Home>Business Lines>SYSTEMS & TECHNOLOGIES>POST-TENSIONING STRAND SYSTEMS

Post-tensioning strand systems

VSL designs, manufactures and installs durable, state-of-the-art post-tensioning systems that comply with international standards and approval guidelines for both new and existing structures.

 

  • Slab modification
    Modifications to a post-tensioned slab in an office building.
    USA - 2006 read more

    PROJECT REFERENCE+

    Slab modification

  • Sea Cliff Bridge
    Supply and installation of VSL post-tensioning for a section of the scenic Lawrence Hargrave Drive.
    Australia - 2006 read more

    PROJECT REFERENCE+

    Sea Cliff Bridge

  • Foothills Water Treatment Plant
    Post-tensioning of a circular concrete tank.
    USA - 2002 read more

    PROJECT REFERENCE+

    Foothills Water Treatment Plant

  • Egg-shaped digester tanks
    Achieving savings by using the VSL Z-Anchorage for all ring tendons, avoiding the need for stressing blisters along the surface.
    Croatia - 2006 read more

    PROJECT REFERENCE+

    Egg-shaped digester tanks

VSL is recognised as a leader in the field of special construction methods. Well-proven technical systems and in-house engineering form the basis of the group’s acknowledged reputation for innovative conceptual designs and engineering solutions that ensure reliability, quality and efficiency.

This has been made possible by the development and the application of the post-tensioning techniques that are VSL’s core business and which provide the foundations for most of the activities and services offered to today’s customers.

For decades, VSL has designed, manufactured and installed durable, state-of-the-art post-tensioning systems that comply with international standards and approval guidelines for both new and existing structures. Its services and products are all aimed at delivering the optimal solution for the customer.

A range of standard solutions is available for projects such as buildings and bridges, but VSL has also developed specialist techniques for more demanding structures including nuclear and LNG containments.

The scope of VSL’s services goes far beyond the supply of components and includes:

  • Design assistance at the conceptual stage to select the best option for the structural system and to provide preliminary sizing and quantities;
  • General and detailed design to incorporate post-tensioning systems into the structure with a constant aim of optimising savings in materials, achieving sustainability of the structure and planning the construction work to reduce the cycle times and resources required;
  • Provision of special equipment for post-tensioning installation, including state-of-the- art monitoring and data recording systems. For the nuclear field, VSL has developed a special Low Force Jack (LFJ) to remove the slack on large and long tendons prior to the start of the stressing process, with force monitoring on each individual strand during stressing;
  • All works for the supply and installation of the post-tensioning materials, including a turnkey package provided by VSL’s highly efficient site teams.

VSL provides a choice of anchorages for post-tensioning systems:

  • The Bondtec system, a monostrand anchorage developed particularly for application in building slabs
  • The VSLAB anchorage for building slabs, for use with two to five strands of 15.7mm diameter. The state-of-the-art anchorage combines the bearing plate and the anchorhead into a single piece.
  • The Gc anchorage is available for between four and 37 strands of 15.7mm diameter. It is the latest development of the standard VSL multistrand anchorage and is the most versatile, designed for use in projects including buildings and bridges.

Click here to zoom image
VSL Gc anchorage
  • The Nc anchorage is designed for special applications in the nuclear field for use with up to 55 strands of 15.7mm diameter. It provides very efficient load transfer to the concrete with its three flanges.

Click here to zoom image
VSL Nc anchorage
  • The AF anchorage is a patented VSL solution for use inside a concrete structure where there is no access to the anchorage zone at the time when the post-tensioning is installed.

Click here to zoom image
VSL AF anchorage

Other systems include:

  • The E anchorage, which was the first multistrand anchorage developed by VSL. It can be used in any structure but is today used mostly for repair or upgrading works.

Click here to zoom image
VSL E anchorage
  • The Z anchorage is for special applications in circular structures. The anchorage does not have a bearing plate and the strands are anchored on either side of the anchorhead, with the forces balancing themselves.

Click here to zoom image
Click here to zoom image
VSL Z anchorage
  • The CS anchorage is for special applications such as use with electrically isolated tendons (EIT). The tendons are completely encapsulated into a plastic shell and protected against the outside environment. Special systems can be incorporated into this anchorage to monitor the ongoing corrosion protection of the tendons.

