基于连续梁振动分析的桥梁冲击系数研究

Study of the impact factor based on the dynamic analysis of the continuous beam

分析计算了2～4跨等截面等跨径连续梁的固有频率和振型,进行了两等跨等截面连续梁振动试验。通过分析和试验,确定梁的前几阶振型最大曲率位置,考虑梁在均布荷载作用下最大正弯矩及最大负弯矩的位置,结合《公路桥涵设计通用规范》讨论计算桥梁冲击系数时结构固有频率的选取。结果表明,计算连续梁桥的冲击力引起正弯矩效应时,应按《桥规》采用基频,计算负弯矩效应时,不应采用基频,应采用二或三阶频率,具体情况应结合振型考虑。

The natural frequencies and mode shapes of 2,3 and 4 spans continuous beam with universal cross section are calculated, and these dynamic parameters of 2 spans continuous beam model are measured. From the analysis and the model test, the locations of the maximum curvatures of the mode shapes are determined, and comparing that with the maximum bending moment of the beam under the action of uniformly distributed load,the selection of the natural frequency of the beam is discussed with the General Code for Design of Highway Bridges and Culverts as the impact factors of the beam is calculated. It is shown from the results of the analysis and the test that, for the impact factor, when the effect of positive bending moment caused by impact force is calculated, the fundamental frequency must be used as shown in the General Code,and the 2 or 3 frequency must be used when the effect of negative bending moment caused by impact force is calculated. The selection of the frequency should be combined with the mode shape into account for the specific circumstances.