[M]aterials should resist mechanical forces and other effects... starting with all types of loading and external forces... and with the mechanical pr… - Eduardo Torroja

Concrete presents, besides a coefficient of , a coefficient of hygroscopic dilation which is more appreciable. While concrete is kept wet... it expands; and as it dries, it contracts, in inverse proportion to the hygroscopic degree of the ambient air. ...The shrinkage ...will vary with the porosity of the concrete and with the thickness used in the structural member. ...Shrinkage is much greater in structures consisting of thin elements subjected to intemperateness of dry climate, and disappears or becomes negligible in underground structures (e.g., foundations).

If you lean on a straight stick... [it] can resist your weight, despite its slenderness, as long as it remains straight; once it starts to bend, it will easily break. The danger of breaking increases with the deflection... [T]he danger of failure will diminish with the increased of the cross section, or if the same are of cross section should be maintained, by distributing the material in a hollow section.

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...