Steel storage pallet racks in seismic zones: Advanced vs. standard design strategies

Steel storage pallet racks are used worldwide to efficiently store goods and products in situations where only limited space is available. Their use has increased remarkably in recent years, owing to the growing importance of the logistics services in the context of the global economy. Despite the quite limited costs of storage racks, essentially due to the extensive use of cold-formed members characterized by high levels of standardization, their safety is of paramount importance. An eventual collapse could in fact result in considerable economic losses and/or loss of human life. The design rules currently adopted, derived from those proposed for more conventional steel buildings, are unable to capture satisfactorily the overall rack response and hence need further improvements, especially for applications in seismic zones. The paper reports the results of a study focussed on the development of more reliable approaches for designing racks against earthquakes. In particular, a wide range of cases of practical interest for routine design has been defined, which is comprised of racks that differ in terms of geometric layout and component performance. For each of them, the load carrying capacity corresponding to different values of the peak ground acceleration has been evaluated via two alternative design approaches: the well-known modal response spectrum analysis approach (MRSA) and an advanced strategy combining non-linear time-history analyses with the assessment of the damage in joints due to the cyclic excursions in plastic range (NLTH-LCF). Based on 56 design cases, requiring in total 1512 structural analyses, the proposed outcomes allow for a direct appraisal of the differences in load carrying capacity. At the same time, the influence of modelling the cyclic joint behavior is highlighted, with reference also to the change in key behavioural parameters, such as flexural strength and rotational stiffness