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

The strap used does not remain in contact with soil, and thus does not transfer any pressure to soil.

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

In conventional design, allowable bearing capacity should be taken as smaller of following two values: i) safe bearing capacity based on ultimate capacity, and ii) allowable bearing pressure on tolerable settlement.

The value of Ks can be found corresponding to a different size and shape for both cohesive and cohesionless soils.

The modulus of elasticity Es used in equation Si = ?0?1 q B (1-?2/Es) is computed from triaxial test data, where
Es = (?1-?3)/?L / L.

In pressure intensity equation q2 = a. qs, if a= 0 we have a triangle with x? = L/3.

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

According to Terzaghi, a foundation is shallow if its depth is equal to or less than its width. In case of deep foundations, depth is equal to or greater than width.

The immediate settlement is elastic settlement and can be computed from following expression based on ory of elasticity,
Si = q B (1-?2/E s) I w.