Experimental and theoretical investigation on RBS reinforced concrete innovative joints with and without floor joists

This study introduces an innovative application of the Reduced Beam Section (RBS) concept in Reinforced Concrete (RC) beam-column connections, aiming to improve seismic performance by controlling the location of the plastic hinge and reducing the beam ends resistance. This reduction could compensate for the additional strength provided by RC joists, ensuring that the beam’s capacity does not increase excessively, which could otherwise negatively impact the beam-column hierarchy criterion. Notably, current design codes do not provide specific guidelines for accounting for the overstrength introduced by joists. While extensively studied in steel structures, the RBS concept remains unexplored in RC systems. To address this gap, six RC beam-column subassemblies, with and without floor joists, were subjected to monotonic and cyclic loading. The experimental campaign demonstrated the significant influence of the floor joists in enhancing the beam's load-bearing capacity and energy dissipation. A theoretical model was also developed to quantify the joist contribution, showing strong alignment with experimental results. The research findings confirm that the proposed RBS design effectively take into account the presence of joists, enhances energy dissipation capacity and allows to prevent undesirable failure mechanisms in RC beam-column joints and columns, offering a promising solution for the seismic design of RC structures. • A novel RBS joint for RC frames is proposed, detailing its design and seismic performance. • Comparative tests highlight the role of floor joists in stiffness and energy dissipation. • An equivalent beam model is developed to quantify the joists’ contribution to resistance.