Arch Bridges Using a rectangular strip of oak-tag (manila folder), bend it into a shape of an arch. Push down as shown in the diagram. What happens? Now try this: Using the same arch, use two piles of books as abutments. • An abutment is the part of a structure that • bears the weight of an arch, • supports the end of a bridge, • or anchors the cables of a suspension bridge.
Suspension Bridges Using 2 textbooks of the same size and a piece of string, tightly tie the tops of each book to its corresponding end of string, then stand the books far enough apart so the string in-between hangs loosely. Press down on the string between the books. What happens?
Suspension Bridges Now try this: Stand two books about 10 inches apart. This time do not tie the string to the 2 standing textbooks. Put a stack of heavy books on each end of string to secure it to the table. Then pass the string over each book. Again let the string hang loosely between the standing books. Now press on the center of the string between the books. What happens? Notice how the stacks of books help to stabilize the bridge.
Beam Bridges Take a thick sponge and cut a notch out of the top and bottom of the sponge as shown, then lay the sponge on top of two piles of books. Press down on the sponge. What happens to the notches? The notch on top closed up because the top of the sponge is in compression. The notch on the bottom stretched out because the bottom of the sponge is in tension.