Isolated footing foundation

The simplest shallow foundation: under each column a footing, a widened block of reinforced concrete that takes the concentrated load and spreads it onto the soil over a larger area, lowering the pressure to values the ground can bear. It is cheap and quick when the soil is good and loads are moderate; the footings are then tied with beams (ground beams) to stiffen them and distribute the horizontal actions.

The isolated footing is the most direct way to found: each column sheds onto its own block of reinforced concrete, widened downward, that bears on the soil. It is the «point» shallow foundation, the cheapest when the soil is strong and uniform and the loads are moderate. Where the ground worsens or the loads grow, one moves to inverted beams or a raft.

The principle is elementary: the column concentrates a large force on a small section; the footing gathers it and spreads it onto a wider base. The wider the base, the lower the pressure on the soil (force divided by area). The plan size of the footing is calculated exactly so: just wide enough for the pressure to stay below the allowable bearing capacity of the soil.

Under the load, the soil reaction pushes the footing up at the edges, which behave as cantilevers fixed into the central stub: they tend to bend and crack at the bottom. This is why the main mesh reinforcement sits at the bottom, near the soil; and punching must be checked, because the column tends to «punch» through the footing with a cone-shaped failure.

Single footings are independent points: to keep them from settling or moving each on its own — especially in seismic areas — they are tied with ground beams that stiffen them and distribute the horizontal actions. Beneath, a blinding layer gives a level casting base; the cover toward the soil protects the reinforcement. Where the column is eccentric (on a boundary), the footing is combined with a beam to prevent overturning.