Whether the theoretical elongation value is calculated correctly mainly includes the elastic transverse quantity of steel tendon, pipe length, duct friction coefficient and Jack friction coefficient K, which must be determined according to the actual situation of the site and the defined value in the specification under the same conditions.
4.
Individual hole plugging caused by a little grout leakage can be stretched out during tensioning without affecting the elongation and grouting.
Correct the bottom formwork settlement, or adjust the preset reverse camber value appropriately.
2.
(3) if the treated foundation still has minimal settlement, the preset camber can be restored by adding mortar to adjust the elevation in the settlement range.
Change the elastic modulus of concrete.
If the long-span beam has inverted top secondary tensioning, the elongation value of the jack shall be subtracted during the second tensioning and the previous control force, and the jacking value of the clips at both ends shall be added.
Bottom formwork (1) generally, the bottom formwork of post tensioned prestressed bottom formwork is prone to bottom formwork settlement under the influence of pressure.
If there is only one place to block the hole, which is not found during tensioning and the elongation value meets the requirements, the blocking hole can not be treated.
Before making the bottom formwork of post tensioned prestressed beam, the stress problem of foundation should be considered first.
Treatment method: check whether the tensioning machines and tools work normally, whether the tensioning technical disclosure is correct, and whether the actual elongation value meets the requirements.
(4) uneven settlement can be treated by overall thickening 10cm concrete (not only serious settlement or compression deformation at both ends).
After the corrugated pipe is blocked, the tensioning elongation value does not meet the requirements and the grouting is blocked.
The tensioning force meets the design requirements, but the elongation value does not meet the requirements, and the tensioning link is also problematic.
3.
If there are multiple blocked holes, the difference of elongation value is very large.
There are four principles for the reserved positions of concrete structure walls, columns and mass construction joints..
When the beam is a negative arch, the stress effect of the beam is not good, and the beam bottom is easy to crack.
The formwork can be sealed only after ensuring that the pipeline is tight.
According to the design age and concrete strength as the standard of whether it can be tensioned, it can be controlled according to the test block strength under the same conditions.
The tension camber is too small or too large.
Correctly locate the bellows coordinates according to the design.
For example, there will be a difference of 3cm for 5m.
Usually, if there is only one blocked hole and the length of the blocked hole is short, the difference of elongation value is small.
Just calculate the blocking position through the elongation value at both ends, open a slurry hole on the left and right of the blocking hole respectively, and fill the slurry.
If the deviation of elongation value does not meet the requirements, reverse calculate the hole plugging position through the elongation value, measure the hole plugging position by using the detection position of single steel strand, hole channel irrigation, impact bell drilling and other methods, then remove the hole plugging material, and then re tension, fill in deficiencies and grouting ~ ~ recommended reading ~ ~ key points of urban engineering road landscaping, do you understand the joint review of construction drawings, design disclosure There are four principles for the difference between the three technical disclosure and the selection of the three connection modes of key point reinforcement, and which parts cannot be welded or bound.
If the elastic modulus of concrete is large, the deformation of concrete is small, resulting in small camber value, which can reduce the particle size of coarse aggregate.
Whether individual steel tendons are not stressed or unevenly stressed, and the steel tendons cannot be wound.
Then, the bearing capacity per square meter of foundation is obtained through experiments, and the size of expanded foundation is determined through these two data.
Calculation of the actual elongation value the actual elongation value shall be subtracted from the elongation value of the tendon in the length section of the jack.
When the beam camber is too large, it occupies the thickness of bridge deck pavement.
The main reasons for the above situation are as follows: the tensioning force may be too small or too large; The actual elastic modulus of concrete is too different from the design; Whether the concrete strength reaches the design age and strength during tensioning; Whether the duct positioning is accurate and smooth; Whether the bottom formwork settles.
Elongation value prestress tensioning usually adopts double control of tensioning force and elongation value to check whether the tensioning is qualified.
The bearing weight of both ends is usually calculated according to the range of 2 ~ 3M at both ends, and the stress at each end can be calculated according to half of the beam weight.
1.
Treatment method: before sealing the formwork, check whether the pipe joint is tight and whether the pipeline is damaged.
(2) in case of soft soil foundation, if the problem cannot be solved by expanding the foundation, it needs to be solved by driving foundation reinforcement measures such as wood pile, powder jet pile or gravel pile at both ends.
