Quantitative Assessment And Improvement Of Seismic Resilience For The Urban Gas Network

The destruction or function loss of the urban gas network under the earthquake disaster will have adverse impact on urban safety,economy,production and so on.With the development of the concept of seismic resilience,the research on earthquake engineering of gas network has been extended to the overall focus on seismic performance and the process of restoration and reconstruction.There are few researches on quantitative evaluation and improvement of seismic resilience for gas network in China,relevant methods still need to be improved.Therefore,from the perspective of the network system,this paper fully considers the various uncertain factors and external constraints in the earthquake resistance and disaster relief of the gas network,and proposes a seismic resilience quantitative evaluation process and a seismic resilience improvement method for the urban gas network.The main contents of this paper are as follows:(1)A process of seismic connectivity fragility analysis based on Monte Carlo simulation is proposed.Firstly,the input ground motion intensity measurements of each site of the gas network were determined based on the ground motion prediction equation(GMPE)conditioned on the given target magnitude.The distribution of random residual was simulated by normal distribution sampling to represent the uncertainty of ground motion.This process was repeated in each round of Monte Carlo simulation to determine the failure probability of each element in the gas network system.Then the loss index of connectivity was determined by the number of blocked nodes in the gas network after the earthquake.Finally,the loss index exceedance probability and the seismic connectivity fragility curve under multiple magnitudes were obtained.The gas network of a city in North China was taken as an example to evaluate the seismic connectivity fragility performance based on the proposed method,and much concern was focused on the influence of uncertainty in the ground motion prediction equation.The calculation results show that the uncertainty of ground motion has a weakening effect in evaluating the seismic capacity of urban gas network,and its impact on the results cannot be ignored.(2)A quantitative assessment framework for three-dimensional seismic resilience of urban gas network considering the uncertainties of multiple links is proposed.Firstly,the destroyed state of gas network after earthquake is calculated based on Monte Carlo simulation which connects the process of seismic connectivity fragility.Then the real-time repair process of the gas network is obtained by randomly allocating the repair resource under each simulated damage condition and the performance recovery curve in three dimensions is given.Repeating the above steps N times,the expectation for the indicators of seismic resilience and the probability distribution of the recovery time for different performance levels are obtained.Taking a northern city of China as an example,the whole procedure was applied to assess the seismic resilience of a gas network system.The results show that the post-earthquake performance of the gas network in three dimensions roughly follows the normal distribution,and the performance recovery time for 75%,90%,and 100% original performance levels in organizational and social dimensions roughly follows log-normal distribution.Neglecting the connectivity of the gas network,the resilience results in the technical dimension underestimate the actual damage level,and the recovery curve is close to linear-type.On the other hand,the results in organizational and social dimensions can better reflect the actual situation of damage and recovery of the gas system function,and are greatly affected by repair order and resource allocation.(3)A computer-simulation-based three-stage optimization strategy is proposed for the resilience enhancement of urban gas network.In stage I,the Fixed Proportion and Direct Comparison Genetic Algorithms(FPDC-GA)are applied to select key pipelines for repair or replacement under limited government funding in preparation for future potential earthquakes.In stage II,pressure testing must be carried out according with the gas leakage situation reported by users or detected by devices.The Multi-Label K-Nearest-Neighbor(ML-KNN)algorithm is used to predict the corresponding failed pipelines and optimize the pipeline pressure test order.In stage III,a strategy based on a greedy algorithm is applied to optimize the pipeline repair sequence.The proposed methods were applied to the gas network of a city in northern China.The following conclusions were drawn from the results: 1.The FPDC-GA method enhanced the resilience robustness and resourcefulness of the urban gas network system to the maximum level within the available government funding budget.2.The pipeline pressure test order calculated using the ML-KNN algorithm was significantly improved compared with a random pressure test order or one based on the empirical failure probability of pipelines.3.After optimization using a greedy algorithm,the recovery curves under different earthquake conditions were shaped as an exponential function,which indicates that the performance of the urban gas network recovered in the most efficient manner.