Earthquake damage to buildings, with the potential for substantial economic losses, highlights a need to focus on developing earthquake resilient and sustainable buildings. As the result of rapid population growth and urban densification, there is a need for taller buildings that are also sustainable and can perform better than simply adequate in moderate to large earthquakes by sustaining only minimal damage. Further, it is critical that such buildings have minimal interruption to allow people to remain in their residences and community following an earthquake event. These types of buildings will be investigated in this project by considering a new type of seismic force resisting system that combines a new technology known as Cross-Laminated Timber (CLT) and a conventional Light Wood Frame System (LiFS). Each of these systems has its own beneficial features that, when combined, will create a more resilient and sustainable structural system for buildings in seismic zones in the United States. This research will address the challenges that arise when combining these two structural systems into a hybridized wood building system. This project will contribute toward a fundamental understanding of long-term loading effects on CLT and develop an optimal combination of CLT and LiFS to produce a financially viable solution for the seismic design of tall wood buildings. The research will produce new basic knowledge needed to design safer, more resilient wood buildings in seismic regions and thus contribute to seismic hazard mitigation in the United States and in other countries that use similar construction.
This research will investigate the seismic performance and optimization of a hybridized, self-centering wood system termed "CLT-LiFS," which uses unbonded post-tensioning tendons, CLT rocking walls, and light-frame wood walls to enable the design of resilient tall wood buildings. In this system, the CLT panel anchored with unbonded post-tensioning will be optimally combined with the light wood frame system to utilize the beneficial features of each. While the unbonded post-tensioning in the CLT will self-center the system, the connections in the light-frame wood will provide the necessary energy dissipation. Preliminary studies on CLT-LiFS have shown its excellent seismic performance with minimal structural damage, but key research challenges focused on its compatibility remain. In order to make this system a reality, optimal configurations of CLT-LiFS systems, performance of connection details between the CLT and the light-frame wood, and long-term behavior of CLT under sustained loading need to be better understood. The fundamental contributions of this research will be the following: 1) experimentally validated analytical models for the creep behavior of CLT under different environmental conditions, and its inclusion into analytical models for tall wood buildings, 2) the use of reliability concepts for performance assessment of the hybrid system, 3) experimental quantification of secondary systems impact on the behavior of tall buildings with CLT-LiFS systems, and 4) development of connections between the CLT-LiFS system and secondary systems. This research will lead to a fundamental understanding of how the hybridized system performs under earthquake loading compared to each of the individual systems, thereby serving as the foundation to develop the seismic design methodology and procedures to meet pre-specified resiliency and sustainability building requirements for this new building type. This research will facilitate a new generation of improved performance-based building systems to achieve resiliency and sustainability goals.
