Creep failure of two historical masonry towers: analysis from material to structure

The collapse of several historical masonry towers has been attributed to gradually increasing mechanical damage, such as creep cracking which occurs under constant stress levels. This paper reviews theoretical, experimental and numerical methods for analysing compressive creep in historical masonry. The investigations focus on creep behaviour in ferruginous sandstone, as results are applied to understand the collapse of two historical towers in Belgium that were both constructed in local sandstone. At the level of the material, cracking, creep strains and acoustic emissions are studied in small-to-medium scale sandstone samples under dry and saturated conditions. Results indicate an acceleration of the degradation process when water absorption takes place during the secondary creep phase. At the structural level, numerical macro modelling is performed to investigate the effect of stress redistributions on creep behaviour of three-leaf masonry. Finally, experimental and numerical results are related to the collapse of two historical towers.