US3619959A - Concrete building - Google Patents

Abstract

AN IMPROVED ELONGATED CONCRETE MEMBER AND A METHOD FOR FABRICATING IMPROVED ELONGAGED PRESTRESSED OR NONPRESTRESSED CONCRETE MEMBERS IN SITAND WITHOUT FORM WORK COMPRISING STRETCHING A SUPPORT COMPRISING A SHEET OR A PLURALITY OF BANDS BETWEEN SPACED END SUPPORTS, APPLYING WET CONCRETE ONTO SAID SUPPORT, AND CURING THE CONCRETE TO FORM A PRESTRESSED OR NONPRESTRESSED CONCRETE MEMBER HAVING A FLAT TOP SURFACE AND A GENERALLY PARABOLIC BOTTOM SURFACE BETWEEN THE END SUPPORTS.

Description

NOV. 16, 1971 PARKER 3,619,959

CONCRETE BUILDING Filed July '7, 1969 2 Sheets-Sheet l INVENTOH 1 SIDNEY A. PAR/(ER @w/ JMWJ u,

ATTORNEYS Nov. 16, 1971 s. A. PARKER CONCRETE BUILDING 2 Sheer, ..5 2

Filed J l 7 L969 INVENTOR A T TORNEYS United States Patent ce- 3,619,959 Patented Nov. 16, 1971 3,619,959 CONCRETE BUILDING Sidney A. Parker, 5820 Diamond Oaks Drive 8.,

Fort Worth, Tex. 76117 Filed July 7, 1969, Ser. No. 839,194 Int. Cl. E04b 1/24 US. Cl. 52-223 1 Claim ABSTRACT OF THE DISCLOSURE An improved elongated concrete member and a method for fabricating improved elongated prestressed or nonprestressed concrete members in situ and without form work comprising stretching a support comprising a sheet or a plurality of bands between spaced end supports, applying wet concrete onto said support, and curing the concrete to form a prestressed or nonprestressed concrete member having a flat top surface and a generally parabolic bottom surface between the end supports.

BACKGROUND OF THE INVENTION This invention relates to concrete structures and to methods of fabricating concrete structures, and more particularly, this invention relates to prestressed and nonprestressed concrete beams, floors or ceilings of novel design and to a method of making such beam, floor or ceiling.

Multifioor concrete buildings are conventionally made by forming one story at a time. In a typical structure, the foundation is formed below ground level and wooden forms or like form work for the walls are set in place. Reinforcing rods may be tied to the foundation and are disposed between the spaced wooden forms. Wet concrete is poured between the wooden forms. After the concrete has set, the Wooden forms, typically plywood panels suitably fastened to one another and retained in position, are removed and by means of scaffolding the wooden forms for the column supports and floor for the next story are positioned. The floor of the next story, which is, also the ceiling of the story below, is formed by providing wooden forms beneath the desired floor, positioning reinforcing rod where desired, and then pouring concrete onto the wooden form to form the floor, which may be of the hat slab or two-way slab types. The wooden forms are removed after the concrete has set and can be reused for the next floor above. However, the wooden forms have only limited life because the use is so hard. It is known from the literature available in the trade that the cost of form work is a major factor in reinforced concrete construction. See, for example, Formwork for Modern Structures, by Sir Frederick Snow, Chapman & Hill 1965.

Notwithstanding improvements in concrete, fabrication of buildings in the fashion stated above is slow, requires much labor and is relatively expensive. For some applications, it has been suggested that the floors which are in the nature of slabs be formed at the site, one atop the other, and then elevated into position by large power rams. The size of the power rams limits this method. Lift slab construction is slow and very hazardous. Slabs have fallen due to either power ram failure or weight distribution being such that slab failure occurred.

Another suggestion (see Chiado Pat. 3,090,165) has been to precast floor sections at a plant and then ship them to the site for assembly. Due to bulk and weight, shipping of large and heavy sections for large distances is not economically feasible. Formation of precast panels at the job site would save shipping costs, but would then require large expenditures for equipment to raise the slabs to the desired elevations.

Yet another method used in buildings is steel deck flooring where approximately 2" of concrete is poured over corrugated steel decking. This system is used primarily in steel buildings to form the floors or ceilings. This system has only been successful with spans up to 5 or 6 feet between expensive steel truss sections. This system is quite expensive and requires a heavy use of steel, and will only stand light floor loading.

