1, when prestressed tendons are tensioned, the strength, elastic modulus and age of concrete should meet the design requirements. Before tensioning, the formwork that limits the displacement of members shall be removed.
2, prestressed tensioning sequence should comply with the design requirements. When the design has no requirements, it should be placed in stages, symmetrically and staggered.
3. The tensioning shall be carried out with a wedge or jack as a whole and meet the design requirements.
4, prestressed tensioning speed should not be too fast.
5. After tensioning, the sequence of cutting off prestressed tendons should start from Zhang Duan and then cut off at the other end.
Second, the tensioning of post-tensioned prestressed concrete members shall meet the following requirements:
1. Before prestressing, check the external dimensions of the members and the compactness of the concrete behind the anchor pad, and clean the mortar in the tunnel.
2, prestressed tensioning procedure should comply with the design requirements. The centralized prefabrication of concrete box girder should be divided into three stages: pre-tensioning, initial tensioning and final tensioning, and the centralized prefabrication of T beam should be divided into two stages: initial tensioning and final tensioning.
3. The strength, elastic modulus and age of concrete in each stage of prestress should meet the design requirements.
4, prestressed tensioning sequence should comply with the design requirements.
5, prestressed tensioning end settings should comply with the design requirements.
6. When prestressing, the anchor pad, anchorage and jack should be located on the same axis. When the two ends are tensioned, the two ends should be synchronized during the prestressing process, and the elongation at both ends is basically the same.
Extended data:
Precautions for prestressed tensioning:
1. The clamp must be stored indoors, and moisture-proof and rust-proof measures should be taken to prevent the conductor from slipping due to the rust of the clamp.
2. When installing the clip, check that the clip hole of the anchor ring should be clean and free of sundries, and the clip should be free of corrosion. It is forbidden to pollute the clamp with dirt and sand.
3. At the beginning of tensioning (15% before tensioning), observe that the anchor ring should be close to the anchor pad, and adjust it in time when problems are found.
4. After tensioning is completed, check the elongation value in time. When it exceeds 6%, suspend the tensioning, find out the reason, and then start construction after adjustment.
5. In any of the following circumstances, the jack and supporting equipment shall be recalibrated:
(1) has been used for more than half a year.
(2) Stretching for more than 200 times.
(3) The prestressed tensioning equipment is abnormal.
(4) After the jack is overhauled.
6. During tensioning operation, steel plates of not less than 4mm shall be set at both ends of the beam body as protective fences, and it is forbidden to stand at the beam end (especially the corresponding steel beam surface) to prevent safety accidents.
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