Abstract:
A joint for connecting together three generally tubular members comprises first and second members and a clamp for joining the two joint members together. Each of the joint members has first and second portions, the first portion of each joint member being a telescopic fit within a respective one of the tubular members. The second portions of the two joint members together form a connector when the joint members are juxtaposed. The clamp is effective to pass around the two second portions of the juxtaposed joint members to fix the connector for coupling a third tubular member.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a joint for connecting together at least three generally elongate structural members. 
     My co-pending U.S. Patent Application Ser. No. 850,252 relates to building structures of the type having a framework covered by sheet material. The framework of these building structures is made up of a large number of generally tubular members, and it is the aim of this invention to provide a joint for connecting at least three such members and which is easy to manufacture and to use. 
     SUMMARY OF THE INVENTION 
     The present invention provides a joint for connecting together three generally tubular members. The joint comprises first and second members and a clamp for joining the two joint members together with each joint member having first and second portions. The first portion of each joint member is a telescopic fit within a respective one of the tubular members. The second portions of the two joint members together form a connector when the joint members are juxtaposed for joining to the third tubular member. The clamp passes around the two second portions of the joint members and is coupled to the third tubular member. 
     Each of the first portions may be arranged to be a friction fit within its respective tubular member, but it is preferable for the first portions to be welded or riveted to their tubular members. 
     Preferably, each of the joint members has a third portion, the two third portions together forming a connector for a fourth generally tubular member. A second clamp may, in this case, be provided for joining the two joint members together, the second clamp passing round the two third portions. 
     Advantageously, the two first portions extend generally in opposite directions and the second (and where provided the third) portions extend substantially at right-angles thereto. 
     The connector formed by the two second portions may be joined to the third tubular member by means of a nut and bolt. Preferably, the bolt passes through the first-mentioned clamp, through the adjoining regions of the second portions, and through a flattened end portion of the third tubular member. Advantageously, the non-threaded end of the shank of the bolt is of square cross-section, and a hole provided in the clamp is of similar cross-section. 
     The connector formed by the two third portions is preferably joined to the fourth tubular member in the same way. 
     In practice, the tubular members to be joined together are each in the form of a compound-braced strut having first and second parallel tubular booms braced together by a series of cross-pieces. In this case, the first booms of the struts are joined together by a first joint, and the second booms of the struts are joined together by a second joint, the first and second joints being of the type defined above. Preferably, the two first members of the first and second joints are joined together by a strut, and the two second members of the first and second jointed are joined together by a further strut. These struts increase the rigidity of the joints. 
     Advantageously, the parts of the joint are made of a high strength aluminium alloy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a joint constructed in accordance with the invention; 
     FIG. 2 is a perspective view of four tubular members connected together by the joint of FIG. 1; and 
     FIG. 3 is a perspective view of four compound-braced struts prior to being joined together by means of joints of the type shown in FIG. 1. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to the drawings, FIG. 1 shows a joint comprising first and second joint members 1 and 1&#39; and a clamp 2. All the parts of the joint are made from a high strength aluminium alloy. Members 1 and 1&#39; are identical, each having a first connector portion 3 and 3&#39; respectively, a second connector portion 4 and 4&#39; respectively, and a third connector portion 5 and 5&#39; respectively. In each case, the second and third connector portions 4 and 4&#39; and 5 and 5&#39; extend at right angles to the corresponding first connector portions 3 and 3&#39;. Each first connector portion 3 and 3&#39; includes an outwardly extending flange 6 and 6&#39; which, when juxtaposed in use, lie in face-to-face engagement as shown in FIG. 1. A re-entrant aperture 7 and 7&#39; is located at each lateral edge portion of flange 6 and 6&#39;, respectively. The purpose of apertures 7 and 7&#39; is described below. 
     As shown in FIG. 1, the two second portions 4 and 4&#39; together form a tab which extends generally perpendicularly to the plane of symmetry of the joint which passes through the center of the first connector portions 3 and 3&#39;. A semi-circular aperture located in each second connector portion 4 and 4&#39; forms a circular aperture 8 when the two members 1 and 1&#39; are positioned as shown in FIG. 1. Each second connector portion 4 and 4&#39; includes a short dowel 9 and 9&#39; which extends outwardly from an inclined front face 10 and 10&#39;. The purpose of these dowels 9 and 9&#39; is explained below. 
     The two third connector portions 5 and 5&#39; are identical to the two second connector portions 4 and 4&#39; and so define a circular aperture 8 and have dowels 9 and 9&#39;. 
