Stay cable systems

VSL’s Stay cables are designed to meet the demanding requirements of modern long span bridge construction but are equally suited for smaller spans or other cable stayed or suspended structures.

  • Baluarte Bridge - Focus: Dampers
    Use of 152 VSL Friction Dampers for vibration control of the world’s highest cable-stayed bridge deck.
    Mexico - 2012 read more

    Baluarte Bridge - Focus: Dampers

  • Second Penang Bridge - Focus: Saddles
    VSL’s installation of a total of 120 saddles along with the 144 stay cables for a major sea crossing.
    Malaysia - 2013 read more

    Second Penang Bridge - Focus: Saddles

  • Torun Viaduct
    Supply and testing of VSL stay cable anchorages that meet very stringent fatigue requirements.
    Poland - 2013 read more

    Torun Viaduct

  • Bugrinsky arch bridge
    VSL’s manufacture and innovative installation of 156 SSI stay cables up to 109m long.
    Russia - 2014 read more

    Bugrinsky arch bridge


VSL – Leading in Stay Cable Technology

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Industrial Ring Road Bridge, Bangkok

Since entering the stay cable market with its strand system in 1978, VSL has been a worldwide leader in stay cable technology and related engineering services with a well-merited reputation for quality and efficiency. Applying the strand / wedge anchorage principles of VSL’s post-tensioning systems, VSL stay cables have a long and successful track record culminating in the most recent SSI 2000 range with its anchorages, saddles and dampers. Continuous development is being carried out to meet the stringent and constantly evolving design, construction and maintenance requirements of modern cable-stayed structures, with a particular focus on durability, fatigue, aerodynamic performance, vibration control, aesthetics and ease of installation.

A fully integrated system

The SSI 2000 system offers high fatigue resistance, enhanced corrosion protection, simple cable force monitoring and adjustment, full inspectability and replaceability as well as modular vibration damping solutions. VSL Stay cables can sustain the most demanding structural configurations in the most severe environments. Individual protection and encapsulation of the strands combined with seamless corrosion protection of the anchorages result in an extremely durable system with reduced maintenance needs. The VSL Saddle allows for strand by strand installation and strand replacement. The specialist strand-by-strand installation methods developed by VSL offer great flexibility for all site conditions combined with fast erection cycles.

Available options:

  • The compact SSI 2000 C standard system for reduced wind drag
  • The dehumidified SSI 2000 D system with drag coefficient comparable to PWS systems
  • The VSL Saddle at the pylon to simplify pylon design and construction
  • VSL Damping systems for stay cables (Friction and R-damper) to mitigate wind or rain induced vibrations

Construction engineering including stage by stage analysis

during the structure’s erection with live calculation of stay force and specific control procedures on site.

Simplified detailing design

with several options of cable dimensions to meet specifications of force and wind drag.

Protection solutions

whether initially during construction or as retrofit measures on existing structures, against excessive vibration, vandalism or blast.

Installation of all the above including methods and specialized equipment

whether as a turnkey or with supervision only

VSL's Products and Services

Bridge construction methods

Design, fabrication, commissioning and operation of specialized construction equipment, such as form travelers for in situ construction, lifting frames for segment erection…

Bridge construction including precasting, segment erection

Bridge protection solutions

Advantages of VSL's Solutions

  • A specialist’s capability: design, supply, installation and monitoring of a state-of-the-art fully integrated system including stays, anchorage, saddle, dampers, monitoring, highly durable and versatile (stay replacement, reduced wind drag) based on over 175 successfully completed stay cable projects and 100 000 precast bridge deck elements.
  • A full partner capability: VSL can bring the project team an extensive experience in bridge construction and is committed to offering clients the ‘best for project’ service with various innovative Partnering and Alliancing arrangements that have proved to be highly successful and mutually beneficial to all parties. VSL is capable of taking over the full bridge construction scope mitigating interfaces for the client.

