US2096921A - Composite beam - Google Patents

Description

Oct. 26, 1937. l 'l yr1. K. o. SAHLBERG 2,096,921"

COMPOSITE BEAMv Filed Nov...18 1935 H92. fy p 59.6

"j"ATToRzEysi I Patented Oct. 26, 1937 n y y Y l v UNITED l STATES PATENT -O-F FICE i i 2,696,921? L .l COMPOSITE BEAM l mu n.0. sauber-g, New york, N411I."V application November 1s,` ms, seria1N.so,42z saumur. (otra-11o) My invention relates to abeamconstruction comnecting members between the concrete-slab and prising a rolled or otherwise fabricated steel beam' the beam. f H 1 s l i `actinghconjointly with a concrete or other slab Figures 3, 5, and .71areyplan Aviews in detail*` resting upon and bonded tothe beam with sufiishowing theconnections illustrated'in Figures 2,

- cientl rigidityv as to restrain the horizontal shear 4, and 6 respectively and Y a f i stresses developed from the load. Said slab to- Figure 8 is a stress diagram indicating the disgether with the steel area above the neutral axis tribution of stresses in the i connection shownforms the zone of compression of thecomposite specically in Figures 6 and 7. f f beam. More specically my invention relates to The composite beam shown in Figure f1 is illus- 10 a beam construction infwhich the slab constitutes trated as a fabricated steel beam with upper chord 10 the oor when the composite members are spacedl I, lower chord 2, a `concrete slab 3,' diagonals in in accordance withload and span. l tension 4,; diagonals inucompression 5 andanchors` Although my improved composite beam pref- 8. ,The anchors shown in Figure 1 correspond erablyv'uses a concrete slab carried by the beam it withithe anchors illustratedy in .Figures 4' and 5 may be rutilized with slabs, vplanks or plates of but other, forms of anchors may, be employed as in 15 other materials capable of restraining compressive v Figures 2 and 3 or Figures 6 and?? or their equiva StreSSeS--; Therefore, when concrete slabs arerelent. n f ferred 4to 4in the following description andclaims v The fabricated beam shown in Flgurel, omit'- I intend to be limited to that particular material ting the anchors andconcrete, slab, is of -well only when such limitation is clearlystated. known dorm, the top andbottom chords ,belngvgo mooiconstructions having steel beams as .load composed of angle ironsfwiththeir verlical'websv bearing members and a concrete or other r,slab 'separated ashort distance for thereception-of the transmitting the load to such beams are afthe tension and compression members 4' and l which present time so designed thatthe stresses in fthe are welded or otherwise rigidly a secured" to the l steel beams shall balance the bending moment angles.; Otherforms of fabricated beams maybe 2:51v without anyhelpful effect fromthe slab between employed instead of the specific construction illusf* thebeams. No helpful elect can be obtainedbetrated in the drawing. v v cause heretofore no provisionhas been made to *T heanchors 6 are carriedupon the upper chord I secure a suiiiciently rigid connection between the of the beam andare preferablysecured vin place beams and the slabs asis the case with my im. byy connections between'the web system and the'sc 1 proved composite beam. j upper chord, as in Figures 2te 5 inclusive-In yBy suiiiciently and eiectivelybonding the conorder to obtain a rigid connection between: the crete slab to the steel Abeam so that the slab will slab 3 and the steel beamfit is necessary .to de-V y beforcedto deform in the same proportionras the velop an anchoring member-6 capable. of retop flange, as will be explained, considerable sav-1v sisting the horizontal shear 'stresses without per-*2.35 ing in .sfteel canbeobtained. yIn thisway the'zone mitting any movement in thelisurface .between o!- compression -willbecomposed of the steel area the slab 3 and the upper chord i. In 'its simplest above the neutral axis of the composite beam in form each anchoringv member. consists ofanzi'ri-y addition to the area of theconcrete slab between verted vT-.section twith the horizontal ange-f i 4 o 'the ,steel beams as compared vto the steel area welded or otherwise rigidly secured to'the topof 40 u alone as with present constructions; the steel beam asindicated in Figures 6 .and

l The vmain object of. my #improved composite Theshear stresses'are heretransmitted through beam is to provide a construction in which will the surface pressure betweenthevertical ange` f 'be developed a connection between the concrete 1, and the concrete slab to the steel `beamfand slab and the top part of the steel beam', said conthe vertical flange 1 lmust have asection modulus .45 i, nection having sumcient rigidity asto withstand of suriicient magnitude to resist the developed` l the horizontal shear developed under the load. bending movement. Y n

