US1360931A - Roof-truss - Google Patents

Description

H. w.` GRAVES.

Roof TRuSs. APPLICATION FILED JAN. 23,-1920.

, UNlTEDfs'TATES PATENToFFIcE.

HENRY W. GRAVES, F CHICAGO, ILLINOIS, ASSIGNOR OF ONE-FIF'IIHEO ALBERT SCHEIBLE, 0F CxHICAGO, ILLINOIS. i l

ROOF-TRUSS.

Specification of Letters Patent.

Patented Nov. 30, 1920.

Application filed January 23, 1920. Serial No. 353,602. i

Chicago, Illinois, have invented certain new and useful Improvements in Iioof- Trusses; and I do hereby declare the fol-l lowing to be a full, clear, and exact description of the invention, `such as wiIl enable others skilled in the art to which it appertains to make and use the same.

My invention relates to roof trusses,l one i of its general objects being that of providinga roof truss which will be unusually light, easy to manufacture, low in cost and easy to erect in proportion to its strength and rigidity. In another aspect, my in- -ven'tion .aims to provide a roof truss for an arched roof, involving 'relatively few compression members, and so designedas to impose relatively light .strains on the tension members.- In a Afurther aspect, my

invention aims to`provide an arched roof truss arranged for automatically distributing unbalanced loads from one lateral half of the truss to the otherl half by 'applying strains equivalent to what would constitute a balancing load; forbwhich purpose, my invention aims to provide a truss divided medially into two halves by a compression member affording pivot means about which the top chord may rock; and by providing separate bracing` for each of the truss halves to resist a distortion of the top chord portion thereof. Furthermore, my invention aims to provide the bracing for each truss half in such a manner as to obviate the-.needof either vertical or oblique struts. Still .further objects4 of my invention will be apparent from the following specification andfrom the accompanying drawings, in which drawings. l

Figure 1 is an elevation of a truss embodying my invention.

Figs. 2, 3 and 4 are enlarged sections taken along the correspondingly numbered lines in Fig. 1.

Fig. 5 is a diagrammatic view of another truss embodying my invention and having a larger number of tension members than of the truss of Fig. l.

Referring to the embodiments of the drawings, I accomplish the purposes of my invention in four ways:

First, by employing only two members having the stiffness required for resisting compressiom'namely an arched upper chord and a single vert1cal strut connecting the center points of the upper and lower chordsY of the truss.

Second, by employing tension'mem'bers radiating respectively from the juncture of the strut with the bottom chord and from the ends or heels of the truss, which tension members all are connected at their other ends to the top chord and are each disposed entirelyAvithin one lateral halfgof the' truss;

Third, by including amon'g these tension members elements arranged vin pairs, with the members of each pair respectively connecting a single point of the top chord with the center of the bottom chord andone end of the bottom chord,

And fourth, by employing a parabolic shape for the to chord and so spacing the points at which t e pairs of tension members are connected tothe top chord that these points will be equally spaced in a direction parallel to the bottom chord.

For example, in the diagrammatic embodiment of-F ig. 5, the top chord 1 is in the form of a parabola having its principal axis vertical, and this axis coincides with the medial line of a strut 2 which connects the middle ofthe top chord l with the middle point of the bottom chord 3. Of these members, both the top chord and the strut are of such angular section as to adapt them to resist compression strains, while the bottom chord is designed for resisting tension only. Radiat-ing from the middle point A of the bottom chord (or from the juncture ofthe latter with the single strut Q) are tension members 4 connected at their other ends to. points on the top chord respectively disposed at right angles to equidistant points on the bottom chord, or on a line parallel to the latter as indicated in Fig. 5. These same points on the top chord in each lateral half of the truss'are alsoconnected by tension membersy 5 to the nearer end of the truss, although such a tension member may be and the nearest pointfrom which the latter is connected to the center point of the boty tom chord. That is to say, the tension members in each 'half of the truss aredisposed in pairs (such as the members 4a and 5 in Fig. l) with the members of each pair connecting a single point on the top chord With the opposite ends of the corresponding l half of the bottom chord; althoughthe comi panion member to the lowest radial tensionelement 4b may be omitted in practice, as 'it would substantially coincide with one end portion of the top chord, and this portion of the top chord is ample in practice to resist the tension strains which would 4ot the truss.

fall upon a corresponding `tension member.

'lVith the truss thus arranaged, the parabolic vformof the top chord automatically distributes the strains due to a load dis.

