Diss. Stockholm : Royal Institute of Technology. Structural Engineering Division, 2003

The work presented in this thesis studies the load and load effects of traffic loads on railway bridges. The increased knowledge of the traffic loads, simulated using field measurements of actual trains, are employed in a reliability analysis in an attempt at upgrading existing railway bridges. The study utilises data from a weigh-in-motion site which records, for each train, the train speed, the loads from each axle and the axle spacings. This data of actual train configurations and axle loads are portrayed as moving forces and then used in computer simulations of trains crossing two dimensional simply supported bridges at constant speed. Only single track short to medium span bridges are considered in the thesis. The studied load effect is the moment at mid-span. From the computer simulations the moment history at mid-span is obtained. The load effects are analysed by two methods, the first is the classical extreme value theory where the load effect is modelled by the family of distributions called the generalised extreme value distribution (GEV). The other method adopts the peaks-over-threshold method (POT) where the limiting family of distributions for the heights to peaks-over-threshold is the Generalised Pareto Distribution (GPD). The two models are generally found to be a good representation of the data. The load effects modelled by either the GEV or the GPD are then incorporated into a reliability analysis in order to study the possibility of raising allowable axle loads on existing Swedish railway bridges. The results of the reliability analysis show that they are sensitive to the estimation of the shape parameter of the GEV or the GPD. While the study is limited to the case of the ultimate limit state where the effects of fatigue are not accounted for, the findings show that for the studied cases an increase in allowable axle load to 25 tonnes would be acceptable even for bridges built to the standards of 1940 and designed to Load Model A of that standard. Even an increase to both 27.5 and 30 tonnes appears to be possible for certain cases. It is also observed that the short span bridges of approximately four metres are the most susceptible to a proposed increase in permissible axle load.