Multi-Tubular Truss Joint and Method of Joining Tube Ends

This invention relates to a mechanical structural joint and particularly one for connecting together the ends of long hollow tubes radiating outwardly from the intersecting points, or nodes, of a multiple tube truss network structure and a method of forming such a joint at the nodes of a truss structure.

Thin-wall hollow tubes are highly advantageous as structural members for creating a lightweight truss structure of large dimensions, particularly one intended for an airborne structure. In such a large truss structure the manner of connecting together the ends of angularly arranged tubes intersecting at the nodes of the truss structure creates a problem. It is normally not desirable to weld together the ends of tube members where they intersect at the truss nodes due to destroying the heat treat condition of the tubes, and other assembly problems. Therefore, some type of mechanical joint must be utilized. Many types of mechanical joints are possible and have been used, such as a central joining piece with arms projecting outwardly at the node in the various directions of the individual tubular members of the truss. However, each tubular member must be separately attached to the central piece, usually a solid forging, requiring a large number of fastenings and resulting in an excessively heavy structure which is expensive and complicated to fabricate. Commonly the ends of the tubes to be joined are completely flattened, the solid flattened ends overlapped and bolted together in the manner of U.S. Pat. No. 4,187,034, USSR Pat. No. 594,269 and European Pat. No. 0 023 721. Various fasteners and central joining pieces have been utilized to mechanically fasten together the ends of hollow tubes at a joint in the manner of U.S. Pat. Nos. 1,582,587, 2,912,075, 4,259,821, 4,322,176 and German Patentschrift No. 237,050.

The object of the invention is to provide a high strength joint for connecting the ends of hollow tubular members. Another object of the invention is to connect the ends of hollow tubes that intersect at the nodes of a truss structure formed from hollow tubes.

A further object of the invention is to provide a manner of joining together the ends of hollow tubular members without disturbing the heat treat condition of the tubular members.

Still a further object of the invention is to join together the ends of a number of hollow tubes arranged in an angular relationship to intersect at a point.

Yet another object of the invention is to join together at the nodes of a truss structure separate sets of co-planar groups of angularly arranged tubes intersecting at the nodes in an angular relationship to one another.

Still another object of the invention is to provide a simple and inexpensive means of connecting together the ends of angularly aligned, hollow tubular members into high strength mechanical joints in the construction of a large, three dimensional light truss network formed of hollow tubular members.

Yet still another object of the invention is to provide a means of joining together the ends of different diameter hollow tubes.

An additional object of the invention is to create a mechanical joint connecting the hollow tubular beams of a complex truss network in a manner to avoid localized stresses and provide an evenly distributed carry-over of loads between the tubular beams of the truss network.

The foregoing and other objects of the invention are achieved in a preferred embodiment of the invention by partially flattening the ends of each of the tubes to be joined into an elongated annular shape of such dimension that the ends of the tubes to be joined will telescopically fit together in a mutually nesting relationship, arranging the tubes to be joined such that the flattened end portions are in an overlapping, telescopically nesting relationship with a hollow splice plate of sandwich construction extending into the space within the interior of the nesting tube ends in engagement with interior surfaces of each of the flattened tube ends, and fastening together the nesting arrangement of the overlapping, flattened tube ends and splice plate by bolts extending transversely of the nesting arrangement through holes at spaced intervals in the flattened tube ends and splice plate.

Other objects and advantages of the invention will hereafter become more fully apparent from the following description and the annexed drawings which illustrate a preferred bodiment of the invention.

FIG. 1 is a perspective view of a two member tubular joint.

FIG. 2 is an exploded plan view of the joint of FIG. 1.

FIG. 3 is an end view of the joint of FIG. 1.

FIG. 4 is a partially exploded perspective view of the splice plate of the joint of FIGS. 1, 2, and 3.

FIG. 5 is a side view of a compound joint of which the two-member FIG. 1 is one component.

FIG. 6 is a plan view of the compound joint of FIG. 1.

