Advantages of Post Tensioning

ADVANTAGES & APPLICATIONS

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FOR LONG SPAN & HEAVY LOADING STRUCTURES:

Post-tensioning has proven to be economical for typical commercial buildings and, to some extent, residential buildings, with spans greater than 7.0m. For a structure with a floor loading of 5.0 kN/m² and spans of approximately 10.0m, there are anticipated savings compared to conventional RCC design.

GREATER HEADROOM:

Due to the efficient design concept of post-tensioning, PT structures are generally thinner than their RCC counterparts. For instance, a typical residential project might use a 250mm thick RCC flat slab, while a PT slab of just 200mm thickness is sufficient.

NEAT & SIMPLIFIED LAYOUT:

For large spans over 10m, RCC design typically requires a ribbed beam framing system, which can be substituted with a PT flat slab or banded slab system. These alternatives are user-friendly for construction and the installation of services.

SPEEDIER CONSTRUCTION:

The simplified structural layout and reduced material usage allow for faster construction with less material wastage. Time savings are primarily attributed to:

• Reduced Steel Quantity: Steel laying is labor-intensive. By decreasing the quantity of steel in PT design, the slab can be readied for concreting sooner. A PT flat slab generally requires about 20 to 35kg/m² of steel, whereas an RCC slab requires 80 to 120kg/m².
• Earlier Stripping of Shuttering: A post-tensioned slab is ready for stressing once the concrete achieves a strength of 28 N/mm². For a concrete grade of 35 N/mm², this usually occurs on the fifth day post-concreting. Once stressing is complete, all slab shuttering can be removed and reused for other pours, allowing for earlier finishing work on lower floors.

IMPROVED DEFLECTION CRITERIA:

Prestressing allows a PT floor slab to "arch" slightly after tendon stressing, reducing the overall downward deflection of the slab. This helps mitigate long-term deflection issues, particularly for long-span structures. If left unchecked, long-term deflection can result in cracking of stiff non-structural members, such as brick walls and floor tiles, within 5 to 10 years post-construction.

ECONOMICAL & SUPERIOR DESIGN:

Post-tensioning provides savings to clients due to its enhanced structural behavior and related advantages. Local builders and developers in India frequently adopt proposals where post-tensioning solutions consistently outperform conventional RCC designs in terms of costs, structural depths, and long-term benefits.

ADVANTAGES:

• Earlier stripping of shuttering.
• Flexibility in providing service ducts and false ceilings.
• Larger column-free spaces.
• Reduced dead loads from thinner slabs leading to cost savings.
• Less workforce needed for post-tensioning works compared to RCC slabs.
• Reduction in reinforcement quantity.
• Post-tensioning allows significant weight reduction for buildings with the same number of floors, decreasing foundation load—a major advantage in seismic areas.
• Reduced occurrence of cracks.
• Better freezing and thawing durability than non-prestressed concrete.
• Post-tensioning is ideal for parking structures due to its flexible column layouts, span lengths, and ramp configurations.
• Increased flexibility for penetrations and openings in floors, both pre- and post-construction.

In summary, post-tensioning provides significant advantages in terms of cost-effectiveness, design efficiency, and long-term performance for a range of building applications.