Fragility Functions for Reinforced Concrete Structures Based on Multiscale Approach for Earthquake Damage Criteria

For seismic risk analysis, reliable predictions and estimations of earthquake damage and seismic behaviour of buildings are essential. A common method is the use of fragility curves. In this paper, fragility functions are developed based on various numerical damage criteria for five defined damage grades, from slight to destruction. The proposed new multiscale approach establishes a correlation between observed damage patterns due to foreign earthquakes and the seismic response of the building using thresholds for material-specific and global characteristics. This approach takes into account various possible damage patterns on different scales more comprehensively than the well-known approach of displacement criteria. Moreover, the approach is universal and adaptable for building classes as well as region-specific material and system characteristics. Several damage criteria with their defined limit values are assigned to the five proposed damage grades, whereby quantity and distribution of the exceeded criteria are relevant, since the first occurrence does not always lead to damage. With the new approach, damages that are not evident in the pushover curve in terms of strength degradation can be detected and taken into account for the damage thresholds. The derived displacement values associated with the damage levels are the basis for developing fragility functions. The results—damage criteria, pushover curves with damage grades, capacity curves as well as fragility functions and parameters—are presented for a four-storey reinforced concrete frame building. These results are discussed and validated with data from the literature. Comparisons to existing fragility functions in the literature show that our developed fragility functions are mostly located in the middle range, graphically as well as for the curve parameters. This specific example was chosen to present our multiscale approach, but for general building classes, numerous simulations with varying characteristics are essential and result in a higher standard deviation of the final fragility curves