Bridge Design Presentation Blog Post

Leonardo Da Vinci designed multiple bridges in his career, each influencing the modern way of designing bridges.

Self-supporting bridge:

Between 1482 and 1499, DaVinci worked in Milan military engineer for his army in the fight against the French. During his first few years working in Milan, Leonardo designed many of the bridges and structures, including several of the bridges being examined here. Like modern engineers, Leonardo became “employed in defense industries in times of real or threatened war” (Moon 38). Leonardo also described his designs as works of beauty, reflecting how “engineers then and now often look at a new creation with a sense of beauty and awe, independent of the moral use of the new technology” (Moon 39).

The first bridge is the self-supporting bridge. This bridge could be built in minutes and be built without fasteners or joints, relying only on the compressive forces on the beams as they crisscrossed each other. The greater the pressure between beams, the greater the stability. Although the bridge was never really used much, it was eventually replaced with more advanced models of this bridge type. This did start a trend as this is on of the first recorded movable bridges. The most common of this type now is the Bailey bridge design (used by the British during WWII), but this was definitely a step towards improving the temporary military bridges. Like many of the other bridges discussed here, it also uses what becomes the foundation of civil engineering by applying compressive forces to its advantage between beams (thus the self-supporting part). It is used to this day in many fairs, parades, and footbridges (such as the one in Morsø, Denmark). It is also used in some classrooms as an easy project to do introduce students to static forces and civil engineering, using popsicle sticks as the beams.

Double decker bridge:

This bridge was designed with the intent to limit the overcrowding and unhealthy streets of medieval towns, where animals often shared the streets with pedestrians. This design was presented in Manuscript B and is closely associated with Da Vinci’s urban studies that he undertook. The purpose of the studies was to improve medieval city layouts and to break down the walls and to have a “space [that] is continuous and infinite rather than discontinuous and finite” (Panofsky 128). Leonardo wished to break from “the medieval space: the space of emplacement” (Foucault 22). The bridge was designed to fulfill Leonardo’s town planning requirements of a utopia of a “city on two levels, with the upper streets 6 braccia higher than the lower ones” (Schofield). The effect of such designs is clearly present even to today. Many bridges are double decker, most notably many of Chicago’s bridges (Chicago’s trucks and delivery vehicles go through the multilevel streets of Chicago, running unbeknownst to the majority of the public). Other famous examples include the Oakland Bay Bridge in San Francisco and Oakland, the George Washington Bridge in New York City (1 of 5 double decker bridges in New York City), and the Fort Pitt Bridge in Pittsburg. Most of these examples make use of many other bridge designs, but it is clear of the effect of Da Vinci’s double decker design on the world of civil engineering as bridges made up to today still apply this technique to sort traffic in a city.

Swing bridge:

As part of his military career under Duke Sforza of Milan, Leonardo designed this bridge, which can swing out from one end of an embankment to the other, allowing boats to pass through or to cut off an end of the canal or river. Its ability to swing away was useful for the military in that it kept enemies one side of the river. It was meant to be a temporary bridge. This bridge used a counterweight to make the turns and uses several physics principals outlined in Leonardo’s “De Ponderibus.” Leonardo worked with balance to create this bridge.

Its modern applications can be seen in some swing bridges that exist around the world, such as one in Okeechobee Waterway, Florida.  These versions are not the same as what was proposed by Da Vinci and are significantly different in look as well as the mechanism for turning. Most modern swing bridges have a single pivot not on any single bank, but as the pier in the center of the bridge and uses no counterweights.

The use of kinematics in the bridge design and the many simple machines to make it work (such as screws) and more complex machines (such as the gear train in the bridge). Using these simple machines, as a modern engineer would, Leonardo creates this bridge. Leonardo also uses “the concept of invariant geometric relationships that are preserved in machine motions when the dimensions, materials and application of the machine or mechanism change” (Moon 78) when designing the geometry of this bridge.

Arched bridge:

After coming to Venice in 1499, Leonardo heard from some Turkish merchants about a bid from the Sultan of the Ottoman Empire for a new bridge to connect Istanbul to Galata across the Golden Horn. In 1502, Leonardo DaVinci submitted a design for such a bridge to Sultan Bayezid II. Leonardo also proposed a cable bridge across the Bosphorus Strait when submitting the design. What Leonardo failed to include was instructions for how to build it, resulting in it never being selected and built.

If it had been built, it would have been the longest in the world, but its true legacy is in the geometry used by the bridge. Leonardo used multiple geometries, such as the parabolic curve, pressed bow, and keystone arch to stabilize the bridge despite not having support beams common in Roman and medieval bridges. The flattened curve that Leonardo used is more akin to most bridges these days that have a greater span between piers than the more circular arches of Roman bridges. How Leonardo designed this bridge became the basis of not just its legacy, but how civil engineering is approached as a whole.

The key to this arched bridge’s success was its use of the stones natural forces to hold itself together. In particular, it uses compression to hold itself together. Civil engineering is based heavily on the idea of statics, which uses compressive forces, and using mathematical methods to balance loads and effectively use the forces. Instead of just piling on more resources and making a big bridge, Da Vinci was using these forces to his advantage ahead of when most bridges were engineered to do be effective and efficient. 

A 1:500 scale model (32 inches long) of the bridge was made in October 2019 by engineers at MIT when they decided to test DaVinci’s bridge designs. Stone, without mortar, was used to create the model in what the MIT engineers assumed would be used at the time. Based on the model and testing data, it was concluded that the design would have worked and would have been capable of surviving even earthquakes. The engineers do not know how much of it was intentional and how much was pure coincidence of his choice, but the compressions and forces of the bridge make its design work.

The difference from today is that engineers today would need to show how this bridge would be stable with math and explain its building methods, but the ideas behind translate well into the modern world. An example of this is in Norway. The bridge design was used as inspiration for the Vebjørn Sand Da Vinci bridge near Oslo, Norway. It is a pedestrian bridge but has led to development of a global project to create pedestrian footpaths and support local artists.

For each of these bridges, Leonardo used his advanced knowledge of geometry to create supportive structures. Leonardo realized that “mathematics was the key to turning observations into theories… the language that nature used to write her laws” (Isaacson 200). Modern engineering is entirely based on these geometries and mathematics.

Leonardo designed many bridges, but these four examples give a good example of the main ones. The most applicable of them is the double decker bridge and the arched bridge, which have many modern applications (the double decker has formed its own category of bridges which makes up the many of the bridges in Manhattan, Pittsburg, Chicago, and across much of the developed world). Although Leonardo’s bridges may have flaws in some of their physics and althoguh many were never implemented, their use of compression, forces, geometry, and math to support themselves is akin to the methods used by modern civil engineers.

Links to COVE resources also by Blake Hakimian:

https://editions.covecollective.org/chronologies/self-supporting-bridge-designs

https://editions.covecollective.org/chronologies/da-vincis-golden-horn-bridge-design

 

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