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Precast,
prestressed concrete lintels
are made of high-strength
concrete and wires of
special steel. Such lintels
rely for their effectiveness
on the properties of and
the interaction between
the concrete and the wires. |
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The
aim of this paragraph
is to give a brief guidance
on the selection of materials
for the proportioning
of concrete, steel specifications,
principles of manufacture,
and sources of design
information and prestressing
equipment. |
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Precast
lintels must meet the
following requirements: |
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They
must contain sufficient
steel to carry the load
once built in. |
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They must
be as light, and therefore
slender, as possible.
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They must
not crack easily when
lifted or handled. |
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It has been
found that the last two
requirements can be met
only if the concrete is
prestressed, i.e. the
concrete is ‘‘precompressed’’
so that it will not crack
easily. Ordinary reinforced
concrete does not work
for such slender shapes.
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The following
equipments are needed:
Suitable moulds
(which may have to be
purpose-made). A jacking
system incorporating a
means of anchoring the
wires, jacks that can
be closely controlled
(for accurately stretching
the wires) and a means
of gripping the wires.
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