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Bars & post-tensioning bar systems

VSL bar systems provides great versatility in geotechnical and construction applications as they cover a full range from hot-rolled bars with grades of 500MPa and 670MPa through to high-tensile alloy steel stressbars up to 1,050MPa.

  • BWI Airport curbside expansion
    Expansion of the main access roads at BWI Airport to improve traffic flow in front of the terminal.
    USA - 2006 read more

    BWI Airport curbside expansion

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  • EuroAirport Basel Mulhouse
    Successful introduction of VSL Threadbar to the Swiss market.
    Switzerland - 2001 read more

    EuroAirport Basel Mulhouse

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  • Wastewater treatment plant
    VSL provides the structural design and post-tensioning of four digester tanks.
    USA - 2013 read more

    Wastewater treatment plant

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  • Honchong Cement Plant
    An application of the VSL SAS-500 Stressbar system.
    Vietnam - 2014 read more

    Honchong Cement Plant

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VSL has been supplying and installing bars for the construction industry since 1971 and can provide an extensive range of hot-rolled products as well as cold-rolled bars.

They have proved to be one of the most popular tools for engineers wishing to control the loads and forces in structures. VSL’s product line complies with international standards, including ISO, Eurocodes, ASTM, Australian Standards and British Standards.

VSL provides a single-source solution for the full range of post-tensioned products and services. It offers threaded bar systems for concrete reinforcing, anchors and form ties as well as products such as soil nails, micropiles and rock bolts for geotechnical applications. VSL bars are available with continuous hot-rolled threads in full 18m stock lengths or as cut sections to meet project requirements.

VSL Threadbar is a high-tensile alloy steel bar with a coarse right-hand thread over its full length. The system has been proven worldwide and offers versatility in a range of applications. The threadbars are hot-rolled, quenched and tempered, followed by a stretching operation (further tempering) to achieve the necessary performance. It is manufactured in accordance with DIN standards and also offers general conformance with BS4486. The system also has been approved to the European Technical Approval (ETA) standard.

Post-tensioning systems are available in grade Y1050 bars from 18mm diameter to 47mm and in grade Y1035 from 57mm to 75mm. CT Stress Bars for use with architectural systems are produced from 26mm to 75mm, which is ideal for the application of post-tensioning forces for relatively short tendons and for stay cable applications.

VSL solid bars are available in grades B500, S670, Y1050/Y1035 and Y1100.

As well as solid bars, VSL also supplies self-drilling, expansion and friction bolts.

Associated services

  • Cutting, bending and torquing in accordance with project specifications.
  • Prefabrication and assembly of the nail-plate inner cap and other fittings corrosion protection, with a choice of available systems.
  • Design, including provision of alternative designs to substitute VSL Bars for conventional reinforcement.
  • Installation on site, whether as a standalone operation or as part of a larger scope including the complete construction project.

Advantages of VSL's offer

Proven technology

VSL bar systems have been successfully used worldwide since 1971.

Durability

The threadbars are extremely durable as their unique design greatly reduces the chance of thread damage during handling and installation.

Complete range

VSL Bars are available in grades of 500MPa to 1,050MPa with diameters from 12mm to 75mm to suit various applications. Non-standard bar diameters and steel grades can be developed for specific project requirements. Additionally, threadbars can be complemented with other VSL components such as hex nuts, couplers, anchorage plates and turnbuckles.

Corrosion protection

Corrosion-resistant systems are available as part of the VSL bar system package. A choice of systems is offered, such as double corrosion protection systems, epoxy coating and galvanising. Equipment rental and sale complete the full range of services offered by VSL. VSL representatives can recommend which system would best suit a particular application and can advise on any bar system equipment needs.

Availability

Bars are stored locally at VSL network locations around the world. This proximity to the construction site allows the bars to be delivered at short notice.

Contributing to sustainable solutions

Saving material

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In construction, VSL bars can be used to substitute conventional passive reinforcement with higher grade steel material:

  • Non-stressed (grade 670) steel bars are used to lower the rebar ratio and so avoid local rebar congestion. At the same time, the total requirement for steel reinforcement is decreased, thus lowering the total carbon footprint of the construction. In many cases, the characteristics of the VSL bars permit the diameters of the standard-quality bar B500 to be reduced by one unit and hence offer more economical solutions.
  • High-tensile stressable bars (grade 1035 and 1050) may also be used to prestress the concrete. This lowers the amount of steel reinforcement required as well as allowing optimisation of the entire design, reducing the concrete volumes as well.
  • Prestressing of the concrete can lower the carbon footprint of the construction by up to 27%. Keeping the structure in compression also means that it is crack-free and less subject to water ingress that might otherwise be responsible for early corrosion.

