The application of post-tensioning led to a new development that was first used in the construction industry in by s Frenchman Eugene Freyssinet, for the Le Havre Marine Station project. Eugene Freyssinet patented the conical anchor technique because of his researches. High-strength steel wire service life to reach the friction of the tensile stress exposed in reinforced concrete structures.
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After II. World War, Eugene Freyssinet has several kinds of research on the creep of concrete. In this way, He produced telegraph poles with pre-tensioning weights to piano wires radiating through the concrete pipe in order to solve dominant creep and shrinkage. It produced pre-tensioning and post-tensioning management with a tension strength of up to 70-80% of yield strength, using C30-40 concrete and strength steel between - MPa values &#;&#;with anchor element, which it was patented in .
In , the 48-meter-long post-tensioning reinforcement Magnel structure produced by the Walnut Lane Bridge project in Pennsylvania, USA, was applied using prefabricated beams.
In this way, post-tensioning became widespread with this project and became the leader in the world with many post-tensioning systems.
Let&#;s look at important projects completed in the history of post-tensioning and pre-stressing;
The Arroyo Seco Pedestrian Bridge (located in Pasadena, California), was built in with a pre-stressed bridge. Using a different technique, the Pre-stressing reinforcement was placed above and below the beam.
In , Prestressed beams were used as a bridge in the Pennsylvania regions of the USA.
In , The first railroad bridge was built in Burlington, USA.
One of the projects that have an important place in benefiting from post-tensioning services in St. Louis, Missouri is the Gateway Arch. This building, which completed on October 28, , was built with reinforced concrete and post-tensioned steel ropes. The outer cover of the Gateway Arch is made of 6.35 mm protectors in stainless steel.
In addition, there is 9.52 mm of structural steel in the inner layers to see its structure. Between these steel layers is concrete. Gateway Arch&#;s prefabricated and 3.7 m length dimensions were increased using 142 stainless steel parts. For this reason, each section is filled with concrete, and prestressing was performed with 252 tensioning units.
Two program studies were carried out between -. A research operation was started under the name of NIST (National Institute of Standards and Technology) and PRESS (Precast Concrete Seismic Structural System) by developing joint designs and methods in the USA and Japan and constructing high pre-production structures against seismic effects.
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In these programs, experiments were carried out according to post-tensioning applied column-beam joints, type, and different reinforcement placements in reinforced concrete buildings.
In addition, post-tensioning frames to prefabricated concrete panels were carried out on the shear wall arrangement.
The use of pre-stressed concrete is common in many parts of the world. Historically in the United Kingdom, the use of prestressed concrete and post-tensioning (PT) in particular has been confined to specialist structures such as car parks, long-span structures, and highway structural engineering and precast hollowcore units.
In the last couple of decades, contractors have identified the benefits of post-tensioning and championed its use.
What is Prestressed Concrete?
Prestressed concrete can most easily be defined as &#;pre-compressed&#; concrete. A compressive stress is put into a concrete member before it begins its working life and is positioned in areas where tensile stresses will develop under working load.
Concrete is strong in compression but weak in tension so the introduction of precompression in areas that will become subject to tension means that the concrete will behave as if it had a tensile strength of its own.
The American Concrete Institute (ACI) code committee stated that Post-tensioned Concrete is concrete in which there have been introduced internal forces of such magnitude and distribution that the forces resulting from given external loadings are counteracted to a desirable degree.
How is concrete post-tensioned?
The precompression may be arranged symmetrically however more common it is applied eccentric to the centroid of the section axis enabling additional efficiencies in construction to be made. Here, the post-tension tendons are installed to follow the bending moment profile. This locally dumps load at peak negative moment areas over supports and results in an uplift force at midspan to balance a portion of the slab self-weight.
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