US3202394A - Prestressing means for slab casting forms - Google Patents

Description

Aug. 24, 1965 T. W. SHOE PRESTRESSING MEANS FOR SLAB CASTING FORMS 2 Sheets-Sheet `1 Filed May 1'?, 1963 KSJ BYRQBERTL. KAHN Aww l mw@ W40 om.

Aug. 24, 1965 T. W. SHOE 3,202,394

PRESTRESSING MEANS FOR SLAB CASTING FORMS Filed May 17, 1963 2 Sheets-Sheet 2 ROBEQTL., KAHMTW United States Patent O pas lltfilENS SLAB Flintlti Theodore W. Shoe, rliroy, Qhio, assigner to The Flexieore Co., nc., Dayton, Ghio, a corporation of New Yori; .Filed Bday 17, 1%3, Ser. No.. 281,312 1 Claim. (Cl. 249-94) This invention relates to prestressing means for slab casting forms and more particularly for slabs of the type disclosed in United States Patent No. 2,299,111, and .the like. Slabs of this character are cast in long forms and are frequently provided with prestressing strands or wires extending the length of the slab for the purpose of imparting desired structural and stress characteristics. While slabs of this character may range anywhere from about 16 feet in length and up, the casting forms for such slabs are generally of the order 40 or 50 feet in length to provide for the maximum slab lengths to be cast.

Where a long casting form is used and where the slab to be cast does not utilize the maximum length of the casting form, it is clear that means must be provided for determining the length of a .slab during the casting operation. in the patent referred to, this means assume the simple form of hav-ing the sides of the casting form provided with regularly spaced apertures to determine the longitudinal position of one bulkhead. The bulkhead, which in this case would be the dead bulkhead, would be anchored in position by pins extending through the apertures in the casting form sides. ln lorder to prevent the sides of the casting from showing the location of such casting forni apertures, it is necessary to provide plugs for filling these apertures. Even then, the side of a casting is not perfectly smooth.

Another means for accomplishing the above involves the use of bulkheads at the two ends of the casting form with an additional bulkhead disposed intermediate the ends of the casting form to form a mud stop which cooperates with one end bulkhead to determine the actual length of a casting. This involves wasting considerable length of presressing wire extending between the mud stop bulkhead and the end bulkhead beyond the casting region.

This invention relates to a bulkhead structure which can be used with casting forms having solid sides but can be positioned at any desired point along the length of a form Without wasting prestressing strands or requiringr any change in the structure of a casting form.

Prestressing strands are tensioned to a substantial de gree. A bulkhead which supports at least three and possibiy ve or six strands tensioned to a substantial amount results in an overall force on the bulkhead which is quite high and requires means for reinforcing the bulkhead and the casting form against collapse. r[his invention provides a bulkhead structure which may be positioned at any desired position along la casting form and which position may be changed easily and which involves a minimum loss of prestressing strand, while at the same time not interfering with the design of the casting forms. The invention involves a bulkhead structure having means for directing the forces created by the tensioning ofthe strands in such a way that the normal casting form structure can withstand the forces without in any way interfering with the normal function of the casting form.

In order that the invention may be understood, it will now be disclosed in connection with the drawings wherein:

FIGURE 1 is a top plan view of a casting form equipped with the new prestressing means.

FIGURE 2 is a side elevation ofthe structure illustrated in FIGURE l, with certain parts broken away.

FIGURE 3 is an end view on hne 3 3 of FIGURE 1.

FIGURE 4 is an enlarged section on line 4-4 of FIG- URE l.

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FIGURE 5 is a View along line 5-5 of FIGURE 1.

FIGURE 6 is a view .along line 5 6 of FIGURE 1.

FIGURE 7 is a perspective detail of the stressing bar forming part of the invention.

