Depending on the location of the span in question the
effective span (Leff) is a function of the slab thickness, the width or
diameter of the supports and the distance between the centre of the supports.
The effective span decreases as the width of the support slab increases.
In a pile-supported slab, a pile head is often situated
on top of the pile, which increases the width of the slab support hence
reducing the effective span. This will reduce the maximum bending moment
induced in the slab.
Effective spans are not
applicable to the design of ground supported slab.