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Seven Wonders of the Modern World

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Construction History

Many lists have been composed of architectural monuments both past and present. In recognition of the greatest civil engineering and construction achievements of the 20th century, however, the American Society of Civil Engineers has designated the following architectural and construction landmarks as the Seven Wonders of the Modern World.


[edit] Empire State Building

Empire State Building
The Empire State Building is a 102-story Art Deco style building situated in central New York City. At 1,250 feet (381 m) high,[1] it is perhaps one of the best-known skyscrapers in the world and remained one of the tallest up until 40 years ago when the first World Trade Center was built in 1972. However, since the attacks of 9/11, the Empire State Building is once again the tallest building gracing the New York City skyline.[2]

The building was designed by the architectural firm Shreve, Lamb and Harmon and was built by Starret Brothers & Eken.[3] What was perhaps one of the more remarkable feats in the construction of the Empire State Building was not its height, but the speed at which this building was actually erected—one year and 45 days without any overtime. A workforce of up to 3,400 workers was employed in the construction during peak periods. Total construction equaled approximately seven million man-hours.[4] Building materials included Indiana limestone and granite, aluminum, chrome nickel steel, and marble imported from Europe.

Construction began in March 1930 and finished in May 1931. Ironworkers set a hectic pace riveting the building’s 58,000-ton frame together in 23 weeks. Masons finished the exterior of the building in eight months. Plumbers laid 51 miles (82 km) of pipe and electricians installed 17 million feet (5.2 million m) of telephone wire.[5] The precision with which the Empire State was so easily erected and constructed set a precedent in the construction industry for tall building projects.

[edit] CN Tower

CN Tower
Located in Toronto, Canada, the CN Tower is the world’s tallest freestanding structure on land. At a height of 1,815 feet or around one-third of a mile high (553 m) it is three times the size of its cousin, the Seattle Space Needle, and is as heavy as 23, 214 elephants.[6]

Foundation work on this structure began in 1973 with giant backhoes excavating more than 62,000 tons of earth and shale from along the shorelines of Lake Ontario. Next pre-stressed concrete and reinforced steel formed the base frame arranged in a Y-shaped pattern measuring 22 inches (56 cm) thick. This part of the construction only took four months to complete.[7]

The actual construction of the tower composed primarily of concrete presented a huge challenge because the actual height had never been met by a technique of poured concrete. To overcome this problem, engineers prepared a mold called a "slip form." Concrete was continually poured for 24 hours a day, five days a week. As the concrete hardened the mold moved upward by means of a ring of hydraulic jacks. The slip form, ascending, decreased in girth, and this gave the tower its unique cylinder-like shape.

At the 1,100-foot (335-m) mark sits the Skypod. The seven-story structure houses two observation decks, a restaurant, nightclub, and broadcasting equipment. Anchored by 12 steel and wooden brackets, the Skypod was built on ground and then pushed up the tower and put into place by 45 hydraulic jacks. Today, visitors can reach the observation decks via high-speed glass elevators who take-off simulating a jet taking off. A glass floor on the observation deck gives visitors a viewpoint of looking 1,122 feet (342 m) down to the ground.

One unique aspect of the CN Tower is that is was also constructed with a pair of 10-ton counter weights attached to a mast or antennae to prevent the tower from swaying in the wind. The tower’s 335-foot (102-m) communication mast was installed on the very top of the tower using a helicopter.

The premise to build the tower in the first place was the fact that Toronto’s skyline was rising and, as a result, signals sent from conventional transmission towers were being bounced or interrupted by the city’s skyscrapers. Today, 16 of Toronto’s media signals are transmitted from the tower.

The CN Tower, completed in 1975, was relatively inexpensive compared to other modern wonder construction projects costing only $57 million dollars to build.

[edit] Golden Gate Bridge

Golden Gate Bridge
Connecting San Francisco to Marin County, the Golden Gate Bridge was noted for being the world’s longest suspension bridge but has since lost that title.

So many people thought the building of the bridge was impossible that the Golden Gate became known as the “Bridge that could not be built.” The vision for such a bridge with wide spans was the vision of an engineer by the name of Joseph Baerman Strauss. Attempts to build the bridge began as early as 1928. Completed in 1937, the bridge only took a little over four years to build at a total cost $35 million.

