Improved Assessment Methods for Static and Fatigue Resistance of Old Metallic Railway Bridges

Abstract

A large number of railway structures in Europe are metallic bridges. The increasing volume of traffic and axle weight of trains mean that, for many structures, the loads today are much higher than those envisaged when they were designed. This paper presents a summary of the different recommendations and advice proposed in European guidelines for assessing load and resistance of railway bridges issued from a research project. The knowledge of the material properties of existing metallic bridges is essential for the resistance assessment and the determination of the remaining lifetime of old metallic bridges. Furthermore, old bridges require more exact and efficient assessment methods that call for a precise description of the material. Among the problems met in metallic structures and material properties estimation, fatigue is the most common cause of failure. To be able to make accurate assessments of existing bridges, it is important to know the behavior of bridges exposed to fatigue and how the old materials behave owing to cyclic exposure. The main question answered in this paper is how to make a safe estimation concerning the remaining life in service. The possible traffic load on steel rail bridges is usually limited by the fatigue resistance, but for certain situations the static resistance also has to be checked. Most design rules for steel structures are applicable also to riveted structures. However, some information is missing on how to deal with the special case when elements are intermittently connected in contrast to welded structures that are connected continuously. Because the traditional methods for assessing the resistance of steel bridges are based on elastic analysis, a method for utilizing a limited redistribution of bending moments based on beam theory is proposed.