US1244641A - Reinforced-concrete floor construction. - Google Patents

Description

kw. M; PRATT. RmNFoncEn coucasre rLo cosrnucnun.

APPLICATIQN FILD MAR. I9, |915.

Patented 00u 30,1917;

3 SHEETS-SHEET I.

WIT/VESSES:

W. M. PRTT. asmronceo coNcnErf lnomi coNsmucnoN.

APPLICATION FILED IMI.l I9. IBIS.

Patented' oet. 30,1917..

3 SHEETS-SHEET 2 Y fw.`M, PkAT.* REINFOBCEDCGNCRETE 'FLOOR CONSTRUCTION. I i APPLIATlON'FIL'ED #n.191 HHS- v 1,244,641. l 'Patented oct. 30,1917.. y

f 3 sHEEIS-SHEET 3.

" ggf' l Walter MP/'ajtt w'ro/vfr l I45 method -of reinforcing,

A50` I" like numbers denote like parts.

UNiriiD STATES -iiifrii.ufr onirica.

wennen in.' r'nn'r'r, or fermoir', inoltre-EN.'

nErNFoncDdoncnErE umoncoNsTnrUcTom--' Taf Zfwhom toizay concern:

e-,it known. that I, Witwen M. PRA'rr, afcl-tizeirnf the United States, and a resi- `dentof the city of Detroit andI State of hichigam-have invented a new and use Improvement in Reinforced-Concrete Floor Construction, of which the following is ing flat slabs have been used. These have ordinarfilywbeenrof .the four-'way vsystem or site directions. This is shown in Fig. 7

theitwqrway system yor a combination of the twofg-'My invention relates primarily to the two-waysys'tem; i. e., a. system in which two` sries'i-f reinforcing members are used at substantially right angles to each other. Notiznnlyhavel developedfan analysis of at=slab.f1stress es, which gives considerable .variamcein placing reinforcing bars as com- 'paned with previous practice, but I have alseffdeveloped', an eeonomy.. in the amount offniateriali and' labor` necessar to the makingiof.the1s'lab'. Some other esigners have 'loftenusedbars of considerable length, which barsfhave .beendiilicult to handle, particuvlarlyin buildings-of several storiesin height. Othershave used bars bent at one, end only,

. ractically all bars in the slab bein bent.

" till,e others have used approximate y one -lralf of the bars-bent, the bent bars usually 40 beingbent at both ends. In all these other "eases,y separate 'supporting bars and some' times concrete blocks have been necessary inzender to keep the top reinforcing in the rmgions above, the neutral' axis. In my fondement for negative moments are selfspporting', and to4 all intents and purposes can not be' .'pla'esi f thed'rawings, Figure l through Fig-.6,

Fig. l is a plan view, showing exterior`- and interior panels. `All concrete isv assumed removed, the bars showing as if restin onv forms.' jig.- 2 is a cross-section on line -A. Fig.

specificati@ of nette'rs'iuifti- Appiicat'ion inegi Maren-19, 1'91'5. i seriaiimislsiy to si'es of exterior panels, or aroundo vView showin' ythe arrangement' o which I emp oy for reinforcing a portion the. floor margins.

all top bars or rein- L than do positive moments. dislodged `from their ,proper a, asian @a life Blais', Fig'. is estetionV on line Eig. G is apers .ective of reinforcing over and A uliacent to uinns. Fig. 7 is an elevation and planwof bars usedin the top region of exterior 'enings whichbreak u the continuity of t e floor construct1on. 'g 8. is an, elevation and lanj of top bars usedover the columns and 'in the top regions between columns andinclsing thepanels..l Fig. 9 is apers active of a' floor including a panel adjacentrone of In my method of construction, all top Patented obese; 1ere.

bars

bars are self-supporting. This isl accomplislied by, extending the to'p reinforcement downward at each end and'then extending each end horizontally and laterallyin oppo'- and Fig. 8, andelsewhere in1the drawings. These out-standing legs may rest` on the forms or on suitable chairs, when it is de the bottom region ofthe slab, o r regio'iisof positive moment. vAt least one top bar'corresponds toone bottom bar. In this way, a virtual connection is formedbetween all bottom and top reinforcement, not onlyat one end of any bottom bar, but at both ends, thus practically doubling. the anchura erelation between top and bottom rein oreement, as compared with any other type that I know of. In addition, it has been' necessary heretofore tri-"provide numerous suports to keep bottoni steel' oil the forms.` Kly method' reduces the number of such supports to a large extent, owingtoj, the fact that the out-standingA legs of top bars form naturalseats or supports for the ends of vall bottom bars.

It is well known that negative moments normally fall off or reduce more' rapidly By .using separate reinforcement for negative moments, rather than byv extending steel used for lpositive moments up intonegative moment regions to take lcare of negative moment stresses, the tonnage of bent steel is reduced, my method' saving -approximately 10% ,in this particular, over any other system. with which I 'am familiar,

Furthermore, positive and negative mo iio `ment, .stresses are? variable quantities. In4 Athe middle of.. the slabatpoints substanl l. tially equidistantfromcolumn centers, there vexist positive moments, 1- TheI stresses due to moments 2cm-taken care of by bars -2lnd tf-and' in theeaberior panelsfby bars Q'and 5.. By exteribr panels are meant those. ad]acent a suppbrting wall or as'upporting beam bordering an opening o r break in the iioor. There is no need tol run these bars to the center lines o fcolumns', and I have used the jlstaggerprmciple?, so common in theuse offplate-gii'ders. y Thus one bar 2 will' be staggered al short distance'as compared withthe next bar 2; similarly for f bars 4f' rIfopbars over-"the columns may i =also befstaggered, thus givingybettershear renforngfln the regions near the column heads.' 'This use 'of'thestaggerfprinciple #My fiat slab makesa 35.

results in a" further economy of material,

-with vno loss' inf-strengthI` L @Agaimmy investigations `indicate that it-is desirableto A'place bottom steel diagonally vin the regions over the columns.

