Devdas Menon

This paper presents details of a nonlinear analysis program capable of tracing the complete load-deflection response of reinforced concrete (RC) beams, frames and grids. The program has been developed in MATLAB using a displacementcontrolled algorithm. The program is capable of handling geometric nonlinearity by using a geometric stiffness matrix in conjunction with a primary stiffness matrix that is constantly updated iteratively. Material nonlinearity is accounted for by making use of prescribed moment-curvature formulations. Stiffness degradation due to cracking of concrete, yielding of steel, tension-stiffening, strain softening and P-A effects is incorporated. The program is computationally efficient and requires only minimal input from the user. The proposed methodology has been validated against experimental data. It is seen that the numerical results generated using the proposed algorithm are in good agreement with the experimental results reported in the literature. Further, the method has been extended to RC grids and RC columns in tension.

This paper presents the results of 15 experimental tests on rectangular slender reinforced concrete (RC) beams. The results reveal limitations in existing theoretical formulations to estimate the failure moment capacity and mode of failure. An improved theoretical formulation is proposed here to predict the critical buckling moment including effects related to nonlinearity and cracking of concrete. Also, following the trends in steel design, an improved measure of slenderness ratio is proposed. Based on a study of 72 test results, it is shown that there is an interaction between flexural tension and instability modes of failure in moderately slender beams. To avoid lateral instability failure, it is suggested that the slenderness ratio be limited to unity. A 'moment reduction factor' is also proposed to account for slenderness effects in RC beams. © 2011 Elsevier Ltd.