GB2313568A - Manufacture of pre-stressed concrete panels - Google Patents

Abstract

A long casting bed (10) is coated with a release agent. Reinforcing cables are stretched along the bed between anchors (17,18) at each end of the bed (10). A plurality of dividers (20) are mounted spaced-apart along the bed (10) to subdivide the bed (10) into a number of panel sections (42). Each divider (20) is of downwardly tapering section having a number of notches 26 in a lower pointed end of the divider (20) for engaging with the prestressed cables. Concrete is prepared and poured onto the bed (10) and cured. After removing the dividers (20) and cutting the cables between the panel sections (42), the panel sections (42) are removed from the bed (10).

Description

Manufacture of Pre-Stressed Concrete Panels Introduction This invention relates to a process and apparatus for the manufacture of pre-stressed concrete panels.

The invention is particularly concerned with manufacturing pre-stressed concrete panels on a long casting bed. Such long casting beds may be 100 metres or more in length.

The beds are usually sub-divided into a plurality of separate panel moulds by dividers which are mounted transversely across the bed. However, these dividers are usually very difficult to remove after casting as upon releasing the pre-stressed cables, adjacent panels are drawn together clamping the dividers therebetween.

Removal of the dividers is time-consuming and the dividers and the panels themselves are often damaged during removal. Further, concrete tends to collect on the dividers making them difficult to handle and adversely affecting the finish on the panels.

The present invention is directed towards overcoming these problems and in providing an efficient process for the production of high quality pre-stressed concrete panels.

According to the invention, there is provided a process for the manufacture of pre-stressed concrete panels comprising the steps : coating a casting bed with a release agent; stretching a plurality of spaced-apart cables between opposite ends of the bed, fixing the cables at each end of the bed between a fixed anchor at one end of the bed and a movable anchor at the other end of the bed; moving the movable anchor away from the fixed anchor to apply a preset tension to the cables; mounting a plurality of dividers at spaced intervals along the bed for sub-dividing the bed into a number of panel sections, each divider being of tapered section, engaging a lower narrow end of the divider with the pre-stressed tensioning cables, clamping the spacers on the bed; pouring concrete onto the bed; vibrating the bed for settling the concrete; pulling a cover over the bed; heating the bed to a pre-set desirable temperature and maintaining said temperature for a preset period for curing the cement to form a plurality of end to end pre-stressed concrete panels on the bed; retracting the cover; removing the dividers; releasing the cables and cutting the cables inter connecting ends of adjacent panels and lifting the panels from the bed.

In another embodiment, the bed has a top surface with a side flap at each side of the top surface defining with the top surface a channel-section mould for forming the concrete panels, the process including mounting the dividers between the side flaps and supporting the dividers spaced above the top surface for forming a narrow neck portion interconnecting ends of the adjacent panels.

In a further embodiment, the process includes removing the panels by tilting an end panel on the bed for breaking the neck portion connecting said end panel to the next adjacent panel, freeing the end panel and then lifting the end panel from the bed.

In another embodiment, the process includes the step of clamping the dividers between side flaps and opposite sides of the bed.

Preferably, the process includes pivoting the side flaps outwardly on the bed after curing the concrete to release the panels on the bed whilst simultaneously engaging and parting the dividers away from the panels this removal of the dividers.

In another embodiment, the process includes the step of engaging each pre-stressed cable with a downwardly facing tapered notch at the lower narrow end of each divider.

In another aspect of the invention, there is provided a divider for a casting bed for forming pre-stressed concrete panels, the divider for mounting across the bed for separating the bed into mould sections of a desired length, characterised in that the divider is of tapered section, a lower narrow end of the divider being engagable with pre-stressed tensioning cables stretched along the casting bed.

In a preferred embodiment of the invention, the lower end of the divider has a plurality of spaced-apart notches for reception of a set of tensioning cables stretched across the casting bed.

Ideally, each notch is tapered inwardly from a mouth of the notch to prevent fouling of the notches with concrete.

Conveniently, the divider has means for engaging the casting bed for supporting the divider above the casting bed.

The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which : Fig. 1 is a plan view of a casting bed for forming pre-stressed concrete panels according to the invention; Fig. 2 is a detail perspective view showing portion of the casting bed with a panel divider mounted on the casting bed; Fig. 3 is a detail perspective view showing adjacent ends of a pair of panels on the casting bed; Fig. 4 is a detail side sectional view illustrating separation of pre-stressed concrete panels after casting on the bed; Fig. 5 is a detail sectional view showing mounting of the divider on the bed; Fig. 6 is a plan view showing the divider mounted on the bed; Fig. 7 is an enlarged perspective view of the divider; Fig. 8 is an elevational view of the divider; Fig. 9 is a plan view of the divider; Fig. 10 is an underneath plan view of the divider; Fig. 11 is an end elevational view of the divider; Fig. 12 is a detail elevational view showing one end of the divider; Fig. 13 is a sectional view showing the divider in use; Fig. 14 is a detail sectional view showing mounting of the divider on the bed; Fig. 15 is an underneath perspective view from one end of a pre-stressed concrete panel formed according to the method of the invention; Fig. 16 is a perspective view of the panel from the side; and Fig. 17 is a schematic illustration of panels formed according to the invention in use for forming a composite floor.

