AU1601383A

AU1601383A - Shear connection truss construction

Info

Publication number: AU1601383A
Application number: AU16013/83A
Authority: AU
Inventors: Emanuel A. Coronis Jr
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-05-10
Filing date: 1983-05-09
Publication date: 1983-12-02
Anticipated expiration: 2003-05-09
Also published as: EP0095614A1; AU561183B2; CA1207974A; ZA833332B; WO1983004064A1

Description

SHEAR CONNECTION TRUSS CONSTRUCTION

The present invention relates to a wide-span truss construc- ^ζ tion and its method of fabrication. More particularly, the present invention relates to truss constructions known as 5 shear connection truss constructions, which are distinctive in the absence of a horizontal reaction or bending moment when disposed on vertical support members.

Description Of The Prior Art:

A variety of truss constructions have existed for many years, that attempt to serve for roof support in wide-span buildings, Certain of these trusses are known as rigid frame trusses, while others purport to be shear connection trusses. The "shear" and "rigid" terminology refers to the nature of the connection between the lateral end of the truss and the ver- tical columns upon which the trusses are supported. In the traditional rigid-frame construction, a moment connection exists between the truss and its supporting columns. This moment connection gives rise to an associated phenomenon at the base of each column which is known as horizontal re- action. A horizontal react-ion will occur at the bottom of a vertical column whenever the top of such column is exposed to a non-vertical or angular moment, generally known as a bending moment. In the field of wide-span construction, the accepted consequence of the presence a horizontal re- action, is that unduly large, and frequently immense, con- crete supports are required to buttress the base of each vertical column against the forces of the horizontal reaction.

Numerous constructions are disclosed in the prior art that attempt to address the need for a simplied wide-span support. As early as 1953, French Patent No. 1,030,371 to Desmery disclosed the splitting of a beam to form a structural ele¬ ment that would permit the resulting split beam to be mounted along two locations on the vertical support structure. While the patent speaks broadly of splitting a beam, it does not contemplate the specific construction wherein the split por¬ tions of the beams are brought together to define an arch, and the unsplit portions are disposed on the vertical support columns. This construction neither takes into account nor cures the long standing problem of the exertion of a horizon¬ tal reaction against vertical support columns.

Numerous other patents are known that have been considered for their possible relevance to the present invention. Thus, U.S. Patent No. 1,419,274 to Lachman, U.S. Patent No. 3,224,151 to Nystro , U.S. Patent No. 2,262,120 te S its, and Australian Patent No. 107,908 to Crockett are represen¬ tative. None of these patents discloses or appreciates the construction set forth later on herein.

One example of a prior art rigid-frame structure which utili¬ zes some of the procedures of the method of the present in- vention, comprises the patent to Temple, United Kingdom Patent No. 692,312 (1953). Temple illustrates the known procedures of longitudinally splitting a construction beam and of form¬ ing an angular displacement relative to the upper and lower chords of such a longitudinally split beam. However, despite the utility which may reside in the use of a truss such as taught by Temple, the ultimate result is still one of a rigid frame structure in which a moment connection exists between the vertical columns and the horizontal truss.

In similar fashion, further prior art patents relating to custom-designed beams, comprise U.S. Patent No. 3,365,852 • to Pitillo and U.S. Patent No. 3,283,464 to Litzka. Each of these patents, while disclosing interesting concepts in

^• the area of beam construction, does not come to grips with the problem of horizontal reaction, which the construction of the present invention eliminates.

SUMMARY OF THE INVENTION

In accordance with the present invention, a shear connection truss construction is disclosed, that, by its particular dimensional conf guration, has been found to eliminate the development of a bending moment or horizontal reaction, when the construction is disposed on vertical support col- umns. The truss construction consists essentially of paired truss members attached to ^"each other in end-to-end abutment, each truss member having an essentially I-shaped cross-section defined by essentially parallel, lo-ngitudinally extending flanges, and a connecting web extending trans- versely between the flanges. Each truss member defines a unitary, unsplit end, and a longitudinally split end, the longitudinally split end defined by an upper chord, located in the same directional plane as the unsplit end, and a lower chord extending at an acute angle with respect to the upper chord, with a web that is discontinuous with the web of the unsplit end. Preferably, the unsplit end of the truss mem¬ ber has a length ranging from 15% to 35% of the total length of the member as measured from the unsplit end to the fur¬ thest tip of the upper chord. Also, the acute angle between the upper chord and the lower ςjiord may range up to about 15° and preferably from about 5° to 15°.

