WO1992003622A1

WO1992003622A1 - Method for fabricating steel-reinforced concrete structures

Info

Publication number: WO1992003622A1
Application number: PCT/FI1991/000258
Authority: WO
Inventors: Seppo RYYNÄNEN
Original assignee: Gesertek Oy
Priority date: 1990-08-21
Filing date: 1991-08-21
Publication date: 1992-03-05
Also published as: FI904137A; FI904137A0; FI89092C; AU8322691A; FI89092B

Abstract

This invention concerns a method for producing a steel-reinforced concrete structure. A reinforcing steel fabric (86, 86a, 50) is stiffened to an essentially self-supporting stage and subsequently fortified by shortcreting (6, 8).

Description

Method for fabricating steel-reinforced concrete structures

The present invention relates to a method in accordance with the preamble of claim 1 for fabricating a steel-reinforced concrete structure suitable for different constructions .

We have disclosed in our earlier patent application

FI 894586 a method for fabricating a composite structure based on the combination of a form-shaped sheet, preferredly a formed steel sheet, with concrete applied by shotcreting. Disclosed in the same patent application is a method for producing adherence in a composite structure as well as the joining of different sheets by forming corrugations into the sheet. Suitable fine-mesh expanded sheet metal fabric fabricated by stretching from thin sheet metal slit by punching is known from US patent 1,864,598 and GB patent 1,409,482. An expanded sheet metal fabric having a dominatingly diagonally oriented coarse mesh fabricated from a thicker sheet metal is known from, e.g., US patent 3,570,086. Another patent application FI 902487 filed by us discloses a method for fabricating concrete floors in multi¬ storey building constructions.

The drawbacks of conventional constructions include, i.a., such difficulties as the fact that large and heavy elements must be hauled to the construction sites necessitating the use of high-capacity lifting equipment. As a rule, prefabricated elements are, however, found incapable of of ering spans of desired lengths. An alternative method is on-site casting. By contrast, this approach requires the use of large mold and scaffolds. Furthermore, on-site casting of structures necessitates erection of temporary supports for taking the load of the unhardened concrete mix. Such erection and dismantling operations cause appreciable impediments in the work progress. Shotcreting through layers of reinforcing steels is a complicated process with conventional methods, and the fill-in of rear spaces behind the reinforcing steels in particular often remains incomplete. The implementation of shotcreting in constructions designed for long spans is cumbersome and generally requires the use of additional support.

It is an object of the present invention to reduce the afore-described drawbacks through the method in accordance with the invention by means of stiffening of the reinforcing steel fabric into a self-supporting shape which is then strengthened by shotcreting.

The invention is applicable to a variety of different embodiments. The following diagrams are intended only to present exemplifying applications which serve to clarify the operating principle of the invention. The illustrated constructions can be oriented in any desired way as appropriate. For the sake of clarity, the description of the illustrated examples refers to the constructions by, e.g., their upper and lower sides, while these aspects might equally well be called the different lateral sides of the construction.

Figure 1 shows a section of a reinforcing steel fabric in accordance with the invention prior to concreting.

Figure 2 shows a section of a reinforcing steel fabric illustrated in Fig. 1 after the attachment of stiffeners to its lower side.

Figure 3 shows the reinforcing steel fabric illustrated in Fig. 1 or 2 resting on a base after the applica¬ tion of concrete. Figure 4 shows shotcreting through the reinforcing steel layers by means of shotcreting jets directed from different directions .

Figure 5 shows a visualization of one possible form of an expanded sheet metal fabric in which diagonally stretched strips are slit from a thin sheet so as to form trestle-like supports.

Figure 6 shows diagrammatically the section of expanded sheet metal fabric illustrated in Fig. 5 after the attachment of the cross-directional stiffeners to its lower side.

Figure 7 shows diagrammatically the section of expanded sheet metal fabric illustrated in Fig. 6 after the attachment of the longitudinal stiffeners to its lower side.

