Dynamic Mechanical Response And Structural Vulnerability Analysis Of PE Buried Gas Pipeline Under Earthquake

Earthquake is one of the important factors for the destruction of buried pipelines.With the advancement of urbanization in China,the construction of buried natural gas pipeline system in cities and towns is also accelerating.More and more attention has been paid to the seismic problem of buried pipelines.In recent years,polyethylene(PE)pipeline has been widely used as buried gas pipeline because of its good corrosion resistance,long service life and simple welding.According to historical earthquake disaster data,PE buried gas pipeline has failed due to earthquake,which has a significant impact on people's lives and property.Therefore,the response analysis and vulnerability analysis,of PE buried gas pipeline under earthquake are carried out in this paper,which provides some theoretical guidance for the early warning of PE buried gas pipeline under earthquake,so as to reduce the loss of life and property caused by secondary disasters of PE buried gas pipeline during earthquake.In this paper,the main influencing parameters of earthquake damage rate are obtained according to the failure law of pipeline.Then the vibration mode superposition method is used to extract the frequency of soil under site conditions and calculate the soil damping.According to the propagation characteristics and incident direction of seismic waves,the seismic waves arc input from the bottom of the soil along the direction perpendicular to the pipe axis(vertical)and parallel to the pipe axis(axial).Then the finite element model of PE buried straight pipe and bend pipe is established,and the response of pipe under different parameters is analyzed by time-history analysis method.Finally,assuming that the structural seismic demand parameters and seismic intensity parameters obey lognormal distribution,combining with the probability performance evaluation framework proposed by the Pacific Engineering Research Center(PEER),the demand model,seismic model and vulnerability model are obtained.The maximum strain of PE straight pipeline is taken as the capacity parameter to analyze its vulnerability.(1)Response analysis of PE buried gas straight pipe and elbow:Under the same intensity of seismic wave,the softer the soil,the easier the pipeline will be damaged.Under the different intensity of seismic wave,the stress and strain of PE straight pipe and elbow pipe will increase with the increase of intensity.With the continuous increase of the pressure in PE straight pipe and bend pipe,the stress and strain of the pipe are also increasing.For the straight pipe segment of PE straight pipe and bend pipe,the stress and strain values calculated by SDR 17.6 pipe are greater than those calculated by SDR11 pipe,while the axial stress value of the bending section of PE bend at SDR11 is greater than that at SDR17.6.The maximum stress and strain of PE elbow bend is at the inner bending point of the pipeline.The maximum stress and strain points of straight pipeline are at the two ends of horizontal direction of pipeline.The displacement calculated by PE straight pipe and bend pipe is related to the displacement of seismic wave,and the change of site condition,internal pressure and diameter to thickness ratio has little influence on the displacement of pipeline.The calculation result of vertical input seismic wave along the soil bottom of PE pipeline is larger than that of axial input seismic wave.(2)Vulnerability analysis of PE buried straight pipeline:Linear logarithmic regression analysis of the calculated maximum strain and peak acceleration is carried out to obtain specific expressions of PE buried pipeline's demand model,seismic model and vulnerability model under earthquake,and vulnerability curve is drawn.The probability of pipeline exceeding each failure grade under different peak acceleration is obtained,combining response analysis.And getting the pipe under the condition of the site I,transcend the probability of failure of the each level less than the exceeding probability of class II.The over-probability of category III site conditions is greater than the over-probability of category II.When the internal pressure is less than 0.4 MPa,the probability of pipeline exceeding each level of damage is less than that of pipeline with internal pressure of 0.4 MPa.When the internal pressure is greater than 0.4 MPa,the probability of pipeline exceeding each stage of failure is greater than that of pipeline with internal pressure of 0.4 MPa.When the diameter-thickness ratio is 17.6,the probability of pipeline exceeding each stage of failure is greater than that of pipeline with diameter-thickness ratio of 11.