LRFD probability data 4

[TimSchrader2]

Been awhile since I used LRFD. A design "based on statistical analysis of probability of failure". Upon rereading I have several simple questions that I do not see readily in the searches. Pls respond if you know or have time. Thanks

1) It seems that this design should not be used for machines or many mechanical designs as these probabilities are not documented or easy to find. So assumptions are made, which makes no sense to me. Is this design is mostly for buildings? Some say if the load factors are properly calibrated (Note this is done with ASD) then the results should be the same. Many disagree.

2) If the probabilty of a certain size load ocurance over a 10 year period is ???? percent, then the allowable stress (PER ASD) can be exceeded by the determined values. True? Some say you should not compare the two designs, but when all is said and done the safety factor/Ultimate resistance load of the members or structure is either less or more.

Some say when the Live load < 3 times the DL dead load, that ASD is too or should i say more conservative. Which is my case by a large margin. And only if the operator makes a big mistake.

I have read or at least scanned several articles and can not find these simple answers. I still have my Blue AISC Steel Manual (7th ed).

Thanks

 

[human909]

So the Chute load would need to be included under the 'servicability' factors and no other formula of LRFD. If I read this correctlly. So the STD deviation formulas are not applicable. Which would be fine.

I think you misunderstood or misunderstand my terminology, or I'm misunderstanding you. What I was trying to say is that chute overfill should be a load considered at ULS but not SLS. Ie your boom shouldn't collapse or plastically deform if the chute fills up but if it exceeds serviceability limits then that is probably ok.

I am quite familiar with the ASD and AISC manual but no so much LRFD.

Overall there isn't a massive difference once you get your head around it. Most structural engineers I know perform LRFD without any thought to probabilities.

Simplistically the main differences are there are two 'safety factors' one on design load and one on the design capacity. Load combination may differ a little too but I don't know enough about ASD to comment further.