Building Turkey’s Longest Bridge
One of the world’s newest, longest bridges owes a large part of its existence to a Luxembourg-based steel manufacturer, and its ongoing health to a pair of Danish and German engineering firms.
ArcelorMittal Galati, located in Romania, supplied 34,000 tons of steel to the construction of the Osman Gazi Bridge in Turkey.
Designer COWI A/S, based in Lyngby, Denmark, built the bridge with earthquake resilience in mind.
And Siemens AG, headquartered in Berlin and Munich, provided the development, installation and commissioning of all bridge structure and traffic control components and systems.
At 2,682 meters (about 8,799 feet) in length, the $1.3 billion structure is said to be the fourth-longest suspension bridge in the world, the second longest in Europe and the longest in Turkey.
The bridge, which opened June 30, crosses 64 meters (almost 210 feet) above the Marmara Sea.
Building Turkey’s Longest Bridge Deck
Named after founder and first sultan of the Ottoman Empire, the Osman Gazi Bridge is part of a 420-kilometer (about 261-mile) highway project that shortens the distance between Istanbul and the northwest city of Izmir by about 140 kilometers (86.9 miles) and cuts a 70-minute drive around the Izmit Gulf to just six minutes.
The bridge project was awarded to a Turkish-Italian consortium NOMAYG—consisting of Turkish companies Nurol, Ozaltin, Makyol, Yuksel, and Gocay, and Italian company Astaldi—which will also operate the bridge for the next 23 years.
The consortium awarded the bridge construction on an Engineering, Procurement, and Construction (EPC) basis to Tokyo, Japan’s IHI Corporation.
IHI, in turn, selected Turkish engineering, fabrication and contracting firm Cimtas as the sole fabricator of both the suspension bridge’s orthotropic steel deck panels and steel tower blocks.
ArcelorMittal said it supplied Cimtas with 34,000 tons of flat steel for the horizontal deck of the structure, shipped in four main lots in a wide range and variety of thicknesses and widths, it noted.
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ArcelorMittal supplied 34,000 tons of flat steel for the horizontal deck of the structure. |
“This project has a special importance for us, given its size,” said Bruno Ribo, chief executive officer of ArcelorMittal Flat Europe, southeast business division.
“Our Galati heavy plates mill facilities produce and supply the requested plates for various applications,” he added. “For the Osman Gazi Bridge, we designed a series of bespoke technical and commercial solutions.”
Constructed entirely out of steel, the six-lane bridge reaches a height of 252 meters (about 827 feet), a width of 35.93 meters (118 feet) and a main span that is 1,550 meters (about 5,085 feet) long.
Overall, Cimtas was responsible for the fabrication of 18,200 tons tower panels and 33,800 tons girder panels—a total of 52,000 tons welded fabrication.
Preparing for Quakes, Monitoring Conditions
Sited in an area considered particularly prone to earthquakes, the bridge was designed by Danish engineering design firm COWI to withstand such movements.
Based on input from COWI's earthquake specialists, the firm made the bridge earthquake resistant by building its pylons on a concrete foundation that rests on a large gravel bed. The pylons can slide on the gravel bed in the event of a major earthquake.
The bridge is thereby partly isolated from the enormous energy released by a major earthquake, the firm explained.
Likewise, Siemens fitted the structure with special technology to alert bridge operators to abnormal events.
The company installed 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, it explained.
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Siemens installed about 390 sensors to monitor bridge conditions and raise the alarm in the event of excessive vibration. |
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, it said.
Additionally, the sensors immediately detect changes and potential damage to the bridge as well, as they also continuously check the steel structure for corrosion.
In the interior areas 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 percent to prevent the steel from rusting in the sea air.
Fast Turnaround
COWI expressed that one of the crucial factors in its high-quality design is the ability to build the bridge on a record short construction period.
Now open to traffic following a 42-month construction period, the new Osman Gazi Bridge can carry more than 40,000 vehicles every day.
