US3435572A

US3435572A - Flat slab construction

Info

Publication number: US3435572A
Application number: US607845A
Authority: US
Inventors: Samuel J Fuchs
Original assignee: SAMUEL J FUCHS
Current assignee: SAMUEL J FUCHS
Priority date: 1967-01-06
Filing date: 1967-01-06
Publication date: 1969-04-01
Anticipated expiration: 1986-04-01

Description

April 1, 1969 S.J.FUHS 3,435,572

FLAT SLAB CONSTRUCTION Filed Jan. 6,1967 v v v Sheet of4 "i l 1 l2 C I52)- s a '15-"; 1 q nu' 3 jzT 8 m 1/ T2 23 I50: 23 R +1?- 'FIGZ (PR/0R ART) INVENTOR. SAMUEL J. FUCHS FIG. 5 BY W .47 rogue-x April], 1969 7 5.4. FUCHS v3,435,572

. FLAT SLAB CONSTRUCTION I Filed Jan. 6, 1967 Sheet 2 of 4 INVENTOR. .s'Am/EL .1. FUCHS ATr /VEt April 1, 1969 s. .1. FUCHS 3,435,572

I FLAT SLAB CONSTRUCTION Filed Jan. 6, 1967 Sheet i of 4 INVENTOR. SAMUEL J'. FUCHS United States Patent f 3,435,572 FLAT SLAB CONSTRUCTION Samuel J. Fuchs, Brooklyn, N.Y. (Box 56, Church St. Station, New York, NY. 100% Filed Jan. 6, 1967, Ser. No. 607,845 Int. Cl. E04b 1/16, /16, 1/20 US. Cl. 52--251 5 Claims ABSTRACT OF THE DISCLOSURE A concrete flat slab building construction having a shear reinforcing structure for relief of excessive stress concentration in flat plate floor portions adjacent columns supporting the slab.

Flat plate construction has been incorporated into a major part of contemporary buildings in preference to other standardized types of construction. The uniformity of slab and smoothness of ceiling around the column head are the characteristic features preferred in flat plate design. By contrast, however, the stress variation within the slab is extremely nonuniform, varying from a low level generally in the intermediate span portions to peak values in immediate proximity to the columns. The structural inefiiciency implied by the maldistribution of stress is recognized by engineers in the art as a long-standing problem of flat plate design, but about which little could be done heretofore.

An object of the invention, therefore, is to provide for a slab of uniform depth and uninterrupted ceiling, but improved over the conventional construction in strength and stress distribution in the column head area.

The approach of the invention, in brief, is to introduce within the slab novel shear stiffening means as further specified, whereby the effect is produced of internal supporting beams for the flat plate flooring.

The invention consists of the features of construction and arrangement of parts which will appear in the following specifications and be recited in the appended claims, reference being had to the accompanying drawings in which the same reference numerals indicate the same parts throughout the various figures and in which:

FIG. 1 is a plan view of a portion of conventional fiat plate floor construction, with parts broken away;

FIG. 2 is a sectional elevation taken at 2-2 in FIG. 1;

FIG. 3 is a plan view of a portion of flat slab plate construction embodying the invention;

FIG. 4 is a sectional elevation taken at 4-4 in FIG. 3;

FIG. 5 is an enlarged sectional elevation taken at 55 in FIG. 3;

FIG. 6 is an enlarged plan view corresponding to the sectional elevation in FIG. 5;

FIG. 7 is a plan view of a form of slab shear reinforcing assembly unit of the invention;

FIG. 8 is a sectional elevation taken at 8-8 in FIG. 6 for demonstration as a model of the invention;

FIG. 9 is a plan view corresponding to the sectional elevation of FIG. 8;

FIG. 10 is a plan of a portion of slab construction embodying the invention as supported on a concrete column; and

FIG. 11 is a sectional view taken at 11-11 in FIG. 10.

Conventional, known flat plate construction, as generally indicated at 10 in FIG. 1 and 2, comprises panel 11, typical of the design generally, together with portions of contiguous similar panels 12. The boundaries of panel 11 are defined according to convention by the rectilinear grid in plan of center-lines mm, n-n, interconnecting the centers of supporting columns 13. The

reinforcing bars

15m, 1511, 23, 115m 115n as in most common usage Patented Apr. 1, 1969 are shown two-way, aligned in parallel with the rectilinear center-lines mm, It is understood that reinforcing

bars

15m, 15n, 23, in proximate relation to the top surface of slab 14 are provided for negative moment whereby the slab assumes an elastic curvature convex downward, and conversely bottom bars m, 115n are provided for positive moment.

