advantages of ceiling diaphragm?

[skavuvie]

what are the advantages of a ceiling diaphragm or are their alternatives to this for a typical wood building with stud walls and wood trusses.

 

[DaveAtkins]

Normally ceiling diaphragms are not used, because it is expensive to place OSB or plywood on the ceiling (since it has to be covered with GWB anyway).

Most of the time the roof and floor sheathing act as the diaphragms. At the walls which are parallel to the trusses, kickers are used to transfer the lateral load to the diaphragm.

DaveAtkins

 

[woodman88]

DaveAtkins, In the IBC 2009 the shear capacity for horizntal gypsum diaphragm ceilings are given in Table 2508.5.
skavuvie, Typically, the roof sheathing is used for the roof diaphragm.

Garth Dreger PE
AZ Phoenix area

 

[skavuvie]

thank you for Garth and Dave

 

[DaveAtkins]

woodman88,

That's good to know! I have always known they contribute something, and it is conservative to ignore them.

DaveAtkins

 

[abusementpark]

How do you ensure that the gypsum ceiling is properly fastened to the ceiling to achieve diaphragm capacity?

 

[DaveAtkins]

The GWB is directly fastened to the bottom chords of the trusses. Like with OSB or plywood, you must make sure loads can transfer to where they need to go.

DaveAtkins

 

[woodman88]

Typically, you nail 2x6 blocking to the wall with 2" into the ceiling for fastening the gypsum board to. See 2009 IBC Section 2508.5.

Garth Dreger PE
AZ Phoenix area

 

[msquared48]

The permissable loads are very low, and in seismic regions, half stresses apply when seismic governs.

Although it is now allowed, I will would not use it. I do it other ways. It provides redundancy up to a point, but the allowed values are so low, to me, they are useless.

It's just my preference.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask