With the continuous rise in population and technological advancement of construction industry, the development of tall buildings is increasingly evident worldwide. In response to this demand and the need for sustainable construction materials, numerous innovative timber-based structural systems have been developed in the past two decades. The "Development of Resilient Timber Buildings" research group is at the forefront of this movement, dedicated to advancing sustainable and resilient timber building design in seismic-prone areas. Our focus lies in proposing, designing, and analyzing innovative timber-based structural systems, leveraging the benefits of timber to meet modern engineering challenges. The group has been committed to push the boundary limits in timber construction by designing tall, safe, durable, and seismic resilient systems. By conducting in-depth research, the group strives to make significant contributions to the field of sustainable construction and set new standards for timber-based building systems in the modern era.
A key part of our work involves the recent development of four innovative tall timber structural systems: the Cross-Laminated Timber Coupled Wall (CLT-CW) system, the Cross-Laminated Timber Shear-wall and Glulam Moment Resisting Frame (CLTW-GMRF) system, Resilient tall timber building with SMA damped-outrigger system, and Buckling-Restrained Brace and Glulam Frame (BRBGF) system. The development of these innovation structural solutions is a testament to our dedication to advancing timber construction and our commitment to create a more sustainable and resilient built environment. We believe that the outcomes of our research will increase the confidence among architects, structural engineers, owners, and contractors in the development of tall mass-timber buildings. The significant results and findings of our group has been published in several prestigious journal publications and conference proceedings, showcasing our contributions to the field.
1. Seismic design and performance assessment of CLT-CW system
Theoretical background: Coupled wall system is one of the classical and efficient types of structural systems that comprises multiple structural walls connected at each storey with coupling beams. Widely utilized in conventional reinforced concrete and hybrid coupled wall systems, this method effectively transforms the base moments of individual walls into axial forces through shear forces in the coupling beams under lateral loads. By extending this classical engineering concept, our research group has proposed a sustainable and resilient timber-based structural solution. Specifically, steel coupling beams with replaceable shear-links are used to coupled multiple CLT balloon shear-walls. This CLT-based coupled wall (CLT-CW) system merges two fundamental concepts - sustainability and resilience - to deliver a high-performance solution for seismic-resistant building construction.
System components: The proposed system comprises glulam beams and columns, CLT floor panels, CLT balloon shear-walls, steel coupling beams with replaceable shear-links, and buckling-restrained brace (BRB) hold-downs. Within this system, the steel coupling beams with replaceable shear-links serve as the primary energy dissipative component. During an earthquake, the inelastic deformation is concentrated within the shear-links, maintaining the elasticity of the beam ends and thereby enhancing the structure's functionality. As a secondary energy dissipation component of the system, the BRB hold-downs demonstrate high seismic performance with substantial ductility and energy dissipation. These BRBs are connectable to the shear-walls through epoxied threaded rods and a gusset plate or bolts with side steel plates. When subjected to lateral force, the wall engages in a rocking motion, effectively transferring axial load to the hold-downs.
Areas of investigation and contribution: As the part of this research, the group has evaluated the feasibility and effectiveness of the coupled system for high-rise timber-based construction. Prescriptive seismic design guideline is developed and applied on a 10-, 15-, and 20-storey CLT-CW system. Linear and non-linear analysis were conducted to examine the performance of the system with varying coupling ratio values, ductility-related seismic modification factors, and coupling beam shear-force profiles. Performance-based design of the system was developed and illustrated on a 20-storey CLT-CW system. Utilizing the FEMA P695 guideline, an appropriate ductility-related modification factor of the system was estimated.
The research has also extended beyond deterministic investigation to include probabilistic assessment of the system, considering uncertainties in connection parameters and design values, along with an optimization scheme. Moreover, the seismic loss and resilience assessment of the system is recently conducted. Findings of the research has shown that the developed system is a promising alternative for high-rise timber construction. The system has exhibited commendable structural behavior under different design parameters. Under seismic events, the system showed significant resilience, making post-event repairs more feasible than complete reconstructions.
Sample Publications:
Tesfamariam S., Skandalos K., and Teweldebrhan B. T. (2021). “Design of tall coupled-wall timber building: Energy dissipating coupling beams.” Kelowna, BC: UBC Faculty Research and Publications. https://doi.org/10.14288/1.0403817.