In order that myinvention may be better Figure 84 shows a pressure diagram based `for understood attention is directed to the accompurposes of illustration upon the form of anchor e' panying drawing forming a part. hereof and in shown in Figure 6. This diagram is governed 50 l which v by various causes and the shape ofthe saine ,l v ,W

Figure 1 is a side view o! my improved composite y therefore varies somewhat by vreason of 'these beam in its preferred construction. causes. However, it may be stated that the rec- Figures 2, 4, and S'are detailviews on somewhat tangular pressure diagram 9 is the maximum larger scale illustrating different forms of conand a triangular diagramk i0 is the minimuml lilikv y gram between the maximum and minimum dia- L ,web system. Y

P of the stresses passes through the center of gravity of the diagram Ii and its distance a from the top of the steel beam is somewhere between one-half and one-third of the height of the vertical flange 1 measured from the bottom of the diagram. 'I'he section modulus of the `vertical flange must be suillcient to resist the moment Pxa. The horizontal flange 8 is connected to the top of the steel beam grams. 'I'he resultant in such a manner that it resists the horizontal force P and a force couple P', acting in opposite directions and at a distance b from each other balancing the moment P xa.

Furthermore, the connection must be developed so as to give a minimumy moment in the top chord. 'I'his result is accomplished ii the re-vsultant P from the pressure diagram coincides with the crossing point I2 ofthe extended center lines of the diagonals l and as indicated by dash and dot lines in Figure 8. It in some cases this ideal `condition cannot be'fully` realized a certain amount of bending moment may be al-l lowed safely without overstressing the top chord byreason of the fact that in the center-of the span (where thevstresses in the top chord are a maximum) the horizontal'. shear stresses are `zero,and at the support (where the shear is a maximum) thestresses from bending moment are zero. The area of the pressure surface 1 is determined by themagnitude of .shear stresses. The anchoring members .6 shown in 'Figures 2, 3 andr4; 5'are also designed in accordance with the above principles. jIn` the :former nguresthe vertical member? is slightly curved and is supportedalog two parallel edges l! and Mythe edge I3 being rigidly connected to the steel beam by the member |11 .which may be welded or otherwise secured to the tension diagonals 4. In Figures 4and 5 each anchor is provided with one horizontalv edge i5 and' one vertical edge IB.. the latterv being thl vertical part of Ya Atongue I8 welded or otherwise secured to the compression diagonals. r i

As stated, the anchoring members 6 are secured tothe steel beam preferably by'welding or in :any-.other wayby which a rigid connection is secured. From whatfhas been sai'dit will be noticed that the member 8 can-be lsecured either to the topchord L, or to the Vweb system l andi ortor the topchord and compression members or to the top chord and hetension members, of the VWith the arrangement of the composite beam above describedl make use of the concrete or other slab as part of therzone in compression for resisting bending "moment By doing this a considerable saving in steel is effected because the steel area in the top flange may be designed to carry only'the weight of the concrete slab and the. weight '01', the steel beam.

greater in percentage than with in the bottom flange is in proportion to these level arms.

My improved beams comprising the top and bottom flanges with a connecting web are preferably manufactured so as to be provided with a slight camber. vBy this I mean that the beam is slightly curved and when apex ofthe curve extends upward. 'Ihis precamber is very` small. being of ythe order of a fraction offan inch, and is so chosen that the weight-of the concrete slab and beam will develop placed onthe Job the a deflection of the steel'beam equal to the pre- Y camber. In this way the steel beamwill be straight and even, when the concreteslab has hardened. 1 I

It is understood that the form of my invention shown and described are merely` representative and that various changes 'in the shape l' and arrangement vof parts departing from the spirit of my invention 'and the scope of the claims hereafter presented.

Havingr now described my invention' what I claim vas new therein and ters Patent is as follows:

1*.' An improved composite vbeamsupported at its ends and comprising a steel beam withupper and lower chord members andan intermediate may be resorted to iwithout desirerto secure'by Let` f` lattice web, a *slab carried bythe beamfor r`e-v sisting compressivev stresses -and anchoring members for anchoring the slab to the beami' said anchoring members being rigidly secured'to the upper chord with such rigidity thatthe slab, Vin cooperation with the upper chord., will form the zone in compression of the compositebeamfand each anchoring membe'rhaving a pressurey meinber supported along a' plurality of edges.-`

' 2. An improved composite beam as'recited in claim 1 said anchoring member being supported along two horizontal edges inthe same levels'.

3. An improved composite beamas recitedin claim 1 said anchoring member having a pressure member supported along one horizontal l and lone vertical edge. -V Y y l l 4.V An improved yc'ompositelbeam as recited 'in claim 1 said anchoring member having a straight Pressure member. f'

pressure member. ROLF K. O. SAHLBERG. l

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