黏滞性阻尼器对千米级斜拉桥纵向减震效果的振动台试验研究

为了研究千米级斜拉桥纵向采用黏滞性阻尼器的减震效果，以一座主跨1 088 m的斜拉桥为工程背景，按相似理论设计制作了一座几何缩尺比为1：35的全桥振动台试验模型，通过改变塔梁间的连接方式，建立了塔梁间纵向无约束的非减震体系和塔梁间纵向采用黏滞性阻尼器的减震体系，选用4条具有代表性的地震动进行了4个振动台纵向一致激励的全桥振动台试验，然后将不同地震动输入下2种体系的试验结果进行对比分析。试验结果表明：千米级斜拉桥纵向无约束体系的地震响应受输入地震动的特性影响较大，对于长周期成分丰富，特别是对应于结构一阶周期的加速度谱和位移谱谱值较大的地震动，结构的地震响应较大；千米级斜拉桥非减震体系的地震响应同样也受输入地震动特性的影响较大；纵向采用黏滞性阻尼器的减震体系可以减小结构的梁端位移、塔顶位移以及塔底钢筋应变，但输入地震动的特性会影响黏滞性阻尼器的减震效果，对于特征周期较长、长周期成分丰富的地震动，黏滞性阻尼器的减震效果较好，而对于有明显速度脉冲的地震动，黏滞性阻尼器的减震效果相对较差，当地震动峰值加速度PGA为0.4g时，在场地人工地震动、Loma Prieta地震动作用下，梁端最大位移分别减小了62.41%、37.75%；对于有明显速度脉冲的地震动，需要选择阻尼系数更大的黏滞性阻尼器。

Shake Table Studies of the Longitudinal Seismic Mitigation Effect of Viscous Dampers on a Kilometer-scale Cable-stayed Bridge

To investigate the effectiveness of viscous dampers in reducing the longitudinal seismic response of a kilometer-scale cable-stayed bridge, a cable-stayed bridge with a center span of 1 088 m was selected as a bridge prototype, and a 1/35-scale bridge model was designed based on experimental similarity theory. Through the use of different tower-girder connections, two types of longitudinal structural systems were considered:a longitudinal floating system and a seismic mitigation system with viscous dampers. Four representative earthquake motions were input as uniform excitations in the longitudinal direction by four shake tables. The test results of the two structural systems were then compared and analyzed. The results show that the seismic response of a kilometer-scale cable-stayed bridge with a longitudinal floating system is significantly influenced by the characteristics of earthquake motions. A large seismic response of the structure is observed when the earthquake motion has abundant long-period components, particularly when the values corresponding to the structural fundamental period in both the acceleration and displacement spectra of the earthquake motion are large. The seismic response of a kilometer-scale cable-stayed bridge with a seismic mitigation system is also influenced by the characteristics of earthquake motions. The longitudinal seismic mitigation system with viscous dampers can reduce the displacements at both the end of the girder and the top of the tower. It can also reduce the rebar strains at the bottom of the tower. However, the viscous dampers are affected by the characteristics of earthquake motions. The seismic performance of viscous dampers is high if the earthquake motion has a relatively long characteristic period and abundant long-period components. However, viscous dampers may not work effectively when the earthquake motion has apparent velocity pulses. When the peak ground acceleration of the input earthquakes is 0.4g, the displacements at the end of the girder are reduced by 62.41% and 37.75% under the actions of artificial and Loma Prieta earthquake motions, respectively. For earthquake motions with apparent velocity pulses, it is suggested that viscous dampers shall have a large damping coefficient.