Earthquake-Resistant Mystery

zyx066 (72)in #science • 5 years ago

Why do buildings fall down when an earthquake occurs? This might seem a silly question, but scientists and engineers are hard at work to find ways to resist nature's immense forces. Maybe they should take a look at the ancient megalithic structures that are found all over the world, and have withstood those forces for hundreds and thousands of years...

_{Twelve-angled stone in the Hatun Rumiyoc street of Cusco, is an example of Inca masonry - source: Wikipedia}

Not too long ago I stumbled upon a video on YouTube about Nikola Tesla that briefly discussed his famous "Earthquake Machine" or Tesla's oscillator;

Tesla's electro-mechanical oscillator is a steam-powered electric generator patented by Nikola Tesla in 1893. Later in life Tesla claimed one version of the oscillator caused an earthquake in New York City in 1898, gaining it the popular culture title "Tesla's earthquake machine".
_{source: Wikipedia}

Although I'm not an expert whatsoever on the subject, I know that part of an earthquake's destructive power comes from the phenomenon of resonance or, more specifically, mechanical resonance and the resonant frequency of a structure. The enormous forces that can be unleashed by a simple thing as resonance, are illustrated perfectly by the destruction of the Tacoma Narrows Bridge in 1940; just watch the video if you've never seen this before, to see a sturdy bridge waving in the wind as if it was a silk ribbon, as well as a short explanation of how the structure succumbed to the accumulating forces of resonance:

_{Why the Tacoma Narrows Bridge Collapsed}

Earthquakes are caused when masses of rock in Earth's crust slip and slide against one another, something that happens mostly in certain regions, along fault lines. The vibrations propagate through the crust as seismic waves that translate into vertical as well as horizontal movement of the ground. Buildings don't collapse due to the vertical movement, as they're built to withstand the vertical force of gravity; it's the horizontal movement that breaks the structure, especially when the frequency of that motion is the same as the structure's resonant frequency:

All buildings have a natural period, or resonance, which is the number of seconds it takes for the building to naturally vibrate back and forth. The ground also has a specific resonant frequency. Hard bedrock has higher frequencies softer sediments. If the period of ground motion matches the natural resonance of a building, it will undergo the largest oscillations possible and suffer the greatest damage.
_{source: IRIS}

Modern buildings have two traits that are absent in the ancient buildings that stood the test of time: the bricks used are regularly shaped and spaced, and they are held together with cement. The use of repeated patterns in the stacking of the bricks ensures that these buildings have a resonant frequency; ancient buildings that have stood for thousands of years, found in Egypt, the far East and South America, all use megalithic stones of irregular shape. These stones are not held together with mortar, but were shaped so precisely that they fit together like pieces in a jigsaw puzzle. In the Inca ruins found in Mexico and South America it's clearly visible that older structures use polygonal masonry as shown in the cover picture, while more recent architecture is made with regularly shaped bricks;

According to official figures, 1,821 Mexican historical monuments suffered some sort of structural damage in the earthquakes that hit Mexico in September 2017, 242 of these being severe. Intriguingly though, THE OLDER THE BUILDING THE LESS DAMAGE IT SUFFERED. In fact, only FIVE ancient archaeological sites suffered, and these only from minor damage. As far as we know, not a single pre-Hispanic construction has ever collapsed in an earthquake or hurricane.
_{source: Mexicolore}

We're starting to catch on though as evidenced by this 2014 article: Ancient Incans Earthquake Proof Walls Inspire These 3-D Printed Modern Structures. Of course, the use of asymmetrical structures and polygonal masonry are not the only things to be learned or to be considered when building structures that can withstand the diverse forces of nature, but I'm sure we can learn a lot by studying the ancient civilizations; it's still a mystery how they were able to move, cut and shape these rocks, so there's still plenty to be uncovered...

_{Lost Ancient Civilizations...In the Middle of Nowhere - The Sumerians & Mesopotamia}

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