Why the Great Pyramids are still standing?

The Great Pyramids at Giza, Egypt are 5000 years old. It is astounding that such old structures are still standing. This is why they are considered among the most notable ancient wonders of the world.

A common question asked by public is that how come such old structure is still standing today yet some modern structures have fallen apart.

Let us understand the engineering principle and philosophy behind these legendary structures.

The pyramids were built as tombs – the resting place of mighty pharaohs!

These pyramids are built of lime stones and granite. Effectively these are huge rocks weighing 2500 kg each on average.

From the engineering point of view, the pyramids are built using compression elements only. A modern concrete building consists of columns, beams and slabs. The columns only carry compression force. However, the beams and slabs carry both compression and tension forces.

If you take a beam, for example, which is subjected to a load on its top, the areas above the center line will experience compression where as the area below the center line will experience tension. Concrete is weak in tension so reinforced steel bars must be placed inside concrete the carry then tension force. Any bending force on any structural member will introduce both compression and tension forces.

Rocks cannot carry tension forces. They will be break if they are designed to carry tension. But, they are extremely good at carrying compression forces! The blocks in pyramids were designed to carry compression forces only. They do not experience any kind of bending force, hence no resultant tensile stress because of this.

Also, as pyramids housed the deads only (excuse the pun), there are no moving mechanisms inside them. A modern house has lots of moving parts like doors, windows (opening/closing), water flowing thru pipes etc. The act of people living inside houses causes some wear and tear.

The pyramids experienced no such wear and tear arising from its inhabitants – because they were dead anyway. However, we need to keep in mind that pyramids experienced great forces of nature in the form of erosion and vandalism by humans over thousands of years.

The other important aspect contributing their longevity is the arid weather in the desert. The lack of moisture in the atmosphere meant there were no water trapped between joints in the structure. The blocks were placed so that they kind of attached to each other like Lego. They did use some mortars though. In other parts of the world, some water would have invariably trapped inside those mortars and would have expanded causing cracks. But in arid weather, there was no such thing of water expansion – because there were no water in the first place.

So to phrase it differently, if the pyramids were built in tropical area, say inside Amazon rain forest, it would have been experienced a different kind of destructive forces like water ingress and roots from trees. In fact, this is how a more modern (comparatively) Ankor Wat temple complex got deteriorated over shorter span of time.

In spite of all these, there is no equivalent yet for the Great Pyramids.


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