Seismic Design of Buckling-Restrained Braced Frames Based on the Modified Equivalent Energy Concept

It has been indicated that the equivalent energy concept (EEC) proposed by Housner contains the following problems: (i) The use of pseudovelocity for estimation of the input seismic energy sometimes underestimates the input energy demand. (ii) The input energy of an inelastic system is not equal to that of the equivalent elastic system. (iii) The plastic to input energy ratio estimated by the EEC is larger than that by time history analysis. In this study a seismic design procedure for buckling-restrained braced frames was proposed based on the EEC which was modified considering the above problems. The design process begins with the computation of input energy from response spectrum. Then the computed plastic energy computed based on the modified EEC is distributed to each story along energy distribution ratio, and the size of each brace is computed so that all the plastic energy is dissipated by the brace. The proposed procedure was applied to the design of 3-, 6-, and 8-story steel frames with buckling-restrained braces for three different performance targets. Twenty earthquake records were utilized for verification of the proposed method. According to analysis results, the top story displacement responses of the model structures corresponded well with the given performance targets.