US1704235A - Metallic joist - Google Patents

Description

March .5, 1929.

w. F. zmaRlsKlE- METALLIC JoIs'r Filed March 5, 1928 anoznurb Palentled Mar. 5; 1929.

Aumn-:D STATES,

PATENT OFFICE.

WILLIAM F. ZABRISKIE, 0F DETROIT, MICHIGAN, ASSIGNOR T0 GABRIEL STEEL COM- IPANY. DETROIT, MICHIGAN, A CORPORATION 0F MICHIGAN.

METALLIC JOIST.

Application filed March 5,

vThe invention relatesl to metallic floor joists ofthatv type comprising an upper chord member formed from a straight bar of structural shape and of greater strength than vrequired for compression stresses only, said bar being reinforced by a lower chord Amember connectedthereto through the medium oi a zig-Zag bent bar or webbing welded at the several points of contact. The principal advantage of this type offstructure is that joists of considerable range of span can all be made Jfrom bars of the same cross section, the only variation being in length and the number of bends or diagonal portibns in the webbing; also on account of the intrinsic strength and rigidity of 'the upper chord member the spacing between points of attachment ofthe webbing is increased so as to diminish the number of welds necessary. Still a further advantage is that the projecting ends of the upper chord member may be used for engaging the supports for the beam and are of sufficient strength and rigidity to take 'care offslight variations in length of span without alteration in the webvbing or lower chord member. 'This is accomplished by permitting Va slight spacing between the portionV of the upper chord l member resting on the support and the point of attachment of the first of the diagonal-- web members. However, it .has ,b'eenfound that there are some objectionsv to the followingv of this practice such as increase inv delection and-vibration of the floor.

It is one of the objects of the presentI invention to obtain a construction-which avoids any spacing betweenthe point of support and the lirst of the diagonal web members 'Y and which at the same time permits of a limited variation in length of span in joists composed of the same-structural elen'iets.

It is a further object'to employ a lowerV chord member which is extended in a straight line beyond the point of attachment to the outermost diagonal web members to be equalin extent to the ceiling and to form a support therefor. l i l With these objects `in,view the invention consists in the construction as hereinafter set forth. 4

In the drawin s; i

Figures l an 2 are diagrammatic side elevations showing my improved joist as adapted for slightly diierent lengths of Span' webbing thereto. `ably'of angle section which 'constitutes the 192s. serial N; 259,226,

l Figure 3 is an enlarged side elevation illustrating the method ot' attaching the web members for variation in length of span while using the same members.

Figure 4 is a cross section'thereof.

Figure 5 is an elevation of a portion of the joist. .g

The upper chord member A is formed of a metallic bar of structural shape Whichis illustrated as a T-head B, a web C, a lower flange D projecting on one side of the web. The opposite side of the web is unobstructed at its lower edge to permit of attaching the E is a straight bar preterlower chord of the truss. and F is the webbing also preferably formed of, angle bars. With joists of this type as heretofore constructed it has been usual to form the end diagonal web members as bent extensions of the lower chord member while intermedi- 'ate these Hend diagonalsv a suitable number of intermediate diagonals are formed from another lbent bar. With such a construction there will be a fixed length between the pointsl of attachment of the end diagonals to the upper chord member so that any variations in length of span will change the relation of these points tothe supports for the beam. With my improved construction the lower chord member is as previously described, a straight bar throughout its length and the'end diagonale of the webbing are formed of separate bars. These are, however, bent tobe integral with 'an oppositely angling diagonal but are separate from the bar forming the intermediate portion of the webbing ifl such is necessaryl Thus, where there are slight variations in length of span the end webbing member F may be spaced slightly from the adjacent webbing member F in its attachment to the upper chord member Vand nrso doing the end diagonal of the member F -may be attached to the member A immediatel'y'adjacent to the support for the beam. This spacing between the web members is not detrimental Y :forA the reason that the depth of the web C,r4 isbsuiiicient to' extend considerably belowA the neutral axis of the chord memberA.

105. i This will 4provide vweld ing.suraces for the to the distance which these lweb members `may* be spaced from each other but that is large enough to provide a considerable variation in length of span. Any further variation must be obtained by changing the angles off the diagonal bars.

Asl shown in detail in F'gure -3 the web member F has its vertical flange overlapping the web C of the chord member A to form a` welding bearing G. In thesame mannenthe web member F overlaps the bar A to form a kwelding .bearing G. These bearings G and G arespaced from each other by a considerable distance but the ex` tension of the center of gravity lines of said! web members indicated by the dotted lines H and I-I will intersect the neutral axis of the bar A indicated by the dotted rline I in a point' J or at least in a point which .will fall within the vertical dimension of said bar. It will be understood that the placing' of the members F, F nearer to each other would be inno way detrimental but it is desirable not to space them further than as indicated in Figure 3.

In addition to the` advantages already given my improved construction has the further advantage that the bar A may be cut to exact length thereby avoiding any waste omaterial in an unnecessary overlapping of the support. Also the bars E may be cutL to exact lengths while the web members F and F may be made of standard lengths.

As shown in Figure 5, the end lweb member Fy is of somewhat,^ greater cross-.section than the intermediate web members YF, Such construction is advantageous in certain cases as the end web-member ,is subjected to hi her stresses than those nearer the center or the span and by reason of the l fact that it is separate from the center` web member, such a change in section' may be readily accomplished.

What I claim as my invention is:

1. A metallic joist comprising a top.

chord member formed of a'structural shape, a bottom chord member and a plurality of web members each having' reversely inclined diagonals extending between and ses curedb to `said top andfbottom chord memf bers, the points of attachment of the adjacent ends of said web members ton/said top chord member being variably spaced tov compensate for. limited variations in the lennth of span but remainlng substantially within the limits where their respective center of gravity lines intersect in a point lying within the vertical dimension of the top chord member.A

2. A metallic oorjoist comprising atop chord member formed of a structural shape Vhaving a T-head, a vertical web and a bottom ange on one side only of said web, a bottom chord member and plurality of web members each formed of a bar bent to form opnositely inclined diagonals, said web members extending lbetween and welded to said top and bottom chord members, and the points of attachment of their adjacent ends to the web of the top chord member being below the neutral axis thereof and variablyspaced to remain substantially within the limits where their center of gravity lines intersect in a point lying within the vertical dimension of said Itop chord member.

3. A metallic floor joist comprising a top chord member formed of a structural shape having a greater strength than required for bending in a vertical plane, a bottom chord Amember and a plurality of web members connecting said bottom chord to said top web members being variabl spaced from each otherin their points o attachment to said upper chord member to com ensate for limited variations in' length o span but within the limits where their center of gravity lines intersect in a point lying within the vertical dimension of said top chord member.

4; A metallic loor joist comprising a top chord member formed of a structural shape having greater strength than required for compression only to ,increase resistance lto bending in\a vertical plane, a bottom chord member and a plurality of web members each having reversely inclined diagonals connecting said bottom chord to said .top chord -member, the adjacent ends of said 'web members being variabl -spaced from Ieach other in their points o attachment tok said upper chord member to com ensate for limited variations .in length o Fspan but within the limits where their center of gravity lines ,intersect in a point 1 ing within the-vertical dimension of saidy top chord member and the outermost of said web members being of a (greater. cross-section than the intermediate web members.

ycompression only to increase resistance to v WILLIAM F. ZABRISKIE.

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