Pad Footing Eccentricity Design

[Muggers]

Hi,

I am currently doing a pad footing design on a brownfields project and am in a situation where I want to avoid extending any existing pad footings where possible.

I have attached a page extract from the Handbook of Concrete Engineering which provides guidance on calculation maximum bearing pressure biaxial eccentricties.

In the instance where the eccentricity ratio L/e falls between 3-6 so not outside the footing but outside the middle third of the footing, can the attached table extract and methodology be used to calculate the maximum bearing pressure providing the stability of the footing (overturning and sliding), reinforcement and bearing pressure are acceptable?

If not, has anyone got guidance on how to approach the situation where the point of load application is still within the footing but outside the middle third and the footing meets the stability, reinforcement and bearing pressure checks?

Cheers,

Nick

 

[KootK]

You should be fine with the table. I believe that the stepped line on the table separates loads that are within the kern (bottom right) from those that are not.

For hand calcs, see this thread: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Muggers]

Thanks for the response KootK. I have limestone fill supporting the footing and I have been reading that having the eccentricity outside the middle third ia acceptable providing the founding material is rock, however in this instance I am unsure I can proceed down that path.

My reasons so far for being able to accept the eccentricity outside the middle third are that the imposed loading causing the eccentricity is an instaneous case and the footing stabilty/bearing pressure/reinforcement checks all meet the requirements.