大跨度铁路悬索桥模态参数研究

Study on Modal Parameters of Long-Span Railway Suspension Bridges

以连镇铁路五峰山长江大桥等国内外典型铁路悬索桥为工程背景,开展桥梁模态参数(自振频率、振型、阻尼比)特征研究。结果表明,通过环境激励法、强迫振动法得到的铁路悬索桥自振频率和振型,与理论计算值均吻合较好;针对双塔钢桁梁铁路悬索桥,正对称横弯、竖弯基频经验公式可表达为主跨跨径的幂函数形式,扭转基频与主跨跨径为线性相关,反对称竖弯基频与公路悬索桥经验公式结果存在较大差别,且离散性较大。五峰山长江大桥采用强迫振动法得到的阻尼比大于环境激励法结果;大桥横弯与竖弯基频阻尼比大于扭转基频阻尼比,这与日本南备赞濑户大桥、大鸣门桥实测结果类似,但在阻尼比具体量值上又存在一定差别;五峰山长江大桥实测振型阻尼比表现为随自振频率增大而减小的趋势。建议在现有移动式线路动态加载车基础上,研发适应性更强的大跨度铁路桥梁模态参数测试激振设备。

Modal parameters of several representative railway suspension bridges including Wufengshan Changjiang River Bridge are studied.The results reveal that the natural frequency and mode shape obtained from ambient vibration and forced vibration correspond well with the calculated values.As for the two-pylon railway suspension bridge with truss stiffening girder,the relationship between the first-mode symmetrical transverse bending frequency and the main span length can be expressed by power function,as is the case for the first-mode vertical bending frequency.A linear function can be used for the relationship between first mode torsional frequency and the main span length.While the values of first-mode asymmetrical vertical bending frequencies of different bridges are scattered with big differences compared to the empirical formula of highway suspension bridges.The damping ratios obtained from forced vibration are larger than the results of ambient vibration.Similar to Minami Bisan-Seto Bridge and Ohnaruto Bridge,the damping ratio of Wufengshan Changjiang River Bridge in first-mode of transverse and vertical bending is larger than the value in first-mode of torsional bending.And the values of damping ratios of those three bridges differ respectively in mode.Another phenomenon is that the measured damping ratio of Wufengshan Changjiang River Bridge tends to decrease with the increase of natural frequency.It is suggested that the adaptable excitation shaker should be developed for long-span railway suspension bridge on the basis of the existing mobile dynamic loading vehicles.