[Towertalk] 'Toes' of a tower concrete base

[blueis@sprintmail.com]

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
RVN BTO