US3050283A - Apparatus for depressing cables - Google Patents

Description

Aug. 21, 1962 F. TUMEY APPARATUS FOR DEPRESSING CABLES 4 Sheets-Shet 1 Filed Jan. 26, 1960 T E-p1 INVENTOR LAWRENCE F. TUMEY BY MM /W4 ATTORNEY Aug. 21, 1962 L. F. TUMEY APPARATUS FOR DEPRESSING CABLES 4 Sheets-Sheet 2 Filed Jan. 26, 1960 QM. mm

LAWRENCE F. TUMEY X) i BY ATTORNEY Aug. 21, 1962 L. F. TUMEY 3,

APPARATUS FOR DEPRESSING CABLES Filed Jan. 26, 1960 4 Sheets-Sheet 5 F'II3 I3 F'II3 '7 F'IE E INVENTOR LAWRENCE F. TUMEY ATTORNEY IOO Aug. 21, 1962 L. F. TUMEY APPARATUS FOR DEPRESSING CABLES 4 Sheets-Sheet 4 Filed Jan. 26, 1960 INVENTOR LAWRENCE F. rune! ATTORNEY 3,050,283 APPARATUS FOR DEPRESSING CABLES Lawrence F. Tumcy, Lakeland, Fla assignor to FIVIC Corporation, a corporation of Delaware Filed Jan. 26, 1960, Ser. No. 4,785 9 Claims. (Cl. 254-61) This invention pertains to apparatus for molding concrete structural members and more particularly relates to apparatus for depressing the cables used in prestressed concrete beams.

Concrete is strong in compression but Weak in tension, consequently, concrete products such as slabs and beams which carry vertical loads must be reinforced in the areas where the most tensile stress occurs. One type of reinforcement frequently employed is steel cables. By tensioning the cables and locating them in the lower regions of the form, a beam having precompressed lower fibers is provided. The amount of compressive stress imposed by the cables is designed to be equal to the tensile stress imposed on the beam by the design load. The stresses counteract each other and therefore, the concrete in a beam supporting the design load will be substantially unstressed.

When the cables imposing compressive prestress are located in the lower portion of a beam throughout the full length of the beam the finished beam arches upward assuming a camber and is horizontal only when subjected to the design load. Beams having cambers often impose difficult construction problems when they are used in buildings and the like. It has been found that by anchoring the prestressing cables at a relatively high location at the ends of a beam and depressing the cables at midspan, the camber of the beam is reduced or completely eliminated while the advantages of prestressing are retained.

An object of the invention is to provide an improved cable depressing device for use with forming apparatus for prestressed concrete structural members.

Another object of the invention is to provide a cable depressing device which has unusually high load capacities.

Another object of the invention is to provide a cable depressing device which can be used in the production of beams of large dimensions.

Another object of the invention is to provide a cable depressing device which is adjustable longitudinally along the beam forming apparatus.

These and other objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective of the cable depressing apparatus of the invention, illustrating a portion of the mold for forming a prestressed concrete beam.

FIGURE 2 is a side elevation of the cable depressing apparatus of the present invention, illustrating the apparatus after cable depression has occurred.

FIGURE 3 is an end elevation of the cable depressing apparatus shown in FIG. 2.

FIGURE 4 is an isometric on an enlarged scale of a clip which is used in depressing several superposed cables.

FIGURES 5, 6, 7, and 8 are fragmentary transverse sections through a typical mold cavity for a stem portion of a prestressed concrete beam, illustrating several successive steps involved in depressing a plurality of prestressing cables within the mold cavity.

FIGURE 9 is a partial side elevation of a modified form of the cable depressing apparatus.

FIGURE 10 is a partial end elevation of the cable depressing apparatus illustrated in FIG. 9.

A portion of a form or mold 12 for a prestressed double-T concrete beam is illustrated in FIG. 1. The form 12 comprises an elongate sheet member 14 (FIGS. 1 and 2) which is bent longitudinally to provide two molding cavities 15 and 16 and to provide flat surfaces 17, 18 and 19 for molding the undensurface of the slab of the double-T beam. The elongate sheet member 14 is supported above a concrete casting bed 22 on a suitable number of longitudinally spaced, transversely extending welded frames, one of which is indicated at 24.

