Seismic Response Analysis Of Continuous Skew Girder Bridges

The complexity of seismic response for skew bridge rises higher seismic-vulnerability relatively in comparison with right bridge. However, there have been no regulations to follow on seismic design of skew bridge at home and abroad for decades. It is necessary to lucubrate the seismic response of skew bridge under strong earthquake so as to provide a theoretical basis for etablishing a reasonable seismic design method for skew bridge.In this paper, the state-of-the-art of earthquake resistance study on skew bridges is reviewed firstly. Then, through the establishment of numerical analytical models of continuous skew girder bridges, the vibration features, displacement of bridge girder and internal force at the bottom of pier, as well as the critical seismic imput angles for skew bridges have been investigated. Main contents and conclusions of seismic studies include:1. Modal analysis is employed to reveal seismic performance of skew bridge under multi-modal spatial coupling dynamic effect. Effect on natural period of vibration, modal shape and modal mass participation factor resulted in skew angle and bearing shear stiffness is obtained. The main vibration modes have shown coupling vibration characteristics interacted by vibrations in longitudinal, transversal directions and rotation around vertical direction. And the larger the skew angle and bearing shear stiffness are, the more obviously the characteristics are.2. Nonlinear time history analyses are employed with two horizontal ground motions in orthogonal directions. Effect on seismic responses from skew angle has been investigated:1) Effect on horizontal displacement of bridge girder and internal force at the bottom of pier from skew angle are obtained. However, there is no rotational displacement observed for skew bridges. Spatial coupling effect of moment and shear at the bottom of pier is found and the effect gets more and more obviously as skew angle increases. Pier yields first at the bottom aears where have been deemed as plastic hinges of the mid span when compares to that of the edge-span. And the distributive trend of plastic hinge is from the pier of the mid span to that of the edge-span.2) It is of importance to point out that large rotational displacement of bridge girder, as well as torque magnified several times at the bottom of pier are obtained for skew bridges when considering impact effect relatively in comparison with seismic responses without considering impact effect. In addition, these two seismic responses increase, not sharply, as skew angle increases.3. The relationships between seismic responses of continuous skew girder bridges and imput angles of ground motions were investigated through nonlinear time history analysises under two horizontal angle-varied ground motions in orthogonal directions. The critical seismic imput angles and a simple method for critical seismic responses were preliminarily provided.This paper can provide a reference for the study of the continuous skew girder bridge's seismic theory and design methods in order to improve its seismic performance.