The casting form to which this invention may be applied may be any one of a number of structures. Thus the casting form may be similar to the ones illustrated in the patent previously referred to or, preferably, may follow the teachings of United States Patents Nos. 3,023,476 and 3,023,477 disclosing one-piece casting forms whose sides are adapted to be bent outwardly and whose bottoms are adapted to be buckled inwardly to release castings. Thus the casting form may consist of at bottom 1@ having sides 11 and 12. Sides 11 and 12 extend upwardly toward top edges 13 and 14 of the casting form. The top portion of each casting form -side is shaped to provide keys in the casting. Parts 15 and 16 ofthe casting form are specifically shaped along the lines shown to provide a keyway. Whether the casting form side is solid lor merely has the interior surface thereof shaped to provide the keyway is not important.

The casting form includes channels 18 and i9 rigidly secured to the outside faces of sides 11 and 12 of the casting form. Channels 13 and 19 have top and bottom franges Ztl to 23 inclusive, these anges extending outwardly away from the sides of the casting form. Top flanges 2t? and 22 of the channels are provided with apertures 25 and 26 disposed at regular intervals along .the length of the flanges. Except for apertures 2S and 26, the casting iorm so far described is .disclosed in Patents Nos. 3,023,476 and 3,023,477 previously referred to.

The casting form has one end, here illustrated as the left end of FIGURE 1, as the front end of the casting form. The front end of the casting form has rigidly attached thereto ilat end bulkhead 23 having overhanging lange 29 extending away from the casting region. As illustrated in the drawings, the casting forrn is adapted to have tive laterally spaced prestressing strands extending along the length of the casting near the bottom thereof fo-r prestressing the casting. Bulkhead 2S is the live bulkhead in that the tension of each of the prestressing strands can be Vadjusted to a desired value.

At each prestressing strand position there is provided threaded nut and bolt means, generally indicated by 3l), and including strand chuck 31 and pulling T .32. A jack or other means for exerting tension on the prestressing strand is coupled to T 32 and strand 33 is tensioned to a suitable degree, assuming that the other end of strand .33 is retained by means to be described. In tensioning strand 33, elongation will occur. The threaded tal e-up means, generally indicated by 39, permits the elongation of the strand to be taken up so that when the tension on pulling T 32 is released, strand 33 will have its tension maintained. The means for establishing and maintaining tension on a prestressing strand is more fully disclosed and claimed in the copending application of Nieber et al., Serial No. 86,689, filed February 2, 1961. It is understood that other means for vestablishing and maintaining tension on a wire strand may be utilized.

The means for maintaining the strand tension at the dead bulkhead generally consists of two parts which -may be combined into one if desired. However, the parts are more conveniently maintained separately with a saving in weight and making the entire bulkhead structure much less cumbersome and easier to handle.

Insofar as function is concerned, the dead bulkhead combination compri-ses strand deiiectin-g bulkhead generally indicated by 4@ and stressing bar .assembly generally indicated by 41. Referring yr-st to the strand detle-cting bulkhead, this comprises .dead bulkhead 45 having Asuitable strand clea-rance openings 46. Dead bulkhead l5 is shaped and dimensioned so that it lies within the casting form vand conforms to the shape of sides 11 and 12 of the casting for-m. Dead bulkhead 45 is rigidly .secured to top plate 4S which is long enough so that ends 49 and 5) thereof overlie top ilanges 20, and 22 `ofthe casting form side channels. Ends 49 yand 50 yof top plate 48 are provided with a numberrof spaced .apertures for accommodating bolts 51 and S2. .By spacing apertures 25 and V26 on the one, hand at one distance and aper- 'turesin ends 49 .and S0 on the other hand .at la different distance, it is possible Vto utilize the 'difference in spacing for obtainingV a fine 4adjustmentrof positioning top plate 4S along the [length of thecasting form. Thus 4as an exa-mple, by having apertures 25 and `26 spaced along three-inch centers and having the .aperture-s in ends y 49 and 50 of top plate 48 .spaced along two-inch centers, it is possible for bolts y51 and 52 to be used along .one inch intervals. Bolts S1 and 52 have nuts .so that .top plate 48 can be Isecurely bolted to top flanges 20 and -722 of the channels. Spacers 54 carried rby top pl-ate 48 rare disposed between .the top anges of .the channel and top plate -48 to take up any separati-on between the two.