The upper chord and the lower chord are integral with the unsplit end at a junction point, and the respective flanges on the upper and lower chord and the adjacent flanges dis¬ posed on the unsplit end are likewise integral. The con¬ struction of the present invention is characterized by the absence of a bending moment at this junction point and the correspondi ng absence of a hori zontal reacti on when the con¬ structi on i s di sposed on verti cal support col umns .

The present truss construction can be prepared in a variety of ways, including the technique of splitting an I-beam to form the upper and lower chords. In a further embodiment of the present invention, the present construction may be assembled from modular components such as plate steel, rather than from pre-for ed I- or T-beams. Further, the geometry of the present truss construction permits a variation in the width of the upper flange with respect to the lower flange, so that the greater compressive stress exerted upon the upper chord relative to the tension exerted upon the lower chord, can be accommodated and an economy in material usage achieved.

Additionally, the present truss construction may utilize an upper flange either greater in cross sectional area or broader in width, than the lower flange by the assembly of the construction from premeasured flat plates.

The adherence to the dimensional limitations expressed herein results in the formation of a truss construction exhibiting no bending moment and therefore an absence of a horizontal reaction exerted against the vertical support members. More¬ over, the capability of fabricating the present truss con¬ struction in a 'modular fashion -confers additional economies of assembly and cost that are not appreciated in the prior art.

It is a principal object of the present invention to provide a wide span truss construction which exhibits an absence of a bending moment and the elimination of the exertion of horizontal reaction upon vertical support members on which the truss construction is mounted. It is a further object of the present invention to provide a truss construction as aforesaid that is capable of a variety of fabrications, including modular assembly from a plurality of premeasured plate members.

It is a further object of t-he present invention to provide a truss construction that eliminates the need for pro¬ viding massive support buttressing to vertical support structures intended to receive truss members.

A still further object of the present invention is to provide a truss construction having a lower ratio of weight per unit length of span than is attainable in prior art trusses such as solid beam or built-up trusses.

Other objects and advantages will become apparent to those skilled in the art from a consideration of the ensuing description which proceeds with reference to t e following illustrative drawings.

DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a side elevational view of a truss construction in accordance with the present invention.

FIGURE 2 is a fragmentary side elevational view partly in phantom of a truss member in accordance with the present invention.

FIGURE 3 is a perspective view of an I-beam useful as starting stock in accordance with a first embodiment of the method of the present invention.

FIGURE 4 is a perspective view showing the partial splitting of the I-beam of FIGURE 3. FIGURE 5 is a perspective view showing the displacement of the split portion of the I-beam of FIGURE 4, to define an upper and a lower chord.

FIGURE 6 is a perspective view similar to FIGURES 3-5, showing the reenforce ent of the junction point between the lower chord and the unsplit end of the I-beam, by the addition of web brace plates thereto.

FIGURE 7 is an exploded perspective view showing the truss member of FIGURE 2 prepared in accordance with -a . further embodiment of the invention.

FIGURE 8 is a cross sectional view of a truss member having flanges of varying width, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the FIGURES, wherein like numerals designate like parts,and particularly .to FIGURE 1, the present inven¬ tion relates to a shear connection truss construction parti¬ cularly suited for roofing applications in wide-span building construction. Thus, truss construction 2 comprises paired truss members that are joined -at their flaired ends, to define, as illustrated herein, the apex of a slanted roof construction.

