Multi-Metal Topology Optimisation (MMTO)

Project Type: Research at UCL (in collaboration with the Technical University Lübeck, Foster+Partners, and Meltio. Project funded by The Bartlett Innovation Fund)

Project Year: 2023

Project Team: Kostas Grigoriadis, Michael Herrmann, Efstathios Damtsas, Alejandro Nieto Jimenez, Marina Konstantatou

Publication: "3D Printing and Material Extrusion in Architecture"

 

MMTO is collaborative research funded by UCL's Bartlett Faculty of the Built Environment Innovation Fund. The project concerns the metal components connecting the different parts of a building's structure and cladding that are standard sized, materially homogeneous elements. Building loads, deflections, and thermal expansion rates, however, are heterogeneous. Using material uniformly in effect is inefficient and increases embodied energy and componentry manufacturing, transportation, and installation costs.

 

The origins of this redundant material use go back to times when mass fabrication was the norm, environmental issues were not a main consideration, and design and fabrication techniques were different from today's practices. Nowadays, CAD methods like topology optimisation offer the possibility of reducing the amount of material in building components to a bare minimum.

 

The novelty of the approach in MMTO is that we aimed to go beyond single materials and investigate multi-metal optimisation and fabrication. More specifically, in single material optimisation, the mass of a carbon steel beam can be halved, while maintaining the same structural properties. A carbon steel like mild steel has a yield strength of approximately 400 MPa and a tensile one of 525 MPa. Our assumption in MMTO was that introducing a second metal in the beam, like tool steel with respective 1,480 MPa and 1,790 MPa yield and tensile strengths, could allow further mass reductions.

 

The overall aim was to minimise embodied carbon. Our optimisations ranged from 90% up to 10% mass reductions. Within this range and in every 10% mass reduction category, it was possible to vary the ratios of mild steel and tool steel from 10% - 90% to 90% - 10% i.e., 90% mild steel and 10% tool steel. Although the optimisations in the 10% reduced mass category had discontinuous material paths, from 20% onwards solid, continuous beams were achieved.

 

Indicatively, compared to a solid S235 steel I beam, an 80% mass reduced mild steel / tool steel MMTO can lower the beam's embodied carbon by approximately 75%. The next step following the topology optimisations was to 3D print (LMD): 1. a conventional mild steel beam, and starting conservatively, 2. its 50% reduced mass equivalent in single mild steel, and 3. another 50% reduced mass dual material beam with 50% mild steel and 50% tool steel.

 

From an environmental point of view and depending on a part's geometry, one issue with 3D printing is the need for added supports, which in this case weighed a total of 2.9kg. A workaround is to optimise with LMD printing constraints in the digital model. The next step is to perform vertical load testing on all three beams at the structural testing facilities of TH Lübeck. This will verify whether the MMTO beam can perform the same as or better than the single TO and conventional beams. On the path to Net Zero, this approach could incur urgently needed building component embodied carbon reductions, hopefully paving the way for widespread applications of MMTO in building construction.