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How
Bridges are Used
All bridges are used for something. Real bridges are usually
used to help something (water, people, cars or trains) cross a valley.
Before these bridges are built, the architect and builder must
understand details like where the bridge will be placed, how much
weight it must support and what it should be made of. Our bridge
was similar. It was used to compete in a contest. So we
will start by looking at how this contest tested bridges.
How our Bridge will be Tested
A picture of a competition tester holding our bridge is shown below.
Let's discuss the pieces of this test setup.
Support
Blocks
Starting at the bottom,
the tester has two support blocks. These hold up the corners of
the bridge. It is important to note that these blocks are not
fastened to the floor. In fact, they slide quite easily so that
they can be adjusted to hold bridges of
different lengths.
Bridge
On top of the blocks is the bridge. One important point is
that the bridge was not allowed to be any taller than 8 inches.
In addition, the bridge is not allowed to weigh more than 150 grams
(5.29 ounces).
The bridge has no roadbed or walkways, since that is not required, and
would just add weight.
Pressure Plate
On top of the bridge is a
rigid
18 inch wide pressure plate. This pressure plate is used to
hold weights, which are Olympic-style free weights.
Support
Pole
In order to
make sure the weights don't fall sideways, the base of the tester has
a pole that passes through the pressure plate and weight plates.
Calculating the Score
Our contest scored bridges
using the following formula:
(Distance
between the support blocks - 19) x weight supported
Our bridge
was 36 inches long. If we needed a quarter inch on each side to
stay on the support blocks, the "Distance between the support blocks" would be
measured as 35 1/2 inches. If
we held 305 pounds (295 pounds of weights plus a 10 pound pressure
plate), our score would be (35.5 - 19) x 305 or 5032.5.
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