Load My S O= t= I Ib 回萨， , +x2 2 4 (a) Reaction (b) 2 +x2 中 白 (c) Fig.7.1-1 Normal,shear and principal stresses in homogeneous uncracked beam.(a)Flexural and shear stresses acting on elements in shear span;(b)distribution of shear stress;(c) principal stresses on elements in shear span(a) (b) (c) Fig. 7.1-1 Normal, shear and principal stresses in homogeneous uncracked beam. (a) Flexural and shear stresses acting on elements in shear span; (b) distribution of shear stress; (c) principal stresses on elements in shear span I My   2 2 1 2 4        2 2 2 2 4      -  ) 2 arctan( 2 1     - VS I b τ