The portal method is based on the assumption that, for each story of the frame, the interior columns will take twice as much shear force as the exterior columns

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.