Comprehensive detection method for simulating in-vivo prestressed duct grouting cavity based on solar radiation infrared and finite element

Abstract

The invention discloses a comprehensive detection method for simulating an in-vivo prestressed duct grouting cavity based on solar radiation infrared and a finite element, and relates to the field of nondestructive testing of prestressed bridges. The method comprises the following steps: firstly, shooting a visible light picture for a concrete bridge, finding out a falling and fading area on the surface of the concrete, and then establishing a finite element simulation model according to the actual size of the bridge; then, an infrared thermal imaging camera is used for shooting the part, not falling and fading, of the surface of the bridge, the position of the defect is found out by observing the temperature abnormal area of an infrared thermal imaging picture, meanwhile, environmental parameters in the shooting time period are collected to serve as boundary conditions of finite element analysis, and then the correctness of a finite element model is verified through test data; and finally, providing a complete temperature field of the bridge through the verified model, and providing detection time windows corresponding to cavity defects with different burial depths by combining test and numerical simulation.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing of prestressed bridges, and in particular to a comprehensive testing method for grouting cavities of prestressed channels in vivo based on solar radiation infrared and finite element simulation. Background Art

[0002] In recent years, internal prestressing technology has been widely used in the fields of new bridge construction and reinforcement of old bridges because of its advantages of effectively reducing the deadweight of the structure, saving materials, and reducing prestress loss. In order to make the internal steel strands bear the force synergistically and avoid environmental corrosion, the pipes are usually grouting. However, due to improper selection of grouting materials or the complexity of construction technology, defects such as cavities, partial cavities and water seepage are prone to occur during construction, making the steel strands more susceptible to erosion and reducing the durability of the bridge structure;

[0003] Moreover, the defects of prestressed duct grouting are concealed projects and difficult to identify with the naked eye. The current detection equipment and methods are mostly point measurements, which require a lot of manpower and slow data processing, making it difficult to timely guide the repair of defects caused during the on-site operation period, which greatly increases the cost of subsequent maintenance. Therefore, how to conduct non-destructive testing of the quality of prestressed ducts in the body during operation has become a difficult problem plaguing the detection field.

[0004] In view of the above, the present application provides a comprehensive detection method for prestressed duct grouting voids in vivo based on solar radiation infrared and finite element simulation to solve the above problems. Summary of the invention

[0005] In view of the above situation, the present invention provides a comprehensive detection method for in-vivo prestressed duct grouting voids based on solar radiation infrared and finite element simulation. The application of this method can greatly improve the efficiency of temperature field measurement of in-vivo prestressed ducts, and improve construction quality and convenience.

[0006] A comprehensive detection method for grouting cavities of prestressed channels in vivo based on solar radiation infrared and finite element simulation, characterized in that firstly, visible light pictures are taken for concrete bridges to find out the areas where the concrete surface is falling off and fading;

[0007] A finite element simulation model was established based on the actual size of the bridge. An infrared thermal imaging camera was used to photograph the non-fading parts of the bridge surface. The defect location was found by observing the temperature abnormality areas in the infrared thermal imaging images.

[0008] Collect environmental parameters during the shooting period as boundary conditions for finite element analysis, and use test data to verify the correctness of the finite element model;

[0009] Finally, the verified model gives the complete temperature field of the bridge, and the detection time windows corresponding to cavity defects with different buried depths are provided by combining experiments and numerical simulations.

[0010] The above technical solution has the following beneficial effects:

[0011] The present invention uses an infrared camera to quickly scan a 2D surface without affecting the normal operation of the bridge. In addition, the remote scanning capability of infrared thermal imaging detection allows the main beam of the bridge and the lower surface of the bridge deck to be inspected without affecting traffic during the inspection process. In addition, heating is only performed by solar radiation without the need for other heat sources, which is simpler and more convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a flow chart of a comprehensive detection method for grouting cavities of prestressed ducts in vivo based on solar radiation infrared and finite element simulation of the present invention;

[0013] Figure 2 It is a numerical diagram of thermal parameters of the material of the present invention;

[0014] Figure 3 An infrared schematic diagram of a prestressed channel surface containing different hole sizes provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The aforementioned and other technical contents, features and effects of the present invention will be clearly presented in the following detailed description of the embodiments with reference to the drawings of the present application. The structural contents mentioned in the following embodiments are all based on the drawings of the specification as reference.

