2)求BC杆的临界力 A=2(D2-42 7(50-402) =707mm2。 4 4 =z(D4-d4 丌(50-404) 64 =181132mm4 64 /181132 -omm 707 x==10×2c030×10 =144.3 162）求BC杆的临界力 A I i = i l  = 707 181132 = =16mm 1.0 = ×2/cos30° 16 ×103 =144.3 4 ( ) 2 2 D d A − =  4 (50 40 ) 2 2 − =  =707mm2 。 64 ( ) 4 4 D d I − =  64 (50 40 ) 4 4 − =  =181132mm4