OVER 50 YEARS OF EXCELLENCE
The pioneering years
More than fifty years of activity have brought with them marked changes to VSL's specialist areas of expertise as well as to the company's organisation. These have been influenced by economics, changes in the business sectors where VSL exercises its skills and by a host of breakthroughs in techniques, technology, methods and the types and details of the structures themselves.
From construction to prestressing
The VSL of today and its reputation worldwide can be traced back to the time of European turmoil in 1943 when the major Swiss builder Losinger saw potential applications for the innovative technique of prestressing. The company acquired nonexclusive rights to use the process throughout Switzerland as a means of increasing production capacity and introducing new solutions to the Swiss market. Losinger founded the company Précontrainte SA in Lausanne in 1954 with the aim of developing and applying the licensed system across Switzerland.
Advent of the VSL wire prestressing system
Losinger’s management faced many obstacles in the pursuit of its objectives and so decided to undertake an intensive programme to research and develop its own customised system. The result was the VSL (Vorspann System Losinger) wire-based system, which was patented in 1954-55 and first employed in 1956 on the Pont des Cygnes bridge at Yverdon, Switzerland.
The technical advantages offered by the new system were so attractive that it very quickly became the solution of choice on many civil engineering projects throughout Switzerland. At the same time, licences were being awarded to representatives in other countries - a move that promoted rapid adoption of the system and created a prominent international profile.
The VSL brand
The trademark was launched in 1958 and the logo soon became recognised throughout the world. The corporate symbol was subsequently revamped in 1989 to create a new design, which is still in use today.
Strands and wedges to enable increased capacity
By 1965, Losinger had several years of operational experience and wanted to meet the increasing demand for higher-capacity cables. The decision was made to develop the VSL strand system to take advantage of an emerging trend for prestressing that used hard steel strands. The novel system was unveiled to the public in Paris at the 1966 International Federation of Prestressing (fib) Congress. Successful completion of the development enabled VSL to introduce a revolutionary system onto the world market. It was based on a purely mechanical approach, characterised by the simultaneous tensioning of cable strands, each individually anchored using wedges held in place solely by friction with the strand. This innovation was highly influential, both in prestressing applications and more generally throughout the construction industry. VSL offered engineers, designers and contractors the flexibility of a system whose cables could accommodate unit forces that at the time spanned the full range from 15 tonnes to 1,200 tonnes, depending on the chosen anchorage. This enabled the company to provided construction engineers with a tool that was adaptable to meet the design constraints inherent in their structures. The versatility of the VSL system provided a wide array of potential solutions, regardless of the structure's size, shape, complexity or applied forces.
Innovation through diversity
The need to identify solutions for highly-diverse projects became apparent from the earliest VSL prestressing system applications, first using wires (1956) and then strands (1965). Requests that came via the network of users and design offices led VSL to innovate, enhance and consolidate its techniques, equipment, services and organisational structure to meet the growing expectations of engineers, clients and project owners. In-house staff worked to implement and master the solutions for all kinds of projects, whatever the level of VSL’s involvement.
Developing a geotechnical approach An idea that germinated during informal discussions with geotechnical specialists was to embed VSL strands and anchorage ties within rock or soil. This extended their use to applications that would previously have used reinforcement rods, such as securing foundations, hydroelectric power plant cavities, dam heightening, flood spillways and soil stabilisation. This type of activity soon became one of the Group’s most prevalent worldwide.
From geotechnical solutions to the VSoL® system A direct result of this expansion into geotechnical engineering and soil stabilisation was that the Group created a retention and consolidation system for embankments. This system, developed in 1981 in the United States, was originally known by the brand "Retained Earth". In time, this technique would evolve into what is now VSoL®.
Sliding formwork for tall structures
In 1966, VSL began focusing on a technique for sliding formwork that would enable further diversification of its activities. The company decided to acquire both the equipment and expertise necessary to provide solutions that would complement its prestressing services for construction projects that involved tall towers or storage structures such as silos and water towers. The technique was ideal for subsequent adoption across the building sector.
