Tensho Bridge

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Tensho Bridge
天翔大橋
Nishiusuki District, Miyazaki, Japan
470 feet high / 143 meters high
853 foot span / 260 meter span
2000

TenshoAerial.jpg

Image by Japanese Soceity of Civil Engineers.


The highest and longest concrete arch in Japan, the Tensho bridge soars across a forested river gorge in the mountains of southern Japan’s Miyazaki prefecture. The bridge is located just south of Takachiho Gorge, a region with more high bridges than any other single location in Japan. These include the highest railway bridge in Japan over the Takachiho gorge as well as the Shintotakachiho and Aoba concrete arches, the Unkai, Ryuten and Seiun steel arches and the Kamiiwato concrete beam bridge. All 8 bridges are more than 328 feet (100 mtrs) in height. If you have just one day to visit high bridges in Japan, Takachiho gorge is the place to be!

The construction of Tensho was somewhat different than similar sized arches whereby a tower is usually erected on either side of the gorge and cables temporarily radiate out from it to support individual sections of the arch until the two halves are joined in the middle. With Tensho, the roadway and support spandrels were built outward at the same time as the arch. To prevent the two halves of the arch from falling into the gorge, several cables were attached from an anchor to the road deck and then down to the arch segments. Once the next vertical spandrel support was built up to deck level and connected to another short span of roadway, then another diagonal cable was connected to the arch rib within the next spandrel and the process repeated itself. When the two sides of the arch were closed in the middle, the temporary cable stays were then removed from the inside of the spandrel panels.

With a span length to rise ratio of just 8 to 1, the Tensho arch is so flat it looks lighter than its size would suggest. This desire to make the bridge an invisible presence is all part of the Japanese ethic to harmonize man and mother nature while maintaining the natural beauty of the environment.

There is no other region in Japan that has as many high bridges than the Takachiho Gorge Scenic Area of Miyazaki Prefecture. Within a distance of just 30 kilometers the Gokase and Iwato River canyons are crossed by no less than 15 high bridges.

Several of these spectacular crossings were the highest in Japan including Tensho, Seiun and Unkai Bridges. The Takachiho Railway Bridge is still the highest railway crossing in Japan even if it not longer operates with regular trains.


TenshoElev.jpg

Tensho Bridge Elevation


日本一高く長いコンクリートのアーチ橋である天翔大橋は、南日本にある宮崎の山間部、森林に覆われた川の谷間を横切り舞い上がります。この橋は高千穂峡谷のほんの南に位置しています。この地域には、他のどの一地域よりも多くの高い橋があります。その橋とは、高千穂峡谷にかかる日本一高い鉄道橋、そして神都高千穂大橋と青葉大橋のアーチ橋、雲海橋、龍天橋と青雲橋の鋼鉄アーチ橋、そして上岩戸大橋コンクリートビーム橋です。この八つの橋はすべて100m以上の高さを持ちます。もし、あなたが一日だけで高い橋をたくさん見たいのであれば、高千穂峡谷地域がお勧めの場所です!

天翔大橋の架設は、同じサイズのアーチ橋と比べて少し違っていました。通常のアーチ橋は、タワーが一方の峡谷に建てられ、そこから一時的に放射上に伸びたケーブル(大綱)が各部分のアーチを支えます。そして二つに分かれているアーチが中央で結合されるまでアーチを支えます。天翔に関しては、道路とサポート・スパンドレルは外側に向けてアーチと同時に造られました。半分に分かれている2つのアーチが峡谷に落ちるのを防ぐため、路面デッキのアンカーから7~8本のケーブルがつながれ、そして、アーチの部分につながれます。そして、次の垂直スパンドレル・サポートがデッキのレベルまで造り上げられ、路面の別のショートスパンにつながると、その後、別の対角線のケーブルが次のスパンドレル内のアーチ骨組みにつながります。この工程が繰り返されます。半分ずつのアーチが中央でつながると、一時的なケーブルステイはスパンドレルパネルの内部より外されます。

スパンの長さとライズの割合は8対1で、天翔大橋のアーチはとても平らでサイズから想像するよりも軽く見えます。自然環境の美しさを保ちながら、人と自然との間に調和をとるために、橋を見えないように造りたいという願いが日本人の倫理感の中にあります。


TenshoElevation2.jpg


TenshoElevationConstruction2.jpg


TenshoSideArch.jpg


TenshoConstruction.jpg

Image by Japanese Soceity of Civil Engineers.


1TenshoBridge.jpg


TenshoCrossSec.jpg


TenshoSatellite.jpg

Tensho Bridge satellite image.


KunimiLocationMap.jpg

Tensho Bridge location map.


MiyasakiBridgesMap.jpg