第10次作业 4-46 5×75 =18.75kN 3Fm3×18.75×1 =0.52MPa≤[r] A2×300×180 4-52 Fl F F=40kN. M =10kN m 、h2 h 69 9×10×106 mEx =208mmb、2×208 =139mm 3FSm_3×40000 =207MPa<[z b=139mm,h=208mm第 10 次作业 4-46 0.52 [ ] 2 300 180 3 18.75 10 2 3 18.75 2 5 7.5 3 .max max .max  =       = = =  = MPa A F F k N S S 4-52 b mm h mm MPa A F mm b mm M h bh h W k N m Fl F F k N M S z S 139 , 208 2.07 [ ] 2 208 139 3 40000 2 3 139 3 2 208 208 , 10 9 10 10 [ ] 9 6 9 10 . 4 40 , .max max 3 6 3 max 2 3 .max max = = =     = = =  = =    = = = = = = =   