US2751776A - Stressed block building slab - Google Patents

Description

June 26, 1956 A. G. STREBLOW T L 2,751,776

STRESSED BLOCK BUILDING SLAB 3 Sheets-Sheet 1 Filed July 21 1950 INVENTORS A1852? G$775AOW 4? .DO/VALD O. MCCAZL BY M June 26, 195 A. G. STREBLOW ET AL STRESSED BLOCK BUILDING SLAB 3 Sheets-Sheet 2 Filed July 21, 1950 INVENTORS ALBERT 6 STEEBZOW Z DOA/4L0 O. M CALL BY My;

ATTOP/VEYS June 26, 1956 A. G. STREBLOW ET AL 2,751,776

STRESSED BLOCK BUILDING SLAB 3 Sheets-Sheet 5 Filed July 21, 1950 INVENTORS A1552? 6 JTFEBAOW &D0A/Az0 0. MCALL ,3

United States Patent STRESSED BLOfiK BUHLDWG SLAB Albert G. Strehlow and Donald 0. McCall, Napa, Calif,

assiguors to The Whitacre-Greer Fireproofing Company, Waynesburg, Ohio, a corporation of Ghio Application July 21, 1950, Serial No. 176,162

4 Claims. (Cl. 72-68) This invention relates to roof and floor construction and more particularly to multi-way reinforced slabs of the type constructed by the assembly and coaction of many relatively small blocks and/0r parts and elements. Our invention comprises at least in part an improvement upon the invention contained in the D. D. Whitacre U. S. Patent No. 2,102,447, issued December 14, 1937.

It is among the objects of our invention to make a roof or floor slab following the broad precepts of the Whitacre patent which, however, in multiple row form will have self-sustaining beam, slab and cantilever strength in any direction. More particularly it is among the objects of our invention to provide a multi-row slab of the Whitacre type that has great self-sustaining strength in substantially all directions and under substantially all conditions of handling, placement, support and use, and is relatively light in weight and low in cost. Another object is to provide a floor slab that accommodates the provisions of stair, elevator, chimney or other openings whether in the middle or in or at the edges of the slab with preservation of all necessary strength in the slab and with wide range of choice and facility of manufacture and erection. Another object is to provide a two-way cantilever roof or fioor slab. Another object is to provide an assembled floor slab that has strength inresistance to skew and twisting as well as bending and shock loads. Another object is to provide an assembled floor slab which by its inherent multi-way strength admits of the assembly, handling, installation and use of larger slab units than have heretofore been practicable. Another object is to provide an assembled multi-way reinforced structural unit having high strength in relation to its weight and cost and of Wide flexibility of adaptation, design and use.

Other objects and advantages will appear from the following description of a preferred and certain modified forms of my invention, reference being made to the accompanying drawings in which Figure l is a perspective of our slab serving as a cantilever roof overhanging a corner in both directions; Figure 2 is a top plan view of the slab shown in Figure 1; Figure 3 is a fragmentary partially broken away perspective view looking downwardly upon the slab of Figures 1 and 2 with various of the blocks and joists removed; Figure 4 is a plan view of a slab embodying our invention and having a central opening; Figure 5 is a transverse partially broken away sectional view taken as if in the plane 55 of Figure 2 but with certain departures from a true section made to illustrate variants in the form of our invention; Figure 6 is a perspective view, partly broken away, showing a modified form of our invention.

To carry out the objects of our invention we take a plurality of blocks B having strength in compression and preferably voided and of light weight such, for example, as the burned clay hollow tile blocks specifically disclosed in the Whitacre patent or so-called cement blocks preferably made with light weight aggregate or any other suitable building blocks or compression ele- "ice ments and treat the longitudinal ends thereof to make them substantially smooth and planar so that compressive loads will be transmitted from block to block with substantially equal unit pressures throughout all areas that are intended to be equally loaded when the blocks are secured together in end to end load bearing engagement as in a beam or slab. Preferably we follow the teaching of the Whitacre patent in treating the ends of the blocks and grind such ends with Carborundum or similar grinding wheels to develop the said smooth substantially planar surfaces. In the preferred practice of our invention we grind the blocks B that are intended to be placed in like transverse alignment in different rows in the slab, not only to planar smoothness on their ends'but also to substantially identical lengths so that when like rows are placed side by side all the planes of abutment P between block B in one row R will align with similar planes of abutment P1, P2, etc., between blocks B in adjacent rows R1, R2, etc., see Figure 2. Where the overall longitudinal length of a row taken transversely of the plane P, P1, P2, etc., requires or is facilitated by using blocks B of different length in one row then We prefer that blocks of like length be given like places in each row to preserve the alignment of the planes P, P1, etc. As will more fully appear below the universal alignment of the planes P, P1, etc., while preferred for its facility may be deviated from without impairing the utility and practice of our invention where the gross overall length of the groups of blocks B disposed between the same transversely extending reinforcing plates or strips 8,81, etc., is preserved.

