Damage Accumulation in Unreinforced Masonry Due to Seismic Loading

Masonry has low cohesive strength and is susceptible to the brittle failure, when subjected to induced tensile stresses. It fails due to lateral tensile stresses even when masonry prisms are tested in uni-axial static compression and the stress-strain curve remains almost linear up to failure. Although masonry normally resists compressive forces, under lateral in-plane cyclic loads some parts of the volume of masonry walls are subjected to tensile stresses, which are sufficient to cause localized brittle failure. However, localized brittle failure does not always lead to a collapse of the masonry wall. The wall after cracking often retains some capacity to deform under the applied load (ductility). This phenomenon shows that masonry is intrinsically neither brittle nor a ductile material. The phenomenological characterization of failure for materials such as masonry is conditional and depends on: (a) the state of stress, (b) the strain rate or loading rate, (c) the temperature, and (d) the amount of accumulated micro-structural damage. Some of these issues for masonry have been addressed; others have not been adequately addressed to this day. This paper reports results of the experimental study on accumulation of the microstructural damage in masonry under seismic loading.