2-21 AD杆: 300×2 NI =300kN,2 2 F,300×103 A1=b:02x A1 NI =1764.7mm O 0 选择80×80×6(9397cm2)2-21 AD杆： 80 80 6(9.397 ) 8.82 1764.7 170 300 10 [ ] 300 ,2 2 300 2 2 2 1 2 3 1 1 1 cm A cm m m F A F k N N N   = =  = = =  = 选择 