US2511761A

US2511761A - Manufacture of prestressed

Info

Publication number: US2511761A
Authority: US
Priority date: 1943-09-28
Publication date: 1950-06-13
Anticipated expiration: 1967-06-13
Also published as: GB581815A; BE459598A

Description

R. s. v. BARBER El AL 2,511,761

June 13, 1950 MANUFACTURE OF FRESTRESSED CONCRETE SLEEPERS AND LIKE BEAMS 2 Sheets-Sheet 1 Filed Dec. 4, 1944 IHIHH IIIIIHH I ifa l mmllnll -IHHIIH II EH II.

IIU H I'NYQNTORS June 13, 1950 R. s. v. BARBER ETAL MANUFACTURE OF PRESTRESSED CONCRETE SLEEPERS AND LIKE BEAMS 2 Sheets-Sheet 2 Filed Dec. 4, 1944 N ToRS Im- M AIII Patented June 13, 1950 MANUFACTURE OF PRESTRESSED. CONe CRETE SLEEPERS AND LIKE BEAMS Ronald Samuel Vernon Barberand Dudley Roger Lester, Malvern, England,- assignors toDowsett Engineering Construction Limited, Malvern,

England, a British company Application December 4, 1944', Serial No; 5665600 In Great Britain Septemberfiii, 1943 This invention: consists of improvements in the manufacture of pie-stressed reinforced concrete sleepers and like: beams and deals particularly with the means for applying tension to reinforcing, wires before a casting operation and for releivingx the external tension on said wires when the castconcrete has set and hardened.

In this specification the expression sleepers is used to includezrailway sleepers and similar beams. In the manufacture of pre-stressed reinforced concrete. sleepers it is customary to employ mass production methods: thus long production lines are arranged to' accommodate a large number of sleeper moulds in series. The

first. step 'is. to* arrange the reinforcingswires in the-productionlines and toapply tension thereto. The distribution of reinforcing wires over the cross-section of thesleeper is a matter of choice or designbut one; known scheme is to use the wires in pairs .andto-Lemploy: anumber of such pairs (say '7v to 12'pairs). Normally there is at each .end of each production line a'sturdy pedestal embodying a: perforated upright. plate through which the wires :are. threaded. At one end of each production line'the ends of the wiresmay be made fastwhil e. at the other end means are provided .fOIi applying and hrelieving tension.

In: onemethodxatpresent in commercial use the wires-at. the: tensioning" end are threaded anchorage; platewhich. is' capable of sliding Iongitudinally in fixed guides.

The. tensioning ofxthe reinforcing wires in this known method. is: carried out intwo stages.

In the first stage; each wire or pair of wires is given a preliminarytension and is secured to the anchorage. plate rsay by the action oi wedges. For, the second stage, hydraulic rams-are introduced. between the pedestal. and the anchorage.

plate. and .oil under pressure pumpedinto the hydraulic rams soas' to force back the-anchorage plate'toaapplythe final tensionzto the reinforcing wires, and distance. pieces, suchaas stout. metal rods, are secured .between. thepedestal and the anchorage plate .to;.keep.the' wires: in tension, the

To enabIe-thedistance pieces to be re-.

2 Claims. (Cl. 25467) moved it has beenfnecessary. to. replace the hy-Q draulic rams and to force the anchorage plate and hardenedin the moulds. This known method of applying and relieving tension is subject to a number of disadvantages in addition tothe one just mentioned. For example, the application.

of the tension through an anchorage plate operated by hydraulic rams may give rise to unequal stresses on the anchorage plate especiallyii' the preliminary tensions on the wires have been'unequal. Again it will be seen with the above arrangement where the anchorage plate moves come the above diificulties both when applying and when relieving tension in the reinforcing wires; and an incidental object is to facilitate the other wires.

plied to the reinforcing wires in one stage. throughra sturdy pedestal and also through an applicationto the. different 'wires'of different ten-j sions according to the requirements of the designer.

According to this" invention the tension is ap- If the wires are used singly, i; e; separated from one another, the desired tension maybe applied to one wire at a time. 'Iraccording-to the usual custom the wires are-used"in" contiguous pairs,

the desired tension may be applied to each pair, onepair at a time.

It-is afeatured this invention that 'in' any particular" arrangementof reinforcing "wires; the tensionin certain wires-may be greater than in According to this'inventi-on at thetensioning end of the production line thereis a stout fixed pedestal or permanent-structure through whichthe reinforcing wires are passed. At the appropriate height forrthe reinforcing wires and at the backof the pedest'al' there is fixed a head also of sturdy-construction and conveniently consisting of' a number (say 8): of short sections of rolled steel'j'oists. Thishead carries one or more hori- J zontally-extending' strong brackets which proand is separated from the head by several (say 3 or 4) stout adjusting screws. Each wire anchorageplatea.is-provided with orifices through :which reinforcing; wires (generally in pairs) are Ida, the uppermost screw I8 of each plate I! bearing against the associated section I la.

Each hole I9 through the anchorage plate I! conveniently accommodates a pair of wires 20 and one method of securing a pair of wires in the anchorage plate I I is to force a wedge 2| between the wires and into the hole.

by a screw-action wedge or by other wire-fixing device.

To prevent any tendency towards tilting of the wire-anchorage plate during the tightening operation, means may be provided for applying the tension to wires symmetrically on both sides of the vertical median line of the wire-anchorage plate. It will be understood that while the tension is being applied and while it is being maintained, the screws which secure the wireanchorage plate in relation to the head are not moved or adjusted: in other words the pedestal, head and wire-anchorage plate are rigid.

