第9次作业 m-m截面 M.=20kN m M1y1_20×10×(-150 =-741MPa 180×1503 =494MPa,c=0,0D=741MPa n-n截面 M.=-22kNm a,=M1y=-25×10×(-150) 9.26MPa 80×150 =-681MPa,ac=0,0D=-926MPa 4-31 M=4F kNm W=2×340.328cm3=680.656cm3 M mx=≤[o] F]=x170×680656 =289×102N=28.9kN 4000 4-36 5F,q×6 3-F×2-F×1 q =202.5kN W=2×6597=13194cm M202.5×10° 13194×10 =1535MPa<[]满足强度条件 M=3.5kNm bh h h≥ 8M 18×3.5×10° =185mm,b=-=62mm第 9 次作业 4-25 MPa MPa MPa I M y M k N m m m B C D A 4.94 , 0, 7.41 7.41 12 180 150 20 10 ( 150) 20 . 3 6 1 1 1 = = = = −    − = = = −     截面 MPa MPa MPa I M y M k N m n n B C D A 6.81 , 0, 9.26 9.26 12 180 150 25 10 ( 150) 22 . 3 6 1 1 2 = − = = − =  −   − = = = − −     截面 4-31 N k N W F W M W cm cm M F k N m z z z 28.9 10 28.9 4000 170 680656 4 [ ] [ ] [ ] 2 340.328 680.656 4 . 2 max max 3 3 max =  =  =  = =  =  = =    4-36 153.5 [ ],满足强度条件 1319.4 10 202.5 10 2 659.7 1319.4 202.5 . 2 3 3 2 1 2 6 2 5 3 6 max max 3 2 max  =     = = =  = =   −  −  −       = + MPa W M W cm k N m q F F F q M z z 4-38 mm h mm b M h bh h W M k N m z 62 3 185 , 10 18 3.5 10 [ ] 18 6 18 3.5 . 3 6 3 max 2 3 max = = =    = = = = 