The Effects of Yield Mechanism Selection on the Performance based Plastic Design of Steel Moment Frame

Abstract

This paper presents the development of performance based plastic design (PBPD) method for steel moment frames with considering the gravity loads and P-Δ effects. In this method the design lateral forces are obtained from energy-work balance equation by using pre-selected target drift and yield mechanism. For further improvement of PBPD method, some solutions are represented to precisely obtain the required moment of columns in order to prevent their yielding that leads to form undesirable mechanisms in the structure. In order to show more validity of PBPD method, two model frames, 5 and 10story, are designed based on PBPD as well as elastic design method. The mentioned frames are evaluated by extensive nonlinear static pushover analysis and dynamic analysis. The results show that the frames designed by PBPD method reach the intended performance objectives in terms of yield mechanism and target drift levels. In contrast, the frame designed by Ed method experience large story drifts due to flexural yielding of the columns. Since PBPD method is a direct design method, little or no evaluation are needed after the initial design because the nonlinear behavior is built into the design process from the start.