are obviously an important consideration in
relation to the selection of concrete as the
structural material for a building.
4.2.2.2 Advantages
Strength
Of the four principal structural materials
reinforced concrete is one of the strongest. It
performs well in skeleton-frame-type structures
and is therefore best used in situations in
which the properties of a frame are required
(planning situations in which the restrictions
of loadbearing walls cannot be accepted). It is
particularly suitable for frameworks on which
the level of imposed loading is high.
Reinforced concrete has tensile, compressive
and flexural strength and can be used to make
all types of structural element. It is capable of
resisting the internal forces which result from
every possible combination of applied load
and structural geometry and is therefore
capable of producing elements with any
geometry. The material itself places no restric-
tion on structural form.
Mouldability
The fact that reinforced concrete is available in
semi-liquid form means that it can be cast into
an almost infinite variety of shapes. This
property, together with its strength characteris-
tics, means that virtually any form can be
created relatively easily in reinforced concrete.
The moulding process also allows structural
continuity between elements to be achieved
relatively easily and the resulting statical
indeterminacy is another factor which eases
the production of complicated forms. In par-
ticular, it allows the adoption of irregular
patterns of vertical support for floor and roof
structures, the cantilevering of floor and roof
structures beyond perimeter columns and the
omission of areas of floor to create voids
running through more than one storey in the
interiors of buildings. It also allows reinforced
concrete structures to be self-bracing.Durability
Reinforced concrete is a durable material
which can be left exposed in relatively hostileenvironments. A wide variety of surface
textures can be achieved, depending on the
type of mould treatment which is specified.
Finishing materials can therefore be eliminated
where concrete structures are used.Fire resistance
Reinforced concrete performs well in fire; it is
incombustible and it retains its structural
properties when exposed to high temperatures.
Cost
Reinforced concrete is relatively cheap and,
when used for frame structures, will usually be
cheaper than steel. It is, however, normally
more expensive than masonry for loadbearing-
wall structures.4.2.2.3 Disadvantages
Weight
Reinforced concrete structures are heavy. The
material has a relatively low ratio of strength
to weight and a reinforced concrete frame is
normally significantly heavier than an equiva-
lent steel frame. It is because of the high self-
weight that reinforced concrete performs best
in situations in which relatively high imposed
loads are involved - for example, for the floor
structures of multi-storey commercial or indus-
trial buildings. It is rarely used where imposed
loads are small, such as in single-storey build-
ings or the roof structures of multi-storey
buildings, except in forms in which the level of
structural efficiency is high, such as form-
active shell roofs.
The relatively high self-weight of reinforced
concrete structures does have some advan-
tages, however. It gives the building a high
thermal mass which eases the problems
associated with environmental control. It also
means that concrete walls and floors are
capable of acting as effective acoustic barriers.Construction
The construction of a reinforced concrete struc-
ture is complicated and involves the erection
of formwork, the precise arrangement of intri-
cate patterns of reinforcement and the careful
placing and compacting of the concrete itself.
The construction process for a reinforced 117Reinforced concrete structures