梁结构疲劳刚度退化对模态频率的影响

为了研究梁结构疲劳刚度退化对模态频率的影响，对预应力混凝土梁进行疲劳试验和动力测试，得到疲劳历程中疲劳刚度和模态频率的演化规律. 建立疲劳全过程变刚度有限元修正模型，并对其进行模态分析. 比较分析试验和模拟结果，讨论模态频率退化规律及疲劳刚度退化对其影响机制. 研究结果表明，梁结构模态频率具有类似抗弯刚度退化的三阶段衰减规律，表明疲劳刚度与模态频率退化存在映射关系；在疲劳作用下，第1阶频率的下降幅度最大，第2阶频率次之，第3阶频率的下降幅度最小；提出的变刚度假设在有限元模拟中运用良好，模拟结果显示第1阶频率模拟值的偏差基本在10%以内. 提出的疲劳全过程动力特性分析方法为梁结构疲劳分析研究提供了新思路.

Influence of fatigue stiffness degradation for beam structure on modal frequency

The fatigue experiment and dynamic test were carried out on the prestressed concrete beam, and the evolution laws of fatigue stiffness and modal frequency during the whole fatigue process were obtained, in order to study the influence of fatigue stiffness degradation for beam structure on the modal frequency. A variable stiffness finite element correction model for the whole fatigue process was established and its modal analysis was carried out. The modal frequency degradation law and the influence mechanism on modal frequency by the fatigue stiffness degradation were discussed, by comparing and analyzing the experiment and simulation results. Results showed that the modal frequency of beam structure had a three-stage attenuation law which was similar to the degradation of bending stiffness, and it indicated that there was a mapping relationship between fatigue stiffness and modal frequency degradation. The first-order frequency had the largest decrease, the second-order frequency was the second, and the third-order frequency had the smallest decrease under the action of fatigue. The proposed variable stiffness assumption was well used in the finite element simulation and the simulation results showed that the deviation of the first-order frequency simulation value was basically within 10%. The proposed full-process dynamic characteristics analysis method provides a new idea for the fatigue analysis of beam structure.