Taiki Saito

Structural pounding in base-isolated buildings can transmit substantial impact forces to the superstructure, potentially causing severe structural degradation during major seismic events. Furthermore, even when base-isolated structures are designed with geometric symmetry, non-uniform mass distributions arising from internal configurations, such as the arrangement of equipment, furniture, and heavy storage, inevitably induce torsional responses that trigger localized pounding at the building corners. This study investigates the seismic performance of reinforced concrete base-isolated buildings subjected to torsional pounding under both pulse-like and long-period ground motions. Nonlinear time-history (NLTH) analyses were conducted using three pulse-like and three long-period ground motion records, scaled to a target isolation layer displacement of 50 cm. The results indicate that torsional pounding acts primarily as a kinematic constraint that restricts the torsional rotation and concentrates the seismic responses at the structural corners. While long-period ground motions trigger high frequency of pounding occurrences, low amplitude impacts, pulse-like ground motions generate severe seismic demands that increase corner story accelerations, resulting in severe localized damage. Specifically, pulse-like motions induce high-velocity impacts that yield large maximum displacement ductility factors on the structural elements. Conversely, long-period ground motions exhibit a highly repetitive, cyclic pounding mechanism, and accumulate extensive energy dissipation, ultimately yielding higher cumulative ductility demands. Consequently, variations in accidental eccentricity must be explicitly integrated into the design phase to maintain the safety of base-isolated buildings against various ground motion characteristics.

This research experimentally and numerically evaluates the effectiveness of viscoelastic (VE) and rotational friction (RF) dampers in enhancing the seismic performance of coupled shear wall (CSW) systems. This study consists of two phases: (1) element testing to characterize the hysteretic behavior and energy dissipation capacity of VE and RF dampers, and (2) shake table testing of a large-scale CSW structure equipped with these dampers under the white noise, sinusoidal and Kokuji waves. The experimental results are validated through numerical analysis using STERA 3D (version 11.5), a nonlinear finite element software, to simulate the dynamic response of the damped CSW system. Key performance indicators, including inter-story drift, base shear, and energy dissipation, are compared between experimental and numerical results, demonstrating strong correlation. The findings reveal that VE dampers effectively control high-frequency vibrations, while RF dampers provide stable energy dissipation across varying displacement amplitudes. The validated numerical model facilitates the optimization of damper configurations for performance-based seismic design. This study provides valuable insights into the selection and implementation of supplemental damping systems for CSW structures, contributing to improved seismic resilience in buildings.

This research experimentally and numerically evaluates the effectiveness of viscoelastic (VE) and rotational friction (RF) dampers in enhancing the seismic performance of coupled shear wall (CSW) systems. The study consists of two phases: (1) element testing to characterize the hysteretic behavior and energy dissipation capacity of VE and RF dampers, and (2) shake table testing of a large-scale CSW structure equipped with these dampers under the white noise, sinusoidal and Kokuji wave. The experimental results are validated through numerical analysis using STERA 3D, a nonlinear finite element software, to simulate the dynamic response of the damped CSW system. Key performance indicators, including inter-story drift, base shear, and energy dissipation, are compared between experimental and numerical results, demonstrating strong correlation. The findings reveal that VE dampers effectively control high-frequency vibrations, while RF dampers provide stable energy dissipation across varying displacement amplitudes. The validated numerical model facilitates the optimization of damper configurations for performance-based seismic design. This study provides valuable insights into the selection and implementation of supplemental damping systems for CSW structures, contributing to improved seismic resilience in buildings.

This study proposes an innovative passive vibration-control system, named the Pulley Damper Multi-story System (PDMAS), which incorporates pulley tackles installed at multiple stories in the successive stories to amplify inter-story displacement. This configuration significantly enhances the energy absorption efficiency of the linked dampers at the middle of the cable by utilizing the cumulatively amplified story displacements via a continuously stretched cable across the entire structure. The proposed system shows notable potential for controlling responses induced by higher vibration modes by customizing the wire installation layout. The aim of this study is to introduce PDMAS and to investigate its seismic-mitigation effectiveness. As a primary investigation of this new system, comparative experimental studies were conducted through shaking-table tests on nine specimens featuring various cable layouts optimized for the first and second structural vibration modes, with or without dampers, under harmonic waves, white-noise waves, and simulated seismic waves. The experimental results demonstrate that the PDMAS effectively accommodates the cumulative amplified story displacement across the structure to match theoretical damper values. Furthermore, the specimens employing PDMAS with a wire layout optimized for the first structural mode reduced both acceleration and displacement by nearly half compared to specimens without PDMAS. Doi: 10.28991/CEJ-2025-011-01-02 Full Text: PDF

This research aims to apply the displacement-based design method (DBDM) for the seismic design of reinforced concrete-coupled shear wall buildings equipped with energy dissipation dampers. The DBDM offers design simplicity by focusing on structural design based on a target design displacement, where the building converts into a single degree of freedom (SDOF) system. The implementation of dampers aims to reduce repair costs and downtime for buildings following significant seismic events. Two types of dampers are utilized in this study: metallic damper and viscoelastic damper. The DBDM procedure begins with determining the target displacement, which corresponds to the specific story drift ratio of the structural system, using a nonlinear static pushover analysis. For the structural wall system considered in this study, a target drift ratio of 1/250 is selected due to the inherent rigidity of the structure. The effective damping factor is then determined from the average energy absorption, which is based on the ductility factor of each structural member. Additionally, the effective period of the building is obtained from the displacement spectrum of the design-level earthquakes. Finally, the required damper shear capacity for the SDOF system is calculated based on the target deformation and effective stiffness. The design earthquakes are generated from the acceleration response spectrum for Level 2 earthquakes, as specified in the Japanese seismic code, utilizing three different sets of phase information: Kobe, El Centro, and random phase records. The effectiveness of the DBDM is scrutinized through a comparison with results obtained from time history analysis. The results obtained for 6-, 12-, and 18-story RC-coupled shear walls with energy dissipation dampers indicate that the proposed design methodology effectively meets the specified design objectives.

Soil-structure interaction (SSI) can significantly influence earthquake responses in base-isolated (BI) buildings, yet it is often overlooked in practice due to the high computational demands of complex analyses. This study investigates SSI effects on reinforced concrete (RC) base-isolated buildings, idealizing SSI with a cone model. Three BI building models of varying heights and soil characteristics were analyzed using modal and nonlinear time history analysis. The base isolation system incorporated elastic sliding bearings, lead rubber bearings, natural rubber bearings, and oil dampers. The SSI model was idealized considering hard, medium, and soft soils. To simulate earthquake input, three artificial ground motions with different phase characteristics were generated to match the design response spectrum according to the Japanese code. The seismic responses of the base-isolated building models with SSI were compared to those of models without SSI. Modal analysis showed that the natural period increased with softer soil profiles. In the first and second modes, the natural period lengthened as the building’s aspect ratio increased. Conversely, in the higher modes with a rocking pattern, the building with the lowest aspect ratio exhibited the longest natural period. Overall, implementing SSI generally reduced seismic responses, notably lowering story drift, acceleration, and force, particularly for buildings on soft soil. However, the SSI effect significantly increased the base rotation angle in high aspect ratio buildings on soft and medium soils. These findings indicate that including SSI in analysis is essential for more realistic seismic response predictions, especially for tall, slender base-isolated buildings. Doi: 10.28991/CEJ-2024-010-11-01 Full Text: PDF