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Structural Concrete Frames 397
Concrete
rectangular
grid floor
Slab spans one way
between main beams
Main beams
Secondary beams
Figure 6.41 Rectangular grid beam and slab floor.
Reinforced concrete column
Solid floor around column to resist shear
Reinforced concrete
main beam
Two-way
reinforcement
floor
Main
beam
Waffle grid floor
Reinforcement
of two-way
span ribs to
waffle floor
Glass fibre plastic moulds nailed
to boarded centring
900
mm
GRP mould
570 mm
900
mm
300 mm
Figure 6.42 Waffle grid in situ cast reinforced concrete floor.
Waffle grid slab floor
If the column grid is increased from about 6.0 to about 12.0 m 2 , or near square, it becomes
economical to use a floor with intermediate cross beams supporting thin floor slabs,
as illustrated in Figure 6.42. The intermediate cross beams are cast on a regular square
grid that gives the underside of the floor the appearance of a waffle, hence the name. The