ʻO ka ʻāpana hollow kahi mea o kekahi geometry i hana ʻia me ka hao a i ʻole ke kila a me kahi mea i loaʻa kekahi ikaika a paʻakikī (e like me ka plastic, aluminika, aniani fiber, etc.) ma o ka ʻōwili ʻana, extrusion, hoʻolei a me nā mea like. Me ke kila angle, ke kila kanal, I-beam, ke kila square, H-beam, etc. he mea ia o kekahi geometry i hana ʻia me ka hao a i ʻole ke kila a me kahi mea i loaʻa kekahi ikaika a paʻakikī (e like me ka plastic, aluminika, aniani fiber. , etc.) ma ka ʻōwili ʻana, extrusion, hoʻolei ʻana a me nā mea like. Me ke kila angle, ke kila channel, I-beam, square steel, H-beam, etc.