To reduce the differential settlement due to live load variations for footings on grained soils, it is desirable to proportion all the footings in such a way that they have equal pressures under the service loads. Thus all footings would settle by equal amounts and the differential settlement would be considerably reduced.
Steps on proportioning footing for equal settlement as suggested by Peck et al (1974)
- Determine dead load of footing.
- Determine the footing subjected to maximum live load.
- Compute the ratio of live load to dead load for each of the footing.
- Identify the governing footing. The footing having maximum live load to dead load ratio is the governing footing.
- Find the area of the governing footing (Ag).
- Ag = (DL+LL) / Allowable bearing capacity.
- Determine service load for all the footings.
- Determine the design bearing capacity (qd) of all the footings except the governing footing.
- qd = Service load of the governing footing / Ag.
- Determine the area under other footings.
A = Service load of that footing / qd.