Fatigue life assessment of multi-span railway masonry arch bridges based on crack growth rate

Abstract

Masonry arch bridges, as critical components of railway infrastructure, are widely scattered throughout the Iranian railway network. Although most of these bridges have been in service for over ninety years, they continue to perform safely while being subjected to increasing traffic demands in recent years. Existing assessment methods mainly focus on ultimate load capacity and do not explicitly address fatigue damage or remaining service life under repeated train loading. Unlike conventional capacity-based approaches, this study presents a fracture-mechanics-based framework that explicitly accounts for fatigue crack growth, enabling quantitative prediction of the remaining service life of masonry arch bridges, which has rarely been addressed in existing numerical studies. A detailed finite element model was developed in ANSYS and calibrated using crack mouth opening displacement (CMOD) measurements obtained from field observations. Fatigue crack propagation was considered by Paris’ law, enabling the relationship between crack length, stress intensity factor (SIF), and number of load cycles to be quantified under realistic traffic scenarios. The results show that for an axle load of 20 ton and 15 train passages per day, the estimated fatigue life of the bridge is approximately 125 years, which decreases to about 94 years when the axle load increases to 25 ton. Based on the critical load position at one-quarter of the main span, a fatigue limit of approximately 0.27 was identified. The proposed methodology extends conventional assessment practices by integrating fracture-mechanics-based fatigue analysis into numerical modeling, providing a practical and service-life-oriented tool for predicting fatigue life and supporting informed decision-making in the structural management of historic railway masonry arch bridges.