  In many cases, beam to column connections in structural frames are semi
rigid, but they are considered to be ideally rigid or pinned due to their
computational complexity and shortage of designing methods. In this paper,
connections are considered as linear rotational springs with variable
stiffness. Moreover, the main contribution of the present study is a
preliminary design method of moment resisting frames, considering semi rigid
behavior of connections, by means of presented diagrams for different frames.
These diagrams relate three features of a frame together; stiffness of frames
connections, geometrical properties of frames elements, and its lateral
displacement. These diagrams can be used when the required stiffness of frames
connections is needed while the desired response of the frame, dimensions of
the frame and the ratio of second moment of inertia of its elements are known.
On the other hand, they could be used to obtain the ratio of beams length to
columns length and the ratio of second moment of inertia of beams to columns
alongside the stiffness of frames connections while the only known data is the
number of frames grids in X and Y directions and its desired response.
