US3036356A - Method of producing prestressed concrete slabs - Google Patents

Description

May 29, 1962 G. G. GREuLlcl-x 3,036,356

METHOD OF PRODUCING PRESTRESSED CONCRETE SLABS Filed June 27, 1957 4 Sheets-Sheet l May 29, 1962 G. G. GREULICH 3,036,356

METHOD 0E PEODUCING PREsTREssED CONCRETE sLABs Filed June 27, 1957 4 sheets-sheet 2 May -29, 1962 G. G. GREuLlcH 3,036,356

METHOD OF PRODUCING PRESTRESSED CONCRETE SLABS Filed June 27, 1957 4 Sheets-Sheet 3 MaY 29, 1962 G. G. GREuLlcH 3,036,356

METHOD OF PRODUCING PRESTRESSED CONCRETE SLABS Filed June 27, 1957 4 Sheets-Sheet 4 United States Patent O 3,036,356 METHOD F PRGDUCING PRESTRESSED CONCRETE SLABS Gerald G. Greulich, Fort Lauderdale, Fla., assigner to Ceco Steel Products Corporation, Chicago, Ill., a corporation of Delaware Filed .lune 27, 1957, Ser. No. 668,506 3 Claims. (Cl. 25--1S4) This invention relates in general to prestressed concrete constructions and more particularly to the novel method of producing prestressed concrete slabs.

In this comparatively young art of prestressed con-crete, the production of prestressed concrete beams has Irisen to substantial magnitude and for certain purposes prestressed concrete slabs have been produced, particularly for road and bridge constructions where the matter of depth or head room is of minor importance. Such slabs have included in their structure integral beams of considerable depth in which the prestressed strands or tendons were embodied. A

For use where load bearing capabilities were of minor importance, shallower prestressed slabs have been produced in which the tensioned reinforcing strands were disposed both longitudinally and transversely of the body of the slab. Such slabs, however, possess insufficient load bearing capabilities to permit their use in large sizes without the employment of supporting beams carried by the building columns and also transverse stringers which afford support for, and prevent exure and eventual rupture of, such slab under load.

In the method of production of such a slab having longitudinal and transverse reinforcing strands, the strands are commonly tensioned in the casting bed by the application of -tensioning st-ress to the strands individually. This is a tedious and consequently expensive procedure, and involves greater time and labor than the production of deeper beams in which the reinforcing str-ands can be tensioned in groups.

One of the primary purposes of my present invention is the method of producing a prestressed concrete slab which is devoid of deep prestressed supporting beams but on the contrary is relatively thin, affording a maximum of head room in building structures and which at the same time possesses sufiicient strength so as to be self-supporting and load supporting without undue flexure and is capable of use to form the floors and ceilings of building structures without the necessity of employing structurally independent supporting beams or stringers.

A further object of my invention is to provide a novel method of producing a prestressed concrete slab of novel construction embodying peripherally and diagonally disposed tensioned strands, together with anchor plates disposed at the corners of the slab and to which all of said strands are anchored.

A still further object is to provide an improved method of tensioning the diagonal and peripheral reinforcing strands of the slab, which method by increasing the distance between the diagonally opposed anchor plates thereby simultaneously tensions not only said diagonal strands but also the peripheral strands attached to said anchor plates.

Other objects and advantages inherent in my invention will be 'readily appreciated as the same becomes better understood by reference to the following description when considered in connection with the accompanying drawings.

Referring to the drawings, FIG. 1 is a plan view of a prestressed concrete slab produced in accordance with 3,036,356 Patented May 29, 1962 ACC my novel method and positioned in a bay area defined by rectangularly spaced columns by which such slabY is supported.

FIG. 2 is a fragmentary sectional View on the line 2-2 of FIG. l.

FIG. 3 is a similar view on the line 3--3 of FIG. 1.

FIG. 4 is a fragmentary sectional view on the line 4-4 of FIG. 1.

FIG. 5 is a fragmentary -section-al view on the line 5 5 of FIG. l.

