The main frame (rigid frame) is the primary structural member of the steel building system, consisting of columns and rafters. Columns transfer loads from main roof beams, trusses, or rafters to the foundations. Rafters are the main beams supporting the roof system. Main frames are normally connected to the foundation using anchor bolts in a configuration described as a pinned condition.
Endwall frames consist of endwall columns and rake rafters. Typically, end-frames only support half as much load as a main frame, so their components are often manufactured using the less expensive process of "cold forming" coils of steel in a roll former. Customers expecting to add to their building can order an expandable endwall. These are designed with the load-bearing capability of main frames so they can serve as interior frames when the building is expanded.
Secondary framing members join the primary framing members together to form building bays and provide the means of supporting and attaching the walls and roof. Secondary framing members consist of eave struts, purlins, girts and bracing. Eave Struts provide attachment and bearing points for the end of the roof sheets and wall sheets. Purlins support roof panels and transfer the roof loads to the rafters. Girts are horizontal structural members attached to sidewall or endwall columns that support paneling. They run horizontally, between main frame columns and between endwall columns. Bracing Steel buildings employ one or more forms of bracing to counteract the constant pressure from forces like torsion, shear, compression, and lift. Flange bracing is standard on all metal buildings, consisting of structural angles connected between rafters and purlins to prevent the rafters form rolling side to side under a load. Diaphragm bracing is created by wall and roof sheeting. ‘X’ bracing uses steel rods or cables to tightly connect various parts of the frame together and strengthen the diaphragm effect. It is useful for extra stresses on a building, such as high winds, heavy snow loads, or even a large number of openings.
Steel plates called clips provide the connection points for attaching the secondary frame components to the main frames and to each other. They are welded on at the factory and have bolt patterns pre-punched .
Bays and Framed Openings
Bays are the spaces between columns. A framed opening is an opening within a bay framed by jams; it can be anything from doors and windows to drive-through vehicle openings.