Classic deformation measurements basically consist in placing reference points, distributed symmetrically as a grid or attached at selected principal points of movement. Measurements points can be determined with a fair precision and a standard deviation of less than a millimeter.
The parsonage of the Parish of San Martino Vescovo, located in Cigole, a small and beautiful town in northern Italy, built approximately in the XVIII century, recently showed major structural failures. The Department
HOW TO DEAL WITH THE PROBLEM
One of the biggest possible measuring volume has been chosen in order to speed up the registration process. Despite of large and continuous surfaces, targeting is not required, the roughness of single coarse stones as well as cracks guides every alignment.
Accuracy of scans in a single session is estimated in a range of 30 microns, overall accuracy in a range of 0.1 mm. Two different measurements sessions, 60 days apart from each other were made to define the movements of the structures analysed. Further measurements will follow.
HARDWARE & SOFTWARE SET-UP
Cronos 3d 400mm
Optical Reveng 2.4
FLUSSO DI LAVORO
1- A calibration of the device on site is required to obtained the most accurate result. The column is directly acquired and automatically registered.
2- Three targets point are placed over the top of the frame in order to consider not only deformations but also wether or not the section is detaching from the entire wall.
3- The window frame and surrounding areas are then acquired and registered. It is necessary to guarantee the equipment a stable environment.
4- Optical RevEng allows intuitive check and optimization of the pointcloud, after a first, coarse registration, a global optimization is performed and a polygonal entity processed.
5- 3D Scan Data is then imported in Geomagic ControlX for the evaluation of any eventual movement. The data obtained during the first session is set as a reference while the latest scan as a test datum for deviations.
6- A Comprehensive understanding of overall deviations is displayed over the deviation map, cross analysis of surfaces, sections and control points allows a direct evaluation of the specific structural failure entity.
3d structured light scanner can be used for the observation of mid to long-term deformations in one of the following methods:
- comparison of grid points;
- comparison of linear structures like sections;
- comparison of whole surfaces.
The equipment has a resolution of less than 250 microns, the smallest detail or imperfection on the surfaces is acquired and analyzed.
The measurement session showed that the column is perfectly stationary while the frame of the window is basically falling forward with
a rate of 13 mm every two months, control points and cracks standing around the frame, allowed to assume that the window is actually moving
because the entire building is falling and torquing backward. The digital record of the column is stored for future restorations.
Open Technologies would like to thank every institution involved in this project for their highly valuable contribution to this case study, Special
thanks are due to Dr. Cartocini Valentina for the priceless support.