PSI - Issue 64

D.B. Zhang et al. / Procedia Structural Integrity 64 (2024) 1997–2004 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

2000

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Safety performance fitting to current regulatory standards Slight damage without affecting safety performance

The height of the external wall is less than 10m; High-rise buildings with paint finish.

Normal maintenance

Riskless

No high-altitude falling-off hazard has occurred, and one of the following conditions is met: External thermal insulation system with service life less than 5 years; Face brick or mosaic facing layer with service life less than 10 years. The proportion of the falling off area to the entire facade is not more than 1%; The proportion of hollow area to the entire facade is not more than 15%, and the proportion of continuous hollow area shall not be greater than 0.1%; In the sampling inspection of bond strength of the external wall, the proportion that meets design requirements is not less than 60%; In the sampling inspection of structure of the external thermal insulation system, the proportion that meets design requirements is not less than 60%; In the sampling inspection of anchor bolt of the external thermal insulation system, the proportion that meets design requirements is not less than 60%; There are visible cracks on the external wall, with a width no more than 0.2mm, and no more than 5 cracks per square meter.

Regular inspection and evaluation

Low risk

Medium risk

Reduced safety performance

Special maintenance

Falling-off hazards endangering public safety

Immediately handle the situation

Other situations.

High risk

Frequent incidents of external thermal insulation system detachment are one of the main forms of falling-off hazards existing in the high-altitude building external walls in China. Subsequent research in this article will focus on

the falling-off hazards of the external thermal insulation systems. 4. 3D laser scanning technology and point cloud data processing

The features of the instrument used in this paper include a maximum scanning rate of 5×10 5 points/s, a maximum scanning distance of 300m, and minimum point spacings of less than 1mm in both horizontal and vertical directions. Additionally, the instrument boasts a target acquisition precision of 2mm. Therefore, the 3D laser scanner can realize the rapid storage of 3D coordinate data of the scanning points. For high-precision coordinate transformation, the fixed targets need to be used. Four fixed targets of varying heights are positioned around the scanning object. The plane defined by the centers of three or more targets is employed as the benchmark for cross-sectional extraction. Point cloud data are discrete geometric points collected by the 3D laser scanner. Due to the interference of human factors or the defects of the scanning instrument, there exist noises and outliers in the point cloud data, which need to be denoised by effective algorithms. The k-nearest neighbor point cloud denoising algorithm as depicted by Saleem et al. (2007) is adopted to denoise in this paper. 5. Identification of falling-off hazards for external thermal insulation system of polyurethane rigid foam spraying 5.1. Construction project profile and testing region of external wall A 19-story residential building in a community in Shanghai has adopted the external thermal insulation system of polyurethane rigid foam spraying. After being delivered for use, the external thermal insulation system of some buildings appeared hollowing and falling, posing a high risk of falling-off hazards. The East facing facade of Building 7 is selected as the research object, as shown in Fig. 1(a), and the ground 3D laser scanner is used to scan the point cloud data. To enhance the efficiency of point cloud data analysis, the point cloud data of three regions, labelled as A, B, and C, are selected as depicted in Fig. 1(b). The heights of the detection regions A, B, and C are all 55.0m, while the widths are 3.7m, 4.5m, 3.6m respectively.