C&B Notes

da Vinci’s Revolutionary Bridge

Leonardo da Vinci responded to a Middle Ages RFP (request for proposal) from the Ottoman Empire for a bridge design.  Alas, the Sultan turned him down.  However, a team of MIT researchers recently demonstrated that da Vinci’s radical design was not misguided but rather just ahead of its time.

Da Vinci’s proposal was radically different than the standard bridge at the time. As described by the MIT group, it was approximately 918 feet long (218 meters, though neither system of measurement had been developed yet) and would have consisted of a flattened arch “tall enough to allow a sailboat to pass underneath with its mast in place…but that would cross the wide span with a single enormous arch,” according to an MIT press statement.  It would have been the longest bridge in the world at the time by a significant measure, using an unheard of style of design.

It wasn’t just length or style that set da Vinci’s bridge apart.  It also had safety features unheard of at the time.  One of the biggest challenges facing any bridge design is that it has to exist in nature no matter the conditions, including wind.  Strong winds have forced many bridges, including relatively modern bridges from the 20th century, into lateral oscillations leading to collapse.  Da Vinci would have added what are known as wing walls, abutments out to the side of the bridge, steadying it during harsh conditions.  They are now common design elements of modern bridges…

He does not specify what materials he would need, but the team assumed that da Vinci was talking about stone — neither wood or brick would have been able to sustain a bridge of that size at the time.  The word “masonry” also tipped off the team to a design strategy.  Like the classic masonry bridges of ancient Rome, with which da Vinci would have been familiar, it would stand solely through the forces of physics and gravity with no need for fasteners or mortar…

“That was not a test to see if his design would work with the technology from his time,” Karly Bast says.  The model is “held together by compression only.  We wanted to really show that the forces are all being transferred within the structure.”  The crucial moment came, as it does in projects like these, with the adding of the keystone.  “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,” Bast recalls.  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 says. “This is a strong concept. It was well thought out.”  Further tests showed that the bridge could have even stood its own against earthquakes to an extent far beyond other bridges at the time.