ASD vs. LRFD? 3

[aswierski]

I'm a young gun starting out his career, and my father (a civil P.E.) taught me how to do all my calcs using the ASD method. I recently bought Salmon & Johnson's "Steel Structures" 5th Ed. and they emphasize LRFD. Is this a trend that is starting to be used more and more? I'd like to know which method is more prevalent throughout the country (my guess is ASD), so let me know what you guys are using.

- Adam

 

[apsix]

"For concrete .... you don't need to recalculate loads to check deflection (because you don't check deflection)."

If you have the experience to judge a deflection check may not be required, but many elemnets should always be checked for deflection.

 

[frv]

I think he was referring to the ACI provision that states that if you have a certain L/d ratio for a given support and continuity condition, deflection need not be checked.

 

[kslee1000]

Deflection is a less critical issue in RC than steel structure, but can not be ignored completely. At least, it is a good indication on how well the structural arrangement is, and a good source to spot troubled areas. These days, with help from computer, service load cases and factored load cases, and load combinations, are not that troublesome to generate as old time before, so it (factor vs non-factor) shouldn't be in the dispute of design methods.

 

[abusementpark]

There is really nothing to learn about either method. It isn't hard to switch from one to the other.

In ASD, you factor one side of the equation.

In LRFD, you factor both sides of the equation.

Am I missing something??

 

[Philip86]

I think this is a trend that will continue. The idea is to approach all engineering problems with the same design framework.

I think since you are young Adam, there is no reason why you cant learn and adopt both methods, either way it makes you are far more rounded engineer.

 

[sandman21]

I can use either it’s truly not that big of a change. Also some of the systems I have checked the sections come out about the same.

 

[aswierski]

Thanks gang. Very helpful.

 

[Lion06]

abusementpark-

Your statement is true of the new ASD vs. LRFD, but not true of the old ASD vs. LRFD.

 

[miecz]

In the old ASD, you checked one or two load combinations. With the advent of the more rational LRFD, you need to check 47. When you need to check so many load combinations, it is no longer feasible to design by hand. Now, those load combinations have found their way into the new ASD. At this point, it really doesn't matter whether you design by ASD or LRFD. You still have to deal with all the #$%^%$ load combinations. You still have to design with a computer. When you turn to a computer to perform the analysis and design, you begin to lose your feel for the mechanics of the material. That, I believe, is the unintended result of the more rational LRFD. We're all becoming less rational.

 

[nutte]

The building code makes us check 47 load combinations, not the steel design method.

Keep in mind the old ASD is 20 years old and wasn't updated from the time it came out until 2005. The difference between the old ASD and the new ASD is merely better information, not a dramatic change in philosophy.

 

[kslee1000]

Always turn the graphics on, and exam the results graphically. In the computer age, one needs to be more sophisticate on interpretating visual displays, and making simple design decisions by intuition.