Structural Design for Architecture
Shell forms have other disadvantages besides
the high cost of construction. They do not
perform well when subjected to concentrated
loads and their use must therefore normally be
restricted to that of providing a free-standing
envelope to which no other substantial compo-
nents, such as services ducts or services
machinery, are attached. The fact that the struc-
tural envelope of a shell-type building is very
thin can produce a number of difficulties for the
designer, which are not present when more
conventional types of structure are used. If, as is
usually the case, the shell is used as the sole
external envelope an obvious deficiency is its
poor thermal insulation and low thermal mass.
Another disadvantage arises from the fact that it
is not possible to accommodate the large
number of systems which occur within a build-
ing, such as wires, pipes, etc., within the very
small structural zone of a shell. This problem
does not arise in buildings which have more
inefficient post-and-beam type structures
because the fairly large structural volume
involved provides a zone within which many
required components (ducts, cable runs) can be
accommodated; where a very efficient structural
form is used these components must be located
elsewhere. The high complexity of the shell
form, combined with its other disadvantages
therefore make it suitable for a rather limited
range of building types.4.4.5 Conclusion
The advantages of reinforced concrete as a struc-
tural material stem from its physical properties
and its mouldability. Its properties allow it to be
used in both compressive and bending-type
structural components and its strength is such
that it can be used to make frameworks in which
fairly large spans are involved. Of the non-struc-
tural physical properties, the good durability and
fire resistance of concrete are probably the most
important; these make it fit for use as a building
support system without the need for extra finish-
ing materials or components. The mouldability
of concrete allows good structural continuity to
be achieved, through the use of cast-m-situ rigid
joints, and makes possible a considerable
variety of geometries.Fig. 4.61 Reinforced concrete lends itself to use in
compressive form-active structural elements. The great
efficiency of this type of structure allows the strength
required for long spans to be achieved with very thin shells- typically between 50 mm and 150 mm. Various types of
hyperbolic paraboloid shell are depicted here.
which can be described by an elementary
mathematical relationship based on the
Cartesian co-ordinate system. Examples are
the cylinder, the sphere, the elliptical parabol-
oid, the hyperbolic paraboloid and the conoid
(see Fig. 4.61 and also Joedicke, Shell Architecture
146 Karl Kramer Verlag, Stuttgart, 1963).