HANGING PIPELINES (EN: hanging pipelines, overhead pipelines; DE: Hangerohrleitungen; FR: conduites suspendues; ES: tuberias colgadas; RU: висячие трубопроводы) is the type of the above-ground overpasses for the pipelines, within which the pipes are tied to the bearing elements, namely, to the ropes, cable-stays, chains, and so on; these pipelines are constructed for the crossing of the gorges, water, and other obstacles, with the width of more than 50-60 metres. There are known the hanging pipelines with the length of the span of up to 200-400 metres and more. They distinguish the following hanging pipelines: flexible, cable-stayed, and in the form of the sagging thread. The flexible hanging pipelines (see the Figure # 1) are constructed with the help of the suspensions, which are attached to one or several carrying ropes, which are slung over the pylons. The single-link variant of the system has the low rigidity, and, in case of the dynamic impacts, easily enters into the oscillatory motion; the double-link system is more rigid. For the cable-stayed hanging pipelines (see the Figure # 2) , they use for the fixation the inclined guy-wires, namely, the cable-stays, or the rope trusses.
Within such schemes, all the elements, as a rule, work only in tension, and form the geometrically unchanging system. The hanging pipelines, which have been made according to this scheme, have much greater vertical rigidity, than the flexible pipelines. The hanging pipelines in the form of the sagging thread (see the Figure # 4) are constructed on the pylons (or without any pylons).
This system is most economical, but has the least rigidity. Within this scheme, the metal of the pipes is stressed significantly more, than within the flexible and cable-stay systems, and there emerge greater oscillations under the influence of the wind flow. There are also constructed the combined systems, for example, the single-link flexible systems with the additional inclined cable-stays.
The hanging pipelines (of all systems) may have the single span, and may have the multiple spans, with the equal spans, and with the spans, which are different in length. In case of the different lengths of the spans, the forces within the carrying ropes (or within the cable-stays) within all the spans must be approximately equal. This goal is achieved using the choice of the determined ratio between the height of the pylons, and the height of the sag of the ropes: in case of the short spans, the ratio of the height of the sag to the length of the span is lesser. They usually specify this ratio within the limits from 1/6 to 1/14. The forces, which are emerging within the carrying ropes, are withstood by the anchored supports. In case of the spans of the small length, the horizontal components of the forces within the ropes may be withstood by the pipeline itself. The pylons of the hanging pipelines are made: rigid, embedded into the supports (usually with the movable supporting pa rts for the attachment of the ropes); flexible, rigidly connected with the supports (with the stationary attachment of the ropes to the tops of the supports); swaying, pivotally connected with the supports, with the stationary attachment of the ropes to the tops of the supports. They construct the pylons of the metallic profiles with the continuous cross-section, or in the form of the flat or spatial latticed trusses, which are made of the reinforced concrete elements. They most often make the supports for the pylons, and for the attachment of the carrying and wind ropes, of the reinforced concrete. On the overpasses of the hanging pipelines, they usually make small observation bridges for the servicing of the pipeline during the operation and in case of the repair. On the hanging pipelines without the small bridge, the observation and repairing works are performed using the observation cart, which is moving along the monorail.
Within the hanging pipelines with the relatively small length of the spans, there is no need for the guy-wires or ropes for the provision of the horizontal rigidity of the span constructions. In case of the spans with the length of 80 metres or more, there is necessary the increasing of the transverse rigidity of the span constructions, for which purpose they construct the horizontal trusses, using the elements of the small operational bridge. They position the paired carrying ropes on the pylons at the distance of several metres, and attach the pipeline to these ropes with the help of the inclined suspensions, or of the special wind ropes. They position the wind ropes and guy-wires at the both sides of the hanging pipelines, and attach them to the special anchored supports, or to the same supports, to which are attached the carrying ropes, with the help of the special console protrusions on the pylons.
The ratio of the height of the sag of the wind ropes to the length of span is usually within the limits from 1/12 to 1/24. For the regulation of the lengths of the carrying and wind ropes, they are provided with the special devices (turnbuckles, screw devices, and others) within the places for the attachment to the supports; the length of the suspensions and guy-wires is regulated using the turnbuckles.
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