Defying the laws of physics with the prestressed concrete
Traction, compression, deformation … these physical forces acting on the structures
The world of construction and public works must continually meet the challenges submitted by the laws of physics.
Human has always manipulated materials and found tips to overcome the obstacles in his path and build solid shelters to protect himself. After wood and stone, concrete and steel have come to reinforce his construction projects.
Thus, for some large constructions, while the beams simply made of concrete underwent too strong loads and ended up cracking on the lower part and breaking because of the forces of pulls which exerted on them, the Human used of his strategists and invented reinforced concrete in the 1850s.
This new steel reinforcement integrated in the concrete structure has demonstrated its solidity in the context of various concrete constructions. This alliance has also made it possible to resist traction efforts much more effectively by limiting their elasticity and elongation. However, the beams thus formed ended up deforming, sometimes dangerously …
But then, how to make sure that the high beams of a bridge do not yield or become subject to deformation under load weight, operating load or climate load?
Engineers and physicists have noticed that, by their very nature, concrete was much more resistant when subjected to compressive forces … Great discoveries followed!
The discovery of Eugene Freyssinet
So, we have seen that in the nineteenth century, civil engineering professionals had already thought to benefit from the best part of the combination metal / concrete, reinforcing it with steel frames: reinforced concrete.
Only during the XX century, a man wishes to go further in the association of these two materials. Eugene Freyssinet, then road and bridge engineer, decided to use the compression effect in concrete parts.
For this, he uses a steel cable composed of strands that he introduced with ease into the concrete. It then ensures that the cable is stretched as far as possible with the help of jacks. In this way we can compress the concrete in proportion to the elongation of the cables and thus better absorb the tensile forces during a tensioning.
This process, very clever for the time is patented by Freyssinet since 1928, then called “prestressing” 5 years later.
In the words of Eugène Freyssinet, “to prestress a construction is to submit it, before the application of the charges, to additional forces […] that the material can withstand indefinitely without alteration”.
All the advantages of prestressed concrete
Over the years, prestressed concrete has given birth to many architectural treasures such as the Grande Arche de la Defense in Paris, the bridge of the Island of Ré in Charente-Maritime and many other prefabricated concrete structures.
In order to create durable structures capable of withstanding heavy loadings, design engineers calculate precisely the physical forces that will be exerted on various points of the structure and can provide manufacturers with the level of prestressing to give to the structure so the compression forces are always higher than the pulling forces, even during periods of concrete creep. The prestressed concrete constructions therefore have a high resistance and are almost infallible.
In addition to being extremely resistant and safe as well as allowing architectural innovations, prestressed concrete is also a clever and practical solution to implement on construction sites. Indeed, the parts needed for the construction of the works are prefabricated in advance in specialized factories and put in prestressing until total hardening of the concrete elements.
The prefabrication processes of our prestressed concrete products were developed in our design offices and then put into practice in our Brive-la-Gaillarde plant.