US3298403A - Wire mat forming method - Google Patents

Description

Jan. 17, 1967 w. D. ALLERS WIRE MAT FORMING METHOD 3 Sheets-Sheet 1 Original Filed April 15, 1963 Ja1 1. 17, 1967 v w, ALLERS 3,298,403

WIRE MAT FORMING METHOD Original Filed April 15, 1963 s Sheets-Sheet 2 Jan. 17, .1967 w. ALLERS 3,298,403

WIRE MAT FORMING METHOD Original Filed April 15, 1963 r 5 Sheets-Sheet 3 m fix rm L U U L -.L i Z3 1 k. ZQ.; E Z9 Z9 v V K1) Q F 42 J" a United States Patent 3,298,403 WIRE MAT FORMING METHOD William D. Allers, 105 W. Harris Ave., La Grange, Ill. 60525 Original application Apr. 15, 1963, Ser. No. 273,227. Di-

vided and this application Nov. 24, 1965, Ser. No.

6 Claims. Cl. 140-921 This application is a division of my copending application Serial No. 273,227, filed April 15, 1963, now abandoned.

j The invention of thisaapplication relates to a method of forming a wire mat particularly suitable for use in prestressing concrete sheets and other members.

In Patent No. 3,084,910, issued April 9, 1963, a method and apparatus are disclosed for forming prestressed concrete sheets. An arrangement of tensors is provided for tensi-oning a plurality of wires over a bed, each tensor in its preferred form comprising a horizontal rod carried by a plurality of arms or shoes which pivot at their ends about a horizontal pivot line parallel with but spaced from the axis of the rod. A power-operated lever is connected to the tensor for slowly pivoting it to shift the horizontal rod downwardly and outwardly away from the bed, thereby stretching andtensioning the wires which are looped about the rod and which span the bed. When the self-locking tensor is fully lowered and the wires have reached maximum predetermined tension, a layer of wet concrete is applied to the bed and, after the concrete has fully hardened, the tensor is disconnected from the exposed ends of the imbedded wires.

For effective stressing of the concrete sheet or other member, it is essential that the stretched and highlytensioned wires be securely anchored within the concrete. Otherwise, the wires would contract as soon as they are cut or disconnected from the tensor and the concrete in which such wires are imbedded would not be stressed. It is for this reason, among others, that multiple strand twisted wire is preferred; the uneven contour of such wire plays an important part in achieving a secure interlock between that wire and the surrounding concrete.

Despite its important advantages, twisted wire has significant disadvantages which makes it difiicult, expensive, and even dangerous to use in forming prestressed concrete members. A particular problem concerns the wide range and dangerously unpredictable level of maximum tension which such wire is capable of withstanding depending upon whether it is tensioned along a straight or curved line. Where'the wire curves sharply, as where it is looped around the horizontal rod of a tensor, the different radii of curvatures for the various strands at any given point of contact with the tensor rod results in unequal stressing of the strands. The outermost strand at any given point is under greater stress and tends to cut into the strand or strands in contact with the surface of the tensor rod. Should one strand be se'vered by an adjacent strand, a type of chain reaction occurs with many strands breaking, often at the same point, and the wire, with its tension suddenly relieved, lashing or whipping about. It should be noted that if any slippage or relative movement occurs between the wire and the smooth surface of the tensor rod during the tensioning step, such relative movement significantly increases the possibility of the self-severing action of the twisted wire.

Another problem relates to the difficulty of determining the stress limits of twisted wire because of the slight st-retchability which inherently results from its twisted character. Even where such wire is cut into precisely equal lengths and each length is provided with its own terminals on opposite sides of the bed, the variations in the stress limits of each stretch of wire over the bed may give rise to breakage problems. Where a single piece of twisted wire is strung back and forth over the bed to form an integral wire mat, the danger of breakage is substantially greater because of the tendency of the various stretches to equalize their tensions, and thereby slip over the smooth rounded surface of the tensor rod, as the tensor is shifted downwardly into its wiretensioning position.

