CN113739963A - Method for testing concrete surface stress - Google Patents
Method for testing concrete surface stress Download PDFInfo
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- CN113739963A CN113739963A CN202110546457.2A CN202110546457A CN113739963A CN 113739963 A CN113739963 A CN 113739963A CN 202110546457 A CN202110546457 A CN 202110546457A CN 113739963 A CN113739963 A CN 113739963A
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- strain
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- strain gauge
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- 239000004567 concrete Substances 0.000 title claims abstract description 65
- 238000012360 testing method Methods 0.000 title claims abstract description 61
- 238000000034 method Methods 0.000 title claims abstract description 24
- 238000010998 test method Methods 0.000 claims abstract description 5
- 238000005553 drilling Methods 0.000 claims description 7
- 238000005070 sampling Methods 0.000 claims description 5
- 239000000853 adhesive Substances 0.000 claims description 4
- 230000001070 adhesive effect Effects 0.000 claims description 4
- 244000137852 Petrea volubilis Species 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 2
- 238000000576 coating method Methods 0.000 claims description 2
- 238000011065 in-situ storage Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
- G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
Abstract
The invention discloses a method for testing concrete surface stress, which comprises the following steps: the method comprises the steps of adhering two strain gauges which are perpendicular to each other to a test point, carrying out segmented stress relief on the test point, recording an initial stress value and a strain value after each segment of stress relief, calculating a stress difference before and after each segment of stress relief, calculating a ratio of two adjacent stress differences as a strain gradient change value, stopping stress relief when three continuous strain gradient change values are smaller than a certain threshold value, and calculating a total strain value. Compared with other stress relief test methods, the method has the advantages that the damage to the concrete can be generally reduced by more than half, the damage to the active concrete is minimum, and the strain value of the active concrete can be rapidly and accurately tested.
Description
Technical Field
The invention belongs to the technical field of engineering geophysical prospecting.
Background
After the in-service concrete is used for years, the strain distribution of the in-service concrete needs to be found out, and a strain gauge embedding mode in the construction period is generally adopted, but the strain gauge cannot meet the actual requirement due to the limited early pre-embedding quantity or failure after many years.
Chinese patent application number isCN201110079624.3The invention discloses an in-situ testing method for the existing stress of a vertical shaft wall, which is characterized in that double holes are formed in the inner surface of the vertical shaft wall, the strain change of the middle part of each double hole is tested, and the existing stress of the vertical shaft wall is calculated according to the change quantity of the strain before and after the holes are formed. The patent opens double holes in the well wall, and has great damage to concrete; in addition, because concrete on two sides of the test point is removed, the influence of side stress is large, and the actual value is difficult to test; for thin plate shapeThe concrete is difficult to implement and use due to the great damage to the concrete caused by the method.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems of inaccurate detection and large damage to concrete in the current concrete stress test method, the stress relief is carried out by punching holes on the surface of the concrete in a more optimized mode, so that the damage to the concrete is minimized, and the strain value of the in-situ concrete is accurately tested.
The technical scheme of the invention is as follows:
a test method for concrete surface stress comprises the following steps: the method comprises the steps of adhering two strain gauges which are perpendicular to each other to a test point, carrying out segmented stress relief on the test point, recording an initial stress value and a strain value after each segment of stress relief, calculating a stress difference before and after each segment of stress relief, calculating a ratio of two adjacent stress differences as a strain gradient change value, stopping stress relief when three continuous strain gradient change values are smaller than a certain threshold value, and calculating a total strain value.
And when the initial three stress differences are smaller than a certain threshold value, determining that the stress is unchanged, and stopping stress relief.
The method for relieving the sectional stress is to vertically install a shallow sampling drilling machine on a test point and relieve the sectional stress by 5mm in section length.
The surface of the concrete is treated by attaching the strain gauge, the stress direction is estimated on the concrete surface according to the design and shape of the concrete, the strain gauge 1 is attached in the estimated stress direction, and the strain gauge 2 is attached in the transverse direction.
