A rigid frame placed in the middle of key building columns in a building is called a portal frame. They are commonly placed in side walls. This is vertical to the width of the main frame of the building.

Portal frames are necessary for the durability of many classifications of steel buildings. They are also the chosen resolution when usual rigid frame and structural bracing cannot be used for a specific project.

Portal frames can be placed into framework in one or two different ways. The best way is for the structural framework to be set with the supports extending to the pad and fastened to the footing with anchor rods. Frame support brackets are then used to affix it to the primary frame at the top of the portal frame. One other approach is for the portal frame columns to stop just short of reaching the footing. The portal frame would then be attached to the primary frame columns at the low and high points. The primary rationale for this secondary procedure is that no increase of the foundation piers will be necessary - a budget and planning savings. The drawback to the second procedure is that the building column bottom must adopt the strength and rigidity commonly provided by the base tethered portal frame.

Clearance and capacity specs can be obtained from the producer of the portal frame. Industry tables serve to calculate the correct minimal clear width that a standard portal frame will need for the proper dimensions for clear height. Bay height and width determine the calculation. There are formulations available if proportions must be figured before a building fabricator is decided upon. This is generally accepted in the public market.

Portal frame couplings can be made to the primary frame column by a single angle bracket. To avoid any twisting or turning (torsion), set up the bracket with the plane of the portal frame. Check that the interior flange for the portal frame is braced by a flange brace or by a pair of horizontal stiffeners to avoid loading restrictions.

A pre-engineered steel structure with reduced eave height needs to have enough room above the top of the opening for a portal frame to adapt. Higher buildings have the difficulty of expanse between eave strut and the summit of the portal frame. Packing this space with X-bracing is greatly favored. With no bowing of the primary frame columns, X-bracing accepts the transfer of any horizontal strains from the eave strut to the portal frame.