The portal frame is the rigid frame that supports the main structural columns in a pre-engineered steel structure. They are usually located in the side walls, in a vertical configuration. Moreover, portal steel frames are small box-like structures, and their inclusion in many classifications of steel buildings is essential to the buildings’ endurance. They are a preferred solution when conventional rigid frame combined with bracing schemes won’t work well for a given application.

An all-steel building can incorporate a portal frame in one of two ways. A common approach is for the structural framework system to be placed so that the columns reach the foundation and then are anchored to it with anchor rods. At the top of the portal frame, brackets lock it to the primary frame columns. Another approach is for the portal frame columns to stop before touching the base. The portal frame would then be fastened to the primary frame pillars at the bottom and the top. A drawback to the second procedure is that it must assimilate the durability and stability of the steel structure pillar bottom that is commonly supplied by a secured portal frame. However, it is a viable alternative if especially strong foundation piers are not required ““ it can save money and engineering effort.

Portal frame couplings can be secured to the primary frame column by means of a single angle bracket. To prevent turning or twisting (torsion), attach the bracket to the plane of the portal frame. By making certain that the inner flange of the portal frame is anchored by a flange brace or by two horizontal stiffeners, the portal frame will not be constrained under loading.

Portal frame placement into a steel building with a reduced eave height requires adequate space above the top of the opening. Vice versa, taller steel buildings will have excess space between the eave strut and the topmost of the portal frame. This can be packed with X-bracing, which transmits any sideways strains from the eave strut to the portal frame, without bending the primary frame supports.

Industry production tables can extrapolate the lowest clear width that the ideal portal frame must provide for the specific clear height, relative to the building bay measurements. Also, the portal frame producer should use industry standard formulas to determine the required size. Be sure that you select a portal frame producer who will provide specifications for adequate clearance and capacity.