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Construction Engineering Research and Innovation Infrastructure and the Built Environment DRSR – Research team specialized in Development and Research on Structures and Rehabilitation

FRP Composites for Seismic Resilience and Self-Centering of Buildings

A futuristic urban scene where a cracked skyscraper stands among modern buildings, evoking a technological disaster.

Abstract

Single shear walls (SSWs) are commonly used in medium- to high-rise buildings to resist seismic forces, but they often suffer significant deformations after earthquakes. This article explores the potential use of Externally Bonded Fiber Reinforced Polymer (EB-FRP) composites to enhance the seismic resilience of SSWs, specifically by reducing residual drift and improving self-centering capabilities. By studying buildings located in Vancouver and Montreal, where seismic conditions vary, this research evaluates the effectiveness of different EB-FRP strengthening techniques. Results indicate that applying EB-FRP composites can significantly reduce post-earthquake residual deformation. These findings suggest that EB-FRP technology offers a cost-effective, minimally invasive solution for improving seismic resilience and self centering of existing constructions.

Introduction

Earthquakes represent a significant threat to buildings in seismic zones, particularly in cities like Vancouver and Montreal, where the nature of seismic events differs dramatically [1]. Single shear walls (SSWs) are a key component in the structural design of medium- and high-rise buildings, providing essential resistance to the lateral forces generated by earthquakes. However, one of the major challenges with SSWs is that after a seismic event, they can experience permanent deformations, especially near the base where plastic hinges form. This permanent drift not only affects the safety of the building but also leads to costly repairs, replacements, and downtime [2].

To address these issues, enhancing the seismic resilience of buildings has become a focal point in modern engineering [3]. One promising solution is the use of Externally Bonded Fiber Reinforced Polymer (EB-FRP) composites [4]. These materials known for their strength, durability, and ease of application [5] are applied to existing shear walls to improve their performance during and after earthquakes.

In this article we investigate the application of EB-FRP composites in two distinct seismic environments: Vancouver, where long-duration, low-frequency seismic events are prevalent, and Montreal, where shorter, higher-frequency events dominate. Through a series of nonlinear time history (NLTH) analyses, the study examines the effectiveness of three EB-FRP strengthening configurations. It evaluates their ability to reduce inter-story drift ratio (IDR) and residual inter-story drift ratio (RIDR) as representative of local residual deformation along the wall height and, hence, indicators of self centering performance.

Enhancing Seismic Resilience of Shear Walls With EB-FRP

In this study, two sets of buildings—20-stories and 15-stories—located in Vancouver and Montreal were analyzed. These cities represent two distinct Canadian seismic zones, offering a comparison of how EB-FRP performs under different types of seismic activity. The walls were designed according to current Canadian seismic codes, and nonlinear time history (NLTH) analyses were performed to simulate their response to real earthquake data.

Three different strengthening schemes were applied to the walls illustrated in Figure 1.

  • R1-SSW: Vertical EB-FRP layers applied on both sides of the wall, with additional wrapping around the wall to improve bending capacity.
  • R2-SSW: Vertical EB-FRP sheets applied to the edges of the wall, with two layers covering 15% of the wall's length and an additional wrapping layer extending from the base to the top.
  • R3-SSW: The most comprehensive approach, with three vertical EB-FRP layers applied to the wall edges, a full wrapping of the plastic hinge zone and additional wrapping in the plastic hinge zone.

Each of these configurations was tested against earthquake scenarios specific to Vancouver and Montreal. The key parameters measured included RIDR and IDR, both critical indicators of seismic performance.

FRP Strengthening schemes
Figure 1 Strengthening schemes used in this study: (a) R3-SSW; (b) R2-SSW; (c) R1-SSW; (d) FRP wrapping of shear walls.

Key Findings

Results demonstrated that EB-FRP composites significantly reduce residual drift in SSWs, with the most notable improvements seen in shorter, 15-story buildings. In Vancouver, where long-duration, low-frequency seismic events are common, the R3-SSW configuration reduced residual drift by up to 17% in 20-story buildings and by 28% in 15-story buildings (see Figure 2 and Figure 3). These results highlight the effectiveness of EB-FRP in mitigating the effects of long-period ground motions, which can cause extensive deformations in taller structures.