    Compactness, single strand installation/replaceability as well as full encapsulation: The very compact anchorages of the SSI 2000 system allow easy installation even in confined locations inside box girders or pylons using light equipment. Anchorages are fully pre-fabricated in VSL’s factories and their installation on site can be carried out off the critical bridge erection path. Single-strand installation and stressing are standard features of this system and the use of lightweight erection equipment minimizes the strain on tower cranes and other heavy erection cranes providing maximum flexibility in the bridge erection cycle. Continuous protection against corrosion of each individual strand is achieved over the entire length of the cable to ensure high performance durability.

  • A state-of-the art saddle, unique on the market allows simplification of pylon detailing and construction

Contributing to sustainable solutions

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VSL Stay cables have a design life of over 100 years even in the most aggressive environments. Elements are fully replaceable without requiring modifications to the structure. All the materials used are carefully selected and all components are detailed to meet the highest durability criteria. In addition, the modular nature of the VSL SSI 2000 Stay cable system helps reduce the environmental impact of maintenance operations by minimizing the amount of waste generated when parts have to be replaced during the structure’s life cycle.

VSL Stay cable system SSI 2000: how it works

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Stay cables on stay cable bridges can be designed according to three different layouts, all connecting the deck to the pylon.

  1. The cables are passing through the pylon which is a solid element to anchor on its opposite side. In this case, cables cross each other in the pylon and are therefore on different plans.
  2. The VSL SSI 2000 stay cables are anchored inside the pylon which is a hollow core structure. The pylon is designed to withstand splitting forces induced by the cable at either side. As such, the structure is generally very heavily reinforced, with passive and active reinforcement
  3. The cables are running through the pylon in a saddle. The VSL SSI 2000 saddle shall withstand differential forces at either side of the pylon which is achieved by friction between the strand and the saddle. This solution has the advantage of simplifying dramatically the pylon detailing and construction.

Anchorages below or above the deck

The lower cable anchorages can either be located below or above the deck. For concrete decks, the anchorage is generally placed below the deck to make use of load transfer mechanisms in compression. A guide pipe runs through the deck in order to create the required void. For steel or composite decks, the anchorages are often placed above the deck in structural attachments transferring the cable forces by tension to the main girder element. The SSI 2000 anchorage with its compact dimensions is ideally suited for both applications.

Durability by full individual encapsulation

The individual encapsulation of each strand avoids the risk of corrosion migration inside the stay. Full individual strand encapsulation in the anchorage zone is achieved by providing each strand with its own protection tube and sealing details in the anchorages at the transition from the free strand length to the wedge anchorage. Combined with injection of the anchorage voids after installation with a bonded and polymerized flexible filler the system becomes fully leak tight.

With its multi-barrier corrosion protection system the SSI 2000 stay cable meets and often surpasses all the requirements of the internationally applicable specifications. The corrosion protection systems on the anchorages have been designed to provide up to 100 years of design life in the most aggressive environments.

Robustness and fatigue performance

SSI 2000 anchorage details are designed to filter vibration and bending stresses in the cable before they reach the wedge anchorage resulting in an outstanding fatigue performance. A tension ring or a guide deviator placed at a fixed distance from the anchorage provides defined deviation conditions at the anchorage exit.

All anchorage elements as well as the cable parts close to deck level are mechanically well protected by either the guide pipe or inside a for each project specifically designed anti-vandalism pipe.

Solutions for reduced wind drag

While the stay pipes of the standard SSI 2000 feature already helical ribs which have been optimized in wind tunnel testing in order to minimize wind drag, two more compact solutions have been developed for long span bridges where the horizontal wind loads on the cables and hence the structure must be further reduced. The SSI 2000-C is a compact stay cable range with significantly reduced stay pipe diameters applying the same corrosion protection system as the standard SSI 2000. Where even lower wind drag is required, the SSI 2000-D offers the most compact strand cable section in the market by eliminating the sheathing of the strands and providing equivalent corrosion protection by permanently de-humidifying the cable.

