Composite Concrete Construction Of Two-way Slabs And Flat Slabs

Abstract

The present disclosure relates to a method and means of building two-way slabs and flat slabs, reinforced concrete floors and roofs employing composite concrete flexural construction which require little or no formwork, greatly reduce the use of temporary stringers and shores, increase the speed of construction, reduce the number of skilled workmen on the job and materially reduce the over-all cost of construction. The bottom layer of the composite concrete floor is formed by using a plurality of thin prefabricated concrete panels of considerable length and of a width in the neighborhood of around 8 feet or so, laid side by side in place on the job site with their ends resting on temporary or permanent supports. The panels are precast with one or more lattice-type girders or trusses extending lengthwise of each panel having their bottom chords firmly embedded in the panel and with the webbing and top chords extending above the top surface of the panel to afford reinforcement in a longitudinal direction from support to support. Transverse reinforcing of the panels is obtained by embedding a plurality of transversely disposed reinforcing rods or bars in the precast panels, the ends of said bars being formed with special upwardly extending return bend hooks which protrude above the upper surface of the panels along the marginal edges thereof, which are joined by the employment of a special splicing means to afford transverse reinforcement from panel to panel. The splice is completed and the transverse reinforcement obtained when the concrete topping applied on the site completely embeds the hooks, splicing link and trusses and has cured and set to form the composite concrete floor slab.

Description

This invention relates to a new method of constructing elevated two-way reinforced concrete slabs and flat slabs for various building structures or the like.

In conventional building constructions employing concrete floors, such floors are formed with the aid of so-called falsework or formwork which is generally made up from horizontal boards or plates supported by stringers and shores, placed at various points along their length and width. After the formwork has been built, prefabricated reinforcement is laid within the formwork and fixed into a predetermined desired position. Finally, the concrete is poured over the reinforcement into the formwork and the formwork remains in place until the concrete has set, solidified and gained sufficient strength to carry itself. In the meantime, the space beneath the floor is cluttered up with the many shores and is unusable during the entire building period.

This method of construction is very inefficient and expensive. The formwork is elaborate and time consuming to erect and later to remove, needing fairly skilled workmen and a large crew of workers. Furthermore, all construction trades must cease their work on the floor below until the formwork is removed. Additionally, the formwork is a constant fire hazard, since it is usually made of wood.

Rapidly increasing costs of construction, combined with continuous labor shortages and inevitable risk of delay due to weather conditions, have generated an increasing interest in prefabrication as a tool looking toward a more economical and efficient structure. While many systems employing prefabrication have been developed in recent years, only a few have found limited practical application. In many instances the prior attempts have been so complex that they outweigh the usefulness of the systems.

The present invention has as its object to make it possible to construct reinforced concrete slabs in a feasible, more rapid and economical manner without the need for the elaborate formwork employed in the conventional concrete slab constructions.

This is accomplished, according to the invention, with the aid of a thin prefabricated panel containing the bottom reinforcing of the floor slabs. This method of construction will be referred to here as the "Wideslab" system. The engineering concept of such a construction is the composite action of a multilayer of one or various materials joined together to prevent any slippage or separation of the layers. This type of a structure properly constructed will, for all practical purposes, act and function as a monolithic unit.

The object is to prefabricate the undersite layer of the floor slab with all the bottom reinforcing in place as a separate thin precast panel, employ these panels on the site as formwork, and after adding the upper portion of the slab on the site, end up with a composite floor or ceiling slab such as that shown in FIG. 1. This invention therefore creates an alliance of precast and poured in place techniques and methods of construction, employing the most desirable and beneficial features of both.

