Static and Dynamic Monitoring of the Notre Dame de Paris Cathedral

Abstract

During the fire which took place on 15th April 2019, the Cathedral of Notre Dame de Paris underwent extensive structural damages: most of the roof was destroyed, part of the stone vaulted ceiling collapsed, and the wooden framework of the north tower was partially burned. After the fire, a list of actions was carried on in order to secure the remaining structure, prevent any further damage and start the rehabilitation. Very early on, a monitoring system was used to assist the project manager in these tasks. With the progress of site works, the monitoring system was updated to provide more insightful information. The present paper focuses on the monitoring system deployed on the towers and the stone vaulted ceiling with the objective to produce a first assessment of the current state and follow the evolution during the reconstruction phase. The monitoring campaign was carried out from December 2020 to December 2021 with two distinct sets of sensors. The first objective was to characterize the current state and identify the dynamic behavior of the structure, for that purpose 48 directional accelerometers were installed on the two towers and the two vaults lane. Acceleration measurements and analytical methods lead to the identification of the fundamental modes of these structural elements. In a second time, to follow the evolution of the vaults, 56 inclinometers were positioned on the outer side of the vaults, constituting 15 inclinometer measuring chains. Set up to transmit data continuously with a 10 min frequency, measurements allow to notify settlements or uprisings and correlate these evolutions with external factors (weather conditions or rehabilitation works).