Rigid-ly secured to the bot-tom of .top plate 48 and to the inside or. rear face tof dead bulkhead 45 .are U-shaped strand deilecting members 60 positioned to register with the lateral position of each prestressing strand 33. -Each strand deflecting member 60 has bottom convex curved ,edgeY 61 shaped :as illustrated in FIGURE 4 to guide strand 33 from its normal position near the bottom of Y.

thecasting form yupwardly atan angle toward the top of rthe lcasting form. Strand de-ecting member -60V is as thick "as the ydiameter of heaviestl strand 33used. A strand presses-against the rear portion of curved edge 61 of the delleoting member. y Y

' To prevent strand 33 from slipping laterally fromV the ,edge lof a stranddeilecting member, retaining plates 63 ,and 64 are rigidly secured .to the bottom part of a strand rdellecting member. These retaining plates extend b ey-ond curve-d edge 61 :and cooperate. therewith to form a U-shaped slot for retaining prestressing strand 33 against .slipping laterally off. The particular shape of vdeflecting member 60 is not important and the particular :shape yof curved edge porti-on 61 is not important except ,that the portion of edge `61 remote` from dead bulkhead v45 should slope upwa-rdly in .a smooth curve.

The .angle at which strand 33 is -deected toward the top of the casting form determines the stress in bolts 51 .and 52. and .also the moment to be resisted by the strand deliection assembly. For best results, it is desir- Y V:able that the resultant of force created at edge 61 by Itensionedvstrand 33 tending to rai-se the stra-nd deflecting lassembly upwardly should intersect the bottom face of top plate 48 in avertical plane defined by the center line extending between the two center apertures in ends 49 and 50, assuming three -apertures :at Veach end as il- :lu-strated. 'This yresultant is shown in dotted lines in FIGURE 4.l This arrangement is on the .assumption that bolts 51 .and 52 pass through the. center aperture at ends 49 .and 50. However, it is contemplated that bolts 51 and 52 can be used with either of the remaining two apertures at both ends of plate 48.V .If such is the caseythen there will be a moment which will be the product lof the resultant from edge -61 multiplied by the This is illustrated in lFIGURE 4 by resultant a and moment 'arm b, .assumingt-hat bolts 51 and 52 are offset to the right as viewed in FIGURES 1 .and 4. If the bolts are Y offset to the left, the resultant will be the same except tor algebraic sign (assuming that the aperture spacing 's i-s the same).

T-o dispose the strand deecting assembly in position, it will .have to be moved in from the open end `of a karm which will be the distance from the center of the f Vaperture containing the bolt to the resultant force.

. a which the strand detlecting bulkhead may be moved lforwardly toward live bulkhead 28 to any desired positron.

Stressing bar assembly 41 includes cr'ossbar 68 extendtures in top .flanges 22 and 2d of the side reinforcing channels. l

Crossbar V68 has upwardly extending blocks 74 laterally spaced .along the length of cross ba-r portion 68 and adapted to be in vertical registration with respective prestressing' strands 33. Crossbar 68 and reinforcing blocks 74 together carry cross end plate 76 having .aperture 77. These apertures .are below crossbar portion 68 and register with .reinforcing blocks 74 and accommodate the prestressing strands. Strand chucks 79 are disposed over the ends of the strands projecting through aperture. 77 of cross end plate 76; Strand chucks 79, when the strands are tensioned, will pre-ss .against cross end'plate 76` with the full force of the tension in strand 33. Thus it Vwill be understood that the construction of. .the entire stressing bar assembly must be sufficiently strong to withstand the tremendous force exerted thereon as a result of the tensions in all strands. In practice, waste strand 'between strand chucks 79 and the dead bulkheadcan be .kept down to no more than about three feet.

By having separate strand deflecting means and stress resisting means, the parts can be made relatively light and designed to resist their respective loads. Thus strand deflecting assembly 40 is subjected to a force component from strands 33 'which tends to raise it above the casting form. The bolts for holding the .strand deilecting bar, can be designed for utmost efliciency to resist the loa-'ding involved. The reduction in weight and increase in strength fmake the pa-rts easier to handle `andless expensive to make.

vBy proper design, the center line of each strand 33 extending upwardly toward stress bar assembly 41 can intersect the line extending between the center lines Aof:

v:apertures 7K1 at the level `of the top faces of the casting form top flanges This will create a substantially pure Vshear force on bolts 72.

