The University of Manchester Research
Design of aluminium alloy beams at elevated temperatures
DOI:
10.1016/j.tws.2019.03.052
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Accepted author manuscript
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Citation for published version (APA):
Su, M., Zhang, Y., & Young, B. (2019). Design of aluminium alloy beams at elevated temperatures. Thin-Walled
Structures, 140, 506-515. https://doi.org/10.1016/j.tws.2019.03.052
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Thin-Walled Structures
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Download date:09. Aug. 2022
Design of aluminium alloy beams at elevated temperatures
Mei-Ni Su
1*
, Yu Zhang
1
and Ben Young
2
1
School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester,
UK. Email: meini.su@manchester.ac.uk
2
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University,
Hong Kong, China (Formerly, Department of Civil Engineering, The University of Hong Kong,
Pokfulam Road, Hong Kong, China)
Abstract
The material properties of aluminium alloys could be affected significantly as temperature rises.
The present study aims to investigate the behaviour of aluminium alloy beams at elevated
temperatures using finite element analyses. The newly developed numerical model was validated
against a total of eight square hollow section beams subjected to three-point bending tests at
elevated temperatures. The validated model was used to generate 120 numerical results in the
parametric study. Three key parameters were considered, including cross-section slenderness
ranging from 8 to 38, temperatures ranging from 24°C to 600°C and two aluminium alloys (6061-
T6 and 6063-T5). Thus, a data pool containing a total of 128 experimental and numerical results
was formed. The appropriateness of the design rules in the American Aluminium Design Manual,
the Australian/New Zealand Standard, Eurocode 9 and the continuous strength method (CSM) for
aluminium alloy beams at elevated temperature are assessed against the newly generated data
pool. In comparison, the design strengths predicted by the four design methods are generally
conservative, whereas the CSM approach is found to be the most accurate and consistent
throughout the full temperature range. Additionally, reliability analysis has also been conducted to
evaluate the reliability level of the aforementioned design methods for aluminium alloy beams at
elevated temperatures.
Keywords: Aluminium alloys; Beams; Elevated temperatures; Flexural design; Numerical study
1. Introduction
Aluminium alloys are used in construction industry widely for its high strength-to-weight ratio,
Su, M.N., Zhang, Y. & Young, B., (2019), “Design of aluminium alloy beams at elevated
temperatures”, Thin-walled structures. 140: 506-515.
ease of fabrication, good plasticity and corrosion-resistant. Aluminium alloy members are
manufactured by extrusion and pultrusion, which enables the production of more complex shapes.
This can be particularly beneficial for enhancing resistance to local buckling through, for example,
the addition of internal stiffeners. A number of studies [1-5] have investigated the flexural
behaviour and proposed the design methods of aluminium alloy thin-walled members with
stiffeners. An urgent concern in the structural design of aluminium alloy members is the safety at
high temperatures or fire conditions, since the material properties of aluminium alloys highly
depend on temperature and vital properties degradation occurs at elevated temperatures. The
response of aluminium alloy becomes increasingly nonlinear at elevated temperatures.
A great number of experimental and numerical investigations on aluminium alloy beams at
ambient temperatures have been carried out, including Lai and Nethercot [6], Moen et al. [7,8],
Zhu and Young [9], and Su et al. [10]. As for the aluminium alloy structural members at elevated
temperature, the majority studies are focused on columns [11-13]. Studies on aluminium alloy
beams at high temperatures are limited. Meulen [14] performed the steady state and transient state
experiments on 6060-T66 aluminium alloy beams of square hollow sections. Steady state tests
were carried out between the range of 250 to 300; transient state tests were conducted at a rate
of either 2.5/min or 10/min. From steady state test results, it was found that the cross-sectional
classification limits in Eurocode 9 (EC9) [15, 16] are applicable for specimens at temperatures
smaller than 250, while EC9 also agrees well with transient state test results if specimens were
heated less than 120 mins. Suzuki et al. [17] performed experiments on aluminium alloy (5083-
H112) H-section beams to investigate the flexural performance at fire and critical temperature.
The critical temperatures predicted by EC9 [15, 16] were found to be conservative. Zheng and
Zhang [18] developed numerical models for aluminium alloy I-section beams and validated
against experimental results on aluminium alloy 5083-H112 conducted by Suzuki et al. [17] and
aluminium alloy 6060-T66 by Maljaars et al. [12].
