Foundation design for Biaxial Momoent

Get a text for either Bowles or Das and create your own, this will instill the process in your mind such that in future cases you'll have a much better understanding of this material.

Regards,
Qshake

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Thanks Qshake ,
But it doesn't give you the equation for biaxial bending. For uniaxial moment one can easily calculate the redistributed pressure and area of footing which is out of contacat with the soil.
I need equations for foundation subjected to BIAXIAL MOMENTS. Pressure diagram would be 3-dim and calculating volume and CG to satisfy the principal equation is really difficult.

Your equivalent footing (in contact with soil) will be: B'xL', where B'=B-2eb, L'=L-2el, eb=Mb/P (Mb=moment in the B direction) and el=Ml/P (Ml=moment in the L direction). The equivalent bearing pressure will then be: (P+Wf)/B'L'. You will also need to use the B' and L' values in your bearing capacity equations. Do you get the idea? Coduto explains this in detail.

SHBH,
I made a spreadsheet to do this recently. It's pretty complicated and requires iterations. You could have a triangle, trapezoid or rectangle with a triangle missing in bearing. You have to figure out which one it is by iteration and solve accordingly. The resulting area is unsymmetrical so you have to use the general formula for stresses due to biaxial bending. If you are just doing a few cases, there are charts available that work very well. I agree with Qshake that you should through the exercise of making the spreadsheet yourself. It will be fun!

Both texts give the treatment for bi-axial loaded footings. Each with the typical treatment of where the resultant is and whether or not uplift occurs.

Additional information can be found using AASHTO which has a graphical interpretation to go along with the equations.

Regards,
Qshake

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