Figure 8 shows diagrammatically the structure illustrated in Fig. 6 or 7 after the application of concrete to its lower part.

Figure 9 shows diagrammatically the section of expanded sheet metal fabric illustrated in Fig. 5 after the attachment of the longitudinal stiffeners to its upper side.

Figure 10 shows a cross-section in which the expanded sheet metal structure shown in Fig. 5 is bent into a corrugated shape and stiffened prior to concreting. Figure 11 shows diagrammatically an expanded sheet metal structure strapped to a base and partially cut/bent on the base prior to concreting.

Figure 12 shows a beam in accordance with the invention having its waist fabricated from concreted and corrugated expanded sheet metal abric.

Figure 13 shows a fine-mesh expanded sheet metal fabric strapped behind a higher-strength coarse-mesh expanded sheet metal fabric.

Figure 14 shows the cross-section of a beam in accordance with the invention during shotcreting.

Figure 15 shows the pushing or pulling of a light-weight trussed bridge girder onto ready-made trestles.

Figure 16 shows the shotcreting operation being carried out from a lift platform.

Figure 17 shows bridge girders in accordance with the invention in place in ^"a stage partially uncoated by concrete.

Figure 18 shows diagrammatically a cross-section of the bridge illustrated in Fig. 17 after completion of concreting.

Figure 19 shows a visualization of an arched bridge with an advantageous form of construction through the application of the present invention.

Figure 20 shows diagrammatically the lifting operation of light-weight elements of a vault bridge. Figure 21 shows the stages of the lifting operation of light-weight elements of a vault bridge.

Figure 22 shows a visualization of a vaulted building.

Figure 23 shows a visualization of a building in which the roof is supported by high-strength vaulted arches.

Figure 24 shows a side view of the building illustrated in

Fig. 23.

Figure 25 shows a visualization of long-span hollow-core girder bridge prior to concreting.

Figure 26 shows a visualization of an underground parking hall.

Figure 27 shows a visualization of a noise abatement barrier along a road.

Figure 28 shows cylindrical reinforcing steel fabrics resting on a base prior to concreting.

Figure 29 shows reinforcing steel fabrics spaced apart prior to concreting.

Figure 30 shows shotcreting between cylindrical rolls.

Figure 31 shows a visualization of an elongated shape of an expanded sheet metal fabric mounted onto a shaped base made of thin sheet metal.

Figure 32 shows a longitudinal section of a shotcreting process performed between endless belts. Figure 33 shows a longitudinal section of a shotcreting process performed between a fabric and an endless belt.

Figure 34 shows interactive function of a diagonally meshed fabric in conjunction with concrete.

It is a primary object of the present invention to achieve a self-supporting composite structure formed by the combina¬ tion of concrete and reinforcing steel using maximally effective work methods and minimal manual labour so that the construction is particularly adaptable to constructions with ^'long spans. The method according to the invention makes it possible to design constructions with a high bending sti fness. Thence, on-site support becomes unnecessary also for constructions with short spans. A f rther o ect of the invention is to diminish on-site transportation and haulage of heavy elements by way of fabricating the final heavy- weight construction typically not earlier than at or near its final location.

Fig. 1 illustrates a section of an elongated shape of reinforcing steel fabric made by cutting and stretching from material called expanded sheet metal. Strips of the expanded sheet metal 86 form a mesh fabric, in which the strips 86 are located diagonally in relation to the longitudinal direction of the fabric. The diagonal strips 86 are aligned to form a network of approximately continuous strands allowing them to transmit loads in a functional manner. The diagonal strips 86 can thus transmit effectively the shear stresses imposed on a structure having, for instance, a shape of a beam. Because all strips 86 of an expanded sheet metal fabric are firmly bound to each other at the nodes of the fabric, the entire fabric has a strong structure. Since the strips 86 are usually slightly twisted about their longitudinal axis during the fabric manufacturing process, even a planar expanded sheet metal fabric exhibits a certain degree of bending stiffness. In the elongated structure illustra yd in Fig. 1, the bending stiffness of the structure has been improved by folding the expanded sheet metal fabric into a wavy structure at its center. Several different shaped forms are possible for the purpose of obtaining an improved bending stiffness for an expanded sheet metal fabric. For optimal strength, the cross-section of the fabric can advantageously have the form of a triangle, trapezoid or rectangle. A structure corresponding to that illustrated in Fig. 1 can also be made from conventional reinforcing steel wire by, e.g., welding the wires together and then bending them into desired shape.