Main components

The SSI 2000 VSL Stay cable system was developed to meet the stringent design, construction and maintenance requirements of cable stayed bridges. It comprises a tendon formed by a bundle of parallel 15-mm diameter high tensile 7-wire steel strands which are hot deep galvanized and generally individually greased or waxed and fitted with a tightly extruded HDPE sheath (except for the SSI 2000 D system), an outer thick-walled protective HDPE stay pipe and factory prefabricated anchorages. VSL has also developed a state of the art fully compatible saddle well suited not only for extradosed cables but also for cable-stayed bridges where the pylons may be subjected to unbalanced loads.

The SSI 2000 System (used for the standard and C version)

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Low drag coefficient and aeroelastic stability Free tension ring Replaceable strang systems in durable stay pipe Anti vandalism protection Individual encapsulation and deviation Compact anchorage High fatigue resistance Anchorage protection cap with flexible del filler

The SSI 2000 Stay Cable System is based on VSL’s proven strand technology. Its wedge anchorages and its tensile members as well as its protective system meet the most stringent requirements for durability, tensile capacity and fatigue performance. Its strand-by-strand technology ensures maximum flexibility and full capability for replacement.

The detailing of all components as well as the material selection has been carried out to provide:

  • highest fatigue performance as confirmed by a multitude of full scale fatigue tests
  • high degree of corrosion protection based on multi-layer system with individual encapsulation of strands in the anchorage zone
  • compact cable dimensions for minimized wind drag
  • easy installation of the cable applying strand by strand methodology with lightweight and compact equipment
  • single strand stressing using extremely light mono strand jacks
  • no requirement for on- or off-site cable pre-fabrication
  • easy tendon force monitoring and adjustment throughout the cable's service life
  • ability to remove and replace individual strands without dismantling the anchorages or the rest of the cable
  • optional installation of anti-vibration dampers during cable installation or as a retrofit solution
  • full compatibility with VSL’s SSI saddle ensuring strand-by-strand functionality while achieving the same level of corrosion protection and fatigue performance as the standard anchorage

SSI 2000-D System - The world’s most compact stay cable strand protected by dry-air

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With the SSI 2000-D system, VSL introduces proven dehumidification technology to stay cables, defining a new standard for the industry (see page …..). The D-system maintains the highest standards of durability while eliminating the need for individual sheathing of the strands and hence allowing a drastic reduction in cable diameters.

A compact bundle of unsheathed strands protected by dry air

With the SSI 2000-D system, VSL offers the most compact parallel strand stay cable in the market. The resulting wind drag is equal to or lower than that of parallel wire cables with equivalent capacity, while the system maintains all the typical SSI 2000 benefits when it comes to installation, inspection and replacement.

Use of SSI Saddles, Catumbela Bridge Angola, 2009

The galvanised, unsheathed strands

Use of SSI Saddles, Catumbela Bridge Angola, 2009

These are placed inside an air-tight enclosure, where any optional dampers can also be accommodated. A dehumidifier unit, typically placed inside the pylon, provides a constant supply of dry air at the pylon anchorages, while maintaining a permanent pressure differential between the inside and the outside of the cable. This prevents any ingress of moisture or other corrosive agents from the outside. All structural elements of the stay cable are protected within this controlled environment where the humidity is maintained below the threshold that would trigger corrosion.

The applied pressure differential ensures that a leak in the system will only result in an increased air demand and will not jeopardise the protective mechanism.

Dry air – a reliable and proven solution
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The concept of dehumidification systems to protect steel bridge decks and suspension cables was introduced in the 1970s and is today a well understood and highly reliable solution, applied to some of the most prestigious bridges around the world. With the SSI 2000-D system, VSL has applied this proven technology to stay cables to offer a state-of-the-art corrosion protection solution. Use of the latest dehumidification equipment keeps operational and maintenance costs extremely low. Running cost estimates can be provided on request.