High tensile strength steel cables 30 (FIG. 1) for stressing the concrete beam are strung horizontally between the ends of the form in the region adjacent the top of the two stem molding cavities 15 and 16. In the particular instance illustrated, six such cables are superposed with respect to each other and comprise the group of cables in each of the stem molding cavities. It is to be noted, however, that each group may consist of other numbers of cables, or in certain cases, a single cable may be employed in each mold cavity. Furthermore, more than one group of superposed cables could be placed in each mold cavity if it is desired.

One or more cable depressing devices 40 (FIG. 1) transversely bridge the form 12. Each device 40 engages the group of cables in each stem molding cavity 15 and 16 and applies downward pressure to these groups of superposed cables to bend the cables so that their center regions are depressed to lower positions in their respective cavities while the cable ends remain fixed in their original high positions.

The portion of the elongate sheet member 14 which defines the stem molding cavity 15 is illustrated in FIGS. 5, 6, 7, and 8. These four figures illustrate four successive steps involved in the depression of the several superposed cables in a stem molding cavity.

The several stressing cables 30 in the superposed group are in planar alignment and are strung in the longitudinal mid-plane of the stern molding cavity of the apparatus 12 (FIG. 1) and with the upper part of the cavity. A cable engaging clip 50 of inverted U-shaped form is next placed over the six cables 30 (FIG. 5). The upper portion of the clip 50 is then engaged by the notched lower end 52 of a downwardly tapered depressing rod 54 (FIGS. 4 and 5) whose upper end is attached to the cable depressing apparatus 40 (FIG. 1). When thus assembled a clip 50 constitutes a detachable lower end for the respective rod.

When actuated by the cable depressing apparatus 40 the depressing rod 54 and the attached clip 50 are moved downward in the stem forming cavity 15 of the form 12 to the final position shown in FIGURE 6. The six cables are held in their superposed relationship by the clip 50 as they are depressed and continue to be so held while the concrete is being poured and while it hardens. Concrete 56 is next poured into the stem molding cavity 15 (FIG. 7) and when the concrete has hardened sufficiently, the tapered rod 54- is vertically withdrawn. The notched lower end 52 of the tapered rod 54 readily re leases the clip 50 and is easily withdrawn upward by the cable depressing apparatus 40. The clip 50 and the several superposed cables 30 remain in the depressed location in the stem portion of the concrete beam and the tapered hole 58 remaining after the withdrawal of the tapered depressing rod 54 may be filled with concrete mortar. With this procedure, cables are depressed at midspan to be positioned in the lower regions of the stems of the double-T beam so that the lower fibers of the beam thus cast are precornpress'ed to increase its efficiency in resisting vertically imposed loads.

Each of the frames 24 which support the sheet member 14 has a pair of short projecting members 60 (FIGS. 1 and 2) welded thereto which members are connected by bolts 62 to the horizontal concrete casting bed 22. The form 12 is leveled by adjusting nuts 66 on the bolts 62.

Each cable depressing apparatus 40 (FIGS. 1-3) includes two upright guide assemblies 70 and 72 placed n opposite sides of the form 12, and includes a cross bridge 75. The upright guide assembly 70 is made from a pair of channel members 76 and 77 and the upright guide assembly 72 is made from a pair of channel members 78 and 79 (FIGS. 13). The channel members of each upright guide are welded to a respective footing plate 80 (FIGS. 1-3) secured by bolts 82 to the casting bed 22.

The upper ends of the channel members of each upright guide assembly 70 and 72 (FIG. 1) carries a vertically movable brace member 86 (FIG. 1). Each brace member 86 comprises a short channel member 88 whose ends are welded to side plates 89 and 90. The side plates lie outside the flange faces of the channel members of the associated upright guide assembly, so that the brace member 86 is guided for vertical movement between the vertical channels.

