A Structural Crack Control Measuring Device and Measuring Method

Abstract

The present invention discloses a structural crack control measurement device and a measurement method. The device is composed of a first steel pipe and a second steel pipe, both of which are internally provided with vibrating wire strain gauges; elastic linings are arranged in a fitting manner on the inner walls of the first steel pipe and the second steel pipe; the two vibrating wire strain gauges are coaxially arranged with the first steel pipe and the second steel pipe where they are respectively located; the opening directions of the first steel pipe and the second steel pipe point to the principal stress of the concrete; the signal cables of the vibrating wire strain gauges are led out of the cast solid structure; the concrete in the cast solid structure is poured to ensure that the concrete in the first steel pipe and the second steel pipe is filled completely; the data of the two vibrating wire strain gauges during the monitoring and measurement are collected, analyzed and crack controlled in real time. The device provided by the present invention has a simple structure and low cost, truly realizes the stress measurement inside the structure, and the measurement process is easier to implement, strengthens the credibility of the crack measurement data, reduces the error range, and can achieve good prevention and control of cracks caused by temperature stress and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering survey and control, and more specifically, to a structural crack control measurement device and a structural crack control measurement method using the device. Background Art

[0002] Mass concrete has large geometric dimensions, long internal heat transfer paths for hydration heat and is not easy to dissipate. Especially for high-strength concrete used in nuclear power plants and the like, the cement consumption is large and the internal hydration heat is high. Construction cracks in concrete often occur, seriously affecting the safety and normal use of the structure. The control of construction cracks in mass concrete is a common technical problem sought to be solved in the domestic and foreign civil construction industries, and also restricts the safe development of major concrete projects (such as nuclear power plants).

[0003] In the construction of mass concrete, temperature stress is an important structural load effect and one of the key factors for structural cracking and failure. Although there are many research literatures on temperature stress, there is currently a lack of effective measurement devices and methods for temperature stress. More often, theoretical calculation methods are used to determine the curing technical conditions under controllable temperature stress, and then measures such as temperature control during the construction process are used to control construction cracks; or strain measurement methods are used to try to distinguish this indirect control method of the restraint strain that restricts crack development.

[0004] At present, the main methods for controlling construction cracks in mass concrete structures are as follows:

[0005] Method 1: The existing patent "201510956216.X A Method for Determining the Construction Curing Method of Mass Concrete Structures". The core idea of this method is to conduct theoretical analysis of the temperature field and temperature stress field of the concrete structure through rigorous finite element modeling and the initial conditions and set technical conditions of the physical project. Compare the structural temperature stress with the allowable tensile strength of the concrete at the corresponding age, adjust and optimize according to the comparison result, and finally determine the specific curing method and corresponding technical indicators of the structure construction as the initial curing technical conditions, and adjust the construction curing measures of the physical project according to temperature and temperature strain monitoring. This method has obvious advantages and has good practical value and guiding significance for determining the initial technical indicators and curing monitoring indicators of concrete curing. However, the measurement of the direct factors affecting concrete cracking, such as temperature stress or restraint stress, is not clearly shown.

[0006] Method 2: For the existing patents "ZL201510342273.9 A Measuring Device and Method for Absolute Stress of Concrete" and "ZL201510342272.4 A Testing Method for Absolute Stress of Existing Concrete Structures", ultrasonic probes are used to measure the absolute stress inside the concrete structure through a combination of embedded or core-taking and assembly methods; this method can also be used for measuring the absolute stress of concrete during the construction of mass concrete. The problem with this method is that since concrete is not a material with good homogeneous properties, especially the internal defects that may be caused during concrete construction will seriously affect the accuracy of the test data. Furthermore, using ultrasonic probes for measurement has a relatively high equipment cost, and core-taking also causes certain damage to the concrete structure, so the engineering application value needs to be considered.

