28 92 2 339 90 90 AASHTO 1996 RC fc =245kg/cm 2 2 fc =280kg/cm fc =280kg/cm 2 2 19 SD42 fy =4200kg/cm 16 SD28 fy =2800kg/cm 2 ASTM 572 GRADE 50 GRADE 50 GRADE 50 GRADE 50 10mm -HS20-44 25 25 (hinge) (roller)