Experimental Studies on Seismic Response of Skew Bridges with Seat-Type Abutments. II: Results

This paper investigates the seismic response of skewed bridges using the comprehensive data set obtained from a family of shake table experiments. To begin, the influence of friction along the abutment on the in-plane rotation of skewed bridges is evaluated. Then the influence of expansion gap size, type of ground motion (near field and far field), and input direction on seismic response is described. It is shown that once impact occurs between the bridge and abutment back wall, significant forces can be generated normal to the back wall due to impact and in the plane of the back wall through friction. These forces cause in-plane rotation of otherwise symmetrical skewed bridges. Both impact and friction should therefore be included in numerical models used to compute in-plane displacements of the superstructure. Moreover, it is shown that bridges with very small or very large gaps experience lower response. It is also shown that numerical models that do not include the gap could give nonconservative results, especially for moderate-sized gaps. Furthermore, skew bridges are more vulnerable to near-field ground motions than far-field motions. Finally, if the major component of the ground motion is applied in the transverse direction alone, comparable maximum displacements and in-plane rotations are obtained for biaxial excitations, but it produces significantly smaller impact forces than for biaxial input due to the contribution of the minor component in the longitudinal direction.