Optimal peripheral drift control of 3D irregular framed structures using supplemental viscous dampers

A methodology for the optimal seismic design of supplemental viscous dampers for 3D irregular framed structures is presented. Optimal design, for which the added damping is minimised and subjected to a constraint on inter-storey drifts at the floor edges, is achieved while considering an ensemble of realistic ground motion records for linear behaviour of the damped structure. A variational approach is adopted for the derivation of the gradient of the constraint, thus enabling the use of a gradient based optimisation algorithm for the solution of the optimisation problem. An optimal design is first attained for one “active” ground motion record. If it fails for other records apart from the original ensemble, additional ground motions (loading conditions) are added one at a time to the “active" set until the optimum is reached. Optimal designs of supplemental dampers are attained for two, 3-bay by 3-bay, 8-storey 3D framed structures. The first has an asymmetric plan whereas the second is a setback structure. The resulting optimal designs are characterised by added damping in the exterior frames only, and full drift utilisation occurs in those storeys with assigned damping.