Mechanics and slenderness limits of sway-restricted reinforced concrete columns

Several aspects of nonslender (short) column limits are considered. Such limits, below which it is acceptable to ignore local second-order effects that may cause a maximum moment to develop between member ends, are generally confined to columns of braced frames, but are also relevant for sway-restricted columns of unbraced frames. Local and global second-order effects are reviewed in this context, and the effect of global second-order effects (sway-modified moments) is discussed, and it is concluded that the end moment ratios of approximate moment magnifier expressions and slenderness limits should be expressed in terms of sway-modified end moments. The need for providing separate slenderness limits, such as in the ACI 318-05 code, for columns of nonsway and sway frames, is questioned. The ACI limits are critically reviewed and several inconsistencies pointed out with respect to their differences and different basis on which they were derived. They are compared with a more comprehensive limit that may replace both of the ACI limits, and comparisons are also made with a summary of nonlinear analysis results.