Preserving excavation faces

VSL bars contribute to the stabilisation of slopes and tunnelling faces when used in geotechnical applications as rock bolts, rock anchors or ground anchors.

They may be used to secure structures such as raft foundations - micropiles avoid the risk of floatation of a structure due to water pressure uplift. Another use is to safeguard buildings subject to overturning.

In this case, ground anchors secure the structure to the ground, avoiding the need for larger gravity structures.

Aesthetics

Architectural stressbars allow for elegant tensile members in situations such as stressing roof membranes and securing glass walls.

How it works

VSL Bars have a wide range of applications in the construction and mining industries. The way they work depends upon how they are used and implemented and ultimately upon their final purpose.

They are usually classified as: geotechnical systems, reinforcing systems, post-tensioning systems, marine-tie rod systems, and form-tie systems.

Geotechnical systems

Available geotechnical systems
Soil nails

The principle of soil nailing is to install reinforcing steel (soil nails) in the undisturbed ground to increase its tensile and shear capacity. As a result, the network of soil nails creates a monolithic composite body with the existing soil, which is comparable with a gravity retaining wall that supports external loads.

Nails are considered to have an efficient cost/benefit ratio, particularly for excavations. VSL supplies nails ranging from temporary to permanent (pre-grouted) types meeting the latest codes and standards.

Ground anchors

Ground anchors can be either unstressed or prestressed. They introduce forces into the ground through their tensile member. The ground anchor is anchored at the bottom to the surronding area by a bond that is provided by a cement grout or resin.

At the top, the ground anchor is tightened or prestressed and secured at the anchor-head. The tension rod ensures a transfer of load from the anchor-head to the bulb that is created by the grout at the bottom.

Additionally, the prestressed anchor prevents stretch deformation caused by loading and also ensures safety by transfering the forces into the grouted bulb at the bottom of the anchor. In turn, the bulb transfers the loads into the stable ground layers underneath.

Micropiles

Micropiles are deep foundation members with small diameters of up to about 300mm. They use skin friction to transfer loads into deeper stable soil layers. They might also be anchored into rock when ground conditions permit.

Micropiles can work either in tension, in compression or with alternating loads.

Main components of geotechnical systems

The main components of soil nails, ground anchors and micropiles are:

  • The anchor-head, including a plate, a nut and an optional cap. A concrete plate with anti-bursting reinforcement might be provided below the anchor-head for ground anchors
  • The tension member, which is a VSL bar
  • The anchor in the ground, made of either an expanding section or a bulb created by injection of a resin or cement-based grout at the bottom of the bar
  • Corrosion protection - optional for temporary anchors. The corrosion protection may be made up of several layers, featuring smooth or corrugated plastic sheathing and cement grout.

The tension members are made of VSL bars :

  • For unstressed applications such as soil nails and micropiles, the bars are typically of grade B500 (for diameters from 16mm to 50mm) or S670 (from 18mm to 75mm in diameter)
  • Stressed or prestressed ground anchors use high-tensile stressbar of grade Y1050 with diameters between 18mm and 75mm

Bar systems are supplied for use in both temporary and permanent applications.

Reinforcing systems

VSL’s lower-grade bars can designed and implemented as conventional concrete reinforcing systems.

Advantages of this solution include the fact that grade S670 allows a reduction in the steel quantities compared to the use of grade B500. Such savings can provide a dramatic advantage in situations with very high reinforcing ratios.

The approach can prove especially suitable for situations including nuclear reactor containment structures, offshore platforms and localised areas on bridges or in high-rise buildings – all of which are traditionally very congested in terms of reinforcement.

