A1 A2 A1 B1 B2 B1 b 1 a b b 3 a b 2 a L2/4 L2/2 L2/4 L2 L1/4 L1/2 L1/4 L1
l1 150mm l2/3 3000m m 150mm l2 l1/3 3000m m
la1 la1 bb/2
0. 4la E la E la E la E la E 0. 4la E
tf b b hw tw hw tf tw hw tw hw tf b tw hw tw D
(a) (b) (c)