Tough for ASD advocates but necessary now even for foundation and footing design, (AISC allows both in steel). When you are done with LRFD design then you can check deflection with unfactored loads.
I'm from the new school and have only know LRFD. It seems logical to apply factors to loading conditions based on how well we know the loading condition and the likelihood that this load will occur. Likewise, using different factors to reduce the capcity of the failure mechanism of a material.
I do perform some of my calculations using allowable stress, such as footing designs. Mainly because the geotechnical surveys are given as allowable and not ultimate, and I can justify whether a foundation is satisfactory based on tried and proven factor of safety.
I still use allowable stress when designing bridge bearings for shear and movement. Mainly because I feel is is appropriate to use manufactures testing data when designing for this material opposed to codified simplifications of the theoretical capacities.
I did my first LRFD analysis (Geotech) for some drilled piers for a bridge. It was a bit of a pain, but mostly because the method used here is very easy to determine bearing capacity with, and I had to update the calculations used after the first draft.
The soils at the location were sandy. The AASHTO code is very vague for these conditions – has you run through 5 different calculations, and then lets you pick a reduction factor based on the capacity your local practice would allow.
Unfortunately, I did not feel comfortable with a factor of 1 (thought it would be difficult to defend in court), so I feel the piers are over designed, based on local practice.
From a geotech point of view, I think the LRFD methods will be difficult due to the variability that we can see in the soils. On the structural side, I have seen things be easier or harder based on the situation.
For the Geotech - in my view, LRFD - how can I say this nicely - "is for the birds." In the end, they calibrate the factors from the traditional method anyway. Glad I won't have long . . .
Load factors (LRFD or ASD) seem to work OK till you get to the soil, where things like bearing pressures, uplift, and overturning safety get a bit murky.
I agree that the structural stuff was calibrated and could be fairly confidently - remember FochtIII's quote of Terzaghi? What is the covariance of steel and concrete - for structures? In the order of 5%, maybe?? In soils it ranges from 10 to 50% - so the calibration is so very much more difficult and, in my view, much less universal. . .
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