Hydraulic jacks for heavy lifting VSL’s expansion into new business areas continued in 1968 when the decision was taken to acquire a licence from a small Swiss contractor to implement a technique for handling heavy loads by means of hydraulic jacks and racks. However, the system had inherent limitations, which led in 1970 to the development of a more efficient approach that made use of axially-holed jacks in conjunction with strands to move very heavy loads either horizontally or vertically. The first major project to use this technique was the roof erection for Munich's Olympic Stadium in 1971.
VSL continued its geographic expansion during these years. One of the most significant developments was the establishment of VSL Corporation, which was set up in the United States in 1966. This company boosted the Group's growth during the 1970s through its promotion of the VSL monostrand prestressing system to the building industry. Use of the “Slab System" was in response to American market demand in a market sector that showed tremendous potential. Similar considerations encouraged VSL Australia to introduce the "Flat Slab System" - slab prestressing using cable injection – into its domestic market. The techniques were then refined through widespread development and their application across a variety of building types.
Following these pioneering years, VSL’s mission was to satisfy everincreasing demands in terms of quality, durability and structural integrity on its projects, with the constant aim of meeting client expectations to an even greater degree. This drive led to successive major breakthroughs that served to bolster the Group's leading position.
Enhanced access and durability
The VSL external prestressing system not only addresses cost considerations - it is also highly effective. It was fundamental in responding to the concerns of structural designers using prefabricated elements by giving them the ability to manage the prestressing throughout a structure's life. Development of external prestressing allowed for greater control of forces and the adjustment or adaptation of the system to accommodate new service loads. Furthermore, all or part of a cable could be replaced at any time should the need arise. The PT PLUS® duct was developed in 1988. It is made of plastic and, with its accessories for prestressing cables, provides a completely waterproof system as well as reducing friction coefficients considerably. The Composite System (CS) made its debut in 1992 and built on recent developments in high-performance concretes and mortars. The Group devised an anchorage with characteristics that reduced both weight and size for ease of application, while improving fatigue and corrosion resistance. The CS PLUS and VSL SUPER systems were also introduced in 1992 to provide the definitive solution to a demand for full protection against corrosion for cables composed of tensioned strands, including complete electrical isolation from the surrounding environment.
Integrating increased levels of complexity
The past decade has confirmed a growing trend for project designers to promote technically-sophisticated bridges, with everincreasing span lengths on projects that showcase the latest technologies while carrying large loads. VSL Group has responded to these challenges by initiating an intensive ongoing programme of research and development into stay cables - a process it has championed since the system first took shape. The work led to the launch of the VSL SSI 2000 (Single-Strand Installation) stay cable system. This marked a major evolution in the technology and responded to the latest requirements in balancing the unit loads per strand as well as enabling control, adjustment and replacement if required. The system is now implemented the world over and is recognised as a market leader in the prestressing industry.
Developing the network
It would be impossible to provide an exhaustive review of the wealth of techniques developed and applied locally, regionally and worldwide over VSL’s 50 years of life. Instead, this publication focuses on the past, present and future of the Group's primary activities as these have served to forge VSL’s reputation, in conjunction with lasting relationships built up with engineers, designers, architects, contractors, project managers, project owners and academics.
Over this period, VSL has helped to solve many commonlyencountered problems. Any project requires unfailing commitment from all parties if their diverse needs are to be met. This demands professionalism, materials knowledge and mastery of the technologies, standards and certifications. VSL has always endeavoured since its inception to uphold these high principles in its role as a valued partner.
VSL, as a Swiss-based firm, initially relied on a network of licensees in other countries to develop applications for its system elsewhere. This mode of operation soon gave way to an organisational structure that was made up of specialist companies, set up in an increasing number of countries to ensure high-quality results.
