OS12F079 Fatigue Life Estimation of Steel Bridges for Extreme Loading using a New Damage Indicator

Abstract

High cycle fatigue (HCF) caused by traffic loading is one of the major modes of failures in steel bridges. During bridge service life, there are extreme loading situations such as typhoons or earthquakes which cause higher amplitude loading than traffic loading. Due to this reason, some of members may undergo overstress cycles in the plastic range. Therefore, such members may be subjected to low cycle fatigue (LCF) during these situations while subjecting to HCF in serviceable condition. Bridges, which are not seriously damaged, generally continue to be used after these extreme loading situations and fatigue life estimation is required to ensure their safety. Therefore, this paper presents a new damage indicator based fatigue model to predict life of steel bridges due to extreme loading. It consists of a modified strain life curve and a new strain based damage indicator. Modified strain life curve consists of Coffin Manson relation in LCF regime and a new strain life curve in HCF regime. Damage variable is based on von Mises equivalent strain and modified by some factors to consider effects of loading non proportionality and loading path in multiaxial stress state. The new damage indicator can capture the loading sequence effect. The proposed model was verified with experimental test results of combined HCF and LCF of three materials; S304L stainless steel, Haynes 188 (a Cobolt superalloy) and S45C steel obtained from the literature. The verification of experimental results confirmed the validity of the proposed model.