Click here to zoom image
VSL CS anchorage
Click here to zoom image
VSL P anchorage
Click here to zoom image
VSL H anchorage
MORE+

VSL’s Products and Services

  • Construction engineering, stage by stage analysis, geometry control
  • A full range of construction services for bridges, buildings and containment structures right through to the management of the full construction project
  • Heavy lifting works
  • Repair and strengthening works
  • Specialised formworks for buildings and bridges.

Advantages of VSL’s solutions

Standard solutions for standard applications: VSL has efficient, reliable and economical post-tensioning systems and equipment for all standard applications, such as bridges and buildings.

Special anchorages and equipment for specialist applications: VSL has a solution for every problem and provides an extensive range of anchorages to respond to every construction configuration and requirement.

The most advanced techniques:VSL provides the nuclear industry in particular with the latest developments in anchorages, equipment and installation methods. This field is highly demanding and VSL has developed unmatched technologies to install post-tensioning, in particular a monitoring system that allows the force in each strand to be read during the stressing works.

Turnkey services: VSL provides post-tensioning solutions as a fully integrated service from design assistance through to the implementation of the entire construction project.

Constributing to sustainable solutions

Click here to zoom image

Today’s construction market has a strong focus on sustainable development and green building solutions. Thanks to its post-tensioning technology, VSL is a valuable partner for owners, developers and contractors seeking to achieve environmentally friendly objectives in terms of greenhouse gas emissions.

Reducing the CO2 footprint

Post-tensioning is a very efficient technology for optimising building designs in terms of the materials used to build the structure as well as for the overall lifetime costs. The reduction of embedded CO2 emissions is a direct consequence of reduced material quantities and is a crucial element in sustainable construction. Other advantages include reduced consumption of natural resources and reduced lifetime costs by enhancing the flexibility of the building’s use through larger column-free spaces. Post-tensioning also cuts the amount of construction waste at the time of demolition. Greenhouse gas emission is a major factor in the market’s move towards sustainable projects and VSL is committed to demonstrating the major advantages that its post-tensioning solutions bring to the development of green building solutions.

Case study:

37% savings in CO2 emissions

A case study was carried out with the objective of comparing the carbon footprints of two technical solutions – one using traditional reinforced concrete slabs and the other designed with VSL post-tensioned concrete slabs. The case study considered a 21-storey building, with a slab area of 1,072m² and floor height of 4m. The building had 12 circular columns of 1m diameter.

Both alternatives were designed to avoid the need for punching shear reinforcement. Column design was calculated using only normal forces and the contribution of core walls was not taken into account as the horizontal loads were not known. In seismic areas, post-tensioning solutions can reduce wall reinforcement even more because the horizontal loads to be withstood are directly linked to the weight of the concrete elements.

Carbon footprint emissions were calculated for both structural designs using the in-house calculation tool CarbonEco®. The calculation is carried out by associating emission factors with each aspect of the project. For a quick and easy calculation, only the main quantities of structural materials need to be entered. Values are calculated using ratios that have been established from test projects.

Click here to zoom image

In terms of material quantities, post-tensioning brings 23% savings for the concrete and a 48% saving in steel compared to the reinforced concrete alternative. The steel savings are made up of a 56% reduction in reinforcement steel offset by an 8% increase in post-tensioning.

The PT steel represents only 7% of the material emissions and 4.9% of the total emissions but post-tensioning allows the whole project to reduce its global emissions by 37%. Offering the client a carbon footprint calculation that demonstrates such large savings can be used to prove post-tensioning’s value as a sustainable solution.

What represents 1.8t equivalent CO2 per person?

  • Return flight Paris New York
  • 7,000km by car, equivalent to a 30km daily commute to work for a year
  • Heating a 45m² office for a year using gas
  • Construction of 7m² of housing
  • Construction of 2m² of a concrete bridge deck
MORE+

CarbonEco®: a software package for carbon audits

CarbonEco® is a software package that gives owners an accurate assessment of the greenhouse gas emissions that will be generated by their projects, from design through to demolition, including the operational phase.

