DE68928472T2 - METHOD FOR PRODUCING TENSIONED CONCRETE BEAMS OR -PLATE ELEMENTS AND REINFORCEMENT DEVICES THEREFOR - Google Patents

Abstract

A prestressed concrete beam (1) is cast with a rectilinear longitudinal profile and a filling piece (13) extending from a surface of the beam (1) to the reinforcing strands (6) is embedded. After hardening of the concrete and removal of the filling piece (13) if necessary, the beam (1) is deflected in a predetermined angle by rotating the beam sections (2, 3) on either side of the recess (4) formed by the filling piece in such a direction that the recess is diminished, following which the beam sections (2, 3) are retained in the predetermined angle. A reinforcement assembly made in two equal halves and connected with a breakable joint may be embedded in the area of the recess to reinforce the beam sections (2, 3).

Description

The invention relates to a method for producing a prestressed concrete beam element or concrete slab element, wherein in this method the reinforcing strands for prestressing the beam are suspended essentially straight through the mold and the element is cast with an essentially straight longitudinal profile.

Beam or panel elements of the above-mentioned type are generally used in buildings, in particular for floor slabs and roof structures, because such elements have good strength compared to their weight and are cheaper to manufacture than, for example, concrete elements with a slack or subsequently tensioned reinforcement or concrete structures cast in place.

However, the previous method does not allow the beam or plate elements to be cast in a roof shape, namely by designing the beam element as two legs forming an angle with each other and the plate element as a roof surface with a ridge with two inclined side surfaces.

Such beam elements can be manufactured by joining two straight prestressed concrete elements by casting them together so that they form an angle with each other and reinforcing the area of the cast joint with cables which are subsequently tensioned after the concrete has hardened. However, this makes the beams more expensive to manufacture and a significant disadvantage is that large V-shaped roof beams are difficult to transport from the production site to the site of the construction due to the fact that existing bridges and overhead cables in the area of the transport route limit the size of the elements.

Furthermore, DK patent B 152 999 discloses a method for manufacturing a concrete beam element or concrete slab element with a prestressed multiple strand reinforcement and with a concave bottom in which the reinforcement is embedded as a tension reinforcement. According to this method, the reinforcement strands extend continuously between the ends of the element and the course of the strands forms one or more bends in which the strands are clamped in a guide intended to take up the transverse forces from the reinforcement at the point or points of bending before pouring the concrete, which guide extends to the compression side of the element and is intended to be fastened to this side of the element after hardening of the concrete.

According to this previous method, the course of the reinforcement strands results in very strong transverse forces on reinforcement guides and shapes when the strands are arranged and prestressed, and in practice this method only allows the production of beam or plate elements with a moderate roof slope.

It is the purpose of the invention to provide a method for producing support and plate elements of the above-mentioned type, which method does not suffer from the disadvantages mentioned.

The invention differs from the above-mentioned method in that

that at least at one point of the element a first filler piece is embedded in the element, the filler piece extending mostly from one side of the element to the reinforcement strands,

that the first filler piece, if necessary, is removed after hardening and prestressing of the concrete, that the element, after hardening and prestressing of the concrete, is bent to a predetermined angle by a relative rotation of the element sections arranged on both sides of the location, so that the recess formed by the first filler piece is reduced, and

that the element sections on both sides of the first filler piece are fastened to each other at the predetermined angle.

The reinforcing strands are usually suspended in a casting bed and in the manufacture of, for example, a beam element the reinforcing strands are arranged in the base of the beam or on that part of the beam which later forms the tension side of the beam, and the filler piece, which is advantageously wedge-shaped, is embedded in the casting mould on the side against which the element sections must be turned during the bending process, and preferably so that it extends into the area of the reinforcing strands. The concrete is then poured and after the concrete has hardened the reinforcing strands are released in order to thereby obtain the desired prestress in the concrete.

The support element now appears as a straight, prestressed concrete element and can be transported in this form to the site of the structure without the risk of bridges, overhead cables and similar installations along the transport route hindering the transport. If the side of the element receiving the filler in this situation forms the compression side of the element, the filler must be designed so that it is able to absorb the resulting compression stress.

