US1762786A

US1762786A - Truss

Info

Publication number: US1762786A
Application number: US257459A
Authority: US
Inventors: John L Mckeown
Original assignee: Individual
Current assignee: Individual
Priority date: 1928-02-27
Filing date: 1928-02-27
Publication date: 1930-06-10
Anticipated expiration: 1947-06-10

Description

June 10, 1930. J. MCKEowN TRUSS Filed Feb. 27. 1928 l A TTORNE Y.

Patented June 10, 1930 UNITED STATES JOHN L. MCKEOWN, OF CHICAGO, ILLINOIS TRUSS Application filed February 27, 1928.

This invention relates to trusses, and relates particularly to trusses of the type commonly known as bow string7 trusses, comprising bowed top chords consisting of pieces of lumber secured together flatwise with their adjacent ends in contact with one another by means of glue, nails, bolts, screws or any combination thereof, to form a plurality of superposed layers, a bottom chord 10 made of steel bars, rods or angle irons which connects opposite ends of said top chord, and web members which connect said top and bottom chords.

As is generally well known, the coefficients of expansion and contraction under heat and cold, of the timber top chords and the metal bottom chords of trusses of the type specified are very different. For example, in the case of a bottom chord made of steel bars (or angles) the elongation and contraction of the bottom chord of a unit truss 100 feet long, between mean summer and winter temperatures is approximately 1 and 1A, inches, whereas the corresponding elongation and contraction of the timber top chord will be comparatively negligible. Obviously, therefore, the elongation and contraction of the bottom chord under variations in temperature will produce a very slight change in the curvature of the top chord, the radius of curvature increasin in length with elongation of the bottom c ord under expansion and decreasing in length with the shortening of the bottom chord under contraction.

Obviously, also, flattening of the top chord, due to elongation of the bottom chord would tend to produce uncalcuable secondary stresses in said top chord, which may very materially reduce its strength and the loads which it will carry.

A principal object of the present invention is to provide a truss having a bowed top chord of the type specified, so constructed that the secondary stresses produced in the top chord by changes of curvature due to elongation and contraction of the bottom chord, will be practically eliminated and the calculated strength of said chord and of the truss will remain substantially constant regardless of temperature conditions,

Serial No. 257,459.

In accordance with the present invention, my improved truss comprises a bowed top chord consisting of pieces of lumber secured together flatwise, and arranged end to end in abutting relation, to form a plurality of superposed layers, the abutting ends of the piece of lumber having interlocking engagement with each other, adapted to rigidly connect the abutting end of said pieces of lumber.

Specifically, interlocking engagement of the abutting ends of the pieces of lumber of different layers of the top chord is effected by making the ends thereof correspondingly curved, one thereof being convex and'the other concave, the axes of curvature thereof being substantially parallel with the axes of curvature of the top chord of the truss.

Also, to provide for bodily fiexure of the truss as a whole, the top chord of the truss also comprises a plurality of sections, which also are secured together end to end in abutting relation, and which have articulated engagement with one another, this being effected by making the abutting ends of adjacent top chord sections correspondingly curved, one thereof being convex and the other concave. Said sections are secured together by means which will connect the sections of the truss to form a unitary structure of sufficient strength to carry the loads which it is designed to sustain in use and, at the same time permitting sufiicient flexibility and play in the joints to permit relative movement thereof to compensate for differences in curvature due to expansion and contraction of the lower chord of the truss under varying temperature conditions.

The means for connecting the sections of the top chord of the truss comprises the various features, combinations of features and details of construction hereinafter described and claimed.

In the accompanying drawings in which my invention is fully illustrated- Figure l is a side view of a truss embodying my invention and improvements.

Figure 2 is a sectional plan view of the truss on the line 2 2 of F ig. l.

Figure 3 is an enlarged fragmentary top plan view of the left hand end of the truss as shown in Fig. l.

Figure 4 is an enlarged fragmentary side View of the truss showing the joint for connecting abutment sections of the top chord of the truss.

Figure 5 is a fragmentary sectional View on the line 5 5 of Fig. 4; and

Figures 6 and 7 are detached detail views.

