A deformed bar can be used to create a formed
restrained-movement joint. It provides load transfer across the joint in the
same way a dowel does. Movement in the joint occurs when the bars yield.
During installation, the bars are set into the formwork
when the first slab is cast, then the second slab is cast around them as they
protrude from the first slab.
The bars bond well to the surrounding concrete due to
their ribbed shape, improving their resistance to being pulled out of the slabs
they are cast in. If the bars were to slide out of the slab with little
resistance, the joint would widen more than the designer intended and the joint
could not be considered as fully tied.
The bar dimensions
are chosen so that the total cross sectional area of the bars across a joint is
roughly equal to that of the fabric reinforcement in the rest of the slab. This
helps to maintain uniform strength properties across the whole floor. The bars
also need an area of 0.08-0.125% of the cross sectional area of the slab. Any
less than this and there is a risk of a joint opening too wide. Any more than
this and the risk of mid-panel cracking increases.