Validation of Code-Specified Girder Distribution for Continuous Steel Girder Bridges

Abstract

Current bridge design codes do not clearly specify the girder distribution factors for continuous bridges. The objective of the paper is to validate the use of code-specified girder distribution factors for the continuous steel girder bridges, and to provide a basis for recommended girder distribution factors (GDF) for interior girders, suitable for evaluation of existing continuous steel girder bridges. This paper presents the procedure and results of 3-dimensional finite element analysis that were performed on five continuous two-lane steel girder bridges to verify girder distribution factors. In the numerical models, the selected bridges were analyzed under fully loaded 11-axle trucks available in Michigan. The analysis results showed that the live load moment distribution is very similar for negative moment region compared with positive moment region in continuous steel girder bridges. It was also found that the GDF’s based on the strain values are similar to those based on the deflection. GDF’s based on the deflection show marginally better distribution. The analysis results confirmed that the code specified GDF's for continuous steel girder bridges are very conservative, for both AASHTO LRFD (1998) and AASHTO Standard (2002). AASHTO Standard (2002) provides more conservative GDF's.