Thus, an object of this invention is to provide an improved concrete floor or ceiling structure and a method for fabricating same in situ wherein deficiencies and disadvantages in prior structures and methods are obviated.

Another object of this invention is to provide an improved concrete floor or ceiling that can be formed in situ in a simple manner without the necessity for wooden forms or similar scaffolding.

A further object of this invention is to provide an improved elongated beam or floor or ceiling which can be supported only at its ends for relatively great lengths and without the number of support columns or girders required in conventional concrete structures.

Yet another object of this invention is to provide an improved method for forming a concrete member in situ without the necessity for wooden forms which comprises securing a support member at its ends in desired position, applying a predetermined quantity of wet concrete onto the support member to tension same to a predetermined value, and curing the concrete to form prestressed or non-prestressed concrete members having a generally parabolic bottom between its ends. Other objects and advantages of this invention will be made more apparent hereinafter.

BRIEF DESCRIPTION OF THE DRAWING Preferred embodiments of the present invention are illustrated in the attached drawing wherein like numerals refer to like elements in the different figures, and wherein:

FIG. 1 is a skeleton of a concrete structure embodying the present invention;

FIG. 2 is a detail view illustrating a sheet-like support member in place between a pair of end supports;

FIG. 3 is a detail view of the connection of sheet-like support member to an end support, with concrete set in place thereabove;

FIG. 4 is a detail view of a concrete floor or ceiling structure illustrating the support member formed from a plurality of strap-like members;

FIG. 5 is a detail vie-w on an enlarged scale of the end support shown at the right in FIG. 6;

FIG. 6 is a perspective view illustrating a plurality of strap-like members attached to end supports and to an intermediate support Where larger spacings are required between end supports;

FIG. 7 is a detail view on an enlarged scale of a modified manner of securing the end of a strap-like member to an end support;

FIG. 8 is a perspective view on an enlarged scale illustrating the connection of the strap-like members to an intermediate member;

FIG. 9 is a cross-sectional view of a concrete member formed in accordance with the principles of the present invention; and

FIG. 10 is a plan view of the concrete member of FIG. 9, illustrating the spacing of bands.

DETAILED DESCRIPTION OF THE PRESENT INVENTION Concrete is in many areas the cheapest material available for carrying compressive loads. Though its compressive strength is high, its tensile strength is only about 10 to 15 percent of its compressive strength and this 3 value is often further reduced to zero by shrinkage cracks which occur during curing.

One prior method of increasing the tensile strength of a concrete member was to incorporate reinforcing rods on the tension side to carry the entire tensile load. The addition of reinforcing bars, made, for example, from steel, gave a member with a low cost material to carry compressive stresses plus steel with a minimum amount of fabrication to carry the tensile stresses. However, a disadvantage of the concrete reinforced with steel bars was that all of the concrete on the tensile side of the neutral axis was useless dead weight, other than serving as a connection between the compressive concrete and the steel. Typically, the reinforcing steel bars have a tensile property of 30,000 p.s.i.

A further improvement in concrete construction was prestressed concrete which goes beyond reinforced concrete. In prestressed concrete structures, all of the concrete on the tensile side of the neutral axis is put under an initial compressive stress of such a magnitude that all design loads which are to be applied to the structure in the future can reduce the stress, but will not put the concrete in tension. Further, the prestress is applied in such a manner that it creates a moment of opposite sign to those which will be produced by applied dead and live loads. In the ideal design, this negative moment carries all the dead load and creates the maximum allowable compressive stress in the concrete on the tensile side of the member. As far as the stresses in the prestressed member itself are concerned, it is then a weightless structure with all its moment-carrying capacity available for live load. Typically, these cables are of high strength steel and are round in configuration, and buried in the center or just olf center of the concrete fiat slab.

The present invention is concerned with a concrete member, as particularly applied to an elongated beam or an extended ceiling or floor structure. Referring to FIG. 1, there is illustrated a skeleton of a building which incorporates the present invention. The foundation 12 is suitably formed in the ground and is of sufficient strength to support the maximum design weight of the building structure. Upright columns 14 are provided to support the weight of the building and the tops of the columns 14 are connected by longitudinally extending beams or end supports 16. The ceiling or floor is provided by the concrete member comprising support means 18 and cementitious material or concrete 19 formed in situ in accordance with the present invention without need for form work.

