Striatus is an arched masonry footbridge composed of 3D-printed concrete blocks assembled without mortar or reinforcement. The 16 x 12 metre footbridge is the first of its kind, combining traditional techniques of master builders with advanced computational design, engineering and robotic manufacturing technologies.

Proposing a new language for concrete that is structurally informed, fabrication aware, ecologically responsible and precisely placed to build more with less, Striatus has been developed by the Block Research Group (BRG) at ETH Zurich and ZHA Computation and Design Group (ZHACODE), in collaboration with incremental3D (in3D) and made possible by Holcim.

Exhibited at the Giardini della Marinaressa during the Venice Architecture 2021, Striatus proposes a new language for concrete that is structurally informed, fabrication aware, ecologically responsible and precisely placed to build more with less.

Optimising the properties of masonry structures, 3D concrete printing (3DCP) and contemporary design, Striatus presents an alternative to traditional concrete construction.

Using a special concrete ink developed by Holcim, this method of 3D concrete printing combines the principles of traditional vaulted construction with digital concrete fabrication to use material only where it is structurally necessary and eliminate waste.

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.

To prevent misalignment between the direction of structural forces and the orientation of material layers that arises from typical shape-agnostic slicing of explicitly modelled geometry, a custom-developed design pipeline was formulated for Striatus to ensure that its printed layers are wholly aligned with the direction of compression forces throughout the entire bridge and also locally through each 3D-printed block. To address issues and challenges that could prevent in-between stability during printing, the coherence and feasibility of the gradually evolving print paths have been modelled using a Functional Representation (FRep) process.

Circular by design, Striatus places material only where needed, significantly reducing its environmental footprint. As the construction is built without reinforcement and does not need mortar, the blocks can be dismantled, and the bridge reassembled at different location.