My intent here is not to raise anybody's blood pressure. However,
yesterday I had a couple of minutes and thought I'd try a quick
comparison between ASD and LRFD. I have a large 2-story structure
(210'x270'). Bay sizes are 21'x27', 10 each direction. I optimized a
typical bay of roof framing using ASD, and then tried LRFD. Know what?
I got the exact same member sizes! I guess that might not be a surprise
to some of you, but it was to me.
The whole thing took me a little longer than ASD (not that its hard or
difficult, just different). It didn't feel right and I certainly didn't
save any money for the client.
Question: When is it that LRFD would produce smaller beam sizes? Maybe
I'll try the same test on the 2nd floor framing, since I have much
higher live loads than on the roof. I'll report my findings if they
Michael Ritter, PE