Precautions For Tension Construction Of Prestressed Anchors
Release time:
2021-06-15
The machines and instruments used for construction prestress should be maintained and calibrated regularly.
1. The machines and instruments used for construction prestress should be maintained and calibrated regularly.
2. When the prestressed tendons are stretched, they should be loaded from zero to the initial tensile force at the starting point of the measured elongation value, and then loaded to the required tensile force in stages.
3. The pre-stressed tensioning must follow the relevant application technical regulations and strictly follow the pre-programmed tensioning operating procedures.
4. The cutting of pre-stressed tendons should be done with a grinding wheel saw, but not with arc cutting.
5. When the steel strands are bundled, they should be straightened out one by one and tied into a bundle without disorder. The extruded anchor or embossed anchor at the fixed end of the steel strand shall be assembled with the bearing plate and spiral ribs in advance.
6. Before the prestressed tendons are stretched, the concrete strength test report shall be provided. When the cubic strength of the concrete meets the design requirements and cannot be lower than the actual strength of the concrete in the anchorage area specified by OVM during tension construction, the prestress can be applied.
7. Before tensioning the prestressed tendons, the surface of the bearing plate should be cleaned, and the quality of the concrete behind the bearing plate should be checked. If the concrete is hollow, it should be repaired before stretching.
8. When the anchor is installed, the anchor plate should be straight, the clip should be tightened, and the position of the clip should be even, but the clip should not be hit too hard to avoid damage to the clip.
9. Before formal tensioning of large-tonnage prestressed tendons, trial tensioning should be conducted with professionals. After confirming that the tensioning process is reasonable, the length of the tension is normal, and there are no harmful cracks, the batch can be tensioned. If necessary, determine the actual channel friction loss.
10. Tension management of prestressed tendons adopts stress control and elongation check. The allowable deviation between the actual elongation value and the calculated elongation value is -5%~10%. If it exceeds this value, the tension should be suspended; after taking measures to adjust, the tension can be continued; if the elongation value is too small, over-tension measures can be taken, but the tension limit shall not be greater than 0.8fptk; in the multi-wave curve In the prestressed tendons, in order to increase the tensile stress at the inner support and reduce the tensile stress at the lower mouth of the anchor after tension, the over-tensioned loosening technology can be adopted.
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