Describing the invention with particular reference to the drawings, A designates the top chord of the truss as a Whole, B the bottom chord thereof, and c Web members which connect said top and bottom chords.

The top chord A consists of a plurality of superposed layers a. consisting of separate pieces of lumber l secured together fiatwise by means of glue, nails, bolts,

` of the top screws, or any combination thereof, the pieces of lumber forming each layer being arranged end to end in abutting relation and the abutting ends of said pieces having interlocking relation so that they will be rigidly connected. in the preferable construction shown, desired interlocking engagement of the abutting ends-of the pieces of lumber forming the different layers, respectively, of said top chord is effected by making the abutting ends thereof correspondingly curved, one thereof being convex and the other concave, as shown at 2, see particularly Fig. 4.

The pieces of lumber l may be of uniform or random lengths.

The lines of severance of the different vlayers a of the truss at the joints 2 will, of

course, tend to weaken the truss somewhat, and to minimize this weakening effect, the pieces of lumber l of different layers a are so proportioned and arranged that said joints 2 of different layers are staggered lor out of line with each other to as great an extent as possible. bviously, weakening chord-and thusl of the trusswill be further reduced by the interlocking character of said joints 2.

As shown, also, the convex and concave ends, respectively, of the pieces of lumber 'forming adjacent layers a of the top chord are oppositely disposed-that is face in op-A posite directions.

In accordance with my invention, the secondary stresses'i'n the top chord produced byivariations in curvature thereof due to 'elongation and contraction of the 'bottoni chord of the truss are practically eliminated by making the top chord A of the truss in separate sections Which are Hexibly secured together, end to end, in abutting relation, the engagement and connection between abutting ends of said top' chord sections being constructed and arranged to form aunitary structure which issufliciently strong to carry its designed loadwhile, at the .same time, permitting lieXure of the joints connecting the abutting ends of said top chord sections under variations in curvature of said top chord.

As shown, said top chord consists of three sections, lcomprising a middle section A and symmetrical end sections A?, A3, the abutting ends of said topjchord sections being correspondinglycurved, onel thereof` being convex and the other concave, as shown at ll, Figs. and el, thus forming joints' which will permit said sections to flex freely with reference to each other under variations of curvature of the top chord. As shown, both ends of the middle top chord section are convex, and the abutting ends ofthe end top chord sections A2, A3, are concave. j

In the preferable construction shown, also, said top chord sections are secured to'- gether by means of splice plates which may include splice plates il, secured tothe sides of the abutting ends of the top 'chord vsections and other splice plates 5 secured to the top and bottom sides of said top chord sections so to overlap thejoints 3 at the abutting ends of said sections. bly invention, however, contemplates' omitting either the side plates 4 or the top and bottom plates 5. f

As shown, said splice plates 4 and 5 are connected together in pairs by means of bolts 6 which extend through holes formed in and through the top chord sections of the truss, which extend through slots 7, see particularly Figs. l and' 5, formed in the 'pairs of splice 4plates 4 and 5, said slots being proportioned both in length and width to permit contemplated iiexure of the joints connecting abutting ends of the top vchord sections, which will be Very slight in anyd event.

Also, in order that said splice plates 4 and shall not bind upon the sides of the top chord sections and-thus -clampabutting Y ends of said top chord sections firmly together so as to prevent relative leXure of the aouttinU ends of said top chord sections at the joints 3, the means for connecting said sections also comprise (see particularly Figs. 5, 6 and 7) bushings 8 seated in sockets 9 formed in the sides-both lateral and top and bottom-of said top chord sections, the relation being such that the outer ends of said bushings will be substantially flush* with the surfaces of the top chord vsurrounding the same.

In the preferable construction. shown, the bushings 8 are made in the form of truncated cones, the bases thereof being disposed outwardly and their inner ends resting against the bottoms of the sockets 9. As shown, also, ribs l() are formed on the bushings 8 which become embedded insides of the sockets 9 when said bushings are" n fil-i forced into said sockets, thus preventing turning of said bushings.

Inserted beneath the heads of said bolts and the nuts threaded thereto are washers 11, and inserted over said bolts between said washers and the ends of the bushings 8 are sleeves 12, said sleeves being sufiiciently longer than the thickness of the splice plates 4 and 5 to insure sufficient clearance between said splice plates and the bushings 8 and washers 11 to permit flexure of the joints 3, while, at the same time, preventing lateral tiexure of said top chord section at said joints.

