Experimental Study on Uplift Behavior of the Footing of Structures during Earthquakes

本文研究了构筑物基础在上拔变形作用下的非线性行为。通过自由振动试验和振动台试验，研究了悬臂梁的上扬振动和摇摆振动的动力特性。在这些测试中，制作了一个三层的1/10比例的模型建筑和一个橡胶底座。振动台试验输入波采用频率正弦波和一些随机地震波。为了与实验响应时程进行比较，进行了数值模拟分析。通过振动试验和分析，得出以下结论：对于自由振动，该系统的周期和阻尼因子收敛到第二个或第三个周期。采用振幅为50 gal或200 gal的平稳正弦波作为输入激励，绘制谐振曲线。当输入量为200加仑时，隆升变形的增长幅度远大于输入量为50加仑时。这种变形在低频和高频范围内尤为明显。随机振动试验采用El Centro (1940) N-S分量或Touhoku Univ (1978) N-S分量。当最大加速度为100 gal时，响应性能呈线性。在300加仑的情况下，发生了隆升变形，非线性特征明显。自由振动实验结果与数值模拟结果吻合较好。该仿真采用碰撞冲击降速系数作为计算参数。

This study deals with nonlinear behavior of the footing of structures concerning uplift deformation. To investigate the dynamic behavior of the uplift and rocking vibration, free vibration tests and shaking table tests were conducted. In these tests, a three stories model building with 1/10 scale and a rubber base were manufactured. As to input waves of these shaking table tests, frequency sinusoidal waves and some random earthquake waves were used. In order to compare with the time histories of experimental response, it was carried out numerical simulation analysis. The following conclusions were obtained by the shaking tests and the analyses.1. For the free vibration, the period and the damping factor of this system were converged until the second or the third cycle.2. Employing the input excitation of stationary sinusoidal waves having the amplitude of 50 gal or 200 gal, it was made resonance curve. For 200 gal input, uplift deformation was grown up fairly more than for 50 gal inplkt. This deformation was especially grown up at the low and the high frequency ranges.3. El Centro (1940) N-S component or Touhoku Univ. (1978) N-S component were used for the random vibration test. As the maximum acceleration was 100 gal, the response performance was linear property. At the case of 300 gal, the uplift deformation was occurred and nonlinear property was clearly observed.4. The experimental results of the free vibration agreed well with the numerical simulation results. That simulation was employing velocity reducing coefficient of collision impact as a calculation parameter.