Accordingly, it is a principal object of the present invention to overcome the aforementioned defects and disadvantages in the methods of forming prestressed concrete members. Another object is to provide a method of forming a wire mat for use in forming prestressed concrete members, such mat having all of the important advantages of twisted wire without the above-described disadvantages thereof. A further object is toprovide a method of forming a mat of twisted wire which may be used in conjunction with the prestressing apparatus and method disclosed in the aforementioned patent without danger that one strand will tend to sever another against the outer surface of the tensor rod.

A further specific object is to provide a method of forming a mat having stretches of wire of substantially identical length and stress characteristics. It is a further object to provide a method which is suitable for forming a single strand of wire into a mat having twisted wire stretches of any desired length.

Other objects will appear from the specification and drawings in which:

FIGURE 1 is a broken top plan view of a bed and wire tensioning apparatus, the apparatus holding in fully tensioned state a wire mat;

FIGURE 2 is a side elevational view of the bed, ap-

paratus and mat shown in FIGURE 1;

FIGURE 3 is an enlarged broken perspective view illustrating in detail the relationship between the tensor of the apparatus and the wire mat;

FIGURE 4 is a broken perspective view illustrating the structural details of the mat;

' FIGURE 5 is a perspective view of an apparatus for use in forming the mat shown in FIGURE 4;

FIGURE 6 is an enlarged broken top plan view illustrating an intermediate step in the formation of the mat;

FIGURE 7 is a top plan view similar to FIGURE 6 but of reduced scale and illustratin a subsequent twisting step in the formation of the mat;

FIGURE 8 is a broken and somewhat diagrammatic plan view of a wire mat prior to the twisting of adjacent stretches thereof;

FIGURE 9 illustrates one way in which the wire shown in FIGURE 8 may be twisted to form a completed mat;

FIGURE 10 illustrates a second way in which the wire of FIGURE 8 may be twisted to form a completed mat;

FIGURE 11 illustrates a third way in which the wire of FIGURE 8 may be twisted to form a completed mat.

Referring to FIGURES 1-11 of the drawings, the numeral 10 generally designates a mat which is formed from a single piece of wire or other filament. The word wire is here used to mean a filament formed of metal or any other material having the requisite characteristics of strength and durability. While in most instances the wire is preferably formed of steel or other suitable metal, it is to be understood that the wire may alternatively be formed of nylon or other plastics.

In FIGURES 1, 2 and 3 the mat is shown in use in conjunction With a bed A and tensor B of the type generally disclosed in Patent No. 3,084,910 to which reference has previously been made. The bed consists essentially of a slab 11 having a top surface 12 in the shape of a concrete member 13 to be formed thereon. In the illustration given, surface 12 is flat and member 13 constitutes a thin concrete sheet. On opposite sides of the bed are upstanding posts 14 and 15. Posts 14 bear against one side of slab 11 and brace the foundation 16 as well as the horizontal rod 17 which is held tightly against the posts by the highly tensioned wires looped thereabout.

The series of spaced upstanding posts along the opposite side of the slab areinterposed between that slab and an inclined platform 18. The platform is horizontally elongated and slants transversely upwardly towards the series of posts 15 to provide an inclined supporting surface for tensor B.

The tensor consists essentially of a horizontal rod 19 which is rotatably supported in the end notches 20 of a plurality of inwardly extending pivot arms or shoes 21. Allof the spaced parallel arms are rigidly interconnected by a connecting bar 22 and the inner ends of the arms are rounded (in vertical planes) and bear against posts 15 and platform 18. Thus, the tensor B is capable of pivoting about a pivot line parallel with and spaced inwardly with respect to the axis of tensor rod 19, the range of pivotal movement being represented in FIG- URES 2 and 3 by the raised position of FIGURE 3 (also shown in broken lines in FIGURE 2) and the lowered position of FIGURE 2.

' When the tensor is in its fully lowered position, the axis of rod 19 is spaced below the pivot line of the tensor and the tension of the stretched wire mat effectively locks the tensor in place. During the wire-tensioning operation, as the tensor is pivoted downwardly, rod 19 is free to rotate about its own axis and within the notches 20* of the pivot arms, thereby eliminating or reducing slipping contact between the wire and the rod. Downward pivoting movement of the tensor is most easily accomplished by connecting a suitable lever extension (not shown) to the tensor to increase the mechanical advantage of the applied force. Such a lever assembly and a form of winch used in connection with its operation are fully disclosed in the aforesaid copending application and, since they form no part of the present invention, need not be described in detail herein.

