Lateral Load Distribution Factors for Military Vehicles on Multi-Girder Deck Slab Bridge Systems

Abstract

American Association of State Highway and Transportation Officials (ASHTO) specifications have prescribed lateral load distribution factors to calculate the bending moments and shear forces for the design of highway bridges for civilian highway traffic. The maximum bending moments and shear forces caused by a wheel line load (or the entire vehicle) placed on the girders are multiplied by the distribution factors to calculate the design forces to include the effect of the load distribution laterally to the girders by the bridge deck. However, the use of these AASHTO distribution factors may not provide accurate estimate of the maximum forces for military vehicles, which usually have significantly different loading pattern than those of the civilian vehicles. Therefore, this study was conducted to develop new formulas for the lateral load distribution factors for military vehicles.

The study considered six different types of military vehicles, three wheeled vehicles and the other three tracked vehicles. The bridge database used for developing AASHTO distribution factors formulas was also used in this study. The focus of this study was to develop the distribution factors formulas for three different types of bridges: steel girder bridges, pre-stressed concrete bridges, and concrete T-beam bridges.

The bridges in each category were analyzed for the six types of military vehicles by the harmonic decomposition approach to calculate the distribution factor. This thesis provides a total of 52 new formulas for different types of vehicles, different types of bridges, bending moment and shear force values, interior and exterior girders, and for single and multiple lane loading cases. The distribution factors calculated with the formulas were compared with those calculated by direct analyses of the bridges to evaluate the accuracy of the proposed formulas. Comparisons were also made between the values calculated by the new formulas, post-LRFD formulas prescribed in 1996 AASHTO Standard Specification, and simple pre-LRFD formulas that were prescribed by AASHTO before 1994.