Buildings: Gandria Church

Case study: SOFO System

Vault Monitoring
Curvature analysis
Crack behavior
Automatic and remote measurements

Project Description

Summary: Crack monitoring under thermal loading and long-term, automatic measurements

Clients: Gandria municipality

Place: Ticino Canton (Switzerland)

Period: 1997 - N/A

Installation: IMM SA

Structure's short description: The church was presumably erected around 1650 and is part of the Swiss national historical monument directory. In the last few years restoration works were carried out on the roof. These interventions are probably the cause of a well visible crack running along the inferior side of the main vault. Other smaller cracks are appearing at ? span on the topside of the vault.

Aim of monitoring: The purpose of the instrumentation is to measure the daily and seasonal variations in the crack openings and vault curvature. This is done in order to point out any irreversible behavior.

Number of sensor: 10

Main Results: The SOFO sensors were selected because of their reliability, precision, ease of installation and the possibility of carrying out automatic measurements: once installed, no direct access to the sensors placed at an height of more than 6m is needed. The measurement can be carried out from the sacristy without disrupting the normal use of the church. Using an optical switching unit, the 10 sensors are automatically measured for a period of a few weeks each three months. Manual measurements are carried out between the automatic measurement sessions. The measurements conducted over about 6 months have pointed to a reversible behavior with crack openings well correlated to the temperature variations. Figure 1 shows the sensor's emplacement. Figure 2 shows the deformations measured on the bottom and topside in one of the measurement sections as well as the temperature variations during the same 3-week period.

Sensor and crack emplacement

Recorded crack openings during two weeks with temperature variations

Bibliography:

Long-term deformation monitoring of historical constructions with fiber optic sensors , D. Inaudi, N. Casanova, B. Glisic, 3rd International Seminar on Structural Analysis of Historical Constructions, Guimaraes, Portugal, November, Univrsity of Minho Publisher, pp. 421-430, 2001

Monitoring of Heritage Structures and Historical Monuments Using Long-Gage Fiber Optic Interferometric Sensors - An Overview , Branko Glisic, Daniele Inaudi, Daniele Posenato, Angelo Figini, Nicoletta Casanova, The 3rd International Conference on Structural Health Monitoring of Intelligent Infrastructure - SHMII-3, November 13-16, on conference CD, 2007

Fibre Optic Methods for Structural Health Monitoring , Branko Glisic and Daniele Inaudi, Johh Wiley & Sons, Ltd, 2007