I am chemical engineer so don't bash me too much but the
way I understand it, there are horizontal forces acting
on a tower's base, albeit less than the vertical
forces. Imagine the tower being blown by the wind, the
top of the tower will tilt toward the leeward side or
away from the wind. The bottom will want to kick out if
it wasn't held fast. In high winds the guys will
stretch, can't prevent it, and the tower will lean.
This is why commercial folks use tapered bases, so that
the leaning tower doesn't put undo compressive load
acting down on the leg away from the wind. Phil KB9CRY
> Obviously we are in disagreement over the magnitude
> of the HORIZONTAL Forces at the Base of a Guyed Tower.
> Please explain the origin of the horizontal forces you are
> concerned about acting on the base.
>
> My contention is that they are quite small (and insignificant)
> compared with the vertical forces. THAT (and NOT LUCK)
> is why towers with minimal lateral support at the base
> do NOT fall down.
>
> Any mechanical or civil engineers wish to resolve this
> debate?
>
> Tom N4KG
>
> On Mon, 7 Oct 2002 Bill Coleman <aa4lr@arrl.net> writes:
> > On 10/7/02 8:53 AM, n4kg@juno.com at n4kg@juno.com wrote:
> >
> > >And what do you see as the problem?
> >
> > Since I sent this to you personally Tom, and you have answered on
> > the
> > list, I'll answer on the list.
> >
> > >The Legs are NOT rusted above the break at ground level,
> >
> > The rusting ground level is of grave concern.
> >
> > >The Legs are braced so they cannot move out or in,
> >
> > Are they? It is hard to tell from the description. What PE did the
> > calculations on the 3 foot pieces of angle iron pounded into the
> > ground?
> > Will they have sufficient strength to hold against all lateral
> > loads?
> > What happens over the next decade or so as they are subject to the
> > corrosive effects of the soil?
> >
> > >The space between ground and the next steps is filled
> > >with H braces at right angles to each other.
> >
> > Is the bracing sufficient to prevent twisting or lateral movement at
> > all
> > conceivable loads? Did a PE do the calculations? Are 2x6 PT boards
> > sufficient?
> >
> > Again, it is difficult to tell from the description, but it doesn't
> > sound
> > like conventional tower construction.
> >
> > >FYI, the tribanders were installed LONG AGO, before the
> > >legs rusted through at / just under the ground,
> >
> > Now THAT is a huge relief! From the way you originally posted the
> > message, it almost sounded the other way around.
> >
> > > AND, the
> > >tower has been climbed without incident in it's present
> > >condition.
> >
> > Again, this sounds like a good TEMPORARY solution for shoring the
> > tower
> > against a topple. It may even be sufficient to allow someone to
> > unstack
> > the tower so that it can be repaired. All things considered, it
> > would
> > likely be safer to use a crane and set the tower down before
> > repairing it.
> >
> > However, you presented this as a PERMANENT solution. I disagree. It
> > sounds unsafe.
> >
> > >Many people seem to fail to recognize that for a GUYED Tower,
> > >nearly ALL of the forces at the BASE are VERTICAL. The
> > >Horizontal forces on a Guyed Tower are carried by the GUY WIRES
> > >which converts them to additional vertical forces on the tower.
> >
> > Guys can only do their work of converting horizontal wind forces
> > into
> > vertical compression IF the base cannot move.
> >
> > Engineers design the towers with just this in mind. That's why bases
> > are
> > fixed laterally as well as vertically.
> >
> > >W1EVT has 19 R25 Towers 140 ft tall sitting on base plates
> > >supported by cinderblocks to place each base at the same elevation.
> > >There is NO lateral support at the base other than friction on
> > >the cinderblocks. These towers have been up for around 40 years
> > >that I know of.
> >
> > W1EVT is DAMNED lucky. (Although real cinder blocks would have
> > corroded
> > the base a LONG time ago, I assume he has them on concrete blocks --
> > in
> > which cases he is really lucky the base plates haven't cracked the
> > concrete blocks in all this time)
> >
> > >It is NOT necessary for a GUYED Tower to have
> > >a base rigidly attached to a large mass of concrete.
> >
> > Show me a PE-stamped tower design drawing that does NOT have the
> > base
> > anchored laterally as well as vertically.
> >
> > >It only needs a base that can support the Vertical Forces from the
> > tower.
> >
> > If that base moves too far, the tower will fall. Lateral anchoring
> > is
> > part of the design.
> >
> > You can show me 50 anecdotal stories of poor installations that have
> > not
> > fallen -- but it doesn't mean it is good practice. Just means people
> > were
> > lucky. So far.
> >
> > Sorry, I'm sticking to the LXC prime directive, and Rohn says
> > NOTHING
> > about concrete block bases or angle iron pounded into the ground.
> >
> >
> >
> > Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
> > Quote: "Not within a thousand years will man ever fly!"
> > -- Wilbur Wright, 1901
> >
> >
>
>
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