US2299070A

US2299070A - Cast slab

Info

Publication number: US2299070A
Application number: US318460A
Authority: US
Inventors: Homer L Rogers; Gayle B Price
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-02-12
Filing date: 1940-02-12
Publication date: 1942-10-20
Anticipated expiration: 1959-10-20

Description

Oct. 20, 19.42.

H. L. ROGERS ETAL CAST SLAB Filed Feb. l2, 1940 2 Sheets-Sheet 2 Patented ct. 20, 1942 CAST SLAB Homer L. Rogers and Gayle B. Price, Dayton, Ohio, assignors, by mesne assignments, to said Price Application February 12, 1940, serial No. 318,460 s claims. c1.72e6) This invention relates to precast concrete slabs.

One object of the invention is the provision of a concrete slab adapted for use in building construction, and having a high degree of strength and rigidity,

Another object of the invention is the provision of a precast concrete slab one surface of which has a very smooth finish so that it may be used to form a nished wall in a building without requiring additional surfacing.

Another object is the provision of a concrete slab the side portions of which are so formed as to provide grout receiving spaces when bottom portions of a series of .similar slabs are arranged side lby side in abutting contact with one another.

Another object is the provision of a precast concrete slab having longitudinally extending pretensioned reinforcing rods.

Another object is the provision of a precast concrete slab having longitudinal passages of large size as compared with the thickness of the slab and so arranged that the slab is of comparatively small weight but well adapted to resist very large bending loads.

Another object is the provision of a precast concrete slab having a prestressed reinforcing structure such that the slab lies substantially fiat when supporting its own weight from points of support at opposite ends of the slab.

Another object is the provision of a series of slabs of the character mentioned, arranged side by side and rigidly connected together to provide a building floor.

Another object is the provisionn ofa precast concrete reinforced slab adapted to be assembled side by side with adjacent similar slabs to form a strong building wall providing a finished ceiling of one chamber of the building, and a floor of another chamber.- ,A

Other objects and advantages of the invention will be apparent from the following description, the appended claims'and the accompanying drawings.

In the drawings, in which the preferred embodiment of the invention has been illustrated in the form o f precast reinforced concrete slabs of generally rectangular cross section, adapted for use in the construction of a building wall or roof, l

Fig. 1 is a perspective view of a portion of a building door formed from a series of precast Fig. 2 is a transverse sectional view through one of the s1abs;`\

Fig. 3 is a section on the line 3--3 of Fig. 2;

Fig. 4 is a perspective view of a series of slabs arranged to provide a floor and a ceiling and showing the slabs in the course of assembly;

Fig. 5 is a top plan view of a portion of the slab series shown in Fig. 4;

Fig. 6 is a section on the line 6 6 of Fig. 5;

Fig. 7 is a side elevation showing the form in which the slabs may be cast, and showing the form support;

Fig. 8 is a transverse section of the form on the line 8-8 of Fig. 7;

Fig. 9 is an end view showing a portion of the form; and

Fig. 10 is a longitudinal section through a portion of the form, taken on the line Ill-I0 of Fig. 9.

vReferring more particularly to the drawings, like parts being designated by the same reference numerals in the several views, I0, Il and I2 designate portions of precast concrete reinforced slabs or beams, arranged side by side and supported at their opposite ends to provide a. oor or roof of a building and to provide the ceiling of a room below the floor or roof. The slabs, as shown, are carried at one end on a flat level surface such as a leveling strip I3 arranged on a suitable foundation I 4 of masonry or other material, the opposite ends of the slabs being carried in a similar manner.

Each of the slabs shown comprises a concrete body I6 of generally rectangular cross-sectional form, having reinforcing rods I1, I8 and I9 extending longitudinally of the slab near its lower side, with additional reinforcing rods 20 and 2| preferably embedded in the concrete near the upper side of thel slab. Longitudinal passages 22 of `large diameter compared to the thickness of the slab extend longitudinally from oneend of the slab to the other. 'I'he slab shown `is twice v as wide as it is thick, with two passages 22 that are of such diameter as to make the total void of theorder of from 40% Ato 50% of the entire slab. The slab is thus provided with strong arches connecting the upper and lower portions so that itsrstrength is very great especially in resisting bending loads. The neutral axis of the slab is quite close to the top of the passages 22, preferably just slightly below the toppf the passages. The slab may be quite long, slabs of 22 feet or longer proving quite satisfactory in a construction in which the vertical slab thickness concrete slabs, embodying the present invention; is 6 inches,

One side 24 of the slab is quite smooth. This is preferably the lower side which is also provided with-smooth curves 25 at its edges, these curves merging with the side surfaces 28 which are adapted to be arranged in abutting relation with the corresponding portions of adjacent slabs. The top surface 21 of the slab is of somewhat less width than the bottom surface so that the upper side surfaces 28 of adjacent slabs are spaced apart to provide a channel, closed at the bottom by the lower portions of the slabs, in which grout may be poured in order that a series of the slabs may be held rigidly one to another. The side surfaces 28 are provided with longitudinally extending grooves 29 so that the hardened grout will be securely interlocked to the ad" jacent slabs and each slab will be rigidified against bending by the other slabs connected to it.

