Effect of the plastic rotation randomness on the moment redistribution in reinforced concrete structures

Design codes allow the moment redistribution in reinforced concrete (RC) beams through the moment redistribution factor. The advantages of performing a moment redistribution are to prevent the congestion of rebars at critical sections along the beams, to allow a more even distribution of rebars along the length and to increase the load carrying-capacity, exploiting the plastic rotation of RC sections. The redistribution requires that sections, in which plastic hinges form, provide the required rotation ductility. The required rotation to perform a plastic analysis with complete moment redistribution and the effective rotational capacity of RC sections are both analytically evaluated with the related load-carrying capacity. A probabilistic analysis by means of the Monte Carlo simulation is performed to assess as the rotation ductility is impacted by the uncertainty in mechanical and geometric parameters and its influence on the ultimate load. The probabilistic analysis shows a greater dispersion in predicting both the rotational capacity and related ultimate load than the member ultimate moment. A reliability analysis on the evaluation of the load carrying capacity of a RC frame according to the Eurocode moment redistribution procedure is performed. Results highlight the Eurocode to be nonconservative suggesting of reviewing the limit on the normalized neutral axis depth to perform a plastic analysis without explicit verification.