Fig. 1 shows only a section of a structure which can have a substantial length, thus making it possible to cross long spans. Such application can be, for instance, bridges and building floors between the storeys as well as any similar structures. Vertically erected structures having the same construction can be made into different kinds of walls and pillars. Excluding the weight of concreting, the inherent weight of the structure is low. By complementing the structure with concreting, a composite structure with vastly improved strength is attained. The structure illustrated in Fig. 1 is lightweight yet sufficiently strong for a plurality of applications.

Fig. 2 shows a shaped expanded sheet metal fabric 86, 86a which has its lower part stiffened solely by means of addi¬ tional reinforcing steels 50 that are aligned in the longi¬ tudinal and transverse directions. In a horizontally aligned beam, the tensional stresses are concentrated to the lower part of the beam, thus necessitating the use of additional reinforcement at this area. When necessary, additional reinforcement can be applied to other parts of the shaped structure as well. To improve the strength of the structure prior to concreting, the additional steels can be attached by, e.g., welding to the expanded metal sheet fabric 86, 86a. As appropriate, the additional steels 50 can also be placed in other directions, e.g., diagonally. The vertically aligned part 86a of the shaped expanded sheet metal structure is made of a similar fabric as the horizontal part 86. The use of a different number for designating this part is only for the sake of clarity. The reinforcing steel structure 86, 86a, 50 has a remarkable capability of holding its shape even prior to concreting. Therefore, the structure 86, 86a, 50 can be lifted to stretch self-supportingly without any dedicated temporary supports over a very long span or instance.

Fig. 3 shows a concrete layer 6 applied to the lower part of reinforcing steel fabric illustrated in Fig. 1 or 2. The upper part of the corrugated reinforcing steel fabric remains above the concrete layer 6. Concrete has been applied while the structure is resting on a base 27. The use of a smooth base 27 achieves a smooth lower surface of the concrete layer 6. An initial shotcreting with only a thin concrete layer 6 attains an effective bonding of the additional reinforcing steels to the structure without compromising the low weight of the structure at this stage. The setting of the concrete layer 6 further improves the strength of the structure thus making it capable of taking higher loads in the next stages. The improved strength makes it possible to add further concrete layers onto the initial concrete layer 6. The base 27 can be an appropriate type of plate which can later be removed or left in the structure as an integral part of it to perform as, e.g., thermal insulation. The reinforcing steel fabric 86, 86a can be entirely covered by concrete layers. Where appropriate, the inner surface of the corrugated structure can be formed into a cavity by coating the surface of the corrugated structure 86, 86a with a fabric of finer mesh which is essentially impermeable to concrete.

