In-vitro calibration method and steel bar diameter algorithm for detecting steel bars inside floor slabs using radiographic method

Abstract

The invention discloses an in vitro calibration method for detecting steel bars inside a floor slab by a ray method, first locating the steel bars inside the floor slab from the upper surface of the floor slab, and measuring the distance a between the upper edge of the steel bars and the upper surface of the floor slab; arranging a calibration plate on the upper surface of the floor slab, recording the size of the calibration plate as the calibration size f, setting up an imaging plate above the floor slab and above the calibration plate, and measuring the setting height b of the imaging plate from the upper surface of the floor slab, setting up an X-ray machine below the floor slab and below the imaging plate; starting the X-ray machine for shooting, and displaying the shooting results on a computer in real time, obtaining the internal structure of the floor slab and an imaging diagram with the calibration plate; measuring the projection size g of the calibration plate and the projection size d of the diameter of the steel bars in the floor slab in the imaging diagram; and calculating the steel bar diameter according to the product of the projection size d and the correction coefficient δ. The invention can obtain the detection result non-destructively and efficiently.

Description

Technical Field

[0001] The invention relates to the technical field of building structure detection, and in particular to an in vitro calibration method for detecting steel bars inside a floor slab using a ray method and a steel bar diameter algorithm. Background Art

[0002] Urban renewal has become an important task in the next decade. Existing old houses will be redesigned, renovated and remodeled to improve their functionality, comfort, safety and aesthetics. The inspection and appraisal of existing buildings is related to structural safety and is a very important part of urban renewal and old town renovation. When renovating or evaluating existing concrete buildings, it is necessary to clarify the configuration of steel bars in concrete components to calculate the bearing capacity of the components. However, many existing buildings were built earlier and the drawings were not properly preserved, so it is impossible to find out the configuration of steel bars through the drawings.

[0003] Accurately measuring the diameter of steel bars inside concrete structures has always been a technical challenge in the field of detection. Traditional electromagnetic induction and radar methods can still guarantee high accuracy in detecting the horizontal and deep positions of steel bars, but there has been no substantial breakthrough in the detection of steel bar diameters. The existing method for detecting the diameter of steel bars in concrete components mainly uses the chiseling method. The chiseling method is to chisel the steel bars out of the concrete to expose them, and use a caliper to directly measure the diameter. Specifically, it is necessary to chisel out a large hole on the surface of the component to expose most of the cross-section of a steel bar to meet the measurement requirements of the vernier caliper. If the protective layer of the steel bar is large, the chiseling range is larger. In order to find out the diameter of each steel bar of a concrete component without a drawing, the component may be chiseled to pieces.

[0004] Especially for concrete floors, there is usually a ceiling underneath and wooden floors, floor tiles and other decorative layers on the upper surface. If the chiseling method is used, in addition to destroying the structural layer of the floor, the ceiling and wooden floors, floor tiles and other decorative layers must also be destroyed. After the inspection, the homeowner must not only repair the structural layer of the floor, but also carry out secondary decoration. For this reason, in many cases, the homeowner does not agree to chiseling, resulting in the inability to conduct the inspection.

[0005] In order to solve the problem of non-destructive detection of the diameter of steel bars inside concrete structures, the Chinese patent document "A method and system for detecting steel bars and defects inside building structural components" with publication number CN117388290A proposes a method for detecting the diameter of steel bars inside structures using X-ray digital imaging technology. According to the principle of X-rays, the projection size of the steel bars on the imaging plate is generally larger than its actual size, and the projection size needs to be corrected to obtain the actual size of the steel bars. To this end, the above patent document provides two correction methods based on geometric principles. The first correction method is to directly calculate the correction coefficient δ and the steel bar diameter c based on the principle of similar triangles when the "distance from the ray source to the steel bars inside the structure" and the "distance from the steel bars inside the structure to the imaging plate" are known at the same time. However, for the special component of the floor slab, there is usually a ceiling under the floor slab, and the parameter "the distance from the ray source to the steel bars inside the structure" cannot be obtained without destroying the ceiling. Therefore, the first correction method is not suitable for floors with ceilings. The second correction method is to use the method of arranging calibration plates outside the body. Calibration plates are arranged on the upper and lower surfaces of the floor slab respectively. Under the premise that the two parameters of "the distance from the steel bar to the upper surface of the floor slab" and "the distance from the steel bar to the lower surface of the floor slab" are known at the same time, the correction coefficient δ and the steel bar diameter c are calculated. However, for the special component of the floor slab, there is usually a ceiling under the floor slab. It is impossible to arrange calibration plates on the lower surface of the floor slab without destroying the ceiling, and it is impossible to obtain the parameter "the distance from the steel bar to the lower surface of the floor slab". Therefore, the second correction method is not suitable for floors with ceilings. In addition, no matter which of the above correction methods is used, the inspection of the steel bars inside the floor slab requires the inspection personnel to work at height, measure the necessary parameters or arrange calibration plates under the floor slab.

