type of construction, all live and dead loads are carried
by the structural-frame skeleton. For this reason, the
exterior walls are nonbearing curtain walls. Roof and
floor loads are transmitted to beams and girders, which
are, in turn, supported by columns. The horizontal
members or beams that connect the exterior columns are
called spandrel beams. If you add additional rows of
columns and beams, there is no limitation to the area of
floor and roof that can be supported using skeleton
construction. However, one limitation of using
skeleton construction is the distance between columns.
Oftentimes, large structures, such as aircraft
hangars, may require greater distances between
supports than can be spanned by the standard structural
steel shapes. In this case, one of several methods of
long-span steel construction is used. One method uses
built-up girders to span the distances between supports.
Two types of built-up girders are shown in figure 8-50.
As shown in the figure, the built-up girder consists of
steel plates and shapes that are combined together to
meet the necessary strength. The individual parts of
these girders are connected by welding or riveting.
Another method, usually more economical, is the
use of a truss to span large distances. A TRUSS is the
framework of a structural member consisting of a top
chord, bottom chord, and diagonal web members that
are usually placed in a triangular arrangement. Figure
8-51 shows many different types of trusses that can be
fabricated to conform to the shape of nearly any roof
A third long-span method, although not as versatile
as trusses, is the use of bar joists. BAR JOISTS are
much lighter than trusses and are fabricated in several
different types. One type is shown in figure 8-52.
Prefabricated bar joists, designed to conform to specific
load requirements, are obtainable from commercial
companies. Other long-span construction methods
Figure 8-50.Typical built-up girders.
Figure 8-51.Typical steel trusses.