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[Towertalk] 'Toes' of a tower concrete base

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Subject: [Towertalk] 'Toes' of a tower concrete base
From: (
Date: Fri, 28 Jun 2002 14:24:55 +0000

IF you make the foundation straight sided at the plan 
base dimension (largest size at bottom) you should have 
no problems as far as your installation is concerned.

I also wondered why they called out a truncated pyramid 
shape for a foundation in soil. It is very hard to shape 
without forming and does very little to increase the 
capacity for the extra effort. (my opinion only)

Hank Lonberg, S.E.,P.E.
> In preparing for the installation of my Rohn HDBX-48 tower I noticed that
> the concrete base diagram showed what I refer to as a 'toe'.  That is, the
> hole for the base is rectangular -- something like 5' x 5' x5'.  However,
> the bottom 12" flared outward creating an "L-shape" when viewed
> cross-sectionally --  similar to   _| |_  .  Being quick to draw
> conclusions, I figured the 'toe section' called for in the diagram provided
> additional leverage or strength.  I compared this effect to that of toggle
> bolts (AKA 'hollow wall anchors').  Once pushed through the small hole, the
> 'wings' spread out and provide strength against tipping or leaning.
> Now that plans have changed to use two AN Wireless towers I've been asking
> lots of questions about installation.  I have been told that you can
> eliminate this "L-shaped" area by simply making the hole rectangular.  (The
> dimensions, of course, would have to be increased in order to make the
> vertical sides match what would have been the very outside edge of the
> 'toe'.)  The reason for the 'toe section', I was told, is NOT mechanical
> advantage or anything like that.  It was to save on concrete costs.  Less
> concrete means less cost.
> My question:  Is this 'L-shape' essential to tower strength?  If I increase
> the horizontal dimension of the hole (to span the distance from left toe
> edge to right toe edge), do I weaken the structure?  Of course, this change
> WILL increase the mass of the concrete used in the base.  It would be
> easier, though, to dig the hole if all I need is a simple rectangular
> volume.
> gary b
> k3gb
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