The multi-strand jack is a double-acting jack that uses double hydraulic cylinders to tension the prestressed tendons and presses the anchors.
Post-Multi-strands Tension Stressing Jack's working principle
When the prestressed tendons are stretched, the oil nozzle of the tension cylinder enters the oil, and the oil nozzle of the top pressure cylinder returns oil. The cover nut, the plug, and the threaded sleeve are connected together to drive the tool anchor to move to the left to stretch the prestressed rib; when the anchor is pressed and the tension is kept stable, the oil nozzle of the pressing cylinder enters the oil, and the piston and protective sleeve are pressed against the pressure. It is connected with the jacking head and moved to the right to force the clip into the anchor ring; at this time, the oil nozzle of the tensioning cylinder returns oil, the oil nozzle of the jacking and pressing cylinder enters the oil, and the tensioning cylinder hydraulically returns. Finally, the oil nozzles of the tension cylinder and the top pressure cylinder return oil at the same time, and the top pressure piston returns to reset under the action of the spring force.
1. Preparation:
First of all, you should understand the tensile requirements of the prestressed bundles in the engineering design, such as the number of steel strands per bundle, the standard strength, the cross-sectional area value, the control stress δk, the required tensile value, and the retraction of the anchorage. value, etc., and then determine the oil pressure value at δk according to the calibration value of "oil pressure value - output force".
2. Installation of jacks and anchors
(1) The steel strand is inserted into the reserved corridor of the structure, and the exposed length of the wire bundle at the tension end is required to be 200-250mm longer than the working length of the jack. The steel strand must be cut with a thin film grinder and must not be scattered or "hairy", so as to avoid difficulty in perforation.
(2) Put on the end of the wire bundle of the working anchor plate, push it to the anchor plate, and fix it with the stop.
(3) Install the working anchor clips: Before installing the clips, use a steel ring to tie each clip together, then push it into the taper hole of the anchor plate along the steel strand, and push it by hand until it does not move.
(4) Install the limit plate: The limit plate is designed according to the working anchor plate and matched with the holes of the anchor plate.
(5) Install the multi-strand jack: first, tie the end of the steel strand bundle with a wire pin, then the jack can be hoisted up and put on the steel bundle, and the support port of the front end cover of the jack is placed on the outside of the limit plate. At this time, the jack can be aligned coaxially.
(6) Install the tool anchor on the bearing stop at the end of the piston.
Operation Precautions:
1. In order to ensure the accuracy of the tension force, the jack should be matched with an oil pump, a pressure gauge, and an external high-pressure hose to calibrate the "oil pressure value - output force". When calibrating, the active working state of the jack shall prevail, and the graded record shall be taken, the average value of three measurements shall be taken, and the chart shall be drawn as the basis for tensioning.
2. In the following cases, the jack should be re-calibrated:
(1) After the jack is disassembled and repaired;
(2) The pressure gauge has collided or malfunctioned;
(3) When updating the pressure gauge;
(4) Reuse the jack after it has been placed for a long time.
3. The oil of the jack should be kept strictly clean, filtered frequently, and replaced regularly
4. When installing the oil pipe, the interface part should be cleaned and wiped clean. Strictly prevent sand and dust from entering the jack, and minimize the number of disassembly and assembly. When the new oil pipe is used for the first time, do not directly connect it with the oil nozzle of the jack. It should be cleaned in advance or cleaned in the oil output by the oil pump before use. After removing the oil pipe, the jack and oil pump should be equipped with dust caps to prevent dirt from being mixed in.
5. The Post tension jack should be run more than three times without load before use to discharge the air in the cylinder.
6. The Post tension jack should be regularly repaired and cleaned according to the actual use situation. If faults, oil leakage, or scratches on the surface of the piston are found during the work, it should be stopped for maintenance.
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