Effect of Continuity on Wheel Load Distribution in Steel Girder Bridges

This paper presents the finite-element results of a study of the effect of continuity on wheel load distribution factors for 78 bridges. Typical two-equal-span, two-lane, straight, composite steel girder bridges were selected for this study. Bridge parameters such as span length and girder spacing were varied within practical ranges, and their influence on the bridge continuity was investigated. The selected bridge cross sections and wheel load positions ensured that interior girders carry more live loads than the outside girders. Results of two finite-element modeling techniques were used to predict wheel load distribution factors, which were similar to the results obtained using the new formula developed as a part of NCHRP Project 12-26. They were, in general, less than the values obtained using the current AASHTO formula (S/5.5). The newly adopted AASHTO LRFD Bridge Design Specifications introduced new wheel load distribution factors based on formulas developed in NCHRP 12-26. The findings of this research encourage the use of the new wheel load distribution formula with a 5% reduction when considering multispan steel girder bridges. The new formula has been shown to be applicable to bridge decks with three girders. The engineer could also adopt an average of 15% reduction when using the AASHTO empirical distribution factor (S/5.5) when analyzing continuous bridges.