US3778946A

US3778946A - Truss and method of making same

Info

Publication number: US3778946A
Application number: US00100282A
Authority: US
Inventors: G Wood; J Mccabe
Original assignee: WOODCO Ltd
Current assignee: WOODCO Ltd
Priority date: 1970-12-21
Filing date: 1970-12-21
Publication date: 1973-12-18
Anticipated expiration: 1990-12-18
Also published as: DE2164417B2; AR195656A1; AU3712871A; DE2164417C3; CA947030A; DE2164417A1

Abstract

Camber is automatically attained in the chords of a truss by means of tensioned tensors and compression members between the top and bottom chords of the truss.

Description

United States Patent [191 Wood et a1.

[ 1 Dec. 18, 1973 TRUSS AND METHOD OF MAKING SAME [75] lnventors: Gordon G. Wood, Glen Ellyn; James L. McCabe, Wheaton, both of 111.

[73] Assignee: Woodco Ltd., Glen Ellyn, Ill.

[22] Filed: Dec. 21, 1970 [21] Appl. No.: 100,282

[52] US. Cl. 52/223 R, 29/155 R, 29/446,

52/640, 52/693, 52/741 [51] Int. Cl. E04c 3/10, E04c 5/08 [58] Field of Search 52/223, 225, 226,

' [56] References Cited UNlTED STATES PATENTS Leland 52/640 Primary Examiner1-1enry C Sutherland Attorney-Donald M, Sell [5 7 ABSTRACT Camber is automatically attained in the chords of a truss by means of tensioned tensors and compression members between the top and bottom chords of the truss.

8 Claims, 13 Drawing Figures PATENTEUUEB 18 ms 3.; 778.946

[\VEYTURS ORDON 6', W000 Mes A. Ma C455 ATTORXE Y5 PATENTEDUEC 18 I915 SHEET 2 OF 2 muss AND METHOD OF MAKING SAME This invention relates to truss structure and more particularly concerns the attainment of camber in a unique manner.

Heretofore camber has customarily been attained in trusses by prebending the chords and then assembling or at least securing the tension and, where employed, compression members in place. Generally the tension members have been rigid structures fixedly and immovably secured to the chords by various expedients such as special hardware, plates and the like whereby to hold the chords in the camber to which they were prebent. This has involved often complex structure, combinations and devices.

Insofar as we are advised, it has heretofore always been necessary to precamber the chords in some manner, such as by constructing the chords to have the desired camber or to place the chords in a fixture or jig during construction to hold them bent to the desired camber while the truss is assembled.

According to the present invention, the foregoing and other disadvantages, defects, inefficiencies, shortcomings and problems in prior truss structures and methods of constructing the same are overcome and a new and improved truss and method of making the same are provided as will hereinafter become apparent.

An important object of the present invention is to provide a novel truss structure.

Another object of the invention is to provide a new and improved method of making trusses.

A further object of the invention is to provide a novel truss structure which automatically attains the desired camber in the truss.

A still further object of the invention is to provide a new and improved method of making trusses wherein the desired camber is attained automatically as an incident to effecting assembly of the truss components.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected 'without departing from the spirit and scope of the novel concepts embodied in the disclosure, and in which:

FIG. 1 is a generally schematic side elevational view of a truss embodying features of the invention;

FIG. 2 is an enlarged fragmentary top plan view taken substantially along the line IIII of FIG. 1;

FIG. 3 is an enlarged fragmentary vertical sectional detail view taken substantially along the line .III--III of FIG. 2;

FIG. 4 is a sectional detail view similar to FIG. 3 but showing a modification;

FIG. 4A is a fragmentary vertical sectional view of another modified tensor securing means;

FIG. 5 is an enlarged sectional plan view taken substantially along the line V-V of FIG. 1;

FIG. 6 is a top plan view taken substantially in the plane of line Vl-VI of FIG. 3;

FIG. 7 is a fragmentary top plan view of a modified truss structure; while FIG. 8 is a side elevational view of the same;

FIG. 9 is a fragmentary top plan view of another modified arrangement of the truss and FIG. 10 is a side elevational view of the same; and

FIGS. 11 and 12 are vectorial diagrams.

We have discovered that camber within a substantial and desirable range can be obtained in trusses and more particularly in floor and roof supporting trusses over any permissible span easily, automatically and with calculable and duplicatable assurance, by simply assembling with the top and bottom chords properly related tensioning means and compression-spacer structure.

