Distribution of Wheel Loads on Highway Bridges

This NCHRP digest presents the findings from NCHRP Project 12-26, Distribution of Wheel Loads on Highway Bridges. The project was initiated in the mid-1980s in order to develop comprehensive specification provisions for distribution of wheel loads in highway bridges. The study was performed in two phases: Phase I concentrated on beam-and-slab and box girder bridges; Phase II concentrated on slab, multibox beam, and spread box beam bridges. Three levels of analysis were considered for each bridge type. The most accurate level, level 3, involves detailed modeling of the bridge deck. Level 2 includes either graphical methods, nomographs and influence surfaces, or simplified computer programs. Level 1 methods provide simple formulas to predict lateral load distribution, using a wheel load distribution factor applied to a truck wheel line to obtain the longitudinal response of a single girder. The formulas developed in this study for the level 1 analysis were based on the standard AASHTO HS truck. Levels 2 and 3 analyses may be applied for trucks outside the AASHTO family of trucks. The major part of this research was devoted to the level 1 analysis methods because of its ease of application, established use, and the surprisingly good correlation with the higher levels of analysis in their application to a majority of bridges.