The major components of a basic type, two member joint of FIGS. 1-3, in which one end of the larger diameter tube 10 is joined to the end of the smaller diameter tube 11 at a node 14 of a truss structure (not illustrated), are illustrated in the exploded plan view of FIG. 4. The ends 10a and 11a of the two hollow, round tubes 10, 11 may be conveniently flattened into an elongated and flat oval shape by placing each tube end between a pair of dies, each of which conforms to the half-contour shape of the flattened tube end, placing a crushable material (e.g. a foamed plastic) within the end portion of the tube and crushing the tube end between the two dies in the jaws of a press. The tube crushing dies gradually taper the cross sectional contour of each tube from the original circular cross sectional shape to an elongated, flattened oval shape a short distance "A" from the tube end as labeled and illustrated by the solid contour lines "B" and "C" on FIG. 2. The outer flattened ends of each tube over the dimension "A" have a uniform cross section so the tubes can be telescopically nested. A pair of doubler plates 12a, shaped to the contours of the upper and lower halves of the flattened end portion of 1Oa of tube 10, are secured to the outer surfaces of the upper and lower halves of the tube flattened end portion 10a by cement or rivets as desired in forming the end of tube 10 into a reinforced flattened end 12. Similarly, a pair of doubler plates 13a are secured to the outer surfaces of the upper and lower halves of the flattened end portion 11a of tube 11 forming the reinforced flattened end 13. Lightening holes 12b and 13b in the upper portions of the doubler plates 12a and 13a reduce weight. As apparent from FIGS. 1 and 3, the height dimensions of the respective reinforced flattened end portions 12 and 13 of tubes 10 and 11 are such that a portion of the flattened end 13 of tube 11 can be inserted within the flattened end 12 of tube 10 (as represented by the phantom lines in the right hand portion of FIG. 2) to place segments of the flattened end portions 12 and 13 of the respective tubes 10 and 11 (represented by the area beneath the dimension "D" of FIG. 2) into a telescopically nesting relationship in which interior surfaces along the top and bottom of flattened end portion 13 are in contact with and overlie outer surfaces of the top and bottom of flattened end portion 12 with the longitudinal axes of tubes 10 and 11 intersecting at the node 14 of a truss structure. Such a structure typically could be of the nature shown in FIG. 1 of U.S. Pat. No. 4,259,821, in which a large number of tubular members are arranged in an angular relationship with the ends of tubes intersecting at nodes to form a complex truss network. Portions of the flattened tube ends 12 and 13 are cut away into the contours illustrated in FIG. 2 so the flattened ends can telescopically fit together in the angular relationship represented by the phantom lines of the assembled tubes at the right portion of FIG. 2 in a manner to avoid interference between the tube flattened end portions 12 and 13 and also to provide clearance for being joined to a second joint of tubes at node 14 in creating a compound joint at the node as will be subsequently described in relation to FIGS. 5 and 6.

A composite, lightweight splice plate 15 fits into the interior of the endmost portions of the flattened end portions 12 and 13 of the tubes 10 and 11 with the upper and lower surfaces of the splice plate 15 in a closely adjoining relation to the overlying surfaces of the flattened end portions 12 and 13 of the tubes 10 and 11. The splice plate 15 comprises a pair of spaced apart upper and lower main plates 16, a portion of each of which are overlapped by a pair of upper and lower riser plates 17 with each set of overlapping main and riser plates being separated by channels 18 secured to the plates by an epoxy adhesive or other convenient manner, lightening holes 19 being spaced apart along the webs of the channels. Lightening holes 20 (only a few being illustrated) are also present in the main and riser plates to reduce weight. Since the interior height dimensions of the oval-shaped flattened end portions 12 and 13 of the tubes 10 and 11 vary to permit the respective tube ends to be telescopically nested one within the other with segments of the two tube ends overlapping, the thickness of different portions of the splice plate 15 immediately underlying each of the tube flattened end portions must differ which is accomplished by the composite construction utilizing riser plates 17 overlapping portions of the main plates 16, as is readily apparent from FIGS. 1 and 3. Bolts 21 having heads 22 and nuts 23 overlying washers 25, extending through holes 24 in the flattened end portions 12 and 13 of tubes 10 and 11 in registry with holes 24a in the upper and lower plates 16 and 17 and the channels 18 of the splice plate, tightly clamp together the nested tube flattened end portions 12 and 13 and the underlying splice plate 15 to form the rigid intergral joint 26 connecting the ends of the angularly arranged tubes 10 and 11 at the node 14. Although the described arrangement of overlapping riser and main plates separated by elongated channels provides a convenient lightweight splice plate of variable thickness serving as an anvil around which the respective tube wall ends are tightly clamped by the bolts 21 into a rigid joint, equivalent construction could be utilized in producing a variable thickness splice plate of the same external contours such as utilizing multiple short lengths of tubing in lieu of channels as separaters between the upper and lower plates of the splice plate. Other equivalent forms of a lightweight splice plate around which the telescopically nesting flattened tube ends may be tightly clamped would be readily apparent to those normally skilled in the art.

