Prestressing Systems- Types of Prestressing Systems

By Aina Parasher|Updated : August 7th, 2022

For major loads and high strength requirements, a setup needs to develop known as prestressing systems. This prestressing system uses high-strength steel with an upper-grade concrete mixture. These prestressing systems based on principal induce high compressive strength internally.

This prestressing system is classified as pre-tensioning and post-tensioning depending on the casting type of beam or member. Both prestressing systems are used in desired construction work.

What are Prestressing Systems?

Nowadays, multi-story buildings and heavy-bearing capacity structures need high strength and high serviceability members. In our practice, the heavy and high-cost members need to be eliminated. For all these causes, a high-strength structure casting method is adopted called prestressing systems.

This prestressing system allows providing high strength and high serviceability by using a high grade of cement with hysd steel bar. These prestressing systems are applicable when the area is less, and the load is high. Also, this is used for the compact design of the structure. In this article, we understand the type of prestressing and what kind of prestressing systems are used.

Difference Between Pre-Tensioning and Post-Tensioning of Prestressing Systems

As per the name, pre-tensioning and post-tensioning are the casting stage of the prestressing systems. We know concrete is able to resist higher compressive strength but weak in tension hence high strength of steel is provided before casting, and after casting, the structure is considered pre-tensioned and post-tensioned.

Pre-tensioning System

Post-tensioning System

In this induced tendons are tensioned before concrete is poured.

In this induced tendons are tensioned after the concrete is poured.

Stress is transferred from steel to concrete.

This concreting is done first by providing a duct for steel.

Pre-tensioning is done in construction facilities

Post-tensioning is done on-site.

This type of prestressing system is more reliable.

This type of prestressing system is less reliable.

In this prestressing system loss is about 17-19%

In this prestressing system loss is about 14-16%

Types of Prestressing Systems

prestressing systems is done with the help of different apparatus and methods. These methods are mechanical and chemical as different machinery is used for different conditions and prestressing systems requirements. All mechanical systems are loaded externally and internally and generate stresses. These are as below-

Gifford Udall Prestressing Systems

This prestressing system is a primary and simple method. In this prestressing system, Gifford provides a stressed wire and is anchored with a cylinder one by one. These anchored cylinders are fixed into the grips called Udall grips. Each grip is divided into two half cones and from this cable anchored in the number of 2,4,6 and 12 etc.

Magnel Blaton Prestressing Systems

This prestressing system consists of a rectangular duct to place steel cables or wires up to a diameter of 8mm. In this, all cables are arranged in as ways as each layer of a duct has a minimum of 4 wires, and these layers may reach up to 16. These layers have a minimum spacing of 4 mm, and spacing will carry on throughout the structure by providing equal blocks.

CCL Standard Prestressing Systems

These prestressing systems are considered individual cable tension. When an individual wire with high tensile strength is stressed, the structure approaches the under yield condition and the load gets satisfied. Maximum 12 no. of cable may be provided with 50mm diameter and these cables having spacing by using 600mm spacers. These spacers avoid frictional resistance from touching with sheathing. At the end knot of the cable, a tapered is provided with an attachment to the duct.

Lee-Mccall Prestressing Systems

These prestressing systems are considered high-strength steel bars with lengths up to 20m and diameters up to 22mm to 30mm provided. In these prestressing tendons, anchoring is done with the help of special threaded nuts. The threaded nuts have a tendency for slippage; hence to avoid this slippage a plate is provided at the end of the structural member to bear this torsional stress. This system is also a simplistic system where semi-skilled workers can also perform.

P.S.C Monowire Prestressing Systems

In this prestressing system when a mono wire with a large diameter (consisting of a high number of small diameter wires) is tensioned This tensioned wire is anchored with a single piece of collet sleeve in a tapered duct. In this duct, mono wire is inserted with the help of a truncated guide, and due to this, a gentle curvature is formed throughout the length. This curvature may also be maintained with the help of spacers or blocks.

Chemical Prestressing Systems

In this prestressing system when we use cement having the property of expansion between the fixed supports provides rigidity and reverse support reaction to confine this prestressing system.By this expansion, concrete gets stressed by compression and member become prestressed member high strength of steel is provided to take the tensile load.

Comments

write a comment

Prestressing Systems FAQs

  • The prestressing system is based on compressive load application where concrete members do not always remain in their initial condition. Due to changes in position, some losses are generated as Instant loss as friction, anchorage slip, and elastic shortening of concrete, and Time-dependent loss as shrinkage of concrete, creep, and relaxation of steel.

  • Generally, prestressing is required for heavy loads, low bearing capacity, and critical zone. When the size of members is restricted and heavy loads are coming to a system is used known as prestressing, where members are constructed with the help of high-grade concrete and high-strength steel with induced pre-applied stresses. This prestressing system provides durability and serviceability.

  • In the application of prestressing systems, high-strength material is used for both concrete and steel. For concrete IS code recommends a minimum M40 mix grade for the pre-tensioning system and M30 for the post-tensioning system while steel HYSD bars have been used with a minimum diameter of 10mm.

  • The prestressing systems have used different types of methods and devices for pre-tensioning and post-tensioning members. These are as below-

    • Gifford Udall prestressing systems
    • Magnel blaton prestressing systems
    • CCL standard prestressing systems
    • Lee McCall prestressing systems
    • P.S.C mono wire prestressing systems
    • Chemical prestressing systems
  • When the prestressing systems apply stresses, the member is loaded as per the line of action of force. This line of action of the force is formed in tendons is known as P-line, and when a line of action of the force is applied as pressure force, known as C-line. These lines are developed in the presence of external load.

Follow us for latest updates