例A-3计算图示型钢组合截面的 形心和对形心轴的惯性矩 46 解:查表A1=395cm2A2=21.3cm2 y 395×10+21.3×(20+1.67) =856.8cm320b S y =14.1cm 1=609.4cm4 A1+A2 169cm 1n=1n+l12=6094+169=7784cm4 2500cm 12=61.1cm4 +A1(y2-y)2+l2+A2(0y2-y) 12 =2500+39.5×(141-102+611+21.3×(2167-14.1)2 4996cm例A -3 计算图示型钢组合截面的 形心和对形心轴的惯性矩 解： 4 1 2 I y = I y + I y = 609.4 +169 = 778.4 c m Sz = A1 y1 + A2 y2 = 14.1c m 1 2 = + = A A S y z c 14b 20b  +  c = c c I I I z z z 2 2 = 2500 + 39.5(14.1−10) + 61.1+ 21.3(21.67 −14.1) 4 = 4996cm 3 = 856.8cm y z 1 z 2 z c y c z = 39.510 + 21.3(20 +1.67) 4 1 I y = 609.4 cm4 2 I y =169 cm 4 1 I z = 2500 cm4 2 I z = 61.1cm 2 1 A = 39.5 cm 2 2 查表 A = 21.3 cm 2 z2 2 2 2 z1 1 1 ( ) ( ) c c = I + A y − y + I + A y − y