US3056183A - Process for the production of lined prestressed concrete hollow bodies - Google Patents

Description

3 8 1. 6 3m S m m qw m P mw mm TLO OFB Ecm www.. IO MH AU E .wm Rm@ N EO TC Dn O F S S E C O R D.. 2 6 9 l 2, .L C 0 4 Sheets-Sheet l Filed Oct. 29, 1959 Oct. 2, 1962 R. A. PlGEoT PROCESS FOR THE PRODUCTION OF LINED PRE- CONCRETE HOLLOW BODIES 4 Sheets-Sheet 2 Filed OCT.. 29, 1959 3,056,183 TION oF LINEE PRE-sTREssE CONCRETE HOLLOW BODIES A. PIGEOT PROCESS FOR THE PRODUC Filed 0G17. 29, 1959 Oct. 2, 1962 4 Sheets-Sheet 3 Oct. 2, 1962 R. A. PlGl-:oT 3,056,183

PROOEss ROR TEE PRODUCTION OE LINED PRE-sTREssED CONCRETE HOLLOW BODIES Filed Oct. 29, 1959 4 Sheets-Sheet 4 United States Patent O 3,056,133 PROCESS FOR THE PRODUCTIN F LINED PRE- STRESSED CGNCRETE HLLOW BDIES Robert Auguste Pigeot, Paris, France, assigner to Entreprises Campenon Bernard, Paris, France, a company of France Filed Oct. 29, 1959, Ser. No. 849,657 Claims priority, application France Dec. 17, 1958 1 Claim. (Cl. Z55- 154) It is already known, more particularly from United States Letters Patent No. 2,048,253 to produce prestressed concrete pipes by a process which consists in expanding in diameter the concrete cylinder enclosing the circular reinforcements or hoops which are to be tensioned, whilst said concrete, which has not yet set, has been brought to a certain state of mechanical strength by vibration and compression. This expansion of diameter is effected by means `of a high pressure acting on the inner face of the hollow concrete body subjected externally to a smaller pressure. In order to carry this process into effect, the concrete is poured into an annular gap between a central expandable mandrel and an outer mould formed of staves or elements separated by radial planes, in such a manner that the said mould is capable of expanding. The circular or helical reinforcements or hoops to be tensioned are placed in the said annular gap before the concrete is poured, so that they can be enclosed by the said concrete and thus made to participate in and tensioned by the expansion of the concrete. This expansion is maintained until the concrete sets and hardens. After setting and hardening, the pressure of the mandrel on the concrete is removed and the concrete pipe, which can then be removed `from the mould, is subjected to radial compressive stresses under the tension force of the circular reinforcements.

In order to obtain longitudinal pre-stressing of the concrete also, it is possible to use conventional means for tensioning longitudinal reinforcements which are placed in the annular mould before the concrete is poured.

Monolithic pipes made of pre-stressed concrete which are produced in this way have exceptional qualities of resistance to mechanical stress and to corrosion resulting from the action of the external environment. Furthermore, they are relatively easy to manufacture near to the places where they are to be used in any region where cement can be obtained, the moulds used in the production of these pipes being relatively easy to construct and install.

On the other hand, they have the disadvantage, due to the very nature of the concrete, of having poor resistance to certain attacks of a chemical nature and consequently of not being suitable for conveying certain liquid or gaseous fluids such as natural hydrocarbons.

Conduits such as long-distance pipe lines which are intended for conveying these fluids over great distances, have hitherto been made of steel, and since they have to satisfy certain strength conditions they are relatively thick and heavy, which entails diiiicult transport from the metallurgical works to the installation site. Transport of this kind is particularly expensive when it is a question of installing conduits, often of considerable length, in countries which do not have a metallurgical industry.

The present invention makes it possible to improve the qualities of pre-stressed concrete pipes so as to overcome this disadvantage, by making them capable of couveying fluids of various kinds, more particularly liquid or gaseous hydrocarbons, whilst retaining the remarkable properties of mechanical strength possessed by these pipes, and their relatively easy construction.

It relates to the novel industrial product constituted by "ice a pipe or hollow element comprising a con-crete body prestressed by circular or helical reinforcements enclosed in the concrete, and an inner relatively thin lining made of metal or plastic material adhering to the concrete which has been poured on to the said lining, which is preferably not subjected to considerable compressive or tractive forces in the condition of rest of the pipe or other hollow body.

This inner lining does not have to have high mechanical strength properties, since it is supported by the prestressed concrete body which surrounds it. It is sufficient if the material constituting the said lining is capable of withstanding considerable elongation without breaking. Since its thickness can be much less than that of bodies made entirely of metal and having to have the necessary mechanical strength themselves, transport from the production Works to the installation site entails much lower costs.

