Building Design and Construction Handbook - Merritt - Ventech!

7.32 SECTION SEVEN
Moment-Resisting Frames. Designers have a choice of several alternatives to X
bracing. Knee braces, shown in Fig. 7.16d, or portal frames, shown in Fig. 7.16e,
may be used in outer walls, where they are likely to interfere only with windows.
For buildings with window walls, the bracing often used is the bracket type (Fig.
7.16ƒ). It simply develops the end connection for the calculated wind moment.
Connections vary in type, depending on size of members, magnitude of wind moment,
and compactness needed to comply with floor-to-ceiling clearances.
Figure 7.17 illustrates a number of bracket-type wind-braced connections. The
minimum type, represented in Fig. 7.17e, consists of angles top and bottom: They
are ample for moderate-height buildings. Usually the outstanding leg (against the
column) is of a size that permits only one gage line. A second line of fasteners
would not be effective because of the eccentricity. When greater moment resistance
is needed, the type shown in Fig. 7.17b should be considered. This is the type that
has become rather conventional in field-bolted construction. Figure 7.17c illustrates
the maximum size with beam stubs having flange widths that permit additional
gage lines, as shown. It is thus possible on larger wide-flange columns to obtain
16 fasteners in the stub-to-column connection.
The resisting moment of a given connection varies with the distance between
centroids of the top and bottom connection piece. To increase this distance, thus
increasing the moment, an auxiliary beam may be introduced as shown in Fig.
7.17d, if it does not create an interference.
FIGURE 7.17 Typical wind connections for beams to columns.