External reinforced concrete beam-column joints subjected to monotonic loading

Abstract

This thesis describes an investigation into the response of external reinforced concrete beam-column joints under monotonic loading. The shear force in joints is of concern since it is much higher than that in the adjacent members. The joint shear force is limited by either joint shear failure or flexural failure in the adjoining beam or column. The objectives of the research were both experimental and computational. The main experimental objectives were to study the influence of beam reinforcement detailing, column axial load and joint stirrups on joint shear strength and the mechanisms of joint shear resistance. The computational objectives were to develop a nonlinear finite element modelling procedure for external beam-column joints and to assess previously developed strut and tie (STM) and empirical design methods. To study these parameters, the author carried out a series of tests in the Heavy Structures Laboratory at Imperial College London. Twelve external beam-column joint specimens were tested in three series of four specimens. Series 1 investigated the effect of beam reinforcement anchorage type and bend radius. Series 2 studied the effect of varying the number of joint stirrups and column axial load. Series 3 studied the provision of intermediate column bars as well as the presence and absence of joint stirrups. The shear transfer mechanisms studied in this thesis comprise aggregate interlock, joint shear reinforcement, tension in the bend of the beam reinforcement at its intersection with the critical shear crack and flexural compression. Digital image correlation was used to determine the opening and sliding displacements of the critical shear crack within the joint of each specimen. These displacements were used to assess the contributions of aggregate interlock and joint stirrups to joint shear resistance. Detailed comparisons are presented between the predictions of the developed nonlinear finite element model and the author’s test results. This assessment includes comparisons of measured and predicted load displacement responses and reinforcement strains. The predictions of various strut and tie models and empirical equations proposed by previous researchers are assessed using a large experimental database and conclusions drawn.