Collapse Fragility Assessment for Structures Under Multiple Earthquakes

Fragility analysis is crucial for seismic risk assessment. Fragility models of structures and infrastructures, nowadays, are more likely to focus on the as-built condition of the structure, neglecting the possibility that they could be subjected to multiple earthquakes sequences (including main shock-aftershock sequence) during their service life. However, considering that this last scenario has a high probability of occurring, in addition to the reality that some buildings’ performances could not satisfy the previous seismic design requirement anymore, it is important to include the effect of past earthquakes in fragility estimation of buildings. In this treatment, the degradation of construction material properties refering to a simplified structure such as the Single Degree Of Freedom (SDOF) system is applied to represent the damage caused by a past earthquake and new deformation capacities (response parameters) will also be obtained using three different approaches. Consequently new analyzes are conducted in order to estimate the fragility of the system already damaged by earthquakes. So in this way it’s possible to include the effect of past earthquakes and, in this specific case, as in the case of low rise RC structures, the new fragility curves could give a more accurate fragility estimate during its service life; this method can be useful to decisional processes after earthquake hits.