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You give a collection of wood logs to the multi-talented genius Leonardo da Vinci, and in a few minutes, he will assemble a bridge from them. No permanent joints, and surprisingly, the more weight on the bridge, the stronger it becomes. Da Vinci designed this self-supporting bridge for troop movement.
Let’s arrange a few wood pieces as shown. It’s clear that the pieces aren’t locking together yet. Now comes the magic. Take one more pair of wood pieces and insert them between the brown pieces. Here the pieces have achieved an interlocking. By repeating this on the other side, we’ve created the smallest Da Vinci bridge possible. This bridge can support a weight.
Now, you might wonder: what happens if I press the brown piece in the center downward? This might seem like it would create a gap and loosen the brown piece, but that’s not what happens. When you press the central piece, these green colored pieces transfer this force to the brown pieces below. This causes the side green pieces to press down, creating a friction lock with the central brown piece. This effect occurs wherever you apply force. The more force applied, the stronger the friction lock. Da Vinci’s thought process is pure genius, right? If you want to make the bridge longer, you can continue with the same assembly process.
We were able to assemble a Da Vinci bridge in less than 10 minutes. I am able to climb this bridge without much difficulty. Remember, no nails or glues in the bridge - just the interlocking due to the friction. Now let’s remove one member of this bridge and see what happens. That was a sudden collapse.
This experiment proves that every element of the Da Vinci bridge plays an equal role in keeping it strong—no over-design.
Here’s an interesting question: what happens if we keep assembling Da Vinci’s bridge for a few more steps? As shown in this animation, it forms a perfect circle. The bridge we saw earlier was actually a segment of that circle.
Now, I have a fully assembled circle. This is a self-supporting circle. Even when I apply significant force to it, nothing happens to it. I can even use it as a wheel. But, just remove one member from it…That was an explosion.
Now, let’s look at how soldiers assembled and launched this bridge in an emergency situation. During assembly, the bridge needs support across its span. These animations show the steps involved in putting it together. Once the assembly is complete, the soldiers remove the support, and the bridge becomes self-supporting. If you try to launch the bridge, you can imagine what would happen. The solution is to secure the joints with ropes. Once tied, the soldiers can lift, tilt and move the bridge to the river. They then rotate the bridge 90 degrees, and it’s launched, connecting both sides of the river. Afterward, they can remove the rope ties. The easy to destroy Da Vinci bridge is ready for use now.
There’s another method of launching this bridge, but it requires a few soldiers to cross the river first and use a ladder—not the most practical solution.
The biggest advantage of this bridge isn’t just its easy assembly but also its quick disassembly. After the bridge has been in use for a while, if the soldiers receive word that the enemy is approaching, all they have to do is pull out one piece, and the bridge is destroyed in under a minute.
Despite being easy to assemble and sturdy, why isn’t Da Vinci’s self-supporting bridge used today? Nowadays, Bailey bridges are commonly used for temporary purposes. The Bailey bridge has a modular design and was invented during World War II by British engineer Donald Bailey. The main issue with Da Vinci’s bridge is its limited span. If you want a longer span, you can’t just keep adding more pieces; that would result in a circle. The only way to extend it is by lengthening the individual pieces—essentially scaling up the entire bridge. But look at the height of this bridge—who could climb that?