Load model for gabled roof rafter

[1asdfghjk]

Hello,

My question is, how do you model the load on a rafter for gabled roof or any angled roof member using the load combinations 4 or 5 for Strength Design? In another word, If I want to use the aforementioned combinations for both wind and gravity, how would I model it since wind is acting perpendicular to the surface while gravity in angle to the included surface. Please see attached picture for clarity.

Thanks,

JN

 

[jayrod12]

What do you mean by model? What program?

Some programs allow you to set the loads by global axes and by local member axes. Using that to your advantage, if possible, would be the easiest. In the program I'm most familiar with, RISA3d, they're differentiated by either capitalized or lowercase X,Y,Z (x,y,z) for Global and local respectively.

Alternately, you could break down the wind load into it's vertical and horizontal components and apply it as two separate components, one directly vertical, and one horizontal.

 

[phamENG]

Since the wind load is orthogonal to the rafter, I'd break down the gravity loads into components based on inclined axes with one axis in the plane of the rafter. Keep in mind that different gravity loads are applied differently. DL is applied along the true length while roof live load is applied on the projection. You'll have to account for those variations, too.