CarbonEco® makes it possible to forecast every project's carbon footprint, enabling VSL’s clients to choose the best design and build options offered by the group. The tool can be applied to all building and civil works projects — whether for construction or renovation - including housing, offices, schools, industrial buildings, engineering structures and tunnels. The software can also be used during the operational phase of a structure, after handover.

VSL is aiming to establish comprehensive carbon footprint accounting throughout its network.

MORE+

How it works?

Concrete is a material that works well in compression, but that has very low strength in tension.

Post-tensioning is a construction technique that consists of inserting active steel reinforcement into a concrete structure to make the concrete work in compression, while the tension forces in the structures are taken by the post-tensioned members. This avoids the concrete coming under tension and so prevents cracking, which is detrimental to the behaviour and long-term durability of the structure.

A traditional reinforced concrete structure

Click here to zoom image

Concrete cracks naturally when under the tension that arises in structural members subjected to bending or tensile loads. This deformation of the structure activates the steel reinforcement members embedded as a matrix within the structural members.

A post-tensioned concrete structure

Click here to zoom image

The structure is first subjected to compression by tensioning cables that are installed in the concrete at appropriate locations. That leads to a pre-compression of the structure, which deforms under these internal compression forces.

When subject to external forces, the structure then experiences additional internal forces.

The design aims to ensure that the resulting sum of all the internal forces inside the structure is such that all the concrete remains in compression, while the steel reinforcement members take the tension.

This can be illustrated as follows:

Bending causes tension + compression

Post-tensioning adds compression (and possibly bending if the post-tensioning members are placed eccentrically in relation to the cross section)

The result is a reduction or elimination of tension – which means that there can be no cracking. Essentially, post-tensioning provides a compressive stress that is introduced into a structural member before it enters service. The compressive stress is introduced at the points where tensile stresses would be expected to develop under service loading.

Force applied eccentrically


Bending causes tension + compression

When the post-tensioning force is applied eccentrically to the structural member, the eccentricity (e) of the prestress force reduces the tensile stress caused by the applied loads and it also prevents the compressive stress from becoming too large.

The internal forces in the structure are therefore better balanced, and - very importantly - the concrete in the structure can remain under compression at all times.

MORE+

The prestressing or post-tensioning components

The prestressing technique requires only one component: the tensile member.

The tensile member is stressed and cast directly into the concrete. The bond developed between the concrete and the strand is sufficient to maintain the stress in the tensile member and, as such, to introduce the required compression into the concrete.

The post-tensioning technique requires additional components:

  • A duct or a pipe, to create a void in the concrete where the tensile member is inserted;
  • Anchorages at both ends of the tendon to transfer the force into the tensile member after stressing;
  • A filling material introduced between the duct and the tensile member. The filling’s primary function is to protect the tensile member against corrosion and it may also be used to bond it to the rest of the structure.

The tensile member

The tensile member is generally made of high-tensile steel bars or strands, but it can also be made from other materials such as carbon fibre reinforcement (CFR).

Click here to zoom image

The guaranteed ultimate tensile strength (GUTS) for such tensile members varies from 950MPa to 2,000MPa or even higher. In comparison, the GUTS for the normal reinforcement materials used in concrete varies between 400MPa and 600MPa.

A wide range of wires, strands and bars is available on the market for use as tension members. Diameters of wires, strands and bars vary depending on the member’s required tensile capacity.

Strand: the tensile member for post-tensioning (PT)

The strand most commonly used for PT has a nominal diameter of 15.2mm or 15.7mm (0.6”) and is made from seven wires that are twisted together.

Other strands are available on the market, including a compact strand of 13mm (0.5”) diameter with an overall capacity of 300kN.

MORE+

Ducts and pipes

Voids in the concrete are created using ducts or pipes. The coefficient of friction between the duct or pipe and the tensile member depends largely on the materials used for these components.

Rigid pipes are generally made of steel, either in straight lengths or in curved sections. They are used especially where sharp deviations in the post-tensioning tendons generate stresses that are too high for the adjacent concrete to widthstand. They are also installed in highly demanding structures such as nuclear power plant containments.

