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Optimal Stiffness Distribution of Steel Moment Frames under Extreme Earthquake Loading

The paper presents a design optimization method for steel moment frames under extreme earthquake loading. Seismic demands of the structures are evaluated using a nonlinear pushover analysis procedure. Least structural weight is taken explicitly as one design objective. The other objective, pursuing uniform ductility demands in all stories, is realized indirectly by imposing an equal limit to the plastic interstory drift ratio of each story. Explicit forms of the objective function and constraints in terms of member sizing variables are formulated to enable computer solution for the optimization model. The proposed design formulation seeks a least-weight design with an optimal lateral stiffness distribution for steel moment frames. The concepts are illustrated for a three-story moment frame example.