A method for on-site detection and evaluation of fire retardant coating thickness of steel structural components

Abstract

The present invention provides a method for on-site detection and evaluation of the thickness of fire-retardant coatings on steel structural components. The method comprises: obtaining a surface model of the steel structure before and after the fire-retardant coating is sprayed, and recording the required spray thickness and spray length of the coating; calculating the overall spray thickness of the coating based on the cross-sectional perimeter of the steel structural component, the spray volume of the coating, and the spray length; obtaining a spray quality map of the fire-retardant coating based on a coating thickness threshold, a minimum defect area threshold, and a point cloud model of the steel structure before and after the fire-retardant coating is sprayed; and evaluating whether the coating thickness is qualified based on the required spray thickness and the spray quality map. The present invention solves the problem of the lack of precise measurement of the thickness of fire-retardant coatings on steel structures in the prior art, evaluates the thickness of fire-retardant coatings on steel structures from two perspectives: overall thickness measurement and local defect detection, and realizes a comprehensive quality evaluation of the thickness of fire-retardant coatings on steel structures.

Description

Technical Field

[0001] The present invention relates to the technical field of non-destructive testing and evaluation, and in particular to an on-site testing and evaluation method for the thickness of a fire retardant coating of a steel structure component. Background Art

[0002] Fire retardant coatings are crucial for improving the fire resistance of steel structures and protecting them from the risk of melting under high temperatures in fires. This extends the service life of steel structures and reduces maintenance costs. However, substandard fire retardant coating thickness can pose significant safety risks. Therefore, during the construction of steel structures, effective measures must be taken to assess the quality of the fire retardant coating to determine whether it meets regulatory requirements.

[0003] Currently, the main methods for on-site coating thickness testing include magnetic stretching, electromagnetic induction, and probe methods. However, these methods mostly measure the coating thickness at a small number of locations, thereby estimating the coating's applied thickness. This makes it difficult to determine the actual coating condition across the entire steel structure. Therefore, a comprehensive on-site testing method for understanding the application quality of fire retardant coating thickness is urgently needed. Summary of the Invention

[0004] In response to the defects in the prior art, the purpose of the present invention is to provide an on-site detection and evaluation method for the thickness of fire-retardant coatings on steel structure components, which solves the problem of the lack of precise measurement of the thickness of fire-retardant coatings on steel structures in the prior art. The thickness of fire-retardant coatings on steel structures is evaluated from two perspectives: overall thickness measurement and local defect detection, thereby realizing a comprehensive quality evaluation of the thickness of fire-retardant coatings on steel structures.

[0005] In order to solve the above problems, the technical solution of the present invention is:

[0006] A method for on-site detection and evaluation of the thickness of a fire retardant coating of a steel structure component comprises the following steps:

[0007] Obtain the surface model of the steel structure before and after the fire retardant coating is sprayed, and record the required coating thickness and spray length;

[0008] Calculate the overall spray thickness of the coating based on the cross-sectional perimeter of the steel structure component, the spray volume of the coating, and the spray length;

[0009] The spray quality map of the fire retardant coating is obtained based on the coating thickness threshold, the minimum defect area threshold, and the point cloud model of the steel structure before and after the fire retardant coating is sprayed.

[0010] Evaluate whether the coating thickness is qualified based on the required spray thickness and spray quality diagram.

[0011] Preferably, the steps of obtaining the surface model of the steel structure before and after the fire retardant coating is sprayed, and recording the required spray thickness and spray length of the coating specifically include: using a three-dimensional laser scanning device to scan the fire retardant coating sprayed area on the surface of the steel structure, obtaining the three-dimensional laser point cloud model of the steel structure before and after the fire retardant coating is sprayed and the steel structure point cloud data PC1 and PC2, and recording the required spray thickness of the coating and the spray length in the direction perpendicular to the cross-section of the steel structure.

