BENDING OF PRETWISTED BEAMS
BROWN UNIV PROVIDENCE R I DIV OF APPLIED MATHEMATICS
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The general theory of pretwisted beams and columns is applied t o the bending of an initially straight and uniformly pretwisted beam of doubly symmetric thin-walled section. Pretwisting brings planes of various bending stiffness into play with a resulting stiffness which may be regarded as averaging the stiffness of the beam in its principal directions. Compared with bending of an untwisted beam in its most flexible direction, a thin strip can have its defelction in the plane of bending reduced 72 by an initial twist of 0.83pi. Simultaneously, lateral deflections of almost equal magnitude are induced. For pretwists above 2 pi, the lateral deflections in the plane of bending are still reduced as much as 44. With increasing initial twist the pretwisted beam becomes more flexible, and for an initial twist of 6.5 pi it is as flexible as the untwisted beam in its most flexible direction. Beams of equal flexibility in all directions become more flexible with initial twist this corresponds to the observations made by Den Hartog Advanced Strength of Materials, 319, McGraw-Hill Book Co., New York, 1952 in some of his experiments.