experience and education by worthy professionals in the engineering industry.

ACEC’s Professional Designation programs set the national standards for business management and leadership excellence in the engineering industry. ACEC offers three professional designations, and each has a different set of criteria for eligibility to capture an individual’s level of experience and education.

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The Management Engineer – MgtEngSM – is designed for professionals working in project, program, or business management roles within an engineering firm or related to the engineering industry.

The Executive Engineer – ExecEngSM – is designed for leaders in the industry. Executive Engineers have attained the highest level of achievement in industry leadership and experience.

The Management Professional – MgtProSM – is designed for non-P.E. managers working in non-profits or government agencies related to the engineering industry or business managers within engineering firms.

Contact Kerri McGovern at kmcgovern@acec.org for more information or visit www.acec.org/education/designations/index.cfm.

You can follow ACEC Coalitions on Twitter – @ACECCoalitions.

October 2012

Performance-Based Design (PBD) is a relatively new and powerful approach to structural engineering born from ongoing efforts to resolve the differences between the actual observed performance and the expected performance of structures. Previously observed differences between the actual and expected performances of structures, especially because of earthquakes, has led to advances in the understanding of system and material performance by the research and practicing community that at times go beyond the prescriptive requirements often found in

the building codes. With the improvements in the capability of relevant analytical tools and computing technology, structural engineers are increasingly using PBD for new design, and for evaluation or retrofit of existing structures, to better predict building performance, provide more economical designs, or address when the prescriptive provisions of the building code just do not apply.

To download a copy of this white paper, visit www.acec.org/case/publications.

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

Home Address on Business Cards With the increasing number of employees working from home, firms have begun to receive requests for business cards that reflect home addresses as the company address. This is not a good idea. Aside from misleading clients, many states require a registration for each place of business. It could also lead to problems with state licensing boards and local business taxing.

An easy solution is to just add email and fax number to the card.

Consequences of a Bad Contract

Ninety-Five Per Cent of Lawsuits Involving Design Professionals are Settled But, frequently, only after years of discovery, countersuits and substantial legal costs. Thus the benefit of having a mediation clause in the contract that requires it before a suit can be filed.

Good mediation language will include the terms “non-binding” with an end date for negotiations. It should also include the possibility of extending the end date or shifting to another form of dispute resolution, if necessary. A lawsuit is always available to parties; with so many cases being settled eventually in mediation, why not start there in the first place.

What are the liability exposures of a bad contract? You might exceed your liability insurance limits, expose yourself to something uncovered by your policy, go beyond your scope of services, expose officers and directors. A good contract will establish the “rules” under which you will play, definitively outline the scope of service and the duties and responsibilities of the parties, properly allocate risks (and rewards) and if a problem arises offer a dispute resolution.

STRUCTURE magazine

CASE is on LinkedIn LinkedIn is a great virtual resource for networking, education, and now, connecting with CASE. Join the CASE LinkedIn Group today! www.linkedin.com.

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CASE is a part of the American Council of Engineering Companies

CASE Business Practice Corner

CASE in Point

CASE Releases Performance-Based Design White Paper

Structural Forum

opinions on topics of current importance to structural engineers

Developing the Next Generation of Structural Engineers Part 2: Structural Engineer Opportunities and Attributes

By Glenn R. Bell, P.E., S.E., SECB This is the second article of a four-part series on the opportunities and challenges we face in developing the next generation of structural engineers, based on the author’s keynote address at the SEI Structures Congress in March 2012.

Structural Engineering Opportunities What does our view of the future world mean for future generations of structural engineers?

I see opportunities on three levels: 1) The creation of all of constructed works needed to meet these global challenges – affordable housing, public transportation, renewable energy, and water distribution and treatment systems – all involve, on some level, structural engineering.

With the possible exception of construction management, structural engineering is the most broadly applicable of the civil disciplines.

