Torsional balance of plan asymmetric structures with viscoelastic dampers

This investigation deals with the torsional balance of elastic asymmetric structures with viscoelastic dampers. Plan asymmetry leads to an uneven lateral deformation demand among structural members and to unbalanced designs with larger capacities in some resisting planes. The analytical and experimental response of stiffness and mass-eccentric structures subjected to different ground motions is investigated herein. Viscoelastic dampers are capable of controlling the lateral–torsional coupling of a structure by placing the so-called Empirical Center of Balance (ECB) of the plan equidistant from all building edges. To improve the damper efficiency, a mechanical deformation amplifier was included in the one-story experimental building model. Results show that the displacement demand at the building edges and that of resisting planes at equal distance from the ECB may be similar if the damper is optimally placed. It was observed that optimal damper eccentricity values tend to increase linearly as the stiffness or mass eccentricities increase, and that response reduction factors ranging from 1.5 to 3 are possible with a small capacity damper. Moreover, viscoelastic dampers are equally effective in controlling lateral–torsional coupling of torsionally flexible as well as stiff structures.