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RE: Flag-Pole Foundations for light framing

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Dennis,
 
I generally use nominal reinforcing just to hold the concrete together.  The HSS column is really doing all the work and the concrete is only adding bearing surface for the lateral soil bearing pressure.  But --  you probably can't find anything in the code that says you don't need any reinforcing.  On small things like this I always let the plan checker win :<)
 
I'm not sure what you mean by the flatwork providing "restraint against rotation" unless you mean providing horizontal resistance at the ground surface.  In that case you have to figure the amount of concrete, its weight and the coefficient of friction to resist the horizontal load (couple).  If there is not enough to resist the force through bearing and shear of the concrete then I add horizontal reinforcing steel around or welded to the column to drag it where I want it.
 
Jim Persing
-----Original Message-----
From: Dennis Wish [mailto:dennis.wish(--nospam--at)verizon.net]
Sent: Wednesday, November 19, 2003 1:03 PM
To: light_framing(--nospam--at)structuralist.net; seaint(--nospam--at)seaint.org
Subject: Flag-Pole Foundations for light framing

I have two Flag-pole foundations designed for the front of a custom home where the forces in each column (lateral force) based on an R of 2.2 is 690-pounds placed at 12’-0” above the top of the foundation. The entry is flatwork which is monolithically placed and is, in my opinion, sufficient to restrain the top of the column. A 18-inch square foundation pier extends up from the flatwork six inches and the foundation is 4’-0” below soil and 30” square. The Column is a TS 6x6x5/16” square tube has approximately 6-inches of flatwork on the two exposed edges of the flatwork (outside edges) and is continuous between columns.

 

The plan check corrections asked for two things:

 

  1. The minimum reinforcement for the concrete foundation
  2. The clearance surrounding the columns to show adequate restraint of the flatwork. It is assumed that the area in front of the columns will also be done in either brick/tile or concrete sidewalks with an area abutting the entry flatwork.

 

Unless the lateral loads were large, I have not in the past provided reinforcement with this much cover around the steel columns. The columns extend through the foundation and are secured to a 12” thick erection pad. The column should be sufficient to handle the moment in the base, and the concrete transfer the bending moment below grade without the need of a cage or vertical rebar. The passive soil pressure should also be sufficient due to the analysis to resist overturning of the columns with such low lateral loading. The erection pad is more than sufficient to support the entry roof dead and live loads.

Am I missing something here? Is there a minimum steel requirement for a flagpole with small lateral loads? Where would I find the information in the 97 UBC that might reference ACI-318 on this issue?

 

I have always used flatwork as a means to offer restraint against rotation of small lateral load columns. What, if any, is the minimum edge requirements to the edge of the foundation especially since the piers extend above a post hole foundation that is 30-inches square and 48” deep?

 

TIA

 

Dennis S. Wish P.E.