Effect of Train Live Load on Railway Bridge Abutments

Abstract

Assessment of lateral excess pressure attributable to train live load on the backfill embankment is one of the main subjects in railway bridge abutment and retaining wall design. Relevant design codes usually define a uniform infinite surcharge on the surface of the embankment to evaluate the lateral live load–induced pressure on the bridge abutments. This simplified method does not consider the actual pattern of operational live load and its induced pressure distribution on the width and height of the wall. In the current study, the operational railway live load pattern LM71 was applied to accurately calculate the laterally induced pressure on the abutment. In this regard, the elasticity-based equations of the laterally induced pressure caused by rectangular area and strip loads were utilized to evaluate the lateral pressure distribution on the abutment attributable to the railway live load. For evaluating the resultant lateral force and moment on the wall, a numerical integration was conducted on the lateral pressure values in the width and height of the wall. Because the laterally induced pressure is related to Poisson’s ratio, a sensitivity analysis was done on this parameter to show its effect on the resultant lateral force on the wall. As an applicable result, it was shown that, in the case in which Poisson’s ratio is equal to 0.3, the induced resultant horizontal forces on the walls with heights of 1.5–7 m are considerably underestimated compared with the values obtained in the current study. Consequently, an analytical equation was proposed for surcharge estimation, which led to a safer structural design of the railway bridge abutments.