lengths of beams.
They are generally used where longitudinal bending moments are a major problem for the foundation design, i.e. in variable ground, soft sub-strata, or where loading is variable in the length of the beam. They are also used in some areas of mining activity etc., where bending from differential subsidence movement is critical but where tensile and compressive ground strains in the foundation can be controlled.
The decision to use a continuous beam strip usually follows the need to
(1) Reduce differential settlements below framework columns.
(2) Combine foundations which would otherwise tend to overlap.
(3) Ease construction by the use of continuous strips rather than separate pads when they are becoming closely spaced.
The decision to use an inverted T rather than a simple rectangular beam would result from bearing pressure
criteria demanding excessive beam widths for bearing when compared to widths required to resist bending and shear.