Numerical Modeling Of Earthquake-damaged RC Frames Retrofitted With FRP And Seismic Performance Assessment

For earthquake-damaged reinforced concrete(RC)frame structures,it is necessary to evaluate their remaining seismic capacity.Retrofit are required for the earthquake-damaged frames which cannot meet the requirements of the current seismic codes and still have repair value.Fiber reinforced polymer(FRP)is widely used for retrofitting concrete structures because of its high strength,light weight and good corrosion resistance capacity.At present,researches on seismic performances of FRP-retrofitted earthquake-damaged RC frames are quite limited,and the existing studies are mainly focused on experimental investigation.The lack of relevant researches limits the engineering applications of FRP in retrofitting earthquake-damaged frames.The current seismic identification and retrofit mainly depend on the test results of the damaged structures and the engineering experience of the designers,and analysis models of FRP-retrofitted earthquake-damaged structural components and structures are quite limited.In order to systematically investigate the seismic performances of FRP-retrofitted earthquake-damaged structural components and structures,the following studies were carried out:(1)Based on the damage states(e.g,number of cracks,concrete spalling,and bare rebars)of RC columns,a finite element modeling method of FRP-retrofitted earthquake-damaged RC columns was developed with considering both the calculation accuracy and efficiency.Based on the comparisons between the numerical predictions and experimental results of FRP-retrofitted earthquake-damaged RC columns,the effects of axial compression ratio,concrete strength,longitudinal reinforcement ratio,FRP wrapping layers and FRP wrapping length on the mechanical behaviors of retrofitted RC columns were investigated.(2)A total of 5120 Pushover analyses of FRP-retrofitted earthquake-damaged RC columns were carried out.Adopting the tri-linear load-displacement skeleton curve model,the influences of damage states on the feature points of the skeleton curve were studied.A calculation model for the skeleton curves of FRP-retrofitted RC columns was proposed by data regression analysis.Comparing with the experimental data and model prediction results,the proposed skeleton curve model showed good prediction accuracy.In addition,the relationship between the damage states and the Park-Ang damage index was established by comparison with the experimental data,which provided a foundation for quantitative investigation of the remaining seismic performances of earthquake-damaged frame structures.(3)Taking a five-layer and three-span RC frame as the research object,Pushover analyses of the intact frame,the earthquake-damaged frame and the FRP-retrofitted earthquake-damaged frame were carried out.The influences of the longitudinal pasted FRP modeled with/without utilizing the MinMax command on the Pushover curve were compared.According to the principles of seismic vulnerability analysis,100 seismic waves were selected,and the vulnerability analyses of the intact frame,the earthquake-damaged frame and the FRP-retrofitted earthquake-damaged frame were carried out by the cloud map method.(4)Considering the changes of the earthquake demand in the subsequent service period,the seismic performance margin ratio was adopted,and a evaluation method for retrofit schemes of earthquake-damaged structures was proposed.Based on the above vulnerability analysis results,taking a 40-year subsequent service period as an example,the seismic performance evaluation for the retrofit schemes was carried out by using the equal evaluation intensity criterion,the equal exceeding probability criterion and the equal average annual incidence rate criterion.