EXAMINATION OF EFFECTIVE LENGTH FACTOR FOR RC COLUMNS IN NON-SWAY FRAMES

摘要

The Canadian Standards Association (CSA) Standard for Design of Concrete Structures (A23.3-04) permits the use of moment magnifier method for computing the design ultimate strength of slender reinforced concrete (RC) columns that are part of non-sway frames. This computed strength is influenced by the column effective length factor K, effective flexural stiffness EI, and equivalent uniform bending moment diagram factor C_m among others. Previous investigations by the authors examined the equations available in literature for computing EI and C_m factor. For this study, nearly 3000 simple non-sway reinforced concrete frames subjected to short-term loads were simulated and used to investigate the effect of using different equations for the effective length factor K when computing the strength of columns in these frames by the moment magnifier approach. An elaborate theoretical model was developed and used for computing the ultimate strength of columns in simulated frames. The theoretically computed column ultimate strengths were compared to the ultimate strengths of the same columns computed from the CSA moment magnifier method using selected equations for K available in literature. For the purpose of analysis, the theoretically computed strengths were divided by the CSA strengths to obtain the so-called strength ratios. The statistical analyses of strength ratios presented in this paper show that, for computing the CSA ultimate strength of columns in non-sway frames, the current practice of using Jackson-Moreland Alignment Chart is the most accurate method for determining the effective length factor.