API LRFD?

[DDP]

Does anyone in practice use this? If not why is practice sticking with ASD if LRFD is more efficient?

 

[Focht3]

Please define "more efficient."

The following represents a combination of my personal opinions and what I have heard from various structural engineers:

ASD has inherent advantages over LRFD when it comes to soil-structure interaction. Soils don't act within the kind of narrow performance bands that apply to manufactured materials (i.e. steel and concrete.) Most marine structures (particularly fixed platforms) have significant foundation issues. Since LRFD principles have not made any real headway into geotechnical areas (for the previously cited reason), designers would have to use LRFD for the structure, then go back to ASD for the foundations and their connections to the structure. That's too much work for most designers - with a lot of uncertainty about whether the structural design is adequate. And it isn't very efficient (to me.)

When will LRFD replace ASD? I'm not sure that will ever happen; look what happened to USD. But that's just my opinion.

 

[DDP]

I guess what I mean by efficient is that if dead load is very large compared to live load (gravity direction-wise, most platforms have this) then LRFD will result in a lighter structure due to less of a dead load fudge factor.

Could you please expand on why piles cannot be designed using LRFD? We can rationally predict soil behavior and pile-structure connections are not complicated. And if soil behavior was erratic, we could just use a large fudge factor in LFRD.

 

[CVCENG]

API RP 2A recommends using ASD for offshore structures. From what I remember it doesn't specifically prohibit using LRFD, but only recommends not using it