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RE: Question on wood Roof Trusses

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Title: Question on wood Roof Trusses
It is common to use braces on individual web members to keep the le / d ratio acceptable.  The usual practice is to use a continuous 2x4 perpendicular to the web plus additional diagonal braces about 20' on center to anchor the continuous brace. 
 
Roger Davis
Architect
SDS Architects, Inc.
 
-----Original Message-----
From: Hyndman, Keith [mailto:KHyndman(--nospam--at)engineeringsi.com]
Sent: Friday, January 12, 2001 6:34 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: Question on wood Roof Trusses

I'm having a problem with a 40' span Howe wood roof truss.  The web members and bottom chords are 2x4's and the top chord is 2x6.  I modeled it in RISA-3D. The interior diagonals are showing compressive forces, yet there le/d > 50 using the 1 1/2" depth. It's member length is about 130".  So I guess my guest ion is how do I analyze this truss?  The slender member can't takes compressive loads, yet my model shows it in compression. Was the truss built incorrectly or am I not understanding how it works?

Ultimately I have to "piggy-back" this truss with another truss to extend the roof line. Essentially turning a gable into a triangle.


Keith Hyndman
khyndman(--nospam--at)engineeringsi.com
Exton, PA