The Raisin and the Bridge

Questions:

If a single raisin is placed at the center span of the bridge shown above, would the weight of the raisin cause the bridge to deflect?

Tiny

What about my pet, Tiny?

If we could convince Tiny to walk to the center span of the bridge and sit, would Tiny cause the bridge to deflect?

Answers:

Yes and Yes.

Tiny weighs about 200,000 pounds. This would cause the bridge to deflect approximately one inch.

A raisin weighs about 1 gram or about .0022 pounds.

The raisin would cause the bridge to deflect about (1/200,000) x .0022 = .000000011 inches.

Not convinced? Think about this.

Tiny's weight is equivalent to the weight of 91,000,000 raisins.

A pile of 91,000,000 raisins would cause approximately the same amount of deflection as Tiny.

Imagine a pile of 91,000,000 raisins placed at the center span of the bridge.

What would happen if you removed the pile of raisins - one raisin at a time?

Definitions:

Deflect - to bend downward or sag due to the applied load.

Tiny is a Diplodocus dinosaur.