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Re: Highway Sign Column Embedment

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I forgot to mention that I also provide ties at the top to take out the tension force:

 

T = fp x b x (d/2) x 0.5

 

S = 8.625 x (36)2/6 = 1,863 in3

 

fp = M/S = 43.01 x 12,000/1,863 = 277 psi

 

T = 277 x 8.625 x (36/2) x 0.5 =21,502 lbs.

 

As = 21,502/(20,000 x 1.33) = 0.81 in2

 

Use (3) #4 Ties (As = 3 x 2 x 0.2 = 1.20 in2)

 

(my math could be off – need to check)

 

Regards,

 

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

V/F (949) 248-8588

San Juan Capistrano, CA

http://members.cox.net/ballense/

 

-----Original Message-----
From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net]
Sent:
Friday, September 12, 2003 8:53 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Highway Sign Column Embedment

 

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.

 

HTH,

 

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

V/F (949) 248-8588

San Juan Capistrano, CA

http://members.cox.net/ballense/

-----Original Message-----
From: M. David Finley, P.E. [mailto:pec(--nospam--at)isgroup.net]
Sent:
Friday, September 12, 2003 8:13 AM
To: seaint(--nospam--at)seaint.org
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
386-752-6400