A bridge to the future: 3D steel printing and load cells [Updated 2023]
Published On: April 26 2023
Back in July 2021, we wrote about how load cells would help monitor an innovative 3D printed steel bridge over the Oudezijds Achterburgwal canal in Amsterdam. Now we’re revisiting the project two years on, to discover more about the impact of this world-first project, and the role of the “digital twin” system.
3D printing steel
If you’re proud of the latest plastic creation magicked from thin air by your new 3D printer, this project takes it to a whole new level.
The first-ever 3D printed bridge was installed over the Oudezijds Achterburgwal canal in Amsterdam in 2021. Many of the cyclists and pedestrians passing over the elegant S-shaped steel structure are probably totally unaware that this ground-braking bridge was constructed layer by layer, using robotic arms and welding torches.
It took four industrial robots, 4500kgs of stainless steel and six months to create the 12m MX3D Bridge. (So no complaining next time your 3D printing projects has to run overnight…) It was the first time that robots had been used to perform metal inert gas (MIG) welding, the process used to construct the bridge. MIG arc welding feeds a heated continuous solid wire just 1.2mm in diameter into a welding gun.
The monitoring system features over 100 sensors and included load cells to monitor movement, vibration, temperature and strain on the bridge when loaded with people and in different weather conditions. As lead structural engineers Arup explained:
“The bridge will be equipped with a sensor network, allowing the partners to gather data which will be used to build a digital twin to monitor the health of the bridge. The digital twin will track performance under different environmental conditions and under changing dynamic loads, including tracking pedestrian use, checking corrosion or studying deflection and support forces, all of which will enable the further development of a data-centric design language. “
“The sensors also measure environmental conditions, including issues relating to natural corrosion, wind, thermal, light, and air quality … Measuring natural corrosion means that if in several years time the strength of this new material started to deteriorate the digital twin will spot this long before there were any visible indicators.”
Big data and its destination
The datas from the bridge’s sensors is sent to servers stored in a basement close to the bridge in Amsterdam. The data is then transmitted directly to a control centre and fed into the digital twin. The bridge’s digital twin is a continuously updated model monitored by a team based at the Alan Turing Institute in London, the UK National Institute for data science and artificial intelligence.
Much of the credit for the involvement of the Turing Institute goes to Lord Robert Mair CBE, Emeritus Professor of Civil Engineering at the University of Cambridge. His goal was to “Persuade members of his profession to measure the performance of what they create”.
Lord Mair is also an advocate of creating a digital twin that mirrors the design process from the very start. Ideally, the digital twin would be in place *before* any construction begins, enabling the model to track every aspect of its manufacture, testing, installation and use.
“One of the things that we found is that the strength characteristics are dependent on the orientation of the printing. But what was in some sense surprising was that the baseline strength was what you would expect of just rolled steel, and it actually increased in some directions.”
The digital twin data will be used by the City of Amsterdam to monitor pedestrian levels and help optimise future designs in terms of material reduction and therefore lowering carbon emissions. It will also help in creating new codes and standards for innovative to materials, such as 3-D printed steel. Furthermore, gathering such data enables what author Hugh Ferguson refers to as generative design.
“By establishing a certain criteria and design constraints and feeding them into the data given out by the digital twin, engineers convention generate money designs that meet the constraints and criteria. This would be a major step forward for structural engineering.”
Why use 3D printing for steel?
Large scale steel 3D printing relies on Robotic Wire Arc Additive Manufacturing (WAAM) software. As leading company MX3D explains:
“(Our process) enables large-scale 3D metal printing by joining together our proprietary technology, a standard industrial robot and a power source.”
It also gives designers more freedom in six axis construction, reduces waste by optimising for weight and strength, and offers a very short CAD to print time, often under an hour!
“The cost for a WAAM printing cell is around 1/5th of an SLM- powder-bed printer. Add to that the cost of the base material is around 10 times lower (€5,- per kg for stainless steel wire against €50,- for stainless steel powder for SLM) and it becomes clear that for large scale printed metal objects, WAAM will often be the technique of choice.”
The finished bridge was craned into place (load cells in action again!), before being formally opened by Her Majesty Queen Máxima of the Netherlands on 15th July 2021.
If you fancy 3D printing your own bridge, MX3D’s co-founder Tim Geurtjens explains how in this video!