Floor Response Spectra in Hybrid Base-Rocking and Reinforced Concrete Wall Buildings

Seismic events such as the Northridge (1994) and Nisqually (2001) earthquakes, amongst many others, have caused significant damage and financial losses to both structural and non-structural components of buildings. In response to this, significant research is being conducted with the aim of achieving higher performance objectives, which include: (i) the reduction and even elimination of structural damage during earthquakes, and (ii) the improvement of seismic risk mitigation for non-structural elements.;To address point (i), several innovative technologies have been proposed that could limit structural damage compared to traditional structural systems in which structural damage serves as a means of energy dissipation. Among these, hybrid base-rocking walls effectively combine unbonded post-tensioning and mild-steel reinforcement to eliminate damage and residual displacements while providing good energy dissipation. In this study, the seismic response of hybrid base-rocking walls is compared to the more "traditional" reinforced concrete (RC) walls, through non-linear time-history analysis of 4, 8 and 12-story case-study buildings. Special attention is given to the floor acceleration response of both structural systems as it pertains to the performance of non-structural elements.;To address point (ii), this study proposes three simple methodologies for estimating acceleration demands on non-structural elements in hybrid base-rocking and RC wall buildings, through a floor response spectrum (FRS) method. In all three procedures, individual modal floor spectra are first generated and then combined through a simplified modal combination approach to generate floor spectra that account for the effects of multiple modes. In order to account for non-linear structural response, the first procedure utilizes the concept of transitory inelastic modes of vibration to generate inelastic modal floor spectra, while the second procedure utilizes empirical modal reduction factors that are used to reduce elastic modal floor spectra based on the expected ductility of the building. The third procedure focuses on how to estimate floor spectra in the early design phases of a building, when the modal characteristics of a building are not known. To this end, the procedure idealizes RC and hybrid base-rocking walls as continuous distributed-mass systems to estimate their modal characteristics, which are in turn used to estimate floor spectra. Each proposed procedure is then tested by comparison to floor spectra obtained from non-linear time-history analysis of 4, 8 and 12-story case-study buildings.