Assuming Metal Roof Deck Rigid Diaphragm
Assuming Metal Roof Deck Rigid Diaphragm
(OP)
I believe I read somewhere that when you use a heavier gage of metal roof deck you can assume the roof diaphragm to be rigid. Has anyone else found this provision. I believe the cut-off between rigid and flexible is 18 gage.






RE: Assuming Metal Roof Deck Rigid Diaphragm
Someone correct if I am wrong, but I do not believe you can make a blanket statement about one gage of deck being 'rigid' and another being 'flexible'. The term is dependant on a diapragms displacement for a given span and width.
SDI, in the Diaphragm Design Manual defines this as G' with units of k/in of dispalcement.
Flexible Diaphragms have a G' of 6.67 to 14.3
Semi-Flexible = 14.3 to 100
Semi-Rigid = 100 to 1000
Rigid = Greater than 1000
RE: Assuming Metal Roof Deck Rigid Diaphragm
If the diaphragm deflects 200% of the average story drift (i.e. deflection of the vertical lateral system) then it is a "flexible" diaphragm per the IBC. If not, then it's "rigid" diaphragm.
Most metal deck diaphragms deflect very little and are thus "rigid" in my experience.
RE: Assuming Metal Roof Deck Rigid Diaphragm
RE: Assuming Metal Roof Deck Rigid Diaphragm
"Diaphragms constructed of untopped steel decking or wood structural panels or similar light framed construction are permitted to be considered as flexible."
In IBC 2006, see 1613.6.1