The bending process can be carried out, for example, by using an assembly crane which lifts the element at its ends and has a secondary winch which is to be installed in the area in the bending point. This area of the element is then raised relative to the ends of the element, for example by lowering the ends until the desired bending angle is reached. Due to its own weight, the element bends in the weakest cross-section, ie at the recess formed by the filler piece. A gap is first formed which extends from the reinforcement strands towards the side of the element opposite the recess, and by continued lifting the gap opens more and more, the element sections on both sides of the bending point being held against each other by the pre-stressed reinforcement strands.

If the filler is made of a deformable material, e.g. a foamed plastic, which is sufficiently rigid to withstand the pressure of the concrete during pouring and its vibration in the mold, but which can be deformed without offering any appreciable resistance to bending of the support element, the filler can remain in its position during the bending operation. If, on the contrary, the filler is made of steel or wood, it must be removed before the bending step.

When the element sections form the desired angle on both sides of the bend, they are held in that position. This can be achieved, for example, by connecting previously embedded holders by welding or in any other suitable way.

Manufacturing the element according to the method described above results in a prestressed concrete element with a curved or angled longitudinal profile, in which element the prestressed reinforcement strands extend continuously from one end of the element to the other. The method according to the invention has the further advantage that the element is given its final shape either at the production site or at the site of the construction, as the case may be. A considerable saving of working hours is obtained if the bending of the element is carried out simultaneously with its erection in its final position.

The method according to the invention not only provides for the production of roof-shaped support or plate elements, but also, for example, portal or frame elements, e.g. as a two-hinged or three-hinged frame with roof and column or cladding parts.

In a preferred embodiment of the invention, the opening between the opposing fracture surfaces, each of which belongs to an element section on both sides of the site, is filled with concrete or a fitting piece attached to the element sections.

Filling the resulting opening with concrete may be advantageous in cases where the element is of simple cross-section and the filling can be effected quickly and without complicated moulding work, and in cases where the sequence of operations allows the elements to be held at the desired angle with respect to each other until the poured concrete has hardened without incurring substantial costs. In other types of such element, a shim may be inserted into the opening formed between the fracture surfaces, causing the element, when no longer lifted at the bending point, to retain its shape and to be immediately capable of transmitting compressive forces from its own weight and possible external influences between the element sections with the result that temporary supports are saved and that the erection crane is quickly released for use in the erection of the next element.

An embodiment of the invention is characterized in that a transverse partition wall extending from the opposite side of the element to the reinforcement strands, is embedded opposite the first filler piece and that the transverse partition is removed during bending of the element. By using a transverse partition as described, a well-defined weakening of the cross-section of the beam is obtained and the surfaces of the beam sections facing each other on both sides of the fracture point can be given a desired shape which, for example, facilitates the reception of a fitting piece.

In this case, the transverse partition and the fitting can advantageously be cast using one and the same set of mould sides, e.g. from concrete. This ensures that the surfaces forming the butt welds between the fitting to be inserted and the curved element fit together exactly.

For beam and plate elements with higher prestressing forces, it is necessary that transverse reinforcement is embedded in the element on both sides of the fracture point. This allows the transverse forces that arise from the change in the direction of the reinforcement strands at the fracture point to be transferred to the compression side of the beam.

If the compressive forces transmitted between the two sections of the element are very strong in the area of the prestressed reinforcement, it is preferable that a reinforcing element with surfaces that are in contact with each other during the bending process is embedded on both sides of the first filler piece.

These contact surfaces of the reinforcing elements can be formed by steel plates to which a specific curvature is imposed so that they roll against each other during bending of the element, and by changing the radius of curvature of the surfaces it is possible to achieve that the prestressing force is kept constant or in a desired manner during bending of the element. This allows the changes in the prestressing force that occur in the initial period after the concrete is poured to be compensated and also other circumstances that affect the prestressing force can be compensated.

A second embodiment of the invention is characterized in that reinforcing elements with guide surfaces are used to hold the reinforcing strands in a specific position, which is different from the position they assume at the ends of the element. In the vicinity of the bending point it is desirable that the reinforcing strands are arranged in a layer extending perpendicular to the direction of the bend, while it is most often desirable to arrange the reinforcing strands at the ends of the element with a fairly large mutual distance and evenly distributed over the cross-section in order to achieve good anchoring of the strands and a suitable distribution of the prestressing force through the concrete.