In a preferred and illustrative form of our invention the blocks B, so treated, are laid out on a fiat surface, preferably but not necessarily remote from the point of ultimate use of the slab, substantially in end to end contact and in a plurality of rows, as for example, rows R to R4, inclusive, Figure 2, with the blocks approximately aligned transversely and with the rows of whatever length is sought in the multiple row slab unit that is to be made. For illustration a slab unit is shown in Figure 2 comprising the rows R-R4, inclusive, and extending between the end plates S and S4. When the blocks are thus generally and loosely arranged then flat preferably steel plates S1, S2 and S3 are sandwiched in between like longitudinally extending groups of blocks in the several rows, which plates extend the full transverse width of the slab unit and stand the. full height of the blocks, see Figure 3. The plates have smooth flat planar vertical surfaces which with the smooth planar end surfaces of the blocks are cleaned free of dirt, scale and foreign matter so that the blocks may abut the plates on opposite sides in intimate tight contact throughout the full height and width of all the blocks contacting the plates as thoroughly as the blocks make end to end contact with each other in the groups between plates. End plates 8 and S4 are then brought to intimate contact with the blocks at the ends of the rows.

As will appear more clearly in Figures 3 and 5, blocks B have lower transverse extensions or lips 10 which, when contacting transversely adjacent blocks, space the upper portions of the blocks transversely apart as at 11, making room for reinforced preferably post-cast joists I to be poured and cast therein at a later stage; the space 11 immediately affording room for longitudinally extending preferably steel reinforcing and tie rods T which at this stage of the slab assembly are passed through aligned holes in the plates SS4, inclusive, and in the spaces 11 where in season they may be bonded into the joints 1.

With the rods passing through the plates and spaces 11 the blocks and rows are brought to close transverse contact and the blocks and plates are ready to be brought to tight longitudinal engagement by the tie rods T. Preferably all the several rods T are of length and extend a little beyond the end plates Sand 54 and the rods are threaded at their ends to receive nuts N which upon being tightened draw up the; several elements of the slab into tight intimate-load bearing engagement and Coaction; the end plates distributing the load widely over the and faces of the immediately adjacent blocks and the blocks B being pre-loaded in compression and ,the several tensioned rods T being pre-loaded in tension up to. a substantial fraction such as A to /3 of the ultimate strength of the elements; the relative efie'ctive transverse arejasof the tension and compression elements being proportioned inversely as their respective strengths and for {host efiicient utilization of the parts respectively.

Meanwhile the intermediate plates S1S3 inclusive are compressed in the direction of the tie rods and securely squeezed and compressed between oppositely abutting blocks B whilst the near faces of the end plates are held in true tight intimate contact with the end faces of the 7 end blocks in, the rows under the influence of the nuts N. This bonding and holding of the several plates S, S1, S2, S3 and S4 so stitfens and supports all the plates and so effectively prevents the plates from buckling or flexing that each plate is forced to deliver to the slab its full strength as a beam in resistance to positive and negative bending moments and in shear however the slab may be loaded or supported; giving, for example, cantilever support to the rows R and R1 when the slab is supported to overhang the wall W1, Figures 1 and 3.

Preferably the tie rods T have a close free sliding fit in" the corresponding apertures .in the plates through which they pass so that the rods are aligned throughout their length and have substantial transverse horizontal as well as vertical contact with the plates at the apertures through which they extend. This gives added resistance to skew load. and transverse horizontal shear and twist of the slab even in its preliminary assembled form prior to having joists I and topping G, see Figure 5, later to be described.

, When the nuts N have been tightened up and the slab pre-loaded as above described all of the compressed elements in each row will be tightly bonded and in tight frictional contact on their abutting surfaces and all the rows will be correspondingly tied together through the several plates S, S1, etc.

