283757893275

Structural Concrete Frames 401
composite action with reinforced concrete topping. The units are 400 or 1200 mm wide,
65, 75 or 100 mm thick and up to 9.5 m long for floors, and 10 m long for roofs. It may be
necessary to provide some temporary propping to the underside of these planks until the
concrete topping has gained sufficient strength.
Precast concrete T-beams
Precast prestressed concrete T-beam floors are mostly used for long-span floors in such
buildings as stores, supermarkets, swimming pools and multi-storey car parks where there
is a need for wide-span floors and the depth of this type of floor is not a disadvantage. The
floor units are cast in the form of a double T. The strength of these units is in the depth of
the ribs which support and act with the comparatively thin top web. A structural reinforced
concrete topping is cast on top of the floor units, which bear on the toe of a boot section
concrete beam.
Precast beam and filler block floor
This floor system consists of precast reinforced concrete planks or beams that support
precast hollow concrete filler blocks, as illustrated in Figure 6.46. The planks or beams are
laid between supports with the filler blocks between them, and a concrete topping is spread
over the planks and filler blocks. The reinforcement protruding from the top of the plank
acts with the concrete topping to form a reinforced concrete beam. The advantage of this
Steel strip lattice
reinforcement
Concrete plank
Bottom
of lattice
cast into
plank
120
mm
up to 12.0 m long
150, 200 or
250 mm
530 mm
Precast reinforced
concrete plank
Lightweight concrete
filler block
225
mm
Structural concrete
topping over filler
blocks, planks and beam
Solid block
perforated
for pipes
or ducts
Stirrups project to
form composite
T-beam with topping
Planks at 600 mm centres
bear on precast beam
Solid blocks
at bearing
Blocks between
planks
Figure 6.46 Precast beam and filler block floor.