In making a truss, the compression-spacer structure is placed between the top and bottom chords, relatively unstretchable but flexible tensioning means are attached to and between the chords to extend diagonally upwardly toward one end of the truss from one side of the longitudinal center of the truss and toward the opposite end of the truss relative to the opposite side of the longitudinal center of the truss, and the flexible tensioning means are tensioned to effect automatic cambering of the chords.

By way of example, a truss 15 (FIGS. 1 and 2) having a top beam or chord l7 and a bottom beam or chord 18, comprises compression-spacer structure in the form of upright" load stress-distributing compression members 19 between the chords; and flexible tension means in the form of relatively unstretchable but transversely flexible tensors 20 attached at respective opposite ends to the chords respectively. At one side of the longitudinal center of the truss 15, the tensors 20 extend diagonally upwardly and toward the end of the truss at that side of the center and at the opposite side of the truss the tensors extend diagonally upwardly and toward the opposite end of the truss. Support for the truss 15 may be provided by any suitable structure between which it is desired to have it span, such, for example, as spaced walls, partitions, piers, posts, beams, or the like, 21. In this instance, the truss 15 is shown as top-chord-supported with the opposite end portions of the top chord 17 in bearing relation over and on the supports 21 and resting on top plates 22 carried on the supports. In this arrangement, the opposite ends of the lower chord 18 are shorter to clear the upper inside portions of the supports 21, with retainer or antisway bars or blocks 23 carried by the supports 21 and closely overlying and secured to the lower chord end portions. However, of course, the truss 15 may be bottom chord supported on the supports 21, and in such case the end portions of the bottom chord 18 would be carried in bearing relation on the tops of the supports.

Spacing of the vertical compression members I9 along the truss is predetermined according to the size, length, material, load-carrying requirements, type of planking or other superstructure to be carried, and like structural characteristics. For example, in trusses especially suitable for residential building floors, having a span between their ends of 26 feet to 28 feet with the chords constructed of 2 inch dimension lumber, the compression members 19 may be set about 24 inches apart and may comprise predetermined lengths of wooden 2 inch dimension lumber. In such trusses the outside to outside height may be from 15 to 1-6 inches. Substantial diminution in height is attainable as compared to at least some prior structures because the width dimensions of the chords is placed in the horizontal direction.

Although the tensors 20 may take numerous and varied forms, a principal requirement is that they be relatively unstretchable or at least strongly resistant to stretching and that their respective opposite ends be attached tothe chords 17 and 18, respectively; but that the tensors be functionally flexible within parameters suitable to attain the desired camber in the truss. In one simple, economical construction, the tensors 20 may comprise metal rods. In trusses of the general dimensions already mentioned, 5/ 16 inch steel rods have been successfully employed. These tensor rods are of a length to extend diagonally from adjacent to the lower end of each of the compression web members 19 to adjacent the upper end of the next adjacent member 19 in the direction of obliquity of the tensor. A desirable attachment arrangement for the respective opposite ends of the tensor rods 20 comprises forming the end portions to extend respectively angularly from the body of the rod at an angle which will place the end portion on an axis normal to the longitudinal axis of the chord with which it is to be assembled. For standardization, thetensor rods may be provided with equal opposite terminal portions 24 (FIGS. 3 and 5) which extend on parallel axes but in opposite directions, whereby to be received in and through respective bores 25 in the chords l7 and 18. For this purpose, the length of the tensor attachment terminals 24 are preferably about the same as the thickness of the chord in each instance. Where the chords are of the same thickness at top and bottom, the terminals 24 can be of the same length. Where one of the chords differs in thickness, suitable complementary revision as to the length of the terminal 24 to be received therethrough may be made.

For wooden chords, means are provided for anchoring the tensor terminals'24 in a manner which will resist compressional deflection of the wood at the respective bore 25 due to deflectional stresses imposed by loading of the tensor. For this purpose, deflection-resisting respective plates 27 (FIGS. 3 and 5) mounted at the inner ends of the bores 25, are thoroughly anchored to the respective chords and provide deflection resistant bearings forthe proximal ends of the terminals 24. In an economical structure, each of the bearing plates 27 may comprise suitable gauge and hardness cast or stamped metal members dimensioned to provide a substantial plate area about a central bearing aperture 28 through which the terminal 24 is received. For increased bearing surface, the bearing aperture is extended by means of an integral rigid ferrule 29 received within the bore 25 to a substantial length. Any suitable means may be employed to secure the plates 27 to the respective chord, such, for example, as sharp tipped drive-in prongs 30 formed integrally with the inner face of the plate and extending in the same direction as but preferably slightly shorter than the ferrule 29. Thereby, the plate can be properly oriented with respect to the bore 25 by starting the distal end of the ferrule 29 into the bore 25, and the plate then driven home by striking it with a hammer, mallet, press or other driving means to cause holding penetration of the prongs 30 into the 7 chord member.

