Research On Failure Mechanism And Design Method Of Interior Joint With Different Depth Beams In RC Frame Structure

With the rapid development of national economy, large-scale structures and long-span structures appear year by year. Accordingly, in order to satisfy the demand of craft and architecture, there always existed abnormal interior joints. An abnormal beam-column joint can be defined as a joint with beams of different depths and the axes of both columns have a horizontal distance. In this type of connection, the top beam bars are arranged with passing through the joint and the bottom beam bars are anchored with a 90 degree hook in the joint.Current deign cod for abnormal joints are based on empirical considerations of the authority. With the aim to ensure the safety of monolithic structure, ten specimens of interior joints with different depth beams were tested under reversed cyclic loading in this p thesis. The experimental study was conducted that focused on the mechanical behavior of abnormal joints. The major contributions of the work presented in this thesis are listed as follows:1. According to the experimental investigation on ten specimens of abnormal interior joints under low cyclic reversed loading, the failure characteristics, mechanical behaviors of abnormal joints such as the load displacement hysteretic loops, rigidity deterioration and energy dissipation are analyzed. The experimental study was conducted that focused on the effect of joint core dimensions, hoop percentage and axial compression ratio on seismic behavior of abnormal joints. Test results indicated that the critical crack load was quite nearly with the ultimate load of abnormal joints. Considering normal practice in a structural analysis to assume that the beam-column connection is rigid, the reinforcing details of the test specimen, which were designed under the guideline of current codes, can not preserve the structural integrity and satisfy the strong joint demand.2. According to the relative relation between the height of column and the vertical depth eccentricity of beam, the abnormal joints can be divided into two types, and the characteristic calculation of them is also put forward.3. Based on the experimental study, the failure process and failure patterns were obtained. An equivalent strut mechanism for this type joint is put forward, and it is assumed that the strength of the joint is provided by an equivalent diagonal compression strut, in which the concrete stress reaching its maximum compression strength is the mark of joint failure. In addition, the shear stress versus shear angle curves of joint core of tested specimens was calculated by using equivalent diagonal compression strut. Good agreement between experimental results and prediction results is achieved.4. An analytical model for equivalent joint core of frame joint under the combined action of axial load and shear is established, and the shear stress versus shear angle curves of equivalent joint core of tested specimens was calculated by using three shear analysis theories: modified compression field theory, rotating angle softened truss model and fixed angle softened truss model. Results indicated that the calculated results by MCFT are better than those of others. The predictions of MCFT are shown to be in close agreement with available test results of beam-column joints without torsion (including ordinary interior joints, exterior joints, and joints with different depth beams).5. The shear strength of equivalent joint core of tested specimens was calculated by using three methods:softened strut and tie model and attaalla model. Results indicated that the calculated shear strength of STM is quite nearly with that of code method, but STM has more definite mechanical model and can reasonable reveal failure mechanism of beam column joint. The predictions of shear strength of joint by STM are shown to be in close agreement with available test data of beam-column joints without torsion.6. Based on both test results and theoretical analysis results, a higher level control of design method and construction measure for abnormal joint is suggested in this thesis, and it can ensure the safety of beam-column joints without torsion in RC frame structure.