Redundancy and equivalent corrosion protection

The principle of multi-barrier protection remains unchanged even though the SSI 2000-D does not make use of individually sheathed strands:

  • The stay pipe provides an airtight enclosure, protecting the tensile element against environmental effects
  • A protective environment of dry air around the strands prevents moisture and corrosive agents from reaching the strands
  • Continuous galvanisation of the bare strand provides a final barrier against corrosion in case of scheduled removal or accidental loss of the other two barriers.
Permanent monitoring of the corrosion protection

The integrity of the corrosion protection system can be monitored permanently through continuous measurement of the corrosion-critical parameters of temperature and humidity inside the cable together with the air pressure. In addition, the protective caps at the anchorages can be fitted with transparent windows allowing a simple visual inspection of the anchorage condition. This significantly reduces the time and cost involved in periodic inspections of the anchorage components.

Combining cable and deck protection

Where the SSI 2000-D is used with steel bridge decks or pylons, the dehumidification can protect both the stay cables and the structural steel elements by suitable sizing of the dehumidification units.

VSL Saddle - Equivalent durability using an injected saddle with replaceable strands

The SSI Saddle is the first saddle in the market with injected but replaceable strands. Each strand is individually encapsulated and the saddle is injected with a polymerised and bonded flexible gel filler, effectively preventing any oxygen or corrosive agents from reaching the strand. Full-scale fatigue tests have demonstrated that the saddle fulfils the same fatigue criteria as the standard anchorages and that no fretting corrosion occurs.

A new generation

VSL has developed a new generation of stay cable saddles combining the advantages of injected saddles with full strand-by-strand functionality based on Ductal® ultra-high-performance concrete.

Individual guiding and encapsulation of the strands allows strand-by-strand installation, inspection and replacement while injecting the guide tubes with a special, polymerised and bonded flexible gel filler prevents any ingress of oxygen, hence eliminating the risk of fretting corrosion. The result is a saddle with fully replaceable strands that achieves the same fatigue performance as standard SSI 2000 anchorages.

The V-effect; maximum friction using wedge action

The SSI Saddle is a steel box filled with Ductal® ultra-high-performance concrete and featuring V-shaped guide voids for each individual strand. This patented geometry provides an efficient wedge action, continuously gripping the strand by friction along the deviated length, while minimising fretting under cyclic loading. The entire saddle is detailed such that the deviation occurs entirely in the strand-to-Ductal® interface with no intermediate layers that could deteriorate over time.

Independently guided and replaceable strands

The saddle allows unrivalled single strand installation, inspection and replacement. Strands can be individually stressed and de-stressed. In the same way that larger anchorage units can have spare strand positions, the saddle can also incorporate additional guide voids to give the option for a future increase in cable capacity.

Seamless integration with the SSI system

The saddle uses the same strand as the standard SSI 2000 system, with no additional treatment required. The removal of the tightly extruded PE-coating on the deviated length inside the saddle is performed on site.

Continuous multi-barrier corrosion protection

The PE-coating of the strands is removed inside the deviated length of the saddle to achieve strand-to-Ductal® contact. As with the other SSI components, multi-barrier protection has been incorporated:

  • An outer casing consisting of a steel box and Ductal® gives protection against ingress of water and corrosive agents
  • Injection of the guide voids with a polymerised, bonded, flexible gel filler gives a reliable seal against moisture and oxygen
  • Galvanisation of the strand provides protection during the installation period prior to the injection
Transfer of high differential cable forces into the pylon

Unbalanced loading between bridge spans results in a need to transfer differential cable forces to the pylon, which is achieved by high friction in the V-shaped guide voids in the saddle. Consistent friction coefficients in excess of 0.4 are attained in laboratories.

Proven fatigue performance
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VSL has carried out extensive fatigue testing with the SSI 2000 saddle in accordance with fib recommendations, including a full scale test using a 6-55 unit.

