US2826800A

US2826800A - Pre-stressing of concrete assemblies

Info

Publication number: US2826800A
Application number: US467392A
Authority: US
Inventors: Myers Van Buren
Original assignee: Raymond Concrete Pile Co
Current assignee: Raymond Concrete Pile Co
Priority date: 1954-11-08
Filing date: 1954-11-08
Publication date: 1958-03-18
Anticipated expiration: 1975-03-18

Description

March 18, 1958 M. VAN BUREN 5,

PRE-STRESSING OF CONCRETE ASSEMBLIES Filed Nov. 8, 1954 vs Sheets-Sheet 1 II II J I INVENTOR MYERS WA/BU/FE/V.

m y 1 NE! E I 3% Z 8w 5 w Q8 S N m N$Mm mm 8 March 18, 1958 M. VAN BUREN 2,82

PRE-STRESSING 0F CONCRETE ASSEMBLIES .0 MW H 2 NB 7 N t AWN W m mm W & M

Filed Nov. 8, 1954 United States Patent 2,826,800 PRE-STRESSING 0F CONCRETE ASSEMBLIES Myers Van Buren, Haworth, N. J., assignor to Raymond Concrete Pile Company, New York, N. Y., a corporation of New Jersey Application November 8, 1954, Serial No. 467,392

3 Claims. (Cl. 25-118) This invention relates to methods and apparatus for forming so-called pre-stressed concrete units and more particularly to methods and apparatus capable of manufacturing a multiple number of such units in end-to-end relationship so that a single stressing operation is suflicient for all units in the group.

Various methods of forming pre-stressed concrete units are presently in use, among them being the method for making hollow piles or pipe described in: U. S. Patent No. 2,609,586, granted to R. M. Parry on September 9, 1952 which comprises running cables through holes provided in the walls of a series of concrete units and applying tension to the extremities of these cables by means of forces reacting against the ends of the assembly of units. The cables are thenbonded in place so that, when the tension applying means have been removed, the cables will remain under heavy tension and act to maintain the v concrete assembly itself under compression, whereby the latter will manifest increased strength when subjected to torsional stress. To effect this bonding, grout is forced into the holes in the concrete units while the cables r ice at the IOU-foot and ZOO-foot marks, thereby forming three 100-foot pressed piles.

running therethrough are maintained under tension, the tension notbeing removed from said cables until after the grout has set, thus permitting bonding the cables under tension throughout their length to the concrete. Practice has shown that the labor costs in such a stressing operation are almost entirely independent of the length of the assembly to be stressed, that is for example, nearly as much labor is required to stress a 50-foot assembly of units as for one 250 feet long. Therefore, substantial economy in both cost and speed can be effected by a procedure which calls for pre-tensioning an elongated concrete structure by a single stressing operation and j so as to form an elongated structure 22 which may be 1 sioning cables are run through aligned apertures provided in both the units and spacer means. T hereupon a single post-stressing or tensioning and grouting operation is performed after which, by virture of the spacer means, the cables may be readily severed, the spacer means removed and a multiple number of pre-stressed concrete assemblies thereby formed. For example, in the manufacture of concrete piles, when it is desired to manufacture relatively short piles of for example 100 feet in,

length, a plurality of concrete units, each having the desired cross-sectional size and configuration and together totaling 300 feet in length are arranged in end-to-end.

relationship with spacers of the type described hereinafter, interposed between adjacent units at the 100-foot and 200- foot marks, thereby forming an elongated concrete structure. Both the units and the spacers are provided with aligned, cable receiving apertures into whichtensiouing According to the invention herein, a spacer is provided Other and more specific objects, features and advantages of the invention will appear from the detailed description given below, taken in connection with the accompanying drawings which form a part of this specification and illustrate by 'way of example the presently preferred embodiments 'of the invention.

