Estimating Remaining Fatigue Life of Critical Members of Steel Railway Bridges using Fatigue Crack Growth Model

Abstract

Fatigue failure of steel structures is one of the most urgent study areas due to the inherent catastrophic nature of the failure. Engineers have made a substantial contribution to the understanding of the fatigue phenomenon through several approaches. Heavy cyclic loads imposed on steel railway bridges have the potential to cause cracks in structurally important members. Initiated cracks propagate during its service and lead to a complete structural failure. Since it is not practical to continuously monitor the structural health of bridges, an accurate life prediction approach is necessary to predict failure. This study proposes the fracture mechanics approach for fatigue life prediction of the critical members of bridges. Standard compact tension C(T) specimens were prepared with a pre-crack to test the fatigue crack growth rate under different stress levels. The crack growth rate da/dN was calculated by plotting the crack length (a) vs the number of cycles (N). According to ASTM E647-15, the stress intensity factor range (ΔK) for the C(T) specimen was determined. Under the conditions of constant amplitude loading, a modified version of the Paris law was used to construct an empirical relationship between da/dN and ΔK. The results of the vibration analysis were used to validate the finite element model of a case study railway bridge in Sri Lanka. The Finite Element (FE) method was used to assess the life of the most critical bridge member, and its estimated remaining fatigue life is 14.5 years.