Fig. 4 shows the method of shotcreting using two concrete jet nozzles 5 so that concrete mix is sprayed to a single spot simultaneously from two different directions . Concrete jets 4 arriving from different directions meet each other behind the reinforcing steel structures 50 thus filling effectively the rear side of the reinforcing structures. The different concrete jets 4 perform in complementary way so that a possible shadow area of one jet is covered by another jet. The partially impinging concrete jets 4 achieve the compaction of concrete both laterally and partially retroactively from behind the reinforcing steel structure 50 toward the structure 50. The filling of the rear side of the reinforcing steel structure is further enhanced by the scattering of the jets from the backing surface 27 possibly placed to the rear of the reinforcing steel structure. This approach allows the use of shotcreting even through thick layers of reinforcing steel fabrics. In place of two concrete jets 4, it is possible to apply even a higher number of concrete jets emitting from several different directions by using several nozzles 5 aimed from different directions. The individual nozzles 5 can be connected to each other with the help of supporting arms 82. If the arms 82 are made movable in respect to each other by means of, e.g., a pivoted joint 89, the attack angle and mutual distance of the jets can be varied as necessary in different conditions. With the help of the described principle, an efficient concreting of the rear sides in different types of reinforcing steel structures is easily implemented. The individual nozzles 5 can be fed from a common feeder pipe from which the flow of the concrete mix is divided by branching unions into the necessary nozzle connection lines. Alternatively, each nozzle can be provided with a dedicated feeder line. A group comprising two or more nozzles can be manually movable, or alternatively, an apparatus resembling a robot with an arm. The use of remote control allows a precise and effective control for a nozzle group having an appreciable weight even at the end of a long arm.

The type of expanded sheet metal fabric shown in Fig. 5 is lexible in both its longitudinal and transverse directions. The diagonal braces 86 form trestles supporting the upper surfaces 58 in both directions. The lower braces 33 secure the diagonal braces 86 to each other in both directions.

Fig. 6 shows a method of stiffening the expanded sheet metal fabric illustrated in Fig. 5 by means of a transverse stiffener 57 of the lower surface which can be, e.g., welded to the lower braces 33, thus allowing them to take tensional stresses of the lower surface in the transverse direction of the structure. The inner side of the diagonal braces 86 can be provided with, e.g., an attached fine-mesh fabric so that the inner space within the supporting trestles 58, 86 remains void during the later concreting stages.

Fig. 7 shows the method of stiffening the lower side of the structure by means of reinforcing stiffeners 57 in both longitudinal and transverse directions;

Fig. 8 shows the method of fortifying the lower part of the illustrated reinforcing structure with the help of a thin concrete layer 6. The concrete layer 6 can further be covered by an additional concrete layer 8. The diagonal braces 86 passing through the different concrete layers 6, 8 bond the concrete layers to each other, thus preventing any possibility of their separation despite the different times of concreting. The diagonal braces 86 can be provided with different anchorage means in order to secure the bonding of concrete to steel. A higher number of concrete layers can be added by shotcreting provided that the earlier applied layers are allowed to set and harden prior to the applica¬ tion of the subsequent layers. This method makes it possible to increase the strength and weight of the structure in a synchronized manner.

Fig. 9 shows the reinforcing of the upper side of the expanded sheet metal fabric in its longitudinal direction by means of reinforcing members 52. Correspondingly, the upper side can also be reinforced in its transverse direction.

Fig. 10 shows an expanded sheet metal structure, similar to that illustrated in Fig. 5 for instance, shaped by bending to have an corrugated form of its cross-section. The bending of the reinforcing structure comprised of diagonal braces 86 into the corrugated form is performed prior to the attach¬ ment of lower side stiffeners 57 and the upper side sti^^eners 52. The sti feners which are attached by welding for nstance give the structure added strength, thus allowing its use as a frame of, e.g, a vault construction. By shotcreting the structure first with a thin lowermost concrete layer 6, a low addition in the weight of the structure bestows a high contribution to its lateral stiffness. The longitudinal stiffness of the structure can be improved by the use of longitudinal reinforcing members 50. The underlying concrete layer can be shotcreted against a fine-mesh expanded sheet metal fabric 10 for instance, or alternatively, a suitable temporary backing can be used to attain a smooth surface f the concrete layer. After the hardening of the underlying concrete layer, the next concrete layers can be shotcreted as necessary. In conventional vault constructions it is customary to cover all reinforcing steels with a concrete layer in order to prevent corrosion attack in the steels. The setting of concrete can be improved by the use of different kinds of accelerating admixtures so that the underlying layer can quickly take the load of the next layer to be applied. The fabric of reinforcing steels can be penetrated by shot¬ creting each point from two or more nozzles aimed from different directions to the same point. When desired, the expanded sheet metal structure can be formed in a similar manner also in its longitudinal direction, whereby it becomes possible to achieve structures of vaulted cupolas.

