Comparison between Calculating Live Load Distribution Factors by AASHTO-LRFD Equations and Finite Element Method of Precast Concrete U-Girder Bridges

Document Type : Regular Paper


1 Department of Civil Engineering, Obour High Institute for Engineering and Technology, Cairo, Egypt

2 Department of Civil Engineering, Elgazeera High Institute for Engineering, Cairo, Egypt

3 Department of Civil Engineering, Faculty of Engineering, Cairo University, Giza, Egypt



The main objective of this study is to make a comparison between calculating live load distribution factors using AASHTO-LRFD equations and the finite element analysis of precast concrete U-girder bridges. The AASHTO-LRFD specifications provide empirical equations for calculating the distribution factors. Little information is available regarding the accuracy of these equations for this kind of bridge girder. As a result, an extensive parametric study was carried out using finite element modelling to evaluate the parameters that influence the live load distribution factors and to verify the accuracy of the AASHTO-LRFD equations to calculate these factors. The parameters considered in this study were bridge span, girder spacing, number of girders, and number of lanes. 52 prototype bridges were analysed using CSI Bridge software to determine moment and shear distribution factors due to the effect of the AASHTO-LRFD live load model (HL-93). All of the bridges studied were assumed to have straight and simply supported spans. According to the study''s results, the length of the girder does not affect the LLDF, while the parameters of the distance between girders, girder count, and lane count have a significant impact. In most cases, the AASHTO equations overestimate the calculated moment and shear distribution factors. Especially for wide bridges, the parametric study found that the difference between AASHTO equations and FEA results for calculating shear distribution factors was 87%. Consequently, it is best to avoid using these equations on wide bridges.

Graphical Abstract

Comparison between Calculating Live Load Distribution Factors by AASHTO-LRFD Equations and Finite Element Method of Precast Concrete U-Girder Bridges


Main Subjects

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