US1840304A - Reenforced concrete structure - Google Patents

Description

Jan. ll2, 1932. s. J. BRANsoN 1,840,304

REENFORCED CONCRETE STRUCTURE Filed Nay 31, 1928' Tin Patented Jan. 12, 1932 UNITED STATES PATENT OFFICE SAMUEL JOSEPH BRANSON, OF EVANSTON, ILLIOIS, .ASSIGNOR, BY MESNE ASSIGN- MENTS, TO THE BR-ANSON SYSTEM, INC., F GHICAGO,`-'ILLINOIS, A. CORPORATION or DELAWARE ApplicationL led May 31,

My invention relates to reenforced concrete structures and it has for its object the provision of'anew and improved form and arrangement of concrete and reenforcing steel whereby both the concrete and the reenforcing steel shall have the maximum efficiency in operation for building up tension, compression, and diagonal tension or shear, Whereby the thickness of the combination floor and ceiling structure may be kept to a minimum consistent with proper strength, whereby the dead weight of the floor structures throughout the entire building may be greatly reduced so as to correspondingly reduce the load to be supported by the girders, columns and foundations of the building and vthus cut down the cost of the entire building structure, whereby the necessity for the use of lath and 'plaster shall be eliminated, and whereby in other respects the cost of production of the building maj7 be reduced.

It is one of the objects of my invention to provide a slab vloor structure, supported by beams or other supports in spaced relation to each other, and formed continuous over such spaced beams, comprising in each slab section between the supports an improved arrangement of concrete and reenforcing steel whereby substantially the full depth of the slab maybe efective depth for developing Y tension and compression, while at the same time 'each of said sections between the supporting beams is kept in the form of a slab strictly speaking, as distinguished -from a A beam' and slab type of construction, Whereby substantially the full depth of the slab may be eiiective also for developing diagonal tension. It is one of the objects of my invention to provide a construction of this type in `which theV positive or bottom tension members are located at the best possible position both with respect to positive or topk compression and alsowith respect to diagonal tension, whereby the greatestpossible depth of slab is effective depth for both of such stresses. For attaining such novel construction by which substantially the full depth of the slab is effective with respect to both positive compression and diagonal tension, I have arranged bottom tension members substantially at the REENFORCED CONCRETE *STRUCTURE` 1928. Serial No. 281,673.

plane of the bottom face of the slab, bonding the tension members to the slab by means of concrete pads or ribs formed integrally with the slab at its bottom face, such pads being of suflicient size to afford the desired protection against fire and corrosion.

It is another object of my invention to provide an improved construction of this type comprising a continuous slabsupported by beams or other supports arranged in spaced relation to each other, with top tension bars in transverse position with respect to the supports and imbedded in the slab sulliciently below its upper face for proper protection against lire and corrosion, in which construction the arrangement may be such as to provide the required compressivel strength for effective cooperation with the top tensioning 4bars for attaining the desired margin of safety. To this end, it is one of the objects of my invention to provide greater compressive strength at the bottomvportion of the slab underneath the top tensioning bars adjacent to said supports than is normally provided hy the slab itself of even. thickness throughout, such increased bottom compressive strenvth adjacent to the supports being provided lay the use of bottom reenforcing bars in transverse position with respect to the supports and located substantially at the plane of the bottom face of the main portion of the slab, such bottom reentorcing rods being bonded to the slab by means of concrete pads or ribs formed integrally with the slab at its bottom face, such pads being of suilicient size to aii'ord the desired protection against tire and corrosion. It is one of the objects of my invention to provide such an arrangement that the saine steel bars act as the bottom compression members for the edge portions of the slab adjacent to the supports and as the bottom tension members for the middle portion of. the span between the supports, the portion of the bar which is not directly active with respect to any particular force which tends to deorm the slab serving as anchoring means for the remaining portions of the bar. ln the arrangement as specified, the bottom reenforcing bars develop high vcompressive stresses in conjunction with the extreme fiber stresses of the concrete.Y

