Design of footing for shear when depth>width

[Buleeek]

Hello everyone,

Assuming square footing (lets say 18"x18", 12" deep, d=9") and column 5"x5", should I check the footing for the wide beam action and two-way action? The distance from the face of the column to the edge of footing is less than "d" which is where I should check the footing section for shear. The code (ACI) doesn't give any information what to do in a such case. Thanks in advance for all the help.

 

[JoshPlumSE]

For cases like this the shear will transfer directly through the slab into the soil, with no real opportunity for shear failure. No real opportunity for flexural failure either for that matter.

 

[Buleeek]

Thank you. So there must be something what determines a depth of a small footing (other than frozen depth). Any suggestions ?

 

[dauwerda]

ACI 318-14 Section 13.3.1.2, "Overall depth of foundation shall be selected such that the effective depth of bottom reinforcement is at least 6 in."

 

[Buleeek]

You're absolutely right. Thanks a lot!

 

[CANPRO]

Buleeek, you don't need a code reference to understand what to do here - draw your column and your concrete footing to scale and then draw a 45 deg line down from the edge of the column. If that line exits at the side of your footing instead of the base, it means you can engage the full width of your footing through direct bearing, without the need for shear and flexure. You could have a little concrete pyramid that is 18"x18" at the base and 5"x5" at the top and it would be no different structurally than full square block of concrete.

JoshPlum - if you happen to be following up on this thread, I was hoping you would comment on this thread

https://www.eng-tips.com/viewthread.cfm?qid=449611

someone posted a screen shot of a connection they designed using Risa3D, was wondering what your thoughts were on this application of the program.