基于元胞自动机的随机车流模拟与桥梁疲劳响应分析

Simulation of Random Traffic Flow and Analysis on Bridge Fatigue Response Based on CA

为了研究类似云南省这样的高原山区低等级公路桥梁实际运营状态下的交通荷载特性及车辆荷载作用效应,首先,基于动态称重获得了云南某低等级公路桥梁的监测数据,得到了该区段车型、车重、车速、车长、轴距和轴重等数学模型。其次,基于传统的元胞自动机模型,对元胞长度、更新步长、换道、行驶的规则及其边界条件做进一步细化研究,提出了适用于山区低等级公路桥梁交通流模型的具体参数值,建立了精细化的元胞自动机模型。最后,根据影响线加载的方式,对该路段上某简支钢箱梁桥在随机车流模拟作用下的荷载效应进行了分析,并且利用雨流计数法整理得出了符合本地区实际交通状况作用下的应力幅和循环次数。结果表明:该元胞自动机模型可以较好地还原车型比例、车速、车长、车头时距等特征参数,模拟车流与实际交通状况吻合较好,从而验证了模型的准确性,该模拟方法可为同类问题提供参考依据。根据随机车流加载得到的车辆荷载效应,对比了《公路钢结构桥梁设计规范》、英国BS5400规范、美国AASHTO规范中的疲劳荷载计算模型作用下的应力幅值。实际交通模拟得到的应力幅值高于规范计算值,表明山区低等级公路由于交通管控不力,导致超载现象严重,桥梁的疲劳问题更加突出。

To study the traffic load characteristics and the vehicle load action effect of low-grade highway bridges in actual operation state in plateau mountainous areas as Yunnan Province, first, the monitoring data of a low-grade highway bridge in Yunnan Province are obtained based on weigh-in-motion, and the mathematical models of vehicle type, vehicle weight, vehicle speed, vehicle length, wheelbase and axle load are obtained. Second, on the basis of the traditional CA model, the cellular length, updated step length, lane changing rule, driving rule and boundary conditions are further studied, the specific parameters suitable for the model of traffic flow on low-grade highway bridge in mountainous area are proposed, and a refined CA model is established. Finally, according to the loading method of the influence line, the loading effect of a simple supported steel box girder bridge on this section with the simulative random traffic flow is analyzed, and the stress amplitude and the number of cycles in accordance with the actual traffic conditions in local area are obtained by the rain-flow counting method. The result shows that the characteristic parameters proportion, speed, length and time headway of vehicles are reproduced very well by the CA model, the simulative traffic flow is consistent with the actual traffic situation, it verified the accuracy of the model, thus the simulation method can provide a reference for similar problems. According to the vehicle load effect obtained by random vehicle flow loading, the stress amplitudes stipulated in Specifications for Design of Highway Steel Bridge, BS5400 and AASHTO specification for the fatigue load calculation models are compared. The stress amplitude obtained by the actual traffic simulation is higher than the calculation values in the specifications, indicating that the low-grade highways in mountainous area are overloaded due to the lack of traffic control, and the fatigue problem of the bridges is more prominent.