h b d t r r 1 (cm 2 ) (kg/m) 5 50 32 4.4 7.0 6.0 2.5 6.16 4.84 6.5 65 36 4.4 7.2 6.0 2.5 7.51 5.90 8 80 40 4.5 7.4 6.5 2.5 8.89 7.05 10 100 46 4.5 7.6 7.0 3.0 10.90 8.59 12 120 52 4.8 7.8 7.5 3.0 13.30 10.4 14 140 58 4.9 8.1 8.0 3.0 15.60 12.3 14a 140 62 4.9 8.7 8.0 3.0 17.00 13.3 16 160 64 5.0 8.4 8.5 3.5 18.10 14.2 16a 160 68 5.0 9.0 8.5 3.5 19.50 15.3 18 180 70 5.1 8.7 9.0 3.5 20.70 16.3 18a 18