Rebars spacing

The distance between reinforcement bars must be such to allow the largest expected concrete size gravel to pass between 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 coarse aggregate dimension plus 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.

These spacing requirements are easily met in slabs and columns. However in beams extra care must be paid mainly at the support and at 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 cases with a combination of them.

Concrete casting in foundation tie-beams is not an easy procedure. These beams are not fixed together with a slab as are superstructure beams; consequently concrete has to be poured down the beam’s narrow top opening and reach the bottom of the beam.
Because of the fact that tie-beams normally have a considerable height and therefore dispose of a large internal lever, it is preferable to place rebars in two or even three layers along their height.