Chapter 3
Figure 3.5 Vulnerability ellipse determination, Step 3 (Basaglia 2015).
The following step consists in considering a random direction for the expected earthquake (see Figure 3.6). A vulnerability index is obtained, which depends on the angle of the earthquake direction. This procedure will be applied for angles from 0º to 360º direction in order to provide an overall view of the city vulnerability.
Figure 3.6 Vulnerability ellipse determination, Step 4 (Basaglia 2015).
By mapping all the vulnerability ellipses, it is possible to plot an overview on the urban settlement’s global response to a seismic event. There could be areas in fact where the ellipses’ sizes are significantly different along different directions, i.e. directions with higher/lesser vulnerability. Having all the vulnerability ellipses it is possible determine the worst seismic scenario. At the end of this stage all the vulnerability indexes are defined. However, there are some considerations to do for masonry buildings. The GNDT method, which is chosen to calculate the vulnerability index shown before, is developed for isolated masonry buildings. However, most of them are usually built in ‘aggregates’ in the urban centres. Therefore, masonry buildings collaborate each other and the possible interaction between adjacent buildings should be considered. Therefore, a seismic analysis of such structural complexes has to take into account the possible interaction between adjacent buildings. 79