Evaluation On Seismic Damages Of RC Bridge Piers Under Long Duration Earthquake Ground Motions

Bridge is a key component of lifeline engineering.Bridge damages or even collapse during earthquake will seriously hinder the progress of the rescue,and bring serious threat to people’s lives.The structure will produce cumulative damages under the action of long duration earthquake ground motions.Research on the influence of long duration ground motion on structure damages can be used for reference both in seismic design and post-earthquake repair.This dissertation focuses on the earthquake damage mechanism of reinforced concrete bridge pier under long duration earthquake ground motion.The main work and conclusions are as follows:1.A numerical model for RC bridge piers based on the Opensees platform was built.The accuracy of the model was verified by comparing with the test results of other researchers.It is found that the proposed model can simulate the response of RC piers under different loading modes.The degradation of strength and stiffness caused by cumulative damages under low cycle loads can be well simulated.Through the simulation of the model under the action of ground motion,it is found that the model can simulate the response of bridge pier under the action of ground motion.2.In order to study the influence of ground motion duration on nonlinear seismic response of RC bridge pier,the long and short duration ground motions matched by spectrum and spectrum are selected.Nonlinear response of bridge piers under different duration motions were analyzed by the proposed analysis model.Considering the influence of aspect ratio and axial load ratio,pier models with aspect ratios of 6 and 4 were established under axial load ratios of 0.05 and 0.1.For the piers with an axial load ratio of 0.05 and aspect ratio of 6,the maximum drift ratio,residual drift ratio and curvature ductility factor of piers e under long durations are1.2-1.3 times,1.6-1.7 times and 1.5-1.6 times of those of piers under short duration ground motions.When aspect ratio is 4,the maximum drift ratio,residual drift ratio and curvature ductility factor of piers under long durationsare 1.6-1.7 times,2.3-2.9times and 2.3-2.6 times of those of piers under short duration ground motions.For the pier with axial load ratio of 0.1 and aspect ratio is 6,the maximum drift ratio,residual drift ratio and curvature ductility factor of piers under long duration are 1.2 times,1.6times and 1.5-1.6 times of those of piers under short duration ground motion.When aspect ratio is 4,the maximum drift ratio,residual drift ratio and curvature ductility factor of piers under long duration motions are 1.5 times,3.0-3.8 times and 2.3-2.7times of those of pier under short duration motions.3.The fragility analysis was conducted for the piers under different ground motions.PGA was selected as the ground motion index,the drift ratio was selected as the seismic performance parameter.The seismic vulnerability curve was drawn based on the clourd map method.In the seismic fragility curve of the model with axial load ratio of 0.05,when PGA = 0.2g,the probability of slight damage and moderate damage of pier with aspect ratio of 6 under long-duration ground motions are 1.2-1.3times and 3.3-4.6 times of that under short-duration ground motions,respectively.The probability of slight damage and moderate damage of piers with aspect ratio of 4under longduration motions are 1.1-1.2 times and 2.7-3.7 times of that under short duration motions,respectively.When PGA = 0.4 g,the probability of moderate damage and severe damage of piers with aspect ratio of 6 under long-duration motions are 1.8 and 2.8 times of that under short-duration motions,respectively.The probability of moderate damage and severe damage of piers with aspect ratio of 4under long-duration motion are 1.9-2.1 times and 3.9-4.3 times of that under short-duration motions,respectively.4.In the seismic fragility curve of the model with axial load ratio of 0.1,when PGA = 0.2g,the probability of slight damage,moderate damage and severe damage of pier with aspect ratio of 6 under long-duration ground motions are 1.2 times、1.9-2.1times and3.3-3.8 times of that under short-duration ground motions,respectively.The probabilities of slight damage,moderate damage and severe damage of piers with aspect ratio of 4 under long-duration motions are 1.3 times,3.2-3.4 times and 8.6-9.4times of those under short-duration motions,respectively.When PGA = 0.4 g,the probability of moderate damage and severe damage of piers with aspect ratio of 6under long-duration motions are 1.3 times and 1.9-2.0 times of that under short-duration motions,respectively.The probability of moderate damage and severe damage of piers with aspect ratio of 4 under long-duration motions are 1.6 times and3.0-3.4 times of those under short-duration motions,respectively.