Environment-assisted fatigue of steel bridges: A conceptual framework for structural integrity/life assessment

Abstract

The purpose of this thesis is to propose a framework/methodology based on a recently proposed fatigue strength curve of corroded steel to assess the life of an existing steel bridge exposed to environment-assisted fatigue. A fatigue assessment using damage accumulation method is performed on an ageing steel bridge located in a marine environment in Sri Lanka. The assessment is performed using both the newly proposed method and conventional approaches covered in the framework. The difference of the estimated fatigue lives emphasizes the importance of considering the interactions of corrosion and fatigue mechanisms.

The newly proposed method includes a formula and corresponding S-N curves to predict fatigue strength of corroded structural elements of steel structures. Parameters of the S-N curve for both marine and urban environments are provided for detail categories in the Eurocode and the DNV-GL code. The formula does not require any other material parameters than the fatigue curves given in the codes. The applicability and significance of this method is discussed by comparison of the fatigue lives obtained by both the conventional method from the Eurocode and proposed method.

Prior to the fatigue assessment, a thorough literature review regarding forms of corrosion on steel bridges, their effects and causes are first studied. Environment-assisted cracking (EAC) and how it affects the structural integrity of steel bridges are introduced. Research gaps and shortcomings in the literature regarding the issue are investigated.