不同跨径比的两跨连续梁的模态分析试验

摘要

Influence of the span ratio of a two-unequal-span continuous beam on vibration mode is introduced, and the option of impact factor values is discussed. Using a channel-shaped continuous beam as the model, the finite element analysis code of Midas and the equipment of DASP are respectively employed for modal analysis, and the first three modals and frequencies of the continuous beam with different span ratios are obtained. Results of the analyses are compared with those of testing, and the vibration mode change is confirmed. The results demonstrate that (1) with the decreasing of the span ratio, the turning points of the 2nd and 3rd order modals may appear and the curvature of the vibration mode at the mid support will change greatly;(2) when the effect of positive bending moment at the mid-point of the span is considered, the impact factor should be calculated according to the fundamental frequencies shown in the standard of bridge construction;(3) when the effect of negative bending moment at the mid-support is considered, the impact factor should be calculated using the 2nd or 3rd order frequency.%介绍两跨连续梁不同跨径比对振型的影响，并讨论冲击系数的取值。采用槽型梁作为连续梁模型，利用Midas有限元分析软件和DASP设备分别对连续梁进行模态分析，得出不同跨径比下连续梁的前3阶振型及其频率，并将Midas计算结果与试验结果进行对比，证实振型变化的真实性。结果表明，第2、3阶振型随着跨径比减小会出现转折，中支点振型的曲率发生变化；考虑跨中正弯矩效应时，冲击系数宜按照《桥规》采用基频计算；考虑中支点负弯矩效应时，冲击系数应采用第二或第3阶频率计算。