The new structure created a forum for international knowledge exchange, enabling problems, solutions and experiences to be shared by all. This approach has accelerated the Group's evolution and enhanced the development of both its systems and equipment. It was in part responsible for VSL's introduction during the 1970s of the strand-by-strand pushing method, which is applied after concreting to run cables through ducts. The technique revolutionised the world of prestressing and changed the method adopted by contractors for all types of structures. It replaced the previous technique of installing fully-prefabricated cables or threading cables on site using winches.
This principle of hosting forums and encouraging communication is now in effect group-wide and continues to generate consistently strong progress thanks to the synergies formed around the world. The same principles are behind the Group’s regular participation in major international construction congresses and in technical and professional commissions, as well as its publication of many highlyregarded technical reports.
VSL has continued to maintain close contact with its clients, to be attentive to their needs and to extend its range of services. The prestressing company of 50 years ago has gradually evolved into a multi-services group specialising in the design and construction of complex turnkey projects. The schemes adopt VSL techniques and processes and often include bespoke building and erection methods such as tailor-made launching gantries for the rapid construction of precast segmental structures. This is especially true in Asia where VSL has, with the support of a versatile technical resources centre, established its position as a specialist capable of devising, manufacturing and operating sophisticated tools to help build civil engineering structures. The Group's companies can augment their local capabilities by drawing on the high-calibre assistance of experienced engineers working in its technical centres, certified for work on large-scale projects. This benefits VSL and its clients alike.
From new construction to renovation
The VSL Group has continued to evolve its organisation over the past half-century, adapting its systems, technologies and methods to new market requirements in order to satisfy updated regulations, meet client expectations or solve problems created by modern largescale construction. Development has been accelerated through the application of VSL’s techniques on structures as diverse as viaducts, railways, nuclear power plants, offshore drilling platforms, reservoirs, LNG tanks and all kinds of extraordinary buildings.
Recent years have seen the emergence of new applications for the techniques already mastered by VSL, in particular relating to the management of post-World War II facilities. Sizeable investments are being made in the maintenance, repair, strengthening and rehabilitation of existing structures. VSL continues to adapt to ensure that it is positioned to provide well-adapted, customised technical solutions for the specific demands of such markets.
Over 50 years of achievements
The VSL Group has for more than 50 years been recognised as a world leader in prestressing and other related industries. Its structure allows it to respond to and satisfy the most stringent of requirements to guarantee project quality, safety and durability. The Group has chosen to direct effort towards the development of technical turnkey proposals to generate optimal solutions.
VSL has successfully erected more than three million square metres of bridge deck in the Asia-Pacific region over the past decade. The Company provides skilled and trained staff with a core of 100 bridge specialists, an experienced technical centre and the ability to develop new methods, equipment and materials. Today, VSL also offers an innovative contractual approach that enables the company and the contractor to focus on what is “best for project”.
VSL is also involved in sustainable construction and many of its innovations help achieve this. Specialist equipment is designed to be as modular as possible to allow reuse in different configurations. Post-tensioned structures consume less energy and the use of post-tensioning allows structures to be reinforced with minimal invasiveness. Structural durability is a critical issue for project owners and the use of external post-tensioning for structural repairs extends the lifespan of structures. The ultra-highperformance material Ductal® provides both fire and explosion protection. The opening of the VSL Academy, a unique posttensioning training centre to ensure the high level of VSL staff know-how in all countries, will provide ongoing development of both individual and corporate knowledge and skills.
Local knowledge is also important: all VSL managers are entrepreneurs with in-depth knowledge of their own markets and are committed to providing creative and safe solutions together with top-quality services. All VSL companies benefit from the exchange of expertise throughout the international network.
VSL continues to focus on the search for methods and technologies that will maintain its competitiveness and ensure its enduring market success. The Group is justifiably proud to present a selection of the most outstanding examples from its extensive portfolio of exciting projects, executed the world over during the last five decades.
The VSL Group cannot ignore its close association - for which it is extremely grateful - with the engineers and designers, the architects, project owners and managers, the general contractors and government administrations, the universities and all the clients it has worked with. Over the past half-century they have demonstrated the confidence in VSL that has been so essential to the accomplishments achieved with their involvement over this long and notable period.