The bridge’s deck spans a total of 1.2 miles (1.9 km) and is held together by two giant 746-foot (227-m) towers with cables each a yard thick. Each cable contains a total of 80,000 miles (128,747 km) of steel wire—enough to circle the equator three times over. Such cables are the largest cables to ever support a bridge.[8] The bridge’s distinguishable orange color was selected to blend the bridge in with the surrounding landscape.

The amount of concrete used to actually cement the bridge to the ocean floor was enough to pave a five-foot (1.5-m) wide sidewalk from San Francisco to New York.[9] The original design of the bridge however was not meant to withstand earthquakes. If the bridge was hit by an earthquake today it would cause considerable damage and possibly close down the bridge altogether. In fact, supercomputers are being used to simulate a possible earthquake’s effects on the bridge.[10]

A five-year plan to retrofit the Golden Gate Bridge to make it earthquake proof is in the works. Several areas are being targeted to strengthen the bridge including work on the structural steel, the approach viaducts, concrete pylons and anchorage houses. The cable saddles on top of the bridge also need to be reinforced and the steel tower shafts and struts will be upgraded.[11]

[edit] Netherlands North Sea Protection Works

View from the 31km Enclosed Dam "Afsluitdijk"
For centuries, the Dutch have fought to save the Netherlands from flooding through the building of dams, floodgates, dykes, or barriers of some kind as the country rests below sea level and its land mass is actually sinking.[12] The Netherlands North Sea Protection Works was one significant project in this ongoing battle. The first portion of the project consisted of building a 19-mile (31-km) long enclosed dam between 1927 and 1932 in the large, coastal tidal inlet known as Zuiderzee, an area particularly prone to flooding. The second step was the Delta project where the Rhine and Meuse rivers meet and break into a delta in the southeastern part of the country.[13]

The construction of the Zuiderzee dam was accomplished using mostly traditional materials. Workers in 1923 began by laying down boulder clay in parallel layers and then filled in the space in between with sand, stones, and handmade mattresses made from brushwood. To ward off erosion, larger sized mattresses with chains and stones were sunk into the estuary channels. The main dam ended up being 300 feet (91 m) wide and 25 feet (7.62 m) high and dredgers, cranes, tugboats, and barges were all involved in the construction process.[14]

The building of the Delta Works occurred after 1953 when the Netherlands was hit by a fierce North Sea storm that broke through dykes and seawalls flooding the country and killing livestock in addition to 1,835 people and forcing the evacuation of 70,000 more.[15] To prevent such a calamity from occurring ever again, the Dutch devised a flood defense system called the Delta Works. The final plan included the damming of four estuaries in the middle of the delta but still leaving open channels to Rotterdam in the north and Antwerp, Belgium, in the south.

The most complicated part of construction project involved building a two-mile (3.2-km) surge moveable barrier in the Oosterschelde estuaries that had tall gates fashioned between massive concrete piers.[16] The project involved building up islands on sandbars within the estuaries and creating work harbors, sites, and material yards on them. A dam was also built between two of the islands to form three separate channels in the estuaries that would each receive a section of the surge barrier.[17]

The barrier included 65 concrete piers that each weighed 18,000 tons, each supported by steel gates weighing 300 to 500 tons. Each pier and corresponding mechanism was constructed on the makeshift islands before being lifted into its precise position in the estuary. The equipment needed to achieve such a magnanimous task had to actually be invented. No machinery existed in the world at the time to carry out the work. Similar to Zuiderzee, modern mattresses, fabricated of layers of sand and gravel and covered with a special space age fabric, were used to stabilize the ocean floor.[18]

The project was finally completed in 1986, but the building of a barrier that protects Rotterdam’s port was since undertaken in 1997. One American trade journal described the scale and breadth of sophistication of the project as one that “approaches the Great Wall of China.”[19]

