钢筋混凝土梁的非线性振动识别研究

通过理论推导和钢筋混凝土简支梁的锤击振动测试实验,证实了钢筋混凝土梁微幅弯曲自由振动存在弱的非线性,且近似为二次非线性,其振动频率随着振幅的减小而加大。利用小波变换时频分析的特点,用Morlet复小波函数对钢筋混凝土梁的自由振动响应进行小波变换,通过脊线所对应的尺度得到瞬时振动频率,通过脊线上的小波系数计算出瞬时振幅。由系统的瞬时频率和瞬时振幅与时间的关系以及它们之间的相互关系,由曲线拟合得到系统的固有频率、阻尼系数和非线性系数。通过实验发现梁的固有频率随着损伤的增大而减小,非线性系数随着损伤的增大而增大。

IDENTIFICATION OF THE NONLINEAR VIBRATION CHARACTERISTICS OF REINFORCED CONCRETE BEAMS

The work presented here investigates the nonlinear vibration characteristics of reinforced concrete beams. It is verified that free small-amplitude bending vibration of reinforced concrete beams contains weak square nonlinear terms by theory deduction and experiment. The instantaneous frequencies decay with amplitudes The wavelet transform is used as a time-frequency representation for system identification. A series of impact-excited vibration tests on a reinforced concrete beam under different damage degree had been conducted. The impulse response of the concrete beam is transformed by Morlet wavelet and the instantaneous characteristics are obtained by the ridges of the wavelet coefficients. The nonlinearities are detected by examining the changes of the frequencies during vibration. The inherence frequency, damping ratios and nonlinear parameter of the system are identified by compound wavelet transform. The tests also demonstrate that the inherence frequency decreases while the nordinear parameter increases with damage.