Experimental Investigation of the Seismic Resistance of RC Beam–column Connections after Freeze–thaw Cycle Treatment

The freeze–thaw cycle (FTC) is one of the major factors leading to damage to reinforced concrete (RC) structures in severely cold regions. The seismic resistance of FTC-damaged RC beam–column connections is critical to the assessment of structural safety. However, studies on the seismic resistance of FTC-damaged RC beam–column connections under severely cold environments are still scarce. In this study, the seismic resistance of FTC-damaged RC connections was investigated in terms of the failure process, hysteresis, energy consumption, core area shear behavior, etc. Furthermore, the effects of FTC action at the microscopic level and macroscopic level and the damage mechanisms of the connections were investigated. The results showed that the shear force ratio of the connections varied via the “diagonal compression strut model” and “truss model” propagation due to the FTC-induced deterioration of the bond performance between the longitudinal rebar and concrete in the beam end; this variation in the shear force ratio, in turn, led to the transformation of the failure mode of the connections. Moreover, as the number of FTCs increased, the ductility of the connections increased slightly, and the shear distortion in the core region as well as its contribution to the whole displacement gradually rose. When the shear–compression ratio is >0.208, increasing the axial force ratio will reduce the load carrying capacity and the shear distortion in the core zone. Based on the test results, a calculation model of the shear force–strain envelope curve of RC connections that integrates the effects of the inhomogeneous temperature field distribution and axial compression ratio was established.