It is another object of my inventiori'to increase still further the bottom compressive stresses at the points adjacent to the supports, or the negative compressive stresses as they are called, in cases in which such further strengthening is required, such reenforcementv being provided preferably by osetting the bottom face of the slab downwardly adjacent to the supports to a slight extent with respect to the bottom face of the main portion of the slab, such downward offsetting serving preferably to bring Vthe bottoni faces of the edge strips of the slabs into alignment with the bottom faces of the pads or ribs. j lt is another-obj ect ofiny invention to pro- *vide an 'improved construction of this type, iv'olvingfthe' use of bottom reenforcing steel running both *ways through they slab between the oppositelyldisposed supports, with such Y "bottom tensioning bars located substantially at the plane ofthe bottom'face of the slab and "with such reenforcing bars bonded to "thes'labbyfpads or ribs of concrete formed integrally 'with the slab at its bottom face, in 'which the protecting and bonding ribs or pads areof such size and shape andare spaced yaft'such intervals with respectto `each other 'thata'n integrally formed mold may readily be v'used for each of the `panels* between the 'ribssothatthe slab bottom portion and the .adj acentiribside portions may benioldled and joined smoothlywithout any occasion yfor d isfliguri'ngimarks in theconcrete, thereby giving";the bottom fface of the slab ,as a whole ianattractive appearance as a paneled molded i ling-and inale'unnecessary the use of lath d plasterer other additional lmoldings in y'conn'eotionwiththe concrete. y

' Itis another object of'my invention to prove structures of kthis type `in vsundry detailsf'hereinafter pointed out.y The preferred means by which I'have laccomplished my sev- Y eral objects are'illustrated in the accompanydrawings and are hereinafter specifically described. 1flhat which Ibelieve to be new and'fde's'iret'o cover by thisapplication isset forth the l'cl-aims.

fFig.- li-s avertical section'tliroughone form ofrmyimfproved floor structure, being a Vfragmentary view-and showing also a portion of oneiof the beams by which the floor structure is supported .at one side;

Fig. 2 is la vertical section taken substanv tially lat line 2-,2 of Fig. l;

Fig. 8 is a view similar to Fig. 2 but show .injg a modified form of construction; and

"Fig, 4 vis :a cross section upon a reduced scale sho-wing the construction as shown at Ref'e'rringno'w particularlyto Figs. 'l and A 2, l0 indicates the beams which stand in spa-ced'relartion toeach other for supporting sired spaced relation for supporting a continuous slab built over and between the supports. In the construction illustrated in liigs. l and 2, the beams 10 are shown vas being` formed integrally with the floor struc- -ture and strengthened by I-beams l1.

The door structure between the oppositely disposed longitudinally extending supports l0 is in the form of a continuousslab 12 of's'ubstantially uniform effective thickness throughout the entire span between the supaorte. f

lt-eac'h'edge Vportieri of Vthe slab adjacent Vto the Isupporting beam, a series -of toptension members 'i3 are provided, such tension members being in the forni of'steel'rods or bars extending transversely across Ithe beams near .thetopv face of the slab, beingpo-sit'ioned as'near 'as possible to the top face ofthe slab consistently with proper protection of the bars bythe concrete against lire and ,corrosion( As is 'best 'indicated yin 2, a plus rality ofthe tension bars lare connected to getherzbynieans of wires ll into the form of 'a' grill, legs 15 of any suitable typebeingprovided on the grill .forsuppor'ting the bars 13 in the desired position upon the form upon which Vthe'concrete-ispoured. For the intermediate portion ofthe sl'ab'between the supports 10, bottoni tensioning rods 16 are piovided, 'located substantially fatthe plane of the fbottom face'of'tlie intermediate portion of the slab l2, -suc'li'bottoni'tensionrods 16 extendnigcontinuously rfrom one support to the other at 1the level indicated Vand serving at theirLend portions vas bottom compression members. zFor bonding the rods 16 to the slab, pads or ribs 17 of concrete are provided on the bottom 'face of the slab-,being 4formed integrallywith the slab, such pads being of sufficient `thickness to 'provide vthe desired protection' ofthe rods against fiire and' corrosion and f-orproviding a strong 'bond between the rods and the slab.

Asis well understood in connection'with a structure of this type comprising a slab extending o'ver andfbetween a series of spaced supports, there is, under'nornial conditions involving substantially equal spacing of theV thepoints of inflection are located at a dis-- tance fromV the supports "corresponding'to approximately one-fifth of the span. The top tension rods 13 are accordingly made of such length as to extend at `each side of a support well beyond the normal ointof iniiection, such rods extending preferably about onefourth of the distance across the span. The

bondjbetween one end portion of a top tension Irod 13 and the concreteslab serves as the anchory for the opposite end portion of the rod.y The bottom tension members 16 also are sufficiently anchored to the slab by their end portions which extend Well beyond the point of inflection at each side of the span. i n

' By reason of the ypositioning of thebottom tension rods 16 directl r at the bottom face of the main portion' o the slab, preferably in centeredposition with respect to the plane of the bottom'face, the'entire thickness of the slab vis-eifective for developing compressive stresses, rendering the structure of maximum eiiiciencywith respect to bot-h the steel and thegco'ncretein this regard.

