LSD versus LRFD 1

[orreng1]

Are these two completely different methods or are they just two different names for the same thing since LRFD is American and LSD is Canadian?

 

[dbuzz]

LSD (Limit State Design) and LRFD (Load and Resistance Factor Dsign) are based on the same philosophy: design load effect <= design capacity.

Generally speaking, in limit state design the nominal load effect is factored up, to account for uncertainitly in the anticipated range of loadings, and the nominal capacity is factored down, to account for uncertainty in material stength or behaviour.

This differs from Allowable Stress Design (also called the Working Stress Method) in which the unfactored stress, calculated from tthe most adverse combination of loads, must not exceed some permissable stress, which is equal to ultimate stress divided by some safety factor.

 

[orreng1]

Thanks for the reply.

But are the calculations very similar? I thought they were basically the same..?

 

[14159]

I think the main difference is that LRFD is actually calibrated using specific reliability techniques and that LSD is not. I could be wrong about this though. From a designer's perspective, I'm not sure there is much difference in philosophy. For example, the 2001 cold-formed steel spec has ASD / LRFD / LSD side by side, just with different factors.

DBD

 

[HgTX]

But LRFD was also calibrated to give more or less the same answers as LFD in many cases, is my understanding.

Hg

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