②求扭矩(扭矩按正方向设) ∑mc=0,71+m2=0 2 3 T=-m2=-4.78kN:m A1B2 C D 72+m2+m3=0, T2=-m2-m2=-(4.78+478)=956kNm T-m=0 7=m4=6.37kNm9 n A B C D m2 m3 m1 m4 1 1 2 2 3 3 ②求扭矩（扭矩按正方向设） 4 78kN m 0 , 0 1 2 1 2 = − = −   = + = T m . mC T m (4 78 4 78 9 56kN m 0 , 2 2 3 2 2 3 = − − = − + = −  + + = T m m . . ) . T m m 6 37kN m 0 , 2 4 3 4 = =  − = T m . T m