As is Well understood in the art, the externalforces which cause failure of a reenforced concrete floor structure by reason of inadequate diagonal tension in the structure are eifective principally at the level of the bottom reenforc-ement for the structure at the point where the failure occurs( It follows accordingly that when deep reenforced ribs are .provided on the bottom face of a slab across the span, such ribs are required by themselves to provide all the diagonal tension necessary for supporting the span, the slab itself assisting very little if any at all in developing effective diagonal tension. By my construction, in which there is no deep reenforced rib or other reenforced or reenforcing structural part between the main supporting members lower than the bottom face of the slab itself, eifectivediagonal tension stresses are developed directly in the slab itself and the full section of the slab is effective for this purpose.

In a reenforced concrete iioor or similar structure, the compressive forces are greatest at' the compressive face and decrease to zero at the neutral axis at some point between the compressive face and the plane of the' centers of the tensioning bars. By the location of the bottom reenforcing bars 16 substantially at thel bottom face of the slab with the depth of concrete in the pads extending below the bars merely suihcient for providing. protection against fire and corrosion, the bot-y tom compressive stresses in the slab adjacent.

to the supporting vbeams are very materially increased, in view of the much greater compressive strength of the steel as comparedy with that of the concrete, steel having a compressivel strength of from ten to fifteen times that of concrete in a similar position.

By the use of my construction, I have provided the maximum vstrength in proportion to theV amount and weight of concrete required. With an allowable steel stress of eighteeny thousand pounds per square inch and an allowable concrete stress of seven hundred pounds per square inch on extreme fiber, my improved slab of a thickness of two and one-half inches will span a distance of ten and one-half feet with a superposed load of forty pounds per square foot in the one-way construction above described. By the development and refinement of the slab structure by which Iam able to span a distance of ten and a half feet without the use of strengthening ribs, I have very materially cut down the amount of concrete necessary as compared with those constructions in which such strengthening ribs are used and I have thus greatly reduced the load to be carried by the girders, columns and foundations of the building. f

Myconstruction has substantially as great an advantage as compared with an ordinary slab construction, in which thebottom tensioning bars are located above the lower surfacefor purposes of fire-proofing and bonding. In such construction,it is necessary that the slab be made from an inch to two inches thicker in order to provide the required positive compressive stresses above such tensioning bars, such increase in thickness serving to increase the amount and the weight of the concrete from forty to sixty per cent. or more.

In some ways, the greatest advantage of all in the use of my construction resides in the fact that thereby the over-all thickness of the combination floor and ceiling is very materiallycut down, both becauseof having the slab structure itself of less depth or thickness and alsozbecause'of 'the fact that no lath and plaster are necessary. If eight inches be saved at each floor, a builder would be able to provide twenty-one stories by the use of my construction as compared with twenty stories by the former constructions, all without in any way weakening the construction.

Referring now to the construction shown in Figs. 3 and 4, beams 18 are provided in spaced relation to each other, with beams 19 also inspaced relation to cach other in crossed position with respect to the beams 18, only one of the beams 19 being shown in the drawings. A column 2O of any approved type is shown as supporting the structure at `the juncture of the beams 18 and 19. The formof the beams 18 and 19 differs from that of the beam 10, but at either point any approved form may be used. The construction shown in Figs. 3 and 4 is substantially the same as that above described in connection with Figs. 1 and 2, except that the construction shown in said Figs. 3 and L1 is what is known as the two-way construction, involving the use of reenforcing members -extendingboth Ways` through. the floor, In Ythis construction-V as- Shown, the ,slabk 21 l,1s

providedwithedge strip portionsQZ off-increased thickness alongeachv otits.; four side edges, such edge strip portions being. ot such increased thickness and ofl such Width as to provide thej desired. bottom --co1npi`essive strength forthe portionsotlieslab adjacent to lthe* beaniisv The bottointension rodsare .preferably placed asnearvaspossible to the piane ofthe bottom face of thema-in portion of the, slab in the construction shown, the

