Verification of shear live-load distribution factor equations for I-girder bridges

The "S-over" Load Distribution Factor (LDF) has been used for many years for determining the distributed moments and shear forces of a girder. Only until recently after the adaptation of the AASHTO LRFD Bridge Design Specification, new LDF equations are proposed using power functions. Although these new equations can more accurately predict the distributed moments and shear forces similar to both field and finite element analysis results, they are complex and they do not represent the fundamental background of LDF but rather based on regression analysis. Therefore, a more fundamental equation such as the S-over LDF is needed for the engineer to have a better understanding of the relationship between the girder sizes and spacing. The primary objective of this study is to develop a simplified S-over LDF for shear for steel and prestressed concrete I-girder bridges. Actual field testing of seven I-girder bridges were evaluated and validated to the developed Finite Element Analysis (FEA) model. A parametric study of bridges with various girder spacing and length were performed to develop the proposed equations. Results show that the proposed equations have excellent correlation with the more exact FEA model as well as the computer-based analysis.