Seismic Performance Analysis Of Corroded Reinforced Concrete Frame Beams In Coastal Atmospheric Environment

Steel corrosion is the main factor affecting the durability of reinforced concrete（RC）structures.Due to the coupling effect of load and environment,there is nonuniform corrosion（pitting）of steel bars in the actual structure to a certain extent,which leads to the decrease of material ductility and seismic performance of components and structures.Due to the high chloride concentration in the coastal environment,there are more pitting corrosions of steel bars in the RC structures.Therefore,this thesis takes the corroded RC frame beam in coastal atmospheric environment as the research object,and focuses on the nonuniform corrosion of longitudinal reinforcement.Based on the experimental data collected in the existing literature,the bearing capacity,deformation,failure mode transformation and energy dissipation performance of corroded RC frame beam are studied by combining theoretical analysis and numerical simulation.The main research contents and results of this thesis are as follows:（1）Based on the general finite element software Msc.Marc,by investigation and summary,the appropriate mechanical model of corroded materials is selected,and the numerical modeling method of mechanical properties of RC beams with pitting corrosion is systematically expounded.The reliability of the modeling method of corroded RC beams is verified by comparing with two groups of existing corroded RC beams.（2）The ultimate bearing capacity,ultimate deformation capacity and failure mode transformation of corroded RC beams under uniaxial loading are studied.（1）The bending performance test data of 92 corroded RC beams under unidirectional loading were collected through literature research.Based on the analysis of test data,the ultimate bearing capacity,ultimate deformation and flexural failure mode transformation of corroded RC beams under bending failure were preliminarily studied.（2）Through theoretical research,based on the plane section assumption,the relationship between the ultimate bearing capacity M_u of corroded RC beams and the critical corrosion rateη_cr of flexural failure mode transformation and the maximum corrosion rateη_max of steel bars is established.On the basis of considering the correction coefficient k of equivalent plastic hinge length of corroded RC beams,the calculation model of ultimate displacement of RC beams considering pitting corrosion is established.（3）Further,through numerical simulation,the effects of different cross-section heights and reinforcement ratios on the critical corrosion rateη_cr and ultimate displacement s_u of the flexural failure mode transformation of corroded RC beams are studied.（3）The ultimate bearing capacity,ultimate deformation capacity and energy dissipation capacity of corroded RC beams under low cyclic loading are studied.Based on the research results of corroded RC beams under unidirectional loading in the third chapter,combined with the experimental data of 23 corroded RC beams subjected to low cyclic loading,the prediction formulas of ultimate bearing capacity and ultimate displacement of corroded RC beams under hysteretic loading are proposed.（4）The changes of the failure mode of corroded RC beams in the actual project in coastal atmospheric environment are analyzed.The main results are as follows.The test data of 168corroded RC beams are collected through literature research,and the calculation formula of shear capacity is selected through comparative analysis.Based on the prediction model of steel corrosion rate obtained from literature research,the time-varying shear capacity model and the time-varying flexural capacity model of corroded RC beams considering pitting corrosion are established.Based on the time-varying model of flexural and shear bearing capacity,the analysis method of flexural-shear failure mode transformation of corroded RC beams in coastal atmospheric environment is established,and a beam in a practical project is taken as an example for case analysis.At the same time,the influence of distance from coastline,stirrup diameter,concrete strength and seismic grade on the failure mode transformation of RC beams in coastal atmospheric environment is explored.