Building Design and Construction Handbook - Merritt - Ventech!

STRUCTURAL STEEL CONSTRUCTION 7.35
resemble the condition illustrated in Fig. 7.18e. In both (d) and (e), the footings
must be designed for such moments.
A common assumption in wind distribution
for the type of light mill building
shown in Fig. 7.19 is that the windward
columns take a large share of the
load acting on the side of the building
and deliver the load directly to the
ground. The remaining wind load on the
side is delivered by the same columns
to the roof systems, where the load joins
with the wind forces imposed directly
on the roof surface. Then, by means of
diagonal X bracing, working in con-
FIGURE 7.19 Braced bays in framing for an junction with the struts and top chords
industrial building.
of the trusses, the load is carried to the
eave struts, thence to the gables and,
through diagonal bracing, to the foundations.
Because wind may blow from any direction, the building also must be braced
for the wind load on the gables. This bracing becomes less important as the building
increases in length and conceivably could be omitted in exceptionally long structures.
The stress path is not unlike that assumed for the transverse wind forces. The
load generated on the ends is picked up by the roof system and side framing,
delivered to the eave struts, and then transmitted by the diagonals in the end
sidewall bays to the foundation.
No distribution rule for bracing is intended in this discussion; bracing can be
designed many different ways. Whereas the foregoing method would be sufficient
for a small building, a more elaborate treatment may be required for larger structures.
Braced bays, or towers, are usually favored for structures such as that shown in
Fig. 7.20. There, a pair of transverse bents are connected together with X bracing
in the plane of the columns, plane of truss bottom chords, plane of truss top chords,
and by means of struts and sway frames. It is assumed that each such tower can
carry the wind load from adjacent bents, the number depending on assumed rigid-
FIGURE 7.20 Braced bays in a one-story building transmit wind loads to the ground.