If the Center of gravity of the load coincides with the centroid of the raft, the upward load is regarded as a uniform pressure, which will be equal to the downward load divided by the area of the raft.

In strap footing, two independent columns are supported by as trap or beam at the bottom.

The weight of the raft is not considered in the structural design because it is assumed to be carried by directly by the subsoil.

The maximum bending moment should be adopted as the design value for the reinforced concrete rectangular footing, which should also be checked for maximum shear and bond etc.

In the pressure intensity equation q2 = a. qs, if a= 0 we have a triangle with xÌ… = L/3.

The raft is subdivided into a series of continuous beams (strips) centered on the appropriate column rows to establish shear failure and moment diagram.

The penetration resistance N values should be taken at 75 cm intervals for a depth equal to width of the raft, below the base of the raft.

Based on the settlement criterion for raft, the net pressure can be calculated from the following equation having its width greater than 6m.

It is assumed that the combined footings are rigid and rests on a homogeneous soil, so as to give rise to a linear stress distribution on the bottom of the footing.

If the resultant of the soil pressure coincides with the resultant of the loads and the center of gravity of the footing, the soil pressure is assumed to be uniformly distributed.