[0006] Therefore, when using X-ray method to detect floors with decorative ceilings below, how to perform in vitro calibration and obtain a high-precision steel bar diameter algorithm while avoiding the need for personnel to climb heights during detection is a technical problem that needs to be urgently solved in this field. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide an in vitro calibration method and a steel bar diameter algorithm for detecting steel bars inside a floor slab by a radiographic method, which can obtain detection results non-destructively and efficiently.

[0008] In order to solve the above technical problems, the present invention provides an in vitro calibration method for detecting steel bars inside a floor slab by a radiographic method, comprising the following steps:

[0009] First, locate the steel bars inside the slab from the upper surface of the slab, and measure the distance a between the upper edge of the steel bars and the upper surface of the slab;

[0010] A calibration plate is arranged on the upper surface of the floor slab, and the size of the calibration plate is recorded as the calibration size f. An imaging plate is set up above the floor slab and above the calibration plate, and the setting height b of the imaging plate from the upper surface of the floor slab is measured. An X-ray machine is set up below the floor slab and below the imaging plate.

[0011] The X-ray machine is started to shoot, and the shooting results are displayed on the computer in real time to obtain the internal structure of the floor slab and the imaging diagram with the calibration plate;

[0012] Measure the projection size g of the calibration plate and the projection size d of the steel bar diameter in the floor slab in the imaging image;

[0013] According to the design data or engineering experience, the estimated value e of the steel bar diameter in the floor slab is given. The correction coefficient δ is calculated based on the estimated value e, distance a, installation height b, calibration size f and projection size g. The correction coefficient δ is calculated according to the following formula:

[0014] ;

[0015] The steel bar diameter is calculated based on the product of the projection dimension d and the correction coefficient δ.

[0016] Furthermore, the calibration plate is in a rectangular shape, with a width dimension of not less than 30 mm and a length dimension of not less than 1.5 times the width dimension; the calibration dimension f of the calibration plate is the width dimension, and the projection dimension g of the calibration plate is the width dimension of the projection image of the calibration plate; the calibration plate is made of lead or copper; the calibration plate is arranged to avoid the steel bars in the floor slab below, and the length direction of the calibration plate is along the direction of the steel bars to be measured.

[0017] Furthermore, the imaging plate is installed at a height of 80 mm to 100 mm from the upper surface of the floor slab, and the effective imaging area of ​​the imaging plate is not less than 300 mm × 400 mm.

[0018] Furthermore, by using radar method or electromagnetic induction method, a distance a between the upper edge of the steel bars inside the floor slab and the upper surface of the floor slab is measured on the upper surface of the floor slab by a handheld high-frequency radar or a large-range steel bar scanner.

[0019] Furthermore, the voltage setting range of the X-ray machine should be able to cover 150kv-250kv. When taking the first picture, the voltage of the X-ray machine is set to 200 kv, and then the voltage value is lowered or increased accordingly according to the imaging effect, such as clear, overexposed or not transparent.

[0020] Furthermore, when there is a suspended ceiling below the floor, the X-ray machine is mounted below the suspended ceiling, and the X-ray machine is lifted and lowered by an electric lifting frame, wherein a pulley is provided at the bottom of the electric lifting frame.

[0021] Furthermore, when measuring the projection dimension g of the calibration plate and the projection dimension d of the diameter of the steel bars inside the floor slab in the imaging image, the average value of the dimensions measured at three locations is used.

[0022] Furthermore, when there are upper and lower double layers of steel bars in the floor slab, the upper and lower layers of steel bars are distinguished by measuring and comparing the projection size of the steel bar diameter in the imaging image, wherein the steel bar with the larger projection size of the diameter is the steel bar of the lower layer, and vice versa.

[0023] Furthermore, the estimated value e of the steel bar diameter in a given floor slab is not greater than the projected dimension d of the steel bar diameter.

