Lifecycle cost optimization of tuned mass dampers for the seismic improvement of inelastic structures

The seismic performance of tuned mass dampers (TMDs) on structures undergoing inelastic deformations may largely depend on the ground motion intensity. By estimating the impact of each seismic intensity on the overall cost of future seismic damages, lifecycle cost (LCC) proves a rational metric for evaluating the benefits of TMDs on inelastic structures. However, no incorporation of this metric into an optimization framework is reported yet. This paper presents a methodology for the LCC-optimal design of TMDs on inelastic structures, which minimizes the total seismic LCC of the combined building-TMD system. Its distinctive features are the assumption of a mass-proportional TMD cost model, the adoption of an iterative suboptimization procedure, and the initialization of the TMD frequency and damping ratios according to a conventional linear TMD design technique. The methodology is applied to the seismic improvement of the SAC-LA benchmark buildings, taken as representative of standard steel moment-resisting frame office buildings in LA, California. Results show that, despite their limited performance at the highest intensity levels, LCC-optimal TMDs considerably reduce the total LCC, to an extent that depends on both the building vulnerability and the TMD unit cost. They systematically present large mass ratios (around 10%) and frequency and damping ratios close to their respective linearly designed optima. Simulations reveal the effectiveness of the proposed design methodology and the importance of adopting a nonlinear model to correctly evaluate the cost-effectiveness of TMDs on ordinary structures in highly seismic areas.