The construction of a framework of structural steel involves two principal operations: fabrication and erection. Fabrication involves the processing of raw materials to form the finished members of the structure. Erection includes all rigging, hoisting, or lifting of members to their proper places in the structure and making the finished connections between members.

A wide variety of structures are erected using structural steel. Basically, they can be listed as buildings, bridges, and towers; most other structures are modifications of these three. Buildings

There are three basic types of steel construction. These may be designated as wall-bearing construction, skeleton construction, and long-span construction.

In wall-bearing construction, exterior and interior masonry walls are used to support structural members, such as steel beams and joists, which carry the floors and roof. It should be noted that while this section of your TRAMAN discusses steel structures, wall-bearing construction is applicable to nonsteel structures as well. Wall-bearing construction is one of the oldest and most common methods in use. Although modern developments in reinforced concrete masonry make the use of this method feasible for high-rise structures, wall-bearing construction is normally restricted to relatively low structures, such as residences and light industrial buildings.

A tall building with a steel frame, such as shown in figure 1-38, is an example of skeleton construction. In this 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. One limitation on using skeleton construction, however, 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 1-39. As seen in this 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, which is usually more economical, is to use a truss to span large distances. As you learned in the EA3 TRAMAN, a truss is a frame-work of structural members consisting of a top chord, bottom chord, and diagonal web members that are usually placed in a triangular arrangement. (See figs. 1-40 and 1-41.) As shown in figure 1-40, trusses can be fabricated to conform to the shape of nearly any roof system.

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 1-42. Prefabricated bar joists, designed to conform to specific load requirements, are obtainable from commercial companies. Other long-span construction methods involve several different types of framing systems, which include steel arches, cable-hung frames, and other types of systems. These methods are beyond the scope of this TRAMAN.

Figure 1-40.Typical steel trusses.

Figure 1-43.Truss bridge.