Diagnostics of historical steel bridges: The case of the Valencian railroad network

Exposure to aggressive environmental agents, aging and extreme weather events can seriously affect the performance of historical steel bridges. In the last decades, the need for diagnostic and monitoring of existing steel bridges became a huge widespread issue, as some recent catastrophic events pointed out (Mississippi River bridge, Minneapolis, Minnesota 2017; Kinzua Bridge State Park, Pennsylvania 2003). In this context, the need for monitoring and risk analysis of existing structures became an important concern for holders and administrators that are responsible for the construction operability and user safety. In particular, the issue of bridge inspections recently arose in the Valencian region (Spain) since a large number of railway riveted steel bridges were built between the end of the19th and the beginning of the 20th Century. Today, after more than 100 years of existence, many bridges need repairing or strengthening interventions due to changes in service requirements or pathologies. This paper proposes a methodology for the identification of an analytical failure tree related to the structural response of the historical steel bridges located in the Valencian railroad network considering different critical phenomena and extreme events. Firstly, a suitable investigation plan has been developed to identify the typological, geometric, material and conservation characteristics of a case study. Subsequently, specific diagnostics (i.e. identification of the critical elements under traffic loads) is performed through a numerical model of the bridge calibrated by using the results of on-site static and dynamic tests. Once the critical elements are identified, some failure scenarios considering corrosion, fatigue and extreme events (e.g. earthquakes) are hypothesized in order to forecast consequence scenarios and achieve a failure tree of the bridge.