imber diaphragms on trussed roofs

huangyhg

timber diaphragms on trussed roofs
i was looking at creating a timber diaphragm in a prefabricated trussed roof to stabilise a wall panel. i can design the diaphragm to work ok however i am aware a top and btm chord are required. as my roof is trussed the most practical option would be to utilise the wallplates at either end of the truss and add a longtitudinal tie above the ceiling joists with bridging between joists in both cases. i am assuming a continuous chord above a below the ceiling joists would serve the same purpose as a continuous chord at the ends - is this correct? are there any issues related to the positioning of the chord i should be aware of?

find a job or post a job opening
any help
i'm not sure i understand your question.  a wood sheathing diaphragm is going to be flexible so you will obviously need chord members to take the tension/compression forces created due to diaphragm bending.  the double top plates of the wall below w/ a tension strap or properly detailed nailing pattern at the splice is the most common chord   
are you trying to make the ceiling that is attached to the underside of the roof trusses into a diaphragm, as well as the existing diaphragm over the top of the roof trusses???
i, too, am comfused...
mike mccann
mmc engineering
the diaphragm will be the ceiling, there is no diaphragm over the truss. i was not sure the wallplate alone would suffice as a top and btm chord and intended adding an additional chord by means of the longitudinal member above the ceiling joists.