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Cable clamp bolt tensioning at Bosphorus bridges with ITH Bolt Tensioning Cylinders

Suspension bridge cable clamp installation at Bosphorus with ITH bolt tensioning cylinders


The cable clamp installations of the suspension bridges over the Bosphorus in Istanbul were finished quickly and precisely with ITH bolt tensioning cylinders. The informative graphic gives an technical overview about the bolt tensioning application. See the impressive pictures from top of the bridge.


Istanbul, Turkey | Tokyo, Japan | Meschede, Germany

There are currently only two highway bridges spanned over the Bosphorus in Istanbul, which are hung by two main cables a with total length of 1,400 Meters (4,593 ft.) and diameters of more than 2.5 Meters (8.2 ft.) each. 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 (d 1 3/8`` x l 28.9``) 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.


Cable clamp at suspension bridges: Installation of the bolts with ITH Bolt Tensioning Cylinders.

Installation of cable clamps and relating bolted joint design

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, USA for example.

These high-strength wires are anchored in concrete foundations on both sides of the coast (anchor blocks). While extended over the two main towers (pylons) of the bridge, the wires are pressed together and by large concrete cable clamps. The Bosporus bridges use two designs of cable clamps:

  1. Cable clamp, two-sided, inner diameter r > 280 mm (11``), 10 x reduced shank bolts M36x734 (d 1 3/8`` x l 28.9``) with cardanic washers
  2. Cable clamp, two-sided, inner diameter r > 290 mm (11.42``), 4 x reduced shank bolts M36x734 (d 1 3/8`` x l 28.9``) with cardanic washers
Suspension bridge cable clamp installation: Bolt tightening of the cable clamp r > 280 mm (11``) with ITH Bolt Tensioning Cylinders. The required preload force is applied simultaneously and with a high precision of ± 2.0%.

Cable clamps are also suspension points for hanger cable

Those cable clamps, which are positioned between two main towers (pylons), 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 in bolted joints

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 other 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. „By 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, Germany. „This is integral for the long-term stability of the bolted joint“. 

Installing cable clamps on suspension bridges with ITH Multi Tensioning: Simultaneous bolt tightening of 4 x reduced shaft bolts with ITH Bolt Tensioning Cylinders type ES 36-470.

Precise implementation of the pre-load forces by ITH Multi Tensioning

Before the bolt tightening 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 ten – respectively four, depending on the application – ITH Bolt Tensioning Cylinders type ES 36-470 were connected to one hydraulic circuit and then connected to the ITH hydraulic pump.  This ensures the pre-load 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“, Frank Hohmann says. „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 main overhaul project of the Bosporus Bridges the Turkish Ministry of Traffic contracted a Japanese construction company, which chose German ITH Bolting Technology for their expertise in bolted joints. Next to on-time project management there were two more decisive factors for the Japanese company:

  1. Extensive technical capabilities of bolting tools and bolted joints
  2. Working safely according to international work safety standards 
The bolts of the concrete cable clamps on the Bosphorus Bridge in Istanbul, Turkey were tightened precisely with 10 x ITH Bolt Tensioning Cylinders type ES 36-470. The bridge connects the European continent with the Asian continent.

International projects are daily busines

„International projects are our daily business. It was beneficial to include our team from ITH Japan into the project“, Frank Hohmann explains, who leads the  worldwide acting  and family-run company ITH Bolting Technology together with his brother Joerg Hohmann. „We are thankful for the trust our customer has set in us and happy that we have met all expectations“. 

And this was not the first time: ITH Bolting Technology maintains long-term relationships to worldwide industry leaders, which trust in the know-how and the experience of ITH Bolting Technology. ITH  bolting tools are used in nearly all industrial areas.

ITH bolting tools have also been used at the Oresund Bridge between Denmark and Sweden and Kattwyk Bridge in the harbour of Hamburg, Germany.

1,400-Meter-main-cables span the 1,000-Meter Bosporus strait / Loads of 400,000 cars per day

The currently only two Istanbul car-highway bridges over the Bosphorus strait

  1.  the „Bogazi Bridge“ (identification 1 BB)
  2. the „Fatih Sultan Mehmet Bridge“ („FSM“, 2 BB)

are loaded with more than 400,000 cars per day. The two main towers (pylons) of each bridge have a total height of 165 Meters (541 ft.) and stand in a distance of 1,074 Meters (1 BB; 3,523 ft.) – respectively 1,090 Meters (2 BB; 3,576 ft.) – on the European continental side and the Asian continental side in Istanbul, Turkey. They are connectin Europe with Asia. The suspension bridges have six-lane traffic-carrying decks which are held by main cables with a total length of 1,400 Meters.

Facts & Figures: bolt tightening of the Bosphorus bridges


  1. Bogazi Bridge (1 BB), Istanbul, Turkey
  2. Fatih Sultan Mehmet Bridge (2 BB), Istanbul, Turkey


  1. concrete cable clamps, two-sided, inner radius: r > 280 mm (11``), 
  2. concrete cable clamp, two-sided, inner radius > 290 mm (11.42``)

Bolt connection

Reduced shaft bolts M36x734 (d 1 3/8`` x l 28,9``); projecting thread > 70 mm on both ends, cardanic washers.

Bolting tool

Single-staged ITH Bolt Tensioning Cylinders type ES 36-470, patented ITH safety concept, spring-loaded turning sleeve, cardanic washer integrated at the support.

Tightening method

„Hydraulic friction-free and torsion-free tensioning“ by „ITH Multi Tensioning“: Simultaneous bolt tightening of two or more bolted joints ensures a high precision of ± 2.0% when applying the preload forces. 

Therefore the Bolt Tensioning Cylinders are connected together to one hydraulic circuit. Then they are pressured by the ITH hydraulic pump ITH Eco-MAX 17.

Press release

Download the press release as a  PDF-file:

Suspension bridge cable clamp installation with ITH Bolt Tensioning Cylinders

Further information

"Hydraulic, friction-free and torsion-free tensioning": The 3D animation video below explains the method with in 49 seconds

Hydraulic, friction-free and torsion-free tensioning: The video explains the method within 49 seconds

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