Nonlinear Behavior of Slender Reinforced Concrete Columns Subjected to Short Term Loading

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Addis Ababa University


When a stress is beyond elastic limit or cracking occurs in reinforced concrete section subjected to axial force and uniaxial bending, the principal axes of the cross section may translate. Because of this phenomenon, axial force applied at the centroid of gross section may have an effect on curvature and bending moment may also have an effect on axial strain at the sectional centroid. In this study, nonlinear second-order analysis is implemented in MATLAB R2019a program to predict the response of reinforced concrete column subjected to axial load and uniaxial bending moment under monotonic short term loadings which takes into account material nonlinearity including tension stiffening and geometric nonlinearity. There has been a lot of research for the nonlinear analysis of slender reinforced concrete columns by adopting analytical methods which assume the deflection curve of a column as a sine wave and then solve the governing differential equations. However, as the load is increased beyond the elastic limit, the post peak deflected response of the reinforced concrete column differs from the deflection curve which is assumed in the analytical method. To overcome these short comings of the analytical methods, the geometrically nonlinear finite element and materially layered cross-section model was adopted in this study. The iterative secant stiffness algorithm is adopted under displacement control. According the results, the application of the analytical method is almost impossible when the columns are existing as a part of a complex structure. The increment of the ultimate load due to the increase of concrete compressive strength was decreased with the increase in the slenderness ratio. The possibility of stability failure for the slender column was increased with increasing concrete strength. The increase of longitudinal steel ratio on the increase of ultimate load of column was more effective for slender columns than for short ones. The effect of tension stiffening on the increases of ultimate load of column was more evident for short columns than slender columns. An increase in the initial eccentricity ratio resulted in a decrease in the ultimate load and an increase in the column deflection at failure.



uniaxial bending, concrete compressive strength, longitudinal steel ratio, slenderness ratio, layered cross-section model, tension stiffening