[0012] Preferably, the step of obtaining the three-dimensional laser point cloud model of the steel structure before and after the fire retardant coating is sprayed and the steel structure point cloud data PC1 and PC2 specifically includes:

[0013] Set the parameters of the 3D laser scanning equipment;

[0014] During the scanning process, the scanner should be close to the area to be sprayed and scan the steel structure surface in all directions;

[0015] After scanning, the point cloud data PC1 of the steel structure before the fire retardant coating is obtained;

[0016] During construction, spray fire retardant coating on the surface of the steel structure. The coating thickness should be D.

[0017] Measure the spray length of the coating in the direction perpendicular to the steel structure section, recorded as l;

[0018] After the fire retardant coating is sprayed or applied manually and dried, the steel structure surface is scanned again to obtain the point cloud data PC2 after spraying.

[0019] Preferably, the step of calculating the overall spray thickness of the coating based on the cross-sectional perimeter of the steel structure component, the spray volume of the coating, and the spray length specifically includes:

[0020] Get the perimeter C of the steel structure section;

[0021] For the portion of the steel structure where the coating has been sprayed, the volume V′ of the area contained in the point cloud PC1, i.e., the volume of the outer contour of the steel structure, is calculated based on the point cloud data PC1 before spraying.

[0022] For the portion of the steel structure where the coating has been sprayed, based on the point cloud data PC2 after spraying, the volume V″ of the area included in the PC2 point cloud, i.e., the volume of the outer contour of the coating, is calculated;

[0023] The volume of the area contained in the PC2 point cloud is subtracted from the volume of the area contained in the PC1 point cloud to obtain the spray volume of the coating V=V″-V′, where V″ and V′ are the model volumes before and after the fire retardant coating is sprayed, respectively, and V is the spray volume of the coating;

[0024] Calculate the overall spray coating thickness of the steel structure using the following formula:

[0025]

[0026]

[0027] Where d is the overall spray thickness of the coating, C is the circumference of the steel structure section, s is the spray volume of the fire retardant coating per unit spray length in the vertical direction of the steel structure section, l is the spray length in the direction perpendicular to the steel structure section,

[0028] V is the spray volume of the coating.

[0029] Preferably, the step of obtaining the spray quality map of the fire retardant coating based on the coating thickness threshold, the minimum defect area threshold, and the point cloud model of the steel structure before and after the fire retardant coating is sprayed specifically includes:

[0030] Fit the surface model of the steel structure without spray coating as the reference surface;

[0031] Calculate the vertical distance from the surface model to the reference plane after spraying the coating to obtain the spray thickness map of the fire retardant coating;

[0032] Based on the coating thickness threshold, spray thickness map and minimum defect area threshold, a spray quality detailed map is obtained.

[0033] Preferably, the step of fitting a surface model of the steel structure surface without spray coating as a reference surface specifically includes:

[0034] The obtained point cloud data PC2 after spraying is registered with the obtained point cloud data PC1, recorded as PC′2, so that the two sets of point cloud data are in the same coordinate system and are comparable;

[0035] Each surface of the steel structure sprayed with fire retardant coating is divided into a region, each region is a curved surface or a flat surface. According to the location of the steel structure, it is first divided into several regions, each region is a plane. For the surface of the double-sided sprayed fire retardant coating, it is considered as two regions.

[0036] The obtained point cloud data PC1 and the obtained point cloud data Pc′2 are segmented respectively, and a set of point cloud pairs (pc1, pc2) are obtained in each area, where pc1 comes from PC1 and pc2 comes from PC′2;

[0037] The point cloud data pc1 of the steel structure surface itself when the coating is not sprayed is fitted into a surface using the least squares method, which is used as the reference surface rp.

