Numerical investigation and design of perforated aluminium alloy SHS and RHS columns
Introduction
Aluminium alloy has been widely used in structural applications such as curtain walls, space structures and bridges owing to its material advantages of high strength-to-weight ratio, excellent corrosion resistance and ease of manufacture. Currently, structural members are often perforated with one or more openings to facilitate the construction assembly, building service and equipment installation. These pre-punched openings usually weaken the sectional dimensions and destroy the geometric continuity of structural members, which result in the deterioration of the elastic stiffness and ultimate strengths of structural members. The shape, size, number and location of openings have a certain degree of influences on the behaviour of perforated structural members.
Finite-element analysis (FEA) is a useful and powerful tool that has been widely used in structural analysis and design. Compared to the physical experiments, FEA is a relatively time-saving and convenient method, especially for the structural members with various cross-section geometries. In order to find an accurate and stable finite-element model (FEM) for the parametric study, it is mandatory to verify the FEM against the corresponding experimental results.
A large number of researches were performed on perforated cold-formed steel compression members. In 2001, Shanmugam and Dhanalakshmi [1] studied the ultimate compressive strengths of perforated cold-formed steel channel stub columns with different plate slenderness ratios, opening shapes and sizes by the FEA. The web plate slenderness ratio and opening area ratio were found to be two main variables on the ultimate compressive strengths. In 2007, Moen and Schafer [2] carried out a series of compression tests on 24 cold-formed steel short and intermediate-length columns with and without slotted web holes. The relationship between the elastic buckling and test response of perforated cold-formed steel columns was investigated. It was found that the post-peak response and ductility were influenced by the slotted holes, the cross-section type and length of the columns. For the short columns with higher hole-to-web width ratio, the slotted holes influenced the post-peak response and reduced the ductility of cold-formed steel columns. For the short columns with lower hole-to-web width ratio and intermediate-length columns, the slotted holes had a small influence on the post-peak response and ductility. Moreover, the existence of slotted holes reduced the ultimate strengths of cold-formed steel columns. In 2012, Yao and Rasmussen [3] researched the effects of different shapes, sizes and spacings of perforations on the inelastic stress distributions, load transfers and failure modes of perforated simply-supported plates and perforated C-section columns in compression. It was found that the perforations changed the stress distributions within the members obviously and triggered the distinct failure modes of inward and outward buckles at the nodal lines of local buckles. In 2013, Kulatunga and Macdonald [4] investigated the influence of perforation positions on the ultimate compressive strengths of cold-formed steel columns with lipped channel cross-sections through the FEA. The ultimate compressive strengths were found to be affected by perforation positions. And the perforation positions near the ends of the columns have a greater weakening effect than the perforations at other positions. Furthermore, Kulatunga et al. [5] also researched the influence of perforation shapes on the buckling behaviour of cold-formed steel columns with lipped channel cross-sections by the FEA. It was found that the ultimate compressive strengths varied greatly with the presence of perforations, which decreased with the increase of the length of perforations.
However, limited researches were conducted on perforated aluminium alloy structural members. In 2010, the experimental and numerical investigations were carried out by Zhou and Young [6] on aluminium alloy square hollow sections (SHSs) with circular holes in the webs subjected to web crippling. The diameter of circular holes was found to be the main factor affecting the web crippling behaviour. In 2015, Feng and Young [7] experimentally investigated the compressive behaviour of aluminium alloy SHS stub columns with circular openings. The ultimate compressive strengths obtained from the tests were used to assess the current design rules. It was found that the current design rules for perforated cold-formed steel members were not suitable for perforated aluminium alloy SHS stub columns. Nevertheless, there is no design rule applicable to perforated aluminium alloy columns. It is worth noting that North American Specification (NAS) [8] provides design rules for cold-formed steel members containing holes.
The main objective of this study is to derive the design guidelines for perforated aluminium alloy square and rectangular hollow section (SHS and RHS) columns under axial compression based on the numerical investigation. Hence, this paper mainly focuses on the development and verification of the FEM, which was used to carry out the parametric study and propose the design equations for perforated aluminium alloy SHS and RHS columns. An accurate and reliable non-linear FEM was developed in this study for aluminium alloy SHS and RHS columns with and without circular openings. The FEM was validated by comparing with the corresponding experimental results, which was then used for the parametric study of perforated aluminium alloy SHS and RHS columns with different geometrical dimensions, as well as diameters, numbers and locations of circular openings. The ultimate strengths of the columns predicted by the FEA are compared with the design strengths calculated using the design rules of NAS [8] and derived by Moen and Schafer [9] for cold-formed steel columns with holes by substituting the material properties of aluminium alloys. The design equations are proposed for perforated aluminium alloy SHS and RHS columns based on the current design rules.
Section snippets
Summary of experimental investigation
The experimental investigation presented by Feng et al. [10] provided the ultimate strengths and failure modes of aluminium alloy SHS and RHS columns with and without circular openings compressed between pin-ends. The test specimens included six different cross-section dimensions with different column lengths ranged from 150 to 3000 mm, which were fabricated by extrusion of SHS and RHS using heat-treated aluminium alloys of 6061-T6 and 6063-T5. The material properties of high strength aluminium
General
The finite-element program ABAQUS [12] was used in the numerical analysis for the simulation of aluminium alloy SHS and RHS pin-ended columns tested by Feng et al. [10]. The material properties, measured geometric dimensions, initial local and overall geometric imperfections of test specimens were all incorporated in the FEM. Residual stress caused by heat treatment was not considered in the FEM since it has little influence on the load-carrying capacities of extruded aluminium alloy profiles
Parametric study
The FEM was verified to accurately simulate the strengths and behaviour of aluminium alloy columns in test series III as presented by Feng et al. [10]. Therefore, the validated FEM was used for an extensive parametric study. The parametric study was performed on 594 specimens that consisted of six different cross-section dimensions with three different wall thicknesses (t) and three different overall lengths (L). The multiple circular openings with four different diameters (d), three different
Current design rules
American Specification (AA) [15], European Code (EC9) [16], Australian/New Zealand Standard (AS/NZS) [17], [18] and Chinese Code [19] for the design of aluminium alloy structures provide design rules for imperforated aluminium alloy columns. It is worth noting that the design rules of AA [15] for calculating the design strengths of imperforated aluminium alloy columns were derived based on the Euler column strength using the gross cross-section area. The influence of material non-linearity was
Conclusions
This paper presents a numerical investigation on perforated aluminium alloy SHS and RHS columns by the FEA. The geometric and material non-linearities of aluminium alloy columns were included in the FEM. The non-linear FEM was verified against the corresponding experimental results, which was used to carry out an extensive parametric study. The parametric study consisted of 594 specimens with different cross-section dimensions, overall lengths, as well as diameters, numbers and locations of
Declaration of Competing Interest
The authors declared that there is no conflict of interest.
Acknowledgements
The authors are grateful for the financial support from National Natural Science Foundation of China (Grant No. 51528803), Natural Science Foundation of Guangdong Province of China (Grant No. 2018A030313208), State Key Laboratory of Subtropical Building Science (South China University of Technology, Grant No. 2018ZA02), and Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen Durability Center for Civil Engineering (Shenzhen University, Grant No. GDDCE 18-5).
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