Study On The Decay Law Of Shear Capacity Of Reinforced Concrete T-beam Considering The Corrosion Process Of Chloride Ion

At present,China is in the stage of vigorously developing infrastructure construction.There are many cross-sea projects.Influenced by the marine high chloride ion environment,most of the concrete structures are corroded earlier and more seriously than those in the mainland.Especially for the reinforced concrete bridges,due to the long-term wind load,automobile heavy load,etc.At this time,if it is in the environment of high chloride ion,it will inevitably cause the durability damage such as steel corrosion,concrete rust expansion cracking when it is less than the design service life.The decrease of bearing capacity of concrete bridge caused by the corrosion of reinforcement also makes the failure mode of the bridge confusing.As the shear failure belongs to brittle failure,once the corrosion of concrete bridge occurs shear failure,it will cause life safety problems and huge economic losses.Therefore,it is urgent to ensure the safety and durability of concrete structure in the chloride corrosion environment question.In this paper,chloride corrosion,steel corrosion,bearing capacity degradation and other issues were studied.The main research contents are as follows:(1)Through a large number of literature research,this paper analyzes the current research status of chloride transport model,reinforcement corrosion model,shear capacity calculation model,shear capacity calculation method of corroded concrete beams,and summarizes and analyzes some problems in the current research.(2)Based on the MCFT,an iterative algorithm for the shear bearing capacity of reinforced concrete T-beams under bending and shear is derived.The accuracy of the model in this paper is verified by collecting test samples,and it is less discrete than various specifications;through statistical analysis of the stress state of longitudinal bars,stirrups and concrete when the T-shaped beam samples are in the shear limit state,the iterative method is simplified to obtain the explicit formula,and the correctness of the explicit algorithm is proved by the experimental data.The explicit formula is the best predictor for T-beams with a shear span ratio of less than 4 and a flange width ratio in the range of 3-6.(3)Introduce the chloride ion diffusion model including steel bar retardation,adsorption reaction,and crack size into the T beam durability study,which more truly reflects the distribution law of chloride ion concentration field in the T beam;Mainly studied the effect of crack size on diffusion of chloride ions.In addition,through the electrochemical theory and COMSOL simulation,the applicability of COMSOL in the corrosion of steel bars was verified.It was found that the initial rust time of the steel bar was correspondingly advanced with the increase of the crack size.When the concentration of chlorine on the surface of the concrete was close to the critical concentration of steel bar corrosion,The cracks have a greater impact on the initial rust time,but have a smaller effect on the corrosion rate of the steel bar,and the corrosion rate has little change from the beginning of the corrosion;Mainly studied the effect of crack size on diffusion of chloride ions.At the same crack,the corrosion rate of the steel bar itself also shows a nonlinear increase with time.(4)Introduce the mechanical parameters of corroded rebar into the explicit formula of the shear capacity of the T-beam,obtain the calculation model of the time-varying shear capacity of the corroded reinforced concrete T-beam,and derive the calculation model of time-varying bending capacity of corroded T-beams based on the existing bending capacity model;collecting test data to verify the correctness of the model in this paper;based on this,the steel surface chloride ion concentration of intact concrete T beams and cracked concrete T beams at 95% confidence level under random chloride ion concentration in the splash zone was analyzed.It is found that the web cracks have a greater effect on the early chloride ion concentration on the stirrup surface.At the same time,the cracking rate of the cracked concrete stirrup is greater than that of the intact concrete stirrup,and the corrosion rate of the stirrup is greater than that of the longitudinal reinforcement.The decline rate of shear capacity of cracked concrete is greater than that of intact concrete;within 15 years of chloride ion corrosion,the failure mode of intact concrete is bending failure,while the cracked concrete is shear failure.