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RE: IBC 2305.1.5

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The issue of distribution of torsion through the diaphragm is mainly intended for open front wood diaphragms (see figure 2305.2.5(1) and (2)) or when the diaphragm qualifies and a rigid diaphragm (see section 2305.2.5). If you do not have either of these conditions (and it appears that you don’t from your description) this section should not be of concern to you.


Ben Yousefi, SE

Santa Monica, CA


From: Jared Lewis [mailto:jared(--nospam--at)]
Sent: Tuesday, December 13, 2005 3:28 PM
To: seaint(--nospam--at)
Subject: IBC 2305.1.5


I am working on an existing three story facility that will have new shear walls positioned 40’ inside the perimeter walls.  The diaphragms consist of plywood sheathing over existing straight sheathing and the existing walls are lightly reinforced concrete and urm.  The above referenced section of the IBC references torsion as an unacceptable force distribution through horizontal trusses and diaphragms.  I suspect that the IBC means flexure in lieu of torsion.  However, flexure seems an inappropriate limitation as all wood diaphragms experience flexure under lateral loading. 


In addition, a steel strap horizontal diaphragm can be designed for this application.  However, I do not feel this is necessary given that the diaphragm depth to span ratio is 2:1.  Does anyone have experience with an alternate solution to this limitation? 




jared lewis


catena consulting engineers

1111 ne flanders street

suite 206

portland, or  97232