Referring to the drawings, a process and apparatus for forming pre-stressed concrete panels according to the invention will be described.

Fig. 1 shows a plan view of a casting bed 10 having a base frame 11 with a top surface 12 on which the pre-stressed concrete panels are formed. A number of side flaps 14 are hingedly mounted at each side of the top 12 for movement between an upright casting position as shown in Fig. 2 and a retracted release position. Reinforcing cables 15 can be drawn from cable spools 16 at one end of the bed 10 along the bed 10 to the opposite end, free ends of the cables 15 being secured in a fixed anchor 17. At the opposite end of the bed 10, the cables are gripped in a movable anchor 18 which is movable by means of rams 19 to stretch the cables 15 along the bed 10 to a required tension.

The bed 10 is over 100 metres long. To separate the bed 10 into mould sections of a desired length, a plurality of dividers 20 are mounted between the side flaps 14 at spaced intervals along the bed 10.

Each divider 20 is shown in more detail in Figs. 7 to 11.

The divider 20 has a body 21 of tapered section, and in this case is generally triangular in section having tapered sides 22,23 extending upwardly from a narrow pointed lower end 24 to a top 25 of the body 21. A plurality of slots or notches 26 are spaced-apart along the lower edge 24 for engagement with a set of prestressed tensioning cables 15 stretched between the anchors 17,18 at each end of the bed 10. It will be noted (Fig. 12) that each notch 26 tapers outwardly from an inner end 27 of the notch 26 towards a mouth 28 of the notch 26.

It will be noted that end faces 30 of the body 21 also taper inwardly and upwardly from the lower edge 24 for close mating with the flaps 14 as shown in Fig. 14, an inner face 32 of each flap 14 being inclined inwardly over the top 12 of the bed 10. Mounting plates 33 at each end of the body 21 extend outwardly for engagement with a flanged upper end 35 of each flap 14. A clamp 36 is engagable between the mounting plate 33 and flanged upper end 35 of the flap 14 to secure the divider 20 in place.

It will be noted (Fig. 13) that when the divider 20 is in place mounted across the bed, the lower edge 24 of the divider 20 is supported a preset distance above the top 12 of the bed 10 thus allowing the formation of a neck 40 of concrete between adjacent panels 42 below the cables 15.

In use, the top 12 of the bed 10 and inner faces 32 of the side flaps 14 are coated with a release agent. Cables 15 are drawn from the spools 16 through the movable anchor 18 for engagement and locking on the fixed anchor 17. The other ends of the cables adjacent the spool 16 are then locked on the movable anchor 18 which is subsequently retracted to stretch the cables 15 to a desired tension.

Plastics spacers may be mounted under the cables 15 at intervals along the top 12 of the bed 10 to support the cables 15 a preset desirable distance above the top 12 of the bed 10.

A plurality of the dividers 20 are then mounted at spaced intervals along the bed 10 to sub-divide the bed 10 into mould sections of a desired length. It will be noted that the dividers 10 engage the side flaps 14 and sit down on top of the cables 15 with the notches 26 receiving associated cables 15. The spacers 20 are clamped to the side flaps 14. It will be noted that the lower edge 24 of each spacer 20 is located a preset desired distance above the top surface 12 of the bed 10.

Concrete is prepared and poured onto the bed 10 between the side flaps 14 to a required depth.

The bed 10 is then vibrated, the bed 10 being on resilient mountings and vibrating motors under the bed 10 being operable to shake the bed 10 for settling the concrete on the bed 10.

Next a cover is mounted over the top of the bed 10, the cover being drawn from a reel 50 mounted on a carriage 51 which is movable along tracks 52 at each side of the bed 10 for deployment of the cover on the bed 10.

Heating oil is then circulated through the bed 10 at a desired temperature for a desired period. For example, the heating oil may be maintained at a temperature of about 1300C for approximately 16 hours for curing the concrete to form the pre-stressed concrete panels 42 extending end to end along the bed 10.

When the concrete has been cured, the cover is rolled up on to the reel 50. Then the side flaps 14 are released and pivoted outwardly to part the side flaps 14 from the pre-stressed concrete panels 42 on the bed 10. It will be noted that the outward pivoting of the side flaps 14 urges the dividers 20 upwardly parting the dividers from the concrete panels 42 and the dividers 20 can subsequently be removed from the bed 10. It will be appreciated that the tapered notch 26 formation at the lower edge 24 of each divider 20 ensures that cement does not collect in the notches 26.

