System-Level Fragility Assessment Under Interdependent Spatial Demand and Structural Capacity

Abstract eng:
Seismic risk assessment is more challenging for infrastructure systems than for single, non-interacting components, especially when network-level interaction is included in the analysis. Accounting for the interdependencies of the spatially distributed demands and of the capacity does significantly affect reliability and risk assessment. The spatial distribution of the ground motion intensity is one of the main sources of dependences among the components’ response, and models for predicting the correlation of the most commonly used intensity measures (peak ground acceleration, spectral acceleration at the fundamental period of vibration, spectral acceleration at multiple periods, etc.) at different locations are available in literature. However, when these models are applied to system-level analysis, it is still to be determined if the capacity of different components (modelled by the fragility function) should be considered as dependent or independent. Dependence can derive from two sources: on one hand, epistemic uncertainty can be common across many components, on the other, the seismic intensity may be just an incomplete summary of the seismic event, not able to capture relevant features of the demand. Because of this, an assessment of the response that only accounts for the interdependence in the seismic intensity may underestimate the actual dependence. To investigate such a loss of information about the correlation between structural responses, we perform non-linear analyses of a RC bridge, using sets of ground motions recorded during the same event at two different locations, and compare actual and predicted interdependence. From the simulations’ results, we investigate the accuracy of system-level analysis.

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