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help: bowstring truss modification (unbraced length problem)

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i am working on an industrial roof that was damaged (read: blew off) during
a windstorm

the structural system is 60' bowstring trusses, 16' o.c., made up of double
angles gapped at 1/2", and 2x10 joists and 1 by decking. the trusses sit on
a multi wythe brick/clay tile wall.
the truss is spliced at the center with bolts instead of rivets to the
gusset plate. otherwise
riveted everywhere else. the center of the span is braced with 'x' bracing
made up of other double angles.

in my analysis, i have found during MWFRS design windload the bottom chord
goes into compression (obviously) and the unbraced length is too long. the
solution seems to be to brace the quarter points of the span. issue here is
how. i am temped to have a 1/2 tab inserted between the chord members and
bolt X's to the top and bottom of it so it is effectively mechanicaly
connected to the bottom chord member. this would have to occur at about 16"
from the theoretical panel point location. i am uneasy about bracing the
truss at a location off the panel point.

is this a bad detail? alternates?

tia

dennis pantazis, pe



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