A view from the leading edge of 3-D-printed infrastructure

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In late 2016 the world’s first 3-D-printed bridge opened in Alcobendas, a small city in the north of Madrid. Directed by ACCIONA, a global infrastructure leader based in Spain, the project marks a significant advance in the application of this technology.

As a structural engineer in Arup’s Montreal office, I’ve been fascinated by 3-D printing for the last decade. After hearing about the bridge, I wanted to learn more about ACCIONA’s experience. Engineer José Daniel Garcia Espinel, who leads the technology transfer team within the firm’s innovation department, agreed to speak with me for Doggerel.


Since this is the first 3-D-printed bridge, I imagine that you needed to develop new skills to make the project viable. Could you discuss?

When we started working on this project more than a year ago, we realized that it wasn’t actually one project, but three. We needed to develop materials. We needed to develop equipment. And what’s more, we needed to develop a procedure for calculations and for the architectural design.

Within ACCIONA we have the capacity to handle some of these challenges, but not all three together. For this reason, we brought in partners. For example, we collaborated with the Institute for Advanced Architecture of Catalonia. They helped us create the architectural design, basing it on biomimetic architecture — mimicking organic forms and geometries that we encounter in nature.

That makes sense. With 3-D printing you can make forms that are more complex, more organic, and a lot more reflective of the structure’s internal forces. Today the way we’re forced to build — especially when it comes to details with complex geometry — uses much more material than is actually needed.

That’s exactly right. One of the key benefits of this technology is the fact that it permits you to construct complicated forms without needing to build a mold or a formwork. This is reflected in the geometry we achieved in this bridge. If we had needed to create a mold to produce these particular forms, it would have been much more expensive than the structure itself.

Approximately how much did this bridge cost compared to a similar project constructed using more traditional methods?

That’s a common question. At the end of the day it’s difficult to calculate, for the simple reason that building this kind of extremely complicated structure using conventional methods would be practically impossible.

To give more context to my answer, I should note that the development of large-scale 3D printing has led to two mega-trends at the global level: the North American school and the European school.

The North American school uses a technology called contour crafting. It was developed in the late ’90s in California by a professor named Behrokh Khoshnevis. This technology uses robotic arms with a nozzle that the material comes out of. It’s oriented toward simple forms.

It’s a fantastic technology for making concrete walls, because the robot releases a line of fresh concrete on top of another line that it’s already made, creating a construction process that goes from the bottom to the top. But the downside is that this limits the geometry that you can create. With this technology you can achieve high yields from a cost perspective, but the geometry is rather limited.

The other style, the European school, is better suited to complex designs. The technology uses a dry material as its base instead of wet concrete. A conglomerate is applied over it to affix it; the geometry is defined by means of contour lines. This gives you complete formal freedom, because you don’t need support material. It allows the architect to do a lot more.

Also, the European school is more sustainable, because you use only the material that you absolutely need — and one of ACCIONA’s core operating principles is sustainability.

How do you think 3-D printing will affect everyday engineering and construction processes?

Working on this project, we realized that we’ve made a huge leap ahead compared to the usual way of doing things.

When you work on a construction project, there’s a design phase. At the end of that phase you think about how to realize the design; you make a plan and you translate it into a set of documents and two-dimensional drawings. These plans are then sent to the job site, where they’re interpreted. And finally, when there’s a contract, all the project stakeholders start to appear.

So in summary, from the moment you start the design to the time the final product is delivered to the client there are many intermediate steps and many people who intervene.

3-D printing allows for a direct link between the initial step — the design phase — and the almost-final step — construction. Imagine the huge number of steps you could remove if you were able to send a digital file directly to the contractor and he could do the fabrication directly from this file.

Think about logistics, for example. It’s no longer necessary to build something in one location and then transport prefabricated pieces to another location, where they perhaps need to be staged 100 or 200km away in order to install the bridge. Imagine, for example, that our 3-D printer could be located in the same site as the project itself and we could send the file there digitally and fabricate it onsite. This would revolutionize transportation logistics. We would only need to bring the primary material to feed the 3-D printer. You’re radically changing the normal way of working in the construction industry.

In my opinion, what 3-D printing allows is the unification of architecture and engineering, which have traditionally collaborated but never worked hand in hand.

What were the main obstacles that you had to overcome to realize this project? For example, the barrier of, “Can this really be done?”

This project was a challenge from the beginning, as much from the technical point of view as from the management point of view.

Not only is this the world’s first 3-D-printed bridge, but it’s the first bridge to use this technology that’s open to the public. This means that a public administration had to authorize it and we had to comply with a series of regulations.

What 3-D printing allows is the unification of architecture and engineering.

With this technology you can make the most avant-garde and complex design in the world, based on biomimetic architecture, following organic forms. But in the end you have to comply with legal norms that require you to modify these forms for safety.

In our case, we didn’t change the geometry, but we had to add safeguards so that a child couldn’t get a hand or foot caught in the structure.

How did the client react when you first said you wanted to build a 3-D-printed bridge?

You expect them to say it’s insane and impossible. But in this case the client, the Alcobendas municipal government, supported us from the outset. We worked very closely with them, searching for the best location for the project. They were really more like a partner than a client.

The reality is that it’s not just businesses that have to be innovators, but also clients. It would have been pointless for us to realize this project in our workshop. The role of the municipality on this project has therefore been critical.


Questions or comments for José Daniel Garcia Espinel or Maria Mingallon? Contact josedaniel.garcia.espinel@acciona.com or maria.mingallon@arup.com.

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