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.