As in standard practice, the parallel bars in each direction provided for negative moment in roximate relation to the top slab surface are grouped in a column band and mid-panel column band classification. The column bands of width aa of such

top reinforcing bars

15m, 15n and 23 in FIGS. 1 and 2 are centered along corresponding center-lines m-m', n-n. Where the column bands cross at right angles over the column heads they intersect to form two-way column band areas of rectangular outline 17, of top reinforcing bars. The mid-panel column bands of top reinforcing bars 23 then comprise the remaining portions of column bands intermediate to the two-way column banded areas.

In said

conventional panels

11, 12, the two-way column bands of reinforcing bars 15m, 1511, are distinguished from the mid-panel column bands of reinforcing bars 23 in that the former are in closer relation and heavier crosssectional design. Notwithstanding the extra concentration of steel sectional area in the column bands, the stress in the bars and concrete of conventional flat plate increases to peak values in proximity to the columns. The capability of the slab in shear is particularly limited in that the increase in bar concentration does not significantly reduce the shear stress.

An object of the invention then is further stated as to improve the capability of the otherwise conventional flat plate in the area of maximum stress enclosed within the rectangular outline 17. The improvement is essentially accomplished by supplementary shear stiffening means of the invention adapted to combine with concrete slab 14 and the usual reinforcing bars in the manner of composite beams.

The invention is generally featured, with reference to the broken-wise sectioned plan and elevation views of FIGS. 3 and 4, in the structural assembly 9 shown typically applied for reinforcing in shear a portion of concrete slab 20 contiguous to an interior supporting column 21. The slab shear reinforcing assembly 9 comprises the twoway column bands of reinforcing bars subdivided as

bars

31m, 3111, 36m, 36n as hereinafter specified, positioned for negative moment adjacent to the top surface of slab 20 and connected as hereinafter set forth to the novel shear stiffening means 19q, 19p of the invention. The shear stiffening means 19q, 19p with further reference to the enlarged sectional view of FIG. 5 and the corresponding plan of FIG. 6, comprise elongated steel bars 18 of upright rectangular section adapted essentially as webs of beams for capability in shear, fitted with

weldment angles

26, 27 as hereinafter detailed. In the form illustrated of the slab shear reinforcing assembly 9, the twoway column bands are centered on and in parallel with the column grid center-lines mm and n-n, and the shear stiffening means 19: and 19p are disposed in plan along the diagonal lines q and p respectively, of the column band rectangle 24 defining the intersection of the two-way column bands.

A shear stiffening means 19q or 19p is provided for each panel shown in part bordering the column grid center-lines mm and nn. The slab shear reinforcing assembly is noted directly supported on steel column 21, which as illustrated is of rolled H-section, preferred for facility in erection, by means of the ordinary shear connecting angles 25 connecting the inner end of each shear bar 18 to column 21.

It is noted that the instant invention offers the advantage with respect to convenient, expeditious erection, in that connection angles 25 may be bolted or riveted to the flanges of column 21, without the need for welding. The mid-panel column band of reinforcing bars 23, aligned and centered in correspondence with the reinforcing bars in the two-way column band area, are conventionally provided similarly as in FIGS. 1 and 2, independently of the slab shear reinforcing assembly 9 featuring the invention.

With further reference to FIG. 3, all reinforcing bars 22m parallel to column center-line 1111n pass directly over all reinforcing bars 2211 parallel to column centerline nn in successive pairs of crossed bars at spaced intervals along the top surfaces of shear web bars 18. In the form of the invention illustrated, preferred as to considerations of erection and prefabrication, the pairs of reinforcing

bars

31m, 3111, 36m, 3611 are selectively connected to shear web bars 181 18-11 at their cross stations over the latter by means of weldment angles 26, as

shown in FIGS. 3, 4, 5 and 6. The weldment angles 26, notched along the angle corners so as to fit vertically over shear web bars 1817, are positioned against and welded to bars 31m, 3111. Each weldment angle 26 is also welded along its notched edges to shear web bars 18. Segments of weldment angles 27, having outstanding horizontal legs and slotted in their vertical legs so as to receive shear web bars 18p on the inner surfaces of their horizontal legs, as seen in the elevation FIG. 5, are welded on their slotted edges transversely to shear web bars 18p at spaced intervals along the bottom edges of the latter, for the purpose hereinafter appearing. Each shear stiffening means 19q, 19p is noted column connected by shear connection angles to column 21.

