Live Load Distribution Factors for Spread Slab Beam Bridges

Abstract

The design and construction of spread slab beam bridges is becoming commonplace in Texas. Although this relatively new class of bridge is somewhat similar to spread box beam bridges, it is unclear whether the existing live load distribution factor (LLDF) equations for the latter system are applicable for the former. Therefore, this paper presents the evaluation and derivation of flexural and shear LLDFs for the new spread slab beam bridge class. Thirty-one variations of these models were used to investigate an array of possible bridge geometries, and shear and moment LLDFs were derived for the design of spread slab beam bridges. Twenty-eight additional geometries were explored to derive correction factors for skew angle, overhang, and vehicle position. Existing AASHTO spread box beam bridge LLDFs range from being unconservative to very conservative when applied to spread slab beam bridges. Therefore, new LLDF expressions are developed to provide an appropriate estimate of load sharing for spread slab beam design in terms of moment and shear.