Joe Bartok
02-12-2005, 10:11 AM
giddonnah, et al:
Sorry about the short response in the Roof Framing Forum last night that didn't really "explain" anything. I didn't intend to be rude, I was having problems posting messages and running out of time as well.
The purpose of the calcs posted yesterday was simply to demonstrate that unequally spaced supports are unequally loaded (we don't really need a calculation to "prove" that, do we?). Here's a bit more detail, the "lecture" requested, and the purlins referenced. Since the topic is also beginning to stray from the original question, this sub-forum seems a more appropriate place to post the data.
I still don't have any specific numbers; they're archived at the company office, and I don't think it would be ethical to broadcast them at any rate. However, the method or process is mine, and here it is. The document LOG_ROOF.pdf illustrates the general idea. The first calculation using the "false" load serves only to assess load distribution (which isn't necessarily symmetrical) about the ridges and purlins. Then we use this data in conjunction with the actual loads psf to solve for the plf along the roof members.
The Sizer 97b program returned values for beams of rectangular section. The attached LOG_BEAM.xls. converts rectangular sections to log beams one to three logs deep, of equal I and depth, with allowance for material removed by scribing and cutting the ridges and purlins. The worksheet's a bit of a mess; it was done on the spur of the moment with notes to myself scattered left, right and center. I wish I knew then what I know now about Excel! Just think of it as the "beta" version.
Also attached is LOG_BEAM_NOTES.pdf, which briefly explains the math my worksheet uses to assess variables such as the First and Second Moments of Area, neutral axis, resisting moment, shear stress distribution, etc. The last page lists empirical methods of checking up on results produced by the theory. (And note that I don't understand why the Log Span Tables compare a circular section to a square rather than an equivalent rectangular section to assess maximum resisting moment. Ditto for maximum shear load).
Rich: If this is "information overload", drag it in your equivalent of a "Recycle Bin". It's your bulletin board, and I don't want to do anything that might seem like abuse of posting privileges. I just thought that perhaps some readers might find this both interesting and useful. The same data is available at my weblog at the link Log Beam Sections.
Sorry about the short response in the Roof Framing Forum last night that didn't really "explain" anything. I didn't intend to be rude, I was having problems posting messages and running out of time as well.
The purpose of the calcs posted yesterday was simply to demonstrate that unequally spaced supports are unequally loaded (we don't really need a calculation to "prove" that, do we?). Here's a bit more detail, the "lecture" requested, and the purlins referenced. Since the topic is also beginning to stray from the original question, this sub-forum seems a more appropriate place to post the data.
I still don't have any specific numbers; they're archived at the company office, and I don't think it would be ethical to broadcast them at any rate. However, the method or process is mine, and here it is. The document LOG_ROOF.pdf illustrates the general idea. The first calculation using the "false" load serves only to assess load distribution (which isn't necessarily symmetrical) about the ridges and purlins. Then we use this data in conjunction with the actual loads psf to solve for the plf along the roof members.
The Sizer 97b program returned values for beams of rectangular section. The attached LOG_BEAM.xls. converts rectangular sections to log beams one to three logs deep, of equal I and depth, with allowance for material removed by scribing and cutting the ridges and purlins. The worksheet's a bit of a mess; it was done on the spur of the moment with notes to myself scattered left, right and center. I wish I knew then what I know now about Excel! Just think of it as the "beta" version.
Also attached is LOG_BEAM_NOTES.pdf, which briefly explains the math my worksheet uses to assess variables such as the First and Second Moments of Area, neutral axis, resisting moment, shear stress distribution, etc. The last page lists empirical methods of checking up on results produced by the theory. (And note that I don't understand why the Log Span Tables compare a circular section to a square rather than an equivalent rectangular section to assess maximum resisting moment. Ditto for maximum shear load).
Rich: If this is "information overload", drag it in your equivalent of a "Recycle Bin". It's your bulletin board, and I don't want to do anything that might seem like abuse of posting privileges. I just thought that perhaps some readers might find this both interesting and useful. The same data is available at my weblog at the link Log Beam Sections.