A system of multiple jacks is utilised for the stressing of Dywidag Multi-Stage Anchors.
The staging of bond lengths, within the fixed anchor length, produces a range of free lengths.

During stressing, each strand exhibits a different rate of extension in proportion to its own length. To accommodate the different rates of extension, whilst ensuring that each strand is equally loaded, a system of pressure-synchronised jacks is used. Each jack is connected via a manifold to a central pump, ensuring equal pressure in all of the jacks.

Allowance is also required for the effect of friction, from adjacent bond lengths, on the free length strands. Friction is generated by the displacement of grout around the staged bond lengths when stressed. The influence of friction can be overcome by using reduced apparent free length acceptance criteria, applying load in smaller increments, or by repeat stressing.

DYWIDAG-Systems International provide on-site stressing and testing services for both temporary and permanent anchors.