After the casting operation is completed and the concrete has set and hardened, the method of releasing the external tension on the wires is to turn the adjusting screws-so as to allow the wire-anchorage plate to approach the head from which it is carried. By this means the release of external tension of the wires is allowed to take place gradually and uniformlyand there is no necessity to apply any further or additional tension to the wires.

When tension of the wires has been relieved to a sufflcient extent, the wires can be released from the wire-anchora e plate by removal of the ferrules, wedges or like securing devices.

It will be understood that the method described for releasing the external tension on the reinforcing wires of one production line involves a movement of the wire-anchorage plate towards the head from which it is carried and therefore at the stage when the tension is applied to the wires,

the anchorage plate must be withdrawn to therequisite extent by the action of the adjusting screws.

In the accompanying drawings which illustrate an example of this invention:

Figure 1 is a front elevation,

Figure 2 is a side elevation,

Fig. 3 is a plan, showing the head, pedestal and tensioning means, other parts being omitted,

Figure 4 is a section on an enlarged scale through one of the holes in the anchorage plate showing the disposition of a pair of wires and the wedge which secures them, and

Figure 5 is a diagram of the production lines.

The pedestal is formed by the upright rolled steel joists I2. joined by horizontal joists I3. The head comprises eight short upright sections I 4 of rolled steel joists secured to the horizontal joists I3. A stout horizontal bracket I5 is secured to each pair of upright'sections I4 and on this bracket I5 (which has guiding fillets I6) there slides a wire-anchorage plate I! which is separated from the head by three stout adjusting screws I8. The horizontally spaced lower adjusting screws I8 bear against upright sections I4 and the upper screw I8 bears against filler block Ma. which rests against upper joist I3. Between Separate means may be provided for supplying and guiding the reinforcing wires to the wireanchorage plate, and when a complete group of wires has been threaded through the holes in the anchorage plate, that group of wires is pulled along the production line by a haulage rope where it is threaded through the head and the anchorage plate at the other end of the production line.

- To accommodate the haulage rope a hole 22 is provided in the anchorage plate I'I,

Referring to Figure 4, it will be seen that when a pair of wires has been subjected to tension a wedge 2! (which may have grooves) is inserted into the hole I9 and between the wires 20 so as to secure the wires in their tensioned position.

In the drawings the wire-anchorage plates I! are shown in an intermediate position of their possible travel but it will be understood that at the time when the tension is applied to the wires, the wire-anchorage plates (by means of the screw adjustment) are withdrawn some distance from the head I4 so that after the concrete in the moulds has set and hardened and the external tension on the wires has to be relieved, there is ample room for the movement of the wire-anchorage plate towards the head.

Referring to Figure 5, moulds 25 are arranged in long straight series and the reinforcing wires 26 pass through the moulds and through the end plates thereof so that when a mould has been filled with concrete the reinforced wires are embedded in the concrete in the mould. In Figure 5 the devices of this invention, viz., the joists I2, I3, I4, the brackets I5, the wire-anchorage plate I7 and adjusting screws I8 are shown only on the right-hand side of the drawing, but it will be I understood that there is a similar arrangement at the opposite end of the production lines.

Beyond the production lines (1. e., outside the pedestals) there are transverse rails 21 on which a wire-tensioning truck 28 can be moved so that the tensioning device thereon (e. g., a fluid-operated ram) can be brought into line with any production line and the truck 28 can then be clamped to the rails 21.

It will be appreciated that when the troughshaped moulds 25 are arranged in series in a production line, and when means for supporting the reinforcing wires 26 are provided as described, these reinforcing wires are secured at one end (say the right-hand end), then tension is applied to the wires (say by means of the wire-tensioning device 28) and then the wire-anchorage devices (not shown) at the tensioning end and are used to secure the wires under tension, but when the concrete in one line of moulds has sat and hardened and when the time arrives for relieving the external tension in the wires 26, the adjusting screws I8 are unscrewed (at either end of the line).

We claim:

1. Apparatus for the manufacture of prestressed reinforced concrete sleepers comprisingmechanism for maintaining under tension for a desired period of time, and thereafter releasing, an intermediate section of each of a plurality of each two adjacent upright rolled sections I4 is o a ed parallel Wires Which 13888 through a secured a horizontally extending rolled section plurality of aligned concrete moulds and whichwires have been initially placed under tension by other means, said mechanism comprising opposed horizontally spaced wire gripping, holding and releasing devices, one such device including an immovable supporting part or standard having a surface disposed substantially in a vertical plane transverse to the direction in which the wires extend and a substantially horizontally disposed plate supporting surface, a stout wire anchorage plate slidably resting upon the plate supporting surface of said standard, said plate being disposed substantially parallel to the vertical surface of the supporting standard and having a series of horizontally extending apertures therein through which the parallel Wires under tension pass, a releasable wire securing element extending into each .such aperture, for laterally gripping and holding against movement relatively to said plate the wire passing through said aperture, and a plurality of screws operatively engaging the plate and the vertical face of. the standard, said screws being adapted to maintain said plate and standard in spaced relationship, and the wires under tension, or to be actuated to permit the plate to move relatively to the rigid part, under REFERENCES CITED i {Ihe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 465,169 Eckley Dec. 15, 1891 191,041 Myers May 30, 1905 1 261590 Moore Apr. 2, 1918 2,171,120 Bullard Aug. 29, 1939 FOREIGN PATENTS Number Country Date 338,864 Great Britain Nov. 18, 1930 581,815 Great Britain Oct. 25, 1946