Shear Flow in Beams


*Example: The nail spacing is 100 mm along a beam with the x-section as shown below.

The force allowed per nail is 1200 N. Find the maximum allowable shear force, Vmax.



The figure below details the nail spacing.


Strategy: Identify the area, A, from where the shear stress is zero to the location where the

shear stress is to be calculated. Evaluate Q recalling that Q = Aybar. Apply the relations for

shear flow and nail spacing q = VQ/I and q = F/s


Consequently F/s = VQ/I so V = FI/Qs


where F = 1200 N, I = (1/12)(260)(310)3 (1/12)(160)(260)3 = 411 x 106 mm4

s = 100 mm

The challenging calculation is for Q.


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