[0038] Preferably, the step of calculating the vertical distance from the surface model of the sprayed coating to the reference plane to obtain the spray thickness map of the fire retardant coating specifically includes:

[0039] Calculate the vertical distance d between each point in the point cloud pc2 and the reference surface rp after the fire retardant coating is sprayed i , that is, the actual spray thickness of the coating. The actual spray thickness value of each point is assigned to the corresponding point to obtain the actual spray thickness point cloud pc3;

[0040] The actual spraying thickness point cloud pc3 is projected onto the reference plane rp in the normal direction to obtain the spraying thickness map f1. The discrete randomly distributed spraying thickness map f1 is resampled into a regular uniformly distributed spraying thickness map f2.

[0041] Preferably, the step of obtaining a spraying quality detailed map based on the coating thickness threshold, the spraying thickness map and the minimum defect area threshold specifically includes:

[0042] Set the coating thickness threshold T D As a threshold, f2 is binarized to obtain the binary image f3 of the spraying thickness:

[0043]

[0044] Where f3 is the binary image of the fire retardant coating spray thickness, d i is the thickness value at each location in the coating thickness diagram. The part where f3=1 is the area where the actual spraying thickness is greater than or equal to the thickness threshold, and the part where f3=0 is the area where the actual spraying thickness is less than the thickness threshold.

[0045] Set the minimum defect area T area As the threshold, the area in the binary image of the spray thickness is larger than T area The unqualified spraying connected areas are considered to be spraying defects, and the spraying quality detailed map is obtained:

[0046] Q={cc|(area(cc)>T area )∩(f3(cc)=0)}

[0047]

[0048] Where f is the spraying quality detail map, the part where f=1 is the area with qualified spraying quality, the part where f=0 is the area with unqualified spraying quality, Q is the spraying defect, cc is each connected domain in f3, area(cc) is the area of ​​each connected domain, and f3(cc) is the value of the connected domain.

[0049] Preferably, in the step of evaluating whether the coating thickness is qualified based on the required spraying thickness and the spraying quality map, the fire retardant coating with qualified spraying thickness should simultaneously meet the following three conditions:

[0050] 1) The overall spraying thickness is greater than 85% of the required spraying thickness and greater than the minimum thickness limit of the fire retardant coating;

[0051] 2) The larger of the minimum fire retardant coating thickness and 85% of the required spray thickness is the spray quality detail diagram obtained under the threshold value, and there is no defective area;

[0052] 3) In the spray quality detail diagram obtained when the spray thickness is at the threshold, the area of ​​the spray defect area measured is less than 20% of the entire spray area;

[0053] The minimum thickness limit of the expansion type fire retardant coating for steel structures is 1.5mm, and the minimum thickness limit of the non-expansion type fire retardant coating for steel structures is 15mm.

[0054] Compared with the prior art, the advantages of the present invention are:

[0055] 1. The thickness assessment method combining overall measurement with local detection is used to conduct a comprehensive construction quality assessment of the thickness of the steel structure fire retardant coating. It has high detection accuracy and a wide range of applications and is suitable for on-site coating thickness construction quality detection.

[0056] 2. Quantitative coating thickness quality assessment based on 3D laser scanning technology can accurately calculate the overall spray thickness of the coating, accurately detect local spray defects, and effectively evaluate the spray quality of steel structure fire retardant coatings with high detection and assessment accuracy.

[0057] 3. The evaluation method of the present invention is a non-destructive test that does not affect the spraying effect of the existing coating. At the same time, the detection results of local spraying defects can provide guidance for subsequent re-spraying. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0059] Figure 1 A flowchart of a method for on-site detection and evaluation of the thickness of fire retardant coatings on steel structural components provided by an embodiment of the present invention;