It is desirable that the reinforcing strands extend through the fracture zones with a suitably large radius of curvature after the bending process. According to the invention, this can be achieved by embedding a second filler piece, preferably made of a deformable material, beneath the reinforcing strands. The second filler piece can have a flat or grooved surface facing the reinforcing strands and can be thickest opposite the fracture point, from which it tapers towards the ends.

The second filler piece can be made of a suitably stiff, foamed plastic, for example. During the bending process, the reinforcement strands will exert pressure on the second filler piece and compress it until the reinforcement strands finally contact the concrete on the opposite side of the second filler piece. A suitable design of the second filler piece ensures that the reinforcement strands are given exactly the desired course during the bending process.

The first filler piece and the second filler piece can, together with reinforcing elements with guide surfaces and stop plates, form a reinforcing arrangement, which can also be joined together with the transverse reinforcement.

The invention also relates to a prestressed concrete beam element or concrete slab element manufactured by the method according to the invention, which element is characterized in that it comprises: a reinforcement assembly consisting of two symmetrical halves, each half of which has a curved lower section made of steel for guiding and positioning the prestressed strands; a stop plate attached to the curved lower section at the end adjacent to the other half; and reinforcing rods designed as open stirrups with anchoring plates at the open ends, the two halves being connected by means of a weak weld which allows easy positioning of the reinforcement assembly in the mold and which breaks when the beam is bent to its final shape, and the reinforcement assembly further comprising a first filler piece inserted between the lower ends of the stop plates and a second filler piece attached to the lower section.

The invention further relates to a prestressed concrete beam element or concrete slab element manufactured by the method according to the invention, the element being characterized in that it comprises a reinforcing arrangement arranged longitudinally between a first filler piece and a transverse partition wall, said reinforcing arrangement comprising a steel element with a U-shaped Cross-section for guiding and positioning the prestressed strands, ribs for transferring the prestressing force between the concrete and the steel element and reinforcing bars designed as open stirrups with anchoring plates at the upper ends.

The ends of the U-profiles are embedded in the concrete for a suitable length on the corresponding sides of the bending point. During the bending operations, the prestressing force is transmitted directly through the continuous U-profile, which is bent to a uniform curvature during the operation while supported by the ribs and the embedded transverse reinforcement.

The invention will now be described in detail using embodiments, with reference to the accompanying drawings, in which:

Fig. 1 is a side view of a part of the carrier or plate element according to the invention,

Fig. 2 a side view of the element according to Fig. 1 after bending,

Fig. 3 is a side view of a support section for forming a corner of a portal or frame,

Fig. 4 the same beam section after bending,

Fig. 5 is a side view of part of a support element according to a second embodiment,

Fig. 6 is a side view of a portion of the support element shown in Fig. 5 on a larger scale,

Fig. 7 is a section along the line VII-VII of Fig. 6,

Fig. 8 is a view corresponding to Fig. 6 after bending of the element,

Fig. 9 is a side view of a reinforcement arrangement according to the invention,

Fig. 10 is an end view of the reinforcement arrangement according to Fig. 9,

Fig. 11 is a side view of part of a support element with a reinforcement arrangement according to a second embodiment,

Fig. 12 is a sectional view along the line XII-XII of Fig. 11, and

Fig. 13 is a side view corresponding to Fig. 11 after the bending process.

Fig. 1 illustrates a portion of a beam or slab element made of prestressed concrete, produced by linearly suspending reinforcing strands 6 through a mold, at the bottom of which a wedge-shaped filler 13 is placed prior to pouring the concrete, the beam or slab element further comprising two reinforcing brackets 7. Fig. 1 shows a portion of the beam element at the stage of the manufacturing process in which the concrete has been poured and hardened and the reinforcing strands 6 have been released. The filler in the element forms a wedge-shaped recess extending to the reinforcing strands 6 and having sides 5.

By lifting the element near the recess in such a direction that the recess has a tendency to close, the beam cross-section at the recess is subjected to a Bending moment of such magnitude that the beam bends sharply, causing the formation of a gap or opening defined by the fracture surfaces 8. By further raising the area of the beam containing the fracture with respect to the beam ends, the two beam sections 2, 3 on either side of the fracture sites are rotated by a certain angle relative to each other. The beam is then held and concrete 9 is poured into the opening between the fracture surfaces 8 as indicated in Fig. 2.

