Simplified live load distribution factor equations for Tennessee highway bridge design

The lateral distribution of live load moment and shear in highway bridge design is commonly determined by using the method specified in the AASHTO LRFD Bridge Design Specifications. This method is generally considered to be accurate; however, the distribution factor equations have restraints on the ranges of applicability for bridge parameters. It is mandated in the AASHTO LRFD that refined methods of analysis are required when the ranges of applicability are exceeded. The main objective of this research was to develop a set of new equations that have little restraints on bridge parameters while retaining the accuracy of the equations. Bridge databases that include bridges used in the NCHRP 12-26 project, actual Tennessee bridges, and a group of hypothetical bridges with structural parameters exceeding the ranges of applicability were assembled. To obtain the analytical results of live load moment and shear distribution factors, rigorous analysis was performed for the hypothetical bridges. A set of new, simplified distribution factor equations (TDOT 2010 equations) was developed based on the evaluation and comparison of existing equations and procedures. Then, a statistical analysis was conducted to examine the accuracy and reliability of the new live load distribution factor equations by comparing them with the analytical results. The study demonstrates that the newly developed equations emphasize ease of application while yielding results comparable to rigorous analysis. The equations also give bridge engineers the flexibility to design bridges with structural parameters outside the ranges of applicability restricted in the AASHTO LRFD Specifications.