A team at Shanghai’s Tsinghua University has built the world’s longest 3D-printed concrete bridge. And, while the bridge is cutting-edge, the team says that it was inspired by China’s oldest standing bridge: the Anji Bridge.
Professor Xu Weiguo’s team unveiled their new bridge, which stretches over a canal in Wisdom Bay Innovation Park, in January. The bridge was 3D-printed by two robotic arms, a process that took just 450 hours split between the two limbs. According to the team, the concrete printing means that its cost was 1/3 lower than a comparable bridge made by more traditional methods. It’s currently the longest concrete 3D-printed bridge in the world, at 26.3 m (approximately 86 feet) long and 3.6 m (approximately 12 feet) wide.
About a thousand kilometers and one and a half thousand years separate it from its inspiration, Anji Bridge. Built by craftsman Li Chun during the Sui Dynasty (starting around AD 605), the bridge is the oldest standing bridge in China today, although the ornamental railings have to be replaced “every 300 to 500 years.” The central arch is made of 28 thin limestone slabs connected with iron dovetail joints.
While the sides of the Anji were made from limestone slabs lifted into place by human workers, the sides of the newer bridge are made of concrete slabs moved into place by robotic arms. The deck of the as-yet-unnamed newer bridge’s deck is made up of 44 concrete units, each approximately 3x3x5 feet. When printing the deck, the researchers used brain coral as an inspiration, creating an organic-looking pattern.
And while the Anji Bridge was groundbreaking at the time for its open spandrels (see below) and a structure that let the bridge shift to accommodate traffic, the new bridge is notable for its special concrete and the design of the robotic arm that helped build it. The bridge is printed from a polyethylene concrete that the team developed specifically for the project, a concrete that the team hopes will keep the structure sound over the years. Because the concrete needs a specific flow rate and drying time, the team developed its own robotic arm injection system and path software to accompany it.
To test whether this new concrete technique works as well as the team hopes it will, the bridge is embedded with sensors to measure its strain. The concrete structure is kitted out with vibrating wire stress meters, which will give a real-time report of how stresses and pressure are impacting it.
Indeed, the team sees the bridge as a test: can 3D-printed concrete structures make the jump from the headlines to the practicalities of everyday construction? “There are quite a few scientific research institutions and construction companies in the world that have been committed to technical research in this area,” says the university’s press release. “But this technology has not really been used in actual engineering. The completion of the pedestrian bridge marks a gratifying step for this technology from research and development to practical engineering applications.”
Hopefully, the bridge can inherit the long life of its inspiration.