HISTORY OF PRESTRESSING
Conception of reinforced concrete structures marked absolutely new construction direction. Due to the development of prestressing technology, designers got the possibility to control the behavior of the structure, to carry out less expensive and more optimal projects with more flexible design and aesthetic qualities of the structure. Today prestressed concrete can be used in almost every field of construction.
Conception of prestressed concrete structures in its modern meaning appeared due to the French engineer Eugène Freyssinet. The idea of prestressed concrete structures was around for a long time, but it was Eugène Freyssinet who finally formed it and put it into practice. Graduated from French Ecole Polytechnique and National School of Roads and Bridges, Freyssinet studied properties and characteristics of concrete structures through his entire career.
His many years’ experience and researches led him to the patent for the technology of building structures using prestressed concrete. He received this patent in 1928 for High Strength Steel Strands stressed in the concrete beam.
First the prestressing steel was used in the concrete member to resist to the tensile force, thus significantly reducing the necessary quantity of steel passive reinforcement. Soon after receiving the patent, Freyssinet opened its first plant for fabrication of prestressed structures in France. It was a great success from a technical point of view, and a great failure from the commercial one, because the start of production coincided with economic recession, and in 1933 he had to shut down the plant. But already in 1935 Freyssinet was able to prove all the advantages of prestressing in practice. Due to this technology he was able to save the marine terminal in Havre (France), the part of which was sinking at the rate of 25,4mm per month. Freyssinet proposed to reinforce the foundation with prestressing. His unmatched success contributed to the development and widespread application of technology.
In the United States it was Gustave Magnel, Belgian engineer and professor, who stood at the origins of prestressing in the USA. Working in his laboratory in Belgium during World War II, Magnel conducted numerous researches and tests of prestressed concrete, among which were the full-scale study of prestressed concrete girders and more detailed study of concrete and reinforcement creep.
Gustav Magnel mainly studied the creep of high strength wires and creep and shrinkage of normal reinforced concrete. Based on his researches it was concluded that high strength prestressing wires creep much less than low-strength mild reinforcing steel used in ordinary reinforced concrete.
By the end of World War II Magnel became one of several engineers who had knowledge in the field of design and construction of prestressed structures. Due to this fact in 1948 Magnel had an opportunity to put his vast theoretical knowledge into practice, when American engineers from Philadelphia asked him to design the first serious construction project with prestressed concrete in the USA, the Walnut Lane Bridge. For this project it was essential to choose the most economic technology, but at the same time save the esthetic part of the project. Thus, the prestressing technology was chosen. From this moment the history of prestressing development in the USA began.