Time-dependent Seismic Fragility Analysis Of Reinforced Concrete Frame Structures Under Chloride Environments At Coastal Areas Of China

Externally China has a vast territory and a long coastline.The chloride salt in the coastal atmospheric environment will cause corrosion of the reinforced concrete structure,resulting in the attenuation of the seismic performance of the reinforced concrete(RC)frame structure.In this paper,multiple RC frame structures designed according Chinese codes are selected as the study cases.Different corrosion degradation models and varying environmental factors are considered and the time-varying seismic fragility curves of the corroded RC frame structure in the coastal salt environment of China analysis.The main research contents are as follows:(1)Based on the available studies,the chloride-induced corrosion process is seperated and the relationship between the service time and the corrosion rate is established with considering the impact of the durability category of the RC structure and the environmental factors.At meanwile,the degradation models of steel and concrete materials’ performance due to corrosion are summarized and classified.The degradation models used in this paper are selected and the differences are compared.(2)A group of representative RC frame structures located at China coastal sites are designed according to Chinese codes using the GEM methods.Based on Open SEES,the finite element(FE)models of the designed RC frames are developed.Further the degradation model of material properties due to corrosion is considered in the FE models.Then the degradation model of corrosion materials is selected to suite this study.The established FE model is verified by comparison with the test data of corroded column.(3)The spectral acceleration is taken as the ground motion intensity measure.Varying material degradation models selected in content(1)are considered.The timedependent seismic fragility curves considering different material degradation models are developed and the effects of different material degradation models are examined and the attenuation relationships of the seismic fragility function parameters with time are generated.(4)Based on the analysis of the first three parts,the time-dependent seismic fragility analysis of the Chinese RC frame structure under the chloride salt environment is comprehensively conducted with considering the influence of structural design variables.The seismic fragility of the corroded RC frames with regards to the distance from the coastline,the type of durability,the duration of service,and the rate of change of the corrosion rate is studied.The effects of various factors on the attenuation of the median value of structural sesimic fragility function were discussed.The time-varying seismic vulnerability curve of a nine-layer structure is obtained.