Seismic Performance of Steel Moment Frames Plastically Designed by Least Squares Stress Fields

摘要

The report presents a new plastic design method for moment resisting frames. The method utilizes the lower bound theories of limit analysis and a stress field termed, 'the least squares stress field.' Member forces are monitored at several points in a frame, and the sum of the squares of the moments is minimized among the member force distributions in equilibrium with the applied design load. The least squares pseudoinverse technique is used to implement this procedure. After reviewing existing plastic design provisions for steel moment frames, two-story frame models with identical configurations are proportioned by the proposed design method considering load combinations specified by three different sets of design requirements used in the United States and Japan. Static and dynamic analyses are carried out on the model frames, and their seismic performances under a severe earthquake are compared. It is found that the relation between the various load factors used for dead, live and earthquake loads greatly influences the collapse mode which occurs under abnormal earthquake load conditions, provided no special consideration is made in the design to control the collapse mode.