The variety of exterior forms in concrete is limited only by the cost of forming; and its thickness is limited only by the size of aggregates, gravel… - Eduardo Torroja

[E]xperimental investigation of stresses in a plane structure is of great interest and merit as applied to shells with single curvature (barrel shells, pipes) and to shells with double curvature (domes, etc.). In these structures similar states of stress are produced and can be determined at any point as acting in a plane tangential to the center layer of the shell.

Before a man can successfully plan a structure... he must study, from every possible angle, the ultimate purpose of his building. Attention must be directed to the basic structural concept before the mathematical process of calculation is undertaken.

Long before... our techniques of today, men could conceive and build structures adapted to the requirements of resistance... because he had observed... the branches of a tree bending under the weight of fruits and the tensioned cords of strings in which children have rocked from time immemorial...