THE EFFECT OF ADDITIONAL DIAGONAL BARS ON THE BOND MECHANISM IN A BEAM-COLUMN JOINT

The inelastic analysis of a beam-column joint is highly dependent on the interaction between the rebars and the concrete.On the one hand,this is caused by the bond-slip effect particularly in the vicinity of the column face that accounts mainly for the stiffness degradation of the whole structural specimen. On the other hand,the bond stresses on the longitudinal bars also affect the shear stress in the panel directly.The proposed use of additional diagonal bars is proved effective to improve the behaviour of interior beam-column joints that are often exposed to the most unfavorable bond condition under reversed cyclic loading.It also avoids congestion of reinforcement in the panel.The presence of diagonal bars prevents the development of both joint cracks and interface cracks,which helps to maintain the stiffness of the joint. The shifting of beam plastic hinge away from the column face may protect the core concrete from yielding penetration and enhance the action of concrete strut.The reduced stresses in the longitudinal bars help to achieve less critical bond condition under the cyclic loading,especially in the lack of column axial force.