Referring now to FIGURE 2, an individual truss member 4 is illustrated and is seen, to comprise a unitary, unsplit end 6 and a longitudinally split end, defined by an upper chord 8 and a lower chord 10. Upper chord 8 extends in the same directional plane as unsplit end 6, while lower chord 10 extends at an acute angle, labeled α. As illustrated generally in FIGURES 3-8, truss member 4 de¬ fines an essentially I-shaped cross section, defined by longi¬ tudinally extended parallel flanges, comprising upper flange 12 and lower flange 14, connected by a transversely extending web 16. Both upper flang.e 12 and lower flange 14 are contin¬ uous throughout the length of truss member 4, with upper flange 12 remaining linear, while lower flange 14 changes direction at the point where lower chord 10 diverges from unsplit end 6.

The point at which lower chord 10 diverges from upper chord 8 is referred to as the junction point 18. As the fabrication of truss member 4 by any of the techniques disclosed herein, results in the formation of a separate portion of web 16 associated with lower chord 10, reenforcement of truss member 4 at the junction point 18 is desirable to integrate the portions of web 16 associated with the respective chords, with the portion of web 16 disposed at the unsplit end. Accordingly, brace plates such as plate 20 are mounted on both sides of the transverse split in web 16, at junction point 18, to combine in sandwich relationship to provide the desired support. Additional bracing is possible and may be provided by one or more lattice members 22 to secure chords 8 and 10 in fixed relationship to each other. If desired, an end plate 24 may be affixed to the free ends of chords 8 and 10 to provide a point of attachment to either the corresponding chords from another truss member, as illus¬ trated in FIGURE 1, or directly to a vertical support struc¬ ture, in a manner not illustrated herein.

A prominent feature of the present invention is that the truss construction and the respective truss members do not exhibit a bending moment, and do not exert a horizontal reaction, in the instance where this construction is mounted by a shear connection, upon one or more vertical support

_ OMPI structures. Thus, the forces transmitted from the present truss construction to the vertical columns, such as columns 26 illustrated in FIGURE 1, are solely vertical in nature, and the possibility of horizontal reaction at the base of the column is eliminated-;

From the viewpoint of structural engineering analysis, the truss construction of the present invention is identified as an "indeterminate structure." The expression "indeter¬ minate", in the field of structural engineering, implies "that which cannot be solved by the application of the laws of statics alone". Various adva'nce methods of struc¬ tural analysis, such as energy principles can be applied to the trusses, using either manual or electronic computer calculation techniques. These techniques, however, tend to become lengthy, involved and expensive, and therefore prohibitive for day to day employment in the routine design of truss members.

One of the features of the present invention is that the unitary unsplit end 6 should preferably have a length ranging from about 15% to about 35% of the total length of truss member 4, as measured from unsplit end 6 to the furthest tip of upper chord 8. In one embodiment of the invention, a preferred range of this length dimension may be from 16% to 29%, and more particularly approximately 20% of the entire length of truss member 4. In an alter¬ nate embodiment, wherein the truss member 4 is prepared by a technique of modular fabrication, the more preferred range of the length of unsplit end 6 may extend from 25% to about 33% of the length of the entire truss member ,4.

A further aspect of the present invention is that the acute angle α defined between upper chord 8 and lower chord 10 may range up to about 15°, and preferably from about 5° to about 15°. The exact value for this angle may vary, de¬ pending upon span loading and truss member selection but will generally range more particularly between 7° and 13°. Thus, for example, the slope or pitch variation between , 5 upper chord 8 and lower chord 10 may vary an average from

1-1/2" to 2-1/2" for eve ry foot of length of the respective chords.

It is been found that, when the foregoing dimensional limi¬ tations are observed, the bending moment, which may be 10 calculated at the junction point 18, will equal 0, and, accordingly, the truss member will not exert a horizontal reaction at the base of vertical members on which it is mounted.

