Notre Dame Cathedral - Restoration Works

The Notre Dame Cathedral – a treasure of French Gothic architecture and one of the most famous symbols of Paris, was engulfed in flames on 15th April 2019. By the time the fire was extinguished, the building’s spire had collapsed, most of its roof had been destroyed, and its upper walls and parts of the vaults severely damaged.

After the devastating disaster, French president Emmanuel Macron vowed to rebuild the cathedral and complete many of the repairs before the city hosts the 2024 Summer Olympics.

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 experts, OSMOS Group, was selected to monitor 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.
 

The OSMOS Group and Senceive project teams combined their expertise and selected Senceive’s FlatMesh™ platform to provide a reliable mesh network of connected sensor nodes. Built around the 2.4 GHz network, the FlatMesh™ platform allows data to flow seamlessly around physical obstructions, to self-heal if elements are damaged, and provides accurate, high-frequency reporting. In addition to the standard cellular FlatMesh™ Gateway, the team installed a second backup Gateway so the flow of data would be uninterrupted in the unlikely event of a Gateway failure.

A total of 70 NanoPlus tilt sensors were mounted on the extrados of the vault. Weighing just 110 g and measuring 45 mm in height, the sensors could be safely and easily fitted to the recently stabilised structure by rope access technicians. The team used flexible Senceive FF-T2P30 mounting plates, which provided the flexibility to fix the sensors with a bespoke lime mortar that would not damage the ancient stones.

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 non-damaged outside walls as a reference.

The 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.

Before and during this critical project, Senceive’s technical and customer services teams provided technical expertise to OSMOS Group's design and operation teams so they could confidently integrate the wireless sensors into their overall monitoring scheme. Despite the COVID-19 pandemic, remote support was provided to guarantee the success of this prestigious project.