All steel building framing systems have a number of similarities and some specific differences. Most require that for the entire structure to work efficiently it needs to have lateral bracing on the rafter’s compression flange. Snow, live, and dead loads create pressure upon the top flange of the primary component framing materials to create compression. Roof purlins, however, provide sufficient bracing. Bottom flanges need stabilization applied because this is the part of the frame under compression from the force of wind uplift. The exact locations of any flange bracing is developed by the engineering department of the specific steel building manufacturer.
With so many choices of primary framing systems available for selection as the supporting structure for steel buildings the question comes down to what is the right application for the chosen structure’s dimension. Most bigger buildings that can include interior columns without jeopardizing floor lay-outs and are not planned for any future expansion can have a multi-span rigid frame system applied because of its overall cost savings applications. Next choice, if interior load-bearing columns are not desired is a single-span rigid frame with a clear-span feature. If the building choice is of a smaller overall dimension there is cost savings involved with choosing a tapered beam option or the use of a wing unit.
The industry trend seems to have the selection of clear-span systems as a priority for most steel building purchasers as the flexibility of the floor plans is inherent in the scheme. The cost of this system must be thought out carefully. If, for instance, portions of the building will be partitioned for any reason the building as operational could preclude the need for the added expense of a clear-span feature. Moreover, the search for the best pricing on large buildings with wide expanses of clear-span area limit’s the manufacturer pool that is able to accommodate the design and production of these bigger structures.
The building purchaser, in coordinating with a designer or architect, needs to make a decision on what type of column will provide the best match to the framing system chosen and for the building’s intended function. This would involve the choice of either tapered, straight, or another type of column application. Straight columns tend to be more costly so if a tapered column selection is feasible this option should be strongly considered.
The proper selection of endwall framing needs to be decided upon. Designs for this frame portion do not tend to vary by much. The load resistance to this area of the building and supporting of wall girts is the endwall’s responsibility. Selection should insure that the columns in the endwalls are of single or double cold-formed channels and with a steel thickness of a minimum of 14 gauge.
The correct choice of framing, in all regards, is crucial for the success of any building project and for the owner’s satisfaction over the serviceable life of the steel structure.