Other objects and advantages inherent in this 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.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which form a part of this application,

FIG. 1 is a fragmentary sectional view through a composite flat slab panel;

FIG. 2 is a perspective view of a precast slab having lattice type girders or trusses extending lengthwise of the panel;

FIG. 3 is a fragmentary sectional view of a precast slab panel with truss and having received a topping of poured in place concrete;

FIG. 4 is an elevational view of a plurality of precast slab panels in place and transversely supported by temporary stringers and shores;

FIG. 5 is a fragmentary perspective view of the special splicing employed between the reinforcing bars of adjacent precast slabs;

FIG. 6 is a perspective view, on a reduced scale and partly broken away, of a precast slab showing the longitudinal extending trusses and transversely extending hooked bars;

FIG. 6a is a fragmentary view of the hook formed on the end of the transverse reinforcing bars;

FIG. 7 is a fragmentary vertical section showing the spliced connection with the topping concrete in place;

FIG. 8 is a perspective view of an imaginary concrete block with the reinforcing rods joined in a conventional lapped splice;

FIG. 9 is a fragmentary sectional view through a composite slab indicating the tension forces and stresses set up in and between the concrete layers;

FIG. 10 is a fragmentary sectional view through a composite slab employing the present invention and indicating the forces present and how they react to the novel splice;

FIG. 11 comprises diagramatic views attempting to show the transfer of load forces resulting from the use of the special splice of this invention;

FIGS. 12 and 13, 14 and 15, 16 and 17, 18 and 19 are perspective and top plan views, respectively of four different forms of splicing links and their use;

FIGS. 20, 21 and 22 are fragmentary perspective, top plan and sectional views, respectively of a further form of splicing link and employing a staggered hook arrangement on adjacent panels;

FIG. 23 is a diagrammatic view of a floor plan employing precast flat slabs of this invention; and

FIGS. 24, 25, 26 and 27 are fragmentary sectional views of details taken on the lines A--A, B--B, C--C and D--D respectively of FIG. 23.

Like characters of reference are used throughout the following description and the accompanying drawings, to designate corresponding parts.

Referring to the drawings, the prefabricated panel 10, in addition to the reinforcing, carries one or more lattice-type girders or trusses 11 cast into them at the time of making the panel. These trusses preferably comprise bottom chords 12, latticed webbing 13 and top chords 14, as best seen in FIGS. 3 and 3a. The height of the truss is usually selected so that the truss will be completely embedded in the concrete slab when the same is installed and completed on the job. They are concreted with their lower chord 12 embedded in the precast slab, and they generally are arranged to run lengthwise of the slab, reinforcing the slab so that they may be made of considerable length and handled in a simple manner without damage, as shown in FIG. 2.

The webbing 13 and top chord 14 of the trusses protrude above the precast slab panel 10 and form reinforcing anchorage tieing together the precast slab 10 with the poured-on the site concrete portion 15, assuring that there will be no slippage between or separation of the layers of the completed composite slab.

The precast panel, together with the trusses, is designed so that it can be used as formwork with temporary stringers 16 and shores 17 spaced far apart (5 to 8 feet) along its length for adequate transverse support, as indicated in FIG. 4.

The proportions of these precast slabs are chosen to keep them light weight, provide needed cover for the reinforcing bars and to permit trucking of the slabs to the job site. The panel length, as well as the size of the trusses to be employed, will be determined by the requirements of the structure to be built. The width of the panels is generally controlled by the trucking width limitations, usually 8 ft. or less, and in some instances, where special trucking permits are obtainable, up to 12 feet. The thickness of the precast panel 10 depends on the size of the reinforcing elements and the protected concrete cover required for the particular job -- for practical purposes from 1 1/4 inches and up.

These precast panels are delivered to the construction site, easily unloaded from the trucks by conventional equipment, such as mobile crane hoists, and erected in place on temporary transverse stringers and shores as mentioned above. Top reinforcing is then added, if necessary, and site concrete is then poured until the required depth is obtained, the webbing and top chord of the trusses now being completely embedded in the poured concrete, as shown in FIG. 3. After the concrete has set and obtained sufficient strength to carry itself, the shores and stringers are removed, leaving the finished composite floor slab.

The underside of the slab is smooth and free from blemish, eliminating the need for refinishing and plastering prior to decoration of the surface. This construction results in a substantial reduction in the over-all cost of construction, faster construction, a reduction in the number of men needed on a construction job, as well as a great reduction in the amount of material to be handled, including the elimination of formwork.

Two-way reinforced concrete slabs employ the principle of reinforcing the slab in two transverse directions. Reinforcing in the longitudinal direction of the slabs runs continuously from support to support and is achieved by casting an adequate amount of bars and trusses in the precast slabs.

