近场竖向地震激励下桥梁支座对竖向碰撞的影响

EFFECT OF BRIDGE BEARINGS ON VERTICAL POUNDING IN BRIDGES UNDER NEAR-FAULT VERTICAL EARTHQUAKES

考虑桥梁支座的作用,针对两跨连续梁桥的竖向碰撞问题,建立了梁-弹簧-杆连续体模型。采用瞬态波特征函数展开法和组合体瞬态内力法,推导了多次竖向碰撞问题的理论解,分析了桥梁支座对竖向碰撞的影响。研究结果表明:桥梁支座直接影响桥面与桥墩的局部碰撞接触刚度,显著影响竖向碰撞响应,包括碰撞次数、竖向碰撞力和碰撞位移响应等。桥梁支座对竖向碰撞具有显著的吸能减震效果,且影响竖向碰撞响应的基本特征,如次碰撞出现的频次和响应的频率。当近场竖向地震激励周期逼近桥梁的固有振动周期时,桥面上抛跳起,与桥梁支座产生剧烈竖向碰撞。由于调节桥梁支座的刚度可以改变桥梁的固有振动周期,因此,合理设计桥梁支座对于降低竖向碰撞的破坏作用,提高桥梁结构抵抗竖向地震的能力,具有重要的价值。

A beam-spring-rod continuous body model was used to simulate vertical pounding in a two-span continuous beam bridge with bearings. The theoretical solutions for multiple vertical poundings were obtained by expanding the transient wave functions in a series of eigenfunctions and using the transient internal force method with the contact interfacial force of combined body, and the effect of bridge bearings on vertical pounding was then investigated. The research results show that the vertical pounding responses including the number of impacts,pounding force and displacements are greatly influenced by the local contact rigidity of the deck and piers, which varies with the rigidity of the bridge bearings. Vertical pounding energy can be absorbed by the bridge bearings and the basic characteristics of vertical pounding can be changed as well, such as sub-pounding frequency and displacement response frequency. As the vertical earthquake period approaches the natural vibration period of bridge, the deck jumps and intense vertical pounding will take place between deck and bearing. Because the rigidity of the bridge bearings can be adjusted to change the natural period of the bridge, it is worthwhile to consider their effects on reducing the destructive effects of vertical poundings and improving of the bridge ability to resist vertical earthquakes when designing the bridge bearings.