Building stability

Do you ever wonder how tall skyscrapers like the Empire State Building, or long suspension
bridges like the Golden Gate Bridge, or huge dome roofs like the Superdome are built so
that they do not collapse under their own massive weight?  In this lesson you will see how
structural engineers decide on the optimum combination of design and materials to build
stable structures like these for the least cost.
Structural stability

"Or I'll huff and I'll puff and I'll blow your house down."  The three Little Pigs

The previous two lessons demonstrated how the structure of space contributes to the
remarkable geometric properties of regular polyhedra and the packing together of atoms in
elements and minerals.  Basically it involves building stable structures as efficiently as
possible.  Similar principles are at work in the design of man-made structures.
You have probably heard the tale of The Three Little Pigs and the big bad wolf.  The first
little pig built his house from straw, which the wolf blew down and then ate him.  The
second little pig built his house from sticks, which the wolf also blew down and then ate
him.  But the third little pig used bricks to build his house, which the wolf could not blow
down.  So the wolf entered down the chimney, fell into a pot of boiling water, and the pig
ate him!  In engineering terms the smart little pig matched the structural material's physical
properties with its intended application - being stable enough to withstand the puffs of the
big bad wolf.  The other two little pigs evidently did not anticipate this kind of load when
they designed their houses and paid for that mistake dearly.  Lives are also at stake when
an engineer designs a massive structure like a bridge or a building.  She or he must
anticipate all of the potential forces that might try to "blow the house down", so to speak,
including the unexpected ones like "wolf puffs".  Then the engineer designs the structure to
be stable, that is, not to break or fall down when it is exposed to the worst possible load
that is anticipated.
The stability of man-made structures depends on two things mainly - the strength of the
individual structural materials (e.g. straw, wood, brick), and the way that they are arranged
together to form the structure (e.g. bundled, nailed, mortared).  In Structure Matters we
showed how the atoms of crystals are arranged to give them the stability to maintain their
shape against both external and internal forces acting on them.  Without that inherent
stability elements could not have survived intact during the fiery conditions present during
the formation of the earth.  And they would not be strong enough to hold together exposed

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