Timing Fragility Analysis of Natural Gas Distribution Stations under Seismic Action

As a critical hub in urban gas distribution networks, natural gas distribution stations consist of multiple functional systems and their subsystems. These systems exhibit distinct time-series failure characteristics under seismic action, yet existing research has not explored their temporal evolution or quantitative assessment. Therefore, this study proposes a research framework for evaluating the timing fragility of natural gas distribution stations. First, based on engineering case studies, the time-series failure sequences of functional systems within the station under earthquake conditions are constructed. By analyzing failure correlations and paths among subsystems, the pressure-regulating system is identified as the most critical functional system. Subsequently, a numerical model of the pressure-regulating system is developed based on an actual engineering case. Structural damage states and seismic intensity levels are defined, and the incremental dynamic analysis (IDA) method is employed to obtain a probabilistic seismic demand model. Through fragility analysis, the damage probabilities of the system under different peak ground accelerations (PGA) are derived, leading to the development of probabilistic fragility curves for the pressure-regulating system, which reflect the overall seismic capacity of the distribution station. The results indicate that a systematic analysis of the seismic event sequence of the gas distribution station yields the failure chronology of consequences for each functional system. Moreover, due to triggering the highest number of event sequences with the most severe consequences, the pressure-regulating system is determined to be the most critical system. Under the frequent occurrence of earthquakes and the action of design earthquakes, the probability of damage to the pipelines of natural gas distribution stations is relatively low. However, under the influence of rare earthquakes, the probability of severe damage to pipeline structures significantly increases, which may lead to large-scale leaks and subsequently result in a serious loss of system functionality. This framework quantitatively analyzes the time sequence of system failures and the extent of damage in critical systems. It provides essential data support and a theoretical basis for optimizing the seismic design of gas distribution stations and formulating protective measures under seismic action.