Development of the Performance Based Plastic Design for Steel Concentric Braced Frames and Evaluation by Energy Methodology

Abstract

This paper presents the development of performance based plastic design (PBPD) method to design steel concentric braced frames (SCBFs). The design base shear is obtained based on energy-work balance equation using preselected target drift and yield mechanism. Also, the energy-work balance can be applied to estimate seismic demands, herein called the energy spectrum method. PBPD method was originally developed to design SCBFs. The results were too conservative. For further improvement, this paper presents some modifications such as C2-Factor method and P-delta effect in energy-work balance equation to give a better estimate of design base shear. For validity, three baselines frames (3, 6, 9-story) are designed according to AISC 2005 seismic provisions (Baseline frames). Then, the frames are designed based on the Original PBPD method (Original PBPD method). Finally, they are designed based on modifications applied on PBPD method (Modified PBPD frames). These frames are subjected to extensive inelastic pushover and time-history analyses. The Results show that the Modified PBPD frames meet all the intended performance objectives in terms of yield mechanisms and target drifts whereas the Baseline frames show very poor response due to premature brace fractures leading to unacceptably large drifts and instability. Also, Modified PBPD frames show that the structures having 20%–25% weight less than the Original PBPD can meet the performance objectives. Moreover, the drift demands obtained from energy spectrum method significantly correspond with the results of time history analyses.