US1973882A - Roof truss - Google Patents

Description

w. M. PRATT ROOF TRUSS Sept. 18, 1934.

Original Filed'se i. 1a. 1929 2 Sheets-Shed 1 INVENTOR Mf fiffra t6 BY Sept. 18, 1934. w RA T 1,973,882

ROOF TRUS S Original Filed Sept. 16, 1929 2 Sheets- Sheet 2 mmvrox (B i i zzter/t- Pra a Patented Sept. 18, 1934 UNITED STATES FATE Application September 16, 1929, Serial No. 392,964 Renewed February 7, 1934 4 Claims.

This invention relates to structural trusses and particularly to trusses having upper and lower built-up chords, the former being substantially parabolic.

5 The tendency of any concentrated load acting upon a truss top chord of parabolic form is to produce a sag at the point of concentration and an elevation of adjacent portions of said chord. To properly take care of concentrated loads, it is therefore desirable to impart to such a chord a considerable stiifness in its longitudinal vertical plane. It is further desirable, so far as possible to efiect a distribution of any concentrated load longitudinally of the top chord to minimize the requisite uniform stiliness of the latter.

One object of the present invention is to build up a parabolic truss top chord of planks or other flat members, elongated in substantially the'direction of curvature of thejchord, some thereof being arranged to primarily-resist vertically acting stresses and others being disposed to primarily resist stresses acting laterally of the truss;

Another object is to provide a parabolic top chord having its upper portion built up of relatively wide planks or the like, primarily taking care of uniform loads and lateral stresses, and its lower portion built up of more narrow members imparting stiffness to resist concentrated loads, and to reinforce said bottom portion by the use therein of planks or the like forming courses substantially coextensive with the chord and arranged on edge to derive their maximum resistance to vertical loads.

A further object is to provide a truss having a series of vertical members forming spaced con nections between its top and bottom chords through which concentrated loads may in part be compressively transmitted from thetop to the bottom chord, the latter having abuilt-up form peculiarly adapting it to transmit such loads from any one of said uprights to other adjacent uprights which may tensilely distribute the load to the top chord at points other thanth at of concentration.

Still another object is to provide for transmission of compression stresses from the top to the bottom chord of a truss (or vice-versa) through tubular members, and to extend rods through each of said members for taking care of such tensile stresses as may arise.

A still further object is to provide an improved means for transmitting end thrust from the top chord of a truss to the bottom chord thereof.

The combining of steel channels of standard form with wooden members to form the chords of a truss is also an object of the invention.

These and various other objects the invention attains by the construction hereinafter described and illustrated in the accompanying drawings, wherein:

Fig. 1 is a view in side elevation of a roof truss embodying the present invention, showing substantially one half of the span of said truss.v

Fig. 2 is an enlargement of a portion of Fig. 1, showing the meeting ends of the truss chords.

Fig. 2a is a top plan View of the truss extremity shown in Fig. 2. r

Fig. 3 is a transverse vertical section of said truss, taken upon the line 3-3 of Fig. 1.

Fig. 4 is a sectional view, corresponding to Fig. 3, of an alternative construction. a

Fig. 5 is a similar section illustrating a further modification in which the top and bottom chords are primarily metallic.

Fig. 6 perspectively illustrates one of two or more metal keys employed in connecting the ends of the top and bottom chords.

Referring now more particularly to the drawings, and initially describing that form of the invention illustrated in Figs. 1 to 3 inclusive, the reference character 1 designates a plurality of planks or like members forming the upper portion of the top chord and arranged end to end in a suitable number of courses, superposed one on another, the joints of said members being staggered in adjacent courses, as best appears in Fig. 1 and said members in adjacent courses being nailed, bolted, or otherwise fastened together, as indicated at 2, to form in effect an arched unit continuous from end to end of the chord. Preferably some of the members 1 have the full width of the chord while others of lesser width are arranged two (or more) to a course with elongated ventilating spaces 3 between same, as best appears in Fig. 3.

The lowerportion of the upper chordis formed by a plurality of courses of planks or the like 4, superposed one on another, of considerably less width than the members 1, and like the 100 latter, have the joints between their ends staggered in adjacent courses. (See Fig. 1). The central longitudinal vertical planes of the described upper and lower portions of the chord coincide so as to derive, in cross-section, a sub- 105 stantial T form.

