By: Harshita Singh Chauhan
The Engineering Marvels Series
Do you often find yourself marvelling at the intricately designed mammoth skyscrapers that line city skylines, or how the long suspension bridge you drove across is able to withstand the weight of so many cars at once? If you do, then the Engineering Marvel series is perfect for you!
From 160 storey buildings to bridges that span 165 kilometres (102 miles), today’s engineering minds and high-end technology have come together to create the impossible. In this series, we explore the thought processes that go behind some of the world’s finest structures and learn more about how daily phenomenon and nature have been an inspiration in many of these creations.
Image 1: Burj Khalifa, the World’s Tallest Building (for now!)
Bridge Building for Dummies
For this month’s article, I want to talk about one of the finest bridges in the world: the Charilaos Trikoupis Bridge.
Image 2: Charilaos Trikoupis Bridge
This seemingly ordinary bridge in Greece is in fact very special. Connecting the coasts of Rion and Antirion (Antirion = Opposite of Rion, pretty neat!), this bridge has significantly reduced travel time between the two towns from over forty minutes to a mere seven minutes.
Image 3: Map of Greece showing Rion and Antirion
However, building this bridge was nothing short of impossible. This region in Greece is exposed to extreme weather conditions: fast winds and frequent earthquakes, which meant that engineers couldn’t just build a regular bridge here, if not the bridge would either crumble during an earthquake or swing wildly like a pendulum due to extremely strong winds. This quirky engineering problem called for quirky solutions. Drawing inspiration from Indian incense plants, can tabs and hammocks, engineers managed to create this marvel which serves up to 30000 cars everyday!
So how on earth is:
Keep reading to find out!
Indian Incense Plant
What is the similarity between a successful couple and a stable bridge? Both have strong foundations!
Speaking of strong foundations, the Rion-Antirion bridge, like all bridges, needed one as well. But there was a problem. The sand under the greek channel is extremely fine, and tends to behave like a fluid when an earthquake hits (in scientific terms, we refer to this as soil liquefaction). As you can imagine, this could spell disaster for the bridge: if the sand under the piers were to give way during an earthquake, the piers would sink in and the bridge might collapse, just like in the houses in the gif below.
GIF 1: Demonstration of soil liquefaction (indeed, a tragedy has occurred)
To solve this, engineers decided to take inspiration from nature. Indian incense plants are known to have long roots that can be up to seven metres long. These long roots helped the plant remain stable along riverbanks. Using this as an inspiration, the engineers gave the piers “roots” as well, in the form of around 25 metre long steel rods that were to be embedded in the sand to make the pier much more stable and less susceptible to earthquakes. While you may notice that the steel rods are not connected to the base of the pier, the effect of introducing the rods is effectively similar to the role of roots in plants as it prevents soil beneath the pier from being displaced significantly.
Image 6: Setting the foundations right
Now that the piers are laid out, design engineers face yet another problem. The hills surrounding the Gulf of Corinth, where the bridge is located, turn it into a wind tunnel - air passing through the gulf can attain speeds as high as 70 miles per hour! Winds at such high speeds can make bridges sway, which is certainly not desirable.
GIF 2: Bridge Swaying due to Strong Winds
To tackle this, engineers took inspiration from sailors. Back in the day, when ships were not so advanced, ship rides were rather rough and as a result, sailors found it hard to sleep on beds in their ship. Instead, they made use of hammocks, which oscillates a lot less than the external driving force (movement of the ship). A simple illustration of this can be seen in the gif below, where the external force (the pendulum bob) simulates the movement of the earth during an earthquake (and by extension, that of a bridge deck connected directly to it). The yellow cones on the other hand are connected to the bob via a string on top and the amplitude of their oscillation is much lower.
GIF 3: Cones driven by an External Driver
Using this principle, engineers decided to suspend the deck completely from the top of the pier, and it is the only bridge in the world to do so.
Stable foundation? Check. Earthquake-proof? Check. But what happens if the very feature that helps the bridge survive tremors makes it even more vulnerable to strong winds?
The full suspension system makes the deck of the bridge more flexible, which works well to withstand earthquakes by reducing the amplitude of its oscillation. However, when faced with strong winds, this can cause the bridge to swing too much and potentially hit the piers, which can be fatal. To prevent the deck from moving during an earthquake, but only where there are strong winds, viscous dampers (to reduce lateral motion) were added to the underside of the deck. Just like how a humble can tab allows for predictable failure, a fuse in the dampers is set such that it breaks during an earthquake. This allows the deck to sway freely only when an earthquake strikes but not when it is windy! This way, the Rion-Antirion bridge is able to not just withstand winds but also earthquakes.
Isn’t it awesome to see how engineers, with their unique ideas stemming from the most bizarre situations, were able to build a bridge in the most challenging of situations? If you found this article interesting, be sure to watch out for the next article in this series, where we will be exploring some more engineering feats!
Image 2: Captcha. (n.d.). Captcha. https://bridgeinfo.net/bridge/index.php?ID=115
Image 6: Engineering Connections: Earthquake Proof Bridge (Richard Hammond) | Science Documentary. (n.d.). YouTube. https://www.youtube.com/watch?v=dQf_vE7tOlw
Image 1: Menon, L. (2020, July 20). Your guide to the 10 best spots to watch the Burj khalifa fireworks. Headout Blog. https://blog.headout.com/burj-khalifa-fireworks/
Image 3: Project. (n.d.). Project development, consulting, project management: Dorsch Group DC Asia. https://dc-asia.dorsch.de/projects/project/dproject/rion-antirion-bridge-traffic-study-greece/show/Project/?no_cache=1
GIF 1: Soil Liquefaction and Subsidence. (n.d.). YouTube. https://www.youtube.com/watch?v=-eH5fh0YEuQ
GIF 2: Tacoma Narrows Bridge Collapse "Gallopin' Gertie". (n.d.). YouTube. https://www.youtube.com/watch?v=j-zczJXSxnw
GIF 3: Barton's Pendulums Resonance and Forced Oscillations - A Level Physics Revision. (n.d.). YouTube. https://www.youtube.com/watch?v=7PMN0WwdEQA