The reinforcing in the transverse direction is cast into the precast slabs in a length equal to the width of the slabs and by splicing in the field are made continuous. In the present invention, a special method of splicing has been developed which is believed to be the key to the economical feasibility of the present system, since these splices occur often and their cost greatly affects the over-all cost of the construction job.

Referring to FIGS. 5, 6 and 7, this splice is made by employing special hooks 18 at the ends of the transverse reinforcing bars 19 in conjunction with a splicing element or member 20, which may take many different forms as hereinafter pointed out. The hooked bars 19 are cast into the prefabricated slabs 10 and the splicing member or link 20 is applied on the job before the concrete topping 15 is poured. The bars to be spliced are cast with their hooked ends 18 positioned upwardly in a vertical plane protruding above the precast slab as shown in FIGS. 5 and 6. The slabs and bars are formed so that the hooked bars in adjacently positioned slabs will be in a predetermined arrangement, preferably with the hook of one slab being directly opposite the hook of the adjacent slab. The splicing is achieved in the field by placing the splice link 20 on top of the precast slabs along the two adjacent hooks and the top concrete is poured to the desired height, embedding the hooks and the link, as shown in FIG. 7.

After the concrete topping 15 has set and hardened, it locks together the two adjacent hooks 18--18 and the splicing link 20, forming the required transverse reinforcing splice. This type of reinforcing splice is particularly well suited for wideslab construction. It is practical, easy to fabricate and set up, very economical and safe in use. It is also a desired and necessary form of splicing since common lapped reinforcing splicing cannot be safely used in this case and other mechanical connections and welded reinforcing splices are prohibitively expensive to employ.

The theory and the need for this special splice will be more readily understood once it is understood how a common lapped reinforcing splice works and why it cannot be used for wideslab construction. Referring to FIG. 8, it will be seen that a common splice of two bars 22 and 23 is achieved by lapping the bars side by side for a determined length and encasing them in concrete. The concrete binds the two bars together by means of bond stress between the concrete and the surface of the bar, and shearing stress of monolithic concrete. We can usually imagine a block of concrete encased around the lapped area of the two lapped bars as shown in this FIG. 8. The strength of such a splice depends on the total bond strength of the bar and the shearing strength of the concrete block along the lapped joint. If we would cut this block along a plane between the bars they will separate together with the halves of the block and no splice will result.

In wideslab construction the splicing is achieved by having the bar and splice link in two separate layers of concrete joined by natural bond. It is therefore obvious that if a common lapped splice would be used the tension force in the bar will have to be transferred through the contact face of the two layers by bond. Since the structural value of concrete bond is relatively small, and since the displacement of the bars will cause tension stress to develop between the layers, this will result in the peeling away and the separation of the layers and the failure of the splice. This is illustrated in FIGS. 8 and 9.

The present special splice provides a practical and economical solution to this problem. The hook 18 at the end of the bars 19 protrudes into the upper layer of poured concrete 15 and ties the two layers 10 and 15 together, the tension force in the bar causes compressive stress between the two layers of concrete of a much greater magnitude than the tension stress tending to separate the layers, as mentioned above. As shown by the arrows in FIG. 10, the compressive stress increases the bond value between the concrete layers 10 and 15 to such an extent that for all practical purposes the two layers are clamped together, particularly in the vital areas, and act as a monolithic body.

In addition, the hook transfers the main tension force upward to the splice link away from the tension face of the slab. The splice link is then capable of transferring the forces from bar to bar and provides additional reinforcement needed at the splice. This will be more readily understood by referring to FIG. 11. The reinforcing splice occurs in the block of concrete contained within the splice link. The transfer or anchorage of the tensile force starts when the bar enters this block and is completed by the bar hook in the middle of the block. The splicing link receives this force starting at the end of the block and ending at the center, it either balances the two forces or transfers them.

The link can be made in a variety of forms, namely, in the elongated ring form shown in FIGS. 5, 12 and 13, in the straight bar form shown in FIGS. 14 and 15, in the hooked bar or link form shown in FIGS. 16 and 17, in the welded wire fabric link form shown in FIGS. 18 and 19 and in the lacing splice link form as shown in FIGS. 20, 21 and 22. In all of these forms, with the exception of the lacing link form, the hooks 18 in adjacent panels are directly opposite to each other. In the lacing link form of FIGS. 20-22 the bars and hooks are staggered slightly with respect to adjacent panels so as to accommodate the serpentine lacing bar 30.

