09.05: Remaining fatigue life of steel railway bridges: Improved models for considering realistic behaviour

Abstract

ABSTRACTMany steel railway bridges will reach the end of their scheduled design service life within the next years. One can also observe some bridges, considerably younger than their scheduled design service life, with insufficient remaining fatigue life and rarely cracks in structural elements. Mostly because of the early applications of the welding technology and sometimes insufficient consideration of fatigue effects, e.g. neglecting of high local secondary stresses. It is a great challenge and very expensive, if a couple of bridges have to be replaced in a short period. Therefore, it is important to have models for realistic fatigue verification to extend the service life.The focus of this paper is to show different approaches – both on the load and the resistance side – to verify an extended service life of steel railway bridges. For example, the big potential of the use of real, measured stress spectra is presented, instead of the common approach according to the Eurocode. In addition, the application of the consequent Miner's rule results in another significant reduction of equivalent stress ranges for application of the fatigue strength curves of the Eurocode.Furthermore, the simplified and conservative assumptions regarding the fatigue resistance in conventional assessment procedures according to the Eurocode (nominal stress approach) are compared with alternative concepts for typical welded joints. For example, the geometric (hot spot) stress concept, the effective notch stress concept and fracture mechanics. The Eurocode already allows the use of the geometric stress concept, but gives little guidance. The practical implementation of these concepts is shown for a representative detail of a steel bridge, considering a variety of geometries.Fracture mechanics approaches are state of the art in mechanical engineering, but still relatively uncommon in civil engineering. These concepts allow for the explicit consideration of real or assumed “non‐detected” flaws or cracks in the component, thereby eliminating the need of an exact knowledge of the past load history, up to the considered defect size. It is shown that the fracture mechanics concept is suitable for steel bridges to determine the remaining fatigue life of critical details.Finally, a multilevel framework is presented to give guidance for engineers to evaluate the service life of a specific steel railway bridge.