Push-off samples are simulated using nonlinear finite element analysis (NLFEA) to evaluate the effects of increased temperatures on the interface shear strength. Firstly, a control shear-key model is created, calibrated, and confirmed against independently published experimental data. Twenty-four NLFEA models are then created with different variables, including temperature (23°C (Room Temperature), 250°C (Raised temperature), 500°C, and 750°C and the number of steel stirrups (none, 1, 2, 3, 4, and 5). The NLFEA results demonstrate that the decreased fracture opening and slide in the damaged shear keys compared to the intact control sample represent the amazing effect of the number of steel stirrups. In addition, it has been revealed that the longitudinal shear force and slide, mode of failure, rigidity, and toughness are all significantly impacted by the degree of heat damage. In particular, a simplified approach is proposed for calculating the shear strength of push-off samples subjected to higher temperatures.