Mat 10 consists of a single strand of wire which extends between the stationary horizontal -rod 17 and tensor rod 19. With the exception of the terminal stretches, all of the stretches of wire which extend back and forth between the stationary rod and the tensor rod are of substantially identical length. Since the rod 17 extends along the same horizontal plane as the uppermost edge portion of platform 18, the stretches of fully tensioned wire extend in the same horizontal plane between spaced points along a pair of spaced parallel lines.

Referring to FIGURES 4, 9 and 1, it will be observed that adjacent stretches of the wire have their intermediate portions twisted together to provide a plurality of paral lel double-strand intermediate sections 23. At one end of each intermediate section is a single-strand loop 24 which, in the illustrations given, is fitted over stationary rod 17. At the opposite ends of the intermediate sections (and along the opposite side of the mat) are a plurality of single-strand loops 25 which interconnect adjacent intermediate sections of the mat. In contrast to bridging loops 25, each of the loops 24 is closed and extends to only a single intermediate section.

The terminal stretch of wire 26 returns to the terminal intermediate section 27 so that such section differs from the other intermediate sections 23 in being formed of three strands twisted together. As a result of such construction, closed loops 24 and 28 are provided at opposite ends of each terminal intermediate section 27. The extreme end of terminal stretch 26 may be aflixed to the remaining strands of the intermediate portion 27 by any suitable connecting means; however, it has been found that if the mat is of sufficient size and the terminal intermediate portion 27 is sufficiently twisted, no additional connection between the three strands of the section 27 is required.

Each of the two-strand intermediate sections 23 has an identical number of twists. The terminal intermediate portions 27 may have one or more fewer twists to comensate for their greater thickness. The result is a mat having a plurality of integral elements (each element consisting of end and intermediate sections) of substantially identical overall or total length.

The mat 10 is formed from a single strand of wire by the method illustrated in FIGURES 5 through 7. The single-strand wire is commercially available on large spools and, as a preliminary step in the formation of the mat, the wire 29 is unwound from the spool (not shown) onto reel 30. The reel may be generally H-shaped composed of a plurality of interconnected side, end, and intermediate members 31, 32, 33, respectively. The reel is rotatably mounted upon a horizontal shaft 34 which passes through the centers of intermediate members 33, thereby facilitating the winding of the Wire 29 under generally uniform tension upon the reel. End members 32 are all parallel with each other and are preferably provided with a series of spaced-apart arcuate recesses 35, each of the recesses being adapted for slidably supporting only a single coil of the wire 29 wrapped about the reel. The wire is wound about the spool with a degree of resistance suflicient to place equal lengths of wire about each turn of the reel.

After the wire is fully wound upon the reel but has not been severed from the supply spool, two series of pulleys 36 and 37 are brought into contact with the inner surfaces of the coils of wire as shown in FIGURE 5. The two sets of pulleys 36 and 37 are rotatable about axes which are parallel with each other and with the end members 32 of the reel. Each pulley is independently rotatable about its own axis, and at least one of the sets is constructed so that the pulleys thereof may also be rotated about the axes of their mountings. In the illustration given, the pulleys of set 36 are independently rotatable about the axles 39 of individual mounting elements 40, although it is to be understood (for reasons which will appear hereinafter) that the pulleys of set 37 may be similarly mounted, rather than being mounted upon a single shaft 38. It will also be noted that the spacing between the pulleys of each set corresponds with the spacing between the recesses 35 of each end member 32. Therefore, as the two sets of pulleys are drawn outwardly in opposite directions, the groove of each pulley receives a portion of a single coil of the wire 29 wound about the reel 30.

