Shear Flow in Thin-walled Members (continued)

Next calculate the maximum shear stress developed in the web. In this case break the
area for Q into two parts such that (See the figure below.)

Q = A₁ y_1bar + A₂ y_2bar

Q for τ_max is: Q = (Area)(y_bar for area about n.a.) = (100)(20)(140) + (130)(20)(65)

Q = 4.49 x 10⁵ mm³

So the maximum shear stress in the web is (100)( 4.49 x 10⁵) / (2.157 x 10⁸)(20) = 10.4 MPa

Note: The average shear stress in the web is the shear force divided by the area of the web.

Area of web = (2)(260)(20) = 10400 mm²

τ_max is: 100000/10400 = 9.62 MPa

Note that the average shear stress in the web provides a reasonable estimate of the maximum

shear stress developed in the web using VQ/It for thin-walled closed sections undergoing shear.

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