Fatigue life estimation of existing steel structures under time-dependent structural degradation

Abstract

The purpose of this thesis is to present a method to estimate remaining fatigue life of steel bridge members subjected to time-dependent corrosion. This method contributes to the further development of the theoretical verification for the available methods and standards in remaining fatigue life of steel structures. The relevant standards for fatigue life and corrosion are evaluated, with focus on fatigue analysis, effects of the loss of the thickness of material due to corrosion and fatigue strength degradation of material due to corrosive environment. A verification of steel bridge structural element in terms of fatigue life is very important for all old bridge construction. The fatigue strength of all structural steel depends on the environmental condition, the type of load and period. The bridge elements can reduce the thickness uniformly or partially. The main cause can be corrosion, where the structure can be subjected to different failure mechanisms during its lifetime. The main focus in this thesis is the introduce a method to estimate fatigue life of bridge members under time-dependent corrosion. Steel plates which are used as bridge elements are subjected to pitting corrosion. Because of this, the plates reduce the thickness irregularly. The plates be modeled and analyzed by using finite element analysis method employed computer program SAP2000. Verification of the introduced method has also done as an objective of this thesis. In principle, the safety of construction generally depends on the design and considers the structural failure mechanism. The main causes of steel structure damage can be fatigue with corrosion and wear in most structural failure. A fatigue failure is one of the time dependent structural failures. Corrosion has a profound effect on the fatigue life of steel structure used in bridge construction. This thesis includes verification of steel bridge members with respect to pitting corrosion and fatigue. To determine the effect of corrosion on a steel element, one must identify reduction of thickness in the material; this is read from the report of the physical research [29]. Eurocodes and UK railway assessment code are mainly used as the basis for all calculations.