Although we have illustrated particularly in Figures 3 and 5 the tie rods T principally disposed in horizontal grooves or splines in the side faces of the blocks B in lateral extensions of the joist spaces 11, these grooves or splines for the rods may well be eliminated, as shown in Figure 5 at the joist space 11b and joist I1, particularly because the aligned apertures in the plates locate and position all the tie rods T both horizontally and yettically in relation to all the compression elements of the slab unit at substantially all times after the rods are tensioned. The elimination of the splines for the tie rods exposes the rods more fully to bonding contact with the concrete to be poured into the joist, and as. shown in the joist J1 permits the upper rods to be located higher in the joist and slab; it being understood that the apertures in,.the transverse plates will be appropriately located for this, purpose. Prior to the time of pouring the joists the positioning ofthe rods in the spaces 11, 11b, etc; by ther el'atively close fit between the rods and the apertures of the transverse Plates preserves the spacing of the rods from the neutral axis of the slab, however the slab may be handled, supported or loaded, defiectedor tended to be deflected prior to the pouring of the joists.

In. the slab of Figures 1-3' the tie rods T are evenly distributed betweenthe upper and lower parts'of the slab and the sizeof the upper and lower rods are shown and may be taken to be approximately equal in size and strength since in this illustration we suggest, inter alia, that the slab: may be put to its intended use with a longitudinal cantilever portion overhanging the wall W2 around the' corner C, Figures. 1. and 3; it being under- 4 stood, of course, that the relative sizes and number of the upper and lower tie rods T will be selected with regard to the negative and phsitive moments to be developed essentially in the direction of the rods in the slab according to its depth, support, load and conditions of use and the specific strength of the rods. Similarly the thickness and quality of the plates S, S1, S2, etc., will be selected with regard to the depth of the slab, its mam ner of support, load and conditions of use. Withal, those ssilled in the art will prudently consider the loadsto which the s.ab will be subjected from the time of its first assembly at, near or far from the place of its ultimate use, until it has been transported and hoisted. or conveyed to the support or supports on which it will ultimately rest and thereafter upon the increased strength to be developed by the joists and/ or the joists and topping and auxiliary reinforcement, if any, inthe topping.

For rule-of-thumb example a roof slab such as suggested in Figures l3, using concrete blocks 7 /2" x8" x 16" of density of 100 pounds per cubic foot of concrete and the overall slab measuring 6 8" x 8" x 18' and overhangfour transverse steel plates A" thick, 6' 8" long and 8 high and using one /2" round tie rod in the upper part of each row and two /2 round tie rods in the bottom of each row, ran 48 pounds per square foot dead load with concrete joists but without topping and readily carried 42 pounds per square foot uniformly distributed live load well within allowable deflections.

In Figure 5 we have taken a section of the slab of Figures 1-3 in the plane P, P1, etc., spaced a block length from the middle plate S2, with variants that would not necessarily appear in any one slab, but are includedto suggest the breadth and adaptability of our invention. For instance, we show the rightward of the blocks 5 numbered 20 with an upwardly facing longitudinally extending central groove 21 open for the reception of a tie rod 22 which may supersede or supplement one or both the upper tie rods T which were previously described and are shown in the upper part of the space or joist channel 11. The rod 22 would extend through an aperture such as 23 in the plate S2 as well as in the other plates in the first instance and would be grouted in with the topping G where a topping is poured, or grouted in flush with the top of the groove 21 if no topping as such were used. If the rod 22 were used without other upper or negative rods in a slab then we prefer that the rod 22 be threaded at both ends and put'in tension upon preliminary assembly of the slab. On the other hand it the slab were tied up with the lower tie rods, or other means compressing the blocks in the slab, at preliminary assembly it would not be impracticable to grout in the rod 22 and bond it into the slab only with the grout after the setting of which the slab could be moved and erected, if not built in situ which is not without the purview of our invention, and in all events the rod 22 would then resist negative moments much as if it were prestressed by nuts on its threaded ends or other tensioning means.

V In theblock 25 of Figure 5 we suggest that upper and lower longitudinally extending voids 26 and 27 be formed to receive additional or alternative tie rods (not shown 7 but like the tie rods T) to supplement or supersede all or part the other tie rods T or aid or serve to tie up the slab longitudinally and resist positive and negative composition, asphalt or mastic; it being more expedient to coat such rods rather than grout them in concrete by first breaking away the blocks adjacent the voids albeit the latter practice is not impracticable especially after the slab is tightly assembled and prestressed as above described.

In Figure 5 we also suggest that the plate S2 especially, since it is the middle plate in the slab, and any or all the other plates S, S1, etc., for that matter have an eyelet 30 formed therein or welded thereto to facilitate hoisting and handling the slab after its preliminary assembly until it has been deposited at its place of use. Alternatively we provide holes H, Figure 3, in the end plates of the slab units disposed opposite the major voids in the blocks B in which the ends of lifting hooks may be inserted so that the slab may be hoisted thereby.

