Expert: Veto Varma - 11/2/2007

Question
I am a graduate engineer and have been given the problem of designing a point load foundation. Due to certain constraints the loading is offset from the centre of the foundation. I have sized the foundation with respect to ground bearing pressure, corrected for eccentricity, and carried out shear checks. My question is what is the calculation for determining the required tension steel in the foundation?

Answer
Hello Jonathon,

For eccentrically loaded foundation you need to determine exact soil pressure distribution. If you are designing for the loading then I assume you design for all compressive soil pressure distribution instead of some tension components, unless you have some size constrains.

Once you know this pressure distribution then you can use cantilever strip of unit width to determine the moment. Because of eccentricity you have two cantilevers of different length on either side of column or loading. You can use the worst case and design the footing for this moment.You can use the help of any standard foundation design book also.

Regards
veto