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1. (WO1979000856) A DEVICE FOR TENSIONING A REINFORCING STRAND
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CLAIMS
1. A device for tensioning a reinforcing strand (11, 2) in a concrete structure by means αf a
ram (l ) attachable to the end of the strand and comprising a cylinder (l6, 62), and a piston (17» 58) cσoperat-ing therewith, c h a r a c t e r i z e d in, that
the device is provided with means (22, 67) adapted to
supply the cylinder with gas obtained by the burning of powder (23» 68) or some similar substance.
2. A device according to claim 1 , c h a -r a c t e r i z e d in, that the device ( 1 k) is adapted to be used for the terminating jerk only, the preliminary, static tensioning being performed by arbitrary known means .
3. A device according to either of claims
1 or 2, c h a r a c t e r i z e d in, that the pressure sequence during the jerk is determined by the composition of the powder charge, so the pressure rises rapidly and then remains constant during the remainder of the jerk.
k.' A device according to either of claims
1 or 2, c h a r a c t e r i z e d in, that the pressure sequence during the jerk is determined by the composition of the powder charge, so the pressure rises rectilinearly to a desired, novel value.
5. A device according to either of claims
1 or 2, c h a r a c t e r i z e d in, that the pressure sequence during the jerk is determined by the composition of the powder charge, so the pressure rises to a novel value, and then is permitted to sink, substantially to the initial value .
6. A device according to claim 1 , c h a r a c t e r i z e d in, that the ram {lk \> , 62) is designed in such a manner that the powder gas may be used for the preliminary, static tensioning, as well as for the terminating jerk.

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7. A device according to claim 6, c h a r a c t e r i z e d in a chamber (15) at least partly forming an axial -extension of the cylinder (16) of the device, a double acting piston (17) being mounted upon a tubular piston rod (18), extending through the cylinder (16) as well as through the chamber (15). means
(22, , kk) being provided for supplying a pressurized gas to the chamber (15). and to submit the piston to the action of said gas at predetermined moments of time.
8. A device according to claim 7> c a r a c t e r i z e d in, that the chamber (15) is formed as an accumulator and that the cylinder (16) is provided with a support determining the innermost position of the piston, said support being formed as a fixed, annular flange (25) provided between the cylinder (16) and the accumulator (15). a cooperating slave piston (27) being adapted to form a temporary seal between the cylinder and the accumulator, said slave piston turning a smaller surface towards the accumulator, than towards the cylinder of the ram.
9. A device according to claim 8, c h a r a c t e r i z e d in a connecting duct (32) having a governing valve (33) for occasionally communicating the accumulator (15) with a space between the support flange (25) and the slave piston (27).
10. A device according to claim 6, c h a r a c t e r i z e d in, that it comprises a stationary piston (56) and a cooperating cylinder (62) axially movable in relation thereto, which at one end is provided with means (63) for the attachment of he ends of a number of strands (52) and at its opposite end is formed with a bottom structure (66) containing at least one loading chamber (67) and a cooperating breech mechanism (69).

11. A device according to claim 10, c h a r a c t e r i z e d in, that the cylinder is provided with a number of exhaust ports (75) in its envelope wall, located at an axial distance from the bottom structure (66) corresponding to the desired stroke of the cylinder.
12. A device according to claim 11, c h a r a c t e r i z e d in the exhaust ports (75) being arranged in series at different distances from the bottom structure, and in a mechanism (77) adapted to maintain, at will, one of said series open, while closing the remainder of the ports.
13« device according to either of claims 10 or 11, c h a r a c t e r i z e d in a firing mechanism (71) attached to the cylinder (72) and communicating with the combustion chamber (70) formed between the cylinder and the .piston by way of a passage (73) » and being adapted to ignite the, or each, stick of powder (68) at its end projecting into the combustion chamber.