283757893275

Structural Steel Frames 335
50 or
75 mm
175
mm
2390 mm
1200 mm
Lengths up to 24.0 m
300–800 mm in
100 mm increments
Prestressed concrete double T-beam
Minimum 50 mm thick
reinforced concrete
topping
Mesh
Reinforced
concrete
column
Minimum 50 mm thick
reinforced concrete
topping
Mesh
reinforcement
Steel
column
Ends of T-beams
bear on toe of boot
section
Double
T-beam
Double T-beam bearing on concrete beam
Ends of T-beams
fixed to steel beam
with angle cleats
Double
T-beam
Double T-beam bearing on steel beam
Figure 5.58 Prestressed concrete double T-beam.
Cold-rolled steel deck and concrete floor
The traditional concrete floor to a structural steel frame consisted of reinforced concrete,
cast in situ with the concrete casing to beams, cast on timber centring and falsework
supported at each floor level until the concrete had sufficient strength to be self-supporting.
The very considerable material and labour costs in erecting and striking the support for the
concrete floor led to the adoption of the precast concrete self-centring systems such as
the hollow beam and plank, and beam and infill block floors. The term ‘self-centring’
derives from the word ‘centring’ used to describe the temporary platform of wood or steel
on which in situ cast concrete is formed. The precast concrete beam, plank and beam, and
block floors do not require temporary support, hence the term self-centring. A disadvantage
of the precast concrete beam and plank floors for use with a structural steel frame is
that it is usual practice to erect the steel frame in one operation. Raising the heavy, long
precast concrete floor units and moving them into position is, to an extent, impeded by
the skeleton steel frame.