FIG. 6 is a fragmentary plan view of a corner of my improved slab with a portion of the concrete removed to exhibit the anchor plate and reinforcing strand arrangement.

FIG. 7 is a sectional View on the line 7-7 of FIG. 6.

FIG. 8 is a sectional view on the line 8 8 of FIG. 6.

FIG. 9 is a somewhat schematic view showing the method of simultaneously tensioning the reinforcing strands by the application of tensioning forces directed diagonally of the slab.

FIG. 10 is a fragmentary View on an enlarged scale of one corner of the disclosure of FIG. 9.

FIG. 11 is a view similar to FIG. l illustrating a modification of my invention.

^ FIG. l2 is a fragmentary View taken on the line 12-12 of FIG. l1.

FIG. 13 is an'enlarged sectional Viewof one of the strand locking clamps. Y

Referring to the drawings more in detail, a prestressed concrete slab constructed in accordance with my invention is indicated generally by reference charac-ter 11. The slab, which is of shallow thickness, is reinforced by any `desired number of peripherally disposed strands 12, 13, 14 and .15 and by diagonally disposed strands '16 extending from corner to corner of the slab, and also by similar diagonally disposed strands 17 extending between the -remaining corners of the slab.

All of the individual strands are preferably composed of stress-relieved individual wires twisted together in cable form, such as is customarily employed in the production of pretensioned precast concrete units.

In Aaccordance with my invention, these strands instead of being individually and consecutively tensioned in a tedious and time consuming oper-ation are all anchored at their ends to corner anchor plates indicated generally by reference character 18. From the enlarged showing of FIG. 6, which illustrates one of the typical plates, it will be observed that the plate comprises a fiat portion or base 19 provided with lan upstanding anchor flange 21 reinforced by upstanding strengthening ribs 22 welded to the base and to the flange. The diagonal strands 16 are passed through the flange 21, as will be apparent from FIG. 8, and anchored 'to 'the plate by suitable end fittings 23 or other preferred commercial anchoring devices.

Each corner plate is also provided with upstanding anchor flanges 24 and 25 reinforced by strengthening ribs 26 and 27, respectively, and to which the peripheral strands 12 and 13 are respectively anchored by conventional end fittings or other suitable means of anchorage.

When the peripheral reinforcing strands or elements extending yalong the margins of the slab from corner :anchor plate to corner anchor plate and the diagonal strands or elements extending diagonally of the slab from corner to corner have been anchored at their ends to the corner plates in tthe manner above described and as illustrated in FIGS.` 9 and l0, yall :of said strands are then tensioned in a manner to be described. g

Each -anchor plate is attached at its outer end as shown in FIG. l0, to a yoke 28 in the form of a clevis by means of a pin 29 extending through the legs of the clevis and an aligned opening in the interposed plate. Each of said clevises, or in some instances all but one which may be stationarily anchored, 4are connected to a powerful tensioning device, such as a hydraulic jack or the like schematically illustrated and designated by reference character 31.

Solidly anchored abutments 30 to take the thrust of the jacks or other tensioning devices are provided at the corners of the casting bed of conventional or preferred form, a port-ion of the vertical walls of which are shown in FIG. l and designated 32.

The base of .the bed will be shaped to produce Va-slab bottom of the desired pattern or coniiguration. For purposes of economy in the use of slab material and of lightness in the finished product, the bed may be shaped to produce slabs shaped as exemplified in FIGS. 2 to 5, inclusive, of the drawings.V Mfarginally disposed grooves or channels adapted -to accommodate peripheral strands such 4as 12 and 14 of FIGS. 2 and 3 result in the dat depending ribs 33 and 34, respectively, and similar ribs along the other two edges of the slab, while Wider diagonally extending grooves `or troughs accommodating the diagonal strands 16 and 17 result in( corresponding diagonal ribs 35 and 36, respectively.

rIlhe intervening spaces between the marginal and diagonal ribs may be left open to present dat downwardly facing surfaces or they may be ribbed in any preferred design, such, for instance, as the longitudinal ribs 37 of FIGS. 2 and 5 or the transverse ribs 3S ofYFVIGS. 3 and 4. In any event, the over-all thickness of my vribbed slab is very materially less than that of the conventional deepbeamed slab of comparable load bearing strength. The attainable thinness of my novel slab is'importautly aduantageous in xthe saving of head room inV tall buildings, thereby in many instances Venabling one or more additional'oors to ybe inclu-ded in abuilding of-xed'height.

