Construction of Turkey’s Yavuz Sultan Selim bridge not only created a third crossing linking Europe and Asia across the mighty Bosphorus Straits, it also marked a major step forward in stay cable technology. The new bridge carries the North Marmara Motorway over the strategic waterway, enabling traffic to bypass the city of Istanbul, boosting highway capacity and relieving congestion on the existing crossings.

  • Name of the owner
    KGM (General Directorate of Highways)
  • Name of the client
    HDSK (Hyundai Engineering & Construction/SK Engineering & Construction JV)
  • Delivery date of the project
    July 2016
  • Partners of the project
    Concessionnaire: ICA (Ictas/Astaldi JV)
    General contractor: HDSK
    Engineer: T-Engineering & Bureau Greisch
Sultan Yavuz Selim bridge

A hybrid arrangement

A traditional suspension bridge form with a shallow deck was chosen for its aesthetics, and to complement the existing Bosphorus bridges. But the need to stiffen the bridge by the addition of a series of super-long, high-strength cables resulted in the creation of a rare, hybrid stay cable technology arrangement.

One of the biggest challenges of the project was to design and build a bridge of this size and complexity in just 36 months. With its main span of 1,408 m, 59 m-wide deck and towers rising more than 320 m above the water, its scale and form were unprecedented.

Added to this was the need to develop and test new equipment capable of erecting, anchoring and restraining the movement of the longest and heaviest parallel strand cables Freyssinet had ever manufactured.

  • 36
  • 1,408
    Length of main span (m)
  • 322
    Height of towers
  • 59
    Width of bridge deck
Installing new stay cable technology on Yavuz Sultan Selim bridge

A heavy load

The highway and rail loads that were predicted meant ultra high-strength strand was needed, leading to the first use of Freyssinet’s 1,960 MPa cable strand – and setting another global record.

A total of 176 stay cables was installed, the longest of which measure more than half a kilometre and contain an incredible 151 strands, weighing in at almost 120 t. The capacity needed to test these cables exceeded that of the world’s biggest testing rigs; even the smallest stays on this project are large when set against those of standard cable-stayed bridges. To manufacture the 9,000 t of high-strength strand needed to produce these cables in such a short time demanded faultless quality control across our supply chain.

Flexible working

This short project time-frame led to additional challenges, with detailed design of certain elements having to be adapted to suit those that had already gone into production. What’s more, the unconventional combination of cable systems led to heavily-loaded stays that were prone to sagging and at higher risk of excitation.

Specially-designed deviators were developed to control the alignment of the cables at the anchorages. These elements had to be tested to provide assurance not only that they would be effective, but that restraint of the cables would not damage the sheathing intended to protect them. Finding the optimum solution for durability was just as important as influencing the structural behaviour.

Yavuz Sultan Selim bridge BB3
Stay cable technology implementation and control

Stay cable technology control

The potential scale of excitation under wind loads demanded damping of the free length of the cables while allowing them to move freely under service loads. Factors such as the size of the predicted movement, the scale of the cable stays and the restricted space available led to the design of 7.4 m-high masts supporting hydraulic pistons with a stroke of ±920 mm.

On site, Freyssinet’s standard procedure for erecting and stressing the strand had to be adjusted to take account of the presence of the main cable directly overhead and the need to work in parallel with many other contractors to meet the programme completion date.

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