Referring to Figures 2 and 5, the practice of our invention comprehends the tieing together of a plurality of slabs as by welding the adjacent ends of the transverse plates S, S1, etc., as and after the slabs are disposed in their ultimate adjacent positions. Then as shown in Figures 2 and 5 the row R5 delineates the near edge or a second slab which may be identical with the slab end ing with the row R4 heretofore described and the transverse plates SS, SS1, SS2, etc., of the second slab will abut respectively the ends of the plates S, S1, S2, etc., where they may be joined as by being welded together, as at 31, especially since the transversely abutting slabs provide an open joist channel 11 corresponding to the channels 11 or ill: interiorly of each slab within which welding can be done easily and quickly when the slabs are juxtaposed. Instead of welding the ends of abutting plates may be bolted together with additional holes and fish plates with similar convenience and results. Thus while we have considered the five rows R to R4, inclusive, as a slab unit from the point of view of initial assembly, transportation, etc., we may take as many rows as desired, R to Rn, inclusive, and by welding or joining slab units together through the transverse plates form a continuous integral slab of any desirable size, while making the initial units small enough to be hoisted and handled with economy and convenience.

Preferably after a plurality of slab units have been welded together to form a complete integrated roof or floor or substantial part, section or bay thereof in its ultimate position of use they and it will comprise a selfsustaining working floor area having much of its ultimate strength in all directions and capable of supporting workmen and materials for additional treatment and construction. Such a floor in the preferred form now being described will ordinarily have exposed the tie rods T in the channels 11, 11b and/or grooves 21 and in the half channels 11a, Figure 5, at the outer exposed edges thereof. Therefore, we prefer to set up a temporary form F closing off the half channel 11a and pour concrete at least into the joist channels 11 and 11b as well as the half channel 11:: and/or the grooves 21 filling the same up at least flush with the top of the blocks B thereby bonding the tie rods into the joists and to the blocks B through the concrete grouting whereby to facilitate extra strength in the slab from the continuous bond between the tie rods at substantially all points throughout the entire length and the adjacent blocks. Similarly the concrete or grout filling the joist channels will encompass the exposed ends of the transverse plates further supporting and reinforcing such plates in the spaces between rows of blocks. With equal facility and preferably after appropriate conduits, pipes, heating element and the like have been laid upon the top surfaces of the blocks we can add a concrete topping G, see Figure 5, in which, if desired, additional negative steel extending longitudinally, transversely or diagonally may also be placed and which topping is preferably as deep as the height of the eyelet 39 to afford a smooth continuous upper surface for the finished floor or roof. Alternatively the eyelets 30 may be cut or burned off if desired. It will be understood, of course, that where a topping G is to be poured that it is preferable to pour it with the joists wherewith to integrate the topping into the floor and into coaction with the steel of the joists.

Where an end plate with the threaded ends of the tie rods are exposed as at the edges of a cantilever roof slab, Figures 1, 2 and 3, we prefer to cast a concrete covering over them with appropriate form work similar to the form F at the time of pouring the joists and/or joists and topping above described. In floor and roof construction it frequently happens that the ends of the slabs characterized by end plates S and S4 will rest on beams, trusses, purlins or girders and be juxtaposed and closely spaced from similar ends of adjacent slabs, and in such event we prefer to pour concrete into the space between such plates covering the exposed surfaces of the plates, the nuts and ends of the tie rods at the time of pouring the joists and topping above described.

