Page 91 - Handbook of Structural Steel Connection Design and Details

Design of Connections for Axial, Moment, and Shear Forces

76 Chapter Two

1 0.5 sin 1.5 (32.5)
1.20°
9.85
D 5 5.90
1.392 3 1.20
3
A / -in fillet weld is indicated, which is less than what was provided. No
8
ductility factor is used here because the loads include a redistribution.
Gusset to column. This connection is ok without calculations because the
loads of Fig. 2.13d are no greater than the original loads of Fig. 2.13a.
Discussion. From the foregoing analysis, it can be seen that the AISC-
suggested procedure for the beam-to-column connection, where the
actual normal force
N |H H | A
BC C D
is replaced by
N max (H , A)
BC c
is justified.
It has been shown that the connection is strong enough to carry the
distortional forces of Fig. 2.13b, which are larger than the elastic dis-
tortional forces.
In general, the entire connection could be designed for the combined
UFM forces and distortional forces, as shown in Fig. 2.13d for this exam-
ple. This set of forces is also admissible. The UFM forces are admissi-
ble because they are in equilibrium with the applied forces. The
distortional forces are in equilibrium with zero external forces. Under
each set of forces, the parts of the connection are also in equilibrium.
Therefore, the sum of the two loadings is admissible because each indi-
vidual loading is admissible. A safe design is thus guaranteed by the
lower bound theorem of limit analysis. The difficulty is in determining
the distortional forces. The elastic distortional forces could be used, but
they are only an estimate of the true distortional forces. The distor-
tional forces depend as much on the properties of the connection, which
are inherently inelastic and affect the maintenance of the angle between
the members, as on the properties and lengths of the members of the
frame. For this example, the distortional forces are [(150 110)/110]
100 36% greater than the elastic distortional forces. In full-scale tests
by Gross (1990) as reported by Thornton (1991), the distortional forces
1
were about 2 / times the elastic distortional forces while the overall
2
frame remained elastic. Because of the difficulty in establishing values
for the distortional forces, and because the UFM has been shown to be
conservative when they are ignored (Thornton, 1991, 1995b), they are

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