基于预紧弹簧系统的桥梁挠度冲击系数量测方法

Measurement Method of the Bridge Deflection Dynamic Load Allowance Based on Preloaded Spring System

为了提高桥梁挠度及冲击系数测试的稳定性,在传统悬锤法基础上,基于弹簧预紧效应,提出了预紧弹簧法。首先依据车-桥耦合振动理论,以简支梁桥为对象推导了车辆-桥梁-预紧弹簧耦合振动方程,进行了室内试验和系统数值验证;在此基础上分别建立了车辆-桥梁-悬锤系统和车辆-桥梁-预紧弹簧系统的有限元模型,利用数值解法分析了横向风荷载对悬锤法和预紧弹簧法测量主梁挠度及冲击系数的影响;根据建立的车辆-桥梁-预紧弹簧耦合振动系统,研究了影响该方法精度的关键性因素,并给出系统参数选型优化经验公式。最后,以一座30 m预制装配式简支箱梁桥为例,在随机车载激励下,进行支架法、悬锤法和预紧弹簧法3种方法的对比试验。研究结果表明:预紧弹簧法与传统悬锤法相比,冲击系数受风荷载影响较小;无风环境下,预紧弹簧法易受铁丝抗拉刚度、弹簧刚度和悬挂长度的影响,而与初始预紧力值无关;通过合理选用参数,预紧弹簧法能够实现主梁与系统同相位振动;工程实例表明该方法与支架法挠度冲击系数平均误差为6.1%,精度高于悬锤法测量结果,该方法也可为桥梁结构静动载大位移测试提供借鉴。

A preloaded spring measurement method is proposed based on the spring preload effect to improve the stability of bridge deflection dynamic load allowance(DLA) testing. Firstly, the vibration equation of vehicle-bridge-preload spring coupled system was derived by the theory of the vehicle-bridge coupling vibration, and then indoor tests and numerical verification of the system were conducted. On this basis, the finite element model of the vehicle-bridge-suspension hammer system and vehicle-bridge-preloaded spring system were established, and the influence of wind loads on the deflection and DLAs measured by the suspension hammer method and preloaded spring method were analyzed by numerical solution method;Based on the established vehicle-bridge-preloaded spring coupled vibration system, the critical factors affecting accuracy of the method were analyzed and an empirical formula for parameter optimization was given. Finally, a 30 m prefabricated assembly box-girder bridge was taken as an example, and the DLAs verification tests of scaffolding method, suspension hammer method and preloaded spring method were carried out under random vehicle excitation. The results show that the DLAs of the preloaded spring method are less affected by wind load than that of conventional suspension hammer method;Under the windless environment, the preloaded spring method is influenced by wire tensile stiffness, spring stiffness, and suspension length, independent of the preloaded force;The preloaded spring method can reflect the girder vibrating in the same phase with the spring system by reasonable parameters. It is verified by engineering examples that the mean error of the DLAs by preloaded method is 6.1% compared with scaffolding method, which is more accurate than the suspension hammer method. The proposed preloaded spring method can also provide a reference for the static and dynamic large displacement test of bridge structures.