[0016] The purpose of the present invention is to provide a comprehensive detection method for in-body prestressed duct grouting cavities based on solar radiation infrared and finite element simulation.

[0017] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] Step 1 First, take visible light pictures of the concrete bridge to find the areas where the concrete surface has fallen off and faded, so as to avoid the fading of the surface concrete causing the emissivity to change and affecting the shooting results of the infrared thermal imaging camera.

[0019] Step 2: When the infrared thermal imaging camera is shooting in real time, the ranging sensor detects the distance between the infrared thermal imaging camera and the prestressed hole in real time, and the temperature sensor records the ambient temperature in time and inputs it into the infrared thermal imaging camera in time, thereby reducing the influence of shooting distance and ambient temperature on detection.

[0020] Step 3 The internal heat transfer model of prestressed concrete structure can generally adopt the Fourier heat transfer formula, and the calculation equation is shown in formula (1.1):

[0021]

[0022] Where ρ, c, and λ represent the density of the material (kg·m -3 ), specific heat capacity (J·kg -1 ·K -1 ) and thermal conductivity (W·m -1 ·K -1 ), T refers to the temperature of the structure surface at a certain time, q v Refers to the heat release rate inside the structure (J / (g·h)).

[0023] The initial condition of the internal heat transfer model of the concrete structure is the initial time of the indoor temperature distribution, which can be written as formula (1.2):

[0024] T0(x,y,z)| t＝0 =T0(x,y,z)(1.2)

[0025]

[0026] In formula (1.2), x, y, and z have the same meaning as in formula (1.1), and all refer to the three-dimensional spatial coordinates of a point in the internal heat transfer model of prestressed concrete. In formula (1.3), Q is the heat release of the internal heat transfer model of the concrete structure.

[0027] The boundary conditions of the internal heat transfer model of the concrete structure are the active heating radiation absorbed by the concrete surface, the heat convection caused by the temperature difference of the surrounding environment, and the long-wave radiation emitted by the concrete surface. The ambient temperature and humidity in the test room are measured around the clock using a radiometer and a thermo-hygrometer.

[0028] The internal heat transfer model of concrete structure assumes that the grouting material is in full contact with the inner surface of the pore, so the heat flow and temperature can be considered to be continuous on the contact surface.

[0029] Q=q s +q c +q r (1.4)

[0030] q s =αG (1.5)

[0031]

[0032] hc=4.687V+10.03,(V≤5m / s) (1.7)

[0033] q r =(T a 4 -T b 4 )εCo (1.8)

[0034] Formula (1.3)qs Refers to solar radiation, q c refers to the ambient convective radiation, q r refers to the external radiation of concrete. In formula (1.5), α refers to the heating radiation absorption rate of the concrete surface, and its value is between 0.5-0.75. G refers to different heating radiation intensities. hc refers to the convection coefficient, which is obtained by empirical formula (1.6). V refers to wind speed (m / s). T a Refers to the ambient temperature, which is measured by the temperature and humidity sensor. b Refers to the temperature of the concrete surface, C O is the Stefan-Boltzmann constant (w·m -2 ·k -4 ), and its value is 5.67×10 -8 , ε refers to the emissivity of the concrete surface.

[0035] The solar radiation, environmental convection radiation and concrete external radiation are calculated by equations (1.5), (1.6) and (1.8). The sum of the three is the heat release Q of the concrete structure. The heat release rate q of the concrete structure can be obtained by taking the derivative of Q with respect to time t. v .

[0036] This model uses the commercial finite element software ANSYS Workbench to establish this simulation model, and the thermal parameters of various materials are Figure 2 The data listed show that the outer concrete, ducts, internal grouting materials and voids are all modeled using three-dimensional solid elements, and the structure is divided into tetrahedral solid grids with a grid size of 3mm to 4cm, 68845 units and 205326 nodes.

[0037] Step 4 verifies the correctness of the finite element model with the measured test data. Finally, the complete temperature field of the bridge is given through the verified model. The test and numerical simulation are combined to provide detection time windows corresponding to void defects of different burial depths (for bridges in actual service, the thickness of the concrete protective layer is different, so the time required for solar radiation during detection is different, and the time suitable for bridge detection will also be different. Providing detection time windows corresponding to void defects of different burial depths through experiments and numerical simulations can improve the temperature field measurement efficiency of the external prestressed duct and improve the construction quality and convenience).

[0038] Please refer to the instruction manual Figure 1-3The method first takes visible light pictures of concrete bridges to find out the areas where the concrete surface has fallen off and faded. Secondly, a finite element simulation model is established according to the actual size of the bridge. Then, an infrared thermal imaging camera is used to photograph the parts of the bridge surface that have not fallen off and faded. The location of the early defects is found by observing the temperature abnormality areas in the infrared thermal imaging pictures. At the same time, the environmental parameters of the shooting time period are collected as the boundary conditions of the finite element analysis. Then, the correctness of the finite element model is verified using experimental data. Finally, the complete temperature field of the bridge is given through the verified model. The detection time window corresponding to the defects of different buried depths is provided by combining experiments and numerical simulations.

[0039] To sum up: the present invention discloses a comprehensive detection method for grouting voids in prestressed channels in vivo based on solar radiation infrared and finite element simulation, which relates to the field of non-destructive testing of prestressed bridges. This system includes temperature and humidity sensors, anemometers, solar radiation meters, laser ranging sensors, infrared detectors, storage areas, controllers and image processing devices. The application of this method can greatly improve the efficiency of measuring the temperature field of prestressed channels in vitro, and improve the construction quality and convenience.

[0040] The above description is only for illustrating the present invention. It should be understood that the present invention is not limited to the above embodiments, and various variations that conform to the concept of the present invention are within the protection scope of the present invention.

Claims

1. A comprehensive detection method for prestressed grouting cavities in vivo based on solar radiation infrared and finite element simulation, characterized in that: First, take visible light pictures of concrete bridges to find areas where the concrete surface is peeling and fading; A finite element simulation model was established based on the actual size of the bridge. An infrared thermal imaging camera was used to photograph the non-fading parts of the bridge surface. The defect location was found by observing the abnormal temperature areas in the infrared thermal imaging images. Collect environmental parameters during the shooting period as boundary conditions for finite element analysis, and use test data to verify the correctness of the finite element model; Finally, the verified model gives the complete temperature field of the bridge, and the detection time windows corresponding to cavity defects with different buried depths are provided by combining experiments and numerical simulations.

2. According to claim 1, a comprehensive detection method for prestressed duct grouting voids based on solar radiation infrared and finite element simulation in vivo is characterized in that: The internal heat transfer model of the concrete bridge structure adopts the Fourier heat transfer formula: In the formula, ρ, c, and λ represent the density, specific heat capacity, and thermal conductivity of the material, respectively; T refers to the surface temperature of the structure at a certain time; q v Refers to the rate of heat release inside the structure.

3. According to claim 2, a comprehensive detection method for prestressed duct grouting voids based on solar radiation infrared and finite element simulation in vivo is characterized in that: The initial condition of the Fourier heat transfer formula is the initial time of the indoor temperature distribution, which can be written as the following formula: T0(x,y,z)| t＝0 =T0(x,y,z) The boundary conditions of the Fourier heat transfer formula are the active heating radiation absorbed by the concrete surface, the heat convection caused by the temperature difference of the surrounding environment, and the long-wave radiation emitted by the concrete surface.

4. According to claim 3, a comprehensive detection method for prestressed duct grouting voids based on solar radiation infrared and finite element simulation in vivo is characterized in that: The ambient temperature and humidity in the test room are measured around the clock using a radiometer and a thermometer and hygrometer.

5. The comprehensive detection method of prestressed duct grouting voids in vivo based on solar radiation infrared and finite element simulation according to claim 1 is characterized in that: When using the infrared thermal imaging camera for real-time shooting, a distance measuring sensor is used to detect the distance between the infrared thermal imaging camera and the prestressed hole in real time, and a temperature sensor is used to record the ambient temperature in time and input it into the infrared thermal imaging camera in time.

6. The comprehensive detection method of prestressed duct grouting voids in vivo based on solar radiation infrared and finite element simulation according to claim 1 is characterized in that: The outer concrete, prestressed duct, internal grouting material and cavity are all modeled using three-dimensional solid units.

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