Experimental investigations on looseness in beam-to-upright connections of CFS storage racks

This paper presents an experimental investigation into the looseness observed in boltless beam-to-upright connections of cold-formed steel storage racks. These connections, formed by tab-insertion mechanisms, are inherently semi-rigid and prone to looseness due to oversize perforations in the uprights, resulting in discontinuities in their structural response under cyclic loading. A total of twelve connection configurations with variations in upright, beam and end-connector geometries were evaluated through single cantilever bending tests as recommended by EN15512. The tests involved alternating sagging and hogging moments to simulate reversal loading conditions, and the looseness was quantified by measuring relative displacements in the connection. Results demonstrated that looseness values ranged from 0.005 to 0.028 radians, correlating to imperfection amplitudes between 1/200 and 1/35. The number of tabs in the end-connector, as well as upright thickness and geometry, significantly influenced the looseness. The study highlights the importance of accounting for connection looseness in rack frame design, as even minor geometric variations can substantially affect connection behavior.