For flat slabs:
(a) The angle of greatest slope must not exceed 45° from the vertical;
(b) The diameter of the column head D measured at a distance of 40 mm below the soffit of the slab should not exceed L/4, where L is the span length.
Total Design Moment for the flat slab is given by:
The absolute sum of the positive and negative moment in each direction is given by
Where,
M
0 = Total moment
W = Design load on the area L
2 × L
nL
n = Clearspan extending from face to face of the columns, capitals, brackets or walls but not less than 0.65 L
1L
1 = Length of span in the direction of M
0L
2 = Length of span transverse to L
1In taking the values of L
n, L
1, and L
2, the following clauses are to be carefully noted:
a) Circular supports shall be treated as square supports having the same area i.e. squares of size 0.886D
b) When the transverse span of the panel on either side of the centerline of support varies, L
2 shall be taken as the average of the transverse spans. In Fig. 1.5 it is given by
c) When the span adjacent and parallel to an edge is being considered, the distance from the edge to the centre-line of the panel shall be substituted for L
2.
Note:
If w is the total load per unit area on a panel, D is the diameter of the column head, L is the span in two directions, then the sum of the maximum positive bending moment and average of the negative bending moment for the design of the span of the square flat slab, should not be less than