The Russky Island Cable-Stayed Bridge : "The Bridge of All Records"
ABSTRACT: Connecting Russky Island and the Russian peninsula in Vladivostok, the Russky Island cablestayed bridge is the longest cablestayed bridge in the world today with its main span of 1,104 m between A-shaped pylons of 320 m in height. It provides a 70 m high navigational clearance through the Bosphor Vostochny Straits, thus symbolizing the new gateway to Russia in the Far East. It is also a bridge of records, i.e. cablestayed span length, tallest pylons, longest stay cable and shortest construction time. The general arrangement and description of the main components of this exceptional structure and its stay cables, which have been the subject of special care in order to improve the bridge response and durability, are presented, and, more particularly, the stay cable technology that uses compact parallel strand cables. Finally, the project construction and methods that were used to aid its completion in less than 4 years in the harsh Eastern Siberian climate are presented with a focus on safety.
Introduction
Standing on the easternmost tip of Eastern Siberia, Vladivostok became the focal point and highlight of Russia in September 2012. In anticipation of Russia’s presidency of the APEC summit (Asia-Pacific Economic Cooperation), the Russian authorities decided back in 2007 that Russky Island, just a stone’s throw from Vladivostok and some 6,000 km from Moscow as the crow flies, would host the event. Construction was completed in time for the international summit (Image 1).
During the Soviet era, the seafaring city of Vladivostok was closed off to foreigners and then neglected in the years following the fall of the USSR. But in preparation for the summit, Russia plowed 20 billion dollars into the city and the Primorsky Krai province to build an international airport, roads, bridges, a new university and amenities (Image 2).
This titanic, yet symbolic project mobilized an army of both native and French designers, engineers and builders to work on the Golden Horn cablestayed bridge (737 metre central span), spanning the bay in the centre of Vladivostok, and the Russky Bridge, which crosses the Eastern Bosphorus Strait and links the Nazimov peninsula to Russky Island, making Vladivostok the home city of two major cablestayed bridges amongst the ten longest in the world.
The Russky Bridge is currently the only land link to the island. As the only gateway to the venue for the APEC 2012 summit, the bridge has firmly cemented its place in the book of records with a central span of 1,104 m, two A-frame pylons with a height of 319 m, the longest stay cable ever (582 m), a design & build time of only four years, and construction work carried out during the Siberian winter with temperatures plummeting as low as -30°C.
The bridge demanded the undivided attention of Russia’s designers, due to its sheer technical complexity, and Russian authorities, in light of the stakes involved in hosting the APEC summit. The bridge was designed by the Russian firm Mostovik and built by the Russian construction company USK Most, who subcontracted the part on the Nazimova peninsula to Mostovik. The construction methods and related detailed analyses were pioneered by Institute Gyprostroimost Moscow and Mostovik.
The Russky Bridge was also a hotbed of French engineering activity and the scene of deployment for the parallel strand stay cable technology pioneered by Freyssinet, which rose to the technical and technological challenge, thereby enabling the extraordinary bridge to be completed in recordbreaking time.
2. Structural description
2.1 General Overview
The Russky Bridge over the Eastern Bosphorus Strait boasts a total length of 1,872 metres. It features 384 metre side spans and a 1,104 metre cablestayed central span, which beats the previous recordholder (the Sutong Bridge in China) by 16 metres for this type of structure (Image 3). The navigational clearance is 450 metres in width and 70 metres in height.
The central span is supported by two lateral planes of stay cables anchored to the tops of the 319 metre high A-frame pylons. The pylons stand on two 13 metre high reinforced concrete pile caps that are linked together with a tie beam and supported by 240 piles with a diameter of 2 metres and lengths varying from 20 metres to 65 metres, anchored in the bedrock.
The stay cables are anchored to the top of the pylon in “anchorage boxes,” which are steel structures fixed to the concrete using studs.
The deck, which has an upsidedown airplane wing shape, has a total length of 25.96 metres and a height of 3.20 metres. Its central span is made from an orthotropic steel box that stretches for 70 metres beyond the towers in the side spans.
Due to the position of the first stay cable, located at 53 metres on either side of the tower’s axis, the steel section in the back span had to be extended to maintain the equilibrium. The steel deck represents 67% of the bridge’s total length. The deck of the central span is built by cantilevering segments of both 12 metres and 24 metres in length.
The side spans stand on reinforced concrete piers and abutments, and vary in length from 60 metres to 84 metres.
In the concrete section of the side spans, the deck is a multicellular prestressed concrete box girder with two 0.6 metre thick side vertical webs and a 0.4 metre thick central web in the main run. The upper and lower slabs have a standard thickness of 0.3 metres.
2.2 The Stay Cable and Damping Systems
The stay cable system used on the Russky Bridge is Freyssinet’s proprietary “parallelstrand” and “compact” system. Invented in the 1970s and initially derived from the technology of prestressing by post tensioning, Freyssinet’s parallelstrand stay cables were used on a large scale for the first time on the Pont de Normandie (the world’s longest cablestayed span in 1994 with 856 metres) and has since undergone a number of significant technological developments.
Compact stay cables comprise individually protected strands that are placed in a parallel fashion inside an outer sheath. Each strand features seven galvanized wires protected by a wax film and a highdensity polyethylene (HDPE) sheath that is directly extruded on the strand in the factory after the wax has been applied. The surface area of a strand measures 150 mm2, and the strand’s guaranteed ultimate strength is 279 kN.
Strands are placed in an extruded HDPE outer sheath, with a UV-resistant outer layer that can be coloured to specification. Furthermore, the sheath is provided with an external helical rib to prevent vibrations under the combined effect of rain and wind, while minimizing the drag coefficient at high wind speeds (CD=0.60). The sheaths for the Russky Bridge were supplied in the colours of the Russian flag - red, blue and white.
