The channel shape cross-section and the rectangular cross-section shown in the Figure Q4 are made of materials with elastic-perfectly plastic behaviour. The yield stress of the material used for the channel shape cross-section is = 451 MPa, whereas that used for the rectangular cross- section is 0.9y. Compute the thickness of the web, t, of the channel shape section if the two cross sections have identical plastic bending moment about the z-axis. In Figure 4, h= 71 mm, b=55 mm, a=9 mm, H=71 mm, d= 55 mm h Z Z H b Figure Q4 d