A post-tension slab consists of laying a grid of high-strength steel strands in bundles to form tendons. After casting, these strands are tensioned at the appropriate pressure to provide compression to the slab and increase its capacity.
In bonded systems, two or more strands are inserted into a corrugated galvanized metal or plastic duct that is embedded in the concrete. The strands are held by steel anchorage devices, when stressed, the anchor will help in diffusing the compression forces into the slab in a uniform manner. The duct is then injected with a cementitious grout that provides corrosion protection to the strand and bonds the tendon to the concrete surrounding the duct.
Post tension bonded systems are used in bridges and buildings. In the latter, they allow for flat slabs eliminating then need of drop beams and increasing the span length while staying more economical then conventional systems such as hourdi slabs or RC solid slabs.
Mega Prefab post tension slabs bring unique architectural freedom when compared to conventional building methods. They allow increased spans to be achieved with thinner concrete sections. By reducing the need for columns, the structure becomes more efficient and functional. In some situations, the height of the building is limited, in which the reduced story height has allowed additional stories to be constructed within the building envelope.
A Mega Prefab designed PT slab contain 20 to 30% less concrete and a minimal quantity of steel reinforcement, leading to significant savings in the overall structure costs.
The main advantages are summarized as follows:
- Increased clear spans.
- Thinner slabs.
- Lighter structures.
- Reduced cracking and deflections.
- Reduced story height.
- Rapid construction.
- Better water tightness
To obtain maximum benefits from post-tension slabs, it is recommended that the system is incorporated into the building structure at early design stages.
- Preliminary design and cost estimation.
- Execution design and shop drawings.
- Supply and supervision / installation of post tensioning systems.
Bonded or Unbonded PT system
Post tensioned slab systems can be constructed using either bonded or unbonded tendons. The relative merits of the two techniques are subject to debate. The following points may be made in favor of each:
- Develops higher ultimate flexural strength
- Does not depend upon the anchorage after grouting
- Localized the effects of damage in case of a severed tendon
- Simple technique for demolishing or providing future opening in slab
- Provides greater available lever arm
- Reduces friction losses
- Can be constructed faster