AISC LRFD Probability of Failure
AISC LRFD Probability of Failure
(OP)
Does anyone know if the AISC Manual indicates the probability of failure in percent when using the LRFD method. Many books that I have do not indicate it. I am suprised that with all the modeling and statistical analyses done with LRFD over the past 25 years this failure ratio issue appears to be very silent. I am sure it must be very small. Any tips will be greatly appreciated.






RE: AISC LRFD Probability of Failure
Pinkham and Hansell, 1Qtr78
Galambos and Ravindra, 1Qtr78
There are probably others, but I would start there.
RE: AISC LRFD Probability of Failure
RE: AISC LRFD Probability of Failure
RE: AISC LRFD Probability of Failure
That is the generic failure probability for any material. One bell curve is the reduced strength curve (this is the peak of one of the bell curves, however, there is the possibility that the strength can go lower due to lower material strength, tolerances in properties, etc... - this is why we use the entire bell curve, not just the peak that we use in calculations).
The other bell curve is the same exact idea, but on the load side. Again, there is some possibility that the ultimate loads could exceed 1.2DL and 1.6LL (or less than), thus the bell curve.
The failure zone is the intersection of the two curves, or where the load curve is greater than the strength curve.
Again, this is just a generic representation and not unique to steel (unless he put a specific number to it, which you said he didn't).
Additionally, I don't think you can put a specific number on it because the LL/DL ratios always change and I don't believe that the 1.2 and 1.6 factors represent an equivalent failure percentage.
RE: AISC LRFD Probability of Failure
RE: AISC LRFD Probability of Failure
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RE: AISC LRFD Probability of Failure
Basically the combination of variabilities between load and φ factors creates an order of probability called a Beta (β) factor. These β factors correlate with the probability of failure.
However, since there are different load combinations and various (rounded off) load factors you get different probabilities of failure that change with different D/L load ratios, etc.