Reverting now to the procedure in practicing my novel method, the anchor plates having been positioned lat the corners of the casting bed and attached to the anchored tensioning apparatus and the strands having been arranged in the various marginal' and diagonal grooves in the bed base, the strands are then anchored to their lrespective anchor platespas previously explained. Before being finally anchored,'however, each strand is drawn taut, whether it be of the straight type or of the draped or slightly sloped type, and anchored under a slight initial tension. Preferably this initial tension under which the strands are anchored to the corner plates'should Ybe subf Y stantially uniform.

y The jacks 31 or'other preferred tensioning devices are now actuated in succession or simultaneously to draw the diagonally Vopposed anchor'plates apart longitudinally of the diagonal strands, thereby tensioningY the diagonal str-andsvto whatever degree may have been determined as preferable for 4the particular slab to be produced.l 1

The outward movement of the `anchor plates diagonally of'rtliebed tensions not only the diagonal Vstrands but also simultaneously tensions rthe l'peripheral strands anuse elsewhere in the interim, until the slab has been poured and set.

After the tensioning operation the casting forms, which in the present inst-ance are merely the movable side walls 32 of the bed, are placed in position around the perimiter of the slab to vbe formed, whereupon the concrete slurry is poured in the usual manner. After sulioient curing to bond the concrete to the strands, the stress is gradually relieved and sustained at the design load by the surrounding set concrete.

The clevises or yokes Z8 are then removed from the anchor plates, whereupon the slab can be lifted out of the form and transported to a storage area. Before being stored, however, the exposed corner 40 of each anchor plate is removed by cutting along the dotted line 41 shown in FIG. l0, the size and shape of the cut-out portion being such that the plate will conform closely to the column `to which it will be subsequently attached. It will be observed from FIGS. 6, 7, 8, and 10 that each corner plate is provided with an upstanding wall 42 providing a darn `for restricting the flow of poured concrete away from the corner of the anchor plate, thus leaving `the corner outside the dam exposed, as will be apparent from BIG. l0.

Since the conventional end :littings heretofore suggested for use are quite expensive and when left in the slab materially increase the cost of production, 1 have illustrated in FIGS. 1l to 13 of lthe drawings a more economical procedure which enables such expensive iittings to be repeatedly reused instead of being permanently embedded in the slabs.

On =FIG. ll of the drawing the plate ythere shown is designated by reference character 51 and the pins which correspond wi-th the pins 29 previously described are designated by reference characters 52, 53, 54, and 55, respectively. The llanges 56, 57, and 58, which in the form of the invention previously described were desighated as the anchor llarrges, are in this instance of lighter construction and serve merely -as guide plates for the reinforcing str-ands which are passed through openings in the plates or are disposed in slots extending downwardly from the upper edges of the plates and in which the strands are positioned.

The upstanding il- anges 59, 61, 62, and 63, which in the form previously described were of light construction and served merely as dams to hold the concrete away from the outer corners of the plates, are in this instance made of heavier material and serve as the anchor plates.

The strands in this form of the invention, instead of being heldV at each end by expensive end fittings, areV anchored to the anges which also serve as the dams.

