Effect of Dampers on Seismic Demand of Short Period Structures in Rock Sites

Seismic behavior of short period structures with dampers founded on rock is investigated. A single bay frame with diagonal damper that represents short period structures is evaluated in response to the excitation of a set of earthquake records. The frame system is modeled as a generalized single degree of freedom system, and is subjected to five earthquake records representative of rock site conditions. The relationship between the force modification factor and the global ductility demand for short period structures founded on rock, in the presence of dampers, tends to approach those of long period ones. Compared with seismic demand under general site conditions, short period structures founded on rock show less seismic demand and less sensitivity to earthquake excitations. Similar to seismic demand in general site conditions, dampers with high damping ratios for short period structures in rock sites tend to keep the structural response in the elastic range even for high values of force reductions. Seismic code provisions should be revised to account for short period effect under seismic excitation.