Cap beam prestress tension problem, super theoretical elongation value 20 20

Let's talk about my opinion, 1. If the oil gauge has been calibrated, the corresponding oil gauge reading and stress formula are correct, then the stress value should be no problem;2. There is such a big gap, I think it should be a theoretical elongation miscalculation, which should be the elastic modulus of the steel strand to take whether there is a problem;3. This problem has not been studied, and I personally think that there should be no such thing, and I have encountered a short beam tension that is larger than the design;4. Now more than 20% theoretically it must be put down to re-analyze the reasons and then stretch, in fact, it should not be done, timely grouting and anchor sealing should be no problem, the possible quality impact may be that the anchor backing plate is easy to crack, and the precamber may be too large to cause cracking at the bottom of the beam.

Personally, I think:

1. Whether the anchor is installed correctly, it is estimated that it is a little crooked, not perpendicular to the bellows.

2. The oil gauge, jack, whether this set of tensioning equipment has been verified.

As for the solution, if the above problems are not there, then the actual elongation value control, that is, the final pull, do not pull 100%, only pull 90%, see, if the actual elongation value reaches the range of the theoretical value, it is OK, that is, with the actual elongation control, not to the oil gauge reading shall prevail!

23 meters is not a short time. If it is tensioned on both sides, such a problem generally does not occur.

1. Is the measurement of the actual elongation value consistent with the calculation end of the theoretical elongation value?

2. Is the coefficient accurate in the calculation of the theoretical elongation value?

The difference between the theoretical elongation value of the prestressed tendon and the actual elongation value of the tendon is ().

a.+10%～-10%

b.+10%～-5%

c.+5%～-10%

d.+5%～-5%

Correct answer: B

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The theoretical elongation of the prestressed tension of the rigid bridge is the same <>

Theoretically, if the anchorage length, prestress magnitude and direction of both ends are exactly the same when the rigid bridge is prestressed and tensioned, the theoretical elongation of both ends is the same. This is because the effect of prestress is to subjecte the concrete to tensile stress, thereby canceling the compressive stress caused by self-weight and external load, so that the whole structure is in a state of compression. In this case, the effect of the prestressing action at both ends on the structure should be the same <>

Is the theoretical elongation of the prestressed tension at both ends of the rigid frame bridge the same?

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The theoretical elongation of the prestressed tension of the rigid bridge is the same <>

Theoretically, if the anchorage length, prestress magnitude and imitation deficit direction of both ends are exactly the same when the prestressed tension of the rigid bridge is pulled, the theoretical elongation of the two ends is the same. This is because the effect of prestress is to make the concrete subjected to tensile stress, thereby counteracting the compressive stress caused by its own weight and external load, so that the whole structure is in a state of compression. In this case, the effect of the prestressing action at both ends on the structure should be the same <>

However, in actual construction, due to various reasons (e.g., material differences, construction errors, etc.) in Doosan, there may be slight differences in the size or direction of the prestress at both ends, so the actual elongation may be slightly different.

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Rigid frame bridge, the main load-bearing structure adopts rigid bridge, that is, the beam and the leg or pier body constitute the rigid connection of the bridge chain. The main load-bearing structure of the rigid frame bridge is the rigid frame structure of the consolidation of the pier of the beam and the bridge, because of the consolidation of the pier girder, the beam and the pier are stressed as a whole, and the pier not only bears the vertical pressure caused by the load on the beam, but also bears the bending moment and the horizontal thrust. Under the action of vertical load, the bending moment of the beam is often smaller than the continuous beam or the simply supported beam of the same span, and its spanning capacity is greater than that of the beam bridge; The consolidation of pier girders eliminates the need for large bearings, and the structure has strong integrity and good seismic performance.

Therefore, prestressed concrete rigid frame bridge is the main bridge type <> of long-span bridges

(1) The tensile control stress of the prestressed tendon should meet the design requirements. When the prestressed tendon needs to be over-tensioned or included in the prestress loss of the anchor ring mouth during construction, it can be increased by 5% compared with the design requirements, but in any case shall not exceed the maximum tensile control stress specified in the design.

2) When the stress control method is used to tension the prestressed tendon, the elongation value should be checked, and the difference between the actual elongation value and the theoretical elongation value should be controlled within 6%, otherwise the tension should be suspended, and the tension can be continued only after the cause is identified and measures are taken to adjust.

10% 20% 100, actual elongation = (20%-10%) + 100%-10%).

The purpose is to reduce the gap error generated during the assembly of steel strands and anchors, and the measured relaxation range can be adjusted according to the length of the steel strand.

Initial sheet = 10%-20%-70%.

Final sheet = 10%-20%-100%.

Four bundles, five bundles, six bundles.