近断层斜拉桥弹塑性索与阻尼器组合横向减震

研究了近断层地震条件下,使用弹塑性减震索和黏滞阻尼器组合体系进行横向减震的斜拉桥的地震响应和减震规律.采用等效脉冲模型对实际近断层地震进行最小二乘拟合.人工合成Ⅱ类场地下的模拟近断层地震波3组,以永宁黄河大桥为工程背景,对人工近断层地震输入进行非线性时程分析,得到在不同脉冲周期的近断层地震作用下,减震措施设计参数对于塔梁相对位移等响应的影响.结果表明,拟合近断层地震下结构响应与实际地震相差较小,可以满足工程计算需求;近断层地震易造成大位移响应,弹塑性索参数设计时应使结构周期避开脉冲周期;容许减震索进入塑性与保持弹性相比,塔梁相对位移并不会明显增加,甚至在一些情况下会减小.

Responses of Cable Stayed Bridge Transversely Isolated with Elasto Plastic Cable Pairs and Fluid Viscous Damper Subjected to Near Fault Ground Motions

The response feature of cable stayed bridge with elastoplastic cable pairs and viscous damper adopted in lateral pylon seismic isolation design under near fault ground motions was investigated. Real near fault ground motions were simulated using the equivalent near fault pulse model, and the three sets of synthetic seismic waves with various pulse periods corresponding to II site condition are synthesized. Based on Yongning Yellow River Bridge, nonlinear time history analysis was performed under the synthetic near fault ground motions, and the effects of variation of design parameters of isolation device on the seismic response of the bridge in terms of relative girder pylon displacement were studied. The results show that the responses under synthetic ground motions are comparable to those records with the same pulse characteristics, which can satisfy the need of engineering practice. Near fault ground motions are likely to cause large displacement response. Therefore, it is strongly recommended that the natural period of the structure should be set apart from the pulse period by properly determining the design parameter of the elastoplastic cables. Allowing certain inelastic behavior of cables does not lead to the increase, sometimes even a decrease, of relative girder pylon displacement response when compared with a hypothetic case where the cables behave elastically all along.