[0024] Also disclosed is an algorithm for detecting the diameter of steel bars inside a floor slab by a X-ray method. Based on the in vitro calibration method described above, a first correction value c1 of the steel bar diameter is calculated according to the product of the projection size d and the correction coefficient δ. The first correction value c1 of the steel bar diameter replaces the estimated value e of the steel bar diameter and is substituted into the calculation formula of the correction coefficient δ to obtain a new correction coefficient δ'. The second correction value c2 of the steel bar diameter is further calculated according to the product of the projection size d and the new correction coefficient δ', and c2 is used as the final calculation result c of the steel bar diameter.

[0025] Beneficial effects of the present invention:

[0026] 1. The in vitro calibration method adopted in the present invention only needs to be operated above the floor, whether it is the setting of the calibration plate or the measurement of the relevant parameters required for the correction calculation; below the floor, it is only necessary to lift the X-ray machine by an electric lifting frame, and there is no need to measure "the distance from the X-ray machine to the measured steel bar" or "the distance from the X-ray machine to the lower surface of the floor", nor is there any need to set a calibration plate on the lower surface of the floor; therefore, the detection method of the present invention will not be affected by the decorative ceiling below the floor, there is no need to damage the ceiling for detection, and there is no need for detection personnel to work at height.

[0027] 2. The in vitro calibration method adopted in the present invention utilizes two distance parameters that can be easily measured above the floor slab, namely, "the distance between the upper edge of the steel bar and the upper surface of the floor slab" and "the distance between the imaging plate and the upper surface of the floor slab", as well as the actual size of the calibration plate and the projection size of the calibration plate after imaging. With the least and most easily measurable original parameters, the geometric principle of similar triangles and the correlation between the parameters are cleverly utilized to derive the correction coefficient based on the specific in vitro calibration method.

[0028] 3. The steel bar diameter algorithm adopted in the present invention only needs one iterative calculation. Even in the case where "the actual steel bar diameter in the floor slab does not correspond to the design data" or "the design data is missing", as long as an estimated steel bar diameter is given, the actual diameter of the steel bar can be accurately calculated, and computer programming can be used to assist the calculation to obtain higher calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the arrangement of the detection equipment and calibration plate for detecting the internal steel bars of the floor slab by the radiographic method of the present invention;

[0030] Figure 2 It is an image of the steel bars inside the floor slab detected by the radiographic method of the present invention;

[0031] Figure 3 It is the projection dimension measurement diagram of the calibration plate of the present invention;

[0032] Figure 4 It is a projection dimension measurement diagram of the steel bar diameter inside the floor slab of the present invention;

[0033] Figure 5 It is a schematic diagram of the position of the distance h from the radiation source to the steel bar and the distance H from the radiation source to the imaging plate of the present invention;

[0034] Figure 6 It is a schematic diagram of ratio relationship based on the principle of similar triangles of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention. Example 1

[0036] An embodiment of the in vitro calibration method and steel bar diameter algorithm for detecting steel bars inside a floor slab by using a radiographic method of the present invention, the floor slab in the embodiment is located in an office building that has been renovated and operated, there is a suspended ceiling below the floor slab, and the upper surface of the floor slab is a wooden floor decoration layer. During the detection, the detection equipment and the calibration plate are arranged as shown in FIG. Figure 1 First, a handheld high-frequency radar was used to locate the steel bars inside the slab from the upper surface of the slab. It was found that there were two layers of steel bars in the slab longitudinally, upper and lower. The distance a between the upper edge of the steel bars and the upper surface of the slab was measured through the radar imaging. The distance between the upper edge of the upper steel bars and the upper surface of the slab was 118 mm, and the distance between the upper edge of the lower steel bars and the upper surface of the slab was 160 mm.