[0060] Figure 2 Detailed flow chart of the on-site detection and evaluation method for the thickness of fire retardant coatings on steel structural components provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0062] 3D laser scanning technology acquires the three-dimensional spatial data source of the target object by emitting a large number of laser beams. It is a non-contact active detection technology with the advantages of high sampling rate, fast scanning speed, and high measurement accuracy. It is widely used in construction engineering, measurement, surveying and mapping and other industries. In terms of detecting the thickness of fire retardant coatings, 3D laser scanning technology can obtain two surface models of steel structures before and after the application of fire retardant coatings. By comparing the two models before and after, the spraying condition of the fire retardant coating can be obtained. To comprehensively evaluate the construction quality of the thickness of steel structure fire retardant coatings, two aspects need to be paid attention to, namely the overall thickness measurement of the coating and the detection of local defects in the coating. On the one hand, the average spray thickness of the fire retardant coating as a whole should meet the specified requirements to achieve the purpose of protecting the steel structure; on the other hand, due to the certain roughness of the surface of the fire retardant coating, there may be local spray defects where the coating thickness is lower than the specified thickness. Such defects need to be detected and subsequently re-coated to ensure that the local coating thickness meets the standard.

[0063] The present invention applies three-dimensional laser scanning technology to the construction quality inspection of the thickness of fire-retardant coatings on steel structures, and proposes a non-destructive and rapid on-site inspection method that combines overall measurement with local detection to comprehensively evaluate the construction quality of coating thickness. The inspection accuracy meets engineering requirements and can realize the rapid inspection of the thickness of fire-retardant coatings on large-area steel structures. It has important application potential in the actual inspection of steel structures.

[0064] Specifically, Figure 1 This is a flowchart of the on-site detection and evaluation method for the thickness of fire retardant coatings on steel structural components provided by an embodiment of the present invention. Figure 2 A detailed flow chart of the on-site detection and evaluation method for the thickness of the fire retardant coating of a steel structure member provided by an embodiment of the present invention is as follows: Figure 1 and Figure 2 As shown, the method includes the following steps:

[0065] S1: Obtain the surface model of the steel structure before and after the fire retardant coating is sprayed, and record the required spraying thickness and spraying length of the coating;

[0066] Use a handheld 3D laser scanning device to scan the fire retardant coating spraying area on the surface of the steel structure, obtain the 3D laser point cloud model of the steel structure before and after the fire retardant coating spraying and the steel structure point cloud data PC1 and PC2, and record the coating thickness to be sprayed and the spraying length in the direction perpendicular to the steel structure section.

[0067] Specifically, targets are placed around the steel structure to be sprayed. The targets should be evenly distributed around the steel structure to be sprayed. A handheld 3D laser scanning device is used to scan the area to be sprayed on the surface of the steel structure to obtain point cloud data PC1 before spraying and point cloud data PC2 after spraying. The specific steps are as follows:

[0068] Step 11: First, set the parameters of the 3D laser scanning equipment, such as sampling point distance, resolution, etc.

[0069] Step 12: During the scanning process, the scanner should be close to the area to be sprayed and scan the steel structure surface in all directions;

[0070] Specifically, the distance between the scanner and the steel structure surface should be less than the maximum scannable object range of the handheld 3D laser scanner. In addition to the area to be sprayed, the scanning process should scan all placed targets as much as possible;

[0071] Step 13: At the end of the scan, the point cloud data PC1 of the steel structure before the fire retardant coating is sprayed is obtained;

[0072] Step 14: Carry out construction and spray fire retardant coating on the surface of the steel structure. The coating thickness should be D;

[0073] Step 15: Measure the spray length of the coating in the direction perpendicular to the steel structure section, recorded as l;

[0074] Step 16: After the fire retardant coating is sprayed or manually applied and dried, scan the steel structure surface again to obtain the point cloud data PC2 after spraying.

[0075] S2: Calculate the overall spray thickness of the coating based on the cross-sectional perimeter of the steel structure component, the spray volume of the coating, and the spray length;

[0076] Specifically, based on the spray length in the direction perpendicular to the steel structure cross section, the perimeter of the steel structure cross section, and the model volume before and after the fire retardant coating is sprayed, the general calculation formula for the coating spray volume is summarized based on various steel structure component cross sections. The overall spray thickness of the coating is calculated. The specific steps are as follows:

[0077] Step 21: Obtain the perimeter C of the steel structure section;

[0078] Usually it can be obtained directly from the specifications of the steel structure without the need for self-calculation.

