| Pipeline,as one of the main mediums for water,oil,and gas transportation,has become a major artery for modern industrial production and urban life.The vast majority of long-distance transportation uses buried pipelines.The biggest natural enemy of buried pipelines is earthquakes,and a large number of earthquake disasters indicate that buried pipelines are vulnerable to earthquakes.The damage caused by earthquakes to buried pipelines not only brings significant economic losses,but also makes it difficult to inspect and repair in the short term.Therefore,the research on seismic fortification of buried pipelines is a very significant event.The underground pipeline network and seismic field constitute the internal and external causes of this problem.In order to accurately evaluate the seismic performance of complex site pipeline systems,it is necessary to take the pipeline and its surrounding soil as an earthquake influence field to study the dynamic response law of the pipeline under seismic action.Due to the geometric and material complexity of the soil pipeline system,the combination of finite element method,boundary element method,and these two methods has become the primary choice for studying the seismic analysis of large three-dimensional and two-dimensional underground pipeline systems.Starting from the theory of dynamic infinite elements and combining with the basic principle of wave method for seismic input,this article derives the input method for seismic motion at the boundary interface of infinite elements under non-uniform excitation.On this basis,a refined three-dimensional finite element infinite element coupling model of buried pipelines was established using dynamic infinite element boundaries.The dynamic response of buried pipelines was analyzed,and some beneficial results were obtained.The main work of this paper is as follows:(1)The progress in research on seismic response analysis of underground pipeline networks was reviewed and evaluated.Different research methods were classified in detail,and their basic principles,development context,advantages and disadvantages were analyzed.The basic principles of finite element method and infinite element method and the coupling method of finite element and infinite element are introduced.The solution process of element Stiffness matrix is emphatically introduced.(2)A detailed introduction was given to the modeling method of the finite element infinite element coupling model,and numerical analysis and comparative discussion were conducted on the value of model dimensions in three directions.Suggested values for important parameters in the finite element infinite element coupling model were given.The hypothetical bedrock surface divided by the shear wave velocity of the soil layer and the thickness of the cover layer serves as the seismic input interface.At this time,the effective depth of the soil layer is taken as H=40m,which can cover most of the geological environment where the pipeline is located.The specific value is determined by the type of site where the pipeline is located,generally H=30m～60m;The value of the effective calculation length L has a great relationship with the actual Seismic wave considered.L should contain at least one wavelength of the predominant period of the ground motion,which can basically reflect the temporal and spatial differences of the ground motion;The effective calculation width W is closely related to the diameter of the pipeline,and the value of W increases with the increase of the pipe diameter.Through comparative analysis of multiple working conditions,40D can be taken as the effective calculation width W.(3)The input method for seismic motion on the boundary of infinite elements was derived,and the seismic motion was transformed into equivalent nodal forces applied at the boundary of the finite element infinite element interface.The input method for seismic motion under non-uniform excitation was further elaborated.The incident problem of external seismic motion is equivalently transformed into an internal problem.On the basis of the stress field generated by seismic excitation,an additional stress field is added to the finite element part to balance the damping stress generated by ABAQUS dynamic infinite element at the boundary node caused by node velocity at the finite element boundary.The basic principle is derived and the input method for seismic motion at the boundary interface of the infinite element is provided.Under the condition of uniform infinite domain,the calculation methods of internal field and equivalent load F2 for oblique and vertical incidence of plane P-waves were elaborated,and the calculation formula for seismic load was derived in detail,providing theoretical basis and methodological support for the input of seismic motion at the boundary interface of the three-dimensional finite element infinite element coupling model.(4)Based on the three-dimensional dynamic finite element infinite element coupling model,various influencing factors(internal pressure,PGA,shear wave velocity of site soil,non-uniformity of site soil,buried depth of pipeline,and interaction between pipeline and soil)of buried pipelines under earthquake action were discussed.Using the seismic response results of typical buried pipelines and the semi empirical and semi theoretical methods proposed by the Chinese seismic design code for buried pipelines,many beneficial conclusions were obtained.By introducing springs and dampers to simulate the stiffness of different interface types,while considering the finite element model analysis of segmented pipelines under different pipe lengths and seismic intensities.The results indicate that under earthquake action,buried continuous pipelines have higher pipe strain than segmented pipelines.Therefore,in segmented pipelines,flexible joints should allow for greater joint displacement,thereby reducing pipe strain;As the stiffness of the joint increases,the strain increases while the relative joint displacement decreases.Except for the slightly higher strain of reinforced concrete pipelines,there is little difference in pipeline strain and relative joint displacement among other materials;As the curvature radius of the curved pipeline increases,the peak value of the principal tensile strain gradually decreases,and a smooth transition at the bend is beneficial for the seismic resistance of the pipeline;In addition to being subjected to axial tension,the three-way pipeline is also subjected to significant tensile and compressive bending effects.The closer it is to the bend position,the more uneven the stress distribution of the pipeline. |
PDF Full Text Request