2) American engineers are well-positioned to take global roles by doing the highervalue, more creative work. We are good at thinking outside the box. America’s national culture facilitates leadership, innovation, and entrepreneurship. A key strategy, then, is positioning our industry and its future professionals to exploit these qualities.

3) Finally, to tackle society’s grand challenges, we need more engineers in leadership roles that are nontraditional: setting policy, leading major societal initiatives, and even politics. The US Congress would work better if it were populated with more engineers and fewer lawyers.

Attributes of the Structural Engineer of the Future If we could fast-forward forty years, the new breed of structural engineer would be unrecognizable to us today.

No. 1: Global Practitioner The successful global practitioner will work with varying technical standards, indigenous materials and construction techniques. Here,

strong technical fundamentals and knowledge of performance-based design will be critical.

Just as important, however, is the ability to embrace different cultures, values, languages, and business practices. Tomorrow’s engineer must be globally aware and adept.

No. 2: Collaborative Leader Tomorrow’s engineers must be able to see their role in its societal context. This entails being able to define society’s important problems, not just solve them – to champion major initiatives and help to craft public policy, not just implement it.

Projects are becoming increasingly complex.

Technical knowledge is exploding. We need to engage stakeholders of many backgrounds. This all demands that the new breed of structural engineer be able to lead collaborative teams. To be a collaborative leader, tomorrow’s engineer must be dynamic, agile, and flexible. Most importantly, great collaborative leaders have to be great communicators – orally and in writing.

No. 3: Creator/Innovator To meet the imperative for resource-responsible construction, tomorrow’s structural engineer will invent new construction materials and systems, as well as innovate new processes and approaches to problems. We need to be creative and entrepreneurial. We all will need a bit of John Roebling or Gustav Eiffel in us.

No. 4: Integrator In engineering problem-solving, we are taught to break problems down into smaller and smaller pieces. Tomorrow’s engineer must be able to engage in lateral, functional thinking as well as vertical, in-depth thinking; to synthesize as well as analyze; to integrate knowledge from a variety of sources; to integrate complex systems. To do this, we must be able to span disciplinary boundaries.

No. 5: Master of Uncertainty The new breed of structural engineer must be able to embrace problems of uncertainty, help others understand it and make good decisions in the face of it. Balancing risk and reward among

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

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project team members is an important strategy for providing value through innovation. We need to accept ambiguity as a new permanent condition.

No. 6: Expert of Technical Fundamentals While many things about the engineer of the future look different, we must not only retain but strengthen our solid expertise in technical fundamentals. Blind reliance on computers can erode our ability to make reasoned judgments that involve common sense and intuition.

Needed Change How do we develop all the competencies of this extraordinary future engineer/leader? We first must take as a given that, tomorrow more than ever, a career in engineering requires a commitment to life-long learning. Comprehensive gain of knowledge and skills will be an intensive, ongoing effort until the engineer retires. Given this, the single biggest need in advancing the development of the next generation of engineers is to sort out what we expect from each of the phases in the career-long spectrum of a professional’s development; from formal university training to pre-licensure apprenticeship to post-licensure professional development.

Presently we have redundancies, gaps, inefficiencies; missed opportunities in our system.

We expect too much from the undergraduate curricula and, as a consequence, it is getting watered down. Firm leaders send mixed messages to academic leaders about our needs and expectations of their graduates. On the one hand, we espouse the virtues of a solid grounding in technical fundamentals and soft skills; on the other, we send recruiters to university job fairs and seek out practice-ready professionals with knowledge of the latest versions of codes and analysis software.

As a general strategy, the earliest material addressed in an engineer’s development should be that which is most fundamental and most likely to be invariant over the course of a career. The changing stuff should be left for later, most particularly on-the-job experience and continued learning.▪ Glenn R. Bell, P.E., S.E., SECB (GRBell@sgh.com), is the Chief Executive Officer at Simpson Gumpertz & Heger in Waltham, Massachusetts.

In the next article, we will consider the industry actions required to bring about the needed changes.