W21 62 (A36) beam. The connection is a shear plate with two erec- tion holes for erection bolts. The shear plate is shop welded to the column flange and field welded to the beam web. The limit states are plate gross shear, weld strength, and beam web strength.
Plate gross shear. Try a plate 1/
2 18
Rgv 0.5 18 0.9 0.6 36 175 kips > 163 kips, ok Plate net shear need not be checked here because it is not a valid limit state.
Weld-to-column flange. This weld sees shear only. Thus ; use 1/
4FW
Weld-to-beam web. This weld sees the shear plus a small couple. Using AISC 13th Edition Manual Table 8-8, l 18, kl 4.25, k 0.24, x 0.04, xl 0.72, al 4.28, a 0.24, c 2.71, and
Thus a 5/
16fillet weld is satisfactory.
D5 163
0.753 2.71 3 18 5 4.46
D5 163
2 3 18 3 1.392 5 3.25 132 Chapter Two
Beam web. To support a 5/
16fillet weld on both sides of a plate, AISC LRFD Manual Table 10.2 shows that a 0.476-in web is required. For a 5/
16fillet on one side, a 0.238-in web is required. Since the W21 62 web is 0.400 in thick, it is ok.
Beam nos. 3 and 4 W21 44 (G50) composite. The flange connection is a full penetration weld, so again, no design is required. Section A-A of Fig. 2.33a shows the arrangement in plan. See Fig. 2.33c. The connection plates A are made 1/
4 in thicker than the W21 44 beam flange to accommodate under and over rolling and other minor misfits. Also, the plates are extended beyond the toes of the column flanges by 3/
4to 1 in to improve ductility. The plates A should also be welded to the column web, even if not required to carry load, to provide improved ductility. A good discussion of this is contained in the AISC 13th Edition Manual of Steel Construction, pp. 12-14 through 12-19.
The flange force for the W21 44 is based on the full moment capac- ity as required in this example, so Mp 358 kips-ft. For gravity moments, the beam moments counteract each other, and the column bending strength is not an issue. For lateral moments, however, the beam moments add, and the column strength may limit the beam moments. The weak-axis column design strength is
Therefore, for lateral loads, the beam plastic moment cannot be achieved because 2 358 > 2 314.
For lateral loads, the maximum beam moment is Mb 314 kips-ft. In summary, for gravity loads, Mb Mp 358 kips-ft and the flange force is
and for lateral loads, Mb 314 kips-ft and the flange force is
Figure 2.36 shows the distribution of forces on the plates A, including the forces from the strong axis connection. The weak axis gravity force of 212 kips is distributed one-fourth to each flange and one-half to the web. This is done to cover the case when full gravity loads are not present on each side. In this case, all of the 212 kips must be passed to the flanges. To see this, imagine that beam 4 is removed and the plate A for beam 4 remains as a back-up stiffener. One half of the 212 kips from beam 3 passes into the beam 3 near side column flanges, while the other half is passed through
Ff 5 3143 12 s20.7 2 0.450d5 186kips Ff 5 3583 12 s20.7 2 0.45d5 212kips Mp5 0.9 3 50 123 83.6 5 314kips- ft
Design of Connections for Axial, Moment, and Shear Forces 133 Design of Connections for Axial, Moment, and Shear Forces
the column web to the back-up stiffener, and thence into the far side flanges, so that all of the load is passed to the flanges. This is the load path usually assumed for gravity loads, although others are possible.
The weak-axis lateral load is distributed one-half to each flange and none to the web. As in the unbalanced gravity load case, all load must be delivered to the flanges. Although no load goes to the web, the stiff- ener would still be welded to the web for ductility purposes.
Merging of stiffeners from strong and weak axis beams. The strong axis beam, beam no. 1, required stiffeners 1/
2 6
1/
2 12
1/
2. The weak axis beams no. 3 and no. 4 require plates A3/
4 8 12 1/
2. These plates occupy the same space because the beams are all of the same depth. Therefore, the larger of the two plates is used, as shown in Fig. 2.33c.
Since the stiffeners are merged, the welds that were earlier deter- mined for the strong axis beam must be revisited.
Weld to web. From the worst case of Fig. 2.36,
Use a 1/
4fillet weld or AISC minimum.
Weld to flanges. From the worst case of Fig. 2.36,
This indicates a 3/
8fillet weld is required. Df 5 22921 932 23 6.25 3 1.392 5 5.60 Dw5 229 21 1072 2 3 11.0 3 1.3925 3.59 134 Chapter Two
Figure 2.36 Distribution of forces on plates A.
In the above weld size calculations, the worst case of gravity loads and lateral loads is used. If it is known that one or the other only exists, only that cases need be considered. When it is not known whether the loads are gravity or lateral, the worst case presumed here must be used.
Note also, that is the weld size calculations, the AISC Specification Section J2.4, which allows for increased strength of obliquely loaded fillet welds, is not used. The compatibility requirements associated with obliquely loaded fillets of different sizes in the same group are complex and are not considered here.
Stresses in stiffeners (plate A). The weak axis beams are G50 steel and are butt welded to plates A. Therefore, plates A should also be G50 steel. Previous calculations involving this plate assumed it was A36, but changing to G50 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 the stiffener strength.
The stiffener stresses for the flange welds are, from Fig. 2.36 (worst case),
and for the web welds
2.3.2.3 Associated shear connections—beams 3 and 4. The specified