[0007] Method 3: Strain gauges are arranged inside the structure or strain gauges or strain gauges are arranged on the surface for measurement. Since the structural strain is very complex, especially during the construction of mass concrete, the temperature strain is the dominant factor. The measured strain obtained by the strain gauges needs to be corrected for temperature. For the construction of mass concrete, the temperature strain and temperature stress obtained after correction do not fully follow Hooke's law, and it is difficult to effectively obtain the factors that truly affect the cracking of the structure, such as restrained deformation or temperature stress.

[0008] Method 4: Other control methods, such as the skip-joint method, reducing the heat of hydration of concrete, temperature control monitoring, etc. These are all qualitative methods or measures and cannot quantitatively measure and control the temperature stress corresponding to cracking.

[0009] Therefore, how to accurately measure the restrained strain and temperature stress, which are the direct causes affecting the cracking of concrete, so as to achieve the control of structural cracking, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0010] In view of this, the present invention provides a structural crack control measurement device and its control measurement method, aiming to solve the above technical problems.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] A structural crack control measurement device includes a first steel pipe and a second steel pipe; one end of the first steel pipe is open and the other end is closed; both ends of the second steel pipe are open; the first steel pipe and the second steel pipe are placed in the concrete structure to be measured; elastic linings are arranged in a fitting manner on the inner walls of the first steel pipe and the second steel pipe; vibrating wire strain gauges are arranged inside both the first steel pipe and the second steel pipe; the two vibrating wire strain gauges are coaxially arranged with the first steel pipe and the second steel pipe where they are respectively located; the inner cavities of the first steel pipe and the second steel pipe are filled with concrete and integrally buried inside the concrete structure to be measured; the signal cables of the vibrating wire strain gauges are led out of the external part of the concrete structure to be measured.

[0013] Through the above technical solution, the device provided by the present invention has a simple structure and low cost, the measurement process is easier to implement, the credibility of the cracking measurement data is strengthened, the error range is reduced, and good prevention and control of the cracking caused by temperature stress can be achieved.

[0014] Preferably, in the above structural crack control measurement device, the vibrating wire strain gauge is suspended and tightened inside the first steel pipe / the second steel pipe by multiple positioning ropes; one end of the positioning rope is bound to the vibrating wire strain gauge, and the other end passes through the outer side wall of the first steel pipe / the second steel pipe and then is tightened. By using the positioning rope to tighten and fix, it can ensure that the vibrating wire strain gauge and the first steel pipe / the second steel pipe are always coaxially arranged during the pouring process, and the measurement accuracy is improved.

[0015] Preferably, in the above structural crack control measurement device, the first steel pipe and the second steel pipe are arranged in parallel and their outer side walls are in contact.

[0016] Preferably, in the above structural crack control measurement device, the outer side walls of the first steel pipe and the second steel pipe are welded and fixed.

[0017] Preferably, in the above structural crack control measurement device, the elastic lining is made of foam plastic material and has a thickness of 10 mm. The elastic lining can ensure that it is tightly attached to the steel pipe wall and the bottom, and ensure that the concrete flow during concrete pouring will not pull off the lining.

[0018] Preferably, in the above structural crack control measurement device, the elastic lining is adhesively fixed to the inner wall of the first steel pipe / the second steel pipe. The lining is adhesively bonded to the pipe wall and the pipe bottom in advance to ensure that the concrete inside the formed steel pipe is columnar and integral, and tightly holds the strain gauge, and can naturally adapt to the characteristics of the free expansion and contraction of the concrete.

[0019] Preferably, in the above-mentioned structural crack control measurement device, the inner diameters of the first steel pipe and the second steel pipe are both 150 mm, and the lengths are both 300 mm, which can meet the size requirements of the device.

[0020] Preferably, in the above-mentioned structural crack control measurement device, the materials of the first steel pipe and the second steel pipe are Q235 carbon steel, which can meet the material requirements.

[0021] The present invention also provides a structural crack control measurement method, including the following steps:

[0022] S1. Place the above-mentioned structural crack control measurement device at the measurement location, and make the opening directions of the first steel pipe and the second steel pipe point to the direction of the concrete principal stress;

[0023] S2. Pour the solid structure concrete to ensure that the concrete in the first steel pipe and the second steel pipe is filled completely;

[0024] S3. Monitor, collect, analyze and control the cracking of the data of the two vibrating wire strain gauges during the measurement in real time.

[0025] Specifically, step S3 specifically includes the following steps:

[0026] a. Measure the first measurement value of the free expansion and contraction strain of the concrete in the stress-free state according to the vibrating wire strain gauge in the first steel pipe;

[0027] b. Measure the second measurement value of the strain of the concrete structure in the direction of the second steel pipe according to the vibrating wire strain gauge in the second steel pipe;

[0028] c. Calculate the difference between the second measurement value and the first measurement value;

[0029] d. Multiply the difference by the elastic modulus of the concrete at the corresponding age to obtain the temperature stress of the concrete structure to be measured;

[0030] e. Compare the measured temperature stress with the ultimate bearing capacity of the concrete material to control the cracking of the concrete.

[0031] Through the above technical solutions, compared with the prior art, the present invention discloses a structural crack control measurement device and a measurement method, which have the following beneficial effects:

[0032] 1. The device provided by the present invention has a simple structure and low cost, truly realizes the stress measurement inside the structure, and the measurement process is easier to implement, strengthens the credibility of the cracking measurement data, reduces the error range, and can achieve good prevention and control of the cracking caused by temperature stress.

[0033] 2. In addition to being used for measuring temperature stress and preventing and controlling cracking during the construction of mass concrete, this device can also be used for accurately measuring the absolute stress of newly built or in-service physical structure projects. For example, for reinforced concrete beam bridges, etc., by arranging monitoring devices along the tensile direction at the tensile part of the beam, the measurement accuracy can be greatly improved, and through efficient temperature correction, the influence of environmental temperature uncertainty can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0035] Figure 1 The drawings are schematic diagrams of the structural crack control measurement device provided by the present invention.

[0036] Wherein:

[0037] 1 - First steel pipe;

[0038] 2 - Second steel pipe;

[0039] 3 - Elastic inner lining;

[0040] 4 - Vibrating wire strain gauge;

[0041] 5 - Positioning rope. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0043] See the appendix Figure 1, an embodiment of the present invention discloses a structural crack control measurement device, including a first steel pipe 1 and a second steel pipe 2; one end of the first steel pipe 1 is open and the other end is closed; both ends of the second steel pipe 2 are open; the first steel pipe 1 and the second steel pipe 2 are placed in the concrete structure to be measured; elastic linings 3 are arranged on the inner walls of the first steel pipe 1 and the second steel pipe 2 in a fitting manner; vibrating wire strain gauges 4 are arranged inside both the first steel pipe 1 and the second steel pipe 2; the two vibrating wire strain gauges 4 are coaxially arranged with the first steel pipe 1 and the second steel pipe 2 where they are located respectively; the inner cavities of the first steel pipe 1 and the second steel pipe 2 are filled with concrete and integrally buried inside the concrete structure to be measured; the signal cables of the vibrating wire strain gauges 4 are led out of the external of the concrete structure to be measured.

[0044] To further optimize the above technical solution, the vibrating wire strain gauges 4 are suspended and tightened inside the first steel pipe 1 / second steel pipe 2 by multiple positioning ropes 5; one end of the positioning rope 5 is bound to the vibrating wire strain gauge 4, and the other end passes through the outer side wall of the first steel pipe 1 / second steel pipe 2 and then is tightened.

[0045] To further optimize the above technical solution, the first steel pipe 1 and the second steel pipe 2 are arranged in parallel and their outer side walls are in contact.

[0046] To further optimize the above technical solution, the outer side walls of the first steel pipe 1 and the second steel pipe 2 are welded and fixed.

[0047] To further optimize the above technical solution, the elastic lining 3 is made of foam plastic and has a thickness of 10 mm.

[0048] To further optimize the above technical solution, the elastic lining 3 is fixedly pasted to the inner wall of the first steel pipe 1 / second steel pipe 2.

[0049] To further optimize the above technical solution, the inner diameters of both the first steel pipe 1 and the second steel pipe 2 are 150 mm and the lengths are both 300 mm.

[0050] To further optimize the above technical solution, the materials of the first steel pipe 1 and the second steel pipe 2 are Q235 carbon steel.

[0051] The manufacturing method of the above structural crack control measurement device includes the following steps:

[0052] S1. Arrange the elastic lining 3 on the inner walls of the first steel pipe 1 and the second steel pipe 2 in a fitting manner;

[0053] S2. Put the two vibrating wire strain gauges 4 into the first steel pipe 1 and the second steel pipe 2 respectively, and coaxially arrange them with the first steel pipe 1 and the second steel pipe 2 where they are located respectively, and keep the relative positions unchanged; lead the cables of the vibrating wire strain gauges 4 out of the external of the casting entity structure.

[0054] The structural crack control measurement method provided by the present invention includes the following steps:

[0055] S1. Place the above-mentioned structural crack control measurement device at the measurement location, and make the opening directions of the first steel pipe 1 and the second steel pipe 2 point to the direction of the principal stress of the concrete.

[0056] S2. Pour the concrete of the solid structure to ensure that the concrete in the first steel pipe 1 and the second steel pipe 2 is filled completely.

[0057] S3. During the monitoring and measurement, collect, analyze and control the cracking of the data of the two vibrating wire strain gauges 4 in real time.

[0058] Specifically, step S3 includes the following steps:

[0059] a. According to the vibrating wire strain gauge 4 in the first steel pipe 1, measure the first measurement value of the free expansion and contraction strain of the concrete structure in the stress-free state.

[0060] b. According to the vibrating wire strain gauge 4 in the second steel pipe 2, measure the second measurement value of the strain of the concrete structure in the direction of the second steel pipe 2.

[0061] c. Calculate the difference between the second measurement value and the first measurement value.

[0062] d. Multiply the difference by the elastic modulus of the concrete at the corresponding age to obtain the temperature stress of the concrete structure to be measured.

[0063] e. Compare the measured temperature stress with the ultimate bearing capacity of the concrete material, so as to control the cracking of the concrete.

[0064] The working principle of this embodiment is as follows:

[0065] If the actually measured strain ε of the vibrating wire strain gauge, the temperature strain ε c of the concrete, the temperature correction coefficient β of the steel string, and the temperature change amount △T, then:

[0066] ε = ε c - β * △T

[0067] If the concrete restraint strain ε r of the concrete, the free expansion and contraction coefficient α c of the concrete, and the temperature change amount △T, then:

[0068] ε r = ε c - α c * △T

[0069] If the concrete temperature stress σ T of the concrete, and the elastic modulus E c of the concrete; then:

[0070] σ T = E c * ε r

[0071] For the first steel pipe, the columnar concrete expands and shrinks freely, and ε r = 0; then

[0072] ε c = α c * △T

[0073] α c = ε c / △T = (ε + β * △T) / △T

[0074] In the past, many scholars determined the thermal expansion and shrinkage coefficient of concrete through laboratory concrete tests, but there was a lack of actual measurements in physical projects, and theoretical data or laboratory data were directly used for approximate processing. The present invention does not need to measure the free expansion and shrinkage coefficient α c of concrete, and can directly correct the restraint deformation of the second steel pipe through the measured free expansion and shrinkage deformation of concrete.

[0075] That is: for the second steel pipe, with the free deformation α c * △T, the restraint strain of the columnar concrete in the pipe is as follows:

[0076] ε r = ε c - α c * △T

[0077] Combined with

[0078] σ T = E c * ε r ≤ [σ] / λ;

[0079] [σ] is the ultimate bearing capacity of the concrete material; λ is the stress safety factor for concrete cracking.

[0080] This gives the restraint strain and temperature stress of the second steel pipe concrete, which is also the temperature stress at the structural measurement point. More preferably, if the device is arranged in the direction of the principal stress of the structure, the measured stress is the principal temperature stress. In practical applications, if the stress in a certain direction needs to be measured, the device is arranged along that direction.

[0081] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts between each embodiment can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description in the method part.

[0082] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A structural crack control measurement device, characterized in that It includes a first steel pipe (1) and a second steel pipe (2); one end of the first steel pipe (1) is open and the other end is closed; both ends of the second steel pipe (2) are open; the first steel pipe (1) and the second steel pipe (2) are placed in the concrete structure to be measured; elastic linings (3) are arranged in a fitting manner on the inner walls of the first steel pipe (1) and the second steel pipe (2); vibrating wire strain gauges (4) are arranged inside both the first steel pipe (1) and the second steel pipe (2); the two vibrating wire strain gauges (4) are coaxially arranged with the first steel pipe (1) and the second steel pipe (2) where they are respectively located; the inner cavities of the first steel pipe (1) and the second steel pipe (2) are filled with concrete and integrally buried inside the concrete structure to be measured; the signal cables of the vibrating wire strain gauges (4) are led out of the outside of the concrete structure to be measured; S1. Place the structural crack control measuring device at the measuring location; make the opening directions of the first steel pipe (1) and the second steel pipe (2) point to the direction of the main concrete stress; S2. Pour the concrete of the solid structure to ensure that the concrete inside the first steel pipe (1) and the second steel pipe (2) is filled completely; S3. During the monitoring and measurement, collect, analyze and control the cracking of the data of the two vibrating wire strain gauges (4) in real time; Step S3 specifically includes the following steps: a. According to the vibrating wire strain gauge (4) inside the first steel pipe (1), measure the first measured value of the free expansion and contraction strain of the concrete in the stress-free state; b. According to the vibrating wire strain gauge (4) inside the second steel pipe (2), measure the second measured value of the strain of the concrete structure in the direction of the second steel pipe (2); c. Calculate the difference between the second measured value and the first measured value; d. Multiply the difference by the elastic modulus of the concrete at the corresponding age to obtain the temperature stress of the concrete structure to be measured; e. Compare the measured temperature stress with the ultimate bearing capacity of the concrete material, so as to control the cracking of the concrete.

2. The structural crack control measurement device according to claim 1, characterized in that, The vibrating wire strain gauge (4) is suspended and tightened inside the first steel pipe (1) / the second steel pipe (2) through multiple positioning ropes (5); one end of the positioning rope (5) is bound to the vibrating wire strain gauge (4), and the other end passes through the outer wall of the first steel pipe (1) / the second steel pipe (2) and then is tightened.

3. The structural crack control measurement device according to claim 1, characterized in that, The first steel pipe (1) and the second steel pipe (2) are arranged in parallel and their outer walls are in contact.

4. A structural crack control measurement device according to claim 2, characterized in that The outer walls of the first steel pipe (1) and the second steel pipe (2) are welded and fixed.

5. The structural crack control measurement device according to claim 1, characterized in that, The elastic lining (3) is made of foam plastic and has a thickness of 10 mm.

6. The structural crack control measurement device according to claim 5, wherein, The elastic lining (3) is fixedly pasted on the inner wall of the first steel pipe (1) / the second steel pipe (2).

7. A structural crack control measurement device according to any one of claims 1-6, characterized in that, The inner diameters of the first steel pipe (1) and the second steel pipe (2) are both 150 mm, and the lengths are both 300 mm.

8. A structural crack control measurement device according to claim 1, characterized in that, The materials of the first steel pipe (1) and the second steel pipe (2) are Q235 carbon steel.

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