Response Analysis Of A Buried Pipeline Crossing The Fault Based On Shell-Model

Firstly, the study of damage of buried pipelines crossing faults is introduced in the first chapter, specially for the damage of PE gas pipeline in 1999 Ji-Ji earthquake, because these kinds of direct evidences of fault ruptures on PE pipe failures were rare in the past. In general, the failure mode of buried pipeline under the fault movement can be divided into two types: (A) Necking Failure, caused by tensional deformation when the crossing angle β is less than 90°; (B) Buckling Failure, caused by compressive deformation when the crossing angle β is larger than 90°. Next, this paper systematically reviews several simplified design methods that have been proposed to obtain the maximum stress or strain in pipelines crossing an active fault. Usually, the buried pipeline is modeled as cable, beam or shell model in these methods. There are the two limitations for both of the cable method and beam method: (1) It can only analyze the response of pipeline under tensile loading (β<90). When the crossing angle is larger than 90 degree, the pipeline would prone to suffer a buckling damage; (2) It cannot be used to analyze the large deformation in the pipe section. Since it is difficult for the cable or beam model to consider the large deformation in the pipe crossing section, the FEM analysis with shell element has been proposed to investigate the response of pipe. Takada (2000) proposed a simplified design formula to obtaining the maximum strain in steel pipes based on the parametrical study using a beam-shell hybrid FEM.To extend Takada's shell method, a 3-dimension shell-spring FEM is proposed to analyze the response of steel pipelines under the large fault movement in the second chapter. Soil springs are used around the pipe including vertical, lateral and axial soil springs to consider the interaction between the pipeline and the surrounding soil. The pipe segment near fault that usually suffers large deformation is modeled with a plastic shell element in order to consider the effect of local buckling and section deformation. To reduce the calculating time of the whole model, an equivalent spring proposed by the author is applied at two ends of the shell model.Compared with other analytical FEM models, it is easy for this model to consider the situation when the soil conditions on the both side of the fault are different ( Kl ≠ K2). In the third chapter, the performance of two fault-crossing steel pipelines with large diameters (Φ2.0 m and Φ2.2 m) at fault crossing in Kocaeli Earthquake and Ji-Ji Earthquake are studied. Thames water pipe (Φ2.2 m) suffered three damages along the pipeline asymmetrically spaced around the fault in Kocaelie earthquake, and the Shigang water pipe (Φ2.0 m) suffered two damages along the pipeline symmetrically spaced around the fault in Ji-Ji earthquake. The failure performance of these two damage cases for large diameter steel pipelines are much different form each other because of the different types of fault movements as well as the type of soil condition on both sides of fault (Kl ≠ K2 and Kl = K2). Compared with the beam model, the shell-spring model proposed in this paper can examine the failure mode of a buried pipeline under the fault movement more clearly. The occurrence of the third damage in Thames water pipeline is specially discussed in Chapter 3. Considering different soil spring models for vertical fault movement and horizontal fault movement, two damage cases of PE pipeline in Ji-JiEarthquake have also been simulated.The large deformation of a buried pipeline under fault movement is investigated in the 4th chapter. To examine the inelastic behavior of buried pipelines, the parametric studies on pipe material property, diameter (D), diameter-to-thickness ratio (D/t), crossing angle (β), as well as soil stiffness, have been conducted using a shell-spring FEM method. For each parametric study case, the fault displacement (A) is up to 7 meters. Through the parametric studies, the inelastic behavior of a buried pipeline differs so much from that of the beam...