In 1502 A.D., Sultan Bayezid II was in search of a bridge design to connect Istanbul with its neighbor city Galata, one that would have been the world’s longest bridge span of its time. inventor Leonardo da Vinci proposed an idea but he did not get the job.
Would it have worked?
Today, 500 years after da Vinci's death, researchers at MIT decided to test whether his concept would have worked. Recent graduate student Karly Bast MEng ’19, along with professor of architecture and of civil and environmental engineering John Ochsendorf and undergraduate Michelle Xie, analyzed all available information from the time and built a detailed scale model to test the structure’s ability to stand and support weight.
The bridge, at the time, would have been about 280 meters long. “It’s incredibly ambitious,” Bast said. “It was about 10 times longer than typical bridges of that time.”
Since Leonardo provided no details about the materials that would be used, Bast and the team researched the time's materials and concluded that the bridge could only have been made of stone. They then had to build a model and demonstrate its stability.
They chose to build it at a scale of 1 to 500 using 126 blocks for their bridge. The individual blocks were made on a 3D printer.
“It was time-consuming, but 3D printing allowed us to accurately recreate this very complex geometry,” Bast said.
Ultimately what the team was trying to test was if the design would work with the technology from da Vinci's time.
Held together by compression
“It’s all held together by compression only,” Bast said. “We wanted to really show that the forces are all being transferred within the structure,” which is key to ensuring that the bridge would stand solidly and not topple.
Similar to an actual masonry arch bridge construction, the pieces of the bridge were supported by a scaffolding structure, and only after they were all in place could the scaffolding be removed to allow the structure to support itself. The final test came when it was time to insert the final piece in the structure: the keystone at the top of the arch.
“When we put it in, we had to squeeze it in. That was the critical moment when we first put the bridge together. I had a lot of doubts” as to whether it would all work, Bast explained. But “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” that makes it work, she said. “This is a strong concept. It was well thought out.”
The design has no practical implications for today's advanced bridge designers but it does underscore da Vinci's brilliance of the time. It also proves, Bast said, that “you don’t necessarily need fancy technology to come up with the best ideas.”