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Re: Drag forces perpendicular to roof trusses and or joists

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Title: Re: Drag forces perpendicular to roof trusses and or joist
Jeff,

You are correct, drag forces perpendicular to the trusses need to be addressed, and detailed,
it is an ugly detail, that is probably why it is unliked. I would first try to get the shear to the outside
walls as to avoid this condition, but if you can not, I use field made or truss panel blocks that transfer
the shear from the roof sheathing down to the shear wall below. you have to treat every panel block as a shear wall with sill nailing/ bolting AND holdowns, although you could detail the interior blocks
to cancel the tie forces, the end blocks will need strap holdowns. I then use a coil strap
on the roof sheathing to tie the blocks and extend it as needed
hope this helps


Tarek Mokhtar, SE
Laguna Beach, CA







Most times interior shear walls tend to run parallel with trusses so it is easy to use roof trusses as drag struts or to transmit drag forces from one wall to the other.  It is also pretty straight forward to design the connection of the drag strut to the shear wall (tension or compression).  However, in the case a drag force runs perpendicular to the trusses, how is the drag strut done to resist any tension loads?  Compression drag loads would be resisted by blocking, etc.  I haven't been able to find anything anywhere mentioning this situation.  I have seen other plans around town that will detail the crap out of the drag forces that conveniently run parallel to the trusses (i.e. drag strut connectors, tension straps, etc.) but then when the shear walls run perpendicular to the trusses/joists the drag ties/struts detailing is mysteriously missing. 
There seems to me that there would have to be at least some blocking working as a collector to: #1 transmit shear forces to the shear walls and #2 it is a diaphragm boundary and blocking needs to be present to edge nail into.  Is there an assumption I am missing here or is this something that since the shear wall is not conveniently oriented with the trusses it gets ignored.  When a shear wall runs perpendicular to the trusses, it gets hard to detail the connection for tension because you have a need for a tension splice every 24" or so.  Just wondering what others thoughts are or what assumptions I am missing.
 
Jeff Hedman 
L.R. Pope Engineers & Surveyors, Inc.
1240 East 100 South Suite # 15B
St. George, Utah  84790
Office: 435-628-1676
Fax: 435-628-1788
email: jeff(--nospam--at)lrpope.com
 

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Tarek Mokhtar, SE
TMM Structural Engineers, Inc
31645 S. Coast Hwy
Laguna Beach, CA., 92651
949-499-6254
949-499-2777 Fax