The recent trend in timber-framed architecture may just be beginning.
SOM’s Timber Tower Research Project has passed a major milestone as the structural system has successfully completed strength testing that validate initial calculations. Launched in 2013, The Timber Tower Research project was established with the goal of developing a new structural system for skyscrapers that uses timber as its primary material. Using these techniques, the research team estimates that the embodied carbon footprint of buildings can be reduced by 60 to 75 percent when compared to a benchmark concrete building.
The proposed solution, called the Concrete Jointed Timber Frame, utilizes mass timber as the main structural elements, reinforcing weak points at connections with reinforced concrete. To validate the system’s potential, SOM partnered with Oregon State University to put the system through a rigorous testing program that has involved nearly 20 tests of varying sizes and configurations. After successful testing of the final full-scale mock-up, SOM has concluded that there is “strong evidence that the timber-concrete composite system can satisfy code requirements and compete with traditional construction methods.”
The 36 foot by 8 foot specimen, modeled after the typical size of a structural bay, was constructed out of a Cross-Laminate Timber (CLT) deck topped with a thin layer of reinforced concrete to “enhance the structural, acoustic, and fire performance of the system.” Specially designed connections were developed to join the two materials together. Around the CLT beams, the topping slab was thickened to create a rigid connection between decks, allowing floors to span between beams with a minimal cross-section.
The system was tested for 2 hours using a hydraulic actuator while being measured using 48 different sensors. Pressure was increased until the system failed at an ultimate load of 82,000 pounds – about 8 times higher than required by code. Stiffness also proved to meet code standards.
SOM Associate Benton Johnson remarked that the successful test “highlights the real benefits of the composite timber approach. We took a small amount of concrete that was necessary for acoustic and fire performance and used it to enhance the structural performance of the floor. This move allows mass timber to reach its full potential, allowing it to compete in the market while also reducing the carbon footprint of cities.”
The system will now undergo further testing for other issues, including fire resistance, as it looks to be approved for use in high-rise buildings.