` Referring rst to the peripheral strands 64, it will'be observed that they constitute a pair consisting of a single strand looped around the pin 52 and secured by end fittrngs to a block 66 abutting against the pin 53 at another side corner of .the slab. VWhen the pins S2 andV 53 have been moved outwardly diagonally of the slab thereby formed, by jacks or other tensioning devices, the tensionedV strands are locked to the anchor flanges 59 and 61 by gripping devices each consisting of a longitudinally split taperedv block 68 provided with internal Ygripping teeth or shoulders 69. After-the strands have been chored'to such plates. The stress exerted upon theV peripheral'strands by the' diagonal movementof the anl chor plates in each inst-ance is equal to the cosine of the angle between thediagonal and peripheral strands at each corner. Thus, by applying to eachY of the corner plates la tensioning stress exerted diagonally of the slab, all of the diagonal and peripheral V'strands Vare simultaneously and speedily tensioned to the requisite degree. Further-V more,Y by tensioning Ythe str-ands' simultaneous-ly in .one

tensioned, these split gripping devices lare forced into the openings or slots71 in the yanchor plates, thereby gripping ythe strands and locking them yunder tension to the anchor plates. i Y

Similarly, the strands 72 are wrapped around the pin Y Y 52, passed through the block 73 to which they are secured bythe endttings 74, and after being tensioned they are locked tofthe anchor plate 63V by the locking devices 68. The diagonal strands, which in the *presentV instance are four in n urnbeL- are held in the desired position by the guideV anges'V 57,*theinner strands 7S being looped around the pin 54 andanchored to the block 76, While Ithe outer strands 77 are wrapped around the pin 52 and anchored to .the block 7 8.

After the strands have been tensioned and locked by the clamping devices in the manner described, and after the concrete has been poured, the strands are all severed with a torch or other cutting means outside the anchor flanges. In other words, they are cut between the points of anchorage and the clevis pins.

The expensive end fittings are thereby released for use in :the production of the following slab, instead of being permanently embedded in the concrete so as to constitute a fixed cost item in each slab. The short pieces of strands resulting from the cutting may be discarded and, since they are of minor importance cost-wise as compared to the end ttings, a substantial saving is made by employing the form of anchorage disclosed in FIGS. 1l-l3, inclusive, in lieu of the anchorage previously disclosed.

Irrespective of the method of tensioning the strands employed, the pouring of the concrete and the subsequent steps of the process are the same as previously described. After the slabs have been completed, and the concrete has become fully set and the slabs are required for use, they are removed from the storage area by suitable hoisting apparatus and transported to the location where they are to be used. Here they are lifted by suitable hoisting apparatus constructed and arranged to hoist each slab in a diagonal position in an open bay and lower it into and position it horizontally in the bay in which it will provide a permanent floor and ceiling.

Referring now to FIGS. l, 6, 7, and 8, it will be observed that the columns 43 defining the area of the bay have fixedly secured thereto, at spaced vertical intervals corresponding to the floor levels, supporting brackets 44 which are permanently attached to the columns by welding or other reliable means of attachment. Each hoisted slab is lowered into position in the bay so as to t between the columns defining its area with each anchor plate of the slab substantially contacting the adjacent faces of the columns to which the plate is then rigidly secured, preferably by welding 45 as indicated in FIGS. 7 and 8. The strengthening ribs 26 and 27 are also rigidly secured to the column, preferably by welding. Access to the edges of the plates and ribs to enable the Welding to be performed is had through the space lying outside the dam 42 by which the flow of concrete 46 has been restricted, as previously explained. After the attachment of the corner anchor plates and ribs to the columns has been effected, the space between the columns and the dams 42, of the plates is filled with poured concrete, as indicated by 47 in FIGS. 7 and 8, thus providing a at top surface for the slab extending entirely to the columns.

While for erection purposes the columns may be temporarily or even permanently tied together by any suitable connecting means, it will be manifest that the slabs constructed and arranged and anchored in the manner described constitute the sole load bearing connections between the columns. 'I'he diagonal and peripheral pretensioned strands impart to the relatively thin slabs suicient stress resistance to enable all load supporting beams and stringers to be dispensed with.

The economy in construction and erection attained by use of my improved method and the saving in time and material employed in the production of my improved slab by my novel method constitute in the aggregate a great saving in building cost. In addition, by reason of the thinness of my novel slabs and the absence of deep beams in the structure, a substantial saving in head room is attained in the building.

