Remote Monitoring of Differential Movements
in Masonry Cavity Walls

Perron Clock Tower, St. Albert, Alberta, Canada


Background

The Perron Street clock tower is a 21 m tall structure located at 53o37’56”N latitude and 113o37’24”W longitude. The tower was built in 1995 by the City of St. Albert in collaboration with the University of Alberta as a research project with a main objective of investigating differential movements in masonry cavity wall systems. Since the clock tower was built primarily for research purposes, it is ideal for implementing and evaluating the effectiveness of the proposed remote monitoring technology.

The tower was tested previously using a mechanical monitoring system. However, this system was not effective for automated data collection and analysis. Therefore, an additional objective of this project is to replace the out-dated, manual monitoring system with a state-of-the-art automated one. This will permit long-term monitoring of displacements in a real structure, providing a unique opportunity to study the behaviour of masonry cavity walls.

The tower is instrumented with 36 temperature-sensing thermistors, 12 linear displacement sensors, and 2 combined temperature and humidity probes. Three thermistors are located at three different heights on each wall. The three thermistors are located at approximately 25 mm, 175 mm, and 240 mm through the wall. The thermistors measure the temperature inside the wall, providing an indication of how much heat is lost through each wall. A combined temperature and humidity probe is installed near the top and bottom of the 12 m instrumented walls in order to track the conditions inside the tower.

Three linear displacement sensors are attached to each wall. One is used to measure the changes in the height of the concrete block wall, another is used to measure changes in the brick wall, and the remaining one provides a check-value by measuring the difference between the concrete block and the brick directly.
The Perron Street Clock Tower, located in St. Albert, Alberta
Clock Tower Section with Sensor Locations

Explanation of Real-Time Displacements

Our "real-time" measurements are updated every six hours (0:00, 06:00, 12:00, and 18:00). The figure to the left shows the vertical displacements in each of the walls at the most recent update. The measurements are compared to the initial readings taken at 0:00 on 01 October 2012. A positive displacement indicates that the wall is taller than it was at 0:00 on 01 October 2012; a negative displacement indicates that the wall is shorter.

Explanation of Real-Time Temperature Profiles

The figures below are plotted from four temperature readings for an elevation of 5.3 m up the wall. The indoor air temperature (left side of the plot) is measured using the temperature & humidity probes. The three thermistors inside the wall provide three more data points. The plots are shown with a cross section of the wall in the background. Grey represents the concrete block, blue represents the Styrofoam insulation, white represents air, and brown represents the clay brick. All walls have 190 mm concrete block and 90 mm brick, but in between these layers, each wall was constructed differently.
North wall: 25 mm insulation, 25 mm air space
East wall: No insulation, 25 mm air space
South wall: 50 mm insulation, 25 mm air space
West wall: 50 mm insulation, 50 mm air space

Real Time Temperature Profiles

Research Team

Adam Lohonyai is a PhD student of structural engineering at the University of Alberta.

Dr. Yasser Korany is an associate professor of structural engineering at the University of Alberta.

Dr. Mustafa Gül is an assistant professor of structural engineering at the University of Alberta.

Nick Trovato is the managing principal of Read Jones Christofferson’s building science division in Edmonton.

Ernest Hawker is the manager of technical service for RJC.

Sean Kelly is a desktop support specialist for RJC.

Acknowledgments

This project was funded from a research grant provided by the Natural Sciences and Engineering Research Council of Canada (NSERC). The project is an undertaking of the University of Alberta in collaboration with industrial partner Read Jones Christofferson (RJC). The research team wishes to also acknowledge technicians Greg Miller and Cameron West, without whom the installation of the electronic sensors would have been impossible. Finally, we wish to thank the City of St. Albert and Mayor Nolan Crouse for permitting us to conduct our research on the Perron Street Clock Tower.