Next, the rams 19 are operated to release the tension applied to the cables 15. The cables interconnecting each pair of adjoining panels 42 are parted by means of a cutter, the cutter being drawn through the groove 60 (Fig.

3) formed by the divider 20 between adjacent panels 42.

It will be noted (Fig. 4) that as a neck 40 of concrete is provided below each cable 15 joining the panels 42 the cutter cannot accidentally damage the top surface 12 of the bed 10. Further, the open grooves 60 readily expose the wires 15 for cutting, a single cut parting the wires without waste.

The panels 42 are then lifted from the bed, starting at one end of the bed 10 and moving along the bed 10. To part adjacent panels 42, the free panel 42 is tilted upwardly to break the neck portion 40 and once freed from the remaining panel 42 the free panel 42 can be lifted off the bed 10. This tilting, illustrated in Fig. 4, provides a clean break between adjacent panels 42 leaving a neat finish to an end of each panel 42.

The panels 42 may be stacked for storage. When the panels 42 have been removed from the bed, the bed can be cleaned and re-coated with release agent for a further casting cycle.

Fig. 15 is a perspective view of a flooring panel 42 formed according to the method of the invention having tapered end faces 60 and tapered side faces 61. Lifting lugs 62 project upwardly from an upper surface of the panel 42 and frames 63 also project upwardly of the top surface of the panel 42 for interlocking adjacent slabs as described with reference to Fig. 17.

Fig. 17 shows a pair of panels 42 mounted on a support beam 65, reinforcing bars 66 are extended between the frames 63 and a reinforcing mesh 67 is mounted above the panel 42 after which structural screed 68 is poured onto the panels 42 to form a composite floor.

It will be appreciated that the process and apparatus according to the invention provides for the production of high quality pre-stressed concrete panels in an efficient and trouble-free manner. The tapered divider sits on top of the cables and engages the cables to accurately locate the cables above the bed. The cables will tend to migrate upwardly during vibration of the bed however the dividers hold the cables down in the optimum location above the bed. The mounting of the dividers above the cables means that the dividers can be removed before releasing cable tension and therefore there is no crushing and damage to the dividers. Further, the tapered sides and the tapered notches facilitates removal and ensures cement does not collect on the dividers. When the dividers are removed the cables are readily exposed for cutting. Also, the neck portion beneath the cables prevents the bed from being damaged during cutting of the cables. The neck portion also prevents crushing and damaging between adjacent panels when the cable tension is released.

The manner in which the cables are presented for cutting and the breaking away of the panels from the bed ensures that a clean and regular end is formed on each panel without the need for further dressing of the panel. Thus, production time is reduced and a better quality product is produced.

Claims (8)

1. A process for the manufacture of pre-stressed concrete panels comprising the steps : coating a casting bed with a release agent; stretching a plurality of spaced-apart cables between opposite ends of the bed, fixing the cables at each end of the bed between a fixed anchor at one end of the bed and a movable anchor at the other end of the bed; moving the movable anchor away from the fixed anchor to apply a preset tension to the cables; mounting a plurality of dividers at spaced intervals along the bed for sub-dividing the bed into a number of panel sections, each divider being of tapered section, engaging a lower narrow end of the divider with the pre-stressed tensioning cables, clamping the spacers on the bed; pouring concrete onto the bed; vibrating the bed for settling the concrete; pulling a cover over the bed; heating the bed to a pre-set desirable temperature and maintaining said temperature for a preset period for curing the cement to form a plurality of end to end pre-stressed concrete panels on the bed; removing the dividers; releasing the cables; cutting the cables inter-connecting ends of adjacent panels and lifting the panels from the bed.

2. A process as claimed in claim 1 in which the bed has a top surface with side flaps at each side of the top surface defining with the top surface a channel section mould for forming the concrete panels, the process including mounting the dividers between the side flaps and supporting the dividers spaced above the top surface of the bed for forming a narrow neck portion interconnecting ends of adjacent panels.

3. A process as claimed in claim 2 in which the process includes removing the panels by tilting an end panel on the bed for breaking the neck portion connecting said panel to the next adjacent panel thus freeing the end panel and then lifting the free panel from the bed.

4. A process as claimed in claim 2 or 3 including the step of clamping the dividers between side flaps at opposite sides of the bed.

5. A process as claimed in any of claims 2 to 4 in which the process includes pivoting the side flaps outwardly on the bed after curing the concrete to release the panels on the bed whilst simultaneously engaging and parting the dividers away from the panels facilitating removal of the dividers.

6. A process as claimed in any preceding claim including the step of engaging each pre-stressed cable with a downwardly facing tapered notch at the lower narrow end of each divider.

7. A process for the manufacture of pre-stressed concrete panels substantially as hereinbefore described with reference to the accompanying drawings.

8. A pre-stressed concrete panel whenever formed according to the process as claimed in any preceding claim.