Shells of double curvature both the synclastic... and anticlastic... a — Thin-shell structure

"has designed some of the most striking thin shells in reinforced concrete of the second half of the twentieth century. He creates thin shells by hanging small membranes in tension and creating smooth curving surfaces that are then inverted and scaled up to create large-scale structures in compression. ...Within the constraint of economy, he discovered new forms from purely structural considerations and demonstrated the unlimited possibilities for thin compression shells to be found in hanging models."

"Very thin shells may be in danger of locally. The problem hardly arises for civil engineering applications over moderate spans, but may be very important if the spans are very large. Local buckling of a thin shell will occur at a typical stress\sigma_{cr} = kE \frac{t}{R}where E is [and R is the minimum radius of curvature of the shell]. The value of the constant k varies from author to author, but a reasonable value is about 0.25. Thus for a concrete shell for which E is about 20 000 N/mm2, and for which \frac{t}{R} is as small as 1/1000, the critical stress is determined as say 5 N/mm2."

"Thin shells — Three-dimensional spatial structures made up of one or more curved slabs or folded plates whose thicknesses are small compared to their other dimensions. Thin shells are characterized by their three-dimensional load-carrying behavior, which is determined by the geometry of their forms, by the manner in which they are supported, and by the nature of the applied load."

"The method of geometric modeling of multi-shell roofs depends mostly on the surfaces properties forming the shell; their curvature, as well as continuity between them. ...s play a specific role, due to their characteristics. Catalan surfaces are s... They are oblique ruled surfaces which can be divided into two groups... second order—hyperbolic paraboloid... [and] of more than second order—s, cylindroids... The difference between hyperbolic paraboloid, conoid, and cylindroid results from different path of movement of a surfaces ruling during formation. In all cases of Catalan surfaces creation... each ruling is parallel to the fixed plane (not containing the surfaces directrices)."

"[M]ost of Candelas structures are almost complete in themselves... the forms and proportions bear witness to his artistic sensibility. ...[B]alanced perfection ...makes a... structure into a work of art. ...[T]he whole must take precedence over any of its parts."

"Candela did not invent the concrete shell; nor is he the first to make use of the hyperbolic paraboloid... Other people... have contributed more to the theoretical analysis of shell structures. But nobody else can claim credit for such an exciting variety of shell structures... [H]e has concentrated his effort in one particular sphere: the construction of light concrete roofs."