Optimal seismic design of multiple-rocking steel concentrically-braced frames in 3D irregular buildings

This paper presents a gradient-based optimization approach for the seismic design of multiple-rocking systems in irregular buildings. The proposed design method tackles general 3D buildings with high torsional and vertical irregularities is developed. The design problem is formulated as an optimization problem that minimizes the construction cost of steel self-centering concentrically braced frames. The constraints are formulated based on current seismic design code requirements and recommendations from the literature. The structural response is computed using nonlinear time history analyses of general 3D models subjected to ensembles of ground accelerations. A dual-phase optimization approach is developed to reduce the computational effort and improve convergence In the first phase, a simplified numerical model is adopted for the analyses while the topology of the framing elements is not optimized. The second phase adopts a more detailed numerical model and starts with fixed location of the rocking sections. This enables topology optimization of the framing elements as well. The design method was implemented for the design of an 8-story building with two setbacks and high torsional irregularities subjected to an ensemble of ground accelerations, each having three components. The results show that this method provides efficient designs of these complex systems with a reasonable computational effort.