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

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This is a matter of judgment on the part of the engineer.  A very
careful evaluation of soil type, frost depth, quality of construction
etc. is required before deciding to take advantage of forces that are
normally ignored.  I provide service for refinery/chemical industry and,
in my experience of several years, I have not had the luxury of soil
investigation reports in many situations. So, while the side friction
forces or availability of passive resistance below a certain depth may
be available to relieve overturning forces on the footing, I choose to
ignore them and provide a slightly larger footing.  I have taken flak in
the process, but most plant officials (many claim to be experts in civil
engineering by practice.  They don't realize that they have been lucky
because civil engineering materials are generally forgiving) accept my
design, sometimes grudgingly.  If someone insists that I reduce the size
of footing by taking into account those type of forces, I demand a soil
investigation.  Considering the extra cost and additional time delays,
usually they backoff.


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 ?