An overview of estimation methods for obtaining the fatigue properties of old metallic bridge materials

Around 38% of structural damage in metallic bridges occurs due to fatigue, with the aggravating factor being a structural phenomenon unknown until some decades ago, which leads to many existing structures being designed without addressing this process of structural degradation. Due to economic and environmental reasons, many metallic railway bridges see their operating time extended, leading to the accumulation of fatigue damage that can be significant and responsible for putting the safety of these structures at risk. Therefore, knowing the fatigue resistance properties of old metallic bridges’ structural materials becomes essential for applying advanced methodologies based on two-stage fatigue global–local approaches. One of these stages is characterised by the crack initiation phase, which is usually evaluated using local approaches based on stresses, strains, or energy. In most cases, only the monotonic tensile strength properties of old metallic bridge materials are known. For this reason, using estimation methods to obtain fatigue strength properties based on monotonic tensile strength properties becomes fundamental for such studies. This study explores various estimation methods for obtaining fatigue strength properties of metallic materials from old Portuguese bridges, revealing that the modified Mitchell method presents the best ranking when analysing all the materials studied.