Aluminium Structural Design

The aluminium and its alloys, from a structural engineering point of view, can be considered as a ‘new’ material (Mazzolani, 1998a). In fact, the first building structures made of aluminium alloy appeared in Europe in the early fifties, when concrete, masonry and steel were the main materials used for civil engineering structures. The aeronautical industry was one of the first fields which benefited of the aluminium alloys physical properties, so much used because there are not other metallic materials which can compete with it. Aluminum alloys are widely and successfully used to build airships, from the early Schwartz and Zeppelin until the modern aircrafts. Nowadays the aluminium alloys are also used in other branches of transportation, such as the rail industry (subway coaches, sleeping cars), the automotive industry (part of cars, containers for trucks, moving cranes) and the shipping industry (civil and military hydrofoils, motorboats). The offshore industry is the largest user of aluminium alloys for structural applications: the helicopter decks and the living quarters of the platforms are an example of structures where aluminium has replaced steel, which in general is the most widely used material for the structural applications. Considering that the first commercial applications of aluminium at the beginning of 20^th Century were objects such as mirror frames, house numbers and servings trays, without counting the cooking utensils, which were a major early market, we can recognize the entering into structural engineering for aluminium alloys was not a very simple and easy process. After many difficulties, today it can be recognized that aluminium and its alloys can be considered as a new and competitive material in civil and structural engineering applications (Mazzolani, 1995b, 1999).

Before we go into the details of the calculation and construction according to the ENV 1999-1-1: 1998 (EUROCODE 9) I want to show you in some slides the advantages of the material aluminium and furthermore some constructions in aluminium.

The design of plated structures involves check of local buckling as well as distorsional buckling of stiffened plates. Local buckling behavior of cross section elements is discussed in section 1. Depending on the width to thickness ratio, the behavior is different, which is considered for in Eurocode 9 by introducing cross section classes. Especially slender webs are treated. In section 2 thin-walled girders in bending are treated and in section 3 stiffened plates in compression. Section 4 deals with orthtropic plates. In section 5 the shear buckling resistance of plate girders with webs without intermediate stiffeners, webs with transversal and longitudinal stiffeners and trapezoidal corrugated webs are discussed. The design rules in Eurocode 9 and some background information are given.

Although a lot of research on aluminium alloys has been carried out in the past, relatively little attention has been given to their structural behaviour. Therefore, in the past most design rules for aluminium alloys were based on design rules for steel.

Fatigue is a phenomenon of progressive damage of materials due to the repetition of applied loads. If these loads were statically applied, then they would not lead to failure. In machine design the critical range where fatigue failures may occur is between 10⁴ and 10⁶ load cycles concerning constant amplitude fatigue, while it is much higher concerning variable amplitude fatigue. So machines and structures may undergo unexpected fatigue failures even after a long in-service life, when their reliability is thought to be proved.

Lightweight materials such as aluminium offer the automotive industry an opportunity to design and manufacture high-performance vehicles that are safe, energy-efficient and environmentally friendly, and much lighter than traditional designs. The introduction of these materials will challenge the automotive design engineers to explore and develop new solutions in design and production technology in order to fully realize the potential that can be gained in the interaction between these materials, product/structural design and the manufacturing process. Even though aluminium is an “old” material, it is relatively new as a load-carrying material in the automotive industry. This implies that material producers and parts suppliers have to develop new knowledge about these materials to gain an increased market share.