黏性剪切阻尼器性能频率依存性对斜拉索多模态阻尼影响研究

Theoretical and experimental studies on multimode cable damping effects provided by a viscous-shear damper with frequency-dependent properties

斜拉索振动是危害缆索桥梁安全性和适用性的一个工程难题,实际中常采用附加阻尼器的方法实现减振。在拉索-阻尼器系统分析中,多将阻尼器系数考虑为常数;现有理论和试验表明,阻尼器动力特性包括刚度和阻尼系数存在明显的频率依存性,相关研究尚缺乏。并且,拉索随着长度的增大,基频降低,分析和设计中更需要考虑索的多模态(多频率)阻尼。因此,研究索阻尼器性能的频率依存性对索多模态阻尼效果的影响。研究选取工程中广泛应用的黏性剪切阻尼器(viscous shear damper,VSD)。首先,开展阻尼器单体试验研究,结果表明在固定位移幅值情况下,随着振动频率的增大,阻尼器的阻尼系数变小而刚度系数增大,系数与频率之间近似呈现指数函数的关系;进一步,采用小垂度拉索附加带刚度阻尼器模型,分析索-阻尼器系统的动力特性,讨论阻尼器性能频率依存性对索多模态阻尼效果的影响;最后,通过实索动力测试得到阻尼器对索多阶模态阻尼效果,与理论分析结果吻合。试验结果表明,实际阻尼器的设计需要考虑阻尼器性能的频率依存性,结合阻尼器单体试验和索-阻尼器系统理论分析是一种精确和实用的方法。

Traditionally,the damper coefficients of the cable damper system installed in cable supported bridges are regularly considered to be constant in analyses.However,existing theories and experiments show that dampers can behave differently when under forced displacements with varying frequency,which has not been investigated thoroughly for cable vibration control.Furthermore,for long cables,vibration control has to consider a number of cable modes,meaning that the damper performance in a wide range of frequency is of interest.In the study,the frequency-dependent properties of cable dampers and their effects on multimode cable damping were investigated.A widely used viscous-shear damper(VSD)was chosen for study.The VSD was manufactured and tested in laboratory under sinusoidal displacement excitation at different frequencies.It is found that when the amplitude of the displacement is fixed,along with the frequency,the stiffness of the damper increases,while the damping coefficient of the damper decreases.The relations between the damper properties and the frequency can be described as exponential functions.Then the dynamic properties of a shallow cable attached with a damper with intrinsic stiffness were analysed.Finally,the manufactured damper was attached to a real cable for field testing.The measured damping ratios are found to be consistent with theoretical prediction results considering the frequency-dependent cable properties.The study demonstrates the importance of taking the frequency-dependent damper properties into account in cable damper design.The method based on the laboratory testing of the damper and complex modal analysis of the cable-damper system is accurate and feasible for practical design.