In this dissertation, a numerical method for predicting the second-order behavior of reinforced concrete columns was developed and the factors affecting the behavior of slender reinforced concrete columns were analyzed by analysis and test. The test results were compared with those of the numerical method and the moment magnifier method of ACI.
Most of the studies for the analysis of slender reinforced concrete columns have adopted the analytical methods which assume the deflection curve of column, and then solve the governing differential equations. As the load is increased beyond the elastic limit, however, the deflection shape of reinforced concrete column becomes gradually different from the deflection curve which is assumed for the analytical methods, and the applications of the analytical methods are almost impossible when the columns exist as a part of complex strucuture. To overcome these shortcomings of the analytical methods, the finite element method was adopted in this study. Because the loading history can not be considered by the nonlayered method, the layered method was employed. The stiffness matrices which ensure the inclusion of second-order effect due to axial load-lateral deflection interaction were used. To analyze the post-peak behavior of reinforced concrete column, the displacement control method was used.
To investigate the effects of concrete strength and longitudinal steel ratio on the behavior of columns, a series of tests were carried out for thirty tied reinforced concrete columns with a 80mm square cross section and three slenderness ratios of 10, 60, 100. Three different concrete strengths of 25.5, 63.5, 86.2MPa, and two different longitudinal steel ratios of 1.98 and 3.95＼% were used. The boundary conditions at the ends were both hinged and the end eccentricities (24mm) were equal and of the same sign.
According the results, while the ultimate load capacity of high-strength concrete column was much increased when the columns were short, that was not when not when the columns were slender. The possibility of stability failure for the slender columns was increased with increasing concrete strength. The effect of longitudinal steel ratio on the increase of ultimate load of column was more evident for slender columns than for short ones and the heavier reinforcement for slender columns led to a more stable columns. These effects of longitudinal steel ratio were more pronounced with increasing concrete strength.
Predicted behaviors of reinforced concrete columns through the numerical method proposed in this study showed good agreements with the test results, and those through the moment magnifier method showed that the moment maghifier method might be unconservative for slender high-strength concrete columns.