Timber Diaphragms on trussed roofs

[engstructural]

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?

 

[engstructural]

Any help

 

[KBVT]

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 member. I don't understand what you are referring to with chords above and below the ceiling joists vs. both ends. Maybe a sketch would help .............

 

[msquared48]

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

 

[engstructural]

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.