[TowerTalk] Fwd: *** - Television tower topples]

[n4kg@juno.com]

N4KG response inserted below.

On Wed, 5 Dec 2001 "Joe Subich, K4IK" <w8ik@subich.com> writes:

	SNIP

> > For (relatively) short guyed amateur towers under 100 feet the  most
> > common failure mode is that of a broken guy support from excessive
> > horizontal forces. While the failure of a top guy of a multi-level
> > guyed tower might constrain the debris radius by allowing top 
> sections to fold around lower guy supports, this would still not be the

> classic downward crumple observed in the TV tower.

	Multiple guy points in each direction are the key to
	allowing a tower to 'fold' in the event of a *single*	
	guy failure.   N4KG
> 
> This would only happen if all they guys on a single side failed at 
> the  same time.  The *only* failure mode in which I could envision a 
> multiple 
> simultaneous guy failure is vandalism (the anchor rod is cut) or if 
> the anchor block were to fail and the anchor pull out of the soil. 

	One scarry scenario would be if the anchor rod were
	to RUST through, unseen by the owner.  Fortunately,
	this seems to be a rare occurance.   This is a STRONG
	argument for TWO anchors in each direction.  N4KG

> If an amateur tower were, for example, have a leg rust out I would 
> expect a crumple or crushing fall just like a commercial tower. 

	NOT exactly. Remember that for a guyed tower,
	almost ALL of the forces at the base are vertical.
	Fortunately and amazingly, even a single tower leg 
	seems sufficient to support a *short* tower but don't
	bet your LIFE on it.  N4KG

	Case in point:  I have two such towers, still standing.
	
	One, a 55 ft TV tower with horizontal braces (NO
	diagonal braces) and roughly 12 inch face width
	where ONE leg rusted through at the ground where
	I had left a string tied around the leg (who knows why).
	I placed a plate under the rusted through leg, drove
	3 ft pieces of angle iron half way into the ground
	on the outside of each leg.  Then I cross braced 
	the legs inside the tower using two pieces of 2X10
	rotated to engage all the legs and nailed together. 

	Two, an 80 ft TV tower of identical construction
	with TWO legs rusted through at the ground.
	(Scared the H*** out of me when I discovered it)
	Both towers were placed in the ground roughly
	30 inches with NO concrete 20 years ago.
	Again, I drove some heavy angle iron around
	each leg, and crossed braced the bottom 
	opening using 2X8's in an H configuration
	stacked on top of each other, up to the first
	step, bracing the bottom of the tower in
	all three axis'.  Both towers are STILL STANDING 
	after 2 years, having survived some quite
	high straight line wind events.  N4KG

	N4AR has a 200 ft Rohn 45 tower that SHEERED
	the legs at the top of his concrete base when
	a tornado twisted the tower with 4 stacked 4L20's.
	It is still standing with an additional concrete
	block poured around the bottom of the tower,
	on top of the original concrete base.  N4KG
	

> > I dare say if the TV tower had suffered the total loss of one of 
> its upwind guy supports, it, too, would have fallen like a giant tree.
> 
	SNIP
> 
> 73, 
> 
>    ... Joe, K4IK 
> 

________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today!  For your FREE software, visit:
http://dl.www.juno.com/get/web/.

List Sponsored by AN Wireless:  AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!!  http://www.anwireless.com

-----
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com