Referring now more particularly to Figure 4 there is illustrated a utilization of our invention for the purpose of affording an opening 0 in a portion of a slab A as for a stair, chimney, elevator or the like. In this instance the slab is shown as supported at its ends and comprising seven rows 40-46 inclusive, corresponding to the rows R, R1, etc., of blocks B with end plates 47 and 48 corresponding to the end plates S and S4 and with middle transverse plates 49 and 50 corresponding to the plates S2 and S3, but with the rows 42, 43 and 44 voided between plates 49 and 50 to define the desired opening. In this form of our invention tie and/0r reinforcing rods 51 corresponding to the rods T, etc., and associated with the rows 40, 41 and 45, 46 extend the full length of the slab, extend through all the plates, have nuts on their extreme threaded ends and are tensioned to tie up and develop the strength of the rows 41, 42 and 46 directly and to bond and secure the plates 49 and 56 into the structure between oppositely abutting blocks B contacting therewith. Tie rods 52 and 53, however, Which are exclusively associated with rows 43, 44 and 45 between plates 47 and 49 at the left and between plates 50 and 48 at the right of the slab extend through such pairs of plates respectively and have nuts on their threaded ends and are tensioned thereby to embrace and compress the blocks B lying in the rows between the respective pairs of plates; the plates 49 and 50 serving as headers for the several parts of the rows 4244 and the plates being supported in their clamped position between the several nuts on the side of the opening 0 and by the smooth ends of the adjacent contacting blocks B against which they are intimately and forcibly held in load bearing contact. The several parts of the rows 42-44 between transverse plates are self-sustaining and are integrated into the slab through the plates. We prefer as prudence suggests that the long tie and reinforcing rods 51 in this form of our invention be relatively stronger and/or more numerous, see Figure 5, than the shorter rods 52 and 53, corresponding to the relative duties imposed upon them and that the plates 49 and 50 be thickened and dimensioned with regard to the loads to be supported having regard for the size of the opening 0 that is desired and for other considerations familiar to those skilled in the art. In all other respects such as the making and assembly of the slab, the joining with adjacent slabs, the pouring of joists and topping and otherwise, our teachings stated elsewhere in this specification may and should with advantage be read with the description of Figure 4.

A modified form of our invention is illustrated in Figure 6 wherein the same broad principles are followed and applied with particular variants as to the form of the blocks, method of making the slab units and other wise as will more fully appear herewith. In this form of our invention the blocks D correspond to the blocks B previously described in substantially all ways except transverse cross-sectional form and are shown for illustration with a large central longitudinal void 60, upper longitudinal grooves 61, lower longitudinal grooves 62 and interfitting book tile side walls to afford a transverse nesting of blocks in adjacent rows. A slab unit in this form, as suggested above, is characterized by a being and use.

plurality of transversely-adjacent rows of blocks D with one or more transverse plates 63, 64 corresponding to any convenient length as measured between end plates 7 63 in the first instance and may have as few or many intermediate transverse plates 64 in relation to the blocks or groups of blocks therebetween as the service required of the slab may demand. In Figure 6 we'suggest for illustration that plates 64 lie between every longitudinal pair of blocks D. a

In this form of our invention the blocks D, plates 63 and 64 with tie rods 65 are first assembled together on a flat surface,- generally but not necessarily remote from the point of ultimate use; the blocks D first being truly aligned longitudinally and transversely of the tie rods 65 under the influence of nuts N threaded onto the ends thereof and bearing on the end plates, tieing the whole slab tightly together with the several parts in their ultimate relation to each other and with the blocks D and plates tightly compressed in the direction of the rods 65 and firmly frictionally bonded together and substantially precompressed, preferably about to the extent of the ultimate working strength of the blocks. Thus under the tension of the rods 65 and the grip of the end plates 63 the slab in this initial condition of assembly and manufacture is a self-sustaining unit capable of holding its form and integrity at least for the purposes of further treatment and perfecting, presently to be described. It may well be noted in passing that the tie rods or bolts 65 pass through aligned closely fitting apertures 63 in the end plates 63 and intermediate plates 64 so that the tie rods will be held against deflection relative to the blocks in this preliminary condition of the slab when the slab is handled, turned upside-down, or otherwise manipulated, stressed or loaded.

As a convenient next step in the manufacture of the slab the upper reinforcing rods 67 may be passed through aligned apertures69 in the plates 63 and 64 to lie in upper grooves 61 where they will be preferably supported above thebottoms and below the tops of the grooves to facilitate the bonding thereof by concrete grout 70 which is thereupon poured in the grooves and appropriately tampedor vibrated into intimate and entire contact and embrace of the rods whereby to bond the rods to the'blocks and plates and integrate them into the slab when the grout sets. As suggested in Figure 6 the rods 67, as well as the rods 66, are of length such that their ends-'lwill li'e substantially flush with the inner faces of the end'plates 63, i.e. flush with the remote end faces of the end blocks adjacent the end plates so that the ends of the rods 66 and 67 will not protrude beyond the ends of the end blocks when, and, if, the end plates are removed.

