Innovations in the use of wood as a structural material have included the invention of engineered wood products including Cross-Laminated Timber (CLT) for which markets are expanding. One such market is residential construction where many structures are built using light-frame construction techniques. These structures have shown vulnerabilities to hazards such as tornadoes; whereas, CLT has shown potential to withstand these hazards.
The project had two main components: an experimental test phase and an analytical phase. Results from experimental debris impact testing demonstrated that 3-ply CLT could reliably resist the debris associated with EF-2 and EF-3 level events while failing approximately 50% of the time when subject to EF-5 level hazards. CLT shear wall tests on assemblies with and without out-of-plane walls sought to quantify the performance of configurations that would likely be present in residential structures with more box-like geometries and behavior. In addition, it was determined that out-of-plane walls could resist the uplift forces that develop due to lateral loads. A simplified analytical method for determining the capacity of CLT shear wall assemblies was proposed based on the connection capacities of the assembly.
The analytical phase of the project included the development of a structural performance model for residential archetypes designed using CLT. Results from this study indicated that the archetypes experienced a 10% probability of failure in EF-4 events. In comparison, light-frame construction has shown vulnerabilities to EF-0 and EF-1 level events. In addition, the hazard assessment of light-frame structures based on historical tornado data showed that significant portions of the United States exhibited a reliability index less than the target reliability described in ASCE 7-16, dropping to nearly 0% when built using CLT. A comparative cost analysis shows that for locations with high tornado hazard, it would take up to 100 years for CLT construction to be economically competitive with light-frame construction considering only the differences in upfront construction costs and tornado-induced losses.
Ultimately, CLT exhibits an increased level of performance compared to light-frame residential construction in tornado events. Further developments in the mass timber market could make such an alternative to light-frame construction more realistic.