In assembling the slabs and before grouting the spaces between adjacent slabs, they may be pulled into liush relationship with one another at one or more points between their supported ends, in the manner more fully set forth in our copending application Serial No. 318,462, filed February 12, 1940, for Building construction. Since the supported ends rest on flat leveling strips I3, these end portions will be flush with one another but the several slabs may not be of exactly uniform i strength and their middle portions may therefore be at different levels when first placed in position. To level the slabs at their middle ori unsupported points, nuts 3| carried by bolts 32 may be placed in the channels between adjacent slabs, being applied from the ends of these channels. 'Ihe bolts carry plates 34 which may be turned to extend transversely of the length of the slab as indicated by the dotted lines in Fig. 6 and as shown in the center of Fig. 5. A frame comprising

angle irons

35 and 36 connected at their ends by connecting plate 31, see Fig. 5, may be moved down against the top of the slabs so as to extend transversely of the slab length, the width of the plates 34 being small enough so that they will be received between the angle iron webs during the positioning of the frame, and the plates 34 are then raised and turned to rest on the webs of the angle irons. The bolts 32 are then turned with a wrench so that one slab is pulled vertically with respect to another adjacent slab that might be at a slightly different level, as the nuts are brought tight against the upper parts of the grooves 29 of the slabs. All of the slabs may thus be brought to a ilush relationship with one another.

After the slabs have been leveled and all of the bolts 32 tightened, the space between adjacent slabs may be filled with grout level with their upper surfaces and after the grout has hardened the bolts 32 are unscrewed, leaving the nuts 3| in place, and the angle iron frames are taken off. If desired, the threaded holes left in the concrete when the bolts 32 are removed may be filled with grout although they may remain if a wood flooring is to be applied to the upper surface of the slabs. The left-hand portion of Fig. 1 shows a wood flooring 38 laid on wood strips 39 secured by bolts 40 threaded to the threaded passages which are left when the bolts 32 are removed.

The concrete slabs are preferably cast in a form, shown in Figs. 7 to 10 inclusive, and in accordance with our copending application Serial No. 318,461, filed February 12, 1940, for Casting slabs. The form has the shape of an open top horizontally extending trough the internal shape and dimensions of which correspond to the slab produced. The lower side of the trough is formed by a smooth metal plate 42 having upwardly turned side walls 43 providing smooth curved fillets 44 at each of the lower corners, which form the smooth curves 25 along the lower side edges of the slab. The

opposite sides

45 and 46 of the form are so shaped as to provide the grout receiving spaces, and the grooves, at 'the opposite sides of the slab. The opposite ends of the form are closed by end plates 55, having holes and 8| of a diameter corresponding to the size of the passages that are cored in the s labs. These holes 88 and 6I receive the ends of tubes 63 which are preferably inflatable rubber tubes of the character disclosed in the patent to Lindas No. 1,949,- 650. Such tubes, when inflated, expand uniformly in diameter throughout their effective length, and shorten in length at the same time. The tubes are applied and then subjected to sullcient pressure to bring the walls of the tubes against the holes 8B and 6I and the pressure supply is then cut oi.

Before the tubes are applied to the form the reinforcing steel structure is first laid in place in the form, this structure comprising the reinforcing rods I1, I8 and I9 which act in tension in the finished product, and the additional longitudinally extending reinforcing rods 20 and 2I which are especially desirable for transportation purposes when the forms are carried in an inverted position. If desired the middle rod I8 may be substituted by a wiring conduit pipe and outlet box that may be embedded in the concrete so that the bottompf the box is even with the lower surface of the slab. The several reinforcing rods, which are so positioned as to be embedded in the concrete near the upper and lower surfaces of the slab and protected on all sides with concrete of suflicient thickness to give a satisfactory protection against flre, are interconnected to one another at spaced intervals along the length of the form by means of wires or stirrups 61, which define a rectangle having a cross sectional form corresponding to the sides of the rectangle defining the total cored area. Extending across the top of the form are a series of straps G8 adapted to be readily removed and applied, and having rod engaging hooks engageable with the rods 20 and 2l to pull them upwardly into their proper position, and also having locating pins 80 engaging the upper sides of the tubes 83 to position these tubes at the proper distance from the sides of the form and at a desired height in the form, since the tubes, being hollow, tend to rise in the concrete mixture applied to the form.