'In the drawings? Fig. 1 is a plan view partly in cross-section, showing a plurality of tubular concrete units aligned in end-to-end relationship in the process of being stressed with spacers v interposed between adjacent groups of units;

Fig. 2 is an enlarged side elevational view of one of the spacers of Fig. l;

Fig. 3 is a sectional view taken on the line 33 of a Fig. 2;

Fig. 4 is. a fragmentary sectional view taken on the line 4-4 of Fig. 2;j

Fig. 5 is a sectional side elevationalview of the spacer of Fig. 3 andfshowing the first step in the method of removing this spacer after the stressing operation has been completed;

Fig. 6 is a fragmentary side elevational view of a portion of the spacer of Fig. 2;

Fig. 7 is an enlarged, fragmentary, side elevational view 1 of a portion of the spacer of Fig. 2, showing one of the tensioning cables passing therethrough;

Fig. 8 is a partial sectional view showing a portion of a modified form of spacer;

Fig. 9- is a sectional view taken on the line 99 of Fig. 8; and y Fig. 10 is a fragmentary, sectional view of another modified form of spacer.

Referring now in more detail to the drawings and particularly to Fig. 1, according to the method of using the invention a plurality of concrete units or groups of units 20 are arranged in end-to-end relationship with spacers 21 interposed between adjacent units (or groups of units) pre stressed inits entirety by a single stressing operation. The concrete units 20 in the form here shown are'tubular and. are provided with a plurality of circumferentially spaced cable-receiving apertures 23, extending longitudinally therethrough. In like manner, spacers 21, as will be described more fully hereinafter, are provided with a 7 corresponding number of similarly, circumferentially spaced, hollow tubes 24 which form cable-receiving apertures extending through the spacers.

In assembling the elongated concrete structure 22, the concrete units and spacers which constitute the same are arranged so that their cable-receiving apertures are aligned and so as to form cavities extending continuously through the elon gated structure 22, and-tensioning cables 25 are then threaded therethrough so that said cables extend continuously through the entire elongated structure 22 with Y the cable ends projecting from each end thereof. Cables 25 are each formed of a plurality of Wires 29 which may be held apart in the desired spaced relationship by cylin "drical wire spreaders 29' (Fig. 7).

3 7 'At this stage of the procedure, the entire structure 22 comprising amultiplicity of units :is subjected to' a stressing operation which may correspond to the operation described in said U. S. Patent No. 2,609,586 in connection with a single group-of'concreteunits. Thus locking devices 26, each comprised of mating'external.and'internal cones 27 and 28, are applied to the'projecting ends'of the cables 25. The externalcone 27 is placed'around the outside of the projecting ends of the cable wires.29 While the internal cone 28 is inserted centrally ofisaid wires. Tension is then applied evenly to the projecting ends of all cables by means of pull-iacks 30 which latter react through external cones 27 against the opposite ends of the elongated concrete structure 22. When the desired tension has been applied 'totthe cables, internal cones 28are forced inwardly bymeans of jack means 31 thereby wedging the wires 29 of each cable against the surfaces of external cones .27. The tension applying pull-jacks are then released whereupon the wires of each of the cables may contract slightly, thereby drawing the inner cones 28 further inwardly into external cones and thus locking the wires, still under tension, between said cones. Each of the inner cones 28 is truncated and provided with a longitudinally extending passage 32 designated to permit the introduction of grout centrally ofthe wires 29 into the cavities in which the cables are disposed. After jacks 30 have been withdrawn, grout may be forced in under pressure around the wires, thereby effectively bonding the cables throughout their length to the concrete structure. At this point in the op eration the elongated concrete structure22has been prestressed in its entirety, that is, since a heavy tension remains in the cables which are in turn adhesively bonded to the concrete structure the latter is maintained under compression. Thereafter, by severing cables 25 at those points in their lengths where they pass through the spacer units and removing those spacer units, a plurality of individual pre-slressed concrete structures are. obtained.

Referring now to Fig. 2, each spacer unit 21 is comprised of a pair of spaced

annular disks

33 and 34 respectively. These discs are releasably and adjustably .secured together in spaced apart relation by a plurality of bolts 35, and each disc is provided with a plurality of circumferentially spaced

holes

36, 36 respectively, pairs of which are axially aligned when the discs are bolted together. Slidably disposed in each pair of aligned holes and extending between the discs of the spacer ista hollow tube 37, the interior of which provides an aperture adapted to permit passage through the spacer of one of the tensioning cables 25. .The spacers 21 are designed to conform to the cross-sectional shape and size of the particular concrete units which are to be stressed and the number and circumferential spacing of the tubes'37 in eachspacer corresponds to the number and spacing of the apertures formed in said concrete units, so that these tubes may be aligned with the apertures in the concrete sections.

