Building Design and Construction Handbook - Merritt - Ventech!

FIGURE 9.58 Continuous cylindrical concrete shell.
CONCRETE CONSTRUCTION 9.135
ness about 5 times that of an eggshell. Because concrete shells are always reinforced,
their thickness is usually determined by the minimum thickness required to
cover the reinforcement, usually 1 to 4 in. Shells are thickened near the supports
to withstand localized bending stresses in such areas. (See also Art. 5.15.)
Shells are most often used as roofs for such buildings as hangars, garages, theaters,
and arenas, where large spans are required and the loads are light. The advantages
of reinforced-concrete thin shells may be summarized as follows:
Most efficient use of materials.
Great freedom of architectural shapes.
Convenient accommodation of openings for natural lighting and ventilation.
Ability to carry very large unbalance of forces.
High fireproofing value due to lack of corners, thin ribs, and the inherent fire
resistance of reinforced concrete.
Reserve strength due to many alternative paths for carrying load to the supports.
One outstanding example withstood artillery fire punctures with only local damage.
Common shapes of reinforced-concrete thin shells used include cylindrical (barrel
shells), dome, grained vault, or groinior, elliptical paraboloid, and hyperbolic
paraboloid (saddle shape).
Cylindrical shells may be classified as long if the radius of curvature is shorter
than the span, or as short (Fig. 9.58). Long cylindrical shells, particularly the continuous,
multiple-barrel version which repeats the identical design of each bay (and
permits reuse of formwork) in both directions, are advantageous for roofing rectangular-plan
structures. Short cylindrical shells are commonly used for hangar roofs
with reinforced-concrete arches furnishing support at short intervals in the direction
of the span.
Structural analysis of these common styles may be simplified with design aids.
(‘‘Design of Cylindrical Concrete Shell Roofs,’’ Manual No. 31, American Society
of Civil Engineers; ‘‘Design Constants for Interior Cylindrical Concrete Shells,’’
EB020D: ‘‘Design Constants for Ribless Concrete Cylindrical Shells,’’ EB028D;
‘‘Coefficients for Design of Cylindrical Concrete Shell Roofs’’ (extension of ASCE
Manual No. 31), EB035D; ‘‘Design of Barrel Shell Roofs,’’ IS082D, Portland Cement
Association; ‘‘Concrete Shell Structures—Practice and Commentary,’’ ACI
334.1R, American Concrete Institute.
The ACI 318 Building Code includes specific provisions for thin shells. It allows
an elastic analysis as an accepted basis for design and suggests model studies for