Experimental Research And Design Method On Performance Of Reinforced Concrete Frame Joints With The Low Concrete Strength

On tall building frame structure design, beams (plates) and columns usually have different concrete grade. The columns'concrete strength is usually higher than the beams'. In the traditional frame joint, the joints'concrete are the same strength as the columns'. This brings many difficulties to the construction. So the frame joints concreted with beams'lower strength concrete is urged intensively by the engineers.Therefor, eleven full-scale specimens in the middle floor with the joints represented by lower strength concrete under cyclic load have been completed by our research group(two interior joints and two exterior joints are completed by the orther of this thesis in the eleven specimens). These eleven full-scale specimens consist of nine interior joints and two exterior joints. All joints are designed according to the shearing strength formula in the Cord[3].Main factors considered in joints design are shear-compression ratio,axial load ratio and concrect strength ratio of beam and column.The collocation of three factors are different with each joint and overlaying the disadvantage conditions in engineering.Based on test result of eleven full-scale specimens in the middle floor with the joints represented by lower strength concrete under cyclic load, In this article, the specimens'seismic behavior on performance of failure mode, load-carrying capacity, ductility, energy dissipation capacity etc were studied. Through comparison with traditional beam-column joints, we can draw some conclusions as follows. Based on these analyse, design method of these joints have been explored and some advices on the engineering also given in this thesis.â‘ The feasibility of the frame joint that the core concrete strength is inferior to that of colimn is validated.Frame's joint that the core concrete strength is inferior to that of colimn must be satisfying the criteria of the applicable Code[1][2][3]and need to be checking calculated with the shearing strength formula in the Cord[3]. If it's the exterior joint or the interior joint whose shear-compression ratio (calculated with the column concrete sthength) is above 0.3, the joint's core should be enhanced.â‘¡Shear-compresure failure mode in the core of these joints is the main failure mode.The failure mode of the frame's joint that the core concrete strength is inferior to that of colimn is as same as the traditional frame joint, Phenomena that concrete in joint region was crushed by axial load were never observed in the eleven joints'test and new failure mode is not appeared.â‘¢The main checking computation content of the frame's joint that the core concrete strength is inferior to that of colimn is shear checking calculation in the joint's core with the shearing strength formula in the Cord[3] .Checking computation contents and methods have been explored in this thesis. When we design these joints, we hould not only carry though the checking computation, but also pay attention to the reasonable constructional details.â‘£Stirrups vertical the shear-action direction in joint core should be pay attention. In the frame's joint that the core concrete strength is inferior to that of colimn, stirrups vertical the shear-action direction revealed lackness a little while.