Parameterized Fragility Assessment of Bridges Subjected to Pier Scour and Vehicular Loads

Abstract

Even though scour-related bridge failures are among the most common causes of bridge failure, the literature lacks studies that have assessed the safety of scoured bridges to carry vehicular loads. As a result, bridge owners often rely on subjective limits of scour depth triggering closure or load limitations. This study focused on developing fragility functions for bridges subjected to pier scour under vehicular loads. For this purpose, fragility functions parameterized on bridge details, scour depth, and vehicular loads were developed to aid management of traffic on scoured bridges and prevent life-threatening accidents. Instability caused by vehicle-induced loads (i.e., vertical gravity loads and longitudinal loads from vehicle braking) was considered. Therefore, failures resulting from lack of bearing capacity and failure of bridge columns, abutments, and bearings as a result of braking loads were studied. To obtain the fragility functions for these failure modes, a set of 3,5 bridge parameter combinations was generated using Latin hypercube sampling (LHS). For all bridge parameter combinations, bridges were modeled in OpenSees, and finite-element analyses were performed to assess the stability of scoured bridges under vehicular loads. The results show that bridges with pier scour are more vulnerable to bearing failure than to failure from longitudinal braking loads. These analysis results were used to develop fragility functions using logistic regression, which were tested on two bridges in New Zealand. To facilitate application of the fragility functions for practical scenarios where multiple soil layers are present, this study developed a soil homogenization procedure. The fragility functions and the soil homogenization procedure were used to study the performance of a case study bridge in Brazoria County, Texas. The results for the case study bridge show the effects of variation in vehicular load, position of the vehicle, and bridge parameters on the fragility of the bridge, highlighting the usefulness of the fragility functions to support decisions on imposing load and lane restrictions and to study the effects of parameter variation on the performance of bridges with pier scour.