US1906683A - Plate girder - Google Patents

Description

May 2, 1933). w H. wElsKoPF Er A1. 1,906,683

PLATE GIRDER Filed May 26. 1931 BY ORN '.Whether a beam is Patented May- 2,

UNITED lsTxrEs PATlazlWl olf- FICE WALTER H. WEISKOF, 0F CEDARHURST, AND JOHN W. PICKWORTH, BRONXVILIE,l

NEW' YORK PLATE GIRDER Application lfed May 26,

Ourpresent invention relates generally to structural elements, and has particular reference toplate girders.

.The design of beams is, of course, pr dicated primarily upon the maximum nad Iwhich is to be supported, and the general objective of the structural engineer is to provide a beam having strength characteristics suflicient to carry the predetermined load and having a 'structural arrangement Awhich is as economical as possible.l y'Economical design requires more thanfmerely keeping the total weight of material to a minimum, since the designer is restricted, from a practical standpoint, to the employment of I-beams, angles, and other structural elements of a character which are readily and inexpensively available on the market.

In steel structures `of thev present skyscraper variety, a `further limitation of economic importance `is imposed upon the designer by virtue of the fact that free and available space in .present-day buildings of this character is so extremely valuable. an inch or more deeper or less deep7., than another beam might appear to be 'a trivial consideration, but .inf present-day structures, of mammoth Aproportions not only in height but also in ground area, a saving of as little as one inch in beam depth represents a total saving throughout an entire floor or floors of many thousands It is a geeralobject of our present invention to provide a structural composite beam of the plate girder variety whereby an increased load carrying capacity 'is provided Within a prescribed jdpth, and whereby,

` conversely, a given load can be proviiled for within aA lesser depth.

Stated in terms of structural engineering, wherein the formula l i :5J

1931. Serial No. 540,094.

prescribes that for a (M) (bending moment being a function of the external load) and a given maximum allowable fiber stress (S), a certain minimum section modulus given bending moment is required, wherein I is the moment of ini Before proceeding to describe the details of our present invention, We will premise that a structural beam of the present character is composed of a pair of opposite flanges connected by a relatively thin web. The

flanges are designed to withstand the maximum bending movement which any particular load imposes upon the beam, and the web is designed primarily to resist the maximum shearing stresses. The flanges are t1ed to" the web by means of rivets, and the rivets' must be so designed as to withstand the maximum shearing stresses which are imposed upon them during the fulfillment of their function to transmit the stresses from ythe flanges into thevweb. One of the limitations coni'ronting the beam designer who is aimmg for economy of depth is due to the fact that the resisting capabilities of a given number of rivets is almost directly proportional to the 'distance of the rivets from the neutral axis of the beam; and, therefore, where, the depth is to be -kept ata predetermined amount, increased carrying capacity may be provided only by increasing the number of rivets or by designing the beam in sucha way that the rivets are subjected to multiple shear along two or more planes. Increasing the number of rivets is -not `al' Wavs feasible, and,.in manv cases, entirely heavier loads impossible due to the limitationsI imposedV by the available sizes of structural elements; and a similar difficulty frequently arises `in endeavoring to design the structure so that the rivets are subjected to multiple shear of a higher order.

For example, in the conventional type of plate girder composed of a single web plate and a pair vof angles tying. one edge of the plate to the flange, the number of rivets that may be employed is, from a practical standpoint, limited to the sizes of angles which are commercially available, and usually only two rows of rivets may be provided form. In endeavoring to support y without increasing depth of beam, efforts have been made vby designers 'to' provide for a multipleshear of higher order in the rivets, as, for example, by employing two additional web plates arranged respectively on the outsides ofy the angles referred to.

Our present invention provides in a simple, efficient, and economical manner for a plate girder which has even greater load carrying capacities, per given depth, than the last-mentioned type of conventional multiple web plate girder.

It is a more particular object of our present invention to provide a plate girder which is so designed that, for a given depth, more Arivets may be employed, and more of the rivets may be efficiently employed under multiple shear. Furthermore, our invention provides simultaneously and in a uniquely efficient manner for .enlarging .the flange area. ,All of these advantageous characteristicsl are attained without any material sacrifice of total weight or of any of the other factors entering into economical design As a result, our present plate girder is. enabled to support a greater load per given depth, or, conversely,'to withstand a given load in a lesser depth and with no increase, and possibly even` a decrease, in total cost of building construction.

We achieve the foregoing objects and advantages, and such other objects and advanT tages as may hereinafter appear or be pointed out, in the manner illustratively exemplified in the accompanying drawing, ,where- 1n u Figure 1 is a cross-sectional view of a plate girder constructeih in accordance with our present invention; s.

Figure 2 isi a fragmentary perspective view of one of the. flanges; and

Figure 3 is a graph illustrating` the ad, vantageoiisJ characteristics of sour present beam as compared with conveutiom'ilplate girders of the character mentioned.

