能量方法 ②应变能: N2( M(x) dx MA(x) dx t dx L 2EA L 2GIp L2EⅠ TR PR(1-coS() Rdo 0 2GIp 0 PR(sm o Rdo 2EI 3P2R3丌PRx 4(× dEl ③外力功等于应变能 P ∴W=fA=U s 3PRI PRT 2 2G1 2EI③外力功等于应变能 ②应变能：    = + + L L P L x EI M x x G I M x x EA N x U d 2 ( ) d 2 ( ) d 2 ( ) 2 2 n 2   + − =   j j j j 0 2 2 2 0 2 2 2 d 2 (sin ) d 2 (1 cos ) R EI P R R GI P R P EI P R GI P R 4 P 4 3 2 3 2 3   = + f U P W = A = 2  EI PR GI PR f P A 2 2 3 3 3    = +