Influence of pounding and skew angle on seismic response of bridges

The seismic vulnerability of skewed bridges has been known since the past few decades. Previous research has found that skewed bridges are more prone to girder unseating than a straight bridge due to the in-plane rotations of the bridge girder which were found to be aggravated by pounding between adjacent spans and abutments. A good understanding of the pounding between girder and abutments of a skewed bridge is crucial for the integrity of the bridge. Most of the past research was performed mainly numerically and without considering movable abutments. Very limited experimental work has been done, and none has incorporated movement of abutments as the surrounding ground moves during earthquakes (movable abutments), influence of girder-abutment pounding, and skew angle at the same time. This study aims to close the knowledge gap through a series of shake table tests performed on a straight bridge, 30° and 45° skewed bridge with abutments on either side of the bridge structure. Abutment movement was considered by subjecting the bridge-abutment model to uniform ground excitations. The results show that ignoring pounding effects could significantly underestimate the bending moments at the piers by up to 1.94 times and the transverse relative displacements by up to 3.43 times. The NZTA recommendation for the seat length was severely inadequate to accommodate for the large displacements of skewed bridges, especially in the transverse direction.