Experimental and Numerical Investigations on Moment Redistribution in Reinforced Concrete Frames Subjected to Vertical Loads

In this study, experimental and numerical investigations of the moment redistribution behaviour in reinforced concrete (RC) frames subjected to vertical monotonic loads are presented. By testing 12 RC single-storey continuous frames over two equal spans of 3000 mm, the evolution of moment redistribution during the whole process of loading was observed, and two-stage moment redistribution that occurred at the serviceability limit state (SLS) and ultimate limit state (ULS) was proposed. The test results showed that with the increase in the yield strength of the reinforcement, the degree of moment redistribution at SLS was improved, which should not be neglected in the prediction of the permissible moment redistribution. Meanwhile, the strain penetration of the high-strength reinforcement was more obvious. This is beneficial to the moment redistribution in frame beams. To further investigate the influence of various parameters on the two-stage moment redistribution quantitatively, a nonlinear finite element (FE) model based on the damage plasticity constitutive law was developed and verified using the teste results. A parametric study was conducted based on 96 simulated specimens and the influential factors included the neutral axis depth factor, yielding strength of reinforcement, concrete strength, geometric dimensions of the frame columns and beams, M-V interaction, and loading patterns. The results indicated that MV interaction had a detrimental effect on the plastic moment capacity, thus promoting the process of moment redistribution in RC structures. Based on the experimental and FE results, new practical calculation formulas that comprehensively reflected the influential factors were proposed to estimate degree of two-stage moment redistribution in RC frames.