Parameter Analysis Of Seismic Behavior And Seismic Fragility Estimation Of Thin-walled Short Piers

The short piers of irregular continuous rigid frame bridges are often vulnerable components in strong earthquakes due to their large pushover stiffness.Especially when located in high-intensity areas or near faults,seismic reinforcement measures need to be taken to reduce the pushover stiffness and improve the ductility and bearing capacity.In this paper,we consider two aspects to improve the ductility of short piers of continuous rigid bridge:On the one hand,we propose a new structural forms small spacing double-shaft piers,which combines the advantages of double-limb piers and single-limb piers,such as good ductility,small site occupation,high thrust bearing capacity,and economic cost;On the other hand,the seismic performance of single-limb piers is improved by using a new material,ultra-high performance concrete(Ultra-High Performance Concrete,UHPC),which has good toughness and energy dissipation capacity,and its high strength can effectively reduce the cross-sectional size and thrust stiffness of short single-limb piers,thus improving their seismic performance.In this paper,in order to investigate the seismic performance of thin-walled short piers,the research is carried out based on the OpenSees numerical simulation and analysis platform,using a combination of experimental studies and numerical simulation calculations,and the incremental dynamic analysis of the finite element model to obtain the susceptibility curves of thin-walled short piers.The main research contents are as follows:(1)Firstly,the seismic performance of their damage morphology,hysteresis curves,displacement ductility,stiffness degradation characteristics and energy dissipation capacity were explored by conducting proposed static tests on small spacing double-shaft piers,UHPC thin-walled piers and reinforced concrete(Reinforced Concrete,RC)single-limb piers.(2)Then the modeling methods for seismic performance analysis of thin-walled short piers with small spacing double-shaft piers and UHPC thin-walled piers based on OpenSees software are given.Comparing the experimental results with the modeling calculation results,the fiber model of thin-walled short piers is verified.It also shows that the finite element analysis is reasonable and reliable for thin-walled short piers of bridges with rigid system.(3)Based on the finite element analysis model of thin-walled short piers established by OpenSees software,two groups of 98 parameters(49 each for small spacing double-shaft piers and UHPC thin-walled piers)were designed by changing the parameters of double limb spacing,axial compression ratio and longitudinal reinforcement rate in combination with the orthogonal test design method,and the corresponding model was established for calculation and analysis.The influence degree of each parameter on the finite element model was determined by the extreme difference analysis,and the parameters of the single-factor variables of longitudinal reinforcement rate,double-limb spacing,wall thickness and axial pressure ratio,which had the greatest influence factors,were analyzed.(4)Finally,according to the canonical response spectrum curve,15 real ground shocks were selected from the strong earthquake database of the Pacific Earthquake Engineering Research Center and input in the form of amplitude modulation.The peak ground acceleration was used as the seismic strength parameter and the ductility coefficient of bridge pier displacement was used as the engineering requirement parameter.The seismic vulnerability of small spacing double-shaft piers,UHPC thin-walled piers,and RC single-limb piers was calculated using incremental dynamic analysis(Incremental Dynamic Analysis,IDA).Based on the results of IDA calculations,the seismic susceptibility curves for the respective different damage states were plotted and compared.