Question 6.17: A built-up plate girder has the dimensions shown in Fig. 1. ......
A built-up plate girder has the dimensions shown in Fig. 1. If the shear force at this cross section is V = 300 kips, what is the shear flow in each fillet weld bead? I_z = 54,800 in^4 .
Plan the Solution Since there are two weld beads that attach each flange to the web, we can use Eq. 6.84 modified by a factor of two.
q_r = \frac{VQ} {I} = \frac{VA^′\bar{y}^′}{I} (6.84)
From Eq, 6.84 (modified).
2q_r = \frac{VQ} {I} = \frac{VA^′\bar{y}^′}{I}where, as indicated, Q is the first moment of the entire flange area, taken about the NA.
q_r = \frac{(300 kips)(20 in.)(1.25 in.)(30.625 in.)} {2(54,800 in^4)}q_r = 2.10 kips/in.
Review the Solution A simple recheck of the calculations is all that is necessary here.
Interesting design information on steel girders and weld beads can be found in Ref. 6-2, but we will not pursue the design of welds further in this text.