ARCHED PIPELINES (EN: arch pipeline; DE: Bogenrohrleitungen; FR: conduites sur cintres; ES: tuberías sobre arcos; RU: арочные трубопроводы) is the type of the overground overpasses, which are created in the shape of the arch; they are constructed above the various obstacles. Most often they construct the arched pipelines, when there is the necessity to provide the specified dimensions of the span at the place of intersection of the transport lines (highways, railways, shipping canals, and so on).
Arched pipelines are constructed also in those cases, when the installation of the intermediate supports significantly increases the cost of construction (during the crossing of the gorges, deep ravines, and so on). The supports of the arched pipelines experience the action of the vertical and horizontal reactions; under the load (of the own weight, and of the weight of the product, which is transported) the structure works mainly against the compression, which permits to increase the length of the span.
They distinguish the arched pipelines according to their design features: without the auxiliary structures; with increased rigidity (either with the help of the struts and guy wires, or because of the combining two or more associated pipelines); with auxiliary constructions, which are increasing the lateral rigidity; with the laying of the pipes along the arched bridge. The action of the vertical and horizontal reactions (thrust) within the arched overpass is passed either directly onto the adjacent pipeline, or onto the special supports. The simplest single pipe overpasses of the arched pipelines do not require the installation of the supports, because the vertical loads (because of the weight of pipeline with product) are transferred directly onto the ground. In case of the significant length of the span, or in case of the construction of pipeline on the soft soils, arched pipelines use the reinforced concrete slabs as the supports.
In order to facilitate the assembly, they usually make the arched pipelines of the straight segments of the pipes with the bent curved inserts. The length of the span, which is overlain, of the arched pipeline, which is made of the single pipe, is determined by the transverse stability of the arch, for the increasing of which, two (or more) pipes are tied together. During the overlaying of the spans of the significant length, instead of the one pipeline, they install two ones of the smaller diameter, which are tied together with struts, and, in case of the necessity, are reinforced with the diagonal braces. The distance between the pipelines depends on the length of the span and on the wind load. The transverse and vertical rigidity, and also the total load bearing capacity of the arched pipelines, are increased with the various auxiliary structures. The transverse rigidity of the single-line overpass is increased with the installation of the auxiliary arches at the sides, which almost completely liberates the primary pipeline from the wind loads. Auxiliary arches have the smaller cross section, and are connected with the primary arch using the struts.
When there are available several lines of the pipeline, each of which has its own mode of work, and also in case of the large variations of temperature of the product, which is transported, they construct the arched pipelines with overpasses, within which the pipelines do not experience the loads; then the arched bridge is usually the load bearing structure. See also the "Overground pipeline overpass" article.
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