[0037] A calibration plate with a known width f of 31.5 mm is arranged on the upper surface of the floor slab, and an imaging plate is set up above the floor slab and above the calibration plate. The height of the imaging plate from the upper surface of the floor slab is measured to be 90 mm. An X-ray machine is set up below the floor slab and below the imaging plate. The X-ray machine is set up below the ceiling surface and is raised and lowered by an electric lifting frame. By raising and lowering the X-ray machine by the electric lifting frame, the inspection personnel do not need to work at heights, and the electric lifting frame with a pulley at the bottom can also be used as a transportation tool for the X-ray machine between different rooms. It can be pushed; the X-ray machine is started to shoot, and the shooting results are displayed on the computer in real time to obtain an imaging diagram of the internal structure of the floor slab, as shown in FIG. Figure 2 As described; measure the projection size g of the calibration plate in the imaging image, refer to Figure 3 As shown, the projection size of the calibration plate is 34.2mm after taking the average value of three measurements; the projection size d of the steel bar diameter inside the floor slab is measured in the imaging diagram. The projection size of the upper steel bar diameter is 9.3mm and the projection size of the lower steel bar diameter is 9.7mm after taking the average value of three measurements of the upper and lower steel bars. Figure 4 As shown in the figure, how to distinguish between upper and lower steel bars depends on the projection size of the steel bar diameter. The X-ray image itself is flat, not three-dimensional. It is impossible to directly determine the upper and lower steel bars inside the floor slab from the image. However, according to the principle of the X-ray method, the farther the steel bar is from the imaging plate, the more the projection size of the steel bar is magnified after imaging. Through this feature, the upper and lower steel bars inside the floor slab can be distinguished. The larger one is the lower steel bar, and the smaller one is the upper steel bar.

[0038] The engineering project in this embodiment has design data, and the design specification of the diameter of the steel bars inside the floor slab is 8 mm. The steel bar diameter is verified by the detection method of this application. According to the design data, an estimated value e of the steel bar diameter inside the floor slab is given as 8 mm. After in vitro calibration, the correction coefficient δ used for calculating the steel bar diameter is calculated according to the following formula:

[0039] (Formula 1);

[0040] Formula 1 is derived by using two distance parameters that can be easily measured above the floor, namely, "the distance between the upper edge of the steel bar and the upper surface of the floor" and "the distance between the imaging plate and the upper surface of the floor", as well as the actual size of the calibration plate and the projection size of the calibration plate after imaging. It uses the least and most easily measured original parameters, and cleverly utilizes the geometric principle of similar triangles and the correlation between the parameters. The specific derivation process is as follows:

[0041] like Figure 5As shown, assuming that "the distance from the ray source to the steel bar is h", assuming that "the distance from the ray source to the imaging plate is H", h and H are both unknown in the detection method of this application. According to the principle of similar triangles, "the ratio of the actual size of the steel bar diameter to the projected size" is equal to "the ratio of h to H", and this ratio is the correction coefficient δ. The calculation formula for deriving the correction coefficient is to replace the unknown "h / H" with the known parameters;

[0042] like Figure 6 As shown in the figure, according to the principle of similar triangles, the ratio between the actual known calibration size f and the projection size g of the calibration plate is equal to the ratio between the distance from the ray source to the calibration plate and the distance from the ray source to the imaging plate, that is: .

[0043] Solving the above formula, we can get , that is, H is replaced by known parameters;

[0044] According to the geometric relationship between H and h, h=Hbae / 2;

[0045] Correction factor , and then Substituting this into equation 1 we can get:

[0046] According to formula 1, the correction coefficient of the upper steel bar is 0.814, and the correction coefficient of the lower steel bar is 0.777.

[0047] When calculating the diameter of the upper steel bar, the first correction value c1 of the steel bar diameter is calculated as 7.6 mm according to the product of the projection size d of the upper steel bar diameter and the correction coefficient δ of the upper steel bar. The first correction value c1 of the steel bar diameter replaces the estimated value e of the steel bar diameter and is substituted into the calculation formula of the correction coefficient δ to obtain a new correction coefficient of 0.814. The second correction value c2 of the steel bar diameter is calculated as 7.6 mm according to the product of the projection size d of the steel bar diameter and the new correction coefficient. Finally, the calculation result c of the steel bar diameter is 7.6 mm.

[0048] The same method was used to calculate the final result of the diameter of the lower layer of steel bars, which was c: 7.5 mm.

[0049] According to the national standard GB / T1499.2-2018 "Steel for Reinforced Concrete Part 2: Hot-rolled Ribbed Steel Bars", the nominal diameter of 8mm steel bars has a nominal size of 7.7mm and an allowable deviation of 0.4mm, that is, steel bars with a diameter size between 7.3-8.1mm can be judged as steel bars with a nominal diameter of 8mm. Therefore, the specifications of the upper and lower steel bars in this embodiment are both steel bars with a nominal mass of 8mm, which is consistent with the design data.

