Seismic Analysis of Integral Abutment Bridge in Tennessee, 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 focus on the effects of two major parameters on the seismic behavior of an integral abutment bridge in Tennessee. The soil structure interaction around the piles and in back of the abutments is considered, namely, clay stiffness (medium versus hard) around the piles and level of compaction (loose versus dense) of the abutment wall backfilling. Modal and nonlinear time-history analyses were performed on a three-dimensional detailed bridge model with the commercial software SAP2000. These analyses clearly showed that (a) compacting the backfilling of the abutment wall will increase the dominant bridge longitudinal natural frequency considerably more than increasing the foundation clay stiffness; (b) the maximum deflection and bending moment in the piles under seismic loading will occur at the pile abutment interface; (c) under seismic loading, densely compacted backfilling of the abutment wall is generally recommended because it will reduce the pile moments considerably, the pile deflection, the abutment displacement, and the moments in the steel girder, except for girder moments at the abutments when the piles are in medium clay; and (d) under seismic loading, when the abutment backfilling is loosely compacted, steel girder moments at the abutments will increase considerably with the foundation clay stiffness.