Experimentally Informed Numerical Modelling of Cementitious Grout-Jacketed RC Columns with Layered Freeze–Thaw Damage

Freeze–thaw deterioration in jacketed reinforced concrete (RC) columns is spatially non-uniform, yet this depth-dependent damage is rarely represented explicitly in structural simulations. This study develops an experimentally informed numerical modelling framework for cementitious grout-jacketed RC columns subjected to freeze–thaw exposure. Unidirectional freeze–thaw tests were conducted on A60 cementitious grout and C30, C45, and C60 concrete. Splitting tensile strength was measured at six depths after 0–320 freeze–thaw cycles, and an empirical layered damage model was established. The measured tensile-strength degradation was then converted into an axial-compressive-strength distribution and implemented in a layered fibre section. The framework further accounts for loss of the severely damaged surface layer, a constitutive model for confined cementitious grout incorporated into OpenSees, and the combined confinement provided by the spiral stirrups in the original column and the jacket. Five jacketed-column tests with different freeze–thaw histories before and after strengthening were used for validation, followed by parametric analyses of pre-existing damage and strengthening thickness. The results showed that strength degradation was greatest near the exposed surface and decreased towards the interior, consistent with coupled moisture and temperature gradients. The proposed model reproduced the measured cyclic hysteretic response, with an average simulated-to-measured peak-load ratio of 0.973 and errors below 5%. The framework provides a material-test-based approach for representing layered freeze–thaw damage in nonlinear analysis of cementitious grout-jacketed RC columns.