Experimental And Analytical Studies On The Failure Mechanism Of CFRP Strengthened RC Beam With Notches

Currently,the fiber reinforced polymers(FRP)are widely adopted in strengthening and retrofitting the reinforced concrete(RC)structures,because of the excellent mechanical properties of the FRP materials.The externally bonding(EB)technic is widely adopted in enhancement of the moment resistance of the RC beams,because of the increased efficiency of construction.The commonly observed failure mode of the EB FRP strengthened RC structures is the interfacial debonding between the bonded FRP plate and the concrete substrate,which has attracted many researchers in recent years.According to previous research,high interfacial stress exists at the interface and the bond strength between the FRP plate and the concrete substrate in turns controls the load-carrying capacity of the FRP strengthened RC concrete beams.In this paper,the author intends to find out the mechanical performance of the FRP strengthened RC beams by the experiments.In order to control the precise location of the debonding initiation and simulate the bending cracks,the vertical notches are precast on the soffit of the RC beam.Both three-point bending and four-point bending are applied on the strengthened beams,to find out the bond performance at different loading conditions.And the RC concrete beams are precast with one and two notches,respectively.During the experiments,the applied loading,deflection and axial deformation of the FRP plate along the axial direction are measured.And the propagations of both cracks on the surface of beam and debonding at the interface are recorded by camera.According to the experimental results,the load-carrying and deformation capacities are dramatically increased by the bonded FRP plate.Based on the experimental observation and interpretation of the measured data,the failure process of the FRP strengthened notched RC beam can be illustrated as follows: First,the deflection of the beam initially increases linearly with the increase of the applied mechanical loading.At this stage,both the interface and the adherends are at elastic deformation stage.The axial stress at the notched section is mainly resisted by the tensile strength of the concrete and the measured axial deformation of the FRP plate is relatively small.Then,with the suddenly propagation of the crack in the RC concrete beam,the tensile stress is transferred from the concrete beam to the bonded FRP plate.At this stage,all the tensile stress at the notched section is resisted by the FRP plate and the deformation of FRP plate increases dramatically as the increase of the applied loading and propagation of the crack in the concrete beam.Afterwards,the interfacial debonding happens at the notched section and propagates along the axial direction.Finally,the failure happens when the interfacial debonding propagates to the plate ends.Based on the comparison of experimental results,the author conducts analytical studies on the load-carrying capacities of FRP strengthened notched concrete beams.The analytical solutions are derived based on the FRP strengthened concrete beam without notch.Then,the recommended safety factors are given based on the experimental results.Figure [58] Table [5] Reference [56]...