桩–土–斜拉桥动力相互作用体系振动反应特性试验研究

Experimental studies on seismic response characteristics of dynamic interaction system of pile-soil-cable-stayed bridges

大跨斜拉桥结构自振频率和阻尼较低,其地震响应可能受桩基础和场地土特性的影响较大,然而目前为止,由于试验条件和技术所限,尚缺乏相关的包括桩基础、场地土和上部结构在内的全模型振动台试验研究。以一座试设计的主跨1400 m超大跨斜拉桥为原型,设计并完成了一座几何相似比为1/70,且包括群桩、人工土和上部结构在内的试验模型,采用多点振动台试验技术,研究了不同加速度峰值和不同频率成分地震作用下桩-土-斜拉桥动力相互作用体系的振动反应特性。试验结果表明:桩-土-结构相互作用对斜拉桥地震响应产生影响,其影响程度与地震输入频谱特性密切相关;在纵向一致激励下,桩-土-结构相互作用受地震动加速度峰值的影响不明显,在横向一致激励下,桩-土-结构相互作用随地震动加速度峰值的增大而减小;主塔高阶振型对其地震响应的贡献明显;地震输入频谱特性影响桩-土-斜拉桥动力相互作用体系的地震响应,特别是在具有丰富长周期成分的Mexico City波作用下主梁竖向地震响应显著增大。

The seismic response of long-span cable-stayed bridges with lower structural frequencies and damping may be significantly affected by the properties of the pile foundation and site soil. However, few experimental studies on the full model for long-span cable-stayed bridges including the pile foundation, site soil and superstructure are available because of the limitations of shaking table testing facilities and technology. A 1/70-scaled full model for a cable-stayed bridge, which includes the pile groups, artificial site soil and superstructure, is designed and constructed according to the trial designed long-span cable-stayed bridge with the main span of 1400 m. The shaking table tests on the full model are conducted to study the seismic response characteristics of the dynamic interaction system of the pile-soil-cable-stayed bridge under uniform earthquake excitations with various frequency components and shaking intensities in the separately longitudinal and transverse directions. The experimental results show that:(1) The pile-soil-structure interaction effects significantly affect the seismic response of the full model for the cable-stayed bridge, but the degree of the influence is closely related to the spectral characteristics of various earthquake waves.(2) The influences of the peak acceleration of the ground motions on the pile-soil-structure interaction effects are not significant when the full model is subjected to the uniform earthquake excitations in the longitudinal direction. However, the pile-soil-structure interaction effects gradually decrease as the peak acceleration of the ground motion increases under transverse uniform earthquake excitations.(3) The higher order mode shapes of the tower make a significant contribution to its seismic response.(4) The seismic response of the dynamic interaction system of the pile-soil-cable-stayed bridge is obviously affected by the spectral characteristics of various earthquake waves. Especially, the vertical seismic response of the girder notably increases when it is subjected to the Mexico City waves with long period components.