ABSTRACT
Seismic events in the northern part of the Netherlands over the past few decades have led to an intense study on the seismic performance of unreinforced masonry structures, ubiquitous in the region. Studies have focused on the safety aspect characterized by the near collapse behavior of the structures, but also on the aesthetic and functional aspect denoted serviceability or light damage state. The latter, triggered by multiple small seismic events until now, has led to economic losses and societal unrest. Experimental studies, detailed in this paper, have looked at the initiation and propagation of visible cracks in clay and calcium-silicate unreinforced masonry specimens. Both materials, replicating samples from existing structures, were surveyed with high-resolution Digital Image Correlation while being subjected to repetitive loading causing horizontal, vertical and diagonal stair-case cracks. Small and full-scale experiments evidenced a difference in behavior between clay and calcium-silicate masonry: where the former only developed cracks along the mortar joints, the latter also exhibited brick-splitting cracks. This mechanism proved extremely brittle and led to a reduced capacity of energy release for the calcium-silicate specimens during cyclic loading, and to their sudden failure. The higher bond-strength between the silicate brick and mortar coupled with the lower strength of the bricks themselves and the overall higher stiffness of the calcium-silicate masonry, in the case of the replicated masonry specific to this study, are suspected of being responsible for the brick-splitting failures. These brittle failures, occurring at low drift levels, set calcium-silicate masonry as more vulnerable than comparable clay-brick masonry in regards to light damage, leading to wider and larger cracks.
