Super Bar Theory and BP System in Super Span Flat Space Frames

In this paper, possible solutions to the constraints of flat space frames in large spans are summarized, including the application of multilayer forms, the introduction of novel simplexes, and the improvement in structural components. Then the base-reinforced pyramid (BP) system, which is formed by reinforcing the base of a rectangular pyramid by crossing bars, is introduced as a successful attempt to reduce maximum bar forces in double-layer space frames without densifying grids. Properties of the BP system are reviewed. Super bar theory is introduced to cope with the buckling and large internal forces of long bars. Therefore, large grids can be realized in super span flat space frames with lightweight and large clear space. Under this concept, either a reciprocal prism or, generally, its derivatives, which are composed of much shorter bars, replace long bars. Factors affecting the efficiency of super bars are analyzed in detail, and their joint design is also recommended. Details of designing bars are clarified. The efficiency of a 200-m-span flat double-layer BP grid employing super bars as long components is proven by case studies. Finally, a new concept with reduced cross-section is developed for a super bar system to achieve a further reduction in weight.