A Study Of Bond Deterioration In Reinforced Concrete Beam Column Joints PDF Download

This study concentrates on two interrelated aspects pertaining to the deformation of beam-column joints under severe cyclic excitations. In the first part of this study, a closed form solution is developed for computing the slip and its distribution along reinforcing steel bars anchored inside a beam-column interior or exterior joint and subjected to generalized boundary steel stress excitations. The main advantage of the developed slip model, under which tremendous computation effort can be saved, is that: 1) it bypasses the local bond stress-slip relationship of unconfined concrete in its descending portion since no reliable experimental data describes this portion, and 2) it ignores the definition of local bond stress-slip relationship under severe load reversals. With its simplicity, the model reproduced quite accurately experimentally observed results and was shown to be in very good agreement with the presumably more accurate finite element prediction models. In the second part of the study, a joint model for describing the moment-rotation relationship of both interior and exterior beam-column joints subjected to inelastic cyclic loading was developed. The model was derived based on idealized hysteretic material models for concrete and for the reinforcing steel bars. Interaction between steel and concrete through bond and slip of reinforcement inside the joint was taken into consideration using the slip model developed in the first part of this investigation. The joint model accounted for the two primary mechanisms responsible for the deformation of the beam relative to the column in the joint. These are: 1) inelastic rotation occurring within an equivalent plastic hinge length extending outside the beam column interface. and more importantly, 2) the fixed-end rotation arising from the slip of reinforcement at the beam-column interface cracks. The joint model allowed prediction of steel stresses and strains, slips, moments, curvatures, inelastic rotation and plastic rotation at any load level during the deformation or load history. Despite some discrepancy, the developed joint model reproduced within a reasonable degree of accuracy the experimentally observed results. On the other hand, with its simplicity in implementation and tremendous efficiency in computation, the developed joint model retained most of the accuracy of results obtained using finite element predictions.