PSI - Issue 64

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

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1. Introduction With the rapid advancement of urbanization in China, there is a huge existing stock of buildings, especially high rise and super high-rise buildings. For example, there are 53 400 high-rise buildings with 8 floors or more at the end of 2021 in Shanghai, including 13 320 buildings using the exterior wall insulation system, over 10 000 buildings using the glass curtain walls, and some buildings cohering the facing bricks as the exterior decoration. In recent years, the high-rise falling-off accidents derived from building external walls have occurred frequently, especially the high altitude detachment of the exterior wall insulation system and the facing bricks, which have become an important hidden dangers to the urban public safety. In March 2021, a high-rise detachment of the external facade happened in a residential building in Shanghai, resulting in the death of a passerby as depicted by Sun et al. (2023). The primary sources of potential falling-off hazards in high-rise buildings are the detachment of external walls and auxiliary facilities, artificially throwing objects from high-altitude, and falling of idle objects on the windowsills and balconies. The latter two can be effectively prevented and controlled through the resident safety education and corresponding management and control measures. However, there are no effective strategies to prevent and address high-altitude falling-off of building external walls, with the difficulty in the lack of rapid and effective methods for identifying and assessing potential risk. As a non-contact active measurement technique, 3D laser scanning can capture point cloud data of the target object for modeling. Due to the advantages such as fast scanning speed, high measurement accuracy, and long measurement distance as depicted by Sholts et al. (2010) and Kilambi et al. (2012) and Ebrahim et al. (2015), the 3D laser scanning technique has important application value in the construction industry. Li et al (2003) have achieved the 3D modeling of building by extracting planar contour information from the point cloud data obtained through the 3D laser scanning technique. Combined with the binarization and connected region labeling methods, Lin et al (2016) have utilized the angle interval histogram of adjacent scan points to extract the external facade point cloud data. Currently, there is little research on the application of the 3D laser scanning technique in the accurate identification of falling-off hazards of

the high-rise building external wall at home and abroad. 2. Type and cause of falling-off hazard of external wall 2.1. Falling-off hazards of external wall

As the increase of the operating time of high-rise building external walls, the natural aging process of the materials used intensifies due to the constant exposure to extreme temperatures, severe cold, storms, rain and snow, and ultraviolet radiation. This leads to problems such as hollowing, cracking, and bond failure on the exterior walls, which may greatly raise the risk of falling-off hazards. Through analysis of actual cases of falling-off accidents, it has been found that the primary risk sources include external wall insulation systems, facing bricks, glass curtain walls, GRC lines, and corresponding auxiliary facilities as depicted by Sun et al. (2023). The potential falling-off hazards of the external walls of existing buildings in China primarily stem from the external thermal insulation systems, external wall facing layer and associated facade attachments, the corresponding defects and contributing causes are presented in Table 1. Table 1. Forms and causes of falling-off hazards of buildings external walls in China Falling-off source Associated defects Contributing causes

External thermal insulation system

cracking, hollowing, bonding failure, detachment, et al

There are various types of external thermal insulation systems, which has problems such as unqualified materials and substandard construction quality, especially the system of inorganic thermal insulation mortar. There exist problems such as aging material, outdated construction techniques and bonding failure for the external wall facing materials, including facing bricks and facing stones. Owing to the absence of unified installation standards and strict oversight, there exist issues for the external facade attachments, including unqualified materials, poor wall substrate quality, and connecting material degradation.

External wall facing layer

cracking, hollowing, water seepage, bonding failure, detachment, et al corrosion, looseness, slippage, deformation, cracking, et al

External facade attachments