Civil Engineering Reference
In-Depth Information
it has low loss of strength at building fire temperatures;
17.2.1.3 Sustainability
Sustainability has become an important factor in the design of
framed buildings, and concrete can contribute to a sustainable
design, especially when the material properties are understood
and used to their maximum. Concrete can contribute to a sus-
tainable building in the following ways:
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strength loss under sustained periods of elevated temperatures
is low.
Guidance on ensuring appropriate fire resistance can be found
in the section on 'cover' below (Section 17.5.1).
17.2.1.5 Acoustics
Concrete is a good insulator of sound, resisting the passage of
both impact and airborne sound; this makes it a useful material
in those situations where sound reduction between spaces is
required and particularly useful for residential, educational
and healthcare buildings.
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Concrete is a local material - reducing travel distances for the
materials used.
Concrete is long lasting - a correctly detailed reinforced concrete
■
building should last comfortably 60 years and would be expected
to last considerably longer even with little maintenance.
Concrete can be exposed - reducing the need for other materials
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to cover it.
Concrete is fire resistant - no fire protection materials are
17.2.1.6 Long spans
A common misconception is that concrete is not suitable for
long span situations. However, the use of prestressed concrete
can greatly enhance the clear spans. prestressed double 'T', hol-
lowcore units and post-tensioned
in situ
floors and beams can
comfortably span 12 to 16 m - further guidance is given below.
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required.
Concrete can be used to minimise energy through the use of its
■
thermal mass - see De Saulles (2006) for more information.
Concrete can be (and is) recycled at the end of its life.
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Concrete can be used to give flexibility for change of use.
17.2.2 Floor system options
Arguably the most important aspect of a buildable concrete
framed building is the choice of floor system, and there is a
vast range of options. The section has highlighted the reasons
why concrete is widely used. However, there is plenty of scope
for innovation and designers should not be constrained by the
options presented here.
Table 17.1
provides guidance on the
various options available.
Materials can be minimised by using prestressing.
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17.2.1.4 Fire resistance
Concrete offers good fire resistance because:
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it is a non-combustible material;
it is a good insulator;
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Slab type
Description
Advantages
Design considerations
Solid flat slab
(Flat plate)
A solid concrete slab of constant
thickness supported directly by columns
without the use of beams. Widely used
because the formwork is simple and
therefore cost effective, suitable for spans
up to 9 m only
Speed of construction
Punching shear capacity
■
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Economy
Delection
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Easy services distribution
Requires continuity
■
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Minimal storey height
Holes should be avoided around
■
■
Easy to install partitions
columns wherever possible
Limited span range
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Aesthetically pleasing soffit■■
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Inherent robustness
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Post-tensioned flat slabs
A prestressed solid concrete slab,
supported directly on columns. The
prestressing is applied after placing
the concrete. The prestressing allows
thinner slabs, or longer spans than for a
reinforced concrete flat slab
Speed of construction
Design is often by specialist
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■
Economy
Increased shrinkage due to
■
■
Minimises the use of materials
prestress
Punching shear capacity is limited
■
Easy services distribution
■
■
Minimal storey height
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Easy to install partitions
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Holes can be formed
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Aesthetically pleasing soffit■■
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Inherent robustness
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Hollowcore units on beams or
walls
Precast, prestressed concrete units
spanning in one direction and supported
by beams or walls. Voids are created
within the units through an extrusion
process during manufacture
Speed of construction
Suppliers use fixed depths for slabs
■
■
Economy
■
Bedding of the units, especially for
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Minimises the use of materials
■
long spans
Usually supplied with pre-camber,
Easy to install partitions
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Low self-weight
■
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which increases with span
Open plan areas
■
Low deflection■■
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Off-site manufacture
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Table 17.1 Concrete floor systems
