沪通长江大桥主航道桥抗震设计

Seismic Design of Main Ship Channel Bridge of Hutong Changjiang River Bridge

沪通长江大桥主航道桥为主跨1 092m的双塔三索面斜拉桥,针对其"塔高、跨大、质重、弱阻尼"的结构特点进行抗震设计。采用MIDAS Civil建立该桥空间有限元模型,对4种典型的塔梁纵向约束体系(阻尼体系、一塔固定一塔活动体系、弹性索体系、半飘浮体系)进行比选,最终选取能够有效耗能的阻尼体系。分析行波效应对该桥地震响应的影响,得出考虑行波效应时桥塔的横向内力均小于一致激励下的计算结果;考虑行波效应时桥塔的纵向响应稍有增大,但满足结构抗震性能要求。阻尼参数设计时,通过假定的线性阻尼系数找到最优值,再根据能量守恒的原则确定非线性阻尼系数,最终确定非线性指数α=0.3,阻尼系数Cα=2 250kN/(m/s)0.3。抗震验算表明结构的抗震性能满足要求。

The main ship channel bridge of the Hutong Changjiang River Bridge is a cablestayed bridge with double pylons,triple cable planes and with a main span of 1 092 m.In the light of the structural characteristics that the pylons of the bridge are high,the spans are long,the mass is great and the damping is weak,the seismic design of the main ship channel bridge has been carried out.In the design,the software MIDAS Civil is used to set up the spatial finite element model for the bridge,4typical longitudinal restraint systems for the pylons and main girder（e.g.the damping system,the system of one pylon being fixed and another being movable,the elastic cable system and the semi-floating system）are compared and the damping system that can effectively dissipate the energy is finally chosen.The influences of the traveling wave effect on the seismic responses of the bridge are analyzed and the calculation results that the transverse internal forces of the pylons are all less than those under the uniform excitation when the traveling wave effect is considered are obtained.When the traveling wave effect is considered,though the longitudinal responses of the pylons increase slightly,the increased responses can meet the required structural seismic performance.When the damping parameters are designed,the optimal values can be found from the assumed linear damping coefficients.Further in accordance with the principle of the energy conservation,the nonlinear damping parameters are determined and consequently the nonlinear exponentα=0.3and the damping coefficient Cα=2 250kN/（m/s）0.3 are determined.The seismic checking calculation shows that the structural seismic performance of the bridge can meet the requirements.