PROBABILITY ANALYSIS OF POUNDING SEPARATION DISTANCE OF BRIDGES SUBJECTED TO EARTHQUAKE EXCITATIONS

To characterize the influence of randomness of ground motion on the pounding separation distance, based on the stochastic vibration theory and the matrix system reliability computing method, a probabilistic approach was proposed to evaluate the required separation length of a bridge system. Firstly, a probability model was developed on pounding separation distance of a bridge under spatially varying seismic loads. Secondly, the finite element model of the bridge pounding system was built, and the conditional exceedance probability relation of the separation distance between the adjacent bridge decks and the earthquake magnitude was obtained. Finally, by using the matrix system reliability computing method, the pounding probability relation of the bridge system and separation lengths of all pounding points (deck-deck and deck-abutment) was obtained. Some important conclusions were drawn that the demand of the separation length nonlinearly increases with the increase in the magnitude; the demand of pounding separation distance on deck-abutment at two ends of employed bridge was almost in agreement and the pounding probability at deck-deck pounding point was about 20% larger than that at deck-abutment pounding point. At a magnitude of 7, the probability of all three pounding points triggered was about 63%, the probability of at least two collision was 95%, and the probability of at least one collision was 100%.