Page 151 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.83

CONNECTIONS

CONNECTIONS 3.83

Weld to Flanges. From Fig. 3.47, the worst-case combined flange loads are 53 kips shear and
29 kips axial. The length of weld is 5.25 in. Proceeding as above, θ= tan (29/53) = 28.7° and µ=
−1
1.17. However, to maintain deformation compatibility, the weld at the flanges can only develop 99%
of its capacity before the less ductile weld at the web fractures (see Art. 3.2.21). Therefore µ is taken
equal to 1.16. Note that in more extreme cases, the more ductile welds (those with small θ) will be
able to develop as little as 85% of their strength before the less ductile welds (those with large θ)
1
fracture. Thus, the weld size in / 16ths is

D = 29 2 + 53 2 = 313
.
f
.
2 × 5 25 ×1 392 ×1 16
.
.
1
Use a / 4-in fillet weld, which is also the AISC minimum.
Strength of Stiffeners (Plate A). The weak-axis beams are Grade 50 steel and are butt welded to
plates A. Therefore, plates A should also be Grade 50 steel. Previous calculations involving this plate
assumed it was A36, but changing to Grade 50 will not change the final results in this case because
the stiffener contact force is limited by the beam no. 1 delivered force, rather than by the stiffener
strength.
Design strength for gross section shear (to resist shear at flange):
φR gv =φ0.60A g F y = 0.90 × 0.60 × 0.75 × 5.75 × 50 = 116 kips > 53 kips OK

Design strength for gross section tension (to resist tension at flange):

φR gt =φA g F y = 0.90 × 0.75 × 5.75 × 50 = 194 kips > 29 kips OK

Design strength for gross section shear (to resist shear at web):

φR gv =φ0.60A g F y = 0.90 × 0.60 × 0.75 × 10 × 50 = 203 kips > 29 kips OK

Design strength for gross section tension (to resist tension at web):

φR gt =φA g F y = 0.90 × 0.75 × 10 × 50 = 338 kips > 107 kips OK

Associated Shear Connections: Beams 3 and 4. The factored shear force for these beams is R =
107 kips.
Weld to Beam Web. As with the strong-axis beam web connection, this is a field-welded con-
nection with bolts used for erection only. The design load (required strength) is R = 107 kips. The
beam web shear R is essentially constant in the area of the connection and is assumed to act at the
edge of plate A (section a–a of Fig. 3.44b). This being the case, there will be a small eccentricity on
the C-shaped field weld. Following AISC Manual Table 8-9, l = 17, kl = 4, k = 0.24, x = 0.04, xl =
1
0.68, al = 4.25 − 0.68 = 3.57, and, by interpolation, c = 2.80. Thus, the required weld size in / 16ths is

D = 107 = 299.
.
0 75 × 2 80. ×17
3
Use a / 16-in fillet weld.
3
Plate B (Shear Plate) Gross Shear. Try a / 8-in plate of A36 steel:
φR v = 0.9 × 0.6 × 36 × 0.375 × 17 = 124 kips > 107 kips OK

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