A Post Tension Primer Post-tensioning is a technique for reinforcing concrete structures. The prestressing steel cables inside the sleeves or plastic ducts are positioned in the forms before placing the concrete. As the concrete gains strength, the cables are stressed to design forces before the application of the service load and are anchored att the outer edge region of the concrete. Post-tensioning is a type of prestressing which means that before the concrete has to support the service load, the steel is pulled or tensioned. The post-tensioned concrete means that the tension is applied after pouring the concrete, however before applying service loads, it is still stressed and hence it is called prestressed.[1] The basic element of a post-tensioning system is called a tendon. One or more pieces of post tensioning strand are coated with a protective corrosion inhibiting coating and a sheathing or bare strands with a duct is used to house them. In order to transmit the forces into the structure, there are anchors on each end of the tendon. The term post-tensioned tendon consists of a complete assembly which contains the strand or bar, anchorage assembly, the duct and any corrosion-inhibiting coating. [2] Strands today consist of seven high-strength steel wires are wound together to form a 270ksi strand. One or more strands would comprise a tendon.[3] Types of post-tensioning Two main types of post-tensioning exist : Unbonded Bonded (grouted) Unbonded tendons In unbonded tendon, the strands are sheathed and not actually bonded to the concrete surrounding it. One of the most common example are monostrand tendons. They contain corrosion inhibiting grease coated seven wire strands. The anchorage has a two-piece conical wedge for gripping the strand and a high strength iron casting. Bonded tendons Bonded systems consist of a metal or plastic duct embedded in the concrete in which two or more strands are inserted. A large multi-strand jack is used to apply stress on these strands and is anchored in a common anchorage device. The most common use of the Bonded system is used in bridges, in cablestayed bridges, in the superstructure (the roadway) and the cable-stays. The heavily loaded beams in buildings make use of bonded systems. Uses of post-tensioned tendons Our bridges, residential foundations, parking infrastructure, walls, columns and commercial or residential buildings make use of Post-tensioning.
The post-tensioned reinforcement technique, when used in floor construction, can result in longer spans between supports or thinner concrete sections. This method proves quite advantageous for the construction of buildings and structures with open spaces. The reduced thickness of the structural floors in the building can decrease the ceiling to floor height of each level and also results in the reduction of the total weight without sacrificing the potential loads. The use of post-tensioned tendons in bridge construction provides design flexibility allowing quite demanding geometry requirements which include significant grade changes, complex curves, and variable super elevation. In stadiums, this technique allows highly creative architectural approach and long clear spans. The technique also helps in eliminating the cracks and shrinkage in concrete. Furthermore, posttensioning can also help in resisting earthquakes. These advantages have allowed for the construction of many or our nations bridges, dams and buildings with modern architectural design and increased functionality and larger open spaces for the users or occupants. For more information please visit here: https://www.infrastructurepc.com/ Infrastructure Preservation Corporation Main Office: 5520 Rio vista Drive, Clearwater Florida 33760 Office: 727-372-2900 Ext.24 info@infrastructurepc.com https://www.infrastructurepc.com/