Shell structure, in building construction, a thin, curved plate structure shaped to transmit applied forces by compressive, tensile, and shear stresses that act in the plane of the surface. They are usually constructed of concrete reinforced with steel mesh . Shell construction began in the 1920s; the shell emerged as a major long-span concrete structure after World War II. Thin parabolic shell vaults stiffened with ribs have been built with spans up to about 300 ft (90 m). More complex forms of concrete shells have been made, including hyperbolic paraboloids, or saddle shapes, and intersecting parabolic vaults less than 0.5 in. (1.25 cm) thick. Pioneering thin-shell designers include Felix Candela and Pier Luigi Nervi.

Shotcrete

Shotcrete, also called (trademark) Gunite, concrete applied by spraying. Shotcrete is a mixture of aggregate and portland cement, conveyed by compressed air to the nozzle of a spray gun, where water is added. The wet mixture is then sprayed in place and may be carved or troweled almost immediately. For structural uses, shotcrete is usually applied over a framework of reinforcing bars and steel mesh. Because it can take any shape, is easily coloured, and can be sculptured after application, shotcrete is used for a variety of fancy concrete structures, including artificial rock walls, zoo enclosures, canopy roofs, refractory linings, pools, and dams. It is sometimes used in tunneling to bind the walls of the tunnel to prevent leaks and fragmentation.

shotcrete-stabilized cliff wall