Effects of soil-structure interaction on longitudinal seismic response of MSSS bridges

This paper presents the results of a comprehensive study on the effect of soil-structure interaction on longitudinal seismic response of existing bridges. FHWA's guidelines for footing foundation on semi-infinite elastic half-space are used to determine translational and rotational stiffnesses at the base of bridge abutments and piers. Similarly, stiffness and strength of abutment backfill soil are determined based on FHWA's procedures. Various stiffnesses at the abutments are then lumped (condensed) into one translational spring at the point of impact between the abutment and the deck. Translational springs at the abutments are bilinear with their yield strength in compression determined based on Mononobe-Okabe method. In tension it is equal to the friction force at the footing. Among the parameters considered is the case of damaged back wall, where it is assumed that due to shear failure at the juncture of the back wall and breast wall the abutment strength and stiffness, as well as mobilized abutment mass, have changed. Results indicate that soil-structure interaction (SSI) has a significant effect on the seismic response in the longitudinal direction. Abutment strength is the most critical parameter. Impact force, deck sliding, and SSI affects all plastic rotations at the base of columns. Thus, it is important that analytical models used in seismic evaluation of bridge systems explicitly consider SSI.