Seismic Performance Of Concrete Piers Subjected To Long Duration Ground Motions

In the recent years,strong long-duration ground motions occur frequently,resulting in great damages to bridges all over the world.The ground motion durations have drawn attentions of researchers.Piers are vulnerable members suffered from the earthquakes.With the increase in the ground motion duration,piers endure more inelastic cycles,and the proportion of fatigue damage become greater among total damage.Meanwhile,with the implementation of precast segmental piers and high-performance materials,research on seismic performance of segmental piers with high-strength reinforcements is now a necessity.Combined with the specimen tests and finite element analysis,this thesis gives a research on the low-cycle fatigue performance of the cast-in-place and precast segmental piers.Specific contents are as followed:(1)Research concerned about low-cycle fatigue,influences of ground motion durations on piers and damage models of RC piers was introduced and summarized.Logical approaches for studying piers damage under long-duration ground motions were put forward,and suitable damage model was selected for piers subjected to long-duration ground motions,(2)Quasi-static and low-cycle fatigue tests on cast-in-place and precast columns were designed and carried out.Phenomena were observed and described.Hysteretic behaviors of two kinds of piers under constant amplitude loads were analyzed.Damage developments of piers under low,middle,high amplitude loads were discussed.(3)Based on Opensees,finite element models were established with fiber sections,to analyze the hysteretic behaviors of specimens under cyclic loads.The methods using discrete materials to simulate the mechanical characteristics were put forward,and were proved to effective and accurate,verified by test results.Finite element models were also established for low-cycle fatigue experiments.(4)Based on Miner criterion,Coffin-Manson fatigue-life equation,the Park-Ang model was modified for long-duration ground motions analysis.The model took first excursion failure and fatigue damage accumulation into consideration and corresponded well with quasi-static test results.