Fig. 3 illustrates a portion of a frame element which is essentially manufactured as a straight prestressed element, similar in principle to the beam element shown in Fig. 1, but with the prestressed reinforcement 6 arranged at the top of the element. On both sides of the filler 13, anchored steel brackets 20 are embedded in the concrete. The filler 13 remains in its position until bending is to be effected and until then it forms part of the compression side of the element during storage and transport. During this step, the brackets 20 serve to transfer forces between the filler 13 and the concrete.

Fig. 4 illustrates the element according to Fig. 3 after the bending operation has been carried out. This operation can be carried out as described with reference to the support element illustrated in Fig. 2. After the bending operation, the element sections 2 and 3 are firmly fixed in the new position by welding the holders 20 together or by connecting them by means of screws. The outer recess formed by the bend can, if desired, later be filled with concrete 9 or another material.

The frame element according to Fig. 4 can be a partial element of a three-hinged frame, a so-called half-frame, with the roof area 2 and the column area 3. The element can also be a two-hinged frame, with Fig. 4 then illustrating one of two symmetrically arranged bending points. The element can, for example, have a third bending point in the center of the element section 2, analogous to Fig. 2.

Fig. 5 illustrates a beam element manufactured like that illustrated in Fig. 1, but with two embedded stop plates 11 adjacent to each other and simply curved in the area of the reinforcing strands 6, whereby they roll against each other during bending of the beam. The figure further shows a first filler piece 13 inserted between the stop plates 11 and a transverse partition wall 14 made of concrete. The transverse partition wall is removed before bending of the beam, thereby providing well-defined "surfaces of refraction" 8 in the beam simultaneously with achieving a well-defined positioning of the bending point. As illustrated in more detail in Figs. 6 and 7, a second filler piece 15, e.g. B. made of a rigid foamed plastic and shaped as a double wedge, embedded below the reinforcing strands 6, the underside of the second filler piece being designed in the form of two inclined surfaces, each curved as a part of a cylindrical surface, thereby giving the concrete beam opposing curved guide surfaces 12a for guiding the reinforcing strands.

Fig. 8 illustrates how a concrete fitting 10 is inserted into the opening between the surfaces 8 on beam sections 2 and 3 on both sides of the fracture after the bending operation of the beam according to Figs. 5 to 7. The surfaces of the transverse partition 14 and the fitting 10 corresponding to the surfaces 8 are cast using the same mould sides so that the sides of the fitting 10 can form tight connections with the surfaces 8. In order to fix the fitting 10, notches can be provided in the above-mentioned mould sides, whereby the surfaces 8 and the corresponding surfaces of the fitting are locked in relation to each other. or grooves can be provided in the connecting surfaces, into which concrete will later be filled.

From Fig. 8 it can also be seen that reinforcement strands 6 have a fully compressed second filler piece 15 during the bending process and then exert a pressure against the guide surfaces 12a, which now form a uniform surface, thereby giving the reinforcement strands a uniform circular path through the fracture zone. It can also be seen that the compression of the second filler piece 15 creates a cavity 16 above the reinforcement strands. This cavity can later be filled with a thin casting material, e.g. cement mortar, through a pouring channel 17 in the fitting piece 10.

As shown in Figs. 9 and 10, the reinforcement assembly 26 is in one embodiment made of steel in the form of two sections joined together by a weak weld 18 which will break during the bending process. The reinforcement assembly includes stop plates 11, reinforcement guides 12 for guiding the reinforcement strands after bending, cross reinforcements 7 and embedded filler pieces 13 and 15.

The arrangement is arranged in the mold before the reinforcement strands are inserted and tensioned. To facilitate the positioning of the reinforcement strands, the transverse reinforcements 7 are designed as open arches with anchoring plates 19 on the top. The anchoring plates 19 also act as guides for the transverse partition wall 14 during the casting process.

Fig. 11 and 12 illustrate a section of a prestressed concrete beam 2, 3 with an embedded reinforcement arrangement 27 of an alternative type. The reinforcement guide in this case is a continuous steel profile 25 of U-shaped cross-section. The ends of the profile are firmly fixed into the corresponding element sections 2 and 3. embedded. The profile is dimensioned to carry the full prestressing force of the reinforcement strands and is provided with ribs 11a to contribute to the transfer of the prestressing load between the channel and the concrete, the transverse reinforcements 7 being welded to the guide. Depending on the size of the desired bending angle, one or more filler pieces 13 with associated transverse partition walls 14 are inserted.