     Clamp 2 includes a generally flattened-oval body portion 2a and a pair of generally disc-shaped members 2b which project beyond the edge of the body portion as shown in FIG. 1. One of the members 2b includes a square hole 2c and the other has a circular hole 2d. The two holes 2c and 2d are aligned and spaced from the edge of body portion 2a. In use, clamp 2 fits over the second connector portions 4 and 4&#39;, to connect the members 1 and 1&#39; together in a manner to be described below. A second, identical clamp (not shown) fits over the third connector portions 5 and 5&#39;. 
     The joint described above with reference to FIG. 1 is used to join together four generally tubular members in the manner described below with reference to FIGS. 2 and 3. Each tubular member 20, 21, 22 and 23 is of generally elliptical cross-section. Members 20 and 21 slide over first portions 3 and 3&#39; of joint members 1 and 1&#39; until their end faces meet flanges 6 and 6&#39;. Members 20 and 21 each have a pair of re-entrant grooves 20a and 21a which form a continuous groove with aperture 7 and 7&#39; of flanges 6 and 6&#39;. Members 20 and 21 are riveted to first portions 3 and 3&#39; so as to form a permanent connection. 
     Member 22 includes a flattened end portion 22a having a hole 22b (see FIG. 3). Clamp 2 is placed over second portions 4 and 4&#39; of joint members 1 and 1&#39;. A bolt 24 having a square-ended shank portion is pulled through square hole 2c in clamp 2, through hole 8 in the tab formed by second portions 4 and 4&#39;, through round hole 2d in clamp 2 and through round hole 22b in the flattened end portion 22a of tubular member 22. A nut (not shown) can then be threaded onto bolt 24 and tightened up to secure member 22 to the joint, thus firmly connecting the two joint members 1 and 1&#39; at the same time. 
     Member 23 is identical to member 22, having a flattened end portion 23a and a bolt hold 23b, and it is connected to the joint in an identical manner. Thus, four tubular members 20, 21, 22 and 23 can be firmly connected together in a very simple manner, using two nuts and bolts and a simple riveting operation. Where the joint is not required to be permanent, the riveting step can be omitted and members 20 and 21 can be arranged to be friction fitted to the first portions 3 and 3&#39;. The use of bolts 24 having square-ended shanks, enables the nuts to be tightened up without the need for the operator to hold the shank of the bolt to prevent it rotating with the nut. 
     As indicated above, the joints are intended particularly for use with the type of building structure described in the specification of my copending U.S. Patent Application Ser. No. 850,252. This specification describes how the sheet material which forms the covering for the framework made up from tubular members such as 20, 21, 22 and 23 is fixed to these members. Briefly, sheets 25 of material are provided at each lateral edge with a beading 26 which can slide in grooves 20a and 21a and by apertures 7 and 7&#39;. In order to stretch the sheets 25, rails 27 may criss-cross diagonally between the tubular members and bow slightly outwardly. Rails 27 in FIG. 2 are friction fitted over dowels 9 and 9&#39; of joint members 1 and 1&#39;. Where rails 27 are not needed, dowels 9 and 9&#39; of joint members 1 and 1&#39; can be omitted. 
     In the specification of my co-pending U.S. Patent Application Ser. No. 850,252, the members forming the framework of the building structure are compound-braced booms and FIG. 3 shows how such booms are joined together using the type of joint shown in FIG. 1. Basically, each of the compound-braced booms includes a pair of tubular booms 20 and 30, 21 and 31, 22 and 32, and 23 and 33, the booms of each pair being braced together by struts 28. The four booms 20, 21, 22 and 23 are joined together by a joint identical to that of FIG. 1. Booms 30, 31, 32 and 33, are joined together by a second joint which has joint members 41 and 41&#39; identical to members 1 and 1&#39; apart from the omission of dowels 9 and 9&#39; which are unnecessary as no sheet material is passed over booms 30, 31, 32 and 33. Joint members 1 and 41 are connected by a strut 42, and joint members 1&#39; and 41&#39; are connected by a strut 42&#39;, these struts increasing the rigidity of the finished compound joint. 
     FIG. 3 also shows a further feature of the invention, namely that the end faces of joint members 1 and 1&#39;, 41 and 41&#39; each include a peg 43 and a matching hole 44, the peg of one member mates with the hole of its counterpart and vice-versa. In this way, accurate alignment of the pairs of joint members is facilitated and ensured. 
     It will be apparent, therefore, that the joint described above enables the tubular members of the framework of a building structure to be joined together in a simple and reliable manner. Moreover, each joint merely requires two standard bolts (and associated nuts) and a conventional riveting gun (where the joints are required to be permanent).