第三吾妻川橋りょう

摘要

第三吾妻川橋りょうはJR吾妻線付替え工事の一環として建設されており，JR吾妻線長野原草津口駅付近で吾妻川を横断する橋長203m，支問長201.7m（22.235m＋159.53m＋19.935m）のバスケットハンドル型複合中路アーチ構造3径間PC下路連続桁の鉄道橋である．本橋は地域のランドマークとなるように考慮するとともに，併走する付替国道145号のニールセンローゼ橋（長野原めがね橋）との景観上の調和を考慮したデザインとなっている．景観デザインとしてアーチ基部の高さを先端部から橋台との連結部に向けて大きくしていくことで構造安定性と安定感，力強さを表現している．また，両端は跳ね上げた形状の斜橋脚として，アーチの連続性を表現し，デザインの流れにリズム感をつけている．%The Third Agatsumagawa Bridge crossing over the Agatsuma River in the vicinity of the Naganohara-kusatsuguchi Station on the JR Agatsuma Line was constructed as part of the replacement work for the JR Agatsuma Line. It is a 203 m-long three-span prestressed concrete continuous girder railway through bridge with a total span of 201.7 m (22.235 m + 159.53 m + 19.935 m) built with a basket-handle compound half-through arch construction.rnThis bridge design was chosen to serve as a landmark for the region, as well as for its aesthetic balance with the Nielsen Lohse bridge (Naganohara Megane Bridge) on the No. 145 national highway that runs parallel Structural rigidity, sense of stability and strength are expressed by steadily increasing the height of the arch base from the ends toward the bridge abutments. A rhythmic sense is also added to the bridge design by emphasizing the continuity of the arch with the diagonal piers with forms that appear to splash up at both ends.rnA unique feature of the bridge design is the use of a CFT structure for the arch rib in order to ensure high rigidity and decrease its dead load; and in making the bridge a half-through arch bridge, the maximum span could be shortened, creating an efficient structural design. This bridge's steel and concrete compound arch structure enabled forms that are rarely seen even in Japan.