Folded plate plywood roof diaphragms 1

[wl2o8]

Does anyone have any methods or literature regarding allowable shear values in gabled (sloped) roof diaphragms (folded plate)? I am trying to figure out how to analyze a roof diaphragm that has an 8:12 pitch. I know that I can't get the allowable diaphragm loads normally given in the tables because there would be bending as well as shear on the plywood panels.

 

[jheidt2543]

I would try the American Plywood Association (AWP) or the Forest Products Lab, in Madison, WI. They are the two that develop the load tables we all use, they would surely have some answers for you.

 

[rccon]

For steep roofs, I analyze a frame consisting of a rafter pair and a stud, under the influence of the horizontal force. The reactions are four: horizontal and vertical at the bottom of the stud, and longitudinal in each rafter. The equations are four: H, V, & M =0 at the bottom of the stud and M=0 at the stud-rafter joint. M is also 0 at the ridge, but this is redundant. The longitudinal reaction multiplied by the length of roof tributary to a gable wall is the unit shear in the roof sheathing, so I compare this with UBC tables for horizontal unblocked diaphragms (or blocked, if necessary). This force is then applied to the gable rafter, which must be tied down.

 

[boo1]

The American Forest and Paper Association; "Wood Frame Construction Manual", 1995 SBC High Wind Edition Table 2.5A, 2.5B, and 2.5C list the allowable unit laterial loads for in-plane shear in gabled roofs.