Verktækni - 01.08.2002, Blaðsíða 18

Verktækni - 01.08.2002, Blaðsíða 18
» Side View 3911 m, 297 m measured from water level. These are the tallest bridge towers in the world. Due to the curvature of the earth surface, the distance between the towers is 93 mm longer at top than at base. Among long-span suspension bridges (>1000 m), the majority of bridges have steel towers. Some bridges have concrete towers, like Great Belt, Runyang (1490 m; dt. 2005), Humber, Jiangyin, Tsing Ma, Höga Kusten: mainly bridges in Europe and China. Main cables and hangers The Akashi Bridge has 2 main cables, each 1122 mm in diameter, a world record. Each cable consists of 290 parall- el-wire ropes, each containing 127 high- strength wires 5,23 mm in diameter. Thus each cable contains 36'830 parallel wires, the total length of those being about 300'000 km. The wires are of special high-strength grade, ultimate tensile stength 1800 MPa (180 kgf/mm2). Thus only 2 main cables are needed, while the previous grade 1600 MPa would need 4 main cables. The 10 mm-diameter poly- aramid fiber pilot rope was carried across the strait by helicopter, a method first time used for a major suspension bridge. The wires of the cables are protected ca- refully agaist corrosion. Also the at- mosphere environment inside the cables is improved by injecting dried air into the cables. Deck and underclearance The deck of the Akashi Bridge consists of strong steel truss girders, width 35,5 m, depth 14,0 m. The effective width of the Akashi Bridge is 30,0 m and the underclearance is 65 m, while the highest underclearance among major suspension bridges (>1000 m) is 70 m of the Ponte 25 de Abril in Lisbon. The deck of the Akashi Bridge accommodates 3 + 3 lanes for motorway traffic, design speed for vehicles 100 km/h, no lanes for light traffic. Depending on loads, the max- imum displacements of the deck may vary within the following ranges: vertically 8 m upwards and 5 m downwards, horizontally 27 m each direction.There are expansion joints at anchorages and hinges at towers. Severe earthquake at Kobe The Akashi Bridge is designed for winds up to 80 m/s and also for severe earthqu- akes of 8,5 on the Richter scale. On 17th January 1995, an earthquake of 7,2 richters occurred in Kobe area and about 6000 people were killed. The epicentre of the earthquake was located close to the south end of the Akashi Bridge, several kilo- metres away from Kobe City itself. The bridge experienced a severe earthquake resistance test, as the magnitude at the bridge site was nearly 8 richters. When the earthquake occurred, the towers and the cables of the bridge were newly complet- ed, and the construction of the deck was to be commenced. Buildings and bridges collapsed even at a distance of 50 km from the Akashi Bridge. It appeared that the Akashi Bridge sur- vived with only minor damages. Because of the movement of the earth, the south tower moved 80 cm southwards, and the tops of the towers tilted 10 cm south- wards. The main span increased 80 cm and became nearly 1991 m. AIso, the south side span increased 30 cm. Accor- dingly, the total length of the suspension bridge increased 110 cm. As a result the sag of the main cables decreased by 130 cm. It is estimated that the damages would not have been this slight had the cables not been already installed. Despite the earthquake, the Akashi Bridge was completed according to the original schedule in Spring 1998.

x

Verktækni

Beinir tenglar

Ef þú vilt tengja á þennan titil, vinsamlegast notaðu þessa tengla:

Tengja á þennan titil: Verktækni
https://timarit.is/publication/957

Tengja á þetta tölublað:

Tengja á þessa síðu:

Tengja á þessa grein:

Vinsamlegast ekki tengja beint á myndir eða PDF skjöl á Tímarit.is þar sem slíkar slóðir geta breyst án fyrirvara. Notið slóðirnar hér fyrir ofan til að tengja á vefinn.