Timber engineers are working to develop the world’s first fully modular timber skyscrapers, creating giant ‘skeleton’ building systems that use cross-laminated timber floors and glulam beams and columns to assemble (and, in time, disassemble) to construct tall timber towers that use ‘plug and play’ construction to rise up to 24-stories in height.
The project—known as MOHOHO—saw a team from the Graz University of Technology work hand in hand with corporate partners Kaufmann Bausysteme and KS Ingenieure to develop the world’s first fully patented building system that can not only be used in new construction but also to add to, repurpose, and retrofit thousands of buildings.
“The construction industry is responsible for 60% of global resource consumption and almost half of all global waste production and global emissions of climate-damaging gases,” according to Christian Keuschnig, TU Graz’s project lead. “That’s why the circular R-strategies, such as refurbishment, repair or reuse, were very important to develop a building system that offers a CO2-reduced alternative to conventional construction methods in high-rise construction and can be used for different purposes for as long as possible.”
Using a combination of modular and skeleton construction, the team prefabricated 3D timber modules that can be stacked next to or on top of each other—like shipping containers at the port. When combined with a supporting mass timber skeleton, these modules allow walls and floors to slide into the skeleton — like draws sliding into a cabinet.
“The prefabricated skeleton modules can be joined quickly and securely using the connection node developed as part of the project. The connection node also enables load redistribution, which means that the failure of individual columns does not lead to the collapse of the entire building,” according to Keuschnig. “This first increases robustness and thus safety, and second enables the targeted repair of individual modules. In addition, an elastomer bearing integrated into the node ensures a high level of sound insulation between the units.”
Wood Central understands that the timber modules have been designed so that a lifting cylinder can be inserted, and shear plates can be lifted and lowered to allow for the supply of electricity, water and heating to be connected to the nodes. “This (also) relieves the pressure on the underlying components and creates the necessary space for the replacement process,” Keuschnig said, adding that individual elements can also be dismantled to ensure repairable construction.
Rising up to 24 stories, Keuschnig said that a concrete podium is “essential” for all buildings beyond six stories: “In MOHOHO, we have combined the advantages of modular wood construction, such as the high degree of prefabrication and the short construction time, with the advantages of skeleton construction.”
“The prefabrication of the modules in a production hall under controlled conditions enables higher quality and traceability of the joints compared to on-site assembly and ensures shorter construction times as well as reduced noise and dirt pollution,” he said. “During dismantling, the modules can be reused directly or separated by type. We are already planning a follow-up project in which we want to test and scrutinize all of these things in practice.”
The German Eco-Box: CLT panels slide into place like shoe boxes
The new system comes after Wood Central reported on a new mass timber prototype that reduces the amount of reinforced concrete used in buildings, which could be an ideal prefab solution for low-rise and mid-rise residential and commercial projects. Dubbed the “Eco-Box,” German-based Züblin, a subsidiary of Austrian firm Strabag, is behind the concept; with the support of the German Federal Ministry of Food and Agriculture, it is working with the University of Applied Sciences in Stuttgart to develop the prototype.
The project, subject to a 36-month demonstrator programme, will see a timber construction system developed to combine a modular design with a decoupled, primary load-bearing system: “The demonstrator will be used to research and implement information on prefabrication and logistics, BIM, building physics investigations and sustainable building service technologies in five work packages,” said Züblin, who spoke to Construction Briefing about the project in September.
According to Züblin, the system differs from traditional prefabrication modules, with the mass timber units sliding into a primary structure rather than individual units stacked on top of each other: “Eco-Box is based on the modular principle, which consists of separating the modular system into a primary and a secondary supporting structure.” In other words, the CLT modular units are placed and fixed to a primary supporting structure rather than the units themselves serving as primary supports: “This construction method means that special uses [like] double storeys can be realised easily and cost-effectively.”
- Click here to learn more about the role of engineered wood products, like cross-laminated timber, in reducing the world’s dependency on concrete-based construction.