Each brace member 86 is adapted to be connected to the associated upright guide assembly 70 or 72 in either of two distinct locations, vertically spaced pairs of holes 96 and 98 being provided in each guide assembly for that purpose. A bolt 94 passing through the flanges of the channel member 88 of the brace member 86 is adapted to connect the brace member to the associated upright guide assembly by passing through either the upper pair of holes 96 or the lower pair of holes 98. The height of a brace member 86 with respect to the associated guide assembly can be changed by removing the bolt 94, sliding the brace member into alignment with the other pair of holes 96 or 98, as the case might be, and then replacing the bolt.

The ends of the cross bridge 75 (FIGS. 1-3) are guided for vertical movement within the upright guide assemblies 70 and 72. The previously described cabledepressing rod 54 and an identical cable depressing rod 55 are connected to the cross bridge 75 at points directly above the centers of the stern molding cavities and 16, respectively, of the form 12 (FIG. 2). The cross bridge 75 is made from two spaced-apart channel members 100 and 102 (FIGS. 1 and 3). Pairs of bearing plates 104 and 106 (FIGS. 1 and 2) are welded to the upper and lower flange surfaces of the spaced-apart channel members 100 and 102 and the bearing plates 104 and 106 are drilled to accommodate the upper ends of the cable-depressing rods 54 and 55, respectively. The upper ends of the cable depressing rods 54 and 55 (FIGS. 1, 2, '6 and 7) are threaded and are disposed in the space between the webs of the cross bridge channel members 100 and 102. The threaded end of each rod 54, 55 carries two adjusting nuts 108 above and below the associated bearing plates 104 or 106, as the case might be, which permit the tapered rods 54 and 55 to be ver- 'tically adjusted relatively to the cross bridge 75. It will be noted that the parts of the cable-depressing rods 54 and 55 that project downward from the cross bridge substantially correspond in length to the depth of the mold cavity. Consequently, the rods 54 and 55 are materially shorter than the cable depressing rods in common use, and they are thus adapted to handle correspondingly heavy loads without buckling.

A bearing plate (FIGS. 1-3) is welded to the top surfaces of the channel members 100 and 102 at each end of the cross bridge 75. A hydraulic jack 122 is placed on each bearing plate 120. The head 126 (FIG. 3) of the piston of each jack 122 bears against the associated brace member 86. The two hydraulic jacks 122 are extended concurrently by manual operation of their handles 124 to force the cross bridge 75, the attached cable depressing rods 54 and 55 and the stressing cables 30 downward to their lower positions in the form (FIGS. 2 and 6-8).

If a cable 30 breaks during its depression, there is little danger that workmen will be hit by the end of the broken cable flying through the because the end will usually fly upward and the jack operating workmen are, of course, positioned not above the forming apparatus but beside it and out of the danger zone.

The reaction force resulting from the depression of the cables 30 acts on the cross bridge 75 considerably closer to the ends thereof where the jacks 122 are placed than incommcnly known cable depressing devices. With this construction, therefore, the amount of bending stress that must be resisted by the cross bridge 75 is reduced. Therefore the cross bridge 75 can be constructed from comparatively light channel members, which, of course, reduces the cost of the apparatus. The relatively small amount of bending stress on the cross bridge 75 allows the present apparatus to be used with apparatus which forms very large dimensioned beams.

It will be appreciated, therefore, that the cable depressing device 40 of the present invention makes it feasible to produce prestressed concrete beams considerably wider and deeper than heretofore.

