Simplified approaches to design medium-rise unbraced steel storage pallet racks. Part 1: elastic buckling analysis.

The design of steel storage pallet racks is quite complex, despite the fact that these structures are built with economical components and manufactured from thin coils or sheets. The most advanced approaches for rack design recommend the use of simplified methods to estimate the key parameters governing both static and seismic design. In the first case, which is the core of this first part of a two-part paper, an evaluation of the elastic critical load multiplier for the sway buckling mode (αcr) is required to select the method of analysis and check member instability. The term αcr can be predicted through simplified approaches, which have been adequately calibrated for traditional steel structures constructed with members having a double-symmetric cross section. Rack uprights (columns) have, in general, an open cross section, with one axis of symmetry, and thus the overall frame response and member behavior is significantly influenced by Wagner’s coefficients, warping torsion, and shear-center eccentricity. Currently, these effects are neglected in routine rack design, owing to the absence of clear indications in standard provisions and the limited availability and knowledge of appropriate software tools supporting this complex design approach. This paper addresses the applicability of simplified approaches for the static design of medium-rise unbraced pallet racks, whereas the second part companion paper considers seismic approaches. A numerical analysis of several racks composed of different geometries, components, and degrees of stiffness of both beam-to-column and base-plate joints has been completed by using an open source finite-element analysis program for academic use, which is characterized by a refined beam formulation accounting for warping effects. Furthermore, the application to model racks of a traditional beam formulation on the basis of the coincidence between the shear center and the cross section centroid allows a direct appraisal of the warping influence on the prediction methods. Finally, to improve the accuracy of the critical load multiplier prediction, a suitable safety factor has been proposed to be used when beam formulations, including warping, are not available for structural analysis.