This j reinforcing provides for reinforcing -due -to the merging of two lines of contra- 'irl'exur'e, an'dthis reinforcing crosses the juncture of theseA lines at 'substantially right angles to the same. In my opinion, thls reinforcing will tend to prevent the unsightly cracks sometimesoccurring in fiat`s'labs in this region.- The bars referred to are marked 15. f

further saving in' that practically all bars are spaced substan-` tially at 'equal intervals apart. For instance, all bars 2 are at equal distances apart.

kSo itis for` bars 5,'or bars 4, or bars 6, or

bars 7, or bars 8. It is true that bars 7 are likely to 'be larger bars than bars'2, 'which is entirely in accord with my analysis. My general scheme gives a simplicity' and ease 'of erection embodied in no other type to the same degree. Heretofore, in two way flat slabs there have been used various meth# ods of proportioning steel in the central portion of the slab. One school groups the bars closet together in this region; another school` groups the bars farthest apart where the first school groups the bars closest together. My method involves the middle groundbetween the twq,land1, I believe, gives ai-better Y vdistribution of the reinforcement.

My improvement' consists in placing' the bars substantially parallel to lines through column centers or to other supports, said bars running in substantially two directions at substantially right angles to each other, and in thev detail placement of said bars or reinforcement intwo separate series using separate bars for negative moment stresses 'as compared with those for positive moment stresses, and as yshown on the drawings accompanying this speciicatlon and forming 'alpart thereof.

`are staggered at their ends.

. My improvement would also apply to the detail use of reinforcement for metal, clay or shale tile, plaster composition, tile rand concrete ioors, with' or without the lise of deepened girders.

Referring to Fig. 1, all concrete is assumed removed, with the bars lying on the forms.

'Light vdotted lines vshow the concrete below. Light lines showbars in the bottom regions. Heavy lines show bas in the top regions. Thebars 2, 5, and 4- are bottom bars, grouped-in'approximately '70% ofthe panel'lwidthijand extending nearly to the column,v centers in length, the bars in any one series beingstaggered. Similarly, bars 3, 6, 9 and 7 are bottom tension bars and n Bars 12, 13 and 14 -areftop bars over columns I or sup.-

ports, and are self-supporting leach, bar for,

itself.' Bars-8 are topbars and zare selfsupporting. Bars 10 are exteriortop'bars and are not only self-supporting, but are sure to develop any stress in them owing to the hook' at the out-side end. All top bars are bent so that their longest dimension is at the proper height od the forms.v Bars 15 are bottom bars running diagonally acrossfthe columns.

The lines -of `contraiexure near the co1-l umn's are approximately at the quarter 0r fifth distance from center to center of columns. Between columns, the lines of contraflexure are at approximately the .156

distance of the distance center to center of" columns. There exist two sets of lines of contraflexure at substantially right angles y to each other. Since all loads Inusttravel along the lines vof reinforcing, each line' of sometimes require additional bottom steel in regions covered by bars 7.

Having thus described my improvedoor system, what I desire'to claim and secure by Letters Patent is asv follows 1. A reinforced concrete floor supported by rows of columns,- and comprising a plurality of slabs each reinforced by two` s eries of long bars extending substantially at lizo `right angles to each other, and adjacent the lower surfaceiof the slab, the adjoining marginal portions of the slabs being reinforced y near the top surface with short bars extending transversely of said portions, the bottom bars extending parallel with* these top bars and overlapping same, said series o f 2. A.- reinforcedv concrete floor, supported by rows of columns,'and comprising'a plurality of slabs, eachreinforced by two series of long-bars extending substantially at right vangles to each -other and adjacent the lower surface of the slab, the adjoining forced near the top surface with-comparatively short barsfextending transversely of said portions, said bottom bars extending substantially parallel with said topv bars and overlapping bars forming a i' heads, diagonal bottom bars being provided over the column heads,4 crossing each other at substantially ,rightangles 'and in substantially the plane of Athe bottom bars.

3. A reinforced concrete floor, supported by rows of columns and comprismg ,a plui rality of slabs, each reinforced `by twoseries of long bars extending substantially at right angles to each other and ad]acent.the

regions above the columns,

the same, said series .of shortgrillage over the column vline of-centers. In testimony whereof I aiix my signa- .ture in' presence, of two, witnesses.

lower surface ofthe slab, of two series of comparatively short bars respectively substantially parallel with' said long bars and arranged adjacent the top of the slab inthe and two bars. arranged substantially in the long bars above the columns, 1n va substantially transverse relation to each. other and in a substantiallydiagonal relation to 'said top bars, providing reinforcing against the' stresses due to merging of the -two lines of contralexure.

4. In a' concrete floor supported -byl c oluriins, a series of short bars crossing a line surface of the Hoor', anda series of :long bars parallel to said short bars andA('sxtendin'gAV adjacent'the bottom surface of 'each of the;l panels adjoining said line of centers, the

neath the short bars into proximity to -said Witnesses:

FRNK S..,PACnARD, Jr. JosnrHL. Bunn plane of said of centers between columns adjacent the top marginal portions ofthe slabs being rein'

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