Modelling fire-induced damage in limestone masonry walls using thermomechanical finite and discrete element method approaches

Fire severely affects the structural integrity of masonry structures, particularly in heritage buildings where post-fire assessment is essential for conservation and restoration efforts. While the fire behaviour of concrete has been widely studied, the thermomechanical response of masonry walls remains less documented. This study explores the behaviour of limestone masonry walls from the literature, subjected to fire and vertical compression, using Finite Element Method and hybrid finite/discrete simulations. These numerical models help analyse deformation mechanisms, crack propagation, and load-bearing capacity after fire exposure. Results show that out-of-plane displacements are highly dependent on boundary conditions and mechanical constraints. Thermal expansion leads to vertical cracking through both stones and joints, with cracks typically initiating near the lateral edges due to high tensile stresses. Post-fire residual behaviour indicates a reduction in compressive strength of about 45%, aligning with experimental data. The stress-displacement curve of the heated wall reveals a complex failure process marked by multiple load drops, associated with crack closure and shear-induced cracking. In contrast, the unheated wall fails primarily through diagonal shear cracks, forming compression struts and confinement cones that influence its load-bearing response. These findings underline the importance of accounting for altered failure mechanisms when assessing and reinforcing fire-damaged masonry. • Numerical models assess post-fire masonry wall behaviour. • Fire exposure reduces compressive strength by 45%, matching experimental findings. • Thermal expansion induces vertical cracks and shear cracks dominate unheated walls. • Heated walls show stiffness loss of 98%.