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In a PRE ENGINEERED BUILDING, Vertical columns bolted with rafters and other metal building parts together in frames to make the primary framing system. Purlins attach from rafter to rafter across the roof of the frames. Girts attach from column to column across the length of the frames. This makes up the secondary framing system. These steel buildings have 6mm thick steel "L clips" bolted strategically on the columns and rafters. These clips are used to fix the Girts and Purlins to the primary framing. A bracing system is a secondary but essential part of a bridge structure.