Pathology in lamellar structures
Introduction
A laminar structure,[1] also known as structural shell,[2][3] is a type of structural element that is characterized by being a three-dimensional solid whose thickness is very small compared to its other dimensions and, in structural terms, because it resists external loads and those generated by its own weight through normal compression and/or traction and tangential stresses, uniform in the thickness of the surface.[4].
Their efficiency is due to their curvature, so they can present great resistance with savings in section, material and weight. They are the most efficient from a structural point of view,[4] allowing large spans without internal supports, thus creating a spacious and unobstructed interior.[5] These elements, typically curved, can be combined to compose large structures. Typical applications for this type of structure include aircraft fuselages, hulls of ships, and decks of large buildings.
Although the first shell structures were built by civilizations such as the Egyptian, Assyrian or Roman, the development of modern shell structures occurred from the 1920s onwards and was due to the fascination with a new material, reinforced concrete, and the need to cover large spans in an economical way. Félix Candela in Mexico, Eduardo Torroja Miret in Spain, Eladio Dieste in Uruguay, Franz Dischinger and Ulrich Finsterwalde") in Germany, Heinz Isler in Switzerland, Anton Tedesko") in the United States and Pier Luigi Nervi in Italy were some of the pioneers in the construction of this type of structures.[2][6].
Structural behavior
The main difference between a laminar structure and a slab or floor is that, without tension, the laminar structure has curvature while the slab is flat. Stress in a laminar structure is caused primarily by coplanar forces, but there may be secondary forces resulting from bending deformations. While a flat slab acts similarly to a beam with bending and shear stress forces, shell structures are analogous to a cable, which resists loads through tensile stresses ("Tension (mechanical)"). However, the ideal laminar structure must be capable of developing both tension and compression.[7].
Essentially, a laminar structure can be obtained from a slab or forging in two ways: by deforming it until it becomes a surface of single or double curvature, or by applying coplanar loads to the slab of sufficient intensity.[8].