ASD/LRFD Wood Design
ASD/LRFD Wood Design
(OP)
Excuse me for being behind the ball a bit. I have just finished up all of my 2001 CBC work and now beginning to look at the new code requirements a little deeper. As I understand it, ASD wood design hasn't changed any (i,e, fa/Fa and fb/Fb), and LRFD is a similar fashion just added adjustment factors.
Now steel is a different animal where ASD is similar to LRFD in the sense that the CSI check is based on M/omega correct?
The reason for my questioning is I have started checking a couple of wood beams with a particular software, and it utilizes an ASD CSI check of Mult vs. M nominal /omega. I am unaware of an omega factor for bending or shear for ASD wood. Am I off base with my questioning? Can you check wood beams using a Moment over omega method, and where is the omega listed in the NDS?
Now steel is a different animal where ASD is similar to LRFD in the sense that the CSI check is based on M/omega correct?
The reason for my questioning is I have started checking a couple of wood beams with a particular software, and it utilizes an ASD CSI check of Mult vs. M nominal /omega. I am unaware of an omega factor for bending or shear for ASD wood. Am I off base with my questioning? Can you check wood beams using a Moment over omega method, and where is the omega listed in the NDS?






RE: ASD/LRFD Wood Design
It appears to me that, the people who write codes and text books are going away from calculating stress and comparing it to an allowables stress even for ASD applications. Instead the trend seems to be the calculation of the member's capacity so that it can be compared to the load requirement.
I've also seen examples where the Demand Capacity Ratio is calculated dividing the load by the member capacity. Your program may be doing something like that.
RE: ASD/LRFD Wood Design
There are no omega values, as far as I can tell, in the 2005 AF&PA NDS for ASD. The code (includes LRFD as well) is cheap enough ($100-$200, including supplemental references) to get a copy of it for little pain.
Jeff
RE: ASD/LRFD Wood Design
RE: ASD/LRFD Wood Design
The conclusion is that it would only apply to seismic design. Neither Jeff or I are Seismic experts, however.
My guess is that it has something to do with the way Seismic forces are calculated today. I think the rational goes something like this, if you calculate your seismic forces using ASCE 7-05 then you must provide, for timber frames, 1.5 times the capacity required to resist those seismic forces.
To me it makes no sense, if you want an increased safety factor then reduce the allowable stress. To me it appears more like LRFD advocates trying to drag every one into their methods.
RE: ASD/LRFD Wood Design
RE: ASD/LRFD Wood Design
Regarding the 1.67 factor are you indicating that your program use that for wood design or only for steel.
RE: ASD/LRFD Wood Design
RE: ASD/LRFD Wood Design
I know very little about the new ASD steel design code. However one post I've read indicated that ASD steel is just another version of the LRFD approach.
I think before long, with the every changing codes, you won't be able to build anything out of wood.
ASD in wood design is still a true ASD method.
RE: ASD/LRFD Wood Design
Jeff
RE: ASD/LRFD Wood Design