| 摘要 |
PROBLEM TO BE SOLVED: To provide a square pipe being light and high in strength and rigidity concretely for piping, a housing and a casing loaded with an internal pressure or an external pressure. SOLUTION: The square pipe made of carbon fiber-reinforced plastic is a square pipe mainly composed of plurality of planes, when a largest plane which constitutes the square pipe is a main surface, and a surface positioned opposite to the main surface and having the same area as that of the main surface or a second large area next to the largest area is a main surface, too each thickness of the peripheries of corner parts in at least four spots of the square pipe is two to five times as larger as the thickness of the main surface.
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