Steel pallet racks - Experimental characterization of the cross- and down-aisle behaviour

Abstract

Prediction of the structural behaviour of pallet racks is known as a difficult task because affected by the particular geometry of their structural components, often exhibiting a highly non-linear behaviour. Due to these peculiarities, specific modelling and design rules are required for such nontraditional steel structures that cannot be considered as classical buildings. This is particularly the case for their seismic design. The most recent design standards propose therefore a combined numerical-experimental approach in which the design structural analysis is supported by specific tests to evaluate the performance of the key components (members and joints). Results presented in this paper are part of a wide research program “Seisracks2 – Storage Racks in Seismic Areas” funded by the European Union (RFCS research program). This research program aims at constituting a scientific background document for the conversion of the Code of practice FEM 10.2.08 to a European Standard. The present paper intends to summarize the current situation of two main aspects of this research: (i) the investigations carried out on the cross-aisle behaviour, with the objective of covering a wide range of configurations (D/Z/X type of cross bracing including different types of connection) and to investigate their consequences on the transverse stiffness, resistance and deformation capacity; (ii) the behaviour in down-aisle direction in presence of eccentric vertical bracings (hybrid frame/braced structural behaviour) with a significant torsional component due to the eccentricity of the bracing system with respect to the centre of mass of the stored goods. The objectives of the study are to provide an experimental corpus available for proper calibration of numerical models and to define testing procedures suitable for the identification of the main structural parameters easily transferrable into numerical models. These various issues are investigated by means of full scale push-over and cyclic testing. In the present study, a more realistic configuration has been chosen consisting in 8 meter high cross-frames tested transversally with 4 load levels equally distributed over the height which correspond to the beam levels of the case-studies, i.e. to levels where the masses are actually present. Vertical side guides prevent the out-of-plane instabilities. Displacement transducers are located at each beam level and at the bottom. The objective is clearly to test the frame in a real loading configuration in terms of shear and overall bending moment distribution. Down-aisle tests consist in 1 span – 1 level frames. The system of the longitudinal bracings is composed of vertical bracings - X bracings with extra uprights and extra horizontal element acting as a rigid frame - and horizontal bracings. The load is applied horizontally by means of an additional beam pushing against steel-stops welded at mid-length of the pallet-beams. The displacements are measured at 10 different positions: longitudinal displacements of the 6 uprights and transversal displacements of the 4 external uprights, all at the pallet-beam’s height.