Experimental Research Of The Inelastic Deformation Behavior Of The Inerion Joint In Earthquake-Resistant Frame Structures

Earthquake damages in China and abroad show that the beam-column joint is the key part to ensure the seismic performance of reinforced concrete frame structure. It has an essential ability to make the frame structure with enough rigidity, better ductility and preferable energy dissipation capacity under strong seismic excitation. Experimental study on joint can be generally divided into two different test methods, loading at beam ends and loading at column end, respectively. However, the influence on mechanics performance and inelastic deformation behavior of the joint zone when testing by the two different methods are not very clear. And there is no comparison experiment or finite element analysis has been found in the present study.In view of the above problems, two rectangular reinforced concrete beam-column interior joints with HRB400 longitudinal bars and two rectangular reinforced concrete beam-column inerior joints with HRB500 longitudinal bars were designed following the guidelines of the China code for design of concrete structures(GB50010-2010). The cyclic loading tests of beam-column joints, of which the relative length of beam longitudinal bar is large, were carried out by the method of loading at column end. Based on the test results, the seismic performance of the beam-column joints was investigated. And the ductility capacity of beam-column subassemblage with HRB400 longitudinal bars or with HRB500 longitudinal bars was comparative analyzed. The slippage of beam longitudinal bars, the joint shear deformation and the hysteresis dissipated energy were investigated. Then, the difference between two kinds of loading methods was analyzed. Based on the test results, the predicted results of longitudinal reinforcement stress-slippage model(the following called ?-s model) were verified. At last, the applicability of the ?-s model was evaluated.The main conclusions are as follows:(1) Test results of four specimens loading at column end show that, the use of high-strength HRB500 longitudinal bar can reduce the displacement ductility of the beam-column subassemblage. The increase of relative length of beam longitudinal bar can significantly improve the bond behavior, and it can also reduce the yield penetration, the bond degradation, and the slippage of beam longitudinal bars. The reduce of shear-compression ratio can slow down the development of the concrete damage in the joint area, delay the crush process of the concrete in the joint core, and improve the energy dissipation capacity of the beam-column subassemblage. The analysis on the contribution of joint shear deformation, longitudinal bar slippage and deformation of beam-column itself to the horizontal displacement of column top show that, with the increase of the horizontal displacement of column top, the contribution of the joint shear deformation and the beam longitudinal reinforcement gradually increased, and the contribution of the deformation of beam-column itself gradually decreased.(2) Comparison of the test results of the two different loading methods show that, the concrete damage is more serious and the crack in the joint core is denser when loading at beam ends, while the concrete crack in the joint core is scarce when loading at column end. With different loading methods, the beam longitudinal peak strains are roughly equivalent, but the development of upper beam longitudinal reinforcement stress is relatively slow under column end loading method. The reason may be that the bottom beam longitudinal reinforcement yield first, and the upper beam longitudinal reinforcement yield then.(3) The experimental results show that, the slippage of beam longitudinal reinforcement bar and the joint shear deformation under the column end loading method are smaller than those under the beam ends loading method. The reason may be that the bending deformation of the beam under the column end loading method is obviously smaller than that under the beam ends loading method.(4) Based on the Open Sees platform, the cantilever beam model is used to calculate the stress of the beam longitudinal bar. Then, the calculated results combined with the beam longitudinal bar slippage measurements are compared with the predicted results of the ?-s model. And the comparison results show that, after the yield of the beam longitudinal reinforcement, the test results of the beam longitudinal reinforcement slippage are significantly smaller than that of the model.The main innovations of this paper are as follows:(1) Through the comparison tests, we got the conclusion that the influence on the mechanics performances of joint core are different between the two loading method, loading at beam ends and loading at column end, respectively. The conclusion is that the concrete damage in the joint core under the column end loading method is smaller than that under the beam end loading method.(2) According to the comparison tests, this paper made it clear that both the slippage of beam longitudinal reinforcement and the joint shear deformation under the column end loading method are smaller than that under the beam ends loading method.(3) Because the column end loading method is more close to the mechanical characteristics of beam column joints in the actual structure, and the measuring method of joint shear deformation and beam longitudinal bar slippage are difference from that under beam ends loading method. Therefore, the ?-s model, which is only built on the experimental data of beam ends loading method, has an undeniable error and should be modified.