Seismic Performance And Fragility Analysis Of Corroded Reinforced Concrete Columns And Frame Structures

The seismic performance of reinforced concrete(RC)structures will degrade with the growth of service life due to the erosion of the environment.The durability environment zoning and the fifth-generation ground motion parameter zoning map of China show that many areas of China are simultaneously in harsh durability environments and high-intensity seismic fortification areas.The corrosion of reinforcements is the main cause of the degradation of the seismic performance of RC structures.Corrosion of reinforcements in RC structures will cause seismic performance degradation of the structure.Meanwhile,the reduced seismic performance of the structure due to corrosion makes the response of the corroded structure may be greater than that of the uncorroded one under the same seismic excitation,i.e.,corrosion amplifies the seismic demand of the structure.Therefore,how to evaluate the safety of existing corroded RC structures under earthquake action has caused widespread concern in the field of earthquake engineering.Since the risk-oriented Performance-Based Earthquake Engineering(PBEE)assessment framework was proposed,researchers around the world have continuously improved the PBEE assessment framework for many years.As a core part of the PBEE framework,seismic fragility characterizes the failure probability of different limit states for a structure under different ground motion intensity levels.During past seismic fragility studies,only one hazard factor of "seismic action" was usually considered.However,the potential hazard factor of "reinforcement corrosion" was usually not considered sufficiently,which makes engineers unable to accurately evaluate the seismic performance of existing RC structures.Therefore,the carry out the seismic fragility research of corroded RC structures is helpful to promote the research and development of life-cycle PBEE.It also helps engineers rationally evaluate the life-cycle earthquake risk of RC structures to serving earthquake disaster prevention decision-making and sustainable development of the city.Based on the above considerations,in this thesis,the RC frame structure is taken as the research object.The seismic fragility of RC frame structure is investigated at the component and structural levels considering the coupling effect of “reinforcement corrosion” and “seismic action”.The main research contents are as follows:(1)This study establishes the corroded RC column experimental database by collecting the quasi-static experiments of corroded RC columns.Based on the phenomenological method,the modified Ibarra-Medina-Krawinkler material model was used to calibrate the model parameters of the specimen in the database.Subsequently,the regression equations of corrosion-induced deterioration coefficients for backbone curve and cyclic deterioration parameter for energy-consuming were established.And then,the hysteretic model of the corroded RC column was established.(2)Considering the difference of accelerated corrosion technologies,the artificial climate environment(ACE)simulation and the electrochemical chloride erosion(ECE)method were used to accelerate the corrosion of 12 reinforced concrete columns.The differences between the two accelerated corrosion technologies were analyzed from the perspective of micro and macro mechanics aspects.The results show that,due to the difference in the corrosion mechanism,the corrosion products,appearance,and seismic performance of the corroded columns obtained by different accelerated corrosion technologies under similar corrosion degrees were different.In addition,the differences in the seismic performance and failure modes of the corroded RC columns with the change of axial load ratio and corrosion damage degrees were discussed.The research results show that the degradation of the seismic performance of the corroded RC columns with low axial pressure ratio was more dependent on the corrosion damage degree,while the corroded columns with high axial load ratio are greatly affected by the axial load ratio before severe corrosion.After severe corrosion,the seismic performance of the test piece deteriorates sharply.(3)Through collection the experiments of RC columns,the database of RC columns designed according to current codes of China was established.The fragility function of columns designed according to current codes of China is obtained based on the FEMA P58 method.A Latin Hypercube Sampling based method for predicting the fragility function of corroded columns was proposed.And the fragility curve intervals of corroded columns that were designed according to current codes of China with different corrosion damage levels were obtained.(4)A RC frame structure was designed as the case study building based on Chinese codes.The lumped plastic model and distributed plastic model consider corrosion effect were established,and then their seismic performance was analyzed.The difference between the lumped plastic model and the distributed plastic model in calculating the seismic fragility of corroded RC structures was discussed.The results show that under the same ground motion intensity,the difference between the fragility exceed probability in a low limit state of uncorroded and corroded structures established by the distributed plastic model was more obvious than that of the lumped plastic model.The probability of exceeding the fragility curve of the lumped plastic model was higher than that of the distributed plastic model at a high limit state.Finally,considering the uncertainty of parameters,a probability model of the case study building was established.The influence of parameter uncertainty on the structure was revealed.