Dynamic Reliability Analysis Of Buried Pipeline Under Fuzzy Random Space - Time Earthquake Load

In order to analyze the response of buried pipeline under seismic load. This paper considered the abnormal load-seismic load and long linear structure of buried pipeline. While the seismic load, which acts on buried pipes has fuzziness, time randomness and space randomness, we called fuzzy stochastic space-time character of seismic load. The attenuation factor of the studying area was obtained by analyzing the attenuation factors of seismic wave, the comparison expression between seismic wave parameters (amplitude, accelerated speed and travel time) and travel distance was given to solve the problem of stochastic space-time characters of seismic load. Then, using the result to analyse the dynamic reliability of buried pipes, the probability of each earthquake damage levels were calculated. However, the total loss of pipes caused by this earthquake was calculated by combining the potential economic lossess related to each earthquake damage levels. Finally, the process of analysis and calculation were given out by a case. The main contents and conclusions are as follows:(1) The causes of the randomness and fuzziness of seismic, the fuzziness of site soil and earthquake damage were analyzed, and the inconvenient and unreasonable caused by these facors were given. Then the mathematical model and calculation method to solve these randomness and fuzziness were showed. The fuzzy stochastic space-time concept of seismic load was given.The causes of the unconventional load were analyzed, and the classification and analysis methods were displaced.(2) The fuzziness of seismic, the spatial randomness of buried pipeline relative to the seismic center and the travel time randomness of seismic load (caused by the difference of the propagation of seismic waves and epicentral distance) sustained by the pipes were studied. The main attenuation factors concerned with the distance of the propagation of seismic waves were considered. The attenuation formula of seismic waves changed with epicentral distance is obtained by analyzing the mainly attenuation factor. In order to obtain the attenuation factor of seismic wave, a simple method is given, which is based on the intensity of input and output seismic wave in study area. Then, the formula of amplitude (accelerated speed, travel time) of seismic wave varied with the epicentral distance x is determined.(3) In order to deduce the formula of axial and bending strain and stress of pipes under the seismic loads and the changing rule with the incidence angle, we simplified the seismic waves that act on the pipes into a simple harmonic plane wave. And known that when the angel of incidence is45, the axial strain and bending strainand stress are both maximum and their absolute values are equals. Then, the occurrence probability of each earthquake damage level of buried pipes is calculated, and the total economic loss values of the buried pipes in study area under this seismic intensity is obtained, or the economic loss values of a pipe within years caused by a potential earthquake can be predicted based on the economic loss values in study area under different level of earthquake damage. Then the seismic risk of pipes in the view of economic can be used to judge whether to accept the loss.(4) The seismic attenuation factor in study area, the probability of each earthquake damage levels and the total economic losses was given, combined with the information of the earthquake (Wenchuan earthquake) and pipelines (Lanzhou-Chengdu-Chongqing product oil transportation pipelines).Then, the result highlights the advantages of fuzzy stochastic space-time by comparing this analysis method with tranditional ones.