EP4177028A1

EP4177028A1 - Apparatus for prestressing reinforcement strands

Info

Publication number: EP4177028A1
Application number: EP21207032.0A
Authority: EP
Inventors: Heikki Lehtonen; Jani Eilola
Original assignee: Elematic Oyj
Current assignee: Elematic Oyj
Priority date: 2021-11-09
Filing date: 2021-11-09
Publication date: 2023-05-10

Abstract

Apparatus (1) for prestressing reinforcement strands (2) in the prefabrication of prestressed concrete products on a casting bed, wherein the apparatus comprises at least one device (17) - preferably a hydraulic cylinder - for moving a strand pulling beam (3) in relation to the casting bed, wherein the apparatus (1) further comprises at least one device (9, 9') for operating locking means (5) - preferably wedges - of the strand pulling beam (3) for locking and releasing the position of the strand pulling beam (3) in relation to the casting bed.

Description

The present invention relates to apparatus for pre-stressing strands in concrete slab prefabrication. More precisely the invention relates to bundle stressing machine wherein plurality of pre-stressing strands is stressed simultaneously in a bundle.
Prefabricated concrete elements, such as hollow-core slabs and solid concrete slabs, are conventionally cast by slipform casting or extrusion casting on long casting beds as a continuous casting process. The length of said continuous casting process is defined either on the basis of the total length of the elements to be cast, or on the basis of the maximum length of the casting bed. The length of casting beds used in casting can be from 50-60 m up to 150-200 m, depending on the size of the element plant. When a casting equipment has cast a continuous slab on a casting bed, the cast concrete slab is allowed to be cured on the casting bed. After the concrete mass has cured, the uniform cast element is cut, generally by sawing, into pieces with predetermined lengths on the basis of the design characteristics of the ready-made elements, and the cut concrete elements are lifted off the casting bed to storage, to wait for transportation to their appointed targets of usage.
Generally concrete elements cast by slipform or extrusion casting are prestressed, i.e. they are provided with prestressed reinforcement strands. These reinforcements strands are prestressed by pulling the strands to a predefined stress before starting of the actual casting with a suitable casting machine.
The stressing of reinforcement strands may be carried out strand by strand, or in a bundle, where all of the required reinforcement strands are connected to a single strand pulling plate or beam after which the plate is moved a predetermined distance with a bundle stressing device in order to achieve the required stressing of the reinforcement strands.
After the strand pulling beam is moved the predetermined distance with the bundle stressing device to stress the reinforcement strand bundle, the beam is typically locked at the pulled position with wedges. This allows the detachment of the bundle stressing device from the beam so that the same bundle stressing device can be used to service a plurality of adjacent casting beds.
Setting of the wedges in the locking of the strand pulling beam during the strand stressing process is manual work, which requires the operator of the bundle stressing machine to leave the cover of the machine and move to the casting bed area, which creates possible work hazards if any of the stressed reinforcement strands happen to break. Further, the area where the wedges are set is also typically uneven and dirty and often oily, which causes additional hazards.
The present invention removes the need for the operator to leave the cover of the bundle stressing device for the locking of the strand pulling beam, as well as other related actions, which significantly increases the work safety. Further, the present invention also allow certification that the locking process, as well as other related actions, are done properly.
The apparatus of the invention for prestressing reinforcement strands in the prefabrication of prestressed concrete products on a casting bed comprises at least one device for moving a strand pulling beam in relation to the casting bed, and at least one device for operating locking means of the strand pulling beam for locking and releasing the position of the strand pulling beam relation to the casting bed. By operating locking means of the strand pulling beam via the device, the operator can release and lock the strand pulling beam from safe location without need to enter in the area of the casting bed.
The at least one device for moving the strand pulling beam is preferably a hydraulic cylinder. Further, the apparatus preferably comprises two of these devices connected to the strand pulling beam on both ends of the beam.
In an embodiment of the apparatus of the invention device for operating the locking means comprise means for gripping and moving a wedge locking the strand pulling beam in relation to the casting bed. These means allow detachable attachment of the wedge to the device and vertical moving of the wedge for raising it from the locking position to released position, and vice versa. Further, there are preferably separate means for each wedge locking the strand pulling beam in relation to the casting bed.
In an embodiment of the apparatus of the invention the at least one device for moving the strand pulling beam is detachably connected to the strand pulling beam, and the apparatus comprises at least one device for detaching the strand pulling beam from the apparatus. In this embodiment the device for detaching the strand pulling beam preferably comprises means for gripping and moving at least one locking pin connecting the device for moving the strand pulling beam to the strand pulling beam. These means allow detachable attachment of the locking pin to the detachment device and vertical moving of the locking pin for raising it from the locking position to released position, and vice versa. Further, there are preferably separate means for each locking pin connecting the devices for moving the strand pulling beam to the strand pulling beam.
In this embodiment of the at least one device for detaching the strand pulling beam is preferably at least partially movably connected to the apparatus for changing the distance between the means for gripping the locking pin and the apparatus. This allows the locking and release of the strand pulling beam to and from the device(s) for moving the strand pulling beam at different positions in relation to the casting bed.
In an embodiment of the apparatus of the invention the apparatus is mounted movably on rails for moving the apparatus between adjacent casting beds.
In an embodiment of the apparatus of the invention the apparatus comprises a cover for an operator operating the apparatus.
More precisely the features defining an apparatus in accordance with the present invention are presented in claim 1. Dependent claims present advantageous features and embodiments of the invention.
Exemplifying embodiment of the invention is explained in greater detail below in the sense of example and with reference to accompanying drawings, where

