Seismic Performance Analysis Of Coastal Reinforced Concrete Frames With Non-uniform Longitudinal Corrosion

The corrosion of steel bars is the main factor affecting the durability of RC structures.Due to the coupling effect of the load and the erosion environment,there is non-uniform corrosion(pitting)in the steel bars of the actual engineering RC structures to a certain extent,which will lead to a decrease in the ductility of the material and the seismic performance reduction of structural members and whole structures.And the non-uniform corrosion of the steel bars in the RC structures in coastal area is more serious as a result of the high chloride ion concentration in the atmosphere environment.But for decades,many studies at levels from material and structural members to the whole structures that have been done by worldwide researchers,are based on uniform corrosion,which deviate from the actual situation of pitting corrosion in steel bars in coastal area.Therefore,the RC frame structure in the coastal area is taken as the research object in this paper.Considering pitting corrosion of steel bars,the seismic performance of corroded RC frame structure is studied by numerical simulation using THUFIBER,a fiber-beam-element package that is developed based on the finite element software MSC.MARC.The main research contents and results are as follows:(1)The effects of chloride salt erosion on the mechanical properties of the corroded longitudinal steel bar and core concrete confined by corroded stirrups are considered.The cross-section corrosion rate of the steel bar is obtained based on the two steel corrosion models,uniform corrosion,coexistence of uniform corrosion and pitting corrosion(pitting corrosion).Based on the relationship model between the mechanical properties of the corroded material and the corrosion rate of the steel barη_s,the mechanical properties of the uncorroded steel and concrete in THUFIBER are modified to obtain the constitutive relationship of corroded materials.(2)Based on the numerical simulation of the fiber beam element in THUFIBER,combined with the material constitutive model summarized in(1),the numerical modeling method of the mechanical properties of corroded RC members is systematically described.Comparing the numerical simulation results with the test results of two sets of existing corroded RC members(a set of beams,a set of columns and 1 set of frames),the effectiveness of the numerical simulation method in this paper is verified and the necessity of considering longitudinal pitting corrosion in the mechanical performance simulation of corroded RC structures is shown.(3)A five-story RC frame structure 200m away from the coast is designed with the offshore atmospheric environment of Luohu District of Shenzhen City as the background.According to the modeling methods in(2),the seismic analysis models for uniform corrosion and pitting corrosion of longitudinal bars are established for structures under different service years.Based on 23 far-field seismic records,the elastoplastic time-history analysis of each model calculation example under different earthquake intensity conditions is conducted,and the seismic performance of each model is investigated.It is shown that,with the increase of service years,the corrosion rate of the RC frame structure increases,the seismic displacement requirements increase,the deformation capacity decreases,and the structural failure mode is gradually transformed from the failure of the compressed reinforcement in the frame column to the failure of the tensile reinforcement in the frame beam;under the same service duration,compared with the uniform corrosion model,the pitting corrosion model has higher seismic displacement requirements,lower deformability and higher probability of collapse.(4)On the basis of the 5-layer pitting RC frame model in(3),considering that the main wind direction may have different corrosion effects on various surfaces and areas of the coastal structure,different reinforcement corrosion parameters for the components in different areas are set to further explore the seismic performance of a more realistic seismic performance of the structure in coastal area.It is shown that,with the increase of service years,after introducing the difference of corrosion caused by wind direction in various regions of the structure,the RC frame structure considering longitudinal pitting corrosion will be easier to change to the failure mode controlled by the failure of the tensile reinforcement in the frame beam under strong earthquake;under the same service duration,after introducing wind direction factors,the collapse probability of RC frame structure considering longitudinal pitting corrosion is higher.