基于影响函数的随机车流作用下大跨度悬索桥风致应力响应分析

为了解决大跨度桥梁在随机车辆荷载和风荷载作用下局部应力求解耗时问题，首先以矮寨大桥为工程背景，建立壳-梁混合单元有限元模型，确定大桥应力的关键位置及关键点，采用分段拟合方法获得随机车辆荷载的影响面函数和风荷载的影响线函数；结合吉茶高速实际交通量特征及随机参数分布特征，采用蒙特卡罗方法，编制抽样程序生成随机车流样本。其次采用风-车-桥耦合振动分析获得典型车辆的等效车辆荷载；引入风荷载动力影响系数，提出了一种简便实用的随机车流下大跨度桥梁风致应力分析方法。最后应用ANSYS计算分析结果验证所提方法的正确可行性，分析矮寨大桥在随机车流和风荷载联合作用下的关键点应力响应。结果表明：风速低于15 m·s^-1时，风荷载引起大桥关键点应力响应远小于车辆荷载引起的应力响应；繁忙车流下应力响应的幅值并不比稀疏车流下的应力幅值大很多，但是繁忙车流下应力响应的峰值数量远大于稀疏车流下的峰值数量，即应力的循环次数多，会增大桥梁的疲劳损伤。

Wind-induced Stress Response Analysis of a Long-span Suspension Bridge Under Random Traffic Load Based on Influence Functions

To solve the time-consuming problem of the local stress analysis of a long-span bridge under the combined action of random traffic and wind loads, the Aizhai Bridge was selected as an example in this paper and a finite element model with shell elements and beam elements for the bridge was established using ANSYS software. The critical locations of the bridge were then determined by refined analyses and the stress influence functions used for calculating the dynamic stress response of the bridge under random traffic and wind loads were calculated by segmented polynomial fitting using the Curve Fitting Toolbox in MATLAB. Based on the characteristics of actual traffic volume and distribution characteristics of random parameters of the bridge, the random traffic flow simulation program was compiled by adopting the Monte-Carlo simulation method and MATLAB software, and random traffic samples were then simulated. The moving equivalent dynamic vehicle loadings were calculated based on full interaction analyses of a single-vehicle-bridge-wind system. By introducing dynamic influence coefficients for wind loads, this paper presented an efficient approach for dynamic stress analysis of a long-span bridge under the combined action of random traffic and wind loads based on the stress influence function. The correctness of the proposed method was verified by comparison with the results of ANSYS analysis. Finally, the local stress responses of the key members of the bridge under the combined action of random vehicle and wind loads were analyzed. The results show that the wind-induced stress response is much lower than that induced by random traffic load when wind speed is less than 15 m·s^-1. The maximum stress amplitude induced by busy traffic flow is not greater than that induced by free traffic flow. However, there are more peak values in the response for busy traffic flow than those for free traffic flow, which will affect the gross number of stress cycles and increase the fatigue damage to the bridge.