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Re: Use of Side Friction to Resist Overturning - Spread Footing

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Robert Rogers wrote:
>  I have recently seen a set of calculations for the design of reinforced
>  concrete spread footings (for a new building) which support building
>  columns which are subjected to large lateral loading.  The spread footings
>  are approximately 5 ft. deep (to bottom of footing), 2 ft. thick, and have
>  a 3' tall square pier which receives the square column.  The calculations
>  assume a value of 500 psf for side friction on the 2' thick footing.  The
>  forces generated by this side friction are supposed to help resist the
>  overturning moment imposed to the footing.  I have never seen this type of
>  analysis used for spread footing design.  I think the methodology is way
>  out in left field !  Any other opinions ?

This not uncommon in the Southwest.  Provided the values are specified
by the Geo-Tech and the concrete is cast against the earth!!  I have
used specified values rangeing from 100 psf to 325 psf to resist uplift
and otm with no rejections from plan reviewers.

Donn Wooldridge RA/SE
Phoenix  AZ