الملخص: The application of aluminium alloy members in building construction has considerably increased in recent years due to their appealing advantages such as corrosion resistance and high strength-to-weight ratio. However, the elastic modulus of aluminium is only one-third of that of steel, making aluminium members being susceptible to various buckling modes including web crippling. To date, only a limited amount of research study has been conducted to investigate the web crippling failure phenomenon in aluminium structural members, and no research has been carried out on the web crippling behaviour of roll-formed aluminium lipped channel sections. Hence, an experimental study was conducted to assess the web crippling behaviour and capacities of unfastened aluminium lipped channel sections under two flange load cases (End-Two-Flange (ETF) and Interior-Two-Flange (ITF)). Forty tests were performed with different bearing lengths, web heights and thicknesses. The results obtained from this study were then compared with the nominal web crippling strengths predicted using the design rules provided by the Australian, European and American Standards. The comparison showed that the current design equations are potentially unsafe and unreliable to estimate the capacity for aluminium lipped channel sections under both ETF and ITF load cases. Hence, suitable modifications were proposed to the available design equations based on the experimental results to accurately predict the web crippling capacities of aluminium lipped channel sections. Generally, it is shown that the web crippling results acquired from the modified equations agreed well with the test results.

الملخص: Aluminium alloys have recently drawn significant attention in structural applications due to its outstanding mechanical characteristics. Thin-walled members fabricated by aluminium alloys can be more competitive in construction industries than the conventional cold-formed steel sections, particularly in areas with high humidity and severe environmental conditions. Nevertheless, they are more vulnerable to various types of instability due to their relatively low elastic modulus compared to steel. Applying high concentrated load transversely on thin-walled members can cause critical damage to the web of the cross section called web crippling. Although a large number of studies has been performed to investigate the web crippling mechanisms on different types of sections, the existing studies are primarily of the empirical nature and thus merits further investigations. To fill the research gap, this study was thus performed based on our previously conducted experimental work to further comprehend the web crippling phenomenon of the roll-formed aluminium lipped channel (ALC) sections under the loading conditions of end-two-flange (ETF) and interior-two-flange (ITF). This was done through numerical investigations followed by a parametric study which are reported herein in details. A wide range of roll-formed ALC sections covering web slenderness ratios ranged from 28 to 130, inside bent radii ranging between 2 mm and 8 mm, bearing lengths ranged from 50 mm to 150 mm, and three sheeting aluminium alloy grades (5052-H32, 5052-H36 and 5052-H38) were considered in the parametric study. The acquired web crippling database was then used to assess the consistency and accuracy of the current design rules used in practice. It was found that the web crippling capacity determined by the current international specifications are unsafe and unreliable, whereas the predictions of the recently proposed equations agree very well. Furthermore, a Direct Strength Method (DSM)-based capacity prediction approach was proposed and then validated against the web crippling database acquired here as well as the experimental and numerical data for cold-formed steel lipped channel sections used in the literature.

الملخص: Thin-walled members in structural systems are highly vulnerable to buckling instabilities, including web crippling. Aluminum alloy members are more prone to this kind of failure due to their relatively low elastic moduli. As shown in the existing literature, limited research has been performed to investigate the web crippling failure of aluminum members. This paper presents the details of an experimental investigation conducted to study the web crippling phenomenon of fastened (restrained flanges) aluminum-lipped channel (ALC) sections. Two loading conditions, end-two-flange and interior-two-flange loading, were considered. Two series of 40 tests were performed using roll-formed aluminum alloy 5052 H36 specimens with different web slenderness and load-bearing lengths. A comparison between the ultimate capacities of the web crippling tests and the predictions from the currently available design rules was performed. The results show that the current web crippling design rules are mostly unsafe and unreliable for fastened ALC sections. Thus, a modified equation is needed to closely and accurately estimate the web crippling strengths for fastened ALC sections under two-flange loading conditions. Furthermore, the effect of restrained flanges on the web crippling mechanism is discussed in detail. It was observed that fastening the flanges considerably strengthened the section web crippling capacity. Hence, a new prediction approach was developed to estimate the increase of the web crippling capacity due to flange restraining.

