ED Sciences Physiques et de l'Ingénieur
Towards an optimal use of the FEM and the DEM for the structural assessment of Historical Monuments subjected to fire
by ALI BOUKHAM (I2M - Institut de Mécanique et d'Ingénierie de Bordeaux)
The defense will take place at 14h00 - amphi 3 A9 campus universitaire Peixotto 33400 Talence
in front of the jury composed of
- Stéphane MOREL - Professeur des universités - Université de Bordeaux - Directeur de these
- Cédric GIRY - Professeur des universités - EPF Engineering School - Rapporteur
- Jose TORERO CULLEN - Professor - University College London - Rapporteur
- Anne-Lise BEAUCOUR - Professeure des universités - CY Cergy Paris Université - Examinateur
- Maria Paola SANTISI-D'AVILA - Maîtresse de conférences - Université côte d'Azur - Examinateur
- Gianmarco DE FELICE - Professor - Roma Tre University - Examinateur
- Pierre PIMIENTA - Docteur - CSTB - Examinateur
This thesis is part of the ANR DEMMEFI project, focused on developing new diagnostic methodologies for the preservation of historic stone buildings. Although representing valuable heritage, masonry structures are vulnerable to fire risks, as highlighted by the incident on April 15 at Notre-Dame Cathedral in Paris. Due to their historical significance, demolishing these public buildings (ERP) after a fire is rarely considered, even in cases of structural concerns, unlike modern buildings. When classified as Historical Monuments (MH), restoration or reconstruction to the original state is required. However, the post-fire stability of these structures remains a critical issue, given the current lack of knowledge and tools to assess their structural condition. To address this challenge, a 3D thermomechanical modeling approach was developed and validated in this thesis using the LMGC90 computational code. At ambient temperature, a hybrid block based approach, combining finite elements and discrete elements, enabled (i) simulating damage within blocks through a model coupling damage and plasticity, and (ii) reproducing joint cracking using a cohesive zone model developed in this thesis. This model accounts for the nonlinear behavior of interfaces (damage and plasticity) as well as the linear elastic behavior of mortar joints. Validation of this modeling approach was performed by comparison with an experimental campaign on walls subjected to vertical loads and monotonic and cyclic shear. At high temperatures, the thermomechanical behavior of "mortar joint + block/mortar interface" assemblies was experimentally characterized through mechanical tests conducted at ambient and elevated temperatures, in both tension and shear/compression of these assemblies after cooling. Equivalent materials were selected to have physical properties similar to those used in Notre-Dame Cathedral. From a modeling perspective, the effect of thermal expansion of the blocks was incorporated through an irreversible, temperature-dependent thermal expansion coefficient. Additionally, the temperature-dependent evolution of the blocks' mechanical properties was also integrated. For the joints, temperature impact is modeled by introducing thermal damage. Validation of the one-way coupled thermomechanical model was conducted through comparison with an experimental campaign on a wall subjected to vertical load and standardized ISO834 fire exposure. The results obtained from this 3D thermomechanical modeling approach are promising: they accurately reproduce typical masonry failure mechanisms and local effects due to friction within joints. Thermal expansion, deflection, and severe cracking resulting from thermal stresses caused by high temperature gradients were precisely captured. Moving forward, the developed approach will be applied to simulate the fire impact on the choir vault of Notre-Dame Cathedral.