A Reliability Based Simulation, Monitoring and Code Calibration of Vehicle Effects on Existing Bridge Performance

This paper summarizes the recent work by the first author’s research group related to vehicle effects on existing bridges, using reliability based performance assessment. The first part presents a simulation framework of fatigue reliability assessment for existing bridges considering the effects of vehicle speed, road roughness condition, equivalent stress range and the constant amplitude fatigue threshold. The second part develops a framework to estimate the extreme structural response due to live load in a mean recurrence interval based on short-term monitoring of existing bridges. The Gumbel distribution of the extreme values was derived from extreme value theory and Monte Carlo Simulation. Studies have shown that the vehicle-induced dynamic allowance IM value prescribed by the AASHTO LRFD code may be underestimated under poor road surface conditions (RSCs) of some existing bridges. In addition, the IM, which is a random variable with certain statistical properties, was modeled as a deterministic constant in the code calibration process. In the third part of this paper, the reliability indices of a selected group of prestressed concrete girder bridges are calculated by modeling the IM explicitly as a random variable for different RSCs. Appropriate IM values are suggested for different RSCs in order to achieve a consistent target reliability index and a reliable load rating for existing bridges.