Reliability based safety assessment of buried continuıus pipelines subjected to earthquake effects

Yavuz, Ercan Aykan
Lifelines provide the vital utilities for human being in the modern life. They convey a great variety of products in order to meet the general needs. Also, buried continuous pipelines are generally used to transmit energy sources, such as natural gas and crude oil, from production sources to target places. To be able to sustain this energy corridor efficiently and safely, interruption of the flow should be prevented as much as possible. This can be achieved providing target reliability index standing for the desired level of performance and reliability. For natural gas transmission, assessment of earthquake threats to buried continuous pipelines is the primary concern of this thesis in terms of reliability. Operating loads due to internal pressure and temperature changes are also discussed. Seismic wave propagation effects, liquefaction induced lateral spreading, including longitudinal and transverse permanent ground deformation effects, liquefaction induced buoyancy effects and fault crossing effects that the buried continuous pipelines subjected to are explained in detail. Limit state functions are presented for each one of the above mentioned earthquake effects combined with operating loads. Advanced First Order Second Moment method is used in reliability calculations. Two case studies are presented. In the first study, considering only the load effect due to internal pressure, reliability of an existing natural gas pipeline is evaluated. Additionally, safety factors are recommended for achieving the specified target reliability indexes. In the second case study, reliability of another existing natural gas pipeline subjected to above mentioned earthquake effects is evaluated in detail.