OC, one of the largest and oldest general contractors in Japan, founded in 1892, has designed the first 3D printed building in the country certified by the Ministry of Land, Infrastructure, Transport and Tourism. Construction has begun on the grounds of OC Technical Research Institute in Kiyose City, Tokyo.

Architectural 3D printing is particularly challenging in earthquake-prone Japan, so that structural safety and performance require special consideration. One goal of the project was to meet the strict construction requirements without relying on conventional reinforcement (e.g., rebars), adopting instead new methods tailored to exploit the characteristics of 3D printing.

The demonstration building thus features a 3D printed envelope made of a special type of mortar, acting both as an internal and external finishing surface, as well as the framework for the load-bearing structure, made of an ultra-high-strength fiber-reinforced concrete (UFC) called “SLIM-Crete®”. This construction method does not require the placement of reinforcing bars nor steel frames, taking full advantage of the 3D printed workflow.

The project is the result of OC’s continued research and development of 3D printing technologies, and represents as step-up from a 2019 prototype, which was at the time the largest 3D-printed structure in Japan.

Having undergone a performance evaluation at the Building Center of Japan, the demonstration building has obtained ministerial approval and has been granted building permission in full compliance with the Japanese Building Standards Law in April 2022. Construction has begun in May, and the building is slated to be completed in November this year. It will be used as an exhibition space, while functioning as a living test piece to evaluate its durability, structural, and environmental performance.

The building shape has been parametrically designed to achieve the best ratio between interior space and material-use reduction, within the printing range of the robotic arm. To fabricate it, a 3D robotic printer will be installed on-site, printing the mortar formwork directly on the foundations. The roof-slab formwork will be 3D-printed indoors in a nearby building, then placed on top of the walls and capped with SLIM-Crete®, making this building the first in Japan being fully 3D printed except for its foundations.

Thereafter, the 3D printer will be placed on top of the roof slab to finish-off the parapet of the walkable deck, demonstrating that it is technically feasible to print a multi-storied building. Equipment such as air conditioning, washbasin, lighting, and an experimental radiating-wall system for climate control will be installed, being an integral part of the building-permit application.

The slab design is a case-in-point when it comes to adapting construction processes to the advantages of 3D printing. Principal stress-lines resulting from structural finite-element analysis (FEA) simulation generated the isostatic ribbed deck, a means of material economy achieving aesthetic and spatial qualities at the same time: this outcome would have been unfeasible using conventional construction methods.

Moreover, the walls are multi-layered, combining load-bearing structure and cavities for insulating material, equipment routing and a system for radiant heating and cooling. In this way, it can be expected that construction time would be reduced in the future, by being able to carry-out simultaneously different construction tasks.

OC hopes that its demonstration building will contribute to the advancement of 3D printing in the AEC industry, and to its increased feasibility as a performative construction method.