梁的剪力与弯矩 截面法过程:切取、替代、平衡 C B E=0:F4-F=0 M F ∑MC=0:M-FAx=0剪力 M 弯矩 ∑F=0:F+F-F=0∑M=0:M-F2x+F(-x)=0 F=F-F=F M=FBx-F(-x)=F梁的剪力与弯矩 一、截面法过程：切取、替代、平衡 F A B a x S A y 0 : A S 0 F F F F F =  = − = M F x M M F x A C 0 : A 0 = x  = − = FA FS C M F FS M FB C S B A y 0: S B 0 F F F F F F F F = − =  = + − = ( ) M F x F(l x) F x M M F x F l x B A C 0 : B 0 = − − =  = − + − =