Equipment for tensioning of dywidag threaded bars

Equipment for tensioning of dywidag threaded bars


FPT – Fluid Power Technology – over the years has developed experience and expertise in various fields of industrial and civil engineering. Historically the hollow hydraulic cylinders were born for the extraction of pins. The same devices have proven to be essential for stressing some bars specifically designed for civil purposes.

For the same bars are available ranges of FPT hydraulic tensioners that allow to reduce to the minimum axial distances of installation and extra lengths for stressing the bars.

The bars mentioned above are usually known as Dywidag. Dywidag® is the trade name of a product developed in Germany by the company named in the past as Dywidag (today DSI acronyms of Dywidag System International).

The Dywidag bars correspond to the class Y1050 in the catalogue SAS and identify the product with the higher resistance values (yeld strength fp0,1k= 950 N/mm2, tensile strength fpk= 1050 N/mm2), over the mentioned bars there are other bars ranges with lower resistance values that cover different applications, the most common ones are:

Bars B500 (corresponding to DSI “Gewi”): yeld strength fp0,2k= 500 N/mm2, tensile strength fpk= 550 N/mm2
Bars S670 (corresponding to DSI “Gewi Plus”): yeld strength fp0,2k= 670 N/mm2, tensile strength fpk= 800 N/mm2
Bars for formworks: yeld strength fp0,2k= from 750 to 950 N/mm2, tensile strength fpk= from 875 to 1100 N/mm2


  • The thread, made during the rolling process, does not affect the entire circumference of the bar, but only two diametrically opposite sectors as can be clearly seen from the drawing shown below. A limit of the thread is the need to tension the bars, putting them in tension and then tightening the anchor nuts.
  • It is also possible to stretch with the use of torque wrenches (manual or hydraulic) but the losses due to system frictions (friction between the thread of the bar and that of the nut) and the high stress of torsions that act on the bar (part of the applied torque due to the mutual frictions between the bar and the nut it is transferred as a torsion to the bar instead of as traction on it) they are not recommended for use when it is desired to obtain tightening values in line with the normal technical requirements (whether they be geotechnical or structural).

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