Simplified Method for the Preliminary Design of Shear-Controlling Rocking-Isolation Podium Systems for Tall Buildings

Abstract

Base dual-mechanism systems that limit both shear force and overturning moment demands are being developed as a new class of seismic force–resisting systems to enhance the control of seismic demands at the base and along the height of tall buildings and to control higher-mode effects. Despite an increasing number of numerical studies that demonstrate the enhanced seismic resilience of tall buildings as a result of better-controlled shear force and overturning moment demands and reduced higher-mode effects through a variety of base dual-mechanism configurations, there are limited design methodologies for buildings with this type of seismic-resistant base system. This paper proposes a simplified method for the performance-based seismic design methodology for these base dual-mechanism systems and the structures above, which consists of (1) designing the dual base-mechanism system using a set of design charts, and (2) protecting the rest of the structure for the maximum expected seismic force demands computed using closed-form equations. The proposed method was used in this paper for the preliminary design of four example core-wall tall buildings with heights of 45, 90, 150, and 300 m. The adequacy of the proposed method was demonstrated using three-dimensional finite-element models. The analysis results were in reasonable agreement with the targeted force and displacement demands estimated using the proposed simplified method for the preliminary design of dual base-mechanism systems.