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RE: Brace connection at mid-point

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No one else responded, so I have to blow the dust off some old references. These are also available on the AISC web site.

I would suggest the following references:

AISC Engineering Journal 1987, 3rd quarter, "Design of Diagonal Dross Bracings Part 1: Theoretical Study"

AISC Engineering Journal 1988, 4th quarter, "Design of Diagonal Dross Bracings Part 2: Experimental Study"

AISC Engineering Journal 1986, 1st quarter, "Effective Length Factor for the Design of X-Bracing Systems"

Basically, the tension brace acts as an out of plane brace for the compression brace. The compression brace buckles in an S shape with the inflection point being the intersection of the X brace. You infer that it appears to be a bad idea, but that is how X braces work. That is what has been used in telecommunications towers also.

For double members, I like to make one of the members continuous from each end.

Harold Sprague

From: <William.Sherman(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: Brace connection at mid-point
Date: Thu, 8 Mar 2007 07:26:17 -0700

In using cross-bracing connected at the mid-point and designed for tension-compression loads, must both braces be "continuous" thru the joint? In tension-only bracing it is common to interrupt one member and connect with a gusset plate at the mid-point, but it is not clear if the same details can be used for tension-compression bracing. In looking thru references on the AISC website, I could not find direct discussion of continuity of diagonal braces. I have seen various articles that discuss the use of the tension brace to laterally support the compression brace with respect to "effective length" - but a discontinued brace would "encourage" buckling at the mid-point vs a continuous brace. If true full lateral support is provided at the mid-point perhaps it should not matter, but reducing the buckling capacity of the compression brace and relying solely on the tension brace to prevent buckling at the mid-point seems like a bad idea.

If possible, please provide references that address this situation.

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