الملخص: Aluminium alloys have recently been utilised in the fabrication of thin-walled members using a roll-forming technique to produce purlins, floor joists and other structural bearers. Such members are often subjected to transversely concentrated loads which may possibly cause a critical web crippling failure. Aluminium specifications do not explicitly provide clear design guidelines for roll-formed members subjected to web crippling actions. Therefore, this study was conducted to investigate the mechanism of web crippling for roll-formed aluminium lipped channel (ALC) sections with flanges attached to supports (fastened) under two-flange loading conditions. Based on the experimental works presented in a companion paper, numerical simulations were conducted including an extensive parametric study covering a wide range of ALC geometrical dimensions, bearing lengths, and 5052 aluminium alloy grade with H32, H36 and H38 tempers. The acquired web crippling data were then used to investigate the influence of the flange restraints on the web crippling mechanism of the ALC sections. Furthermore, a detailed assessment of the consistency and reliability of the currently available design rules used in practice was carried out. The predictions of the web crippling design guidelines given in the Australian, American and European specifications were found to be unsafe and unreliable, whereas a good agreement was obtained between the predictions of our recently proposed design guidelines and acquired web crippling results. Further a suitable Direct Strength Method (DSM)-based design approach was developed in this study with associated equations to predict the elastic bucking and plastic loads of fastened ALC sections under two-flange loading conditions.

الملخص: Web crippling is a form of localized failure that thin-walled members are susceptible to in structural systems. The available literature shows limited experimental studies conducted to investigate the web crippling behaviour of aluminium members. Hence, an experimental study was carried out herein to investigate the web crippling phenomenon of fastened (flanges restrained to supports) rollformed aluminium lipped channel sections. A total of 40 web crippling tests were carried out under twoflange load cases of End Two-Flange (ETF) and Interior Two-Flange (ITF). This paper presents the test results including the load-displacement curves, failure modes, ultimate loads and the effect of restraining flanges to the support in the web crippling behaviour. It also presents the comparison of ultimate loads from tests with the current design rules and discuss the details of the development of the new design rules. The comparison showed that the current design rules are unconservative and unreliable to predict the web crippling capacities of fastened aluminium lipped channel sections, while the new design rules can accurately predict the web crippling strengths of fastened aluminium lipped channel sections under two-flange load cases.

الملخص: Web crippling is a form of localized failure that thin-walled members are susceptible to in structural systems. The available literature shows limited experimental studies conducted to investigate the web crippling behaviour of aluminium members. Hence, an experimental study was carried out herein to investigate the web crippling phenomenon of fastened (flanges restrained to supports) rollformed aluminium lipped channel sections. A total of 40 web crippling tests were carried out under twoflange load cases of End Two-Flange (ETF) and Interior Two-Flange (ITF). This paper presents the test results including the load-displacement curves, failure modes, ultimate loads and the effect of restraining flanges to the support in the web crippling behaviour. It also presents the comparison of ultimate loads from tests with the current design rules and discuss the details of the development of the new design rules. The comparison showed that the current design rules are unconservative and unreliable to predict the web crippling capacities of fastened aluminium lipped channel sections, while the new design rules can accurately predict the web crippling strengths of fastened aluminium lipped channel sections under two-flange load cases.

الملخص: The use of thin-walled aluminium alloy members in construction has significantly increased during the recent years due to its appealing characteristics. However, they are highly susceptible to web crippling failure due to its lower elastic modulus. In addition to the experimental study conducted by the authors, a numerical study was carried out to further investigate the web crippling phenomenon of unfastened aluminium lipped channel sections under two flange load cases. Subsequently,a detailed parametric study was conducted to thoroughly investigate the web crippling bearing capacities of a wide range of aluminium lipped channel sections including different material properties, sectional geometric parameters and bearing lengths. The extensive FE web crippling capacity data were then used to assess the accuracy of the web crippling design rules provided by the Australian design guidelines for aluminium structures. It was found that the current equations are unconservative and unreliable to predict the web crippling capacity of aluminium lipped channel sectionsunder two flange load cases. Thus, suitable modifications were proposed to the current web crippling design equation. It is shown that the modified design rules closely predicted the web crippling strengths for aluminium lipped channel sections.