PSI - Issue 64

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

1999

3

2.2. Causes analysis of falling-off hazards The potential danger of high-altitude falling-off of existing building external walls primarily stems from the service life, the construction materials and design of external walls, and the maintenance and operation management of the response as depicted by Ma et al. (2023). The external wall is continuously subjected to the combined effects of gravity load, wind load, and temperature variations. As the service life increases, the issue of material aging intensifies, and the problem of bond failure becomes more prominent, resulting in high-altitude falling-off hazards of building external wall. For the construction materials and design of external walls, there is a wide range of problems, such as uneven material quality, unreasonable design, insufficient setting of isolation joints, unstable anchoring methods, etc. Especially, the resin adhesives are predominantly used for fixing external wall insulation and decorative materials. Unfortunately, these adhesives only have a lifespan of 10 to 15 years, resulting in falling-off hazards of external wall due to bond failure. The objective factors that pose a high risk of falling-off hazards of the external thermal insulation system include significant disparities in the thermal conductivity and deformation coefficients of the materials used, the inability to balance the thermal and mechanical properties of the insulation materials, long-term exposure to environmental changes and so on. Corresponding, the human factors include poor design, irregular layout of grid cloth, absence of isolation joints, improper waterproofing, substandard construction techniques and so on. The main reasons of external wall facing layer with a high risk of falling-off hazards are affected by the environmental change and the effects of thermal expansion and contraction. Through field research on 128 cases of falling off accidents of the external wall facing layer that have occurred in Shanghai, the causes of falling-off accidents of the external wall facing layer are summarized, and the proportion distribution of different influencing factors is shown in Table 2. The falling-off reasons of the GRC lines for building facade decoration are lack of frost resistant, waterproof and alkali-resisting. In 2019, the use of GRC, EPS, XPS and other decorative components which are easy to fall off is banned in Shanghai.

Table 2. Cause analysis of falling-off accidents of the high-rise building external wall facing layer in Shanghai Falling-off cause Number of cases Percentage/% Freeze thaw effect of water seepage 22 17.2 Artificial damage such as drilling, impact 9 7.0 Typhoon, storm and other natural disasters 6 4.7 Defects in the quality of facing layer materials, adhesive materials, and other related materials 15 11.7 Construction quality defects of cohesiveness and leveling layer 27 21.1 Differences in thermal expansion and cold shrinkage of various materials 31 24.2 Material aging 18 14.1

The drop of external air conditioning rack in the auxiliary facilities of the building facade is basically caused by the aging and corrosion of the rack, except for the non-standard installation. Currently, the safe service life of the ordinary angle steel for installing the air conditioner is only 5~7 years, while many air conditioner supports in old residential areas have exceeded the effective service life, resulting in the high risk of falling off. 3. Risk classification of falling-off hazards of building external walls Based on the statistical analysis results of the falling-off accidents of building external walls happened in China, the risk levels of typical falling-off hazards of the external walls are classified, as shown in Table 3, which can provide the basis for the assessment of high-rise falling-off hazards.

Table 3. Risk level of falling-off hazards of external walls of high-rise building

Treatment countermeasure

Risk level Classification criteria

Typical characteristics