The cross bridge 7 5 may be locked in the extreme lower position or cable-depressing position (FIGS. 2 and 6) or in any intermediate position between the positions illus trated in FIGURES 5 and 6, respectively, by threaded hold-down devices (FIGS. 1 and 3) one of which is connected to each end of the cross bridge 75. Each holddown device 140 comprises an elongate bolt 142 connected to a plate 144 (FIGS. 2 and 3) welded to the under surface of the cross bridge channel members 100 and 102 adjacent the associated end thereof. Each bolt 142 is threaded throughout its entire length and extends through a hole in an abutment member 146 (FIGS. 1 and 3) welded between the channel members of the associated upright guide assemblies 70, 72. A nut 148 on each bolt 142 may be adjusted to retain the bolt 142 and the corresponding end of the cross bridge 75 in any depressed position. The two abutment members 146 are located to also act as stop members, limiting the downward travel of the cross bridge 75.

If the two hydraulic jacks 122 used with the cable depressing apparatus 40 cannot be extended sufiiciently to depress the cables 30 to the desired location, when the braces 86 are fastened to the upright guide assemblies 70 and '72 at the level of the upper holes 96, the cables '30 can be locked in place by the hold-down devices 140 while the braces 86 are lowered to be connected at the holes 98. With this construction complete cable depression can be achieved with relatively inexpensive hydraulic jacks 122 having stroke lengths that are insufi'icient to fully depress the cables when the cross brace members 86 are connected at holes 96. When complete cable depression is achieved the nuts 148 of the cable hold-down devices 140 are tightened against the respective abutment members 146 and both hydraulic jacks 122 can be removed, with the result that jacks are not required to maintain the cables depressed while the concrete in the form 12 is hardening. A hook 150 (FIGS. 1 and 2) is centrally connected to the upper surface of the cross bridge 75 and is provided for lifting the cross bridge and the attached cable depressing rods 54 and 55 when the concrete has hardened.

It is sometimes desirable to have the cross bridge and the upright guide assemblies movable longitudinally along the concrete forming apparatus 12, so that when the length of a beam is changed the depressing apparatus can be located at midspan of the beam to be cast. To make this longitudinal adjustment of the cable depressing device possible, a modified form 160 (FIGS. 9 and of an upright guide assembly is provided for use at each end of the disclosed cross bridge 75. The modified upright guide assembly 160 includes two vertical channel members 162 and 164. The lower portion of each of the channel members 162 and 164 is welded to a guide block 166 and a guiding angle member 168. The guide block 166 and the guiding angle member 168 are spaced apart sufliciently to accommodate a guide rail 170 therebetween. The upper surface 172 of the guide block 166 contacts and can he slid along the lower surface 174 of the guide rail 170. A pair of locking bolts 178 engage nuts 180 which are welded to the guiding angle member 168. The bolts 178 are tightened through the nuts 180 against the upper surface 175 of the guide rail 170 and lock the upright guide assembly 160 in the selected longitudinal location along the guide rail 170.

Each upright guide assembly 160 includes one of the previously described hold-down devices 140. The guide assemblies 160 receive the cross bridge 75 and operate in the manner described in connection with the cable depressing device 40 (FIGS. 1-3).

The guide rail 170 is illustrated as being cast as an integral part of the edge of forming apparatus 190. This form 190 is made from concrete and includes a metal forming sheet 191. A guide rail 170 extends for a considerable distance along each side of the apparatus 190, and it will be apparent that the guide rails 170 could be made as a part of a separate framework which would be placed along each side of the form 12 (FIGS. 1 and 2), for example, and bolted down to the casting bed 22.

It will be understood that modifications and variations of the invention disclosed herein may be resorted to without departing from the scope of the invention as defined by the claims.

The invention having thus been described, that which is claimed as new and which is desired to be protected by Letters Patent is:

1. Apparatus for depressing stressing cables in a prestressed concrete molding form comprising a vertically movable bridge spanning the concrete molding form, guide means adjacent each end of the bridge adapted to guide the bridge during vertical movement thereof, a

cable engaging rod extending downward from the bridge, hydraulic means connected between said guide means and said bridge for forcing the cables downward in the form, and means connected to the bridge for locking the bridge and depressed cables in a selected vertical position.