The particular carriage means used to support each set of pulleys for outward movement with respect to the reel may vary considerably depending upon the size, location and capacity of the particular installation. Whatever the design of the particular carriage means, it is essential in forming a rectangular mat that the axes of the two sets of pulleys remain at all times in parallel relation with each other. Since the wire 29 remains connected to the supply spool (not shown), and since the wire is 3 freely slidable Within the recesses 35 of end members 32, outward movement of the two sets of rollers produces longitudinal sliding movement of the wire 29 about the reel. Additional wire, as it is required, is provided by the supply spool. Outward movement of the pulleys is continued until the stretches of wire extending back and forth between the parallel rolls of pulleys are of a preselected length. The wire is severed from the supply spool and, with opposite ends of the wire entrained about the pulleys anchored securely in place, a predetermined outward force is applied to the two sets of pulleys 36 and 37 to produce uniform tension in all of the stretches 29 of w1re.

Where only a relatively small mat is desired, the wire may be wound upon the reel in uniformly tensioned condition, and thereafter removed from the reel, by disassembling, partially collapsing, or otherwise reducing the size of the reel, for placement of the wire upon an arrangement of opposing pulleys.

Thereafter, each of the pulleys 36 is rotated about a radial axis generally parallel with the stretches of wire extending therefrom (FIGURE 7). The pulleys 36, with the possible exception of terminal pulleys 36a, are rotated an identical number of turns in the same or different direction. The terminal pulleys 36a may be rotated one or more fewer turns in the same or different direction because of the fact that the terminal intermediate sections 27 comprise three strands of wire rather than only two strands as in intermediate sections 23. When the wire is fully twisted, the looped end sections 24, 25 and 28 are removed from the pulleys. The result is a mat formed of wire having generally parallel elements of equal length, each element consisting of a double strand intermediate section (except for the terminal elements) and single strand end sections.

Since the end sections are only of single strand construction, they may be looped about the horizontal movable tensor rod 19, or the stationary vertical tensor rods 17, of the apparatus illustrated in FIGURE 1, and the wire elements of the mat may then be stressed or stretched without danger that one strand might sever another strand in contact with the tensor rods. Furthermore, since the elements of the mat are of identical length, with all of the two-strand intermediate portions having an identical number of turns or twists, there is no appreciable longitudinal sliding movement of the wire over the tensor rods during a tensioning operation. These important results are achieved while at the same time providing a mat having wire elements with twisted intermediate sections. Such sections constitute the principal length of each wire element and are essentially the only sections imbedded in the concrete member formed thereabout. Therefore, because of the twisted character of the imbedded wire, the chances of wire slippage in the finished concrete product are substantially eliminated.

FIGURES 8 through 11 illustrate different Ways in which the same wire, previously stretched and preformed by the means illustrated in FIGURES and 6, may be twisted to form mats of different configuration. Starting with the wire with parallel stretches 29 as illustrated in FIGURE 8, the looped ends designated by the letters A, B and C may be rotated by pulleys 36 in the manner already described to form the completed mat (FIG- URE 9) in which A, B and C become closed loops 24. Loops D-G, supported by pulleys 37 all carried upon the same shaft 38, form open loops 25 and closed loop 28 in the final mat 10.

The same wire of FIGURE 8 may be twisted differently to form the modified mat 10 illustrated in FIGURE 10. Mat 10' is formed by superimposing loops D and E, and twisting them simultaneously while holding loops A, B and C stationary. Loops F and G are separately twisted in the same manner as composite loops D, B. As in mat 10, the intermediate portions 23' of mat 10 are twisted the same number of turns, whereas the terminal intermediate portion 27' has a lesser number of turns to form twisted elements of equal length. One advantage of mat 10' over mat 10 lies in a more secure connection between the terminal stretch 26' and the remaining wire portions which form the terminal element.

The mat 10" of FIGURE 11 is similar to the mat 10' of FIGURE 10 except that the pulleys supporting loops A, B and C have been rotated as well as the pulleys supporting loops D-E, F and G. In other wonds, mat 10 is formed by twisting the wire of FIGURE 8 from all of the looped ends, the apparatus for performing such an operation consisting, as already indicated, of opposing sets of independently mounted pulleys 36.

