Abstract: The authors investigate the seismic fragility of typical civil defense engineering structures built in soft soils. A nonlinear dynamic analysis model of the soil-civil defense engineering structure system is developed using the ABAQUS finite element platform. Numerical simulations are conducted to determine the most appropriate intensity measure for seismic fragility analysis, taking into account the nonlinear characteristics of the soil and the uncertainty of input ground motion. Subsequently, seismic fragility curves for typical civil defense engineering structures in soft soils are established. The findings indicate that: (1) Peak ground acceleration is the most effective and practical intensity measure for the seismic fragility analysis of civil defense engineering structures. (2) The seismic fragility of these structures increases with softer soil conditions. (3) Civil defense engineering structures in soft soils are highly likely to suffer extensive damage during earthquakes, with the exceedance probability for each damage state approaching 100% as seismic intensity increases.

Key words: civil defense engineering, soft soils, seismic fragility analysis, intensity measure