Seismic risk assessment of piping systems, as a group of vulnerable facilities in oil refineries, is mostly based on the single-variable fragility curves. However, it is well-known that the fragility curves, developed based on a single intensity measure (IM), are not much reliable. For increasing the confidence level of seismic risk assessment of piping systems, it was tried, in this study, to develop double-variable fragility functions by using peak ground acceleration (PGA) and peak ground velocity (PGV) together as the IMs. For this purpose, the piping system of the ISOMAX Unit of Tehran oil refinery was considered, and modeled by a powerful finite element analysis program under various loadings, including gravity, pressure and seismic loads. For seismic analyses 157 set of three-component earthquake records were employed, with PGA and PGV values varying respectively from around 0.1 g–0.6 g and 10 cm/s to 60 cm/s. By using the nonlinear time histories analyses results, two single-IM fragility curves and one double-IM fragility surface were developed based on the probability of exceedance of the maximum created stress, considered as the ‘damage index’, from the allowable stress. The results indicate that using PGA and PGV jointly, as the IMs in the development of fragility functions, provides more reliable vulnerability estimations. For example, the single-IM fragility function gives, for PGA = 0.2 g, a probability of exceedance of 75%, while by using the double-IM fragility function this probability may change from 30% for PGV = 10 cm/s to 95% for PGV = 60 cm/s.

作为炼油厂中一组易受攻击的设施，管道系统的地震风险评估主要基于单变量脆性曲线。但是，众所周知，基于单一强度测量（IM）绘制的脆性曲线并不是很可靠。为了提高管道系统地震风险评估的置信度，在本研究中，尝试通过将峰值地面加速度（PGA）和峰值地面速度（PGV）一起用作IM来开发双变量脆弱性函数。为此，考虑了德黑兰炼油厂ISOMAX装置的管道系统，并通过强大的有限元分析程序对各种载荷（包括重力，压力和地震载荷）进行了建模。为了进行地震分析，采用了157组三分量地震记录，PGA和PGV值分别在0.1 g-0.6 g和10 cm / s到60 cm / s之间变化。通过使用非线性时间历史分析结果，根据超过最大允许应力（称为“破坏指数”）的概率，绘制了两条单IM脆性曲线和一个双IM脆性表面。结果表明，结合使用PGA和PGV作为脆弱性功能开发中的IM，可以提供更可靠的脆弱性估计。例如，对于PGA = 0.2 g，单IM脆性函数给出的超出概率为75％，而通过使用双IM脆性函数，该概率可以从PGV = 10 cm / s的30％变为95 PGV的％= 60 cm / s。通过使用非线性时间历史分析结果，根据超过最大允许应力（称为“破坏指数”）的概率，绘制了两条单IM脆性曲线和一个双IM脆性表面。结果表明，结合使用PGA和PGV作为脆弱性功能开发中的IM，可以提供更可靠的脆弱性估计。例如，对于PGA = 0.2 g，单IM脆性函数给出的超出概率为75％，而通过使用双IM脆性函数，该概率可以从PGV = 10 cm / s的30％变为95 PGV的％= 60 cm / s。通过使用非线性时间历史分析结果，根据超过最大允许应力（称为“破坏指数”）的概率，绘制了两条单IM脆性曲线和一个双IM脆性表面。结果表明，结合使用PGA和PGV作为脆弱性功能开发中的IM，可以提供更可靠的脆弱性估计。例如，对于PGA = 0.2 g，单IM脆性函数给出的超出概率为75％，而通过使用双IM脆性函数，该概率可以从PGV = 10 cm / s的30％变为95 PGV的％= 60 cm / s。从允许应力出发，被视为“损坏指数”。结果表明，结合使用PGA和PGV作为脆弱性功能开发中的IM，可以提供更可靠的脆弱性估计。例如，对于PGA = 0.2 g，单IM脆性函数给出的超出概率为75％，而通过使用双IM脆性函数，该概率可以从PGV = 10 cm / s的30％变为95 PGV的％= 60 cm / s。从允许应力出发，被视为“损坏指数”。结果表明，结合使用PGA和PGV作为脆弱性功能开发中的IM，可以提供更可靠的脆弱性估计。例如，对于PGA = 0.2 g，单IM脆性函数给出的超出概率为75％，而通过使用双IM脆性函数，该概率可以从PGV = 10 cm / s的30％变为95 PGV的％= 60 cm / s。