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 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. Typical steel trusses. Steel truss fabricated from angle-shaped members. Clear span bar joists.