EP0117167A1 - Method for lifting a structure - Google Patents

Abstract

1. A method of lifting a structure having a substantially horizontal and substantially airtight surface (3), said method being of the type relying on the provision of a closed space (19) beneath the top surface (3) of the structure, termed the thrust surface and contributing to the closing off of said space (19), for the injection of compressed gas, characterized in that the compressed gas is used to provide a lifting force different from the load of the structure ot be lifted, said difference being taken up by mechanical pushing or pulling means.

Description

The invention relates to a method for lifting a structure with a generally horizontal surface that is substantially sealed, or made waterproof. By lifting, it is understood that a movement from the bottom upwards is more particularly designated (which will be the most frequent application of the process), but also, if necessary, from top to bottom. Indeed, the realization of certain structures is often simplified by an execution at a level lower than the final level? a lifting operation is then necessary. The described method is adaptable to an execution at a level higher than the final level followed by a descent; it can be advantageous for any movement of load having a support surface made watertight.

In the case where the loads are fairly well distributed, it is very advantageous to have a lifting means developing a distributed force; the forces in the structure are then low and do not require (or little) reinforcements for this phase.

Document FR-A-2 215 519 discloses a lifting process according to which a closed space is created beneath the surface, called the pushed surface, of the structure, which is supplied with gas under pressure, said surface participating in the closing from space.

This gas is preferably air. The air overpressure generates a uniformly distributed force independent of the differences in levels of the wall receiving the thrust. Air is a free fluid, having no nuisance on the materials constituting the structure or surrounding. In order for the air to provide lift for the pushed surface in an essentially vertical direction, the pushed surface should have sufficient horizontal projection. That's what we hears at the top of this thesis when speaking of a structure with a generally horizontal surface.

The process disclosed in the aforementioned document could not have been continued, because it is purely utopian: any attempt to lift by this process is doomed to failure because of the instability of the pushed surface, which tends, under the slightest external stress, to be taken from the heel, by damaging on this occasion the flexible membrane which closes the volume of thrust.

The object of the invention is to provide a stable and therefore viable lifting method.

This object is achieved according to the invention in that by means of the pressurized gas a lifting force different (however generally close) is exerted from the load of the structure to be lifted, the difference being taken up by mechanical means of thrust or traction towers.

According to one embodiment, the pressure of the gas serves to support part of the load, preferably between 90% and 99.5% thereof, the rest being taken up by mechanical means also ensuring the lifting movement.

According to another embodiment, the gas pressure is used to push the surface with a force greater than its load, the rest being taken up by traction means also ensuring lifting.

To achieve the air overpressure, it is necessary to completely close the volume under the application surface by a system compatible with the displacements of the structure.

Advantageously, the closed space is formed of a base constituted by a fixed and sealed bearing surface, preferably substantially parallel to the pushed surface, of a sealed peripheral skirt compatible with the variation in spacing between the surface of support and the pushed surface during lifting, and, of course, of the pushed surface itself.

Advantageously, the peripheral skirt is a flexible cover which can be rubberized or plasticized.

It may be necessary to provide bearing surfaces for this sheet, in order to prevent the formation of pockets having large radii of curvature causing high tensile forces.

The tarpaulin must be difficult to tear, flexible, easily repairable in the event of an accident, It can be glued or pinched with a foam cord on the edges of fixed and mobile surfaces,

Ires support surfaces of the tarpaulin do not, in general, entirely in construction they are therefore made for this operation; they must be parallel, spaced about ten centimeters from each other, a value compatible with construction tolerances, the smooth running of the sheet and low tensile forces. Generally, they will be vertical, but in the case where the lift must be accompanied by a horizontal displacement, they can be oblique.

The skin of the support frame must be very careful to avoid pinching of the tarpaulin and piercing.

The elements are advantageously removable in order to allow possible repairs to the tarpaulin.

The structure of this support frame can be formed by formwork elements or by a mesh specially designed for this purpose.

Air intake and deflation holes are arranged in the tarpaulin or in the structure.

Another solution is to provide two sealed, parallel, smooth surfaces, provided with a seal attached to one and sliding on the other.

Cracks in concrete on fixed and moving surfaces can cause air leaks; however, their intensity is low and does not compromise the functioning of the entire air cushion.

Advantageously, vertical guides are installed to avoid translations and rotations; complementary jacks ensure the adjustment of the horizontality and emergency supports, such as stays, prevent at any time the fall of the structure in case of rupture of the peripheral skirt.

The vertical guides have the task of balancing the horizontal actions acting on the raised structure, the origin of which can be notably the wind, the pressure of the tarpaulin on the bearing surfaces in the event of accidental or design asymmetries, or even the tilt of the cylinders and was.

