Finding the displacement of wood structure in heritage building by 3D laser scanner

Abstract

ABSTRACT:Heritage buildings are highly prone to long term damage from the microclimate, scourge and vandalism, which can result in damaged materials, structures, painting and cultural heritage items. This study will focus on finding the displacement of wood structural members through the use of a 3D laser scanner and the 4D concept of time. The results will compare the scans from different periods to find the difference (if any) in the structural member position. Wood structures usually consist of numerous wood members connected to form the structure. However, these members can be damaged in various ways such as physical mechanisms, chemical reactions, and biological corrosion. When damage to the wood structure occurs, the structural displacement can be affected, and if affected severely, can lead to a building collapse. Monitoring of the structural displacement is the best way to discover damage immediately and to preserve the heritage building. However, the Cultural Heritage Preservation Law in Taiwan prohibits the installation of monitoring instruments (e.g strain gauge, accelerometer) in historic structures (heritage buildings). Scanning the wood structure with 3D lasers is the most non-intrusive method and quickly achieves displacement through visualization. The displacement scan results can be compared with different periods and different members to analyze the severity of damage. Once the 3D scanner is installed, the whole building is scanned, and point clouds created to build the visual building model. The structural displacement can be checked via the building model and the differences are measured between each member to find the high risk damaged areas or members with large displacement. Early detection of structural damage is the most effective way means of preservation.

Displacement Study of a Large-Scale Freeform Timber Plate Structure Using a Total Station and a Terrestrial Laser Scanner

“…These survey markers were used for the registration of the scans. Their spherical shape prevents axis mapping mistakes [22]. Scans were acquired for both tests before and after loading.…”

“…The resulting point cloud presented in Figure 8b contains about 34 million points and is illustrated for an area of 1 × 1 cm in Figure 9. According to Lee et al [22], mapping errors of the sphere reference points need to be below 1 cm to ensure sufficient total accuracy of the measurements, in the few millimetres range for the present study. Registration were thus refined manually using the open source software CloudCompare [31] by aligning four point pairs manually picked from the reference cloud and the cloud to be compared.…”

“…However, they allow measurements on a limited number of target points. More recently, three-dimensional (3D) terrestrial laser scanning has also been used for several applications [21][22][23][24]. With this technique, coordinates of millions of points forming a point cloud are collected.…”

Photogrammetric Measurement of a Wooden Truss

“…There are many works promoting the usability of terrestrial laser scanning (TLS) in the measurement of timber structures. Interesting applications have been presented, e.g., by (Bertolini et al, 2015), (Lee et al, 2015) or (Perria et al, 2017).…”

Documentation for the Conservation of Built Heritage: Analysis of Recording Methodologies

“…237 One final note of analysis is that there was one case study by Lee et al to measure the displacement of columns that did not use either of the two base methodologies. 238 Instead, the authors established a datum line along the center of the column of interest, and compared the displacement between point clouds from 2006 and 2013. 239 If the deformation reaches an established critical angle, then the structure will collapse.…”