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Post-Tensioned slab

Reasons why smart builders are using Post-Tensioned slab (PT slab) for constructing 2/3bhk apartments in Hyderabad

Builders in Hyderabad are increasingly using Post-Tensioned (PT slab) for giving the benefit of more chic, flexible and smart-looking 2/3 BHK in Hyderabad and elsewhere. The home buyers need to know what a PT slab means, and how it impacts them financially and in terms of design-related elements like safety and aesthetics.

Post-Tensioned slabs are a huge respite for an architect, besides being a delighter for the developers. PT slabs are not only a fantastic tool for the builders, but are also environment-friendly.

Over the last few decades, the PT technology has advanced tremendously, and is used for mid to high-rise buildings- both commercial and residential.

In this article, we shall discuss-

Let’s begin exploring…

What is a slab?

Slab is a moulded layer of ‘reinforced concrete’ used to create flat and useful surfaces such as floors, roof, and ceilings of a building. The slab made up of concrete is flat (horizontal), usually of uniform but sometimes of variable thickness, and is supported by columns, walls, beams or the ground.

A slab is generally several inches thick and supported by beams, columns, walls, or the ground.

Reinforced concrete slab

[Source- https://i0.wp.com/theconstructor.org/wp-content/uploads/2018/09/Reinforced-concrete-slab.jpg?resize=450%2C284&ssl=1]

What are Post-Tension slabs?

The post tension slab is an integral part of modern architecture. Builders today cannot craft magnificent skyscrapers, long bridges and beautiful structures without using PT slab. Having the right skill and experience is one of the key requirements to making PT slabs.

YouTube video given here demonstrates the phenomena of PT slab very neatly-

  • Post-tension slab is the one where the concrete is made strong using tendons. Tendons are inserted along the slab, and these tendons act as ‘reinforcements’ to make the floor strong. These strings/tendons go through ducts and is made-up of ‘steel wires’ (not bars). The wires are initially loosely suspended, and are later pulled after the concrete has been hardened. This means that the slab is made to bend upwards.
Monostrand Post-Tensioning System | AMSYSCO Post Tensioning

[Source- http://www.amsyscoinc.com/wp-content/uploads/2011/11/monostrand620x349.jpg]

Unbonded Post-Tensioning System - Post Tension Services India Pvt. Ltd.

{Source- https://ptsindia.net/wp-content/uploads/2020/12/Unbonded-Post-Tensioning-System-Page.jpg]

  • So, in Post-tensioned concrete, the tendons (wires) are ‘tensioned’ after the surrounding concrete structure has already been cast
  • The beauty of PT slab is that these wires/tendons are not allowed to come in direct contact with the concrete. Instead, they are enclosed in a protective duct just like a covered wire. At each end of a tendon, an anchorage assembly is provided. This anchor is firmly fixed to the surrounding concrete
  • Once the concrete is poured, and starts solidifying (set), the tendons are they pulled using a machine. This pulling makes the slab get ‘tensioned’ (stressed). This activity of pulling creates a significant permanent compression to the concrete, especially once the tendon gets locked at the anchorage

Advantages of PT slab

The use of post-tensioning helps us gain: i) thinner concrete sections, ii) longer spans/spaces between supports, iii) sturdier and stiffer walls to resist lateral loads, and iv) firm foundations to undo the adverse-effects of shrinking and/or swelling soils

Concrete possess, what the engineers refer to as ‘compressive’ strength. This means that it can easily bear its own weight within a certain structure. 

Post tension slabs are advantageous in many ways. Some of the major benefits of post tension slabs are as follows.

1. Extremely strong and durable

  • PT slab is a very strong substitute of the normal concrete
  • PT slab lasts longer, and is high on performance and ability to withstand the building weight with easy making it safe and strong simultaneously
  • Quality assurance has increased its durability
  • Corrosion protection has further enhanced its use in residential and commercial buildings

2. Reduced cost

  • With Post tension slabs, builders can construct much stronger structures at an affordable price point, passing on the benefits of savings to home buyers
  • There are many structures like parking garages as well as stadiums, since they are required to hold much more weight than average buildings, this slab becomes a viable option.

3. Tremendous architectural Flexibility enabling ‘column-free spaces’

  • A PT slab is sleek ranging between 4 to 6 inches in thickness
  • Designs made with PT slab are also sleek. They require lesser space and engineers can achieve dynamic contouring (with complex design elements). This is in fact the best part!
  • Post-tensioning allows complete flexibility and freedom on the shape of structure to be constructed
  • Creativity in spaces is possible, and 2/3BHK homes can be made without worrying about presence of additional columns since the area available in unrestricted
  • PT slabs are ideal to express creativity, especially to create open-kitchen, unconventional shapes and contouring of rooms and spaces
  • It also reduces environmental impact, construction time, use-of-materials and costs
  • It allows even for ‘change of use’ of the given space under the PT-slab i.e. a residential home can easily be re-adjusted to change the spaces/walls inside the residence, and also convert it into modern commercial spaces in future

4. Lesser usage of materials

  • With post tension slab is sleek and much thinner, yet stronger, lesser materials are used to achieve high tensile strength of the floor/ceiling
  • The PT slab does not need bulky materials

5. ‘Specific structural advantages’ as compared to ‘standard reinforcing steel’ (rebars):

  • PT slabs reduces or eliminates shrinkage cracking. This means that are fewer joints in the slabs which makes it stronger
  • It is far more crack-resistant since the slab is held together tightly
  • PT slab are other corresponding walls can be thinner, allowing for more space
  • PT slabs can be built on soft soils
  • PT slabs allow having longer spans i.e. more space
Site
ConcreteNetwork.com

[Source- https://static.concretenetwork.com/photo-gallery/images/550x412Exact_0x4/site_26/concretenetwork-com_12454.jpg]

Pre-requisites to casting a strong and sturdy PT slab

  • The builder and structural engineers doing the job must be knowledgeable. More important, the tendons and wires used in the PT slab must be corrosion-resistant, with no scope of being exposed to water
  • Skilfully and professionally laid and cast PT slab can be stronger than conventional concrete slabs. The masons deployed by the builder must be well-trained and experienced in laying PT slab
  • Filling of the wiring and tendons completely is an important element of PT slab

Thus, many benefits accrue by adopting a post-tensioned approach, especially in a mid-rise structure. In Hyderabad, smart builders are using it to include flexibility of design, faster construction pace, and lower material costs.

In the long run, they are extremely sturdy, and it help reduce maintenance costs, and offers potential for re-structuring or even increasing future loading.

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