#4 Ties (As = 3 x 2 x
0.2 = 1.20 in2)
(my math could be off – need to
T. William (Bill) Allen, S.E. (CA #2607)
V/F (949) 248-8588
San Juan Capistrano, CA
From: Bill Allen
Sent: Friday, September
12, 2003 8:53 AM
Subject: RE: Highway Sign Column
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
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
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
Mcap = 30.72 x 16.8 /12 = 43.01
For f`c = 2,500 psi:
Fp = 0.3 x 2,500 x 2 x 1.33 =
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
From: M. David Finley, P.E.
September 12, 2003 8:13 AM
Subject: Highway Sign Column
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