Tension anchors2018-02-28T10:20:49+02:00

metodi_tiranti_02Tension anchors are structural elements operating in traction that transmit power to the ground through a steel strand armor or self-drilling rods (or hollow bars) with improved adherence.

The most common use of the anchors is inside the supporting structures of the excavations, together with micropiles or piles (in berliner walls) or with diaphragm in c.a.; by increasing the tension anchors class it is possible to carry out excavations even at high depth without making very heavy vertical structures.

The scope of the tie rods varies depending on the number of strands, from 15 to over 120 tons, or on the diameter of self-drilling rods.


These are the functional parts of a tie rod:

  • The armor is divided into the anchor bulb (part of naked strand anchorage in the ground) and a free part (part of strand coated with sheath). A series of steel wire strands (that make up the armor) allows varying the tensile force transmitted from the tie rod to the support structure;
  • an anchoring head, composed by the anchor plate, transfers the load in traction from the strand to the restraint structure;
  • the injection tube ensures proper casting of mortar under pressure sealing of the hole for the entire length. If needed, injection tubes can be equipped with valves for reinjection.

Based on the temporary life of their action, anchors can be classified in: – provisional, with a time-limited function, as it is no longer required once the structure is completed and – permanent, which need adequate protection against corrosion as to guarantee a duration equal to that of the supporting structure.

The installation phases of anchors can be summed up as follows:

  • Drilling by rotation or rotary percussion with hydraulic probe, likely with hole coating;
  • Laying of the armor;
  • Mortar pressure casting through canes (using special cement grouts or high resistance expanding resins);
  • Testing to be made after jet maturation reaches a load equal to 1,2vv the working load;
  • Tightening ad required project load.

metodi_tiranti_01Tie rods are structural elements operating in traction, used to secure rock faces and anchor to the ground bulkheads and retaining walls.

In general, the function of the anchor is to ensure that the work is static, in areas where the soil offers the possibility of absorbing the stresses.

We consider anchoring tie-rods those structural elements connected to the ground or to the rock that act to get traction. Traction forces are applied to anchored structure by means of a distribution plate (with anchor head).

Depending on type of stress, tie rods can be:

  • Passive anchors, in which tensile stress rises after deformation of the anchored work;
  • Active anchors, in which tensile stress is totally or partially linked to the anchorage work;

Depending on the duration of the exercise, tie rods can be:

  • Provisional ties, with a time-limited function
  • Permanent ties, which function is linked to useful life of the work anchored.

To sum up, ties are essential and basic construction means in special foundation works than transmit large tensile forces to almost all types of soil.

It should be noted that the consolidation of rocky friable or cracked surfaces, request injection works.


Strand anchors

Strand anchors are composed of three main parts: steel anchor (strand), anchor head and grout body. The steel anchor is mounted in a hole with a diameter of 80-150mm and joined to the rock with a quick-setting cement suspension. Then, stretching is induced through a hydraulic press. The power passes from the construction to the steel anchor through the head and is gradually transmitted to the ground, acting on the structure or on the consolidated land.

Injections anchors

Injections anchors are steel pipes in casted steel with external thread that can be galvanized to increase protection against corrosion. The pipe acts as a boring bar, consolidation bar and injection pipe. The external thread and the screwing possibility allow an extension with sleeves, addition of various crowns and the fixing of plates and nuts.

Injection anchors are used as rock anchors, as nails for the soil (consolidation of sprayed concrete walls) or as piles for special foundations.

Dywidag threaded bar anchor

This type of anchor is used for the slopes long-term stabilization (through a shotcrete wall), because its robust composition (certified pre-stressed steel) and because it protects against corrosion (protection mass, ribbed or smooth PVC sheaths). The assembling of spacers allows to obtain homogeneous injection distribution, and consequently an increase in stability and protection against corrosion.

Threaded rods of the anchors can reach variable lengths when using valve sleeves.