Comparative Seismic Assessment and Strengthening of Two Storey URM Dwellings in Kruja Insights from Four Case Studies

This paper examines four two-storey unreinforced masonry (URM) houses in Kruja, Albania, all of which were heavily damaged during the 26 November 2019 earthquake. Although the buildings were constructed at different times and by different owners, they share similar materials, wall configurations and construction practices. Because of this, they also show comparable weak points when exposed to strong seismic shaking. The study combines field observations, crack pattern documentation, and nonlinear static (pushover) analysis to understand how these dwellings behaved during the earthquake and why their performance was inadequate. Across all four houses, the most common issues include poor-quality mortar, a lack of proper connections between walls and floor slabs, discontinuous diaphragms, and the absence of any confinement elements. These weaknesses contributed to diagonal cracking, corner separation, partial out-of-plane failures, and significant permanent deformation. Based on the similarities identified in the case studies, a single strengthening concept was developed for the group. The proposed retrofit, which relies mainly on perimeter reinforced-concrete columns, diaphragm improvements, and local wall rehabilitation, aims to address the recurring problems found in this type of construction. The results indicate that this unified approach can substantially increase lateral strength and deformation capacity, particularly in the transverse direction where the original buildings performed poorly. By treating these four dwellings as part of the same typology, the study shows that a consistent and replicable retrofit strategy can be applied to a wider stock of URM houses with similar characteristics in the Kruja region.