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Single-Storey Frames, Shells and Lightweight Coverings 259
Chord angle welded to
plate welded to top
chord of beam and
bolted to wall panel
Wall
panel
Bearing plate bolted
to seat angle welded
to plate and studs
cast in wall panel
Connection of roof beams to
wall panel
Anchor bars cast
in panels are
welded to bars
cast in site slab
Wall
panel
Site slab
Figure 4.98 Connection of wall panels to site slab.
ties. A shell structure is more expensive than, for example, a portal-framed structure covering
the same floor area because of the considerable labour required to construct the centring
on which the shell is cast. Shell structures cast in concrete are also difficult to insulate
economically because of their geometry and so are mainly suited to unheated spaces.
Shell structures tend to be described as single or double curvature shells. Single curvature
shell structures are curved on one linear axis and form part of a cylinder in the form of
a barrel vault or conoid shell; double curvature shells are either part of a sphere as a dome
or a hyperboloid of revolution (see Figure 4.99). The terms are used to differentiate
the comparative rigidity of the two forms and the complexity of the formwork (centring)
necessary to construct the shell form. Double curvature of a shell adds considerably to its