Beam to column rigid connection

The main objective of a fixed connection is to eliminate any relative rotation between column and beam. In other word when a beam a connected to a column by one of the methods shown in the figure, the bending moment transfers to the column without any reduction. In simpler words, you can assume that beam and column function together as if they cast together in the factory.
I think it is a good idea to explain how the bending moment is transferred to the column. Wings of the beam apply to axial forces in opposite directions and since there is distance between their lines of application, it causes a bending moment
Bending moment is transferred in shape of a couple of axial forces applied by the wings, and shear shear forces are transferred by the beam web. Depending on the magnitude of loads, it may be necessary to design some stiffeners to strengthen the critical areas of the column.
When do we design a rigid frame?
On case that require design of rigid frames is plastic design. Another application of rigid frames is when the section are compact and we are allowed to apply a 10 percent reduction in the amounts of bending moments. In both cases the connections must be able to reach their plastic capacity. As a result we need to use fixed connection between beams and columns.
The necessity of vertical stiffeners
As it is mentioned earlier, the wings applied axial forces to the column. If the beam is connected to the wings of the column, these forces may cause distortion or crippling in the adjacent area of the column. So sometimes using some stiffeners seems necessary to secure the connection.
In our future video lessons I design and analyze many connections, so that you can learn how to design a safe and optimized connection.