3. Before tensioning operation, warning signs should be set around, and designated persons should be responsible for site safety. The fan-shaped danger zone radiated by the 45-degree included angle between two outer steel strands at both ends of the base. Tensioning and anchoring operators must stand in a safe position on the side. It is forbidden to watch and other personnel enter the tensioning operation area to prevent the steel strand from slipping and hurting people.
4, tensioning operators should not be frequently replaced, should be relatively stable and trained to operate.
5. All temporary power consumption requires "tn-s" wiring, and all temporary distribution boxes (boxes) must be equipped with sensitive leakage protectors. 6, all kinds of motor machinery must have a grounding device. Check regularly to ensure trouble-free use. In case of power failure or rest after work, the switch must be locked. The motor is connected in strict accordance with "one machine and one brake". 7. During on-site construction, the power supply of construction equipment, lighting power supply, office power supply and electric light power supply must be marked with electric panels respectively. When disconnecting the power supply, the full-time electrician shall be responsible, and other personnel shall not disconnect it at will. 8. In case of storm, lightning attack, dense fog and gale of magnitude 6 or above, the construction operation should be stopped. Construction method 1, steel strand blanking length Before steel strand blanking, the blanking length should be considered when calculating the pedestal length, anchor fixture length and exposed length of components according to the specific conditions of pedestal equipment. When blanking, straighten the steel strand first, and then measure it with a steel rule. The blanking shall be carried out on a flat site, and the cutting shall be carried out with a grinder. 5cm on both sides of the cut-off point shall be tied with iron wire to prevent the steel strand from coming loose after being cut off. The steel strand is manually put into the mold, and the threading sequence is from inside to outside. Both ends of each steel strand shall be marked and numbered, and plastic pipes shall be installed according to the drawings for prestress failure treatment after threading. 2. Tension procedure The tension procedure is 0 → initial stress → σcon (anchorage with load for 2min), where σcon is the control stress value during tension, including prestress loss. 3. When calculating the theoretical elongation value, the actual elongation value should be measured and checked with the theoretical elongation value. Calculation formula of theoretical elongation of prestressed tendons: where: PP- average tension of prestressed steel strand (N)L- length of prestressed steel strand (cm)AP- cross-sectional area of prestressed steel strand (mm2) EP-elastic modulus of prestressed steel strand (N/mm2). Suppose there are two types of tensioning platforms: 64.5m and 52.5m. Effective length of steel strand in tensioning platform = length of tensioning platform+width of two steel beams+length of decompression sandbox+anchorage length at both ends of 64.5m. Effective length of steel strand in tensioning platform L = 64.5+1.3+0.5.1= theoretical elongation of 66.4m. = 475mm 52.5m Effective length of steel strand of tensioning platform L = 52.5+1.3+0.0.34+0.1= 54.24m Theoretical elongation δ L =1395× 54.24×10000. There should be three tensioning operators, one to measure the actual elongation of steel strand with a steel ruler, one to record and one to operate the oil pump. Integral tensioning: at the integral tensioning end, two 250T jacks are used to push the movable anchor box for integral tensioning. In order to ensure the balance of the movable anchor box during the tensioning process, the method of simultaneous jacking by two jacks is adopted. When stretching to 80%, the calculated elongation cannot be achieved due to the short stroke of the jack, so it is necessary to use large blocks to keep the stroke between the movable anchor box and the mooring anchor box, return oil to the jack, add two blocks under the jack, and then stretch to 105%. After tensioning is completed, anchor with nut, return oil with jack, loosen the connecting sleeve, and move the movable anchor box and jack to another production line for tensioning. First of all, check whether the oil circuit is normal, check the safety facilities and ensure the safety of personnel. The oil pump drivers cooperate closely to control their respective oil pumps. When the oil pump is pulled to 105% σ k, it will return for 5 minutes with load, and then pull to 100% σ k .. to mark the steel strand, relax the stress and re-tension. After tensioning is completed, re-check the tensioning machinery and equipment used for tensioning. Observe and measure the pedestal and pressure column. Steel plug support, jack unloading. Insert steel plugs with different thicknesses between the bearing box and the end beam, plug the anchorage with thin steel plugs to make the anchorage stress uniform, and then unload the jack. After the steel strand is tensioned, the failed tube should be closed to prevent concrete slurry from flowing back into the failed tube during concrete pouring, which will affect the failure effect. Concrete pouring must be completed within 48 hours after tensioning. (1) Anchorage installation: firstly, install the passive tension end anchorage, straighten each steel strand in the same group, then install the active tension end anchorage, and then tighten the anchor pins at both ends. When installing, it should be operated by special personnel, and the anchorage should be strictly checked. The anchorage model should meet the requirements. (2) Install the jack; Jack should be checked and calibrated before use, and each jack should have an oil pump calibration curve. Put the jack into the bearing housing and install it in place. The installation position of the jack shall ensure that the line of action of the jack is consistent with the center of mass of the I-beam compression bar. (3) Initial tensioning: Check whether all parts of jack supporting equipment are complete and up to standard. Start the oil pump for initial tensioning and oil the tensioning cylinder of the tensioning jack. The initial tensioning control stress is10% σ k. Before tensioning, the steel strand shall be marked with original recording points. After the tension reaches the control stress, the ejector pin is anchored and unloaded. During the tensioning process, each group of steel strands shall be tensioned symmetrically, so as to ensure the balanced stress on the pedestal and accurate and clear marking. The steps and technical requirements for adjusting tensioning are consistent with the requirements for initial tensioning, except that the tensioning stress is adjusted to 40% σ k. In addition, the difference between the tensile force value of the steel strand after tensioning and the theoretical calculation value should not exceed 5%. After meeting the above requirements, the overall tensioning work can be carried out. (4) When the concrete specimen reaches more than 80% of the design strength, it can be demoulded. When releasing tension, the oil pumps must be loaded slowly, and the readings of oil standards of each oil pump should be similar, and the unloading time of the jack should not be less than l0min. (5) Cutting steel strand: The steel strand incision should be close to the member with the spacing of 1-2 cm. Grinding wheel saw should be used when cutting, and electric welding cutting is strictly prohibited. If oxygen-acetylene flame is used for cutting, the flame shall not barbecue the surface of the component during cutting, and the exposed steel strand at the cutting place must be coated with antirust paint and blocked with concrete with the same label as the component.