Ducts can be made of steel (galvanised generally) or plastic. VSL has developed PT PLUS™, its own propriatary duct system that provides many advantages for the tendons, including a high degree of corrosion protection and lower friction coefficients.

MORE+

Post-tensioning anchorages

The anchorages are placed at both ends of the tendons to secure the forces once the load has been released from the stressing jack.

Anchorages are generally composed of:

  • Wedges - the critical item that transmits the stressing force from the strand to the anchorage
  • The anchorhead - a key component that transfers the post-tensioning force from the wedges to the bearing plate. The head is drilled with holes and wedge cavities to allow the strand to pass through and be secured. At the exit of the head, plastic bushings may also be inserted to reduce the friction between the strand and the anchorhead, thus enhancing the anchorage’s fatigue behaviour.
  • A bearing plate, which is generally embedded into the concrete and that transfers the post-tensioning force from the anchorage to the concrete structure
  • Anti-bursting reinforcement, located around the bearing plate to confine the surrounding concrete so that it can withstand the compression forces. Typically these forces are in excess of two or three times the ultimate capacity of the concrete.
  • A cap on the top of the anchorage to protect the anchorhead and the wedges

VSL has developed a wide range of post-tensioning anchorages for internal and external post-tensioning. These include:

  • The Gc anchorage: the most common and the most versatile anchorage for multi-strand tendons, whether internal or external. Sizes range from 6-4 to 6-31. Ultimate capacity varies between 1,116kN and 10,323kN.
  • The Nc anchorage, for special applications in the nuclear field, where tendon sizes are up to 55 strands with an ultimate capacity of 15,345kN
  • The VSLAB anchorage for flat tendons, generally installed into flat members (slabs), with sizes varying between 6-2 and 6-5 and ultimate capacity from 558kN to 1,395kN
  • The AF anchorage, a patented VSL solution that allows the anchorage to be installed into the concrete in an inaccessible area, with the strands installed and stressed at a later stage
  • The CS anchorage, which allows total encapsulation of the tendons for enhanced durability

These anchorages are tested and approved in accordance with international standards, especially the European ETA.

Filler materials

The filler materials that surround the tensile and anchorage members are an essential part of the post-tensioning system, as they provide long-term protection for these compoenents and as such ensure the durability of the structure. A great deal of attention needs to be paid in choosing, testing and using these materials to ensure their final quality.

The filling materials can be:

  • Cementitious, with a high pH that inherently protects the steel components. The design and installation has to ensure that all voids are filled, especially at the high and low points. Special methods of installation should be developed and tested on a mock-up prior to implementation on the permanent structure.
  • A petroleum-based material, grease or wax can also be used but may need to be heated before installation.

Active reinforcement: prestressing and post-tensioning systems

Click here to zoom image

General overview of the different techniques for prestressing and post-tensioning:

There are two basic types of active reinforcement systems, depending on when the tensioning of the tensile member is carried out.

Click here to zoom image

Prestressing

The term prestressing is used when the tension is applied to the tensile members (strand) before the concrete is poured. Once the concrete is cured and the strands have bonded to the concrete, the tension on the strands is released, which introduces the force from the strands into the concrete.

The construction sequence
Click here to zoom image
  • Small diameter wires are generally used due to their better bond characteristics. Strands are also widely used for large precast concrete elements.
  • As the bond is important, the steel must be extremely clean. Full compaction/vibration of the concrete is also necessary.
  • Prestressing is suitable for factory production off-site where permanent casting beds can be set up, particularly for casting a large number of identical units.
  • Specialised curing techniques including the use of steam can be used to enable early stress transfer
  • Sizes and weights are limited only by transport capabilities.
  • Wires are generally straight, which means they are not making the most efficient use of the prestressing force.
Click here to zoom image

The casting set-up includes a bench that is used to take in compression the forces that are applied to tension the strands before the concrete is poured.

Click here to zoom image

The strands are stressed into the formwork before the concrete is poured.

As the concrete is poured, it comes in contact with the strand. Once the concrete has cured, the strands are bonded to the concrete matrix.

Once the concrete has set, the force in the strand is activated and the precast element freed from the form.

MORE+

Post-tensioning

Post-tensioning is the technique where the tension is applied to the tensile members (strands) after the concrete has been cast and has cured to reach the minimum required strength.