Fig. 11 shows a planar expanded sheet metal fabric 86 of diagonal strips from which a part 86a has been cut and bent upright to provide anchorage between the different layers of concrete. The base 27 is attached by straps 13 to the reinforcing steel fabric 86. The base 27 can be appro¬ priately spaced by hanging for instance from the fabric 86 in order to make the formation of a smooth concrete surface possible. The shotcreting performed from different direc¬ tions can easily penetrate the reinforcing steel fabric 86.

Fig. 12 shows a lightweight beam produced so that its waist section is formed from a reinforcing steel fabric 86 of diagonal strips that has a good capability of taking shear forces when attached by, e.g., welding to a lower flange 57 and upper flange 52. The waist section can be straight in the longitudinal direction of the beam, or alternatively corrugated according to Fig. 12. The reinforcing steel fabric can be complemented with a fine-mesh fabric 10 which serves for preventing concrete jets from penetrating the structure. The waist section of the beam is fortified with a concrete layer 6 which also acts as corrosion protection. Prior to shotcreting, the frame construction of the beam is lightweight which makes it easy to transfer on-site into frame structures of, e.g., large constructions. Strength increase is attained by shotcreting the structure with concrete 6 not earlier than at its final or nearly final location.

Fig. 13 shows the method of attaching a fine-mesh fabric 10 by straps 13 to the coarse-mesh reinforcing steel fabric 86 of diagonal strips in order to prevent concrete from penetrating the structure. The fine-mesh fabric can be provided with stiffening corrugations 49 in order to improve the stiffness of the structure.

Fig. 14 shows the method of shotcreting the waist of the beam having the structure illustrated in Fig. 13. The lower flange 57 and the upper flange 52 of the beam are made of joined angle steels spaced by an attached fabric 86 of diagonal strips. The flange parts of the beam are concreted in order to prevent corrosion and improve strength. The flange parts 52, 57 can be provided with different kinds of anchorage means such as pegs or corrugations to ensure bond anchorage between steel and concrete. Concreting is advan¬ tageously performed not earlier than at the final installa¬ tion site or, when necessary, for strength improvement.

Fig. 15 shows the pulling or pushing of a lightweight bridge girder 86b, 10 to its final location on prefabricated supporting trestles 60. The reinforcing steel cage according to the invention can be made lightweight in relation to its span. Initially, the structure only has to take the load of its own weight. Weight and strength is adαed not earlier than in the final location by shotcreting the combination structure of reinforcing steel cage and girder construction implemented using the methods described above. The truss members 86b can be made of beams, while the fabric 10 is fabricated according to, e.g., the method illustrated in Fig. 13. Initially, the fabric serves as a working platform. After the shotcreting of the core structure, the hardened concrete can again be used as a working platform. The necessary pulling or pushing force 63 can be produced by means of, e.g., pull cables or hydraulic rams. In comparison to a conventional solution, the transfer operations are performed on a construction with appreciably lighter weight. The construction can be complemented with longitudinal beams with upper and lower flanges 57, 52. The thicknesses of shotcreted layers can be varied in the different parts of the construction. A thicker layer of concrete is shotcreted in places where higher stresses occur. In areas of lower stress the construction weight can be reduced by the use of thinner concrete layers. By contrast, the conventional methods of mould casting offer no easy approach to the optimization of layer thicknesses. The necessary minimum thicknesses for shotcreted layers can be indicated prior to shotcreting with the help of, e.g., elevated markings which will be covered by concrete. In general, shotcreting of a bridge construction is advantageously performed not earlier than having the girder structures already transferred to their final locations, while it is also possible to fortify some parts of the reinforcing steel cage 86b, 10 in order to achieve sufficient strength increase for transfer. The tops of the supporting trestles 60 are provided with conventional transfer mechanisms such as different types of rolls for instance.

