REINFORCED CONCRETE BEAM-COLUMN JOINT:INTERACTION OF ULTIMATE STRENGTHS AND FORCES AT MEMBER ENDS

Abstract

The author proposed a new mathematical model which predicts the ultimate behavior of two-dimensional reinforced concrete beam-column joints. The model is based on a kinematic model named nine DOF model combined with non-linear biaxial constitutive relation of concrete and steel to bear simple algebraic expressions for the ultimate moment capacity and moment at balanced failure. It is applicable to symmetric interior beam-column joints subjected four symmetric moments transmitted among the four adjacent members. This paper extends the model such that it could consider the interaction of ultimate strength and axial force, shear force transmitted from adjacent members framed into the joint as well as the amount of joint shear reinforcement in a beam-column joint designed by weak beam-strong column concept for Capacity Design. It is concluded from the theory that the factors increasing the moment capacity of beam-column joints include (1) axial force, (2) margin of moment capacity of column to beam, (3) confinement by joint shear reinforcement, (4) confinement by mid-layer bars in columns, the effect of which are followed by a simple combination rule in a simple algebraic equation form. It is also shown that the theory predicts that the factorsabove have little effect on the moment at balanced failure while (5) the concrete strength and (6) the ratio of the bar distance to the depth of member have large effect.