To secure the terminals 24 to the respective chords, any suitable means that will effectively prevent withdrawal of the terminals under functioning loads may be employed. One such means comprises respective threaded nuts 31 secured on a suitably threaded distal I end portion area 33 of the respective terminal (FIG. 3).

to receive the, nut 31 and also desirably at least a metal washer, but preferably means which will distribute the nut thrust over a relatively wide area about the bore 25 to resist to maximum extent desirable any tendency for the material of the chord to yield under stress of the nut pressure or tension loads that may be imposed on and through the tensors 20 in service. For this purpose, respective force distribution plates 34 (FIGS. 3 and 6) are provided to engage a substantial area of the outer face of the associated chord about the respective counterbore 32 and provided with an inset 2S complementary to and received in socketed relation within the counterbore 32 and of an inside diameter to afford ample clearance for a wrench to be engaged with and about the nut 31. In the bottom of the inset 35 is provided a bearing aperture 37 for projection therethrough of the distal end portion of the terminal 24 and equipped with a bearing surface ferrule extension 38 extending into the bore 25. Any suitable means for anchoring the plate 34 may be provided, such as integral sharpened inwardly extending securing prongs 39 enabling the plate to be attached by hammering it into anchored position by suitable driving means.

For conditions involving possibty lower magnitude stresses, attachment of the tensor terminals 24 to wooden chords may be effected at both opposite ends in the manner depicted in FIG. 4, wherein thedeflection load distribution plate 27 is provided simply with a bearing surface 28' about an opening through the plate through which the terminal extends, the bore 25' of the chord l7 (and the chord 18 as well) being dimensioned to receive the terminal 24 closely. Although the outer deflectional load distribution plate 34' may have the inset portion 35' received in the socket counterbore 32, the inset is provided merely with a simple bearing aperture 37 through which the distal end portion of the terminal 24 extends for securement purposes. While securement may be accomplished similarly as shown in FIG. 3 by means of a threaded nut, a simple and effective securing means for the lesser load conditions comprises one or more inwardly fingered annular disk press nuts 40. For this purpose the distal end portion of the terminal 24 is left in its original cylindrical form so that the inwardly directed biting, gripping fingers of the press nut disk will effect a positive retaining grip. We find that these press nuts can be applied in multiples to multiply proportionately the power of retention of the terminal 24 against withdrawal from the respective chord. For example, if one of the press nuts 40 will withstand a pull of 1,000 lbs. against separation of the terminal 24, two of the nuts will withstand about 2,000 lbs. pull. Instead of a plurality of thinner press nuts, a single heavier gauge press nut may be employed.

In FIG. 4A is depicted another desirable securing means, having the advantage that counterboring of the respective chord is avoided and requiring only the straight through bore 25. This comprises a combination bearing and nut plate or disk 34" having an inwardly extending integral bearing ferrule 38" which has internal threads 33a retainingly engaging the threads 33 of the terminal 24. For driving the disk 34" it has peripheral wrench notches 340.

Other types of retaining structures may also be employed where expedient, such as pins, weldments, upset heads, and the like.

In making a truss employing the tensor rods 20, the chords 17 and 18 are first connected together by securing the terminals 24 of the tensor rods in the respective preformed bores 25 in the chord with the supplementary hardware provided by the

plates

27 and 34 or 27 and 34', as the case may be. Initial inside spacing of the chords will be determined by the juncture bends between the respective terminals and the body of each of the tensor rods serving as limiting stops during assembly of the components. By having all of the tensor rods standardized as to dimensions the chords 17 and 18 will be in straight parallel relation, as shown in dash outline in FIG. 1, after the tensor rods have all been completely assembled therewith. Thereafter the load distributing, compression-spacer web members 19 are assembled with the truss. If no camber is desired in the truss, the length of the compression members 19 will be predetermined to be just equal to the assembled spacing between the inside faces of the chords l7 and 18, with the thickness of the plates 27 serving a snugging function between the ends of the members 19 and the chord. If desired, the members 19 may be provided with respective notches 41 (FIG. 3) to clear the adjacent end portions of the tensor rod bodies, where the particular disposition of the tensors would interfere with proper compression load-supporting function of the members 19 when fully assembled with the chords.

