Seismic displacement analysis of free-standing highway bridge abutments

Seismic displacements of two typical highway bridge abutments used in Taiwan are examined based on the input ground accelerations suggested by both new and old aseismic design codes. A pseudo-static-based multi-wedge method is used in conjunction with Newmark's sliding block theory to evaluate seismic displacement of these bridge abutments. It was found that (1) the design peak ground acceleration specified in the new code are significantly greater than those used in the old code for some near-fault areas in Taiwan; (2) for the gravity-type bridge abutment, the seismic displacement under both level 2 and level 3 design earthquakes are beyond the permissible displacement suggested in the literature, indicating the vulnerability of the gravitytype bridge abutments to medium-large earthquakes; (3) A vertical-to-horizontal ground acceleration ratio, λ = 0.67 used in the new code gives slightly conservative seismic displacement evaluations compared to those calculated using λ = 0.25 measured at near-fault seismographs; (4) the passive resistance in front of the gravity-type bridge abutment may significantly reduce the seismic displacement of the abutment. Regular integrity inspections for passive zone or pre-earthquake reinforcement program is suggested for the gravity-type abutments to avoid excessive horizontal seismic displacements.