Comparison of S670 bars and conventional B500 bars
  • higher utilisation due to rearrangement
  • increasing of the percentage of reinforcing from 9 to 20% redundancy, when 670 N/mm² is under utilized
  • S670 and B500 are both weldable
  • S670 bars of diameters up to 43mm can be bent
  • B500 bars of diameters up to 50mm can be bent
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Additional advantages are :

  • screw-threaded ribs are provided along full length of the bar
  • robust, site-proven, self-cleaning thread
  • cutting or extension can be carried out at any position along the bar
  • mechanical threadbar splicing up to 100% allowed in one section
  • threadbar diameters of 12mm to 50mm are approved for use in most countries
  • galvanised or epoxy-coated bars are available together with accessories
  • the B500 reinforcing threadbar coupling system can replace many other bar connection systems
  • customised individual bar lengths are available
  • a simple and low-cost solution

Post-tensioning systems

VSL stressbar is a high-tensile alloy steel bar with a coarse right-hand thread over its full length. The system has been proven in use worldwide and offers versatility in a wide range of applications.

Stressbars are prestressed to between 50% and 80% of their ultimate tensile strength (UTS), whether they are being used in temporary or permanent applications.

Advantages of VSL post-tensioning systems

  • Compared with hot-rolled bars, the cold thread (CT) bars offer lower draw-in after stressing (1mm to 1.5mm compared with 3mm). This can make a dramatic difference when short bars are installed.
  • Use of a post-tensioning system allows pre-deformation to be introduced to the construction member by the application of a compressive force. Such compressive force prevents any cracks from developing when external forces are applied.
  • The prestressing generally allows a reduction in the size of construction elements as well as an increased ability to withstand higher loads than when conventional passive reinforcement is used.
Standards and sizes

Manufacturing is carried out in accordance with DIN standards and the system also offers general conformance with BS4486. It has also received ETA approval.

The threadbars may be hot-rolled, quenched and tempered, followed by a stretching operation (further tempering) to achieve the necessary performance. Alternatively, they may be cold-threaded.

Post-tensioning systems are available as grade Y1050 bars for diameters from 18mm to 47mm and in grade Y1035 from 57mm to 75mm.

CT stressbars with architectural systems are available from 26mm to 75mm, which is ideal for the application of post-tensioning forces on relatively short tendons and for stay cable applications.

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Marine tie rod systems

The bars are used as tie rods to brace embankments, sheet-piles, shed roofs and frame structures, as well as tie-back retaining walls.

Form-tie systems

Form-tie systems are used widely to fasten formwork during concreting or to secure formwork and other temporary works against existing structures.

VSL form-ties are available in grade Y1100 and come in two types - FA (weldable) and FS – in diameters of 15mm, 20mm and 26.5mm. A complete range of accessories is also available, including nuts, couplers, plates, anchor-heads and expansion sleeves.

Architectural bars

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Suvanrnabhum Airport, Bangkok, Thailand, 2007

Architectural bars provide an aesthetic solution that allows tensioning of tent roofs, glass walls and other architectural structural members.

Low-tensile architectural bars (MT 600) have threads at their ends and are available in grade 620 from 30mm diameter to 60mm.

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Gibraltar airport, Spain, 2011
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Murcia airport, Spain, 2011

Applications for the VSL bar system

There are many fields of applications for the VSL bar system, from geotechnical to general construction work. Applications include:

Buildings

  • Prestressed beams and columns, which may use prestressed bars or bars of grade S670 to reduced rebar content and avoid congestion
  • Precast connections, where mainly prestressed bars are used.
  • Micropiles
  • Architectural stressbars for tensioning roof membranes and glass walls

Bridges

  • Cable-stayed bridges, where prestressed bars are used at the pylon and at the anchorage zones in the deck. This is an efficient method of introducing stay cable forces into the structure, reducing the requirement for passive reinforcement.
  • Hangers
  • Temporary or permanent use in the assembly of segments
  • Local strengthening
  • Precast connections, where mainly prestressed bars are used.
  • Connections for temporary works and heavy specialist equipment
  • Tension piles and micropiles

Wharves and jetties

  • Stressed deck planks
  • Marine tie-backs

Tunnelling and mining

Rock bolts are used for:

  • Stabilising galleries during excavations
  • Stabilising unstable rock or soil

Soil nails are used for:

  • Slope stabilisation
  • Retaining wall strengthening

Other applications

Ground anchors have many applications in providing stability against overturning effects for:

  • Retaining walls
  • Buildings
  • Wind turbines
  • Deep excavations
  • Tower cranes
Barajas Airport, Spain Hong Kong stadium, Hong Kong
Euro Airport in Basle Mulhouse, Switzerland

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