Minimum-Cost Optimal Design of Nonlinear Fluid Viscous Dampers and Their Supporting Braces for Seismic Retrofitting

Abstract eng:
In this paper, we present a new methodology for achieving economical retrofitting design solutions of 3-D irregular frames. Nonlinear fluid viscous dampers and their supporting braces are optimally distributed in irregular 3D frames and optimally sized. For generating optimal design solutions useful for practitioners, a realistic cost formulation is chosen as the objective function to be minimized. Constraints are imposed on interstory drifts at the peripheries. These are evaluated with nonlinear time-history analyses considering realistic ground acceleration records. The behavior of each damper-brace system is defined based on the Maxwell’s model for viscoelasticity. A fractional power-law is used to describe the nonlinear force-velocity relation of each damper, and the stiffening contribution of the supporting brace and of the damper is represented by linear springs. The damper-brace elements are divided into size-groups, that is, elements with the same mechanical properties. The properties of each size-group of dampers (damping coefficient and supporting brace stiffness), and the dampers’ distribution in the structure are optimally defined in the optimization process using Genetic Algorithms. The capability of the proposed methodology to achieve economical designs is demonstrated in a practical case. The numerical results establish also important benchmarks for other, more efficient, methods to be developed.

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