Figure 1 shows schematically an embodiment of the apparatus of the invention,
Figures 2A and 2B illustrates the operation of a device for operating locking means of a strand pulling beam with the apparatus of figure 1, and
Figures 3A-3C illustrates the operation of a device for detaching a strand pulling beam from the apparatus of figure 1.

Figure 1 shows schematically an embodiment of the apparatus of the invention, which apparatus is a bundle stressing machine 1.
When prestressing reinforcement strands 2 in a bundle in the production of prefabricated concrete products, the strands are first connected to a strand pulling beam 3, which is then pulled backwards with the bundle stressing machine 1 to a predetermined distance to achieve the required prestressing of the reinforcement strands before the concrete casting phase is started.
Since the forces acting of the reinforcement strands 2 during the prestressing can be up to 3000 kN, there is always a possibility that one or more reinforcement strands break during the prestressing, which would cause a significant danger to the personnel of the prefabrication site. Thus, when the reinforcement strands 2 are prestressed, personnel are evacuated from the area of the casting bed, and the operator of the bundle stressing machine 1 is behind the cover 4 of the machine. The bundle stressing machine 1 also typically gives sound and light alarms when the strand pulling is about to start and when it is ongoing.
When the strand pulling is done, i.e. the bundle stressing machine 1 has pulled the strand pulling beam 3 the predetermined distance, the strand pulling beam is locked at this position with wedges 5, which are inserted in the slots 7 formed in the abutment section 6 of the end of the casting bed. After the wedges 5 are at their locking places, the pull on the strand pulling beam 3 is slowly released and the strand pulling beam will rest against the wedges, after which the bundle stressing machine 1 can be detached from the strand pulling beam 3 and moved to another adjacent casting bed via rails 8 for a new reinforcement strand prestressing process.
The bundle stressing machine 1 is equipped with devices 9, 9' for operating locking means of the strand pulling beam, which devices comprise arms 10, 10' with gripping portions 11, 11'for gripping the wedges 5. The operation of these devices 9, 9' are discussed in more detail later with reference to figures 2A and 2B.
The bundle stressing machine 1 is also equipped with devices 12, 12' for detaching the strand pulling beam from the bundle stressing machine, which devices comprise arms 13, 13' with gripping portions 14, 14' for gripping locking pins 15. The operation of these devices 12, 12' are discussed in more detail later with reference to figures 3A and 3B.
Figures 2A and 2B illustrates the operation of the devices 9, 9' for operating the locking means, i.e. the wedges 5, of the strand pulling beam 3 with the bundle stressing machine 1 of figure 1. In figures 2A and 2B the machine 1 is shown both as a side view and as a top view.
During the prestressing process of the reinforcement strands 2, i.e. when the strand pulling beam 3 is being pulled, the wedges 5 are in lifted position, as shown in figure 2A. In this lifted position the wedges 5 are supported with the gripping portions 11, 11' of the devices 9, 9', which gripping portions in this embodiment are formed as forks opening towards the sides of the abutment section 6 of the casting bed, wherein the prongs of the forks set themselves on both sides of the wedges 5 in grooves formed in the wedges.
When locking the strand pulling beam 3 at its pulled position the wedges 5 are lowered with vertical downward movement of the arms 10, 10', which inserts the wedges into the slots (7 in figure 1) formed in the abutment section 6 of the casting bed, as shown in figure 2B.
In the position of figure 2B, wherein the wedges 5 are located in their locking position in the slots, the devices 9, 9' can be moved horizontally towards each other along the rails 16 in order to move the forks away from the wedges and thus detach the wedges from the gripping portions 11.
Release of the locking of the strand pulling beam 3 is done in similar manner but in opposite order, once the concrete product cast on the casting bed is cured and the strands connected to the strand pulling beam are cut.
Figures 3A-3C illustrates the operation of the devices 12, 12' for detaching the strand pulling beam 3 from the bundle stressing machine of figure 1. Similarly than in figures 2A and 2B, the machine 1 is shown both as a side view and as a top view in figures 3A-3C.
The ends of the piston rods of the hydraulic cylinders 17 of the bundle stressing machine 1 used to create the pulling force to the strand pulling beam 3 are connected to the beam with removable locking pins 15.
When the strand pulling beam 3 is released, such as when the bundle stressing machine 1 is moved between the different casting beds along rails 8, the locking pins 15 are in lifted position, as shown in figure 3A. In this lifted position the locking pins 15 are supported with the gripping portions 14, 14' of the devices 12, 12', which gripping portions in this embodiment are formed as forks opening away from the bundle stressing machine 1 in the longitudinal direction of the casting bed, wherein the prongs of the forks set themselves on both sides of the locking pins 15 in grooves formed in the locking pins.
When locking the strand pulling beam 3 is attached to the ends of the piston rods of the hydraulic cylinders 17, the ends of the piston rods are first moved to the strand pulling beam, after which the locking pins 15 are lowered with vertical downward movement of the arms 13, 13', which inserts the locking pins into and through holes formed at the ends of the strand pulling beam and fastening lugs at the ends of the piston rods into the position shown in figure 3B.
The attachment and detachment of the gripping portions 14, 14' to and from the locking pins 15 is achieved with horizontal movement of the devices 12, 12' along the rails 18, 18'. Further, the rails 18, 18' also allows the devices 12, 12' to be moved at suitable position for detaching and attaching the ends of the piston rods of the hydraulic cylinders 17 from and to the strand pulling beam 3 when the beam is located at the opposite end of the abutment section 6 of the casting, as shown in figure 3C, or along any position along the abutment section. Before moving the devices 12, 12' in horizontal direction with the rails 18, 18', the devices 9, 9,' are moved towards each other along the rails 16, with the wedges 5, in order to avoid collision between these devices.
The specific exemplifying embodiment of the invention shown in figures and discussed above should not be construed as limiting. A person skilled in the art can amend and modify the embodiment described in many evident ways within the scope of the attached claims. Thus, the invention is not limited merely to the embodiment described above.

