Figure 2.1-7. Beam Interface Attachments The second joint (upper center of Figure 2.1-7) involving increased complexity occurs when two tribeams intersect at 90° to each other having a common base plane and apex centerlines lying normal to each other in a plane parallel to the base plane. The resulting joint is a compound 60® bevel, 90° miter-type joint. Fortunately, the four base plane corners of the tribeam intersection are identical and are oriented progressively at 0® (360°), 90°, 180°, and 270* (i.e., 90® apart in rotational orientation). The fitting is attached at four places by fasteners to the sheet metal element at the juncture of the sheet-metal flanged braces. Quick connect fittings located on the tubular structure and the ends of the two intersecting sheet metal elements permits automatic assembly of the intersection. A third joint (upper right Figure 2.1-7) is the most complex joint required to produce the entire SPS frame (except at the rotating joint and transmitting antenna). This intersection occurs when tribeam trusses in the same plane cross at an angle of 60° to each other. The vertex sheet metal elements of each truss form this particular joint. Due to symmetry of reflection or inversion of this joint, all parts of the frame structure intersecting at 60° or 120° may be connected. Quick-connect fitting halves are installed in the tubular members and the ends of the sheet-metal elements to be connected such that subsequent automatic assembly can be achieved. The results of the historical search for lightweight structures is illustrated by Figures 2.1-8 through 2.1-10. The utilization of the Vierendeel truss applied to square columns by the Akron and Macon dirigibles is shown by Figure 2.1-8. Framing and wire rigging is dramatically shown in Figure 2.1-9.
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