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RE: Bolt force in round column

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Thank you all for your responses.  I got to thinking about this after I sent the note and came up with the same basic conclusion.  What through me off at first was the compression forces are bearing of the column, not the bolt.  I was looking at it as a column baseplate with tension bolts, only all the tension bolts were in different locations.  I guess if I look at it as just the bolts taking compression and tension I will get an answer pretty close to the real life situation of bolts in tension and column steel bearing in compression.





From: M. David Finley, P.E., P.A. [mailto:davidfinley(--nospam--at)]
Sent: Wednesday, January 11, 2006 6:59 AM
To: seaint(--nospam--at)
Subject: RE: Bolt force in round column




T = P/A + MC/I.  You can use that to find the forces in every bolt.


If you are looking for the maximum tension or compression, then it simplifies to


Bolt_Group_Inertia = (Number of Bolts /  8) x (Bolt_Circle_Diameter)^2


Section_Modulus = (Bolt_Group_Inertia) / (Bolt_Circle_Diameter / 2)


Bolt_Force = (Moment / Section_Modulus) + (Axial Load / Number of Bolts)      Use correct signs for loads.


I forget the minimum number of bolts for which this is applicable ( 4? ), but from your description, it should be applicable.


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

-----Original Message-----
From: Rich Lewis [mailto:seaint03(--nospam--at)]
Sent: Tuesday, January 10, 2006 5:53 PM
To: seaint(--nospam--at)
Subject: Bolt force in round column

I have a large diameter round column with bolts at about 6 inches on center around the perimeter of the base.  I know the axial load and the bending moment.  The bending moment is large.  The virtual eccentricity is larger than the column diameter so I know I have tension in some of the bolts.  Can someone direct me to a reference, or give me a formula, to calculate the maximum tension in the individual bolts?