Controlled filtering of angular deviations at the saddle exit

Stay cable anchorages and saddles can be subjected to non-negligible angular deviations at their exits as a result of installation tolerances, vibrations and variations in cable forces. This could cause gradual deterioration of the protective layers of the strand or result in premature fatigue damage. The SSI saddle avoids this by incorporating a defined exit where each strand is individually deviated with the same characteristics as in a standard anchorage, without introducing unwanted stress into the pylon surface.



The tensile member of the tendon is made of a 15.2- or 15.7-mm diameter, high-tensile, 7-wire steel strand, low relaxation that is manufactured as per VSL specifications. It is delivered on coils to site and the tendon is assembled strand by strand. No large and costly on- or off-site pre-fabrication facility is required to carry out the works. By adjusting the installation procedures to the specific requirements of each site, the SSI 2000 provides an extremely versatile solution for all structures.

For the SSI 2000 and the SSI 2000C systems, these strands are galvanized, greased and extruded into a HDPE plastic sheathing.

For the SSI 2000 D systems the strands are only galvanized and additional protection is provided by the dry ambient atmosphere that is maintained inside the HDPE pipe around the tendon.


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The strands are encapsulated into continuous HDPE pipes that provide the ultimate corrosion protection to the tendon. The diameter of the pipe depends upon the tendon size and the implemented system, the pipe for C and D systems is such that the strands are tightly arranged inside leading to a substantially more compact stay cable with reduced wind drag.

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Optional components
VSL Friction Damper
  • Coloured HDPE stay pipes with helical rib: The outer stay pipe is fabricated with double helical ribs, which have been optimised in wind tunnel tests for maximum efficiency and minimum drag against vibrations induced by rain and wind. HDPE pipes can be co-extruded with a coloured outer layer. VSL provides a choice of standard colours that have been tested against ageing and UV phenomena.
  • Anti-vibration dampers, generally at deck level for easy maintenance and designed to provide high performance and easy installation on both new and existing bridges. The VSL Friction Damper dissipates energy by friction whereas the VSL R-damper makes use of high damping rubber acting in shear, friction or rubber, provided at construction stage or after.
  • Anti-vandalism, fire or blast resistant systems, custom designed. Where cables are close to traffic or anchorage zones easily accessible, robust anti-vandalism systems for fire or impact protection are provided to prevent accidental damage to the cable or its anchorage.
VSL R-damper during installation


The strand-by-strand installation methods developed by VSL offer maximum flexibility and can be adapted to the specific needs of each project. All SSI 2000 cables are installed strand by strand using extremely compact equipment and can be inspected and replaced if necessary in the same manner.

The main advantages of the VSL strand-by-strand system installation

  • Absolute flexibility to adjust the cable length during construction to address variations in the bridge geometry or late changes to the deck erection methodology
  • No requirement for provision of off-site prefabrication facilities
  • No significant additional construction loads on the partially-completed structure as light and compact equipment is used.
  • Fast erection cycle and mitigation of cable sag with partial and staged installation of cables for light composite deck assembly
  • No additional requirement on the project’s critical path for the use of tower and deck cranes during cable erection, thus reducing the risk of delay
  • Lightweight anchorages can be pre-installed during deck and pylon construction
  • Easy second stage stressing with monostrand jacks, providing greater flexibility to designers and contractors by avoiding the relocation of heavy stressing and access equipment
  • Improved site safety due to reduced component weights and simplified access arrangements
  • Full strand-by-strand replacement
  • Fully compatible with the VSL Saddle

An optimised solution to streamline complex bridge erection cycles

The equipment can be handled manually at the anchorage location inside or outside the pylons, whatever their shapes. The strand reels are light and compact compared with prefabricated cables and can be easily lifted, transported and handled. This renders the cable installation largely independent of the logistics of deck and pylon construction. As a significant part of the installation can be carried out off the critical path, tower crane usage is reduced, resulting in cost and programme savings.

