Inelastic analysis-based design optimization of eccentrically braced steel frames

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The objective of the proposed research is to develop an inelastic analysis-based design optimization methodology for eccentrically braced steel frames under earthquake loading.      The state-of-the-art design method for eccentrically braced frames (EBFs) is the capacity design approach, where the links are sized for code-specified forces while all other members are proportioned for the forces generated by the fully yielded and strain hardened links. The capacity design approach has four main shortcomings: 1) it is implemented by hand calculations instead of by computers; 2) it is unable to determine, with confidence, the internal forces for the columns in braced bays; 3) it cannot account for instability effect; and 4) it cannot identify inelastic behaviors outside the links.      These shortcomings of the capacity design approach can only be possibly overcome by employing an inelastic analysis-based design procedure. There exist two inelastic analysis methods for seismic design, i.e., nonlinear dynamic time history analysis and pushover analysis. None of these methods are pitfall free. Considering the relative simplicity of pushover analysis, this proposal will adopt pushover analysis as the main tool to evaluate seismic demands for EBFs, while the time history analysis is employed to verify the design solutions if necessary. In light of the tremendous computational efforts required for a design process using an inelastic analysis, a computer-aided tool specially developed for EBFs is indeed desirable.      Minimization of both structural weight and earthquake damage will be the design objective. The capacity design concept will be realized by imposing constraints on the plasticity demand for steel members. For example, yielding in the frame members outside the links will be prohibited, or strictly controlled if unavoidable.      The proposed research work will not only liberate design engineers from arduous hand calculations but also significantly improve the performance of the EBFs designed by the proposed methodology.