§7.3 Shear Stress Distribution 161 dz Element B dx dy Element A o =(M +dM)y I (a) (b】 (c} Fig.7.7.Horizontal shear in flanges. This force being reacted by the shear on the element shown in Fig.7.9(c), ttdx L [dm rtdx ·ytdz L dM 1 and r= dx'It tdzy dM But tdz.y=Ay and =0. dx QAy t= (7.110 It Thus the same form of expression is obtained to that of eqn(7.2)but with the breadth b of the web replaced by thickness t of the flange:I and y still refer to the N.A.and A is the area of the flange 'beyond'the point being considered. Thus the horizontal shear stress distribution in the flanges of the I section of Fig.7.8 can$7.3 Shear Stress Distribution 161 (a) (C) Fig. 7.7. Horizontal shear in flanges. This force being reacted by the shear on the element shown in Fig. 7.9(c), = Ttdx z and But .. T=- dM - 1tdz.y dx 'It z dM dx tdz.y = Aj and ~ = Q. (7.11) Thus the same form of expression is obtained to that of eqn (7.2) but with the breadth b of the web replaced by thickness t of the flange: 1 and y still refer to the N.A. and A is the area of the flange 'beyond the point being considered. Thus the horizontal shear stress distribution in the flanges of the I section of Fig. 7.8 can