ABSTRACT
Isostatic, or statically determinate, structures made up of beams are widely used in civil and industrial constructions. As will emerge more clearly later, the internal stresses induced by mechanical loads are greater in the isostatically constrained structure than in the structure that is redundantly constrained and consequently rendered hyperstatic by further constraints. On the other hand, the internal stresses induced by the so-called thermal loads (variations of temperature, uniform or otherwise, through the depth of the beam) are zero in isostatic structures, whereas in certain cases they are considerable in hyperstatic, or statically indeterminate, structures. From this, it is possible to deduce the importance, also from a practical point of view, of considering isostatic beam systems. In fact, often the mechanical loads that the structure will have to support are known to the designer, at least with a certain degree of approximation, while the thermal variations and the constraint settlements that the structure will undergo are not reasonably foreseeable, even as regards the order of magnitude. In these cases, an isostatic structure shows ample possibilities of settling with the intervention of rigid movements only (translations and global rotations), whereas a hyperstatic structure, in view of its redundant degree of constraint, will undergo deformations also of a mechanical nature, and thus internal stresses different from zero.
