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Single-Storey Frames, Shells and Lightweight Coverings 261
Tied arch with glazing
h
H
H
Square dome
shells
Conoid
shells
L
S
W
Perimeter
tie beam
Glazing
Conoid shell roof
L somewhat less than half S
H about sixth and h ninth of S
Square Dome Shell roof
radius of domes about six-fifths of W
H one-tenth of w
W
Barrel vault
Spandrel
glazing
H
R
H
S
L
W
Hyperboloid of revolution
W about seventh of S
R about same as W
H about twentieth of S
Barrel vault shell roof
H about eighth of W
L one-fifth of W
Figure 4.99 Some typical shell roof forms.
stiffness, resistance to deformation under load and reduction in the need for restraint
against deformation.
Centring (or formwork) is the term used to describe the necessary temporary support
on which a curved reinforced concrete shell structure is cast. The centring for a single
curvature barrel vault is less complex than that for a dome, which is curved from a centre
point. Advances in computer software have made the design of shell structures and the
setting out of formwork much easier; however, there is still a considerable demand on
labour to make and erect the centring, and the more complex the shape, the greater the
amount of cutting and potential waste of material. The simplest, and hence most economic,
of all shell structures is the barrel vault, constructed in concrete or timber.
Reinforced concrete barrel vaults
These consist of a thin membrane of reinforced concrete positively curved in one direction
so that the vault acts as both structure and roof surface. The most common form of barrel