Ducts are laid into the concrete before it is poured. Once the concrete has cured, the strands are threaded into the ducts. They are then tensioned and anchored at the ends of the tendons using post-tensioning anchorages embedded into the concrete.

In order to protect the strands against corrosion, the space between the ducts and the strands is then injected either with:

  • a cement-based grout, in which case the PT becomes bonded to the concrete
  • grease or wax, which does not bond the strand to the structure. In this case, the PT is unbonded.
Click here to zoom image

Bonded (non-replaceable) post-tensioning

The construction sequence is as follows:

  • Empty ducts are placed into the formwork before concrete is placed, creating a hollow void for the PT strands.
  • Strands are threaded into the ducts either before or after pouring the concrete.
  • Concrete is poured and allowed to cure to reach a required strength, generally 25MPa
  • Strands are stressed. The force is secured into the tendons by anchorages at both ends. Stressing can be done at one or both ends of the tendons, depending on the shape and the design requirements.
  • Ducts are injected/grouted with a cementitious grout to bond the strand to the rest of the structure and to provide corrosion protection.
The construction sequence
Click here to zoom image
Click here to zoom image
Click here to zoom image
Ducts are placed within the rebar cage in the formwork before the concrete is poured.
The operation is similar for a flat slab, where the ducts have a profile that is determined during design to suit the internal force envelope.
MORE+

Unbonded (non-replaceable) post-tensioning

Click here to zoom image

Unbonded internal PT

The construction sequence is the same as for the bonded system.

However, in order to maintain the strand’s freedom to move relative to the concrete structure, it has to be surrounded by a non-adhesive material that provides its protection against corrosion. Grease is normally used for this purpose.

There are two basic arrangements to achieve unbonded tendons:

Greased and sheathed strand
  • The strands are greased and individually extruded into a plastic sheath – the strands are described as greased and sheathed. These are then threaded into the ducts and the spaces between the ducts and the greased and sheathed strands are injected with a cement-based grout.
  • The strands are stressed and secured at each end of the tendons using PT anchorages.
  • A cap is placed over the anchorages and injected with grease to protect the steel against corrosion.

Note that the strands can also be inserted directly into the formwork without ducting before the concrete is cast. These are known as mono-strand structures.

Click here to zoom image
Greased and sheathed strand
Bare strand injected with grease
  • Bare strands are threaded into the structure.
  • They are tensioned and secured.
  • The void left between the strand and the duct is then injected with grease or a wax that serves to protect the tensile member against corrosion.

External PT

Click here to zoom image
External post-tensioning: Gautrain project, South Africa

External tendons are installed outside the concrete section. However, they are anchored at the ends of the concrete structure in such a manner that they introduce compression into the structure. Detailing of the connection between the tendon and the structure has to ensure that the tendon can be removed and replaced if necessary.

This technique is also widely used for so-called ‘future tendons’: the structure is detailed and built with additional anchorages but without the tendons. The tendons can be installed at a later stage if the structure needs strengthening due to an increase in traffic or changes in the design regulations.

Bridges

Post-tensioning techniques have contributed to extraordinary developments in concrete bridges in terms of bridge types, erection methods and span lengths.

Tendons are typically installed as internal and external post-tensioning. They allow different construction techniques, including but not limited to:

  • Precast balanced cantilever erection
  • Precast span-by-span erection
  • In-situ balanced cantilever installation
  • The incremental launching method
  • Full-span precasting
Click here to zoom image
Click here to zoom image
The Gateway Bridge in Brisbane, Australia, was built by the cast-in-situ balanced cantilever method, with its precast approach spans built in balanced cantilever using an overhead gantry.
The West Tsing Yi structure in Hong Kong was built as a balanced cantilever erected with lifting frames.

Buildings

Post-tensioning is widely used in building all over the world.

The primary application is for slabs, where passive steel reinforcement is largely replaced by post-tensioning. This allows the structure to be lighter, or the spans to be longer, while enhancing durability as the concrete remains uncracked throughout the life of the structure.

