Portal frame is a construction technique where vertical supports are connected to horizontal beams or trusses via fixed joints with designed-in moment-resisting capacity. The result is wide spans and open floors.

Portal frame structures can be constructed using a variety of materials and methods. These include steel, reinforced concrete and laminated timber such as glulam. First developed in the 1960s, they have become the most common form of enclosure for spans of 20 to 60 meters.

Because of these very strong and rigid joints, some of the bending moment in the rafters is transferred to the columns. This means that the size of the rafters can be reduced or the span can be increased for the same size rafters. This makes portal frames a very efficient construction technique to use for wide span buildings.

Portal frame construction is therefore typically seen in warehouses, barns and other places where large, open spaces are required at low cost and a pitched roof is acceptable.

Generally portal frames are used for single-story buildings but they can be used for low-rise buildings with several floors where they can be economic if the floors do not span right across the building (in these circumstances a skeleton frame, with internal columns, would be a more economic choice). A typical configuration might be where there is office space built against one wall of a warehouse.

Portal frames can be clad with various materials. For reasons of economy and speed, the most popular solution is some form of lightweight insulated metal cladding with cavity masonry work to the bottom 2 m of the wall to provide security and impact resistance. The lightweight cladding would be carried on sheeting rails spanning between the columns of the portal frames.

Portal frames can be defined as two-dimensional rigid frames that have the basic characteristics of a rigid joint between column and beam.

The main objective of this form of design is to reduce bending moment in the beam, which allows the frame to act as one structural unit.