New analytical method for computing moment redistribution in RC beams under concentrated load

ABSTRACT Computing the moments in RC structures after the yield by linear elastic analysis can lead to an inaccurate assessment of the behaviour due to the nonlinear behaviour. Therefore, it can become necessary to use more advanced methodologies to achieve a higher degree of performance optimisation of structures than those resulting from the simplified approaches adopted by existing design codes based on linear elastic analysis with redistribution of internal forces. The moment redistribution is supposed to start after occurring the cracks of concrete, but with small ratio. In this study, the moment redistribution before the yielding will be neglected, and the redistribution is focused after the yield. This paper suggests a mathematical model to investigate the moment redistribution in RC beams after yielding analytically. In the suggested mathematical model, the beam after forming the plastic hinges is converted into a virtual beam that can be analysed by structural linear analysis. The plastic hinges in the virtual beam will be represented as rotational springs having a linear rotational stiffness against the induced moment. The actual moments can be found through derived relationships in the mathematical model between it and the virtual moment. The mathematical model was verified and it gave values of moment matching experimental results. Also, a comparison for degree of moment redistribution among the suggested mathematical model and several design codes was performed. The analytical results indicate that the proposed mathematical model can be used for analysis of moment redistribution of RC beams.