TATARA BRIDGE MAP

TATARA BRIDGE MAP

Crossing Seto Inland Sea, Hiroshima-Ehime, Japan Designer/Engineer Honshu-Shikoku Bridge Expressway Company Completed 1999 Span 2,919 feet (890 meters)

Materials Steel, concrete Type Cable-stayed

Engineers reduced wind turbulence by adding a raised pattern to the outer cables.

On May 1, 1999, the Honshu-Shikoku Bridge Expressway Company (HSBE) completed its titanic bridge campaign, which saw the completion of seventeen major spans, several of them world record holders, in less than three decades. On this day, the Tatara Bridge, then the longest cable-stayed bridge in the world; the Shin-Onomichi Bridge; and the Kurushima-Kaikyo Bridges, a trio of suspension bridges, opened in Japan. The bridges are five of the nine long-span bridges on the 29-mile (46.6-kilometer)-long Nishi-Seto Expressway, which connects seven islands.

The Tatara is the westernmost of the three bridge routes between Honshu and Shikoku (see here and 113). With a central span of 2,919 feet (890 meters), the Tatara was the longest cable-stayed bridge for nine years, until China’s Sutong Yangtze River Bridge opened in 2008.

In cable-stayed bridges, the deck is attached with cables directly to the pylons and supported by the cables, pylons, and onshore abutments, thus bypassing the need for the vertical suspenders, main cables, and anchorages of suspended spans, which are the largest, most costly type of bridge. Although the Tatara was originally planned in 1973 as a suspension bridge, the HSBE ultimately decided a cable-stayed design would be less costly and less invasive to the environment of the Seto Inland Sea, a national park dotted with some three thousand islands and inlets.

Unlike their vertical counterparts, skyscrapers, bridges are wholly exposed to the elements and subject to daily onslaughts of traffic, wind, and weather. To test the Tatara’s response to wind, a significant consideration for tall structures (in this case, one the height of a seventy-story building), engineers ran wind tunnel tests on a 1:200 scale model, which confirmed that its gust response at midspan was within an acceptable range. The wind tunnel testing also showed that indenting the exterior surfaces of the cables would limit, if not prevent, turbulence.

With the exception of the Shin-Onomichi Bridge, all of the bridges on the Nishi-Seto route accommodate pedestrians and cyclists. The Shimanami Kaido Highway cycling route, the most popular in Japan, is about 44 miles (71 kilometers) long, hovering over the emerald Seto Inland Sea, which is often compared to the Mediterranean. Drop-ins are welcome, thanks to numerous rent-a-bike stations along the way.

The Kurushima-Kaikyo crossing consists of three successive suspension bridges, the only such grouping in the world. All three are stiffened box girder spans, with a total of six spans, six towers, and four anchorages that stretch 2.5 miles (4.0 kilometers) between Oshima Island and the city of Imabari. The cable-stayed Ikuchi Bridge (1991) features two delta-shaped towers. Constructed with composite girders, it has a 1,607-foot (490-meter) center span and 492-foot (150-meter) side spans. Lessons learned on this bridge, the longest cable-stayed bridge when it opened, were applied to the Tatara. Enthusiasm for the impressive scale of the HSBE bridge links was tempered by the severe budget deficit of the late 1990s and the growing perception among the Japanese that such outsize public works were consuming the country’s wealth and inviting environmental devastation. According to a 1997 New York Times article by Andrew Pollack, the mood was one of reassessment, both of the need for construction of this magnitude and of the country’s once-admired bureaucracy. Nonetheless, the opening of any major bridgehere, five major crossingsis an occasion to celebrate the vision, cooperation, and enormous ingenuity these structures represent. More than physical connections between two points of land, bridges serve as valuable links between societies, cultures, and political ideologies. As such they warrant our protection.

China’s Zhangjiajie National Forest Park, with its exquisite rock outcroppings, has always been like catnip for tourists. Their numbers increased exponentially when the Zhangjiajie Bridge (2016) opened. The 20-foot (6.1-meter)-wide bridge is a gossamer fi lament, stretched 1,410 feet (430 meters) long. The big draw is its vertigo-inducing, fully transparent glass deck, which provides views 984 feet (300 meters) down into a deep canyon. Demand so far exceeded the bridge’s eight-thousand-person daily capacity that it had to close shortly after it opened. Once reinforced, it reopened.