A restoring force model for a novel type of precast beam-to-column joints using mechanical connections

To investigate the restoring force model (RFM) for a novel type of precast beam-to-column joints using a mechanical connection (PBCJ-MCs), the low-cycle cyclic loading test of three PBCJ-MCs was first performed in this article. Subsequently, combined with the shape of the test hysteresis curves and skeleton curves, three key characteristic points of cracking point, yield point, peak point and a key parameter at the strength degradation stage, stiffness were defined in the theoretical skeleton model. Using the regression approach, a four-line skeleton curve model for PBCJ-MCs was fitted by the dimensionless test skeleton curve data. Then, a mathematical model for strength degradation of PBCJ-MCs at the same loading displacement was established based on the damage index. By the analysis of the hysteresis path, the hysteresis rules applicable to PBCJ-MCs were formulated. The RFM for PBCJ-MCs considering the slipping and pinching effect was determined by fitting and properly defining the inflection point, pinching point, unloading stiffness and reload stiffness of the hysteresis curve in the unloading-reloading path. Finally, the theoretical skeleton curves, hysteresis curves and energy dissipation capacity were compared with test results. The results illustrated that the proposed RFM for PBCJ-MCs can better consider the pinching effect of PBCJ-MCs. The theoretical hysteresis curves of the proposed RFM considering the damage effect were more consistent with the test hysteresis curves, which can be used for further theoretical analysis and engineering applications.