Warping influence on the static design of unbraced steel storage pallet racks

• Standards do not cover adequately rack modeling nor minimum requirements for the finite element analysis programs are defined.
• The critical load multiplier and the safety index of the verification checks are significantly influenced by warping effects.
• Warping effects influence significantly internal forces and moments, together with the frame deformability.
• Inappropriate beam element formulations neglecting warping could lead to unsafe data for structural verification checks.

The use of thin-walled steel members has significantly increased in the last decades, especially in the field of logistics. Goods and products are frequently stored in pallet racks, i.e., in structural framed systems assembled from components manufactured from cold formed steel coils. The great convenience in using rack systems is, however, counterbalanced by a complex local and global structural behavior, often difficult to predict accurately. Owing to the light weight of the key structural components, rack design requires high engineering competence. A structural failure of these structures may result in a very great economic loss. Several research programs are currently in progress worldwide; their outcomes are expected to contribute significantly to the improvements of design rules. Standards, however, do not seem to cover adequately the modeling phase of the framed systems nor minimum requirements for the finite element (FE) analysis programs to be used for analysis. These two points are fundamental pre-requisites for guaranteeing an adequate safety level in design.A research project aimed at improving the reliability of the design rules for steel storage pallet racks and at developing suitable approaches for preliminary calculations is currently in progress. Main results of a numerical study carried out on typical medium-rise unbraced pallet racks are summarized here with the goal of investigating the key features of the warping influence on the structural frame behavior under monotonic loading; the seismic response of rack is considered in a separate paper.