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[amrutha_N]

How to design ISOLATED SQUARE FOOTING under a biaxial column??
We generally consider service axial load then check for one way and two-way shear and design flexural reinforcement.Whether we need to take the biaxial moment in column while designing FOOTING? If yes then how to do it?

[sakumar79]

Dear Er Amrutha,
    The footing size is calculated by finding the pressure at the four corners of the footing as P/A +/- Mx/Zx +/- My/Zy. If the lowest value is more than 0 and the highest value is less than SBC, then the footing size is okay. Once the size is confirmed, design load of Max Pressure x A /1.1 can be considered as Axial Load for footing thickness and reinforcement design.

Hope that helps
Arunkumar

[vikram.jeet]

Nicely explained by Er Arun,,

In case some economy in footing size desired,, then Some upliftment of footing can be taken,, about 20% on Firm soil /rock strata  and lesser in medium and poor soils  UNDER NORMAL CASE  and 33% upliftment of footing area under Wind /Eq Cases.

However for Bridges,, No upliftment of footing area permitted
For foundations resting on Soils, but for Foundations on Rock it is permitted as stated above.

You can refer Teng's Charts for Design of Footings subject to bisxisl moments with upliftment of footings as given in book ' The Foundations Design by Wyane C Teng'

[vikram.jeet]

In continuation to above post :-

However Maximum base pressure shall be within permitted  Sbc

[amrutha_N]

Thank you Er.Arun .Checking for SBC WITH maximum pressure takes BIAXIAL MOMENT into account for the design of FOOTING. Will you say how to Assume SBC OF SOIL IN a place without SPTvalue . Given the depth of FOOTING to be 5feet below GL???