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Construction of the Osman Gazi Bridge

The Osman Gazi Bridge is the largest suspension bridge in Turkey and the fourth largest in the world but was constructed in just 42 months. This was achieved by combining the technical capabilities that the IHI Group acquired through its extensive record in the Honshu-Shikoku Bridge project and overseas projects.

The construction was broadly divided into five areas: ① Anchorage work on the north and south coasts, ② main tower foundation work, ③ manufacture and installation of the main towers, ④ cable installation, and ⑤ manufacture and installation of stiffening girders (where the cars drive).

① The anchorages that secure the cables to the ground are gravity-based concrete structures at the north and south ends. As the ground is solid on the north coast, the ground was excavated and the concrete poured directly. The softer ground on the south coast was backfilled and surrounded by a diaphragm wall to form a concrete body.

② For economy and safety, the main tower foundation construction adopted concrete caissons filled with seawater combined with steel-concrete composite shafts. After manufacturing the lower half on land and the upper half on the sea, seawater was injected to sink to the design level and install it on a crushed rock layer spread on the sea floor. This is the world's first seismic isolation mechanism for a suspension bridge.

③ Concrete main towers are mainstream in overseas suspension bridges. However, to shorten the construction period, steel main towers were adopted so that blocks could be manufactured in parallel with construction of the main tower foundations. The blocks were produced at Turkey's steel structure factory. The lower half of each main tower was erected by lifting the blocks with a 1,200-tonne floating crane and the panels of the upper half were erected using a jib climbing crane installed on a lower level horizontal beam. The two north and south main towers were completed in just six months.

④ The cable installation work was performed on catwalks constructed as aerial scaffolding. The prefabricated parallel wire strand (PPWS) method was adopted for this construction. (In this method, factory-made parallel strands and steel wires pre-bundled to a certain size at the factory were extended between north and south on site to form thick cables.)

⑤ The steel stiffening girders have a flat hexagonal cross-section, which is less susceptible to vibrations due to wind. The blocks for the parts near the main towers were erected by a 1,200-tonne floating crane, while the majority of the blocks were lifted directly off the barge by a lifting device installed on the cable. As a result of working simultaneously at a total of four locations (two each at the north and south ends), approximately 2 km of stiffening girders were installed in just three weeks. Furthermore, performing and managing other tasks such as pavement construction and installation of lighting columns in parallel enabled the bridge to open to traffic just two months later, a record-breaking pace.

Construction of this bridge has also attracted attention in Turkey, and everyone was excited that the President and other senior government officials would visit the site. In the opening ceremony held on the eve of opening the bridge, we were able to thank the labor force that completed this difficult construction project.

It was feared that Japan might be losing its technological edge, as no long suspension bridge has been constructed there in more than 15 years since the Honshu-Shikoku Bridge, but engineers who worked at that time, young Japanese engineers, and Turkish engineers worked together to complete the construction. This has greatly contributed to the handing down of technologies, the generations and to the transfer of technology to Turkey.

Outline of construction project

Client トルコ共和国 運輸海事通信省 道路総局
Location トルコ共和国 イズミット湾
Completed in 2016
橋長 2,682m
鋼重 70,490t(主塔、橋桁、ケーブル)
特長 トルコ最大の都市であるイスタンブールと第3の都市であるイズミルを結ぶ全長420kmの高速道路の一部として建設された、世界第4位の中央経間長1550mを有する3経間連続長大吊橋。

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