It will be apparent that the invention is not limited to pipes but also covers any other hollow bodies, such as containers.

The process for the production of the novel pipe or hollow body often forms part of the subject of the invention.

This process derives from the process by expansion which has been mentioned hereinbefore. It is characterized in that the pressure exerted on the inner face of the concrete, before setting and hardening, in order to compress the concrete, expand the diameter thereof and at the same time tension the enclosed circular reinforcements, is exerted by means of the sleeve which is to form the inner lining of the pipe, the central mandrel before the concrete is poured into the mould.

The description which now follows ywith reference to the accompanying drawings given by way of non-limitative example, will make it easy to understand the various features of the invention and the way in which they are carried into effect, any feature brought out either from the text or from the figures being understood to come within the scope of the present invention.

PIG. l is a diagrammatic `vertical half-section of a mould for carrying the invention into effect.

FIG. 2 is a partial cross-section thereof taken on II*II.

FIG. 3 is a diagrammatic vertical half-section of a modified form of embodiment of the mould.

FIG. 4 is an axial half-section of a pipe constructed according to the invention.

FIG. 5 is an explanatory diagram which is not drawn to scale.

FIGS. 6, 7 and 8 show various constructional forms of joints which can be used to connect pipes according to the invention.

The mould illustrated in FIGS. 1 and 2 comprises a rigid cylindrical central core l made of concrete for example, of smaller diameter than the internal diameter of the pipe to be produced, and an outer mould formed of a certain number of staves or elements 2 juxtaposed on radial planes 3. Arranged about the core l is an inatable iiat annular tube 4 which is made of rubber for example and whose interior communicates with a duct 5 formed in the core and can thus be connected to a hydraulic pump permitting the introduction of Water under high pressure to the interior of the said flat tube. This tube 4 and the core 1 thus form together an expandable mandrel.

The staves 2 are surrounded themselves by a certain number of annular tubes 6 (or by a single annular chamber similar to the tube 4 or any other system such as hydraulic jacks) wherein it is also possible to introduce water under pressure by means of connections to a common duct 7a. About these tubes and at a certain distance from the staves, the value of which distance is greater than the radial displacement to which the staves are subjected during the production of the pipe, as will be explained hereinafter, there is arranged a strong cylindrical frame 8 used to support the tubes 6 when they are subjected to pressure by way of the duct 7a.

With this arrangement, when the central tube 4 is pressureless and the tubes 6 are inflated by the water at a certain pressure in order to hold the staves clamped against one another in `the position shown in PIG. 2, there is fitted over the tube 4 the metal or plastic sleeve 9 which will form the inner lining of the finished pipe, the circular reinforcements il@ are arranged in the annular gap between the said sleeve and the inner face of the staves, and also, if appropriate, longitudinal reinforcements are arranged in position, and then the lower annular plug lll which forms a bottom closure for the said gap is put in position, said plug possibly consisting, for example, of a series of sectors of a circle or a plastic ring made of cellular rubber or an equivalent synthetic product, and then the concrete is poured into the said gap. During this pouring operation, the concrete is subjected to vibrations in order to achieve perfectly uniform filling and to eliminate excess water which leaks through the joints of the mould, more particularly along the planes 3 at which the staves contact one another. When filling is completed, the upper plug l2 (which can be composed in the same way as the aforementioned plug) is put in position. Vibration is continued and water is introduced under pressure into the tube d through the duct 5 without relaxing the pressure which prevails in the tubes 6 surrounding the staves. The concrete is thus put in compression and the sleeve is expanded. As a result, the residual excess water is driven out through the joints of the mould. The compacting of the concrete is caused on the one hand by the vibration which arranges the solid particles, reducing the intervals between them to the minimum, and on the other hand is due to the compression which produces a veritable squeezing drying action on the concrete, and as a result the coefficient of internal `friction of the fresh concrete is considerably increased. It is then possible to commence the second phase of the process, wherein by increasing the water pressure in the central tube 4 and progressively draining the outer tubes 6, Whilst keeping the pressure in these tubes constant, there is obtained not only an additional expansion of the diameter of the sleeve 9 but also an expansion of the concrete which has not yet hardened and finally of the outer mould formed of the staves 2, which are driven out radially, widening their joints 3. Joint covers formed of ordinary vertical strips i3 can be provided along the joints 3 of the staves in order to prevent the concrete from flowing through these joints, whilst allowing the excess Water to pass through. The expansion of the concrete is transmitted to the circular reinforcements Mi which are thus put in tension since the concrete, although it has not yet set, has sufficient resistance to the penetration of the reinforcements owing to the compression force to which it is subjected. When the expansion of diameter reaches the value corresponding to the tension which it is desired to give to the circular reinforcements 1t), the pressure increase in the central tube 4 is stopped at the same time as the draining of the tubes 6 is stopped. The apparatus is left in this state until the concrete has set and hardened, which can be accelerated by heating the mould, for exF ample by circulating steam through ducts formed in the staves near the inner surface of the said staves. When hardening is complete, the central tube 4 is emptied and the outer tubes 6 are emptied and the hollow body constructed is removed from the mould.

