Cable Suspended Bridges

الكبارى المعلقة

Akashi - Kaikyo Bridge Akashi - Kaikyo Bridge

JAPANENG.\ Mahmoud zaghlal

SITE MAP The Akashi Strait, which connects Osaka Bay and Harimanada, is about 4 kilometers wide. The segment spanned by the bridge has a maximum depth of 110 meters and a maximum current speed of 4.5 meters per second. The Strait has been a productive fishing area since ancient times, and is an important waterway, used by over 1,400 vessels a day. To ensure the safety of marine traffic, an international water-way 1,500 meters wide has been set by marine traffic safety law. Several severe conditions were encountered, such as strong currents, deep water in which divers were unable to explore the seabed. It was also necessary to preserve the fishing area and to ensure the safety of marine traffic. Those difficulties were conquered through investigations and technical examinations .SOIL PROFILE

3 SPAN – 2 HINGED TRUSS GIRDER

The Great Hanshin Earthquake, a great epicentral earthquake caused by an active fault, measured 8.5

magnitude on the Richter scale at 300km from this point

WATER VELOCITY

MAX RICHTER SCALE

WIND SPEED

PHYSICAL CONDITIONS

(Main Elements)

1-Foundations2-Two towers3-Two suspension cables4-Hangers5-Deck (Steel or R.C)6-Four Anchorages

SYSTEM RESISTING INTERNAL FORCES

Foundations

Tower

Crane

Inner Elevator

DAMPERS

Each tower contains damping devices to counteract deflective and torsional vibration caused by wind. Weighing about 10 tons each, 20 of the devices are distributed on the 17th, 18th, and 21st tiers of the towers.

Passive -- This is an uncontrolled damper, which requires no input power to operate. They are simple and generally low in cost but unable to adapt to changing needs. Active -- Active dampers are force generators that actively push on the structure to counteract a disturbance. They are fully controllable and require a great deal of power. Semi-Active -- Combines features of passive and active damping. Rather than push on the structure they counteract motion with a controlled resistive force to reduce motion. They are fully controllable yet require little input power. Unlike active devices they do not have the potential to go out of control and destabilize the structure. MR fluid dampers are semi-active devices that change their damping level by varying the amount of current supplied to an internal electromagnet that controls the flow of MR fluid.

Dampers are used in machines that you likely use every day, including car suspension systems and clothes washing machines.damping systems use friction to absorb some of the force from vibrations.A damping system in a building is much larger and is also designed to absorb the violent shocks of an earthquake. The size of the dampers depend on the size of the building. There are three classifications for dampening systems:

• Depending on the size of the building, there could be an array of possibly hundreds of dampers. Each damper would sit on the floor and be attached to the chevron braces that are welded into a steel cross beam. As the building begins to shake, the dampers would move back and forth to compensate for the vibration of the shock. When it's magnetized, the MR fluid increases the amount of force that the dampers can exert.

• Buildings equipped with MR fluid dampers will mitigate vibrations during an earthquake.

Note: Water Depth 60 m The foundations of the main towers transmit the 120,000 ton weight of the bridge from the main towers to the support ground. The support ground, 60 meters under water, was excavated by grab bucket dredger. Various high-tech devices, such as the Remotely Operated Vehicle System, were used to overcome the challenging conditions in the Strait, including strong currents and deep water, as well as waves that caused the grab bucket to vibrate during excavation. Ultimately, the excavation was finished within the vertical variation of +/-10 cm needed for caisson installation.

The caissons were installed using the "setting down method," which entailed manufacturing the caissons beforehand at a factory, then towing them to the site, submerging them, and finally filling them with underwater and standard concretes. The circular shape of the caissons has no directional property, and therefore makes them more stable and easier to handle in the strong currents of the Strait. A new type of underwater concrete, "underwater nondisintegration concrete," was developed for the foundations.

CASTING FOUNDATIONS UNDER WATER

TOWER & HANGERSAND BRACING SYSTEMS

HANGER

CABLE

TOWER CROSS SECTION

DECK

CABLES

CABLE300,000 KM LONG OF WIRES

Each cable is composed of 290 strands, each strand containing 127 wires made of high tensile galvanized steel

and measuring 5.23 millimeters in diameter. The strands are hexagonal in shape and factory produced beforehand, in what is known as the prefabricated strand [PS] method. One of the biggest technological advances achieved in constructing the bridge was the improvement in wire

tensile strength. Although prior to construction of this bridge the wire tensile strength was only 160 kgf/mm2, a

new wire with an increased tensile strength of 180 kgf/mm2 was developed . This slight increase in tensile strength

made it possible to use only one cable per side instead of two, reducing the weight and making construction easier.

The length of the wire used totals 300,000 kilometers, enough to circle the earth 7.5 times.

WIRES TO STRAND TO CABLE

SADDLES OVER TOWERS

SADDLE

CABLE

CABLE INSTALLATIONThe first stage of cable installation was pilot rope spanning, which was done by helicopter so as to avoid the affects of currents or interference with marine traffic. Using light-weight, high strength poly-aramid fiber rope measuring 10 mm in diameter, the pilot rope was installed over each span in succession.

CROSS SECTION IN DECK

PROFILE OF BRIDGE

STIFFENING GIRDERS 90,000 tons of steel was used in constructing the stiffening girders. Due to the tremendous size of the bridge, the wind load they sustain is greater than that of any other bridge in existence. Using high tensile strength steel for the girders made them very strong but relatively light, and therefore more economical. The stiffening girder construction, by the plane block method, began at the main towers and anchorages, where a floating crane was used to install 6 panel blocks on the towers, and 8 on anchorages. The truss members that had been assembled in panel shape at the factory were transported to the construction site, where they were erected inwards from the anchorages and from the towers.

* Wind At stiffening girders:--------------------------------------------------------------------------To reduce stiffening girder torsional vibration caused by wind, stabilizing plates were installed under the median strip of the deck. The stabilizers act to guide the wind, reducing torsional vibration by achieving a balance between pressures on the bridge lower and upper surfaces. The effect of the stabilizers was verified in large scale wind tunnel tests. Stiffening Girder Specifications .

windwind

wires

cable

saddle

ANCHORAGE DETAILS

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