The Research Of Reliability For The Reinforced Concrete Beams Strengthened With FRP Laminates

Fiber Reinforced Plastic(FRP),which has the advantages of light weight,high strength,corrosion resistance and fatigue resistance,has been widely used in civil engineering field.From the 90 s of last century,extensive research on FRP reinforced concrete structure technology,including the force characteristics and failure mode,FRP material parameters,the uncertainty of the calculation model and the impact of loads combinations on the reliability of the Reinforced concrete beams(Reinforced Concrete Beams,referred to as the RC beams),has been carried out by domestic and foreign scholars,and a series of progress has been made.But these studies mainly focused on the new and old part of the reinforcement as a whole to analyze its reliability.However,the failure of FRP reinforced RC beams is often caused by low reliability of the new or old part(the original reinforced concrete or added FRP).As so far,there is little research on the reliability and the remaining life of FRP reinforced RC structure considering the compatibility and durability of the new and old parts,so it is necessary to study it in depth.In this paper,the factors affecting the reliability of the new and old parts after the reinforcement were studied by considering the coordination problem of the two parts.The residual life of the structure was predicted by establishing the time-dependent reliability model of each part,and the design of the reliability based on the remaining life was put forward.The main research contents and results are as follows:(1)For the structural members in service for several years,based on the existing reinforcement codes,considering the difference between the new and old structure,the time-varying effect of steel and concrete and the characteristics of the secondary force,the bearing capacity formula have been improved,and reliability calculation formula for each part of RC beams have been derived.(2)The effects of FRP material properties,the amount and other parameters on the reliability and the consistency of the old and new parts were studied.The results show that the reliability of the old part remains basically unchanged and the reliability of the new part can be improved by improving the performance and quantity of FRP material.By adjusting the parameters,the reliability of the new and old parts can be harmonized which avoids structural failure due to low reliability of one part.(3)Based on the long-term performance of each part of reinforced RC beams,the time-dependent reliability models for each part were established.The influences of the factors such as the attenuation of bond strength between concrete and reinforcement on time-dependent reliability and residual life were analyzed.(4)The residual service life of structures with different types of FRP,different unloading degree and different reinforcement area were predicted and the reliability design method of FRP strengthened RC beams based on residual life was proposed.This paper provides a useful theoretical support for the reliability design of FRP reinforced concrete structures and the evaluation of the remaining life of reinforced concrete members.This is the first time to consider the coordination problem of the new and old parts in the study of FRP strengthened RC beams,which has certain practical value.