Fabricator's Economic Perspective on Steel Bridges

Frank Russo, Ph.D., PE,
Project Manager
URS Corporation
Philadelphia, PA

John C. Huang, Ph.D., PE,
Principal
CHC Engineering, LLC
Herndon, VA

Highway bridges are vital links in the nation’s transportation network. Approximately 96% of nation's nearly 600,000 bridges have spans that are less than 120 feet, and roughly 66% of the bridge population have a total length that is less than 120 feet. Furthermore, the Federal Highway Administration estimates nearly one-third of bridges in the nation need to be repaired or replaced. Therefore, the majority of bridges that we are going to deal with are short-span bridges that provide important links for state, county and municipal roads. The structural advantages of using steel include its lighter weight, which means lighter foundations and lower erection costs. Steel is ideal for short-span bridges because of its durability, ease of maintenance and ease of construction.

To build cost-effective steel bridges is a challenge that faces today's designers, fabricators, contractors and owners. The objectives are not only to provide the most cost-effective solution for initial bridge construction, but also to provide a long maintenance-free life. Although the total project cost (the initial construction cost and the life cycle cost) is affected by many decisions in the various stages of design, fabrication, erection and maintenance during the structure's life span, the decisions made at the design stage account for more than 80% of the influence on both the total project cost and the service life performance quality.

This course focuses on the short span bridges with spans less than 120 feet. The following factors, which have major influences on the bridge economics, will be discussed to show you how design and details impact fabrication cost and maintenance cost from fabricator's perspective.

• Type of Steel
• Paint
• Integral/Jointless Bridge
• Bearings
• Girder Spacing
• Splicing
• Web, Connection and Bearing Stiffeners
• Bracing
• Welding

This course provides some real fabrication costs and cost comparisons that can be used in the actual design process. Several new developments in High Performance Steel are also presented here. These new developments may come to play in bridge economics in the future. Several useful references have been included in this course for those who need help in making decisions with respect to cost-effective bridge design and details and for those who search for more detailed information. An expanded presentation on Cost-Effective Steel Bridges by Bob Nickerson, formerly with FHWA and a consultant for AISI, is available on video tapes and can be purchased through American Iron and Steel Institute.

The followings are some of the cost saving measures recommended in this course from fabricator's economic perspective. Those recommendations are relevant only to the short span steel bridges and shall not be misconstrued as blank statements as to what to do and what not to do. The designers must use their own judgments in deciding what is the best design from both the engineering and the economical standpoints on a case by case basis.

• Use uncoated weathering steel
• Use jointless and integral structures if possible
• Avoid expensive bearings and use elastromeric bearings if needed
• Increase girder spacing
• Avoid welded girder splices and/or bolted field splices if possible, and make splices optional if required
• Avoid web shear stiffeners and use thicker web if necessary
• Avoid bolted tabs and cutting-short for cross-frame connection stiffeners and use fillet weld to connect stiffener with flanges
• Use simple cross frames
• Use single pass weld if possible

In this lesson, you need to view the slide show: Fabricator's Economic Perspective, which provides the detailed information on cost-effective design and details for short span steel bridges.

Once you finish viewing the slide shows and studying the FAQ, you need to take a quiz to obtain the PDH credits.

 

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Additional Technical Resource and Further Readings:

1. American Association of State Highway and Transportation Officials, Manual for Condition Evaluation of Bridges, Washington, DC, 1994.

2. American Association of State Highway and Transportation Officials, Standard Specification for Highway Bridges, 1996, Edition, 1997,1998 and 1999 Interim Specifications - Bridges, Washington, DC.

3. American Association of State Highway and Transportation Officials, Guide for Painting Steel Structures, Washington, DC, 1997.

4. American Iron and Steel Institute, Steel Bridge Bearing Selection and Design Guide, by Profs. Charles Roeder, PE, and John Stanton, PE, 1996. (Available from the National Steel Bridge Alliance, Chicago, IL).

5. Federal Highway Administration, Uncoated Weathering Steel in Structures, FHWA Technical Advisory T5140.22, Washington, DC, 1989.

6. Missouri Highway and Transportation Department. Task Force Report on Weathering Steel, January 1996.

7. Rubeiz, C.G., and Gorman, C.D., Pre-Engineered Short Span Steel Bridges, ASCE Structures Congress, Atlanta, GA, 1994.

8. Taavoni, S., Comprehensive Package for the Design of Short Span Steel Bridges, National Symposium on Steel Bridge Construction, Atlanta, GA, 1993.

9. AASHTO, Guide Specifications for Highway Bridge Fabrication with HPS70W Steel, Washington DC 2000.

10. AISI Short Span Bridge Design Software: AISIBEAM Version 3.0.

11. AISI Bridge Girder Splice Design Software: AISISPLICE Version 3.0

12. Federal Highway Administration, High Performance Steel.

13. F. Ibrahim, Guide for bolted Field Splices, Clarkson University, 1999

14. Dennis Mertz, Bridge Designer's Guide to Intermediate Cross-Frame Diaphragms, AISI, 2000

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Acknowledgment:

PDHonline.com acknowledges the sponsorship of American Iron and Steel Institute (AISI) for this online course.

 

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DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDHonline.com or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered professional engineer. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.