When the body is removed from the mould, the sleeve 9, which in the preceding operations was interposed between tlle elastic central tube 4 and the inner surface of the concrete, must remain adhering to the concrete.

Now, the circular reinforcements or hoops 16 are generally made of hard steel having a very high elastic limit, enabling them to be subjected by the process described hereinbefore to elastic tractive forces much greater than kg./mm.2. When the concrete has set and hardened and when the pressure in the central tube 4 is cancelled, the diameter of the pipe diminishes slightly owing to the elastic shrinking of the concrete as a result of the tension of the circular reinforcements. In this way there is produced in the reinforcements a decrease in tension in accordance with the moduli of elasticity of the concrete and of the steel. lf the sleeve 9 were made of a steel of the same quality as that of the hoops, it would be brought during the moulding operation to a substantially equal tension, but once the pressure is relaxed in the central tube 4, its residual tension, of the same order of magnitude as that of the hoops owing to the small difference in diameters, would be supported by the adhesion of this sleeve to the concrete. There would therefore be a risk of detachment. In order to avoid these risks, and in order that the inner-lining sleeve remains adhering to the concrete, it is necessary that tractive forces existing in this sleeve when the pressure is relaxed in the central tube 4 and when the concrete has undergone its elastic shrinking, should be sufficiently small so that the force whereby the sleeve adheres to the concrete remains dominant. For this purpose, it is advantageous to select for the sleeve a material whose elastic limit is distinctly lower than that of the hoops, but which is capable of an adequate elongation before rupture to withstand the expansion imposed by the central elastic mandrel during the course of the operations described hereinbefore. Materials of this kind are, for example, mild or non-rusting steels which are commercially obtainable in the `form of thin sheets.

The mechanical features of these sheets and more particularly their elastic limit and their elongation are compatible with the working conditions required by the process according to the present invention. Plastic materials not liable to be attacked by the liquid or gaseous fluids transported can also be suitable.

The diagram shown in FIG. 5 (which is not drawn to scale) shows the phenomena which occur. In this diagram, the tractive forces in the sleeve and in the circular reinforcements have been plotted as ordinates, and the elongations as abscissae. When the expansion ofthe sleeve 9 commences at the beginning of the operation of compressing (squeezing) the concrete, the point representing the state of the sleeve is displaced from O along a straight line OB. When the expansion continues in the second phase of the process, the circular reinforcements are elongated in their turn and the law connecting the tractive force to the elongation in these high-elastic-limit reinforcements is shown by the straight line O'D, whilst the sleeve assumes a permanent elongation from the point B where the elastic limit of the metal :of the sleeve is exceeded. The law connecting the elongation of the sleeve to the tractive force then follows the straight line BC which is much less steeply inclined. The abscissa O'a represents the value of the elongation of the circular reinforcements (Oa represents the elongation of the sleeve in the diametral sense) at which the pressure increase is stopped in the central elastic mandrel. This value corresponds to a tension load Tc in the sleeve and a much higher tension load Td in the circular reinforcements. When the pressure is relaxed in the elastic mandrel 4 and in the outer tubes 6 about the staves in order to enable the hollow body to be removed from the mould, the tension load of the `circular reinforcements falls from Td to Te owing to the elastic shrinking of the concrete, at the same time as the tension in the sleeve tends to diminish along the straight line CC in accordance with well-known phenomena. If the abscissa of the point E, representing the elastic elongation existing in the circular reinforcements coincides with that of the point C', as has lbeen assumed in the diagram, it will be seen that the sleeve will have neither a compressive stress nor a tractive stress. \If the abscissa of the point E is greater than that of the point C', the sleeve will remain in tension, and if it is smaller the sleeve will be in compression. By an appropriate choice of the tension imparted to the circular reinforcements and of the material of the sleeve, it will generally be possible to arrange that there only remain in the sleeve tractive forces compatible with the value of the adhesion of the sleeve to the concrete or residual compressions which do not detrimentally affect the principle of the process.

The form of embodiment of the mould illustrated in FIG. 3 differs from the preceding form by the elimination of the rubber tube 4 on the central core, the inner lining sleeve 9 being used to transmit to the concrete first of all the pressure used for drying and compacting `the concrete and then the stronger pressure intended to expand the concrete together with its reinforcements and the outer mould formed by the staves. The sleeve 9 is arranged at a certain interval from the rigid central core 1 and concentrically with the said core, the said interval 1a being closed at its ends by annular packings 15 which provide sealing-tightness when the gap is supplied with water under pressure through the duct `5. These packings can be made of highly elastic rubber and can be suciently compressed initially between the core and the sleeve to maintain the sealing-tightness when the sleeve 9 expands under the action of the water pressure. They can also be constituted by hollow rubber pads inilated by the same water pressure or by U-section leathers of the type generally used in hydraulic work.