2. Apparatus for depressing stressing cables in a prestressed concrete molding form comprising a vertically movable bridge spanning the concrete molding form, guide means adjacent each end of the bridge adapted to guide the bridge during vertical movement thereof, a cable engaging rod extending from the bridge into the form, means connected between the rod and the bridge for adjusting the extension of the rod with respect to the bridge, hydraulic means connected between said guide means and said bridge for flexing the cables within the form, and means connected to the bridge for locking the bridge in a selected position and the cables in the corresponding flexed position.

3. Apparatus for depressing a stressing cable in a prestressed concrete molding form comprising vertically movable means spanning the concrete molding form, cable engaging means carried thereby, means adjacent each end of the spanning means for guiding the same in vertical movement, hydraulically actuated means engageable with each end of the spanning means and with the associated guide means and operable to depress said spanning means and the engaged cable with respect to the form, and means located at each end of the spanning means for locking it and the engaged cable in a selected depressed position.

4. Apparatus for depressing a stressing cable in a molding form comprising a vertically movable beam spanning the concrete molding form, a cable engaging member carried by the beam, guide means adjacent each end of the beam, hydraulically actuated means adapted to be interposed between each end of the beam and the respective guide means, said hydraulically actuated means being operable to depress said beam and the engaged cable with respect to the form, means for adjusting the position of the cable engaging member with respect to the beam, and means located at each end of the beam for locking it and the engaged cable in selected position.

5. In apparatus for manufacturing prestressed concrete beams including an elongate form for molding a beam, and a plurality of concrete stressing members in planar alignment within said elongate form, the combination of a movable stressing member depressing device spanning said form, means for guiding the depressing device in movement toward and away from said elongate form, means engaging said depressing device for forcing said device toward the form, a clip embracing said stressing members for maintaining said alignment thereof, and a rod secured to the depressing device and engaging the clip to depress the stressing members in the form upon operation of said forcing means, said rod being releasable from the clip to leave the clip in embracing relation with the stressing members upon movement of the depressing device away from the form.

6. In apparatus for manufacturing prestressed concrete beams including an elongate form for molding a beam, and a plurality of concrete stressing members in planar alignment within said elongate form, the combination of a movable stressing member depressing device spanning said form, means for guiding the depressing device in movement toward and away from said elongate form, means for guiding the depressing device in movement substantially parallel to said elongate form, means engaging said depressing device for forcing said device toward the form, a clip embracing said stressing members for maintaining their alignment, and a rod engaged with the clip and connected to the depressing device to depress the stressing members in the form upon operation of said forcing means, said rod being releasable from the clip to leave the clip in embracing engagement with the stressing members upon movement of the depressing device away from the form.

7. Apparatus for depressing cables in a concrete molding form comprising a vertically movable bridge spanning the molding form, guide means adjacent each end of the bridge, each of said guide means being mounted for movement along said form and adapted to guide the bridge during its vertical movement, a cable engaging rod extending downward from the bridge, hydraulic means connected between each guide means and said bridge for forcing the cables downward in the form, and means connected to the bridge for locking the bridge and depressed cables in a selected position.

8. In apparatus for manufacturing prestressed concrete beams including an elongate form for molding a beam, the combination of a guide rail mounted adjacent each side of the form and extending parallel thereto, a cable depressing device spanning said form, guide means for said depressing device mounted on each of said rails for longitudinal movement along said form, said guide means engaging said cable depressing device for guiding said device in a plane perpendicular to the form, and adjustable means adapted to be connected to said guide means for engaging the cable depressing device and moving it in said plane.

9. In apparatus for manufacturing prestressed concrete beams including 'an elongate form for molding a beam, the combination of a guide rail mounted on each side of the form and extendingparallel thereto, a cable depressing device spanning said form, guide means for said depressing device mounted on each of said rails for longitudinal movement along said form, each of "said guide means engaging a respective end 'of said cable depressing device for guiding said device in a plane intersected by the form, adjustable means adapted to be connected to said guide means for engaging the cable depressing device and moving it in 'said plane, and means connected between the cable depressing device and the guide means for retaining the device in selected position of adjustment on said guide means.

References Cited in the file of this patent UNITED STATES PATENTS

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