The upper portion of the described chord (formed by the members 1) is primarily designed to take care of uniform loads and of lateral stresses, and the lower portion (formed by 110 the members 4) serves primarily to resist concentrated loads.

To further increase the stiffness of the chord, one or more facings consisting of planks 5 or like members are appli d to each side of the lower portion of the chord, the same being nailed or otherwise fastened to the members 4 as indicated at 6 (Fig. 3). The members 5 are arranged on edge, that is to say with their width vertical, and each thereof preferably contacts at its ends with the overlying upper portion 1 of the chord, said portion curving up from said members between their ends to form elongated .restricted spaces 7 having a ventilating value. The lower edges of the members 5, are substantially tangent at their mid length to the bottom face of the lower portion 4 of the chord. Preferably a number of bolts 8 are employed in addition to the nails 6 to hold the members 5 securely against the portion 4 of the chord, said bolts being effective on both outside faces of the members 5.

The lower chord of the described truss is formed by a plurality of planks or like members 9 ar-' ranged side by side, on edge, as best appears in Fig. 3 so that their width is utilized to derive a maximum stiffness resisting vertical loads. Said members are arranged end to end to form courses coextensive with the chord and the joints between. said members are staggered in adjacent courses. Nails 10 or the like are employed to fasten together the laterally adjoining members 9, adapting them to form in effect a unitary structure. V i

The ends of the bottom chord are beveled, as

indicated at 11, to form seats for the ends of he top chord and the two chords are rigidly connected by one or more vertical bolts 12. The end thrust exerted by the top chord is primarily transmitted to the bottom chord by heavy sheet metal yokes 13 the parallel arms of which terminally embrace the lower chord and are firmly bolted thereto as indicated at 14, their closed ends providing abutmentsfor the ends of the members 1.

To supplement the yokes 13 in transmitting thrust from the top to the bottom chord of the truss, it is preferred to provide at each end of the truss a key member 15 consisting of a T- rail, having its head imbedded in the meeting faces of the two chords, and its stem extending between said faces toward the adjacent end of the truss. Thus, the heads of said key members strongly resist relative longitudinal movement, of the two chords, and their stems maintainthe proper vertical position of said heads and powerfully resist any lateral tilting of said key members.

The improved truss further comprises aplurality of vertical connections between the two chords, suitably spaced longitudinally of the truss. Each of said connections comprises a tubular metallic compression member 16 terminally abutting the top and bottom chords, and a tension member 17 consisting of a rod passing through said tubular member and through both chords,

- the ends of said rod being threaded for engagement by nuts 18 clamping washers 1 9 against the top and bottom faces of the truss. Preferably, a pair of washers 2c is also mounted on each of said rods between the ends of the associated tubular member and the two chords. A metal or wood facing plate 2% may be applied to the under face of the bottom chord throughout the length thereof and held in place by the lower nuts 18. y

The type of truss illustrated in Fig. 4 is simisaid planks to the units 22.

posed upon one another in courses coextensive with the chord, the meeting ends of the planks in adjacent courses being relatively staggered. Said units are bolted as indicated at 23 to the top unit 1 of the chord, which corresponds to that of the preceding description. Between the units 22 is arranged a reinforcement formed by a plurality of relatively wide planks (or like members) 24 arranged on edge, that is to say, with their wide faces vertical, bolts 25 being extended transversely of the truss to rigidly connect The meeting ends of the courses formed by the planks 2a are staggered in adjacent courses similarly to the planks 5, and said courses further correspond to the planks 5 in forming elongated ventilating spaces 26 between their top edges and the top portion or the chord.

In the further modification illustrated in Fig. 5, a truss of primarily metallic construction is shown. This comprises a top chord, its upper portion formed by a plurality of flat metal plates 27 coinciding as to their longitudinal vertical plane, but reduced in length from the uppermost to the lowermost, and welded to each other throughout their length (or at suitable intervals), as indicated at 28. The lower portion of said chord comprises two or more pairs of reversely disposed upper and lower channel beams 29 having their flanges welded together throughout their length (or at suitable intervals.) as indicated at 30, wood filler beams 31 being continuously extended within said channels, or a plurality of such beams being arranged end to end within the channels. Said channels preferably have a width somewhat less than that of the lowermost plate 27, and the uppermost of said channels is welded to said plate at each side thereof throughout the length of said channel (or at suitable intervals) as indicated at 32. One or more facing strips 33 of sheet metal is applied to each lateral face of the unit formed by the two channels, and a plurality of bolts 34; rigidly secure said strips to said unit.

