(mlD-m)×4+mb×2 +mn×2=0 解得 2 m =0.557m A端的反力偶m4=m-mn=0443m即 解得 端的反力偶 ( ) . . m m m m m m m A m m m m D D D D A D −  +  − +  = = − = = − = 4 2 1 2 0 2 4 0 557 0 443 4 4  