Lifeline systems are intricately linked with the economic well-being, security, and socialrnfabric of the communities they serve. When earthquakes or other hazards strike lifelinernsystems, they disrupt the flow of resources and provision of services that sustainrncommunities. rnMany Lifeline systems are long-span structure. These structures are extended horizontallyrnto allow people, goods, electric power, gas and other item to move freely between locations.rnWhen seismic ground motion strikes, these structures may be affected and, consequently,rnthe economy aspect of a country can be disrupted there by leaving people at risk. rnThe purpose of this thesis has been to investigate the influence of soil-structure interactionrnon a dynamic property of above-ground pipeline (as an example of long-span structuresrnand lifeline facilities) for five different support conditions. rnThree-dimensional (3D) linear finite element analysis of above-ground pipeline for arndifferent base conditions have been made with the help of general purpose softwarernABAQUS. For this study, a 12m nominal length of a pipeline with API 5L X80 materialrngrade has been used and models have be studied for Kobe 1995 earthquake ground motion.rnDashpot and the spring coefficient for a typical foundation have been establish for use inrnsubstructure approach for the analysis. From analysis, it has been noted that, therndisplacement of pipelines on the soft soil to be larger than the displacement of pipeline laidrnon other type of soil support. It has also been observed that, when the base conditionrnbecome more flexible, the values of all response increased. rnIn a view of these observation, therefore, considering SSI effects in seismic design ofrnabove-ground structures resting on flexible support conditions like soft soil deposit isrnessential to minimize the potential damage of earthquake. rnFrom this thesis, it is recommended that, incorporating SSI for lifeline systems (similar tornabove-ground pipeline structure) is important in order to assure the safety of the structure.