Where, as is generally the case, camber is desired in the chords l7 and and 18, the compression members 19 are predetermined in length, desirably uniform, to be greater than the initial spacing between the chords l7 and 18 after assembly of the tensors 20 therewith. Then, as the members 19 are placed in assembly in the truss, the desired camber is automatically attained by virtue of placing the tensors 20 under tension. Since the opposite ends of the tensors 20 are secured in fixed positions on the respective chords, vectorial forces are developed by the forcing of the chords apart to cause the upward camber bowing of the chords. The longer the compression members 19 are relative to the initial spacing between the chords, the greater will be the camber, and this can be calculated with some degree of accuracy and is attainable repetitively to meet various design and production standards and requirements.

To illustrate the vectorial phenomenon, reference may be had to FIGS. 11 and 12. FIG. 11 represents the vectoric conditions prevailing where the chords 17 and 18 are in straight parallel relation and the compression members 19 are of the same length as the straight parallel spacing between the chords, represented by L. In such condition, pivoting tendency under load with respect to the ends A C of the tensor 20 will be about the deflection radius represented by the are A C at the point A. Pivoting of the chord sections A B and B C will be on the arcs A' B and B C, respectively. When the compression member length L is increased as represented in FIG. 12 while the distances A B, A C and D C remain constant, the arcs A B and D C, respectively, also remain constant, but the deflection radius are A C shifts to the opposite point C of the tensor 20 as shown, and the desired camber is attained as indicated.

Numerous and varied practical arrangements of the compression members 19 and the tensors 20 may be provided to meet design and load requirements. For example, in the form of FIGS. 1 and 2, the two compression members 19 nearest the longitudinal center of the truss 15 are spaced on centers nearly but slightly less than the spacing on centers between the compression members 19 toward each respective end of the truss from such central compression members. Also, the tensors nearest the ends of the truss are provided in parallel pairs while the remaining tensors inwardly therefrom toward the center of the truss are singles. In this instance where five tensor sections are provided each way from the center, the two sections nearest the ends of the truss comprise a pair of the tensors 20 while the three sections nearest the center in each half of the truss comprise a single tensor. This ratio may, of course, be varied to suit the circumstances, or all of the tensor sections may be double or even triple or more, or all may be singles, as may be best suited for the particular structural application. In this instance, also, it will be noted that all of the compression members 19 are oriented as webs with their width across the axis of the truss.

In FIGS. 7 and 8, the two centermost of the compression members 19 are relatively close together, and could, if preferred comprise a single member of possibly greater transverse dimensions to compensate for singularity as compared to the plurality of central members. In this instance, also, the compression members are oriented with their width in the direction of the axis of the truss. By thus orienting the compression members, the anchored ends of the tensors 20 can be located in the most desirable relation to the respective axes of the compression members, the ideal being coincident with the compression member axes. In this instance it is possible to place the anchored ends at least in transverse alignment with the axes of the compression members and relatively close thereto. This also facilitates efficient drilling of the bores 25 in the top and bottom chords at the same time for uniform quality production. Further, in this arrangement increased loading capacity is attained by having the top chord ends of the endmost tensors 20 advantageously located as nearly as practicable over the center of the end bearing supports for the truss. In this instance respective compression members 19a are mounted as transverse webs between the respective opposite endmost portions of the chords l7 and I8. Suitable means such as nails 42 may be employed to secure the compression members 19 and 1% against displacement relative to the chords.

Another representative example of adaptability of the present invention is depicted in FIGS. 9 and 10 wherein it will be observed that the topmost tensors 20 of the top chord supported truss have their upper end terminals located efficiently substantially centered over the support 21. To enable this centering, means such as a bearing plate 43 having tensor clearance grooves 44 may be provided. Thereby the most efficient loading capacity for the truss is attained, especially where the multiple tensor arrangement is employed.