Claims

Apparatus (1) for prestressing reinforcement strands (2) in the prefabrication of prestressed concrete products on a casting bed, wherein the apparatus comprises at least one device (17) for moving a strand pulling beam (3) in relation to the casting bed, characterized in that the apparatus (1) further comprises at least one device (9, 9') for operating locking means (5) of the strand pulling beam (3) for locking and releasing the position of the strand pulling beam relation to the casting bed.
Apparatus (1) of claim 1, wherein the device (9, 9') for operating the locking means comprise means (10, 11, 16; 10', 11', 16) for gripping and moving a wedge (5) locking the strand pulling beam (3) in relation to the casting bed.
Apparatus (1) of claim 1 or 2, wherein the at least one device (17) for moving the strand pulling beam (3) is detachably connected to the strand pulling beam, and the apparatus (1) comprises at least one device (12, 12') for detaching the strand pulling beam from the apparatus.
Apparatus (1) of claim 3, wherein the device for detaching (12, 12') the strand pulling beam (3) comprises means (13, 14; 13', 14') for gripping and moving at least one locking pin (15) connecting the device for moving the strand pulling beam to the strand pulling beam.
Apparatus (1) of claim 3 or 4, wherein the at least one device (12, 12') for detaching the strand pulling beam (3) is at least partially movably connected (18, 18') to the apparatus (1) for changing the distance between the means (14, 14') for gripping the locking pin (15) and the apparatus.
Apparatus (1) of any of claims 1-5, wherein the apparatus (1) is mounted movably on rails (8) for moving the apparatus between adjacent casting beds.
Apparatus (1) of any of claims 1-6, wherein the apparatus (1) comprises a cover (4) for an operator operating the apparatus.