The rods I1, I8 and I8 are comparatively close to the bottom surface of the slab and thus act effectively in resisting bending loads when the slabs are supported at their opposite ends. These rods end in threaded lugs 82 having head portions 83 welded to the ends of the rods, and having threaded extensions 84, the plates 55 having openings located opposite the threaded extensions 84 and of such size as to receive tensioning nuts 85 adapted for threaded engagement with the extensions 84. The tension nuts 85 are tightened before pouring the concrete into the form, so as to stretch the rods and thus pretension them to give a predetermined initial elongation, the nuts `85 being turned by a suitable wrench to apply a known amount of torque in order that the required predetermined amount of pretension may be given to the rods. The tensioning nuts 85 are not unscrewed until after the concrete poured into the form has set and created a secure bond to the rods throughout'their length. The head portions 83 prevent any possibility of the rods slipping with respect to the concrete' with which they are bonded.

'I'he rods are pretensioned to some point below their elastic limit, the degree of pretensioning preferably being .such that the finished slabs, when supported at ytheir opposite ends and carrying their own weight, will be prevented from sagging in their middle portions, and will extend substantially horizontally between the slab supports. With the rods under some predeterminedl initial tension the normal form of the slab is slightly bowed in a longitudinal direction when the slab rests on its side, the contracting 'force of the pretensioned rods curving the side 24 into a slightly concave shape and producing a corresponding convex curve along the surface 21. This curve is preferably such that when the slabs support their own weight they rest perfectly horizontally when supported at their opposite ends with the surfaces 21 uppermost, the rods at this time being under some very considerable tension even though the axis of the rods may be perfectly straight. 'Ihe downward -deflection of the slabs, when subjected to large loads is thus resisted by the rods to a far greater degree than the resistance exerted by rods that are normally untensioned. The slabs are therefore very rigid and oer great resistance to bending or sagging.

Before filling the form with concrete, those surfaces of the form to which the concrete mixture is applied are preferably rst oiled so that the concrete, when set, can be readily separated from the metal parts of the form. The concrete mixture is poured or shoveled into the form until it comes level with the top of the form, the concrete mixture being a suitable mixture or mass to provide a hard strong compound formed by concretion or coalescence of the particles. A mixture of one part cement and five parts of a mixture of sand and gravel, thoroughly mixed together with water constitutes a very satisfactory mix. After the form is filled it is supported for vibratory movement and vibrated rapidly for a short time, The traps 68 are then removed, and the upper surface of the concrete mixture leveled off flush with the top of the form after the concrete has set, the tubes 63 are removed, the nuts 85 unscrewed and the form disassembled. When the nuts 85 are removed the threaded ends of the rods Il, I8 and I9 are accessible for use in connecting other parts to the ends of the slabs, if desired.

The vibratory movement imparted to the concrete mixture causes air bubbles to rise rapidly in the mixture and be eliminated, increasing the density and strength of the concrete slab produced due to air elimination especially from the bottom of the concrete mass. This increase of strength amounts to about 10% to 15% where the vibration is such as to eliminate about 90% of the air bubbles that would otherwise remain. The vibratory movement of the mixture causes the mixture to entirely .ll all the crevices and come into intimate contact with all surfaces of the form, tubes, reinforcement. etc., resulting in a very smooth surface on those portions of the slab that are formed by engagement with the metal bottom. The lower surface of the finished slab will thus have a smoothness comparable to the smoothness of the smooth sheet metal plate which forms the lower part of the form as it will be substantially free of pits caused by air bubbles, and the curved lower corner portions 25 will be very smooth so that the lower `sides of the slabs may be usedy without additional surfacing to formv the nished ceiling of a room. The need for lath and plaster is thus entirely eliminated and there is no possibility of the ceiling cracking or falling. For decoration purposes mere painting may be used. The upper sides 21 of the slabs have a flatness so that: they may be used without additional covering or additional surface treatment, as a roof or floor, although the top surface may be ground smooth to show up the outlines of the stone portions employed in the mix, as indicated in the upper right portion of Fig. 1.

