Seismic Design and Behavior of Ductile Knee-Braced Moment Frames

Abstract

The design and behavior of a ductile structural system called a knee-braced moment frame (KBMF) are presented in this paper. The design of this structural system is based on a capacity-design concept that results in ductile behavior. For this system, the frames are designed so that the knee braces will yield and buckle under seismic loads; this is followed by plastic hinging of beams at the ends of the beam segments outside the knee portions. Through this concept, inelastic activities are confined to the designated elements. The knee braces also provide much less obstruction than the braces of conventional systems, making this structural system architecturally attractive. The design concept of this new structural system is addressed first. Results from an experimental study into the seismic behavior of the proposed system are then presented. Two approximately half-scale KBMF specimens were tested. The load-deformation characteristics obtained from the test indicate that the newly developed system can be a viable alternative to conventional structural systems. Finally, results from dynamic analyses of an example KBMF structure designed by the proposed method are provided.