Teweldebrhan B.T. and Tesfamariam S. (2022). "Performance-based design of tall-coupled cross-laminated timber wall building." Earthquake Engineering & Structural Dynamics, 51(7): 1677–1696. https://doi.org/10.1002/eqe.3633.
Teweldebrhan B.T., Popovski M., McFadden J.B., and Tesfamariam S. (2022). "Development of ductility-related modification factor for CLT-coupled wall buildings with replaceable shear link coupling beams." Canadian Journal of Civil Engineering, 50(5), 362-374. https://doi.org/10.1139/cjce-2022-0257
You T., Teweldebrhan B.T., Wang W., and Tesfamariam S. (2023). "Seismic loss and resilience assessment of tall-coupled cross-laminated timber wall building." Earthquake Spectra, 39(2), 727-747. https://doi.org/10.1177/87552930231152512
Teweldebrhan B.T., Goda K., De Risi R., and Tesfamariam S. (2023). "Multi-variate seismic fragility assessment of CLT coupled wall systems." Earthquake Spectra, 87552930231190687. https://doi.org/10.1177/87552930231190687
2. Seismic design and performance assessment of CLTW-GMRF coupled system
Theoretical background: Employing a dual or coupled structural system offers improved stability and load resistance, especially against lateral forces such as earthquakes and wind. This system efficiently distributes the load demands across its various components, utilizing their distinct advantages to enhance the building's safety and resilience. In line with this concept, our group has developed the Cross-Laminated Timber Shear-wall and Glulam Moment Resisting Frame (CLTW-GMRF) coupled system. In this system, the CLT shear-wall panels provide lateral stability and distribute seismic forces effectively, while glulam frames contribute to the overall ductility and energy absorption of the structure. This synergy ensures robust seismic performance, complemented by the aesthetic and environmental benefits of the timber-based construction.
System Components: The proposed system comprises glulam beams and columns, CLT floor panels, CLT balloon shear-walls, beam-column joints with replaceable steel dampers, buckling-restrained brace (BRB) hold-downs, and column-base joints. The utilization of replaceable steel damper, functioning similarly to a fuse, in the beam-column joint provides high ductility with large energy-dissipative capacity. Moreover, the replaceable of the steel dampers enhance the post-earthquake recoverability of the system. The BRB hold-downs further contribute to the system's ductility and energy dissipation. Given the system's low moment demand at the column base, conventional column-base joints with lagscrewbolts fastened to steel bottom plates are used. To further improve the resilience of the system, hybrid beam-column joints made up of post-tensioned tendons and mild steel dissipators along with hybrid brace hold-downs made up of pretensioned tendons and friction surfaces were also employed as part of the research.
Areas of Investigation and Contribution: In this research, the feasibility of the coupled system was explored, and the potential interaction between the two systems under seismic loading was investigated. The research introduced a versatile seismic design method congruent with existing codes and design standards, while offering flexibility through adjustable wall-to-frame moment proportions. Utilizing the proposed seismic design procedure, 6-, 10-, 15-, and 20-storey CLTW-GMRF system were developed. Linear and non-linear analysis were performed to examine the performance of the system with varying moment proportion, ductility-related seismic modification factors, hold-down, and beam-column joint types. The ductility-related modification factor of the system was also estimated using the FEMA P695 guideline.
Findings of this research suggested that CLTW-GMRF system offers a promising solution for sustainable high-rise timber buildings. Its coupled nature allows to fully exploit the potential of CLT shear-wall and glulam frames, addressing the challenges often faced in a single timber-based structural system. When utilizing these systems, the research underlines the need for careful consideration of the interaction between the individual systems. The system has exhibited commendable structural behavior under different design parameters. Specifically, the system’s performance has significantly improved by using self-centering energy-dissipative beam-column and hold-down systems. Moreover, the system has showed resilience at both the design and maximum considered earthquake levels.
Sample Publications:
Tesfamariam S. and Teweldebrhan B. T. (2023). “Seismic design of tall timber building with dual CLT-Shear wall and glulam moment resisting frame systems.” Kelowna, BC: UBC Faculty Research and Publications. https://doi.org/10.14288/1.0431446.
Teweldebrhan B. T. and Tesfamariam S. (2023). "Seismic Design of CLT Shear-Wall and Glulam Moment-Resisting Frame Coupled Structure". Journal of Structural Engineering, 149(12), 04023169. DOI: https://doi.org/10.1061/JSENDH.STENG-1269.
