预应力混凝土梁自振频率的疲劳演变

为了研究预应力混凝土（PC）梁自振频率的疲劳演变规律，理论推导了抛物线型布筋的后张无黏结预应力梁疲劳历程自振频率的计算公式. 针对Euler梁、Timoshenko梁和预应力梁等3类梁，分析剪转效应、预应力效应对梁自振频率的疲劳演变规律的影响. 通过对预应力混凝土模型T梁的疲劳试验和动力测试，对比分析3类梁理论频率计算公式的适用性. 研究结果表明，抛物线型布筋的预应力不影响整个疲劳历程中梁的偶数阶频率. 梁的第1阶频率退化速率随着疲劳荷载幅值的增大而增大，随着预应力的增大而减小. 在实际工程应用中，对于偏心布筋无黏结预应力梁结构，须考虑预应力对基频的增强效应.

Fatigue evolution of natural frequency for prestressed concrete beam

The calculation formula of natural frequency during fatigue process for post tensioned unbonded prestressed beam with quadratic parabolic reinforcement was theoretically derived in order to analyze the fatigue evolution law of natural frequency for prestressed concrete (PC) beams. The effects of shear-rotation and prestress on the fatigue evolution law of natural frequency for beams were analyzed for Euler beams, Timoshenko beams and prestressed beams. The applicability of the theoretical frequency calculation formulas of three types of beams was compared and analyzed through the fatigue test and dynamic test on the prestressed concrete model T-beams. Results show that the prestress with quadratic parabolic reinforcement does not affect the even order frequencies during fatigue process of the beam. The first-order frequency degradation rate of the beam increases with the increase of fatigue load amplitude and decreases with the increase of the prestress. The strengthening effect of prestress on the fundamental frequency should be considered for the unbonded prestressed beam structure with quadratic parabolic reinforcement in practical engineering application.