Fragility Curve Estimation

Fragility curve estimation produces a function that gives the probability that an asset reaches or exceeds a defined damage state as a function of a hazard intensity measure, such as peak ground acceleration or spectral acceleration. It is the central conditional-probability link in disaster risk assessment, sitting between hazard (how strong the shaking is) and loss (what the damage costs), and is almost always parameterized as a lognormal cumulative distribution defined by a median intensity and a logarithmic standard deviation. Tiziana Rossetto and Amr Elnashai's 2003 work derived empirical fragility and vulnerability functions for European reinforced-concrete buildings from large post-earthquake damage databases, while Jack Baker's 2015 paper formalized efficient maximum-likelihood fitting of fragility functions from dynamic structural analyses. The method spans empirical fitting to observed damage, analytical fitting to simulated response, and expert-based judgment when data are scarce. Its output, a small set of curves indexed by damage state, is the reusable vulnerability building block consumed by loss-estimation and catastrophe-modeling pipelines. Estimating these curves well is what makes downstream risk numbers credible rather than arbitrary.