PSI - Issue 64

Alex Carpenter et al. / Procedia Structural Integrity 64 (2024) 319–326 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Conservation efforts in the 1930s and 1940s added concrete walls and slabs into the lower tower, while the 1990s introduced steel framing to support the spire and reduce the load on the timber central mast. The addition of concrete into the historic structure led to several complications, such as moisture entrapment in the tower which is visible against the interior concrete walls during storm events. Preliminary structural models indicate the need to determine whether the steel tie rods are acting in tension before proceeding with future work on the spire’s central timber mast , ensuring that conservation efforts will not add to the mast ’s load . In addition to these considerations, there are structural concerns over cracking near the tower’s eastern pinnacles and the wind-induced tilt of the spire. This structure is situated in the heart of a city facing the second-highest child-poverty rate in Canada, standing at 23.1% (Statistics Canada, 2017). The Cathedral of the Immaculate Conception holds significant regional importance for its faith-based community and serves as a welcoming hub for Saint John’s immigrant families to engage with their cultural traditions. The cathedral ’s prioritisation of funds towards supporting these communities leaves limited resources for conservation initiatives, necessitating an SHM system to inform critical conservation efforts.

3.2. Sensor selection & staging

Fig. 1. Eastern elevation for Phases 1 and 2 sensor placements in the Cathedral of the Immaculate Conception with images of Phase 1 sensors.

The sensor selection for the Cathedral of the Immaculate Conception focuses on sensors in Section 2 deemed beneficial for long-term monitoring and assessing conservation while being cost-effective and adaptive, forgoing sensors beneficial for monitoring buildings at seismic risk, performing AVT, or experiencing nearby construction. The cracked pinnacles and the bell tower’s structural system required immediate monitoring. The suite of sensors selected to meet these criteria include crack metres; tilt metres; strain gauges; temperature, relative humidity, and wind sensors; and FBGs (see Figure 1 and Table 2). Phases 1 and 2 sensors will be used for a decade of monitoring. Installation of these sensors is divided into three phases: Phases 1 and 2 were completed in January 2024 and June 2024, respectively, and Phase 3 is planned for the summer of 2025. The timing of these phases allows for a swift response to areas of immediate concern in Phase 1. Phase 2 provides a more global understanding of the