While I have shown and described that embodiment of my invention which at present seems preferable, it should be understood that various modifications and details of procedure may be resorted to Within the scope of my invention as dened in the following claims.

I claim:

l. The method of producing a shallow prestressed concrete slab, comprising arranging in a casting bed groups of horizontally spaced reinforcing strands positioned to extend peripherally about the slab and other groups positioned to extend diagonally of the slab, providing each corner of the bed with an anchoring plate having anchoring flanges, connecting an end of each group of said peripheral strands together by anchoring same to one of said anchoring flanges on its anchoring plate at a corner of the bed and connecting an end of each group of said diagonal strands to another of said anchoring flanges on said last mentioned anchoring plate, connecting the other end of each group of said peripheral strands to one of the anchoring flanges on the anchoring plate at an adjacent corner of the bed and connecting the other end of each group of said diagonal strands to one of the anchoring flanges on the opposite corner of said bed, applying to each of said corner anchoring plates a tensioning stress exerted longitudinally of said diagonal strands for simultaneously and equally tensioning the individual peripheral and diagonal strands anchored to said anchoring flanges, placing a casting form about `the perimeter of the slab to be formed, surrounding said strands with concrete slurry to form a slab, and releasing the tension on said strands after the concrete has set.

2. The method of producing a shallow prestressed concrete slab for forming the floor and ceiling in rectangular bays defined by angularly spaced columns to which the slab is rigidly secured and supported thereby and affording the sole load bearing connection between the columns of the bay, comprising arranging in a casting bed parallel reinforcing strands disposed in horizontally spaced relation at each side along the periphery of the slab and other parallel reinforcing strands arranged in horizontally spaced relation diagonally of the slab for increasing the load bearing capabilities of the slab and making it self-supporting, providing each corner of the bed with an anchor plate each having angularly arranged anchoring flanges for anchoring an end of adjoining peripheral and diagonal reinforcing strands, individually anchoring an end of said peripheral and diagonal strands at each corner under slight initial tension to the anchoring flanges of said anchor plates at the corners, applying to each of the corner anchor plates a tensioning stress exerted diagonally of the slab to simultaneously and uniformly tension the peripheral and diagonal strands anchored to the flanges, placing a casting form about the casting bed, pouring a concrete slurry into said casting bed to form a slab in which the peripheral and diagonal strands are embedded, and releasing the tension on esaid strands after the concrete slurry has set.

3. The method of producing a prestressed substantially rectangular concrete slab for forming a shallow oor and ceiling of a building structure with said slab affording a maximum of head room and possessing sufcient strength to be self-supporting and load-supporting without undue flexure, comprising the steps of locating in a casting bed an anchor plate at each corner of the slab to be formed with each anchor plate having plural upstanding flanges, positioning spaced reinforcing strands peripherally and others diagonally of said slab, individually anchoring the opposite ends of each of said peripheral strands along one side to the flanges of adjacent anchor plates, individually anchoring each of said diagonal strands to the flanges of those anchor plates located at diagonally opposite corners of the slab, simultaneously and equally tensioning all of said peripheral and diagonal strands anchored to said flanges of one corner plate by applying a tensioning stress exerted diagonally of the slab, placing a casting form about the bed for retaining the concrete, surrounding said strands with a concrete slurry to form a slab, and releasing the tension on said strands after the concrete has set with the stress gradu- 7 ally relieved and sustained at the desired load by the sur- V1,444,806 Sty Feb. 13, 1923 rounding set concrete. Y 1,559,837 Allen Nov. 3, 1925 Y '2,172,703 Freyssinet Sept. 12, 1939 References Cited'in the le of this patent 2,234,663 Anderegg Mar. 11, 1941 UNITED STATES PATENTS 5 FOREIGN PATENTS 634,986 Mami oct. 17, 1899 820,576 Germany Nov. 12, 1951 1,417,774 Schuster May 30, 1922

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