Slenderness of Columns in Braced Frames

Abstract

Moment-magnification factors for columns in braced frames are dependent upon column slenderness and the flexural stiffness of restraining beams. A column bent in single curvature has a flexural stiffness that can be as little as one-third that of the same column bent in reverse curvature. Column slenderness ratios (\IL\N/\IR\N) above which reverse curvature moments must be magnified are significantly higher than those for which single-curvature moments would require magnification. This paper shows that when loading conditions are considered together with framing restraints, magnified moments from the single-curvature condition rarely generate moment values as high as moments unmagnified from the reverse-curvature loading condition. Thus, without need for moment magnification, column slenderness ratios can be significantly higher than the limit ratios traditionally derived for single-curvature bending conditions of columns.