Abstract: An index in terms of vulnerability index is proposed to assess structural damage due to earthquake based on conventional seismic fragility analysis. The methodology of assessing earthquake consequences at the regional scale using the damage index is adopted and the numerical expectation of the damage index is calculated to quantify the vulnerability index of an individual building, where the damage state probability is derived through analytical seismic fragility analysis. Two groups of RC frames of 8- and 10-story height are considered as study cases, each of which includes frames designed to various seismic fortification levels. Seismic fragility curves, damage state probability curves, vulnerability index curves and vulnerability indices at frequent earthquake (FE), design-based earthquake (DBE) and maximum consider earthquake (MCE) intensities are computed separately. The results show that the RC frames designed according to the current Chinese codes can basically satisfy the performance requirements of "no damage under FE", "no unrepairable damage under DBE" and "no collapse under MCE". At MCE intensities, the reference frames illustrate good performance of controlling the occurrence of severe damages. Structural resistance against earthquake is enhanced due to the increase of seismic fortification level; however the conditional seismic vulnerability indices upon FE, DBE and MCE are increased accordingly.