# Seismic Vulnerability Assessment of Historical Masonry Buildings in Croatian Coastal Area
## 4 Discussion  
A seismic vulnerability assessment approach based on the calculation of the seismic vulnerability indexes of the buildings was applied to the historical center of Kastel Kambulovac, a Croatian city settlement placed along the coastal Dalmatian area. The approach consisted of the following stages:  
* Identification of architectural, structural, and material characteristics of the buildings through the investigation of historical and archival documentation, literature, visual inspection, and thermographic imaging;
* Characterization of the soil type through a geophysical survey;
* Calculation of seismic vulnerability indexes for all buildings in the area;
* Calculation of the peak ground accelerations for early damage and collapse states of the buildings through non-linear static (pushover) analysis of representative buildings;
* Development of a new damage-vulnerability-peak ground acceleration relationship, which estimates the damage of the buildings under specific seismic action;
* Risk analysis in terms of seismic damage;
* Demonstration of seismic vulnerability and seismic risk using seismic vulnerability index maps and damage index maps. Two main results were obtained from the investigation. The first one is the proposal of a methodology that allows the damage assessment of the building stock on a territorial scale for a certain seismic action expressed in terms of peak ground acceleration. This result was achieved by combining an expeditious empirical method based on vulnerability index calculation and detailed non-linear pushover analyses. The second result is the evaluation of vulnerability and risk in terms of the damage to stone masonry buildings in a typical historical city center located along the Croatian part of the Adriatic coast. Furthermore, the relevant findings of this analysis are detailed as follows. The obtained vulnerability indexes showed that most buildings (72.4%) belonged to medium-high (45 < I_v < 60) and high (I_v > 60) vulnerability classes. The reasons for such a high vulnerability are that these buildings cannot effectively bear the seismic load due to the fact that they were constructed with unconfined stone masonry walls, flexible wooden floors and roofs, and poor connections between the walls and floors. Additionally, irregularities in the plan and elevation, age, and the degree of general preservation of the building contribute to their high vulnerability. It has also been shown that reconstructed buildings have significantly lower vulnerability indexes. For example, one of the reconstructed buildings has a vulnerability index of 11.1. The non-linear static (pushover) analysis carried out on 11 typical buildings indicated the low capacity of the buildings in terms of collapse peak ground acceleration (between  
Figure 20: Map of the damage index for PGA = 0.22 g and a return period T = 475 years. 0.078 g and 0.183 g), as well as low accelerations of early damage states (between 0.029 g and 0.103 g). Generally, numerical predictions of the collapse acceleration by means of non-linear static analyses showed that no building meets the seismic requirement equal to a\({}_{\text{g}}\) = 0.22 g for T = 475 years in either direction. Moreover, a significant number of buildings achieved collapse at accelerations that are lower than the demand acceleration of a\({}_{\text{g}}\) = 0.11 g for a return period T = 95 years. These evaluations rely on the analysis of the global structural response. Evaluation of the local failure mechanisms for the Public Library building and a few other buildings showed that the lowest critical acceleration was obtained for the global response. Therefore, the yield and collapse acceleration and the associated damage for all buildings were estimated based on the global response of the structure. The motivation for this is that, considering that our final aim is a large-scale vulnerability assessment of the area, a global structural analysis is acceptable.