Research On Seismic Behavior Of Reinforced Concrete Frame Side Joint Assembly Of Beams

The reinforced concrete frame structure is the most widely used form of buildingstructure in our country, and beam-column joint is an important part of the framestructure. For its hub location and complexity of the stress state, the beam-column jointhas long been paid attention both at home and abroad. The exterior joint only hasunilateral beam constraints, therefore the damage of the exterior joints are more seriousin the earthquake compared with interior joint. In this paper, experimental study andfinite element analysis are carried out on the exterior joint beam-columnsubassemblages. The main contents are as follows.(1) The reversed cyclic loading tests were carried out on five exterior jointbeam-column subassemblages. Through different axial load ratios, stirrup ratios in jointcore area and the percentages of longitudinal steel in beam, the shear capacity, theenergy dissipation capacity, the ductility and the mechanics characteristic of stirrupwere comparatively analyzed under the condition that the end of the beams weredestructed. Experimental results indicated that the stirrups participate in the trussmechanism and the confinement mechanism, and the stress of stirrups in differentlocations present inhomogeneity. The higher axial load ratio can slightly improve theshear capacity and the energy dissipation capacity of the subassemblage, but theductility would be affected. The shear value of the joint core area designed inaccordance with the current criterion is low, and it tends to be unsafe when applied tothe practical engineering.(2) With the finite element analysis software ABAQUS, the mechanicalperformance and the failure mode of the exterior joint beam-column subassemblagewere studied. Parametric study is carried out by analyzing108finite element models.The main analysis parameters include shear compression ratio, axial load ratio, stirrupratio of the joint core area and concrete compression strength. The numerical resultsshow that the effect of the axial load ratio on the seismic performance of exterior joints can’t be simply determined because it is too complex. The stirrup ratio of the joint corearea is the key effect factor to affect of the shear capacity of exterior joint, and theultimate failure mode of the exterior joint beam-column subassemblage has muchrelationship with the shear compression ratio and the stirrup ratio of the joint core area.The destruction of the concrete in the core area means the exterior joint destroyed, andthe ductility will be declined while enhancing the concrete strength in the core areaimproves the shear capacity. There are three types of failure modes of exterior jointbeam-column subassemblage, including the beam flexural failure mode, theinclined-tension failure mode of the joint core area and the inclined-compression failuremode of the joint core area. The latter two failure modes can be subdivided into twotypes: the failure mode with the yield of beam longitudinal steels and the failure modewithout.(3) Through the analysis of the transfer mechanisms in the exterior joint core area,the main transfer mechanisms consist of the diagonal strut mechanism, the trussmechanism and the confinement mechanism. According to the transfer mechanisms inthe core area, the calculation models applied to the analysis of the shear capacity of thejoint core area contain the modified compression field theory, the rotating anglesoftened truss mode, the modified rotating angle softened truss model, the fixed anglesoftened truss model and the softened strut-and-tie model. By comparison, the softenedstrut-and-tie model can clearly represent the transfer mechanisms in the exterior jointcore area. The accuracy of the softened strut-and-tie model is verified by thecomparative analysis of the calculate values and the experimental values in this paper.Based on the analytical results, the softened strut-and-tie can be used as the calculatedmodel of the exterior joint core area. Combined with the experimental research, thefinite element analysis and the calculated model, the rationalization proposals to theshear strength calculation formula of joint core area in current standard are put forward.