Mat foundation, what "strip width" to design for

[N Andersen]

A four column footing, columns space 20' each way, supported on a 26' square footing. i.e. edge distance outside columns is 3'-0".

Footing approx. 2'-6" thick, all pedestals are 2'-0" square.

To design for shear & moment by strips, I read in an old textbook that rule of thumb for strip width is Pedestal + 3d, which gives strip 2' + 3(2'-2") = 8'-6" wide.

Sounds reasonable, but looking for any possible references to confirm.

 

[civilperson]

I would just duplicate the outside width and use 6 foot strips between/beyond columns, (including the diagonals).

 

[DaveAtkins]

I would either design this as a two way slab, using the ACI rules, or analyze it with a finite element computer program.

DaveAtkins

 

[VoyageofDiscovery]

Concentrate reinforcing under the columns within a band as specified by Code.

HTH

VOD

 

[BAretired]

You could take a six foot wide strip centered on each of the four columns. The 14'x14' slab in the middle could be reduced in thickness in order to save material (your option). It would be designed as a two way slab spanning between all four beams.

Any reasonable assumption would be okay.





Best regards,

BA

 

[N Andersen]

Thankyou to all for your input.

As I did not have access to a F.E. program last week, I designed 6' wide strips along all four column lines, and reduced the reinforcing somewhat for the 14x14 interior.