[0079] Step 22: For the portion of the steel structure where the coating has been sprayed, the volume V′ of the area included in the point cloud PC1 is calculated based on the point cloud data PC1 before spraying, i.e., the volume of the outer contour of the steel structure.

[0080] Step 23: For the portion of the steel structure where the coating has been sprayed, based on the point cloud data PC2 after spraying, calculate the volume V″ of the area included in the point cloud PC2, i.e., the volume of the outer contour of the coating;

[0081] Step 24: Subtract the volume of the area contained in the PC1 point cloud from the volume of the area contained in the PC2 point cloud to obtain the spray volume of the coating;

[0082] The specific formula is: V = V″-V′

[0083] Where V″ and V′ are the model volumes before and after the fire retardant coating is sprayed, and V is the spray volume of the coating.

[0084] Step 25: Calculate the overall spray coating thickness of the steel structure;

[0085] The calculation formula for the overall spray thickness d of the coating on the steel structure is:

[0086]

[0087]

[0088] Where d is the overall spray thickness of the coating, C is the circumference of the steel structure section, s is the spray volume of the fire retardant coating per unit spray length in the vertical direction of the steel structure section, l is the spray length in the direction perpendicular to the steel structure section, and V is the spray volume of the coating.

[0089] S3: Obtain the spray quality map of the fire retardant coating based on the coating thickness threshold, minimum defect area threshold, and the point cloud model of the steel structure before and after the fire retardant coating is sprayed;

[0090] Specifically, the point cloud model of the steel structure before and after coating spraying is registered to obtain the coating thickness map of the steel structure. Based on the coating thickness threshold and the minimum defect area, the coating spray quality map of the local spray defects is obtained. The specific steps include:

[0091] Step 31: Fitting the surface model of the steel structure without spray coating as the reference surface;

[0092] Specifically include:

[0093] 1) The obtained point cloud data PC2 after spraying is registered with the obtained point cloud data PC1, recorded as PC′2, so that the two sets of point cloud data are located in the same coordinate system and are comparable.

[0094] 2) Each surface of the steel structure sprayed with fire retardant coating is divided into an area, each area is a curved surface or a flat surface. According to the location of the steel structure, it is first divided into several areas, each area is a plane in itself; for the surface of the double-sided sprayed fire retardant coating, it is considered to be two areas.

[0095] 3) Segment the obtained point cloud data PC1 and the obtained point cloud data PC′2 respectively, and obtain a set of point cloud pairs (pc1, pc2) in each area, where pc1 comes from PC1 and pc2 comes from PC′2.

[0096] 4) The point cloud data pc1 of the steel structure surface itself when the coating is not sprayed is fitted into a surface using the least squares method, which is used as the reference surface rp.

[0097] Step 32: Calculate the vertical distance from the surface model after spraying the coating to the reference plane to obtain the spray thickness map of the fire retardant coating;

[0098] 1) Calculate the vertical distance d between each point in the point cloud pc2 and the reference surface rp after spraying the coating i , that is, the actual spray thickness of the coating. The actual spray thickness value of each point is assigned to the corresponding point to obtain the actual spray thickness point cloud pc3;

[0099] 2) The actual spraying thickness point cloud pc3 is projected onto the reference plane rp in the normal direction to obtain the spraying thickness map f1. The discrete randomly distributed spraying thickness map f1 is resampled into a regular uniformly distributed spraying thickness map f2.

[0100] Step 33: Obtain a spraying quality detailed map based on the coating thickness threshold, the spraying thickness map, and the minimum defect area threshold.

[0101] 1) Set the coating thickness threshold T D As a threshold, f2 is binarized to obtain a binary map f3 of the spraying thickness.

