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 associated with design like they have perforations to facilitate assemblage within the system, driving them to more not easy to analyze by cold-formed steel structures design codes. There are several design codes proposed through the manufacturers associations, as the specifications of Rack Manufacturers Institute (RMI), applied in the nation along while using specification of your American Iron and Steel Institute (AISI). These codes propose experimental stub columns tests for the determination of your resistance. In this particular work, the commercial software, ANSYS, is employed for material and geometric non-linear analysis of these columns, and the results are compared with experimental data obtained by stub column tests, for a typical part of racks made in Brazil.

Introduction
Cold-formed steel sections have become usual inside kinds of structures, and consequently much numerous studies have been carried out to understand their behaviour so you can 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 a great amount of products in reduced areas, due using their vertical design. Besides, they also allow great accessibility towards the stored materials. Many companies are using methods to store their product in massive.

There are several commercial models that fit to the stipulations demanded for each product pertaining to being stored their available space in your home. These models vary from simple shelves to automated structures of above 30 m height. Among these several models, it is worth mentioning the Pallet and Drive-in Tactics. 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 relocate inside the structure and the presence of perforations on the columns to facilitate montage. Fig. 1 shows a Pallet and a Drive-in rack in operation [1].

The Brazilian Association of Handling and Logistic provides some recommendations for designing rack systems that, in the future, get used in the Brazilian code. This work presents an analysis of typical columns of commercial Brazilian racks, using industry 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 from the columns is also assessed.

Section snippets
The rack column
The analyzed column is constructed of cold-formed steel [5], the place that the cross-section shape is a thin-walled «rack». One all those cross sections and the nomenclature used for the identification of its parts are presented in Fig. 2. It has as particularity rear flanges that allow fitting the braces, making it easier to assemble the structure.

The main characteristic of the column, however, is the presence of perforations along its height that allows fitting the connections of braces and also structural

Design concept
The regarding thin-walled sections can give rise to 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 slow up the resistance of these members. The design rules created these members use minimum geometric properties and experimental results to predict the behaviour of framework.

For the evaluation of the load capacity of the column by the RMI specification it is

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

Experimental results
Ultimate compressive strength was evaluated. The experimental program consisted of four years old specimens tested by the «stub column test», described in Section 3. Fig. 6 shows the average actual size of the cross sections tested and the gravity center of the minimum net area,
. Table 2 shows the experimental results of the ultimate axial load,
. As prescribed your stub column test just 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 examine the influence of imperfections, perforations and material properties on the roof mode and supreme strength of rack cold-formed steel sections submitted to axial compression. In the model, shell, solid and contact finite elements were acquainted with represent the stub column analyzed coming from the experimental device. The finite element model also used nominal and experimentally derived stress–strain relationships and geometric imperfection

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