Prestressing steel

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Ducts for prestressing steel in the base plate of the bridge superstructure
Finished tension cables with coupling anchors

Prestressing steel is high strength steel , which, especially in the prestressed concrete for biasing is used. Prestressing steel mostly belongs to the group of unalloyed steels. Its high strength values enable great elastic elongation during pretensioning. In prestressed concrete construction, this reduces the loss of tension due to creep and shrinkage of the concrete , which reduces the pre-stretching and thus reduces the initially applied pre-tensioning force.

Properties and shapes

The prestressing steels are named according to their strength:

The modulus of elasticity for prestressing steel may be assumed for strands with E = 195,000 N / mm² and for rods and wires with E = 205,000 N / mm². In Germany, prestressing steels are subject to building authority approval.

Prestressing steel is used in various product forms and strengths. So there is it today in Germany, for example:

  • as hot-rolled bars, smooth, with thread or thread ribs, diameters from 26 to 40 mm and strengths from 835/1030 to 1080/1230 N / mm²
  • as tempered round wires (smooth or ribbed) with a diameter of 5.2 to 14 mm. (In the case of quenching and tempering, a lightly alloyed hot-rolled wire is brought to the desired property by means of multi-stage heat treatment .)
  • as cold-drawn round wires (smooth or profiled), with diameters from 4 to 12.2 mm with strengths from 1370/1570 to 1660/1860 N / mm². (The cold-drawn wires are brought to the desired properties by a multiple drawing process.)

The best-known prestressing steel is the tension wire, which is made from 3 or 7 stranded, cold-drawn round individual wires with diameters of 6.9 to 18.3 mm.


Anchor plate with the trumpet of the duct and spiral reinforcement

If the prestressing takes place against the hardened concrete, the prestressing steel is installed as a sliding tendon in the component to be prestressed. To do this, he receives a protective cover (metal or plastic corrugated pipe ) that separates the prestressing steel from the concrete. In addition, the prestressing steel is provided with anchors at its ends. Prestressing steel, duct and anchorage together are referred to as tendons . The pre-tensioning is done with hydraulic presses .

Cladding tube

The tendons are delivered on a cable drum either as a finished unit and installed or assembled on site. The individual prestressing steel wires or strands are shot one after the other through the duct and then threaded into the anchor. The cavity in the profiled ducts is either grouted with cement mortar ( subsequent bond ) or is already filled with grease at the factory ( without bond ) to protect the corrosion- sensitive prestressing steel, as is the case with the monostrand .

Tension anchor with anchor plate, anchor head and wedge anchoring of the tension wire strands

Tendon anchorage

The anchorage has the task of transmitting the forces of the tendon to the concrete. This is usually done with anchor plates to which the prestressing steel transmits the forces through wedge anchoring, upset heads or nuts .

One distinguishes

  • tensionable (movable) anchors that are accessible and at which tensioning takes place, as well as
  • Fixed (immovable) anchors to which the prestressing steel is anchored during installation.


  • Manfred A. Hirt, Rolf Bez, Alain Nussbaumer: Steel construction . Presses polytechniques et universitaires romandes, Lausanne 2007, ISBN 978-2-88074-702-2 .
  • Peter Marti, Orlando Monsch, Birgit Schilling: Engineering concrete construction. 1st edition. Society for Civil Engineering, Zurich 2005, ISBN 3-7281-2999-2 .
  • Hans-Gustav Olshausen, VDI-Gesellschaft Bautechnik (Hrsg.): VDI-Lexikon Bauingenieurwesen . Second revised and expanded edition. Springer Verlag, Berlin / Heidelberg 1997, ISBN 3-642-48098-5 .
  • Klaus-Wolfgang Bieger, Jürgen Lierse, Jürgen Roth: Reinforced concrete and prestressed concrete structures. 2nd revised and corrected edition. Springer Verlag, Berlin / Heidelberg 1995, ISBN 3-540-58799-3 .

See also

Web links