The horizontal shear per unit length q is VQ/I, where q also equals the shearing force divided by the horizontal shear distance. To find V, q, Q, and I must be computed.
First, I compute q:
Q is the moment of the area above the shearing plane:
The moment of inertia is of the entire
cross section. A table is often useful as a help in keeping the quantities
ordered:
 |
d (mm) | A (mm2) | Ad2 (mm3) | total I (mm4) | |
| each plate |  |
 |
(12)(175) =
2100 |
4.057x107 | 4.0599 x 107 |
| beam | 71.1 x 106 | N/A | 5720 | N/A | 71.1 x 106 |
The total, after multiplying the plate moment of inertia by two, is 1.523 x 108 mm4.
Substituting, I get