After the grout 70 has set, and we prefer to use quick setting cement and accelerate the setting as by steam curing, the slab is turned upside-down and the rods 66 grouted into the grooves 62 in the same way that the rods 67 were grouted and bonded into the grooves 61. After the grout in both the grooves 61 and 62 isfully set and cured the rods 65 and end plates 63 may be removed either at the place" of manufacture or at or near the place of ultimate use and location of the slab in or on the building structure where the slab is to have its final place of I The slab without the end plate and tie rods 65 has much or substantially the same characteristics as the slab illustrated in Figures 1-5 inclusive, with two-way reinforcement and self-sustaining strength in substantially all directions and develops the inherent strength of its constituent-elements in much the same way. For substantially all practical purposes the relative size and strengthof the reinforcing rods, transverse plates and blocks of this slab may be calculated and apportioned on the same principles and in'substantially the same wa as is taught herein with respect to the preferred form of our invention. V a p As shown in Figure 6 eyelets '71 may be provided at appropriate points along the upper edges of the transverse plates 64 to facilitate handling of the slab. Ordi narily a concrete topping not shown, but similar to the topping G, may be poured over the slab, or plurality of adjacent slabs welded together as above described; the topping embracing the eyelets 71 and whatever additional reinforcing steel, longitudinal, transverse, circular or diagonal, that may be desired to be added to strengthen the finished slab, roof, floor or building structure.

While we mentioned the passing of'the rods 66 and 67 through apertures 69 in the transverse plates, it is not impracticable to notch especially the intermediate transverse plates at the same places so that the rods may be laid in the notches and located in the grooves 61 and 62 in the same relation as mentioned above.

The slab of Figure 6 and its method of manufacture may also be modified within our invention and with the advantages thereof by having the rods 66 and 67 with threaded ends, not shown, extend through the end plates 63 and receive nuts. thereon and serve as tie rods in the first instance doing the same workof the rods 65 above described. Under such circumstances the tie rods 65 need not necessarily be included or used in the first instance or permanently, although their concomitant em-' plo-yment for initial assembly and/ or permanent use may be of advantage. We may use the rods 66 and 67 as permanent tie and reinforcing'rods retaining also the end plates 63 at all times much as our practice was described with relation to Figures 1-5. In that event only. the lower rods would necessarily be grouted in before erec-' tion of the slab; the upper rods being advantageously grouted in situ especially in instances where a topping is to be added. Alternatively the rods 66 and 67 can be used as tie rods, exclusively or .with the rods 65, prestrcssing the slab while the'grout in the grooves 61 and 62 is setting, and then after the rods are bonded into the slabs through the grout 70 the nuts may be removed 7 from the ends of the rods 66 and 67, the plate 63 also removed, and if desired, the exposed threaded ends of the rods snipped ofi leaving the slab unit of Figure 6 in much the same finished state as first above described, except that the rods 66 and 67 will have been pre-" stressed directly and ordinarily to a greater degree than would follow from pre-stressing the slab through the'rods 65 alone as first above mentioned in respect to Fig ure 6.

One further variant may be employed with advantage in respect particularly to the form of Figure 6, to wit, that the blocks instead of being ground truly at right angles to the horizontal plane of the slab may be ground at a slight deviation therefrom to impose a corresponding arch or camber, positive or negative for all or part the 7 length of the rows as may be desired, when the blocks are Although we have specifically illustrated and described our slab units and slabs comprising multiples thereof with the transverse plates extending all the way across all ,of

the units and all of the slabs which comprise a plua rality of units, it is often practicable and economical to omit various of the transverse platesin certain of the units of a multiple slab unit and/or to employ less than full length plates in certain slab'units. Conversely,

it is often desirable to add transverse plates that need' not necessarily extend the whole width of a single unit or of an assembly of units, i. e. as between points X and Y of Figure 4 if the lower, as viewed, part of the slab were to overhang its support. In either event we prefer to use correspondingly longer blocks in the rows from which the plates are omitted to maintain uniform compression and/or pre-compression upon all the blocks in the slab or slab unit as the case may be.

Slabs or other structures employing our invention have unique strength and advantage from, among other things, the coaction of the element that can perhaps be most easily visualized in the relation and interplay between the longitudinal rods and the transverse plates. For example, a floor slab unit several rows wide and about three times longer than its width with five transverse plates, including end plates, and with top and bottom rods piercing the plates, if supported at its ends and given a concentrated load in a small area in the longitudinal and transverse middle, will support the load and resist deflection by spreading the eifect of the load immediately and transversely by and through the middle plate thereby drawing all the rows to the aid of the middle row, or obversely, deflection of the middle row cannot take place, except by edgewise deflection of the plate, without inducing similar deflection of other rows and thereby stressing the rods in the rows remote from the load in aid of the rods in the row or rows adjacent the load. Tension in the rods, of course, reflects compression in the blocks and/or blocks and joists and consequently squeeze upon the sides of the plates thereby stiffening the plates and more effectively insuring that they support and distribute the load. That is to say, we employ the very forces generated by the load to strengthen the structure to distribute and support the load. What we have noted with particular reference to the middle plate in the instant example also pertains to the other plates and withal the rods in their coaction with the plates tend to be mutually cooperative in both supporting and distributing the load throughout the structure.

