VStructural, LLC (VSL) -- the technical leader in the design, manufacture and installation of post-tensioning systems and components for the construction industry - is celebrating 50 years in 2006.
Best known today for high-profile post-tensioning projects throughout the United States, VSL can actually trace its roots to a major Swiss contracting firm, Losinger, in 1953. Frustrated by the dramatic raw material scarcity resulting from the war, Losinger experimented with prestressing techniques. This new method of construction promised considerable material savings. After spending several million Swiss francs on research and development, Losinger applied the new system - which came to be widely known as the VSL (Vorspann System Losinger) Wire System - for the first time commercially in 1956 on the Pont des Cygnes bridge in Switzerland.
In order to spur further development of the technology, VSL initiated several licensee organizations. In 1966, VSL Corporation was formed in the United States. From this point, VSL Corporation grew rapidly. "In the 1960s, with the development of higher strength steel, better attachment hardware, improved construction techniques and simplified design methods, the use of post-tensioning to reinforce structures became more popular," said VSL President Scott Greenhaus. "By the early 1980s, the mystery of post-tensioning subsided with further refinements to the tensioning process, the development of more corrosion-resistant anchorages and the widespread dissemination of design software. Because of these factors, post-tensioning has become a preferred method for reinforcing concrete today. VSL is proud to have reached this milestone and we look forward to continued technology development and meeting the needs of owners today and tomorrow."
Key to longevity and continued growth of VSL is a commitment to research and development. According to John Crigler, PE, Vice President and Technical Manager of VSL, though post-tensioning has been a proven solution in the marketplace for five decades, older systems focused more on obtaining the desired prestress force and less on durability. Today, however, the industry has evolved to offer systems that deliver the desired prestress force while providing improved durability. These advancements in corrosion protection are especially important in areas that experience significant exposure and damage from freeze-thaw cycles, de-icing salts, seawater, salt spray and other deterioration mechanisms. "Since post-tensioning was first introduced in the United States, the industry has seen many technological advances, including seven-wire strand, low relaxation strand, improved analysis techniques and design software, the use of banded tendons, extruded sheathing, encapsulated anchors, plastic duct systems, as well as the development of non-bleed grouts," said Crigler. "Today, many owners and designers also are looking at post-tensioning as a solution that offers the high level of structural flexibility necessary to meet changing user requirements."
Possibly one of the greatest advancements is the progress made during the last decade in corrosion protection. When some of the earliest unbonded post-tensioned buildings started to experience corrosion problems, it was apparent that some tendon sheathings and coatings could not adequately resist corrosion in the most aggressive environments, such as where de-icing salts are applied to slab surfaces or in coastal areas that have a high salt content in the air. One means to protect unbonded post-tensioning systems is with a combination of corrosion inhibitor and seamless extruded plastic sheathing. While this technique protected the tendons along their length, it did not address protection of the anchorages. In the late 1980s, VSL's first generation of encapsulated components, CP+TM, was introduced. Although this technology allowed for great advancement in durability, it did not completely address encapsulation at construction joints. As such, VSL recently launched Enhanced Protection PlusTM (EP+ ) – a new generation of systems offering end-to-end protection of the tendon. The EP+TM System features a unique tendon coupler that carries the encapsulation across construction joints, improving constructability, durability and quality. Best known today for high-profile post-tensioning projects throughout the United States, VSL can actually trace its roots to a major Swiss contracting firm, Losinger, in 1953. Frustrated by the dramatic raw material scarcity resulting from the war, Losinger experimented with prestressing techniques. This new method of construction promised considerable material savings. After spending several million Swiss francs on research and development, Losinger applied the new system - which came to be widely known as the VSL (Vorspann System Losinger) Wire System - for the first time commercially in 1956 on the Pont des Cygnes bridge in Switzerland.
In order to spur further development of the technology, VSL initiated several licensee organizations. In 1966, VSL Corporation was formed in the United States. From this point, VSL Corporation grew rapidly. "In the 1960s, with the development of higher strength steel, better attachment hardware, improved construction techniques and simplified design methods, the use of post-tensioning to reinforce structures became more popular," said VSL President Scott Greenhaus. "By the early 1980s, the mystery of post-tensioning subsided with further refinements to the tensioning process, the development of more corrosion-resistant anchorages and the widespread dissemination of design software. Because of these factors, post-tensioning has become a preferred method for reinforcing concrete today. VSL is proud to have reached this milestone and we look forward to continued technology development and meeting the needs of owners today and tomorrow."
Key to longevity and continued growth of VSL is a commitment to research and development. According to John Crigler, PE, Vice President and Technical Manager of VSL, though post-tensioning has been a proven solution in the marketplace for five decades, older systems focused more on obtaining the desired prestress force and less on durability. Today, however, the industry has evolved to offer systems that deliver the desired prestress force while providing improved durability. These advancements in corrosion protection are especially important in areas that experience significant exposure and damage from freeze-thaw cycles, de-icing salts, seawater, salt spray and other deterioration mechanisms. "Since post-tensioning was first introduced in the United States, the industry has seen many technological advances, including seven-wire strand, low relaxation strand, improved analysis techniques and design software, the use of banded tendons, extruded sheathing, encapsulated anchors, plastic duct systems, as well as the development of non-bleed grouts," said Crigler. "Today, many owners and designers also are looking at post-tensioning as a solution that offers the high level of structural flexibility necessary to meet changing user requirements."
In the early 1990s, VSL pioneered the use of fully integrated plastic duct systems for bonded tendons with the introduction of the P-T PlusTM duct system. It features a robust plastic duct combined with couplers, anchorage connections, grout caps and vents to completely encapsulate bonded tendons. The development of new technologies is likely to continue to expand the acceptance and growth of the post-tensioning method. Electronic monitoring is one example of these technologies. The embedded electronic sensing devices, designed to monitor a structure over time, are becoming increasingly popular as they allow for the determination of when and where a tendon breakage occurs. Another growth area may be tall buildings -- 20 stories and higher -- where most framing historically has been structural steel. Post-tensioned concrete offers significant performance benefits in tall buildings, particularly in the areas of fire resistance, sound transmission and floor stiffness. Post-tensioning the floors and frames of tall concrete buildings minimizes their weight and, combined with the use of high-strength concrete, makes this a realistic solution.
In addition to being at the forefront in post-tensioning technology, VSL also is known as an industry leader. Coincidently, Greenhaus has been selected to serve as the 2006 president of the Post-Tensioning Institute (PTI). Established in 1976, PTI is a non-profit organization for the advancement of post-tensioned, pre-stressed concrete design and construction. “It is my great honor to serve as president of PTI during the 50th anniversary year of VSL,” said Greenhaus. “The post-tensioning industry is experiencing an explosion of growth, coinciding with the robust economy in the United States. It is the mission of PTI to ensure that post-tensioning is the preferred method of reinforcement for all types of concrete structures. VSL is also committed to this goal and to providing high quality post-tensioning materials and service in keeping with our heritage of fine Swiss craftsmanship.”
VSL is part of the Structural Group - one of the nation’s leading specialty contractors. From 20 operating centers around the United States, the Structural Group businesses perform a wide range of projects involving industrial facilities, commercial properties, public infrastructure and municipal buildings. Structural Group is comprised of three dynamic and diversified companies. Structural Preservation Systems is the largest specialty contractor focusing on structural repair and strengthening. And, Pullman Power leads the industry in chimney, silo, and stack construction, maintenance, and repair. For more information about Structural Group, please visit http://www.structural.net/.