The stress value of the strain gage 1 is recorded as epsiloniThe stress value of the strain gauge 2 is recorded as εhiStrain difference of i-th section is Deltaepsiloni＝εi-εi-1The absolute value of the strain difference is Delta-epsiloni∣，Δ∣εi∣＝∣(∣εi∣-∣εi-1| if the absolute value of the difference of strain of three consecutive numbers Δ | epsilon1∣、Δ∣ε2∣、Δ∣ε3And if all the values are less than 5 mu epsilon, the test point is unstrained, and the test is terminated.
Strain gradient change value TεiThe calculation formula is Tεi＝Δεi/Δεi-1When T isεi-2、Tεi-1、TεiAnd when the number of the three continuous samples is less than 0.5, calculating the arithmetic mean value delta T of the gradient change of the strain, stopping the stress release to the ith section, and terminating the test.
Total strain value of concrete ═ epsilons 2+εh 2)1/2，
Presumed strain value epsilon of stress direction of concretes＝εi+Δεi×(1/(1-ΔT))-Δεi，ΔT＝(Tεi+Tεi-1+Tεi-2)/3
Strain value in vertical direction epsilonh＝εhi+Δεhi×(1/(1-ΔTh))-Δεhi
ΔTh＝(Thi+Thi-1+Thi-2)/3
In the formula: epsilonhStrain value of concrete strain gage 2 εhiStrain value of strain gauge 2 of i-th section, Δ εhiStrain difference, Δ T, of strain gage 2 of section ihGradient arithmetic mean, T, of strain gage 2hiGradient value of strain gauge 2 of section i, Thi-1Gradient value of strain gage 2 of section i-1, Thi-2Gradient change value of the strain gage 2 of the i-2 th segment.
Strain gauge 1: the length of the first-level concrete strain gauge grid wire is more than 75mm, and the length of the second-level mixed concrete strain gauge grid wire is more than 100 mm; strain gauge 2: the length of the grid wire is about two thirds of the length of the grid wire of the strain gauge 1.
The difference value of the inner diameter of the drill bit of the sampling drilling machine minus the outer edge diameter of the adhered strain gauge is larger than 10 mm.
Before the strain gauge is adhered, the surface of the test point is polished by a polisher or sand paper, so that the test surface is smooth, and the test surface is cleaned and dried.
Respectively and uniformly coating adhesives on the concrete test surface and the bottom surface of the strain gauge, adhering the strain gauge on the test surface, connecting a resistance strain gauge with the test, and recording the initial reading epsilon of the strain gauge 10Initial reading epsilon of strain gauge 2h0(ii) a Before each section of stress is relieved, the resistance strain gauge is disconnected, after each section of stress is relieved, the drill bit of the drilling machine is lifted to leave the concrete surface, and the strain gauge is connected with the resistance strain gauge for testing
The invention has the beneficial effects that: compared with other stress relief test methods, the method has the advantages that the damage to the concrete can be generally reduced by more than half, the damage to the active concrete is minimum, and the implementation and the application of the method are facilitated; the method can quickly and accurately test the strain value of the in-service concrete.
Drawings
FIG. 1 is a schematic diagram of a strain gage pasting and borehole decompressing position.
Fig. 2 is a flow chart of the present invention.
Detailed Description
Example 1:
(1) the stress direction is presumed on the concrete surface according to the design and shape of the concrete.
(2) And (3) polishing the surface of the test point by using a polisher or sand paper to enable the test surface to be flat and smooth, and cleaning and drying the test surface.
(3) The strain is tested by using a strain gauge with a certain grid wire length, adhesives are uniformly coated on a concrete test surface and the bottom surface of the strain gauge respectively, the strain gauge 1 is attached in the stress direction, the strain gauge 2 is attached in the transverse direction, and the strain gauge is firmly attached to the test surface. The length of the grid wire of the first-grade concrete strain gauge 1 is not less than 75 mm; the length of the grid wire of the secondary grading concrete strain gauge 1 is not less than 100 mm; selecting the strain gauge by the method that the length of the grid wire of the strain gauge 2 is about two thirds of the length of the grid wire of the strain gauge 1; the concrete test surface and the bottom surface of the strain gauge are respectively and uniformly coated with adhesives, and the strain gauge 1 is attached to the presumed stress direction, the strain gauge 2 is attached to the transverse direction, and the strain gauge is firmly attached to the test surface.