From the foregoing, it is believed apparent that mats having single strand looped end portions and twisted intermediate elements may assume a variety of configurations. All of the elements of such mats are of substantially identical length and, therefore, there is no appreciable longitudinal sliding movement of the wire over the tensor rods during a tensioning operation. Since the portion of the mat imbedded in the concrete consists primarily of twisted wire, the mat is firmly anchored in place and is well able to perform its essential function in prestressing the surrounding concrete body.

While several embodiments have been disclosed in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

I claim:

1. In a method of forming a mat for use in prestressing concrete members, the steps of extending a single strand of wire back and forth between spaced opposing series of pulleys, each pulley of one of said series being associated with an individual mounting, each of said mountings being independently rotatable, urging said series of pulleys apart while simultaneously holding the ends of said wire against longitudinal movement to tension uniformly the stretches of wire between said pulleys, and thereafter rotating said mountings to twist adjacent pairs of said stretches of wire together to form a mat of interconnected wire elements having twisted intermediate sections and untwisted single-strand end loops.

2. The method of claim 1 in which said pulleys are arranged in two spaced parallel series, said adjacent pairs of said stretches of wire being twisted equally to provide a mat having wire elements with intermediate sections of equal numbers of turns.

3. In a method of forming a mat for use in prestressing concrete members, the steps of extending a single strand of wire back and forth between two spaced opposing series of pulleys, each pulley of one of said series being associated with an individual mounting, each of said mountings being independently rotatable, separating said series of pulleys while at the same time permitting longitudinal movement of said wire to extend the length of the stretches of wire between said pulleys, urging said series of pulleys apart while simultaneously holding the ends of said wire against longitudinal movement to tension uniformly said stretches of wire, and thereafter rotating said mountings to twist adjacent pairs of said stretches together to form a mat having interconnected wire elements with twisted intermediate sections and untwisted single-strand end loops.

4. The method of claim 3 in which said series of pulleys extend with their axes along spaced parallel lines, said adjacent pairs of said stretches of wire being twisted equal numbers of turns to form a plurality of substantially identical interconnected wire elements.

5. In a method of forming a mat for use in prestressing concrete members, the steps of winding a single strand of wire about a reel to form a plurality of substantially identical coils of wire, expanding each coil by urging opposite portions thereof outwardly in opposite directions 7' 8 while at the same time permitting longitudinal movement References Cited by the Examiner of the wire thereofluniformly tensioning said coils by UNITED STATES PATENTS urging said opposite portions outwardly in opposite directions while preventing longitudinal movement of the 3 'ggx 1351; end portions of said wire, and thereafter twisting each 5 coil of wire to form a plurality of elongated and inter- FOREIGN PATENTS connected wire elements having twisted intermediate sec- 319 555 3/1920 Germany, tions and untwisted single-strand end loops. 661,155 11/1951 Great Britain.

6 The method of claim 5 in which all of said coils I other than the terminal coils are twisted an identical ml CHARLES LANHAM Pnmary Examme" number of turns. L. A. LARSON, Assistant Examiner.

Claims (1)

1. IN A METHOD OF FORMING A MAT FOR USE IN PRESTRESSING CONCRETE MEMBERS, THE STEPS OF EXTENDING A SIGLE STRAND OF WIRE BACK AND FORTH BETWEEN SPACED OPPOSING SERIES OF PULLEYS, EACH PULLEY OF ONE OF SAID SERIES BEING ASSOCIATED WITH AN INDIVIDUAL MOUNTING, EACH OF SAID MOUNTINGS BEING INDEPENDENTLY ROTATABLE, URGING SAID SERIES OF PULLEYS APART WHILE SIMULTANEOUSLY HOLDING THE ENDS OF SAID WIRE AGAINST LONGITUDINAL MOVEMENT TO TENSION UNIFORMLY THE STRETCHES OF WIRE BETWEEN SAID PULLEYS, AND THEREAFTER ROTATING SAID MOUNTINGS TO TWIST ADJACENT PAIRS OF SAID STRETCHES OF WIRE TOGETHER TO FORM A MAT OF INTERCONNECTED WIRE ELEMENTS HAVING TWISTED INTERMEDIATE SECTIONS AND UNTWISTED SINGLE-STRAND END LOOPS.

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