[0102]

[0103] Where f3 is the binary image of the fire retardant coating spray thickness, d i The part with f3=1 is the area where the actual spraying thickness is greater than or equal to the thickness threshold, and the part with f3=0 is the area where the actual spraying thickness is less than the thickness threshold.

[0104] 2) Set the minimum defect area T area As the threshold, the area in the binary image of the spray thickness is larger than T area The unqualified spraying connected areas are considered as spraying defects, and the spraying quality detailed map is obtained. area It can be set to twice the square of the scanner resolution.

[0105] Q={cc|(area(cc)>T area )∩(f3(cc)=0)}

[0106]

[0107] Where f is the spraying quality detail map, the part where f=1 is the area with qualified spraying quality, the part where f=0 is the area with unqualified spraying quality, Q is the spraying defect, cc is each connected domain in f3, area(cc) is the area of ​​each connected domain, and f3(cc) is the value of the connected domain.

[0108] 3) Repeat steps 32 to 33 for all areas to obtain detailed drawings of the spraying quality of all areas of the steel structure.

[0109] S4: Based on the required spraying thickness and spraying quality map, evaluate whether the coating thickness is qualified.

[0110] Specifically, the coating spray quality is judged based on the overall spray thickness, spray quality detailed map, required spray thickness, and coating thickness threshold. For coatings that fail to meet spray quality standards, re-spray the defective areas as shown in the spray quality detailed map. The specific steps for spray quality judgment are as follows:

[0111] 1. For the spray quality of qualified intumescent fire retardant coating, the following three conditions should be met at the same time:

[0112] 1) The overall spraying thickness is greater than 85% (85% D) of the required spraying thickness and greater than 1.5 mm.

[0113] d≥max(85%D,1.5)

[0114] Where d is the overall spray thickness, and max(a, b) is the larger value of a or b.

[0115] 2) The larger value of 1.5 mm and 85% of the required spray thickness (85% D) is obtained under the threshold value. In the spray quality detail diagram obtained, there is no defective area.

[0116] T D =max(85%D,1.5)

[0117] 3) In the spraying quality detail diagram obtained when the spraying thickness is the threshold value, the measured defect area is less than 80% of the entire spraying area.

[0118] T D =D

[0119] 2. For non-expansion fire retardant coatings with qualified spray quality, the following three conditions should be met at the same time:

[0120] 1) The overall spraying thickness is greater than 85% (85% D) of the required spraying thickness and greater than 15 mm.

[0121] d≥max(85%D,15)

[0122] 2) The larger value of 15 mm and 85% of the required spray thickness (85% D) is the spray quality detail obtained under the threshold value, and there is no defective area.

[0123] T D =max(85%D,15)

[0124] 3) In the spraying quality detail diagram obtained when the spraying thickness is the threshold value, the measured defect area is less than 80% of the entire spraying area.

[0125] T D =D

[0126] For coatings that fail to meet the spraying standards, the spraying thickness should be set as the threshold (T D =D) as shown in the spray quality details, the defective areas are re-sprayed.

[0127] Among them, the minimum limit of fire retardant coating thickness should refer to the national standard. According to the current national standard "Steel Structure Fire Retardant Coating" GB14907-2018, the minimum limit of thickness of expansion type steel structure fire retardant coating is 1.5mm, and the minimum limit of coating thickness of non-expansion type steel structure fire retardant coating is 15mm.

[0128] Compared with the existing technology, the present invention proposes a non-destructive, comprehensive and high-precision on-site detection and evaluation method for the thickness of steel structure fire retardant coating. The method of the present invention includes two parts: overall coating thickness measurement and coating local defect detection. The overall coating thickness measurement refers to estimating the overall spray thickness of the steel structure coating based on the volume difference of the three-dimensional model before and after spraying the fire retardant coating, that is, the spray volume of the fire retardant coating, the cross-sectional size of the steel structure itself and the spray range. The local coating defect detection refers to accurately measuring the thickness of the fire retardant coating at various locations on the surface of the steel structure by comparing the three-dimensional laser point cloud model before and after spraying the coating, detecting local defects where the coating thickness does not meet the standard, and re-spraying the defective area. The present invention ensures a comprehensive assessment of the thickness of the fire retardant coating and provides operational guidance and measurement basis for the assessment of construction quality.

