BAR JOIST

Bar joists form a lightweight, long-span system used as floor supports and built-up roofing supports, as shown in figure 3-18. Bar joists generally run in the same direction as a beam and may at times eliminate the need for beams. You will notice in figure 3-19 that bar joists must have a bearing surface. The span is from girder to girder. (See fig. 3-20.)

Prefabricated bar joists designed to conform to specific load requirements are obtainable from commercial companies.

TRUSSES

Steel trusses are similar to bar joists in that they serve the same purpose and look somewhat alike. They are, however, much heavier and are fabricated almost entirely from structural shapes, usually angles and T-shapes. (See fig. 3-21.) Unlike bar joists, trusses can be fabricated to conform to the shape of almost any roof system (fig. 3-22) and are therefore more versatile than bar joists.

The bearing surface of a truss is normally the column. The truss may span across the entire building from outside column to outside column. After the trusses have been erected, they must be secured between the BAYS with diagonal braces (normally

Figure 3-18.-Clearspan bar joists (girder to girder) ready to install roof sheeting.

Figure 3-19.-Bar joists seat connection.

Figure 3-20.-Installing bar Joists girder to girder.

round rods or light angles) on the top chord plane (fig. 3-23) and the bottom chord plane (fig. 3-24). After these braces are installed, a sway frame is put into place. (See fig. 3-25.)

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