PROBLEM TO BE SOLVED: To provide a beam capable of being reduced in weight, while securing strength and rigidity.;SOLUTION: This beam includes a sub reduction hole 5 punched in a web 3 by avoiding a neutral shaft a in addition to main reduction holes 4a, 4b, 4c, 4d, 4e, 4f and 4g punched to cross the neutral shaft a of the web 3 in which bending stress becomes zero, and thereby the beam can be reduced in weight by the sub reduction hole 5. Maximum stress to be generated becomes larger as a cross section coefficient is smaller in a cross section on which bending moment acts, but the cross section coefficient can be made larger than that of a conventional beam punched with a hole part of the same diameter by making opening area of the sub reduction hole 5 punched by avoiding the neutral shaft a smaller than the main reduction holes 4a, 4b, 4c, 4d, 4e, 4f and 4g. As a result, the maximum stress of the cross section can be lowered, and lowering of strength and rigidity can be prevented.;COPYRIGHT: (C)2011,JPO&INPIT
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