The Safety And Reliability Of Prestressed Concrete Beams Under Freeze-thaw And Rusting Damage Studying

In the process of using prestressed concrete components,not only is it subject to external forces,but also damaged by harmful chemical substances.In addition to the degradation of the structure's own performance,many prestressed concrete structures exhibit varying degrees of disease conditions.In the cracks are too large,increasing deflection,etc.,making the bearing capacity of many reinforced concrete structures do not meet the requirements.Corrosion of steel bars and damage of freeze-thaw cycles are two extremely important factors that affect the reliability of concrete structures.Therefore,it is particularly important to study the safety and reliability of prestressed concrete members under corrosion of steel bars and freeze-thaw cycles.There are relatively many studies on the reliability of structural single-factor damage at home and abroad,but few studies on the structural reliability under coupled damage,especially the related studies of prestressed concrete members under coupling damage.This paper is based on the coupled damage test of corrosion and freeze-thaw cycle of prestressed tendons of unbonded prestressed concrete beams carried out by the research group,and combines existing research results to study the safety and reliability that prestressed concrete beams under coupled damage of steel strand corrosion and freeze-thaw cycles.The main research content are as follows:(1)Research on basic theory of reliability.It mainly discusses the basic concept of reliability,the development direction of reliability,the evaluation method of reliability,the basic principle of reliability,and the calculation method of reliability.Focuses on the principles and steps for the calculation of reliable indicators by the JC method and the Monte Carlo method.(2)Focused on the relevant experiments carried out by the research group,including:steel strand corrosion test of unbonded prestressed concrete beams,freeze-thaw cycle damage test and coupling damage test of steel strand corrosion and freeze-thaw cycles.Then,according to the test results,the relationship between the effective prestressing of the damaged components and the corrosion rate,the number of freeze-thaw cycles,and the coupling between them was revealed.The corresponding function model was fittedaccording to the data processing software,and the fitting effect was good.It provides the basis for the study of structural resistance after damage in the limit state of the bearing capacity.(3)The static load test of the prestressed beam after pre-stressed tendon corrosion and freeze-thaw cycle coupled damage was introduced.According to the test results,it was found that the damage of the beam after freeze-thaw cycle gradually became super-reinforcement with the increase of the number of freeze-thaw cycles.The characteristics of damage are as follows: After the corrosion of steel strands,the damage of the beam body gradually becomes a feature of less rib failure as the corrosion rate increases.(4)Study on reliability of limit state of prestressed concrete beam bearing capacity under coupling damage.The probabilistic model of load effect was statistically analyzed.The relationship between the mechanical performance index of concrete and steel reinforcement under coupling damage and the corrosion rate and the number of freeze-thaw cycles was analyzed.Based on this,the flexural resistance expression of components containing corrosion rate and freeze-thaw cycles was deduced.Then,the ultimate state function function of load carrying capacity containing damage factors was established,and the program flow of using JC method to obtain reliable indicators was given.The JC method was used to calculate and analyze the reliability of the 16 damaged beams in this experiment,and the formula for the reliability under the damage deduced in this chapter was verified.The rules of the reliability index along with the corrosion rate and the number of freeze-thaw cycles were analyzed.The analysis shows that the effect of coupling damage on the reliability of the structure is greater than the effect of the single factor superposition.(5)Coupling damage of prestressed concrete beams in normal service limit state reliability study.Considering the maximum crack width and maximum deflection of structural members as the object of reliability study,the calculation formulas for maximum crack width and maximum deflection of prestressed concrete beams with damage factors were established,and the resistances based on the specified limits were established as the components.Taking the maximum crack width and deflection as the structural function function in the load effect,each parameter in the function is considered as a random variable,and the Monte Carlo method is used to solve the structural failure probability method,which solves the limitation of the specification.The value is treated as a constant problem,and the calculation steps are given.