The Vulnerability Assessment For Reinforced Concrete Bridge Piers Subjected To Near-fault Earthquake Motions

Compared to the far-field ground motion, the near-fault ground motion have clearly pulse wave of speed, and accompany by strong vertical ground motion, which two reasons causing more serious damage of bridge structure. In order to reasonably evaluate the earthquake vulnerability of typical reinforced concrete piers under the action of near-fault ground motion, a common medium span reinforced concrete pier located in the near of fault zone in our country is selected to as the research object. Considering the uncertainty of material strength and basing on the OpenSees aseismic analysis software platform, 13 dynamic elastic-plastic finite element models of reinforced concrete piers is established by using the Latin hypercube sampling, then combinating randomly with the 13 seismic records with significant velocity pulse choosing form PEER seismic database, forming ―Ground motion-bridge pier‖ samples. First, through the pushover analysis, the paper determine damage parameter values of the curvature ductility coefficient, displacement ductility coefficient and displacement Angle in good condition, basic intact, slightly damaged, moderate injury and severe damage(five kinds of damage state in bridge); Then, nonlinear time-history analysis was carried on the pier subjected to 8 far-field ground motion records to obtain the response in bridge pier in small earthquake, medium earthquake and strong earthquake, and then compared with the calculation results of near-fault ground motion, the results prove that the pier damage is bigger than far-field vibration effect under the near-fault ground motion; Last, by using incremental dynamic analysis method the paper anylzes 13 Ground motion-bridge pier samples under the combination action of horizontal and vertical ground motion, as well as gives the vulnerability curve of the displacement ductility coefficient of pier top, low control section curvature ductility coefficient and the displacement Angle, and compared to the vulnerability curve under the action of far-field ground motion. the The results show that reinforced concrete bridge piers under the action of the near-fault ground motion present a more severe earthquake response than the action of far-field ground motion.The Paper make innovations and acquaintanceships in the following aspects:(1)Identified the damage value for the selected models in this paper under different damage states;The paper makes a conclusion about the velocity pulse characteristics of the typical near-fault ground motion, and gives the principle of selecting near-fault ground motion and the selecting results, then on basis of above works do dynamic time history analysis respectively, to contrast and verify the difference between two types of ground motion on seismic performance of reinforced concrete piers.(2)Making comparative analysis of several damage parameters between near-fault ground motion and far-field ground motion;Based on the analysis of damage criteria about displacement ductility coefficient, the curvature ductility coefficient and the displacement Angle, the paper separately gives vulnerability of pier curve under the three criteria, and finally to compare the differences of its seismic performance, and gives the corresponding conclusion.(3)Establish the vulnerability curve of the reinforced concrete bridge piers under the action of near-fault ground motion;The paper gives the theory of vulnerability curve about the near-fault ground motion and the far-field ground motion under the same damage index, then contrast the earthquake vulnerability of reinforced concrete piers, and to evaluate the difference of effects and conclusion.