基于疲劳损伤累积的中小跨径公路桥梁的限载分析方法

Overloaded vehicles have become the main reason for the deterioration of load-carrying capacity and the shortened operation life of bridges. Proposing scientific and reasonable standard for vehicle weight limits is critical for securing safe operation of bridges. However, current research and regulation in the area of vehicle weight limits have two drawbacks: ignoring the deterioration of bridge structure resistance induced by fatigue damage accumulation and underestimating the dynamic effect of overloaded vehicles on the bridge under poor road surface condition. This will result in larger vehicle weight limits and aggravate the fatigue damage and failure of bridge structures. In this research project, analytical vehicle models that can represent the main dynamic properties of typical overloaded vehicles will be first developed and the dynamic effect of vehicle loading will be accurately considered based on refined analysis of bridge-vehicle coupled vibration. Taking the short- and medium-span highway bridges as the research object, methods for obtaining the time-history curves of dynamic stress of critical steel components of bridges under the action of the random traffic flow during the deterioration process of road surface condition will be developed. The effect of fatigue damage accumulation on the resistance deterioration of critical steel components of bridges will be accurately considered. A rational load limit analysis method that can accurately consider the resistance deterioration of critical steel components of bridges and the dynamic effect of vehicle loading will be proposed. The research results from this project will fill in the gaps in the current vehicle weight limit analysis method in which the bridge true resistance is overestimated while the dynamic effect of vehicle loading is underestimated, will enhance the reasonability and reliability of the analysis method for vehicle weight limits, and will provide scientific support for the management of vehicle weight limits.

车辆超载运输已成为桥梁承载能力劣化和运营寿命缩短的主要原因。提出科学合理的公路桥梁限载标准对保障桥梁安全运营具有重要意义。然而，目前关于桥梁限载的研究和标准中存在两大缺陷，即忽略了疲劳损伤累积导致的桥梁抗力的衰减和低估了桥面状况差时重车荷载对桥梁的动力效应，导致桥梁限载取值偏大，从而加剧桥梁结构的疲劳损伤破坏。为此，本项目拟建立各类典型重车的动力分析模型，通过车桥耦合振动精细化分析准确考虑车辆荷载的动力效应；以中小跨径桥梁为研究对象，研究在桥面状态不断劣化过程中随机车流作用下桥梁重要钢构件的应力时程的获取方法，进而准确考虑疲劳损伤累积对桥梁重要钢构件抗力衰减的影响；提出能准确考虑桥梁抗力衰减和重车动力荷载效应的限载分析方法。研究成果将弥补现有桥梁限载分析方法高估桥梁真实抗力、低估车辆荷载动力效应的不足，提高桥梁限载分析方法的合理性和可靠性，为我国中小跨径梁桥的限载管理提供科学依据。

针对国内钢结构桥梁疲劳损伤评估缺乏适用于不同交通荷载的疲劳车模型、UHPC正交异性桥面板采用确定性疲劳评估的不足、钢构件绝对应力和混凝土剩余强度识别难等问题，提出了一种确定疲劳车辆模型的新方法，该方法可应用于交通载荷组成不同的各个站点的疲劳损伤计算，可为国内桥梁疲劳评估提供参考，所提方法对其他地区高精度的疲劳车辆模型的开发具有借鉴意义; 提出了一种基于可靠度UHPC正交异性桥面板疲劳评估方法，可为LWCD系统的设计和维护提供参考; 提出了一种基于深度学习的钢结构绝对应力和混凝土剩余强度的评估方法，突破了传统方法只能获取结构应力而无法获取结构实际应力以及无法获取混凝土剩余强度的技术瓶颈;提出了一种确定钢主梁极限承载能力可靠度的新方法，该方法能考虑车辆荷载引起的疲劳累积损伤对钢主梁极限承载力的影响。研究结果表明: (1)提出的3 轴疲劳车模型和 4 轴疲劳车模型比规范中规定的疲劳荷载在疲劳评估方面具有更好的准确性和实用性。特别是4轴疲劳车车辆模型用于评估交通繁忙的测点的钢构件疲劳损伤时均方根误差在5%以内，明显低于调整后的疲劳荷载III模型;(2) 基于确定性方法和可靠性方法对COSD系统和LWCD系统的疲劳性比较发现，与COSD系统相比，LWCD系统可将桥面板的疲劳寿命延长至少60%。基于确定性方法明显高估了桥面板实际的疲劳寿命，考虑路面的整个生命周期时，基于确定性方法计算的 COSD 和 LWCD 的疲劳寿命比基于可靠性方法的疲劳寿命长 65% 到 110%；(3) 在最佳参数组合下深度学习Faster R-CNN模型对六种不同应力的平均识别精度达89.67%，对五种不同腐蚀程度的混凝土剩余强度评估的平均准确率达98.98%;(4) 获得了钢主梁极限承载力的可靠指标与疲劳设计车日均通行量的关系。

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