Other applications include:

  • Transfer plates, used where a building layout changes from floor to floor, for example where offices or residential properties are above shopping centres that require larger open spaces. VSL has built up extensive experience of the use of transfer plates, especially in Hong Kong where this type of construction is very popular.
  • Post-tensioned transfer beams and transfer plates to provide spacious, column-free, architecturally pleasing spaces such as entrance halls, lobbies and convention rooms
  • Post-tensioned raft foundations to produce more economical solutions with improved deflection and better performance in terms of shear and soil pressure
  • Post-tensioned concrete walls such as building cores and masonry walls that allow the architect and engineer to design with more flexibility and produce more pleasing aesthetics
  • Post-tensioning in structural members such as the mega-trusses of high-rise buildings designed to withstand wind-generated overturning moments
  • Precast structures built using post-tensioning to allow the structure to be built more quickly

The benefits of the solution

Owners benefit from:
  • Savings in materials for both structures and foundations, leading to more economical construction
  • Reduced financing costs due to shorter construction periods
  • Less need for maintenance because of crack and vibration control
  • Provision of more useable space within the available heights limits
  • Reduced structural deflection
Click here to zoom image

Architects have more aesthetic freedom and greater options arising from the creation of larger column-free spaces that generate more flexibility for offices, houses, car parks and similar structures.

Contractors gain through:
  • Shorter construction time as formwork is often simpler due to the integration of the main beams into the slab thickness
  • Reduced cycle times as post-tensioning allows the structure’s formwork to be stripped earlier leading to an overall reduction in the construction programme
  • Lower energy consumption
MORE+
Click here to zoom image
Click here to zoom image
Lugo Hospital, Spain - 2005
Venetian Macao Resort Hotel, China - 2007
Click here to zoom image
Hang Seng Bank New Headquarters, Hong Kong, 1989
Click here to zoom image
Click here to zoom image
Burj Residence, Dubai, U.A.E., 2007
Liverpool Tower, UK, 2006, Transfer plate/beams construction

Prestressed slab on grade

Click here to zoom image

Placing a prestressed slab directly on the ground – known as slab on grade - is the preferred solution for installation in large areas such as container terminals and distribution centres. Use of the slab on grade technique combines economy, long-term durability and a flat finish for smooth vehicle operations.

Slabs on grade

VSL post-tensioning techniques bring benefits to large indoor and outdoor areas where the slab foundation is placed directly at ground level. The approach delivers advantages in warehouses, distribution centres, container storage terminals, train and shipping terminals, airports, manufacturing facilities and as floor bases for liquid-retaining structures.

Benefits to the owner:
  • Elimination of joints - owners and operators benefit from cost savings brought by the elimination of most or all of the joints in the slab, as the use of VSL’s technologies allows a reduction in their number.
  • Shorter construction times, compared with ordinary reinforced concrete slabs. The use of VSL’s technologies leads to less excavation, a thinner slab, little or no reinforcement and few if any joints. Large areas in excess of 2,500m2 can be concreted, which results in a shorter construction time and contributes to a very competitive initial cost.
  • 'Crack free’ performance as initial stressing can prevent shrinkage cracks. Post-tensioning compresses the slab and counteracts the tensile stresses that would otherwise cause cracking under the worst combinations of loads or in poor soil conditions.
  • Shorter curing time - the curing time of VSL’s post-tensioned slab on grade is very short compared with any other type of slab. This leads to a shorter overall construction programme, which also helps reduce financing costs.
  • High impact and abrasion resistance - the compression resulting from post-tensioning combined with an optimum concrete strength and surface treatment reduces general wear and tear and subsequent maintenance costs.
  • Low maintenance - the significant reduction in the number of joints means that less maintenance is required, giving great improvements in operational efficiency.
MORE+
Click here to zoom image
Click here to zoom image
Hangar Mosnov, Czech Republic - 2007
Walmart, Mexico - 2007

Containment structures

Post-tensioning techniques are particularly well suited for containment applications as they provide a primary structural member to take the tension forces generated by the pressure applied inside the containment, while keeping the structure airtight and watertight.

The advantages apply to all types of containment structures, including nuclear containments where the post-tensioning plays a vital role in the event of a nuclear accident. Similarly, post-tensioning in an LNG structure keeps the gas inside the tank in the event of a failure of the primary containment structure. Water tanks and silos benefit from the same security.

