deflection of sloped rafters

[scherry]

Ok, here goes. I am designing a great many sloped members for a complex roof with all kinds of slopes and some fairly heavy loads - different ones of course. I know how to use flat or sloped beam methods for moment and shear and what is conservative and what is not (Breyer). Any tips on conservative simplified deflection analysis for sloped wood beams? I am assuming that with steeper pitches I would need to consider a secondary deflection due to sort of a p delta effect because of the axial component of the load. Any suggestions, rules of thumb, (anything...) about when this becomes a critical issue? or should I just shut up, sit down, and analyze the heck out of all of them? Some of the members have miscellaneous point loads as well, and many of the members are cantilevered. if three in a group are exactly alike, I cheer. They are also using #2 SPF...say they cannot get anything else cause this is the boonies. any help, suggestions, shoulders would be apprecitated immensely.

 

[RARWOOD]

My gut feeling is that any deflection which may result from a P Delta effect will be small. One thing you could do is just run some of the members on a frame program.

 

[JAE]

We don't ever consider PDelta for wood deflection calculations. We use the horizontal projection span length for gravity loads, and the sloped length for wind.