STEP2 concrete stair fabrication starts

The STEP2 Unit at NEST will feature a unique staircase with fibre-reinforced concrete steps only 2 cm thick. The pioneering project demonstrates the potential of polymer 3D-printed formworks for free-form geometry. The complex topology is designed to minimise material, expressing an innovative structural and tectonic concept based on discrete prefabricated concrete steps assembled with shape memory alloy prestressing bars. Ultra-high-performance concrete enables the striking slender design with steps weighing only 54 kg, circa 60% less than a conventional alternative. Image: Digital Building Technologies, ETH Zurich

Read more: Go-ahead for digitally manufactured concrete staircase (

The precast steps of the STEP2 staircase are assembled with shear keys and pre-bent post-tensioning bars. Video: Digital Building Technologies, ETH Zurich

A reusable formwork part for the concrete steps, 3D-printed in PET reinforced with 15% carbon fibre. Image: New Digital Craft

The first prototypes of the steps in the construction hall of Empa. Image: Empa

Empa experts subjected the concrete steps to structural load tests. Image: Empa

Stair design: Digital Building Technologies – ETH ZurichROK Architects
Fabrication system: Digital Building Technologies – ETH Zurich, SW Umwelttechnik
Formwork development and 3D printing: Digital Building Technologies – ETH Zurich, BASF Forward AMNew Digital Craft
Structural design: WaltGalmarini
Precast concrete: SW Umwelttechnik
Post-tensioning systemre-fer
Project management: ROK Architects