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This paper presents a performance-based plastic design (PBPD) methodology for the design of steel concentric braced frames. The design base shear is obtained based on energy-work balance equation using pre-selected target drift and yield mechanism. To achieve the intended yield mechanism and behavior, plastic design is applied to detail the frame members. For validity, three baseline frames (3, 6, 9-story) are designed according to AISC (Seismic Provisions for Structural Steel Buildings, American Institute of Steel Construction, Chicago, 2005) seismic provisions (baseline frames). Then, the frames are redesigned based on the PBPD method. These frames are subjected to extensive nonlinear dynamic time-history analyses. The results show that the 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.

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.

This article presents the results of a study in which a newly developed performancebased plastic design (PBPD) methodology was applied to steel special concentric braced frames (SCBF). In PBPD method, pre-selected target drifts and yield mechanisms are used as performance limit states. The design base shear for selected hazard level(s) is calculated by equating the work needed to take the structure monotonically up to the target drift to that required by an equivalent elastic-plastic single degree of freedom system to achieve the same state. In addition, a new lateral force distribution has been developed based on the relative distribution of maximum story shears obtained from inelastic dynamic analysis. Plastic design method is performed to detail the frame members and connections to achieve the intended yield mechanism and behaviour. Results of inelastic dynamic analyses carried out on example frames designed by PBPD method showed that the frames met all the intended performance objectives in terms of yield mechanisms and target drift levels. On the other hand, when designed by current seismic design code as SCBF, they showed very poor response due to premature brace fractures leading to unacceptably large drifts and instability. Reliability-based assessment based on FEMA 351 indicated that PBPD frames have much higher confidence levels against global collapse than those of corresponding SCBFs designed by current seismic codes. Finally, the results are proved by determining the seismic fragility curves of model frames.

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