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:  Britec :  2011-07-10
:  Youngjong Bridge

The Incheon International Airport Expressway was completed in December 2000, after about five years of work. The construction work was the first privately invested SOC (social overhead capital) project in Korea. Samsung Corporation was the main contractor of this project.
The two-story Youngjong Bridge, built by Samsung Corporation, lies on the expressway. The upper floor of the 4,420m-long bridge is a six-land road, while the lower floor consists of a four-lane road and a double-track railroad. As a result, this bridge is capable of handling the world's largest traffic volume. In particular, a self-anchored suspension part is situated at the center of the long bridge. The bridge heralds the advent of a three-dimensional self-anchored suspension bridge in the world. In its July issue of 2000, an internationally known engineering magazine ENR gave prominent coverage to the self-anchored suspension Youngjong Bridge. The magazine described the bridge as a success story in the category of self-anchored suspension bridges, and highly praised Korea's technology, Samsung officials say.
Features of the bridge
The Youngjong Bridge is featured with a self-anchored suspension part. Three-dimensional cables were applied to the construction of the bridge for the first time in the world. Such cables can be applied to the construction of a self-anchored suspension bridge which are 2000 meters long or more. Only when three-dimensional cables are applied, a long bridge can be built. In this regard, the completion of the Youngjong Bridge drew keen attention from civil engineers across the world.
The Youngjong Bridge is the longest self-anchored suspension bridge in the world. Unlike suspension bridges (both ends of the cables are fixed to the anchorage blocs made of concrete), the cables are supported by the body of the bridge. The bridge's self-anchored suspension part is 550 meters long, 10 meters longer than the Konohanabashi Bridge in Osaka, Japan, which was built in 1987. The adoption of three-dimensional cables and self-anchored suspension, this time, is designed to provide foreign visitors with a glimpse of the beauty of the curved eaves of traditional Korean tiled roofs. The diamond-shaped main tower comes from a similar consideration.
In addition, the bridge is capable of resisting strong winds at 65 meters per second for more than 100 years, and earthquakes with 6 on the Richter scale. The whole upper floor of the two-story bridge is set aside for vehicles. But the lower floor has a double-track railroad, in addition to a four-lane road for vehicles. In consideration of this, the Automatic Ultrasonic Test technology was applied to the construction of the bridge. It enables us to conduct a three-dimensional probe into sound waves of the bridge and record them.
New construction methods
Three kinds of unique construction methods were applied to the construction of the Youngjong Bridge, according to Samsung officials.
First, the seabed on which the bridge was built has a strong tide at 2.5 meters per second. Moreover, the difference between the rise and fall of the tide reaches 8.5 meters. Under these difficult circumstances, Samsung used the Pneumatic Caisson methods to lay the groundwork to erect pillars, since the company had to meet a tight construction schedule. The bridge should have been dedicated no later than November 2000 to meet the opening of the newly built Incheon International Airport, which was slated for 2001. The Pneumatic Caisson methods are remote-controlled excavation methods, which were implemented for the first time in Korea.
By adopting these methods, workers dug out 72 tons to 96 tons of soil per day. They worked underwater. But it felt like working on the ground, regardless of the difficult conditions. As a result, work to erect the pillars ended three months earlier than scheduled.
Second, the large bloc erection method was employed. Works to make the bridge's main tower weighing 27,000 tons, truss and others were delayed because of a lack of space to produce them. So Samsung used a 3,000-ton crane, the largest crane in the country, to implement the large bloc erection method. The 107m-high main tower was divided into three blocs (one bloc weighs about 1,200 tons), and then installed. The truss of the self-anchored suspension part was divided into eight blocs (one bloc weighs 1,200 tons. It is 70 meters long, 35 meters wide and 12 meters high on average) and then produced.
Third, Samsung employed three-dimensional Air Spinning methods with regard to the cable work for the first time in the world. The cable is made of 6,720 wire strands. One wire strand is 5.1mm in diameter. The combined length of the wire strands is equivalent to 10 round trips between Seoul and Busan and weigh 1,300 tons. NW