huangyhg

window/dormer cuts wall collector
our architect has provided me a wood truss, wood stud church. there are are dormers with windows that start below truss bearing, continuing above truss bearing, cutting the traditional double top plate collector/chord (depending on the load direction) that typically runs the length of the building. the condition exists on both sides of the building, cutting the collector/chord on the long length of the building (parallel to the ridge of the building.)
for longitudinal wind, i have a short diaphragm to shear walls on either end of the building. for transverse wind, i'm thinking that there needs to be drag struts at the location of the cut chords, forming smaller diaphragms between the larger diaphragms. these drag struts would not rest on shear walls, but server to transfer the load from the larger diaphragm to the smaller one back to the larger one. i have no idea on how to compute deflections of this irregular diaphragm. am i on the right track here? did i mention scissor trusses and a 12:12 roof pitch?
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you have mentioned one possible solution.
another possibility--can you treat the diaphragm for transverse lateral loads as two separate three sided diaphragms (each open on the side at the dormer)?
daveatkins
the condition occurs 3 times in the roof, so i would have a couple of isolated diaphragms with the 3 sided diaphragms. i don't think that that option will work. always open to suggestions though.
tricky problem. somehow you need to get those chord forces around the dormers. if the chord force is small, perhaps some of the roof sheathing can do the job (i believe this is not a "kosher" way of taking chord forces, but i have done it for small forces). or perhaps use blocking between the trusses, and use simpson straps to tie the pieces of blocking together.
daveatkins
are you saying that, at the thinnest part of the whole roof, use that as a diaphragm width, creating the chords the full length of the building using the strapped blocking parallel to the ridge. i think that could work. it would be uniform and deflections would be simple.
yes. and you would not necessarily need to run the strapping the whole length of the building, if at the ends of the building the wall top plate can start taking the chord force.
daveatkins

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