Selection of Input Motion for Seismic Analysis of Scoured Pile-Supported Bridge with Simplified Models

Potential scouring scenarios around the foundations of bridges that pass over water could have adverse effects on the seismic response of both the site and the structures. In this study, a two-step methodology is proposed to estimate the seismic response of pile-supported structures accounting for these effects. The first step was to calculate the seismic response of the free field and obtain the acceleration and displacement responses of the site considering the effects of scouring on ground motions. The second step was to perform seismic analysis on the pile-supported structure on the basis of a simplified model, using the acceleration response of the free field as a uniform input along the pile nodes. The responses of four different input motion choices were compared to determine the best choice for the seismic analysis of bridges with scour in their foundations. To validate the accuracy of the proposed approach, the results were compared with an integrated soil-pile-structure numerical model and with shake table test data. It was found that the simplified method could effectively estimate the bending moments of the pier and piles, as well as the acceleration response of the superstructure and pile cap. It was shown that the best input motion choice for the simplified model was to use the ground acceleration response of the free field after scouring.