SEMI-RIGID BEAM-TO-COLUMN CONNECTIONS FOR BRACED FRAMES

Braced frames, including those that are designed to resist seismic or large wind loads, traditionally have been analyzed and designed as trusses with all joints pinned. However, braced frames using gusset plates are actually braced-moment frames because the presence of a typical gusset plate creates a rigid joint zone generally larger than that of a moment frame connection. Described herein is a semi-rigid flexure connection design for braced frames which eliminates the undesirable effects caused by rigid beam-gusset-column connections that typically cause large moments and shears in the beams and columns. With a proper design of the strength and flexibility of this semi-rigid beam-to-gusset-to-column connection, the required axial force capacity in the beams and columns is maintained. The frame moments and shears are reduced so that both the beams and columns remain elastic at the target story drifts and support primarily only gravity and frame axial loadings. After a seismic event that damages the braces, the frame may be repaired by removing and replacing the braces and, if required, repairing or replacing the elements of the semi-rigid connection without having the residual frame drift caused by the inelastic distortion of the beams and columns which is consistent with the concept of the design of “damage tolerant structures”.