Some observations on energy demand spectra for single-degree-of-freedom systems equipped with fluid viscous dampers

Abstract

The ability of structural elements to absorb input energy through inelastic deformation and supplemental damping is a primary factor in determining structural damage during earthquake excitation. This study proposes an energy methodology for the seismic evaluation of single-degree-of-freedom (SDOF) systems, considering the effect of fluid viscous dampers (FVDs). The FVD is characterized by supplemental damping ratio, ${\xi }_{add}$ , and velocity power $\alpha$ . A computer algorithm is developed for the numerical simulation of SDOF systems using nonlinear time history analysis, which is verified through a number of validation examples. This study focuses on issues related to input and hysteretic energies $\left(E_I \text{and }{E}_H\right)$ with particular emphasis on near-field records and their interrelationship with seismic response demand, which is defined as non-dimensional indices for SDOF systems without FVD and those equipped with FVD. The energy indices ( $\zeta$ and $\gamma$ ) are the ratios of input and hysteretic energies to maximum displacement demand, respectively. The results show that the natural period $T_n$ , ductility level $\mu$ , ${\xi }_{add}$ , and $\alpha$ have a significant effect in the determination of energy spectra $\left(E_I \text{and }{E}_H\right)$ . The non-dimensional $\zeta$ is a more stable and reliable indicator than $\gamma$ to quantify the damage potential of ground motion. Finally, the observations of the energy approach provided in this study indicate that it can be used as a useful tool for developing energy-based guidelines for structures incorporating FVDs.