During the construction of cast-in-place beams, the steel strands need to be pre-stressed tension, which is a core link. When calculating the theoretical elongation of the prestressed tension of the steel strand, the distance between the anchor points at both ends of the steel strand should be used as the calculated length of the steel strand. The following is the method of calculating the tension value of prestressed concrete steel strands
1. When the steel strand for prestressed concrete is stretched by the stress control method, the elongation value is used to check, and the difference between the actual elongation value and the theoretical elongation value meets the design requirements. If the design is not specified, the actual elongation value and the theoretical elongation The difference between the values should be controlled within 6%, otherwise, the tensioning should be suspended, and the tensioning can only be continued after the cause is found out and measures are taken to adjust.
2. The theoretical elongation value (mm) of the prestressed tendons can be calculated by multiplying the tensile strength by the cross-sectional area of the steel strand.
3. When the steel strand for prestressed concrete is stretched, adjust it from the fixed end to the initial stress σ0, which is 10% of the tension control stress σcon, and the elongation value is measured from the initial stress. Straighten the prestressed steel strand, tighten the anchoring end and the connector, select a suitable position on the prestressed concrete strand to mark as the base point for measuring the extension, and then tension from the tension end to control the stress To 20% of σcon and measure the elongation value.
4. Holding load, select the holding time 2~5min according to the type of prestressed concrete steel strand, so that the prestressed concrete steel strand can be partially relaxed, and the complete amount is about 20% to 25% of the total amount to reduce The stress loss after the steel wire is anchored.
5. Before anchoring, makeup or relax the tension of the prestressed steel strand to control the stress. Measure and record the extension of the prestressed steel strand, and check the actual measured value and the theoretically calculated value. The error should be within ±6%. If it does not meet the requirements, find out the reason and deal with it in time. Therefore, the measured value of the steel strand is between 462mm and 522mm.
6. After the tension meets the requirements, anchor the prestressed steel strand and the jack to return oil to zero.
7. When the prestressed tendons are stretched and relaxed, fill in the construction records.
8. Corresponding to the reading of the oil gauge when tensioning at each stage.
The tension of the prestressed concrete strand can increase the bearing capacity, so the calculation of its tension value is very important. If you still have some doubts after reading the above, you can contact us for more detailed solutions.
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