Efficiently designed 3D printed bridge could reduce CO2 emissions in concrete construction

The 3D-printed concrete bridge from a partnership between Switzerland and Austria has been unanimously selected as the first AJ100 Innovation of the Year winner by a jury from The Architects’ Journal, an architectural magazine. British architecture. The jury praised the lightweight design, which avoids waste. Even better, the bridge can also be taken apart and rebuilt elsewhere.
The 3D-printed concrete bridge was built as the Striatus project for the Venice Architecture Biennale and was on display at the Giardini della Marinaressa until November 2021. ‘Striatus’ in Latin means ‘grooved with grooves’ and refers to the surface texture related to the production of 3D concrete printing.

It is a pedestrian bridge that spans an area of ​​16 by 12 meters in the shape of an arch. Characteristic of the shape is a bifurcation on both sides, giving the bridge four access points. To make the slope practicable, the accesses are organized with wooden stairs. The bridge is a response to the huge CO2 emissions in concrete construction and was designed according to the principles of “reduce, reuse and recycle”.

ancient building method

What is revolutionary in the 3D printed bridge is the combination of a traditional technique with advanced computer design, engineering and robotic manufacturing technologies. The arch of the bridge is based on a traditional construction method used in ancient times. Consider the construction of the dome of the Pantheon in Rome. The arches were defined using methods originally developed for the structural assessment of historic masonry vaults. Examples include boundary analysis methods, equilibrium methods, and shear network analysis.

The Block Research Group (BRG) of ETH Zurich and the Zaha Hadid Architects Computation and Design Group (ZHACODE) participated in the design of the 3D printed bridge. It was implemented in collaboration with the Innsbruck spin-off incremental3D (in3D) and the building materials producer Holcim. The jury’s praise: “Architects tend to equate innovation with applications. What I like is that it’s a fully integrated view, from materiality to printed structures to aesthetics, and it promises a massive reduction in material costs overall.

3D printed bridge in Eindhoven, Netherlands
3D printed bridge Striatus (c) Naaro

Outstanding efficiency

“The extraordinary efficiency of the design is explained by the additive manufacturing process”, explains Johannes Megens, co-founder of in3D in Innsbruck. He and his company were involved in the development of new concrete printing technology. 3D printing helps to optimize the shape, he says. The structural depth of the components can be achieved without a solid section. The material is only used where it is structurally needed, he said. As a result, the amount of material required is less than casting or subtractive manufacturing methods, he said. Subtractive manufacturing methods include grinding, milling, and turning. 3D printing concrete can theoretically reduce material consumption by up to 70%.

53 individual components

Combining traditional construction methods with innovative 3D concrete printing, the company has achieved a load-bearing capacity not apparent in the streamlined design. This is due to 53 individually designed components, each with a specific geometry and predefined position. The compressive forces within the load-bearing structure are created by the geometry and the structural elements themselves, explains Megens. “Concrete can be considered a reconstituted stone that behaves better under compression. In arch and vault structures, the material can be precisely placed so that the forces are transferred to the columns in pure compression,” says Megens.

Concrete can be considered an artificial stone that works best in compression. In arched and vaulted structures, material can be precisely placed so that the forces are transferred to the columns in pure compression.

Johannes Megens, co-founder Incremental3D

Dry assembly

To capture the horizontal shear force of the vault, a massive foundation is required. However, Striatus’ pioneering project was only a temporary installation. Therefore, this function was performed by fragmentary elements connected to steel tension bands. Mortar is not needed for the construction of the 3D printed bridge. The blocks were assembled dry. Neoprene pads are placed between the blocks to compensate for local irregularities and avoid local stress concentrations. A method reminiscent of the use of lead plates or soft mortars

This method is reminiscent of the use of sheets of lead or soft mortar in historic masonry construction.

3D concrete printing technology

Conventional concrete bridge construction uses steel reinforcement to increase the bearing capacity. 3D printer concrete is not yet suitable for reinforcement – although there are already first approaches. The traditional construction method and the specially developed 3D printing technology provide the necessary rigidity and the reinforcement can be omitted. It is good insofar as the CO2 the impact of reinforcement is significant, says Megens. Its production generates more than ten times more carbon per unit mass than standard concrete.
In3D’s proprietary 3D concrete printing technique has blocks printed in layers and at right angles to key structural forces to create compression.

Short construction time

Overall, the construction of the 3D-printed bridge, including pouring the foundation, assembling and installing the stairs and wooden deck, took just 35 days. Concrete 3D printing is relatively fast. For example, it only took 84 hours to produce the 53 blocks. With the pioneering product, the blocks still had to be printed in a controlled environment as it required a certain temperature and air humidity. However, he says, there is already talk of developing forms of mobile products that can be produced locally. This would eliminate transportation costs and reduce CO emissions2 emissions.

Reuse and recycle

An interesting side effect of the vault construction method is that it is easily removable, with dismantling being done in the same way as construction. You lift the deck slightly so the blocks can be loosened and easily removed. This would allow the bridge to be rebuilt elsewhere. The design ensures that the 3D blocks are under low stress when in use. Structural integrity is maintained. The external fixings are easily accessible and can be easily maintained. This results in a longer service life of the entire structure.

By eliminating the steel reinforcements, the 3D printed bridge is made entirely of concrete. Thus, the blocks can be easily crushed and recycled.

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