There are many benefits of using a large number of small dia bars than a small number of large dia bars. The reasons are as follows.
- to provide ductility to the structure, i.e. (beam and slab ) which is not available in the concrete.
- to provide stability to the structure as the bars have rib design on it which helps to prevent the bars from slippage as we have to provide enough development length.
- also because of the complicated shape of the structure we have to provide small dia bars.
and because of these reasons, it is not possible to provide all these factors using a single bar, and therefore we have to provide a small number of large diameter bars.