POST TENSION SLABS (PT SLABS)

Post Tension Slab - Part 1.

One of the most important and improving systems in construction methods is Pre-stressed concrete which covering all structural elements(horizontal & vertical).
the main concept for the pre-stressed concrete is to creating resisting force for the deflection shape as shown the figure.
the same method can be applied to all structural elements with little difference depends on the element itself and the method of fixing.

There is two kinds of Pre-stressing concrete.
  • Pre-tension.
  • Post-tension.
Pre-tension concrete elements must be prepared in the factory then to be shifted to the construction areas to be fixed by cranes under qualified supervision and engineering team, different fixing methods are following depending on the element shape and size as shown the figure


Post tension concrete elements usually prepared at site due to it's size so it cannot be manufactured in the factory then shifted to sites like slabs or rafts.
  
Post tension slabs must be installed and cast at site, in the below lines will explain the components of the PT slabs.

-Steel Strands.

The steel strands which is usually used in the slabs and beams are 7 wires of low relaxation steel
It's coming in different diameters, 12.7mm , 15.2mm, 15.7mm.

-Ducts.

It's working as tube to install the strands inside it and protect the strand and make gap between strands and the concrete to allow stressing after slab concerting, it coming in different shapes as shown. 


- Anchorage system.

It's the most important and critical part in the PT slabs and it contains three items.
  1. Anchor head to carry the concentrated force in stressing stage.
  2. Anchor block to distribute the strands at the end.
  3. Wedges to allow the strand to move in one way and not to lost the force after completing the stressing.
     

   - Bar Chairs.

The bar chairs are used to give the required shape to the tendon (tendon profile) before concreting.

After all this items fixed in the correct way we will get the below shape of the tendon.
After fixing all this components as required by the approved design to make the required shape of profile in both directions as shown 

Then the PT slab is ready for casting.
Once the concrete gains the required concrete strength as required and calculated by the designer we can apply the stressing force.

After stressing completing and approved by the designer, then we can cut the stressing length and prepare for grouting the tendons.

Comments

  1. drayayoussefAugust 20, 2019 at 10:58 AM

    valuable informations , thank you

    ReplyDelete
  2. MaherAugust 22, 2019 at 11:49 PM

    Great work.. wow

    ReplyDelete
  3. ISLAM HELALAugust 24, 2019 at 2:33 AM

    A clear, easy and concise explanation with the help of real site pictures of the tools used and the method of implementation of a very important and economical topic to solve many problems and difficulties in many important structural designs.
    Thanks

    ReplyDelete

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