Published Tue 26th Mar 2024
The sight of flames towering above the iconic gothic roof and spire of the Notre Dame d’Paris shocked the world in April 2019. Despite the efforts of 400 firefighters it took 8 hours to bring the fire under control. By that time the massive blaze had devastated the roof and spire and caused damage that threatened the structural integrity of the building. When the French president declared just hours after the fire that the cathedral would be “more beautiful than ever” within five years it was not hard to find words of doubt amongst the world’s building conservation community. But with the announcement of a planned re-opening date of December 8th 2024 it seems that the ambitious programme is still pretty much on track.
In this article we look back to the immediate aftermath of the fire and the big part played by some very small wireless sensors.
Challenges Faced by Repair Teams Post-Fire
In the days following the fire, repair teams tasked with restoring the fifteenth century vaulted stone roof of Notre Dame cathedral faced many challenges. Amongst them was the need to ensure that the remaining structure was not further damaged by the recovery and restoration works.
The first step for Notre-Dame’s roof and spire reconstruction was the safety phase, which started in the summer of 2019 and lasted until November 2020. From the start of the project, structural health monitoring monitoring was needed for the weakened areas of the cathedral to ensure the safety of the 60 to 70 workers on site each day. As the work progressed, scaffolding was built around the cathedral to restore the spire, protective coverings were installed above the vaults, gargoyles were wrapped, and the flying buttresses were reinforced.
In these conditions, the use of wired sensors quickly became impractical. A new technology had to be deployed to provide reliable data in the crowded space of the church.
Innovative Solution: Wireless Remote Monitoring Technology
NanoPlus sensors provided an easy to install and reliable solution where classic wired and optical solutions were not a viable option. The compact design and triaxial capability of the NanoPlus made them the perfect technology for this challenging setup. A total of 70 Senceive NanoPlus tilt sensors were installed on the extrados of the vault. Weighing just 110 g and measuring 58 mm in height, the tilt sensors could be safely and easily fitted to the structure by rope access technicians. The team fixed the sensors using a bespoke lime mortar that would not damage the ancient stones.
Ensuring Structural Integrity: Real-time Data Collection and Analysis
The soft-touch installation approach was completed in just a few days and the precise movement data was shared with stakeholders planning, and then carrying out the repair works. Cumulative calculations allowed the project team to display the convergence of each arch in the nave and the transept wings in data visualisation software. Their stability was compared to the undamaged external walls as a reference.
Engineers were able to proceed with greater confidence armed with updates every few minutes and with the knowledge that the system would deliver automated alerts in the event of any movements outside pre-set thresholds.
Before and during the critical project, Senceive’s technical and customer services teams provided technical expertise so specialists so they could confidently integrate the wireless sensors into their overall monitoring scheme. The monitoring programme continued through 2020 despite the COVID-19 pandemic with remote support provided for the site team.
Utilising Wireless Monitoring in Restoration Projects
The Senceive wireless remote monitoring technology used at Notre Dame can play a key role wherever there is a need to safeguard valuable buildings and structures after events such as fire and flooding and during the delicate restoration activity that follows. The project demonstrated the advantages of Senceive wireless monitoring technology for this type of emergency response monitoring application. It was quick and easy to install immediately after the fire and it delivered data within minutes of installation. The NanoPlus tilt nodes could be mounted at any orientation to virtually any part of the structure and the sensors could be moved around the building to provide data wherever it was most-needed in the following months.
