Thin–Walled Structures 157 (2020) 107091 Available online 20 September 2020 0263-8231/© 2020 Elsevier Ltd. All rights reserved. The infuence of strain-hardening on the ultimate behaviour of aluminium RHS-beams under moment gradient Elide Nastri * , Vincenzo Piluso University of Salerno, Department of Civil Engineering, Italy A R T I C L E INFO Keywords: Aluminium alloys Rotation capacity Ultimate resistance RHS beams FE simulation Empirical formulations ABSTRACT In this paper, the infuence of strain-hardening on the ultimate behaviour of aluminium beams made of rect- angular hollow sections (RHS) and subjected to non-uniform bending is investigated by analysing different aluminium alloys. The strain-hardening behaviour is related to the Ramberg-Osgood exponent of the constitutive stress-strain law of the material. A wide parametric analysis has been accomplished referring to both cooled, heat-treated and naturally-aged alloys. The results of comprehensive regressions analyses ftting the results obtained from numerical FE models are presented. Therefore, the main outcome of the work is the proposal of empirical relations for the prediction of the ultimate behaviour of RHS aluminium beams, accounting for the fange slenderness, the fange-to-web slenderness ratio, the non-dimensional shear length and the Ramberg- Osgood exponent. The proposed mathematical relationships allow a quick estimation of the ultimate non- dimensional fexural resistance and both total and stable part of plastic rotation capacity. 1. Introduction Aluminium alloy structures can provide convenient solutions in civil engineering applications in those situations where the lightness and the corrosion resistance constitute winning properties. This is the case of long-span roof systems, such as latticed space structures, single layer and double layer reticular domes, especially for the construction sites where the self-weight of the structures constitute the greatest part of the gravitational loads. Lightness is of primary importance also in case of movable bridges and foodgates where corrosion resistance is an addi- tional key point, as it generally occurs for structures located in highly corrosive or humid environments. Aluminium is used in external fa- cades, roofs and walls, in windows and doors, in staircases, railings, shelves, and other several applications. Deteriorated bridge decks re- placements, residential area bridges and structures situated in inacces- sible places far from the fabrication shop [1,2] are also typical applications. Moreover, in the framework of seismic applications aluminium alloys can assume different tasks being used as fuses, dissi- pative shear walls or seismic links [3–8]. Recently, columns made of an aluminium alloy have also been applied for the construction of a resi- dential building in a seismic area [9]. In the last years, signifcant work has been promoted by the Euro- pean Community aiming to the updating of structural Eurocodes. An important novelty concerning aluminium alloy structures is included in Eurocode 8 where for the frst time a section dealing with the seismic design of aluminium structures will be provided. It is well known that, under seismic forces, structural members are often subjected to double curvature bending. This is the main reason why the ultimate behaviour and the plastic rotation capacity of metal members are usually investi- gated by referring either to a cantilever scheme or to the three-point bending testing scheme [10,11]. In this way, the response under dou- ble curvature bending is interpreted considering the infuence of the so-called shear length which is practically coincident with the distance between the point of zero moment and the section where the maximum bending moment occurs, i.e. the section where the development of the plastic hinge is expected. Within the framework of the activities of CEN TC250/SC9, i.e. the committee encharged of the revision of Eurocode 9, a signifcant gap of knowledge compared to steel members was recognized dealing with the ultimate resistance and the plastic rotation capacity of aluminium members. Such a gap of knowledge is even more important as soon as it is considered that aluminium alloys are a wide family of materials whose mechanical properties are signifcantly affected by the chemical composition and the heat treatments, covering both low-yielding high- hardening alloys and high-yielding low-hardening alloys. In particular, strain-hardening plays a fundamental role both on the ultimate * Corresponding author. E-mail addresses: enastri@unisa.it (E. Nastri), v.piluso@unisa.it (V. Piluso). Contents lists available at ScienceDirect Thin-Walled Structures journal homepage: http://www.elsevier.com/locate/tws https://doi.org/10.1016/j.tws.2020.107091 Received 17 June 2020; Received in revised form 19 August 2020; Accepted 24 August 2020