地震作用下双薄壁高墩刚构桥桥台处的碰撞效应及减碰措施

针对双薄臂高墩连续刚构桥两侧桥台处主梁与背墙的碰撞现象,基于桥台-背土作用简化模型和Kelvin碰撞模型,采用非线性时程法研究碰撞对双薄臂墩地震剪力、弯矩、曲率和位移,以及支座纵向变形的影响。提出可牺牲背墙、阻尼器、加强型横系梁等三种减碰措施,并对比分析其减碰效果。研究表明:碰撞会显著增大高墩的地震内力和曲率响应,降低墩顶位移和支座的纵向变形;碰撞刚度的变化对碰撞效应的影响在20%以内;可牺牲背墙和阻尼器两种减碰措施均可大幅降低桥墩的地震内力和曲率,使其接近不考虑碰撞时的状态,阻尼器同时还可以保护支座不超过容许变形,而可牺牲背墙则会导致支座的地震破坏;加强型横系梁不能发挥减碰作用,反而会增大桥墩的地震响应。

Analysis of the Pounding Effects and Countermeasures at the Abutments of a Rigid-frame Bridge with High, Double Thin-walled Piers During Earthquakes

The pounding between the abutment and superstructure has a significant influence on the seismic response of bridges during major earthquakes, especially in the case of flexible bridge systems, such as the continuous rigid-frame bridges with high, double thin-walled piers. Compared with the pounding effect between superstructures, the aforementioned pounding phenomenon is far more complicated because of the abutment-backfill interaction. In this paper, the pounding effect on the seismic behavior of high thin-walled piers was specifically examined. A simplified analytical model of abutment-backfill interaction was proposed, and the Kelvin impact model was applied to formulate the pounding between the abutment and superstructure. By using the nonlinear time history method, the effects of pounding on the seismic shear force, moment, curvature and displacement responses of high thin-walled piers were investigated, along with the longitudinal deformation of the pot bearings. Three countermeasures, which were elaborated as sacrificial back-wall, viscous damper and strengthened link beams, were suggested for reducing the pounding effect. The efficiencies of the three countermeasures were also compared in detail. The results showed that the pounding significantly increases the seismic force and curvature responses of high piers; the pounding also decreases the top displacement and results in the longitudinal deformation of pot bearings. The variation of impact stiffness has an influence of less than 20% on the seismic response of the bridge structure. Using the sacrificial back-wall and the viscous damper as countermeasures, the seismic force and curvature responses of high piers can be reduced sharply to magnitudes that are close to those obtained without considering the pounding effect. The viscous damper can also protect the pot bearings from exceeding the deformation limits, whereas the sacrificial back-wall tends to damage the pot bearings. The application of strengthened link beam as a countermeasure is proved to be ineffective in mitigating the pounding effect; on the contrary, it can actually increase the seismic response of high piers.