Investigation Of Compressive Behavior And Damage Assessment Of Predamaged Concrete Confined With Fiber-reinforced Polymers

Earthquake can cause great damage to the building structures,because of economic and social reasons,a large number of structures can not be rebuilt after earthquake damage,and it is an effective method to reinforce these damaged structures.Fiber-reinforced polymers(FRP)are widely used in the field of civil reinforcement in civil engineering for its excellent properties such as light weight,high strength,corrosion resistance and easy construction.However,there is little research concerning the axial compressive properties of FRP-confined predamage concrete.Among the man-made fibers,basalt fiber has good corrosion resistance and chemical stability,high thermal stability,good affinity with epoxy resin,abundant raw material and low cost.At the same time,with the increasing awareness of environmental protection in the world,it is of great significance to study the use of plant fiber instead of artificial fiber as the reinforced fibers for strengthening structures.Therefore,the experimental studies on the axial compressive properties of the BFRP and the JFRP confined damaged and undamaged concrete were carried out.Acoustic emission(AE)was monitored for the damage process of FRP-confined concrete during the axial compressive process.The main research contents are as follows:(1)The mechanical properties of two kinds of FRP,such as tensile strength,elongation at rupture,elastic modulus and stress-strain curve,were obtained through the unidirectional tensile study of BFRP and JFRP sheets.(2)The axial stress,axial strain and hoop strain of 34 FRP confined standard concrete cylinders(150×300mm)were measured with different FRP types and layers as well as predamage of concrete as the research parameters.The experimental results showed that the compressive strength and ultimate strain of predamaged concrete can be improved by FRP confinement,and the initial predamage levels had an adverse effect on the compressive strength and elastic modulus of FRP confined concrete.However,the predamage had little effect on the ultimate strain of FRP confined concrete.(3)The strength and ultimate strain models of BFRP confined damaged and undamaged concrete were studied.Firstly,the experimental results were compared with the classical strength model and the ultimate strain model of FRP confined concrete.Then,the strength and ultimate strain models of the BFRP confined damaged and undamaged concrete were proposed.Finally,the test results of JFRP and BFRP confined concrete were compared.(4)The stress-strain models of BFRP confined damaged and undamaged concrete were studied.Firstly,the test curves with five different forms of calculated model curves were compared.Then,the stress-strain model of BFRP confined damaged and undamaged concrete were proposed.(5)The characteristics of AE signal of some specimens were analyzed briefly,and the damage characteristics of FRP confined concrete under axial compressive loading were described.