InfraStructures - November 2015 - The Bolts of Bosphorus Bridge Were Tightened Precisely Using ITH Bolting Technology

The Bolts of Bosphorus Bridge Were Tightened Precisely
Using ITH Bolting Technology

Franz Niklas Gampe, on behalf of ITH GmbH & Co. KG
Special Collaboration

The Bosphorus Bridge and the Fatih Sultan Mehmet Bridge are currently the only 2 suspension bridges spanning the Bosphorus strait in Istanbul, Turkey, with the Yavuz Sultan Selim Bridge under construction.

Connecting Europe and Asia, they are gravity-anchored suspension bridges with steel towers and inclined hangers.

The Bosphorus Bridge, built in 1973, has a total length of 1,560 m. Its 2 main cables each measure 2.5 m in diameter. These main cables consist of numerous, smaller and high-strength steel wires which are pressed together by 84 concrete cable clamps. During a main overhaul project nearly 700 reduced shank bolts M36 x 734 (36 mm x 734 mm) of all 84 cable clamps were tightened precisely and reliably. ITH Bolting Technology provided bolting tools, engineering know-how, professional project management and fulfilled all requirements of this international large-scale project.

Tightening cable clamp bolts precisely with ITH Bolt Tensioning Cylinders
To carry the various loads (self-weight, working load, dynamic loads) efficiently, main cables of suspension bridges are often made out of numerous single steel wires. This concept is also used at the Golden Gate Bridge in San Francisco, California, for example.

These high-strength wires are anchored in concrete foundations on both sides of the coast (anchor blocks). While extended over the 2 main towers of the bridge, the wires are pressed together and held by large concrete cable clamps.

The clamps also provide a suspension point for the series of vertical hanger cables, which carry the deck. At the suspension point, the cables are seated in a spherical bearing while anchoring in a cast iron plate when fixed to the traffic-carrying deck.

Using cardanic washers when bolting cable clamps
Compared to steel parts in machine engineering the production tolerances in steel construction and the tolerances of the concrete-composite cable clamps are relatively high. The supporting surfaces were not machine processed. This and parameters of the design of the clamps lead to a certain vertical misalignment of the reduced shank bolts. This effect was compensated by the use of cardanic washers, which were included between the nuts and the supporting surface.
Accordingly, the ITH Bolt Tensioning Cylinders were designed with integrated cardanic washers as well.

“With this customized design we ensure that the required preload forces are applied evenly and with a high precision,” explains Frank Hohmann, general manager of ITH Bolting Technology. “This is essential for the long-term stability of the bolted joint.“

Precise implementation of the pre-load forces by ITH Multi Tensioning
Before tightening the bolts of the cable clamps, the main cable was pressed together by a hydraulic press. After that, all bolted joints were tightened simultaneously by using the “ITH Multi Tensioning” method.

Therefore 10 (or 4 depending on the application) ES 36-470 type ITH Bolt Tensioning Cylinders were connected to an hydraulic circuit and then connected to the ITH hydraulic pump, ensuring the preload forces are transferred into the bolted connection with a tight tolerance and high precision of ± 2.0%.

International industry leaders trust in ITH Bolting Technology
“Infrastructure projects of this size create a certain public attention, because it affects the people’s lives,“ says Mr. Hohmann. “Obviously, no project partner could afford any time delays. We are happy that all sides were satisfied with project management and bolting job performance by ITH.”

For this major overhaul project of the Bosphorus Bridge, the Turkish Ministry of Traffic contracted a Japanese construction company, which chose ITH Bolting Technology for their expertise in bolted joints.

“International projects are our daily business. It was beneficial to include our team from ITH Japan into the project,“ explains Frank Hohmann. “We are thankful for the trust our customer has set in us and happy that we have met all expectations.“

ITH Bolting Technology maintains long-term relationships to worldwide industry leaders, which trust in the know-how and the experience of ITH Bolting Technology. Among other industry sectors ITH bolting tools are used in all power generating industries like wind turbines, construction and mining machines, oil & gas, offshore industries, general engineering companies and more. ITH bolting tools have also been used at the Oresund Bridge between Denmark and Sweden and the Kattwyk Bridge in the harbor of Hamburg, Germany.

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