The plugs 11 and 12 are arranged between Vthe sleeve 9 and the staves 2.

FIG. 3 shows two steel rings 16 which are relatively thick and are each Welded to one of the ends of the sleeve 9 externally of the said sleeve, that is to say at the concrete side. These rings are enclosed in concrete only over part of their length. They will be used to constitute joints for connecting the pipes to one another as idnicated hereinafter. FIG. 4 shows a finished pipe. 17 indicates the outer concrete body pre-stressed by the circular helical reinforcements which have been tensioned as indicated hereinbefore, and 9 is the inner lining sleeve provided with end rings 16. The ends of the sleeve 9 and of the rings 16 project from the concrete body to facilitate the execution of joints between pipes.

As has been stated, the pipe can be provided with longitudinal reinforcements, that is to say reinforcements parallel to its axis. These reinforcements will be arranged in the annular gap between the expandable central core and the staves before the concrete is poured in. They can be put in tension and elongated elastically before the concrete is `poured if it is desired to pre-stress the concrete longitudinally. -For this purpose, there will be used the conventional means known in the pre-stressing of concrete, such as jacks bearing on the mould or on external elements. The reinforcements will be held ytensioned until the concrete sets and hardens. If they are attached in the tensioned state to the exterior of the mould, the plugs 11 and 12 will be adapted to permit `the passage therethrough of these reinforcements.

It should be noted that the inner lining sleeve 9 can act as a longitudinal reinforcement, permitting a reduction in the cross-section of those which `are to be enclosed in the concrete.

In case where the sleeve is constituted by a metal sheet, the sleeve with its entire cross-section plays an important part in the resistance of the pipe to pressures to which the pipe is subjected during use.

FIG. 6 shows one form of embodiment of a joint between pipes. The ends of two pipes to be collected -together are at t1 and t2. The end rings 16 of the two pipes, which advantageously have bevelled ends 18, are connected together by a welded seam 19 executed between these ends. The projecting portions of the rings and the welded seam are enclosed in concrete 20 reinforced by hoops 21 and poured into the gap between the concrete bodies 17 of the two pipes to be connected.

It is also possible to have a conventional interlocking joint (FIG. 7) by welding a female conical ring 22 to the end ring 16 of one of the pipes, the ring 16 of the other pipe forming the male portion which is engaged in the ring 22 with interposition of an elastic or plastic packing ring 23. Concrete can be poured into `or a protective plastic lining sprayed on to the gap between the concrete bodies 17 of the two pipes.

FIG. 8 shows the construction of a flanged joint. A ring 24 carrying the flange 25 with holes 26 for connecting bolts is Welded at 27 to the end ring 16 of each of the pipes.

What is claimed is:

In the art of manufacturing prestressed concrete pipes and hollow bodies and like articles by radially expanding a mass of moist concrete contained in `a radially-expansible annular mold and embedding at least one annular reinforcing member of high tensile steel having a high elastic limit, the steps of (a) pouring the moist concrete around a tubular member which defines the inner wall of said annular mold and which is formed of a substance having an elastic limit substantially lower than that of said reinforcing lmember and capable of substantial radial expansion without rupture,

(b) `applying internal pressure forces to said tubular member to expand it uniformly radially-outwardly, -thereby applying radially expansive forces to the concrete in the mold and the reinforcing member therein, the pressure forces applied internally to said tubular member having a magnitude suflicient to expand radially said .tubular member `bey-ond its elastic limit without rupture but insuicient to stretch said reinforcing member radially-outwardly beyond its elastic limit,

(c) permitting said concrete to set,

(d) releasing said internal pressure, and

(e) removing the thus-formed article from said mold.

References Cited in the file of this patent UNITED STATES PATENTS 1,910,643 Sherrard May 23, 1933 1,965,748 Mitchell July 10, 1934 2,048,253 Freyssinet July 21, 1936 2,138,946 Trickey Dec. 6, 1938 2,236,107 Miller et al Mar. 25, 1941 2,382,171 Pomykala Aug. 14, 1945 2,401,092 Miller et al May 28, 1946 2,579,801 Crom et al. Dec. 25, 1951 2,585,446 Edwin et al Feb. 12, 1952 2,730,783 Kennison lian. 17, 1956 2,913,798 Breguet Nov. 24, 1959 FOREIGN PATENTS 1,072,441 France Mar. 17, 1954 1,113,484 France Dec. 5, 1955

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