In FIG. 6a is shown a preferred method of forming and determining the bend of the hooks 18 of the transverse reinforcing bars 19. The bar 19 at each end has the hook formed by bending the end on a relatively true circular arc of at least 180.degree. and preferably somewhat greater, as shown. The diameter D of the bend should be at least 3 inches or more depending on the thickness of the composite concrete slab being formed and the return arm A should be at least six times the diameter of the rod 19 being used and preferable longer.

The precast slabs 10 with reinforcing hooks are formed at the plant in long, U-shaped in cross section, steel forms. These forms may be as long as 300 feet or longer. The width of the form would depend on the width of the panel to be formed, for example 8 feet. Bulkhead rails are laid crosswise of the steel form to divide the form into the desired panel lengths. The forms are cleaned, oiled or waxed or a releasant applied, after which spacer chairs are placed in the forms for the hooked bars. The hooked bars are placed on the chairs with the hooks positioned vertically upward, and the lattice girders and longitudinal bars are next placed on the hooked bars and fastened in place by wires or the like fasteners to run lengthwise of the panels. If desired the reinforcing assemblies can be assembled in advance and dropped into the steel form.

Freshly mixed concrete is now poured into the form, spread over the assembly to a predetermined thickness and then vibrated in place to eliminate air pockets and the like. After the concrete has set and properly cured, the panels are removed from the form and stored until they are needed on a construction job. The completed precast concrete slabs can be stacked for storage, the hooks not interfering with the stacking and unstacking operation.

In FIG. 23 is illustrated a practical example of a wideslab flat slab layout, showing the positioning of the slabs with reference to the main supporting columns 50 and associated transverse beams. In this view the reinforcing is not shown. FIGS. 24 through 27 are sections taken on lines A--A, B--B, C--C and D--D, respectively, of FIG. 23 showing details of the construction.

In FIG. 23 it will be seen that the slabs 10 are laid in place with their ends 51-52 supported on the line of permanent concrete columns 50. This is shown in section B--B in FIG. 25. The slabs are placed in close abutting relationship with the adjacent slabs as shown in section A--A in FIG. 24 with their hooks properly aligned so that the workmen can drop the splicing links over and adjacent the hooks as previously described.

Before the concrete topping is placed over the slabs, service pipes and conduits for electricity, waste water and ceiling heating are positioned on top of the slab. All holes and cut-outs in the floor can be provided in the factory precasting operation or they can be formed in the field.

Columns 50 supporting the floor above are poured after the slabs on the floor below are in place. For example, referring to FIG. 26, a detail showing a joint at a supporting column 50, a section taken on the line C--C of FIG. 23, the column 50 is formed to the point 55 only, then the panels 10--10 are put into the position shown with their ends resting on the column, then the concrete is poured on the slabs and the column then poured and extended to the next floor position above. It will be noted that the precast slabs 10 have their ends 51 and 52 formed with an undercut, the preferred undercut being at about 15.degree. from the vertical as shown. It has been determined that shear stress at the supports will be fully developed as in a monolithic slab.

In FIG. 27 a detail is disclosed of a joint between a panel 10 and a horizontal concrete beam 60, an undercut being used here on the panel in similar manner to that described with reference to the supporting column 50.

While there has been shown and described various embodiments of the present invention which at present seem preferable, it should be understood that various modifications and details of structure and procedure may be resorted to within the scope of this invention as defined in the following claims.

Claims

What is claimed is:

1. A composite concrete slab structure composed of a lower layer formed of a plurality of prefabricated two-way reinforced concrete panels arranged in abutting relation wherein said panels are provided with embedded transversely disposed reinforcement rods having their ends formed in upwardly disposed return bend hooks extending above the surface of the prefabricated panels with the hooks of one panel disposed oppositely to the hooks in the adjacent panel, a splicing link laid in place on the upper surface of said panels across the abutting edges and in close association with each pair of adjacently disposed hooks to form a reinforcing splice therewith and a poured in place concrete topping layer covering said prefabricated slabs and completing the composite concrete slab construction and entirely embedding the hooks and splicing links to complete the splice and provide adequate reinforcing in a transverse direction of said constructed composite slab by transferring tension forces in said rods to compression forces in said concrete to adequately prevent separation of said concrete layers.