. of the top vchord in Fig. 5, this load would tend to cause a downward deflection or. fiattening of the left-hand half of the top chordth,ereby tending to rock this top chord about lits medial point C 'and correspond- .inglyvtending to cause an upward bulging orgreater convexing of the right-hand half of the top chord. However, anysuch -upward bulging tendency will be resisted by the tension members 4 in ythe right hand half of the truss. and the vertical components of the tension due to the resulting strains on these normally unloaded tension' members will producean -upwardly directed stress on the strut 1l, thereby placing the members 5f and 5e under tension. Likewise, the upward bulging tendency of the righthand halic of the top chord will place the members 5 and 5d under tension, sothat the members 4 and 5 in the right-hand half of the truss will all exert downward strains on the 'top chord having a Joint effect equ1va'- lent to that of placing a balancing load on the right-hand halt' of the top chord.

Moreoven'since the top chord is parabolic -in shape and since the tension members lead from the end of the right-hand halt ot' the bottom chord to points so spaced along the top chord as to correspond* in spacing to equal strain distributions 'in a parabolicv chord.y (namely to points at right angles tov -50 equidistant points on the bottom chord) there will be no resulting strains requiring either vertical or oblique auxiliary struts to resist the same.

load distribution on the roof without employing any struts other than the-strut 2,

which str ,it divides the truss into two halves and whic `rigidly spaces the center points of the top and bottom chords so as to afford a leverage about which an unbalancedload on one-half of the truss can rock the top4 I am therefore able to` .take care of the strains due to an uneven the medial vertical member of the truss, I `am able to reduce the weight and cost of the truss considerably over` that required for the'types of roof trusses heretofore in use. Moreover, since the tensionmembers ot' my truss are normally unloaded (owing to the parabolic form ofthe topchord, the mathematically proportioned vspacing of the connecting points on'each haltl of, the top chord, and the arrangement of thesetension members in pairs), I can employ tension members of relatively light weight and cost. Furthermore, sinceeach of the tension members is disposed entirely in one lateral half ofthe truss, -I not only greatly reduce the weight of these members. over that required i n trusses employing tension members reaching from one lateral half of a truss into the other, but also greatly reduce the strains on sucli members'due to lunbalanced load effects on the top chord. Consequently, I can further decrease thecrossfsectiona-l size and cost-of these tension members as compared with those required for 4trusses in which the tension members are not each confined to'a'single lateral half of the truss.

liVhile various elements of the truss are connected to onejanother theoretically at the same points, it will be understood that in practice some of these connections'may be made through gusset plates or the like as in# termediaries'; and it will'also be obvious that the cross-sectional shapes of different members of my truss may conform lto common practice in truss construction. For example, in the truss of. Fig. 1, the top chord is bent fromv a pair of steel angles G bolted to each other at their centers throughgussetplates 7 and at their .ends through heelplates 8, which heel plates also afford the connectionsv between the two ends ofl thetop chord and i the bottom chord. This bottom chord is here shown as a single angle bar 9, and has an. other gusset plate l0 riveted to its middle. The gusset plates 7 and 10 also form the connections from the top and bottom chords to the vertical strut which forms the-medial compression member' of the truss and which is here shown as consisting of two angle bars 11 riveted to opposite sides of the gusset plates Q7 and 10. The latter plate also` forms the means of @onnectng the tension membersfl to the center point of the bottom chord that is to say, the lower ends of these tension members 4 are all riveted to the gusset plate 10 at suchpoints that the members 4 radiate from the middle point A in the angle-bar forming the lower chord. The upper 'ends of the tension members 4' and of the 4companion tension members 5 are here shown as interposed between the two angle bars 6 forming the top chord and as'jointly riveted to these angle bars, after the manner of Fig. 3, thus affording single connections between the topchord and the pairs of associated tension members.' However, at

the centerv of the truss, the longest tension members c and 5f desirably are riveted to which the upward vertical component of the tension on all of the members 4. is transmitted by the strut 11 to the longest tension members 5c and 5f. i

IVhile the truss illustrated in Fig. l only has tension members radiating from' the point A to two points ineach half of the top chord, it will be obvious that the number of such connected points maybe varied in accordance with the relative height and spread of the trusses and `with the floads for which the latter is designed. However, `the shortest tension members 5d may be omitted in practice, as' being too nearly coincident with the adjacent end portions of the top chord. Furthermore, While I have complied With the Astatutes by illustrating and describing the truss 'of my invention 'in a desirably commercial embodiment, I do 'not Wish to be limited to the details of the construction and arrangement thus disclosed,

nor to the use of t-he mentioned materials,l it being `obvious that the same might be modied in many Ways Without departing from the spirit ot' my invention -as disclosed in the appended claims. Neithendo I Wish to be limited to an exact conforming of the arch member of my truss to fa parabolic curve, since this can only be approximated in the practical construction of such trusses.