The truss construction of the present invention may be fab- 15 ricated by different techniques, and two such techniques are disclosed herein. In particular, FIGURES 3-6 refer in general to a first technique for fabrication, wherein a unitary I-beam 28 is provided having a length predetermined to co¬ incide with the desired longitudinal dimension of the truss. 20 member to be formed. . I-beam 28 comprises essentially para¬ llel upper flange 12 and lower flange 14, and transversely extending web 16. In this method, a longitudinal split or cut 30 is made in web 16 to alength that will correspond to the length desired for upper chord 8, shown clearly in 25 FIGURE 5. As shown, both upper chord 8 and lower chord 10 are formed by the provision of split 30, and are seen in FIGURE 5 to possess essentially T-shaped cross sections. The point at which cut 30 is stopped corresponds to the junction point 18, described earlier. At this point, a j3Q transverse cut 32 is made to sever the portion of web 16 adjacent lower chord 10 from the remainder of web 16 associated with upper chord 8 and unsplit end 6, as clearly

O PI shown in FIGURE 5-, Thus, lower chord 10 remains connected to unsplit end 6 by lower flange 14 that remains integral.

Lower chord 10 is then bent or deflected at a predetermined angle α away from upper chord 8, and paired brace plates 20 are then affixed to the adjacent surfaces of the portions of web members 16 to secure the web members to each other in a sandwich relationship. Finally, though not shown, a plurality of latice members 22 may be provided to give further support between upper chord 8 and lower chord 10. The exact number and positioning of the latice members 22 may vary with the load requirements of the particular construction.

Though not illustrated herein, a modification of the above fabrication sequence may be followed, wherein, T-beams may be brought together to form the final I-beam shape of the truss member. Specifically, the above sequence would be modified by the deletion of t e splitting of the I-beam, as only the transverse cut 32 in one of the T-beams would be necessary. Thus, one of the T-beams could be transversely cut and then bent to the predetermined angle, and subse¬ quently the uncut T-beam could be appropriately mated there¬ with to form the structure shown in FIGURE 5. The web members 16 could be joined at the unsplit end by a variety of known techniques, including butt welding and the like, and the invention is accordingly not limited to a specific such joining technique.

A further embodiment of the present invention comprises the fabrication thereof from a plurality of modular components, as illustrated herein in FIGURE 7. In such instance, a plurality of planar sheets of material could be individually fashioned to conform in all dimensions, including shape, to that of their respective component parts. Thus, flanges 12 and 14 could be fashioned as continuous strips, with flange.14

OMPI bent appropriately to define the angular displacement of lower chord 10. Web member 16 might be prepared in two sections, the first comprising an essentially L-shaped member for unsplit end 6 and upper chord 8, and a separate, ^s5 approximately rectangular portion for lower chord 10.

Alternately, it would be possible to fashion a continuous flat plate conforming to the ultimate shape of web 16 in the final truss member. In such instance, it would only be necessary to weld the respective upper and lower flanges

10 against the corresponding lateral edges of the web to complete the formation of the basic truss member. There¬ after, additional brace plates and lattice members, if desired, could be added. The foregoing techniques are presented for purposes of illustration of this embodiment 5 of the invention, and are not presented by way of limita¬ tion.

A wide variety of construction grade materials may be utili¬ zed to fashion the truss members and the truss construction of the present invention. The materials useful in 0 this regard are all well known, including the widely employed structural steels, and the like. The variety of ways in which the present truss construction may be fabricated, allows a correspondingly broader variety of metals to be utilized, as one is not limited tb the use of specific metals 5 suited for the manufacture of an I-beam.

A further advantage conferred by the use of the modular fabrication method disclosed herein, comprises the ability to vary the width of the flanges with respect to each other, to permit economies of material to be made without sacrifice ^Q in structural integrity. Thus, it is possible to prepare truss members having broader, heavier or thicker upper flanges 12, while utilizing lower flanges 14 of reduced dimension. A schematic illustration of this is shown in

OMPI FIGURE 8, wherein a cross section of an essentially I-shaped member is shown, embodying this differential. While this construction is eminently suited for the instance where the beam is assembled by a modular fabrication technique, it is to be understood that I-beams having variant flanges may likewise be fabricated and formed into truss members in accordance with the present invention, so that they, too, may appreciate this variation in flange size. The invention is therefore not limited to a particular mode of fabrication, but encompasses all variations of such modes within its scope.

