High-resolution monitoring of the initial development of cracks in experimental masonry shear walls and their reproduction in finite element models

Induced seismicity in the north of the Netherlands has recently exposed unprepared, unreinforced masonry structures to considerable earthquake hazard. While the ultimate-limit state capacity of the structures is vital to assess the individual's risk, their behaviour during more frequent, lighter earthquakes leading to 'light damage', has shown to be strongly linked to economical losses and societal unrest. To study the effect of these repeated light earthquakes, the behaviour of masonry structures, typical of the region, needs to be investigated when subjected to multiple small cycles. In particular, insight into the potential aggravation of the light damage is sought. Hence, shear walls of replicated clay brick masonry have been tested in the laboratory and exposed to a high number of low in-plane drift cycles. The experiments show, under inspection with high-resolution Digital Image Correlation, how stair-case, diagonal cracks initially distribute in multiple cracks running in joints at the centre of the walls, but later localise into a single, visible, wider crack. The tests are used to establish an interval over which light damage can be expected for these types of walls. Furthermore, this initial distribution of strains in 'bands' and subsequent localisation, previously observed only with computational finite element models and which could not be verified experimentally, is compared and reproduced with improved models both at the composite continuum scale (macro-model) and the brick-to-brick micro scale. The models are calibrated based on the quasi-static, cyclic experimental results and later used for extrapolation in dynamic nonlinear settings to assess the influence of natural ground motion excitations.