A second story may be provided in the building structure by extending columns or beams 20 upwardly from the floor defined by the concrete 19 and support means 18. Securing the tops of the columns 20 to one another are the elongated beams or end supports 22. The second floor ceiling or roof in the case of a two-story building is comprised of support means 24 disposed between the adjacent end supports 22 and concrete 25 poured onto the support means and permitted to cure. It should be noted that the ceiling of the first and second floors could be poured simultaneously since no vertical scaffolding is required.

Referring now to FIGS. 2 and 3, there is illustrated a method of securing a support means, for example, sheet \18 to the end supports 16. As shown, the end supports 16 may comprise an I-beam. Secured to each I-beam 16 or formed integrally therewith is a retainer which comprises an elongated channel-like member having a bentover portion 32 which is adapted to receive and cooperate with the complementary elongated bent-over portion 34 on the sheet 18. The sheet 18 may be joined to the end supports 16 so that there is no prestressing of the sheet 18. However, if it is preferred that a predetermined prestressing be applied to the sheet 18, the specific manner of calculating the degree of prestressing will be considered hereinafter.

Suifice it to say that preseressing of the sheet 18 to a predetermined value prior to adding the wet concrete will permit a resultant beam or floor or ceiling structure that has a flat top with parabolic contour beneath of predetermined center thickness after the concrete is set.

It is readily apparent from the foregoing explanation as to FIGS. 1-3 that fabrication of a concrete building structure in accordance with the present invention will obviate the need for form work for the floor or ceiling structure. Thus, there are very significant savings in the cost of the material that normally goes into the wooden form work set in place before pouring the concrete and in the labor in setting up the form work and then removing same after the concrete has cured. Furthermore, there is a savings in concrete by use of the present invention, for in normal practice it is an economical necessity to utilize a constant cross-section the full span distance in order to gain the desired thickness in the center of the span. This is because of the extreme cost of contour carpenter work. In the present invention it will be noted that the top of thespan of the floor will be fiat, whereas the bottom thereof will be generally parabolic. There is less dead weight concrete in a beam or floor or ceiling structure made in accordance with the present invention. Since it will be apparent that a floor of one-story is also the ceiling of the story below, these terms may hereinafter be used interchangeably. Further, a floor is an extended beam and therefore in considering any cross-section or portion of a floor, the term beam will be used interchangeably.

Turning now to FIGS. 4, 5, 6, 7 and 8, there are illustrated modifications of the present invention, wherein the support means is comprised of a plurality of separate straps or bands, rather than a single sheet. In FIG. 4 it is seen that the upright columns 114 are adapted to support beams or end supports 116, 117. The lower ends of the upright columns 114 are adapted to be secured to the foundation or to a floor below. The end supports 116, 117 are supported on the top of the columns 114, as, for example, by having projections or reinforcing rods extend upwardly from the columns 114 through openings in the end supports 1'16, 117 into the end supports 116, 117. Secured to the end supports 116, 117 are a plurality of straps or bands 118. Concrete 119 is carried on top of the bands 1118 with the result that a floor structure having a parabolic bottom results in a manner similar to that of FIGS. 1, 2 and 3. Since the bands 118 are spaced laterally from one another, a filler material 140 such as a film or sheet of wood, or plastic, for example, polyethylene may be placed over the bands 118 in order to cooperate with the bands 118 to retain the wet concrete during the curing process.

The bands 118 are preferably fabricated from a material having very high tensile strength, for example, a hardened strip steel with a bainitic structure made by Sandvik and sold under the trade name Hard-flex.

FIGS. 5 and 7 illustrate details of the end supports. The end support 116, as shown in FIG. 7, is provided with a reinforcing rod 142 positioned longitudinally thereof and secured in place by means of the upwardly extending reinforcing rods 143 from the columns 114. A strap 118 is adapted to pass through an opening in the flange 144 of the end support 116 and then through the end wall 146 of the end support 116 over and about the extended reinforcing rod 142 and then clamped in place by a band or retaining member 148. It will be appreciated that each of the bands 118 are spaced along the length of the end support 116 in generally parallel relationship to one another. These bands 118 are generally transverse to the end support and extend through openings in the flange 144 and openings in the side 146 and are secured to the reinforcing rod 142 by means of retaining members or clamps 148. A basket weave design (not shown) could be used, with sets of parallel bands 1l18 crossing each other at approximately The support 117, as shown in FIG. 5, is of the type adapted to be disposed centrally of a wall member. Specificially, it is intended that there be an end support 116 to the left and to the right of the intermediate beam 117, as shown in FIG. 4. The strap 118 extending from the left and secured to the end support 116, as shown in FIG. 4 is adapted to pass over the intermediate supports 117 through an opening in the flange 145 and an opening in the flange 150 and be bent over on itself so as to be secured by a member or clamp 152. The strap 118 from the right hand support (not shown) passes over the'top of the intermediate end support or beam i117 and down through similar openings in flanges 145 and 150 and is likewise secured by a retaining member or clamp I152. It is apparent from this arrangement that there is a balancing of the forces applied to the intermediate support 117 so that no undesirable moments are applied thereto.