[0129] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A method for on-site detection and evaluation of the thickness of fire retardant coatings on steel structural components, characterized in that: The method comprises the following steps: Obtain the surface model of the steel structure before and after the fire retardant coating is sprayed, and record the required spray thickness and spray length of the coating. Specifically, this includes: using a 3D laser scanning device to scan the fire retardant coating spray area on the steel structure surface, obtaining the 3D laser point cloud model of the steel structure before and after the fire retardant coating is sprayed and the steel structure point cloud data PC1 and PC2, and recording the required spray thickness of the coating and the spray length in the direction perpendicular to the cross section of the steel structure; Calculate the overall spray thickness of the coating based on the cross-sectional perimeter of the steel structure component, the spray volume of the coating, and the spray length; Based on the coating thickness threshold, minimum defect area threshold, and the point cloud model of the steel structure before and after the fire retardant coating is sprayed, the spray quality details of the fire retardant coating are obtained, including: Fit the surface model of the steel structure without spray coating as the reference surface; Calculate the vertical distance from the surface model to the reference plane after spraying the coating to obtain the spray thickness map of the fire retardant coating; Based on the coating thickness threshold, spraying thickness map and minimum defect area threshold, a spraying quality detailed map is obtained; Evaluate whether the coating thickness is qualified based on the required spray thickness and spray quality details.

2. The on-site detection and evaluation method for the thickness of the fire retardant coating of a steel structure component according to claim 1 is characterized in that: The steps of obtaining the three-dimensional laser point cloud model of the steel structure before and after the fire retardant coating is sprayed and the steel structure point cloud data PC1 and PC2 specifically include: Set the parameters of the 3D laser scanning equipment; During the scanning process, the scanner should be close to the area to be sprayed and scan the steel structure surface in all directions; After scanning, the point cloud data PC1 of the steel structure before the fire retardant coating is obtained; During construction, spray fire retardant coating on the surface of the steel structure. The coating thickness should be D. Measure the spray length of the coating in the direction perpendicular to the steel structure section, recorded as l; After the fire retardant coating is sprayed or applied manually and dried, the steel structure surface is scanned again to obtain the point cloud data PC2 after spraying.

3. The on-site detection and evaluation method for the thickness of fire retardant coating of steel structure components according to claim 1 is characterized in that: The step of calculating the overall spray thickness of the coating based on the cross-sectional perimeter of the steel structure component, the spray volume of the coating, and the spray length specifically includes: Get the perimeter C of the steel structure section; For the portion of the steel structure where the coating has been sprayed, the volume V' of the area contained in the point cloud PC1, i.e., the volume of the outer contour of the steel structure, is calculated based on the point cloud data PC1 before spraying. For a portion of the steel structure where the coating has been sprayed with a length of l, based on the point cloud data PC2 after spraying, the volume V" of the area contained in the PC2 point cloud, i.e., the volume of the outer contour of the coating, is calculated; Subtract the volume of the area contained in the PC2 point cloud from the volume of the area contained in the PC1 point cloud to obtain the spray volume of the coating V=V″-V′, Wherein, V” and V’ are the model volumes before and after the fire retardant coating is sprayed, respectively, and V is the sprayed volume of the coating; Calculate the overall spray coating thickness of the steel structure using the following formula: Where d is the overall spray thickness of the coating, C is the circumference of the steel structure section, s is the spray volume of the fire retardant coating per unit spray length in the vertical direction of the steel structure section, l is the spray length in the direction perpendicular to the steel structure section, and V is the spray volume of the coating.

