1轴向拉压的应变能 V=-F·M= 2EA 轴力沿变化:=-5 (15.5) 对桁架结构:V=∑ Fsl 2E A 2扭转应变能 T Tl E 2 gLp 7(x) (15.6) 2G11.轴向拉压的应变能 l l EA F l V F l N N 2 2 1 2 = = 轴力沿x变化: = l N EA F x dx V 2 ( ) 2 对桁架结构: = i i i Ni i E A F l V 2 2 (15.5) 2.扭转应变能 T T l GIP T l V T 2 2 1 2 = = dx GI T x V l P = 2 ( ) 2 (15.6)