2. A composite concrete slab structure as defined in claim 1 wherein said splicing link comprises an elongated ring type link laid over each pair of oppositely disposed return bend hooks.

3. A composite concrete slab structure as defined in claim 1 wherein said splicing link comprises a straight splice rod laid adjacent each pair of oppositely disposed return bend hooks.

4. A composite concrete slab structure as defined in claim 1 wherein said splicing link comprises a hooked type splice link encompassing each pair of oppositely disposed return bend hooks.

5. A composite concrete slab structure as defined in claim 1 wherein said splicing link comprises a welded wire fabric link encompassing each pair of oppositely disposed return bend hooks.

6. A composite concrete slab structure as defined in claim 1 wherein said return bend hooks are disposed in a slightly staggered relation in adjacent panels and said splicing link comprises a lacing splice bar formed in serpentine form.

7. A reinforcing splice for the abutting lateral edges of two precast two-way reinforced panels which are to receive a top layer of poured concrete to form a two-way slab, said precast panels having embedded therein transverse reinforcing rods having their ends formed into reverse hook-like bends near the marginal edges of said panels with the reverse bend of said hooks extending upwardly above the surface of said panels, the hooks along the marginal edges of one panel being positioned opposite to the hooks in the adjacent panel, a splicing link placed upon the surface of the two adjacent panels over or adjacent to each pair of said oppositely disposed hooks, and a top layer of poured on the job concrete covering the precast panel and completely embedding the reverse hooks and associated splicing links to complete the reinforcing splice and provide adequate reinforcing in a transverse direction of said constructed composite slab by transferring tension forces in said rods to compression forces in said concrete to adequately prevent separation of said concrete layers.

8. In a building structure in the course of erection, the combination therewith for support by permanent columns, of a composite concrete floor slab comprising a lower concrete layer formed of a plurality of thin precast concrete panels of considerable length and width and containing lengthwise and transverse reinforcing and laid in abutting relationship side by side with their ends resting on said permanent supports, the transverse reinforcing in said panels being formed of transversely disposed reinforcing bars embedded at spaced intervals therein and provided with return bend hook ends which protrude above the surface of said panels near the marginal side edges thereof, said hook ends being disposed in a definite predetermined relationship with respect to adjacent panels, a reinforcing splicing link laid on the surface of said panels across the abutting edges of two adjacent panels and closely encompassing said adjacently disposed hook ends of adjacent panels and an upper layer of poured on the site concrete covering the precast concrete panels and completely embedding the return bend hook ends and associated splicing links to complete the splice and provide adequate reinforcing in a transverse direction of said constructed composite slab by transferring tension forces in said rods to compression forces in said concrete to adequately prevent separation of said concrete layers.

9. The method of constructing a composite two-way girderless concrete slab or floor, comprising the steps of forming the permanent columns for the structure, positioning in abutting relationship a plurality of precast thin concrete panels with the short ends of said panels resting on said permanent columns, said panels being of the type having longitudinally extending trusses with their lower chords embedded in said panels to give reinforcing in a longitudinal direction of the panels and having transverse reinforcing hooked bars embedded at spaced intervals transversely along the length of said panels with the hooked ends extending above the surface of the panels in a reverse bend, laying in place upon the panel surfaces across the abutting edges of adjacent panels a splicing link in close association with each pair of oppositely disposed hooks of adjacent panels, using said precast panels as formwork and pouring therein a topping layer of concrete over the upper surfaces of said precast concrete panels to the desired depth to fully embed the longitudinally extending trusses and the hooked ends and associated splicing links and temporarily supporting said panels at spaced intervals along their length until the poured concrete has set and cured and provide adequate reinforcing in a transverse direction of said constructed composite slab by transferring tension forces in said rods to compression forces in said concrete to adequately prevent separation of said concrete layers.

10. The method defined in claim 9, wherein service pipes and conduits for electricity, water, heating and cooling facilities for the structure being erected are positioned on top of the precast panels prior to pouring the topping layer of concrete.