Following a construction period lasting 42 months, Turkey’s new Osman Gazi Bridge has opened, halving travel time between the cities of Istanbul and Izmir.
The six-lane tolled suspension bridge, with separated maintenance lines, extends 1.8 miles (3km) across the Sea of Marmara, and is part of a freeway project linking the cities of Istanbul and ?zmir in western Turkey. The fourth longest suspension bridge in the world by center span, it also has the highest toll fee in the world, costing US$30.77 to travel one way, plus an additional charge of 5 cents per kilometer.
The construction of the bridge and the 254-mile (409km) long highway between Istanbul and ?zmir is part of the largest freeway project in Turkey to date. Otoyol Yatirim ve Isletme AS (Nurol-Özaltin-Maykol-Astaldi-Yüksel-Göcay) has been appointed under the terms of a built-operate-transfer (BOT) contract to plan and operate the new motorway over a period of 22 years. Expected to carry more than 40,000 vehicles every day, the new six-lane bridge connection will cut the travel time between the two cities from eight to four hours.
Constructed entirely from steel, and with a main span of 5,090ft (1,550m) and overall length of 8,799ft (2,682m), the bridge is suspended 211ft (64m) above the Sea of Marmara to the south of Istanbul, a region which is considered particularly prone to earthquakes. The structure therefore had to be fitted with special technology that continuously measures vibrations, movements, and loads, and to give alarms to the bridge operators for all abnormal events. Working on behalf of the Japanese construction company that built the bridge, IHI Infrastructure System Co., Siemens took on the role of electro and mechanical contractor, with responsibility for the development, installation and commissioning of all the bridge structure and traffic control components and systems.
Siemens has equipped the bridge with about 390 sensors that constantly monitor its condition and raise the alarm in the event of excessive vibration. The sensors continuously measure longitudinal and lateral strain, as well as the stress loads on the road sections leading up to the main span. Special GPS sensors fitted to the bridge register oscillations of the bridge piles down to the last millimeter, while wind and temperature measuring units are also provided.
Changes and potential damage to the bridge are also immediately detected by the sensors, for instance to check the steel structure continuously for corrosion. In the interior chambers of the bridge, in the bridge towers and bridge decks, as well as on the sheathed suspension cables, a special system controls and regulates atmospheric humidity, ensuring it remains below 40% to prevent the steel from rusting in the sea air.
Siemens has also supplied state-of-the-art traffic control technology, including all the communication and camera equipment, energy supply, lighting and ventilations, together with an integrated operations, emergency call and traffic control center. A SCADA (supervisory control and data acquisition) system will be used for the process monitoring and control of the system.