(4) Connecting resistance strain gauges and tests as required, and recording the initial reading epsilon of the strain gauge 10Initial reading epsilon of strain gauge 2h0。
(5) Vertically installing a shallow layer sampling drilling machine at the test point, carrying out sectional stress relief by 5mm in section length, testing, and respectively recording the strain epsilon of the i-th section of strain gage 1iOf strain gage 2Strain epsilonhi。
(6) Strain difference of i-th section is delta epsiloniHaving a value of Delta epsiloni＝εi-εi-1
In the formula: delta epsiloni-strain difference of section i in units μ ∈; epsiloni-strain value in i-th section in units μ ∈; epsiloni-1Strain values in section i-1 in units μ ∈.
Strain gradient change value TεiThe calculation formula is as follows:
Tεi＝Δεi/Δεi-1
in the formula: t isεi-the i-th segment gradient change value; delta epsiloni-strain difference, μ ∈, of section i; delta epsiloni-1-strain difference, μ ε, of section i-1.
(7-1) when the test point is not strained, testing the initial reading epsilon0And 1 st stage ε12 nd stage ε23 rd stage ε3Calculating the absolute value of strain difference in the i-th section as Delta | epsiloni∣：
Δ∣εi∣＝∣(∣εi∣-∣εi-1∣)∣
In the formula: delta | epsiloni-absolute value of strain difference, μ e, of the ith segment; | epsiloni-absolute value of strain value, mu epsilon, of the ith section; | epsiloni-1| the absolute value of the strain value, μ ε, of section i-1.
If the absolute value of the strain difference of three consecutive numbers Δ |. epsilon1∣、Δ∣ε2∣、Δ∣ε33And if all the values are less than 5 mu epsilon, the test point is unstrained, and the test is terminated.
(7-2) when there is a change in strain at the test point, Tεi-2、Tεi-1、TεiAnd when the number of the three continuous samples is less than 0.5, calculating the arithmetic mean value delta T of the gradient change of the strain, stopping the stress release to the ith section, and terminating the test.
Presumed strain value epsilon of stress direction of concretesComprises the following steps:
εs＝εi+Δεi×(1/(1-ΔT))-Δεi
ΔT＝(Tεi+Tεi-1+Tεi-2)/3
in the formula: epsilons-strain value of concrete in units of μ epsilon; epsiloni-strain value in i-th section in units μ ∈; delta epsiloni-strain difference of section i in units μ ∈; Δ T — arithmetic mean of gradient change; t isεi-the i-th segment gradient change value; t isεi-1-gradient change value of segment i-1; t isεi-2-gradient change value of segment i-2.
Strain value epsilon of concrete strain gage 2hComprises the following steps:
εh＝εhi+Δεhi×(1/(1-ΔTh))-Δεhi
ΔTh＝(Thi+Thi-1+Thi-2)/3
in the formula: epsilonh-strain value in units of μ epsilon for the concrete strain gauge 2; epsilonhi-strain value, μ ∈, of strain gauge 2 of section i; delta epsilonhi-strain difference, μ ∈, of strain gauge 2 of section i; delta Th-the arithmetic mean of the gradient changes of the strain gage 2; t ishiGradient change value of the section i strain gauge 2; t ishi-1Gradient change value of the strain gage 2 in the i-1 th section; t ishi-2Gradient change value of the strain gage 2 of the i-2 th segment.
Total strain value of concrete ∈:
ε＝(εs 2+εh 2)1/2
in the formula: epsilon-total strain value of concrete, unit. mu. epsilon; epsilons-strain value epsilon of soil in the direction of stress estimations；εh-strain value of the concrete strain gauge 2.
Claims (11)
1. A test method for concrete surface stress is characterized by comprising the following steps: the method comprises the steps of adhering two strain gauges which are perpendicular to each other to a test point, carrying out segmented stress relief on the test point, recording an initial stress value and a strain value after each segment of stress relief, calculating a stress difference before and after each segment of stress relief, calculating a ratio of two adjacent stress differences as a strain gradient change value, stopping stress relief when three continuous strain gradient change values are smaller than a certain threshold value, and calculating a total strain value.
