Load Reduction in Steel Girder Bridges
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Volume 7, Issue 1
Abstract
This paper presents the finite-element results of a study investigating the effect of multipresence of design vehicles on three- and four-lane steel girder bridges. A total of 220 bridges were analyzed using the computer program SAP2000. Typical three- and four-lane, straight, composite steel girder bridges were selected for this study. Bridge parameters such as span length, girder spacing, one span, two equal spans, design loads in all lanes, and design loads in two out of three, three out of four, and two out of four lanes were investigated. The finite-element analysis (FEA) results were used in calculating the maximum wheel-load distribution factors (DF), which were later compared with the simple AASHTO DF formula, and the formula developed as part of NCHRP project 12-26. The 10% reduction suggested by AASHTO bridge specifications for three-lane bridges appears to be developed by loading two lanes of the three-lane bridges. It was also observed that the calculated wheel-load distribution factors from the FEA-DF due to live loads in three out of four lanes were similar to the 10% reduction of the calculated FEA-DF results obtained by placing live loads in all four lanes. Also, the FEA-DF due to live loads in two of the four lanes were similar to the 25% reduction of the FEA-DF results due to fully loaded four-lane bridges. This paper demonstrates that the multiple lane reduction is built into the DF formula presented in the NCHRP 12-26 final report. The finite-element results suggest a 10 to 20% reduction factor in three-lane bridges and 20 to 25% reduction factor in four-lane bridges when using AASHTO DF depending upon the girder spacing and span length. Finally, this paper can assist engineers in quantifying the adjustment factors used in analyzing and designing multilane steel girder bridges.
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References
AASHTO. (1994). LRFD bridge design specifications, Washington, D.C.
AASHTO. (1996). Standard specifications for highway bridges, 16th Ed., Washington, D.C.
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SAP2000 user’s manual. (1998). Computers & Structures Inc., Berkeley, Calif.
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Published In
Practice Periodical on Structural Design and Construction
Volume 7 • Issue 1 • February 2002
Pages: 37 - 43
Copyright
Copyright © 2002 American Society of Civil Engineers.
History
Received: Mar 20, 2001
Accepted: May 9, 2001
Published online: Feb 1, 2002
Published in print: Feb 2002
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