A recent article in Buildings introduced a numerical model of an 18-story reinforced concrete frame with a core tube and a double-layer seismic isolation system. Designed using YJK (3.0) and simulated in ABAQUS, the model was used to evaluate how high-rise buildings respond to three different seismic waves.
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Background
To minimize earthquake damage, engineers have developed various structural systems based on seismic isolation principles. These systems reduce the amount of seismic energy transferred to a building’s superstructure by dissipating energy through isolation layers, thereby lowering the seismic response.
However, as buildings grow taller with larger height-to-width ratios, conventional single-layer isolation systems face performance limitations. To address these challenges, dual-layer isolation systems have emerged, combining the benefits of both base and inter-story isolation.
Unlike traditional approaches, dual-layer isolation introduces a different seismic response mechanism, necessitating a detailed investigation into its behavior, performance characteristics, and potential for real-world applications.
Methodology
The study modeled an 18-story concrete frame-core tube structure designed per China’s Code for Seismic Design of Buildings, with a seismic fortification intensity of 8 degrees. Structural components such as beams, columns, and walls used C40 concrete, while slabs were made of C30.
Two categories of models were analyzed:
- Single-layer isolation models, including base and inter-story configurations.
- Double-layer isolation models, with isolation layers placed at the first and, sixth, ninth, or twelfth floors.
A fixed-base scenario was included as a control, and isolation bearings were represented using a bilinear restoring force model. The study employed two types of lead rubber bearings: LRB600 for upper isolation layers in double-layer systems, and LRB700 for all other configurations. Soil–structure interaction was not considered.
Damping effects were modeled through Rayleigh damping, material hysteretic damping, and frictional damping at joints. Key metrics included structural ductility, cumulative damage, and the shear performance of non-structural components. Three seismic waves—two natural and one artificial—were selected based on regional seismic characteristics, epicentral distance, and duration.
Results and Discussion
According to China’s seismic code, isolation bearings must maintain tensile stress below 1 MPa and compressive stress under 30 MPa during rare earthquake events. In all simulations, compressive stress remained under 30 MPa, and no tensile stress was recorded—demonstrating that all isolation configurations met code requirements.
Base-isolated models showed lower minimum compressive stresses compared to the lower isolation layer in double-layer systems. However, double-layer isolation systems notably minimized the risk of tensile stress, enhancing structural resilience during high-severity seismic events and reducing the likelihood of progressive collapse.
The study also assessed overturning moments to evaluate the anti-overturning capacity of each system. Under the Imperial Valley-06 earthquake (magnitude 6.54), the one-six double-layer configuration showed significantly lower inter-story overturning moments than both base and inter-story isolation systems.
Conversely, the one-nine and one-twelve configurations experienced higher overturning moments in the lower third of the structure than base-isolated models.
Still, under the Loma Prieta (6.54 magnitude) and artificial “ArtWave” seismic scenarios, all double-layer configurations consistently outperformed single-layer systems in reducing overturning moments. This reduction helps lower the risk of upper structural deformation due to bending under extreme seismic forces.
Conclusion
This study successfully conducted elastoplastic time-history analyses to compare different isolation strategies under rare seismic conditions.
Results show that dual-layer isolation can effectively lengthen the natural vibration period, thereby reducing seismic forces. However, the higher the second isolation layer is placed, the weaker this period-lengthening effect becomes.
More notably, double-layer systems substantially decreased overturning moments compared to single-layer isolation, improving the stability of tall buildings against bending-induced failure.
Future research should focus on multi-hazard resilience, smart isolation technologies, life-cycle analysis, and parametric optimization to further enhance performance and reliability.
Journal Reference
Zhao, G., Zhang, L., Liu, D., & Shen, K. (2025). Seismic Response Analysis of Double-Layer Isolation Structures in High-Rise Buildings. Buildings, 15(8), 1292. doi: 10.3390/buildings15081292. https://www.mdpi.com/2075-5309/15/8/1292
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