In accordance with my invention, also, the bottom chord B of my improved truss consists of spaced members, comprising central sections 13 and

symmetrical end sections

13, 132, the ends of which, respectively, are rigidly connected to opposite bottom chord sections 13 and which are bent between their ends to form stirrups, as shown at 14, which form abutments for the ends of the top chord A and through which stresses are transmitted to the bottom chord of the truss.

Preferably the

chord members

13, 13, 182, are made of steel bars or angles and are rigidly connected in spaced relation by means of spacing members 15 inserted between opposite sides of said bottom chord at intervals and riveted or otherwise rigidly secured thereto.

In the preferable construction shown, the stirrups 14, instead of forming separate members or elements, as heretofore has been common, are formed directly by the

end sections

13, 132, thus providing for making the bottom chord of the truss of structural steel bars of standard commercial lengths and eliminating the expense of mal'- ing separate stirrups and providing means for anchoring the ends of the bottom chord of the truss thereto.

The web members c preferably consist of angle bars secured to the outer sides of the top and bottom chords, the lower ends of which are riveted or otherwise rigidly connected to opposite side members of the lower chord and the upper ends of which are sccured to the sides of the top chord A by means of bolts. As shown, said web members comprise upright members 16 and oppositely inclined members 1G', 162, arranged substantially as shown. Preferably, also, corresponding web members on opposite sides of the truss are connected by means of spacing blocks 17 riveted or otherwise rigidly secured to the web members which they connect. The construction of the truss, as regards the arrangement of the web members c, may be variously modified, as may be desired, Within the scope and contemplation of my invention.

I claim:

1. A truss of the general type specified,

comprisingl a bowed top chord consisting of pieces of lumber secured together flatwise to form a plurality of superposed layers, the pieces of lumber forming said layers, respectively, being arranged end to end in abutting relation and having interlocking engagement with one another.

2. A truss as specified in claim l, in which the abutting ends of adjacent pieces of lumber are correspondingly curved, one thereof being convex and the other concave and the axes of curvature thereof being substantially parallel with the axis of curvature of the top chord of the truss.

3. A truss as specified in claim l, in which the abutting ends of adjacent pieces of lumber are correspondingly curved, one thereof being convexv and the other concave and the axes of curvature thereof being substantially parallel with the axis of curvature of the top chord of the truss, and the pieces of lumber forming adjacent layers ofthe top chord being arranged with their convex and concave ends, respectively, disposed toward opposite ends of the truss.

4. A truss as specified in claim 1, in which the pieces of lumber forming different layers of the top chord of the truss are arranged so that the pieces of lumber of each layer will overlap the joints at the abutting ends of adjacent layers.

A lower chord for a truss of the type specified, made of spaced metal bars and comprising a central section and substantially symmetrical end sections, and spacing members secured between and which ri gidly connect the spaced bars forming each of said sections respectively, said end sections being formed by separate bars bent liictwcen their ends to form stirrups forming abutmcnts for the ends ofthe bowed top chord, the ends of the bars forming the end sections of said bottom chord being rigidly secured to the opposite ends of bars forming the middle section of said bottom chord.

G. A truss as .specified in claim 1, in which the top chord of the truss comprises a plurality of sections arranged end to end in abutting relation, and means for connecting said sections constructed and arranged to permit fiexure of said top chord at the abutting ends of said sections to compensate for variations in the curvature thereof corresponding to variations in the length of the bottom chord due to temperature changes.

7. A truss as specified in claim 1, in which the top chord of the truss comprises a plurality of sections arranged end to end in abutting relation and having interlocking engagement with one another, and means for connecting said sections constructed and arranged to permit fiexure of said top chord at the abutting ends of said sections to compensate for variations in the curvaturel n oo thereof corresponding to variations in the length of the bottom chord due to temperature changes. i

8. A truss of the general type specified, comprising a bowed top chord made of lumber and a metal bottom chord, said top chord consisting of a plurality of sections arranged end to end in abutting relation, and means for connecting said sections constructed and arranged to permit flexure of said top chord at the abutting ends of said sections to compensate for variations in the curvature thereof correspondingr to variations in the length of the bottom chord due to temperature changes.

