Partial Diaphpam
Partial Diaphpam
(OP)
Got a building where it has a bowstring truss roof. Off to one end, they added on a small addition to make a L shaped building. The addition had a flat roof, wood joists and decking.
Now its being rehabed into a strip mall, and the flat roof will be torn off, and trusses added. Leaving the flat roof is not an option. The new roof will be a regualar truss roof with standing seam roofing.
Is it possible to deck the underside of the truss for a diaphram? I dont see why not, its no different than what is there now.
The big question is, does the whole thing need to decked, or can I do a perimeter 'beam' type pattern, thus the plywood still transfering the load to the sides?
Thanks
Now its being rehabed into a strip mall, and the flat roof will be torn off, and trusses added. Leaving the flat roof is not an option. The new roof will be a regualar truss roof with standing seam roofing.
Is it possible to deck the underside of the truss for a diaphram? I dont see why not, its no different than what is there now.
The big question is, does the whole thing need to decked, or can I do a perimeter 'beam' type pattern, thus the plywood still transfering the load to the sides?
Thanks






RE: Partial Diaphpam
Mike McCann
MMC Engineering
RE: Partial Diaphpam
RE: Partial Diaphpam
RE: Partial Diaphpam
However, being in a high seismic zone myself, I would definitely say no if the ceiling diaphragm was sheetrock.
Mike McCann
MMC Engineering
RE: Partial Diaphpam
That said, you could do a perimeter diaphragm as you've drawn but what are you really saving? As a diaphragm is essentially a deep beam taking strong and weak axis bending loads you're essentially breaking that up into 4 smaller, less efficient beams. You'll need tension and compression chords for each partial diaphragm, edge nailing (or screws) around all the edges, possibly blocking due to the small size, and you'll only save just the diaphragm material and field nailing in the middle. Much better just to make it a normal ceiling diaphragm and call it good.
As Mike pointed out if this has high seismic you're not going to be able to use sheetrock for a ceiling diaphragm which means you'll need wood decking. As you need wood decking on the exterior of the roof trusses you're probably better off just designing a typical sloped diaphragm.
Maine EIT, Civil/Structural.
RE: Partial Diaphpam
He said the new roof will be standing seam, so there is no need for wood sheathing on the slope.
RE: Partial Diaphpam
Maine EIT, Civil/Structural.
RE: Partial Diaphpam