As noted earlier, the truss construction of the present in¬ vention facilitates economies and manufacture and use. Thus, the elimination of bending moment and horizontal reaction as described earlier, permits the present truss construction to be "simply supported". In other words, because of the absence of adverse bending moments, the only transfer of force from the truss construction to the vertical supports is vertical in nature. This permits a far simpler and economically more practical type of support approach to wide-span truss constructions that has been heretofore possible. For example, the present truss construction may be easily bolted or otherwise secured to the load-bearing columns_* as shown in FIGURE 1. Alternately, the truss con- struction may be rested upon a pair of masonry or concrete walls, not shown, and simply boJted vertically downward thereinto.

Connections of the type described above are exceedingly simple and easily performed. This feature renders the pre- sent truss constructions particularly well adapted for field construction, in the instance where the sections of the truss construction are prefabricated in the contractor^'s plant. As mentioned earlier, the connectionsbetween the lateral termini of the truss construction and the vertical support members are not rigid and thus the complex body of engineering analysis that accompanies and governs all rigid-frame concepts is avoided. Accordingly, massive buttressing of vertical supports is eliminated, and a simpler "normal" foundation can be utilized herewith.

Though not shown herein, it is to be noted that the upper flanges 12 of each truss member 4 may be provided with clips to receive wood roof purlins. An advantage of the present truss construction is that the loading of the purlins on top of the upper flanges is not limited to panel points, as in the instance of the prior art. This limitation has, in the past given rise to extreme diffi- culty in the shipment of prior art truss constructions of all types. The present truss construction permits a degree of practical flexibility in the spacing of purlins that has been unattainable in the prior art as, for example, each upper flange can be designed to receive a variety of sizes, loadings and slopes, all of which are highly valuable in the design of modern ceiling systems.

As mentioned earlier, the present truss constructions, and the individual truss members, may. be utilized in a variety of applications, either together'-in a truss construction, or individually with variant vertical support members. TJius, for example, individual truss members may be mounted with their flaired ends adjacent a central vertical support mem¬ ber in cantilever fashion, utilizing such central support exclusively. Moreover, truss constructions can be placed on existing wall structures without the need for further support or reenforcement of those vertical load bearing structures, so that reduced expense of retrofitting the present truss construction renders building renovations less expensive and more desirable. The present truss-

OMPI constructions can thus be seen to offer a variety of appli¬ cations in the building industry.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are suitable of modif¬ ication of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within the spirit and scope and defined by the claims.

CMPI

-A . W T.I J-.-P-----OV----/

Claims

WHAT IS CLAIMED IS:

1 1. A shear connection truss construction comprising:

2 A. paired truss members attached to each other in 3 end-to-end abutment;

4 B. each of said truss members having an essentially

5 I-shaped cross-section defined by generally

6 parallel, longitudinally extending flanges and

7 a connecting web extending transversely there¬ in between;