In initially assembling the elongated concrete structure 22, described above, two or more concrete units 20, or groups of such units, of the desired length are arranged in end-to-end relationship, with adjacent units being axially spaced apart a sufficient distance to permit insertion of a spacer 21 therebetween. Laterally projecting arcuate flanges 38 and39, provided on the

discs

33 and 34, respectively, of each such spacer and corresponding in shape to the external surface of units 20,

serve to center the spacers relative to the units. The spacers are then angularly adjusted relative. to the units so as to align hollow tubes 37 with the cable-receiving apertures, thereby providing continuous cavities extending through the entire concrete structure 22 for the reception of cables 25. Once this alignment has been achieved, means are provided on each spacer to maintain the angular positioning of said spacer relative to the concrete units. This retaining means consists of a plurality tween discs 33 and '34 of each spacer. These assemblies are each comprised of a pair of

blocks

41, 42 having oppositely inclined

abutting surfaces

43, 44 each of which is formed with a cut-out

portion

45, 46, respectively, which cut-outs cooperate to form a tapered aperture extending through the assembly and designed to receive a tapered pin 47. As shown, these

blocks

41, 42 are held in position between the

discs

33, 34 by means of U-shaped

wire braces

48, 49 welded to the discs and adapted to slidably embrace the blocks on three sides. The braces 48, as shown in Fig. 4, are secured to discs 33 with :the open end of the U facing radially outward of: said disc, while the braces 49 are secured to disc 34 with the open end of the U facing radially inward of said disc.

Wedge blocks

41, 42 are therefore adapted to he slid radially from opposite directions through the openends of the U-shaped braces into and out of position between discs 33' and 34. When the spacers 21 are initially interposed between adjacent concrete units 20 as aforesaid, the blocks are positioned in their braces and the tapered pin 47 is lightly tapped part way into the aperture formed by'the cut-outs in the

abuttingsurfaces

43, 44. After thespacer has been angularly adjusted so that its hollow tubes are aligned with the cable-receiving apertures 24,

bolts 35 are removed or loosened and tapered pins 47 are driven firmly into the aperture extending through the assemblies 40, thereby keying the wedge blocks and assuring that assemblies 40 will have parallel external faces a definite distance apart. It should be noted that in order to insure a uniform gripping relationship between the spacer discs and the adjacent concrete units, the outer sides of

discs

33, 34 may be provided with facings of

compressed sheet asbestos

50, 51 bonded to said discs by means of a

suitable adhesive

52, 53, such as rubberbonded packing means of some suitable well-known material (Fig. 7). With the spacers in this tight, gripping relationship with the units, maintenance of the alignment of the hollow tubes 37 and apertures 24 throughout the stressing and grouting operation is assured.

After the stressing operation has been completed on the elongated structure 22 as described above, by then severing the tensioning cables at the points where they pass through the spacers 21 and removing the spacers from between adjacent units, a plurality of pro-stressed individual units (or groups of units) may be obtained. 'To accomplish the above, it is necessary first to sever the hollow tubes 37 so as to provide access to the cables 25. To this end,a burner torch 54 (Fig. 5) maybe provided to cut through these tubes 37, and the cables 25 may then similarly be severed by burning after the tubes have been cut in half. As soon as all of the tubes 37 of the spacer, together with the cables passing therethrough have been severed as indicated at 55, the spacers maybe removed from between adjacent concrete units, thereby leaving those units completely separated and pre-stressed'as desired. When it is desired to re-use spacers 21 for another stressing and grouting operation, it will of course be necessary to replace the hollow tubes 37. which have been destroyed by the burning operation. Once such a new set of tubes has been installed in a spacer, the same will be ready for use once again in the above-described manner.

If it is desired to avoid the necessity of burning the spacer tubes in half in order to obtain access to the tensioningcables for severing the same, the modified form of spacer 60: shown in Fig. 8 may be employed. This type of spacer comprises similarly spaced

annular discs

61 and 62 having aligned apertures 62', 63, but in place of the one-piece tubes'37 of spacers 21,-the tubes 64 of this type spacer are .formed in two parts 65, 66, each welded in position in the hole of the disc at which it belongs. The spacing of the

discs

61, 62 and the length of the tube parts65, 66 are so designed asto provide a aes soo in! a) space 67 between the ends of these tubes to permit relative movement therebetween during the procedure of inserting the spacer between adjacent concrete units as has been described above. This space 67 between the tube part is closed by means of a split clamp 68 which is provided with a rubber lining 69 designed to form an efiective seal between the parts 65, 66, but also adapted to permit lateral sliding of the tube parts when the discs of the spacer are expanded.