Fig. 16 shows the shotcreting operation being carried out from a lift platform. When desired, the lift platform can be braced onto the stiffened reinforcing steel fabric, or alternatively, onto an already shotcreted construction such as the bridge deck for instance. Shotcreting of large or high-raised objects can be performed using high-capacity shotcreting robots. These robots use a long arm to take the shotcreting nozzle to the actual worksite vv ere it is remote-controlled without the need for the presence of workers at the actual worksite.

Fig. 17 shows the trussed reinforcing steel girders 86, 57, 52 prior to shotcreting. The rear part of the structures is shown shotcreted with vertically aligned concrete layers 8 and horizontally aligned concrete layers 6. The bridge deck 80 can be concreted onto the load-carrying girders using a fabric 10 as the foundation for concreting.

Fig. 18 shows diagrammatically a cross-section of the bridge illustrated in Fig. 17 after concreting. All lattice elements are coated with concrete 6, 8. This method disposes of any later paintwork on metal elements.

Fig. 19 shows an arched bridge which can be advantageously implemented through the application of the method in accordance with present invention. Conventional methods are clumsy for the erection of long and heavy vaulted arches 84. The method in accordance with the invention can be used for first erecting relatively lightweight, stiffened reinforcing steel lattices shaped to the form of the vaulted arches 84 that are concreted not earlier than at their final location. The relatively lightweight, stiffened reinforcing steel lattices shaped to the form of the vaulted arches 84 can be assembled, e.g., on the ground and the lifted to their final position. This method avoids the transfer of very heavy structures. The fluid concrete mix is easy to transfer by pumping to great distances and elevated locations as well. Shotcreting is started first on areas requiring an initial strength. Generally, the lower sides of vaulted arches are advantageously concreted first. The possible underwater structural parts can be prepared prior to the installation of the actual reinforcing steel lattice structure.

Fig. 20 shows diagrammatically the start of erection operations for a vaulted arch comprised of elements 84a and 84b preassembled on ground. The elements 84a and 84b of the vaulted arch are assembled to be stiffly supported by pivotal support joints 89 at their ends. The elements are aligned partially overlapping. Between the elements 84a and 84b is arranged some kind of a gliding mechanism 96, e.g., a roller assembly which makes it possible for the elements to glide in relation to each other along a glide surface 42. A lift force 64 backed by a suitable type of support is exerted on the lower element 84b. In waterways the support can be provided by, e.g., a pontoon. The arch elements 84a and 84b are later lifted up by rotating them about the pivotal joints 89 so that the ends 11, 11 of the arch elements finally become supported by each other. The elements of the vaulted arch to be lifted are still at the stage of erection in the form of relatively lightweight stiffened reinforcing steel lattices. The bridge construc¬ tion illustrated in Fig. 19 can also be erected using the described method. The trestles 61 of the bridge deck 80 illustrated in Fig. 19 can be attached to the vaulted arch already while the arch is in its lower position prior to the erection.

Fig. 21 shows the progress of the erection of the vaulted arch elements 84a and 84b illustrated in Fig. 20. When lifting from underneath in a long span is not further possible, the arch elements 84a and 84b can be lifted self- supportingly by exerting a pull force 63. This orce tends to attract the ends of the elements 84a and 84b, whereby the center part of the vaulted arch is erected. The pull force 63 can be accomplished by the use of different kinds of hydraulic mechanisms and even as simply as using tackles. When necessary, the use of an auxiliary extension 78 is possible in order to allow for an easy butting of the ends of the elements 84a and 84b in their upper position.

Fig. 22 shows a vaulted structure 84 ready concreted. The structure can be, e.g., a hall construction or a bridge element.

Fig. 23 shows a completed hall construction, in which the supporting vaults 84 of the hall ends are implemented using the method according to the invention. Guy cables 61 which take the supporting load of the roof are attached to the vaulted arches 84.

Fig. 24 shows in a side view use of vaulted arches 84 in an inclined position which would be difficult to implement with the methods of conventional technology. The reinforcing steel lattice of the vaulted arch 84 can be assembled on the ground 23 while the lattice is still resting horizontally. Next, the ready-assembled, stiffened reinforcing steel lattice of the vaulted arch 84 can be lifted in relatively lightweight stage to its final position and ultimately shotcreted here to give it its final strength.

Fig. 25 shows diagrammatically a stiffened reinforcing steel lattice 86 of a hollow-core girder bridge placed onto supporting trestles 60 prior to concreting. The structure can be complemented with pretensioning steels 61 already prior to concreting. When desired, the pretensioning steels 61 can be used for the support of the reinforcing steel lattice 86. In order to retain the shape of the structure, reinforcing steels are advantageously placed at the edges of the hollow-core girder prior to concreting. Pretensioning steels can also be added between the shotcreted layers. Fig. 26 shows an underground parking lot implemented using the method according to the invention. The parking lot site is first prepared by excavating a ground pit, after which the self-supporting reinforcing steel lattices formed to the shape of the vault 84 are erected to their places. This method avoids the preparation of temporary supports and moulds as well as offers substantial savings in construction time in respect to a conventional approach. The entire construction is fortified by shotcreting up to its final strength, after which the excavation can be filled with earth materials. A corresponding method is applicable to the implementation of, e.g., traffic tunnels and underground caverns up to very long spans.

Fig. 27 shows a hollow-core noise abatement barrier imple¬ mented roadside using the method according to the invention. Cavities 92 remaining in the center of the concrete structure 9 are advantageous for weight reduction on unstable ground, thus contributing to reduced need for ground consolidation. When desired, the cavernous structure can be covered with a layer of soil capable of supporting planted vegetation. The noise abatement barrier can easily be designed to include different kinds of elevated shapes 88 as well as depressions and notches.

Fig. 28 shows cylindrical reinforcing steel fabrics 86, 10 placed resting adjacently parallel on a base 45. Fortification of the set of reinforcing steel fabrics by shotcreting forms them into, e.g., continuous hollow-core wall structure which can be used as a support wall, noise abatement barrier or quay for instance. When desired, the cavity 92 can be filled with earth for instance immediately after the setting of the shotcreted concrete. Fig. 29 shows the reinforcing steel fabrics 86, 10 spaced apart by a distance 28. This arrangement allows shotcreting also between the cylindrical reinforcing steel fabrics . Thence, the method is applicable to an advantageous fabrication of water or oil tanks for instance.

Fig. 30 shows shotcreting between two cylindrical rolls 96. When desirable, the rolls can also be shaped to have a conical or other suitable contour. Shafts 94 of the rolls are tied to each other by means of a bracing assembly 51.

The rolls 96 are movable along the direction of the desired structure, and they are generally moved toward the shot¬ creting nozzles 5. The shotcreting jets 4 penetrate compactingly into the gap between the rolls 96. The rolls shape the surface 9 of the final structure into a desired contour. The rolls 96 are freely rotating about their shafts thus avoiding any friction between the rolls and the concrete surface 6. When necessary, the rolls can also be spun in a desired direction to attain a brushing effect. The surfaces of the rolls can be smooth, whereby also a smooth final surface 9 is obtained. By contouring the rolls 96 with different kinds of raised or sunken patterns, the final surface 9 of the structure can be patterned. The rolls 96 can be moved forward in desired directions by means of different control mechanisms. A linear forward motion of the rolls 96 produces a linear surface 9 of the final structure. Use of, e.g., an undulating control curve for the motion of the rolls 96 results in a correspondingly undulating final shape 9 of the structure. By arranging the bracing mechanism 51 to have such a spacing control that makes the mutual distance of the shafts 94 variable, final structures 9 of variable thickness can be produced. The structure can further include different kinds of reinforcing steel arrangements not shown in the figure. Moreover, additional materials such as thermal insulations can be fed between the rolls when desired. Complicated reinforcing steel structures are preferably shotcreting using a greater number of the nozzles 5. When suitable, the operation can also be implemented single-sidedly using only one roll 96.

