The methodologies to predict the safety levels of highway bridges must consider suitable live load models from real and critical traffic conditions. This research is focused on the reliability assessment of prestressed simply supported Mexican bridges, which are the most common structures for short and medium spans in Mexico. The safety levels of highway bridges are determined to show the impact generated by two different kinds of live models on using prestressed type AASHTO I beams in Mexico, with spans of 10, 15, 20, 25, 30 and 35 m. These safety levels are obtained using a probabilistic approach based on the reliability theory. Selected highway bridges are designed according those procedures proposed by the Mexican Institute of Transportation rules and AASHTO LRFD bridge specifications, which are commonly used by Mexican bridge designers. For all the cases, results of IMT-66.5 live load model achieve higher safety levels than T3-S2-R4 truck. Shear reliability analyses indicate high level overdesign using Mexico City design code, leading to high safety levels for all evaluated cases. For bending moment analysis, the bridges with spans higher than 20 m have reliability indices under 3.5 for both live load models and a traffic scenario with 35% trucks. Therefore, we propose new live load factors for bridges with spans longer than 20 m to achieve the target reliability index of 3.5. For traffic scenarios with 18% and 35% trucks, proposed live load factors for IMT 66.5 and T3-S2-R4 trucks have increments of 6.7% and 7.8%, and 16.7% and 16.8%, respectively. An overall methodology was also proposed to be applied in other places with similar truck overloading problems for evaluating new and current bridge infrastructure.

中文翻译：

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墨西哥预应力混凝土桥梁的可靠性分析：评估和活荷载系数建议

预测公路桥梁安全水平的方法必须考虑来自真实和关键交通条件的合适活荷载模型。这项研究的重点是预应力简支墨西哥桥梁的可靠性评估，这是墨西哥中短跨最常见的结构。确定公路桥梁的安全等级以显示两种不同实况模型对墨西哥使用预应力型 AASHTO I 梁产生的影响，其跨度为 10、15、20、25、30 和 35 m。这些安全级别是使用基于可靠性理论的概率方法获得的。选定的公路桥梁是根据墨西哥交通运输协会规则和 AASHTO LRFD 桥梁规范提出的程序设计的，这些程序通常被墨西哥桥梁设计师使用。对于所有情况，IMT-66.5 活载模型的结果比 T3-S2-R4 卡车实现了更高的安全水平。剪切可靠性分析表明使用墨西哥城设计规范的高水平过度设计，导致所有评估案例的高安全水平。对于弯矩分析，跨度大于 20 m 的桥梁对于活荷载模型和具有 35% 卡车的交通场景的可靠性指数均低于 3.5。因此，我们为跨度超过 20 m 的桥梁提出了新的活荷载系数，以实现 3.5 的目标可靠性指标。对于具有 18% 和 35% 卡车的交通场景，IMT 66.5 和 T3-S2-R4 卡车的拟议活载系数增量分别为 6.7% 和 7.8%，以及 16.7% 和 16.8%。