I cant understand this math. ive been over and over it. Each time I get a little further, then I loose it again.
ref:
How to calculate rafter thrust? -Help! at http://www.eng-tips.com/viewthread.cfm?qid=105386
Can someone help me figure cable load?
4/12
24″ rafter spacing.
No rafter ties at all. A few existing collar ties.
ceiling joists run parallel to ridge.
house is 27′ x 30′(ridge).
7/8″ roof planking and asphalt shingles.
thanks,
pa
Replies
It's all about the squaw on the hippopotamus.
Hint: Consider what happens if the rafters spread one inch -- how far does the ridge fall? The spreading force is equal to the force on the ridge divided by how far the ridge falls (in inches). For a 12/12 pitch the ratio is 1:1.