Minimum spacing between reinforcement bars
The distance among reinforcement bars must be
such to allow the concrete’s gravel to pass be-tween them. In order to
have properly anchored reinforcement, it is mandatory for rebars to be
surrounded by concrete.
The minimum spacing between two reinforcement
bars should be at least equal to the maximum aggregate grain dimension
with a margin of 5 mm. For Greece, the maximum aggregate grains
dimension for usual concrete, is 32 mm and for self compacting concrete
is 16 mm.
Usual Concrete
Self Compacting Concrete
Example:
Usual Concrete
Beam 4Ø20
Stirrups Ø10
Coating =30 mm
Self Compacting Concrete
Beam 4Ø20
Stirrups Ø10
Coating =30 mm
These spacing requirements are easily met in
slabs and columns. However in beams extra at-tention must be paid mainly
to the support and the joint areas. The problem in beams is related to
the concrete’s casting and it can be dealt with three different ways or
in certain occasions with a combination of them.
For satisfactory results it is very important
not only to use the vibrator in the proper way but also to avoid
over-vibrating the concrete of the elements.
a) Large beam width b) Use of the second layer, which is placed in contact with the stirrups. c) By placing rebars on both outer sides of the beam’s main body.
Connecting beams in foundation
Concrete casting in foundation connecting
beams is not an easy procedure. These beams are not fixed together with a
slab as are superstructure beams; consequently concrete has to be
purred down the beam’s tight top opening and reach the bottom side.
Because of the fact that connecting beams
normally have a large height as well as a large internal lever, it is
preferable to place rebars in two or even three layers along their
height.
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