Experimental assessment of the seismic behavior of unbraced steel storage pallet racks

Steel storage racks are typically made of thin-walled cold formed steel profiles, which prove to be the most versatile, economic and sustainable elements for industrial rack construction. Their lightweight structural systems are usually designed to resist heavy load units, reaching considerable heights. However, the global behavior of storage racks under seismic actions is much less predictable than the behavior of steel buildings made of standard steel profiles and connections, mainly due to the perforations in their thin walled upright columns, and their semi-rigid beam-column and base plate joints. Full scale experimental investigations are greatly needed in order to understand and quantify the global performance of storage racks, and improve their design for seismic actions. For the first time in Europe, thanks to the funding provided by Research Fund for Coal and Steel (RFCS), an extensive full-scale push-over testing program has been carried out on 8 fully-loaded pallet racking specimens (4 unbraced and 4 braced racks), provided by 4 different international rack producers. This paper presents the experimental results of full scale push-over tests performed in the down-aisle (longitudinal) direction on fully-loaded unbraced specimens. In particular, experimental global capacity curves of the tested specimens are presented, discussing the key factors influencing the racks’ response, as well as the failure mechanisms of the different rack typologies. Furthermore, the behavior factor (q) values of each specimen are derived from re-analysis of the test results. Vulnerability of unbraced racks to soft-storey mechanism is demonstrated, highlighting its causes. Design guidelines are provided in order to guarantee a globally homogenous ductility under seismic actions, along with the new safety requirements for the design of the floor connections of unbraced racks.