Montreal's seismic events, while shorter and higher in frequency, also Present challenges to building resilience. The study found that the EB-FRP applications reduced residual drift by up to 13% in a 15-story wall, with the R3-SSW configuration again showing the best performance. The taller wall depicted elastic behavior (see Figure 4 and Figure 5).

residual inter-story drift ratio for 20 stories in Vancouver
Figure 2 Reduction of RIDR in 20-story SSW due to strengthening schemes, in all earthquakes used in NLTH.
residual inter-story drift ratio for 15 stories in Vancouver
Figure 3 Reduction of RIDR in 15-story SSW due to strengthening schemes, in all earthquakes used in NLTH.
residual inter-story drift ratio for 20 stories in Montreal
Figure 4 Reduction of RIDR in 20-story SSW due to strengthening schemes, in all earthquakes used in NLTH.
residual inter-story drift ratio for 15 stories in Montreal
Figure 5 Reduction of RIDR in 15-story SSW due to strengthening schemes, in all earthquakes used in NLTH.

In both cities, the use of EB-FRP also resulted in significant reductions in inter-story drift, with decreases of up to 11% observed in Vancouver. This reduction in IDR is critical as it correlates directly with the likelihood of permanent structural damage. In Eastern Canada, where seismic events tend to be of lower intensity, the study found that tall shear walls, particularly 20-story structures, exhibited predominantly elastic behavior during earthquakes. The relatively low ground motion did not induce significant residual deformations in these walls, with maximum permanent drift observed at less than 0.05% in the 20-story walls and 0.13% in the 15-story walls. This suggests that in regions with moderate seismic activity, such as Montreal, the need for extensive strengthening in taller shear walls may be reduced, as their elastic response ensures they remain largely undamaged even during seismic events.

Comparison of Results: Vancouver vs. Montreal

While both Vancouver and Montreal face seismic risks, the nature of these risks is quite different. Vancouver’s seismic profile, dominated by low-frequency, long-duration earthquakes, places substantial demands on the lower portions of SSWs, especially near the base. The application of EB-FRP composites in this context proved highly effective, especially in shorter walls, where residual deformations were most pronounced.

In Montreal, where seismic events are shorter and dominated by high frequency waves, the strengthening schemes were effective only in shorter wall. However, the challenges presented by high-frequency ground motion were different. In taller structures, the potential for secondary plastic hinge formation in upper stories became a concern, but the EB-FRP configurations, particularly R3-SSW, performed well in reducing drift fluctuations along the wall height.

Impact on Shear and Bending Demands

Applying EB-FRP composites to shear walls increases both shear force and bending moment demands. This is driven by the fact that the strengthening schemes reduce the structural vibration period by increasing wall stiffness, which amplifies shear demand during seismic events. As a result, shear demand increased by 4% to 16%, while bending moment demand increased by up to 11%. However, despite these force increases, the walls' enhanced capacity using EB-FRP fully accommodates the added demands.

Conclusion

Our research demonstrates that EB-FRP composites are highly effective in enhancing the seismic resilience of single shear walls. By reducing both inter-story drift and residual drift, these advanced materials help buildings recover more effectively after an earthquake, minimizing the need for costly repairs and replacements. The R3-SSW configuration, notebly was the most successful in reducing post-seismic damage, especially in shorter buildings.

As seismic events increase, especially in high-risk regions like Vancouver, the use of EB-FRP in both retrofitting and new constructions can offer a practical and cost-effective solution. Further research could explore the long-term durability of these materials and their performance in a wider range of seismic conditions, but the potential benefits of EB-FRP for enhancing building safety are clear.

Additional Information

For more information on this research, please read the following articles: Abbaszadeh, A., & Chaallal, O. (2024). The Use of Externally Bonded Fibre Reinforced Polymer Composites to Enhance the Seismic Resilience of Single Shear Walls: A Nonlinear Time History Assessment. Journal of Composites Science, 8(6), 229.

[1] J. Adams, S. Halchuk, T. Allen, and G. Rogers, "Canada’s 5th generation seismic hazard model, as prepared for the 2015 National Building Code of Canada," in 11th Canadian conference on earthquake engineering, 2015, pp. 21-24.

[2] A. Abbaszadeh and O. Chaallal, "Resilience of medium-to-high-rise ductile coupled shear walls located in canadian seismic zones and strengthened with externally bonded fiber-reinforced polymer composite: Nonlinear time history assessment," Journal of Composites Science, vol. 7, no. 8, p. 317, 2023.

[3] M. Bruneau and A. Reinhorn, "Overview of the resilience concept," in Proceedings of the 8th US national conference on earthquake engineering, 2006, vol. 2040, pp. 18-22.

[4] H. El-Sokkary, K. Galal, I. Ghorbanirenani, P. Léger, and R. Tremblay, "Shake table tests on FRP-rehabilitated RC shear walls," Journal of Composites for Construction, vol. 17, no. 1, pp. 79-90, 2013.

[5] F. A. Fathelbab, M. S. Ramadan, and A. Al-Tantawy, "Strengthening of RC bridge slabs using CFRP sheets," Alexandria Engineering Journal, vol. 53, no. 4, pp. 843-854, 2014.