Repair & Strengthening

Repair and strengthening of structures because of load capacity upgrades, changes of use, changes in design codes, slab openings, construction defects or damage caused by deterioration.

  • Renovation project
    Use of CFRP for strengthening around new slab penetrations.
    USA - 2005 read more

    Renovation project

  • Acude Bridge
    VSL’s execution of major repair work on a 1,940m-long bridge.
    Portugal - 2012 read more

    Acude Bridge

  • Meuse Bridge
    Bridge strengthening using VSL external post-tensioning.
    Netherlands - 2008 read more

    Meuse Bridge

  • Parking Les Tilleuls
    Provision of the complete solution for the refurbishment of an underground car park suffering from severe cracking.
    Switzerland - 2012 read more

    Parking Les Tilleuls


Turnkey services for repair and/or strengthening of structures

The need for repair and strengthening may arise from deterioration, changes in use, changes in the relevant design codes, structural defects or seismic conditions. VSL uses the latest technologies to develop innovative strategies to restore or add load-carrying capacity to bridges, buildings, parking facilities, silos and other structures.

Rehabilitation, strengthening and protection of concrete structures all require thorough investigations, clearly defined procedures, expert execution and systematic quality control. Through its wide range of construction and engineering services and systems, VSL provides engineers, contractors, consultants and owners with the specialist service they need. VSL inspects and assesses civil engineering works, buildings, bridges and industrial structures both to determine present condition and to initiate any measures found necessary for restoration to full service condition. In many cases, VSL also undertakes the project management for the rehabilitation work as a turnkey service.

VSL’s products and services

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VSL offers a wide range of specialist services in each of the main areas of structural investigation, repair, strengthening and protection for bridges, office buildings, homes, industrial buildings, factories and warehouses. Repair and strengthening of structures may be required because of load capacity upgrades, changes of use, changes in the relevant design codes, slab openings, construction defects or damage caused by deterioration including cracking.

VSL provides turnkey services for repair and strengthening including:

  • Inspection
  • Condition evaluation, assessed through in-situ destructive and non-destructive testing such as the detection of prestressed tendons, rebar orientation, concrete defects and grout voids in prestressed tendons
  • Design of repairs
  • Project planning
  • Project management

Design and build repair services can be provided for:

  • Concrete and structural repairs including
    • Crack repair
    • Repair of concrete honeycombing, delamination and spalling
    • Repairs to corroded embedded metals
  • Concrete fireproofing repairs
  • Structural supports and shoring
  • Protective coatings and linings
  • Re-anchoring of prestressing tendons
  • Restoration of historic structures
  • Reinforcement repair
  • Expansion joint replacement
  • Structural bearing replacement

Design and build strengthening systems and services include:

  • Passive strengthening systems
    • Enlarging the structural members
    • Steel plate bonding
    • Addition of carbon fibre reinforced polymer (CFRP) composite systems such as
      • Vwrap® CFRP fabrics
      • Vplates® CFRP plates
      • Vrod® CFRP rods
    • Use of Hardwire® steel reinforced polymer (SRP)
  • Active strengthening systems:
    • External and internal post-tensioning systems
    • Carbostress® prestressed FRP
  • Reconfiguration of structures

Advantages of VSL’s solutions

  • The experience of an international specialist, to provide turnkey services for the planning and implementation of schemes for mitigation, repair and strengthening
  • State-of-the-art systems and technologies to remedy defects and strengthen any structure
  • Worldwide provision of services from within the VSL network

Contributing to sustainable solutions


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Precise assessment of critical potential damage at an early stage allows adequate preventive measures to be implemented before the damage become too costly to repair or before the state of the structure’s deterioration demands demolition.


Repairs and regular preventive actions serve to extend the life span of a structure, which leads to financial savings and reduced wastage of materials.

Providing structures with a second life

Repair, strengthening or reconfiguration can give a new life to existing or ageing structures that might otherwise be demolished and replaced.

