Mackinac Bridge
45.816388888889 - 84.7275Koordinaten: 45 ° 48 '59 "N, 84 ° 43' 39 " W
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Mackinacstraße
The Mackinac Bridge (pronounced ' mækɪnɔ ː bɹɪdʒ ), also known as the " Mighty Mac " or " Big Mac", is an all access roads eight -kilometer, four-lane road bridge that carries Interstate 75 over the Mackinacstraße. With the bridge for the first time a direct connection between the main area of the U.S. state of Michigan and its upper peninsula was created. It connects the towns of Mackinaw City on the south and Saint Ignace in the north.
The construction of a bridge had been discussed since the 1880s, but could be started only after many decades. The design of the suspension bridge finally exported comes from the American engineer David B. Steinman.
History
Early 1880s had railway companies a ferry service across the Mackinacstraße started but could not be maintained all year round. Soon after, the area became a popular holiday destination, particularly the nearby Mackinac Iceland with the 1875 created Mackinac National Park, which also houses the Fort Mackinac is located.
After the inauguration of the Brooklyn Bridge in New York, the population began to imagine that there would be a similar construction of practical use. In 1884, a shopkeeper from St. Ignace had a newspaper advertisement published with an artistically designed reprint of the Brooklyn Bridge and the headline: " Proposed bridge over the Mackinacstraße ".
On July 1, 1888, at a meeting of the directors of the Grand Hotel of Mackinac Iceland, beat Cornelius Vanderbilt II, grandson of the famous entrepreneur Cornelius Vanderbilt, the construction of a bridge across the waterway in front to extend the holiday season the hotel. He was thinking similar to this time in Scotland across the Firth of Forth Forth Bridge built on a bridge. The proposal to build a bridge was also discussed in the Parliament of Michigan, partly inspired by the construction of the Brooklyn Bridge.
Despite the recognized need for a bridge went decades without a concrete plan. 1920 suggested the Commissioner for State Highways in Michigan for the construction of a floating tunnel. At the invitation of Parliament CE Fowler presented from New York City a plan for a series of dams and bridges, starting from Cheboygan, which is 27 kilometers southeast of Mackinaw City, several islands to Saint Ignace.
In 1923, Parliament passed the State Highway Department commissioned to set up a permanent ferry. Because these but until 1928 was very expensive, commissioned the then Governor Fred Green, a feasibility study for a bridge. The Department thought the idea feasible and estimated that the cost of a bridge with two lanes plus a rail for the rail transport 32.4 million U.S. dollars would not exceed.
The Parliament of Michigan created in 1934 by the Mackinac Straits Bridge Authority to pursue the feasibility of the bridge on, and authorized this, bonds for the project to sell. The mid-1930s, the authority tried twice in vain to get money from Washington, even though they had the approval of the U.S. Army Corps of Engineers and the then U.S. President Franklin D. Roosevelt. Nevertheless, you put 1936-1940 set a route and carried out holes for a detailed geological study.
Because of World War II delayed the project. The Authority was established in 1934 and abandoned in 1947 by the Parliament, but later established again ( in June 1950). You got the order to deal with three leading specialists in conjunction and seek their advice. According to the report of the engineers of January 1951, the Authority was entrusted with the sale of 85 million U.S. dollars in bonds for bridge on April 30, 1952. A weak stock market in 1953 led to a renewed one-year delay before the bonds could be issued.
David B. Steinman was commissioned in January 1953 with the development of the project. By the end of 1953 clarified the funding and negotiated the necessary contracts. Construction finally began on May 7, 1954., The American Bridge Company and United States Steel Corporation received an order for 44 million dollars to build the steel superstructure. The construction took two and a half years and cost the lives of five workers. Time on 1 November 1957, the newly built bridge was opened to traffic. The inauguration was held to 28 June 1958 by 25. The hundred -millionth crossing took place on 25 June 1998, exactly 40 years after the inauguration of the Mackinac Bridge.
The design of the bridge was directly affected by the catastrophic failure of the first construction Tacoma Narrows Bridge, which collapsed due to instability in high winds in 1940. Three years after the disaster Steinman published a theoretical analysis of stability issues with suspension bridges. He recommended to use in future designs high rigid track support to prevent vibration of the bridge deck, and an open timber in order to reduce wind resistance. Both techniques have been incorporated in the construction of the bridge.
