Leaderboard

Answer is simple. Top columns have less axial load and more moment. That means more in the tension region of interaction diagram.

You need to size the slabs for long term deflections. Forget these tables.

There is a great discussion on eng-tips about it that you can follow. http://www.eng-tips.com/viewthread.cfm?qid=223271

WA, 1. Basic information regarding bucking analysis of structural steel elements is generally available in the books dealing with the stability of steel structures. For example, "Guide to Stability Design Criteria for Metal Structures', 6th edition by Ziemian, 2010. 2. Specifically, in relation to Eurocodes, following links may be helpful in providing the desired information:- a. Design of Steel Structures: Eurocode 3 b. Designers’ Guide to Eurocode 3: Design of Steel Buildings c. Buckling resistance of steel & composite bridge structures-SCI 2012 d. Guide on second order analysis-2009 HTH Regards.