应力 T O max p p 强度条件、≤[a max A ≤[z] 变形 △l O EA E 刚度条件 180 max max ≤[] G p
应力 强度条件 变形 刚度条件 p I T = p max W T = [ ] p max W T A FN = [ ] N,max A F EA F l l N = E = GI p Tl = [ ] π 180 p max max = GI T
2-3 FM=-20kN. FM =-10kN Fm=10kN 10KN F 20×10°N 100MPa , 200mm 10KN 10×103N 20KN N2 33.3MPa 300mm F310×103N n3 = 25MPa A3 400mm
2-3 FN1 = −20k N, FN 2 = −10k N, FN3 = 10k N MPa m m N A FN 100 200 20 10 2 3 1 1 1 = − − = = MPa m m N A FN 33.3 300 10 10 2 3 2 2 2 = − − = = MPa m m N A FN 25 400 10 10 2 3 3 3 3 = = = 10kN (+) (-) 10kN 20kN
2-19 FN=2×(F+P)=60N A=2×4058=811.6mm2 O=2M60×103 =73.9MPa<[o] A811.6
2-19 73.9 [ ] 811.6 60 10 2 405.8 811.6 2 ( ) 60 3 2 = = = = = = + = MPa A F A m m F F P k N N N
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
AB杆: F=2×300=600kN F600×10 242=M2 =15294mm O 170 A1=1765cm2 选择100×100×10(19261cm2)
AB杆: 100 100 10(19.261 ) 17.65 1529.4 170 600 10 [ ] 2 2 300 600 2 2 1 2 3 2 2 1 cm A cm m m F A F k N N N = = = = = = 选择
第3次作业: 2-7 F F F 1F23 n3 3 △= EA EA EA F Fl F Fl Fl BEA 3EA3EA 3EA D △Z → 3EA
第3次作业: 2-7 F F F EA Fl EA Fl EA Fl EA Fl EA l F EA l F EA l F l N N N 3 3 3 3 3 3 3 1 2 3 + = − = + = + + ( ) 3 = = → EA Fl u l D