Raising allowable axle loads on railway bridges using simulation and field data

Abstract

The European railways continue to reduce its share of the transport sector, a large proportion going to road transport. Raising allowable axle loads is regarded as a means of making the railways more competitive as raised axle loads result in more goods being transported per train. This has many positive effects including increasing line capacity, reducing overhead costs, more efficient use of energy and increased productivity. It is therefore of interest to increase the allowable axle loads on existing railway bridges with a minimal cost for society. This thesis studies the possibility of increasing allowable axle loads on existing railway bridges from the current 22.5 to 25 tonnes without the need for strengthening of these same bridges. The work studies the case of simply supported bridges and found that this was possible, within the framework of this study, for bridges designed to the Load Model 71 and the SW/2 traffic loads of the Swedish bridge code and whose span exceed 8 metres. The thesis considers the case of purely static loads and does not consider the effects of increased fatigue rates or increased dynamic stresses. The study builds upon a traffic load model presented by The European Rail Research Institute, ERRI. The work presents three load models for Monte-Carlo simulations of railway traffic loads with increased axle loads. Traffic load effects are obtained from the simulations and results are analysed using a combination of extreme value theory and reliability theory. The work also details results from months of field measurements of axle loads and train configurations. Data from over eleven thousand trains have been collected. The data is used to simulate trains crossing bridges and “real traffic” load effects are thus obtained. The real traffic load effects are then compared with the theoretical traffic load models. The study suggests that the special transport trains should be treated separately and that once these transports have been omitted it is the block trains (typically iron-ore) that constitute the dimensioning case for the bridges.