基于振型动能法的大跨度斜拉桥振型分析和模态识别

Mode Shape Analysis and Identification of Long-span Cable-stayed Bridge Based on the Method of Computing the Proportion of Kinetic Energy in Each Mode Shape

针对拉索的自身振型以及与塔梁相互间的模态耦合作用被人为忽略和单凭振型图难以识别出主梁的主振型两大问题,采用多段索单元模拟拉索以便能准确地计算结构模型。通过动力计算分析振型参与的动能比例,实现了振型识别功能,得出斜拉桥的自振频率和振型。分析结果表明:斜拉桥的自振特性表现出明显的三维性和相互耦合的特点,主梁、桥塔、斜拉索之间相互影响;在一个较宽的频率范围内,许多振型都可能被动力荷载激起强烈的振动;为识别出主梁振动为主的振型和主振型方向分析振型参与的动能比例,应采用10阶以上的振型情况分析,为动力测试提供理论数据。

Aiming at two problems that the coupling action of the cable with tower and girder is neglected and the mode shape of girder are difficult to be identified only from the mode shape curve, the multi-cable element was adopted to simulate the cable in order to calculate the dynamic characteristics more exactly. By analyzing the proportion of kinetic energy in each mode shape, the mode shape was identified, the natural vibration frequencies and mode shape of the cable-stayed bridge were obtained. The result enunciates that （ 1 ） the dynamic characteristics of cable-stayed bridge are three-dimensional and coupled with each other; （2） many mode shapes can be triggered by dynamic loads in a wide frequency range; （3） in order to recognize the mode shape of girder and the proportion of kinetic energy in each mode shape, tenth and above order mode shapes must be used to provide the calculation data for the dynamic test.