It will be-noted from Fig. 5 that the bracing ofthe arch is eiiected entirely by Web` members forming triangles connect-ed at their apices to thearch and each having half of themain chord as .its base. (In this aspect, the central 'strut 2 forms a side of two of the triangles). The bracing is therefore quite simple, and by employing a parabolic arch With the connections to it spaced.

as described, I reduceV the strains on the Webs so that these can'be unusually light in proportion to the size ofthe archl and the load for which the latter is designed. By making these connections to the arch at an odd numbervof points, I can readily use the medial web as a means for distributing` an unbalanced load from one half of thearch to the other, -vvhile the radialy disposition of part of the tension members prevents an undue bulging or' deiecting ofthe-arch 1 with such an uneven load distribution.

Moreover, I do not Wish to be limited to the employment of the structureo my .in-t

vention as a rooiC truss, since it' could obviously be used `With equal facility as a bridge truss or as a girder for other purnoses. f

of the parabola,

truss and connecting the 'arch with the main chord, and bracing means-associated with each half ofthe trussfor resisting an increased convexing of one-half of the arch by an excessiveloading of the other halt` thereof.A n

2. Aroof truss -as per claim 1, the bracing means for .each truss half conin which sists entirely `of tension members connecting the ends of the bottom chord portion of that trnss'half with vpoints on the top chord portion of the same truss half, which points are `respectively at right angles to the bottom chord opposite equidistant points on the latter. l

v3. A roof truss as'per claim 1, in which the bracing means for each truss half con'- sists entirely of tension members disposed oblique` to the Abottom chord and connecting the top chord portion of the same truss half with the ends of the bottom chord portion of the same truss half. l

4. A roof truss comprising a top chord curved in the -form ofV a parabola, a bottom chord disposed at right angles to the axis a strut connecting the center of the top member and the bottom chord and tension members arranged in pairs, the members of each pair connecting thesame point onv the top chord respectively with the lower end ofthe strut and the nea-rer heel of the truss.

A roof truss comprisinga substantially parabolic compression top chord, a bottom ch'ord at right angles to the axis of the parabolawdefined by the top chord, members connecting the center of the top chord respectively with thecenter and the tWo ends` of the bottom chord, and other members arranged in pairs with the members of each Vpair connecting the same point of the top .parabola defined bythe top chord, a strut connecting the centers of the top and bottom chords, tension members connecting the cen ter` of the top chord respectively with the ends of the bottomxchord, and other tension members each disposed entirely in one lateral halt1 of the truss; the said other tension members all connecting points .on the top chord with ends of that half of the bottom chord which is opposite the said points.

7. A roof truss comprising a substantially parabolic compression top chord, a bottom ioo chord at right angles-4to Vthe axis ofthe parabola defined by the toprchord, a strut connecting lthe centers of the top and bottom',`

chords, tension members connecting the cen- 4,ter of the top chord respectively With the ends of the bottom chord, andothervtensioi members each disposed entirely in' one lateral halfof the truss; the said other tension :members all connecting points' on the top chord With ends of that half of the bottom vchord which is opposite the said points and 'including'pairs of members respectively conxnecting the same points of the top chord with' the nearer half-bottom-chord ends. i

8. A truss structure comprising an arch, a lmain chord. for the, same, Web members Vconnectingthejmiddle of -the 'chord with v various points on 4the'arch, and web' members respectively connecting the same points with the nearer end of the chord.

` ,1.9. A truss structure comprising a' sub- I 4'stantialkly parabolic arch, and Web members arranged in pairs all connecting a single A4point axial of the arch with the ends-of the i secutively spaceduniformly from each otherV land -fromfthe end sof'the arch in a` direc- ,Y tion parallel tothe chord, andWebs con- .necting each of the same nearer end of the chord. v

-Yarch, ,the members of each pair being sub-. stantiallyv jointly connectedv to each other and to the arch. u .1 l y 10. A'truss structure comprising a para l bolic arch, a' main chordatright angles` to` the axis thereof, Webs connecting the middlel p of the'chorduwith points on the arch cone points with the A truss structure comprising a parabolic arch, and web members radiating from the ends -of the arch and from a point axial thereof, Y. the said Web ymembers being con- I nected in pairs to each other and to the arch at an odd number of pointson the-latter'consecutively spaced uniformly from each other and from theends of the arch in aydirec-gI `in a direction at right anglesto the -axis of -vthe arc'hfthe Web members including a compression member axial of thearch, all other web members being'tension members.

13. A truss structure including a para` boliclarch, a bottom chordfor the same, ano i secondary chords connecting each end of the arch `with points on "the 'arch" respectively disposed on equidistant lines normal tothe bottom'chord v 14. A truss structurecomprisi'ng an arch,

`a main chord, and auxiliarybracing members consistingI entirelyl 'of web members forming La plurality'ofl triangles vconnected at their apices to the arch and eachhaving yhalf of the mainchord as its base.

' "Signed at' Chicago, January 21st, l920.

.HENRY W. GRAVES.

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