斜交连续T梁桥的动力特性分析及试验

Analysis and Experiment on Dynamic Characteristics of Skew Continuous T-beam Bridge

以某三跨连续斜交T梁桥工程为背景,应用Midas Civil建立三跨连续斜交T梁桥空间梁格模型进行有限元模拟,分析了不同斜交角度对该类结构动力特性的影响变化规律,并考虑斜交角度影响,对现行《桥规》中连续梁桥冲击系数计算采用的基频通用计算公式进行了修正,最后通过实桥动载试验对所提出的基频修正公式进行了验证。研究表明:对于斜交连续T梁桥,随着斜交角的增大,前三阶竖弯振型从固有振型的一、三、五阶变化到了一、三、七阶,斜交角的变化对前两阶竖弯振型没有影响;当斜交角小于30°时,结构基频值与正桥相近,可以按正桥考虑;当斜交角大于30°时,基频计算应计入斜交角影响;当斜交角小于40°时,前三阶竖弯振型对应的自振频率值仍满足比例关系:π~2:3.55~2:4.3~2,与正桥相同;在实际斜交连续梁桥工程中,可利用实测得到的一阶自振频率通过这一比例关系得出第三阶自振频率,作为在计算因冲击力引起的负弯矩效应时采用的自振频率值;实桥动载试验验证了本研究所提出的基频修正公式计算结果是合理的;T梁之间采用刚接或铰接的连接方式,对结构动力特性几乎无影响,本研究结论适用于主梁之间为刚接或铰接的中小跨径三跨连续斜交T梁桥结构。

The spatial grillage model based on a three-span skew continuous T-beam bridge engineering is built using Midas Civil,and the influencing rules of different skew angles on the dynamic characteristics of this kind of structure are analyzed. Considering the effects of skew angle,the formula of fundamental frequency for calculating the impact coefficient of continuous bridges in current specification is modified.Finally,a dynamic load test of factual bridge is conducted to verify the correctness of the modified fundamental frequency formula. The study shows that（ 1） the first 3 orders vertical bending vibration modes of skew continuous T-beam bridge are changed from the first,third and fifth orders of natural vibration modes to the first,the third and the seventh orders as the skew angle becomes larger,and the change of skew angle has no influence on the first two vertical bending vibration modes;（ 2） when skew angle is less than 30°,the fundamental frequency approaches to right bridge,it can be considered as that of right bridge;（ 3） when skew angle is greater than 30°,the effect of skew angle on the calculation of fundamental frequency should be considered;（ 4） when skew angle is less than 40°,the natural frequencies corresponding to the first 3 orders vertical bending vibration modes still meet the ratio of π~2∶ 3. 55~2∶ 4. 3~2 as the same as right bridge;（ 5） inreal skew continuous bridge engineering,the third-order natural frequency can be obtained from the measured first-order natural frequency based on the ratio,which can be used as the natural frequency value in calculating the negative moment effect caused by the impact force;（ 6） the dynamic load test of the real bridge shows that the calculation result of the modified fundamental frequency formula is reasonable;（ 7） the dynamic characteristics of skew T-beam bridge can hardly be affected whether the connection between T-beams is rigid or hinged. The conclusions are applicable to the small and medium 3-span continuous skew T-beam bridge with rigid or hinged connections between main girders.