Implements or apparatus for applying pushing or pulling force – Pipe or rod jack – Tie rod tensioner
Patent
1979-11-16
1983-03-15
Ramsey, Kenneth J.
Implements or apparatus for applying pushing or pulling force
Pipe or rod jack
Tie rod tensioner
60632, 60 39461, 91402, 254 93R, B28B 2304, F01B 101
Patent
active
043765270
DESCRIPTION:
BRIEF SUMMARY
Reinforcing strands in concrete structures are often subjected to a tensioning action during the erection. On those occasions when the reinforcing strands are located in passages in the concrete structure, and the casting of the latter is completed before tensioning is applied to the strands, it will, especially with long strands, and with strands which do not run rectilinearly, be found that friction against the walls of the passages causes a very uneven stress distribution along the length of the individual strand. The tension is highest at the end where the pulling force is applied, and the tension will be reduced in the direction away from said end.
In order to bring about a levelling of the stress distribution along the strand the inventor has previously proposed to terminate the static, stepwise tensioning by a sudden stress change, which causes a shock wave to pass along the strand. During a short moment of time this shock will release the local frictional grips between the passage walls and the strand.
When this activity is terminated the passage is filled with concrete slurry so the strand will be firmly bonded to the structure.
This shock wave has been caused by a hydraulic ram, sometimes subjected to the action of a pressurized gas, stored in a container. A shock wave for causing the desired stress relieving in the strand has a very short duration--it is a question of parts of a second--and experience has shown that it is very difficult to accelerate the means for jerking the strand. The rapid sequence will further make it necessary to use short conduits and large flow areas.
A substantial simplification of the handling is obtainable according to the invention by using a device for tensioning the strands and being provided with means adapted to supply the cylinder with gas obtained by the burning of powder or some similar substance.
A satisfactory tensioning of a strand will comprise a static tensioning, usually performed in several steps, followed by at least one jerk.
For the static tensioning a double acting ram of arbitrary type may be used, and the aim of the present invention is, in the first hand, to propose a device for causing the jerk, which in a simple manner may be devised so it can be used for the static tensioning also.
According to a development of the invention the device may include an accumulator, at least one portion of which forms an axial extension of its cylinder. A support determining the inward movement of the piston into the cylinder is then formed as a fixed annular flange between the cylinder and the accumulator, and a cooperating slave piston is 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.
A connecting duct having a governing valve may be provided for occasionally communicating the accumulator with a space between the support flange and the slave piston.
The means for governing the length of the piston stroke may comprise a stop member, cooperating with the piston rod and determining the return movement of the piston into the cylinder. Alternatively series of exhaust openings may be provided in the cylinder wall, a slide being arranged to maintain, at will some openings free and others closed.
The device may alternatively include a stationary piston and an enclosing cylinder, which at one end is formed with means for the attachment of the ends of a number of strands, while its other end includes a bottom structure comprising at least one loading chamber, which may be closed by a breech mechanism.
The cylinder is preferably provided with a number of exhaust ports in its shell, located at a distance from the bottom structure corresponding to the desired stroke.
The exhaust ports may be arranged in series at varying distances from the bottom structure, and a closure means is provided to select one series, while closing the remaining ports, to make possible a variation of the stroke length.
The cylinder may be provided with a firing mech
REFERENCES:
patent: 4048706 (1977-09-01), Ludvigson
LandOfFree
Device for tensioning a reinforcing strand does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for tensioning a reinforcing strand, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for tensioning a reinforcing strand will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1656706