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RE: Layout Prevents use of Drag Struts

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Are your windows, mitered glass corners or are there mullions? Assuming that
you are designing by tributary area, you can treat each jog in the diaphragm
as line of shear if you have some location in each line to embed a couple of
cantilevered columns. I assume that you can drag the entire length of the
diaphragm in each line of shear. For example at one end of the roof, the
diaphragm may be only 20 feet deep. Twenty feet away in the next line of
shear, the diaphragm depth increases to 40 feet (or whatever). My assumption
is that there is some wall (interior or exterior) that lies close enough to
the physical jog in diaphragm depth as to allow the full length of the
diaphragm to be dragged into this shear element.

By spacing the shear elements (even a 6" rectangular tube section) in
adjacent lines of shear close enough together the reaction for the wind load
on the tributary width should not exceed the diaphragm capacity - especially
for interior shear elements where you can collect shear from both sides of
the diaphragm and virtually double the maximum shear capacity (i.e., if a 10
foot long wall needs to accumulate 4800 pounds of shear in a diaphragm
designed for 240 plf - you only need to connect the top plate of the ten
foot wall section and nail the diaphragm with 8d Commons at 6" on center in
two rows - staggered. The 10 foot wall will collect 480 plf of shear or 4800
pounds total.

I'm not sure if I am helping or not since I don't know your level of

I guess it comes down to - if you don't have enough wall, consider either a
braced frame or embedded (cantilevered) columns to do the job.

Dennis S. Wish, PE
SEConsultant(--nospam--at) <mailto:SEConsultant(--nospam--at)>
(208) 361-5447 Efax