Preliminary Observations on Historical Castle Trakošćan (Croatia) Performance under Recent ML ≥ 5.5 Earthquakes

Snježana Markušić,Davor Stanko,Radmila Šalić,Domagoj Trajber,Davorin Penava

doi:10.3390/geosciences11110461

Snježana Markušić, Davor Stanko + Show 3 more

Open Access

https://doi.org/10.3390/geosciences11110461

Copy DOI

Abstract

Trakošćan Castle, built on a rocky peak in the late 13th century, is a cultural heritage site protected as a historical entity by the Republic of Croatia. The Castle is constructed as a highly irregular masonry structure with timber or shallow masonry arches, vaults or dome floors. It was substantially renewed, upgraded and partially retrofitted from the 16th century until the year 2000. The M5.5 (VIII EMS) and M6.2 (VIII-IX EMS) earthquakes, which struck the city of Zagreb on 22 March 2020 and the Pokupsko-Petrinja area on 29 December 2020, strongly shook the Castle’s structure. Earthquake damage was observed and assessed by visual inspection accompanied by ambient vibration measurements. The slight cracks that appeared on masonry arches were found to be critically positioned, and can likely lead to the arches’ collapse if their spreading is not prevented. Ambient vibration measurements, which were compared to pre-earthquake ones, revealed the decrease in the fundamental frequencies of the Castle’s central tower unit and the second floor, thus possibly indicating the loss of structural stiffness as a consequence of the earthquake damage.

Highlights

Trakošcan Castle is protected as a cultural heritage site and an important historical entity by the Republic of Croatia (Figure 1)
This paper presents initial steps/analyses that were taken towards assessing Trakošcan Castle’s seismic hazard and vulnerability
Dinetgailiend stehisimsicphaapzaerrd, aintaslyhsoisuld be mentioned that wiitlsl bseepiesrmforimc ehdaizncalurddinagnpdrobvaubillnisetircaabndilistcyenawriiol-lbabseedfaunratlyhseisraes vwaellluaasttehde dien- detail in the frame of tseeoremnngiinnoaotiirnodngeroCtfolrococoaralrtesiciattelnyreeSsvpcaoliuneasntee.cFtehuerFtgholeourbnaelxdtseeanitssimiovienc 3vDRulennesornea-ablirinlciethayroPsftatrhtoiecjebaucnitaldly(iIsnPigs,i2is.e0f.o,2rie0ts--02-3531): Seismic risk staruscsteusraslmpeernfotrmoafnccue.ltural heritage buildings in Croatia (SeisRICHerCRO)

Summary

Introduction

Trakošcan Castle is protected as a cultural heritage site and an important historical entity by the Republic of Croatia (Figure 1). As observed during the Petrinja M6.2 earthquake, and higher accelerations (e.g., local site effects in the Trakošcan area), combined with the lack of ductility in historical buildings, may play a significant role in collapse or heavy damage, if the frequency content of given input motions is similar to the fundamental frequency of the structure itself. This study, together with previous ones of the Trakošcan area [13,14], is the basis for future studies of the Castle’s seismic performance and protection for the purpose of ret-rofitting to withstand future earthquakes. This requires careful interpretation by the use of theoretical analysis and empirical data. Further extensive 3D non-linear static analysis is foreseen in order to correctly evaluate the seismic vulnerability of the building, i.e., its structural performances

Seismicity of the Wider Trakošcan Area

Ambient Vibration Measurements

Discussion and Conclusions