Behaviour of top and bottom angles for beam-to-column connections.

In the design of multistorey steel frames, a common method of analysis is to assume that, for vertical loads on the beams, the joints at the ends of the members are flexible and allow the members to rotate freely at the ends. The same frame, however, when analyzed for lateral loads, is assumed to have rigid connections. Building connections, in general, are neither perfectly rigid nor completely flexible, but belong to a category that is intermediate between these two extremes and are known as semi-rigid joints. [...