基于基频法的预应力混凝土箱梁疲劳刚度退化试验

开展了基于基频法的预应力混凝土箱梁桥模型疲劳试验; 详细介绍了基于基频法的疲劳多级变幅试验加载过程及疲劳加载方案和采集方案; 梳理了动刚度和静刚度的基本原理、基于基频的动刚度计算方法和基于挠度的静刚度计算方法; 对预应力混凝土箱梁的疲劳动刚度和静刚度退化规律进行了研究。结果表明:箱梁构件疲劳裂缝分布、裂缝走向和破坏敏感位置与矩形梁不同,模型梁均首先在腹板产生斜裂缝,腹板斜裂缝主要分布在从支座到1/4跨范围内,不断向顶板和底板斜向延伸; 预应力混凝土箱梁疲劳动刚度和静刚度二者退化规律相同,均呈现为先快速、后平稳的2阶段变化规律; 在疲劳初期,动刚度和静刚度退化率均在40%以上; 疲劳荷载上限值是桥梁结构疲劳刚度退化的一个重要影响因素,疲劳荷载上限值越大,动刚度和静刚度退化幅值就越大,且疲劳剩余刚度越小; 因为二者计算原理不同,所以计算的动静刚度数值也不同,但二者刚度退化规律相同,可相互对比、补充、验证,共同来探究预应力混凝土箱梁疲劳刚度的退化规律。

Experiment on Fatigue Stiffness Degradation of Pre-stressed Concrete Box Girder Based on Fundamental Frequency Method

The model fatigue test of pre-stressed concrete box girder bridge based on the fundamental frequency method was carried out. The loading process of fatigue multi-stage variable amplitude test based on the basic frequency method, as well as the fatigue loading scheme and collection scheme were introduced in detail. The basic principle of dynamic stiffness and static stiffness, the calculation method of dynamic stiffness based on the basic frequency and the calculation method of static stiffness based on deflection were combed. The degradation law of fatigue dynamic stiffness and static stiffness of pre-stressed concrete box girder was studied. The results show that the trend and sensitive position of fatigue crack of box girder are different from those of rectangle girder. The oblique crack of web is mainly distributed in the range from support to 1/4 span, extending to roof and floor. The degradation laws of fatigue labor stiffness and static stiffness of pre-stressed concrete box girder are the same, both of them are fast first and then stable. In the early stage of fatigue, the degradation rate of dynamic stiffness and static stiffness is more than 40%. The upper limit value of fatigue is an important factor of fatigue stiffness degradation of bridge structure, the higher the upper limit value of fatigue, the greater the degradation amplitude of dynamic stiffness and static stiffness, the less residual stiffness. Because of their different calculation principles, the calculated dynamic and static stiffness values are also different, but their stiffness degradation laws are the same, which can be compared, supplemented and verified with each other to explore the degradation laws of fatigue stiffness of pre-stressed concrete box girder.