Eshima Ohashi: The bridge that looks vertical

The two-lane Eshima Ohashi Bridge in Japan — dubbed as the “Rollercoaster Bridge” — is a marvel of civil engineering that puts vertigo-induced terror firmly in the driving seat.

It’s been nicknamed the ROLLER COASTER BRIDGE because of its a super steep slope and appearance of being a bridge to the sky due to optical illusion.

Eshima Ohashi Bridge is a large rigid-frame bridge that connects Matsue in the Shimane Prefecture and Sakaiminato in the Tottori Prefecture over Nakaumi lake. Built between 1997 to 2004, the bridge is also known as Betabumizaka (Acceleration Bridge) for it’s the rather steep looking slope.

This bridge is the largest rigid frame bridge in Japan, and even third-largest in the world and stretches about a mile long with a height of about 144 feet. And It has a gradient of 6.1 % on the Shimane Prefecture side and 5.1 % on the Tottori Prefecture side, making it appear like the apex of a rollercoaster. But thanks to civil engineering and expertly employed high fences, the roller coaster bridge doesn’t look that scary to drive on.

It was constructed as a bridge that straddles the bridge with a total construction cost of about 23 billion yen.

Need to build Eshima Ohashi Bridge:

Previously, a road bridge built on the Nakaura water gate on the south side connected Ejima and Sakaiminato, which could only be crossed by ship, and was used by about 14,000 vehicles a day. However, because the lock is built as a drawbridge, traffic was interrupted for about 7 to 8 minutes when the ship passed, which was an obstacle to traffic, and large vehicles of 14 tons or more could not pass.

Therefore, the Eshima Ohashi Bridge was constructed to solve the traffic problem of the Nakaura Water Gate.

Why is the Eshima Ohashi bridge so steep?

The structure was built to service two cities on the northern coast of Honshu Island. Located in Shimane Prefecture, Matsue’s town is known as the “Water City” due to its lakes and canals.

Some 12 miles further east is the relatively small city of Sakaiminato in Tottori Prefecture — the hub of western Japan’s fishing fleets. Its international seaport is vital to the country’s economy and has been trading with the outside world.

Between the two cities is the sprawling saltwater lake of Nakaumi, whose name means “middle sea.” The Eshima Ohashi Bridge was built to span Nakaumi’s waters, but there was one big problem: the height of passing ships.

In engineering, the “elegant solution” to a problem is the one that’s the most straightforward and most direct. Thus, the Eshima Ohashi Bridge was designed to climb rapidly to 144 feet, facilitating both ships and ground vehicles’ uninterrupted flow with its steep slope on both sides.

Structural Aspects of the bridge

The structural type is a PC5 span continuous hinged rigid frame box girder bridge.

The Eshima Bridge has a maximum height of 44.7 meters and a central span of 250 meters, making it the largest bridge in the Orient with a prestressed concrete rigid frame structure. It is a construction method that achieves high strength by building strength with a frame, embedding a steel wire in concrete, and applying a tightening (compressive) force to the concrete by the steel wire’s tension.

The construction of the main bridge superstructure of the Eshima Bridge was carried out by the overhanging erection method using a mobile work platform. The overhang erection method is a method of extending the pier while balancing left and right from the pier.

Construction outline:

1) Dimensions of the bridge:

• Bridge length: 660m (55m + 150m + 250m + 150m + 55m)
• Total width: Standard part 11.3m (Effective width: Sidewalk part 1.5m + Roadway part 7.5m + Sidewalk part 1.5m)
• Emergency parking zone 15.3m (effective width: sidewalk 3.0m + roadway 10.0m + sidewalk 1.5m)

2) Long large span, broad cross-section:

• The span length of 250 m between the central spans is Japan’s largest span length for a concrete girder bridge.
• The girder height of the stigma is 15.5 m, and the thickness of the lower floor slab is 2.55 m, which is a broad cross-section.
• As a PC steel material, 156 12S15.2 and 56 12S12.7 are arranged on the stigma.
• A steel pipe sheet pile with a diameter of about 31 m is used for the foundation of the main pier (the third largest in Japan).

3) Rapid construction:

The bridge was expected to be constructed by 2006, but early completion is strongly required as part of regional development in both prefectures. Therefore measures were taken to shorten construction period resulting in the opening of Eshima bridge in 2004. Some of the steps were:

• Larger mobile work platform: Regarding the construction of the bridge girder of the main bridge, the wagon used for overhanging erection has been enlarged (super-large wagon) to improve the construction capacity.
• By performing day and night construction, the block construction cycle is shortened.

Today, the bridge has become a tourism spot and draws a lot of attention from people as they like to feel the speed. Here’s a spoiler for the speed devils: the bridge’s speed limit is a crawly 40 km per hour.

The Eshima Ohashi Bridge opening promotes tourism cooperation with Yatsukacho’s Button Garden and Matsue and improves logistics efficiency in trade using Sakaiminato. Not only this, but the bridge had also made traffic in the eastern part of Shimane Prefecture smoother and had various effects such as reduction of transportation costs and shortening of transportation time.

Although it is an impressive and brilliant example of modern civil engineering, Japanese bridge-building is an ancient and sophisticated tradition.

Author: Diksha Patil

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