弯幽应力( Stresses in Beams) (1)当中性轴为对称轴时 实心圆截面W d 64 d d/2d/2 32 b 矩形截面、I.bh3/12b2 /2h/2 z ID3 空心圆截面W=(1-a)a= d 32(Stresses in Beams) （1）当中性轴为对称轴时 矩形截面 实心圆截面 空心圆截面 b h z y z d y z D d y 32 π / 2 π / 64 / 2 4 3 d d d d I W z = = = / 2 6 /12 / 2 3 2 bh h bh h I W z = = = D d α D W = (1− ) = 32 π 4 3 