How it works

Repair and strengthening work varies depending on the existing state of the structure, the conditions it is subjected to and future requirements. This makes the preliminary evaluation extremely important. VSL carries out a proactive review of the as-built drawings and performs reverse calculations to determine the existing capacity of the structure. Some tests - destructive or non-destructive - may also be conducted on site to confirm the structure’s condition and any design assumptions. Future conditions and requirements such as loadings and environmental exposure are obtained from interviews with the client as well as from site visits. The evaluation leads to the consideration of various alternative repair and strengthening approaches in order to produce the best solution. VSL implements repair and strengthening solutions using a variety of techniques.

Post-tensioning systems

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GC anchorage

VSL applies the post-tensioning technique mainly to improve the serviceability condition of the strengthened structure. This includes reducing the structural deflection, stresses and crack widths. The active force induced by the post-tensioning is also useful in increasing the structural capacity against ultimate conditions. The post-tensioning can be applied externally or internally using steel strands or VSL stressbars.

FRP composite systems

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The main reason for applying externally bonded FRP composites is to increase structural capacity in a passive manner. FRP plates and rods are used to provide strengthening for beam/slab sagging moments while FRP rod or tape is used for the beam/slab hogging moment. FRP wrap on the columns works well to enhance load-bearing capacity. Carbostress®, a prestressed FRP system, is a technology jointly developed by VSL and Sika. It combines the advantages of CFRP plate with a conventional prestressing system to increase the structural capacity and at the same time improve the serviceability conditions. Using in-house design methods, VSL produces efficient designs that comply with the appropriate design guidelines (ACI 440, TR55, and FIB), depending on the client’s requirements.


Hardwire®, also known as steel reinforced polymer (SRP), is the latest generation of externally bonded reinforcement systems. It is made up of uni-directional cords consisting of tightly wound ultra-high-strength steel wires embedded within a polymer resin. The application of Hardwire®, for strengthening is very similar to normal FRP and it has been used in a variety of applications including flooring reinforcement, historical building restorations and retrofits, laminates in the boating industry and to strengthen bridges and buildings. Hardwire®, is also used as an advanced composite armour and infrastructure-protection solution.

Structural enlargement

One of the most basic strengthening solutions is the use of section enlargement. For steel structures, enlargement takes place by welding new steel sections or stiffeners to the existing steel members. For concrete elements, the enlargement can be achieved using normal reinforced concrete as well as internal post tensioning.

Plate bonding

The concept of plate bonding is very similar to FRP. Steel plate, being a solid material, has the advantage over FRP of being able to be drilled and anchored to the existing structure. These anchors provide additional safety to ensure better bonding.

Structural reconfiguration

Structural reconfiguration may be considered as an alternative when too much strengthening would be required. VSL can draw on a range of structural reconfiguration techniques including span shortening, load isolation and the addition of new beams. VSL conducts a sophisticated yet comprehensive analysis to come up with the best reconfiguration solution to achieve strengthening with minimal disruption - or none at all - to the adjacent structural elements.

Other techniques

VSL also uses other techniques for the repair of structures, such as chemical/epoxy injection and the routing and sealing of cracks.

Commercial, civil and public structures

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Hai Van tunnel, Vietnam, 2006

VSL provides repair, strengthening and protection for concrete structures including bridges, office and residential buildings, factories and warehouses. It has the expertise and technical competence needed to solve problems requiring surface repairs, strengthening, stabilisation, waterproofing and protection. VSL’s ‘toolbox’ contains solutions that are ideal for the repair of all structures, including airports bridges, buildings, high-rise buildings, parking structures, plazas, tunnels and historic structures.

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St Andre de Cubzac: external post-tensioning using twenty record-breaking 486m-long cables was used to reinforce this ageing bridge. The solution avoided the installation and tensioning of additional anchorages.
Trançao viaduct repair, Portugal, 2010
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Column displacement, Spain, 2010
Kai Tak airport, Hongkong, 2010
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Culvert repair, Brunei, 2010, before
Culvert repair, Brunei, 2010, after
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Bridge inspection, Washington, USA, 2010
Historical building restoration using Hardwire®: Hippodrome Theatre, USA, 2003
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Figueira da Foz bridge, Portugal, 2005
Pisa leaning tower, Italy

Case Studies from the carbostress® brochure

Hütten Bridge, Werthenstein, Lucerne (Switzerland)

Structure and Problem

The Hütten Bridge was built in the 1950’s and was designed for vehicles with a maximum total load of 28 tonnes. The management of the surrounding forests now required the bridge to carry heavier loads of timber on trucks up to 40 tonnes. Neither of the two main bridge beams on the three span bridge could take this stress and had to be strengthened for bending and shear.


