Bridges

1. Bridges By : Lisa Runt

2. Types of Bridges Beam – the simplest type of bridge. It is made of two or more supports which hold up a beam. Arch – weight is carried outward along two paths, curving toward the ground. Suspension/Cable – the deck of a suspension bridge is hung by cables which hang from towers. The cables transfer the weight to the towers, which transfer the weight to the ground. Cantilever – two beams support another beam, which is where the deck is. The two beams must be anchored.

3. Bridge in Literature Bridge to Terebithia is a book about a two kids who go over a bridge and make up their own world.

4. Bridge in a Movie The Lovers on the Bridge is one of the most exhilarating motion pictures of the 1990s.

5. Bridge Disasters – The Tay Bridge On December 28, 1879, there was great storm with gale force winds topping 70 mph at right angles to the bridge. It was 7:15 PM when the Tay Bridge collapsed into the Firth of Tay at Dundee. A Court of Inquiry set out to determine the reason for failure. “The Court of Inquiry report concluded that, ‘The fall of the bridge was occasioned by the insufficiency of the cross bracing and its fastenings to sustain the force of the gale.’”

6. Bridge Disasters – The Quebec Bridge The Quebec Bridge Company and Phoenix Bridge Company of Pennsylvania contracted to build the Quebec Bridge over the St. Lawrence River. The project called for a cantilever bridge with a main span of 1800 feet. This would pass the Forth Bridge and take the title for the longest bridge in the world. The actual bridge weight exceeded the design by 8 million pounds. This extra stress was determined to be within tolerances and work continued. Two girders were misaligned by a couple of inches and appeared to be bent. The workers progressed without permission and the bridge failed. In the summer of 1907, the south arm of the bridge collapsed taking the lives of 76 workmen.

7. Bridge Disasters - The Tacoma-Narrows Bridge On July 1, 1940, the Tacoma Narrows Bridge in Tacoma, Washington was completed after two year of construction. It was the longest suspension bridge of its time spanning over 5939 feet with a center span of 2800 feet. This massive bridge connected the Tacoma and Gig Harbor. Relying on the shear and bending stress in the main cables, the engineers designed the bridge with a new method of calculations. This method allowed them to design a less expensive, lighter bridge. However, this design wasn't adequate in any respect.

8. Famous Bridges – Brooklyn Bridge Located in New York Spans the East River Constructed from 1869-1883

9. Famous Bridges – Forth Rail Bridge Located in Edinburgh, Scotland Spans River Forth Constructed from 1882-1889 Spans 1.5 miles

10. Famous Bridges – Sydney Harbor Bridge Located in Sydney, Australia World’s Largest Bridge

11. Physics in Bridges When forces are applied to a structure and added together, the sum of the forces is defined as a load. Two types of load engineers must consider when designing bridges are known as dead and live loads. A dead load, also known as a static load, includes the weight of the bridge or stationary objects on the bridge. A live load, also known as a dynamic load, includes objects in motion as well as natural forces such as the wind or an earthquake. Live loads are the most difficult to design for because they are always changing. It is crucial that engineers account for all types of loads when designing a bridge because the magnitude of loads will affect the material selection and possibly the type of bridge engineers choose to build. As stated above, for all forces acting on a bridge, there must be a counter force pushing or pulling in the opposite direction. These forces are defined as either compression or tension forces. A force of tension will lengthen or pull on a material while a compression force will squeeze or push a material together.