Reinforced Concrete Beam-Column Joints: An Overlooked Failure Mechanism

This paper proposes a new set of general and rational concepts useful in identifying and defining the ultimate behavior of two-dimensional reinforced concrete beam-column joints subjected to lateral load. It is based on a model that reflects observations of the crack pattern at failure and its compatible kinematic field overlooked in previous research. The kinematic model, called a nine-parameter model, is combined with nonlinear constitutive relations for concrete and steel. New concepts of ultimate moment capacity and moment at balanced failure of beam-column joints are defined. The upper bound value of reinforcement precluding joint failure before yielding of longitudinal reinforcement is also defined. In addition, this paper demonstrates how the concepts are used to derive a set of simple algebraic expressions that can be applied to design, taking as an example the simplified case of a symmetric interior beam-column joint subjected to symmetric couples transmitted through the four connected members without joint shear reinforcement or mid-layer longitudinal reinforcement in the column. The factors affecting the moment capacity and the upper bound value of reinforcement are identified by comparing the mathematical prediction to the results of the example. [PUBLICATION ABSTRACT]