# Destructive M6.2 Petrinja Earthquake (Croatia) in 2020--Preliminary Multidisciplinary Research
## 6 Earthquake Performance of Buildings
In addition, according to the current probabilistic seismic hazard map, wherein a _PGA_ value of 0.16 g is assigned for that county, the contemporary code provisions EN1998-1:2004 [34] do not allow unreinforced masonry construction without vertical confining elements for \"simple masonry buildings\" (see Tables S1 and S2 in the Supplementary Materials). According to further examination of the building code requirements from 1965 to 1981 [37] and from 1982 to 1998 [38], the consideration of horizontal confining elements in masonry construction was mandatory. However, vertical confining elements were mandatory only in the case of IX (violent) MCS intensity designated areas, e.g., the Zagreb area. Even so, masonry buildings were constructed from the start (or with post-war retrofitting) in Sisak-Moslavina County with the implementation of vertical confining elements (at least in the building's corners), contrary to the building code requirements, which enabled them to successfully endure earthquakes, thereby mitigating other potential structural flaws. The cost of vertical confining element construction is less than 3% of the costs of the whole house (e.g., 150,000 EUR), which is far less than the earthquake damage restoration costs. The described problems are related to the relationship between the education of construction workers, construction company managers and code enforcement staff and the earthquake performance of structures. Strategies should be implemented to improve the education of, and existing training methods for, construction workers and building inspectors. The M5 foreshock with a _PGA_ value of 0.05 g, which occurred at almost the same location on 28 December 2020, caused damage of grades that spanned from Grade 1 (DG 1) to Grade 3 (DG 3) to vulnerability class B building stock, while buildings that belonged to vulnerability classes C, D and E sustained Grade (DG 1) damage or no damage at all. The M5.3 earthquake that struck the capital city of Zagreb and its surroundings on 22 March 2020 [51] caused Grade 4 (DG 4) to Grade 5 (DG 5) damage to the old city centre three- to five-storey unreinforced masonry buildings, which dated from the Austro-Hungarian monarchy to 1920 (vulnerability class B [43]). The prevalence of Grade 4 (DG 4) to Grade (DG 5) damage to vulnerability class B buildings was also evident in the aftermath of the M6.4 2019 Durres, Albania earthquake, which had a _PGA_ value of 0.19 g [52]. However, buildings that were built in compliance with contemporary codes such as masonry infilled RC frames (vulnerability classes C and D [43]) experienced Grade 1 (DG 1) and Grade 2 (DG 2) damage to RC frame structures but not Grade 4 (DG 4) or Grade 5 (DG 5) damage, namely very heavy damage or collapse, respectively, of masonry infill walls (prevailing out-of-plane damage). The M5.3 202 Zagreb earthquake did not cause damage to RCframes but caused occasional Grade 1 (DG 1) damage, namely negligible to slight damage to masonry infill walls. The M6.2 Petrinja earthquake caused Grade 1 (DG 2) and Grade 2 (DG 2) damage, namely negligible to slight and moderate damage, respectively, to the masonry infill walls. The prevailing failure mechanisms of masonry construction that experienced Grade 4 (DG 4) and Grade 5 (DG 5) damage were diagonal tension cracking and bed-joint sliding in accordance with FEMA306 guidelines [53]. By comparing them to the period-building relationship of \(T=0.016H\), as presented in [51], these periods correspond to family houses and 3- to 4-storey (B1) and 4- to 15-storey buildings (C1) in the city of Zagreb and to 1- to 3-storey buildings in Sisak-Moslavina County. Buildings of special or outstanding historical or cultural heritage significance or value, such as St. Nikola church and St Vid's Roman Catholic parish in the village of Zazina, Lekenik municipality (17 km from Petrinja), which were built in the late 18 th century, mostly collapsed or became unserviceable during the earthquake.