In FIGS. 6 and 8, there is shown an alternate support arrangement for spanning between adjacent beams 116 and; 117. An intermediate member 160 is disposed between a pair of adjacent end supports and in generally parallel relationship thereto. The straps or belts 118 are adapted to be secured at one end to the member 160 in the fashion shown, for example, in FIGS. 6 and 8. The straps 118 extend through openings 162 in the elongated intermediate member 160 and are bent upon themselves and-secured by means of a clamp 152.

Briefly, in utilization of the present invention, the up rights or columns 114 are secured at the lower end to a foiindation and extended upwardly in a vertical plane. The beams 116, 117 are suitably afiixed to the upright columns 114 and then the desired straps 118 are tensiolned between the end supports. Since it is intended that the straps 118 be spaced from one another, a sheet filler as, for example, a film of plastic 140 is disposed on top of the straps and concrete is then poured onto the filler material. It may be desired to use a wire mesh 141 over straps if the strap spacing is such that too great a sag might develop by filler 140. The weight of the concrete causes the straps 118 to deflect downwardly to a generally parabolic form as best seen in FIG. 4, resulting in a prestressed or nonrestressed concrete beam structure after the concrete cures. No distinction is intended between prestressed and non-prestressed concrete insofar as the invention is concerned.

Those persons skilled in the art will be familiar with texts describing the differences in prestress and non-prestress concrete, for example, Modern Prestressed Concrete by H. Kent Preston and Norman J. Sollenberger, McCraw-Hill 1967 and Design of Prestressed Concrete Structure" by T. Y. Lin, John Wiley & Son, Inc., 1967. It, is evident to those skilled in the art that structures made as shown in the drawings and description thereof will produce a non-prestressed structure. However, if temporary compression members or spreaders placed between beams 16 (FIG. 2) or 116 and 117 (FIGS. 4 and 6) are employed and then removed after the concrete has cured, then the horizontal structure will be prestressed. For high floor loading designs, strap 118 or sheet 18 may require pre-tensioning before the wet concrete is poured in place.

The roof of my new building structure may be formed from materials other than concrete, for example, the roof might be gypsum tarred to form an acceptable waterproof roof. Other lightweight roofing could be used.

Designers using the system of this invention have at their disposal many design flexibilities. The decision whether to use a non-Prestressed system or a prestressed system will depend on the economics of the building under construction and the type of loading on the floor. Also the type of filler material such as high strength concrete, lightweight concrete, gypsum, etc., is a design consideration.

By use of this invention, there is no necessity for the normal wooden form work beneath the beam as utilized in conventional concrete construction. The amount of concrete utilized may be reduced considerably from the present practice of utilizing a constant cross-section the full distance in order to gain the desired thickness at the center of the expanse of beam or floor.

The concept of the present invention may best be understood from the following discussion. The variables that may be controlled for a desired contour of beam and center thickness of such beam are:

By definition, the desired section thickness at the center of the span would be:

For steel straps, the equation relating the above listed variables is as follows:

2 Y 2 Y 4 b=1.3333F 2) [53,000,000 A-3.2F

Center section thickness Y -i-h The equation solves for strap spacing, b. Strap tensile stress may be calculated as follows:

Strap tensile stress=%+E[2.667( 6.4( a 1 The formula, which might be modified slightly for practice allowances in a situation, may be used in the following manner. Assume a structure as depicted in FIG. 9. Straps will be made of steel having a yield strength of 100,000 p.s.i., and a stress of 80,000 p.s.i. will be applied. Assume further that the straps to be. used are 1.0" wide by 0.062" thick-(0.062) in. area). Concrete density (wet) is lb./ft. or 0.0897 lb./in. It can be shown that for a problem as described, the volume of steel cannot be reduced or increased by merely changing strap dimensions, i.e. the stress values dictate a given volume of steel strap or sheet. The value for a given yield strength would be as follows:

By use of Equation 3 the preload can be calculated:

EL i -80,000 30,0 4240)] E A 30,000 p.s.i.

thus F =(30,000) (.062)=1860 lb.

