Performance-Based Seismic Design of Eccentrically Braced Frames Using Target Drift and Yield Mechanism as Performance Criteria

A new performance-based seismic design procedure for eccentrically braced frames (EBF) based on pre-selected yield mechanism and target drift is proposed in this paper. The design base shear is derived from a modified energy balance equation. A new seismic lateral force distribution based on nonlinear dynamic behavior is also presented. Two EBF (3-story and 10-story), which were used in a recent related study where they were designed by following current design practice and IBC 2000 provisions, were re-designed by the proposed performance-based design methodology by using the same basic design spectral values as used for the code designed frames. The proposed design procedure was validated by extensive non-linear dynamic analyses for a number of ground motion records. Comparisons are made between the responses of the code designed frames with the ones designed by the proposed method. The results confirm the validity of the proposed method for the study EBF in terms of meeting all the performance design objectives, such as target drifts, and intended yield mechanism, in other words, yielding occurring in a controlled manner in pre-selected elements. Thus, yielding was confined to the shear links only, and plastic hinging in the columns was eliminated except some occurring at the column bases, which was expected. This resulted in superior performance of the frames designed by the proposed method over that of the code designed frames. The total weight of steel used in the frames designed by the two approaches was the same. No attempt was made to compare the costs because of many factors that may affect them.