ISU

As already mentioned the longitudinal passages in the slabs are of large diameter. If they are made so large as to reduce the weight of the slab substantially in excess of 50% the slab strength will be adversely affected, and if made small enough to reduce the weight substantially less than 40% the increased weight of the concrete employed willalso adversely affect the slab strength. Within the range of from 40% to 50% void space, however, the slab strength and rigidity will be a maximum. As one specic example of a slab construction that has proved quite satisfactory and of great strength, the slab has outside dimensions of 6 inches by 12 inches with two passages of 4% inches diameter spaced apart :V4 inch and spaced inch from the sides and 'V8 inch from the top, three reinforcing rods of 1/2 inch diameter spaced 1/2 inch from the bottom being employed. Assuming a safe elastic limit for the steel rods of 20,000 pounds per square inch, and a safe compression strength of 1500 pounds per square inch for the concrete itself, the deflection produced by a uniformly distributed load of pounds per square foot in a 14 foot span will be less than .46 inch. In such a slab the total cross sectional area of the passages will be slightly less than 50% of the cross sectional area of the entire slab.

While the article herein described constitutes a preferred embodiment of the invention it is tovbe understood that the invention is not limited to this precise article, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A precast concrete slab comprising an elongated body of concrete generally rectangular in cross-section, of greater width than thickness and having a plurality of longitudinally extending cylindrical passages of such diameter compared with the slab thickness as to `provide a total void of at least 40% and not substantially in excess of 50% of the slab section, the passages being located substantially closer to the bottom of the slab than to the top, the bottom portion of the slab having a greater width than the top, upper longitudinally extending reinforcement embedded in the upper portion of the slab, and lower longitudinally extending reinforcing rods embedded in the lower portion of the slab, such lower rods being pretensioned and of such cross sectional area as to assume substantially the entire tension forces due to live load, the cross sectional area of the pretensioned reinforcing rods and the diameter ofthe passages being so coordinated as to locate the neutral axis of the slab closely adjacent the tops of the passages.

2. A precast concrete slab comprising an elongated body of concrete generally rectangular in cross-section, having a width substantially twice` its thickness and having two longitudinally extending cylindrical passages of such diameter compared with the slab thickness as to provide a total void of at least'40% and not substantially in excess of 50% of the slab section, the passages being located substantially closer to the bottom of the slab than to the top, the bottom portion of the slab having a greater width than the top, the upper side portions of the slab each having a recess extending longitudinally of the slab,

upper longitudinally extending reinforcing rods embedded in the upper portion of the slab, and lower longitudinally extending reinforcing rods embedded in the lower portion of the slab, such lower` rods being of such cross-sectional area as to assumek substantially the entire tension forces due to live load and having such pretension as to provide a longitudinal upward bend between the slab ends of such extent that the\ slab is substantially straight when it supports its own weight from its opposite ends, the cross seclocated substantially closer to the bottom of the slab than to the top, the bottom portion of the slab having a greater width than the top and having a cast concrete surface of a smoothness comparable to thatof a. smooth metal plate with smooth rounded corner portions merging into the sides of the slab and entirely devoid of edges, the upper side portions of the slab each having a recess extending longitudinally of the slab, upper longitudinally extending reinforcement embedded in the upper portion of the slab, and lower longitudinally extending reinforcing rods embedded in the lower portion of the slab, such lower rods being pretensioned and of such cross-sectional area as to assume substantially the entire tension forces due to live load, the cross-sectional area of the pretensioned reinforcing rods and the diameter of the passages being so coordinated as to locate the neutral axis of the slab closely adjacent the tops of the passages.

4. A precast concrete slab comprising an elongated body of concrete generally rectangular in cross-section, having a depth substantially twice its thickness and having a pair of longitudinally extending cylindrical passages of such diameter compared with the slab thickness as to provide a total void of at least 40% and not substantially in excess of 50% of the slab section, the bottom pretension as to provide a longitudinal upward bend between the slab endswhen the slab is free of load. and said lower rods being of such cross sectional area as to assume substantially the entire tension forces due to live load, the crosssectional area of the pretensioned reinforcing rods and the diameter of the passages being so coordinated as to locate the neutral axis of the slab closely adjacent the tops of the passages.

5. A precast concrete slab comprising an elongated body of concrete generally rectangular in cross-section, of greater width than thickness and having a plurality of longitudinally extending cylindrical passages of such diameter compared with the slab thickness as to provide a total void of at least 40% and not substantially in excess of 50% of the slab section, the passages being sume substantially the entire tension forces due to the live load, the. cross sectional area of the pretensioned reinforcing rods and the diameter of the passages being so coordinated as to locate the neutral axis ot the slab closely adjacent the tops of the passages.

HOMER L. ROGERS. GAYLE B. PRICE.