In 1502, Leonardo da Vinci sketched out a design for what would have been the world’s longest bridge at the time — 280 meters (918.6 feet). Although the bridge itself was never built, engineers at the Massachusetts Institute of Technology have tested the design to see if it would work.
Karly Bast, a recent MIT graduate student, with the scale model she created. Credit: Gretchen Ertl
Da Vinci submitted his innovative bridge sketch when Sultan Bayezid II, ruler of the Ottoman Empire from 1481 to 1512, put out a request for bridge designs that could span across the Golden Horn. This natural river estuary separated the cities of Galata and Istanbul.
Da Vinci’s proposal was not selected. Now, a cable-stayed bridge is in place. But what would it have been like if da Vinci’s design had been constructed?
MIT engineers studied his drawing, as well as the materials he would have had available, and construction conditions at the time. They built a scale model to test its stability and how it might react to different conditions.
At the time of his concept, the bridge would have been a novel design compared to popular semicircular arches. These arches needed piers placed along the bridge’s span to support its length. But da Vinci proposed a flattened arch, still reaching a height so that ships could pass beneath it, but using one gigantic arch to help people cross from Istanbul to Galata.
“It’s incredibly ambitious,” said Karly Bast, a recent MIT graduate student. “It was about 10 times longer than typical bridges of that time.”
“But it was also quite sophisticated geometrically, with much more curvature and three-dimensionality than typical arch bridges,” said John Ochsendorf, MIT professor of architecture and civil and environmental engineering.
In order to stabilize the bridge against lateral sway and earthquakes, da Vinci wanted the bridge’s supportive abutments on either end of the arch to spread outward. He knew the area might experience earthquakes, as it had in the past.
At the time, stone would have been the primary material used to build a bridge of such length because wood or brick would not have been practical. The researchers didn’t find any details by da Vinci for the construction of the bridge, but believe the stones would have been fitted together without mortar.
Their model included 126 3D-printed blocks fitted together for a 32-inch long bridge. When a bridge was constructed in this Roman style, scaffolding was used to keep the stones in place. Once the final keystone was in place, the scaffolding could be removed. The researchers did the same thing with their model.
“When we put it in, we had to squeeze it in,” Bast said. “That was the critical moment when we first put the bridge together. I had a lot of doubts. When I put the keystone in, I thought, ‘This is going to work.’ And after that, we took the scaffolding out, and it stood up. It’s the power of geometry. This is a strong concept. It was well thought out.”
Previous attempts to create the bridge — such as a pedestrian bridge in Norway — used modern materials.
Ochsendorf said if the bridge were constructed today, it would likely be made with steel or concrete. But the researchers wanted to know if da Vinci’s design would have been viable at the time of its creation.
The engineers also tested the bridge’s stability by simulating what might have happened if the soil was weakened by earthquakes. The bridge withstood the simulations.
Could the bridge be used today? Bast said lighter, stronger designs for bridges, based on available materials, would win out. But it highlights the brilliance of da Vinci’s design.
“What we can learn from Leonardo da Vinci’s design is that the form of a structure is very important for its stability,” Bast said. “Not only is Leonardo’s design structurally stable, but the structure is the architecture. It is important to understand this design because it is an example of how engineering and art are not independent from each other.”
Ochsendorf said the team wanted to know if da Vinci’s idea “could actually have stood up.”
“It would not have been easy to build, in the 16th century or today, but we have now proven that his ideas on bridge design were well ahead of his time,” he said. “It is unlikely that it will ever be built for reasons of cost and practicality, but it could inspire future designers to dream big.”