Precautions For Tensioning Of Anchorage Prestressed Tendons
Release time:
2021-06-17
When determining the tension sequence of the prestressed tendons, the overturning moment and eccentric force should be reduced as much as possible
1. When determining the tension sequence of the prestressed tendons, the overturning moment and eccentric force should be reduced as much as possible, and the prestressed tendons near the center of gravity of the pedestal section should be stretched first. It should be stretched in batches and symmetrically.
2. When the prestressed tendon is over-tensioned, its maximum over-tension should meet the following requirements: cold-drawn Ⅱ～Ⅳ grade steel bar is 95% of the yield point; carbon steel wire, scored steel wire and steel strand are the strength standard values 80% of it.
3. When tensioning by controlled stress method, the elongation value of the prestressed tendons should be checked. When the actual elongation value is greater than 10% of the calculated elongation value or less than 5% of the calculated elongation value, the tension should be suspended, and the cause should be found out and measures have been taken to adjust it before further tensioning.
4. When multiple prestressed tendons are tensioned at the same time, the initial stress must be adjusted in advance to make the stress consistent. The deviation of the stress value during the tension check shall not be greater than or less than 5% of the total value of the prestress of all steel wires of a component.
5. The number of pre-stressed steel fractures or slippages in the structure is strictly prohibited to exceed 3% of the total number of steels in the same section of the structure for post-tensioned components, and only one steel wire is allowed in a bundle; for pre-tensioned components, it is strictly prohibited to exceed 5% of the total number of steels in the same section of the structure, and it is strictly forbidden for two adjacent pre-stressed steels to break or slip off. The pre-tensioned steel material that breaks or slips off before the concrete is poured must be replaced.
6. When anchoring, the shrinkage of the prestressed tendons at the tension end shall not be greater than the construction specifications. After tensioning and anchoring, the deviation of the prestressed tendons from the design position shall not be greater than 5mm, and shall not be greater than 4% of the short side dimension of the component section.
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