usd ` lsd ` lrfd

huangyhg

usd ~ lsd ~ lrfd
can some one explain in terms of reinforced concrete design? are these three design methods same or not? if not, what is the basic difference?
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okay, great theoretical design engineering question, and i'll give you an answer as best as i understand the situation...
pretty much everything used to be usd (ultimate stress design, aka allowable stress design, aka working stress design).  there are occationally some minor differences between the three, but essentially they are the same animal.  basically you find the stress in a   
i have never heard of usd explained in terms of ultimate stress design but rather ultimate strength design...and i seem to recall it is noted that way in several codes...
ultimate strength design here in the states is really about limits and is similar to limit state design which was more popular name in the uk for the method.  usd comes with the provisions that certain elements need to be checked via service limits states such as cracking in concrete.
regards,
qshake
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limit state design (lsd) is a design methodology that incorporates ultimate and serviceability limit states--conditions for which the structural system or element becomes unfit for its intended purpose. aisc 360 implements a lsd methodology and calls it lrfd. aci 318 implements a lsd methodology and calls it strength design method, formerly known as ultimate strength design (usd) method.
i am suprised to hear usd as a limit state code... i had thought ultimate strength design was a turn of the 19th century design procedure replaced by asd & wsd...  this should show the danger of international engineers dicussing matters with abbreviations more than anything else!
the core item for limit states, no matter what the name, is probability curves.  these methods are based on probability of failure, and/or, the probability of people dying in an ultimate limit state event.  if memory serves the national building code of canada has codified 1:50000 as a probability of death in a uls event.
regards,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
ys
my vote also is for usd as a limit state method, based on aust/brit experience. you're right about the confusion that can arise due to regional differences.