Do Roof diaphragm and ceiling diaphragm work together?

[SeanStructural]

In a one story wood frame building in a high wind area, is it acceptable to assume that the ceiling diaphragm and the roof diaphragm work together? and therefore add their plf values together.

 

[msquared48]

Never done that before, but it is an interesting thought.

However, in that ceilings are sheetrock, and roof diaphragms are plywood, the ceiling diaphragm should fail before the roof diaphragm. When that happens everything goes into the roof diaphragm anyway. That's why the code generally does not allow you to combine dissimilar materials in a shearwall system.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MiketheEngineer]

Traditionally, only used the roof plywood.

As M^2 noted- once you lose the drywall ceiling - you are left with the roof only.

 

[hokie66]

This is more a matter of philosophy than of structural design. In Australia, solid plywood roof sheathing is not typically used. Ceiling diaphragms are the norm, combined with some diagonal bracing at the roof level.

If you lose the ceiling, there is not going to be much left of the building anyway.

 

[woodman88]

For the roof and ceiling diaphragms to act together they both have to deflect the same amount under the load applied. Since for the same amount of deflection they will resist difference loading you can only add the loads that gives the same deflection. I have never felt that it was a worthwhile calculation to do.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.