ABSTRACT
The analysis and design of building steel frames in practice has long been based on simplified assumptions
concerning the behavior of beam-to-column connections as two idealized models, fully rigid and ideally
pinned, even though the semirigid concept was introduced many years ago. The first model implies
displacement and slope continuity between the column and the beam, together with the full transfer of
bending moments. The latter one, on the other hand, implies that rotation continuity is nonexistent and,
consequently, no bending moment may be transmitted to the column by the beam. Although adoption of
such idealized models leads to great simplification in structural analysis and design, it by no means
represents the actual behavior of the connections. Consequently, the predicted structural responses may
be inaccurate as a result of disregarding the true behavior of beam-to-column connections. To date,
numerous experimental investigations on connection behavior have clearly demonstrated that a pinned
connection possesses a certain amount of rotational stiffness, while a rigid connection possesses some
degree of rotational flexibility. Most beam-to-column connections commonly used in practice actually
exhibit semirigid behavior characterized by the moment-rotational relationship as shown in Figure 23.1.