# Destructive M6.2 Petrinja Earthquake (Croatia) in 2020--Preliminary Multidisciplinary Research
## 6 Earthquake Performance of Buildings  
In the design of earthquake-resistant buildings with regard to the peak ground acceleration _PGA_, in accordance with the official probabilistic seismic hazard map for the Republic of Croatia for a return period of 475 years, the strong ground motion that is designated for Sisak-Moslavina County should not exceed a _PGA\({}_{ROCK}\)_ of 0.16 g [32]. However, the recent M6.2 event exerted ground motion with a _PGA\({}_{ROCK}\)_ of approximately 0.3 g [33], thereby exceeding this limit by approximately 0.15 g and placing the buildings in the higher category of earthquake demand grade in compliance with building code EN1998-1:2004 [34] requirements (including [35; 36] provisions). The highest historical intensity occurred in the county in 1999, and it was estimated as VIII MCS scale. In addition, a question arises regarding the vulnerability of buildings that were constructed prior to the implementation of contemporary building code EN1998-1:2004 [34] in 2013, which can be divided in principle according to the periods of development of building code regulations (until 1964, from 1965 to 1981 [37], from 1982 to 1998 [38] and from 1998 to 2012 [39; 40; 41]). The update of the building codes was related to consequences of the 1963 Skopje, North Macedonia and 1979 Montenegro earthquakes (the first two earthquake code eras) and the establishment of the Eurocodes. According to the Disaster Risk Assessment for the Republic of Croatia [42], buildings that were built before 1964 (pre-earthquake code era) were not designed for earthquake resistance at all, while in later periods the values of horizontal accelerations or the corresponding calculated horizontal force, depending on the observed location, were much lower. As discussed in [42], buildings' earthquake resistance for the corresponding periods of construction, building regulations periods and vulnerability classes with respect to the EMS-98 scale [43] (unreinforced masonry with timber floors, namely class B; unreinforced masonry with reinforced concrete (RC) floors and horizontal confining elements, namely class C; confined masonry, namely class D; RC frame ductility class low (DCL), ductility class medium (DCM) and ductility class high (DCH), namely classes C, D and E, respectively) could be estimated as follows:  
Buildings that were built before 1945 possessed approximately 5% earthquake resistance, as required by [34]. They were built as unreinforced masonry buildings with timber floors and without considerations of earthquake action (no building codes). According to the type of structure, they belonged to vulnerability class B in compliance with EMS-98 [43]:  
Buildings that were built from 1946 to 1964 were approximately 10% earthquake resistant, as required by [34]. They were unreinforced masonry buildings with predominantly reinforced concrete slabs without confining elements, which ultimately resulted in poor earthquake performance. An order on temporary technical regulations for building loads was introduced in the stated time period [42]. Such buildings also belonged to vulnerability class B in compliance with the EMS-98 scale [43]:  
Buildings that were built from 1965 to 1981, in the aftermath of the M6.9 1963 Skopje, North Macedonia earthquake, were constructed under the Ordinance on Temporary Technical Regulations for Construction in Seismic Areas [37], which introduced the first building codes that considered earthquake action, including the earthquake hazard map from 1964. These buildings were designed and constructed with reinforced concrete or masonry with vertical and horizontal confining elements. However, they had low earthquake resistance of up to 30-50%, as required by [34].