I'm considering freestanding platforms with no cross bracing. I'm using k=2.0, but was looking into using a lower k. Our platform legs are welded to a baseplate which is bolted to the floor with 4 anchor bolts.
The question seems to be the restraint at the base. If the base is fixed k=1.2 and if it is assumed to be pinned k=2.0, per Table C-C2.1 (c) and (f). Is your design going to be for a standard product to go just about anywhere, or a one time design to be installed in a place you are familiar with? Based on my 11 years experience in a Plant Engineering department you shouldn't design things too close. Sometimes fork truck divers use bldg steel, racks, etc. for brakes. Personally I would use k=2.
I don't know why you don't just calculate K based on the AISC Manual. It's very easy and you could've done that by the time we sent all these posts back and forth.
Also, K=2 is not a catch-all conservative effective length factor. If you have a fixed base, then K=2 is the upper limit. If you have a pinned base, then K will likely exceed 2. There's no substitute for actually calculating the correct value.
I think I understand Bagman2524s issue here. Having worked 11 years in plant engineering and 10 years as a designer of structural products, I can testify that there is a different mindset associated with each. When you are designing equipment for your own use you want it to work. If it doesn't then it will cost more time, money, and downtime to fix the problem. On the other hand, when you are designing a standard product it shouldn't contain any extra costs, because that cost will be incurred over and over again.
Theoretically a column fixed at the top and bottom with sidesway will have k=1.2 per case(c). If the base were properly shimmed, grouted, and bolted down then that would be the appropriate value. If the bolts would loosen up however, the pinned base assumption would be more accurate. And there are probably many onsite reasons why bolts may not stay tight.
Remember that if you design the base as fixed, the footing will have to be designed for any moment you apply and will have to be to accomodate your column with almost no rotation. If your footing rotates then your fixity is gone whether or not the bolts loosen.
I would use k=2 as a starting point and then when you get some preliminary members I would go back and use the logarithmic charts given in the AISC manual to choose a more accurate k. Keep in mind there are a lot of assumptions built into those k charts so they aren't necessarily the "theoretically correct" tools we sometimes assume. The main thing is to provide for your assumptions. If you assume nonsway or braced frames for instance then the top of the column needs to have translation prevented to such a degree that your assumption is correct, and the same for the base fixity at the footing.
