Patent GB-1293290-A (GB)
Title: Method of producing composite concrete-steel pipes and joints, and pipes and joints obtained by means of said method
IPC: B28B21/60
Filed: 1964-11-11
Abstract: 1293290 Steel; concrete pipes SOC D'ETUDE DU TRANSPORT ET DE LA VALOR ISATION DES GAZ NATURELS DU SAHARA 11 Nov 1964 [25 Nov 1963] 46054/64 Headings F2G and F2P  A composite concrete-steel pipe comprises an inner mild steel sleeve surrounded by a layer of concrete, a reinforcement including inner rib structures disposed longitudinally and fixed to the outer surface of the sleeve, and at least one hooping constituted by a winding of coils of hard steel wire encompassing both the sleeve and the rib structure and embedded at least partially in the concrete. In the embodiment shown in Fig. 2, the inner sleeve 1 is constructed from mild steel sheets bent and welded together, and has welded to it rib structures consisting of two corrugated metal bars 2a, 2b welded to a longitudinal metal bar 2c. These bars are of work hardened steel. The rib structures can also be formed from thin bent sheet. Two apertured rims 3a, 3b between which extend wires or rods 4 for producing longitudinal pre-stressing are secured to the sleeve 1 adjacent its ends, these wires being flattened at their ends and held in the rims by screwed sleeves 5 whereby it is possible to put the wires under tension. The outer hooping is provided by two windings 6, 7 of hard steel wire separated by a helical steel wire or rod 8. The sleeve thus equipped constitutes a skeleton which is conducted by mechanical handling means to an injection station. At this station (Fig. 4), the ends of the skeleton 13 are closed by closing means 20 supported by carriages 21 which are movable along slideways 22 by hydraulic jacks 23. A drying or draining shell structure 25 composed of three hinged part-cylindrical segments consisting of staves of wood is carried by a bar 15c supported above the skeleton 13 by winches 15a, 15b from two gantries 14a, 14b movable along runways parallel with the skeleton 13. Toggle devices 26 disposed between the bar 15a and the shell structure 25 comprise links articulated in such a manner that the segments of the shell structure 25 close around the skeleton 13 on being lowered into positions, the closure being completed by the action of two horizontal jacks (not shown). The shell structure 25 is hooped by binding cables 28 provided at their ends with tightening means. When the shell structure 25 is fixed in position around the skeleton 13, concrete is injected into the annular space between the sleeve 1 and the shell structure 25 from an injection vessel 17 through pipes 24 and a closing means 20. The pipes 24 are then disconnected and the assembly comprising the shell structure 25, the skeleton 13 and the closing means 20 is conveyed by the gantries 14a, 14b to a horizontal press 12 and placed between two opposed clamping jacks 30. Apertures in the closing means 20 leading to the interior of the sleeve 1 are connected to a source of water under pressure and the sleeve 1 is then filled with water, the pressure of which is raised progressively. Under the effect of the internal pressure, the concrete is dried or drained through the shell structure 25 and the hooping placed under tension. The hardening of the concrete is accelerated by stoving by means of steam for some hours. The stoved pipe is then emptied of water and this results in a partial release of the stress on the bars and wires which have a high elastic limit and on the sleeve whose elastic limit was exceeded under the effect of the pressure. In this way, a triple stressing of the concrete is achieved. The pipe according to a second embodiment (Fig. 7, not shown) has the outer hooping provided by contiguous coils (41) wound about the longitudinal bars (2c) to form a cylindrical outer wall which is covered by a protective covering (42) of, for example, epoxy resin or glass fibre-reinforced polyester resin. In the production of this pipe, the contiguous coils (41) constitute the outer wall of the mould and the shell structure (25) is no longer necessary. The protective covering is applied when the pipe has just been extracted from the injection station and is still hot. In either of the above embodiments, the longitudinal stress can be obtained without the longitudinal wires or rods 4 by clamping each closing means 20 to the sleeve 1 by jacks disposed in a ring. The internal hydraulic pressure then causes not only radial expansion of the sleeve but longitudinal extension as well, this longitudinal extension creating after the hardening of the concrete and the elimination of the hydraulic pressure, a longitudinal compression of the concrete. A joint interconnecting two pipes of the type having contiguous coils (Fig. 8, not shown) employs bare end portions (Ea, Eb) of the sleeves (la, 16), which portions are welded together at (51). The annular joint (J) which surrounds the end portions (Ea, Eb) comprises an annular support (52) provided with an injection aperture (53), a hooping (54) having contiguous coils, and a flexible annular chamber (55) provided with an injection pipe (56) and surrounding a protecting ring (57). After concrete (58) has been injected into the joint, the chamber (55) is filled with a hardening substance which is introduced under pressure by way of the pipe (56). This expands the chamber (55), whereupon the concrete undergoes an inner radial compression and is dried and furthermore puts the hooping (54) under tension. The internal pressure is maintained until the substance filling the chamber (55) hardens.