Unbonded External Post-tensioning

DYWIDAG external unbonded post-tensioning systems strengthen wide-span bridges and wind towers.

The systems use tendons with strands and wires—or DYWIDAG Threadbars™.   

The systems, which have low induced stress range   and less fretting fatigue  can be prefabricated or assembled on site.  Corrosion protection with flexible fillers contributes to the structural durability.   

Our post-tensioning tendons with strands, wires and DYWIDAG Threadbars™ are inspectable and replaceable  and can be restressed if required . Deviation solutions are available. Our engineers can also configure the monitoring of stressing forces to support our Infrastructure Intelligence service. 

External strands and wires  

Typical applications for external tendons with strands and wires include bridge construction projects, where they are used as longitudinal tendons between bulkheads, and in the pre-stressing of concrete and hybrid wind towers, where they are used as vertical tendons.   

Strand systems of up to 55 strands and wire systems of up to 84 wires are available.  

External mono-strands 

Special applications for external mono-strands include round tank walls.  The tendons form a closed ring, arranged in either a circular or semicircular pattern.  A circular arrangement is also possible using a single-strand floating coupler.    

External DYWIDAG bars 

A significant field of application for DYWIDAG bars is in increasing the shear capacity of structures where bar tendons are arranged vertically outside webs—to replace any missing stirrup reinforcement.  Bar systems are available up to diameters of 47mm.  


  • Strand systems up to 55 strands and monostrand systems

  • Bar systems up to diameters 47mm

  • Wires systems up to 84 wires

  • Corrosion protection with flexible fillers contributes to the structural durability

  • Low induced stress range 

  • Less fretting fatigue 

  • Monitoring of stressing forces 

  • Restressing possible, if required 

  • Inspectable and replaceable 

  • Deviation solutions available

  • Prefabrication resp. site assembly possible

Commercial & Industrial

Wind Towers


Cast-in-place Method


Uncoilers, designed for the reels and tendon types, support precise timings for the safe and fast delivery of coiled tendons to the job site.   
Unbonded external bar tendons can be installed either inside or outside the cross-section of a structure to provide additional compression force.