Our client had primarily considered building the bridge with the balanced cantilever erection method, due to the topographical conditions and restrictions inherent to the tunnels that did not allow to launch the bridge from downhill.

However, the tight schedule, cost, and innovative approach of Freyssinet drove the final choice to the Incremental Launching Method which could be rethought to enable bridge launching from uphill.

While the bridge was made of two parallel roadways, the decks consisted of prestressed cell box girders fixed on two piers.

  • Owner
    Ministry of Transport in Turkey
  • Client
    KOLIN Construction
  • Delivery date
    2018
Cayirköy Environmental challenges - Incremental launching

Environmental challenges

The Cayirköy viaduct, located next to Izmit city, on the Marmara Sea, is part of the Northern Marmara motorway. It is a large Turkish project of 431 km of highways in the Istanbul region which aims to ease the traffic flow in the congested Istanbul area and to link the western part of the country to the city and its new airport.

Due to the viaduct’s location in unpropitious geographical settings, the project’s major issues remained in the earthquake loads to be considered during construction, and the significant launching downhill, with a -2.8% slope.

Rethinking the construction method

While decks are typically launched uphill, it was decided to launch the viaduct decks downhill, due to a space issue as they were too close to the Ankara side tunnel. This unusual configuration required the specific design of a braking system to block the deck during stop phases and prevent both sliding due to self-weight and unexpected movements due to earthquakes, and to hold it back during launching phases.

The braking system would work in both directions, i.e. uphill and downhill, by preloading the launching and braking strands. At certain stages, the deck could be blocked on fixed piers, using high friction plates.

Cayirköy viaduct - Preparation for the incremental launching method

Preparation and controls, key success factors of the incremental launching method

The thorough preparation undoubtedly played a major role in the effective execution of the project: accurate design and careful planning ensured that controls would only result in minor adjustments and easy monitoring of the smooth running of the operation at each phase.

Launching phases required to check the measurement of the deck position both at the beginning and at the end of each launching operation, measurement of the longitudinal displacement of piers as well as control of launching forces to prevent any sliding pad or jack issue.

Stop phases entailed checking of the position and level of casting beams, segment length, settlement of temporary supports and level of the deck at each pier.

Since the level of casting beams was a major parameter to watch regularly, as a change could introduce cracks in the deck, casting beams had been designed to be adjustable in height.

Valuable time and cost savings of the Incremental launching method

A major advantage of the incremental launching method remains in its simple execution and minimum equipment requirements. Therefore, most of the items were reused from a former project (KMO1) and adapted to match the main characteristics of the viaducts:

  • The launching nose was fully recalculated and slightly modified to adapt to the vertical forces exerted on it, which were higher than those considered in the former project’s original design.
  • Among the necessary four pulling sticks, two of them were reused and the two others were adapted (400 mm longer), since the left deck had a vertical curve at the end, which increased the deck height.
  • Temporary bearings, last launching device and guiding device – to transversally guide the deck during launching (wind and deck curvature) and stop (wind and earthquake) phases – were all reused from another project as well.

These adjustments enabled us to reduce both cost and fabrication planning of the main temporary equipment.

To reduce the overall time frame for construction, the two parallel carriageways were launched simultaneously. Decks were fabricated in a precast yard behind the abutment and organized in a casting area – where the reinforced concrete deck could be cast and partially post-tensioned –  and a buffer area, where the full prestressing necessary for launching was applied.

An efficient construction cycle of 5 days for a half-span was ultimately achieved on site.

  • 27,300t
    Deck weight
  • 1,496m
    Two decks length
  • 1,850m
    Horizontal radius
  • -2.83%
    Longitudinal slope (launching downhill)
  • 160t
    Longitudinal slope (launching downhill)

We, at Freyssinet, always consider challenges as opportunities. This is typical of the true Freyssinet spirit that drives us every day. Cayirköy was one of a kind, with a limited precast yard and a considerably heavy deck to be launched downhill. We achieved the viaduct’s construction thanks to great teamwork with Freyssinet Technical Department. I am proud to be involved this project!

Baran  
Special Projects Director

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