Just as we think it’s taking off, another spanner has been thrown in the works for tall timber construction.
Results from a joint research project by America’s Skidmore, Owings & Merrill and Oregon State University concludes that there is strong evidence that a timber-concrete composite construction system can satisfy code requirements and compete in terms of structural performance with traditional construction methods.
The team have been considering the possibility of using a hybrid concrete timber structure for skyscrapers since 2013 when they launched their Timber Tower Research project. The project was launched to develop a new structural system for skyscrapers that uses timber as its primary material because of its environmental benefits.
Now, three years on, the team have proposed a solution called the Concrete Jointed Timber Frame, which utilises mass timber as the main structural elements but reinforces weak points at connections with reinforced concrete.
An 11m by 2.5m model was constructed out of a Cross-Laminate Timber (CLT) deck topped with a thin layer of reinforced concrete and tested by Oregon State Uni under load pressure from an hydraulic actuator. The system was tested for two hours under 48 different sensors and the pressure was increased until the system failed at an ultimate load of nearly 40,000kgs which is about 8 times higher than required by code in the US.
According to the study, the topping slab effectively creates a rigid connection between the decks which allows floors to span between beams with a minimal cross-section.
The use of concrete, says SOM, also enhances the acoustic and fire performance of the material, two commonly heard arguments against using CLT for tall buildings.
In the video above, SOM Associate Benton Johnson says the 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.”