What is portal steel frame structure?

The portal frame is generally used for plant design, while some of the design of additional floors also use portal frame, portal frame is composed of steel beams, steel columns, columns can be made into articulated foot, can also be made into a solid knot, portal frame in the portal frame in the plane of the stiffness is greater, while the longitudinal stiffness is smaller, and the biggest difference with the steel frame is that the portal frame in the longitudinal direction mainly rely on the inter-column bracing and rigid bollards to transfer the horizontal force.