Reinforced concrete floor slabs account for about 40% of buildings’ embodied carbon emissions. Until now, however, there has been no practical alternative for complex, multistory buildings.

Using a construction demonstrator, researchers at the University of Stuttgart have shown for the first time how floor slabs can be built sustainably with an innovative timber-concrete composite system.

The demonstrator, tested in June as part of the Future Cleantech Festival in Remscheid, showcases “UniversalTimberSlab”—the first point-supported timber-concrete composite flat slab for long, two-way spans.

“With the UniversalTimberSlab, we aim to make multistory timber-concrete composite construction significantly more flexible, performative and adaptable. The demonstrator is the result of several years of research at the University of Stuttgart and is based on innovative digital design and manufacturing methods,” says Achim Menges, professor and director of the Institute for Computational Design and Construction (ICD) and spokesperson for the Cluster of Excellence “Integrative Computational Design and Construction for Transformative Architecture” (IntCDC).

A timber-concrete composite flat slab for multistory mixed-use buildings

“UniversalTimberSlab” is as slender and performative as a reinforced concrete slab but significantly more sustainable. The system relies largely on wood, a renewable resource, as well as material-efficient construction and circular design.

Compared with conventional post-and-beam timber floor slab systems, which require deep beams for larger two-way spans, the compact “UniversalTimberSlab” reduces the structural height by 30 to 70 centimeters (12 to 28 inches). That offers a significant cost advantage: With the same floor-to-ceiling height, a building can accommodate more stories, and the facade area is reduced by up to 20%.

“UniversalTimberSlab” also sets new standards for design possibilities in timber construction. The structural system is based on point supports, meaning building loads are transferred through columns that can be spaced relatively far apart. Load-bearing partition walls are not required; walls can be arranged freely as needed. In mixed-use buildings, this allows for flexible layouts tailored to retail, dining, offices and residential spaces.

Floor plans can also be reconfigured later if the building is repurposed. The new floor slab could thus help expand timber construction in urban areas.

The game-changers: New slab segmentation and digital design methods

In timber construction, larger slabs are divided into individual prefabricated elements. Previously, these elements and their supports had to be arranged along rigid grids for technical reasons. The “UniversalTimberSlab” system makes it possible to build both regular and irregular floor slab geometries.

The approach is based on a new, patent-pending segmentation method. Glued-laminated timber segments with straight laminations that are easy to prefabricate help keep costs down. The fibers in the floor slab are arranged to follow the flow of forces, optimizing the system’s load-bearing capacity.

The project also developed new digital design methods for timber buildings. During planning, AI-powered tools generate detailed models for numerous floor plan and building variations and assist with design optimization. For example, if a planner moves a column, the impact on costs, slab height and sustainability can be shown immediately.

Milestone: Successful demonstrator in Remscheid

“What was particularly exciting for us was that the first load test wasn’t conducted in the lab, but in front of the approximately 200 visitors at the Future Cleantech Festival in Remscheid. This made it possible to verify the load-bearing capacity required for construction under real-world conditions,” says Jan Knippers, professor and director of the Institute of Building Structures and Structural Design (ITKE).

For the structural test, the team built a full-scale floor slab demonstrator measuring 9 x 5 meters (30 x 16 feet), with a two-way span of 8 x 4 meters (26 x 13 feet), in just three months. At just 36 cm (14 inches) thick, it was as thin as a reinforced concrete slab with an equivalent load and span, yet required about two-thirds less reinforced concrete.

As a preliminary step, the researchers performed computer-aided calculations—so-called FEM simulations—to investigate how the floor slab deforms and vibrates under load. In the structural test, the demonstrator was loaded with a total of 20 metric tons in addition to its own weight. This allowed the team to test the load-bearing capacity for a heavily used office building with finish loads of 1.4 kN/m² and a live load of 3.0 kN/m².

The measurements confirmed the simulations, with a maximum deformation of only 12 mm. With a natural frequency of over 8 Hz—that is, eight oscillations per second—the floor slab met the deflection and vibration requirements for multistory buildings.

Prospects for rapid technology transfer: First pilot project in the planning stages

With the successful feasibility test, the researchers have reached a crucial milestone toward widespread use of “UniversalTimberSlab” in multistory wood construction. “The system builds on the existing manufacturing expertise of the wood construction industry. This means it has the potential to be rapidly deployed in larger construction projects once further development work is successfully completed,” says Hans Jakob Wagner, group leader at the ICD and head of the EIC Pathfinder project “UniversalTimberSlab.”

The first pilot building is already in the works: The town of Oberkochen in the German state of Baden-Württemberg is planning the “Zukunftsforum,” a three-story, 1,400 m² (15,000-square-foot) building constructed using the “UniversalTimberSlab” method. The building is intended to house exhibitions, workspaces, makerspaces, workshops and laboratories.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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