Fig. 31 shows a stiffening reinforcing steel fabric 86a, 86 attached onto a shaped metal base 1 of thin sheet metal by riveting or welding, for instance. The sheet metal base can be provided with different types of anchorage systems for improvement of bond anchorage to the concrete. In the illustrated case the anchorage is provided by a flat-top corrugated ridge 22.

Fig. 32 shows a method of shotcreting into the slot between two endless belts 96a in a manner similar to that illustrated in Fig. 30 for shotcreting between two rolls.

Fig. 33 shows a method of shotcreting into the slot between an endless belt 96a and a fabric 10 in a manner similar to that illustrated in Figs. 30 and 32. Using only a single endless belt it is easy to implement, e.g., the fabrication of a horizontally laying structure, whereby the endless belt 96a initially takes a partial load of the weight of the wet concrete 6. A load-carrying reinforcing steel fabric (not shown) which will be embedded in the concrete mix 6 also bears a partial load of the concrete weight.

Fig. 34 shows the action of concrete 6 filling the openings in a reinforcing steel fabric 86 comprised of diagonal strips. The shape of opening becomes stabilized even against pull forces applied to the opposite corners of the opening. Thus, stresses within the reinforced structure are effectively transmitted throughout the structure.

Claims

WHAT IS CLAIMED IS:

1. A method for fabricating a reinforced concrete structure, c h a r a c t e r i z e d in that a reinforcing steel fabric (86, 86a, 50) is stiffened to a stage essentially self-supporting and subsequently fortified by shotcreting (6, 8) .

2. A method in accordance with claim 1, c h a r a c - t e r i z e d in that the reinforcing steel fabric (86,

86a, 50) is essentially formed from diagonally placed and mutually bonded steels.

3. A method in accordance with claim 1 or 2, c h a r a c - t e r i z e d in that the reinforcing steel fabric (86,

86a, 50) is essentially formed from an expanded sheet metal fabric (86, 10) fabricated from thin sheet metal by slitting and stretching.

4. A method in accordance with any of the foregoing claims 1...3, c h a r a c t e r i z e d in that the reinforcing steel fabric is formed into a shape having a corrugated cross-section.

5. A method in accordance with any of the foregoing claims 1...4, c h a r a c t e r i z e d in that additional stiffening reinforcing steels (50, 57, 52) are attached to the reinforcing steel fabric (86, 86a) of diagonal strips.

6. A method in accordance with any of the foregoing claims 1...5, c h a r a c t e r i z e d in that the reinforcing steel fabric (86) is tilted to an inclined position (86a) corresponding to the prevalent orientation of the construction.

7. A method in accordance with any of the foregoing claims 1...6, c h a r a c t e r i z e d in that the shotcreted concrete (4) is sprayed from two or a greater number of nozzles (5) from different directions to the same area.

8. A method in accordance with any of the oregoing claims 1...7, c h a r a c t e r i z e d in that a roll (96) or an endless belt (96a) is used for forming the surface (9) of the shotcreted concrete (6, 8) .

9. A method in accordance with claim 8, c h a r a c ¬ t e r i z e d in that the roll (96) or the endless belt

(96a) is contoured to have raised or sunken patterns.

10. A method in accordance with claim 8 or 9, c h a r ¬ a c t e r i z e d in that the position of the roll (96) or the endless belt (96a) is controllable in all directions.