foundation system of burj al arab

Factors Affecting Width of Cracks in Reinforced Concrete

In reinforced concrete, reinforcement contributes to limit cracks number and their width. We know if steel reinforcement is anchored at the end properly, a tension member like beam will not collapse prematurely even after entire span allow slip due to failure of bond; but wider cracks are formed.

We know two types of steel are available based on surface deformation. When beams are reinforced with round and smooth bars, the cracks of greater width are observed under tension relative to member reinforced with deformed bars.

Interestingly when beams are reinforced with deformed bar providing good resistance against slip, shows more number of cracks relative to that reinforced with plain bars.

Thus when crack number is increased crack width becomes less; more precisely fine cracks are found which are almost invisible under naked eyes. This is achieved by used steel having proper surface deformations.

Plain bars, stated above, are now almost replaced by deformed bars, due to importance in crack distribution and also limiting of the same.The spacing requirements and minimum projection from surface of bar are provided by ASTM specification (ASTM A615, A 996 and A706).

Crack formation, definitely, make concrete section weak, but if they allow environmental agent to penetrate through them, section is severely damaged. The next factor is stress applied to reinforcement. 

Studies on relation between crack width and steel stress confirmed that this width is proportion to exponent of steel stress i.e. w α fsn


fs= steel stress,

n=exponent ranging from 1.0~1.4.