Effect of vertical ground motion on gravity-resisting columns in RC core shear wall buildings

This study shows a significant gap in the seismic design requirements for vertical excitation in the National Building Code of Canada (NBCC), making many code-designed structures more vulnerable to damage than anticipated. Contrary to the assumption that the gravity load combination in the code adequately accounts for vertical excitation, our study shows otherwise. We identified a potential increase in axial load, particularly on the gravity-resisting system, due to the absence of seismic design requirements incorporating vertical excitation. To understand this deficiency, we analyzed a 30-story residential RC core shear wall building commonly used on Canada’s West Coast. By evaluating provisions in the LATB and ASCE 7 standards, we propose a new load combination to address the shortcomings of the current code. Additionally, our research introduces a simplified procedure to enhance nonlinear time history (NTH) analyses when considering the effect of vertical excitation, helping structural designers better assess buildings’ seismic resilience.