Internal Unbonded Post-tensioning System Using Strand

DYWIDAG’s internal unbonded post-tensioning system using strand tendons is a high-performance solution for improving the structural integrity and load-carrying capacity of concrete structures. The system follows the anchorage principles of bonded post-tensioning, but instead of grouting with cement grout, the tendons are protected against corrosion with grease or similar corrosion protection compounds in plastic sheaths.

The internal unbonded tendons are not rigidly bonded to the surrounding concrete, which offers benefits such as a low induced stress range, less fretting fatigue, easy monitoring of stressing forces, with re-stressing and replacement of the strands possible, if required. The tendons can be checked for stressing force using lift-off tests or built-in load cells, and can be re-stressed later provided the stressing anchors are accessible.

The use of grease, flexible filler, or gel in a plastic duct provides excellent corrosion protection for the tendons, and the system can be used in a variety of applications, including tanks, silos, and buildings.

This system provides the highest quality of corrosion protection in prefabrication applications, as the corrosion protection is usually prefabricated with the tendon, delivered to site, and installed. Additionally, the system provides more favorable conditions for decompression checks and meets requirements for crack widths as on reinforced concrete members.

  • High-strength steel strand tendons with up to 55 strands for enhanced load-carrying capacity and reduced reinforcement requirements

  • No grouting operations required on site, for faster installation times

  • Diameters available include: 0.5" (12.7mm), 0.6" (15.2mm), 0.62” (15.7mm)

  • Customizable system with prefabrication or on-site production possible and curved or straight tendon profiles

  • Replacement and restressing of the tendons is possible depending on the systems.

  • Electrically isolated version available

  • Corrosion protection available with flexible filler

  • Engineered coupler to couple all strands within the tendon available

Main standards for steel nuances

Europe: Y1770, Y1860

North America: 270 ksi low relaxed strand per ASTM A416

North America: Florida DOT Approval

Tank & Silos
Commercial & Residential Buildings
Industrial Buildings