Analytical And Experimental Study On The Strength And Ductility Of FRP-Reinforced High Strength Concrete Beam

Recently,the fiber reinforced polymers(FRP) have been widely used in strengthening and rehabilitating the existing reinforced concrete structures due to their superior properties, including their high strength,light weight,good corrosion resistance and simplicity in use. However,most of the researches have been concentrated on the RC members with a normal compressive strength between C30 and C40,but works related to that with the high strength can rarely be found.The high strength concrete has been extensively used in the building industry in recent years,and therefore the structure strengthening/rehabilitation is inevitable. It is believed that the techniques of externally bonded FRP sheets/plates are also the effective methods for the strengthening of high strength concrete structures.Therefore,analytical and experimental studies on the strength and ductility of FRP-reinforced high strength concrete beams were carried out in the thesis.The main contents of the thesis include:(1) A series of comprehensive analytical and experimental studies were carried out to investigate the bond behaviors of FRP-bonded high strength concrete specimens.A single shear test of 123 FRP-bonded high strength concrete specimens and four different types of FRP materials is conducted to investigate the bond-slip behavior of the specimens.Strain distribution along the bonded FRP was obtained based on the strain gauges installed on the FPR strips.Thereafter,three bond-slip relationship models of FRP-bonded high strength concrete are established based on the strain profile of FRP strips.Finally,an anchorage strength model for FRP sheet bonded to high strength concrete is proposed according to the fracture mechanical analysis.(2) An analytical and experimental study was carried out on the shear strengthening of high strength concrete(HSC) beam with externally FRP bonded.A total of 23 high strength concrete beams reinforced with FRP were properly designed to test the shear contributions and behaviors of FRP.Based on these experimental data,a simple and credible expression of calculating the critical shear crack angle was developed.As a result,a shear strength model of FRP reinforced high strength concrete beam was established with very high accuracy when compared with the experimental results.Finally,a design method for high strength RC beams bonded with Carbon FRP(CFRP) for shear reinforcement was proposed correspondingly.(3) An analytical and experimental study is carried out on the FRP reinforced high strength concrete beams in bending.A total of eight high strength concrete beams flexural reinforced with FRP were properly designed to test the bending contributions of FRP.Two bending strength models corresponding to the flexural failure and the failure of intermediate crack(IC) debonding were established,respectively.Based on the concrete failure criterion and the fracture energy release rate failure criterion,two methods for the prediction of the bending capacity of FRP-reinforced high strength RC beams corresponding to the failure of FRP end debonding were finally developed.(4) An experimental study on the ductility of FRP reinforced high strength concrete beams was carried out.A new technique for increasing the ductility of high strength concrete beams by applying the FRP confinement to the compression side of the beam in the plastic hinge zone was provided first.A total of four high strength concrete beams with FRP wrapped in their plastic hinge zone were tested.The results indicated that such technique has remarkably increased the ductility of high strength concrete beams and thus it was effective to increase the ductility.After an analysis on the mechanism of the ductility increment,some effective anchorage measures were finally proposed to enhance the FRP confinement when FRP is bonded to the concrete beam in form of U jacket which is usually the case in reality.(5) A study on the ductility of high strength concrete beam reinforced with FRP bars was finally carried out.A new concept of achieving ductility through compression yielding(CY) was firstly introduced.In a CY beam,a CY block is placed on the compression side of the member in the plastic hinge zone to replace the concrete.The ductility of a CY beam is achieved through the compression yielding of the CY block instead of the tensile yielding of the reinforcing bars.As the plastic deformation of a CY beam is concentrated in the plastic hinge zone,the ductility is remarkably increased and the rupture of FRP will be prevented. Therefore,the ductility problem of high strength concrete beam reinforced with FRP bars can be solved by adopting this technique.Based on the results from the numerical simulations and the theoretical derivations,the influences of the parameters of the CY block on the ductility of a CY beam were firstly investigated and finally an optimal ductility design method of a CY beam was given out with the objective of displacement ductility.