Seismic Analysis of Integral Abutment Bridges Including Soil-Structure Interaction

Integral abutment bridges are jointless bridges in which the deck is continuous and connected monolithically with the abutment walls supported typically by a single row of piles. Part of the research results from an ongoing project is presented in this paper, which focuses on the effects of two major parameters on the seismic behavior of an integral abutment bridge in Tennessee by considering soil-structure interaction around the piles and in back of the abutments: (1) clay stiffness (medium vs. hard) around the piles, and (2) level of compaction (loose vs. dense) of the abutment wall backfilling. Modal and nonlinear time history analyses were performed on a three dimensional detailed bridge model using the commercial software SAP2000, which clearly showed that (1) compacting the backfilling of the abutment wall will increase the bridge dominant longitudinal natural frequency considerably more than increasing the clay stiffness around the piles; (2) the maximum deflection and bending moment in the piles under seismic loading will happen at the pile-abutment interface; (3) under seismic loading, densely-compacted backfilling of the abutment wall is generally recommended since it will reduce the pile deflection, the abutment displacement, the moments in the steel girder, and particularly the pile moments; (4) under seismic loading, when the piles are located in firmer clay, although the pile deflection, the abutment displacement, and the maximum girder moment at the pier and the mid-span will decrease, the maximum pile moment and the maximum girder moment at the abutment will increase.