While our description has been pointed largely in the direction of roof and floor slabs the principles of our invention suggest utility and advantage in other structural forms. A slab unit may well serve in a load bearing or other wall whether employed with the rods or plates vertical. Similarly the rows need not necessarily be but one layer deep; for example, a structure one or two rows wide and two or more deep, depending on the shape of the blocks, with plates the full Width and depth of the unit and the tension rods located or concentrated advantageously remote from the neutral axis lends itself to employment as a beam or column having many of the advantages of our invention. In such a structure the blocks will be arranged with regard to their voids or groove or joist spaces to facilitate the desired location of the steel and the grouting of all or part of the steel into the whole unit according to the precepts of our invention. -t may clarify the nature of the novel mode of operation of our invention to suggest that the plates have the function of acting as both positive and negative multi-lateral stirrups for the tension rods, restraining the rods from deflection in any direction in the structure. It also follows that single row structures may profitably employ our invention, regard being had for the size and shape of the blocks, the disposition of the longitudinal rods and the transverse plates with respect to the compression and bonding elements of the structure and the coaction of all the parts according to the teaching and practice of our invention.

While we have illustrated and described a preferred and certain modified forms and variants of our invention, changes, further modifications and improvements will occur to those skilled in the art who come to understand the precepts hereof and practice our invention. Therefore we do not care to be limited in the scope and effect of our patent to the specific forms herein exemplified and described to illustrate our invention nor in any 10 manner inconsistent with the advance that our marks over the state of the prior art.

We claim:

1. A stressed wide, long, thin and flat prefabricated load bearing slab for building construction made of a plurality of preformed blocks arranged side by side and end to end, the slab having width and length not substantially less than several times its thickness, said slab comprising a plurality of parallel longitudinally extending rows of preformed blocks arranged end to end in each row and side by side in adjacent rows, plates extending transversely of the slab traversing said rows of blocks and tension means aligned with said rows of blocks traversing said plates and extending longitudinally of the slab; the blocks having uniform depth and width and having equal lengths and having smooth, flat, load bearing end faces and having strength in compression and stressed endwise in compression by said tension means, said blocks being disposed in stressed end to end contact with each other and with said plates in each row and aligned side by side with their end faces in parallel transverse planes, said plates having smooth, flat side surfaces engaging end faces of adjacent blocks and having strength in tension, compression and shear and being relatively more flexible in side bending than edge bending and having aggregate width approximately equal to the thickness of the slab and aggregate length approximately equal to the width of the slab adjacent the plate, at least one of said plates being forcibly squeezed in the slab between proximate smooth, flat end faces of adjacent blocks disposed on opposite sides of said plate, said plates bridging between transversely aligned smooth, flat end faces of blocks lying side by side and being forcibly frictionally bonded to said end faces and being both prestressed and stressed under load into tight bonding engagement with said end faces, and said plates resisting relative motion, bending and shear between and distributing load between side by side blocks in said slab, said tension means forcibly maintaining stressed and prestressed compression in and between said blocks and plates in the longitudinal direction of said slab and forcibly frictionally bonding said plates to said end faces of said blocks, said blocks and tension means conjointly and actively supporting said plates against flexure and stiffening said plates and said plate stiffening and strengthening said slab, said blocks carrying endwise compression load as working beam elements when the slab is loaded as a beam supported at its ends, and said slab having monolithic strength as a beam supported at either its ends or sides or as a cantilever at least in the direction of its width.

2. A stressed wide, long, thin and flat prefabricated load bearing slab for building construction made of a plurality of longitudinally extending rows of preformed blocks arranged end to end in each row and side by side in adjacent rows, plates extending transversely of the slab traversing said rows of blocks, and tension means aligned with said rows of blocks traversing said plates and extending longitudinally of the slab; the blocks in the rows having equal aggregate lengths between plates and having smooth, flat, load bearing end faces engaging said plates and having load bearing strength in compression and stressed endwise in compression with said plates by said tension means, said blocks being aligned side by side with their smooth end faces engaging said plates in parallel transverse planes, said plates having smooth, flat side surfaces engaging end faces of adjacent blocks and having strength in tension, compression and shear and being relatively more flexible in side bending than edge bending and having aggregate width approximately equal to the thickness of the slab and aggregate length approximately equal to the width of the slab traversed by the plates, at least one of said plates being forcibly squeezed in the slab between proximate smooth, flat end faces of adjacent blocks in the same row disposed on opposite sides of said plate, said plates bridging between invention transverselyz aligned' smooth, flatiend facesnf. blockszlyingtside by side in adjacent. rows-and? being forciblyi'frictiona ally bonded to said end faces and being bothtpr'estressed and stressedunder load into tight bonding engagement withsaidiend faces, and said plates resisting relative motion, bending and shear between. and distributing load between side by side blocks in'said slab, said tension means forcibly maintaining stressed and prestressedfcompression' in and between said blocks and plates in the longitudinalidirectionof saidslab and forcibly frictionally bondingisaidplates to saidiend faces of'said blocks, said blocksiand' tension. means conjointly and actively supporting; said plates against fiexure and stificning' said plates and said; plate stiffening and" strengthenin gfsaid" slab;