vbottoni tension'vmembers 'running in one direction being located .their VVcenters slightly-belowsuch plane and the bottom tension' rods Qlsrunuing invtheepposite di: rection being positioned with thei-rvcenters slightlyl above suchplanej; this being. necessary in order vtro-allen?. such bars 23 and 2d to pass each other. In ther construction shown, a .single lbottoni tensimiing rod is used in l'ieuiof the,l two vbottom. v.tensinning rods idas-shownin Fig. l. In .the forni shown in said Eigs.3..anzd 4, top tensioning rods areemployed in transverse positionavith respect to leachjofthe beams I8- andit',A theV top tensioning bars.d in yone .direction being indicated by :the numerals. Q5 andthe iop tensioning bars,v inthe cross direction being' indicated bythe numerals 2.6, a.iplurality toward thegpoints off inflection. By reason of making. the edge stripsr of the slab oi increased thickness, With the bottoni faces of the edge strips preferably in alignment' with the bottomy faces of the padsv or ribs 117'the eiiectivewthickness. of .the slab underneath the top tension bars-13 is-inade to correspond substantially to the thickness of the. slab?, above the bottom. tension .rods wat-the center olif the span Where the topfcompressive stresses are the'greatest. The edgestrips '712: of in-v creased thickness are made of such Width as to extendinvvardly towardthe points of 1n-l flection .to such` a distance -as-to. provide the n desired. compressive strength forsuch edge.

portions By reason of theY decrease in, the compressive stresses toward lthe. point of inflectio'n,V itis notl necessary thattlie increased. thickness be continued..thegfull distance to they points ofiniection even when such; strips u of'inc'reased thickness are used. M'In any case main portion Vo the slab ,develops the re'- quifredcornpression Vin cooperation with kthe bottom compression bars yfor providing the required support..V it will beunderstood that in many casesitjsnot necessary fto make the edgestrips of increased thicknessbut that in such cases edge strips of a thickness corresponding to the; thickness of them/ain portion of the slahderelop fthe required. conipressive stresseseven at thev points adjacent to the aces ofthe supporting beams. .Y By the use of the two-Way construction k1n- Volvingthe :pads Vor ribs28 extending in crossed. relationship toeach other,and either With or Without the edge strips, .22 of increased thiekness correspondingto,the combined thickness ot the pads andthe main port-ion ofthe slab,y a very attractive paneled ceiling.. is provided. vByusng care With respect to the contour of the forms against which the yedges ofthe pads and theedgesof thev strips 22 areinoidedy a decorative eiiect is .produced Without'rieti-acting in any Vivay .iroin the eiiectiveness ,of the structurel mech anicaliyiA The. arrangement is such 'that upon the removal of thev forms the structureis ready `for receiving its iin'al coats, of paint orY other decorations Without the necessity for employing iathsor plasterupon the bottoni` face of the slab, thisA being made possihl'e lley* reason ofthe `fact-thatv the individual slab face sections are. ofsuch size that they can bevcast readilyupon integrally formed molds pressed ronirsheet metalinto'shape Without joints or ribs of anytyqiie7 the parts ofthevniold against Which-the edge vportions of the ribsfor pads/are castheing also formed integrally with the .mold for the slab face sectio'n. n 'n f y By theuse oinly improved construction as describedy in connection. WithFigs. 8 and 4, I amV abl'et'o span a distance of approximately sixteen and a half feet both stays between the supporting beams7- with an'allowable steel stress of eighteen thousand poundsper square inch and an allowable concrete stress of seven hundred lpounds perinch on eXtreme liber, Without the'duse of strengthening ribs.V Y I am able thus to make a Vradical saving in the amount oil concrete required', with its cor responding saving. throughoutl the structure.

While l prefer to employ the form of construction as illustrated in Vthe*drawings. it

is tobej. understood that I *do not limit' the:l

invention to the forni shownexcept' so far as the'claiinsjin'ayfbe so limited by the prior art.

clain'ii--UM` 'f" j l". In'l ay reen'torcedand fire-,proofconcrete structure, the' combination of a'plu'ra'lity of' longitudinally extending' supports in spaced relation to each otlien. a slab'of' concrete eX- tendinggfroniV one support to' the other, re-

enorcing rods extending, in spaced relation to eachother between said ksupports atsubstantially the plane of the bottom face' of the slab, and pads of concrete formed-integrally with saidslabon its bottom face and serving to imbed said reenforcing rods between the slab and the pads, said slabv otconcrete and' said imbedded rodsserving by themselves.

