Flexural response of aluminium alloy SHS and RHS with internal stiffeners

Abstract

Tubular profiles, such as square and rectangular hollow sections (SHS and RHS) are widely used in a range of structural engineering applications. Their thin-walled nature means that local buckling is a key design concern, which is usually addressed by adhering to specified slenderness limits. An alternative approach is to employ local plate stiffeners, which can be practically achieved in extruded aluminium alloy sections through the introduction of internal cross stiffeners. The flexural behaviour and design of aluminium alloy SHS and RHS with internal stiffeners is the subject of investigation of the present paper. The primary aims of the study are to generate experimental and numerical data for these new types of cross-section in bending, as well as to assess the applicability of different approaches to their design at cross-sectional and system levels. First, an experimental investigation was performed on aluminium alloy SHS and RHS beams with internal stiffeners subjected to three-point bending, four-point bending and five-point bending (i.e. continuous beams over three supports) of three different configurations. Finite element (FE) models were also developed and validated against the presented test data. Once validated, the models were employed to generate additional data through numerical parametric studies. Comparisons are then made between the experimental/numerical capacities and the Su, M., Young, B. and Gardner, L. (2016), "Flexural resistance of aluminium alloy SHS/RHS with internal stiffeners", Engineering Structures, design capacities predicted using international design specifications for aluminium alloy structures, as well as the continuous strength method (CSM). The design strengths predicted by the American and Australian/New Zealand specifications were found to be conservative, while improved predictions were achieved by Eurocode 9. The most accurate and consistent predictions were obtained using the CSM, which was able to capture the significant observed strain hardening at the cross-sectional level and moment redistribution at the global system level.

The continuous strength method for the design of aluminium alloy structural elements

“…The CSM enables collapse loads beyond those determined from traditional plastic design through a systematic exploitation of strain hardening [12,13]. The CSM design procedure for indeterminate structures is summarised as follows:…”

“…In this section, the aforementioned design methods [6-8 and 12] are used to predict the ultimate capacities of a series of five-point bending specimens [11][12][13], and hence to assess the accuracy of the design rules for indeterminate aluminium alloy structures. The comparative results are summarized in Tables 4 -5 and plotted in Figures 10 -11.…”

“…These specifications provide design rules for a range of structural components and applications though, in some areas, including the capacity of aluminium alloy compression and flexural members, design provisions are often conservative [9][10][11][12][13][14][15][16][17]. In the case of Class 1 and Class 2 cross-sections [8], this conservatism is largely attributed to the lack of account for strain hardening and moment redistribution.…”

Classification of aluminium alloy cross-sections

“…For cross-sections in bending, 53 experimental data points obtained from three-point bending tests on SHS/RHS and I sections [18][19][20], as well as 38 data points from four-point bending tests on SHS/RHS [17,18,19,21,22] have been assembled. In addition, a total of 192 numerical results from validated finite element models of aluminium alloy beams (half in three-point bending and half in four-point bending) have been collected [18 and 19].…”

“…For continuous beams, data from an experimental program featuring 46 SHS/RHS test specimens with and without internal cross stiffeners [19,23], have been collected. The beams were tested in three symmetrical five-point bending configurations.…”