Nuclear and liquefied gas: stringent requirements to ensure exceptional reliability

Click here to zoom image
Uljin nuclear power plant, Korea

VSL carried out comprehensive tests on a full-scale mock-up of the latest generation of nuclear power plants to verify compliance with specific client post-tensioning requirements. VSL demonstrated that its systems, equipment and procedures meet the stringent requirements for all operations on various types of 360° tendons.

The construction of tanks for LNG and LPG (liquefied natural and petroleum gas) requires cryogenic testing of tendons. They are subjected to temperatures down to -196°C and are tested in accordance with international standards including ETAG. As a result of such testing, VSL is in a position to supply its post-tensioning systems to any LNG or LPG project around the globe.

Unique VSL anchorages for economical solutions

Well-designed structures are practically crack-free and, most importantly, they are economical. Thanks to the variety of its post-tensioning anchorage systems, VSL offers versatile solutions for engineers and contractors to optimise costs and construction times. Some of VSL’s wide selection of anchorages are particularly suited for use in containment structures.

Offshore structures

Prestressed concrete is the preferred choice for many other types of engineered concrete structures.

Click here to zoom image
Click here to zoom image
Troll Platform, Norway
N’kossa barge, France

Special structures

Click here to zoom image
Thun Bypass Tunnel, Switzerland – 2008

Without post-tensioning, many special structures could only be built with great effort - if indeed they could be built at all.

This also applies to many other type of structures, where the post-tensioning is used to strengthen the concrete. Applications are endless, and include stadiums, tunnels, water drainage pipes and penstocks

Repair and strengthening

Post-tensioning is an ideal technique for retrofitting and strengthening concrete structures, as it can be installed externally to the structure. Many applications have been carried out on different types of structure including:

Replacement of external post-tensioning in bridges

Click here to zoom image

The external tendons that reinforced the 1974-built 1,102m-long Saint-Cloud Bridge near Paris showed signs of corrosion and the client decided to replace them. As a first precautionary step, shock-absorbers were fitted at each side of the deviators before the tendons were cut and the anchorages removed or adapted. New external tendons were then installed by VSL.

Repair of bridges

Click here to zoom image
Figueira de Foz Bridge, Portugal – 2005

VSL, in partnership with a local contractor, carried out repair works including external post-tensioning, strengthening of the abutments with bars and replacement of expansion joints. There was also retrofitting of structural bearings and seismic devices, including the installation of 4 x 500kN shock-absorbers at the abutments.

Strengthening of historical buildings

Click here to zoom image
Las Arenas Bullfighting Ring, Spain, 2007

One of the many examples in Barcelona where VSL has assisted with engineering and specialised site works is this former bull ring, built in 1898, which has been transformed into a leisure and entertainment complex. VSL carried out engineering and post-tensioning works in connection with the transfer slab and beams of the Neo-Mudéjar façade. The project involved post-tensioned floors with spans of between 12m and 17m and the supply of other VSL products such a neoprene bearings and studs.

Click here to zoom image
The Leaning Tower of Pisa, Italy - 1993

VSL strengthened the world-renowned Leaning Tower of Pisa with 18 specially-developed monostrand hoop tendons. The optimum solution consisted of a marble-coloured PE-sheath and galvanized, non-greased 0.6" strand with a centre stressing anchorage, allowing force adjustment and monitoring during and after the stressing operation.

Strengthening of a nuclear power plant

Click here to zoom image
Gösgen Nuclear Power Plant, Switzerland, 2005

A carbon fibre tendon system was used for the seismic upgrade of the emergency feed building at the Gösgen nuclear power plant. The system consists of carbon CFRP plates and head and is well suited for seismic and other strengthening measures where post-tensioning forces are needed in very thin tensile members.

Silo repair and strengthening

Click here to zoom image
Blue Circle Cement Silo, Singapore, 2001

The 60m-tall silo was strengthened using a VSLengineered solution of externally wrapped, bonded tendons each with four strands of 0.6”. The 66 tendons are encapsulated in flat high-density polyethylene ducts and anchored into special stressing brackets.