One of the main features of our present invention lies in providing a structure wherein the flange is. a substantially T-sliaped, preferably (composite, member wherein the cross bar of the T is provided with at least three depending stems.` In the drawing, we have illustrated a preferred construction wherein the T has three stems, and it is a particular and essential feature of our invention `to construct the middle stem iiitegrally with the cross bar of the T. In Figi ure 2, for example, it will be noted that the flange is composed of the integral T-shaped member 10 having the cross bar 11 and the main depending stem 12. A cover plate 13 is preferably arranged upon the outer sui'- face of the cross bar 11. To the under surface of the cross bar 11, and on opposite sides of and spaced from the main stem 12, we provide a pair of auxiliary stems 14 and 15 which may conveniently be provided by the employment of angles of the character shown, these angles being made part of the flange construction by means of rivets 15.

Rivet holes 16 are provided in the auxiliary stems, and weY have illustratively shown two parallel rows of these holes. Two rows of rivet holes 17 aligned with the holes 16 are provided in the main stem 12. In accordance with our invention, the main stein 12 is appreciably longer than the outer stems of the T, and we provide at least one additional l'ow of rivet holes, such as the two rows 18, in this main stem.

To connect thetwo flanges thus constructed, we employ at least two web plates arranged in parallel, spaced relationship on opposite sides of the main stern 12. In the drawing, for example, we have shown two web plates 19 and 20, these plates being arranged in alternate lapped relationshipl with vthe three depending stein portions of the substantially T-sliaped flanges. Suitable rivet holes having been provided in these web plates, the assembly is completed by the rivets 21 and 22, and it'will be noted that the rivets 21 of the two rows closest to the flange are each in multiple shear along four planes, while the rivets 22 of the two rows which are relatively farther from the flange are each in double shear. i

By means of this simple and compact and obviously inexpensive construction, a plate girder is provided which has greatly in- `creased capabilities per given depth. In Figure 3, for example, we have chartered the depth in feet which is `necessary in a plate girder to permit-the rivets, regardless of how they may be arranged, to withstand the shear imposed upon them by a given load. The line 23 represents the characteristics 'of the present beam lasv illustrated in Figures 1 and 2, and it will benoted that for a given shear of, say, 1,000 tons, the present construbtion requires a depth of only 5% feet orgslightly less in order that the rivets may be capable of withstanding the shear imposed upon them `by this load. The

dot-and-dash line 24 has been shown for comparative purposes and represents the capabilities and characteristics of the conventional type of plate girder having a single web and two angles connecting one edge of the web to a flange. Regardless of the amount ofmaterialthat may be embodied in the flange of thisconventional construction', or in the web thereof, the structural arrangement of parts is such that a depthof at least 10 feet, and, in fact, -considerably greater than this, would be necessary to permit the rivets to withstand the shear iml posed uponthem by the 'illustrative load of 1,000 tons.

VThe dot-and-dash line 25 represents the capabilities' of the conventional plate girder referred to wherein ltwo additional web plates have been mounted alongside of the original plate for the purpose of subjecting the rivets to multiple shear of a higher order. This line, which to our knowledge represents the maximum capabilities of constructions of this character up to the present time, indicates that a depth of at least 62/3' feet would be required to enable the rivets, regardless of how theyI might beI arranged, toysustain the same given load.`

It is to be noted that our present invention, even in its simplest form as illustrated in Figures 1 and 2, has greater load carrying capacities'. than the multiple web. arrangement of the conventional type of plate girder. By adding. two .additional web plates to the construction of our present )invention (thereby ymaking a total of four web plates), we are enabled to provide aconstruction whose characteristics are designated by the dot-and-dash line 26 of Figure 3, from which it will be seen that the sheer of 1000 tons chosen for purposesL of comparison could be sustained within a depth as low as 41fet.e t The gaph of Figure 3 is the result of mathematical computation based 4upon the use of one-inch rivets aligned verticallyom all gauge lines and with the minimnumy allowable rivet pitch of three inches. The formula employed is the welll known formula for rivet pitch L Y i nRd gr'ws where-.-P is the spacing in inches'between successive` rivet lines; R is the maximum allowable single shear on each rivet, in tons; n is the` number of instancesl of single shear on a vertical line; (ZK-is the distance m'inches between the center of gravity ofthe rivets at one flange` and the center of gravity of the'rivets at the lopposite'iiange; S is` the total shear on the girder, in ton A According to some authorities, 'd in the above. ormula is more correctly stated as being the distance in inches between the plate 13 may be entirely center ofgravity of one flange and the center of gravity of the opposite ange. The

Ad value employed usually makes little difference in computations involving ordinary conventional plate girders, but it may make. some difference vin girders, of the Ipresent type, and a graph of the character illus-- trated in Figure, if plotted on the basis of the d value between the centers of gravity of the two opposite flanges, results in demonstrating 4even more markedly the advantages of the present construction.

