Statistical Law Of Inelastic Deformation In Beam-column Joint And Its Effect On The Seismic Response Of RC Frame

Reinforced concrete beam-column joint experiments indicate that, after thelongitudinal bar of the beam end yield, with the increasing of the spectra, the bend crackon the beam end first widen and later gradually close, the additional rotation angle ofbeam end caused by longitudinal bar through beam-column joint and joint sheardeformation gradually account for the main proportion of the total rotation angle ofbeam end, this proportion will be larger than50percent when the beam-column jointfailure for shear. How will this kind of nonlinear deformation of the beam-column jointzone affect the seismic responses of the RC frame when comes the strong earthquake?Based on the above questions, the following four aspects of research work areproceeded:①Data of domestic39reinforced concrete middle beam-column joint and12reinforced concrete side beam-column joint expriments have been collected. Cantileverbeam model for calculating stress of the longitudianl bar of the beam end prove to befeasible, then the tress of the longitudinal bar of beam end is acquired. From therelationship of caculated stress and measured slippage of the longitudinal bar, thestress-slippage qualitative model have been presented.②Nonlinear fitting is gone on for the relationship between stress and slippage ofthe longitudinal bar, then a quantitative stress-slippage constitutive model which cantake all main beam-column joint parameters into account is acquired. Simulation of13middle beam-column joint and4side beam-column joint expriments with different jointparameters is done, this work can prove the degree of accurancy and reliability of thequantitative stress-slippage constitutive model.③In order to take beam-column joint shear deformation into account, sheardeformation of the bean-column joints is transformed into additional slippage under theprinciple of equal additional rotation angle of beam end. Then a quantitative constitutivemodel which can consider both longitudinal bar slip and beam-column joint sheardeformation is achieved. Simulation of13middle beam-column joint and4sidebeam-column joint expriments with different joint parameters is done, this work canprove the degree of accurancy and reliability of the quantitative stress-slippageconstitutive model.④Under the strong earthquake ground motion records, nonlinear dynamic response analysis of three reinforced concrete frame model (consider neitherlongitudinal bar slip nor beam-column shear deformation which is called conventionalanalytical method, only consider longitudinal bar slip, consider both longitudinal barslip and beam-column joint shear deformation) which reinforced with HRB400steelbars is done, then compare the response of the whole frame, the distribution regularityof plasstic hinge and section hysteresis rule of element end.The main conclusions are as follows:①With the modeling method for a zero-length section element considering bothlongitudinal bar slip throuth beam-column joint and its shear deformation attached tothe beam end, mechanical and deformation performance of beam-columnsubassemblage in joint tests can be accurately simulated. The modeling method take themain joint parameters into account and can be conveniently used in seismic responseanalysis of frame.②Compared with the conventional analytical method, when consider bothlongitudinal bar slip and beam-column joint shear deformation, base shear reduce21.1percent, plastic hinge rate of the beam end reduce80percent and the column end61percent.③Under the analysis with convensional analytical method, when the maximumdrift of the frame is less than0.02, there is no need to consider longitudinal bar slip andbeam-column joint shear deformation; when the maximun drift of the frame is largerthan0.02, it is necessary to take longitudinal bar slip and beam-column joint sheardeformation into account, otherwise, it is not safe of the maximun lateral displacementand drift of the frame.④Designed according to the latest standard “Code for design of concretestructures”(GB50010-2010) and “Code for seismic design of buildings”(GB50011-2010), beam-column joint member failure and shear failure are not appeared inthe analysis with8strong earthquake ground motion records.