Bridge Load Rating With Model Updating And Stochastic Analysis Of Vehicle Bridge Interaction

[Truncated abstract] Many load rating methods have been developed in recent years to evaluate the safety and serviceability of existing bridges. In general, the rating of a bridge is carried out by comparing the factored live load effects of nominated rating vehicles with the available bridge capacity. Therefore, accurate and practical approaches to calculate the live load on bridges resulting from moving vehicles and to estimate the bridge load carrying capacity are essential for bridge load rating. The research described in this thesis aims to develop a load rating procedure for accurately estimating the load carrying capacity of existing bridges. It involves three main parts of work. First, to obtain a reliable Finite Element (FE) model of the bridge under the current condition, FE model updating analysis is carried out to refine the bridge model based on the field measured vibration data. Second, detailed static nonlinear Finite Element Analysis (FEA) based on the updated FE model is carried out to determine the bridge load carrying capacity. In this part, the dynamic vehicle-bridge interaction is only approximately modelled by using the code specified Dynamic Amplification Factor (DAF) or Dynamic Load Coefficient (DLC). In the third part, to more precisely model dynamic vehicle-bridge interaction and predict the DAF, nonlinear stochastic dynamic response analysis of an equivalent hysteretic Single Degree of Freedom (SDOF) system subjected to a non-stationary non-zero mean excitation are carried out. The equivalent SDOF system is derived from the actual bridge conditions. The advantages of these approaches are that they can model the actual current condition of a bridge by applying the model updating method and take into account the effects of road surface roughness, single or multiple vehicles-bridge interaction and material nonlinearity of prestressed or reinforced concrete. ... At last, based on the principle of equivalent dissipated energy, the resulting load-displacement relationship may be simplified as a bilinear hysteretic model which defines the stiffness of the equivalent SDOF system. The excitation force of the equivalent SDOF system is a non-stationary stochastic process with non-zero mean, which is caused by the vehicle weight and vehicle-bridge interaction. This thesis presents a novel approach to the evolutionary spectral analysis for the random response of a coupled vehicle-bridge system. The proposed method is capable of taking into account the random characteristics of vehicle-bridge interaction induced by road surface roughness and effect of multiple vehicles-bridge interaction. In addition, this method allows each vehicle to be modelled using a mass-spring-damper system with 4 Degrees Of Freedom (DOF). The resulting stochastic dynamic interaction force can be transformed to an excitation force of the equivalent SDOF system by applying the principle of virtual work. Once the mass, damping, stiffness and excitation force of the equivalent SDOF system are determined, the equation of motion of this SDOF system can be solved using the equivalent linearization method. The entire proposed rating procedure is applied to rating of a practical bridge located in the Shire of Roebourne in Western Australia. Also, parametric studies are conducted in this research to investigate the effects of the length ratio, vehicle to bridge frequency ratio, bridge damping ratio, vehicle to bridge mass ratio, vehicle speed, vehicle number and road surface condition on the DAF and DLC.