三跨斜交连续小箱梁桥动力特性分析

Dynamic characteristics analysis of three-span skew continuous small box girder bridge

以三跨连续斜交小箱梁桥为例,应用有限元软件Midas Civil分别建立了斜交角度为0~60°(步长为5°)的上部结构模型,分析了不同斜交角度对桥梁结构固有频率和振型的影响,对现有《公路桥涵设计通用规范》中用于连续梁桥冲击系数计算的基频计算公式给予修正。分析表明:三跨连续斜交小箱梁桥前三阶竖弯频率均随斜交角度的增大而增大,其中一阶竖弯频率所受影响最为显著,当斜交角度大于15°时,斜交角的影响不能忽略,其增大值最大可达103%。此外基于正桥模型得出的等跨等截面三跨连续梁桥的前三阶竖弯频率的比值关系(π^(2)∶3.44^(2)∶4.3^(2))在斜交角度小于15°时仍然适用;当斜交角度大于15°时,两者误差逐渐增大,最大可达57.8%,因此该比例关系不再适用于大角度斜交梁桥。本文提出的计算连续梁桥冲击系数的基频修正公式经实桥试验验证是正确的。

In this paper,a three-span continuous skew box girder bridge is taken as an example.The finite element soft⁃ware Midas Civil is used to establish the superstructure model with skew angle of 0~60 degrees(step length 5°).The ef⁃fects of different skew angles on the natural frequency and mode shape of the bridge structure are analyzed.The formula of the fundamental frequency used in the calculation of the impact coefficient of the continuous girder bridge in current bridge specification is modified.The analysis shows that the first three-order vertical bending frequency of the three-span continuous skew box girder bridge increases with the skew angle.The first-order vertical bending frequency is significant⁃ly affected.When the skew angle is greater than 15°,the maximum value can reach 103%.The influence of skew angle cannot be ignored.In addition,based on the bridge model,the ratio(π^(2)∶3.44^(2)∶4.3^(2))of the first third-order vertical bending frequency of the three-span continuous beam bridge with equal cross-section is still applicable when the skew angle is less than 20°.When the skew angle is greater than 20°,the errors have gradually increased to 57.8%,so the ratio is no longer suitable for large-angle skew bridges.The basic frequency correction formula for calculating the impact coef⁃ficient of continuous beam bridge proposed in this paper is verified by the bridge experiment.