The two member joint 26 described above with reference to FIGS. 1-4 represents a simple basic joint of the invention connecting the ends of two co-planar tubes. However, the same basic construction of the two member joint can be utilized in connecting ends of three or more co-planar tubular members intersecting at a node. As in the two member joint 26 described above, an end of each of the tubes to be joined is flattened to an elongated annular shape in the manner described for the two member joint with the dimensions of each of the flattened tube ends varying to the degree that the respective tube ends of the multiple tubes are arrangable into a telescopic, mutually nesting relationship. A multi-layered splice plate fits into the interior of the telescopically nested flattened tube ends in an immediately adjoining relationship with the interior surfaces of each flattened tube end and, in a preferred embodiment, comprises a pair of sets of plates in which the number of plates in each set is equal to the number of tubes in the joint with the plates comprising each set of the pair arranged in an overlapping manner and the two sets of plates are separated by elongated channels in the same general manner as FIG. 4.

FIGS. 5 and 6 illustrate a compound joint 27 at node 14 comprising the intersection of a first set of co-planar tubes, such as tubes 10 and 11 connected by the joint 26 illustrated in FIG. 1, and a second set of co-planar tubes 28 schematically illustrated by phantom lines in FIG. 5, in which the flattened ends of each of the tubes 28 are connected by the joint 29 of which the splice plate 30 is an integral portion (schematically illustrated by phantom lines in FIGS. 5 and 6). The phantom lines in FIGS. 5 and 6 represent a set of co-planar tubes angularly arranged in the common plane 36 with their telescopically nesting flattened ends overlying a splice plate to form a connecting joint 29 basically equivalent to the one described with respect to FIG. 1. Upper and lower brackets 31 are rigidly connected to members comprising each of the joints 26 and 29 that respectively join the ends of each of the two sets of co-planar tubes 10, 11 and 28 intersecting at node 14. As best seen in FIGS. 5 and 6, each bracket 31 includes a faceplate 32 contoured to overlie the flattened end portions 12 and 13 of joint 26 and at the end of the face plate adjacent the node 14 and end plate 34 extends upwardly at the angle subtended between plane 35 of co-planar tubes 10 and 11 and plane 36 of the co-planar set of tubes 28. Several upstanding L-shaped gussets 37 extending across each faceplate 32 are welded to the face plate and end plate 34 of the brackets 31. Bolts 21 extending through and joining together the flattened tube ends and the splice plate of joint 26 and bolts 38 which extend through the flattened end portions of the second set of tubes 28 and splice plate 30 in forming the second tube joint 29, rigidly connect the members comprising each of the two tubular joints 26 and 29 to the upper and lower brackets 31 to form the compound joint 27 at the node 14. Lightening holes 33 of the general nature illustrated in FIG. 6 may be incorporated in various components of the brackets 31. Obviously brackets having more than the two angularly arranged plates 32 and 34 of bracket 31 that connect the respective joints of the two sets of tubes as illustrated in FIGS. 5 and 6 can be formed to connect the joints of each of three or more co-planar tube sets intersecting at a common node.

The configurations of the joints illustrated and described in FIGS. 1-6 have been chosen as sample of the simle embodiments of the invention to promote an easy understanding. Although round tubes are utilized as the members of most truss structures, trusses utilizing hollow tubes of other than a circular cross section could be joined by this invention in the same manner as the illustrated hollow tubes by deforming the ends of the tubes to be joined into elongated contours which can be telescopically nested together with their inner surfaces in overlying contact with a splice plate fitting within the deformed tube ends. In utilizing this invention in joining hollow tubes of any cross-sectional shape, round or otherwise, the ends of the tubes to be joined need not be deformed into the elongated oval shape described with respect to FIGS. 1-6 but can be deformed into any shape whereby the tube ends can be telescopically arranged in a nesting relationship, e.g. the contour of the flattened tube ends could be rectangular.

Various modifications of the invention are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined by the amended claims.