Experimental Evaluation of Unreinforced Brick Masonry Mechanical Properties by the Flat-Jack Method - an Extensive Campaign in Croatia

Several strong earthquakes hit Croatia in 2020. Such earthquakes, after a long absence of strong seismic activities in the country, in combination with material degradation, lack of maintenance and structures that were built before modern seismic regulations, culminated with extensive damage to the existing building stock. Existing unreinforced masonry (URM) structures are quite vulnerable to earthquakes, largely due to a lack of connectivity between structural parts. The numerous damaged buildings emphasize the need to preserve, restore and strengthen URM structures, especially the ones under heritage protection. The main focus of this paper is on the first step of the assessment process, which is to determine the mechanical properties of masonry. For that purpose, the flat-jack method is used. Through stress transfer from a flat-jack to the masonry useful information can be obtained. The results of the extensive post-earthquake flat-jack tests (single, double and shear) on 17 case studies in Croatia are presented. The results are critically discussed and the mechanical properties of brick masonry in Mediterranean Europe are presented. The goal of the present work is to increase the confidence level in the definition of mechanical properties and, thus, to favorably influence the necessary reconstruction.