Stable and flexible: DYWIDAG Strand Anchors with restressable Anchor Heads secure Steyr Viaduct

A total of six bridge structures in lengths between 83m and 278m and heights between 25 and 50m were built during the widening of the A 9 Pyhrn Motorway near the Klaus Tunnels in Austria. The bridges also serve as access roads for the construction of the second tunnel tubes, which began at the end of 2014.

In the jobsite areas, there are many river valleys with steep slopes. The geology is characterized by gravel, loose sediments, carbonates and psephites. The construction of the second tube for the 2.2km long Klauser Tunnel required the construction of bridge No. PY51.2, also known as the Steyr Viaduct, at the Klaus Interchange. The construction of the bridge required several excavation and slope stabilizations as well as supporting structures due to the unstable foundation soil.

DSI Austria produced and supplied selfdrilling DYWI® Drill Hollow Bar Anchors and accessories for the permanent stabilization of the deep river valley. A total of, 2,000m of R32-400 DYWI® Drill Hollow Bar Anchors as well as 480m of R32-280 DYWI® Drill Hollow Bar Anchors were installed including accessories.

Furthermore, an anchor beam had to be tied back near the northern abutment using permanent DYWIDAG Strand Anchors with 8 strands. For this purpose, DSI supplied DYWIDAG Strand Anchors with newly developed, restressable anchor heads.

The anchor heads can be restressed at any  time if necessary to ensure a permanent stabilization even in changing geological conditions. DSI has received an approval in Austria for the new restressable anchor heads. To tie back the anchor beam at the bridge abutment, the following products were successfully installed:

  • 6 permanent, 41.5m long DYWIDAG Strand Anchors
  • 14 permanent, 31.5m long DYWIDAG Strand Anchors
  • 6 permanent, 26.5m long DYWIDAG Strand Anchors

In addition, DSI supplied 26 restressable anchor heads as well as 5 anchor load plates with design loads of 1,250kN and rented the tensioning equipment.


ASFINAG Bau Management, Austria

Contractor Bridge Construction

STRABAG AG, Direktion IC Ingenieurbau, Austria

Contractor Rock Engineering

STRABAG AG, Direktion AC Verkehrswegebau, Gruppe Felstechnik, Austria

Geotechnical Engineering

INSITU Geotechnik ZT GmbH, Austria

DSI Unit

DYWIDAG-Systems International GmbH, Austria

DSI Scope

Production, supply, technical support

DYWIDAG Products

2,000m of R32-400 DYWI® Drill Hollow Bar Anchors, 480m of R32-280 DYWI® Drill Hollow Bar Anchors, 26 permanent DYWIDAG Strand Anchors with 8 strands and restressable anchor heads, 5 anchor load plates, stressing equipment

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