Foundation slab profiling for uniform soil pressure: How should the thickness of a footing vary from the column face toward the edge to maintain practical and economical stress distribution?

Introduction / Context:Footings are designed to safely spread column loads onto soil while controlling bending, shear, and punching. Although the soil pressure is governed by load and plan area, the slab’s thickness profile strongly influences internal forces and economy. Textbook practice uses thicker concrete near the column (where bending/shear are highest) tapering toward the edge.

Given Data / Assumptions:

• Isolated spread footing under vertical load and uniform bearing capacity.
• No unusual edge loads or moments beyond typical soil reactions.
• Conventional reinforced concrete detailing and code-compliant cover.

Concept / Approach:

Bending moment and shear are maximum near the column face and reduce toward the edge. A variable depth section satisfies strength where needed and saves material elsewhere. While soil pressure distribution is a function of plan geometry and load, the footing thickness taper improves structural efficiency and constructability without compromising bearing performance.

Step-by-Step Solution:

Verification / Alternative check:

Design charts and code clauses for one-way shear, punching shear, and bending confirm higher required effective depth near the column, permitting a slope (haunch) or step down toward the edges.

Why Other Options Are Wrong:

Uniform thickness wastes concrete or may be unsafe near the column; increasing thickness toward the edge is structurally illogical; “zero” thickness at the edge is impossible; arbitrary variation is poor engineering practice.

Common Pitfalls:

Ignoring minimum cover and edge thickness; not checking punching shear at the column face; over-simplifying soil pressure as affected by thickness profile.

Final Answer:

Decreased gradually toward the edge