When building bridges with very large spans, the drag force caused by the wind becomes the most critical factor when sizing the towers and their foundations, meaning that every effort must be made to reduce the drag force to a minimum. To achieve this aim, Freyssinet has masterminded the “compact” stay cable technology that, unlike other technologies, allows more strands to be fitted inside the same diameter sheath, thereby reducing drag by around 25%.
In the deck and the pylon heads, each strand is individually anchored using custom designed wedges in anchorages featuring patented devices that ensure the strand’s fatigue resistance and minimize unwanted stresses due to cable movements. Furthermore, Freyssinet’s anchorages are fitted with a system that guarantees a perfect seal. The exposed parts of the strands and the internal parts of the anchor block are injected with wax to protect against corrosion. Thanks to all of these devices and systems, combined with corrosion protection for the external metal parts of the anchorages, Freyssinet’s stay cable system offers unrivalled durability.
3. Bridge construction
3.1 Works Schedule
Construction works on the bridge were carried out over a 47-month period.
The construction works could only be completed within such a short time by working 24 hours a day, 365 days a year.
3.2 Manufacturing and Installing the Stay Cables
The design of Freyssinet’s compact stay cable system used for the Russky Bridge came in for close scrutiny to ensure that the cables would withstand the harsh conditions in the Primorsky Krai region (marine environment, subzero temperatures down to -30°C, high wind speed during construction, etc.), while meeting the project’s major technical requirements (Image 4).
The easiness of installation, while maintaining the required production output, was ensured with the use of:
- Light plant equipment to improve the process of installing the steel segments
- Suitable fitting methods and tensioning tools geared towards the long stay cables used, while minimizing installation times
3.3 Harsh Operating Conditions
To comply with the extremely tight schedule for such a major feat of engineering, a dedicated technical structure had to be set up and incorporated into the Vladivostok work crew in order to promptly meet the need for suitable execution methods.
Freyssinet developed new equipment for the installation phases that could be used for working in low temperatures, especially since stay cables could be fitted at any time of day or night in temperatures down to -30°C. To work around the schedule constraints, the installation methods were redefined, particularly the process for lifting long stay cable ducts. The aim was to guarantee the workers’ safety when lifting the longest ducts to a height of 320 metres, while guaranteeing the ducts’ integrity, bearing in mind that having to replace any ducts would put work significantly behind schedule.
3.4 Safety
Stay cables had to be installed around the clock without any interruptions, meaning that a safety plan was needed to minimize the risks associated with installing the stay cables, working at night and working in extreme weather conditions, since the apparent temperature could fall below -30°C depending on the wind speed. Furthermore, the Eastern Bosphorus region is prone to abrupt changes in visibility and wind, with a likelihood of sudden swirling gusts of wind, especially on the island.
Risk analysis and training formed the backbone of the quality and safety management system throughout the stay cable installation process.
The risk analysis highlighted the operational difficulties and risks inherent in working in cold conditions and at night.
Three types of risk were analyzed:
- Equipment risks related to equipment failure without any effect on project progress
- Operational risks affecting the progress of the installation phase
- Human risks related to operations and the environment
To minimize each risk, a specific set of methods, resources and tools was created.
In terms of equipment risks, new equipment was designed for the cablestaying operations. In particular, low temperature operating winches were developed to allow hoisting operations to continue in temperatures down to -40°C. All hydraulic equipment was also insulated.
In terms of operational risks, new installation procedures were defined to take account of the environment and the compact size of the sheaths, combined with their record breaking lengths.
In terms of human risks, an indepth study was carried out on the effects of cold temperatures on human behaviour and work efficiency. The findings were used to create the best possible working environment and reduce the impact on the work cycle. The study also helped ensure that the appropriate resources were provided for carrying out work both safely and efficiently.
Because of the operational difficulties and risks inherent in working in cold conditions and at night, new methods and resources were developed to keep the pace with the project’s high work rate. Technical training specific to the project also had to be developed and delivered. In all, 200 hours of training divided into 88 sessions were given.
A detailed review was conducted into each workstation, especially those outside the tower during the strandhoisting phase, and a specific set of procedures was defined accordingly. One such procedure was the requirement for people to work in teams of two or more, the idea being for each member to watch the other for any warning signs of cold weather exposure. Heated shelters were also set up on the platforms to allow teams to work in shifts.
By July 2012, and right on schedule, the stay cables had been installed, the dampers fitted and the stay cable monitoring system implemented, all of which without a single accident. The bridge opened to traffic in September 2012 (Image 5).
4. Conclusions
Designing and constructing the Russky Island Bridge within the record period of 4 years and in the harsh Siberian environment of Vladivostok was a challenge to bridge engineering. The use of Freyssinet’s parallel strand cables contributed to this achievement by allowing an early start to the cable erection works before fully completing the assembly of the steel segments, thus placing most of the cable erection works out of the critical path. Finally, the enhanced durability and inspectability of the parallel strand cables will allow the 100 year design life and maintenance criteria of the bridge to be achieved.
5. Acknowlegments and references
5.1 Acknowledgements
This article was written with the valuable contributions of Mr. Valery Kurepin of Mostovik, Omsk, who designed the Russky Island Bridge, and Mr. Sergey Gorbachev of Institute Gyprostroimost Moscow, who designed its main construction methods.
5.2 References
- CIP Recommendations on cable stays, 20 June 2002
- FIB Bulletin 30, Acceptance of stay cable systems using prestressing steels, January 2005