Further illustrated in FIG. 6, weldment angles 26 for similar interconnection of the crossed reinforcing bars 36m, 3611 to shear bar 18q are in staggered spaced relationship to the weldment angles 26 interconnected to shear bar 18p. Reinforcing bars 31111, 3111, as shown, are connected by weldment angles 26 to shear stiffening means 18p and reinforcing bars 36m, 3611 to shear stiffening means 18:]. Thus, all reinforcing bars 3611 shown cross-connected by weldment angles 26 to shear stiffening means 18: at even numbered spaced stations 0, 2, etc., in FIG. 6 are seen to mesh with the remaining parallel reinforcing bars 3111 connected to shear stiffening means 1811 at odd numbered spaced stations 1, 3, etc., and to traverse unconnected over the latter means. Conversely, reinforcing bars 3111 connected to shear stiffening means 18 at odd numbered stations traverse unconnected over stiffener means 18q, meshing with reinforcing bars 3611 connected to means 18q.

The invention in the form set forth permits of the shear stiffening means 18 18p with their integrally

crossconnected reinforcing bars

31m, 3111 or 36m, 3611 to be erected, without the need for field welding, as prefabricated assembly units of the slab shear reinforcing assembly of FIGS. 3 and 4, designated in FIG. 7.

As shown in FIG. 7, slab shear reinforcing assembly unit 30 of the invention is represented as taken from the assembly of similar units in FIGS. 3 and 4 and from the fragmentary view of FIG. 6. Corresponding to the shear stiffening means 19p which is disposed on diagonal p of the pair of shear stiffening means 19: 19p illustrated in FIG. 6, the assembly unit 30 is shown to include its selected portion of reinforcing bars 31m, 3111 integrally connected at odd numbered, spaced stations to shear stiffening means 19p. In plan, reinforcing bars 31m, 3111 present a generally L-shaped formation of a pair of bands intersecting near their ends on diagonal line 32, designated L-band formation for convenience of reference. The shear stiffening means 19p is noted adapted for column connection by means of connecting angle 25 at the end of shear web bar 18 proximate to the re-entrant angle of the L-band. The ends of reinforcing bars 31m, 3111 terminate on the rectangular outline 33 which corresponds to the two-way column banded rectangular outline 24 of FIG. 3. It is evident that an assembly unit corresponding to shear stiffening means 19g of FIG. 6, of L-shaped band plan symmetrically opposite to that shown in FIG. 7 but of staggered spacing of reinforcing bars 3612 in relation to the parallel reinforcing bars 3111 of assembly unit 3%, can be designed similarly within the rectangular outline 33. It is understood that all reinforcing bars parallel to column grid center-line mm in both units pass directly over those parallel to column grid center-line 12-11.

The complete slab shear reinforcing assembly of FIG. 3 can be erected readily in assembly units typified by 30 in FIG. 7, and by symmetrical counterparts of 30 with staggered bar spacing, without the need for field welding. The assembly units can be positioned and column connected in rotational sequence, the reinforcing bars of staggered spacing in each alternate unit falling in mesh with the similarly oriented bars of the preceding unit and crossing over or under the right-angle oriented reinforcing bars of the latter unit. In the complete assembly the reinforcing bars form the two-way column bands of conventional design of reinforcing bars provided for negative moment in proximate relation to the top surface of the slab, but with their added function of being crossconnected to their respective shear stiffening means of the invention. It is understood that the invention places no other restriction on the conventional design of all reinforcing bars of the slab or of the actual slab.

