A small seaside park in Venice, Italy, was recently upgraded to include an innovative new concrete pedestrian bridge from the research arm of the global contemporary design firm Zaha Hadid Architects. Like many of the firm’s signature projects, it has swooping lines, smooth curves, and the vaguely futuristic shape of something that seems built either by or for space robots.
What’s important about the concrete bridge is what it doesn’t have. Using a building technique inspired by ancient masonry, the bridge requires neither steel reinforcements, binding mortar, nor the large amount of carbon-intensive concrete that a conventionally built structure would require.
The bridge is able to stand, and indeed to carry the weight and forces of regular use, through a highly detailed and computer-driven design that used 3D printing to precisely generate 53 hollow chunks of concrete that stack together into a structure as strong as stone.
The bridge was designed by Shajay Bhooshan, co-founder of Zaha Hadid Architects Computation and Design Group ZHACODE and Philippe Block, a professor in the Institute of Technology in Architecture at ETH Zurich, in collaboration with 3D printing company incremental3D and the global building materials company Holcim. Like ancient stone bridges and cathedrals, the structure was designed in an old style but with new material precision. Installed as part of the current Venice Architecture Biennale, the bridge is an attempt to prove that ancient and modern techniques can be combined to create better structures.
“Many masonry structures are standing after centuries because of their capacity to move and to settle. They’re still there, they’re very robust but not in a way that modern engineering enables,” says Block. Arched stone bridges from Roman times, for example, have stood intact for centuries due to their sheer compression and weight. “This is a beautiful thing that we want to reintroduce into modern architecture and engineering practice.”
The pieces of the bridge were 3D printed to be discrete chunks that are mostly hollow, with only small concrete braces within. Computational design was used to determine how each piece could support weight on its own, and how all 53 pieces of the bridge could fit together and provide structural strength entirely through compression. This approach cuts down the amount of concrete and eliminates the need for the steel reinforcing bars that concrete structures require. Fewer materials lower the overall cost of building, and the relative ubiquity of concrete means this type of construction could potentially happen anywhere.
“You’re placing material exactly where it is needed,” says Bhooshan, who developed the design as part of his PhD research at ETH Zurich.
Rather than the typical 3D printing approach that lays a uniform line of mixture over and over again to build simple walls, Bhooshan and Block worked with Holcim to develop a special 3D printing approach that can lay a variable width of material, enabling a more complex structural form while using less steel and concrete. The non-parallel forms open up new aesthetic opportunities for 3D printing concrete. “It’s really about starting from the design and thinking about how the materials want to be used in the best way,” says Francis Steiner, Holcim’s head of digital design and fabrication. “This is where we see the future of 3D concrete printing.”
Constructed earlier this summer over a simple wooden bracing structure, the bridge also has small concrete pads and steel tension ties at the five points where it meets the ground, and steel steps. Because the bridge requires no mortar or glue to hold it together, it is capable of being disassembled and rebuilt elsewhere as needed (there may come a time when buildings and infrastructure have to be moved quickly for cities to adapt to climate change). Block says the team is currently in the process of finding a second home for the bridge.
Despite its location in the lagoon city of Venice, the bridge is situated in the middle of a park and doesn’t actually cross water. But that hasn’t stopped it from being used, according to Bhooshan. Since opening, it has been popular with kids, people walking dogs, and park visitors walking up just for a perch to stare out at the ocean. “It turned out to be a very social space,” he says. “That was quite a surprising and pleasant and happy coincidence to discover.”