Additive manufacturing, also known as 3D printing, is one of the most fascinating technological developments in recent years. Originally developed for rapid prototyping, using plastics, the technology has developed to the extent that steel can now be printed – which means it’s possible to 3D-print structures such as bridges.

But how safe is a bridge printed by robotic arms, as opposed to being constructed in the tried and tested methods used in civil engineering for centuries? We can now answer this question thanks to a pedestrian bridge installed over the Oudezijds Achterburgwal canal in Amsterdam’s city centre.

The bridge was partially developed by The Alan Turing Institute, as part of its data-centric engineering (DCE) programme, under the aegis of the Institute's Chief Scientist, Mark Girolami, who was DCE programme director at the time. It was designed and built by Dutch company MX3D, using robotic technology for wire arc additive manufacturing that it developed itself.

Girolami describes the process, saying: “What happens in welding is you get two pieces of metal and a rod is heated electrically. The metal becomes liquid and fills the gap between the two pieces of metal that you want to join. The same principle takes place here, where you now have a welding rod, but you just let the molten metal run along and solidify. Then you run molten metal along that as well, layering it up. It's a bit like icing a cake.”

As a new process, existing design protocols and standards didn’t apply, so Arup collaborated on ensuring safe design standards were used. However, the project still had to undergo rigorous stress testing to guarantee the bridge’s integrity.

But the bridge has another technological trick up its sleeve, in the shape of embedded accelerometer sensors that measure vibration and the levels of stress. “What that allows us to do is to gather data, both instantaneously and over time, as to how the structure responds to certain forces, whether it's people walking over it or jumping on it,” Girolami explains. “That provides a living stethoscope on how the bridge is performing over time. We can then monitor the data that comes from these sensors to assess any changes taking place and if these changes are indicative of any potential problems that may arise.”

Alongside these sensors is a digital twin of the bridge that couples the physical bridge with a digital representation. This computational model gets data direct from the real bridge, so it can be updated and used to play out potential scenarios that the physical structure might have to deal with and respond to.

As Girolami says: “This digital twin is very exciting because it takes us away from just monitoring and doing computational modelling. Putting them together gives you something which, from an engineering and an operational perspective, means that we can operate more safely, more economically and open up potential business opportunities.”

This sensor-led approach to safety can also apply to more conventionally built structures. Girolami says that more traditional rail bridge projects undertaken with Cambridge University, where he is the Sir Kirby Laing Professor of Civil Engineering and holds the Royal Academy Research Chair in Data Centric Engineering, have involved embedding fibre optic sensors in concrete as it is being poured, making it self-sensing.

This kind of development means that existing bridges can use new technology retrospectively to enhance safety and potentially even extend their life.

CIHT has explored the use of data in the transport sector in the whitepaper ‘Growing up quickly’ available here.

Photo credit: Shutterstock

CIHT has explored the use of data in the transport sector in the whitepaper ‘Growing up quickly’ available here.