4. The on-site detection and evaluation method for the thickness of fire retardant coating of steel structure components according to claim 1 is characterized in that: The step of fitting the surface model of the steel structure surface without spray coating as the reference surface specifically includes: The obtained point cloud data PC2 after spraying is registered to the obtained point cloud data PC1, which is recorded as PC ' 2. Make the two sets of point cloud data in the same coordinate system and comparable; Each surface of the steel structure sprayed with fire retardant coating is divided into a region, each region is a curved surface or a flat surface. According to the location of the steel structure, it is first divided into several regions, each region is a plane. For the surface of the double-sided sprayed fire retardant coating, it is considered as two regions. Separately split the obtained point cloud data PC1 and the obtained point cloud data PC ' 2. Each region obtains a set of point cloud pairs (pc1, pc2), pc1 comes from PC1, pc2 comes from PC ' 2; The point cloud data pc1 of the steel structure surface itself when the coating is not sprayed is fitted into a surface using the least squares method, which is used as the reference surface rp.

5. The on-site detection and evaluation method for the thickness of fire retardant coating of steel structure components according to claim 1 is characterized in that: The step of calculating the vertical distance from the surface model of the sprayed coating to the reference plane to obtain the spray thickness map of the fire retardant coating specifically includes: Calculate the vertical distance d between each point in the point cloud pc2 and the reference surface rp after the fire retardant coating is sprayed i , that is, the actual spray thickness of the coating. The actual spray thickness value of each point is assigned to the corresponding point to obtain the actual spray thickness point cloud pc3; The actual spraying thickness point cloud pc3 is projected onto the reference plane rp in the normal direction to obtain the spraying thickness map f1. The discrete randomly distributed spraying thickness map f1 is resampled into a regular uniformly distributed spraying thickness map f2.

6. The on-site detection and evaluation method for the thickness of fire retardant coating of steel structure components according to claim 1 is characterized in that: The step of obtaining the spraying quality detailed map based on the coating thickness threshold, the spraying thickness map and the minimum defect area threshold specifically includes: Set the coating thickness threshold T D As a threshold, f2 is binarized to obtain the binary image f3 of the spraying thickness: Where f3 is the binary image of the fire retardant coating spray thickness, d i is the thickness value at each location in the coating thickness diagram. The part where f3=1 is the area where the actual spraying thickness is greater than or equal to the thickness threshold, and the part where f3=0 is the area where the actual spraying thickness is less than the thickness threshold. Set the minimum defect area T area As the threshold, the area in the binary image of the spray thickness is larger than T area The unqualified spraying connected areas are considered to be spraying defects, and the spraying quality detailed map is obtained: Q={cc|(area(cc)>T area )∩(f3(cc)=0)} Where f is the spraying quality detail map, the part where f=1 is the area with qualified spraying quality, the part where f=0 is the area with unqualified spraying quality, Q is the spraying defect, cc is each connected domain in f3, area(cc) is the area of ​​each connected domain, and f3(cc) is the value of the connected domain.

7. The on-site detection and evaluation method for the thickness of fire retardant coating of steel structure components according to claim 1 is characterized in that: In the step of evaluating whether the coating thickness is qualified based on the required spraying thickness and the spraying quality detailed drawing, the fire retardant coating with qualified spraying thickness should meet the following three conditions at the same time: 1) The overall spraying thickness is greater than 85% of the required spraying thickness and greater than the minimum thickness limit of the fire retardant coating; 2) The larger of the minimum fire retardant coating thickness and 85% of the required spray thickness is the spray quality detail obtained under the threshold value, and there is no defective area; 3) In the spray quality detail diagram obtained when the spray thickness is at the threshold, the area of ​​the spray defect area measured is less than 20% of the entire spray area; The minimum thickness limit of the expansion type fire retardant coating for steel structures is 1.5mm, and the minimum thickness limit of the non-expansion type fire retardant coating for steel structures is 15mm.

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