There are many types of compression members in a typical building including: columns; top edges of beams; top edges of joists; wall studs; top chords and cantilevered bottom chords of wood trusses, and compression webs of trusses. the image below could easily be a line of wall studs; a row of truss top chords; a row of cantilevered bottom chords, or a line of compression webs.
Often, compression members will require some sort of lateral brace to prevent the member from buckling under load. For example, the top edge of a dropped built-up wood beam will be braced laterally by the floor joists that sit on it. In the case of a wall, the studs may be braced laterally by a row of girts or by rows of strapping. Trusses are generally braced using rows of 2×4 material for top and bottom chord strapping or web bracing. Refer to Figure 2. This sketch could illustrate among other things, a wall with a row of girts at mid-height, or a row of truss webs which require a single lateral brace.
If a truss web requires a single row of lateral bracing, simply installing the row of bracing is not enough to properly brace the trusses. Figure 3 illustrates that even with the lateral brace installed, all of the webs can buckle in the same direction.
In order to prevent the webs from buckling, the lateral brace must be tied off so that it is prevented from
shifting sideways. This is often accomplished by installing X bracing as shown in Figure 4. It is important to note that the X brace must be securely anchored at both the top and bottom and it must be properly fastened to the lateral web brace. Generally, this X bracing detail will be repeated at 20 foot intervals.