| Buried pipelines for transportations of oil and gas function in complex environments, such as Arctic and sub-Arctic regions. In addition to the normal operational loading conditions, for example, the internal pressure, buried pipelines are subject to various types of imposed deformations. The objectives of this work are to develop a predictive approach for the behavior of pipelines under imposed deformations and to establish associated criteria for design, maintenance and assessment of pipelines. The standard procedure for analysis of buried pipelines at the present time, which has been developed by industry, is based on an elastic-plastic beam model for the pipeline, combined with elastic-plastic soil springs for the surrounding soil. A design criterion commonly used is the buckling strain criterion. This criterion has been demonstrated to be overly conservative, in general, by both experimental and analytical studies.;The predictive approach developed in this study is based on the fact that local buckling of pipe walls interacts with overall response of the line of pipe. A two-step predictive approach has been developed. These are denoted as segment analysis and line analysis. The segment analysis is based on a three-dimensional shell model simulating a pipe segment. The line analysis models the pipeline by using a pipeline-beam element, developed in this study, acting interactively with the soil. To integrate the local behavior into the overall behavior, representative cross-sectional stiffness is abstracted from the segment analysis and is then fed into the line analysis.;For the segment analysis, a solution technique based on an improved arc-length controlled equilibrium iterative method is developed. A solution procedure based on a direct search technique is explored as an alternative. The results of segment analyses demonstrated the softening behavior in postbuckling regions. Two basic buckling modes, referred to as diamond and bulging modes, and significant cross-sectional distortions have been predicted.;A program ABP has been developed for the line analysis. It is based on the ISPDR and RMDI techniques, defined herein, which include and exclude the effects of local buckling, respectively. Responses of lines of pipe, characterized by localization of deformation, have been predicted and analyzed. Results demonstrate great influence for effects of local buckling and the strengths of bearing and uplifting springs.;Based on the predicted behavior, criteria for design and assessment of pipelines are proposed on a more rational basis. The procedures for establishment and application of these criteria have been illustrated. |
