Estimation of the Fatigue Life of Railroad Joint Bars

This paper investigates the influence of physical track conditions in the vicinity of a rail joint on the fatigue life of the joint bars. Recent derailments due to broken joint bars, such as the Minot, ND accident in January 2002, have highlighted the need for better understanding of the effects of joint conditions on premature joint bar failure. Fatigue life estimates can be used to guide the selection of inspection intervals for joint bars in service. Engineering approximations are used to infer the dynamic load factor at a rail joint due to joint characteristics including: • rail end gap; • joint efficiency (looseness); • track stiffness (vertical foundation modulus). A three-dimensional finite element analysis of a rail joint is conducted and the dynamic load is applied to develop an estimate of the live (bending) stresses at the joint due to passing wheels. These stresses are then used to estimate the fatigue life of the joint bars. The methodology is demonstrated for 132RE rail with companion joint bars. The effect of thermal expansion (or the temperature difference below the rail neutral temperature) is investigated. Typical wheel loads and railcar speeds are considered and results are presented for a baseline a joint condition.