IMPACT LOAD MODEL ANALYSIS ON THE VEHICLE-TO-PIER COLLISION

Abstract

As the key member of the bridge substructure, the pier is always the most concerned part under variety of hazards, among which the vehicle-induced impact is a rare but an extreme load hazard that may result in significant structural damage, even full failure of the bridge pier. This study overviewed the previous studies in vehicle-to-pier collision and found the design in AASHTO code conservative. Based on the explicit finite elemental method, the sensitivities to the impact load values of different parameters of bridges and vehicles are analyzed by LS-DYNA@. The impact load is the most sensitive among various parameters, including impact velocity, concrete strength, pier diameter, pier length, impact height, axial force, and cargo mass. Two simplified impact load models are suggested for improvement of the design values of the impact load: the simplified mass-spring model and response surface model. The simplified mass-spring model is applied to the explicit analyses on reduced vibration system to obtain the impact load following appropriate assumption. On the other hand, the response surface model is based on mathematic experiment with large quantities of data to find fitting function of the impact load according to the variation of the sensitive parameters. Both methods can give approximate solution for the dynamic peak impact load and the static equivalent impact load. Comparatively, the response surface model is more efficient in design by giving the function of the impact load. The reliability of the pier under the impact load has been analyzed based on Monte-Carlo simulation and response surface model. For light-weight and medium-weight trucks induced impact events, the failure probability of the pier could be controlled to a very low level (i.e. 0.137%, reliability index equal to 3) by appropriately increasing the resistance of the pier. For the heavy truck induced impact load, the most efficient way to reduce the failure probability is to limit the impact velocities, while the cost for increasing the resistance of the pier is uneconomic. In conclusion, the suggested simplified impact load model based on the parametric study could be applied to future analyses and designs for the truck-to-pier impact hazard.