New research reveals how frictional base isolators can protect timber buildings from collapse during major earthquakes—without the need for expensive anchor tie systems.
Study: Seismic Collapse of Frictionally Isolated Timber Buildings in Subduction Zones: An Assessment Considering Slider Impact. Image Credit: anatoliy_gleb/Shutterstock.com
A recent study published in the journal Buildings explored the seismic performance of mid-rise light-frame timber buildings (LFTBs) equipped with frictional base isolation systems.
The researchers focused on slider interactions with perimeter protection rings during seismic events, particularly in subduction zones such as Chile, where seismic risk is significant. They demonstrated that frictional base isolation could significantly enhance the resilience of timber structures. The findings offer a cost-effective alternative to conventional continuous anchor tie systems (ATS), enhancing earthquake resistance without increasing structural complexity or costs.
Sustainable Timber Construction and Seismic Isolation
LFTBs are becoming a popular choice in sustainable construction, valued for their low carbon footprint and fast, efficient assembly. In particular, their adoption is growing in seismically active regions like Chile, Japan, and the United States—places where there's a clear need for building solutions that balance environmental responsibility with structural safety. That said, their broader use in earthquake-prone areas is still limited, largely due to the high cost of continuous Advanced Timber Systems (ATS), which are traditionally needed to handle seismic forces.
In this context, frictional base isolation systems present an efficient alternative by decoupling the superstructure from ground motion. Unlike elastomeric bearings, frictional isolators offer lateral flexibility and weight-dependent restoring forces, making them suitable for lightweight timber structures.
These systems play a key role in reducing peak floor accelerations (PFAs), inter-story drift ratios (IDRs), and nonstructural damage. However, under strong seismic loading, slider–ring impacts can occur, which may affect the overall isolation performance. This issue is especially relevant for compact isolator designs and is not yet explicitly covered in national design codes like Chile’s NCh2745.
This study aims to address that gap by investigating the collapse behavior of mid-rise LFTBs subjected to ground motions typical of subduction zone earthquakes.
The Study
To evaluate the seismic performance of frictionally isolated LFTBs, the research team developed four archetype five-story residential structures representative of Chilean timber construction practices. Each building incorporated strong wood-frame shear walls (SSWs) constructed with 38 × 135 mm studs and 11.1 mm-oriented strand board (OSB) sheathing, supported by rigid diaphragms made of 302 mm deep I-joist beams.
The isolation system comprised 25 double concave friction pendulum (DCFP) bearings installed under a grid of concrete beams. The bearing featured radii of curvature of 1.0 m and 2.0 m, with friction coefficients of 0.06 and 0.12 achieved using polyethylene terephthalate (PET-P) polymer plates under axial loads. Structural analyses were performed using SAP2000 v19 for linear modeling and OpenSeesPy for nonlinear collapse simulations.
The seismic performance of the buildings was assessed using incremental dynamic analysis (IDA) with 26 two-component ground motion records, comprising 18 subduction and eight crustal events. These records were scaled to the spectral acceleration at the fundamental period corresponding to maximum considered earthquake (MCE) conditions. Collapse was defined as exceeding a 3 % peak inter-story drift ratio or demonstrating dynamic instability.
Collapse margin ratios (CMRs) were derived to quantify safety margins relative to MCE demands. Archetype BLD-1 achieved a CMR of 1.24, indicating good collapse resistance despite reduced wall density and the absence of an ATS. BLD-2 and BLD-4 demonstrated superior performance, with CMRs of 1.35 and 1.55, respectively. BLD-4 maintained strong seismic resilience due to its higher wall density and consistent use of double OSB sheathing across all stories.
In contrast, BLD-3, designed with a higher peak drift ratio (0.7 %), approached the limits of acceptable performance, demonstrating marginal performance with a CMR near 1.0. This highlights the potential risk of exceeding code-defined drift limits without compensating for increases in wall strength, redundancy, or connection detailing. Additionally, the fragility analyses validated that BLD-2 and BLD-4 maintained collapse probabilities below 20 % at MCE intensity.
Study Findings
The findings highlight the viability of frictional base isolation as a cost-effective protection strategy for mid-rise timber buildings. By eliminating the need for continuous ATS and reducing wall density, these systems offer substantial construction savings while enhancing safety.
The study demonstrates that bearings with optimized friction coefficients can provide sufficient displacement capacity and energy dissipation, even under impact conditions. Although slider–ring impact can intensify demands at high displacements, the archetypes were able to maintain adequate collapse resistance when the stiffness of the isolation system and the superstructure were properly balanced.
Researchers found that the friction coefficient has a secondary influence on overall performance, provided the stiffness balance between the isolation system and superstructure is maintained. This outcome enables project-specific optimization of isolator design based on structural constraints.
Furthermore, they emphasized the need for realistic numerical modeling to capture the complex dynamics of isolated timber structures. The study used a simplified linear-elastic model to simulate slider–ring impact, which did not account for energy dissipation from the perimeter ring. This conservative assumption may underestimate the isolation system’s true performance under extreme events.
Additionally, the models did not include axial load effects or three-dimensional coupling in the shear walls, both of which could enhance collapse resistance. These modeling limitations present opportunities for refinement in future research.
Importantly, the collapse margin ratios reported are conservative, as the study did not apply the FEMA-specified 1.2 adjustment factor typically used for 3D numerical models. Inclusion of this factor would likely increase the reported safety margins further.
Conclusion
This research takes a fresh look at how we can make timber buildings more resilient to earthquakes by integrating frictional base isolation into mid-rise LFTBs. It shows that it’s possible to achieve collapse safety without relying on ATS, and that even compact isolators as small as 40 cm could be enough to support timber construction in high-seismic areas.
The findings are promising, but a few limitations are worth noting.
The study didn’t include the vertical component of seismic ground motion, which might impact peak floor accelerations and inter-story drift. The DCFP bearing models weren’t validated against physical testing, and all building archetypes had the same plan and number of stories, meaning the results might not apply across the board. Future work should look at how vertical motion, axial forces in timber shear walls, and more advanced modeling techniques could influence performance.
While a full lifecycle cost analysis wasn’t part of this study, the results suggest that frictional isolation could help cut construction and repair costs, mainly by removing the need for ATS and reducing nonstructural damage. Ongoing research into lifecycle performance and real-world testing of compact DCFP bearings will help refine these findings and shape more effective design strategies.
In short, this study highlights frictional base isolation as a practical, cost-efficient way to improve the seismic performance of timber buildings. By tackling challenges like slider impact and collapse risk through detailed analysis, it adds to the growing body of work supporting safer, more sustainable construction in earthquake-prone regions.
Journal Reference
Quizanga, D., Almazán, J, L., & Torres-Rodas, P. (2025, October). Seismic Collapse of Frictionally Isolated Timber Buildings in Subduction Zones: An Assessment Considering Slider Impact. Buildings, 15(19), 3593. DOI: 10.3390/buildings15193593, https://www.mdpi.com/2075-5309/15/19/3593
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