Triangles Under a heavy load, a square distorts into a parallelogram. A triangle cannot be deformed without changing side lengths.
Truss Bridges The truss transfers the weight of the road deck to the piers. Rocks Village Bridge , Massachusetts Dump Road Bridge , Minnesota Sellwood Bridge, Oregon
Truss Bridges These are a few common types (notice the location of the roadway colored gray in each): Howe Kingpost Truss Deck Truss Warren Truss Pratt or Through Truss
Truss 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.
Challenge • Team of 2 create truss bridge • 30 straws and tape (straws may be cut, tape on joints only) • Height and Span: 4 in. < Height 3 in. < Width Must cover 8 in. span • Bridge will be loaded until failure Objective: Carry maximum amount of weight prior to collapse