While dead bulkhead 45 has been illustra-ted as part lof the strand detlecting assembly, it may be separated therefrom.

In .such case, ends 49 and 5d require only one bolt ,aperture each. The dead bulkhead is lightly loaded .and can be .adjusted to 'any desired location from the strand deilecting assembly by means .of .spacer blocks.

vAlso Vone stress bar assembly has been illustrated for all strand-s in a slab, Where wide slabs are being made or if lmany strands are used, it is possible to have two stress bar assemblies, laterally olset along the length of .the casting form. VOne vstress bar assembly could .accommodate certain strands and the other stress bar assembly couldV accommodate the remainder.

What is claimed is: In combination, means for providing `a casting region :of adjustable length for prestressed slabs in a casting form having a maxi-mum length of about 40 feet, said casting form being of `,steel having .a generally'U-shaped section with the sides reenforced by steel channels on the `outside thereof extending the length of said form, each channel Vhaving a flange adjacent .the top edge `ot the Vform side with the tlange extending outwardly away laway from 'the form, the lianges having regularly spaced apertures therethrough, at least one bulkhead `assembly for mounting alo-nfy a desired region along the length of said casting forni, said 'assembly 'being capable of handling the total load of a plurality of tensioned steel strands with .a minimum lof waste of excess lengt-h of .steel strand, said lassembly comprising two :sub-assemblies, one sub-assembly being a strand deflecting subassembly yand the other being a strand stress bar subassembly, said strand deecting sub-assembly comprising a generally flat steel plate extending :across the casting for-rn `and being long enough to overlie the top ilange-s Iof the casting forni channels, said plate having apertures therethrough for registration Wit-h the channel tlange apertures, bolts for anchoring said steel plate in ldesired position along the top of said casting form, a dead bulkhead supported from said plate and extending into the casting forni to define the end of a casting region, said dead bulkhead having apertures therethrong-h for accommodating prestressing strands, strand deecting guides depending from the plate :and extending from the outer face lof said dead bulkhead and provided With guide slots for guiding the tensioned strands upwardly from the 'bottom of the casting form while retaining .said strands in their norm-al positions laterally lof the form sides so that looking down upon a casting forni in normal casting position all strands appear straight, said stress bar Sub-assembly comprising a bar extending across said casting form and havin-g its ends overlying said apertured channel anges, the cross bar ends being apertured to register with the channel ange apertures, Abolts for anchoring said cross bar in desired position along the casting form, said stress bar subassernbly being anchored at ya region beyond the dead bulkhead and outside of the casting region, :a cross end plate rigidly secured to said cross 'bar and having apertures therethrough for sai-d tensioned strands, said bar apertures being :about level With the casting form edges and Ibeing 4alined with lthe :strand guide slots to permit strands to continue straight as seen in plan, :sai-d cross end plate yand -cross bar together providing a structural angle Iless than 90, `said stress bar sub-assembly 'being oriented so that the cross end plate will .receive the upwardly guided strands substantially norrnal thereto when spaced a predetermined short distance from the strand deecting sub-assembly, said cross end plate having an outer face remote fro-rn the IStrand deecting sub-assernbly for laccornrn@dating strand chucks to seat against said louter face, .the strand length from the dead bulkhead to the lchucks being Waste.

References Cited by the Examiner UNITED STATES PATENTS 2,721,368 10/55 Landrum 25-121 2,95 0, 517 8/60 Brinkman 25-118 XR 2,958,507 11/60 Hartup 50-130 3,041,702 7/62 Schwab Q5-118 XR 3,049,786 8/62 ones 25-1l8 3,070,867 1/63 Belle 25-118 FOREIGN PATENTS 162,538 4/55 Australia.

WILLAM I. STEPHENSON, Primary Examiner.

ROBERT P. WHITE, MICHAEL V. BRENDESI,

Examiners.

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