PSI - Issue 64

2001 5

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

Fig. 1. Point cloud data of east facing facade (a) photo; (b) zoned point cloud data; (c) point cloud imaging; (d) defect identification.

After denoising the point cloud data of the external thermal insulation system, the average value z m of z coordinate is calculated. By setting the threshold z 0 , the difference between the z coordinate value and the average value z m of each point is calculated. The specific criteria are shown in Table 4. The image utilizing the 3D point cloud data is depicted in Fig. 1(c). By observing the colour intensity, the hollowing area in the x - y plane can be effectively identified.

Table 4. Criterion for identifying abnormal points Criteria Region status

0 m z z z −  0 m z z z −  0 m z z z − 

Normal

Hollowing Falling off

5.2. Analysis of testing results Set the threshold value z 0 =15mm, the point cloud data of regions A, B, and C is processed respectively to obtain the distribution of hollowing hazards in the x - y plane as shown in Fig. 1(d). Three hollowing regions are found in the x - y plane in region A, which are A1 to A3 respectively. Area B exhibits a hollow region near the window, which aligns with the actual lintel, and a hollow area in the lower right corner. In area C, there is a continuous hollowing region C0 in the upper right corner, corresponding to the convex part of the external wall, covering an area of approximately 1.79m 2 , representing about 0.9% of the total external wall region. Based on the risk classification method of falling-off hazards of the building external walls as outlined in Table 3, the external wall is categorized as high risk, and effective measures should be taken immediately to dispose this hazard. To validate the efficiency of 3D laser scanning technique in identifying hollowing defects in the external thermal insulation system of polyurethane rigid foam spraying, the infrared thermal imaging of the facing facade is conducted during the heating phase as depicted by Zhang et al. (2021). As depicted in Fig. 2, the regions with light color indicate high temperature and the presence of hollowing. Upon comparison, it is evident that hollowing regions labeled as A1, A2, A3 in Fig. 1(d) correspond closely to defects labeled as A1, A2, A3 in Fig. 2, which validates the practicality of 3D laser scanning technique in discerning hollowing hazards.