Dynamic interaction between merchandizes and supporting structure in steel storage racking system

Abstract eng:
When static steel storage racks are subjected to seismic action, a specific limit state must be considered additionally to classical resistance and stability criteria, i.e. the fall of pallets with subsequent damage to goods, to people and to the structure itself. From an analysis point of view, this requires to account both for the sliding motion of the pallets with respect to the supporting beams and, if relevant, for the rocking motion of the stored goods. Further, since the mass of the merchandizes is usually very important compared to the mass of the structure itself, their sliding and rocking motion introduces a strong dynamic interaction between the stored objects and the supporting structure. The objective of the present contribution is to investigate this coupled behavior and to study its consequences on the structural safety in the perspective of deriving design recommendations. To this purpose, a parameter study is performed with a specifically developed numerical tool. Regarding the sliding behavior, it can easily be stressed that if the amplitude of the relative motion is not too important, in such a way that pallets can remain on the rack, the sliding effect can benefit to the structure since it is limiting the horizontal seismic forces transferred to the rack to a maximum intensity equal to the friction force at the interface between pallet and beam. In this contribution, it is evidenced that a reduction factor can thus be applied on the seismic load and that this reduction is depending on the structural typology (and in particular on the first natural frequency of the system) and on the ratio ag/μ between the design acceleration of a structure with the additional masses supposed to be fixed and the friction coefficient of the pallets.

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