FIG. 8 represents a further sectional view taken at 8-8 in FIG. 6, and FIG. 9 the corresponding plan view thereof, shown in partial concrete embedment, of shear stiffening means 19p of the invention, as a model for demonstration of its function. Under the load P shown schematically as an arrow vector applied downward to the horizontal leg of weldment angle 27, shear stiffening means 19p bends in negative moment as a centilever connected to column 21, with a curvature convex downward. As a result, all points on its upper surface undergo a small displacement away from column 21 and all points on its lower surface displace conversely toward the column. Weldment 26 in its displacement takes with it locally the integrally cross-connected pair or reinforcing bars 31m, 3111, and tends also, by concrete bond, to displace locally the contiguously meshed pairs of bars 36m, 3611. The reinforcing

bars

31m, 3111, 36m, 3611, being embedded in the concrete slab shown broken sectioned 20, resist along their lengths their displacement at weldment 26. Their accumulated resistance is represented schemat ically by the arrow vectors denoted T in FIG. 9. The axial components, denoted T, of the diagonal forces T as exerted against the top surface of shear stiffening means 19p by weldment 26, as viewed in FIGS. 8 and 9, constitute effectively the tensile flange action of a composite beam.

Conversely, angle 27 presents a vertical leg surface abutting the concrete, on which a compressive force is accumulated, denoted by the arrow vectors C in the figures, resisting the displacement of angle 27. The axial components, denoted C in FIG. 8, of the diagonal compressive forces C exerted against the bottom portion of shear stiffener means 19 by the compressive force accumulation angles 27, as viewed in FIGS. 8 and 9, again constitute effectively the compressive flange action of a composite beam.

The overall effect produced as for the model portion, is of an internal supporting beam along the line of action of shear stiffening means 19p, with continuity maintained across the supporting column. With further reference to FIG. 3, each shear stiffening means 19q, 19p, because of its relative stiffness as the web of an effective beam, draws to itself a major portion of a superposed slab load, main- 1y received on the horizontal leg surfaces of the pressure force accumulation angles 27. The load is then transferred by shear directly to column 21, relieving the adjacent slab of shear and moment, and resulting in a stress dis tribution essentially improved over conventional construction.

As understood from the above demonstration of the model of FIG. 8, shear stiffener means of the invention are not necessarily restricted to the form shown as 19q, 19p in FIG. 3, as to their lengths outward from the column and corresponding connected portions of the column bands of reinforcing bars; FIG. 3 illustrating a preferred embodiment of the invention.

Negative moment in a concrete slab in relation to a column support or other local reaction is understood, for purposes of this specification, to correspond to a local curvature of the slab under load, convex when viewed in a direction opposite to the direction of the columnar or other reaction. For the usual column support of a floor slab under downward superposed floor load, the reaction of the column is upward, hence the curvature is locally convex when viewed downward, and reinforcing bars for negative moment are provided in proximate relation to the top surface of the slab. Where the superposed slab load is applied upward, as in the case of an invert slab on the ground with ground pressure upward, the column reaction is downward, the curvature of the slab locally around the column is convex upward, and reinforcing bars for negative moment are provided in proximate relation to the bottom surface of the slab.

FIGS. and 11 represent fragmentary views illustrative of the alternative usage of a concrete column 61, preformed with reinforcing bars 62, for support of slab 20 reinforced according to the invention by shear stiffening means 19 19p, together with their cross-connected reinforcing

bars

31m, 31n, 36m, 36a similarly as in FIG. 3. Shear bars 18, provided at their column ends with sole plates 63, are shown set into pockets 64 preformed with column 61, for subsequent embedment in slab 20, shown broken-wise sectioned from column 61.

It is understood that the foregoing figures and accompanying context are intended as illustrative only and not restrictive of essentially equivalent variations of form and arrangement of parts such as are apt to occur commonly to persons skilled in the art.

What is claimed is:

1. A structural reinforcing assembly unit for embedment within a reinforced concrete slab supported at spaced intervals, in a portion of the slab adjacent one of the supports, said unit comprising tensile flange means, said tensile flange means consisting of a pair of bands of reinforcing bars, each band comprising a plurality of parallel bars for embedment adjacent one surface of said slab, said bands intersecting adjacent their ends in an L-band formation substantially L-shaped in plan, the parallel reinforcing bars of one band crossing over the parallel reinforcing bars of the other band in a substantially rectangular two-way reinforced area, a shear resisting member of upright section effective as the Web of a beam disposed along a diagonal of said two-way reinforced area interconnecting the reentrant and opposite salient corners of said L-band formation positioned in upright abutting relation to the tensile flange means, said tensile flange means crossing in successive pairs of intersecting reinforcing bars at spaced intervals along said diagonal being connected at said intervals to adjacent portions of the shear resisting member for transfer of tensile flange shear thereto, said shear resisting member being adapted for connection at the end thereof adjacent the reentrant angle of the L-band formation to a near side of said support, compressive flange means comprising bar means distributed along the shear resisting member positioned for embedment in proximity to the other surface of said slab and having surface portions for accumulation thereon of compressive axial flange force and of transverse shear force, said bar means being secured to adjacent portions of the shear resisting member at spaced intervals for transfer of compressive flange shear.and transverse shear.

