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Bracing of vertical webs

Bracing of vertical webs

Bracing of vertical webs

(OP)
Recently had a project where trusses were located directly above a separation wall in the attic space (i.e. separating two units of a townhome).  These trusses consist basically of 2x4 vertical webs at 12" o.c with maybe a maximum height at the peak of around 10'.  Problem came up when the contractor needed to know how to achieve fire rating around all of the bracing called out in the truss package for several of the vertical webs in the trusses.

As these trusses are lightly loaded (maybe 2' of roof) and are continuously supported on wall below, we asked the truss company for clarification.  Answer came back that truss design software specifies bracing for all webs where L/d ratio exceeds 50, and actual loads/stresses are not considered.

Is this how the various programs work?  I thought they were more sophisticated in their operation.

RE: Bracing of vertical webs

I believe the L/d ratio less than 50 comes from the NDS.  I would start by checking those requirements.  That's analogous to bracing steel members with L/r > 200 regardless of load.

RE: Bracing of vertical webs

I would like to know what software program is being used. MiTek, Alpine....?
 Most webs over 8'-0" in length will require bracing despite the loads applied to the truss. It sounds like you have some of those with a 10'-0" peak.
 I would be surprised if the design program DOES NOT take the actual loads into consideration.

RE: Bracing of vertical webs

You can get around the dreaded continuous lateral brace by scabbing another 2x member to the webs that require braces.  Can be in the configuration of an L, T, or flat scabbed, depending on the axial load in the web and the L/d ratio.

RE: Bracing of vertical webs

Dear prblmfxr, you cannot add the "L" or "T" member then try to drywall both sides of the truss!!!

However, a lot of times the L/d ratio is so minimal, that a 3" wide by 12" long truss plate added to the center of the web will actually elimate the need for a brace. Challenge the truss engineer. If he knows what he is doing, he will agree.

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