Pre-stressed concrete is installed using ready-made fabricated strands, commonly referred to as tendons.
Pre-stressed concrete is a material made from reinforcing steel and concrete. Reinforcing steel provides the tensile strength to resist tension, compression or both. Concrete resists compression loads but has relatively poor tensile strength unless reinforced with thin walled steel forms or steel strands called tendons, encased in ducts formed into the concrete section. The section is then stressed (placed under tension) before it hardens through pulling on the tendons by jacks using hydraulic pressure. Once hardened, this increases the compression strength of the concrete section. Pre-stressing makes a beam more resistant to bending moments caused by overloading tensile stresses, such as those due to earthquakes, as well as countering some effects of shrinkage and temperature-induced compressive stresses and tensile stresses imposed. Purpose-made high strength steel tendons are used which can be stressed to approximately two-thirds of their ultimate tensile strength, without suffering from creep because of the internal stresses as is the function of the high strength steel tendons. Pre-stressed concrete structures are widely employed in structures such as bridges, parking garages, railroad ties and power plants that require structural strength and resist not only compressive stresses, but also enough space for bending movement caused by the forces that it will have to support. It allows larger clear spans than would otherwise be possible at a given width and height with comparable overall structural rigidity.
In general, pre-stressed concrete can be divided into two large categories: "stress-controlled" and "crack-control". In stress-controlled or ordinary external pre-stressing, each tendon is stressed to a level that achieves the specified compressive strength in the concrete. In crack-control, however, the tendons are stressed to levels greater than those needed for sufficient compressive strength of the surrounding concrete. The resulting stress level prevents cracks from opening up due to shrinkage.
Once hardened, pre-stressed concrete is much stronger than regular reinforced concrete due to its high compressive strength properties. It also has virtually no shrinkage problems because its low tensile strengths prevent cracking.
The most common structures that utilise pre-stressed concrete are: residential and commercial buildings, water tanks, bridges and highways, parking decks and plazas, overpasses and flyovers.
At home, pre-stressed concrete is commonly used for slabs, metal bands, beams, columns and walls so that the concrete mix reaches long term durability, required strength and longer unsupported spans.If cared for properly, pre-stressed concrete has an extremely long life span. The average compressive and flexural strengths in a well-designed structure are usually between 50 and 70 megapascals (MPa). In cases where the loading is extreme in service loads, dead load and external load, or the structure must meet specific seismic requirements, the ultimate strength of pre-stressed concrete and concrete construction can be as high as 160 MPa.
Post-tension tendons are similar to regular prestressed tendons, but these are used in conjunction with "jacketed" structural steel bars. First, the jacketed bar is positioned at the desired location. Next, holes are drilled into both sides of this bar and post-tensioning cables are inserted into them. The end of each cable is then connected to its corresponding tendon on either side of the structure wherever it needs reinforcement, especially steel reinforcement. Finally, the jacked bars are pulled taut with high tension stress so that any designated amount of force can be applied between them and the concrete without causing damage to either material.
The most common structures that utilize post-tensioning include: residential and commercial buildings, bridges and highways, parking decks and plazas, overpasses and flyovers. At home, post-tensioning is commonly used for floor slabs, floor beams, columns and walls.
Pre-stressed concrete is a type of concrete that uses a pre-tensioning process with steel cables or bars that are stretched prior to the concrete being poured. During later stages, this material that has undergone pre-tensioning will then be put under compression, which gives it sufficient strength than conventional concrete. Conventional reinforcement is an important element in such strengthening procedures. Post-stressed concrete, on the other hand, is a technique where steel cable or rods are tightened after the pour. They allow engineers to create a pre-stressed concrete beam and slabs with specific amounts of curvature, twist and tension. Post-tensioned tendons are used in conjunction with jacketed structural steel bars. First, a jacketed bar is positioned at the desired location. Holes are then drilled into both sides of this bar and post-tensioned cables are inserted into them. The end of each cable is then connected to its corresponding tendon on either side of the structure wherever it needs reinforcement. Finally, by pulling the jacked bars with high tension stress any designated amount of force can be applied between them and the concrete without causing damage to either material.
Post-tensioned tendons are strong, steel cables that connect areas of a structure requiring reinforcement and transmit tension from one to another. Such as: a structural, larger beam span, slabs and columns. Post-tensioning is typically accomplished by pulling these tendons very tight with hydraulic jacks and then fixing them in place to ensure they do not slip once the concrete hardens.