Behavior of braced and unbraced semi-rigid frames

The state-of-the-art limit states specification for structural steel buildings explicitly acknowledges the semi-rigid nature of most connections by allowing for the construction of semirigid frames under its Type PR (Partially Restrained) Construction provision. The construction of semi-rigid frames differs from that of rigid frames in that connection behavior must be taken into consideration in the analysis and design process. This paper attempts to shed light on the subject by outlining a methodology for semi-rigid frame analysis. Analytical studies of both braced and unbraced semi-rigid frames are presented. It is found that the use of bracings not only increases the strength and stiffness of semi-rigid frames, but it drastically reduces the sensitivity of the frames to differences in connection behavior. It is further demonstrated that for design application the assumption of linear connection behavior is quite adequate for braced semi-rigid frames.