Live Load Distribution Factors for Cast-in-Place Concrete Box Girder Bridges: Fid-Bau Portal

Live Load Distribution Factors for Cast-in-Place Concrete Box Girder Bridges

Doerrer, Ryan / Hindi, Riyadh

This paper presents a comparison between the live load distribution factors of cast in place concrete box girder bridges based on the AASHTO-LRFD 2007 specifications and finite element analysis for continuous bridges. In this comparison, the range of applicability limits specified by the current AASHTO-LRFD specifications is fully covered and investigated in terms of span length, girder depth, girder spacing, and number of cells. To cover all the limits of the AASHTO-LRFD specifications, a variety of bridges were each modeled with different geometric properties that pushed the limits of what the specifications allow. Bridges previously modeled by others were modeled again using SAP 2000 version 10.0.2, and their results were compared to the results from the finite element analysis in order to gain faith in the correct application of the modeling. The live loads used in the analysis are as specified by AASHTO-LRFD. Lanes were defined along the span of the bridge and moved transversely across the width of the bridge. This load was then moved longitudinally along the lanes defined on the bridge. All possibilities of one lane, two lanes, and three lanes loaded were investigated. The distribution factors obtained from the finite element models were compared to the AASHTO-LRFD distribution factors. The results from AASHTO-LRFD were overly conservative for a vast majority of the bridges when compared to finite element analysis. Several figures are developed to assist bridge engineers finding the live load distribution factors for certain bridge parameters and using the differences between the AASHTO-LRFD and finite element analysis to decide if a refined method of analysis is necessary.