Portal Frame

A portal frame is a structural frame of columns rigidly connected to a beam or rafter so that the joints transmit moment, giving the assembly its lateral stability and enabling large, clear, column-free spans. The classic single-bay pitched-roof steel portal is the workhorse of industrial sheds, warehouses, factories and large halls; multi-bay and multi-storey rigid frames extend the concept.

In steel (IS 800) portals are usually designed plastically — the frame is proportioned so plastic hinges form at the eaves and apex/mid-span at the collapse load, an efficient use of material; haunches are added at the moment-rich eaves. Pre-Engineered Building (PEB) construction is essentially optimised tapered-member portal framing. Design must address sway stability, lateral-torsional buckling of rafters/columns, haunch design and base-fixity assumptions; RCC portal frames (for tanks, subways, hangars) follow IS 456 frame analysis.