Self-weight of footing in foundation design: How should it be treated in pressure and sizing calculations?

Introduction / Context:
In shallow foundation design, the base pressure equals the total downward load divided by the plan area. The total downward load includes the superstructure load transferred at the column base plus the self-weight of the footing and the weight of soil backfill over the footing. Recognizing these components is essential to size the footing correctly and to compute base pressure for bearing and settlement checks.

Given Data / Assumptions:

• Isolated or combined shallow footing on soil with allowable bearing capacity.
• Dead load of footing concrete and overburden soil are present.
• Service-level bearing pressure design by classical approach.

Concept / Approach:

Upward soil reaction must balance the total downward load. Therefore, footing self-weight and backfill are included both in pressure computations and in determining the required area A = (P_struct + W_footing + W_soil) / q_allowable. Neglecting these terms underestimates base pressure and can undersize the footing.

Step-by-Step Solution:

Verification / Alternative check:

Iterative design often assumes A, estimates W_f, recomputes q, and adjusts A until convergence. This confirms the inclusion of self-weight is necessary in both pressure and area sizing.

Why Other Options Are Wrong:

(a) and (c) omit significant downward loads, leading to unconservative designs. (d) combines a correct statement with an incorrect one. (e) is too restrictive; self-weight matters for pressure and strength, not only settlement.

Common Pitfalls:

Ignoring self-weight; forgetting water table effects on buoyant weight; failing to include footing weight when checking sliding and overturning for retaining structures.

Final Answer:

Also considered for calculating the upward pressure on the footing