Developing sustainably constructed buildings is an urgent concern as cities look to decrease their ecological footprint. SOM sought to address this issue by exploring the potential of mass-timber to reduce the embodied carbon footprint of high-rise buildings. SOM and Oregon State University (OSU), with support from the Softwood Lumber Board, developed a comprehensive physical testing program that, to date, has included nearly 20 tests of varying sizes and configurations. On August 8th, the successful test of the final full-scale specimen provided strong evidence that the timber-concrete composite system can satisfy code requirements and compete with traditional construction methods.
The tested floor specimen—36 feet long by 8 feet wide—was modeled on a portion of a typical structural bay. The tested element was a Cross-Laminated Timber (CLT) deck topped with a thin layer of reinforced concrete to enhance the structural, acoustic, and fire performance of the system. The two materials were joined and made composite with connectors specifically designed for this application. The reinforced concrete topping slab was thickened at the supporting CLT beam to form a rigid connection between CLT decks, a feature which allows floors to span between beams with a relatively thin cross-section. For the test, the specimen was loaded with a hydraulic actuator and was recorded by 48 different sensors over the course of two hours.
The floor system provided greater stiffness than required by code and supported an ultimate load of 82,000 pounds—approximately eight times the required design load. The initial results are promising and will serve as the basis for verification testing—a series of tests that will address issues such as fire resistance—which will be required before the system can be used in high-rise buildings.