Seismic response of bridge abutments on surface foundation subjected to collision forces

Abstract

Bridges are important components of the roadway and railway networks, as they must remain operational in the aftermath of the seismic event. Permanent movements of the backwall and the backfill soil and rotational deformations of the abutment-backfill system are well known failure modes that potentially may incite deck unseating mechanisms. However, only a few studies dealt with the modeling of deck-abutment-backfill pounding effect. In this framework, an extended parametric study was conducted on a simplified abutment-backfill analytical model. A typical seat-type abutment was analyzed using 2D nonlinear FE model in Plaxis. Simultaneously, a refined abutment-backfill model was built in commercial software SAP2000 in view to highlight significant parameters of the interaction aiming at identifying the effect of collisions on anticipated damages of the abutment. The assessment of the deckabutment-backfill response was performed on the basis of longitudinal maximum and residual movements and rotations of the abutment that may affect both the integrity and the postearthquake accessibility of the bridge. SSI effects due to the interaction of the deck with the abutment and the backfill soil were considered; analyses showed that large seismic movements during an earthquake and permanent movements of the abutment are deemed to put in danger the abutment itself, the integrity of the end spans and finally the accessibility of the bridge. Comparison of different seat-type abutment models in Plaxis and SAP2000 revealed that modeling of bridge abutments with emphasis on the geotechnical design should be properly made. Poor design assumptions may have a serious impact in the assessment of the response of the abutment-backfill-bridge system.