by theircooperation -to support theirown weight from said supports and also to carry a predetermined additionalload.v e 1 2.In a reenforced and Ylire-proof 'concrete structure,the combination ofa pluralityr ott longit-udinally extending supportssin spaced relationto each other, a slab `ot concrete extending from one supportto the other,'reen`- f forcing` rods extending 1n, spjaced relation to each other between each two successive supports at substantially the plane of the bottom face*l of the slab atfthe central portionthereot servingfas the bottom tension members for the intermediate portion ofthe slab and extendingv only yslightlyeither above or below said plane atany point throughout their effective tension portions whereby substantially rthe full section of the slab above such' rods is cffective Vfor developing; positive compression,

and pads .of concreteformed integrally withV said slab onits bottom vface-and serving-to imbed saidreenforcing rods between the slabv and the pads, saidslab of. concrete andsaid imbedded rods serving by themselves Iby their'y cooperation to support their own-weight from mined additionalload. e. f n v 3.]In a reenforced. and lire-proofed 'con-v crete structure, the combination. of a plurality Vof longitudinally extending, supports y inA spaced relation to each other,:as1ab ofcon-v said supports and also` to crete' extending from. one. .support to` the other, reenforcing rods-extending in spaced Vrelation to each other between saidsupports and each located atsubstantially the plane of the bottom face of the slab andalsoat the lowermost point of eilective Astresses in said struc- ;ture', and pads of concrete formed integrally with said slab on its bottom face andserving to imbed 'said reenforcing rods between the slab and the pads. f. V. V.

4. In jay reenforced Vand .lire-proofconcrete structure, the combination of a'plurality ofy longitudinally, extending supports yin Ispaced relation to each other,I a slab of concrete ex'y tending from one support to theother, reen- `forcing rods for said slab extendingfin spaced relation to each other between each two successive supports,y with the 'lowermost reen= forcing rods located substantially at.. the plane of the bottom face-of the slab at thel edge f portions ofthe slab Yadjacenttothe supports `whereby the slab itself veloping diagonal tensiomandpads'of conis efective tor de-y creteformed integrally v,with said slab onits bottom face and serving to. imbedusaid re'v enforcing rodsbetween the slab,A and the pads, said slab, of'conorete and said fimbeddedrods carry af-predeterspaced relation to eachother,-

bottom face ot the slab, and pads of concrete formed integrally with said slab on its bottom face and servingte imbed said reenforcing rods between the slab and the pads throughout'the full span from one support to the other, the central portions of the rods serving as the bottom tension members for the intermediate' portion of the slab and extending only slightly either above or below the plane ofthe bottom face of the slab at anypoint throughouttheir effective tensioning portions whereby substantially the full section of the slab above saidreenforcing rods is effective for developing positive compression,y and the end portions of the rods serving as thev lowermost reenforcing elements of the structure adjacent to said su ports whereby the slab itself is effective orv respect to the yslab as to cause substantially the full-.depth of the concrete of the slab to' be 'effective for building up both positive compression anddiagonal tension. 4 Y 7. ln a reenforced and tire-proofed concretestructure, the combination of a 'plurality of longitudinally extending supports in a slab of concrete extending from one support to the other,

reenforcing'rods extending in spaced relationl to each other between said supports in a single horizontal plane, and pads of concrete formed `integrally with said slab on its bottom face and serving to imbed said reenforcing rods between the slab and the pads,tbe arrange- =.ment being sucht that substantially the full depthy of the concrete of the slab is effective for developing top compression at the middle portiono'f the slab and for developing diagonal tension in the portions ot proaching the supports. f

8. In areenforced and tire-proofed conthe slab. ap-

crete structure, the combina-tion of a plurality of longitudinally extending` supports in .spaced relation to each other, a slab'ofconai: mamma dbi mev ,am

way paneled bottom face on the slab ready for decoration, said slab comprising at its edges adjacent to said supports edge strips of substantially as great thickness as the combined thickness of the pads and the intermediate portion ot' the slab.

