ASD vs LRFD
ASD vs LRFD
(OP)
This question is related to one I posted earlier:
Going to be working on a project designing connections where the EOR gives the shear reactions in ASD and gives the moment reactions in LRFD. He basically states ASD = 0.8*LRFD and LRFD = 1.5*ASD. In looking at these formulas I would think that the most advantageous method would be convert everything to LRFD because there isn't a large reduction in the other direction. In general, is this a correct statement?
Such a simple question and yet for some reason I am a little confused. I'm so stupid!
Going to be working on a project designing connections where the EOR gives the shear reactions in ASD and gives the moment reactions in LRFD. He basically states ASD = 0.8*LRFD and LRFD = 1.5*ASD. In looking at these formulas I would think that the most advantageous method would be convert everything to LRFD because there isn't a large reduction in the other direction. In general, is this a correct statement?
Such a simple question and yet for some reason I am a little confused. I'm so stupid!






RE: ASD vs LRFD
Depending on the type of structure LRFD should result in a lighter structure. But, with regard to connection design service loads (ASD connection design) or factored loads (LRFD), should result in the same connection. There are some minor issues with conversion factors (1.4-1.6), so the EOR usually chooses a conservative factor.
You can inform your client that this process is not the most efficient/economical presentation. But, from the fabricator's perspective the final connections will not be much different.
www.FerrellEngineering.com
RE: ASD vs LRFD
RE: ASD vs LRFD
If you convert the ASD shear reactions to LRFD using the relationship LRFD = 1.5*ASD you will be conservative, so I would agree with that tactic.
BA
RE: ASD vs LRFD
and LL = 30 kips
The factored LRFD force is 1.2(20) + 1.6(30) = 72 kips
With a phi factor for steel connections at 0.75 the "safety factor" is 72 / 50 / .75 = 1.92
With equal DL and LL you get a safety factor = 1.86
With ONLY DL you also get 1.86 (using the 1.4DL combination)
Not sure how 1.5 works here.
RE: ASD vs LRFD
RE: ASD vs LRFD
If DL = 20 kips
and LL = 30 kips
The factored LRFD force is 1.2(20) + 1.6(30) = 72 kips
The "safety factor" is 72 / 50 = 1.44
With equal DL and LL you get a safety factor = 1.40
With DL = 20 and LL = 60 you get 1.5
This is probably how the 1.5 was derived - based upon a ratio of LL to DL
RE: ASD vs LRFD