In charting the lines shown in Figure 3, the ordinates represent values of S, and the abscissae represent the distance in inches between the backs of the flange angles in the conventional type-of construction and the backs of the T-shaped flanges of the present construction. The distances represented by the abscissae of the chart of Figure 3 can be readily computed from :Z ofthe formula. p

We attribute the advantages of the present construction to the provision of a substantially T-shaped flange having atr least three spaced stem portions with the middle stem or stems integral with the cross bar of the T. Where four stem portions are einployed, both middle portions are made longer than the outer stems, and correspondingly greater load capabilities may be providedfor. Y

Obviously, our construction is susceptible to a variety of modifications.` The cover omitted, or it may be augmented by additional cover plates. Spacing plates may be inserted between the angles and the under surface of the cross bar 11. The sizes of the respective parts may be altered to suit vdiffering requirements.

Preferably, though'not necessarily, the T- shaped member 10is provided by splitting a.,unitary I-beam of commercially available type along a transverse line which passes through the neutral axis where the I-beam is, symmetrical. Under certain lcircumstances, it may be found desirable to leave such I-beam intact.

Obviously, changes in the details herein described and illustrated for the purpose of explaining the nature of our invention may be made byMthose-skilled in the art without .departing fromthe spirit and scope of the invention vas expressed in the appended claims. It is 'therefore intended that these rivets comprising tworparallel, spaced plates arranged respectively within the spaces between said stem portions, and rivets for \tying the web to the fiange, certain of said rivets extending through all three stem portions and being thereby subjected to'multiple shear along four planes, certain other of said rivets extending only throughsaid middle stem portion.

2. In a plate girder, a substantially T- shaped flange with three spaced, parallel stem portions, the middle portion being appreciably longer than the other two, a web comprising two parallel, spaced plates arranged respectively within` the spaces between said stem portions, and four rows of rivets for tying the web to the iange, the of ltwo of said rows extending through all three stem portions and being' thereby subjected to `multiple shear along fourplanes, the rivets of the other two rows extending only through said middle stein portion and being thereby subjected to double shear.

3. In a plate girder, a composite, substantially T-shaped flange with three spaced, parallel stem portions, the middle lstem portion beingintegral with the crossbarof the T, the outer stem portions being rivete to said cross bar, a web comprising two par. llel, spaced plates arranged respectively between said outer stem portions and said middle stem portion, and rivets extending, through said stem portions and web plates to tiecthe web to the ange.

4. Ina plate girder, 'a compos1te, substanl tially T-shaped fiangewith three spaced,

parallel stem portions, the middle stem portion being appreciably longer than the others and being integral with the cross bar of the T, the outer stem portions being riveted to said vcross bar, a web comprising two parallel, spaced pla-tes arranged respectively between said outer stem portions and said middle stemportion, rivets relatively close to said cross bar and vext-ending through said stem portions and web plates, and other rivets relatively farther from said cross bar and extending through said web plates and only the middle stem portion;v

5. A plate' girder comprising an` I-beamfl split transversely to provide a pair of opposed T-shaped members, a pair of angles secured to the underside of each T cross bar on opposite sides of and spaced from the main stem ofsaid T so as to provide afpair *of auxiliary stems on each cross bar, `said auxiliary stems being of appreeiably iesser depth -than 'that of saidfmain stem, a pair of spaced, parallelviweb plates arranged respectively in the spaces on, each side of said main stems, and a plurality of rows of rivets, the rivets of'at least one row extending through all three stems and both interposed web plates, the rivets of at least oneA other row extending only through the main stem of each T-shaped member and the web plates on each side thereof.

6. In a plate girder, a composite, substantially T-shaped flange with three spaced, parallel stem portions, the middle stem portion being integral with the cross-barof' the T, a web comprising two parallel, spaced plates arranged, respectively, between said outer stem portions and said middle stem portion, and rivets extending through all three stem portions of the flange and through both web plates, thereby tying the web of the girder to the flange thereof.

7. In a plate girder, a composite, substantially T-shaped fiange with three spaced, parallel stem portions, the middle stem por.- tion being integral with the cross-bar of the ,T and the outer stem portions being riveted. to the cross-bar of the T, a web comprising two parallel, spaced plates arranged, respectively, between said outer stem portions and said middle stem portion, and rivets extending through all three stem .portions ofthe (Seal) CERTIFICATE oF CORRECTION.

Patent No. 1,906,683. May 2, 1933.

WALTER H. WEISKGPF, IET AL. Y

It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correction as follows: Page l, line 67, for "movement" read "moment"; page 2, line 15, for "form" read "for"; and line 117, for "chartered" read "charted"; page 4, commencing with line 25, strike out all to and through line 35, which comprises present claim 3; same page, lines 36, 51, 69 and 80 respectively, for the claim numbers "4, 5, 6, and 7" read "3, 4, 5, and 6"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 8th day of August, A, D. 1933 M. J. Moore.

Acting Commissioner of Patents.

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