Deformation measurements

and analysis at the Vicarage of Saint Martin Parish Church

TARGET

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. However, these procedures takes account only of the movements of the measuring points and sometimes, accuracy may not be enough.
Movements among the measuring points cannot be determined. Interpretation is more difficult, ancient building have very rough surfaces,  hapes are complex. Structured light scanning  ffers the benefit of a complete  eformation analysis on  uildings detail.


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 of Civil, Environmental, Architectural Engineering and Mathematics (DICATAM) of the University of Brescia wants to keep under monitoration these failures in order to provide a conservation work for this building. These  easurements will be used in a
restoration thesis entitled  Which sustainability for the restoration? A proposal for the conservation works for the  ectory of Cigole” edited by Dr. Cartocini Valentina.


Cronos 3D was helpful to  onitor the movements of the frame of a window, in relation with its surrounding surfaces, and the changes of the fissures on the surface of a column in the internal patio.

The purpose of this measurements is to derive changes from 3d scanner data at different epochs.

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  ontinuous 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, verall 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 AND SOFTWARE SET-UP

  • Cronos 3d 400 2.0 Mpx
  • Tripod
  • Portable workstation
  • Optical Reveng 2.4
  • Geomagic ControlX

WORKFLOW

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.

marker case study

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  egistration, a imization is performed and a polygonal entity processed.

inspection 3d scanner

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.

inspection 3d scanner

CONCLUSION

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.

inspection 3d scanner

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