Large-sized aqueduct prestressing force construction method

[0023] The implementation process of the present invention is as follows:

[0024] 1. Material entry: steel hinge line entry inspection, setting out, off-line, numbering; fixed end anchorage production, bundling, classification; anchorage inspection, warehousing, classification placement; bellows inspection, stacking.

[0025] 2. Bellows installation: When the bellows are installed after the bottom net steel bars and lateral steel bars are bound, control the coordinate size of the section and the vector height of each hole marked on the template according to the drawing, and the measurement allowable error is ±5mm , Fix the bellows on the stirrups with the erecting steel bars, and control the left and right positions of the bellows to weld the erecting steel bars and the stirrups to prevent the bellows from shifting or floating. During installation, special bellows joints are used for the extension of the bellows, and the outer edge of the lap joint is tightly wrapped with sealing tape.

[0026] 3. Tension end anchor plate installation: After the bellows are installed in place, put the neck of the anchor plate on the bellows, and the overlapping length of the bellows and the anchor plate shall not be less than 30mm. The outer edge of the lap joint is tightly wrapped with adhesive tape, and bound to the fixed anchor pad with soft steel wire, and the spiral reinforcement should be inserted before installation. After the anchor is installed, the spiral reinforcement is fixed on the steel bar close to the anchor backing plate. The outlet end of the anchor backing plate must be perpendicular to the center line of the corrugated pipe, and the inclination angle of the end surface must meet the design requirements. For the lower horizontal tension end, a tapered groove should be reserved under the surface of the structure according to the design drawings. After the end formwork is erected, the anchor plate is fixed on the formwork with screws.

[0027] 4. Installation of p-type anchors at the fixed end: finally, according to the actual situation on site, use extrusion anchors and pressure-bearing plates to fix them. The method is to thread the steel strand into the corrugated pipe, insert the restraint ring, spiral reinforcement, anchor plate, and reserve a length of 1.5m from one end in sequence, and then anchor the extrusion sleeve on the steel strand with an extrusion machine. Squeeze the extrusion sleeve and the anchor plate tightly, install the pressure plate and tighten it with screws. When positioning, put the whole beam into the position, and accurately position according to the coordinate requirements.

[0028] 5. Reserved hole protection: After the corrugated pipe is bound in place, other operations should be very cautious. Care should be taken during the binding of the reinforcement. Carefully protect the shape and appearance of the reserved hole position. During the electric welding operation, it is strictly forbidden for the electric spark to touch the bellows and the tape, and the welding slag shall not pile up on the surface of the bellows.

[0029] 6. Steel strand threading: After the steel strands are braided into bundles, wrap the front end with tape to avoid damage to the bellows when threading the bundles, and it is also easy to thread. Install the beam ring on the front end of the bellows, and then use the beam threading machine combined with manual threading. During the threading of the steel strands, the steel strands should be prevented from twisting, and attention should be paid to the upper and lower marks at the end of the steel strands.

[0030] 7. Install the exhaust pipe: When the corrugated pipe with the reserved hole is ready to be installed, install the exhaust pipe at the appropriate position of the corrugated pipe according to the needs. There is an exhaust pipe in the middle. (2) If there is an upward arch structure in the reserved channel of the curved beam, an exhaust pipe must be installed at the wave crest. (3) The exhaust pipe is required to be connected to the upper surface of the prestressed concrete and exposed for more than 300mm. Number the outer end, stick it firmly with tape, and wrap the exhaust pipe and the corrugation tightly with sealing tape.

[0031] 8. One-layer silicon pouring: re-inspect the installation height before sealing the mold: check the corrugated pipe for damage before opening the warehouse, and conduct hidden process acceptance. Strengthen the vibration of the anchor backing plate during pouring to ensure that the vibration is compact and prevent the grout from leaking into the anchor backing plate.

[0032] 9. Pouring of second-floor bricks: Prior to pouring, it is important to check whether the corrugated pipe at the interface is damaged or not, and it can only be poured after passing the inspection.

[0033] 10. Stretching: When the strength of the brick structure reaches 80% of the design strength, it can be stretched.

[0034] 1) Before applying the prestress, the jack and the oil gauge should be calibrated, and the accuracy of the pressure gauge should be within ±2%.

[0035] 2) Stress control is the main method of tensioning, and the elongation value is used as a verification: when the theoretical value and the measured value exceed the specified range of design (±6%), the tensioning must be suspended, the reason is analyzed, and measures can be taken before continuing.

[0036] 3) Tensioning sequence: Arrange the tensioning sequence on the principles of synchronization, symmetry, and simultaneity. The general sequence is first longitudinal to horizontal and then vertical, advancing from both sides to the middle.

[0037] 4) Stretching steps: the tension control force of the steel beam is δcon=0.7×fPtkMpa, and it is stretched in four steps;

[0038] The first step stress is pretensioned by 0-15% δcon single root;

[0039] The second step of tension can be carried out after the second step of stress is held for 5 minutes by 15%-30% δcon;

[0040] The third step stress is 30%-60% δcon;

[0041] In the fourth step, the stress is changed from 60% to 103% δcon, keep 103% δcon, and lock after holding the load for 2 minutes.

[0042] 11. Hole grouting: after the tensioning is completed, the hole is grouted in time. The design of this project requires the use of vacuum-assisted grouting for construction.

[0043] 1) Equipment preparation and instrument calibration: Calibrate the pressure gauges used for grouting pumps and vacuum pumps.

[0044] 2) Pipeline sealing and anchor pressing: After the tensioning is completed, if the elongation value calculated by experience is within the design requirement range, the steel strand can be cut off, leaving a length of about 3 cm at the anchorage end, and the anchor is sealed with a wet cement mass.

[0045] 3) Channel dredging: Use high-pressure air to dry the accumulated water in the pipe before installing the anchor fixture, and clean up the impurities before proceeding to the next step.

[0046] 4) Conduit connection: install a vacuum tube at one end, install a grouting tube at the other end, turn on the vacuum pump to press the grout, and reach the vacuum degree requirement of -0.06 to -0.09MPa.

[0047] 5) The cement slurry is stirred strictly according to the proportion to make slurry: open the valve of the slurry inlet pipe and press the slurry. After the cement slurry enters the exposed vacuum pipe, close the ball valve of the slurry outlet pipe and pressurize to 0.5-0.8MPa. Press the grout upwards, control the pressure at 0.3-0.4MPa, and keep the pressure constant for 2 minutes.

[0048] 6) For the pipeline grouting process with multiple peaks, the vent holes should be opened and closed in sequence, and the grouting should be carried out slowly and evenly without interruption.