The effects of increasing axle loads on rail integrity are examined in this paper. In the present context, rail integrity refers to the prevention and control of rail failures. Rail failures usually occur because cracks or defects develop and grow from cyclic forces caused by the repeated passage of wheel loads over the rails, i.e. metal fatigue. Once a crack or defect has formed, it may grow to a critical size and cause a sudden fracture of the rail. Moreover, a broken rail may cause a train to derail.
Rail integrity evaluations are performed in this paper by applying a framework developed previously to estimate track capacity. The framework is exercised using two different criteria while varying axle loads: (1) allowable rail deflections and bending stresses, and (2) metal fatigue characterized in terms of propagation life (also referred to as slow crack-growth life). The engineering analyses based on these criteria are described. Results from these analyses are used to provide the rational basis for estimating the minimum rail size under heavy axle loads.