JOINT FOR THREE-DIMENSIONAL GRID STRUCTURES

Abstract: A joint for three-dimensional grid structures composed of pyramidal and tetrahedral modules; the joint being composed of two solid semispherical caps (1, 3) with ovoidal seats (19), and of a central plate (2). By means of four perpendicular grooves (11) on one cap (1) and four perpendicular grooves (20) on the other (3), and by inserting a single central pin (9) screwed to an external nut (10), the caps (1, 3) and central plate (2) enclose the ends (4, 14) of rods (7, 18, 8) extending in all directions; which ends (4, 14) are screwed to the rods (7, 18, 8) by means of a respective welded conical fitting (6) and a respective lock nut (5).

Description: JOINT FOR THREE-DIMENSIONAL GRID STRUCTURES TECHNICAL FIELD The present invention relates to a joint for three-dimensional grid structures, and in particular to a joint composed of steel elements (two semispherical caps) connected by means of a central through pin, and in which converge the cylindrical ends of tubular rods which, however oriented and connected by the joints, provide for forming three-dimensional grid structures. The present invention applies in particular to heavy-duty steelwork for wide-span constructions subjected to exceptional stress. BACKGROUND ART Three-dimensional grid structures, or grid structures composed of pyramidal and tetrahedral modules, are special structures normally made of steel; are composed of a number of joints and rods; and are characterized by the convergence, in each joint, of eight or twelve rods, four of which located in the same horizontal plane to form a square grid, and eight of which extend obliquely in all directions, four on each side of the plane containing the horizontal rods. European Patent n. 0053582 and Italian Patent n. 1209778 issued on 30/8/1989 and filed by the present Applicant relate to a joint of the aforementioned type, wherein: the joint is composed of two hollow slotted caps; the ends of the rods are spherical; the conical rod fittings are screwed on to the rods. The above joint presents the following drawbacks: when subjected to tensile stress by the rods, the hollow caps tend to open, thus resulting in collapse of the structure; being spherical, the ends of the rods, when subjected to severe tensile stress, become wedge-shaped and withdraw from the caps, thus resulting in collapse of the structure; - when subjected to compressive stress, the spherical ends, being tangent to one another, transmit the localized stress, thus resulting in permanent deformation of the stressed portion; during assembly, the four horizontal rods must be locked due to difficulty in assembling all twelve rods simultaneously with the central pin. DISCLOSURE OF INVENTION It is an object of the present invention to provide a joint for three-dimensional structures, designed to overcome the drawbacks typically associated with known joints of the aforementioned type. According to the present invention, there is provided a joint for three-dimensional grid structures composed of pyramidal and tetrahedral modules, and in which joint converge eight or twelve horizontal and oblique rods extending in all directions; characterized by the fact that the joint is composed of two solid semispherical caps and a solid, central truncated-cylinder-shaped plate interposed between said semispherical caps; each said rod presents a hammer-shaped end; each semispherical cap has respective flat face which presents four perpendicular ovoidal seats and four truncated-cone-shaped grooves for connection with a respective said hammer-shaped end of said rod; said semispherical caps, central truncated-cylinder-shaped plate and hammer-shaped-ends being connected by means of central pin. BRIEF DESCRIPTION OF DRAWINGS A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows an exploded view in perspective of a joint in accordance with the present invention; Figures 2, 3 and 4 show larger-scale plan views of details of the Figure 1 joint; Figures 5 and 6 show sections along lines A-A' and B-B' in Figures 2 and 3 respectively; Figure 7 shows larger-scale details of Figure 1; Figure 8 shows the Figure 4 detail in a specific operating condition. BEST MODE FOR CARRYING OUT THE INVENTION More specifically, Figure 1 shows an exploded view of the joint composed of eight converging rods prior to assembly by means of a central pin 9 locked by an external nut 10. Figure 2 shows a plan view of the solid bottom cap 3 having a central hole 12 and with reference to Figure l, an at least internally prismatic peripheral recess 13, and in which the hammer-shaped ends 4 of the horizontal rods 7 and 18 converge inside seats 19 and grooves 20 formed in the solid cap 3. Figure 3 shows a plan view of the solid top cap l having a central hole 12 and a peripheral recess 13, and in which the hammer-shaped ends 14 of the oblique rods 8 converge inside seats 19 and grooves 11 formed in the solid cap 1. Figure 4 shows a plan view of central plate 2, which presents grooves 20', an at least internally prismatic peripheral lip 15, ovoidal seats 19' for receiving the hammer-shaped ends 4 of the horizontal rods, a hexagonal recess 16 for housing an intermediate nut for partially locking the rods, and a central hole 17 for passage of central pin 9. Figure 5 shows a section A-A' of the three parts, through the horizontal rods in the case of eight converging rods. Figure 6 shows a section B-B' of the three parts, through the oblique rods in the case of eight converging rods. Figure 7 shows the hammer-shaped ends 4, 14 of the horizontal and oblique rods 7, 8 respectively, screwed to the conical fittings 6 welded to the rods, and locked by nuts 5. Figure 8 shows a plan view of central plate 2 in the case of twelve converging rods, in which case it houses ends 4 of the horizontal rods, and, by means of lip 15, connects two symmetrical caps 1, 3 for the eight oblique rods 8. The joint according to the present invention provides for overcoming the drawbacks of known joints by virtue of the following characteristics; with the exception of the seats for the hammer-shaped ends of the rods, steel caps 1 and 3 of which the joint is composed are solid; the hammer-shaped ends 4, 14 of the rods are embedded entirely inside the cap, thus preventing any possibility of the rods withdrawing from the joint; the contact surface between the end of the rod and the joint extends over the entire bottom portion of the hammer-shaped end, thus preventing permanent deformation due to compressive stress; when assembled, the peripheral recess 13 on the caps mates with the peripheral lip 15 on the central plate, thus preventing the caps from opening; in addition to connecting the two caps, the central plate also provides, during assembly, for locking the first four rods by means of a central intermediate nut housed in seat 16. As compared with similar systems, the main advantage of the joint according to the present invention is that it provides for withstanding severe tensile and compressive stress - even in the order of hundreds of tons - on the rods of which the structure is composed, by virtue of the characteristic hammer-shaped ends of the rods, which, when inserted inside the solid steel caps and central plate, have virtually no possibility of withdrawing. As such, the present invention provides for achieving constructions featuring exceptional spans and stress as compared ' with normal three-dimensional structures. A further advantage of the system according to the present invention - in addition to enabling assembly by means of one fastening element, providing for a perfect joint, and enabling adjustment of the length of the individual rods - is that the two solid caps, symmetrical in relation to the central plate, also enable rotation of the converging rods in the plane perpendicular to the pin, thus enabling the formation of virtually any number of both curved and flat structures. To those skilled in the art it will be clear that changes may be made to the joint as described and illustrated herein without, however, departing from the scope of the present invention.