2. A structural reinforcing assembly unit as in claim 1, wherein said L-band formation comprises outstanding leg portions, said leg portions being of lengths to extend beyond the far sides of said support into adjacent portions of said slab.

3. In a reinforced concrete slab supported on spaced support means, slab shear reinforcing means embedded within a portion of said slab adjacent one of said support means, said slab portion being reinforced for negative movement by two-way bands of reinforcing bars positioned proximate to one surface of the slab, said two-way bands comprising one band of parallel reinforcing bars crossed substantially at right angles to a second band of parallel reinforcing bars, the two bands intersecting in a substantially rectangular two-way reinforced area adjacent said support means, said slab shear reinforcing means comprising in combination with said bands of reinforcing bars a shear resisting member adapted for shear as the web of a beam disposed along a diagonal of the two-way reinforced area, said shear resisting member being positioned in depth in upright abutting relation to the two-way bands of reinforcing bars, a plurality of intersecting pairs of reinforcing bars of said two-way bands being connected at successive spaced intervals along said diagonal to adjacent portions of the shear resisting member by means adequate for transfer of tensile flange shear thereto, the shear resisting member being connected at the inner end thereof to said support means, compressive flange means comprising bar means distributed along the shear resisting member positioned in depth in proximity to the other surface of said slab and having surface portions for the accumulation thereon of compressive flange and transverse shear forces, said compressive flange means being secured to adjacent portions of the shear resisting member at spaced intervals for transfer of compressive flange shear and transverse shear to said shear resisting member.

4. In a reinforced concrete slab supported on spaced support means, slab shear reinforcing means embedded within a portion of the slab adjacent one of the support means, said slab portion being reinforced for negative moment by a two-way bands of reinforcing bars positioned proximate to one surface of said slab and comprising 'one band of parallel reinforcing bars crossed substantially at right angles to the other band of reinforcing bars, the two bands intersecting in a substantially rectangular two-way reinforced area adjacent said support means, said slab shear reinforcing means comprising in combination with said bands of reinforcing bars, a shear resisting member adapted for shear as the web of a beam disposed along a diagonal of said two-way reinforced area, said shear resisting member being positioned in depth in upright abutting relation to the twoway bands of reinforcing bars, a plurality of intersecting pairs of reinforcing bars of the two-way bands being connected at spaced intervals along said diagonal to adjacent portions of the shear resisting member by means adequate for transfer of tensile flange shear thereto, the shear resisting member being connected at the inner end thereof to said support means, compression flange means positioned in depth in proximity to the other surface of said slab and comprising bar means secured to the shear resisting member adapted as a compression flange of said beam disposed along said diagonal and for accumulation of transverse shear force thereon.

5. In a reinforced concrete slab supported on spaced support means, slab shear reinforcing means embedded within a portion of said slab adjacent one of said support means, comprising in combination, a plurality of bands of reinforcing bars adjacent one surface of said slab for resistance to moment, a shear resisting member adapted for shear as the web of a beam connected at the inner end thereof to said support means and disposed in plan along a line traversing said bands of reinforcing bars out- Wardly of said support means, said shear resisting memher being positioned in depth in upright abutting relation to said bands of reinforcing bars, a plurality of reinforcing bars of said bands being connected at spaced intervals along said line by means for transfer of tensile flange shear to adjacent portions of the shear resisting member, compression flange means positioned in depth adjacent the other surface of said slab and comprising bar means secured to the shear resisting member adapted as a compression flange of said beam disposed along said diagonal and for accumulation thereon of transverse shear force.

References Cited UNITED FOREIGN PATENTS France.

US. Cl. X.R.