Feb 5, 2019 | By Cameron
The construction industry is one of the greatest contributors of greenhouse gasses as one-third of global emissions are attributable to the building sector. A large chunk of those GHG are embodied in the concrete used for flooring systems, so there are various ongoing efforts to reduce the usage of concrete throughout buildings. The key to using less material without sacrificing strength is geometry. An arch is a great example: weight pressed onto the top of the arch gets distributed throughout the whole shape because it resolves forces into compressive stresses while eliminating tensile stresses. A team of researchers from Block Research Group, the Institute of technology in Architecture, and ETH Zurich has used 3D printing to apply that same principle to concrete floors.
Due to their layered nature, 3D prints have tensile strengths lower than most materials in the construction industry, but their compression strength is rather high. By designing ribs and arches into the flooring system, the team can convert thrust forces into compressive forces; this is known as a funicular system. Led by Philippe Block and Tom Van Mele, the engineers used an ExOne S-Max 3D sand printer with a build volume of 1.8 × 1.0 × 0.7m to 3D print five pieces that connect together. “No mechanical connection was used between neighbouring elements. Instead, the compression dominant structural shape of the prototypes allowed for a simple interface design using only male–female interlocking features to guarantee alignment,“ the paper states.
To generate the funicular forms, they used Thrust Network Analysis (TNA) and its software implementation RhinoVAULT; they simulated hundreds of different configurations before fabricating one. The first 3D printed sand floor was fabricated and put through the rigorous tests that ensure materials are up to code and safe for people to use. It faired well but came just 3% shy of the required load standard, so the ribs were modified slightly for the second 3D printed sand floor, which did meet load standards. The third iteration was a different design that had a higher load limit but experienced greater deflection, an issue the team calculates could be solved with additional preloading.
Their experiments reveal flooring systems can be produced using these geometries that require 70% less material than what is used in traditional concrete slabs. They continued their research and used traditional FDM 3D printers to create molds that would allow them to incorporate the funicular forms directly into a concrete floor to be placed in the NEST HiLo (high performance, low energy) project apartment that features sustainable and high-tech building methods. It’s being constructed in Dübendorf, Switzerland and will accommodate visiting ETH faculty.
These 3D printed flooring systems free up not only materials but also space that could be used for wiring and conduits. Block Research Group is working with Architecture and Building Systems lab at ETH to determine if HVAC (heating and cooling) systems can be integrated into the floors, which seems likely. It’s a shame the floors will be covered because the patterns are aesthetically pleasing.
The geometries that reduce material usage are often impossible to fabricate without 3D printing. It’s not that architects and building engineers didn’t know that these shapes could be used in concrete floors to make them stronger, it’s that those shapes are incredibly expensive or impossible to create through traditional means. 3D printing has been around for some time now, but some industries that face strict regulations and have long-established supply chains and workflows are slower to adopt new technologies. It’s safer for the construction industry to have waited for strong validations of the applications for 3D printing in architectural components, but with the 3D printed houses, 3D printed bridges, and other concrete-reducing methods enabled through 3D printing, those validations are piling up and the industry is taking notice.
Posted in 3D Printing Application
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Wait...so they 3D printed sand + phenolic resine three prototypes; so weak 5 MPa material. And then made molds (milling, wire cutter) to cast concrete? The video seems to have nothing to do with the paper. Why are the parts so white (pic 4-5); seems like foam and not sand.
Missilevania wrote at 2/6/2019 7:33:58 AM:
The analysis and thought that went into this project is amazing, and while it's possible that a "thrust" analysis was performed, I think it's somewhat more likely that a truss network analysis was what the writer meant. This is a network of trusses like you'd find on bridges. The mechanical advantages could be extrapolated to make concrete or steel structures stronger and stiffer if desired, so the material here is unimportant, save for the fact that the students managed to make something stronger with plastic than you'd typically find in concrete. Nice Work!
The truth will out wrote at 2/6/2019 4:31:38 AM:
And in earthquake conditions where the forces are everywhere vs the designed for axis they are 70% weaker.
Dan wrote at 2/6/2019 2:41:31 AM:
Plastic - Remember fire will kill the strength! Plan well.
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