Residual Performance Prediction And Its Capacity Catastrophic Degradation Behavior Simulation Of Seismic-damaged RC Columns

Quantitative evaluation of the residual performance of seismic-damaged reinforced concrete(RC)structures is an important part of urban reconstruction after disasters,and it plays a vital role in guiding reconstruction decisions.The damage degree and damage distribution of seismic-damaged RC structures are the direct theoretical basis for quantifying the residual performance of earthquake-damaged RC structures,and it is also a challenging task.The research results on the damage levels of seismic-damaged RC structures are relatively rich,but the research on the quantitative analysis of its residual performance is relatively lacking.Obtaining the actual load-displacement response of seismic-damaged RC structures is an important basis for quantitative description of earthquake damaged RC structures,but there is no relevant research.Based on the damage distribution model,the residual performance evaluation method of seismic-damaged RC columns is proposed in this paper,and the simulation of catastrophic degradation behavior of RC column bearing capacity is nested in the method.This method can directly obtain the actual load-displacement response of the seismic-damaged structure through modeling and analysis based on the macroscopic damage phenomenon of the seismic-damaged structure,and fully describe the remaining performance of the seismic-damaged structure.The main contents of this research work are listed as follows:1)The corresponding relationship between damage index and observable damage phenomenon is established.By analyzing the corresponding relationship between the damage index of each loading history of the RC column and the accompanying damage phenomenon,and referring to the existing research results,the range of the damage index corresponding to different damage levels and the macroscopic failure phenomenon of RC members under each damage level are determined.Finally,a reference table of the corresponding relationship between the damage index and the macroscopic damage phenomenon is obtained.2)The damage distribution model of potential plastic hinge area of RC column is proposed.Taking 8 RC columns as the research objects,the cumulative damage index of each loading cycle is calculated according to the experimental hysteretic curve data,and then the maximum compressive strain of the concrete at the outermost edge of the core area in each loading cycle is extracted.Finally,the relationship between the strain ratio and the damage index is obtained by data fitting method.According to the existing research results and using the material strain ratio as an index,the damage of the material is divided into non-destructive,invisible damage and observable damage,and a damage distribution model is established.The damage distribution model proposed in this paper is checked and verified with the test data of the other four RC columns,and the bond-slip effect of steel bars is initially considered.3)Based on the existing material constitutive model,the constitutive model of seismic damage material is proposed.According to the assumption of “peak-oriented”reloading,the maximum strain of the material during the loading process is regarded as the peak strain of the seismic-damaged material.By modifying the existing material constitutive model,a constitutive model suitable for materials with different degrees of seismic damage is proposed.4)The definition of catastrophic degradation behavior and its judging conditions are proposed.By observing the existing tests,the nonlinear degradation process of RC columns is divided into progressive degradation and catastrophic degradation.Based on the experimental hysteretic curves of 18 RC columns,this paper gives the criteria of the above two degradation modes.5)Based on the existing material constitutive model,the constitutive model of kernel concrete considering the effect of de-confined is proposed.Based on the analysis of the existing research results and the failure phenomena of the existing tests,the catastrophic degradation behavior of RC columns is attributed to the transformation of part of the core concrete(kernel concrete)from the restrained state to the unconstrained state.Based on 18 RC columns,a numerical inversion method is used to determine the proportion of kernel concrete and core concrete.This paper defines the triggering conditions for the state transition of the kernel concrete from the confined state to the unconfined state,and obtains the constitutive model considering the de-confined effect of the kernel concrete by modifying the existing constitutive model of the confined concrete.By comparing the analysis results of finite element modeling analysis of existing specimens based on the model in this paper with the test data,it can be seen that: the proposed model has high accuracy in predicting and analyzing the residual performance of seismic-damaged RC columns,and can evaluate the performance of seismic-damaged RC structures and guide the formulation of repair schemes.