Page 155 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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CONNECTIONS

CONNECTIONS 3.87

connection. Since the column is usually continuous at this cross section, this moment will have no effect
on the column. If the column is in compression, the moment M c will cause increased compressive stress
at one column flange, and a tensile stress which decreases the column compressive stress at the other
flange. This decreased column compressive stress will prevent any yielding from occurring on the column
cross section as a whole and the moment M c can therefore be neglected. If the column is in tension, the
same argument applies. In Art. 3.7.4, M c will have an effect because there is a connection at this point.
To complete the picture, the free moment on the gusset needs to be calculated. This can be done
by multiplying the distance from the intersection of the brace force line and the gusset-to-column
force line to the gusset-to-beam line by the gusset-to-beam force. Multiplying the distance from the
intersection of the brace force line and the gusset-to-beam force line to the gusset-to-column line by
the gusset-to-column force will yield the same results. When simplified, this leads to
(
M =−β( H + α( V = e V − e H) (3.72)
)
)
(
)
g
c
b
c
b
In this case M b is equal to M g , so no moment can exist at the gusset-to-column interface. Therefore,
the calculated moment M c must exist internal to the column.
When taken to the extreme, ∆V b = V b , the result is Special Case 2 (Fig. 3.49), illustrated in the
AISC Manual.

FIGURE 3.49 Force distribution for Special Case 2 of uniform force method. (Source: A. R. Tamboli,
Handbook of Structural Steel Connection Design and Details, McGraw-Hill, 1999, with permission.)

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