Friday, November 21, 2008

Structural Engineering for Kids 2 - Shaping Up Humpty Dumpty

You may be wondering why Humpty Dumpty fell from the wall if he has legs and hands. Well this is because of his shape which is very unstable. When he sat on the wall, he is not anymore supported by his legs and a little push will make him roll and thus he fell from the wall. If Humpty Dumpty is an inverted triangle, he will be more unstable. He will stand on the tip of the triangle and he has to balance himself otherwise he'll fall. But a rectangular or upright triangle- shaped Humpty Dumpty will be difficult to be overturned even if he is not supported by his two legs since the bottom side is flat for both shapes and the center of mass is near the bottom.

Shapes play a major role in the behavior of structures. Observed that because of the stable upright triangular shape, the Pyramids of Egypt and the Eiffel Tower have remained structural wonders. In earthquake design of structures, rectangular and upright triangular shaped buildings and towers are more preferred because of their regular shape. To build tall skyscrapers like the Taipei 101, the floor area has to be reduced as it goes up. An inverted triangle is the worst type of configuration for a building because it will behave like an inverted pendulum where the inertia forces will be concentrated at the top and there is very little resistance to lateral movements. The overturning moment will be too large such that it can easily be toppled down. Irregularly shaped structures, of course, can still be built provided they are properly modelled, analyzed and designed.


  1. That's a nice idea - The Wolrd of Humpty Dumpty!

  2. I was thinking about a book by Dr. Orense wherein he used the concept of building sand castles to better understand soil properties. I think it's good idea for the next issue of Structural Engineering for Kids. What do you think?