Efficiency of Viscous Damping in Seismic Energy Dissipation and Response Reduction

Input energy accumulates at a specific rate, and viscous damping dissipates the accumulated input energy at a slower pace. The difference between the two energy time histories at a time t is the vibration energy E_v(t), which is the sum of kinetic and potential energies at time t. Maximum displacement occurs shortly after E_v attains its maximum value during the following cycle when potential energy is maximum and kinetic energy is zero. An efficient damping produces lower E_v, accordingly lower maximum displacement. We choose to define the damping efficiency as the ratio of dissipated energy E_D to input energy E_I at the time t_max when E_v(t) attains its maximum value for a SDOF system with period T. The influence of earthquake magnitude, fault distance, soil type and fault type on damping efficiency are assessed here under a large set of earthquake ground motions that represent the distribution of such characteristics effectively. A large set of free-field strong motion records are selected from the NGA database. Damping ratio, soil class, distance to epicenter (R_epi), moment magnitude (M_w), and fault mechanism are selected as the basic parameters in order to characterize source and site properties of ground motions. Based on the employed GM database, it has been found that damping efficiency is affected most by the earthquake magnitude, soil type, and expectedly by the damping ratio.