Post Tensioned Concrete Slab

It is the process of Post Tensioned Concrete slab after it has been poured and cured by means of a compressive force. High-strength steel tendons are used to form a network within the concrete that is then anchored to the foundation. The resulting post-tensioned slab provides structural rigidity at relatively low costs compared with most other types of construction, especially given its size.

Post-tensioned slabs have been proven in research to offer higher performance than conventionally reinforced slabs.

Introduction to post-tensioning and its advantages in concrete slabs

Post-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands, known as tendons. When compared to unbonded post-tensioning, it has the following advantages.

A technique of applying compression after pouring concrete and the curing process (in situ) is known as bonded post-tensioned concrete. The concrete is wrapped around a plastic, steel, or aluminum curved duct to prevent stress in the element.

Filled with tendons, the duct is pushed through it. Hydraulic jacks react against the concrete member after it has hardened to tension the tendons.

After the jacks are removed, the tendons are wedged in position and maintain tension after being stretched according to design requirements (see Hooke’s law), transferring pressure to the concrete.

The duct is then grouted to prevent the tendons from rusting. This technique is frequently utilized in areas where wide soils (such as adobe clay) make conventional perimeter foundations difficult to install.

Prior to the installation of the curtainwall, a wall with integrated supporting cables was erected. This method provides greater strength and resistance, and it reduces conventional post-tensioning requirements by eliminating the need for additional hardware in this application. The entire tensioned slab supports the structure without significant flexure owing to pre-tensioning. In addition, various bridges

The benefits of this method over unbonded post-tensioning are:

  1. Tendons, unlike other structure components, do not require traditional reinforcement. In accidents, they are unable to de-stress and thus cause a reduction in required reinforcements.
  2. Tendons may be readily ‘woven’ to generate a more effective design method.
  3. Increased ultimate strength resulting from the connection between the strand and concrete.
  4. There are no long-term concerns about maintaining the anchor/dead end’s integrity.

Post Tensioned Concrete Slab Benefits

  1. Slabs can be made with longer clear spans and thinner slabs.
  2. For the same floor-to-floor height, lower the building height.
  3. Allows for a high degree of adaptability in pillar layouts, span lengths, and ramp configurations.
  4. Traditional reinforcement standards may be reduced owing to the fact that tendons do not relax in accidents.
  5. The strand’s resistance to UV radiation contributes to its ultimate strength, as does the strong connection between it and the concrete.
  6. Concrete slabs are not generally subject to concurrent live loads, which means that the need for additional reinforcing is reduced. Concrete slabs also eliminate the need for timber piles or steel piles, both of which can be expensive and time-consuming to install. In addition, post-tensioning can significantly cut costs because of:
  • Reduced cracking and deflections
  • Height is reduced in the narrative.
  • Better water tightness.

Tendons Placement

  • Casting and block-outs are fixed to the edge formwork or construction joint formwork.
  • Support bars must be made in advance.
  • Lay the tendons according to their tendon layout as shown in the plans.
  • Tendon repairs utilizing support bars and chairs, as well as tendons with grouting ports and hoses, to correct profiles
  • Prepare each installation report according to the supplied format.
  • Tendon profiles should be tolerated as follows:
  • Vertical = + 5 mm (at the lowest and highest points)
  • Horizontal = + 100 mm

Conclusion:

It is a structural technique in which tendons are stressed from their relaxed position with hydraulic jacks to improve the performance of concrete, especially for large-scale projects.

In this method, reinforcement bars or tendons are placed in tension in a controlled manner by hydraulic jacks and then anchored at each end in sheaths.

This technique is used to achieve greater strength and durability.

Post-tensioning is a relatively new procedure, gaining recognition as an accepted practice following World War II. The first major project implemented using post-tensioning was the San Francisco Bay Bridge which involved post-tensioning.

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