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RE: Highway Sign Column Embedment

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I’ve always done this using the concept of bearing and never had any problem with it.


M = Moment at the top of the footing.


b = flange width or diameter of pipe


d = embedment depth of column into the footing


Fp = Allowable bearing stress on concrete = 0.3 x f`c x min(A2/A1,2) x 1.33


Where A2 is the bearing area (in this case A2 = b) and A1 is the total area (in this case footing diameter)


S = b x d2/6


F = M/S


Rearranging –


dreq’d = (M x 6/(b x Fp))0.5 (make sure units are consistent)


For example, using the capacity of an 8” STD pipe, A-53 Grade B:


Fb = 0.66 x 35 x 1.33 = 30.72 ksi


Mcap = 30.72 x 16.8 /12 = 43.01 ft.-k


For f`c = 2,500 psi:


Fp = 0.3 x 2,500 x 2 x 1.33 = 1,995 psi


dreq’d = (43.01 x 12000 x 6/(8.625 x 1,995))0.5 = 13.41 in. << 36 in. O.K.


As you can see, providing just a reasonable amount of embedment (I never use anything less than two feet) will be satisfactory.




T. William (Bill) Allen, S.E. (CA #2607)

V/F (949) 248-8588

San Juan Capistrano, CA

-----Original Message-----
From: M. David Finley, P.E. [mailto:pec(--nospam--at)]
Friday, September 12, 2003 8:13 AM
Subject: Highway Sign Column Embedment


I'm working on a project with several multi-column highway signs.  The columns (W6's, W8', or 8" pipe) are directly embedded 6'-0" into the drilled shaft foundations.  The foundations are reinforced and are typically 3'-0" in diameter by anywhere from 8' to 12' in length.


The Owner's representative has requested design calculations substantiating the column embedment.  Can anyone direct me to a reference for determining the fixity that can be developed this way? 


M. David Finley, P.E.
2086 SW Main Boulevard - Suite 111
Lake City, FL  32025