Post-tensioned concrete has made significant progress since its first applications – particularly in the areas of performance, quality assurance and reliability, as well as corrosion safety. But what exactly is this technology?
What is Post Tensioning Concrete?
It is concrete that has been affected by compressive stresses that make an opposite reaction to the tensile stresses expected to occur from the weight of the concrete element. This leads to preventing the formation of cracks, by fading tensile stresses in the element in critical areas and improving its condition to withstand other loads.
Prestressed uses
It is widely used in bridges, bridges, floor slabs, silos and residential buildings.
The Post Tension system has spread at the present time to distinguish it from other traditional systems as follows: –
- Reduce the iron used.
- Speed in executing and dismantling the ceiling.
- The thickness of the concrete slabs is less compared to the rest of the systems, and thus the amount of concrete used for ceilings is reduced.
- Less weight of the slab, and its benefit appears in reducing the total weight of the building and thus improving its performance on earthquake resistance.
Components of the Post Tension implementation process
There are ten main tools used in the implementation of Post Tension work.
- Chairs are the same as the chairs used in a regular ceiling, and are used to place ducts on top of them to form the cable profile and the probe for the Bending Moment.
- Pipes – Ducts: There are two types of pipes, plastic and sheet metal, which are considered as hoses for the wires. Their aim is to protect the wires / Strands from entering any concrete. They are located at the project site with lengths ranging from 4 meters to 5 meters and are collected by making a joint (coupler) from another bag to bridge any Places that allow concrete to reach the weirat.
- Cables – Strands It is called (Wire). One cable consists of 7 strands (a core surrounded by six strands). The wires are mostly made of nickel, and there are diameters of 12.7, 15.24, and 15.7.
- Cast – Live End It is used to tighten the wires after the completion of casting and breaking the cubes, and in order to allow the wires to be tightened easily, a length of 40 cm to 50 cm is left in one wire from the end of each roof, and in some cases, such as wide seas, the wires are tightened from both sides.
- Anchor Head / Anchor Cast is called “the palm”. It consists of a hollow piece of iron that is fixed to the duct with adhesive tape. A piece of iron is placed in the front with a number of holes according to the number of wedges in one duct. It is known as the Anchor Head and to prevent concrete from reaching the wedges as well. To facilitate the cleaning process, a piece of cork is placed in the sides of the ceiling joinery.
- Wedges The aim of the wedges is to seal the welds after the tensioning process and to prevent the wire from bouncing back after tensioning, so they are placed after cleaning the surface of the anchor head.
- Stirrups & Spiral RFT Alkanes Spiral Alkanes are placed at the beginning and end of each Tendon to avoid cracks or fractures in the concrete during the tensioning process.
- Onions – Dead End (in tiles). At the end of each group, it is attached to one duct with an iron skewer, which is the end of the Tendons.
- Injection Tubes – Injection Tubes are placed at equal distances of (2-3) meters and at the beginning or end of the duct to ensure the success of the injection process and the absence of obstruction in the course of the duct. tensile strength and adoption.
- The main iron grid is used to prevent cracks in the ceiling, and it is mostly Shrinkage Bars.