Bolted moment connections in drive-in and drive-through steel storage racks

Often unbraced, the stability of steel storage racks may depend solely on the pallet beam to upright connector and on the stiffness of the base plate to floor connection ([1]). This paper presents experimental results from cyclic tests performed on portal beam to upright bolted moment connections intended for cold-formed steel drive-in and drive-through storage racks. In storage racks, portal beams are typically connected to uprights by “tab connectors”, which are costly to manufacture and experience initial looseness. By simply bolting the portal beams to the uprights, bolted moment connections may represent a cost effective alternative to “tab connectors”. A literature review shows that bolted moment connections between cold-formed steel members are economical and feasible. However experimental results show a significant amount of looseness in the connection after an initial high moment-rotational stiffness. Being slender structures, storage racks are sensitive to second-order P-Δ effect, and international racking specifications require the initial looseness of the tab connectors to be considered when analysing the stability of the rack in the down-aisle direction (sway motion). The non-linear cyclic behaviour of bolted moment connections is presented and explained herein. Based on Finite Element results it is shown that for drive-in and drive-through racks, the looseness in bolted moment connections can be ignored in ultimate limit states design. Finally, the paper concludes with proposing two methods, with different degree of complexity, for the design of drive-in and drive-through racks with bolted portal beam to upright bolted moment connections.