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RE: reducing rod deflection with tension force
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: reducing rod deflection with tension force
- From: "Chan, David" <DCHAN(--nospam--at)ladpw.org>
- Date: Thu, 28 Aug 2003 07:20:23 -0700
don't know much about queen post trusses, but a 1" rod spanning 22 feet between
panel points sounds like a pretty high slenderness ratio.
I have a queen post truss with 1" rods for the
bottom chord. The spacing between the panel points is 22 feet.
According to our calculations, the 1" rods would sag about 10" under their own
weight if they are not in tension and free to move at their ends. I
would like to find out how much tension will need to be applied to reduce the
self-weight deflection to a reasonable amount - say 1/2".
I see from Roark's formulas - Table 12 Case 3
that if the ends can't move, then the force on the ends would be about 1100
pounds and the deflection of the rod would be about 1 1/2".
While this is helpful, this formula does not get
me the force required to bring the rod up that remaining 1" to get the
deflection down to 1/2". I understand that it is not possible to get the
deflection to zero and expect that as one approaches zero the force qets quite
high. What I don't want to do is to specify that the erector have to
take more sag out of the rod than is reasonable - thus inducing huge tension
Thanks in advance for your help.
Kenneth S. Peoples, P. E.
Technical Associates, Inc.
1584 Weaversville Road
Phone: (610) 262-6345
Fax: (610) 262-8188