For structural strength is it better or not make any difference if you set the top end of a rafter on a bevel on top of a ridge beam or cut a bird mouth to set on the ridge beam? Do maximum rafter stregth does it make any difference? I am sure for many applications it make no difference, but in a heavy load application does it matter?
I know a beam requires maximum strength mid span (hence you do not bore holes mid span), and that in theory a beam requires little thickness at the tails, therefore ….
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rafter on a bevel on top of a ridge is stronger - e.g breaking point will be the same or higher than a bird mouth.
lateral shear is sometimes the governing factor. Notch causes a stress riser.
Thanks
As one would think, but then again as your favorite quotes states, sometimes our tortured reasoning is just that.
Rafter Strength
I'm not sure that your statement "you do not bore holes mid span" is true. At least, IIRC, in the case of engineered joist, larger holes are allowed in the middle third where the bending forces are greater than in the end thirds where the vertical shear is greater.
This is not necessarily true with standard lumber. You can bore in the middle third, but not notch in the middle third. I think that the limits for notching and boring of these joist / rafters is set forth in the IRC. Notching and boring is mostly determined by the debth of the joist / rafter and which third of the span.
Junkhound mentioned lateral / horizintal shear. It is my understandting that this is not usually a factor except in short spans with very heavy loading. It is not usually a concern in residential construction.
What say ye junkhound? :-)