High-rise buildings have innate susceptibility to higher-mode effects, which can significantly magnify seismic demands but are not fully addressed in the current National Building Code of Canada (NBCC) or design codes worldwide. This gap leads to code-prescribed design being inadequate and structures undergoing substantial unintended damage. The authors developed a novel uncoupled rocking and shear mechanisms system, named MechRV3D, for mitigating higher-mode effects and achieving seismic resilience of high-rise buildings during major earthquakes. This paper presents an analytical investigation on modal response of high-rise buildings with the MechRV3D system incorporated at the base acting as flexible supports. A cantilevered continuum beam analogy was used, with the rocking and shear mechanisms represented using idealized springs. Response spectrum analyses were then conducted on families of flexibly supported cantilevers. Results of these analyses provided verification of the MechRV3D’s efficacy of damage control, new insights on higher-mode effects, and an analytical basis for designing the MechRV3D system for high-rise buildings. These findings address the shortfall of Canadian and international design codes and open a new direction towards resilience-based seismic design.