A.C. ISFELD
Postdoctoral Scholar, Department of Civil Engineer, University of Calgary, Schulich School of Engineering,
Calgary, Alberta, T2N 1N4 and Canada acisfeld@ucalgary.ca
ABSTRACT
The Prince of Wales Fort was constructed in the 18th century in Churchill, Manitoba, in the Vauban style. The perimeter walls consist of two wythes of cut ashlars and a rubble core which have shown signs of deterioration. During conservation work to rebuild damaged wall sections other sections of wall, previously thought to be in good condition were found to be undergoing significant displacements and were added to the project scope. Subsequently a more thorough understanding of the causes of failure was desired so work could be done to prevent further problem areas.
To test the hypothesis that failure was initiated by degradation of the mortar within the walls, micro-modelling using both the Discrete (DEM) Finite Element (FEM) and Random Finite Element (RFEM) methods was implemented. The DEM approach involved simplified geometry; the model was used to determine if a transition could be made from instability to stability by increasing the bond alone. The FEM used a detailed micro modelling approach, modelling the units, mortar, and unit mortar interface. A parametric analysis of both the grouts compressive and bond strength was completed. The RFEM was used to randomize the material properties, which had been parametrically evaluated through the FEM.
The research identifies a new general mechanism of failure for multi-wythe masonry walls, and their susceptibility to environmental conditions. The numerical results predicted that the stone-grout bond was the most critical parameter in the proposed intervention, and that in the grouted wall sections, collapse would be avoided and lateral displacements stabilized.
KEYWORDS: masonry, grout injection, discrete element model, finite element model, historic structures