Both beams were strengthened with prestressed CFRP plates up to 30 metres long on both sides. The end anchorage of the prestressed plates consisted of continuous shear connectors through the beams which introduced the tensioning forces into the beam in concentrated form. CFRP fabric loops were used for the shear strengthening. Slots were first cut vertically in the deck slab so that the loops could completely surround the tension and compression zones of the beams. The loops were inserted in several layers and bonded.

Sports Hall Roof, Thörl (Styria / Austria)

Structure and Problem

The roof of the sports hall at Thörl secondary school (Styria, Austria) had to be strengthened to repair damage and to meet current standards. Assessment showed that the tensile resistance and flexural stiffness in the transverse beams across the sports hall were insufficient. An on-site in-spection and the results of the structural analysis showed a need to strengthen these roof support beams longitudinally. Due to deflection under the existing loads, a solution involving prestressing was the only practical and viable option.


The VSL® Carbo Stress® pre-stressing system was selected to fulfil the refurbishment and strengthening requirements. The load bearing capacity and flexibility in design of the end anchors of the VSL® Carbo Stress® system gave the engineer sufficient choice in the anchor positioning to ensure safe and secure transmission of the loads. The final decision to use this system was made on the basis of its comparatively low cost and the fact that it could be installed very quickly and without damaging the existing reinforcement.

Fire Station, Visp (Switzerland)

Structure and Problem

Visp fire station was built in 1974. The load bearing design of the structure was now seriously defective in terms of earthquake resistance to the latest standards. The reinforced concrete frames of the gable end walls, with masonry infill, would be unsafe in earthquakes and could not transfer the seismic forces to the ground. The works also had to cause minimum disruption to the normal daily operation of the fire station.


Increased earthquake resistance of the gable end walls was achieved with 4 vertical CFRP plates on the ends of each wall. The plates were anchored and tensioned in the roof and in the basement walls. The extra vertical force of the prestressed CFRP plates was sufficient to increase the shear resistance of the masonry and provide earthquake resistance in accordance with the latest standards.

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Vehicular bridge strengthening using Carbostress® and Hardwire®
Vehicular bridge strengthening
External post-tensioning using stressbars

Industrial structures

VSL is a leading provider of specialist structural repair, strengthening and protection solutions for industrial facilities and so understands the unique challenges faced by industrial owners and operators.

Repair works typically take place while the facilities remain in use and VSL recognises the need to ensure continuous operation of the plant. Executing repairs under these conditions requires an experienced industrial contractor that employs a team approach. With VSL, every project is carefully preplanned in close coordination with plant operations, maintenance and safety personnel.

VSL carries out the work safely and with the least possible impact on critical manufacturing, processing or production activities. VSL’s teams develop safety-oriented solutions for challenging environments and provide turnkey project delivery.

Heavy lift of stack External post-tensioning using PT strands: Cement silo, Singapore
Heavy lift of stack, Singapore
External post-tensioning using PT strands: cement silo, Singapore
Structural maintenance work in petrochemical plants
Structural maintenance work in petrochemical plants
Plant structural inspection works
Plant structural inspection works, Thailand

Underground structures

Tube à manchette installation, Hongkong

Intrafor, the ground engineering and foundations specialist subsidiary of VSL, is able to provide a full package of design and construct solutions for enhancement, improvement or remedial works to any foundations.

Intrafor has its own design department and in-house testing company and so can address all technical challenges raised in the difficult task of underground structural diagnosis and repair. Projects range from simple waterproofing grouting of earth-retaining structures to full-scale foundation rehabilitation using load transfer and pile replacement.

Compensation grouting shaft J, Hongkong
Diaphragm wall repair, Hongkong

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