Experimental Study On The Behaviors Of Exterior Joints Of Rc Frame Under Low Cyclic Reversed Loading

In this thesis, a total of 6 nearly full-scale exterior beam-column joints of RC frame, with different shear-compression ratio and axial compression ratio, were tested under low cyclic reversed loading. The damage developing process of the joint core zone was carefully monitored and investigated. The exterior joints had some failure characteristics differing from the interior joints, such as: (a) the direction of the cracks in the exterior joint core zone were apt to be vertical; (b) the shear cracks of exterior joint extend into the inside of the column; (c) the concrete of the exterior joint, where no confinement could be provided by the lateral beam, would have more serious damage.The shear capacity, the energy-dissipation capacity, the deterioration of the stiffness and the ductility, were all analyzed by comparing the 6 exterior joints which were conducted by the author, and another 3 exterior joints which were tested by Mr. Chen Cheng, a member of the author's research group. Under different shear compression ratio, effect of axial compression ratio on seismic behavior of the joint was evaluated. Under same shear compression ratio, effect of horizontal stirrup ratio on seismic behavior of the joint was also evaluated. The comparison showed that: under shear compression ratio, axial force. When the shear compression ratio was above the average, the axial force would disbenefit the seismic behavior of the joint. When the shear compression ratio was at lower-middle level, the axial force would improve the ductility of the joint. At the same shear compression ratio level, the horizontal stirrup can improve the ductility of the joint. Generally speaking, the seismic behavior of the exterior joint of RC frame is weaker than the interior joint.According to the characteristics of the exterior joints, the axial compression ratio, the shear compression ratio and the stirrup ratio were considered to be the most affecting factors to the seismic behaviors of the exterior joints. And the horizontal stirrups in the joint core can strengthen the ductility of the joint. However, by re-identifying the"seismic capacity", the two-term shear capacity equation in Chinese Code GB50010-2002 is not reasonable. And it is found that the seismic design of exterior joints is somewhat dangerous.In this thesis, it is underlined that the static shear of a member is different from the seismic shear of a member designed according to capacity design philosophy both in prerequisites and in controlling criteria. In the case of static shear, the bearing capacity is the controlling criteria, it is required that the bearing capacity is greater than acting shear, while for the case of seismic shear, it still requires that no significant deterioration in bearing capacity occurs when ductility or deformation capacity is maintained. That is to say, the seismic shear requires more strict terms.According to the bridge ductile seismic theory and design method, we find that seismic capacity considering the ductility of the joint is more accurate than the traditional shear capacity when measuring the comprehensive seismic behavior of the joint. Based on the experiment results, a design criterion, which is suitable for both of the exterior joint and the interior joint, is proposed.