Influence of the RFS Geometry on the Performance of Dissipative Slim-Floor Beam-to-Column Joints

The slim-floor solution, consisting of a shallow cross section, moment-resisting beam-to-column connection, and a reduced lower flange (Reduced Flange Section) has been experimentally and numerically validated for its feasibility in steel framed structures designed for seismic zones. The experimental tests, conducted on cyclically loaded specimens, proved good seismic performance. Notably, the joint achieved a rotation capacity of ±45 mrad at Significant Damage, with the dissipative zone of the slim-floor beam providing the highest contribution to the joint rotation. The key components for an adequate seismic behaviour are the dissipative zone of the slim-floor beam, along with the non-dissipative bolted connection and strong column web panel. To ensure this adequate behaviour, a crucial factor is reducing the wider bottom flange of the beam, ensuring seismic energy dissipation in this component and a balanced flexural response. This challenge is compounded by partial concrete encasement. Since the dissipative zone plays a critical role in joint performance, and Eurocode 4 offers limited guidance for slim-floors, this paper presents results of Finite Element Analyses investigating the Reduced Flange Section geometry. The parametric study aims at identifying the optimal geometry for reliable connection design, adhering to capacity design principles. The key findings and conclusions from this analysis are presented within this paper.