Honshu-Shikoku Bridges: Shin-Onomichi Bridges

On the other end of the Nishi-Seto Expressway are the Onomichi and Shin-Onomichi Bridges. They cross the Onomichi-Suido Strait and connect Honshu to Mukaishima Island.

The Onomichi Bridge (on the right) was built in 1968 and was the first modern cable-stayed bridge in Japan. Ownership transfered to the Honshu Shikoku Expressway in 1988.

Because the Onomichi Bridge had only two lanes, the new Shin-Onomichi Bridge was begun in 1993 and completed in 1999. It has two single-legged towers and it was designed not to disturb the aerodynamic stability of the older bridge. Cranes were positioned at the ends of the deck farthest from each tower to lift the steel box girder segments into place.

Both bridges are strange mixtures of reinforced concrete and structural steel. The older bridge is completely steel except for the bottom of the towers. The new bridge has a steel superstructure supported by reinforced concrete towers.

Honshu-Shikoku Bridges: Shin-Onomichi Bridges by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Honshu-Shikoku Bridges: Kurushima Bridge (2)

Bridge building can be a dangerous profession. There were 27 deaths building the Brooklyn Bridge including the death of the designer, John Roebling. There were 16 deaths building the Sydney Harbor Bridge.

The Kurushima Bridge was designed so that some of the back spans (spans 6, 7, and 9) were supported on piers rather than from the suspension cables. These spans were incrementally launched from the anchorages onto temporary steel platforms. A week before we visited the bridge, they were dismantling a platform when it suddenly slipped from it's cables, sending seven workers to their death. After the accident, the platform lowering system was replaced using ground-based cranes.

Unfortunately, it sometimes takes an accident before improvements can be made. A safety commission conducted a study of the accident and made recommendations to improve the safety of this widely used incremental deck launching system.

Although bridge construction remains a dangerous profession (about 60 deaths per 100,000 workers) it is eclipsed by pilots (70 deaths per 100,000 workers), fishermen (71 deaths per 100,000 workers), and loggers (118 deaths per 100,000 workers).

Honshu-Shikoku Bridges: Kurushima Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Honshu-Shikoku Bridges: Kurushima Bridge (1)

The rest of the bridges on the Honshu-Shikoku Expressway were in various stages of construction when I went on my tour in 1998.

Like the previously studied Ohmishima and Tatara Bridges, the Kurushima Bridge is part of the Nishi-Seto Expressway. It is the westernmost bridge and connects Shikoku to Oshima Island across Kurushima Strait in the Inland Sea. I say bridge, but its really three suspension bridges with four anchorages and six towers. In total, it's the world's longest suspension bridge at 4015 m (13173 ft). It's similar in construction to the west spans of the San Francisco-Oakland Bay Bridge, which has four towers and a third anchorage in the middle of the bridge.

Because of occasional rough seas and to protect the waters in the Kurushima Strait, several of the towers have energy absorbing devices to protect them and ships that may possibly collide with the towers. This has become a heated issue, especially after single hull oil tankers collide with bridges. Bridge owners are usually blamed for the resulting oil spill, even when the shipping channel under the bridge is wider than 600 m. In any event, the use of energy absorbing devices is suppose to prevent ship damage, although it is likely that a tanker going at 16.5 knots (the speed of the Exxon Valdez) would be seriously damaged by a stationary object, with or without the use of energy absorbing devices.

Honshu-Shikoku Bridges: Kurushima Bridge (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Honshu-Shikoku Bridges: Tatara Bridge (3)

A last look at the Tatara Bridge. The Honshu-Shikoku Bridge Authority kindly took me on a boat trip in 1998 to look at construction of their expressway. The Tatara Bridge was complete except for some final work on the deck. It was a rainy day and clouds had descended to the tops of the towers.

The main span of the Tatara Bridge is a 890 m steel box girder. The side spans are 270 m and 320 m long and are prestressed concrete box girders at their ends to balance the weight. More information on fabrication of the bridge is provided by Uesugi Hideo and information on the erection of the bridge is provided by Satou Yoshyuki.

Honshu-Shikoku Bridges: Tatara Bridge (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Honshu-Shikoku Bridges: Tatara Bridge (2)

Private corporations own, maintain, and collect toll revenue on most of the expressways in Japan. The Hanshin Expressway Corporation owns a dozen expressways in the Kansai region including the Wangan Expressway along Osaka Bay. The Honshu-Shikoku Bridge Expressway Company owns three expressways that connect Honshu to Shikoku. This includes the westernmost Nishi-Seto Expressway (National Highway 317). The expressway is 46.6 km long and includes nine long-span bridges that connect seven islands. We looked at the Ohmishima Bridge on the Nishi-Seto-Expressway two days ago. Just north is the Tatara Bridge, which had the longest main span (890 m) of any cable-stayed bridge when it was built in 1999. We also studied this bridge before (on February 8, 2009).

It crosses over the Tatara Strait between Ikuchijima and Ohmishima Islands. It was originally planned to be a suspension bridge, but advances in cable-stayed technology eventually made this bridge a more economical and environmentally friendly alternative. It took nine years, from August 1990 to May 1999, for the Tatara Bridge to be built.

Honshu-Shikoku Bridges: Tatara Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Honshu-Shikoku Bridges: Akashi-Kaikyo Bridge (3)

One more look at the bridge with the longest main span in the world. Cable-stayed bridges are getting bigger but there are no plans to build a longer suspension bridge than the Akashi-Kaikyo Bridge in the foreseeable future. At 2 km long between 300 m tall towers, this is one big bridge.

There is something interesting about big structures. The sculptor Claes Oldenburg took common objects like clothespins and made them hundreds of times their normal size in order to see them anew. Perhaps something like that takes place when we view a really big bridge.

John Ruskin, the 19th century art critic wrote about how landscape art creates an intense aesthetic experience because familiar details are transformed when seen at a distance and because the object is changed by the distorting effect of the the atmosphere.

These are just my first thoughts on the pleasures of looking at big bridges and other structures. I'd like to hear what you think!

Honshu-Shikoku Bridges: Akashi-Kaikyo Bridge (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.