A Seismic Fragility Assessment Method for Urban Function Spatial Units: A Case Study of Xuzhou City

Cities that experience earthquake disasters face a lot of uncertainties and unsustainability resulting from the fragility of their infrastructure, which should be considered in engineering. This study proposes a seismic fragility assessment framework for urban functional spatial units in order to improve the traditional structural fragility assessment criteria that are currently applied in urban planning. First, appropriate spatial units are classified for the study area, the functional categories of the study area are determined using urban Point of Interest (POI) data, and the functional proportion of the spatial units is calculated. Secondly, considering the classification of different seismic fortification levels represented by different construction ages, and considering the possible building forms and HAZUS’s classification system of building structures in order to establish the correlation between building functions and building structures, the methods of a field survey and a questionnaire survey are adopted to match the functions with the most likely building structures. After this, based on the assumption of the lognormal distribution of ground motion intensity, a mixed method is adopted to calculate the mean value μ ¯ for the fragility of functional space units. The Monte Carlo method is then used to discretize the data and statistically obtain the standard deviation β ¯ for the fragility of functional space units, and the fragility curve is then fitted. A district in Xuzhou City, China, was used as a case study to verify this assessment framework. The results showed that: (1) the fragility of functional space units was greatly affected by the proportion of defense standards in different periods in the unit, which reflected the average level of fragility within the unit. (2) The unit loss index of units built after 2001 with a proportion of less than 50% is basically above the average loss level of the study area. (3) The simulated damage ratio of the assessment results under the three levels, namely frequent earthquake, fortified earthquake and rare earthquake, is consistent with the previously experienced earthquake damage. The paper concludes that it is helpful to design and utilize seismic fragility predicting formulas and technologies at the functional spatial unit level for urban planning, which is meaningful for the formulation of planning strategies, reducing risks to infrastructure and delivering sustainable development.