Seismic Design Optimization of Steel Building Frameworks

This paper presents a multicriteria optimization method for the performance-based seismic design of steel building frameworks under (equivalent static) seismic loading. Minimizing structural cost (interpreted as structural weight) is taken as one objective. The other objective concerns minimizing earthquake damage which, since uniform postelastic ductility demand over all stories generally avoids local weak-story collapse, is interpreted as providing a uniform interstory drift distribution over the height of the building. That is, the overall objective for the design of a building framework is to have minimum structural weight and uniform plastic ductility demand while, at the same time, meeting displacement and strength constraints corresponding to the various performance levels. Explicit forms of the objective functions and constraints in terms of member sizing variables are formulated to enable computer solution for the optimization model. The concepts are illustrated for three-story and nine-story steel building frame examples.