are parallel to one another, it is necessary to
brace the structure with a limited number of
walls running in the orthogonal direction;
these can normally be located around stairs
and service cores.
The advantages of reinforced concrete over
masonry for this type of structure is that it
allows the structural plan to be simpler and
gives much more planning freedom generally:
it is, for example, possible to omit some of the
loadbearing walls at occasional locations and
bridge the gap by reinforcing the wall above so
that it acts as a deep beam.^13 The disadvantage
of reinforced concrete is that it is almost
invariably more expensive than the equivalent
masonry structure.
4.4.2.6 Summary of cast-in-situ forms
\n situ reinforced concrete structures perform
best in circumstances in which imposed loads
are high and they are therefore used principally
to support multi-storey commercial and indus-
trial buildings and only rarely as the structures
for low-rise domestic-type buildings or single-
storey buildings.
The main alternative to reinforced concrete
for the multi-storey building is steel and the
particular advantages of reinforced concrete
are that it allows complex and irregular forms
to be achieved more easily than with steel and
that it is both durable and fire resistant, which
eliminates the need for finishing materials.
4.4.3 Structural forms - precast forms
4.4.3.1 Introduction
In precast concrete construction the structural
components are cast in a location which is
different from that which they will finally
occupy in the structure. They are normally
manufactured in a precasting factory which is
remote from the site but they may sometimes
be cast on the site. The advantage of the latter
is that it removes the constraints imposed by
the need to transport the components to the
site. In either case the main advantage of
precasting is the achievement of higher quality
control, which results in higher strength, better
durability and better surface quality than is
possible with equivalent in situ concrete. It also
reduces the time required to construct the
building on site.
The particular advantages and disadvantages
of precast concrete are summarised below.Advantages
1 Almost all of the advantages of in situ
reinforced concrete are obtained. The mater-
ial has relatively high strength in compres-
sion, flexure and tension and is therefore
suitable for all types of structural element
and for skeleton-framework arrangements. It
is also durable and fire resistant, which
facilitates the exposure and expression of
the structure.2 The precasting of concrete allows better
quality control to be achieved. The material
is therefore stronger than equivalent in situ
concrete and has a better standard of
surface finish. Structural elements can
therefore be more slender and are less likely
to require the application of a finishing
material to bring them to a satisfactory
visual standard.3 Precasting allows greater complexity of the
form of individual components to be
achieved. This characteristic can be
exploited in several ways. In heavily serviced
buildings, in which a large number of
service ducts are required, it allows precast
concrete columns and beams of complex
cross-section to be used as frame elements
and as service ducts. Precast concrete
frames have therefore been fairly widely
used for building types, such as hospitals
and laboratories, in which the provision of
services is a major factor in the design. The
precasting technique has also been widely
used for the manufacture of proprietary
components with complex cross-sectional
shapes.Reinforced concrete structures14113 The most famous building in which this technique was
exploited was perhaps the Highpoint flats by Lubetkin
and Arup.