دانلود رایگان مقاله تاثیر اعوجاج پالت راک برای فشار ترکیب شده و خمش

ABSTRACT

A pallet rack is a structure in which the beams and uprights are cold-formed steel sections. The beam-upright connections are normally clipped in order to select the beam levels required and for ease of assembly. For this reason, the uprights contain holes and perforations distributed along their length. The complexity of these components, with local, distortional and torsional/flexural buckling behaviour, represents a challenge in structural design. The loads acting on the structure are induced by the weight of pallets to be stored, and transmitted to the uprights by the semi-rigid connection system. Therefore, the uprights are thin-walled singly symmetrical perforated open cross-sections bearing axial load and bending moment simultaneously. The main objective of this paper is to analyse the influence of the bending moment on the load bearing capacity of rack uprights subject to axial load together with bending moment. Bending is induced by means of axial forces eccentrically applied. The influence of bending on the strength capacity of rack uprights is analysed through finite element analysis, where residual stresses and strength enhancement induced during cold forming of sections are also considered. Experimental tests have been performed reproducing the load conditions in order to validate the FEA results. The ultimate load has also been calculated according to the European Standards and compared to experimental results.

6. Conclusions

A study of the structural behaviour of a rack upright subjected to combined compression and bending load has been presented. Two different methodologies have been analysed in order to determinate the load carrying capacity through the finite element method. The results obtained have been validated by experimental values. First of all, the experimental tests show that the influence of the bending moment induced by an axial force eccentrically applied on the load carrying capacity of the upright can be very relevant. Therefore, it is essential that finite element analysis reproduces this influence in order to obtain accurate predictions. Two different FEA methodologies have been described to correctly simulate this load cases. The first methodology presented does not take into account the residual stresses and the strength enhancement due to the manufacturing process. The results show that an initial geometrical imperfection has to be included into the nonlinear analysis for all eccentricities to obtain accurate results if a distortional column length is analysed. Moreover, the shape of this initial geometrical perturbation is only relevant to obtain accurate results if the failure mode obtained is different to the experimental one