Hubba:
MiTek and others hold their cards pretty close to their vest when it comes to their design and analysis programs, and it is becoming more and more difficult to do some simple calcs. to verify their controlling reactions and member stresses and sizing, etc. What with all the load combinations, variable wind loadings and nonuniform snow and drift loading, and then add earthquake loadings, and who knows but that a different load combination doesn’t control every single member in the truss. I expect that, in another generation or so of code changes a simple building will be impossible to design and analyze by what we used to call rational engineering methods. You won’t ever get past trying to summerize the potential different load combinations, let alone know how to factor them up or down, and in wood, don’t forget all those adjustment factors also. And, then if you use different programs, you most likely will get different answers, because the various programmers interpreted an un-interpretable bunch of probabilistic babel differently, and none of them is really wrong; but their solutions are maybe more exacter (?) than slide rule solutions were 50 years ago, they just need sixty more pages of printout to get there. And, you needed more time to compile the load combinations now than I did to design the whole roof system. They have ten decimal place answers, that must be gooder, but my building is still standing after 50 years, so who is righter? If that roof structure knew what contortions you and they went through to prove it might stand up under load, it would fall down from sheer exhaustion or sheer exasperation. That’s different than horiz. shear stress, but is going to be included in the next version of the NDS. And, LEED says it’s greener too, when you use more trees to produce the paper for the paperwork and computer printouts than you do to produce the actual roof trusses.
