Experimental and analytical assessment of RC joints with varying reinforcement detailing under push-down loading before and after fires

Abstract

This paper examines the behaviour of RC beam-column joints with different reinforcement detailing arrangements under pushdown loading before and after fires. The thermal responses of the RC joint specimens are firstly described, including the development of the temperature fields and the horizontal reactions as well as the deflections during the heating and cooling phases. Subsequently, displacement-controlled push-down tests are performed, and the vertical load, horizontal reactions as well as detailed deformations are monitored. The bending moment-rotation relationships are derived from the test results, together with an account of the observed failure modes. The mechanical behaviour is also discussed in detail, including the rotational capacity, with emphasis on the effect of different reinforcement detailing arrangements as well as the post-fire condition. Particular attention is given to comparing the experimental axial-moment strength interaction curves and theoretical predictions under ambient conditions so as to examine the underlying mechanisms. In order to support practical application, a simplified analytical method is proposed for simulating the push-down response, based on the combined loading states and idealised constitutive relations, taking into consideration the restraint effect due to horizontal restraint or fire conditions. The suggested analytical procedure is shown to be a reliable and effective approach for representing the behaviour. Based on the findings of this investigation, practical considerations for enhancing the rotational capacity of RC joints are highlighted.