7 Finally, the computation of strap spacing is as follows using Equation 2.

and

**b= 1.793 inches Since the strap spacing is larger than strap width the arrangement will function. The volumes and weight of steel straps for costing purposes can be calculated as follows:

Width of Structure 2;t0

No. of straps b =l34 Vlurne=AlN= (.062) (240)(134)=1993.92 in.

and

**b= 1.706 inches Again, the strap spacing is larger than strap width.

No. of straps=240/1.706= 141 Volume: (.024) (240) 141) :813 in.

Weight: 8 13) (.283 :230 lbs. steel (200,000 p.s.i. yield strength) The savings in concrete used between supports in the improvement of this application and prior constructions having a constant cross-section is determined as follows: The parabolic section below supports in FIG. 9 has a cross-sectional area (A AD mnx) 9 0 111.

Above the supports, the area (A,) is:

A,:h l=(4) (240)=960 in.

and Total Cross-sectional area:960+960=1920 in.

Total Volume (V is:

4 9291249 (1728) 9.89 cubic yards Volume with a constant thickness of 10 would be:

The concrete savings for the illustrated structure as compared to prior known constructions would be:

l2.369.89=2.47 cubic yards =12.36 cubic yards There is a percent savings in concrete resulting from 8 use of the present invention for the specific example given.

The present invention has widespread applicability in the building industry. It can be effectively used for the ceilings of single story structures wherein extended beam lengths may be desired without intermediate column support, as well as in multi-story buildings. Much of the interior column supports for carrying the load of the floor above in a multi-story building are obviated by use of the concept of the present invention, providing increased usable floor space. There is no need for the form work commonly made of wood used to form a slab floor and the savings in material costs is substantial. Furthermore, there are large labor savings since there are no wooden forms to be set up and then taken down. As pointed out above, the concrete beam is not uniform in cross-section, but rather is contoured to the most desirable form (a flat top with a parabolic bottom between supports). This results in a savings in concrete costs.

There has been provided a novel method for forming a concrete beam in place in a building which is relatively inexpensive as compared with comparable known methods. The resultant beam structure contains less concrete since it is automatically contoured to an optimum design profile and it is prestressed or non-prestressed for providing maximum economy and all the other advantages as described earlier.

It will be obvious to those skilled in the art that changes may be made in the method and beam. structure without departing from the true spirit and scope of my invention, and it is not my intention to limit the invention to the specific form shown and described other than as necessitated by the scope of the claims.

I claim:

1. A concrete member comprising a support means made at least in part from a material having a high tensile strength and a cementitious material carried on top thereof, the top of the concrete member being flat and the bottom of the concrete member being parabolic as viewed in cross-section, the support means comprising a plurality of bands made of high tensile strength steel and spaced from one another in accordance with the following formula:

References Cited UNITED STATES PATENTS 619,769 2/1899 Lilienthal 52-335 704,933 7/1902 Riley 52-326 830,494 9/1906 Collins 52-327 1,671,946 5/1928 Govan et al. 52-335 2,096,629 10/1937 Farrar et a1. 52-335 2,233,291 2/1941 Leebov 52-335 OTHER REFERENCES Modern Plastics: March 1957, p. 252.

FRANK L. ABBOTT, Primary Examiner H. G. SUTHERLAND, Assistant Examiner US. Cl. X.R. 52326, 327, 335

Patent No. 3,619 ,959 Dated November 16 1971 Inventor(s) Sidney A. arker It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 28, "wire" should read wide same column 7, lines 31 and 32, the two top lines of the computation should read 1 Total stress-50,000

160 ,000-50, ODO=11O 000 PSI Signed and sealed this 2nd day of May 1972.

(SEAL) Attest:

EDWARD Z LFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents ORM PC1-1059 (10-59) USCOMM-DC 6O376-P9 1: U 5 GOVERNMENT PRNTING OFFICE 1969 O355-334

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