1. I don't agree in that the reduced stiffness not need to be used in the member checks; if you have required to introduce the diminished stiffness for a particular member to derive the appropriate solicitations, it is inconsistent not use the same stiffness approach for the checks.
2. Also, P-? effects is automatically accounted in the code checks UP TO the tolerances permitted for steel shapes being sold in the market. Hence use of K=1 and dividing the -initially surmised notionally straight- compressed members in a number of segments and using segment length for the checks should work to capture P-? effects.
3. By AISC 360-05 it is clear that initial imperfections are to be considered and that out of plumbness should be taken 1/500 or equivalent notional floor level loads.
4. But it is not as clearly stated what would be the out of straightness to be considered -and need to be considered per 7.2 and 7.3- for compressed members, neither are the notional loads to be considered substitutively for the analysis. In my view it would be inconsistent in the frame of the regulation of the industry to enforce for the checks out of straightness above of the tolerance permitted for members to be placed at the works; if exceeding the tolerance should be rejected. So my view is then resumed respect the thing as stated in point 2.
5. If by constitutive geometry, like in bent or curved members (arch elements) or by protection against some degree of accidental out of straightness it is wanted a bigger sagitta than the 1/1500 permitted in the USA (Note the 1/1000 in the EU wouldn't be covered by the AISC P-? member checks, these things happen when mixing international practices) by the tolerance for straight members, the appropriate corrective measures in whatever the way need to be taken.
6. For members theoretically straight initially, in my view this would encompass representing the expected imperfection directly, better than including a load more difficult to derive to mimick it; that is, except one is wanting to believe elephants fly.
7. And all this would be fine if 360-05 was the end of the matter; but it is not; 360-10 has appeared, I have to read it well but it becomes apparent it has reduced the applicability of the the direct analysis method to buildings with tiered levels; portal frames, gable type, have then dissappeared from the scope of direct design. In my view this reduction on the scope of the method may not to be warranted as a proper description of the same be included in the code; in my view, either you are confident that direct analysis is able to produce a sound and safe design, and AISC has retracted in 10 what in 05 accepted us to believe.
8. This more so because even if developing later as a consequence of theoretical and computing development, the alternative method of first order design with amplified moments should be thought to have appeared due to the means of the era not being able to produce what direct analysis can deliver. It has a sound track of practice, but you are closer to the behaviour in direct analysis than in first order with moment amplification.
