The Eiffel Tower is an iron lattice tower located on the Champ de Mars in Paris. The tower was named after the engineer Gustave Eiffel, whose company designed and built the tower. Built in 1889 as the entrance arch to the 1889 World’s Fair, it was initially criticized by some of France’s leading artists and intellectuals for its design, but has become both a global icon of France and one of the most recognizable structures in the world.

The tower is the tallest structure in Paris. The tower is 324 meters tall, about the same height as an 81 story building. The material used for the design of the tower included a puddle iron structure that weighs 7,300 tons, while the entire structure, including non-metal components is approximately 10,000 tons. One of the considerations when Eiffel began to plan out the design of the structure was wind. Eiffel and his engineers, as experienced bridge builders, understood the importance of wind forces and knew that if they were going to build the tallest structure in the world they had to be certain it would withstand them. Eiffel used empirical and graphical methods accounting for the effects of wind rather than a specific mathematical formula.

The Eiffel tower also was built to accommodate tourists and others in the area. When built, the first level contained three restaurants and an Anglo-American bar which was later converted to a 250 seat theatre. On the third level there were laboratories for various experiments and a small apartment served for Gustave Eiffel to entertain guests. This apartment is now open to the public, complete with period decorations and lifelike models of Gustave and some guests. Being a very tall and well known landmark the maintenance was a large part of the design. Maintence of the tower includes applying 50 to 60 tons of paint every seven years to protect it from rust. An interesting fact is that the height of the Eiffel Tower varies by 15 cm due to temperature. More than 250 million people have visited the tower since its construction in 1889. The Eiffel Tower is the most-visited paid monument in the world and that is why it is incldued as an amazing wonder in our world.

http://en.wikipedia.org/wiki/Eiffel_Tower

http://www.engineering.com/Library/ArticlesPage/tabid/85/ArticleID/62/Eiffel-Tower.aspx

http://www.livescience.com/29391-eiffel-tower.html

The Space Shuttle Challenger disaster was one of the most horrific events in the 1980’s. It took seven astronaut’s lives and left America confused as to what went wrong. The reason for the explosion of the Challenger was a seal, called an O-ring that failed at liftoff. This then let in pressurized hot gas that leaked from within the booster. Because of the high temperatures, it singed strut connecters, which caused pieces of hardware to break down. It only took 72 seconds to absolutely demolish the Challenger. Hydrogen atoms were burning at an accelerating rate in the failed tank section combining with liquid oxygen. Once the demolition happened, pieces of the space shuttle sprinkled across the Atlantic Ocean.

After scientists looked into the disaster, they noticed what exactly went wrong. Cold weather was the sole reason to the destruction of the challenger. NASA then made the conclusion that the shuttle should have never lifted off in cold temperatures. The O-ring does not have the durability to withstand extreme temperatures. There were several delays before the lift-off at 11:38 a.m. on January 28, 1986. The delays made NASA skeptical but they furthered the launch anyways.

This disaster could have been avoided if NASA decided to fully delay the launch for another date. The early morning delays were a warning sign that the Challenger should not have launched. Another alternative to the design is that the O-ring could have been designed better to withstand various temperatures. When there is a billion dollar project and seven people’s lives on the line, it is important that everything is 100% perfect. NASA learned from their mistakes and improved future space ships.

http://en.wikipedia.org/wiki/Space_Shuttle_Challenger_disaster

http://www.history.com/topics/challenger-disaster

The Tacoma Narrows Bridge is a pair of twin suspension bridges that span the Tacoma Narrows in Pierce County, Washington. These bridges connected the city of Tacoma with the Kitsap Peninsula and carry State Route 16 over the entire strait. The Tacoma Narrows Bridge was a name applied to the original bridge which was nicknamed Galloping Gertie, which opened in July 1940. The bridge unfortunately collapsed because of aeroelastic flutter four months after it was opened.

The damage done on the bridge was crazy. During the collapse the main suspension cables were thrown violently side to side, twisted, and tossed 100 feet into the air. The cables then slipped from their respective positions in the cable saddles atop each tower. The main towers, including the bracing struts, were twisted and bent. Stress beyond the elastic limit of the metal resulted in buckling and permanent distortion. After the disaster the only value of the towers was as scrap metal.

The collapse of the 1940 Tacoma Narrows Bridge stunned everyone, especially engineers. People asked how the most modern suspension bridge of its time suffer catastrophic failure in a relatively light wind. The pivotal event in the bridge’s collapse was the change from vertical waves to the destructive twisting, torsional motion. This event was what cause the cable band to slip. When the bands slipped the bridge became imbalanced the bridge slowly began to collapse. The collapse of Galloping Gertie revealed the limitations of the deflection theory. Now, engineers no longer believe that suspension bridges needed to be stiffened only against the stress of moving vehicles and the minor effect of wind.

http://www.wsdot.wa.gov/tnbhistory/machine/machine3.htm

http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridges

http://www.eng.uwo.ca/people/esavory/tacoma_narrows_bridge_collapse.htm