Striatus is the First 3D Printed Bridge Built Without Reinforcement

Striatus exhibited at the Giardini della Marinaressa during the 2021 Venice Architecture Biennale is a 16 x 12 metre arched masonry footbridge, constructed using 3D printed concrete blocks assembled without mortar or reinforcement. The precise integration of design, engineering, fabrication and construction devised through the Striatus model has led to a redefinition of the standard interdisciplinary relations.

The footbridge developed by the BRG (Block Research Group) at ETH Zurich and ZHACODE (Zaha Hadid Computation and Design Group) in collaboration with incremental3D and Holcim is a novel concept synthesising customary techniques of master builders with advanced computational design, engineering and robotic manufacturing technologies. Further, through the use of ‘COMPAS’ – an open-source computational framework ensured high accuracy and transparency during data exchange between the different designers of the project working together from five countries, at a time when travelling was restricted.

‘Striatus’ the title, contemplates on the creation of a “striated” compression-only structure wherein the concrete material is printed in orthogonal layers to the main structural forces. Circular by design, it only carries material where needed contrary to the inefficient deposition of building materials. Through the construction of Striatus, arises the extensive 3Rs of sustainability which includes:

● Reduce- emphasising on the relevance of using lower-strength, less-polluting printable materials for building while also drastically reducing the amount of steel reinforcements.

● Reuse- rising the possibility of dry assembled design without the use of binders or glue, ensuring easy access and maintenance of external ties resulting in longer lifespan of the structure.

● Recycle- by avoiding waste and expenses linked to single-sue moulds with the additional possibility of using various material components that are separate and separable due to the application of mechanical connections.

Due to the distinctive geometry of unreinforced concrete employed on Striatus, the concrete is regarded as an artificial stone performing best during compression. Specifically in arched and vaulted structures, precise placing of materials can be formulated to allow movement of forces to the various supports.

The peculiar fractionalized deck geometry is site responsive while the funicular shape has been defined by limit analysis techniques and equilibrium methods. Also, the crescent profile encompasses the thrust lines that trace compressive forces through the structure for all loading cases. Neoprene pads positioned between dry assembled blocks eliminate stress concentrations and regulate friction properties of the interfaces.

In contrast to the classic extrusion 3D printing (done in simple horizontal layers), Striatus uses 2k (two-component) concrete ink with corresponding printing head and pumping organization to exactly print non-uniform and non-parallel layers through a 6-axis, multi-DOF robotic arm. Also, to prevent disorder between direction of compressive structural forces and the orientation of material layers, a custom developed design pipeline termed as FRep (Functional Representation) process is used. FRep encodes and checks rules of minimum overlap and maximum cantilever between the different print layers, speed and length.

Importantly, Striatus therefore also proposes an alternative to the standard inefficient floor slabs within any building. The advanced floor system here enables the use of low-embodied-carbon concrete that contains 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. Further, the digitisation of fabrication and digital augmentation of skilled assembly and construction techniques makes historically-accrued knowledge easily available to future younger generations, thereby allowing a systematic upgrade towards industrialised construction through the use of computational and robotic technologies.

• Text by Nikitha Sunil, Contributor at A+D