The characteristic formula of viscous damper force is often the nonlinear viscous element model in seismic time history response analyses of structures having the dampers, but it is not always accurate. Damping force depends on properties of viscous material and its components, but the formula is not compounded from them. To make the formula more correct, the previous thesis had demonstrated some viscous material characteristics with detailed experiments. It indicated that viscous force depended on strains and frequencies, and its hysteresis loop was like that of viscoelastic in small strains. This paper shows modeling of viscous material properties with viscoelastic theories that are fractional derivative and mechanical elements models.
