Different bridge designs can be found throughout the world. You can find truss, arch, cable, beam, suspension and cantilever bridges in different areas. The type of bridge used largely depends on the distance it must cover and the amount of load it must bear. Geometric design is important in bridge design. Properly used, geometric figures can create extremely strong bridges. Though some bridges may use more geometric concepts than others, all bridge designs evenly distribute weight for proper bearing.
Truss bridges rely heavily on triangles. Used properly, triangles evenly distribute weight throughout the bridge. Triangles are used on the sides and sometimes even the top of the bridge. The top of a truss bridge may have an "x" design, where four triangles create enough support to bear a great deal of weight. Students can use simple wooden craft sticks to create a truss bridge strong enough for the teacher to stand on. A well-designed bridge is less about the materials and more about the design.
Arches are used to create arch bridges. According to PBS.org, "Arch bridges are one of the oldest types of bridges and have great natural strength. Instead of pushing straight down, the weight of an arch bridge is carried outward along the curve of the arch to the supports at each end." It may be a one-arch bridge, or there may be several arches side by side to create the support needed.
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Connector plates are used to help strengthen connecting points on bridges. A connector plate is most commonly shaped as either a square or a triangle. They are made of steel and bolted onto intersecting points on a bridge. The shape of the plate adds strength to these areas of the bridge. When pressure is added to the point of intersecting, the connector plate distributes the pressure. There are different-sized plates and most have a galvanized coating to help prevent rust corrosion.
Symmetry is a geometric concept that is used in bridge design. Symmetry is where one half of a figure is the mirror image of its other half. Symmetry is important in bridge design because the entire length of the bridge must be able to bear weight. An asymmetrical bridge can cause the bridge to collapse. Each arch on an arch bridge must be symmetrical. The triangles on a truss bridge must be symmetrical. Even the spacing on cable and suspension bridges must be even and symmetrical.