Experimental investigation of adjustable circular steel connectors for modular steel beam splices

This study proposes an Adjustable Circular Steel Connector (ACS) for beam-to-beam connections in modular steel structures, which enables continuous on-site length adjustment through the threaded engagement of two cylindrical shanks. The load path through the connection was first examined by finite element analysis, and one monolithic beam and three ACS specimens with connector lengths of 450, 500 and 535 mm (RCS-450, RCS-500 and RCS-535) were then tested under monotonic four-point bending. The threaded engagement remained intact in all tests, with no pull-out or thread stripping; inelastic deformation developed instead in the end bracket and in the adjacent portion of Shank B. Across the tested range of adjustment, the three specimens developed 94%, 86% and 82% of the peak moment (316.9 kN m) and 92%, 84% and 80% of the maximum load (633.8 kN) of the monolithic specimen. Increasing the connector length reduced strength and rotational stiffness but increased rotation capacity. All specimens exceeded a ductility index of 3.0, although in the two specimens exhibiting the larger initial slip the index is affected by the identification of the yield displacement. On-site length adjustment can therefore be accommodated without a disproportionate loss of flexural resistance, with connector length acting as a design parameter that trades strength against deformation capacity.