lil. ln a reen'liorced and tire-prooted concrete structure, the combination of two longitudinally extending supports in spaced relation to each other, two other longitudinally extending supports in spaced relation to each other and in cross relationship to said iirst named supports, a slab ot concrete extending between said several supports, recntorcing rods extending in spaced relation to each other between two of said supports, other reenforcing rods extending in spaced relation to each other between the other two supports, all ot said reenforcing' rods being positioned substantially at the plane of the bottom face ot the slab, comparatively shallow and narrow pads ot' concrete formed integrally with said slab on its bottom face serving to imbed said reenforcing rods between the slab and the pads and serving to provide a two-way paneled bottom face on the slab ready. tor decoration, and other reenforcing rods imbedded in the slab and bonded therewith near the top face ot the slab at the edge portions adjacent to said supports serving as the top tension members for said edge portions of the slab, said slab comprising edge strips of substantially the same thickness underneath said third named reentorcing rods adjacent to said supports as the combined thickness ofthe pads and the intermediateportion of the slab, said edge strips being of such width transversely from the supports to provide adequate compressive strength with respect to said top tension rods.

l5. ln a reentorced and tireproofed concrete structureythe combination ot a longitudinally extending support, a slab of concrete supported at one edge by said support and evtendinn` laterally therefrom, a reentorcing rod alongside ot' said support in spaced relation thereto at substantially the plane ot the bottom face of the slab` and a Dad ot concrete formed integrally with the slab on its bottom face about saidy rod and serving` to bond the rod directly to the slal whereby substantially the full depth ot the concrete ot tbe slab is eiective tor developing top compression with respect to the rod at its middle portion and tor developing diagonal tension at the end portions ot the rod.

lo. ln a reentorced and tireproo't'ed conrete structure.v the combination ot a longitudinally extencinfr support, a slab of concrete eitending laterally from the support at both sides tbereot and supported thereby at the parts adiacent thereto` reentorcino alongside ot said support at opposite sides thereof respectively in spaced relation thereto at substantially the plane of the vbottom face of the slab, and pad-s of concrete formed integrally fwithvth'e'lslrab fon its bottom tace about saiclrodsserving to bo-nd the rods directly to tlieslabwhereby substantially the tu-l-ldepthof the concrete of the slab is effective for developing top compression with res pec'tto-the rods at their middle portions and for developing diagonal tension at the end portions ofthe r'odsjv p '17. In a reenforced and lireproofed concrete structure, the combination of a plurality of 'longitudinally eirtending supports in spaced relation toeach other-,transverse supporting means 4connecting said first named supports inseries, `a slab of concrete extending over thefiiitermediate spaced supports and connecting 'the outermost spaced supports alongside of said transverse supporting means, reenforcing rods extending between adjacent spaced supports in spaced relation to the transverse supporting means at substantially the plane ot the bottom face of the slab, and pads of concrete formed integrally with the slab on its bottom face about said rods serving to bond the rods directly to the slab whereby substantially the full depth of the concrete of the slab is effective for developing top compression with respect to the rods at their middle portions and for developing diagonal tension at the end portions of the rods.

18. In a reenforced and ireproofed concrete structure, the combination of two longitudinally extending supports in spaced relation to each other, two other longitudinally extending supports in spaced relation to each other in crossed relationship to said rst named supports, a slab of concrete extending between said several supports, reenforcing rods securely connected between each two spaced supports at opposite marginal portions of the slab in spaced relation to the cross-positioned supports, each of said four reenforcing rods being positioned substantially at the plane of the bottom face of the slab. and pads ot concrete formed integrally with the slab on its bottom face serving to imbed the several reentorcing rods between the slab and the pads.

19. A reeniorced concrete structure comprising in combination a slab of concrete, a second slab of concrete of smaller depth formed integrally therewith, a reenforcing bar extending across said thinner slab portion at substantially the bottom face thereof and extending into said thicker slab portion, and a pad of concrete formed integrally with said thinner slab portion surrounding said reentorcing bar serving to bond said bar directly with said thinner slab portion and merging at its end with said thicker slab portion.

20. A reenforced concrete structure comprising in combination a slab of concrete, a

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second slab of concrete of smaller depth formed integrally therewith,I a series of reenforcing bars extendingacross said thinner slab portion at substantially the bottom face thereof and extending into said thicker slab portion at spaced intervals therealong, pads of concrete 'formed integrally with saidV thinner slab portion and surrounding said reenforcing bers for bonding vthem directly to said thinner slab portion, said pads merging at their ends with said thicker slab portion, and a series of negative reenforcing bars extending across said thicker slab portion Y and into said thinner slabportion adjacent to the upper face of said united slab strucn ture,v said second named bars being in substentially parallel Yposition With respect to said first named reenforcing bars.V`

SAMUEL JOSEPH BRANSON.

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