Load Rating of Pile-Supported Bridges Susceptible to Scour

Bridge load rating is traditionally done based on the load-carrying capacity of the superstructure components. Only in some rare instances does the bridge load rating consider the load-carrying capacity of the substructure. However, the authors believe that for bridges over waterways, which are susceptible to scour, the load-carrying capacity of the substructure must be evaluated to assess the need for reduced load rating and posting limits. The results in this paper attempt to address the importance of assessing the substructure load rating. Case histories for bridges susceptible to scour are analyzed. The analysis and evaluation of the actual bridges presented demonstrate that the bridge load rating is limited by the substructure load-carrying capacity and the tolerable deformation. The examples clearly illustrate that reduced load rating is experienced when scour occurs. Thus, bridges impacted by scour need to be judged based on both the super- and substructure components. The findings suggest the need to augment the current bridge load rating procedures to include the substructure load rating in a quantitative manner.