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268 Barry’s Advanced Construction of Buildings
Conoid and hyperboloid shell roofs
Reinforced concrete conoid shell
In this shell form, the curvature and rise of the shell increases from a shallow curve to a
steeply curved end in which the north light glazing is fixed, as illustrated in Figure 4.99.
The glazed end of each shell consists of a reinforced concrete or steel lattice, which serves
as a stiffening beam to resist deformation of the shell. Edge beams resist spreading of the
shell as previously described.
Hyperbolic paraboloid shells
The hyperbolic paraboloid shells provide dramatic shapes and structural possibilities of
doubly curved shells (see Photograph 4.26). The name hyperbolic paraboloid comes from
the geometry of the shape: the horizontal sections through the surface are hyperbolas and
the vertical sections parabolas, as illustrated in Figure 4.107 and Figure 4.108. The structural
significance of this shape is that at every point on the surface, straight lines, which
lie in the surface, intersect so that in effect, the surface is made up of a network of intersecting
straight lines. Thus the centring (formwork) can consist of thin straight sections of
timber, which are simple to fix and support.
Reinforced concrete hyperbolic paraboloid shell
Figure 4.109 illustrates an umbrella roof formed from four hyperbolic paraboloid surfaces
supported on one column. The small section reinforcing mesh in the surface of the shell
Photograph 4.26 Hyperbolic paraboloid shell roof.