3. A-' stressed wide, long thin. and flat prefabricated load bearing slab for buildingtconstruction made of a plurality of longitudinally extendingrows-of preformed blocks arranged end to end ineach row and side by side in adjacent rows, at least'one plate extending transversely offthe slab traversing said rows of blocks, and tension means aligned with said rows iofblocks traversing said plate and extending. longitudinally of the slab; saidiblocks having smooth, flat, load bearing end faces engaging said plate and having. load bearing strength in endwise compression and fstressed'endwise in compression by said tension means, said blocks being aligned side by side adjacent said plate with. their smooth end faces engaging said plate in parallel transverse planes, said plate having smooth, flat side surfaces engaging end faces of adjacent 7 blocksand having strength in tension, compression and shearand'being relatively more flexible in side bending than'edge bending and having aggregate widthapproximately equal-to-the thickness of the slab and aggregate length approximately equal to the width of the slab, said plate being forcibly squeezed in the slab between proxi mate: smooth, flat end faces-of adjacent blocks disposed on opposite sides of'saidplate, said plate bridging between transversely aligned smooth, fiat end faces of blockslying side by side and being forciblyfrictionally bonded to said end faces and being both prestressedand stressed under load into tight bonding engagement with said endfaces, and said plate resisting relative motion,

bending and shear between and distributing load between side by side blocks in said slab, said tension means forcibly maintaining stressed and prestressed compression in' and between said blocks and plate in the longitudinal direction of said'slab and forcibly frictionally bonding said plate to said end faces of -said'blocks, said'blocks and tension means conjointly and-actively supporting said plate-against flexure andstitfening said plate and said plate stiifening and strengthening said slab.

4. A stressed Wide, long, thin and fiat prefabricated load bearing slab for building construction made of a plurality of longitudinally extending rowsof stressed'preformed blocks arranged end to end in each row and side by sidein adjacent rows, stressed plates" extending trans verselylofrthe' slab traversing said rows, of blocks, and: stressed tension means aligned with said rows'of b1ocksJ traversing said plates and extending longitudinally of the slabythe rows of blocks having equalaggregate lengths between plates and the blocks having smooth, flat, load bearing endifaces' engaging said plates in tight, stressed,

bonded engagement, the blocks having load bearing strength in endwise compression and stressed with said plates in endwise compression by said tension means,

blocks adjacent said plates being aligned side by side with their end faces engaging said plates in parallel transverse planes, said plates having smooth, fiat side surfaces engaging end faces of transversely adjacent blocks and having strength in tension, compression and shear and being relatively more flexible in side bending than edge bending and said plates having aggregate width approximately equal to the thickness of the slab and.ag-'

gregate length approximately equal to the width of the slab, said blocks being forcibly squeezed longitud'nially in the slab between proximate smooth, fiat side surfaces of adjacent plates disposed on opposite ends of rows of blocks, said plates bridging between transversely aligned smooth, fiat end faces of blocks lying side by side in adjacent rows and being forcibly frictionally bonded to said end faces andtbeing both prestressed and stressed under load into tight bonding engagement with said end faces, and said plates resisting relative motion, bending and shear between and distributing load between side by side blocks in said slab, said tension means forcibly maintaining stressed and prestressed compression in and between said blocks andtplatesin the longitudinal direction of said slab and forcibly frictionally bonding said plates to said endrfaces of said blocks, said blocks and tension means conjointly and actively supporting said plates'against fiexure and stiffening said plates, and said plates stifiening and strengthening said slab, said slab having load bearing strength as a beam supported at either its sides or ends and as a cantilever at least in the direction of said plates.

References Cited in the file of this patent;

UNITED STATES PATENTS

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