The properties of the cross section for
a W 8 x 28 are taken from Appendix C:
| d = 8.06 in | tf = 0.465 in | Ix = 98.0 in4 |
| A = 8.25 in2 | tw = 0.285 in | bf = 6.535 in |
The moment of the two forces about b is:
Also, P = 90 kips, and V = 20 kips.
Because point b is on the N.A., the normal stress does not include a bending moment term:
To obtain the shearing stress, I have to
compute Q:
| section | Ai (in2) | 
(in) |
(in3) |
| flange | bftf = 3.039 | d/2 - tf/2 = 3.7975 | 11.54 |
| half web | tw(d/2 - tf) = 1.016 |  |
1.811 |
| totals | 4.0548 | 13.35 = Q |
Now I can compute the shearing stress:
To summarize, the element at b has these stresses:
Mohr's Circle can now be sketched:
From the circle, I have:
