The structural safety and durability of existing reinforced concrete bridges can be considered as one of the current most important research topics in structural engineering, especially after the numerous collapses that have occurred in recent years. Considering the Italian context, it is important to highlight that most of these structures were built in the 1960s and 1970s and, consequently, the effects of materials degradation phenomena have reduced their vertical and horizontal load-bearing capacity.

This paper presents an efficient procedure for the collapse mechanism evaluation of existing reinforced concrete motorway bridges under horizontal loads, considering the corrosion effects due to carbonation through a simplified model that takes into account the steel rebars reduction and applying a multi-modal pushover analysis approach. In this study, three different (slight, moderate and high) corrosion scenarios are considered for two existing reinforced concrete bridges characterized by frame piers. The results of the numerical analyses, which consider both brittle and ductile failure mechanisms, highlight a significant decrease of the seismic capacity of the structures as the corrosion level increases, especially for brittle collapse mechanisms that are strongly affected by the bridge maintenance condition. Such a procedure allows identifying the first structural elements reaching the collapse, providing useful information for the maintenance of existing bridges in terms of repair and strengthening interventions.

现有钢筋混凝土桥梁的结构安全性和耐久性可以被认为是结构工程中当前最重要的研究课题之一，尤其是在近年来发生了多次倒塌事故之后。考虑到意大利的情况，重要的是要强调指出，这些结构大多数是在1960年代和1970年代建造的，因此，材料降解现象的影响已降低了它们的垂直和水平承载能力。

本文提出了一种有效的程序，用于评估现有钢筋混凝土高速公路桥梁在水平荷载下的倒塌机理，并通过简化模型（考虑了钢筋的减少）并考虑了碳酸盐化造成的腐蚀影响，并采用了多模式下垂分析方法。在这项研究中，考虑了两种现有的以框架墩为特征的钢筋混凝土桥梁的三种不同（轻度，中度和高度）腐蚀情况。兼顾脆性和延性破坏机理的数值分析结果表明，随着腐蚀水平的提高，结构的抗震能力显着下降，特别是对于受桥梁维护条件强烈影响的脆性坍塌机制。