Expert: Veto Varma - 6/30/2006

Question
sir,
I know the design of isolated footings incase the loads are transmitted from columns.How is the design of foundation(shallow) done in case of an ordinary residential building?(the type of footing selected is...?)what are the considerations or factors taken into account?

Answer
Hello Dency,

For a residencial building you should consider Location of footing, Bearing capacity, moments transferred etc. Size of the footing is straight forward i.e. load divided by Bearing capacity, but the shape may be sometimes tricky. Such as if it is located on the property edge, then you will look for eccentric footing. if no space constrains, just go for square or rectangular one.

Important point to consider in design is shear of the footing, that gives you the thickness of the footing. Usually two way shear is always governing but you should check for one way shear too. Usually in building with more than one storey you will get combined footing too. In that case don't forget to check for flexure reinforcement requirement between the two columns.

Depth of footing from ground depends on local soil conditions, water table etc, but if there is no such constrained minimum depth usually taken in Americas is 4 feet. Type of concrete in foundation is alwaye type 50 i.e. Sulphor resistance. Strength of concrete is usually 25-30 MPa.

Hope this may help. if you have any questions sand me an email

regards
Veto