3D printed bridge with NO connections! | Striatus

STRIATUS, an innovative 3D printed masonry bridge recently opened to the public as part of the Venice Architecture Biennale. The bridge was built by BRG at ETH Zurich, Zaha Hadid Architects, incremental 3D and Holcim

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Chapters
0:00 Introduction
0:31 3d modeling
1:49 Roman Arch
2:30 Nubian Arch
2:41 3D printing
3:34 Assembly
4:15 Pros
5:38 Cons
6:48 Conclusion

A basic 2d form was decided on and the bridge was extruded and analyzed in 3D modelling software. Thrust network analyses created force diagrams for every design iteration. At the ideal curvature and extrusion of 2 meters, balustrades or railings were designed 3 meters high. A Stereotomy mesh divided up the bridge into 53 voussoirs or wedge-shaped blocks. Advanced discrete element analysis calculated the structural load at different points on the bridge and the effect they would have.

The bifurcating decks and balustrades transfer loads to the 5 steel footings or base supports. Since these footings want to move outward and flatten the bridge, underground steel tension ties were added to pull the footings together, absorb the horizontal thrust of the arches and keep the bridge intact. Once the design was optimized and finalized each of the 53 blocks were sliced in non-parallel layers that are orthogonal to the dominant flow of forces.

As a whole, the bridge behaves as a series of leaning voussoir arches, similar to a Roman arch. During construction, arches are supported by a temporary wooden frame. Wedges are stacked around the frame until the central keystone is placed at the top of the arch. The keystone bears almost no weight, but is the center of redirecting the weight of the structure down and outwards. Once the rest of the pieces are in place, the formwork can be removed and the arch remains standing.

Unlike typical extrusion 3D printing in simple horizontal layers, Striatus uses a two-component concrete ink. Each of the blocks was printed in non-uniform and non-parallel layers via a 6 axis, multi-DOF or degrees of freedom, robotic arm. This new generation of 3D concrete printing allows the resulting forms to be used structurally without any reinforcement or post-tensioning. Compared to conventional concrete construction where beams and floor slabs are solid, heavy blocks, the bridge uses just 30% of the total volume of concrete and 10% of steel. Strength is achieved through geometry rather than mass. Every section of the bridge is hollow, thus minimizing material and reducing transportation and labor costs.

The forms were printed in Germany in an indoor, controlled environment. Once cured, they were strapped to pallets and transported to Venice, Italy. A laser cut osb formwork was on site, ready to receive the 3d printed concrete forms. Once the steel footings and tension ties were in place, a cane carefully lifted the voussoirs. The pieces do not interlock and are not attached in any way to each other. A neoprene pad is all that separates them. Once all the pieces were in place, the formwork was disassembled. Wooden stairs and a walkway were the last components to be built.

The bridge follows the 3 Rs that I mentioned in an earlier video, reduce, reuse and recycle. It uses minimal material for maximum strength with no waste. All components are designed to be disassembled and reused at another location. It can also be easily recycled because it doesn’t use any reinforcements, glue or binders. There are a few drawbacks. The bridge isn’t wheelchair accessible. The designers were probably constrained by the dimensions of the site, and since ramps need a lot more space, they couldn’t make it work. Also, since the 53 modules or wedges were so lightweight and fragile, 3 of them broke during the shipping and installation process. They had to be re-printed in Switzerland, allowed to cure and shipped separately to Italy. This caused massive delays because the bridge is built sequentially. The last issue is the clash between the precision of machines and 3d printers and human inaccuracy. There was a 2 cm difference between some of the foundations, so the workers on site had to use a good old-fashioned chainsaw to level it.
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SOURCES
   • Introducing Striatus - the first of i...   Holcim
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#3dprinting #zahahadid #robotics #architecture #construction #bridge #future #3dprinter