An arched, unreinforced masonry footbridge composed of 3D-printed concrete blocks and assembled without mortar is on exhibition at the Giardini della Marinaressa during the Venice Architecture Biennale 2021.

Representing a design collaboration involving the Block Research Group (BRG) at ETH Zurich and Zaha Hadid Architects Computation and Design Group (ZHACODE) in partnership with incremental3D (in3D) and Holcim, the 16-metre x 12-metre footbridge, Striatus is made from concrete 3D-printed in layers orthogonal to the main structural forces to create a ‘striated’ compression-only funicular structure that requires no reinforcement. 

Combining the traditional techniques of master builders with advanced computational design, engineering and robotic manufacturing technologies, Striatus establishes a new language for concrete that is digital, environmentally advanced and circular by design.

In traditional arched and vaulted structures, material is placed precisely to allow forces to travel to the supports in pure compression. Strength is created through geometry, rather than an inefficient accumulation of materials as in conventional concrete beams and flat floor slabs. This presents opportunities to significantly reduce the amount of material needed to span space as well as the possibility to build with lower-strength, less-polluting alternatives.

Striatus’ unreinforced concrete structure achieves strength through geometry. The footbridge optimises the interrelated properties of masonry structures, 3D concrete printing (3DCP) and contemporary design, presenting an alternative to traditional concrete construction by minimising material use without compromising on strength, performance and aesthetics. The concrete is unreinforced, holding through compression, structurally informed, fabrication-aware and ecologically responsible, setting a blueprint for building in the future.

Striatus places material only where needed, significantly reducing its environmental footprint. Built without reinforcement and using dry assembly without binders, Striatus can be installed, dismantled, reassembled and repurposed repeatedly; demonstrating how the three Rs of sustainability (Reduce, Reuse, Recycle) can be applied to concrete structures.

Unlike typical extrusion 3D printing in simple horizontal layers, Striatus uses a two-component (2K) concrete ink with corresponding printing head and pumping arrangement to precisely print non-uniform and non-parallel layers via a 6-axis, multi-DOF robotic arm. This new generation of 3D concrete printing in combination with the arched masonry design allows the resulting components to be used structurally without any reinforcement or post-tensioning. For Striatus, Holcim developed a specific, custom-made proprietary 3D-printing ink from its Tector 3D Build range of mortar inks.

Striatus offers a blueprint for building more with less. Compared to typical reinforced concrete flat floor slabs, this new floor system uses only 30% of the volume of concrete and just 10% of the amount of steel. The very low stresses within the funicular structure also enable the use of low-embodied-carbon concrete that incorporates high percentages of recycled construction waste. Prefabricated and dry-assembled, and therefore fully demountable and reusable, this floor system is easily and cleanly recyclable at end-of-life. 

Striatus’ game-changing design and construction principles can truly disrupt the built environment, transforming it for the better.

Striatus is on display at the Venice Architecture Biennale until November 2021.

Photography: Naaro