Impact of ground floor openings percentage on the dynamic response of typical Dutch URM cavity wall structures

Unreinforced masonry (URM) buildings with cavity walls, typically constituted by the assembly of a loadbearing inner leaf weakly coupled to an outer veneer with no structural functions, are widely present in a number of regions exposed to tectonic or induced seismicity, including the Groningen province (The Netherlands), which has lately experienced low-intensity ground shaking due to natural gas extraction. Recently, experimental evidence has shown that the lack of seismic details, and, above all, the presence of large ground floor openings, makes these structures particularly vulnerable towards horizontal actions. In this endeavour, advanced discrete element models, developed within the framework of the Applied Element Method (AEM), are employed to investigate numerically the impact of ground floor openings percentage on the dynamic behaviour of cavity wall systems representative of the typical Dutch terraced houses construction, namely low-rise residential URM buildings with rigid floor diaphragms and timber roof. Firstly, the model is validated through comparison with a shake-table test of a full-scale building specimen, tested up to near-collapse. Then, a comprehensive numerical study, which featured several combinations of ground-floor openings and the application of various acceleration time-histories up to complete collapse, is undertaken. The ensuing results allowed a comparison of the fragility associated with each of the considered openings layouts, showing how the presence of large ground floor openings may significantly increase the seismic vulnerability of typical URM Dutch terraced houses.