Experiment And Theoretical Analysis Of Shear Capacity Of Beam-column Joints With FRC

Under the seismic excitation?beam-column joint is a key component to ensure thestability and reliability of reinforced concrete frame structure. Based on "strongcolumn-weak beam" mechanism, beam-column joints were strictly designed accordingto specifications in the Chinese seismic design code of concrete structures, which resultsin reinforced congest and construction difficulties. Due to high toughness, high damagetolerance and excellent deformation capacity of FRC material, shear performance andseismic performance of beam-column joints can be improved, and the amount ofstirrups in joint core can be reduced moderately. So steel reinforcement is saved, andconstruction is convenient. Therefore, the study of seismic performance and designmethod in FRC beam-column joints will have better theory signification and practicalvalue.To study the shear performance of FRC beam-column joints, three FRC specimensand one ordinary concrete specimen were carried out by quasi-static tests. With varyingaxial load ratio and FRC compressive strength, developing process of crack and failureprocess under low cyclic reversed loads was observed, the hysteretic behavior, stiffnessand strength degradation, energy dissipation capacity, and the hysteresis characteristicof shear-deformation in the joint core and moment-curvature of beam end was studied..Under the seismic excitation, the longitudinal reinforcement strain increasedquickly and extended to the joint core after the longitudinal reinforcement of the beamadjacent to joint core yielded, which caused the increasing of the principle tension strainof joint core, therefore, shear capacity in joints was dropped by reducing of the effectivecompressive stress of concrete. In this paper, the additional strain of joint caused byyield strain of beam longitudinal reinforcement extending to the joint core was analyzed,the joint principle tension strain was calculated, and the reduction coefficient of concrete compressive strength according to the principle tension strain was determined.On this basis, the strut-and-truss model was used to establish the calculation model ofthe shear capacity of the beam-column joint in which joint shear deformation was alsoconsidered. Based on properties of FRC material, this calculation model of the shearcapacity of the FRC beam-column joint is improved and established, and the calculationresults agreed well with the experimental results.