Reliability of AASHTO LRFD parameters in multilane reinforced concrete slab bridges

Abstract

Empirical expressions for estimating live load bending moments are typically specified in AASHTO bridge codes. This paper will evaluate the reliability levels that are inherent in the simplified empirical equations in the AASHTO LRFD to design concrete slab bridges. Typical one-span, multilane, straight bridges, with various span lengths are modeled using finite element analysis (FEA) and subjected to AASHTO live loads. FEA results are compared with LRFD moments to quantify biases that might result from the simplifying assumptions in AASHTO. The reliability index ␤ for bridge cases using AASHTO procedures and FEA results were quantified. The results of this analysis showed that current live load factors in AASHTO LRFD procedures were below the required levels of reliability index (␤ < 3.5) for one-lane bridges, and those indices were higher for multilane bridges, yet did not reach the required level, thus proposing to increase the AASHTO live load factors.