Wood Diaphragm Gable End.

[EngStuff]

I have a manufacture building that spans about 107'x75'. It used to have a steel roof, spanning the 107' (partition wall in the center).. burned down, and they ended up going with Gable wood trusses. The wood trusses are spanning the 75' length, peak at gable height is 18 feet, the wall height is about 16 feet. Total building height is about 34'-0". Truss spacing is at 24" o.c. no ceiling or anything below the bottom chord members to help act as a diaphragm. refer to the Image below.

Also, I understand we still are required to design for seismic, but wind controls here and R=2.

I already designed the connections, bond beams, checked the existing walls and foundations due to the new loadings. designed the diaphragm as well. I had a question about the wall that has the gable end above. There is a hinge point, so what are the best way to brace these. kickers to the roof? or a sub diaphragm at the bottom truss chords? or just typical blocking into 1 to 2 truss bottoms are enough?

Thanks

 

[XR250]

Difficult problem. Threading kickers thru trusses is hard and puts a huge up/down load on the trusses and the wall.
This is a big building.
I would be looking at a partial plywood ceiling diaphragm. Might be able to add a bunch of X or V bracing on the bottom chords to get hinge the load out. The devil is in the details, though.

It scares me that you are asking about blocking one or two truss bays. What on earth will that do?

 

[GC_Hopi]

Block back and turn the truss bays into a horizontal truss or continue masonry to the roof line. You will likely need kickers to brace the end truss for the out of plane wind loading regardless.

Also try using the search on Eng Tip. I found the gem below.

 

[EngStuff]

XR250

Thanks for the info, I should of been a little more clear on blocking part. I meant use blocking, but also sheath the blocked portions up from one side to the other side of the building. it would essentially act like a deep beam. Perhaps blocking up to two trusses in isn't enough, but essential as much blocking to create a deep beam? where the gable end transfers the loads to the sheathing and into the walls.

GC_Hopi,

Thanks for the image, I found the thread you provided the image in. I did use search, but used the wrong search words. That document helps a lot! I also spoke with the PE in the office about it and showed me the book it came from. it helps a lot!


Also, Out of curiosity, this is a side question. Is there somewhere in the code books where if your roof pitch is a certain slope, you have to use an additional factor for lateral loading to transfer the diaphragm loads into the wall?

Thanks