Claims: CLAIMS 1) A joint for three-dimensional grid structures composed of pyramidal and tetrahedral modules, and in which joint converge eight or twelve horizontal and oblique rods extending in all directions; characterized by the fact that the joint is composed of two solid semispherical caps (1, 3) and a solid, central truncated-cylinder-shaped plate (2) interposed between said semispherical caps (1, 3) ; each said rod presents a hammer-shaped end (4, 14); each semispherical cap (1, 3) has respective flat face which presents four perpendicular ovoidal seats (19) and four truncated-cone-shaped grooves (11 ' ,- 20) for connection with a respective said hammer-shaped end (4, 14) of said rod; said semispherical caps, central truncated-cylinder-shaped plate (2) and hammer-shaped-ends (4, 14) being connected by means of central pin (9) . 2) A joint as claimed in Claim 1, characterized by the fact that said central plate (2) presents at least one flat face with four perpendicular seats (19') , and presents also two peripheral lips (15) designed to mate with respective peripheral recesses (13) of said caps (1, 3). 3) A joint as claimed in Claim 2, characterized by the fact that said peripheral recess (13) and said peripheral lip (15) are at least internally prismatic. 4) A joint as claimed in Claim 1 or 2 or 3 , characterized by the fact that said central plate (2) provides for receiving the hammer-shaped ends of the horizontal rods in the case of twelve converging rods; and presents an intermediate nut (21) for partial assembly. 5) A joint as claimed in at least one of the preceding Claims, characterized by the fact that each end of the horizontal and oblique rods (7, 18, 8), composed of threaded hammer-shaped elements (4, 14), is screwed to a conical fitting (6) welded to the respective rod, and locked by means of a nut (5) .

Inventors: VENTRELLA ETTORE, VENTRELLA, ETTORE
Applicants: VENTRELLA ETTORE, VENTRELLA, ETTORE
Application year: 1993
Main classification: E04B1
IPC codes: E04B1