Description
Suspension bridge
The central building of the crossing of the Mackinacstraße is a suspension bridge with a span of 1158 m ( 3800 ft) in the main opening and each 549 m (1800 ft) in the two side openings. Differently than usual are located at the outer ends of the side openings do not anchor blocks, but only pillars with cable saddles over which the supporting cable is directed downwards to 149 meters away, the anchor blocks in which they are widely mounted beneath the platform girder. Steinman's original design, a conventional suspension bridge had provided. To save costs, he had indeed the main port unchanged, but prolonged the side openings and shifted the position of the anchor blocks further to the outside so that this 36 m long, 20 m wide and founded on bedrock concrete structures could be built closer to the shore where the bedrock has been encountered earlier. In the side view therefore differs the Mackinac Bridge with her in a wide curve outward drawn supporting cables clearly from other suspension bridges such as Ammann's George Washington Bridge with short, almost in a straight line to the anchor blocks strained supporting cables.
The road carrier is a 11.6 m high and 20.7 m (68 ft) wide truss structure, on which the 16.5 m (54 ft) wide four-lane roadway is elevated as an independent structural element. These dimensions make the move away from the design principles of the Tacoma Narrows Bridge clearly. While this had a ratio of 1:355 between its span of 853 m and the height of the roadway support of only 2.40 m, this ratio is at the Mackinac Bridge, only 1:100. In wind channel tests a timber with a wind-permeable possible side view was developed. Furthermore, the two inner tracks and the center sill of an open steel grids were made may flow through the air, so that approaches are connected to aeroelastischem flutter. The two outer lanes are each 3.7 meters wide (12 ft), the two inner lanes 3,4 m (11 ft). Footpath and railings take 0.9 m ( 3 ft ) wide on each side.
The pylons are 168.25 meters (552 ft) above the water level high. They consist of slender steel stems that are connected and stiffened by paneled timber trusses.
The suspension cable each consisting of 12580 wires were bundled and compressed air in the spinning process to parallel wire cables with 62.23 cm diameter.
The choice of color from green ( in the Steinman preferred sound) for the track support and the support cable and ivory for the towers to go back to an advertisement in the magazine Fortune in July 1954 in an artistic representation of the future bridge served as a background graphic.
The suspension bridge has a clear height of 47 m (155 ft). It is thus still slightly higher than the Ambassador Bridge. For this first bridge over waterways in the Great Lakes region above the Niagara River has a greater height than had been required for the bridge on the east coast. There, the Brooklyn Bridge had with a clear height of 135 ft (41 m) set the standard.
Access bridges and roads
In the south, a 1741 m long leads, supported at regular intervals on concrete piers steel truss bridge from the anchor block to the shore at Mackinaw City. There is a 180 m long high bridge connects, crossing a big parking lot and the North Hudson Avenue. It is a conventional reinforced concrete girder bridge on concrete piers.
In the north, a 1097 m long truss bridge connects the local anchor block with an approximately 1074 m long causeway that leads to the shore. From there, a roughly 1320 m long road through the toll station to the center of the distributor between Interstate 75 and U.S. Highway 2
Length specifications
The frequently mentioned length of the bridge of 8038 m or five miles is the distance from the center of the distributor in the north, including the road with the toll and the dam up to the abutment at the end of the concrete viaduct at North Hudson Avenue in Mackinaw City.
The steel bridge construction of the suspension bridge and the two truss bridges driveway is 5464 m ( 17926 ft ) long.
The suspension bridge is the anchor blocks including 2626 m ( 8614 ft) and between the anchor blocks 2554 m ( 8380 ft ) long. Your spans of 549 m 1158 m 549 m yield a spanning length of 2256 m.
Record length between anchorages
The span of the bridge between the pylons of 1158 m is significantly shorter than that of the Golden Gate Bridge at 1280 m. To but in order to also show a record that you chose the length including the anchor blocks of 2626 m ( 8614 ft ) to the Mackinac Bridge as "the world's longest bridge between anchorages " denote the order is longer than the Golden Gate Bridge and also longer than the western suspension bridge in the San Francisco-Oakland Bay Bridge, which is equipped with an additional anchor in the middle.
The Mackinac Bridge is still the longest bridge between two anchorages in the Western Hemisphere, but now fallen world. In 1998 she had the top spot in the Japanese Akashi Kaikyo Bridge that shall with a span of 1991 m holds the record at 3911 m total length between the anchors. The span of the Mackinac Bridge is 1158 m ( 3800 ft). This is the Mackinac Bridge, the world's fifteenth longest suspension bridge, and third longest in the U.S. after the Golden Gate Bridge and the Verrazano -Narrows Bridge.
Others
The bridge is a toll road. The speed is limited to 72 km / h (45 mph). It is not approved for cyclists and pedestrians. However, pedestrians, cyclists and their bikes can be transported for a fee with a motor vehicle over the bridge.
In October 2013 330 610 vehicles drove over the bridge.
Each year, Labor Day two lanes for participants of the Mackinac Bridge Walk will be blocked.
The bridge was taken by the American Society of Civil Engineers in the List of Historic Civil Engineering Landmarks in 2010.