Depending on the shape of the structure, there will be 2, 3 or more guides.

A system can consist of two rollers placed on either side of a rail stiffened by a metal trellis structure; the rail is integral. of the fixed structure, the rollers linked to the mobile structure or vice versa.

If the rollers are free to move on their axis, only the force perpendicular to this axis is balanced, so four guides of this type are needed to cope with a horizontal action of any direction.

Structural deformations must be assessed in the different phases (with and without overpressure).

It may be necessary to change the position of the rollers during lifting by small hydraulic cylinders.

It is advantageous to provide vertical guidance by the lifting cylinders if the examination of deformations and forces allows.

The horizontal actions, the difference in position between the resulting thrust and the center of gravity generate a reversal torque which must be balanced by secondary cylinders,

• - la poussée de l'air équilibre la charge totale moins la poussée des vérins ;
• - la poussée de l'air équilibre la charge totale plus la traction des vérins ou des cables,

One calculates the forces necessary to bring center of gravity and resulting thrust on the same vertical; there are two possibilities:

• - the air pressure balances the total load minus the pressure from the cylinders;
• - the air pressure balances the total load plus the traction of the cylinders or cables,

In the first aspect - of the invention, the gas pressure is used to sustain most of the char- ^g e of the structure, preferably between 90% and 99.5% thereof, the remainder being taken up by mechanical means also ensuring the lifting movement,

The amount of air in the cushion should be increased as it is lifted; the overpressure must be constant so as not to modify the load on the cylinders.

A servo system consists in regulating the pressure to a constant value with a low tolerance by a pressure regulator. A variation less than or equal to + 2 millibars is possible.

The hydraulic cylinders control the lifting provided that their speed is compatible with the air flow supplied by the compressor; the oil pressure in the cylinders is therefore monitored.

The variation of the load carried by the air is an additional load on the cylinders. The cylinders must be able to balance all random vertical actions during lifting (e.g. wind suction, variations in rolling resistance of the rollers).

The number of cylinders depends on the structure to be lifted, it is at least equal to 3.

The lift heights at 3 points are compared; level corrections are made by the cylinders.

It is possible to install an automatic unevenness correction system.

The air pressure values, forces by cylinders calculated are checked when the structure is detached,

The eccentricity of the center of gravity of the structure to be lifted can be reduced by placing counterweights on it.

The deformations of the structure during lifting and during support at the end of movement generally make it desirable to interpose hooped elastomer plates between the stays and jacks and the support structure.

The raised structure rests on the safety struts; horizontal stability may need to be reinforced to take account of long-term wind actions.

The sealing system is then dismantled and the construction of the final supports undertaken,

According to the second aspect of the invention, the gas pressure is taken up more than 100% of the load, for example 102% of the load, and the structure is retained by tensile forces.

The problem of buckling is then eliminated, cables can be used and lifting can be envisaged over great heights; the fixed structure must be provided for these actions.

The traction in the cables can be obtained by winches or counterweights with pulleys.

Another advantage of this solution is to create a greater return torque than with the previously developed solution, due to the greater distance of the points of application of the resulting forces directed upwards and downwards.

• - la figure 1 est une vue partielle en coupe de la partie supérieure d'une structure réalisée conformément à l'invention.
• - la figure 2 est une vue schématique de dessus montrant la répartition des étais et des vérins.
• - la figure 3 est une vue en coupe partielle de la structure montrant la bâche et l'ossature d'appui, avant levage.
• - la figure 4 est une vue analogue à la figure 3, en fin de levage.

The invention will be better understood on reading the following description of a particular embodiment, referring to the accompanying drawings in which

• - Figure 1 is a partial sectional view of the upper part of a structure produced in accordance with the invention.
• - Figure 2 is a schematic top view showing the distribution of the props and jacks.
• - Figure 3 is a partial sectional view of the structure showing the sheet and the support frame, before lifting.
• - Figure 4 is a view similar to Figure 3, at the end of lifting.

Figure 1 shows the upper part of a structure produced in accordance with the invention. This structure intended to cover a nuclear reactor essentially consists of two external cylindrical enclosures 1 and internal 2, covered respectively with external domes 3 and internal 4 with the same curvature opposite.

To give an idea of the dimensions of the structures which the invention may relate to, it can be specified that in a particular example, the domes 3,4 have an arrow of approximately 9m, for a diameter of about fifty meters. They are spaced from each other by two meters and the external dome culminates at more than 60 m above the ground.

