Shear stiffness of pallet rack upright frames

Pallet rack uprights are braced in the cross-aisle direction forming a frame, which behaves like a built-up column. Currently two approaches prevail in the racking industry to determine the shear stiffness of these frames. The Rack Manufacturers’ Institute (RMI) code uses a theoretical formula whereas the Federation Europeenne de la Manutention (FEM) code requires testing. There is a considerable difference in the stiffness values determined by the two approaches. A literature review showed that the stiffness predicted by the RMI code could be up to 20 times higher than the experimental stiffness. The shear stiffness of the frames is influenced by the bracing pattern and the connections between the elements. Local distortion of the thin walled open section upright, joint eccentricity and slip due to bolt clearances all affect the behaviour of the frames. The present paper describes experimental and numerical studies conducted at Oxford Brookes University to evaluate shear stiffness.