Suspension bridges have been in existence since ancient times and evolved in different civilisations with no relationship between them. They may have developed initially from having a single cable with a basket suspended from it crossing a valley. It may then have progressed to three cables, one for walking on and two for handrails. Many primitive forms of suspension bridge are still in use today e.g. isolated areas in Nepal.
Suspension bridge, bridge with overhead cables supporting its roadway. One of the oldest of engineering forms, suspension bridges were constructed by primitive peoples using vines for cables and mounting the roadway directly on the cables. A much stronger type was introduced in India about the 4th century ad that used cables of plaited bamboo and later of iron chain, with the roadway suspended.
Common Bridge Types
The designer of a railroad bridge must allow for forces that result from the concentrated impact that occurs as a train moves onto the bridge; the pounding of wheels, the sidesway of the train, and the drag or push effect as a train is…
Build a Bridge
Take a flat eraser or a small sponge and slice a shallow notch across the top and bottom. Create a beam bridge by supporting each end of the eraser or sponge with a stack of books. Press down on the center of the bridge. What happens to the top and bottom notches? Notice how the top notch squeezes together in compression, while the bottom notch spreads apart under tension.
Bridge Types: Suspension Bridge Spans, Section A-A; Cantilever Truss Spans, Section B-B; Through Truss Spans, Section C-C; Deck Truss Spans, Section D-D – San Francisco Oakland Bay Bridge, Spanning San Francisco Bay, San Francisco, San Francisco County, CA
Suspension bridges are the longest-spanning bridges in the world. Prior to the record set by the Golden Gate Bridge in 1937, 4,200 ft (1,280 m), the longest-spanning bridge in the world was the George Washington Bridge, with a span of 3,500 ft (1,067 m). Today, the longest-spanning bridge in the world is the Akashi Kaikyo Bridge in Japan, with a span of 6,352 ft (1,991 m).
The Severn Bridge (Fig. 15.13d) employs a 10-ft-deep torsion-resisting box girder to support an orthotropic-plate deck. The deck plate is stiffened by steel trough shapes, and the remaining plates, by flat-bulb stiffeners. The box was faired to achieve the best aerodynamic characteristics.
As a journalist and editor for several years, Laurie Brenner has covered many topics in her writings, but science is one of her first loves. Her stint as Manager of the California State Mining and Mineral Museum in California’s gold country served to deepen her interest in science which she now fulfills by writing for online science websites. Brenner is also a published sci-fi author. She graduated from San Diego’s Coleman College in 1972.
Bridges come in many shapes and sizes. When you consider the types of materials used, the style of construction and the main use of the crossing, you find that bridges can take many forms. Bridges can be simple wooden beams over small streams or massive steel and concrete suspension structures crossing miles of open water and shipping channels. The best-known bridges in the Portland area span the Willamette and Columbia rivers, but there are also smaller structures that cross the Sandy River, Johnson Creek, Beaver Creek and other waterways, as well as roads, highways and railroads.