To understand what is meant by structural elements, it is convenient to start by considering a whole structure made of various components assembled together with the aim to satisfy various functional and cost criteria. Depending on the domain of application, the terminology used to designate such assemblies varies; they are referred to as buildings, civil engineering works, machines and devices, vehicles etc. In most cases, the shapes of such structures are so complicated that the appropriate way to make a mathematical model feasible, is to identify simpler structural elements, defined according to a few generic response properties. Such a theoretical approach closely follows the common engineering practice of selecting a few appropriate generic shapes to build complex structures. Since the architects and engineers of the Roman Empire, two geometrical features have been recognized as key factors to save material and weight in a structure. The first one is to design slender components, that is, at least one dimension of the body is much less than the others. From the analyst standpoint this allows to model the actual 3D solid by using an equivalent solid of reduced dimension. Accordingly, one is led to distinguish first between 1D and 2D structural elements. The second geometrical property of paramount importance to optimise the mechanical resistance of structural elements is the curvature of the equivalent solid. Based on these two properties structural elements can be identified as:

1. Straight beams, modelled as a one-dimensional and rectilinear equivalent solid.

2. Plates, modelled as a two-dimensional...