The development and application of aluminium alloys have been supported by existing
international design rules, such as the American Aluminum Design Manual (ADM) [19], the
Australian/New Zealand Standard (AS/NZS) [20] and Eurocode 9 (EC9) [15]. The thermal
properties including thermal expansion and reduction factors are included in Appendix 4, Part I of
ADM [19] and Part 1-2 of EC9 [16]. Substituting the reduced material properties into design
equations in ADM, AS/NZS, EC9 and CSM, the strengths of aluminium alloy structural members
at elevated temperatures could be obtained. Gardner [21], Gardner and Ashraf [22] and Su et al.
[23] proposed a deformation - based design approach, the continuous strength method (CSM) for
aluminium alloy members. The result comparison revealed that the CSM can increase the
accuracy and consistency of the prediction by adopting the new base curve showing the
continuous relationship between cross-section deformation capacity and slenderness. The
appropriateness of the CSM approach for aluminium alloy members at elevated temperatures can
also be assessed by adopting the material properties at corresponding temperatures.
The present paper aims to investigate the flexural behaviour and design of aluminium alloy beams
at elevated temperatures. The aluminium alloy beam tests [14] and tensile coupon tests [24]
conducted at elevated temperatures were collected from literature. A numerical model of
aluminium alloy beams on square hollow sections was developed using ABAQUS programme [25]
and validated against experimental results [14]. The validated finite element (FE) model was used
to conduct parametric study based on the tensile coupon test results of normal and high strength
aluminium alloys [24]. A total of additional 120 numerical results of aluminium alloy beams at
elevated temperatures were generated from parametric study. Both the collected experimental
results and newly generated numerical data were utilised to assess the existing design equations in
the ADM, the AS/NZS, EC9 and the CSM. Reliability analysis was also performed to assess the
reliability and safety of existing design rules.
2. Data collection
The data at elevated temperatures collected and used in this paper are three-point bending tests
performed by Meulen [14] and tensile coupon tests conducted by Su and Young [24].
2.1 Three-point bending test results
A total of eight three-point bending tests on aluminium alloy beams at high temperature were
conducted by Meulen [14]. The beams were extruded by aluminium alloys 6060-T66. The cross-
sections of the beams were square hollow sections with nominal outer dimension of 100 mm and
nominal thickness of 3 mm, 4 mm or 5 mm. Two lengths of 1000 mm and 2000 mm were
considered. Table 1 summarized the cross-section diameters, material properties obtained at
corresponding temperatures and the loading capacities. The symbols presented in Table 1 are
defined as follow: B and H are the outer dimension, t is the thickness, L is the beam length, D is
the length of the supporting insulation at middle of span, E is the Young’s modulus, f
y
is the yield
stress, which is taken as 0.2% proof stress, f
u
is the ultimate stress, T is the temperature at which
the test was conducted and P
exp
is the experimental ultimate force, which is taken as the maximum
force that the specimen can endure. The experiments were conducted by steady state method at
250℃ and 300℃. Details of the test setup can be referred to Ref. [14]. The results summarized in
Table 1 are used to validate the newly developed finite element model in this study as detailed in
Section 3.1 of this paper.
2.2 Tensile coupon test results
Su and Young [24] reported material properties of normal strength aluminium alloy 6063-T5 and
high strength aluminium alloy 6061-T6 at elevated temperatures ranging from 24 to 600°C Both
static state tests and transient state tests were performed by Su and Young [24], but only results
from steady state tests are collected and used herein. In steady state tests, specimens were loaded
to failure at a constant temperature, while in the transient state tests, specimens were heated up to
failure at a specified load level. In steady state tests, the specimens were heated up under 10
various nominal temperatures ranging from 24 to 600 with intervals of 50 or 100. The
upper end of specimen was fixed while the lower end was free for expansion during the process of
heating until it reaches to the required temperature. After the required temperature was stabilized
for ten minutes, the lower end of specimen was gripped. The load to the specimens was given
through displacement with a constant loading rate of 0.3 mm/min until failure. Key material
properties at elevated temperatures reported by Su and Young [24] are summarized in Table 2 and
used to conduct the parametric study as detailed in Section 3.2 of this paper.
3. Numerical study
Finite element (FE) model for three-point bending beams was developed using ABAQUS
![Table 3. Comparison between experimental [14] and numerical results of three-point bending beams](/figures/table-3-comparison-between-experimental-14-and-numerical-2gt0ozb6.webp)
