A portal frame is a rigid frame that is installed between the primary structural supports in a building. They are normally placed in side walls, vertical to the main frame girth of the building.

Portal frames, also known as small equilateral steel frames, are critical to the soundness of many classifications of pre-engineered steel buildings. When the reinforcement ability of the existing rigid frame is insufficient, portal frames can be the remedy.

A steel building can incorporate a portal frame into its supporting structure in one of two ways. The most popular way is for the supports of the portal framework to reach to the base, and then it is attached to the base with anchor rods. Supports are then installed at the top of the portal frame to secure it to the primary frame columns. The other procedure is to install the portal frame pillars so they do not reach the footing. The portal frame is fastened to the top and bottom of the primary frame pillars. The drawback to this second procedure is that the chief steel pillar bottom must accept the rigidity and strength commonly provided by the base-secured portal frame. The prime reason for choosing the second alternative is that enlargement of the pad piers are not required, which can save design time and money.

The portal frame manufacturer can provide details about the required clearance and capacity. Industry tables provide information as to the minimum clear width that the standard portal frame will support relative to the precise clear height. This calculation is controlled by the building bay size. Before accepting a bid from a steel building company, ascertain the actual desired proportions to determine if formula adjustments are required. This is a critical step to avoid “one size fits all”� bids that may not include all of the hidden costs.

Installing a portal frame into a steel building with a short eave height requires sufficient space above the top of the opening for the portal frame to work properly. In taller structures, the distance between eave strut and the uppermost of the portal frame can cause complications, which can be addressed by filling this space with X-bracing. X-bracing allows any horizontal stresses to be dispersed from the eave strut into the portal frame without bending the primary frame pillars.

Portal frames can be bonded to the primary frame column by a single angle bracket. Adjusting the plane of the portal frame bracket is necessary to prevent the possibility of any twisting or turning. An additional problem can be caused when a portal frame that is subject to loading is not properly restricted. This dilemma can be solved by checking that the interior flange for the portal frame is anchored by a flange brace or by twin horizontal stiffeners.

Portal frames are a critical support component, and there are many ways that your building can benefit from their use.