The preferred option for cable inspection or replacement under traffic

The compact equipment allows for inspection and replacement of the entire stay cable with minimum impact on the bridge traffic, as a single lane closure is typically sufficient to provide a safe working space. For cable replacements if ever required due to accidental damage during the service life., only very light equipment needs to be mobilised to site and replacement works can be carried out with minimal impact on bridge traffic. In addition, the strand-by-strand replacement makes the loss of cable force during the works negligible, allowing unrestricted vehicle movements.

A matching saddle

The SSI Saddle has been specifically designed to allow application of the same strand-by-strand principles for installation, inspection and replacement of the stay cables. All strands are individually encapsulated and guided within the saddle assembly, which combines the advantages of a saddle solution with the benefits of a strand system.

Specialist equipment and procedures

The continuous stay pipe is welded on site from elements of standard length. The strands are delivered to site in compact coils and are installed one by one using a small winch system. They are individually stressed by a lightweight monostrand jack from either the deck or the pylon end. The VSL AMS system provides fully automatic control, recording and data management for the stressing operation on site. Specialist procedures are implemented to ensure an equal final force in all strands and safe anchoring of low cable forces at intermediate stressing stages. The system provides absolute freedom to engineers to specify stressing either to a cable force or cable length, depending on the characteristics of the structure. It is even possible to change the cable length during construction if required. Final tuning of the completed cables

VSL stay cables have been designed to meet the demanding requirements of modern long span bridge construction but are equally suited for smaller spans or other cable stayed or suspended structures such as large roofs.

Single or multiple cable planes on bridges

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Two planes arrangement on Zwolle Bridge Netherlands, 1999

The Stay cable can be arranged in one or multiple axial planes or in two lateral planes. The distance between cables and anchorages must take into account the deck erection methodology. Light and compact cable erection equipment allows tight spacing of adjacent planes while still allowing full replaceability.

Fan, harp and semi-fan system arrangement

Several geometrical solutions can be applied for the arrangement of the stay cables in the structure. Applying the fan system, the upper anchorages of all cables are concentrated in the upper part of the pylon. With the harp system, the stay cables are parallel to one another and their upper anchorages are distributed over the available pylon height. A combination of both principles results in semi-fan arrangements typically used for long span cable-stayed bridges because of its efficiency and the high level of geometrical freedom that it provides. Where additional lateral stabilization must be provided, special arrangements with partially inclined cable planes might be selected and combinations of suspended and cable stayed systems can be used.

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Harp system arrangement on Val de Renne Bridge France, 1988.
Fan system on Evripos Bridge Greece, 1988

Pylon arrangement and jacking clearances

The shape of the bridge towers or pylons varies depending on the chosen cable arrangement and other factors.

Pylons can be inclined and back stayed, solid or hollow, single or multiple shaft etc. The VSL SSI 2000 system offers great flexibility in the arrangement of the anchorages. Minimal required equipment clearances and the possibility of stressing cables either from the top of the bottom allow adaptation of the cable installation process for all possible applications.

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Fan system on Evripos Bridge Greece, 1988
Saddle design on Wadi Leban Bridge Saudi Arabia, 1997
Back-stay cables on Safti Bridge Singapore, 1995

Compact pylon design

In order to achieve a compact pylon arrangement and a more efficient load transfer into the structure deviating cable saddles instead of pylon anchorages might be selected. VSL’s SSI saddle design offers individually guided strands, full adjustability and replaceability of the cable, a superior and tested fatigue behaviour as well as outstanding durability.

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Anchorage below the deck on River Leven Bridge UK,1995
Anti-vandalism pipe, Baluarte Bridge, Mexico,2011
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Neva Bridges Russia, 2003
Yiling Bridge China, 2001
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Masang Xi Bridge China, 2000
Batam Tonton Indonesia, 1998
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White HDPE pipe, Baluarte Bridge, Mexico,2011
Merida Arch Spain, 1991
Anti-vandalism pipes on John Paull II Bridge Poland, 2003 Click here to zoom image
Anti-vandalism pipes on John Paull II Bridge Poland, 2003
Suspended Roof, Alamo Dome USA, 1993

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