For AISC, which method, LRFD, or ASD, should one use ? ? 2

[bertyboy]

For AISC, which method, LRFD, or ASD, should one use ?

I am a Structural Engineer in the oil and gas industry, in Aberdeen, Scotland, U.K.
In this industry we use some of the American codes, e.g. the AISC codes.

ASD is the allowable stress design. I have the 'green book', 9th edition, dated 1997.
Has this method been replaced by LRFD ?
Presumably this is a Load Factor Design method ?
When did this method come out ?
Is ASD still valid ?
Which of these 2 codes is the most commonly used code, in the U.S.A. ?
In terms of column design ( combined compression, and bending ), is there any difference between the methods in these 2 codes, aside from load factoring ?

 

[HgTX]

State highway departments and the FHWA are requiring design by AASHTO LRFD. Have they said anything about items that fall under the scope of AISC? Is there any highway work done under AISC codes?

vmirat: If neither code is specifically required, you pick one and follow it. You are under no ethical obligation to do multiple calculations and pick the "safer" one. If it were all about "bigger is better", you'd be under some kind of obligation to just provide the biggest member that can fit into the space available--nothing prevents you from oversizing members beyond code requirements. As long as you follow any one of the allowable codes, the liability is not on you any more than it would be if there were only one allowable code. LRFD has been used to reanalyze structures designed with ASD when a potential overload problem arises.

pmkPE: the simplicity of ASD (within AISC anyway) is about to go away, as others have said. The calculations will be the same for either "method" (one can hardly call them separate methods any more); only the factors are different.

 

[metljakt]

I'm presently one of many engineers working on the design of 5.5 billion dollar glassification plant in Washington State for the Dept of Energy. The umbrella statement for structural steel design was made a couple of years ago that stated

"All steel will be designed to ASD"

Peace berty