After having mounted in a traditional manner, the enclosures 2,3 and the internal dome 4, the latter was used as formwork for the external dome 3 (fig, 3) taking care to have between the two domes 3,4 a laminate 5 allowing thereafter the passage of air and the separation of the domes. This laminate can consist in a known manner of a superposition of welded mesh, chipboard and plastic sheets; or geotextiles with a high percentage of vacuum covered with plastic material.

The construction of the belt 6 of the external dome 3 can be facilitated by the use of predales 7 of suitable shape which avoids the problem of a cantilevered formwork. This pre-slab also has the advantage of naturally creating a draft and an air circulation interval without interposition of laminate. It promotes the implantation of the skirt fixing inserts.

Is fixed under the base of the belt 6 of the outer dome 3 of the vertical elements 8 of a peripheral support frame, interposed between the two enclosures 1 and 2, and on which will be able to support a flexible waterproof cover 9 making the tour of the structure. This cover 9 is tightly fixed on the one hand to the periphery of the external dome, for example at 10, at the level of the fixing of the support frame 8 on the belt 6, and on the other hand, at 11 , on the periphery of the internal dome.

This waterproof fixing, obtained for example by nailing, under a strip and joint, or gluing, is carried out so that the cover 9 forms a pocket 12 downwards, which will allow the cover to follow the elevation movement of the dome by absorption of said pocket,

The support frame comprises vertical elements 8 spaced peripherally from 1 to 2 m, as well as horizontal elements (not shown) spaced half a meter apart and forming a metal mesh on which it is possible to hang plates 13 plywood which will form the solid support on which the pressure sheet will bear. This arrangement has the advantage of being very flexible and light; it allows rapid disassembly and repairs in situ for the purpose of plugging a leak in the tarpaulin, for example.

One can however choose to replace all or part of this device with formwork elements already available on the site.

The vertical elements 8 of the support frame are provided with a member 14 such as a roller or a sliding shoe, allowing them to rest on the external enclosure 1 permanently, including during the movement d elevation of the external dome 3.

During the pouring of the belt 6, provision has been made to reserve by thirty-six sleeves 15 a housing for six jacks 16 and thirty vertical struts 17, distributed over the periphery and spaced about 4.40 m apart (cf. fig. 2 ) The cylinders are themselves fitted with a safety nut.

The jacks 16 and struts 17 rest, by means of an elastomeric support 18, on the enclosure 1.

To carry out the lifting of the external dome 3, the closed space 19 reserved between the two domes 3, 4 and the peripheral cover 9 is supplied with compressed air. This is at a regulated pressure to ensure the recovery of most of the average load; between 95% and 99.5%. These values are not critical, however, and can be changed depending on a variety of factors; this is how a strong wind can create an upward suction force exerted on the external dome and making it desirable, for reasons of stability, to resume by air pressure only about 90% of the charge.

The lifting proper is carried out by the jacks 16. To take account of the possible imbalance of the load, resulting either from its constitution or from external actions (winds), the jacks are divided into three groups of two jacks 16a, 16b, 16c, supplied at pressures which may be different,

In order to ensure total safety of the process, the external dome must be able to rest at any time without falling on emergency supports. This is the role of the props 17 constituted by bars or tubes 17a threaded externally on the height of the lift and fitted with a nut 17b which is screwed in progress ascent,

At the end of lifting, the dome 3 rests on the safety struts 17 (approximately 100 tonnes per strut).

The invention applies to the lifting or vertical or oblique movement of all kinds of large-scale structures, in particular in the field of construction of engineering structures or industrial structures.

Claims (7)

1. A method of lifting a structure with a generally horizontal surface (3) which is substantially sealed, of the type according to which a closed space (19) is created under the surface (3), called the pushed surface, which is supplied with gas under pressure. , said surface (3) participating in the closing of the space (19), characterized in that a lifting force different from the load of the structure to be lifted is exerted by means of the gas under pressure, the difference being taken up by mechanical means of pushing or pulling. 2. Method according to claim 1, characterized in that the gas pressure is used to support part of the load of the structure, preferably between 90% and 99.5% thereof, the rest being taken up by means mechanical (16) also ensuring the lifting movement. 3. Method according to claim 1, characterized in that the gas pressure is used to push the surface with a force greater than its load, the difference being taken up by traction means. 4. Method according to any one of claims 1 to 3, characterized in that the gas pressure is regulated to a constant value. 5. Method according to any one of claims 1 to 4, characterized in that the space (19) is closed in particular by a peripheral skirt constituted by a flexible cover (9) associated with a support frame (8,13 ). 6. Method according to any one of claims 1 to 5, characterized in that there is provided a guide (8,14) of the structure in the direction of lifting. 7. Method according to any one of claims 1 to 6, characterized in that there is provided a safety support system (17).

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