The lower chord of the metallic truss is somewhat similarly formed by a pair of channel beams 35 reversely disposed with their flanges approaching each other, a wooden filler beam 36 (or the equivalent) being enclosed in the space formed by .said channels, and a plurality of bolts 37 rigidly connecting said channels to each other and said. beam.

In each of the described alternative constructions, the. upper and lower chords are connected in conformance with the first described truss.

In the use of the described truss, the members 1 (or 1) of the upper chord primarily take care of uniform loads and stresses transverse to the truss, whereas the members 4 impart to the top chord requisite stiffness to withstand concentrated loads, said members in accomplishing this function being reinforced by the members 5.

The bottom chord of the described truss does not act as in most parabolic trusses merely as a tie member between the ends of the top chord, but assists in distributing loads concentrated at any point of the top chord some distance to each side of said point. Thus the tubular memher (or members) 16 lying close adjacent to any point of concentration of load compressively transmit a portion of such load to the bottom chord, which by virtue of its unusual vertical stiffness is adapted to transmit such load longitudinally in each direction to adjacent tension rods 1'7 whereby it may be returned at various points to the top chord. By thus providing for distribution of concentrated loads, the uniform stiffness of the top chord may be considerably less than would otherwise be essential. That form of the improved truss which is illustrated in Fig. 5 is well adapted to be incased in concrete, and may be thus reinforced and to a considerable extent fire-proofed.

The stiffness of the described truss in its various forms may be further materially increased by the use of some adhesive between the components of the built up members of the two chords, such as glue, varnish, paint, or the like.

Fig. 1 illustrates in dash line at 37 the possibility of triangulating the truss between its vertical members to further increase its stability.

It is a feature of the disclosed truss that the top chord thereof is not divided into two half sections, as is 'the present common practice, and consequently the construction has much greater lateral strength than most trusses employing composite chords, and requires less lateral bracing for the top chord.

Said truss is desirably light in comparison with its strength and affords large open spaces between its top and bottom chords for installation of pipes or wire or for passage ways. The numerous small ventilating openings tend to keep the chords dry and prevent any decay of their wooden members. Said truss is suitable for supporting roofs, bridges, or any like structures.

While it will be apparent that the illustrated embodiments of my invention herein disclosed is well calculated to adequately fulfill the objects and advantages primarily stated,.it is to be understood that the invention is susceptible to variation, modification, and change within the spirit and scope of the subjoined claims.

What I claim is:

1. A truss top chord comprising upper and lower units, the former consisting of several superposed arched courses of elongated members arranged end to end, with their width transverse to the chord, and latter consisting of similar arched courses of members less wide than those forming the upper unit, said chord further comprising elongated straight members arranged end to end against the sides of said lower unit, said members adjoining in an obtusely angular relation to adapt them to conform to the arched form of the chord and ventilating air spaces being formed between the straight upper edges of said members and the arched bottom face of the upper unit.

2. A truss top chord consisting of upper and lower units, the former comprising several superposed arched courses of elongated members, arranged end to end in each course, with their width transverse to the chord, and the latter comprising similar arched courses of members less wide than the upper unit, and further comprising a series of elongated straight members arranged end to end, and adjoining each other in an obtusely angular relation in a polygonal conformity to the arch of the chord, ventilating air spaces being formed between the straight upper edges of the last named members and the arched bottom face of the upper unit.

3. A truss top chord consisting of upper and lower units, the former comprising several superposed arched courses of elongated members, arranged end to end in each course, with their width transverse to the chord, and the latter comprising two spaced assemblies of elongated members forming superposed arched courses, and further comprising a series of elongated straight members arranged end to end between said spaced assemblies, adjoining each other in an obtusely angular relation and so conforming to the arch of the chord, ventilating air spaces being formed between the straight upper edges of the last-named members and thevarched bottom face of the upper unit.

4. A truss comprising an arched top chord and a bottom chord terminally seating said top chord, of an anchorage member interposed between each end of the top chord and the seating face of the lower chord, said anchorage member consisting of a length of standard steel T bar extending transversely of the truss and having its head set jointly into the upper and lower chord and having its stem extending between said chords.

WALTER M. PRATT.

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