Non Linear Analysis of Steel Storage Racks Submitted to Earthquake Loading - Assessment of the Interstorey Drift Sensitivity Coefficient and of Its Use in Simplified Analyses

Abstract eng:
Static steel pallet racks are used for the storage of various types of goods in areas of retail warehouse stores and other facilities, possibly accessible to the public. Storage racks are composed of specifically designed cold-formed steel elements permitting an easy installation and later reconfiguration, consistent with the merchandising needs of a warehouse retail store. Static steel pallet racks can be considered as part of the most flexible structures constructed nowadays, in particular for what concerns the so-called down-aisle (i.e. longitudinal) behaviour. Since rack structures are highly flexible, ULS requirements (stability and resistance) can be fulfilled even if sway displacements are significant. However, this requires of course that the second order geometrical effects be duly taken into account in the global structural analysis. In Europe, the main reference document is the FEM 10.2.08 "Recommendations for the design of static steel pallet racks under seismic conditions" issued by the European Racking Federation. The recommendations of this document are mainly based upon the philosophy of EN 1998-1 (Eurocode 8) although the peculiar dynamic behaviour of racking structures and of their stored unit loads is taken into consideration. Given that the design rules take root in the Eurocode 8, the management of the PDelta effects is based on the so-called θ-parameter or interstorey drift sensitivity coefficient. The paper deals specifically with down-aisle frames of rack structures and follows three definite objectives: (i) Evaluate the sensitivity parameter θ for rack structures such as designed in practice. To this purpose, a database of 18 more or less flexible real structures is developed; (ii) Evaluate the actual impact of the second order effects in seismic context for such flexible structures. This assessment is done through static and dynamic non linear analyses of the 18 structures; (iii) Compare different methods of global analysis and, in particular, assess the accuracy of the simplified approach proposed by FEM 10.2.08 for intermediate values of θ.

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