Buckminster Fuller's “Tensegrity” structures and Clerk Maxwell's rules for the construction of stiff frames
Résumé
Maxwell has shown that b bars assembled into a frame having j joints would, in general, be simply stiff if b = 3j−6. Some of Buckminster Fuller's “Tensegrity” structures have fewer bars than are necessary to satisfy Maxwell's rule, and yet are not “mechanisms” as one might expect, but are actually stiff structures. Maxwell anticipates special cases of this sort, and states that their stiffness will “be of a low order”. In fact, the conditions under which Maxwell's exceptional cases occur also permit at least one state of “self-stress” in the frame. Linear algebra enables us to find the number of “incipient” modes of low-order stiffness of the frame in terms of the numbers of bars, joints and independent states of self-stress. Self-stress in the frame has the effect of imparting first-order stiffness to the frame, and it seems from experiments that a single state of self-stress can stiffen a large number of modes. It is this factor which Fuller exploits to make satisfactory structures.
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