Analysis of steel storage rack columns

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Storage rack systems are structures composed of cold-formed steel structural members that are used as columns, beams and bracing. The rack columns present peculiar features in their design because they have perforations to facilitate assemblage of the system, driving them to more challenging to analyze by cold-formed steel structures design codes. Opportunities design codes proposed by the manufacturers associations, as the specifications of Rack Manufacturers Institute (RMI), applied in the nation along a problem specification for this American Iron and Steel Institute (AISI). These codes propose experimental stub columns tests for your determination their particular resistance. In this work, industry software, ANSYS, is useful for material and geometric non-linear analysis of these columns, and the results are compared with experimental data obtained by stub column tests, to get a typical section of racks manufactured in Brazil.

Introduction
Cold-formed steel sections are usual in most kinds of structures, and therefore much reports have been done to understand their behaviour and to develop design procedures. Among these structures, may the storage systems, usually called racks, widely used throughout the world for storing materials in distribution people. These systems provide high storage density, allowing the storage of lots of products in reduced areas, due using their vertical mood. Besides, they also allow great accessibility on the stored resources. Many companies are using these systems to store their product in massive.

There are several commercial models that fit to the conditions demanded each product to be stored the actual world available space in your home. These models vary from simple shelves to automated structures of more than 30 m height. Among these several models, it deserves mentioning the Pallet and Drive-in Systems. The Pallet rack is the most prevalent storage rack used in Brazil. The Drive-in model presents peculiar structural concepts: the deficiency of transversal beams to allow trucks to move inside framework and the presence of perforations more than a columns to facilitate installation. Fig. 1 shows a Pallet and a Drive-in rack in operation [1].

The Brazilian Association of Handling and Logistic offers some recommendations for designing rack systems that, in the future, will be used in a Brazilian prefix. This work presents an analysis of typical columns of commercial Brazilian racks, using the commercial finite element software ANSYS [2]. The results are weighed against experimental data, based on prescriptions of RMI [3] and from previous work (Oliveira [4]). The influence of the perforations and geometric imperfections on the resistance of the columns is also assessed.

Section snippets
The rack column
The analyzed column is made of cold-formed steel [5], the location where the cross-section shape is a thin-walled «rack». One all those cross sections and the nomenclature employed for the identification of its parts are presented in Fig. two. It has as particularity rear flanges that enable fitting the braces, making it easier to assemble the muscle.

The main characteristic from the column, however, is the existence of perforations along its height that allows fitting the connections of braces various other structural

Design concept
The use of thin-walled sections can result in specific design problems as a result of failure modes such as local buckling and distortional buckling [6]. The rack sections usually contain perforations and imperfections that decrease the resistance of the members. Account when selecting rules aimed at these members use minimum geometric properties and experimental results to calculate the behaviour of framework.

For the evaluation of the load capacity of the column together with RMI specification it is

Finite element analysis
This item presents the constructional procedures of the finite element model for the proposed non-linear analysis using the software ANSYS. The prototype of the cold-formed steel column and its cross section presented in Fig. 2 can be simulated the shell . To consider the shape of this perforations in the mesh, a triangular mesh was used, with automatic adjust and fine rate, generating small elements may easily be avoided exactly contour the perforations. Fig. 5 presents the finite element meshes

Experimental results
Ultimate compressive strength was evaluated. The experimental program consisted of 4 specimens tested by the «stub column test», described in Section 3. Fig. 6 shows the average actual dimensions of the cross sections tested and the gravity center of minimal net area,
. Table 2 shows the experimental results among the ultimate axial load,
. As prescribed by the stub column test only the ultimate compressive load was measured.

By using Eq. (3) and the experimental results the form factor

Conclusions
A finite element analysis has been developed to learn the influence of imperfections, perforations and material properties on the collapse mode and ultimate strength of rack cold-formed steel sections submitted to axial pressure. In the model, shell, solid and contact finite elements were acquainted with represent the stub column analyzed by the experimental device. The finite element model also used nominal and experimentally derived stress–strain relationships and geometric imperfection

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