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Re: Lateral Brace Deflection[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: Re: Lateral Brace Deflection
- From: "Ed Workman" <eworkman(--nospam--at)fix.net>
- Date: Mon, 16 Aug 1999 16:12:45 -0700
-----Original Message----- From: Ed Fasula <tibbits2(--nospam--at)metro.lakes.com> To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org> Date: Saturday, August 14, 1999 7:26 PM Subject: Lateral Brace Deflection >I know that many use a factor of 0.02 of the design load on a compression >member to brace it, but what kind of deflection criteria should be used? This brings to mind a comment regarding bracing from Jack Boukamp. who said something like "A brace to an initially straight member could be a piece of cardboard, since the buckling force is nil until the chord is allowed to move" > >I'm bracing the top chord of a bowstring truss for a bridge (discussed >earlier on this list) with a diagonal fastened to an outrigger. The >outrigger extends 6' out, so it will deflect close to an inch under the 3 >kip vertical reaction from the brace (using a TS6x6x9/16 Clearly, the chord IS allowed to move in this case, but why so much?: An inch for a 72 inch outrigger is, on the face of it, L/72, and seems quite flexible. Obviously, "seems flexible" doesn't establish a criteria, but isn't a numerical evaluation of the top chord for p-delta fairly simple? Assume a parabolic shape and find the incremental deflection due to 3 inch lateral movement. If this additional deflection is "slight" it's OK if not, stiffen the outrigger. See the slender wall procedures in the Masonry section of the UBC for help in determining "slight" that denotes convergence.
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