2. The method for testing the surface stress of the concrete according to claim 1, wherein: and when the initial three stress differences are smaller than a certain threshold value, determining that the stress is unchanged, and stopping stress relief.
3. The method for testing the surface stress of concrete according to claim 2, wherein: the method for relieving the sectional stress is to vertically install a shallow sampling drilling machine on a test point and relieve the sectional stress by 5mm in section length.
4. The method for testing the surface stress of the concrete according to claim 3, wherein: the surface of the concrete is treated by attaching the strain gauge, the stress direction is estimated on the concrete surface according to the design and shape of the concrete, the strain gauge 1 is attached in the estimated stress direction, and the strain gauge 2 is attached in the transverse direction.
5. The method for testing the surface stress of the concrete according to claim 4, wherein: the stress value of the strain gage 11 is recorded as epsiloniThe stress value of the strain gauge 2 is recorded as εhiStrain difference of i-th section is Deltaepsiloni＝εi-εi-1The absolute value of the strain difference is Delta-epsiloni∣，Δ∣εi∣＝∣(∣εi∣-∣εi-1| if the absolute value of the difference of strain of three consecutive numbers Δ | epsilon1∣、Δ∣ε2∣、Δ∣ε3And if all the values are less than 5 mu epsilon, the test point is unstrained, and the test is terminated.
6. The method for testing the surface stress of the concrete according to claim 5, wherein: strain gradient change value TεiThe calculation formula is Tεi＝Δεi/Δεi-1When T isεi-2、Tεi-1、TεiWhen the number of the three continuous samples is less than 0.5, calculating the arithmetic mean value Delta T of the gradient change of the strain, and relieving the stress to the secondSegment i is stopped and the test is terminated.
7. The method for testing the surface stress of the concrete according to claim 6, wherein: total strain value of concrete ═ epsilons 2+εh 2)1/2，
Presumed strain value epsilon of stress direction of concretes＝εi+Δεi(1/(1-ΔT))-Δεi，ΔT＝(Tεi+Tεi-1+Tεi-2)/3
Strain value in vertical direction epsilonh＝εhi+Δεhi(1/(1-ΔTh))-Δεhi
ΔTh＝(Thi+Thi-1+Thi-2)/3
In the formula: epsilonhStrain value of concrete strain gage 2 εhiStrain value of strain gauge 2 of i-th section, Δ εhiStrain difference, Δ T, of strain gage 2 of section ihGradient arithmetic mean, T, of strain gage 2hiGradient value of strain gauge 2 of section i, Thi-1Gradient value of strain gage 2 of section i-1, Thi-2Gradient change value of the strain gage 2 of the i-2 th segment.
8. The method for testing the surface stress of the concrete according to any one of claims 1 to 6, wherein the strain gauge is selected from the group consisting of: strain gauge 1: the length of the first-level concrete strain gauge grid wire is more than 75mm, and the length of the second-level mixed concrete strain gauge grid wire is more than 100 mm; strain gauge 2: the length of the grid wire is about two thirds of the length of the grid wire of the strain gauge 1.
9. The method for testing the surface stress of concrete according to any one of claims 1 to 6, wherein: the difference value of the inner diameter of the drill bit of the sampling drilling machine minus the outer edge diameter of the adhered strain gauge is larger than 10 mm.
10. The method for testing the surface stress of concrete according to any one of claims 1 to 6, wherein: before the strain gauge is adhered, the surface of the test point is polished by a polisher or sand paper, so that the test surface is smooth, and the test surface is cleaned and dried.
11. The method for testing concrete surface stress according to claim 10, wherein: respectively and uniformly coating adhesives on the concrete test surface and the bottom surface of the strain gauge, adhering the strain gauge on the test surface, connecting a resistance strain gauge with the test, and recording the initial reading epsilon of the strain gauge 10Initial reading epsilon of strain gauge 2h0(ii) a And (3) disconnecting the resistance strain gauge before each section of stress is relieved, lifting the drill bit of the drilling machine away from the concrete surface after each section of stress is relieved, and connecting the strain gauge with the resistance strain gauge for testing.
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2021
- 2021-05-19 CN CN202110546457.2A patent/CN113739963A/en active Pending
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