瓦斯管線受震的災損評估

DAMAGE EVALUATION OF GAS PIPELINES UNDER EARTHQUAKES

利用既有的理論方法與收集的災損數據，本文建立一個評估天然瓦斯管線震後災損的方法。研究成果可作為震前風險評估與震後損失估算的依據。文中考慮三種主要的損壞機制，即斷層錯動、震波傳遞、以及土壤液化。管線的損壞程度以破壞指標反映之。破壞指標的定義為須修復的管線長度與管線總長度的比值。災損評估時的重要參數包括破壞長度、最大地表速度和液化潛能指數。文中配合集集地震時天然氣管線的災損資料，假設易損曲線為一個具兩參數的常態分佈函數。準此，即可建立不同最大地表速度與最大地表加速度下管線的易損曲線與破壞指標。同時，依計算的液化潛能指數，可以探討土壤液化對管線的影響。最後，本文建議一種合理方案，以評估不同地震強度下管線系統的可能損失。

By utilizing the available theoretical methods and collected damage data, this paper develops an approach to evaluate the damage of natural gas pipelines under the earthquake threat. The outcome can serve as a basis for seismic risk analysis and damage cost assessment. Three major damage mechanisms, namely fault rupture, wave propagation, and soil liquefaction, are considered. The degree of damage is justified by the pipeline’s damage index. Such a damage index is defined as the ratio of the repaired length to the total length of pipelines. The key parameters associated with damage evaluation consist of damaged length, peak ground acceleration, and liquefaction potential index. In accordance with the damage data of gas pipelines collected in the Chi-Chi earthquake, the study assumes that the empirical fragility curves can be expressed in the form of two-parameter normal distribution functions. Consequently, the fragility curves and damage indices for gas pipelines can be constructed as functions of PGV and PGA. Meanwhile, through the calculation of the liquefaction potential index, the impact of soil liquefaction on pipeline’s performance is examined. Finally, a rational strategy is suggested to estimate the possible loss of a pipeline system under a particular intensity of ground motion.