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RE: Bracing Requirements

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2 - 10% is what I have been told by many eng's. in the past. My relatively untrained eyes were surprised to see that this can be accomplished with a less than 1/4" dia. tie rod:
2% of 40k is 800#. Tn=Fy x Ag yields a req'd. Ag of .022, 
k-brace=2 x Pn / h yielding an Ag of .022, using Pn=200k, and h=23'.
I was atop this as yet complete fixture today and was tempted to jump clear of it when I felt it swaying.
Thanks for the help.
-----Original Message-----
From: S. Gordin [mailto:mailbox(--nospam--at)]
Sent: Monday, September 12, 2005 3:02 PM
To: Seaint@Seaint. Org
Subject: Re: Bracing Requirements

I would think that in your situation, "Guide for Stability Design Criteria for Metal Structures" by T.V. Galambos et al. is a must-see reference. 
Particularly, they refer to the brace force at 2% of the column force as a "usual conservative practice."
Steve Gordin SE
Irvine CA
----- Original Message -----
Sent: Monday, September 12, 2005 2:40 PM
Subject: RE: Bracing Requirements

Yes, that is the plan. Now, how to rationally size the members. There is little to no redundancy in this fixture. Loads are on the order of 20k at each col. with an overall ht. of 23'. Intermediate horz. beam is provided. Col. sects. are dbl. 8x8x.250 HSS.
I have one one approach outlined by Charles G. Salmon & John E. Johnson, Steel Structures, 4th Ed. Stiffness of brace, k, in the horz. dir. is  equivalent to 2x the column cap., Pn, divided by story ht., h.
-----Original Message-----
From: Gerard Madden, SE [mailto:gmadden(--nospam--at)]
Sent: Monday, September 12, 2005 2:21 PM
To: seaint(--nospam--at)
Subject: RE: Bracing Requirements

Cross brace it (chevron or X bracing) for in-plane rigidity and if you are trying to eliminate buckling of the columns, provide horizontal cross pieces to reduce the unbraced length of the column (KL/r).