From the foregoing it will be apparent that the present invention greatly simplifies the construction of trusses in which camber is a desirable or necessary attribute. While for economy and expediency wood is the structurally acceptable material for many installations, other materials may be employed in the chords and/or the compression members, such, for example, as steel, reinforced plastic, aluminum, or combinations of these and other materials with wood. Other materials than rod stock may be found structurally acceptable for the tensors, such as wire or cable in fixed or continuous lengths, or even wooden members, as long as functional flexibility is present to enable the chords to camber when the tensors are placed under tension. Tensors stiffness,'span, and the like. Advantageous versatility and adaptability is indicated. Further, according to the principles of the present invention the truss height can be substantially reduced as compared to at least many prior constructions .to accomplish the same purposes. it will be understood that variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

We claim as our invention:

l A method of making a truss comprising assembling top and bottom truss chords in generally parallel relation to one another by securing relatively unstretchable flexible tension means to and between said chords to extend diagonally toward one end of the truss at one side of the longitudinal center of the truss and toward the opposite end of the truss at the opposite side of said longitudinal center of the truss, and thereafter inserting stress-distributing spacer structure between said chords and forcing said chords to a greater than initial spacing thereby automatically cambering said truss as an incident to its assembly.

2. A method according to claim 1, comprising drilling tensor-anchoring bores in beams to provide said chords, shaping tensor rods with anchoring terminals to provide said tensioning means, securing the anchoring terminals of the rods in said bores, and thereafter assembling between the chords compression members of greater length than the initial assembled spacing of the chords and tensors to provide said spacing structure and force the chords apart to automatically attain the camber of the chords.

3. A method for assembling a truss so that camber is induced as an incident to its assembly comprising (a) joining top and bottom chords in generally parallel relation to one another with unstretchable tensor members which are capable of limited flexure under tension load, the tensor members on each side of the truss center being oppositely diagonally disposed, (b) then forcing said chords to a spacing greater than their initial spacing and flexing said tensor members by the insertion of compression members therebetween thereby automatically cambering said truss.

4. A method according to claim 3 wherein said compression members extend between said chords with the upper and lower ends of each compression member being proximal to the upper and lower ends of adjacent tensor members.

5. A method according to claim 4 wherein said tensor members are stiff rods having their end portions angled from the main body portions thereof and secured in bores in said chords.

6. A method according to claim 5, said chords having reinforcing structure about said tensor member end portions. 1

7. A cambered truss comprising generally parallel cambered upper and lower chords interconnected to and spaced from one another by means of upright compression members and diagonally disposed elongated metal tension members having their end portions angled from the main body portions thereof and being relatively 'unstretchable while capable of flexure under tension at the juncture of the end portions to the main body portions thereof, said chords having bores therethrough and having reinforcing plate means at the entrances and exits of said bores, means securing said plates to said chords, said tension member end portions.

extending into said bores and terminating therein below the outer surfaces of said chords and means anchoring said end portions in said bores, to said plate means said tension members being of generally equal length, said tension members at each side of the truss center line extending diagonally upwardly toward the end of the truss nearest thereto and being generally equidistantly spaced from one another, said compression members extending between said chords and having their ends engaging said chords proximal to said tension member terminal end portions, said compression members being longer than the normal uncambered vertical distance between said chords, said compression members maintaining said tension members under tension load thereby automatically maintaining the camber of said truss.

8. A truss according to claim 7, wherein said tension members are relatively flexible.

Claims

1. A method of making a truss comprising assembling top and bottom truss chords in generally parallel relation to one another by securing relatively unstretchable flexible tension means to and between said chords to extend diagonally toward one end of the truss at one side of the longitudinal center of the truss and toward the opposite end of the truss at the opposite side of said longitudinal center of the truss, and thereafter inserting stress-distributing spacer structure between said chords and forcing said chords to a greater than initial spacing thereby automatically cambering said truss as an incident to its assembly.

6. A method according to claim 5, said chords having reinforcing structure about said tensor member end portions.

7. A cambered truss comprising generally parallel cambered upper and lower chords interconnected to and spaced from one another by means of upright compression members and diagonally disposed elongated metal tension members having their end portions angled from the main body portions thereof and being relatively unstretchable while capable of flexure under tension at the juncture of the end portions to the main body portions thereof, said chords having bores therethrough and having reinforcing plate means at the entrances and exits of said bores, means securing said plates to said chords, said tension member end portions extending into said bores and terminating therein below the outer surfaces of said chords and means anchoring said end portions in said bores, to said plate means said tension members being of generally equal length, said tension members at each side of the truss center line extending diagonally upwardly toward the end of the truss nearest thereto and being generally equidistantly spaced from one another, said compression members extending between said chords and having their ends engaging said chords proximal to said tension member terminal end portions, said compression members being longer than the normal uncambered vertical distance between said chords, said compression members maintaining said tension members under tension load thereby automatically maintaining the camber of said truss.