Iconic Bridges Dazzle

Turkchem 26 Apr 2018 41 6 dk okuma

TURKCHEM

Golden Gate, USA

The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, a 1.6 km strait connecting San Francisco Bay and the Pacific Ocean. The bridge connects San Francisco, the northern tip of the San Francisco Peninsula, to Marin County, carrying both the strait crossing, US Route 101, and California State Route 1. The bridge is one of the most important symbols of San Francisco, California, and the United States. The American Society of Civil Engineers has declared it one of the wonders of the modern world. Many authorities describe the Golden Gate Bridge as "probably the world's most beautiful bridge, certainly the most photographed." At its opening in 1937, with a length of 1,280 meters and a total height of 227 meters, it became the world's longest and tallest suspension bridge. It retained the title of longest suspension bridge until 1964. The weight of the bridge roadway is supported by 250 pairs of vertical suspender ropes attached to two main cables. The main cables pass over two main towers and are anchored in concrete at both ends. Each cable is made of 27,572 wires. The total length of galvanized steel wire used to manufacture both main cables is estimated at 80,000 miles (130,000 km). The original color of the bridge is a reddish-orange tone known as vermilion. This color was selected in consultation with architect Irving Morrow; it complements the natural environment and increases the bridge's visibility in fog. Aesthetics was the most important reason for the rejection of the initial design by chief engineer Joseph Strauss. For this reason, the bridge construction plan was revised, and details such as lighting were added to depict the bridge's cables and towers. The bridge was originally painted with red lead primer and lead-based topcoat paint. In the mid-1960s, a program was launched to remove the original paint and repaint the bridge with zinc silicate primer and vinyl topcoats to improve corrosion protection. Since 1990, acrylic topcoats have been used due to air quality concerns. The program was completed in 1995, and currently severely worn areas are periodically inspected and repaired by 38 specialist painters.

Tower Bridge, England

Tower Bridge is a combined bascule and suspension bridge built in London between 1886 and 1894. The bridge spans the Thames River near the Tower of London and has become an iconic symbol of London. For this reason, Tower Bridge is sometimes confused with London Bridge, located approximately 0.5 miles (0.80 km) upstream. The construction process of the bridge lasted eight years. To support construction, two large cofferdams containing more than 70,000 tons of concrete were sunk into the river bed. More than 11,000 tons of steel were used for the towers and walkways. Subsequently, Cornish granite and Portland stone were laid to protect the underlying steel work and give the bridge an attractive appearance. The bridge was officially opened on 30 June 1894. Tower Bridge consists of two bridge towers connected at the upper level by two horizontal walkways designed to resist the horizontal tension forces that the suspended sections of the bridge apply to the sides of the towers. The vertical components of forces in the suspended sections and the vertical reactions of the two walkways are carried by two solid towers. The bascule pivots and operating machinery are located at the base of each tower. Before its restoration in the 2010s, the bridge's color scheme was changed to red, white, and blue in 1977 for Queen Elizabeth II's Silver Jubilee. The colors were later changed back to blue and white, the bridge's original colors. The bridge is 240 meters long, with two tower legs each 65 meters high. The 61-meter central span between the towers is divided by two equal bascule leaves that can be raised to an angle of 86 degrees to allow river traffic to pass through. The bascules, each weighing more than 1,000 tons, are counterbalanced to minimize the required force and allow raising within five minutes.

Millau Viaduct, France

Millau Viaduct is a cable-stayed bridge near Millau in southern France. Millau Viaduct is part of the A75-A71 motorway axis from Paris to Béziers and Montpellier. The construction cost was recorded at approximately EUR 394 million. The planning and design process for this remarkable structure naturally extended over an important period. In July 1996, the jury decided on a cable design with multiple spans, as proposed by the Sogelerg consortium directed by Michel Virlogeux and Norman Foster. Following construction work lasting three years, the viaduct was officially opened on 14 December 2004, with traffic flowing two days later. The structure has been continuously recognized as one of the greatest engineering achievements of all time and received the 2006 Outstanding Structure Award from the International Association for Bridge and Structural Engineering. Two important challenges were identified in the construction of the structure: crossing the Tarn River and spanning the large gap from one cliff to another. A unique solution—using seven pylons instead of the traditional two or three—overcame what seemed like an impossible task. With this pylon design, a height several meters greater than the Eiffel Tower was achieved. Renowned British architect Norman Foster was responsible for the viaduct's appearance. The structure was designed to look as delicate and transparent as possible. Each section is 342 m wide, and its columns span 75 m to 235 m above the Tarn River. Millau Viaduct's seven pylons consist of pyramidal-shaped reinforced concrete shafts, divided into an inverted V configuration, with their decks anchored and distributed with semi-harps. The project construction employed hundreds of high-pressure hydraulic cylinders to push deck spans into place, pumps, and a PC synchronized lifting system to raise auxiliary scaffolding. Interestingly, Millau Viaduct is not straight. A completely flat road spanning such a large gap could create perception difficulties for drivers. A slight curve in the design has addressed this potential problem. The curve has a 20 km range and a slight 3% gradient to improve road visibility and driver comfort.

Eshima Ohashi Bridge, Japan

Eshima Ohashi Bridge is a rigid frame bridge in Japan connecting Matsue, Shimane Prefecture and Sakaiminato, Tottori Prefecture across Lake Nakaumi. It was constructed between 1997 and 2004. Images of the bridge became widely popular on the internet because it appears very steep from a short distance, but it actually has a 6.1% gradient on the Shimane side and a 5.1% gradient on the Tottori side. This interesting and unusual bridge appears to stretch from the ground to the sky. With this characteristic, it frequently appears in Japanese television commercials. Along with its popularity, this highly functional bridge with a height of 45 meters allows even large ships to pass underneath it with ease.