Fig. 13 illustrates the same element after completion of the bending process, which, moreover, is similarly effected by the same means as previously described. Filler pieces 13 are in this case made of a durable and resiliently resilient material, e.g. rubber, which is left in the element and forms a uniform curved transition between the element sections 2 and 3 and a piece 22 arranged between the transverse partition walls. During the bending process, the U-profile is cold-formed in the fracture zones. Fitting pieces 10 with embedded supports 23 are finally inserted between the anchoring plates 19 and can be locked in position, for example by welding. Such locking can also be obtained by a suitable design of the corresponding surfaces of the butt joints between the element sections and the fitting pieces. The reinforcement strands are located on the underside of the U-profile and the cross-section of the U-profile is designed so that its center of gravity is positioned exactly in relation to the reinforcement strands, so that when bent, a desired setting of the prestress is achieved in the fracture zones.

Claims (10)

1. Method for producing a prestressed concrete support element or concrete slab element (1), wherein in this method the reinforcing strands (6) for prestressing the support are suspended essentially straight through the mold and the element (1) is cast with an essentially straight longitudinal profile, characterized in that a first filler piece (13) is embedded in the element at least at one point on the element (1), the filler piece extending largely from one side of the element (1) to the reinforcing strands (6), that the first filler piece (13) is removed, if necessary, after hardening and prestressing of the concrete, that the element (1) after hardening and prestressing the concrete, while the prestressing is maintained over the entire length of the element (1), is bent to a predetermined angle by a relative rotation of the element sections (2, 3) arranged on both sides of the point, so that the recess (14) formed by the first filler piece (13) is reduced, and that the element sections (2, 3) are attached to both sides of the first filler piece (13) with respect to one another at the predetermined angle. 2. Method according to claim 1, characterized in that the opening between the opposing fracture surfaces (8), which each lead to an element section (2 or 3) on both sides of the site, is filled with concrete or a fitting piece (10) attached to the element sections (2, 3). 3. Method according to one of the preceding claims, characterized in that a transverse partition wall (14) extending from the opposite side of the element (1) to the reinforcing strands (6) is embedded opposite the first filler piece (13) and that the transverse partition wall (14) is removed during bending of the element. 4. Method according to claim 3, characterized in that the transverse partition wall (14) and the fitting piece (10) are cast using one and the same set of mold sides, e.g. made of concrete. 5. Method according to one of the preceding claims, characterized in that a transverse reinforcement (7) is embedded in the element (1) on both sides of the bending point. 6. Method according to one of the preceding claims, characterized in that a reinforcing element (11) with surfaces (11b) which lie against one another during the bending process is embedded on both sides of the first filler piece (13). 7. Method according to one of the preceding claims, characterized by the use of reinforcing elements (12) with guide surfaces (12a) for holding the reinforcing strands (6) in a specific position which is different from the position they assume at the ends of the element. 8. Method according to one of the preceding claims, characterized in that a second filler piece (15), which preferably consists of a deformable material, is inserted between the reinforcement strands (6) and the guide surfaces (12a). 9. Prestressed concrete beam element or concrete slab element (1) manufactured by the method according to claim 1, characterized in that the element comprises: a reinforcing assembly (26) consisting of two symmetrical halves, each half of which has a curved lower portion (12) made of steel for guiding and positioning the prestressed strands (6); a stop plate (11) fixed to the curved lower portion (12) at the end adjacent to the other half; and reinforcing bars (7) designed as open brackets with anchor plates (19) at the open ends, the two halves being connected by means of a weak weld (18) which allows easy positioning of the reinforcing arrangement in the mold and which breaks when the beam is bent to its final shape, and the reinforcing arrangement (26) further comprising a first filler piece (13) inserted between the lower ends of the stop plates (11) and a second filler piece (15) attached to the lower portion (12). 10. Prestressed concrete beam element or concrete slab element (1) manufactured by the method according to claim 1, characterized in that the element comprises a reinforcing arrangement (27) arranged longitudinally between a first filler piece (13) and a transverse partition wall (14), which reinforcing arrangement (27) comprises a steel element (25) with a U-shaped cross-section for guiding and positioning the prestressed strands (6), ribs (11a) for transmitting the prestressing force between the concrete and the steel element (25) and reinforcing rods (7) designed as open brackets with anchoring plates (19) at the upper ends.