[0050] In the calibration plate used above, the calibration plate is rectangular in shape, and the length dimension is specified to be not less than 1.5 times the width dimension. Such a limitation can make the projection of the calibration plate directional after the image is taken, and identify the steel bars in the slab that are consistent with its direction according to the length direction of the calibration plate projection. The width dimension of the calibration plate is not less than 30 mm in order to reduce the calibration error. The calibration work is carried out by manually selecting the upper and lower edges of the calibration plate in the width direction in the imaging image. There will be certain errors when manually selecting points, so the calibration size needs to exceed 30 mm to reduce the relative error. When arranging the calibration plate, avoiding the steel bars in the lower slab can prevent the boundary between the steel bars and the calibration plate in the width direction in the imaging image from being doubled, which hinders the calibration.

[0051] In the setting requirements of the imaging plate, the height of the imaging plate from the upper surface of the floor slab is 80mm-100mm. Under the premise of clear imaging, the closer the imaging plate is to the X-ray machine, the clearer the imaging is. The calibration plate and the imaging plate can be separated by a sufficient distance, so that the actual size of the calibration plate is significantly different from the projected size, achieving the effect of accurate calibration. It is stipulated that the effective imaging area of ​​the imaging plate is not less than 300mm×400mm, so that the calibration plate and the measured steel bar are more likely to appear in one imaging picture.

[0052] During the shooting process of the X-ray machine, the voltage setting range of the X-ray machine should be able to cover 150kv-250kv. The voltage of the X-ray machine is set to 200 kv for the first shooting, and then the voltage value is lowered or increased accordingly according to the three situations of clear, overexposed or not transparent imaging effect. The thickness of the structural layer of the floor is usually between 100-140㎜, but in the case of decoration, there are additional layers and decorative layers on the upper part of the structural layer of the floor. The additional layers are more complex and may include different structural layers such as bonding layer, leveling layer, waterproof layer, and insulation layer. Therefore, the total thickness of the floor cannot be measured without opening the ceiling under the floor, and the detection method and calculation formula in this application do not need to involve the thickness of the floor; therefore, it is impossible to set the appropriate voltage at one time according to the actual measured thickness of the floor. Here, according to the experience of engineering inspection, the voltage of the X-ray machine can be set to 200kv. If a clear image can be obtained in the first shot, the next step of measurement can be carried out; if the image effect of the first shot is displayed as a white area, and there is no projection outline of the steel bar, it is judged that the voltage is too high and overexposure occurs, and the voltage needs to be lowered; if the image effect of the first shot is displayed as a black-gray area, and there is no projection outline of the steel bar, it is judged that the voltage is too low and the light is not through, and the voltage needs to be increased. In the same type of floor decoration, after the first floor adopts the trial method to select the appropriate voltage, the subsequent similar floor can refer to the above voltage setting value. According to engineering experience and test results, the voltage adjustment range of 150kv-250kv can meet the needs of various floor conditions.

[0053] Embodiment 2:

[0054] Assuming that the engineering project in Example 1 lacks design data, and due to the lack of engineering experience of the inspection personnel, an unreasonable estimated value e of the steel bar diameter in the floor slab is given as 20 mm, then the calculated correction coefficient of the upper steel bar is 0.809, and the iterative process for calculating the diameter of the upper steel bar is as follows: the first correction value c1 of the steel bar diameter is calculated as 7.5 mm according to the product of the projection size d of the upper steel bar diameter and the correction coefficient δ of the upper steel bar, and the first correction value c1 of the steel bar diameter is substituted for the estimated value e of the steel bar diameter into the calculation formula of the correction coefficient δ to obtain a new correction coefficient of 0.814, and the second correction value c2 of the steel bar diameter is calculated as 7.6 mm according to the product of the projection size d of the steel bar diameter and the new correction coefficient. The final calculation result c of the steel bar diameter is still 7.6 mm, which is consistent with the final calculation result when the estimated value e of the steel bar diameter is set to 8 mm in Example 1. This means that even in the case where "the actual steel bar diameter in the floor slab does not correspond to the design data" or "the design data is missing", as long as an estimated steel bar diameter is given, even if the given estimated steel bar diameter has a large deviation from the actual steel bar diameter, as long as the algorithm provided by this application is used, only one iterative calculation is required to accurately calculate the true diameter of the steel bar, and computer programming can be used to assist in the calculation to obtain higher calculation efficiency. However, in the actual detection process, the given estimated steel bar diameter e is generally not larger than the projected size d of the steel bar diameter. The correction coefficient δ is calculated after the image is taken. At this time, the projected size of the steel bar diameter is already known. According to the principle of the ray method, the actual size of the steel bar must be smaller than its projected size. Therefore, even in the absence of design data, the estimated steel bar diameter can be used as a reference based on the previously measured projection size and is not larger than the projection size of the steel bar diameter.