9. A truss as specified in claim 8, in which the abutting ends of the top chord sections are correspondingly curved, one thereof being convex and the other concave, the axes of curvature of said abutting ends being substantially parallel with the axis of curvature of said top chord.

10. A truss as specified in claim 8, in which the means for connecting the top chord sections consists of plates bolted to opposite sides of the abutting ends of connected sections provided with slots to receive said bolts and which extend substantially at right angles to radii of said top Chord passing through said bolts.

11. A truss as specified in claim 8, in which the abutting ends of the top chord sections are correspondingly curved, one thereof being convex and the other concave, and the means for connecting the top chord sections consisting of plates bolted to opposite sides of the abutting ends of connected sections provided with slots to receive said bolts which extend lengthwise of the top chord, the length and width of said slots being proportioned to permit contemplated flexure of the top chord at the abutting ends of the sections thereof.

l2. A truss as specified in claim 8, in which the abutting ends of the top chord sections are correspondingly curved, one thereof being convex and the other concave, and the means for connecting the top chord sections consisting of plates. bolted to opposite sides of the abutting ends of connected sections provided with slots to receive said bolts which extend lengthwise of the top chord, the length and width of said slots being proportioned to permit contemplated f flexure of the top chord at the abutting ends of the sections thereof, said connecting means also comprising spacing sleeves adjusted over said bolts between the heads thereof and the nuts threaded thereto, respectively, and the sides of said chord sections, said sleeves being proportioned to permit contemplated relative flexure of connected chord sections.

13. A truss as specified in claim 8, in which the abutting ends of the top chord sections are correspondingly curved, one thereof being convex and the other concave, and the means for connecting the top chord sections consisting of plates bolted to opposite sides of the abutting ends of connected sections provided with slots to receive said bolts which extend lengthwise of the top chord, the length and width of said slots being proportioned to permit contemplated flexure of the top chord at the abutting ends of the sections thereof, said connecting means also comprising spacing sleeves adjusted over said bolts between the heads thereof and the nuts threaded thereto, respectively, and the sides of said chord sections, said sleeves being proportioned to permit contemplated relative flexure of connected chord sections and in which, also, bushings are secured in sockets formed at the ends of the bolt holes, against which the spacing sleeves adjusted to said bolts abut.

14. A truss as specified in claim 8, in which the abutting ends of the top chord sections are correspondingly curved, one thereof being convex and the other concave, and the means for connecting the top chord sections consisting of plates bolted to opposite sides of the abutting ends of connected sections provided with slots to receive said bolts which extend lengthwise of the top chord, the length and width of said slots being proportioned to permit contemplated fiexure of the top chord at the abutting ends of the sections thereof, said connecting means also comprising spacing sleeves adjusted over said bolts between the heads thereof and the nuts threaded thereto, respectively, and the sides of said chord sections, said sleeves being proportioned to permit contemplated relative fiexure of connected chord sections and in which, also, bushings are secured in sockets formed at the ends of the bolt holes, said bushings forming truncated cones and the sockets in the top chord which receive them being correspondingly tapered.

A truss as specified in claim 8, in which the abutting ends of the top chord sections are correspondingly curved, one thereof being convex and the other concave, and the means for connecting the top chord sections consisting of plates bolted to opposite sides of the abutting ends of connected sections provided with slots to receive said bolts which extend lengthwise of the top chord, the length and width of said bolts being proportioned to permit contemplated iiexure of the top chord at the abutting ends of the sections thereof, said connecting means also comprising spacing sleeves adjusted over said bolts between the heads thereof and the nuts threaded thereto, respectively, and the sides of said chord sections, said sleeves being proportioned to permit contemplated relative exure of connected chord sections and in which, also, ribbed bushings are secured in sockets formed at the ends of the bolt holes, said bushings forming truncated cones and the sockets in the top chord which receive them being correspondingly tapered.

In Witness that I claim the foregoing as my invention, I aix my signature this l5 day of February, 1928.

JOI-IN L. MCKEOWN.