考虑双向地震作用的无柱地铁车站振动台试验研究

Shaking table tests of column-free subway stations considering bidirectional earthquake actions

国内地铁车站一般采用有柱形式,目前尚无针对无柱地铁车站,考虑水平以及竖向地震作用下的抗震性能研究。以南宁地铁五号线金桥无柱地铁客运站为研究对象,开展多种工况下考虑土–结构相互作用以及水平和竖向地震作用下,无柱大跨地铁车站模型的地震振动台模拟试验,研究该类车站模型结构和周围土体地震响应的一般规律。试验结果表明:(1)模型地基加速度响应随着地震动幅值的增加而增大;在地基深处地震动主要以竖向Z方向加速度分量为主,在土层表面,则以横向X方向加速度分量起主导作用。(2)随着地震动幅值的增加,结构的基本频率呈现逐渐下降的趋势;在水平地震动作用下,水平方向测点加速度反应傅里叶谱在20~40 Hz高频成分逐渐增大,而低频成分逐渐被滤掉。(3)竖向地震动作用下无柱地铁模型结构中板变形较大,且双向地震作用下模型结构的加速度峰值均大于单向地震。(4)当地震动作用较大时,土与结构相互作用剧烈,底板与土体出现了脱离现象,模型结构底部的土压力出现了降低趋势。(5)在大震作用下,模型结构的破坏主要集中于顶板与侧墙交接处,且沿着加载方向出现了细微裂缝,车站顶板与侧墙连接处以及中板为该类车站结构薄弱位置,在设计中应对这些部位进行加强处理。(6)无柱地铁车站的中板应力增幅受双向地震作用下的影响较大,在加速度峰值为0.484 g的EL Centro波作用下,中板处的应力峰值为单向地震作用下的2.5倍左右;而加速度峰值可为单向地震作用下的1.4~1.5倍,故双向地震作用对无柱地铁车站的影响不可忽视。

Due to that domestic subway stations are generally constructed with columns,there are rarely studies on the seismic performance of column-free stations under bidirectional earthquake actions. Taking a column-free subway station as the objective,large-scale simulation shaking table test of a long-span column-free subway station under different loading conditions was carried out considering soil-structure interaction and bidirectional earthquake actions to investigate dynamic responses of the station structure and the surrounding soil. The results show that the acceleration response of the model foundation increases with increasing the magnitude of the ground motion, and that the acceleration components in vertical and horizontal directions respectively play a leading role in the depth of the foundation and on the surface of the soil layer. As the magnitude of the ground motion increases,the fundamental frequency of the structure gradually decreases. Under the action of the horizontal ground motion,the 20-40 Hz high-frequency component of the Fourier spectrum of the acceleration response in the horizontal direction at the measuring points gradually increases and the low-frequency component is gradually filtered. The deformation of the middle plate of the model structure is large under the vertical earthquake action. The peak acceleration of the model structure under the bidirectional earthquake actions is greater than that under the unidirectional earthquake action. When the earthquake action is large,the soil and the structure interact violently,the bottom plate and the soil are separated and the earth pressure at the bottom of the model structure decreases. Under the action of earthquakes,the damage of the model structure is mainly concentrated at the junction of the roof and the side wall where slight cracks occur along the loading direction, indicating that the connection between the roof and the side wall of the column-free subway station and the middle plate are structurally weak locations and should be strengthened. Under the action of EL Centro wave with a peak acceleration of 0.484 g,the peak stress and the peak acceleration at the middle plate are respectively about 2.5 and 1.4–1.5 times of those under the unidirectional seismic action,so the influence of bidirectional seismic actions on the column-free subway station cannot be ignored.