These spacers 60 may be employed in similar manner to spacers 21 described above, that is, they are inserted between adjacent concrete members 20, their tubes aligned with the cable-receiving holes of the units and the stressing and grouting operation performed. After the grout has set and it is desired to divide the elongated structure 22 into individual pre-stressed units, the clamps 68 may be removed from the tubes 64, thereby providing access to the cables 25 through space 67. These cables may then be severed by a conventional means, such as sawing without destroying the tubes themselves. Therefore, the spacer 60 remains intact in its entirety and may be re-used for an indefinite numberof stressing operations. I

As described above, during the stressing operation, the hollow tubes of the spacers are aligned with the cablereceiving holes formed in the concrete units, thereby forming cavities extending continuously throughout the elongated structure 22. When grout is introduced through passage 32 at one end of the elongated structure 22, it will be forced into these cavities throughout the length of the concrete structure itself. However, when it is desired to provide an additional grout entry passage at intermediate points along the length of the elongated structure 22 so as to further insure a uniform dispersion of the grout, spacers of the type 60 may be provided with nipples 70, which communicate with the opening 67 and thence the interior of tube parts 65, 66. These nipples 70 may then be used to introduce additional grout through the spacers into the holes formed in the concrete units.

Referring now to Figure 10, a portion of an alternate embodiment of a spacer according to this invention is therein disclosed.- This spacer 70 is comprised of a plurality of cylindrical plugs or blocks 80 having central passages 81 formed therein, which are designed to be aligned with the cable-receiving apertures 24 formed in the adjacent concrete units. The number and location 81 of eachspacer 80 will, of course, coincide with the number of cable-receiving apertures provided in the concrete units. These spacers 80 may be formed of a material such as is easily cut or sawed, such as wood, wood fiberboard, plaster of paris, etc., so that after the stressing operation has been completed, as aforesaid, the tensioning cables units 20 by sawing first through the spacers 80 themselves and then through the cables. If desired, the spacers 80 can be formed of any material such as wood, which is capable of being removed by self-sustaining combus- 24 may be severed between adjacent concrete tion. 0n the other hand if desired, the spacers can be formed of a material which may be melted by the application of heat, such as sulfur, rosin and various thermosetting resins. In any event, spacers of this type 80 are designed for one use only, since after a single stressing operation, as described above, these spacers 80 must be destroyed to provide access to the tensioning cables for severing the same.

The invention is particularly Well adapted for use in the economical construction of concrete pipe as well as hollow concrete piles.

The invention is also adapted to be used in cases where the wire cables are contained in metal sheaths such as shown in U. S. patent to Upson No. 2,677,957, granted May 11, 1954.

Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, various further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

'1. A re-usable spacer for use in the prestressing of a plurality of concrete units comprising a pair of spaced discs adjustably secured together, at least one hollow cable-receiving tube extending between said discs, and wedging means interposed between said discs and adapted, when the spacer is interposed between adjacent concrete units to be stressed, to key said discs apart.

2. A re-usable spacer for use in the prestressing of a plurality of concrete units comprising a pair of spaced discs adjustably secured together, a pair of aligned apertures one in each disc, a hollow cable-receiving tube slidably received in said pair of aligned apertures and extending between said discs, wedging means interposed between said discs.

3. A re-usable spacer for use in the prestressing of a plurality of concrete units comprising a pair of spaced discs adjustably secured together, a pair of aligned apertures, one in each disc, a hollow tube extending between said discs and connecting said apertures, said tube comprising a pair of spaced tube parts, one secured to each disc concentrically with the aperture of said disc, and a removable clamp slidably embracing said tube parts and extending across the space therebetween, and wedging means interposed between said discs.

References Cited in the file of this patent UNITED STATES PATENTS 2,609,586 Parry Sept. 9, 1952 2,677,957 I Upson May 11, 1954 FOREIGN PATENTS 489,515 Canada Ian. 13, 1953 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,826,800 Myers Van Buren It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let cers Patent should read as corrected below.

March, 18,- 1958 Column 1, line- 34, for "torsional stress" re'ad e -tensional stress,

Signed and sealed this 24th day of June 1958.,

Attest:

KARL HMAXLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents