Force distribution analysis of self-centering coupled-beams for moment-resisting-frames without floor elongation

The self-centering (SC) coupled beam (CB) is an innovative system that can avoid floor elongation. The internal force distribution of SC-CBs is also different with conventional posttensioned (PT) connections. This paper first presents a non-uniform factor (Ω) for measuring the uneven force distribution at the beam ends of SC-CBs. Theoretical formations of the factor Ω are driven using structural analysis. Sensitivity analysis for a one-story one-bay frame is conducted to identify the significant parameters for the mitigation of uneven force distribution in the SC-CBs. The frames are also modelled in OpenSees where material and geometrical nonlinearities are taken into account. The numerical results for Ω match well with the theoretical values. A prototype six-story building is designed to evaluate the influence of three design parameters on the Ω value at different stories. Nonlinear dynamic analyses of five moment-resisting frames using SC-CBs with different combinations of design parameters indicate that the decreasing axial stiffness ratio of the upper beam component to the lower beam component can significantly mitigate the uneven force distribution at the two beam ends. Based on those analytical results, a simple regression equation is proposed for predicting the factor Ω.