Structural Concrete - Hassoun

CHAPTER13
FOOTINGS
Office building under construction, New Orleans,
Louisiana.
13.1 INTRODUCTION
Reinforced concrete footings are structural members used to support columns and walls and to
transmit and distribute their loads to the soil. The design is based on the assumption that the footing
is rigid, so that the variation of the soil pressure under the footing is linear. Uniform soil pressure is
achieved when the column load coincides with the centroid of the footing. Although this assumption
is acceptable for rigid footings, such an assumption becomes less accurate as the footing becomes
relatively more flexible. The proper design of footings requires that
1. The load capacity of the soil is not exceeded.
2. Excessive settlement, differential settlement, or rotations are avoided.
3. Adequate safety against sliding and/or overturning is maintained.
The most common types of footings used in buildings are the single footings and wall footings
(Figs. 13.1 and 13.2). When a column load is transmitted to the soil by the footing, the soil becomes
compressed. The amount of settlement depends on many factors, such as the type of soil, the load
intensity, the depth below ground level, and the type of footing. If different footings of the same
structure have different settlements, new stresses develop in the structure. Excessive differential
settlement may lead to the damage of nonstructural members in the buildings or even failure of the
affected parts.
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