Different Input Direction Based The Critical Response Of Skew Bridges To Earthquake Excitation

ABSTRACT:Due to the randomicity and complexity of seismic motion, it is difficult to determine the seismic input direction accurately when calculating seismic response. The plane irregularly of skew bridge leads to bending-torsion coupling, it’s harder to determine the critical seismic input angles. Therefore, it is meaningful to lucubrate the seismic response of skew bridge under multi-directional earthquake and present simplified calculation theory of the seismic reaction of the skew bridge, so as to make sure the safety of skew bridge in earthquake.In this paper, the critical seismic response studies on skew bridges are summarized firstly. Then, through the establishment of30numerical analytical models of continuous skew girder bridges with different span, skew angle and collision situation, the critical seismic response of skew bridges have been investigated. Main contents and conclusions of seismic studies include:1.The relationships between seismic responses of different characteristics of continuous skew bridges with input angles of ground motions were investigated through multi-directional nonlinear time history analysises under two horizontal angle-varied ground motions in orthogonal directions:the input angle of ground motions have a big influence on seismic displacements at the top of pier and seismic reactions at the bottom of pier, some seismic responses change as sine or cosine curve approximately with the increase of the input angle, and the changing rules of transverse or longitudinal responses are opposite. The seismic responses from conventional directional nonlinear time history analysises are different from the theoretical calculation results, it may greatly underestimate some responses of the skew bridge.2. Seismic response spectrum analysis of combination methods are used to calculate critical seismic response of skew bridge, which are proposed by relevant specification, including100/30,100/40and SRSS combination rules. The probability of underestimation is used to estimate the accuracy of each combination rule. Combined with the results of multi-directional nonlinear time history analysises, putting forward a simple method for critical seismic responses.3. Based on the theory of elastic-plastic static analysis method, compositing the two perpendicular Pushover results to get the multi-directional capacity spectrum curves, then draw them in the same coordinate axis with the reduced demand spectrum curve to simulate multi-directional Pushover analysis. Analyzed the demand-capacity relationships of multi-directional Pushover analysis.