[0055] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. An in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method, characterized in that: The steps include: First, locate the steel bars inside the slab from the upper surface of the slab, and measure the distance a between the upper edge of the steel bars and the upper surface of the slab; A calibration plate is arranged on the upper surface of the floor slab, and the size of the calibration plate is recorded as the calibration size f. An imaging plate is set up above the floor slab and above the calibration plate, and the setting height b of the imaging plate from the upper surface of the floor slab is measured. An X-ray machine is set up below the floor slab and below the imaging plate. The X-ray machine is started to shoot, and the shooting results are displayed on the computer in real time to obtain the internal structure of the floor slab and the imaging diagram with the calibration plate; Measure the projection size g of the calibration plate and the projection size d of the steel bar diameter in the floor slab in the imaging image; According to the design data or engineering experience, the estimated value e of the steel bar diameter in the floor slab is given, and the correction coefficient δ is calculated according to the estimated value e, distance a, erection height b, calibration size f and projection size g. The correction coefficient δ is calculated according to the following formula: ； The steel bar diameter is calculated based on the product of the projection size d and the correction coefficient δ; The estimated value e of the steel bar diameter in a given floor slab is not greater than the projected dimension d of the steel bar diameter.

2. The in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method as claimed in claim 1, characterized in that: The calibration plate is in the shape of a rectangle, with a width of not less than 30 mm and a length of not less than 1.5 times the width. The calibration dimension f of the calibration plate is the width dimension, and the projection dimension g of the calibration plate is the width dimension of the projection image of the calibration plate. The calibration plate is made of lead or copper. When arranging the calibration plate, avoid the steel bars in the floor slab below, and the length direction of the calibration plate is along the direction of the steel bars to be measured.

3. The in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method as claimed in claim 1, characterized in that: The imaging board is installed at a height of 80㎜-100㎜ from the upper surface of the floor slab, and the effective imaging area of ​​the imaging board is not less than 300㎜×400㎜.

4. The in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method as claimed in claim 1, characterized in that: Using radar method or electromagnetic induction method, the distance a between the upper edge of the steel bars inside the slab and the upper surface of the slab is measured on the upper surface of the slab by a handheld high-frequency radar or a large-range steel bar scanner.

5. The in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method as claimed in claim 1, characterized in that: The voltage setting range of the X-ray machine should be able to cover 150kv-250kv. When taking the first picture, the voltage of the X-ray machine is set to 200 kv, and then the voltage value is adjusted down or up accordingly according to the imaging effect, such as clear, overexposed or not transparent.

6. The in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method as claimed in claim 1, characterized in that: When there is a suspended ceiling below the floor, the X-ray machine frame is arranged below the suspended ceiling surface, and the X-ray machine is lifted and lowered by an electric lifting frame, and the bottom of the electric lifting frame is provided with a pulley.

7. The in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method as claimed in claim 1, characterized in that: When measuring the projection dimension g of the calibration plate and the projection dimension d of the diameter of the steel bars inside the floor slab in the imaging image, the average value of the dimensions measured at three locations is used.

8. The in vitro calibration method for detecting steel bars inside a floor slab by using a radiographic method as claimed in claim 1, characterized in that: When there are upper and lower layers of steel bars in the floor slab, the upper and lower layers of steel bars are distinguished by measuring and comparing the projection size of the steel bar diameter in the imaging diagram. The steel bar with the larger projection size of the diameter is the steel bar in the lower layer, and vice versa.

9. An algorithm for detecting the diameter of steel bars inside a floor slab using a ray method, characterized in that: Based on the in vitro calibration method described in any one of claims 1 to 8, a first correction value c1 of the steel bar diameter is calculated according to the product of the projection dimension d and the correction coefficient δ, the first correction value c1 of the steel bar diameter replaces the estimated value e of the steel bar diameter and is substituted into the calculation formula of the correction coefficient δ to obtain a new correction coefficient δ', and a second correction value c2 of the steel bar diameter is further calculated according to the product of the projection dimension d and the new correction coefficient δ', and c2 is used as the final calculation result c of the steel bar diameter.

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