The main bar is the bar which is placed at the shorter span of the slab. It usually placed at the bottom of the slab.
The distribution bar is the bar that is placed in the long span of the slab. It is placed above the main bar.

The main bar is the bar which is placed at the shorter span of the slab. It usually placed at the bottom of the slab.
The distribution bar is the bar that is placed in the long span of the slab. It is placed above the main bar.