[edit] Itaipu Dam

Itaipu Dam
Built between 1975 and 1991, the Itaipu hydroelectric power plant took 16 years to complete and is the largest development of its kind in the world. Representing the efforts and milestone achievement of two neighboring countries, Brazil and Paraguay, the Itaipu Dam connects the cities of Foz deo Igiaci, Brazil with Ciudad del Este in Paraguay. The dam is comprised of a series of different types of dams spanning a total distance of 25,407 feet (7,744 m) with a crest elevation of 738 feet (225 m).[20] The main dam, as high as a 65-story building, was constructed of hollow concrete with flanked wings comprised of earth rock fill.[21]

During the first stages of construction workers had to actually change the course of the seventh largest river in the world. This involved excavating and removing 50 million tons of earth and rock to dig a 1.3-mile (2.1-km) bypass.[22] The dam deployed the use of more than 15 times the volume of concrete in its construction than was used in the building of the Channel Tunnel between France and England or in the building of the Hoover Dam fives times over.[23] The amount of steel and iron used in the construction of the Dam’s structure was comparable to building 300 Eiffel Towers.[24]

Perhaps the most impressive part of the Itaipu Dam is its powerhouse, a single building half a mile (0.8 km) long and submersed half underwater, containing 18 hydroelectric generators each 53 feet (16 m) across with the capacity to generate 12,600 megawatts, which is enough to power most of California.[25]

The scope of the project is best demonstrated in the fact that in 1995, the dam supplied 25 percent of Brazil’s energy supply and about 78 percent in Paraguay.[26]

[edit] Channel Tunnel

Entering a shuttle train in the Chunnel
The Channel Tunnel, or Chunnel, as it is often referred to, links France to Britain and is comprised of three interconnected concrete tunnels that measure 31 miles (50 km) long, of which 23 miles (37 km) are located directly under the English Channel[27] at an average depth of 150 feet (46 m) below the seabed[28]. Two high-speed rail tunnels each with a diameter of 25 feet (7.6 m) are adjoined to a smaller central service tunnel measuring 16 feet (4.8 m) in diameter.[29] Construction of the tunnel started with the signing of a treaty in 1986 and ended in 1994 when the tunnel was opened to the public.

The construction of the tunnel entailed drilling through the chalk marl strata under the English Channel using tunnel-boring machines. In total it took three years to drill from France to Britain and 85 percent of the tunnel was drilled and constructed in the chalk marl. A huge undertaking, 13,000 workers were employed in constructing the tunnel.[30]

Eurotunnel, who signed a 55-year concession after the tunnel’s completion, currently operates the tunnel. The company has experienced financial difficulty ever since the tunnel’s opening, as digging the tunnels proved to me more expensive than first anticipated and traffic levels have been substantially lower than forecasted. Construction of the tunnel cost an estimated $15 billion dollars.[31]

[edit] Panama Canal

Panama Canal
Pegged as one of civil engineering’s greatest triumphs, the Panama Canal cuts across the Isthmus of Panama connecting the Atlantic Ocean via the Caribbean Sea and Pacific Ocean. The canal is approximately 40 miles (64 km) long from shore to shore and 51 miles (82 km) long between each of its channel entrances and has a minimum depth of 41 feet (12.5 m).[32]

The building of the canal was first undertaken in 1880 by the French and proved to be no easy task. After 20 years of attempting to construct the canal under the direction of Ferdinand de Lesseps, the French were defeated by disease and financial problems.

In 1903, the United States made a second attempt when they signed a treaty with Panama to resume with the canal’s construction. The massive project took 10 years to finish and cost $387 million at the time.[33] The project was led by such visionaries as John F. Stevens and Col. George W. Goethals and Col. William C. Gorgas.[34]

A total of 42,000 workers dredged, blasted and excavated from Colon to Balboa moving enough earth to bury the entire island of Manhattan to a staggering depth of 12 feet (4 m) or enough to build a 16-foot (5-m) tunnel to the middle of the Earth.[35]

Construction of the Panama Canal also posed a series of engineering, sanitation and organizational problems for it was the largest dam on earth to be built in its day. No dam with such massive canal locks and large swinging gates had ever been constructed of such proportion and it set a precedent. After it was completed the United States invested an additional US$3 billion in the Canal enterprise.[36]

[edit] References