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RE: Tension only thrust restraint

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	-----Original Message-----
	From:	Bill Sherman [SMTP:SHERMANWC(--nospam--at)cdm.com]
	Sent:	Friday, October 09, 1998 8:57 AM
	To:	seaint(--nospam--at)seaint.org
	Subject:	Tension only thrust restraint

	I have a pipe thrust restraint problem which I could use some advice
on.  I 
	have 21 kips of pipe thrust 20 feet above grade, which I would like
to
	resist 
	by use of a 30-ft long horizontal cable or rod from a vertical pipe
support 
	back to a building structure.  I am trying to avoid thrust at the
vertical 
	pipe support since its support structure below is not adequate to
carry the 
	base reactions if the thrust is included.   
	 
	I was thinking of using a cable - but in order to minimize cable sag
as well 
	as minimize pipe movement under load, I would need to pretension the
cable.  
	But this in turn puts a horizontal load on my vertical pipe support
when
	there 
	is no pipe thrust, which is the same as what I was trying to avoid
in the 
	first place.  So does anyone know of a way to resist such tension
due to 
	thrust without inducing tension due to the catenary effect?  Would a
steel
	rod 
	act much different from a steel cable? 
	 
	 
	For 30' span, probably not (Section properties of a rod are so low).
Sounds like you need a horizontal stiffleg.  What about a pipe sized to span
10' unsupported, and  a 4-way queen post arrangement at the 1/3 points of
the distance, similar to what I've seen done with long spans of pneumatic
conveyors?