WHEEL LOAD DISTRIBUTION ON SIMPLY SUPPORTED SKEW I-BEAM COMPOSITE BRIDGES

This paper presents distribution factor expressions for wheel-load distribution to interior and exterior girders of concrete on multisteel beam composite bridges of medium span length. These expressions were derived from finite element analysis of 36 bridges: with 9 ft spacing of girders, different spans (75, 100, and 125 ft), different widths (39, 57, and 66 ft), different skew angles (0-degrees, 20-degrees, 40-degrees, and 60-degrees), and different spacing and size of intermediate cross frames. The analysis recognizes the three-dimensional interaction of all bridge members, places the bearings at their actual location, and considers the effect of the restraining forces at the bolster and rocker bearings. To test the validity of the adopted discretization scheme, its results were validated by testing an actual 137 ft. span four-lane, 59.5-degrees skew bridge. The derived distribution factor expressions give values that are generally much lower than the current American Association of State Highway Transportation Officials (AASHTO) values, particularly for skew bridges. In addition to the girder spacing, these distribution factors recognize the effect of skew, span length, deck slab width, number of girders, and number of loaded traffic lanes, as well as the probability that positioning all the standard AASHTO trucks in locations to produce maximum flexure effects is reduced as the number of loaded lanes exceeds two.