9 C. said truss members each defining a unitary, 0 unsplit end, and a longitudinally split end, said 1 longitudinally split end defined by an upper chord and a lower chord, said upper chord residing in the directional plane of said unsplit end, and said lower chord extending at an acute angle to said upper chord, and having a web discontinuous with the web of said unsplit end; D. said unsplit end of said truss member having a length ranging from 15% to 35% of the length of said truss member; E. said upper chord and said lower chord integral with said unsplit end at a junction point, the flanges on said upper chord and said lower chord integral with the respective adjacent portions of the flanges disposed on said unsplit end; F. paired support plates straddling the broad sur- faces of the webs defined by said chords and said unsplit end, said paired support plates rigidly attached thereto to provide a sandwich-type fixed retention of said webs therebetween; G. the acute angle subtended by said upper chord and said lower chord ranges from about 5° to about 15°; and H. wherein the bending moment exerted at the said junction point is zero.
2. The truss construction of Claim 1 wherein said unsplit end of said truss member has a length ranging from about 16% to about 29% of the length of said truss member.
3. The truss construction of Claim 1 wherein said unsplit end of said truss member has a length ranging from about 25% to about 33% of the length of said truss member.
4. The truss construction of either of Claims 1 or 2 wherein said unsplit end has a length of about 20% of the length of said truss member.
5. The truss construction of Claim 1 wherein said acute angle ranges from about 7° to about 13°.
6. The truss construction of Claim 2 wherein said acute angle ranges from about 7° to- about 13°.
7. The truss construction of Claim 1 wherein said upper and said lower chords are attached to a transverse end plate at the opposite ends thereof from said junction point, and the webs of said upper and said lower chords are coπ- nected by at least one lattice member disposed in over- lapping relationship therebetween.
8. The truss construction of Claim 1 wherein said truss construction is suspended between two vertical loadbearing supports.
9. The truss construction of Claim 1 wherein said lower flange is smaller than said upper flange.
10. A truss member for use in a shear connection truss

OMPI 2 construction,said truss member comprising:

3 A. generally parallel, longitudinally extending 4 flanges and a connecting web extending trans¬ 5 versely therebetween, so that said truss mem¬

6 ber defines an essentially I-shaped cross-

- 7 • section; 8 B. a unitary, unsplit end, and a longitudinally 9 split end, said longitudinally split end de¬ 10 fined by an upper chord and a lower chord, 11 said upper chord residing in the directional 12 plane of said unsplit end, and said lower 13 chord extending at an acute angle to said 14 upper chord, and having a web discontinuous 15 with the web of said unsplit end; 16 C. said unsplit end having a length ranging-fro 17 15% to 35% of the length of said truss member; 18 D. said upper chord and said lower chord integral 19 with said unsplit end at a junction point, the 20 flanges on said upper chord and said lower chord

21 integral with the respective adjacent portions

22 of the flanges disposed on said unsplit end; 3 E. paired support pl-ates straddling the broad sur¬ 4 faces of the webs defined by said chords and 5 said unsplit end, said paired support plates rigidly 6 attached thereto to provide a sandwich-type fixed 7 retention of said webs therebetween; 8 F. the acute angle subtended by said upper chord 9 and said lower chord ranges from about 5° to 0 about 15°; and 1 G. wherein the bending moment exerted at the said 2 conjunction point is zero.
1 11. The truss member of Claim 10 wherein said unsplit end

2 has a length ranging from about 16% to about 29% of the length of

3 said truss member.

OM
12. The truss member of Claim 10 wherein said unsplit end of said truss member has a length ranging from about 25% to about 33% of the length of said truss member.
13. The truss member of either of Claims 10 or 11 wherein said unsplit end has a length of about 20% of the length of said truss member.
14. The truss member of Claim 10 wherein said acute angle ranges from about 7° to about 13°.
15. The truss member of Claim 11 wherein said acute angle ranges from about 7° to about 13°.
16. The truss - member . of Claim 10 wherein said upper and said lower chords are attached to a transverse end plate at the opposite ends thereof from said junction point, and the webs of said upper and said lower chords are con- nected by at least one lattice member disposed in over- lapping relationship therebetween.
17. The truss member of Claim 10 wherein said truss - construction is suspended between two vertical loadbearing supports.
18. The truss member of-Claim 10 wherein said lower flange is smaller than said upper flange.
19. The truss construction of Claim 1 wherein said upper flange, said lower flange and said web are integral with each other prior to the fabrication of said truss member.
20. The truss member of Claim 10 wherein said upper flange, said lower flange and said web are integral with each. other prior to the fabrication of said truss member.

-£UR£

OMP
21. The truss construction of Claim 1 wherein said upper flange, said lower flange and said web comprise planar plate materials that are joined together to form said truss member.
22. The truss member of Claim 10 wherein said upper flange, said lower flange and said web comprise planar plate materials that are joined together to form said truss member.