RESTORING FORCE MODEL OF FREEZE-THAW DAMAGED RC FRAME JOINTS

To research the aseismic behavior of reinforced concrete (RC) frame joints damaged by freeze-thaw cycling, the hysteretic behavior of 6 RC frame joint specimens were investigated experimentally, which have been damaged by the freeze-thaw cycles under low cyclic reversed loading. Based on the test results, a trilinear skeleton curve model of frame joints was established, and the key parameters of the skeleton curve were determined. The limiting work ratio I of RC frame joints was expressed through regressive analysis, which considered freeze-thaw damage. The cyclic degradation indexes of RC frame joints based on freeze-thaw damage was proposed, so as obtained to describe the degradation law of specimens' mechanical properties such as yield load, hardening stiffness, unloading stiffness. And then, a restoring force model of RC frame joints based on freeze-thaw damage was established. The specific hysteretic rule was developed. The results show that the bond performance degradation of longitudinal reinforcements of a joint beam is obvious under the freeze - thaw, that the cumulative energy dissipated is decreased as the increase of cyclic numbers of freeze-thaw, and that the effect of pinching is affected by considering stiffness and strength reduction, which can well reflect the practical purpose. The study results will shed light on the theoretical research about the elastic-plastic dynamic analysis of RC structures.